6 Bones and Skeletal Tissues

(1)

6

Bones and

Skeletal Tissues

Cartilage

• Location and basic structure

• Found throughout adult body • Ear and epiglottis

• Articular cartilages and costal cartilage • Larynx, trachea, and nose

• Intervertebral discs, pubic symphysis, and articular discs Cartilage

• Is surrounded by perichondrium • Consists primarily of water

• Resilient tissue—it springs back to original shape

Types of Cartilage

• Hyaline cartilage (glassy)

• Most abundant cartilage

• Provides support through flexibility

• Elastic cartilage—contains many elastic fibers

• Able to tolerate repeated bending

• Fibrocartilage—resists strong compression and strong tension

• An intermediate between hyaline and elastic cartilage Cartilages in the Adult Body

Growth of Cartilage

• Appositional growth

• Chondroblasts in surrounding perichondrium produce new cartilage

• Interstitial growth

• Chondrocytes within cartilage divide and secrete new matrix

(2)

Tissues in Bone

• Bones contain several types of tissues

• Dominated by bone CT

• Contain nervous tissue and blood CT • Contain cartilage in articular cartilages • Contain ET lining blood vessels

Function of Bones

• Support—provides hard framework

• Movement—skeletal muscles use bones as levers • Protection of underlying organs

• Mineral storage—reservoir for important minerals • Blood-cell formation—bone contains red marrow • Energy metabolism—osteoblasts secrete osteocalcin

Bone Tissue

• Bone tissue

• Organic components—cells, fibers, and ground substance • Inorganic components—mineral salts that invade bony matrix Extracellular Matrix

• Unique composition of matrix

• Gives bone exceptional properties • 35%—organic components

• Contributes to flexibility and tensile strength • 65%—inorganic components

• Provide exceptional harness, resists compression Cells

• Three types of cells in bone produces or maintain bone

• Osteogenic cells—stem cells that differentiate into osteoblasts • Osteoblasts—actively produce and secrete bone matrix

• Bone matrix is osteoid

• Osteocytes—keep bone matrix healthy Cells

• Osteoclasts

• Responsible for resorption of bone

• Are derived from a line of white blood cells

(3)

Classification of Bones

• Long bones—longer than wide; a shaft plus ends • Short bones—roughly cube-shaped

• Flat bones—thin and flattened, usually curved

• Irregular bones—various shapes, do not fit into other categories

Gross Anatomy of Bones

• Compact bone—dense outer layer of bone

• Spongy (cancellous) bone—internal network of bone

Structure of a Typical Long Bone

• Diaphysis—―shaft‖ of a bone • Epiphysis—ends of a bone

• Blood vessels—well vascularized

• Medullary cavity—hollow cavity filled with yellow marrow • Membranes

• Periosteum, perforating fibers (Sharpey’s fibers), and endosteum Structure of a Long Bone

Structure of Short, Irregular, and Flat Bones

• Flat bones, short bones, and irregular bones

• Contain bone marrow but no marrow cavity • Diploë

• Internal spongy bone of flat bones Gross Anatomy of Bones

• Bone design and stress

• Anatomy of a bone reflects stresses

• Compression and tension greatest at external surfaces Bone Markings

• Superficial surfaces of bones reflect stresses on them • There are three broad categories of bone markings

• Projections for muscle attachment • Surfaces that form joints

• Depressions and openings

(4)

• Compact Bone

• Contains passage ways for blood vessels, lymph vessels, and nerves

• Osteons—long cylindrical structures • Function in support

• Structurally—resembles rings of a tree in cross-section Microscopic Structure of Compact Bones

• Osteons contain:

• Lamellae • Central canal • Perforating canals • Canaliculi

Microscopic Structure of Compact Bones

• Spongy Bone

• Is less complex than compact bone

• Trabeculae contain layers of lamellae and osteocytes • Are too small to contain osteons

6

Bones and

Skeletal Tissues

Bone Development

• Ossification (osteogenesis)—bone-tissue formation

• Membrane bones—formed directly from mesenchyme • Intramembranous ossification

• Other bones—develop initially from hyaline cartilage • Endochondral ossification

Intramembranous Ossification Endochondral Ossification

• All bones except some bones of the skull and clavicles • Bones are modeled in hyaline cartilage

• Begins forming late in the second month of embryonic development

(5)

• Continues forming until early adulthood

Stages in Endochondral Ossification Anatomy of Epiphyseal Growth Areas

• In epiphyseal plates of growing bones:

• Cartilage is organized for quick, efficient growth • Cartilage cells form tall stacks

• Chondroblasts at the top of stacks divide quickly • Pushes the epiphysis away from the diaphysis

• Lengthens entire long bone

Anatomy of Epiphyseal Growth Areas

• Older chondrocytes signal surrounding matrix to calcify • Older chondrocytes then die and disintegrate

• Leaves long trabeculae (spicules) of calcified cartilage on diaphysis side

• Trabeculae are partly eroded by osteoclasts

• Osteoblasts then cover trabeculae with bone tissue

• Trabeculae finally eaten away from their tips by osteoclasts Organization of Cartilage within

Epiphyseal Plate of Growing Long Bone Postnatal Growth of Endochondral Bones

• During childhood and adolescence:

• Bones lengthen entirely by growth of the epiphyseal plates • Cartilage is replaced with bone CT as quickly as it grows • Epiphyseal plate maintains constant thickness

• Whole bone lengthens

Hormonal Regulation of Bone Growth

• Growth hormone—produced by the pituitary gland

• Stimulates epiphyseal plates

• Thyroid hormone—ensures that the skeleton retains proper proportions

• Sex hormones (estrogen and testosterone)

• Promote bone growth

(6)

Postnatal Growth of Endochondral Bones

• As adolescence draws to an end:

• Chondroblasts divide less often • Epiphyseal plates become thinner

• Cartilage stops growing • Replaced by bone tissue

• Long bones stop lengthening when diaphysis and epiphysis fuse Bone Remodeling

• Bone is dynamic living tissue

• 500 mg of calcium may enter or leave the adult skeleton each day

• Cancellous bone of the skeleton is replaced every 3–4 years

• Compact bone is replaced every 10 years Postnatal Growth of Endochondral Bones

• Growing bones widen as they lengthen

• Osteoblasts—add bone tissue to the external surface of the diaphysis

• Osteoclasts—remove bone from the internal surface of the diaphysis

• Appositional growth—growth of a bone by addition of bone tissue to its surface

Bone Remodeling

• Bone deposit and removal

• Occurs at periosteal and endosteal surfaces

• Bone remodeling

• Bone deposition—accomplished by osteoblasts • Bone reabsorption—accomplished by osteoclasts Remodeling, Spongy Bone

Osteoclast—A Bone-Degrading Cell

• A giant cell with many nuclei • Crawls along bone surfaces • Breaks down bone tissue

• Secretes concentrated HCl

(7)

• Derived from hematopoietic stem cells Repair of Bone Fractures

• Simple and compound fractures • Treatment by reduction

• Closed reduction • Open reduction

Stages of Healing a Fracture Common Types of Fractures Disorders of Bones

• Osteoporosis

• Characterized by low bone mass

• Bone reabsorption outpaces bone deposition • Occurs most often in women after menopause Osteoporosis

Disorders of Bones

• Osteomalacia

• Occurs in adults—bones are inadequately mineralized

• Rickets

• Occurs in children—analogous to osteomalacia Disorders of Bones

• Paget’s disease

• Characterized by excessive rate of bone deposition

• Osteosarcoma

• A form of bone cancer

The Skeleton Throughout Life

• Cartilage grows quickly in youth

• Skeleton shows fewer chondrocytes in the elderly • Bones are a timetable

• Mesoderm

• Gives rise to embryonic mesenchyme cells • Mesenchyme

• Produces membranes and cartilage • Membranes and cartilage ossify

(8)

The Skeleton Throughout Life

• Skeleton grows until the age of 18–21 years

• In children and adolescents, bone formation exceeds rate of bone reabsorption

• In young adults, bone formation and bone reabsorption are in balance

• In old age, reabsorption predominates • Bone mass declines with age

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Bones, Part 1:

The Axial Skeleton

The Skeleton

• Consists of:

• Bones, cartilage, joints, and ligaments

• Composed of 206 named bones grouped into two divisions

• Axial skeleton (80 bones)

• Appendicular skeleton (126 bones) The Axial Skeleton

• Formed from 80 named bones

• Consists of skull, vertebral column, and bony thorax

The Axial Skeleton The Skull

• Formed by cranial and facial bones

The Cranium

• Is the body’s most complex bony structure • Formed by cranial and facial bones

• The cranium

• Encloses and protects brain

• Provides attachment for head and neck muscles The Face

(9)

• Form framework of the face

• Form cavities for the sense organs of sight, taste, and smell • Provide openings for the passage of air and food

• Hold the teeth in place • Anchor muscles of the face Overview of Skull Geography

• Facial bones form anterior aspect

• Cranium is divided into cranial vault and the base

• Internally, prominent bony ridges divide skull into distinct fossae

Overview of Skull Geography

• The skull contains smaller cavities

• Middle and inner ear cavities—in lateral aspect of cranial base • Nasal cavity—lies in and posterior to the nose

• Orbits—house the eyeballs

• Air-filled sinuses—occur in several bones around the nasal cavity

Overview of Skull Geography

• The skull contains approximately 85 named openings

• Foramina, canals, and fissures

• Provide openings for important structures • Spinal cord

• Blood vessels serving the brain • 12 pairs of cranial nerves

Cranial Bones

• Formed from eight large bones

• Paired bones include • Temporal bones • Parietal bones

• Unpaired bones include • Frontal bone

• Occipital bone • Sphenoid bone • Ethmoid bone

(10)

• Parietal bones form superior and lateral parts of skull • Four sutures of the cranium

• Coronal suture—runs in the coronal plane

• Located where parietal bones meet the frontal bone

• Squamous suture—occurs where each parietal bone meets a temporal bone inferiorly

Parietal Bones and Sutures

• Four sutures of the cranium (continued)

• Sagittal suture—occurs where right and left parietal bones meet superiorly

• Lambdoid suture—occurs where the parietal bones meet the occipital bone posteriorly

Sutural Bones

• Small bones that occur within sutures • Irregular in shape, size, and location • Not all people have sutural bones

The Skull— Posterior View Frontal Bone

• Forms the forehead and roofs of orbits

• Supraorbital margin—superior margin of orbits

• Glabella—smooth part of frontal bone between superciliary arches

• Frontal sinuses within frontal bone

• Contributes to anterior cranial fossa

Occipital Bone

• Forms the posterior portion of the cranium and cranial base • Articulates with the temporal bones and parietal bones • Forms the posterior cranial fossa

• Foramen magnum located at its base

Occipital Bone

• Features and structures

• Occipital condyles • Hypoglossal foramen

(11)

• Superior nuchal lines • Inferior nuchal lines

Inferior Aspect of the Skull Temporal Bones

• Lie inferior to parietal bones

• Form the inferolateral portion of the skull

• Term ―temporal‖ comes from Latin word for time • Specific regions of temporal bone

• Squamous, temporal, petrous, and mastoid regions Lateral Aspect of the Skull

The Temporal Bone

• The mastoid process

• Site for neck muscle attachment • Contains air sinuses

• Petrous region

• Projects medially, contributes to cranial base • Houses cavities of middle and internal ear

• Contributes to the middle and posterior cranial fossae

The Temporal Bone

• Foramina of the temporal bone

• Jugular foramen

• At boundary with occipital bone • Carotid canal

• Formane lacerum

• Internal accoustic meatus

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Bones, Part 1:

The Axial Skeleton

The Sphenoid Bone

• Spans the width of the cranial floor • Resembles a butterfly or bat

(12)

• Consists of a body and three pairs of processes • Contains five important openings

• Is the ―keystone‖ of the cranium

The Ethmoid Bone

• Lies between nasal and sphenoid bones

• Forms most of the medial bony region between the nasal cavity and orbits

• Cribiform plate—superior surface of the ethmoid bone

• Contain olfactory foramina

• Crista galli—attachment for falx cerebri

• Perpendicular plate—forms superior part of nasal septum

• Lateral masses—contain air cells • Superior and middle nasal conchae

• Extend medially from laterial masses The Ethmoid Bone

Facial Bones

• Unpaired bones

• Mandible and vomer

• Paired bones • Maxillae • Zygomatic bones • Nasal bones • Lacrimal bones • Palatine bones

• Inferior nasal conchae Facial Bones

Mandible

• The lower jawbone is the largest and strongest facial bone • Composed of two main parts

• Horizontal body • Two upright rami

(13)

Mandible

Maxillary Bones

• Articulate with all other facial bones except the mandible • Contain maxillary sinuses—largest paranasal sinuses • Forms part of the inferior orbital fissure

• Are the ―keystone‖ bones of the face

Other Bones of the Face

• Zygomatic bones

• Form lateral wall of orbits

• Nasal bones

• Form bridge of nose

• Lacrimal bones

• Located in the medial orbital walls

• Palatine bones

• Complete the posterior part of the hard palate Other Bones of the Face

• Vomer

• Forms the inferior part of the nasal septum

• Inferior nasal conchae

• Thin, curved bones that project medially form the lateral walls of the nasal cavity

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Bones, Part 1:

The Axial Skeleton

Special Parts of the Skull

• Orbits • Nasal cavity • Paranasal sinuses • Hyoid bone Nasal Cavity Nasal Septum

(14)

Paranasal Sinuses

• Air-filled sinuses are located within

• Frontal bone • Ethmoid bone • Sphenoid bone • Maxillary bones

• Lined with mucous membrane • Lighten the skull

Orbits

The Hyoid Bone

• Lies inferior to the mandible

• The only bone with no direct articulation with any other bone • Acts as a movable base for the tongue

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Bones, Part 1:

The Axial Skeleton

The Vertebral Column

• Formed from 26 bones in the adult

• Transmits weight of trunk to the lower limbs • Surrounds and protects the spinal cord

• Serves as attachment sites for muscles of the neck and back • Held in place by ligaments

• Anterior and posterior longitudinal ligaments • Ligamentum flavum

Regions and Normal Curvatures

• The Vertebral column has five major regions

• 7 cervical vertebrae of the neck region • 12 thoracic vertebrae

(15)

• Sacrum—five fused bones • Inferior to lumbar vertebrae • Coccyx—inferior to sacrum Regions and Normal Curvatures

• Curvatures of the spine

• Cervical and lumbar curvatures • Concave posteriorly

• Thoracic and sacral curvatures • Convex posteriority

Regions and Normal Curvatures

• Curvatures increase resilience of spine • Thoracic and sacral curvatures

• Primary curvatures • Present at birth

• Lumbar curvature

• Develops when baby begins to walk Ligaments of the Spine

• Major supporting ligaments

• Anterior longitudinal ligament

• Attaches to bony vertebrae and intervertebral discs • Prevents hyperextension

• Posterior longitudinal ligament • Narrow and relatively weak • Attaches to intervertebral discs Intervertebral Discs

• Are cushion-like pads between vertebrae

• Composed of

• Nucleus pulposus • Anulus fibrosus Intervertebral Discs

• Nucleus pulposus

• Gelatinous inner sphere

• Absorbs compressive stresses

• Anulus fibrosus

(16)

• Inner rings formed of fibrocartilage • Contain the nucleus pulposus General Structure of Vertebrae

• Common structures to all regions

• Body

• Vertebral arch • Vertebral foramen • Spinous process • Transverse process

• Superior and inferior articular processes • Intervertebral foramina

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Bones, Part 1:

The Axial Skeleton

Regions Vertebral Characteristics

• Specific regions of the spine perform specific functions • Types of movement that occur between vertebrae

• Flexion and extension • Lateral flexion

• Rotation in the long axis Cervical Vertebrae

• Seven cervical vertebrae (C1–C7)—smallest and lightest

vertebrae

• C3–C7 are typical cervical vertebrae • Body is wider laterally

• Spinous processes are short and bifid (except C7) • Vertebral foramen are large and triangular

• Transverse processes contain transverse foramina • Superior articular facets face superoposteriorly

The Atlas

(17)

• Lacks a body and spinous process • Supports the skull

• Superior articular facets receive the occipital condyles

• Allows flexion and extension of neck

• Nodding the head ―yes‖ The Axis

• Has a body and spinous process

• Dens (odontoid process) projects superiorly

• Formed from fusion of the body of the atlas with the axis • Acts as a pivot for rotation of the atlas and skull

• Participates in rotating the head from side to side

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Bones, Part 1:

The Axial Skeleton

Thoracic Vertebrae (T1—T12) • All articulate with ribs

• Have heart-shaped bodies from the superior view

• Each side of the body of T1–T10 bears demifacts for articulation

with ribs

• T1 has a full facet for the first rib • T10–T12 only have a single facet Thoracic Vertebrae

• Spinous processes are long and point inferiorly • Vertebral foramen are circular

• Transverse processes articulate with tubercles of ribs • Superior articular facets point posteriorly

• Inferior articular processes point anteriorly

• Allows rotation and prevents flexion and extension Lumbar Vertebrae (L1—L5)

• Bodies are thick and robust

• Transverse processes are thin and tapered

(18)

• Vertebral foramina are triangular

• Superior and inferior articular facets directly medially • Allows flexion and extension—rotation prevented

Sacrum (S1—S5)

• Shapes the posterior wall of pelvis • Formed from 5 fused vertebrae • Superior surface articulates with L5

• Inferiorly articulates with coccyx • Sacral promontory

• Where the first sacral vertebrae bulges into pelvic cavity

• Center of gravity is 1 cm posterior to sacral promontory • Ala—develops from fused rib elements

Sacrum

• Sacral foramina

• Ventral foramina

• Passage for ventral rami of sacral spinal nerves • Dorsal foramina

• Passage for dorsal rami of sacral spinal nerves Coccyx

• Is the ―tailbone‖

• Formed from 3—5 fused vertebrae

• Offers only slight support to pelvic organs

7

Bones, Part 1:

The Axial Skeleton

The Thoracic Cage

• Forms the framework of the chest • Components

• Thoracic vertebrae—posteriorly • Ribs—laterally

• Sternum and costal cartilage—anteriorly

(19)

• Supports shoulder girdle and upper limbs • Provides attachment sites for muscles

Sternum

• Formed from three sections

• Manubrium—superior section

• Articulates with medial end of clavicles • Body—bulk of sternum

• Sides are notched at articulations for costal cartilage of ribs 2– 7

• Xiphoid process—inferior end of sternum • Ossifies around age 40

Sternum

• Anatomical landmarks

• Jugular notch

• Central indentation at superior border of the manubrium • Sternal angle

• A horizontal ridge where the manubrium joins the body • Xiphisternal joint

• Where sternal body and xiphoid process fuse • Lies at the level of the 9th thoracic vertebra Ribs

• All ribs attach to vertebral column posteriorly

• True ribs - superior seven pairs of ribs • Attach to sternum by costal cartilage • False ribs—inferior five pairs of ribs • Ribs 11–12 are known as floating ribs Disorders of the Axial Skeleton

• Cleft palate

• A common congenital disorder

• Right and left halves of palate fail to fuse medially

• Stenosis of the lumbar spine

• Narrowing of the vertebral canal • Can compress roots of spinal nerves Disorders of the Axial Skeleton

(20)

• Scoliosis—an abnormal lateral curvature • Kyphosis—an exaggerated thoracic curvature

• Lordosis—an accentuated lumbar curvature; ―swayback‖ The Axial Skeleton Throughout Life

• Membrane bones begin to ossify in second month of development

• Bone tissue grows outward from ossification centers • Fontanels

• Unossified remnants of membranes Fontanelles

The Axial Skeleton Throughout Life

• Many bones of the face and skull form by intramembranous ossification

• Endochondral bones of the skull

• Occipital bone • Sphenoid • Ethmoid bones

• Parts of the temporal bone

The Axial Skeleton Throughout Life

• Aging of the axial skeleton

• Water content of the intervertebral discs decreases

• By age 55, loss of a few centimeters in height is common • Thorax becomes more rigid

• Bones lose mass with age

8

Bones,

Part 1: The Appendicular Skeleton

The Appendicular Skeleton

• Pectoral girdle

• Attaches the upper limbs to the trunk

• Pelvic girdle

(21)

• Upper and lower limbs differ in function

• Share the same structural plan The Pectoral Girdle

• Consists of the clavicle and the scapula

• Pectoral girdles do not quite encircle the body completely

• Medial end of each clavicle articulates with the manubrium and first rib

• Laterally—the ends of the clavicles join the scapulae • Scapulae do not join each other or the axial skeleton The Pectoral Girdle

• Provides attachment for many muscles that move the upper limb

• Girdle is very light and upper limbs are mobile

• Only clavicle articulates with the axial skeleton

• Socket of the shoulder joint (glenoid cavity) is shallow • Good for flexibility, bad for stability

Articulated Pectoral Girdle Clavicles

• Extend horizontally across the superior thorax • Sternal end articulates with the manubrium • Acromial end articulates with scapula

Clavicles

• Provide attachment for muscles • Hold the scapulae and arms laterally

• Transmit compression forces from the upper limbs to the axial skeleton

Scapulae

• Lie on the dorsal surface of the rib cage • Located between ribs 2–7

• Have three borders

• Superior

• Medial (vertebral) • Lateral (axillary)

(22)

• Lateral, superior, and inferior The Upper Limb

• 30 bones form each upper limb • Grouped into bones of the:

• Arm • Forearm • Hand Arm

• Region of the upper limb between the shoulder and elbow • Humerus

• The only bone of the arm

• Longest and strongest bone of the upper limb • Articulates with the scapula at the shoulder • Articulates with the radius and ulna at the elbow Arm

• Humerus

• Many structures of the humerus provide sites for muscle attachment

• Other structures of the humerus provide articulation sites for other bones

Forearm

• Formed from the radius and ulna

• Proximal ends articulate with the humerus • Distal ends articulate with carpals

Forearm

• Radius and ulna articulate with each other

• At the proximal and distal radioulnar joints

• The interosseous membrane

• Interconnects radius and ulna

• In anatomical position; the radius is lateral and the ulna is medial

Ulna

• Main bone responsible for forming the elbow joint with the humerus

(23)

• Hinge joint allows forearm to bend on arm

• Distal end is separated from carpals by fibrocartilage • Plays little to no role in hand movement

Proximal Part of the Ulna Radius and Ulna

Radius

• Superior surface of the head of the radius articulates with the

capitulum

• Medially—the head of the radius articulates with the radial

notch of the ulna

• Contributes heavily to the wrist joint

• Distal radius articulates with carpal bones • When radius moves, the hand moves with it Distal Ends of the Radius and Ulna

8

Bones,

Part 1: The Appendicular Skeleton

Hand

• Includes the following bones

• Carpus—wrist

• Metacarpals—palm • Phalanges—fingers Carpus

• Forms the true wrist—the proximal region of the hand • Gliding movements occur between carpals

• Composed of eight marble-sized bones

Carpus

• Carpal bones

• Are arranged in two irregular rows • Proximal row from lateral to medial

(24)

• Scaphoid, lunate, triquetral, and pisiform • Distal row from lateral to medial

• Trapezium, trapezoid, capitate, and hamate • A mnemonic to help remember carpals:

• Sally left the party to take Carmen home Bones of the Hand

Metacarpus

• Five metacarpals radiate distally from the wrist • Metacarpals form the palm

• Numbered 1–5, beginning with the pollex (thumb) • Articulate proximally with the distal row of carpals • Articulate distally with the proximal phalanges Phalanges

• Numbered 1–5, beginning with the pollex (thumb)

• Except for the thumb, each finger has three phalanges

• Proximal, middle, and distal

Bones of the Appendicular Skeleton Pelvic Girdle

• Attaches lower limbs to the spine • Supports visceral organs

• Attaches to the axial skeleton by strong ligaments

• Acetabulum is a deep cup that holds the head of the femur

• Lower limbs have less freedom of movement • Are more stable than the arm

Pelvic Girdle

• Consists of paired hip bones (coxal bones) • Hip bones unite anteriorly with each other • Articulates posteriorly with the sacrum

Bones of the Pelvic Girdle

• A deep, basin-like structure • Formed by:

(25)

The Pelvic Girdle

• Consists of three separate bones in childhood

• Ilium, ischium, and pubis

• Bones fuse, retain separate names to regions of the coxal bones

• Acetabulum

• A deep hemispherical socket on lateral pelvic surface Ilium

• Large, flaring bone

• Forms the superior region of the coxal bone • Site of attachment for many muscles

• Articulation with the sacrum forms sacroiliac joint

Ischium

• Forms posteroinferior region of the coxal bone • Anteriorly—joins the pubis

• Ischial tuberosities

• Are the strongest part of the hip bone Pubis

• Forms the anterior region of the coxal bone • Lies horizontally in anatomical position • Pubic symphysis

• The two pubic bones are joined by fibrocartilage at the midline

• Pubic arch—inferior to the pubic symphysis

• Angle helps distinguish male from female pelves Lateral and Medial Views of the Hip Bone

True and False Pelves

• Bony pelvis is divided into two regions

• False (greater) pelvis—bounded by alae of the iliac bones • True (lesser) pelvis—inferior to pelvic brim

• Forms a bowl containing the pelvic organs

8

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Part 1: The Appendicular Skeleton

Pelvic Structures and Childbearing

• Major differences between male and female pelves

• Female pelvis is adapted for childbearing

• Pelvis is lighter, wider, and shallower than in the male • Provides more room in the true pelvis

Female and Male Pelves The Lower Limb

• Carries the entire weight of the erect body

• Bones of lower limb are thicker and stronger than those of upper limb

• Divided into three segments

• Thigh, leg, and foot Thigh

• The region of the lower limb between the hip and the knee • Femur—the single bone of the thigh

• Longest and strongest bone of the body

• Ball-shaped head articulates with the acetabulum Structures of the Femur

Patella

• Triangular sesamoid bone

• Imbedded in the tendon that secures the quadriceps muscles • Protects the knee anteriorly

• Improves leverage of the thigh muscles across the knee

Leg

• Refers to the region of the lower limb between the knee and the ankle

• Composed of the tibia and fibula

• Tibia—more massive medial bone of the leg • Receives weight of the body from the femur • Fibula—stick-like lateral bone of the leg

• Interosseous membrane

(27)

Leg

• Tibia articulates with femur at superior end

• Forms the knee joint

• Tibia articulates with talus at the inferior end

• Forms the ankle joint

• Fibula does not contribute to the knee joint

• Stabilizes the ankle joint

Structures of the Tibia and Fibula The Foot

• Foot is composed of

• Tarsus, metatarsus, and the phalanges

• Important functions

• Supports body weight

• Acts as a lever to propel body forward when walking

• Segmentation makes foot pliable and adapted to uneven ground Tarsus

• Makes up the posterior half of the foot • Contains seven bones called tarsals

• Body weight is primarily borne by the talus and calcaneus • Trochlea of the talus

• Site of articulation with the tibia

• Other tarsals are:

• Cuboid and navicular

• Medial, intermediate, and lateral cuneiforms Metatarsus

• Consists of five small long bones called metatarsals • Numbered 1–5 beginning with the hallux

(great toe)

• First metatarsal supports body weight

Phalanges of the Toes

• 14 phalanges of the toes

• Smaller and less nimble than those of the fingers

• Structure and arrangement are similar to phalanges of fingers • Except for the great toe, each toe has three phalanges

(28)

Arches of the Foot

• Foot has three important arches

• Medial and lateral longitudinal arch • Transverse arch

• Arches are maintained by

• Interlocking shapes of tarsals • Ligaments and tendons

• ―Keystones‖ of arches

• Talus—medial longitudinal arch • Cuboid—lateral longitudinal arch Lower Limb and Pelvis

Disorders of the Appendicular Skeleton

• Bone fractures • Hip dysplasia

• Head of the femur slips out of acetabulum

• Clubfoot

• Soles of the feet turn medially

The Appendicular Skeleton Throughout Life

• Growth of the appendicular skeleton

• Increases height

• Changes body proportions

• Upper/lower body ratio changes with age

• At birth, head and trunk are 1.5 times as long as lower limbs • Lower limbs grow faster than the trunk

• Upper/lower body ratio of 1 to 1 by age 10 Changes in Body Proportions

The Appendicular Skeleton Throughout Life

• Few changes occur in adult skeleton until middle age, when

• Skeleton loses mass

• Osteoporosis and limb fractures become more common

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Joints

• Rigid elements of the skeleton meet at joints or articulations • Greek root ―arthro‖ means joint

• Structure of joints

• Enables resistance to crushing, tearing, and other forces Classifications of Joints

• Joints can be classified by function or structure

• Functional classification—based on amount of movement

• Synarthroses—immovable; common in axial skeleton

• Amphiarthroses—slightly movable; common in axial skeleton • Diarthroses—freely movable; common in appendicular skeleton

(all synovial joints) Classifications of Joints

• Structural classification based on

• Material that binds bones together • Presence or absence of a joint cavity • Structural classifications include

• Fibrous

• Cartilaginous • Synovial Fibrous Joints

• Bones are connected by fibrous connective tissue • Do not have a joint cavity

• Most are immovable or slightly movable • Types

• Sutures

• Syndesmoses • Gomphoses Sutures

• Bones are tightly bound by a minimal amount of fibrous tissue • Only occur between the bones of the skull

• Allow bone growth so the skull can expand with brain during childhood

• Fibrous tissue ossifies in middle age

(30)

Syndesmoses

• Bones are connected exclusively by ligaments • Amount of movement depends on length of fibers

• Tibiofibular joint—immovable synarthrosis

• Interosseous membrane between radius and ulna • Freely movable diarthrosis

Gomphoses

• Tooth in a socket

• Connecting ligament—the periodontal ligament

Fibrous Joints

Cartilaginous Joints

• Bones are united by cartilage • Lack a joint cavity

• Two types

• Synchondroses • Symphyses Synchondroses

• Hyaline cartilage unites bones

• Epiphyseal plates

• Joint between first rib and manubrium Symphyses

• Fibrocartilage unites bones; resists tension and compression • Slightly movable joints that provide strength with flexibility

• Intervertebral discs • Pubic symphysis

• Hyaline cartilage—present as articular cartilage

Symphyses Synovial Joints

• Most movable type of joint • All are diarthroses

• Each contains a fluid-filled joint cavity

(31)

• Articular cartilage

• Ends of opposing bones are covered with hyaline cartilage • Absorbs compression

• Joint cavity (synovial cavity)

• Unique to synovial joints

• Cavity is a potential space that holds a small amount of synovial fluid

General Structure of Synovial Joints

• Articular capsule—joint cavity is enclosed in a two-layered capsule

• Fibrous capsule—dense irregular connective tissue, which strengthens joint

• Synovial membrane—loose connective tissue

• Lines joint capsule and covers internal joint surfaces • Functions to make synovial fluid

• Synovial fluid

• A viscous fluid similar to raw egg white • A filtrate of blood

•

Arises from capillaries in synovial membrane

• Contains glycoprotein molecules secreted by fibroblasts

• Reinforcing ligaments

• Often are thickened parts of the fibrous capsule

• Sometimes are extracapsular ligaments—located outside the capsule

• Sometimes are intracapsular ligaments—located internal to the capsule

• Richly supplied with sensory nerves

• Detect pain

• Most monitor how much the capsule is being stretched General Structure of Synovial Joints

• Have a rich blood supply

• Most supply the synovial membrane

• Extensive capillary beds produce basis of synovial fluid • Branches of several major nerves and blood vessels

(32)

Synovial Joints with Articular Discs

• Some synovial joints contain an articular disc

• Occur in the temporomandibular joint and at the knee joint • Occur in joints whose articulating bones have somewhat

different shapes

9

Joints

How Synovial Joints Function

• Synovial joints—lubricating devices

• Friction could overheat and destroy joint tissue • Are subjected to compressive forces

• Fluid is squeezed out as opposing cartilages touch • Cartilages ride on the slippery film

Bursae and Tendon Sheaths

• Bursae and tendon sheaths are not synovial joints

• Closed bags of lubricant

• Reduce friction between body elements

• Bursa—a flattened fibrous sac lined by a synovial membrane • Tendon sheath—an elongated bursa that wraps around a

tendon

Bursae and Tendon Sheaths

Movements Allowed by Synovial Joints

• Three basic types of movement

• Gliding—one bone across the surface of another

• Angular movement—movements change the angle between bones

• Rotation—movement around a bone's long axis Gliding Joints

• Flat surfaces of two bones slip across each other

• Gliding occurs between

(33)

• Carpals • Articular processes of vertebrae • Tarsals Angular Movements

• Increase or decrease angle between bones • Movements involve

• Flexion and extension • Abduction and adduction • Circumduction

Rotation

• Involves turning movement of a bone around its long axis • The only movement allowed between atlas and axis vertebrae • Occurs at the hip and shoulder joints

Rotation

Special Movements

• Elevation—lifting a body part superiorly

• Depression—moving the elevated part inferiorly

• Protraction—nonangular movement anteriorly • Retraction—nonangular movement posteriorly

• Supination—forearm rotates laterally, palm faces anteriorly • Pronation—forearm rotates medially, palm faces posteriorly

• Brings radius across the ulna Special Movements

• Opposition—thumb moves across the palm to touch the tips of other fingers

9

Joints

(34)

• Inversion and eversion

• Special movements at the foot • Inversion—turns sole medially • Eversion—turns sole laterally Special Movements

• Dorsiflexion and plantar flexion

• Up-and-down movements of the foot

• Dorsiflexion—lifting the foot so its superior surface approaches the shin

• Plantar flexion—depressing the foot, elevating the heel Special Movements

Synovial Joints Classified by Shape

• Plane joint

• Articular surfaces are flat planes • Short gliding movements are allowed

• Intertarsal and intercarpal joints • Movements are nonaxial

• Gliding does not involve rotation around any axis Plane Joint

• Hinge joints

• Cylindrical end of one bone fits into a trough on another bone • Angular movement is allowed in one plane

• Elbow, ankle, and joints between phalanges

• Movement is uniaxial—allows movement around one axis only Hinge Joint

• Pivot joints

• Classified as uniaxial – rotating bone only turns around its long axis

(35)

• Proximal radioulnar joint • Joint between atlas and axis Pivot Joint

• Condyloid joints

• Allow moving bone to travel

• Side to side—abduction-adduction • Back and forth—flexion-extension

• Classified as biaxial—movement occurs around two axes Condyloid Joint

• Saddle joints

• Each articular surface has concave and convex surfaces • Classified as biaxial joints

• 1st carpometacarpal joint is a good example • Allows opposition of the thumb

9

Joints

• Ball-and-socket joints

• Spherical head of one bone fits into round socket of another • Classified as multiaxial—allow movement in all axes

• Shoulder and hip joints are examples Ball-and-Socket Joint

Factors Influencing Stability of Synovial Joints

• Articular surfaces

• Shapes of articulating surfaces determine movements possible • Seldom play a major role in joint stability

(36)

• Hip joint, elbow joint, and ankle

• Ligaments

• Capsules and ligaments prevent excessive motions

• On the medial or inferior side of a joint – prevent excessive abduction

• Lateral or superiorly located—resist adduction Factors Influencing Stability of Synovial Joints

• Ligaments (continued)

• Anterior ligaments—resist extension and lateral rotation • Posterior ligaments—resist flexion and medial rotation

• The more ligaments, usually stronger and more stable

• Muscle tone

• Helps stabilize joints by keeping tension on tendons • Is important in reinforcing:

• Shoulder and knee joints

• Supporting joints in arches of the foot Selected Synovial Joints

• Sternoclavicular joint

• Is a saddle joint

• Four ligaments surround the joint

• Anterior and posterior sternoclavicular ligaments • Interclavicular ligament

• Costoclavicular ligament

• Performs multiple complex movements Selected Synovial Joints

• Temporomandibular Joint

• Is a modified hinge joint

• The head of the mandible articulates with the temporal bone • Lateral excursion is a side-to-side movement

• Two surfaces of the articular disc allow • Hinge-like movement

(37)

9

Joints

Selected Synovial Joints

• Shoulder (glenohumeral) joint

• The most freely movable joint lacks stability • Articular capsule is thin and loose

• Muscle tendons contribute to joint stability Glenohumeral Joint

Glenohumeral Joint

• The rotator cuff is made up of four muscles and their associated tendons

• Subscapularis • Supraspinatus • Infraspinatus • Teres minor

• Rotator cuff injuries are common shoulder injuries

The Shoulder Joint The Shoulder Joint

• Elbow joint

• Allows flexion and extension

• The humerus’ articulation with the trochlear notch of the ulna forms the hinge

• Tendons of biceps and triceps brachii provide stability

Wrist Joint

• Stabilized by numerous ligaments

• Composed of radiocarpal and intercarpal joint

• Radiocarpal joint—joint between the radius and proximal carpals (the scaphoid and lunate)

(38)

circumduction

• Intercarpal joint—joint between the proximal and distal rows or carpals

• Allows for gliding movement Selected Synovial Joints

• Hip joint

• A ball-and-socket structure • Movements occur in all axes

• Limited by ligaments and acetabulum • Head of femur articulates with acetabulum

• Stability comes chiefly from acetabulum and capsular ligaments • Muscle tendons contribute somewhat to stability

• Knee joint

• The largest and most complex joint • Primarily acts as a hinge joint

• Has some capacity for rotation when leg is flexed • Structurally considered compound and bicondyloid • Two fibrocartilage menisci occur within the joint cavity

• Femoropatellar joint—shares the joint cavity

• Allows patella to glide across the distal femur Knee Joint

• Capsule of the knee joint

• Covers posterior and lateral aspects of the knee • Covers tibial and femoral condyles

• Does not cover the anterior aspect of the knee • Anteriorly covered by three ligaments

• Patellar ligament

• Medial and lateral patellar retinacula

Anterior View of Knee Knee Joint

• Ligaments of the knee joint

• Become taut when knee is extended

(39)

• Fibular and tibial collateral ligament • Oblique popliteal ligament

• Arcuate popliteal ligament Posterior View of Knee Joint Knee Joint

• Intracapsular ligaments

• Cruciate ligaments

• Cross each other like an ―X‖

• Each cruciate ligament runs from the proximal tibia to the distal femur

• Anterior cruciate ligament • Posterior cruciate ligament Anterior View of Flexed Knee Knee Joint

• Intracapsular ligaments

• Cruciate ligaments—prevent undesirable movements at the knee • Anterior cruciate ligament—prevents anterior sliding of the

tibia

• Posterior cruciate ligament—prevents forward sliding of the femur or backward displacement of the tibia

Stabilizing function of cruciate ligaments The “Unhappy Triad”

• Lateral blows to the knee can tear:

• Tibial collateral ligament and medial meniscus • Anterior cruciate ligament

The “Unhappy Triad” Selected Synovial Joint

• Ankle joint

• A hinge joint between

• United inferior ends of tibia and fibula • The talus of the foot

• Allows the movements

(40)

The Ankle Joint

• Medially and laterally stabilized by ligaments • Medial (deltoid) ligament

• Lateral ligament

• Inferior ends of tibia and fibula are joined by ligaments • Anterior and posterior tibiofibular ligaments

Disorders of Joints

• Structure of joints makes them prone to traumatic stress • Function of joints makes them subject to friction and wear • Affected by inflammatory and degenerative processes

Joint Injuries

• Torn cartilage—common injury to meniscus of knee joint • Sprains—ligaments of a reinforcing joint are stretched or torn • Dislocation—occurs when the bones of a joint are forced out

of alignment

Inflammatory and Degenerative Conditions

• Bursitis—inflammation of a bursa due to injury or friction • Tendonitis—inflammation of a tendon sheath

Inflammatory and Degenerative Conditions

• Arthritis—describes over 100 kinds of joint-damaging diseases

• Osteoarthritis—most common type of ―wear and tear‖ arthritis • Rheumatoid arthritis—a chronic inflammatory disorder

• Gouty arthritis (gout)—uric acid build-up causes pain in joints

• Lyme disease—inflammatory disease often resulting in joint pain

The Joints Throughout Life

• Synovial joints develop from mesenchyme

• By Week 8 of fetal development, joints resemble adult joints

• Outer region of mesenchyme becomes fibrous joint capsule • Inner region becomes the joint cavity

The Joints Throughout Life

• During youth—injury may tear an epiphysis off a bone shaft • Advancing age—osteoarthritis becomes more common

(41)

• Exercise—helps maintain joint health

10

Muscle Tissue

Muscle

• Muscle—a Latin word for ―little mouse‖ • Muscle is the primary tissue in the:

• Heart (cardiac MT)

• Walls of hollow organs (smooth MT)

• Skeletal muscle

• Makes up nearly half the body’s mass Overview of Muscle Tissue

• Functions of muscle tissue

• Movement

• Skeletal muscle—attached to skeleton

• Moves body by moving the bones

• Smooth muscle—squeezes fluids and other substances through hollow organs

Overview of Muscle Tissue

• Functions of muscle tissue (continued)

• Maintenance of posture—enables the body to remain sitting or standing

• Joint stabilization • Heat generation

• Muscle contractions produce heat

• Helps maintain normal body temperature Functional Features of Muscles

• Functional features

• Contractility

• Long cells shorten and generate pulling force • Excitability

• Electrical nerve impulse stimulates the muscle cell to contract • Extensibility

(42)

an opposing muscle • Elasticity

• Can recoil after being stretched Types of Muscle Tissue

• Skeletal muscle tissue

• Packaged into skeletal muscles • Makes up 40% of body weight • Cells are striated

Types of Muscle Tissue

• Cardiac muscle tissue—occurs only in the walls of the heart • Smooth muscle tissue—occupies the walls of hollow organs

• Cells lack striations

Similarities of Muscle Tissue

• Cells of smooth and skeletal muscle

• Are known as fibers

• Muscle contraction

• Depends on two types of myofilaments (contractile proteins) • One type contains actin

• Another type contains myosin

• These two proteins generate contractile force

Similarities of Muscle Tissues

• Plasma membrane is called a

sarcolemma

• Cytoplasm is called sarcoplasm

Skeletal Muscle

• Each muscle is an organ

• Consists mostly of muscle tissue • Skeletal muscle also contains

• Connective tissue • Blood vessels • Nerves

Basic Features of a Skeletal Muscle

• Connective tissue and fascicles

• Sheaths of connective tissue bind a skeletal muscle and its fibers together

(43)

• Epimysium—dense regular connective tissue surrounding entire muscle

• Perimysium—surrounds each fascicle (group of muscle fibers)

• Endomysium—a fine sheath of connective tissue wrapping each muscle cell

• Connective tissue sheaths are continuous with tendons

• When muscle fibers contract, pull is exerted on all layers of connective tissue are tendon

• Sheaths provide elasticity and carry blood vessels and nerves Connective Tissue Sheaths in Skeletal Muscle

• Nerves and blood vessels

• Each skeletal muscle supplied by branches of • One nerve

• One artery

• One or more veins

• Nerves and blood vessels (continued)

• Nerves and vessels branch repeatedly • Smallest nerve branches serve:

• Individual muscle fibers

• Neuromuscular junction—signals the muscle to contract Basic Features of a Skeletal Muscle

• Muscle attachments

• Most skeletal muscles run from one bone to another • One bone will move, other bone remains fixed

• Origin—less movable attachment • Insertion—more movable attachment Basic Features of a Skeletal Muscle

• Muscle attachments (continued)

• Muscles attach to origins and insertions by CT • Fleshy attachments—CT fibers are short

(44)

• Indirect attachments—CT forms a tendon or aponeurosis • Bone markings present where tendons meet bones

• Tubercles, trochanters, and crests Microscopic and Functional Anatomy of Skeletal Muscle Tissue

• The skeletal muscle fiber

• Fibers are long and cylindrical

• Are huge cells—diameter is 10–100µm

• Length—several centimeters to dozens of centimeters • Each cell formed by fusion of embryonic cells

• Cells are multinucleate

• Nuclei are peripherally located Diagram of Part of a Muscle Fiber Myofibrils and Sarcomeres

• Striations result from internal structure of myofibrils • Myofibrils

• Are long rods within cytoplasm • Make up 80% of the cytoplasm

• Are a specialized contractile organelle found in muscle tissue • Are a long row of repeating segments called sarcomeres

(functional unit of Skeletal MT) Sarcomere

• Basic unit of contraction of skeletal muscle

• Z disc (Z line)—boundaries of each sarcomere

• Thin (actin) filaments—extend from Z disc toward the center of the sarcomere

• Thick (myosin) filaments—located in the center of the sarcomere

• Overlap inner ends of the thin filaments • Contain ATPase enzymes

Sarcomere Structure

• A bands—full length of the thick filament

• Includes inner end of thin filaments

• H zone—center part of A band where no thin filaments occur • A bands and I bands refract polarized light differently

(45)

• A bands—anisotropic • I bands—isotropic

Sarcomere Structure (continued)

• M line—in center of H zone

• Contains tiny rods that hold thick filaments together

• I band—region with only thin filaments

• Lies within two adjacent sarcomeres Sarcomere Structure (continued)

Sarcoplasmic Reticulum and T Tubules

• Sarcoplasmic reticulum

• A specialized smooth ER

• Interconnecting tubules surround each myofibril

• Some tubules form cross-channels called terminal cisternae • Cisternae occur in pairs on either side of a

t tubule

Sarcoplasmic Reticulum and T Tubules

• Sarcoplasmic reticulum

• Contains calcium ions—released when muscle is stimulated to contract

• Calcium ions diffuse through cytoplasm • Trigger the sliding filament mechanism

• T tubules—deep invaginations of sarcolemma

• Triad—T tubule flanked by two terminal cisterns Mechanism of Contraction

• Two major types of contraction

• Concentric contraction—muscle shortens to do work

• Eccentric contraction—muscle generates force as it lengthens • Muscle acts as a ―brake‖ to resist gravity

• ―Down‖ portion of a pushup is an example Mechanism of Contraction

• Sliding filament mechanism

• Explains concentric contraction

• Myosin head attach to thin filaments at both ends of a sarcomere

(46)

• Then pull thin filaments toward the center of the sarcomere

• Thin and thick filaments do not shorten

• Initiated by release of calcium ions from the SR • Powered by ATP

Sliding Filament Mechanism

• Contraction changes the striation pattern

• Fully relaxed—thin filaments partially overlap thin filaments • Contraction—Z discs move closer together

• Sarcomere shortens

• I bands shorten, H zone disappears • A band remains the same length Microscopic and Functional Anatomy of Skeletal Muscle Tissue

• Muscle extension

• Muscle is stretched by a movement opposite that which contracts it

• Muscle fiber length and force of contraction

• Greatest force produced when a fiber starts out slightly stretched • Myosin heads can pull along the entire length of the thin

filaments The Role of Titin

• Titin—a spring-like molecule in sarcomeres

• Resists overstretching

• Holds thick filaments in place • Unfolds when muscle is stretched Innervation of Skeletal Muscle

• Motor neurons innervate skeletal muscle tissue

• Neuromuscular junction is the point where nerve ending and muscle fiber meet

• Axon terminals—at ends of axons • Store neurotransmitters

• Synaptic cleft—space between axon terminal and sarcolemma The Neuromuscular Junction

(47)

Motor Units

10

Muscle Tissue

Types of Skeletal Muscle Fibers

• Skeletal muscle fibers are categorized according to two characteristics

• How they manufacture energy (ATP) • How quickly they contract

• Oxidative fibers—produce ATP aerobically

• Glycolytic fibers—produce ATP anaerobically by glycolysis

• Skeletal muscle fibers

• Are divided into three classes • Slow oxidative fibers

• Red slow oxidative fibers

• Fast glycolytic fibers

• White fast glycolytic fibers

• Fast oxidative fibers

• Intermediate fibers

• Slow oxidative fibers

• Red color due to abundant myoglobin

• Obtain energy from aerobic metabolic reactions • Contain a large number of mitochondria

• Richly supplied with capillaries

• Contract slowly and resistant to fatigue • Fibers are small in diameter

• Fast glycolytic fibers

• Contain little myoglobin and few mitochondria • About twice the diameter of slow-oxidative fibers

• Contain more myofilaments and generate more power • Depend on anaerobic pathways

(48)

• Fast oxidative fibers

• Have an intermediate diameter

• Contract quickly like fast glycolytic fibers • Are oxygen-dependent

• Have high myoglobin content and rich supply of capillaries • Somewhat fatigue-resistant

• More powerful than slow oxidative fibers Disorders of Muscle Tissue

• Muscle tissues experience few disorders

• Heart muscle is the exception • Skeletal muscle

• Remarkably resistant to infection • Smooth muscle

• Problems stem from external irritants Disorders of Muscle Tissue

• Muscular dystrophy

• A group of inherited muscle destroying disease

• Affected muscles enlarge with fat and connective tissue • Muscles degenerate

• Types of muscular dystrophy

• Duchenne muscular dystrophy • Myotonic dystrophy

Disorders of Muscle Tissue

• Myofascial pain syndrome

• Pain is caused by tightened bands of muscle fibers

• Fibromyalgia

• A mysterious chronic-pain syndrome • Affects mostly women

• Symptoms—fatigue, sleep abnormalities, severe musculoskeletal pain, and headache

Muscle Tissue Throughout Life

• Muscle tissue develops from myoblasts

• Myoblasts fuse to form skeletal muscle fibers

(49)

Muscle Tissue Throughout Life

• Cardiac muscle

• Pumps blood three weeks after fertilization

• Satellite cells

• Surround skeletal muscle fibers

• Resemble undifferentiated myoblasts

• Fuse into existing muscle fibers to help them grow Muscle Tissue Throughout Life

• With increased age

• Amount of connective tissue increases in muscles • Number of muscle fibers decreases

• Loss of muscle mass with aging

• Decrease in muscular strength is 50% by age 80 • Sarcopenia—muscle wasting

11

Muscles of the Body

Muscles of the Body

• Skeletal muscles

• Produce movements

• Blinking of eye, standing on tiptoe, swallowing food, etc.

• General principles of leverage

• Muscles act with or against each other • Criteria used in naming muscles

Arrangement of Fascicles in Muscles

• Skeletal muscles—consist of fascicles

• Fascicles—arranged in different patterns

• Fascicle arrangement—tells about action of a muscle Arrangement of Fascicles in Muscles

• Types of fascicle arrangement

• Parallel—fascicles run parallel to the long axis of the muscle • Strap-like—sternocleidomastoid

(50)

• Convergent

• Origin of the muscle is broad

• Fascicles converge toward the tendon of insertion • Example—pectoralis major

• Pennate

• Unipennate—fascicles insert into one side of the tendon • Bipennate—fascicles insert into the tendon from both sides • Multipennate—fascicles insert into one large tendon from all

sides

• Circular

• Fascicles are arranged in concentric rings • Surround external body openings

• Sphincter—general name for a circular muscle • Examples

• Orbicularis oris and orbicularis oculi

Lever Systems: Bone-Muscle Relationships

• Movement of skeletal muscles involves leverage

• Lever—a rigid bar that moves • Fulcrum—a fixed point

• Effort—applied force • Load—resistance

• Bones—act as levers • Joints—act as fulcrums

• Muscle contraction—provides effort

• Applies force where muscle attaches to bone

• Load—bone, overlying tissue, and anything lifted

• Levers allow a given effort to

(51)

• Move a load farther

• Mechanical advantage

• Moves a large load over small distances

• Mechanical disadvantage

• Allows a load to be moved over a large distance Lever Systems: Bone-Muscle Relationships

• First-class lever

• Effort applied at one end • Load is at the opposite end

• Fulcrum is located between load and effort Lever Systems: Bone-Muscle Relationships

• Examples—seesaws, scissors, and lifting your head off your chest

• Second-class lever

• Effort applied at one end • Fulcrum is at the opposite end

• Load is between the effort and fulcrum

• Examples—wheelbarrow or standing on tiptoe • An uncommon type of lever in the body • Work at a mechanical advantage

• Third-class lever

• Effort is applied between the load and the fulcrum • Work speedily

• Always at a mechanical disadvantage

• Most skeletal muscles are third-class levers

• Example—biceps brachii • Fulcrum—the elbow joint

• Force—exerted on the proximal region of the radius • Load—the distal part of the forearm

Organization Scheme Based on Embryonic Development