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Chapter 6 The Muscular System Be Able To


Academic year: 2020

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Chapter 6 The Muscular System

Be Able To

• Describe the similarities and differences in the structure and function of the three types of muscle tissue.

• Explain the role of endomysium,

perimysium, epimysium, tendon, and aponeurosis.


Overview of Muscle Tissue

• Muscles are responsible for essentially all body movements because of their ability to contract or shorten.

• Muscle cells are called fibers because they are elongated.

• The ability to contract depends on myofilaments.

• Skeletal muscle tissue is made of long, striated, multinucleate, muscle fibers

controlled voluntarily.

• Cardiac muscle tissue is made of spirally arranged striated muscle fibers controlled involuntarily by the heart.

• Smooth muscle tissue is made of single nucleated spindle-shaped fibers with no striations that are controlled involuntarily such as in the visceral organs.

Match the muscle fiber to the muscle.


Gross Anatomy of Skeletal Muscle

• Each skeletal muscle fiber is

enclosed in a delicate connective tissue sheath called an


• Several muscle fibers are organized in bundles called a fascicle which are covered by a fibrous membrane

called a perimysium.

• Fascicles are bound together in a

dense fibrous connective tissue called the epimysium, which surrounds the entire muscle.

• The deep fascia is a sheet of fibrous connective tissue that binds muscles together.

• The epimysium blend into a strong cordlike tendon or aponeuroses that attach muscles to bone, cartilage, or other connective tissue coverings.


Muscle Functions

1) Skeletal movements are

responsible for all locomotion and manipulation, whereas cardiac muscle is responsible for the beating of the heart and smooth muscle is responsible for

squeezing materials through tubes.

2) Skeletal muscles maintain body posture.

3) Skeletal muscles stabilize joints.

4) Muscles generate body heat.

• Functionally muscles are

excitable, contractile, extendable, and elastic.

How do muscle help these triathletes finish their race?


Chapter 6 The Muscular System

Be Able To

• Describe the microscopic structure of skeletal muscle.

• Explain the role of actin- and

myosin-contracting myofilaments.


Microscopic Anatomy of a Skeletal Muscle Fiber

• The plasma membrane of a skeletal muscle fiber is

called the sarcolemma.

• Its cytoplasm or

sarcoplasm contains high amounts of glycogen and myoglobin, which is a red pigment that stores oxygen in muscle fibers.

• There are hundreds to thousands of rodlike myofibrils in a single muscle fiber.


Microscopic Anatomy of a Skeletal Muscle Fiber

• The dark bands or A bands polarize visible light.

• The light bands or I bands are nonpolarizing.

• Each A band has a lighter stripe in the middle called the H zone.

• Each H zone is bisected by a dark M line.

• The I bands are interrupted in the middle by a dark Z disc.

• A sarcomere is a region of a myofibril between two

successive Z discs.

• Sarcomeres are the smallest

contractile units of a muscle fiber


Microscopic Anatomy of a Skeletal Muscle Fiber

• Within the sarcomere are thick central filaments that extend the entire length of the A band and thin lateral filaments the extend across the I band and part of the A band.

• The Z disc is a protein sheet that anchors thin filaments and connects each myofibril to the next.

• Thick filaments are composed of myosin which has a head and tail.

• The heads or cross bridges link the thick and thin myofilaments during contraction.

• The heads contain ATP binding sites and ATPase enzymes.


Microscopic Anatomy of a Skeletal Muscle Fiber

• Thin filaments are composed of actin.

• Actin bears active sites for the myosin cross bridges.

• Tropomyosin is a rod-shaped protein on the actin core that inhibits the binding of the

myosin heads.

• Another protein called

Troponin helps bind calcium ions required for contraction.

• The sarcoplasmic reticulum regulates intracellular levels of calcium by storing and releasing on demand.


Chapter 6 The Muscular System

Be Able To

• Describe how an action potential is initiated.

• Describe the events of muscle contraction.

• Define graded response, tetanus,

isotonic and isometric contractions, and muscle tone.

• Describe 3 ways in which ATP is regenerated during muscle activity.


Skeletal Muscle Activity:

Stimulation and Contraction of Single Skeletal Muscle Cells

• Skeletal muscle cells must be stimulated by nerve

impulses to contract.

• A motor unit is one neuron and all of the skeletal

muscle cells it stimulates.

• junctions between axonal terminals and the

sarcolemma are

neuromuscular junctions.

• The gap at this junction is the synaptic cleft.


Skeletal Muscle Activity:

The Nerve Stimulus and Action Potential

• The neurotransmitter acetylcholine or ACh stimulates muscle cells.

• ACh, released by the axonal

terminals, binds to receptors on the sarcolemma.

• Large amounts of ACh increase the permeability of the sarcolemma for Na+.

• An increase in positive charge

generates an unstoppable electrical current across the sarcolemma

called an action potential which results in contraction.

• The cell returns to rest by (1) K+ ions diffusing out and (2) the Na-K pump returning the cell to initial conditions.

Motor unit


Skeletal Muscle Activity:

the sliding filament theory

• Upon stimulation, cross bridges attach to binding sites on thin actin filaments.

• ATP energizes the cross bridges to attach and detach several times

during contraction.

• This coordinated event occurs along the entire length of the muscle fiber resulting in shortening of the muscle.

• Binding requires Ca+, and upon

nerve stimulation the sacroplasmic reticulum releases stored Ca+ in the sarcoplasm.

• During relaxation Ca+ is reabsorbed.

• A single nerve impulse produces one contraction.

Relaxed muscle

Myosin heads bind to actin

Myosin heads “springs the trap”


Skeletal Muscle Activity:

contraction of a skeletal muscle as a whole

• Muscles, not muscle cells, react to stimuli in different degrees of shortening also known as a

graded response.

• Graded muscle contractions occur by changing: (1) the

frequency of muscle stimulation or (2) the number of muscle

cells stimulated.

• Complete tetanus or tetanic contraction occurs through rapid stimulation with no

evidence of relaxation.

• The role of tetanus is to create smooth sustained contractions.


Chapter 6 The Muscular System

Be Able To

• Describe 3 ways in which ATP is regenerated during muscle activity.

• Define oxygen debt and muscle fatigue and list the possible causes of muscle fatigue.

• Describe the effects of aerobic and resistance exercise on skeletal muscles of other body


• Demonstrate different types of body movements.


Skeletal Muscle Activity:

Providing Energy for Muscle Contraction

• Muscles only supply 4-6

seconds of ATP, therefore it must be regenerated


• Working muscles regenerate ATP in 3 pathways:

1) Creatine phosphate or CP transfers a phosphate to ADP

making ATP (20 sec supply of CP).

2) Aerobic respiration generates 36 ATP molecules from glucose.

3) Glycolysis and and lactic acid fermentation (poor source of ATP).

Where do world class sprinters get their ATP from?


Skeletal Muscle Activity:

muscle fatigue and oxygen debt

• A muscle is fatigued when it is unable to contract even though it is still being


• During oxygen debt, a

person is unable to to take in oxygen fast enough.

• An increase muscle acidity and lack of ATP causes the muscles to contract less


• How do you pay back your oxygen debt?


Skeletal Muscle Activity:

types of muscle contraction

• Isotonic contractions produce

shortened muscles, e.g. bending of the knee.

• Isometric contractions do not

produce shortening of the muscles, instead they produce tension.

• Muscle tone is a state of continuous partial contractions.

• Muscles that do not receive stimuli eventually atrophy.

• Aerobic exercise produce stronger, more flexible, and less resistance to fatigue muscles.

• Resistance training increases muscle size and strength.

Which one is more fit?


Skeletal Muscle Activity:

Types of Body Movements

• The origin of a muscle is the

attachment site to an immovable or less movable bone.

• The insertion point of a muscle is the site of attachment to a movable bone.

• During muscle contraction the insertion moves toward the origin.

• Common types of body movement:

1) Flexion brings two bones together

2) Extension increases distance between two bones

3) Rotation movement around

4) Abduction movement away from midline.

5) Adduction movement toward midline

6) Circumduction combination of movements common in ball-and-socket joints.

Triceps extension exercise


Skeletal Muscle Activity:

Special Body Movements

1) Dorsiflexion and plantar flexion e.g.

lifting up and pushing down the foot at the ankle.

2) Inversion and eversion e.g. turn sole medially and laterally.

3) Supination (turning back) and pronation (turning forward) .

4) Opposition e.g.

touching the thumb to other fingers.

Pronation Supination


Types of Muscles

• The prime mover is the muscle that has the major responsibility for a particular movement.

• Antagonists are muscles that oppose or reverse a movement.

• Synergists help prime movers by

producing the same movement or reducing an undesirable movement.

• Fixators are specialized synergists that hold a bone still.

• Muscles are named by:

1) Direction of muscle fibers 2) Relative size

3) Location

4) Number or origins

5) Location of insertion and origin 6) Shape

7) action Muscles can only pull.


Chapter 6 The Muscular System

Be Able To

• Identify the major muscles of the human body and state their action.


Gross Anatomy of Skeletal Muscles

Head and Neck Muscles

• Facial muscles permit facial expressions.

• Chewing muscles or muscles of

mastication physically broken down food.

Facial Muscles

• Frontalis covers the frontal bone running from the cranial aponeurosis to the skin of eyebrows for wrinkling of the forehead.

• Orbicularis Oculi fibers run in circles around the eyes for blinking, squinting, and winking.

• Orbicularis Oris is the circular muscle of the lips that allows closing of the mouth.

• Buccinator runs horizontally across the cheek and inserts into the orbicularis oris for flattening of the cheek, e.g. whistling.

• Zygomaticus extends from corner of the mouth to the cheekbone and allows


Locate the facial muscles on this diagram

Cranial aponeurosis


Gross Anatomy of Skeletal Muscles

Head and Neck Muscles

Muscles of Mastication

• Masseter covers the lower jaw from the zygomatic process of the temporal bone to the mandible for closing the jaw.

• Temporalis overlies the temporal bone and is a synergist for closing the jaw.

Neck Muscles

• Platysma is a single sheetlike muscle covering the anterolateral neck originating in the chest and inserting into the area

around the mouth producing downward sag of the mouth.

• Sternocleidomastoid are paired muscles on each side of neck arising from the

clavicle and sternum and inserting into the mastoid process of the temporal bone both acting to flex the neck or rotation.

Locate the neck muscles and muscles of mastication on this



Gross Anatomy of Skeletal Muscles

Head and Neck Muscles









Gross Anatomy of Skeletal Muscles

Trunk Muscles

Anterior Muscles

• Pectoralis major or pecks cover the upper chest and originate from the shoulder girdle and the first 6 ribs and inserts into the proximal end of the humerus and acts to adduct and flex the arm.

• Intercostal muscles are

the deep muscles of the ribs that depress the rib cage to move air out of the lungs.

Some move the vertebral column, ribs, head, and arms; abdominal muscles form the girdle of the abdominal wall.


Gross Anatomy of Skeletal Muscles

Trunk Muscles

Muscles of the Abdominal Girdle

Rectus Abdominis are paired superficial

muscles that run from the pubis to the rib cage to flex the vertebral column and compress the abdominal contents for defecation and


External obliques are paired superficial

muscles that run posteriorly and medially from the last 8 ribs to insert at the ilium to flex the vertebral column and to rotate and bend laterally.

Internal Obliques are paired deep muscles that run at right angles to the external obliques and originate from the iliac crest and insert into the last 3 ribs.

Transverse Abdominis is the deepest muscles of the abdominal wall and run horizontally

across the abdomen by originating from the lower ribs and inserting into the pubis for compression of abdominal contents.

Fibers of each muscle or pair run in different



Gross Anatomy of Skeletal Muscles

Posterior Muscles

• Trapezius muscle originate from the occipital bone and cervical & thoracic vertebrae and insert into the scapular spine and clavicle where they extend the head and aid in scapular movement.

• The paired latissumus dorsi are large flat muscles covering the lower back that

originate on the lower spine and ilium and insert at the proximal humerus and are important for moving the arm downward.

• Erector spinae group are deep muscles of the back that are the prime movers of back extension.

• The longissimus, iliocostalis, and

spinalis span the length of the vertebral column and provide resistance for bending at waist.

• Deltoid muscles are triangular shaped muscles of the shoulder that originate at the scapular spine & clavicle and insert at the deltoid tuberosity of the humerus

where it abducts the arm.




Gross Anatomy of Skeletal Muscles

Muscles of the Upper Limbs Muscles of the Humerus

• Biceps brachii originates by two heads from the shoulder girdle and insert into the radial tuberosity to act as prime movers for flexion of the forearm.

• Brachialis lies deep to the biceps muscle where its origin at the distal humerus and insertion at the coronoid process of the ulna acts in forearm flexion.

• The brachioradialis originates at the distal end of the humerus and inserts a the styloid process of the radius and acts as a synergist of forearm flexion.

• The triceps brachii has three heads that

originate at the scapula, posterior and medial head of the humerus and inserts at the

olecranon fossa for forearm extension.




Gross Anatomy of Skeletal Muscles

Muscles of the Lower Limbs

• Cause movement at the hip, knee, and foot joints.

• Longest & strongest specialized for walking and balance.

• Muscles of thigh are massive to act against gravity.

• Thigh muscles cross the knee and cause flexion and extension.

• Various muscles with origins on the leg cause assorted

movements and the ankle and toe joints.


Gross Anatomy of Skeletal Muscles

Muscles at hip joint

• Gluteus maximus is the largest and most superficial muscle of the buttock; origin in sacrum and iliac bones and insertion on gluteal tuberosity of femur; action hip extensor and extremely important for climbing and jumping.

• Gluteus medius is a thick muscle covered largely by gluteus maximus; origin on ilium and insertion on greater trochanter of

femur; action hip abductor and important for steadying pelvis during walking.

• Iliopsoas is a fused muscle composed of the lilacus and psoas major; origins on iliac bone and lower vertebrae and

insertion on lesser trochanter of femur;

action prime mover for hip flexion and keeps body upright when standing.

The adductor group have origins on pelvis and insertion on proximal femur and adduct or

press thighs together.





Gross Anatomy of Skeletal Muscles

Muscles at knee joint

• Hamstrings are the 3 fleshy muscles of the posterior thigh that cross both the hip and knee joints.

• The hamstrings are prime movers of thigh extension and knee flexion.

• Name comes from old butchers’ practice of using the tendons of this group to hang hams for


• Hamstrings are composed of the biceps femoris, semimebranosus, and semitendinosus.

• Biceps femoris has 2 heads and is the most lateral of the group.

• Semitendinosus is largely a tendon and lies medial to biceps femoris.

• Semimembranosus is deep to the semitendinosus.



Gross Anatomy of Skeletal Muscles

Muscles at knee joint

• Sartorius is a thin straplike muscle that is the most superficial of the thigh; origin anterior iliac crest insertion medial side of tibia; action weal thigh flexor.

• Quadriceps group consists of four muscles.

• As a whole act to extend the knee powerfully.

• Rectus femoris is the most superficial and runs straight down the leg from the pelvis.

• Vastus lateralis forms lateral thigh and is used for intramuscular injections in


• Vastus medialis forms inferomedial thigh.

• Vastus intermedius lies between lateralis and medialis.

All quads insert into the tibial tuberosity via the patellar





Gross Anatomy of Skeletal Muscles

Muscles at ankle and foot

• Tibialis anterior is a superficial muscle of the anterior leg; origin upper tibia

insertion tarsal bones; action dorsifexes and inverts the foot.

• Extensor digitorum longus is lateral to the tibialis anterior; origin lateral tibial condyle and proximal fibula insertion

phalanges of toes 2-5; action prime mover of toe extension and dorsiflexion of foot.

• Fibularis muscles are composed of the peroneus tertius, brevis, and longus;

origin fibula insertion metatarsals; action flexes and everts foot.





Gross Anatomy of Skeletal Muscles

Muscles at ankle and foot

• Gastrocnemius is a superficial posterior lower leg pair; origin one each side of distal femur insertion through calcaneal

tendon; action prime mover for plantar flexion of foot.

• Soleus is deep to the

gastrocnemius on posterior calf;

origin superior tibia and fibula insertion calcaneal tendon;

action strong plantar flexor of foot.


Developmental Aspects of the Muscular System

• Muscular dystrophy is an inheritable disease that enlarges specific muscle groups due to fat and connective tissue deposits and degeneration of muscle fibers.

• Duchenne muscular dystrophy inflicts primarily male children between 2-6

years of age.

• The disease spreads from the extremities upward and by age 12 most are wheel chair bound until their death.

• Observing a baby’s muscle control indirectly tests their nervous system.

• Myasthenia gravis is a rare muscular adult disease that involves a shortage of Ach receptors ultimately leading to death.


Deep Muscles of the Torso

Rhomboideus minor Atlas #5 Pg 84

– Origin is the posterior end of spinous process of C7 through T1

– Insertion is the vertebral border of the scapula at the medial end of the scapular spine

– Action is to retract the shoulder and rotate downward Building:

– Refer to the Atlas

– form a tube of clay long enough to reach the attachments

– Roll the tube flat with a roller and place the piece of clay over the area where the muscle will be located

– Cut the pattern of the shape of the muscle with your wooden knife and remove the clay and cut out portion of the muscle.

– Place the muscle to its attachments

* You should be able to look underneath this muscle


Deep Muscles of the Torso

Rhomboideus major Atlas #5 Pg 86

– Origin spinous process of vertebrae T2 through T5 – Insertion medial border of the scapula

– Action is to retract the shoulder and rotate downward


– Refer to the atlas

– Build this muscle as you did with the Rhomoideus minor muscle except this muscle is much wider


Deep Muscles of the Torso

Levetator Scapula Atlas #5 Pg 90

– Origin transverse process of vertebrae C1 through C4

– Insertion superior medial border of the scapula

– Action elevates scapula and/or bends the neck and rotates the head “shrugging”


– Refer to the atlas

– This muscle is a flat ribbon of clay and it rotates from its attachments to the neck vertebrae


Deep Muscles of the Torso

Quadratus Lumborum Atlas #5 Pg 60

– Origin transverse processes of L1 through L4 and lower marging of 12 rib

– Insertion iliac crest of pelvic bone

– Action flexes vertebral column laterally Building:

– Refer to the atlas

– Modify the distal attachment to end before the hip screw for now.


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