Nervous System

(1)

Neuron

Nerve Circuit

PNS

Brain

(2)

Role of nervous system

▪ _{To transmit information rapidly}

▪ _{Information sent as electrical impulses}

through a nerve circuit

▪ _{Nerve circuit consists of neurons passing}

electrical messages to each other

▪ _{Electrical impulse is the way neuron}

(3)

The Neuron

▪ _{Nerve: a group of}

neurons bundled together

▪ _{Neuron: nerve cell}

▪ _{Mature neurons lose}

ability to undergo cell division

(4)

Components of a neuron

(5)

Components of a neuron

Component Description Function

Cell body Contain nucleus & organelles

Carries out basic cell functions

Dendrites

Multiple short, branched

extensions

Receives input from other neurons

Axon Single long

extension

(6)

Myelin Sheath

▪ _{Myelin sheath (lipid) insulates the axon}

▪ _{Not found on other parts of the neuron}

(7)

Fig. 48.2a

Dendrites

Cell body

Axon

Synaptic terminal

Neuron Function

▪ _{Conducts electrical impulses from dendrite}

(8)

Neuron Function

▪ _{Electrical impulse is sent from the axon of}

(9)

The Basic Nerve Circuit

1. Detection of stimulus

2. Processing in brain

3. Response in other part of body

Fig. 48.1

Sensory neurons

(10)

The Basic Nerve Circuit

2. Processing

Central Nervous System Brain and Spinal Cord

Peripheral Nervous System

1. Sensory Input 3. Motor Output

Effector cells

Involuntary muscle Voluntary muscle

Motor Neurons

External Senses Internal Senses

Sensory receptors

(11)

Components of the Nerve Circuit

Function Description Components

Sensory Input Detect stimulus Sensory receptors Sensory neurons

Processing Analyze

information Brain & spinal cord (CNS)

Motor Output

Response in body

(12)

Simplest type of nerve circuit

▪ _Reflex

▪ _{rapid, involuntary responses to stimuli}

▪ _{Processing of the stimulus}

▪ _{doesn’t happen in the brain} ▪ _{occurs in the spinal cord}

▪ _{processing of stimulus is faster}

▪ _{body responds automatically without “thinking”}

(13)

Examples of reflexes

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▪ _{Withdrawal (nociceptive) reflex}

▪ Knee-jerk (patellar) reflex

▪ Gag (pharyngeal) reflex

▪ _{Blink (corneal) reflex}

(14)

Peripheral Nervous System (PNS)

▪ _{Composed of all the neurons that}

communicate between the body and the

central nervous system (brain & spinal cord)

▪ _{Relays information:}

(15)

Organization of the PNS

Fig. 48.17

Peripheral Nervous System

(16)

Types of senses

▪ _{Sensing the external environment}

▪ _{Eyes: vision}

▪ _{Ears: hearing, equilibrium} ▪ _{Nose: smell}

▪ _{Tongue: taste}

▪ _{Skin: touch, temperature}

▪ _{Sensing the internal environment}

(17)

Sensory Receptors

▪ _{Detect a specific type of stimulus}

Examples Stimuli External Internal

Mechanoreceptors Pressure, movement

Skin,

muscles, ears

Blood vessels, stomach, lungs, bladder

Photoreceptors Light Eyes

Chemoreceptors Chemicals Nose, mouth Arteries Thermoreceptors Temperature Skin Organs

(18)

Organization of the PNS

Fig. 48.17

Peripheral Nervous System

(19)

Effector Cells

▪ _{Carries out body’s response to a stimulus} ▪ _{Voluntary system: sends signals to skeletal}

muscles

▪ _{Involuntary system: sends signals to smooth}

(20)

Central Nervous System (CNS)

▪ _{Composed of the brain and spinal cord}

▪ _{Protected by bone: skull and spine (vertebral}

column)

▪ _{Surrounded by cerebrospinal fluid (CSF):}

▪ _{Shock absorber (cushioning)} ▪ _{Transports chemicals}

(21)

Anatomy of the Brain

▪ _{2 hemispheres}

▪ _{4 lobes}

Left

hemisphere

Right

(22)

Brainstem

▪ _{connects brain to spinal cord}

(23)

Cerebellum

▪ _{Coordination of movement and balance}

▪ _{Example: hand-eye coordination}

Fig. 48.20

“little

(24)

Anatomy of the Brain

▪ _{Mostly highly evolved structure in}

mammalian brain

▪ _{Many folds to increase surface area}

(25)

4 Lobes of the Cerebrum

Fig. 48.24b

Frontal

• Integrate and process

information from other lobes

• Short-term memory

Temporal

• Hearing

• Long-term memory

(26)

Neurological Disorders

(27)

Parkinson’s Disease

▪ _{Progressive degenerative disorder of the CNS}

▪ _{Cause: inability to adequately produce a}

chemical (neurotransmitter) needed in impulse conduction

▪ _{Major symptoms:}

▪ _Tremors

▪ _{Muscle rigidity / Stiffness} ▪ _{Stooped posture}

▪ _{Slow movements}

(28)

Alzheimer’s Disease

▪ _{Progressive degenerative brain disease}

▪ _{Neurons deteriorate}

(29)

Cortex

▪ _{Motor skills}

▪ _{Ability to control}

the five senses

▪ _{Ability to retain}

(30)

Hippocampus

▪ _{Formation of new}

memories (amnesia)

▪ _{Retrieval of}

(31)

Due to large number of brain cell death, ventricles grow

(32)

Symptoms

▪ _{A form of dementia that causes problems}

with memory, thinking and behaviour

▪ _{Difficulty forming new memories} ▪ _{Disorientation}

▪ _{mood and behavior changes}

▪ _{deepening confusion about events, time and}

place

▪ _{unfounded suspicions about family, friends and}

(33)

What is Multiple Sclerosis?

▪ _{Multiple = many}

▪ _{Sclerosis = scars}

▪ _{Axons demyelinated}

▪ _{Axon withers}

▪ _{No electrical impulse}

▪ _{Lost myelin replaced}

with scar tissue:

▪ _{Blocks formation of new}

myelin

▪ _{Slows down electrical}

signals

(34)

Cause

▪ _{Idiopathic (no definite cause)}

▪ _{Suspected to be an autoimmune disease}

▪ _{Immune system views myelin sheath as foreign}

and attacks