Chapter 8: Nervous System

The most complex organ system

1

Three General Functions:

Sensory, Integrative, and Motor

1) Sensory function

Sensory receptors at ends of peripheral neurons

gather info by detecting change

External: light, sound

Internal: temperature, oxygen

Convert info into nerve impulses

2

Three General Functions:

Sensory, Integrative, and Motor

2) Integrative Functions:

When sensory impulses become

perceptions

Signals brought together

Added to memory

3

Three General Functions:

Sensory, Integrative, and Motor

3) Motor function: used to act on the

conscious or subconscious decisions

resulting from integrative functions

- peripheral neurons carry impulses from CNS

to effectors = muscles and glands that respond

to stimulation

4

5

Two Major Divisions

1) Central Nervous System (CNS)

Brain and spinal cord

Integrates and coordinates processing of

sensory info

Transmits motor commands

Higher functions:

Intelligence

Memory

Emotions 6

Two Major Divisions

2) Peripheral nervous

system (PNS)

All neural tissue outside

of CNS

7

Two Divisions of PNS

1) Afferent – takes info from PNS to CNS

Info detected by receptors

af = to

ferre = carry

2) Efferent – CNS sends motor commands to

PNS

To muscles and glands (effectors)

ef = from

8

See p. 248!

Get to know the

info on this!

9

Efferent Division:

Motor Commands - 2 Types

1) Somatic Nervous System

Consciously controlled

Controls skeletal muscles

2) Autonomic Nervous System

Involuntary

Controls heart, smooth muscle b. vessels,

various glands

Maintains homeostasis

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Divisions of Autonomic NS

1) Sympathetic – prepares body for energy

expending, stressful, or emergency situations

“flight or fight”

Ex: increases breathing and heart rates

2) Parasympathetic – operates under normal

control

Brings body back to normal after emergency

“rest and digest”

12

Types of Cells

1) Neuron – basic units within system

Essential for communication

Most can NOT divide

2) Neuroglia – “glia” or glial cells

Most CAN divide

Outnumber neurons

13

Neuron Structure – 3 common

characteristics

1) Cell Body

2) Dendrites

3) Axon

See p. 249,

251, 252

Diagrams

* Test*

14

3 Common Characteristics

1) Cell Body

Contains nucleus and other

organelles but:

Most have no centrioles. . .

Meaning???

No movement of organelles

during mitosis . . .

Meaning????

NO cell division . . .

Meaning????

Can NOT be replaced!

Uh oh.

15

1) Cell Body

Nissl bodies –

clusters of RER

and ribosomes

“Chromatophilic

substance”

Give gray color to

cell bodies

Account for gray

matter in CNS 16

3 Common Characteristics

2) Dendrites

Short, highly branched

Main receptive surface

Sensitive to chemical,

mechanical, and

electrical stimulation

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3 Common Characteristics

3) Axon

Originates as single

structure

May branch =

collaterals

Directs nerve

impulses AWAY

from cell body

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3) Axon

Axon hillock –

thickened region of

cell body

Action potential begins

here

Synaptic (axon)

terminal – tips of

axons

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I like this diagram . . . FYI ;)

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Neural Stem Cells

Cells can divide

Typically inactive

except in nose and

in hippocampus

(part of brain)

Being studied

Why are these

important? 22

Structural Classification of Neurons

1) Bipolar

2 processes

One on each end

1 = axon

1 = dendrite

Rare

Ex: Eyes, nose, ears

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Structural Classification of Neurons

2) Unipolar

Single process extending from cell body

Peripheral process = branches into dendrites

Central Process = axon

Most PNS sensory neurons

Form in ganglia- masses of neuron cell bodies

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Structural Classification of Neurons

3) Multipolar

One process is axon

All other processes

dendrites

Most neurons in CNS

All those that interact

with skeletal muscle

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Functional Classification of Neurons

1) Sensory = afferent

Carry impulses from PNS to CNS

Get info from sensory receptors

Triggered by external or internal changes

Most are unipolar, some bipolar

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Functional Classification of Neurons

2) Interneurons = association

In CNS

Multipolar

Link other neurons

More complex = more neurons

Distribute sensory info

Coordinate motor activity

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Functional Classification of Neurons

3) Motor neurons

Multipolar

Carry nerve impulses out of CNS to effectors

Stimulate muscle contraction (somatic) and

gland secretion (visceral)

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Diagram like that on p. 248!

Important!

Drawing on board; not in book

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Neuroglial cells = Neuroglia

Fill spaces

Support neurons

Structural framework

Produce myelin

Fatty material that covers some nerve fibers

Phagocytosis

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4 Types of neuroglial cells (CNS)

1) Microglial Cells

Scattered in CNS

Support neurons

Phagocytize bacteria

and cellular debris

Smallest and rarest

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4 Types of Neuroglial cells

(CNS)

2) Oligodendrocytes

In rows along nerve

fibers

Form myelin sheaths

(insulating layers)

around axons w/in

CNS

33

4 Types of Neuroglial Cells

(CNS) 3)Astrocytes

B/w neurons and blood

vessels

Structural support

Join cellular processes

Secrete chemicals that

help protect CNS

Repair damage

Form scar tissue

Largest

Most numerous

34

4 Types of Neuroglial Cells

(CNS)

4) Ependymal Cells

Form epithelial-like

membrane (ependyma)

Some produce

cerebrospinal fluid

(CSF)

Line central canal of spinal

cord and ventricles of brain

Cover choroid plexuses

Form lining of spaces w/in

CNS

35

Neuroglial Cells (PNS)

Two types:

1) Schwann Cells

Form myelin sheath

around axons in PNS

Cover every axon in

PNS

2) Satellite cells

Surround and support

neuron cell bodies

36

Myelinated Axons in PNS

Enclosed in sheaths of Schwann cells

Myelin sheath- Inner layer

made of myelin (lipoprotein)

Neurilemma – outer surface of Schwann cell

surrounds myelin sheath

mostly of cytoplasm and nuclei

outer living layer

Axons in PNS can often regenerate

37

Myelinated Axons in CNS

Appear glossy white = white matter

Myelinated by oligodendrocytes

no neurilemma (outer living layer)

Usually do NOT regenerate

Nodes of Ranvier – gaps between myelin coverings

38

Unmyelinated Axons

No myelin around axon

In CNS groups of unmyelinated axons and

neuron cell bodies form gray matter

39

8.3 Cell membrane potential

Cell membrane surface usually polarized =

electrically charged

Positive and negative charges are held apart

Excess negative charge on inside of cell

membrane

Important for conducting nerve impulses

40

Ions

Potassium ions (K+) pass thru membrane more

easily than sodium (Na+)

Potassium major contributor of membrane polarization

Calcium (Ca 2+) ions cross less easily than

potassium or sodium (Na+)

41

42

Resting Potential

Separation of charge (potential difference)

Due to active transport: high concentration

of Sodium ions outside cell, and high

concentration of potassium ions inside

Inside = excess negative charge

Outside more positive charge

43

Potential Change

Nerve cells = excitable = respond to

changes in environment (stimuli)

Stimuli affect resting potential

44

Potential Change:

Depolarization

Occurs when resting potential decreases

Inside of cell membrane becomes less negative

compared to outside of membrane

45

Potential Change

Threshold

Result of summative stimulation

Each subpotential is added to next until

threshold is reached

Ion channels open; Sodium ions diffuse freely

inward and cause Action Potential

46

Action Potential

Occurs when a series of subthreshold

stimuli summate and reach threshold

A rapid sequence of events

Also called a nerve impulse

47

Nerve Impulse

48

Action Potential

Sodium ions diffuses inward, membrane

loses negative charge (becomes

depolarized)

At same time, potassium ion channels open

and allow potassium ions to leave the cell

and membrane becomes repolarized

Resting potential is established

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Action Potential

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Nerve Impulse

Conducted as action potential is reached

Spreads by current flowing down fiber

New areas reach action potential

51

Local Anesthetics

Decrease membrane permeability to

Sodium ions

Prevents impulse from passing thru affected

region

No sensation of touch or pain

52

Impulse conduction

Unmyelinated axon – conduct over entire

membrane surface

Myelinated axon – conduct from Node of

Ranvier to Node of Ranvier

Much faster

53

Nerve Impulse

Larger diameter of axon = faster conduction

of impulse!

54

All-or-None Response

If neuron responds = completely

Greater intensity of stimulation = more impulses per

second NOT stronger impulse

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8.4 Neuronal Pool

Within CNS

Groups of connected neurons that work

together to perform a common function

Receive input

Generate output

56

Convergence

Axons from various locations come

together at the same neuron in CNS

Allows info to be collected, processed, and

responded to in a special way

57

Divergence

In CNS

Axon of one neuron may stimulate two or

more other neurons

Spreads the impulse to many neurons

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Convergence / Divergence

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Nerve Axon = “Nerve Fiber”

Nerve = bundle of nerve fibers

Remember:

Muscle fiber = entire cell

Nerve fiber = neuron axon only

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3 Types of Nerves:

1) Sensory – conduct impulses into CNS

2) Motor - carry impulse to muscle or gland

3) Mixed – sensory and motor together

= most nerves

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8.9 Nerve Pathway

Route of nerve impulse as it travels through nervous system

Reflex Arc – simplest pathway

Few neurons

Constitutes a Reflex

automatic, subconscious

response to stimuli changes (internal or external)

62

Reflex

Help maintain homeostasis

Heart rate

Breathing rate

Blood pressure

Digestion

Automatic actions

Swallowing

Sneezing

Coughing

Vomiting

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Knee-jerk reflex (Patellar reflex)

Simple reflex

2 neurons

Sensory

Patellar tendon is striked

Motor

Quadraceps is stimulated, contracts

64

Knee jerk reflex

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Withdrawal Reflex

Occurs when unexpected touch of hot or painful substance

Skin receptors send impulse to spinal cord

Impulse passes to interneurons

Then Directed to motor neurons

Cause muscle to contract, hand to withdraw

At same time, other interneurons stimulated

Become aware; may experience pain

*Protective!

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8.5 The Meninges

Membranes

Between bone and soft tissue of CNS

Protect brain and spinal cord

3 layers

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3 Layers of Meninges

1) Dura mater

“hard” “mother”

Outermost

Tough, white, fibrous connective tissue

Many blood vessels and nerves

2 layers

Outer layer is fused to periosteum of skull

Inner layer hold brain in position

In vertebral column:

surrounds spinal cord

Not fused to bone here 69

3 Layers of Meninges

Epidural space – bw dura mater

and bony wall of vertebral canal

Protection

Contains:

Loose connective tissue

Adipose tissue

Blood vessels

Where epidural block is given

70

Epidural Space

71

Epidural Block

Produces temporary

sensory and motor

paralysis

Affects only nerves by

injection site

72

3 Layers of Meninges

2) Arachnoid Mater

Thin, web-like

membrane

No blood vessels

Between dura and pia

maters

Does not dip into

grooves

73

3 Layers of Meninges

Subarachnoid space

Between arachnoid

and pia maters

Contains

cerebrospinal fluid

(CSF)

Clear, watery fluid

74

CSF

Surrounds brain and spinal

cord

In subarachnoid space

Support and protection

Maintains stable ion

concentration in CNS

Pathway for blood to rid

wastes

Pressure usually constant

75

3 Layers of Meninges

3) Pia Mater

“delicate” “mother”

Very thin

Many nerves and blood

vessels

Nourishes cells of brain

and spinal cord

Hugs surfaces; follows

high and low areas

76

Interesting Fact:

At REST, the 3.1

pound brain uses as

much oxygen as 61.6

pounds of skeletal

muscle!!!!!!!!!!!!!

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78

8.6 Spinal Cord

Slender nerve column

Begins at foramen

magnum

Ends between L1 and

L2

~ 18 in. long

79

Spinal Cord Structure and

Function

31 segments

Each contains pair of

spinal nerves

1) conduct nerve

impulses

2) center for spinal

reflexes

80

8.7 The Brain

Largest, most complex part

of nervous sys.

Weighs ~ 3 lbs

98% of neural tissue in body

About 100 billion multipolar

neurons

Males’ generally larger

Size NOT correlated to

intelligence

81

The Brain

6 major regions:

1) Cerebrum

2) Diencephalon

3) Midbrain

4) Pons

5) Medulla Oblongata

6) Cerebellum

82

Cerebrum Structure

Cerebrum = largest part

2 cerebral hemispheres connected by corpus callosum = deep bridge of nerve fibers

On surface:

Gyri = convolutions = ridges

Grooves that separate ridges = Sulci

shallow groove

Fissure = deep groove

Longitudinal – separates R and L hemispheres

Transverse – separates cerebrum from cerebellum 83

Cerebrum Function

Sensory and motor

function

Higher mental function:

memory and reasoning

personality

84

Lobes of Cerebrum

Named after bones

1) Parietal

2) Frontal

3) Temporal

4) Occipital

5) Insula

* diagrams p. 270, 271 important!

85

Label Handout and keep in notes:

86

Add information to worksheet:

87

Cerebral Cortex Structure

Thin layer of gray matter

Outermost portion of cerebrum

Thick “blanket” that covers lateral and superior

surfaces

Contains 75% of all neuron cell bodies in

Nervous system

Mind games

88

Cerebral Cortex Function

Functions overlap:

1) Motor – controls movement

2) Sensory – creates feelings and sensations

Touch, pressure, pain, temp

3) Association – analyze and interpret

sensory experience

Oversees memory, verbalizing, judgment,

emotion

89

Functional regions of cerebral

cortex:

Motor: Broca’s area

motor speech area

Frontal eye field

Sensory: Visual area (in occipital lobe)

Auditory (in temporal lobe)

Association: Parietal, frontal, temporal, occipital lobes

General Interpretive areal – complex thought processing Where parietal, temporal, and occiptial lobes

meet 90

91

Hemispheric Lateralization

92

Each ½ responsible for specific functions

Still function as a unit; not independent of each

other

Left

Reading, writing, speaking

Analytical tasks: math, logic

Right

Nonverbal functions, spatial relationships

Ex: facial recognition, emotion, 3-D objects

Hemispheric Lateralization

90% dominant = left

Lots of musicians

and artists are left-

handed

What might this

mean?

93

Corpus Callosum

White nerve

fibers connecting

hemispheres

>200 million

axons

4 billion

impulses/second!

94

Brain Song

Brain parts song 2 min

Brain parts 3 min

95

Electroencephalogram

EEG

Used to diagnose brain

disorders

Record of electrical

activity of brain

Brain waves

4 types

See p. 274

96

Clinical Death

Flat EEG

Could a

person still

function?

97

Limbic System

Functional grouping, not

anatomical

Establishes emotions

Links conscious functions

with unconscious functions

Stores and retrieves long term

memories

Alzheimer’s patients have

problems with this part

*Makes you WANT to do

things

98

Ventricles

Cavities within brain stem

and cerebral hemisphere

Contain CSF

Choroid plexuses –

extend into ventricle and

secrete CSF

Capillary masses from pia

mater

99

Spinal Tap (lumbar puncture)

Used to check for presence

of abnormal cells,

microorganisms, color,

and/or pressure of CSF

Hollow, fine needle

inserted into subarachnoid

space bw 3rd and 4th or 4th

and 5th lumbar vertebrae

WHY here????

100

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Diencephalon

Surrounds 3rd ventricle

Between cerebral hemispheres

Above midbrain

102

Diencephalon

Contains:

Epithalamus

Contains pineal gland – secretes melatonin

Thalamus – sorts and directs sensory info

Coordinates motor commands

Hypothalamus – maintains homeostasis by regulating

Heart rate, body temp

Water, hormone, and electrolyte balances

Hunger, weight, growth, reproduction, sleep

103

Diencephalon

104

Brainstem

Consists of:

1) midbrain – just below

diencephalon

2) pons – middle; bulges

3) medulla oblongata –

connects brain with spinal

cord

105

Reticular Formation

Scattered throughout

brainstem

Regulates sleep and wake

cycle

Low activity = sleep

High activity = awake

Damage can result in a coma

106

Parkinson Disease

Controlled by midbrain nuclei

Become more active

Increase in muscle tone

Muscle groups don’t relax

Hard to start voluntary movements

Takes extreme effort and

concentration

107

Cerebellum

Coordinates skeletal muscle activity and position

Mostly white matter

If damaged: (ex: stroke)

Tremors

loss of balance, control of voluntary movement, muscle tone

Awkward walk

Ataxia – disturbance in balance

Alcohol affects this region

108

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8.8 PNS

Made of cranial and spinal nerves that arise in CNS and travel to rest of body

Divisions:

1) somatic = connect CNS to skin and skeletal muscle

Conscious activity

2) autonomic = connect CNS to viscera (heart, stomach, etc)

Unconscious activity

110

Cranial nerves

12 pairs, all numbered and named

Most are mixed nerves

Communicate w/ head, neck and trunk

1st pair arises from underside of cerebellum

All others from brainstem or diencephalon

111

112

Spinal Nerves

31 pairs

Names

correspond with

vertebral column

113

8.12 Aging

114

Changes begin around age 30

Accumulate

Reduction in:

Brain size and weight

# of neurons

Blood flow

Synaptic connections

Increase in abnormal proteins

in cells

Affects: hearing, smell, sight,

reactions, and reflexes

Alzheimer Disease

Loss of cerebral function:

Memory

Verbal and reading skills

Emotional control

Causes senility

Normally appears around age

50-60

15% in US over 65

~100,000 deaths per year

No cure

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