Nervous System

Part 1

Chapter 17

Nervous System

Control System

3/24/2011 NS 3

Also a

Communication System

3/24/2011 NS 4

Pattern Of Control

stimulus - response

input - integration - output

3/24/2011 NS 5

Pattern Of Control

stimulus response

input - integration - output

3/24/2011 NS 6

3/24/2011 NS 7

Neurons

• the nervous system is made up of

two types of cells:

• neurons - irritable (responsive),

conductive

• glial cells - protective, supportive

& nourishing

3/24/2011 NS 8

Neuron Structure

3 main parts:

• dendrites - receiving area

• cell body - integrating area

• axon & terminals - sending area

3/24/2011 NS 9

Neuron Structure

3/24/2011 NS 10

Neuron Structure

• the nerve impulse or action potential is

the information sent from one nerve to

another

• it travels from the dendrites to cell

body to axon

3/24/2011 NS 11

Neuron Structure

• some neurons are “myelinated” and

some are not (unmyelinated)

• myelinated neurons have a fatty

myelin sheath around the axon

3/24/2011 NS 12

Neuron Structure

• myelinated axon

• myelin sheath

• node of Ranvier

3/24/2011 NS 13

Myelin Sheath

3/24/2011 NS 14

Classes Of Neurons

sensory (afferent) -

carry information

from sense organs

(eyes, ears) to CNS

3/24/2011 NS 15

3/24/2011 NS 16

Classes Of Neurons

e.g. optic nerve

auditory nerve

neurons carrying temperature

& pain sensations

• short axons

• long dendrites

3/24/2011 NS 17

Classes Of Neurons

• interneurons (association)

carry information between other

neurons inside the CNS

they often form tracts

3/24/2011 NS 18

Classes Of Neurons

e.g. corpus callosum,

spinal cord tracts

• short dendrites

• long or short

axons

3/24/2011 NS 19

Classes Of Neurons

• motor neurons (efferent)

carry information from the

CNS to the effector organs

(muscles & glands)

3/24/2011 NS 20

Classes Of Neurons

e.g. nerves to skeletal

muscles, viscera & glands

• short dendrites

• long axons

3/24/2011 NS 21

Impulse Or Action Potential

• neurons carry information

• neurons are arranged in pathways

• impulses travel along the pathways

from one neuron to another neuron

3/24/2011 NS 22

3/24/2011 NS 23

3/24/2011 NS 24

Resting Membrane Potential

• electrical event

• difference in charge across the resting

cell axon membrane (- 60 to -70mv

inside)

3/24/2011 NS 25

Resting Membrane Potential

3/24/2011 NS 26

Resting Membrane Potential

• +ve sodium ions outside

• +ve potassium &

-ve proteins inside

3/24/2011 NS 27

Resting Membrane Potential

• Na/K pump keeps ion balance

3/24/2011 NS 28

Resting Membrane Potential

3/24/2011 NS 29

Ion Movements Across

Resting Neuron Membrane

3/24/2011 NS 30

Action Potential

• stimulus to nerve causes

• an electrical change which travels down

the axon due to

• Na+ moving in then

• K+ moving out

3/24/2011 NS 31

Action Potential

• Depolarization – change in charge across neuron membrane from –60 mv to + 40 mv inside

• Repolarization – restoration of membrane back to resting level of – 60 mv inside

• Threshold Potential – level of depolarization that must be reached to trigger an action potential

3/24/2011 NS 32

Action Potential

4

3/24/2011 NS 33

Resting Membrane Potential

3/24/2011 NS 34

Depolarization Begins

3/24/2011 NS 35

Depolarization Ends

Repolarization Begins

3/24/2011 NS 36

Repolarization Complete

3/24/2011 NS 37

Action Potential

• Action Potential

3/24/2011 NS 38

Action Potential

3/24/2011 NS 39

Action Potential

2 parts:

upswing down swing

depolarization repolarization

3/24/2011 NS 40

Action Potential

2 parts:

upswing down swing

Na+ inflow K+ outflow

depolarization repolarization

3/24/2011 NS 41

Action Potential

• Na+/K+ pump in membrane

• pumps the Na+ out & the

• K+ in after the action potential is over

3/24/2011 NS 42

Action Potential

• the depolarization at one point of the

membrane acts as a

• stimulus for the next point on the

membrane which then depolarizes

and so on down the membrane

3/24/2011 NS 43

Refractory Period

• the period following one stimulus when

the neuron cannot respond to another

stimulus

• so each action potential is a separate

event

3/24/2011 NS 44

Action Potential

• the action potential is

ALL OR NONE - it either happens fully

or not at all

- it cannot be partial

3/24/2011 NS 45

Nerve Conduction Speed

• larger, myelinated axons conduct

faster by

• “saltatory conduction” where action

potential jumps from node to node

3/24/2011 NS 46

Saltatory Conduction

3/24/2011 NS 47

Synapse

• information passes from one neuron

to another

• across synapses using

• chemical transmitters

• synapses are one way only

3/24/2011 NS 48

Synapse• a synapse can be between

• 2 neurons or between a

• neuron & its effector organ

• it is at synapses that mood

altering drugs affect

the nervous system

3/24/2011 NS 49

Synapse

• neuron -

neuron

synapse

• axon terminal

3/24/2011 NS 50

3/24/2011 NS 51

Summation & Integration

• all sensory input to the neuron cell body

at any time is added together or

“summated”

• if there is enough stimulation an action

potential will be triggered

3/24/2011 NS 52

Neurotransmitters

• acetyl choline (ACh) -

destroyed by cholinesterase

• nor-adrenaline

(nor- epinephrine) - destroyed by

monoamine oxidase (MAO)

3/24/2011 NS 53

Neurotransmitters

3/24/2011 NS 54

Neurotransmitters

• low nor- epinephrine (adrenaline) levels

• are linked with

3/24/2011 NS 55

Neurotransmitters

• can be

excitatory e.g. ACh, norepinephrine,

serotonin or

inhibitory e.g. GABA & glycine

3/24/2011 NS 56

• there are also naturally occurring

• painkillers or opiates - such as

those which give a “runner’s

high”

Neurotransmitters

3/24/2011 NS 57

Nervous System - Structure

2 regions:

• central nervous system

- brain & spinal cord

• peripheral nervous system

- everything else…..

3/24/2011 NS 58

Organization Of The Nervous

System

CNS PNS

brain cranial nerves*

(12 pairs)

spinal spinal nerves*

cord (31 pairs)

* and associated ganglia

3/24/2011 NS 59

Ganglia & Nuclei

Collections of neuron cell bodies in the:

• CNS - nuclei (gray matter)

3/24/2011 NS 60

Ganglia & Nuclei

• PNS - ganglia (spinal ganglia &

autonomic ganglia)

3/24/2011 NS 61

Spinal Cord

• central canal filled with CSF

• outer white matter - myelinated tracts

• inner gray matter - cell bodies &

unmyelinated tracts

3/24/2011 NS 62

Spinal Cord Functions

• reflex centre part of the spinal reflex

arc

• communication between the brain &

the peripheral nervous system

(many tracts )

3/24/2011 NS 63

Spinal Cord• spinal reflex

ventral

root

dorsal

root

interneuron

3/24/2011 NS 64

Brain

• ventricles

• white matter (tracts)

• gray matter ( nuclei & tracts)

• different functions in different areas

3/24/2011 NS 65

Brain - Cerebrum

Prefrontal

lobe

3/24/2011 NS 66

Brain

3/24/2011 NS 67

Brain & Spinal Cord

• hollow - filled with cerebrospinal fluid (CSF)

• covered with 3 membranes –

• meninges

• both are protective

& supportive

3/24/2011 NS 68

Parts Of The Brain

(from highest to lowest)

• cerebral hemispheres

(4 lobes)

• diencephalon

(thalamus/hypothalamus)

• limbic system

• cerebellum

3/24/2011 NS 69

Parts Of The Brain

(from highest to lowest)

brain stem

• midbrain

• pons

• medulla oblongata

• reticular formation

(in brain stem)

3/24/2011 NS 70

Structure Of Cerebrum• 2 hemispheres joined by the corpus

callosum

• basal ganglia help control skeletal

muscles

3/24/2011 NS 71

Structure Of Cerebrum

4 lobes

1) frontal

2) parietal

3) temporal

4) occipital

3/24/2011 NS 72

4 lobes

Brain Functions

3/24/2011 NS 73

Cerebral Cortex

• outer layer of the

cerebrum = the cortex

• gray matter

• motor, sensory and

association areas

3/24/2011 NS 74

Cerebral Cortex

3/24/2011 NS 75

1) frontal - motor control &

highest mental functions

2) parietal - skin senses

e.g. pain, touch, temperature

Brain Functions

3/24/2011 NS 76

Brain Functions

3) temporal - sound & smell,

sensory interpretation

4) occipital - sight

3/24/2011 NS 77

Brain Functions

Cerebrum (cerebral

hemispheres)

• highest functions

e.g. memory, learning,

perception, awareness

3/24/2011 NS 78

Brain Functions

Diencephalon

• thalamus - sensory filter

• hypothalamus - homeostasis

(many functions)

e.g. hunger, body temperature

3/24/2011 NS 79

Brain Functions

Cerebellum

• balance , posture

3/24/2011 NS 80

Brain Functions

Brain Stem –

sensory & motor tracts, reticular

formation

• midbrain - nuclei e.g. (balance)

• pons - respiratory centres

• medulla - vital centres

3/24/2011 NS 81

Brain Functions

• reticular formation

network which contains the

• Reticular Activating System

which controls alertness/sleep

3/24/2011 NS 82

Chapter 17: Part 1

Internet Resources:

• http://yucky.kids.discovery.com/noflash/body/pg000136.html

• http://users.tpg.com.au/users/amcgann/body/nervous.html

• http://faculty.washington.edu/chudler/introb.html

• http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/C/CNS.html

• http://www.bartleby.com/107/183.html