B17 ns03part1

transcript

Nervous System

Part 1

Chapter 17

Nervous System

Control System

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Also a

Communication System

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Pattern Of Control

stimulus - response

input - integration - output

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Pattern Of Control

stimulus response

input - integration - output

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Neurons

• the nervous system is made up of

two types of cells:

• neurons - irritable (responsive),

conductive

• glial cells - protective, supportive

& nourishing

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Neuron Structure

3 main parts:

• dendrites - receiving area

• cell body - integrating area

• axon & terminals - sending area

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Neuron Structure

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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

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Neuron Structure

• some neurons are “myelinated” and

some are not (unmyelinated)

• myelinated neurons have a fatty

myelin sheath around the axon

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Neuron Structure

• myelinated axon

• myelin sheath

• node of Ranvier

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Myelin Sheath

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Classes Of Neurons

sensory (afferent) -

carry information

from sense organs

(eyes, ears) to CNS

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Classes Of Neurons

e.g. optic nerve

auditory nerve

neurons carrying temperature

& pain sensations

• short axons

• long dendrites

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Classes Of Neurons

• interneurons (association)

carry information between other

neurons inside the CNS

they often form tracts

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Classes Of Neurons

e.g. corpus callosum,

spinal cord tracts

• short dendrites

• long or short

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Classes Of Neurons

• motor neurons (efferent)

carry information from the

CNS to the effector organs

(muscles & glands)

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Classes Of Neurons

e.g. nerves to skeletal

muscles, viscera & glands

• short dendrites

• long axons

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Impulse Or Action Potential

• neurons carry information

• neurons are arranged in pathways

• impulses travel along the pathways

from one neuron to another neuron

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Resting Membrane Potential

• electrical event

• difference in charge across the resting

cell axon membrane (- 60 to -70mv

inside)

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• +ve sodium ions outside

• +ve potassium &

-ve proteins inside

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• Na/K pump keeps ion balance

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Ion Movements Across

Resting Neuron Membrane

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Action Potential

• stimulus to nerve causes

• an electrical change which travels down

the axon due to

• Na+ moving in then

• K+ moving out

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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

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Action Potential

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Depolarization Begins

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Depolarization Ends

Repolarization Begins

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Repolarization Complete

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Action Potential

• Action Potential

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Action Potential

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Action Potential

2 parts:

upswing down swing

depolarization repolarization

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Action Potential

2 parts:

upswing down swing

Na+ inflow K+ outflow

depolarization repolarization

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Action Potential

• Na+/K+ pump in membrane

• pumps the Na+ out & the

• K+ in after the action potential is over

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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

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Refractory Period

• the period following one stimulus when

the neuron cannot respond to another

stimulus

• so each action potential is a separate

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Action Potential

• the action potential is

ALL OR NONE - it either happens fully

or not at all

- it cannot be partial

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Nerve Conduction Speed

• larger, myelinated axons conduct

faster by

• “saltatory conduction” where action

potential jumps from node to node

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Saltatory Conduction

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Synapse

• information passes from one neuron

to another

• across synapses using

• chemical transmitters

• synapses are one way only

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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

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Synapse

• neuron -

neuron

synapse

• axon terminal

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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

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Neurotransmitters

• acetyl choline (ACh) -

destroyed by cholinesterase

• nor-adrenaline

(norepinephrine) - destroyed by

monoamine oxidase (MAO)

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Neurotransmitters

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Neurotransmitters

• low norepinephrine (adrenaline) levels

• are linked with

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Neurotransmitters

• can be

excitatory e.g. ACh, norepinephrine,

serotonin or

inhibitory e.g. GABA & glycine

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• there are also naturally occurring

• painkillers or opiates - such as

those which give a “runner’s

high”

Neurotransmitters

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Nervous System - Structure

2 regions:

• central nervous system

- brain & spinal cord

• peripheral nervous system

- everything else…..

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Organization Of The Nervous

System

CNS PNS

brain cranial nerves*

(12 pairs)

spinal spinal nerves*

cord (31 pairs)

* and associated ganglia

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Ganglia & Nuclei

Collections of neuron cell bodies in the:

• CNS - nuclei (gray matter)

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Ganglia & Nuclei

• PNS - ganglia (spinal ganglia &

autonomic ganglia)

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Spinal Cord

• central canal filled with CSF

• outer white matter - myelinated tracts

• inner gray matter - cell bodies &

unmyelinated tracts

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Spinal Cord Functions

• reflex centre part of the spinal reflex

• communication between the brain &

the peripheral nervous system

(many tracts )

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Spinal Cord• spinal reflex

ventral

dorsal

interneuron

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• ventricles

• white matter (tracts)

• gray matter ( nuclei & tracts)

• different functions in different areas

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Brain - Cerebrum

Prefrontal

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Brain & Spinal Cord

• hollow - filled with cerebrospinal fluid (CSF)

• covered with 3 membranes –

• meninges

• both are protective

& supportive

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Parts Of The Brain

(from highest to lowest)

• cerebral hemispheres

(4 lobes)

• diencephalon

(thalamus/hypothalamus)

• limbic system

• cerebellum

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Parts Of The Brain

(from highest to lowest)

brain stem

• midbrain

• pons

• medulla oblongata

• reticular formation

(in brain stem)

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Structure Of Cerebrum• 2 hemispheres joined by the corpus

callosum

• basal ganglia help control skeletal

muscles

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Structure Of Cerebrum

4 lobes

1) frontal

2) parietal

3) temporal

4) occipital

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4 lobes

Brain Functions

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Cerebral Cortex

• outer layer of the

cerebrum = the cortex

• gray matter

• motor, sensory and

association areas

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Cerebral Cortex

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1) frontal - motor control &

highest mental functions

2) parietal - skin senses

e.g. pain, touch, temperature

Brain Functions

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Brain Functions

3) temporal - sound & smell,

sensory interpretation

4) occipital - sight

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Brain Functions

Cerebrum (cerebral

hemispheres)

• highest functions

e.g. memory, learning,

perception, awareness

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Brain Functions

Diencephalon

• thalamus - sensory filter

• hypothalamus - homeostasis

(many functions)

e.g. hunger, body temperature

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Brain Functions

Cerebellum

• balance , posture

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Brain Functions

Brain Stem –

sensory & motor tracts, reticular

formation

• midbrain - nuclei e.g. (balance)

• pons - respiratory centres

• medulla - vital centres

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Brain Functions

• reticular formation

network which contains the

• Reticular Activating System

which controls alertness/sleep

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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

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