Coordinates and regulates the function of all other body systems

2 major divisionCentral Nervous System (CNS)

Brain Spinal Cord

Peripheral Nervous System (PNS) Nerves

carry sensory info to the CNSMotor commands from CNS to muscles

2 types of cellsNeurons

transmit nerve impulses between parts of the nervous system

Neuroglia Support and nourish neurons Maintain homeostasis Form myelin Help in signal transmission

3 types of neuronsSensory neurons

Take messages to the CNS Sensory receptors detect changes in the

environment Interneuron

Receive input from the sensory neurons before communicate to motor neuron

Motor neuron Takes message away from CNS to rest of body

(organ, muscle or gland)

Fig. 17.1b

glands

brain

sensory neuronssensoryreceptors

motor neurons

skeletalmuscles

other motor neuronssmooth muscle

cardiac muscle

Peripheral nervous systemCentral nervous system

Anatomy of a neuronCell bodyDendrites

Receive signals from other neurons and send them to cell body

Axon Conducts nerve impulses away from the cell

body and send them toward other neurons

Myelin SheathFormed by Schwann Cells around the

axonGaps between Schwan Cells are called

nodes of Ranvier

Myelin Sheath gives nerves white colour

Helps protect and insulate the nerve Helps conduct nerve impulse

axon

node ofRanvier

myelin sheath

cell body

dendrites

Sensory neuron

direction ofconduction

axon

node of Ranviersensoryreceptor(in skin)

cell body

dendrites

axon

Interneuron

axon terminal

cell body

dendrites

Motor neuron

node of Ranvier

direction ofconduction

axon

nucleus ofSchwann cell

(neuroglial cell)

effector(muscle)

cell body

cell body

cell body

dendrites

dendrites

dendrites

Motor neuron

node of Ranvier

direction ofconduction

axon

effector(muscle)

Interneuron

axon terminal

Sensory neuron

direction ofconduction axon

node of Ranviersensoryreceptor

(in skin)

Nervous system uses a nerve impulse to send information

When an axon is not conducting a nerve impulse we call it at resting potential More negative inside the axon Positive outside the axon

Difference in polarity is due to ion concentrationMore Na+ ions outside the axonMore K+ ions inside the axon

Sodium-potassium pumps Actively transport Na+ out of axon and K+ into

axon 3 Na+ for every 2 K+

K+

Na+

+

recordingelectrodeInside axon

axonalmembrane

inside axon

outside axon

a. Resting potential: more Na+ outside the axon and more K+ inside the axon causes polarization.

gated K+

channel

referenceelectrodeoutside axon

gated Na+

channel

+ + + + + + + +

+

+

+ + + + + + + +

Action potential Rapid change in polarity across the axon Nerve impulse

During an action potential DEPOLARIZATION

Sodium channels open up Sodium enters the axon Axon becomes more positive

REPOLARIZATION Potassium gates open K+ moves outside of axon Axon returns to original negative charge

open Na+

channel

b. Action potential be gins: depolarization occurs when Na+ gates open and Na+ moves inside the axon.

direction of impulse

+

+ + + + + + + +

+

+

+ + + + + + + +

+

direction of impulse

open K+

channel

c. Action potential ends: repolarization occurs when K+ gates openand K+ moves outside the axon.

+

+ + + + + + + +

+

+

+ + + + + + + +

+

Refractory periodReturns K+ to the inside of cell and Na+

outside through pump returning the neuron to its normal polarized

state

Time (milliseconds)

Vo

ltag

e (m

V)

threshold

+60

+40

+20

0

–20

–40

–60

0

actionpotential

K+ movesto outsideaxon

Na+ movesto insideaxon

restingpotential

1 2 3 4 5 6

dep

ola

riza

tio

n

repo

larization

d. An action potential can be visualized if voltage changes aregraphed over time.

https://www.youtube.com/watch?v=7EyhsOewnH4