1. Nervous System

2. Nervous system
Coordinates and regulates the function of all other body systems
2 major division
Central Nervous System (CNS)
Brain
Spinal Cord
Peripheral Nervous System (PNS)
Nerves
carry sensory info to the CNS
Motor commands from CNS to muscles
Both systems are functionally distinct but they work together and are connected to each

3. Basic Divisions of the Nervous System

4. Nervous system 2 types of cells Neurons Neuroglia
transmit nerve impulses between parts of the nervous system
Neuroglia
Support and nourish neurons
Maintain homeostasis
Form myelin
Help in signal transmission

5. Neurons 3 types of neurons Sensory neurons Interneuron Motor neuron
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)
Sensory receptors are specialized endings that detect changes in the environment

6. Central nervous system Peripheral nervous system
Fig. 17.1b
brain
sensory neurons
sensory
receptors
motor neurons
skeletal
muscles
other motor neurons
smooth muscle
cardiac muscle
glands
Central nervous system
Peripheral nervous system

7. Neurons Anatomy of a neuron Cell body Dendrites Axon
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

8. Neurons Myelin Sheath Formed by Schwann Cells around the axon
Gaps between Schwan Cells are called nodes of Ranvier
Myelin Sheath gives nerves white colour
Helps protect and insulate the nerve
Helps conduct nerve impulse
Schwann cells wrap themselves around an axon

9. Neurons

10. axon
node of
Ranvier
myelin sheath

11. Sensory neuron
cell body
direction of
conduction
node of Ranvier
sensory
receptor
(in skin)
axon
dendrites

12. axon
cell body
Interneuron
dendrites
axon terminal

13. cell body
dendrites
Motor neuron
node of Ranvier
direction of
conduction
axon
nucleus of
Schwann cell
(neuroglial cell)
effector
(muscle)

14. Motor neuron node of Ranvier Interneuron effector (muscle)
cell body
dendrites
Motor neuron
node of Ranvier
direction of
conduction
axon
Interneuron
cell body
effector
(muscle)
dendrites
axon terminal
cell body
direction of
conduction
sensory
receptor
(in skin)
node of Ranvier
axon
Sensory neuron
dendrites

15. Nerve impulse 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
Electrical potential of a neuron

16. Nerve impulse Difference in polarity is due to ion concentration
More Na+ ions outside the axon
More K+ ions inside the axon
Sodium-potassium pumps
Actively transport Na+ out of axon and K+ into axon
3 Na+ for every 2 K+
Why there is a more positive charge outside compared to inside the neuron

17. reference
electrode
outside axon
recording
electrode
Inside axon + + + + + + + + + +          
axonal
membrane +          + + + + + + + +
inside axon K+
Na+
gated K+
channel
gated Na+
channel
outside axon
a. Resting potential: more Na+ outside the axon and more K+ inside
the axon causes polarization.

18. Nerve Impulse Action potential During an 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
Due to concentration gradient
Not Sodiium channels will close
Potassium opens and it becomes negative again inside the axon

19.   + + + + + + + + + +        
direction of impulse + +           + + + + + + + +
open Na+
channel
b. Action potential be gins: depolarization occurs when Na+ gates
open and Na+ moves inside the axon.

20. + +           + + + + + + + +
direction of impulse   + + + + + + + + + +        
open K+
channel
c. Action potential ends: repolarization occurs when K+ gates open
and K+ moves outside the axon.

21. Nerve Impulse Refractory period
Returns K+ to the inside of cell and Na+ outside through pump
returning the neuron to its normal polarized state

22. +60
+40
Na+ moves
to inside
axon
K+ moves
to outside
axon
action
potential
+20
depolarization
repolarization
Voltage (mV)
–20
–40
threshold
–60
resting
potential 1 2 3 4 5 6
Time (milliseconds)
d. An action potential can be visualized if voltage changes are
graphed over time.

23. Nerve impulse