1. Biology Powerpoint #3 Unit 8 – Chapter 35
Nervous System
Biology
Powerpoint #3
Unit 8 – Chapter 35

2. Structures of the Nervous System:
Brain
Spinal Cord
Peripheral Nerves: Neurons

3. Function of Nervous System:
Coordinates the body’s response to changes in its internal and external environments.

4. 1. The Central Nervous System
Relays messages, processes information and analyzes information.
Brain
Spinal Cord

5. 2. Peripheral Nervous System:
Sensory Division: transmits impulses from sense organs to central nervous system.
What are sense organs?
Organs designed to pick up stimuli.

6. Peripheral Nervous System:
Motor Division: transmits impulses from the central nervous system to muscles.
Network of Neurons makes up the peripheral Nervous System.

7. Neurons Structure and Conduction of a Nerve Impulse

8. Basic Organization Sensory Input triggered by stimuli Integration
sensory receptor (sensory input)  integration  (motor output)  effector
Sensory Input triggered by stimuli
conduction of signals to brain
Integration
interpretation of sensory signals by brain
Motor output
conduction of signals to effector cells (i.e. muscles, gland cells)

9. Neuron
Dendrite - conducts “signal” toward the cell body -- [input zone]
often short, numerous & highly branched
signal comes from sensory cell or neighboring neuron
Axon - usually a single fiber -- [conducting zone]
conducts signal away from cell body to another neuron or effector cell
Axon Ending
a cluster of branches (100’s to 1000’s)
relays signal to next neuron / effector cell

10. How a nerve impulse is transmitted
1) Resting - The neuron is POLARIZED.
There is a slightly negative charge on the inside, and a positive charge on the outside
The outside contain excess Na+ (sodium)
The inside contain excess K+ (potassium)
This balance is maintained by the sodium-potassium pump

11. Cells have voltage! – – + +
Opposite charges on opposite sides of cell membrane
membrane is polarized
negative inside; positive outside
charge gradient
stored energy (like a battery) +
This is an imbalanced condition.
The positively + charged ions repel each other as do the negatively - charged ions. They “want” to flow down their electrical gradient and mix together evenly.
This means that there is energy stored here, like a dammed up river.
Voltage is a measurement of stored electrical energy. Like “Danger High Voltage” = lots of energy (lethal). – – +

12. How a nerve impulse is transmitted
2) Action Potential - stimulus causes opening of Na+ gates & closing of K+ gates, allowing Na+ to rush in
This changes the neuron from polarized to de- polarized
This is all-or-none, meaning a stimulus must exceed a threshold for the action potential to occur

13. How does a nerve impulse travel?
Stimulus: nerve is stimulated
reaches threshold potential
open Na+ channels in cell membrane
Na+ ions diffuse into cell
charges reverse at that point on neuron
positive inside; negative outside
cell becomes depolarized – +
Na+

14. How does a nerve impulse travel?
Wave: nerve impulse travels down neuron
change in charge opens next Na+ gates down the line
“voltage-gated” channels
Na+ ions continue to diffuse into cell
“wave” moves down neuron = action potential
Gate + –
channel closed
channel open – +
Na+
wave 

15. How a nerve impulse is transmitted
3) Repolarization – K+ moves outside, Na+ stays inside
4) Refractory period – When the Na+/K+ balance returns to normal
During this time the neuron will not respond to new impulses

16. How does a nerve impulse travel?
Re-set: 2nd wave travels down neuron
K+ channels open
K+ channels open up more slowly than Na+ channels
K+ ions diffuse out of cell
charges reverse back at that point
negative inside; positive outside + –
Na+ K+
wave 
Opening gates in succession =
- same strength
- same speed
- same duration

17. How does a nerve impulse travel?
Action potential propagates
wave = nerve impulse, or action potential
brain  finger tips in milliseconds! + –
Na+ K+
wave 
K+ gates open more slowly than Na+ gates

18. Nerve Impulse Transmission

19. The Synapse Action potential happens
Neurons DON’T touch
The gap between the axon of one neuron, and the dendrites of another is called the SYNAPSE
Action potential happens
Neurotransmitter is released by axon ending
Neurotransmitter is a chemical that sends a signal
Neurotransmitter binds to dendrite membrane of next neuron
Excitation or inhibition of the membrane occurs
Neurotransmitter is ‘recycled’

20. The Synapse

21. Myelin Sheath Resembles chain of beads
Allows signal to travel faster because impulse “jumps” from node of Ranvier to node of Ranvier (with myelin sheath (225 mph / without 11 mph)
MS  destruction of myelin sheath by own immune system (progressive loss of signal conduction, muscle control & brain function)
Myelin Sheath