1. Human Anatomy & Physiology NERVOUS SYSTEM
BioH

2. Nervous System Functions
Control & coordinate functions throughout the body
Respond to internal & external stimuli
Provides fast communication between body systems and parts

3. Nervous system cells Neuron a nerve cell Structure fits function
signal
direction
dendrites
cell body
Structure fits function
many entry points for signal
one path out
transmits signal
axon
signal direction
synaptic terminal
myelin sheath
dendrite  cell body  axon
synapse

4. Neuron Basic Structure
Messages sent by the nervous system are electro-chemical signals (impulses) carried by neurons (nervous system cells)
Impulses always travel from dendrites, through the cell body to the axon terminal

5. Neuron Anatomy
Dendrites – short, branched extensions that receive impulses from the environment or other neurons toward the cell body
Cell Body – the largest part of a neuron, containing most of the cytoplasm and the nucleus
Axon – the long extension that carries an impulse away from the cell body
Myelin (myelin sheath) – insulating membrane surrounding most axons (roduced by Schwann cells) separated by small gaps (Nodes of Ranvier = “nodes”)
Axon terminals – branches at the end of an axon
Neurons may have many dendrites and axon terminals, but only one axon
Nerve – bundle of axons and dendrites from many neurons

6. Fun facts about neurons
Most specialized cell in animals
Longest cell
blue whale neuron
10-30 meters
giraffe axon
5 meters
human neuron
1-2 meters
Nervous system allows for 1 millisecond response time

7. Neuron Types
If you painfully stub your toe, what is the sequence of neurons that the stimulus would follow?
Sensory Neuron – carries impulse from sense organs to brain & spinal cord
Motor Neuron – carries impulse from brain to muscles & glands
Interneuron – connects sensory and motor neurons

8. Nerve Impulse
HOW does a signal travel along an neuron?

9. Transmission of a signal
Think dominoes!
start the signal
knock down line of dominoes by tipping 1st one
 trigger the signal
propagate the signal
do dominoes move down the line?
 no, just a wave through them!
re-set the system
before you can do it again, have to set up dominoes again
 reset the axon

10. Transmission of a nerve signal
Neuron has similar system
protein channels are set up
once first one is opened, the rest open in succession
all or nothing response
a “wave” action travels along neuron
have to re-set channels so neuron can react again

11. Resting Neuron
When a neuron is resting (NOT transmitting an impulse), the outside of the cell has a net positive ion charge, while the inside has a net negative charge.
Na+ ions are pumped out of the cell while K+ ions are pumped into the cell, using active transport

12. Na+ K+ pumps (active transport) and leakage channels
This creates a difference in charge between the inside and the outside of a neuron = resting potential

13. Measuring cell voltage
Voltage = measures the difference in concentration of charges.
The positives are the “hole” you leave behind when you move an electron.
Original experiments on giant squid neurons!
unstimulated neuron = resting potential of -70mV

14. Moving Impulse
The neuron remains in a “resting state” until it receives a stimulus large enough to start an impulse (“All or nothing response”) from the environment or another neuron.
The electrical imbalance between the inside and the outside of the neuron is reversed as the impulse travels along the axon toward the axon terminals = ACTION POTENTIAL (nerve impulse)
If the stimulus does not reach a threshold (minimum amount of energy to cause an impulse), the impulse does not happen. (Think dominoes!)

15. What happens at the end of the axon?
Impulse has to jump the synapse!
junction between neurons
has to jump quickly from one cell to next
How does the wave jump the gap?
Synapse

16. The Synapse
The action potential travels along the axon (“jumping” from node to node) until it reaches an axon terminal and the gap (synapse) between it and another cell
Chemicals (neurotransmitters) travel between the axon terminal and the next cell through the synaptic cleft (synapse)

17. Action potential graph
Resting potential
Stimulus reaches threshold potential
Depolarization Na+ channels open; K+ channels closed
Na+ channels close; K+ channels open
Repolarization reset charge gradient
Undershoot K+ channels close slowly
40 mV 4
30 mV
20 mV
Depolarization
Na+ flows in
Repolarization
K+ flows out
10 mV
0 mV
–10 mV 3 5
Membrane potential
–20 mV
–30 mV
–40 mV
Hyperpolarization
(undershoot)
–50 mV
Threshold
–60 mV 2
–70 mV 1
Resting potential 6
Resting
–80 mV

18. Divisions of the Nervous System
Central Nervous System (CNS) – brain and spinal cord
“Coordination/communication center”
Receives most impulses and determines “next steps”
Sends communication along spinal cord
Peripheral Nervous System (PNS) – all the nerve cells not part of the CNS
Receives internal and external sensory input
Receives and sends impulses to muscles or glands
Reflex arcs
Autonomic Nervous System – regulates activities that are involuntary

19. CNS and PNS

20. Reflex Arc
Impulse pathway travels directly from sensory neuron to spinal cord, interneuron and back to muscle or gland

21. Summary – Brain Basics & Neuroscience