1. The Neuron An everyday (every second!) use of active transport
OPENER  Do the wave!

2. The Nervous System
Controls and coordinates functions throughout the body and responds to internal and external stimuli.

3. What makes up the Nervous System?
The basic unit of structure and function of the nervous system is a neuron (nerve cell).

4. Structure of a Neuron
4. Myelin sheath: insulating membrane *increases speed of impulse*
1. Cell body: Contains the nucleus and other cell organelles
Axon terminals
4. Myelin sheath
Nodes
1. Cell body
3. Axon
Nucleus
2. Dendrites
3. Axon: long, thin extension of the cell body
*Function: sends nerve impulses away from the cell body*
(Remember “A” for away!)
2. Dendrites: Short, branched extensions of the cell body
*Function: receive stimuli*

5. 3 Main Types of Neurons 1. Sensory Neurons (sensory = of the senses)
-send impulse from sense organs to spinal cord & brain
2. Interneurons (inter- = between)
-relay messages between sensory and motor neurons
3. Motor Neurons (motor = causing motion)
-send impulse from brain and spinal cord to effectors
(glands or muscles)

6. Which are sensory? Which are motor neurons?
Top arrows = sensory; bottom arrows = motor

7. How do Neurons Communicate?
1. Dendrites receive the signal (action potential) which then travels down to the axon of the first neuron.
2. When the signal reaches the end of the axon, the axon releases chemicals called neurotransmitters.
ex. acetylcholine, norepinephrine, dopamine, serotonin
3. Neurotransmitters enter into the space between the 2 neurons, called the synaptic cleft.
4. Neurotransmitters bind to receptors on dendrites of the next neuron thereby passing on the signal.

8. The Neuron
The internal “solution” of the cell has a characteristic concentration of sodium versus potassium ions
called: RESTING POTENTIAL
More Na+ outside, more K+ inside
Takes Energy to maintain this
A signal is produced when this internal “solution” changes
Called: ACTION POTENTIAL

10. The Resting Neuron When a neuron is at rest
There is a certain amount of ions inside & outside of cell
This difference in charges is called the resting potential (-70mV)
The nerve cell membrane pumps sodium (Na+) out of the cell and potassium (K+) into the cell
Works by active transport
Net result = more K+ inside the cell and more Na+ outside the cell
The cell membrane leaks K+ back out of the cell
Diffusion
Causing the negative charge inside the cell
Also, organelles inside contribute to the negative charge

11. The Moving Impulse
An impulse begins when a neuron is stimulated by another neuron or by the environment
Causes movement of ions across the membrane
Na + rushes in
What kind of transport is this?
This is called an action potential
Also called “depolarization (+30mV)
Impulse travels down axon away from the cell body to the axon terminal
at 110 m/sec (225 mph)
After impulse passes, K+ flows out of the cell
“repolarization” (-70mV)
Passive transport (high to low)

12. What is an action potential?
A sudden reversal of membrane potential.
“Resting” is when the pump is active
“Action” is when the sodium is diffusing into axon

13. Threshold Strength of impulse is always the same
It is an all or nothing response
Minimum level of stimulation to cause an impulse is call the threshold
What happens when the action potential reaches the end of the axon?

14. The Synapse The area where an impulse is transferred between 2 neurons
Synaptic cleft separates the axon terminal from the dendrites of the adjacent neuron

15. The Synapse
The terminals contain tiny sacs (vesicles) that contain neurotransmitters
 chemical signals
Impulse triggers release of neurotransmitters into the synaptic cleft (via exocytosis)
Neurotransmitters diffuse across gap & bind to receptors on the adjacent neuron
Cause the impulse to continue
(if threshold is reached)
Neurotransmitters are either broken down or recycled
This is where drugs interfere

16. Dendrite of adjacent neuron
The Synapse = junction between two neurons
Section 35-2
Direction of Impulse
Dendrite of adjacent neuron
Axon
Receptor
Vesicle
Axon terminal
Synaptic cleft
Neurotransmitter