1. Nerve Impulses

2. Neuron Physiology
Action Potentials- nerve impulses which are sent by a change in electrical charge in the cell membrane. Depends on ions:
Sodium (Na+) highly concentrated outside of cells
Potassium (K+) highly concentrated inside cells
Ion movement
Ions move from high
concentration to a low
concentration passively
Na+/K+ pumps move ions
actively using ATP

3. Creating a Resting Potential
Protein pumps
open and close
let ions through
Active pumps
Ions move against a gradient
Use ATP to work
Passive pumps
Ions move with the gradient
Ions move from high to low concentration
Active transport
Passive transport

4. Action Potential

5. Resting Membrane Potential (-70mV)
Stage 1: Resting Potential

6. Depolarization and Threshold Potential
Stage 2: Depolarizing neuron (-62mV)
Sodium rushes in when channels open which are stimulated by neurotransmitters
Stage 3: Threshold is reached once enough sodium rushes in (-55 mV)

7. Stage 4: Neuron continues to depolarize as sodium continues to rush in.
Stage 5: Repolarization occurs as K+ channels open and K+ moves outward causing inside of membrane to become negative again.
Na+
Na+
0mV to +20mV K+
Potassium channels open
-70mV

8. A Nerve Impulse- a series of action potentials

9. Refractory Period
For a short period after the passage of an impulse, the threshold for stimulation is raised, so it limits the frequency of impulses and ensures uni-directional travel of impulse.

10. Action Potential

12. What happens when the nerve impulse reaches the end of the axon?
Axon terminals
Are found next to another neuron (as shown) or a muscle or gland
The gap is called a synapse
Synapse Action
Neurotransmitters are released at the synapse to pass the message to the next neuron.

13. Synapse

14. Neurotransmitters released at synapse

15. Saltatory nerve impulse conduction
The action potential jumps large distances from node to node, a process that is called saltatory propagation.

16. Myelinated vs. unmyelinated neurons

17. Speed of a Nerve impulse
Temperature - higher the temperature= faster speed. Warm-blooded animals have faster responses than cold-blooded.
Axon diameter - larger the diameter= faster speed. Marine invertebrates, (who live at temperatures close to 0°C), developed thick axons to speed up their responses. This explains why squid have their giant axons.
Myelin sheath - Only vertebrates have a myelin sheath surrounding their neurons. The voltage-gated ion channels are found only at the nodes of Ranvier, and between nodes myelin sheath acts as a good electrical insulator. Increases the speed of propagation dramatically.
unmyelinated neurons –travel at about of 1 meters/second
myelinated neurons-travel at about 100 meters/second
Depending on the type of fiber, modern measurements are from 6-122m/s

18. All or None Response
The strength of a response of a nerve cell or muscle fiber is not dependent upon the strength of the stimulus. If a stimulus is above a certain threshold, a nerve or muscle fiber will fire. Full response or no response at all.
"The all-or-none law guarantees that once an action potential is generated it is always full size, minimizing the possibility that information will be lost along the way."

19. Multiple Sclerosis
Autoimmune disease-body’s natural defenses breaks down myelin in CNS
Degeneration inhibits normal nerve impulse transmission, may slow or even stop in some cases.

20. Characterized by seizures Causes vary:
Epilepsy
Sudden disorderly discharge of brain neurons-impulses fire continuously.
Characterized by seizures
Causes vary:
by injuries , infections, tumors, with drawl from drugs, etc.