1. Neurons, Neurons, Neurons!
Mrs. Hartley
Anatomy and Physiology

3. Remember:Divisions of Nervous System

4. Neurons Primary structural and functional unit of nerve tissue
Responsive cells that conduct impulses at great speeds
Cell body, axons, dendrites, myelin sheaths, synaptic terminals
Direction of impulse: dendrites to cell body to axon to axon terminal to synaptic end bulb

5. Cell Body: cytoplasm enveloped by plasma membrane
Prominent nucleus/nucleolus
Many functional organelles (mitochondria, Golgi, etc.)

6. Axon Conducts impulses away from the cell body
Terminal end communicates with the next cell

7. Dendrites Thin, branching extensions of cell body
Receive impulses from adjacent neurons
Uni-directional: only towards cell body

8. Myelin Sheath (pink) White, fatty insulating barrier
Aids in nerve impulse conduction

9. What Goes Wrong in MS?
When myelin is damaged, dense, scar-like tissue forms around nerve fibers throughout the brain and spinal cord. These scars, sometimes referred to as sclerosis, plaques, or lesions, can slow down or completely prevent the transmission of signals between nerve cells. Messages from the brain and spinal cord cannot reach other parts of the body. Damage, or scarring, occurs in many places throughout the central nervous system, hence the term "Multiple Sclerosis."

10. Nodes of Ranvier
Gaps in myelin sheath
Aid in impulse conduction

11. Information from one neuron flows to another neuron across a synapse
Information from one neuron flows to another neuron across a synapse. The synapse is a small gap separating neurons. The synapse consists of:
1. a presynaptic ending that contains neurotransmitters, mitochondria and other cell organelles, 2. a postsynaptic ending that contains receptor sites for neurotransmitters and, 3. a synaptic cleft or space between the presynaptic and postsynaptic endings.

12. So…How Are Impulses Created?
Excitability: neurons have the ability to respond when a stimulus becomes great enough to alter the resting membrane potential of a particular region of a membrane
Uneven distribution of ions (electrically charged particles) of sodium and potassium causing an electrical gradient

14. Depolarization and Repolarization
Rapid change in membrane’s permeability to sodium ions causing the electrical charge inside the cell to become more +positive
Soon after, resting membrane potential is restored
Potassium flows out of the cell and sodium stops flowing in

15. Action Potential
Depolarization + rapid repolarization results in an action potential or nerve impulse
Rapid at 1/1000s and in rapid succession

17. Myelinated vs. Unmyelinated
Unmyelinated: impulse continues along the length of the neuron unimpeded
10 m/s
Myelinated
Nodes of Ranvier
Myelin disrupts impulse…saltatory conduction….impulse skips, quickening the impulse
130 m/s

18. So Let’s Play a Game! “Saltatory Conduction” “All or None Game”
All or None response: if stimulus is large enough, impulse will be conducted along the entire length of the neuron