1. A NERVE CELL?

2. Classification

3. Glial cells
nonconducting cells important for structural support and metabolism of the nerve cells

4. Neurons Sensory neurons Interneurons Motoneurons
Nerve cells that conduct nerve impulses
Sensory neurons
Neurons that carry impulses from sensory receptors to the CNS (aka. afferent neurons)
Interneurons
Link neurons within the body (primarily in CNS)
Integrate and interpret information
(aka. Association neurons)
Motoneurons
Neurons that carry impuses from the CNS to effectors
(aka. efferent neurons)

5. Anatomy of a Motor Neuron

6. Dendrite Cell body (soma) Axon
Projections of cytoplasm that carry impulses toward the cell body
Cell body (soma)
Location of the nucleus
Axon
Extension of cytoplasm that carries nerve impulses away from the cell body

7. Axons Myelin sheath Schwann cells Nodes of Ranvier Neurilemma
Insulated covering over the axon of a nerve cell that increases the speed of the impulse
Schwann cells
Special type of glial cell that produces myelin sheath
Nodes of Ranvier
Regularly occurring gaps between sections of myelin sheath along the axon
Action potential jumps the gap speeding up the travel of the impulse
Neurilemma
Surrounds the axon and promotes the regeneration of damaged axons
Axons

9. A Neuron’s ‘Language’

10. An action potential (nerve impulse) is an ‘all or nothing’ response.
A threshold must be reached before an action potential is sent.
A weak stimulus will not trigger an impulse but a stronger stimulus will trigger the same size of impulse no matter how intense.
Analogy: light switch
Ions exist in the bloodstream and in and around all your cells (we will focus on potassium, sodium, and chloride)
Before we begin…

11. Resting Potential More sodium outside the cell
Overall, negative charge inside the cell (polarized membrane)
= -70 mV
Due to effect of:
Sodium/potassium pump
3 sodium ions pumped out for every 2 potassium ions pumped in.
Differences in permeability
The cell is more permeable to potassium leaving the cell than to sodium entering the cell.

12. Depolarization Positive charge from soma reaches the axon hillock
If threshold is reached, the sodium channels open and sodium goes into the cell down it’s concentration gradient and the electrical gradient.
Cell becomes positive
= +40 mV

13. Repolarization Sodium channels close.
Potassium gates are opened (K+ leaves
the cell)
Sodium/potassium pump pumps 3 sodium ions out of the cell for every 2 potassium ions it pumps in (ATP fueled).
Original polarity of the nerve membrane restored

14. Hyperpolarization/ Refractory period
Resting potential is overshot and the neuron falls to a -90mV state.
Neuron returns to resting potential
Recovery time required before a neuron can produce another action potential.

15. Textbook Diagram Propagation Triggers Page 420 Page 421 pH
Change in pressure
Chemicals

16. Saltatory Conduction

17. Synaptic Transmission
Synapse
Regions between neurons, or between neurons and effectors
20 nm
Neurotransmitters
Chemicals released from vesicles into synapses
Located in the end plates of axons
Rely on diffusion (slow)
Explains speed of reflex verses problem solving

19. Neurotransmitters
Synaptic vesicles in the end plate of the presynaptic neuron release neurotransmitters by exocytosis.
Neurotransmitters attach themselves to the postsynaptic membrane (causing either depolarization or hyperpolarization).

20. Summation
The accumulation of messages received by a postsynaptic neuron
A postsynaptic neuron may need more than one neuron worth of neurotransmitter to reach threshold and trigger an action potential.
A postsynaptic neuron may receive inhibitory and excitatory messages that cancel the effect

22. Follow up
Page 417 #5, 6
Page 426 #1, 5, 10
Handout