1. Introduction to the Nervous System

2. Basic Divisions of the Nervous System
Figure 12.2

3. Central Nervous System (CNS): --brain and spinal cord
Peripheral Nervous System (PNS):
                   pairs of spinal nerves
                   pairs of cranial nerves

4. THREE BASIC FUNCTIONS OF THE NERVOUS SYSTEM
Sensory -  gathers info
Integrative - information is brought together
Motor - responds to signals, maintains homeostasis

5. Peripheral Nervous System
SOMATIC NERVOUS SYSTEM - skeletal muscles, under voluntary control AUTONOMIC NERVOUS SYSTEM - smooth muscles, glands, involuntary

6. Parasympathetic System
Brain & Spinal Cord
Afferent System
Efferent System
Sensory Receptors
Somatic System
Autonomic System
Stimulus
Sympathetic System
Parasympathetic System
Smooth muscles, glands
Skeletal muscles

7. Neurons

8. Dendrites – shorter, more numerous
Dendrites – shorter, more numerous. Form the receptive surfaces of neurons
Axon – single, long fibre which conducts impulses away from the cell body. End has many fine branches.

9. Neuroglial Cells 
- support cells for the neurons 1. Microglial : scattered throughout, digest debris or bacteria 2. Oligodendrocytes: provide insulation around the axons in CNS 3. Astrocytes: connect blood vessels to neurons 4. Ependymal Cells: form a membrane that covers certain cavities in brain

10. 5.  Schwann cells:  form the insulating sheath around the neurons within the PNS
*Myelin Sheaths - necessary for insulation of neurons

11. Supporting Cells in the CNS
Creates the myelin sheath that insulates axons

12. Supporting Cells in the CNS

13. Supporting Cells in the CNS

14. Supporting Cells in the CNS

15. Neuron Structure
Myelin -insulation surrounding axons
Nodes of Ranvier - gaps in the insulation

16. White vs Grey Matter
Myelinated (white matter) – myelinated axons
Unmyelinated (grey matter) - unmyelinated

17. Interesting Facts about the Neuron
Longevity – can live and function for a lifetime
Do not divide – fetal neurons lose their ability to undergo mitosis; neural stem cells are an exception
High metabolic rate – require abundant oxygen and glucose
The nerve fibers of newborns are unmyelinated - this causes their responses to stimuli to be course and sometimes involve the whole body.  Try surprising a baby!

18. END OF INTRO NOTE!!!

19. Electrochemical Impulse
- weak electric current.
- a series of action potentials along a nerve fiber.

20. Resting Potential -inside of a neuron's membrane has a negative charge
a Na+ / K+ pump uses energy from ATP to pump Na+ out of the cell and K+ into it
the cell membrane is a bit leakier to K+ than it is to Na+, so K+ ions leak out of the cell
the inside of the membrane builds up a net negative charge relative to the outside called membrane potential
if electrodes placed across the cell membrane, the resting membrane potential is about -70mV
- this difference in charge means the membrane is polarized

21. Sodium- Potassium Pump
For every 3 Na+ out, 2 K+ come in
Uses ATP (splits into ADP and inorganic phosphate) to alter pump shape

22. Action Potential
1. Neuron membrane maintains resting potential (-70mV)
2. Threshold stimulus is received.
3. Volate-gated Na+ channels open.
4. Na+ ions diffuse inward, depolarizing the membrane (+40mV)
5. Na+ channels close and voltage-gated K+ channels open
K+ ions diffuse outward, repolarizing the membrane
Membrane becomes hyperpolarized to – 90mV.
K+ channels close.
Na+/K+ pump restores resting potential
During refractory period, membrane cannot undergo another action potential. Entire process continues along length of axon until it reaches the end.

24. Myelinated Neurons
Action potentials only occur at nodes of Ranvier, which contain many voltaged-gated channels
When Na+ ions enter cell, they move quickly through cytoplasm to next node.
This reduces net charge, causing a threshold stimuli that elicits depolarization.
Since depolarization just occurred at previous node, it is in refractory period and cannot depolarize thus preventing action potential from moving backwards.
Action potentials jump from node to node = SALTATORY CONDUCTION
Travels at a rate of 120m/s versus 0.5m/s in unmyelinated neurons.

26. The Synapse Synapse - junction between two communicating neurons
To complete the signal, a NEUROTRANSMITTER is released at the gap to signal the next neuron

27. Structure of a Synapses

28. Neurotransmitters
Excitatory - allow positive ions to flow into postsynaptic membrane causing depolarization
Inhibitory – allows potassium ions to flow out causing hyperpolarization

30. Types of Neurotransmitters
Acetylcholine - stimulates muscle contraction
Monoamines - Norepinephrine & Dopamine (sense of feeling good, low levels = depression)
Serotonin (sleepiness)
Endorphins (reduce pain, inhibit receptors)