IA Study Session 6

.What you need to know:
1. CNS
- Composed of the BRAIN and SPINAL cord

2. PNS
- Composed of the NERVES and GANGLIA

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TWO SUBDIVISIONS

What you need to know:
- 1 ) Visceral- INVOLUNTARY
- Visceral Motor - Ex. glands, cardiac muscle, smooth muscle
- Visceral Sensory - Ex. Lungs, Heart, Stomach

- 2) Somatic - VOLUNTARY
- Somatic Motor - Ex. Skeletal muscle
- Somatic Sensory - Ex. Skin, bones, joints, muscles

SENSORY --> AFFERENT --> ARRIVING in the CNS
MOTOR --> EFFERENT --> EXITING the CNS.

RULE BREAKER:
-Reflexes
- Technically INVOLUNTARY but can involve muscles that we can VOLUNTARY control.

Functional DIFFERENCE between subdivisions

What you need to know:
- 1) Sensory Neurons
- sends INFO to CNS

- 2) Interneurons = 90% of neurons
- Lie WITHIN the CNS
- Bridge the two neurons.

- 3) Motor Neurons​
- Receives INFO from CNS
- Muscles and glands act on signal

Functional Classes

What you need to know:
- Dendrites - MAIN site for signal acceptance.
- Axon Hillock- Axon originates; Electrical signal is produced.
- ​Axon Terminal- Where the neurotransmitters are found.
- communicate with other neurons.
- Myelin Sheath- insulation around axon.
- Helps signal travel faster.
- Nodes of Ranvier- Small gaps between myelin sheath.
Help by allowing signal to "JUMP" from one gap to the next one.

Typical Structure of a Neuron

What you need to know:

​- Glial cells SUPPORT neurons. They protect, provide nutrients, clean waste, and help repair injuries.
1) Oligodendrocytes- Makes MYELIN in CNS.
- Myelinates MULTIPLE
2) Ependymal Cells- Secretes and circulates CSF.
3) Microglia- Defends and Disposes.
4) Astrocytes- Support and Nourishment.


1) Schwann Cells- Makes MYELIN in PNS
- myelinates ONE.
2) Satellite Cells- Support and Nourishment.

6 Types of Glial Cells

Signal depends on DIAMETER and PRESENCE/ABSENCE of myelin!

What you need to know:
- Myelinated- Signal is FASTER; it "JUMPS"
-SALTATORY Conduction

- Unmyelinated- Signal is SLOWER; "Gradual"

​ - Continuous Conduction

What you need to know:
- Presynaptic Neuron - Nerve that SENDS the signal
- Synapse- The CONNECTION POINT of TWO cells.
- Postsynaptic Neuron - Never that RECEIVES the signal.
- Synaptic Vesicle- Tiny sacs that hold NT.
- Neurotransmitters (NT) - Chemical messengers that carry SIGNAL ACROSS the synaptic cleft.
- Synaptic Cleft- SMALL gap between pre- and post-synaptic neurons.

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Synapses/Synaptic Junctions

What you need to know:
- Chemical - Sends NT signal
- Has a SYNAPTIC CLEFT
- Depending on NT can excite/inhibit.

-Electrical - Diffusion of IONS.
- Is joined by GAP JUNCTIONS.
- NO DELAY of NT release/binding

Electrical vs. Chemical Synapses