Nervous System 4 (WS 10)

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1

Cell to cell communication

Neurocrines- chemicals that convey information from neuron to other cell
could be from neuron to neuron, could be other cell
Types:
1. Neurotransmitter- fast, released from axon terminal, acts as a synapse. Is local
influences another neuron or effector
EX: allows us to move our fingers fast
2. Neurohormones- Released to blood by the neuron, travels to target.
Are typically rapid acting (fast) and systematic
3. Neuromodulators- slow acting
Alters response of cell to a neurotransmitter (potentiates or inhibits)
Binds to non-synaptic sites

2

Chemical types of neurocrines

First three are all catecholamines

1. Amines- Norepinephrine
2. Amino acids- EX: Glycine, Glutamate (both involved in CNS)
3. Gases- Nitric oxide (NO); sticks around for a short amount of time, causes blood vessels to open up
4. Others- Acetylcholine, purines, lipids; hang around longer

3

Synapse

A connection point pre-synaptic neuron and post-synaptic cell

Two types:
1. Electrical Synapses
2. Chemical Synapses

4

Electrical Synapses

Ions move across a border; involves gap junctions (heart)
They need a place of low electrical resistance
are very fast
Involved in- the cardiac muscle and CNS
is bidirectional in some paths of flow

5

Chemical Synapses

Chemical crosses synaptic space (cleft)
Post synaptic gap
Involved in- neurotransmitters

6

Synthesis and recycling of Acetylcholine

1. ACh is made from choline and acetyl CoA
2. In the synaptic cleft, ACh is rapidly broken down by the enzyme acetylcholinesterase
3. Choline is transported back into the axon terminal by cotransport with Na+
4. Recycled choline is used to make more ACh

7

Neurotransmitter release

1. an AP depolarizes the axon terminal
2. The depolarization opens voltage- gated Ca2+ channels, and Ca2+ enters the cell
3. Calcium entry triggers exocytosis of synaptic vesicle contents
4. Neurotransmitter diffuses across the synaptic cleft and binds with receptors on the post synaptic cell
5. Neurotransmitter binding initiates a response in the post synaptic cell

8

Inactivation of neurotransmitters

Recycled/broken down or diffuse away

Enzymatic degradation-
1. Acetylcholine
2. Catecholamine's (aka Norepinephrines)
a) COMPT: Catecholamine methyl transferase
b) MAO: monoamine oxidase
a) and b) are enzymatic compounds that speed up destruction

9

Neurotransmitter Termination

neurotransmitter action terminates when the chemicals are broken down, are taken up into cells, or diffuse away from the synapse
1. Neurotransmitters can be returned to the axon terminal for reuse or transported into glial cells
2. Enzymes inactivate neurotransmitters
3. Neurotransmitters can diffuse out of the synaptic cleft