Neuro Physiology And The Synapse

Front 1

Normal resting potential

Back 1

-70mv

Front 2

threshold needed to open channels

Back 2

-55mv

Front 3

Na/K pump

Back 3

pushes 3 Na's outside for every 2K's inside

Front 4

Chemically gated channels

Back 4

opened by a neurotransmitter

found at the synapse

also called neurotransmitter dependent channels

Front 5

Voltage gated channels

Back 5

open in response to nearby changes in charge

more numerous in most neurons

Front 6

Synapse

Back 6

where the axon of the first neuron plugs into the next neuron

Front 7

Axodendritic synapse

Back 7

axon plugs into dendrite

Front 8

axosomatic

Back 8

axon plugs into cells body

Front 9

synaptic cleft

Back 9

the small space between the axon terminal and the membrane of the next neuron

Front 10

Impulse transmission

Back 10

1. the action potential or nerve impulse from the first neuron opens Ca+ channels.

2. Calcium triggers exocytosis of synaptic vesicles containing neurotransmitter

3. neurotransmitter diffuses across the synaptic cleft and attaches to receptors in next neuron's membrane

4. Na+ channels open allowing NA to rapidly diffuse into the cell

5.neurotransmitter pops out and is not replaced, Na gets shut out again.

Front 11

Acetylcholinesterase

Back 11

the enzyme that degrades acetylcholine so that the channel can close

Front 12

"All or None rule"

Back 12

Either all will depolarize or none at all

Front 13

Graded potentials

Back 13

even when depolarization occurs it is not guaranteed to become an action potential. this graded potential weakens as K+ leaks out diluting the charge differential.

Front 14

Axon hillock

Back 14

the start of the axon

In order for the action potential to become self propagating, in must reach the axon hillock and move down the entire neuron to the end.

Front 15

Action potentials

Back 15

voltage gated channels open;full depolarization follows until we have a self-propagating action potential.
Oppositely charges ions are attracted to the depolarized area bringing the next portion of the membrane to threshold and its Na+channels open up.

Front 16

Nervous impulse :step by step

Back 16

-an action potential opens Ca+ channels , triggers exocytosis of neurotransmitter
-neurotransmitter diffuses across the synaptic cleft and binds to receptors that open the NA+ channel gates
-Na-rushes in causing depolarization
-outer activation gates of Na+ channel gates open if depolarization reaches the axon where we have voltage regulated channels.
-Inactivation gates are open(both gates need to be open for Na to rush in and cause depolarization
-After depolarization, inactivation gates close and K+channels open.
-K+ rushes out and repolarization occurs

Front 17

Nervous impulse cont'd: repolarization

Back 17

Gates of K+ channels are slow and stay open an extra millisecond
Therefore repolarization undershoots the resting potential causing hyperpolarization of the membrane.
-the inactivation gate of Na+ must reopen and the K+ channels must closebefore another stimulus can cause depolarization. (relative refractory period)

-the Na/K pumps are also working to restore the ion balance of the resting potential. in 1-2 ms the neuron is ready for another stimulus

Front 18

Myelinated neurons

Back 18

Why myelination speeds up conduction
no leaking of K+from myelin covered parts of the membrane and practically all of the gated Na+ channels are at the node of Ranvier

The next place from which the ions will be pulled toward depolarized area is at the next node of Ranvier so the area where Na+ channels can open is at the next node, the action potential appears to skip the entire myelinated section.

Front 19

Inhibitory postsynaptic potentials (IPSPs)

Back 19

hyperpolarize the membrane often by opening up K+channels, so you have to open more Na channels to reach threshold

"Second neuron"-postsynaptic neuron

Front 20

Excitatory postsynaptic potentials (EPSPs)

Back 20

hypopolarize the membrane by opening up Na+ channels so you have to open fewer Na channels to reach threshold
Second neuron is the only one you can regulate.

First neuron is the "presynaptic neuron.

Front 21

Neurotransmitters

Back 21

not all neurotransmitters open Na+ channels some activate "second messenger systems" that lead to changes in membrane permeability. Result is slower and longer lasting stimuli.

Front 22

Biogenic amines (norepinephrine, dopamine, serotonin)

Peptides (endorphins, substance P, somatosin, and CCK)

Dissolved gasses (nitric oxide and carbon monoxide

Back 22

use the indirect mechanism of transmitting.

CNS

Front 23

Amino acids

Back 23

can be neurotransmitters
Use the direct mechanism.

Even ATP can be a neurotransmitter CNS

Front 24

Circuits

Back 24

Neurons need other neurons to be useful

Front 25

Diverging circuits

Back 25

a way that one neuron can stimulate many

Front 26

Converging circuits

Back 26

a way for different thoughts or stimuli to trigger the same effect

Front 27

Parallel after-discharge circuits

Back 27

less well understood, may play a role in abstract thought

Front 28

Reverberating or oscillating circuits

Back 28

regulatory

found in the CNS in area that control rhythmic activities such as breathing.