nervous system - ms. kropac...saltatory conduction the action potential can move along the axon by...

Nervous System Saltatory Conduction and Synaptic Transmission

Thursday, December 7, 17

Neuron Structure


Neuron Structure

dendrites receive impulses from other neurons or sensory receptors.

relay impulse to the cell body


Neuron Structurecell body: contains the nucleus and is the site of the cell's metabolic activity

processes input from dendrite

if input is large enough, the action potential will be initiated in the axon


Neuron Structureaxon: conducts impulse away from cell body

terminal end branches into dendrites

releases NT's to communicate with adjacent neurons, glands or muscle

some are enclosed in a myelin sheath


Neuron Structuremyelin sheath: the fatty, insulating layer around the axon, composed of Schwann cells

(a cell that wraps itself around the axon)

speeds the rate of nerve impulses


Saltatory Conduction

the transmission of an action potential along a myelinated axon


Saltatory Conduction

the action potential can move along the axon by jumping from node to node which allows for a quicker transmission of the impulse


Synaptic Transmission

explains how impulses move between two neurons.

A synapse is only 20 nm wide.



Presynaptic neuron carries the impulse to the synapse


Synaptic Transmissioncontains the synaptic vesicle

neurotransmitters (NT's) are the chemicals that are released from vesicles into the synaptic cleft.



Postsynaptic neuron carries the impulse away from the synapse


Synaptic TransmissionDendrites have receptors for the NT's that diffuse across the synapse.

Dendrites become depolarized upon receiving the NT's into their receptors.



1) The action potential triggers Ca2+ channels close to the synapse



2) Ca2+ follows it’s concentration gradient and flows into the cell.



3) Calcium causes vesicles filled with NTs to fuse the the presynaptic cell membrane.



4) NT travel across the synapse and bind to receptors on the postsynaptic cell.



5) Receptors open Na+ ion channels on postsynaptic cell, the action potential continues.



The time it takes for the NT's to diffuse across the synapse slows the transmission of the nerve impulse. A greater number of synapses creates a longer time for the impulse to reach its destination


NeurotransmittersCan be excitatory, inhibitory or both.


Neurotransmitters

Acetylcholine is as an excitatory NTcan cause postsynaptic neurons to open Na+ channels, generating an action potential never gives the neuron a chance to repolarize


Neurotranmitters

cholinesterase (an enzyme) gets released and destroys acetylcholine and results in the Na+ channels closing and the recovery phase starts


NeurotransmittersAcetylcholine is also an inhibitory NT

make postsynaptic membrane more permeable to K+K+ ions flow out of neuron making it more negative (hyperpolarized)takes more Na+ channels to open to achieve depolarization and an action potential.


nervous system - ms. kropac...saltatory conduction the action potential can move along the axon by...

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