Nervous Communication Flashcards
(23 cards)
Motor neurone goes from _______ to ______
CNS
To effector tissues
What connects motor and sensory neurones?
Relay neurones
What do sensory neurones do?
Connect receptors to the CNS
In four points describe the structure of a neurone
Long
Ion channels (Ca2+ , Na+ , K+)
Sodium potassium pump
Mitochondria
What are dendrites ?
Long branched elongations coming off the dendron
What is the dendron part of the neurone?
From the dendrites to the cell body
What is the axon of a neurone?
From the cell body to the end of the neurone
What is meant by myelination?
Several layers of membranes and cytoplasm wrapped around a neurone
In-between myelinated Schwann cell you find?
Nodes of ranvier
The fact that current can only be generated in the Schwann cells is given the term?
Saltatory conduction
Describe how a resting potential is formed
Na+/K+ pump pump three Na+ out for two k+ in
Some potassium leak through channel proteins
Proteins have negtive charges
Therefore there is an overall negative charge inside the neurone of -60mV
Describe how a current is formed at the generator region of a neurone
Synapse triggers the Na+ channels to open
Na+ goes into the cell
Causes a generator potential
If enough generator potentials occur they can be summed and meet the threshold
Overall depolarisation will occur
Describe how the inital opening of sodium ion channels leads to positive feedback
The depolarisation from the generator potential causes the opening of the voltage gated sodium channels
Causes more depolarisation
After a set delay since gated sodium channels have opened what happens?
They close again
Describe how re polarisation occurs why there is a refrcactory period and how the resting potential is regained
K+ ion channels open
K+ diffuse out of the cell
Causes hyperpolarisation as sodium potassium pumps take time to start working so the voltage drops down very qucikly
Once sodium potassium pump is working it will regain the resting potential
Explain how the propagation of an action potential is Unidirectional
[Na+] is high behind the action potential still
Na+ is far more likely to diffuse forward than backward
In a myelinated neurones where can Na+ and K + channels be found?
In the nodes of ranvier
Explain how myelination increases the speed of nervous communication
Myelin acts as an insulator
Depolarisation only occurs at the nodes of ranvier which elongates the local circuits and results in saltatory conduction
An action potential is an all or nothing response
How therefore is the intensity of the signals coded for?
By the frequency of signals
Describe the movement of nervous signals across a synapse
Action potential arrives at the synaptic knob
Voltage gated Ca2+ channels open and ions diffuse into the synaptic knob
Cause vesicles with acetylcholine to fuse to the membrane of the pre synaptic knob. Exocytosis then occurs
Acetyl choline binds to recptor sites on Na+ channels on the post synaptic membrane
Na+ ions diffuse through the post synaptic membrane
Excitatory post synapctic membrane potential
How is acetylcholine removed from receptors?
Acetylcholineesterase is an enzyme that braks acetylcholine down into ethanoic acid and choline
Once broken down by acetylcholinease what happens to the products of this reaction?
Ethanoic acid and choline diffuse back to the synaptic bulb where they are recombined using ATP to form acetylcholine
Why must the Ca2+ ions be gated?
Otherwise Ca2+ would be released all the time and would bind to the receptors sending inappropriate impulses
