Topic 9 Nervous system Flashcards
what do all three neurones have in common
Axon
cell body
dendrons
Axon
long fibre that carries the nervous impulse along the neurone
Dendrons
carry the action potentials to surrounding cells
cell body
where proteins and chemicals are made
What do schwann cells do? (SENSORY NEURONE)
they wrap around the axon to form myelin sheath, which is a lipid therefore does not allow charged ions to pass through it
what are the purpose of nodes of ranvier
they are gaps, which allow the action potential to jump from node to node (saltatory conduction), which means the action potential travels along the axon faster as it doesnt have to generate an action potential along the entire length, just at the nodes of ranvier.
what is the function of a relay neurone?
these neurones carry impulses between the sensory and motor neurones. they have multiple short axons and dendrons
What does the motor neurone do?
These carry the impulse from a relay or sensory neurone to th effector (muscle or gland) to carry out a response. they have one long axon and multiple short dendrons.
Sensory receptors. what do they do? Name examples
sensory receptors detect a stimulus
there are different types of sensory receptors, and each type can detect a different stimulus
eg photoreceptors (rods and cone cells) detect light (stimulus).
Resting potential
when a neourone is not conducting an impulse, there is a difference between the electrical charge inside and outside the neurone, this is known as the resting potential.
there are more positive ions, Na+ and K+, outside compared to inside, therefore the inside of the neurone is more negtaive. at -70mV.
Establishing resting potential
the resting potential is maintained by a sodium-potassium pump, involving active transport and ATP.
the pump moves 2 K+ ions in and 3 Na+ ions out.
this creates an electrochemical gradient causing K+ to diffuse out and Na+ to diffuse in. (through their channel proteins).
however there are more potassium ion channels than sodium ion channels, and more potassium ion channels are open, so the membrane is more permeable to K+ so more are moved out of the protein channels resulting in the -70mV.
so as a result you have more postive ions out, than inside hence -70mV.
Action potential overview
if there is a stimulus it can result in an action potential. this where the neurones voltage increases beyond a set point from the resting potential. An increase in voltage, or depolarisation, is due to the neurone membrane becoming more permeable to Na+ so more sodium ions diffuse into the axon, due to their postive charge this will bring the voltage to be more and more postive , once an action potential is generated, it moves along the axon, triggering an axon potential at each node of ranvier after.
process of action potential generated
All or nothing principle
if the depolarisation does not exceed -55mv, an action potential and impulse are not produced. (NOTHING)
Any stimulus that does trigger depolarisation to -55mv will awalys peak at the same max voltage (ALL). bigger stimului increase the frequency of action potentials
Refractory period
After an action potential has been generated, the membrane enters a refractory period where it can’t be stimulated, because sodium channels are recovering and can’t be opened.
This ensures that discrete impulses are produced. An action potential cannot be generated immediately after another and this makes sure that each is seperate.
Also ensures action potentials travel in one direction
