transmission within neurons Flashcards
what do sensory neurons do
carry info from the body
what do interneurons do
link sensory and motor neurons
what do motor neurons do
send info the body
important for movement
what are neurons
- 1 of 2 types of cell
- do all the info processing and transmitting
- many different types
- 86 billion neurons
what is the soma
- cell body
- contains the nucleus
what are dendrites
they receive messages
what are axons
they carry info from the soma to terminal buttons
what is the myelin sheath
wraps around the axon
what are the terminal buttons
at the end of axon branches
what are glia
- supporting cells
- number of glia is equivalent to number of neurons
- 3 types of glia
what are the 3 types of glia
- astrocytes
- oligodendrocytes
- microglia
what are astrocytes
- star shaped
- provides structural support to neurons
- hold neurons in place
- help providing nutrients to neurons
- surround the synapse - help limit dispersion of neurotransmitters
what are oligodendrocytes
- produce the myeline sheaf
- one cell can produce 50 segments of myeline sheaf
what are micoglia
- smallest of supporting cells
- clear dead or dying neurons
- act as the brain’s immune system - attack foreign tissue and repair damage cells
what is transmission within a neuron
an electrical process
- results from movement of ions across a membrane
- all cells have an electrical charge - more negative on the inside than the outside
- this results in a resting potential
- neurons can reverse their electrical charge
what is the cell membrane
- all cells are covered in a membrane
- two layers of phospholipid molecules
what are phospholipid molecules
- head of the molecule is a phosphate - hyrophillic - attracted to each other and to water
- the tails are fatty acids - hydrophobic - they point away from the water - inwards to each other
what are ions
- charged molecules
what are the 2 types of molecules and their charge
- cations - positive
- anions - negative
what ions does intercellular fluid contain
- potassium
- anions
what ions does extracellular fluid contain
- sodium
- chloride
what is the membrane potential
- the difference in electrical potential inside and outside the cell
what is the membrane potential balanced by
- diffusion
- electrostatic pressure
how do organic anions impact membrane potential
- concentrated inside the cell
- cannot cross the membrane
- make cells negatively charged
how do potassium ions impact membrane potential
- concentrated inside the cell
- they want to move out the cell - diffusion
- but attracted to the inside - they are positive
- balanced
how do chloride ions impact membrane potential
- concentrated on outside the cell
- want to move in - diffusion
- repelled from the inside because they are negative
- balanced
how do sodium ions impact membrane potential
- concentrated outside the cell
- wants to move in - diffusion
- attracted to inside - positive
- potassium is forced into cell
- kept under control by sodium-potassium pumps
what is the resting potential of a neuron
-70mV
why is maintaining the resting potential important
so the neuron can respond rapidly to a stimulus
what is an action potential
a reversal in the potential and is how information is sent through an axon
- a rapid change in the membrane potential
- an all or none process (fires or not fire) and stays the same size throughout transmission
what is depolarization
decrease from normal resting potential - brings membrane closer to 0
what is hyperpolarization
increase relative to resting potential - more negative
what does the membrane have to reach to start an action potential
around -50mV
what happens when -50mV is reached
the membrane continues to depolarize - becoming more positive
when does the membrane continue to depolarize until
about +40
what happens when the membrane reaches about +40
- it reverses
- repolarization - all the way back down to the resting potential
what happens after the membrane has repolarized
- it hyperpolarizes a little bit - more negative than usual - below -70 and then returns to resting state
what happens in the first stage of action potential
- reached threshold of excitation
- sodium channel starts to open
- sodium begins to enter the cell - diffusion because they are positively charged
- causes depolarization
what does the channels being voltage dependent mean
- they only open at a certain point of membrane potential
what happens in the second stage of action potential
- potassium channels start to open
- voltage dependent
- require more depolarization
- potassium starts to leave the cell
what happens in stage 3 of the action potential
- sodium channels close and become refractory - can’t open again
- stops sodium entering
- peak action potential
what happens at the fourth stage of action potential
- potassium channels are still open
- potassium continues to leave the cell
- causes the repolarization
what happens in the fifth stage of action potential
- potassium channels close and sodium channels reset
what happens in the sixth stage of action potential
- slight hyperpolarization
- lots of potassium around the membrane which will eventually diffuse away and allow membrane to go back to it’s resting state
what is propagation
- the action potential is transmitted down an axon via propagation
- action potential is regenerated at points down the axon due to the entry of sodium ions at the neighbouring point - only goes in one direction because of refractory sodium channels
what is saltatory conduction
action potential regenerated along the axon at nodes of ranvier
what are the benefits of saltatory conduction
- fast conduction
- more energy efficient
