HPS111 Lecture Notes - Lecture 5: Membrane Potential, Acetylcholine, Neurotransmitter
WEEK 5: Micro-Neuronanatomy
Intro :
- About the cells of the brain
- Information travels across the brain
- Communication of information across nervous system
Basic structure and function of neurons:
oNerve cells
oFundamental to nervous system
oHighly integrated- all connected
oNeuronal connectivity
oGlial cells as well- have different ones (nutrients and structure)
oSensory neurons- transmit information from sensory receptors to the brain processing
omotor neurons- transmit instructions from the brain to the muscles and organs in the
body
ointer neurons- transmit information between neurons (mostly in the brain)
ostructure:
nucleus (all of the DNA, control house)
myelin (insulate the electrical signal, white fatty substance)
body (soma-the work is being done here)
dendrites (receive information from other neurons)
axon (transmitting electrical information from cell body to terminal button)
axon hillock and node of ranvier (action potential-electrical signal propagated)
synapse (chemical signalling)
othey don’t touch other neurons
oonly travels one way
ostructure types:
unipolar neuron- one projection
bipolar neuron- two projection (visual)
multipolar neuron- most common
sudiopolar neurons- only one but both dendrites and axon (sensory long ones)
owhite matter (myelinated, transmission between cell bodies (grey matter))
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ogrey matter (cell bodies-outside in the cortex, where brain process information)
ostep a- understanding dendrites and cell body reception, all or nothing (electrical-
within)
ostep b- from axon hillock to the terminal buttons (electrical-within)
ostep c- how electrical signal becomes chemical, between terminal buttons across
synapse
STEP A- Dendrites to the Axon Hillock
- electrical signalling within the neuron
- ions- molecule that has a charge (postivie- cation, anion-negative)
- diffusion- passive movement of a substance to high concentration to low concentration passive
attraction to opposite (attracted to their opposite charge, repulsed by their own charge)- make
ions move due to concentration/electro static pressure, the occur naturally
- electrostatic pressure-
the membrane
ointracellular space-inside the cell
oextracellular space outside
othese are separated by the cell wall/membrane
ocell membrane- semi permeable, some things can pass through others can not
ofacilitated by ion channels, and they can be opened or closed by electrical stimulation
oat rest- neuron nor stimulated- over negative within, positive outside
othe cell kicks positively charged ions out to remain negative
othis is called the membrane potential, the resting is because of the ions across the
membrane
oopen up channels in the membrane so positive charged ions can move, they will want to
enter the cell (diffusion, electrostatic pressure)
odiffusion-
oelectro static pressure-
omembrane potential will shift to be more positive
ocan also get the opposite effect, more negative
oopen and close ion channels, change the charge
oresting membrane potential -70 mv
oif the effect means more positive than negative, depolarise, excitatory signal or more
negative, hyperpolarise, inhibitory signal
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- electrical transmission
- receiving information from other neurons, change the cell membrane, cause different signals
due to the charge – from uptake of either negative or positive, they pass passively, the amount
of the charge conductive is how strong the initial signal was
- they can cancel out if both excitatory and inhibitory
- dendrites and cell bodies received signals from adjacent neurons
- these manipulate the permeability of the membrane
- this changes the membrane potential: depolarising (excitatory, positive) or hyperpolarising
(inhibitory, negative)
- these potentials are “graded” (they vary in level and strength)
- these can sum or cancel each other out
STEP B- The action potential
- transmission of electrical signal across and within the neuron
- getting the neuron to fire
Graded vs action potential
ograded: dendrites to axon hillock, involve changes inion concentration and membrane
potential, can vary in size, can vary in direction
oaction potential: axon hillock to terminal buttons, involve changes in ion concentration
and membrane potential, all-or-nothing, always the same
othe neuron either fires or doesn’t
What causes it
ocreating an action potential:
oexcitatory and inhibitory potentials converge on axon hillock
ograded potential sum
oin the membrane potential reaches the threshold of excitation (-55 to -65)
oaction potential occurs if not then membrane potential doesn’t reach this then nothing
happens
oinhibitory pushes it further way from the threshold, excitatory closer
oaction potential- all or nothing, the same way, changes in the concentration of ions
positively and negatively charged, along the axon membranes
Time course
ocharacteristic time course
omembrane potential changes over the time
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Document Summary
Step b- the action potential transmission of electrical signal across and within the neuron getting the neuron to fire. Time course: characteristic time course, membrane potential changes over the time o, it triggers different ion channels to open at different times, first, depolarisation, negative to positive, then they return, repolarise, then hyperpolarised. Graded potentials from part a are summed at axon hillock. If exciation does not reach excitatory threshold nothing happens. If there is then an action potential occurs at axon hillock. Saltatory communication, action potential is propagated by, down the axon with new action potential occurring at each node of ranvier. Neurotransmitter: chemical signals, lots of types, cause either epsp or ipsp, neurons specialise and release only one type of neurotransmitter. Some anti-anxiety medication also target this: dopamine. Addiction, schizophrenia (drug treatment block dopamine), parkinson"s disease (movement from low levels, buildings blocks of dopamine: serotonin. Targeted in treatment of depression (increase serotonin, block reuptake of serotonin, not simple: acetylcholine.
