Neurology & Cytology Flashcards
what are neurons?
these are highly specialised cells of the brain and nervous system
what do neurons communicate?
they communicate information in electrical and chemical form
what is the broad classification of neurons?
glia
dendrites - what do they do?
they receive signals from other neurones
what does the cell body of the neuron do?
makes proteins which are essential for neuronal function
what does the nucleus of the neuron do?
contains the genetic material (chromosomes) of neuron cell
what does the axon hillock part of the neuron do?
plasma membrane generates the impulse
what does the axon of the neuron do?
it conducts electrical impulses along the neuron cell
myelin sheath of neuron?
insulate the axon to help protect the neuron cell and speed up transmission of electrical impulses
what is the myelin sheath made up of?
schwann cells
gap between schwann cells?
nodes of ranvier
axon terminal of neuron?
transmits electrical and chemical signals to other neuron cells
afferent neuron?
sends signal through axon - signal is processed at cell body of neurons and sent to axon terminals
what does the motor division of PNS involve?
voluntary movement by skeletal muscles
AND
involuntary body responses, such as heart rate, blood pressure, respiration, digestion and sexual arousal
sensory division of PNS includes?
vision, hearing, smell or taste, touch, pain and temp
what do the Schwann cells (of PNS) and oligodendrocytes ( of CNS) do?
insulation and myelination
what do satellite cells (of PNS) and astrocytes (of CNS) do?
for support of the neurons
what do the microglia of the CNS do?
immune support, phagocytosis
what do the ependymal cells of the CNS do?
creating CSF
cerebral spinal fluid
myelin sheath is essential for?
for electrical insulation and to speed up action potential propagation
what is the axon terminal designed to do?
to convert the electrical signal into a chemical signal in a process called synaptic transmission
what do motor proteins do?
they ‘walk’ along the microtubules carrying material away from the soma (anterograde transport) or back to the soma (retrograde transport)
what does an axon terminal refer to?
it refers to the axon endings that are somewhat enlarged and often club or button shaped
what do axon terminals do that are part of a nerve cell?
they make synaptic connections with another nerve cell or with an effector cell
what does an axon end in?
a synapse but it is a neuromuscular junction in muscle
what does the axon terminal contain?
it contains vesicles of neurotransmitter
e.g. ACh, noradrenaline, dopamine and serotonin
as nerve impulses travel down axon - what happens?
vesicles fuse with pre-synaptic membrane
neurotransmitter diffuses across synaptic cleft & interacts w/ post-synaptic receptor
how do neurons send messages?
electrochemically
meaning that chemicals (ions) cause an electrical signal
the important ions in the nervous system are sodium and potassium
At rest, describe the concentrations of Na and K:
a higher conc of Na+ is kept outside the cell and higher conc of K+ inside, creating a voltage difference called resting potential
what happens to the Na+ and K+ conc when an impulse moves down an axon?
Na+ move into the cell, creating a reversal in voltage called an Action potential
what happens when a second stimulus is applied to a neuron less than 0.001 second after the first?
it will not trigger another impulse
the membrane is depolarised and the neuron is in its refractory period
how is repolarisation first established?
by the opening of potassium channels and the facilitated diffusion of potassium ions (K+) out of the cell
what happens to Na+ during repolarisation?
they are actively transported back out of cell
in some neurones, how long can the refractory period last?
only 0.001-0.002 seconds - meaning that the neuron can transmit 500-1000 impulses per second
What is happening during nerve conduction/signal transduction?
neurons have a resting potential
the neuron ‘fires’ if a threshold potential is reached
signalling - all or nothing
increased frequency of firing increases intensity of signal
excitatory neurons move the resting potential towards the threshold
inhibitory neurons make resting potential more negative away from threshold
in response to the signal (action potential) what happens to the soma end of the axon?
it becomes depolarised
as the depolarisation spreads down the axon - what is happening?
the first part of the membrane repolarises
Na+ channels are inactivated and additional K+ channels have opened, the membrane cannot depolarise again
the action potential continues to travel down the axon
what does an excitatory postsynaptic potential (EPSP) do?
increases the likelihood of a postsynaptic action potential occurring and are induced by excitatory neurotransmitters (Glutamate)
what does an inhibitory postsynaptic potentials (IPSP) do?
it decreases the likelihood of a postsynaptic action potential occurring and are induced by inhibitory neurotransmitters (GABA)
what is the postsynaptic response a result of?
possibly thousands of synaptic events from many neurones
how is the postsynaptic neuron brought to action potential threshold?
via temporal or spatial summation
spatial summation?
activation of multiple presynaptic terminals can cause summation
temporal summation?
high frequency activation of a single presynaptic terminal can cause summation if interval between impulses < 15 msec
botox?
botulinum toxin
the formation of an action potential can be divided into 5 steps - what is the 1st step?
a stimulus from a sensory cell or another neuron causes the target cell to depolarise toward the threshold potential
the formation of an action potential can be divided into 5 steps - what is the 2nd step?
if the threshold of excitation is reached, all Na+ channels open and the membrane depolarises
the formation of an action potential can be divided into 5 steps - what is the 3rd step?
at the peak action potential, K+ channels open and K+ begins to leave the cell. At the same time, Na+ channels close
the formation of an action potential can be divided into 5 steps - what is the 4th step?
the membrane becomes hyperpolarised as K+ ions continue to leave the cell
The hyperpolarised membrane is in a refractory period and cannot fire
the formation of an action potential can be divided into 5 steps - what is the 5th step?
the K+ channels close and the Na+/K+ transporter restores the resting potential
Describe how synapses function before an action potential occurs:
precursors are taken up and transmitters are synthesised. The transmitter is stored in vesicles and any surplus transmitter is degraded.
Describe how a synapse functions, starting with an action potential:
Action potential
Influx of Ca2+ and release of neurotransmitter which diffuses to the post-synaptic membrane
This NT then interacts with postsynaptic receptors
Once the neurotransmitter has interacted with the postsynaptic receptors - how does the synapse function?
inactivation of transmitter and then reuptake of neurotransmitter
Uptake of neurotransmitter by non-neuronal cells which interact with pre-synaptic receptors
how can neurotransmitters be classified?
by chemical structure e.g. ACh, dopamine
by functional role e.g. excitatory/inhibitory
what molecules are neurotransmitters typically?
typically small, rapid-acting molecules
they are either excitatory e.g. glutamate, acetylcholine
inhibitory e.g. GABA, glycine
or others e.g. noradrenaline, serotonin, histamine, dopamine
