Module 5.3 Flashcards
Neuronal communication
what are sensory receptors
specialised cells that can detect changes in our surroundings
most are energy transducers
what is a transducer
converts one form of energy into another
what is a pacinian corpuscle
pressure sensor that detects changes in pressure on the skin
structure of a pacinian corpuscle
series on concentric rings of connective tissue wrapped around the end of a nerve
How does a pacinian corpuscle work
when pressure on the skin changes the connective tissue rings deform which pushes against the nerve ending
function of a sensory neurone
carry the action potential from a sensory receptor to the CNS
function of a motor neurone
carry an action potential from the CNS to an effector such as a muscle or gland
structure of a relay neurone
dendrites
cell body
axon
synaptic endings
function of a relay neurone
connect sensory and motor neurones
structure of a motor neurone
dendrites
cell body
axon
axon terminals
structure of a sensory neurone
sensory receptor
dendron
cell body
axon
synaptic ending (in the CNS)
difference between types of neurone
motor neurones have their cell body in the CNS and have a long axon
sensory neurones have a long dendron which goes to the cell body just outside the CNS then a short axon going into the CNS
relay neurones have many short dendrites and a short axon
what makes neurones myelinated
schwann cells wrap around the neurone forming a fatty sheath
function of myelinated neurones
most sensory and motor neurones associated with schwann cells
prevent the movement of ions across the membrane so it can only occur at the nodes of ranvier
impulse jumps from one node to the next which is faster
function of non-myelinated neurones
also associated with schwann cells but one schwann cell wrap around several neurones
impulse moves along the neurone in a wave which is slower
advantages of myelination
quicker transmission
100-120 m/s vs 2-20 m/s
carry action potentials over longer distances
carry impulse from receptor to CNS and from CN to effector
non-myelinated often used in coordinating body functions where speed is not needed
what is the resting potential voltage
60-70 mv
what do sodium potassium pumps do at rest
pump 3 sodium ions out for every 2 potassium ions that are pumped in
what do voltage-gated sodium channels do at rest
they are closed
what do potassium channels do at rest
some are open so membrane is more permeable to potassium than sodium
What is a node of ranvier
areas of the neurone between schwann cells where ions can diffuse across the membrane
how is an action potential started
generator potential from synapse or stimulus in the generator region of a neurone
what happens to the voltage gated-sodium channels when generating an action potential
a few open allowing sodium ions into the cell
produces a small depolarisation
sodium ions diffuse causing other voltage gated channels to open
What voltage is an action potential
+40mV
what voltage is the threshold potential
-50 mv
what happens after an action potential
sodium channels close
potassium channels open
What is repolarisation
potassium ions diffuse out of the cell making the cell negative again
What is hyperpolarisation
potential difference overshoots slightly to over the resting potential
ensure the action potential does not flow backwards
What is the refractory period
after an action potential the sodium and potassium ions are in the wrong place
it is impossible to stimulate the neurone into another action potential for a short time until cell is restored by odium potassium pumps
also stops action potential travelling wrong way
what are local currents
when sodium ions are allowed to flood into the neurone causing depolarisation
sodium ions move down concentration gradient to other regions
propagation of action potential in unmyelinated neurones
local currents
movement of sodium ions away from point in membrane causing other sodium channels to open allowing for more sodium ions to enter
which depolarising the surrounding membrane causing more opening of sodium channels etc
propagation of action potential in myelinated neurones
saltatory conduction
ionic movement only occurs at the nodes of ranvier
sodium ions diffuse from one node to another
the action potential jumps
advantages of saltatory conduction
speed of transmission is increased
what is the intensity of all action potentials
+40mv
how is intensity of a stimulus conveyed
higher frequency of action potentials
what is the pre-synaptic bulb
the end of a presynaptic neurone before the synapse
What are the specialised features of the pre-synaptic bulb
many mitochondria for ATP
large amount of smooth ER for packaging NTs in vesicles
Large number of vesicles
Large number of voltage gated calcium channels on the plasma membrane
specialisations of the post-synaptic membrane
specialised sodium ion channels that can respond to acetylcholine
channels have specific receptor site for NT
What happens in the presynaptic bulb to transmit a signal
action potential opens voltage gated calcium channels
calcium ions diffuse into synaptic bulb
calcium ions cause vesicles to move to and fuse with the presynaptic membrane
Acetylcholine is release through exocytosis
What happens on the post synaptic membrane to transmit a signal
acetylcholine binds with receptor sites on sodium ion channels
sodium ion channels open
sodium ion channels diffuse into post synaptic neurone
generator potential/excitatory post-synaptic potential is created
if threshold potential is reached new action potential is created
what does acetylcholinesterase do
hydrolyses acetylcholine into ethanoic acid and choline so acetylcholine left in the cleft is not constantly opening sodium channels on post synaptic membrane
products are recycled
What is an excitatory post synaptic potential
makes the neurone more likely to continue the action potential
depolarises membrane
alone is not sufficient to produce an action potential in a post synaptic neurone
what is summation
when several excitatory post synaptic potentials combine together to increase the membrane depolarisation to reach the threshold
What is temporal summation
when summation results from several action potentials in the same presynaptic neurone
what is spatial summation
when summation results from actions potentials arriving from several different presynaptic neurones
What is an inhibitory post synaptic potential
reduce the chance of an action potential in the post synaptic neurone
reduce the effect of summation
