5.3 neural communication Flashcards
define sensory receptors
specialised cells that can detect changes/ of internal or external environments and can create an action potential
define transducer
a cell that converts one form of energy into another
what type of signal is created in the form of electrical energy
nerve impulse
define pacinian corpuscles
a pressure sensor that detects changes in pressure on the skin
what do photoreceptors(cones/rods) detect and where
changes to light intensity
retina
what do audio receptors detect and where
changes to sound/ vibrations
ear/cochlea
what does the pacinian corpuscle detect and where
changes to pressure
skin
what do oflactory cells detect and where
chemicals in the air
nose
what do chemoreceptors detect
changes to chemicals in food/air etc.
describe the structure of a pacinian corpuscle
oval shaped
series of concentric rings of connective tissue
around the end of a nerve cell
what happens when pressure on the skin changes
pacinian corpuscle rings of connective tissue deforms which pushes against nerve ending
how are nerve impulses generated
when pressure changes/ PC deforms = sodium channels are forced open
sodium cells diffuse into the cell
generator potential produced
Na+/K- pump in the membrane pumps 3 sodium out for every 2 potassium in
creates concentration gradient conc. of sodium outside increasing
conc. K inside increasing
membrane is more permeable to K- so some leak out
result of these ionic movements is a potential gradient across the cell membranes
cell is negatively charged
what is depolarisation
movement of ions across the membrane creates a change in the potential difference/ charge across the membrane
the inside of the cell becomes less negative compared to outside than usual
what causes an action potential to be initiated
larger stimulus so more gated channels will open
if enough are open then enough sodium ions enter the cell
potential difference changes significantly and will initiate an AP
what is a myelinated neurone
has an individual layer of myelin around it
what is the myelin sheath composed of
schwann cells
what are nodes of ranvier
gaps in the myelin sheath
what is a non-myelinated neurone
has no individual layer of myelin
what does a myelin sheath do
insulates myelinated neurones
function of sensory neurone
carries an impulse from receptor to CNS
structure of a sensory neurone
a long dendron
carry action potential from a sensory receptor to cell body
short axon carrying action potential into the CNS
function of a relay neurone
carries impulse from sensory neurone to motor neurone
structure of a relay neurone
connects sensory to motor neurone
many short dendrites and a short axon
function of a motor neurone
transmits impulse to the effector
structure of a motor neurones
cell body in the CNS
long axon that carries the action potential to effector
structure of a cell body
nucleus
many ER, mitochondria and ribosomes
structure and function of a dendron
extension from cell body
transmits impulses towards cell body
structure and function of a dendrite
connects to other neurones
carries impulses towards the cell body
structure and function of an axon
long nerve fibres
transmits impulses away from cell body
what do neurones maintain a potential difference across
cell surface membrane/ plasma membrane
advantage of neurone structure
long - transmit action potential over a long distance
many gated ion channels - control the entry of ions
define resting potential
the potential difference across the membrane whilst the neurone is at rest
how is resting potential established
Na+ ion gates fully closed
K+ ion gates are leaky/ more permeable = inside is more negative
sodium potassium pump
pumps out 3Na+ ions and pumps in 2K+ ions
using active transport
so inside becomes more negative
what is resting potential at
-60mV
where does the exchange of Na+K happen in myelinated neurones
nodes of ranvier
how do you generate an action potential
higher conc. of Na+ outside the membrane
some Na+ open = Na+ diffuse down the conc. gradient
(membrane depolarises)
if large enough = passes threshold = action potential caused
voltage gated Na+ channels open
depolarisation reaches +40mV inside the cell
stages of an action potential
membrane in resting state (polarised with -60mV inside)
higher Na+ inside, higher K+ outside
Na+ channels open = some Na+ diffuse into cell
membrane depolarises = becomes less negative (threshold -50mV)
positive feedback causes voltage gated Na+ ion channel to open
more Na+ = inside more positive (+40mV)
Na+ channels close and K+ open
K+ diffuse out
potential difference inside now negative (repolarisation)
potential difference overshoots = cell hyperpolarised (-70mV)
original resting potential restored (resting state)
explain how positive feedback works when an action potential is generated
when there is sufficiant generator potentials to reach threshold = more Na+ gated channels open
describe what the refractory period is
after an action potential = Na+ K+ are in the wrong places
concentration of them is restored by the sodium potassium ion pump
during this time another action potential cannot occur
what does the refractory period stop from happening
the action potential going in the wrong direction
it keeps it going in one direction
how is an action potential moved down a neurone
local currents caused by Na+ cause depolarisation
describe how an action potential is moved down a neurone by local currents
when Na+ channels open and Na+ diffuse in
Na+ diffuse sideways along neurone (away from the area of higher concentraion)
this is the local current
causes slight depolarisation further down
causes Na+ voltage gated channels to open
the open channels allow rapid influx of Na+
causes a full depolarisation
why doesn’t an action potential reverse its direction
concentration of Na+ behind the action potential is still high
describe saltatory conduction
ionic movement only occurs at nodes of ranvier, cannot occur over myelin sheath
Na+ diffuse along from nodes of ranvier to the next
action potential jumps from one node to the next
advantages of saltatory conduction
conducts action potential more quickly
what is the all or nothing rule
an impulse/ action potential are all the same intensity and will all produce a depolarisation of -40mV
what is the significance of the frequency of transmission in an action potential
stimulus at higher intensity = more sodium channels are open in the sensory receptor = more generator potentials produced
= more frequent action potentials produced
what is a cholinergic synapse
a synapse that uses acetylcholine as a neurotransmitter
what is a neurotransmitter
chemical used as a signalling molecule between two neurones in a synapse
what is a synapse
the junction between two or more neurones where they can communicate with/signal to each other
what is a synaptic cleft
gap between two neurones
structure of a cholinergic synapse
acetylcholine as neurotransmitter
synaptic cleft between neurones
what is the pre synaptic bulb
the end of a pre synaptic neurone
features of a pre synaptic bulb
many mitochondria
large amount of smooth endoplasmic reticulum - packages neurotransmitter into vesicles
lots of vesicles
voltage gated calcium ion channels
describe the post synaptic membrane
contains specialised sodium ion channels
receptor that is specific to acetylcholine
acetylcholine present in synaptic cleft = sodium ion gate opens
transmission across the synapse
action potential arrives at bulb
voltage gated calcium ion channels open
calcium ions diffuse into synaptic bulb
calcium ions causes synaptic to move and fuse with pre synaptic membrane
acetylcholine is released (exocytosis) diffuses across cleft
binds to receptor sites on sodium ion channels in post synaptic membrane
sodium ion gates open
sodium ions diffuse into post synaptic membrane
generator potential created
new action potential created if above threshold
what is the role of acetylcholinesterase
enzyme in synaptic cleft that stops the transmission of signals
by hydrolysing acetylcholine into ethanoic acid and choline (recycled into it) so no more action potentials continue to happen
how is neural communication an example of cell signalling
transmitter released by pre synaptic membrane and post synaptic neurone responds to it
what is summation
occurs when effects of several excitatory post synaptic potentials are added together
excitatory post synaptic potential
one action potential only causes a few vesicles to move on and fuse with pre synaptic membrane = few acetylcholine molecules diffuse across = small depolarisation = not sufficient to cause action potential in post synaptic neurone
inhibitory post synaptic potentials
an impulse which can reduce the effect of summation/ prevent an action potential in the post synaptic neurone
temporal summation
several action potentials in the same pre synaptic neurone
spatial summation
action potentials arriving from several different pre syanptic neurones
how can an action potential be transmitted to several parts of the nervous system
one pre synaptic neurone might diverge to several post synaptic neurones
explain what happens if we become habituated to stimulus
after repeated stimulation a synapse may run out of vesicles containing neurotransmitter = habituated to it
