5.1.3 - neuronal communication Flashcards
stimulus
changes in the internal and external environment
neurones
transmit electrical impulses rapidly around the body so that the organism can respond to changes in its internal and external environment
cell body of a neurone
contains the nucleus surrounded by the cytoplasm
lots of ER and mitochondria
dendrons
short extensions which come from the cell body - responsible for transmitting electrical impulses towards the cell body
axons
singular elongated nerve fibres that transmit impulses away from the cell body - can be very long
sensory neurones
transmit impulses from a sensory receptor cell to other neurones
one dendron and one axon
relay neurone
transmit impulses between neurones - lots of axons and dendrons
motor neurones
transmit impulses from a relay/sensory neurone to an effector.
one axon and many short dendrons
myelin sheath
covers axons of some neurones, made up of many layers of plasma membrane and acts as an insulating layer
advantages of a myelienated neurone
faster transmission
features of all sensory receptors
- specific to a single type of stimulus
- act as a transducer - convert a stimulus into a nerve impulse
pacinian corpuscle
specific sensory receptors that detect mechanical pressure
most abundent in the fingers and soles of the feet
structure of a Pacinian corpuscle
neurone ending surrounded by many layers of connective tissue. each layer of tissue is separated by a layer of gel.
steps of how the Pacinian corpuscle converts mechanical pressure into a nervous impulse
- resting potential
- pressure is applied and the corpuscle changes shape - causing membrane to stretch
- sodium channels widen, sodium ions can diffuse in
- influx of + sodium ion causes depolarisation
- action potential
- action potential transmitted along sensory neurone
resting potential
when a neurone is not transmitting an impulse - the outside of the membrane is more positively charged than inside, so it is polarised
resting potential ion movement
- sodium potassium pump - ACTIVE TRANSPORT - 3Na+ pumped out, 2K+ pumped in
- sodium ion channels are CLOSED so cannot diffuse back in
- potassium channels are OPEN so can diffuse back out
= more positive outside the membrane
action potential ion movement
- sodium channels OPEN - Na+ can diffuse in
- the mmore that diffuse in, the more that open - positive feedback causing influx of na+ ions
- potassium ion channels CLOSED
= DEPOLARISATION
repolarisation
the neurone returning back to the resting potential.
hyperpolarisation
initially lots of potassium ions diffusing out of the axon, resulting in the inside of the axon becoming more negative than in its normal resting stage
propagation of an action potential - non myelinated neurone
first region is depolarised, then this acts as a stimulus for the depolarisation of the next region of the membrane, this process continues due to a localised current of sodium ions
refractory period
short period of time after an action potential when the axon cannot be excited again.
why is the refractory period important?
prevents the propagation of an action potential backwards along the axon as well as forwards - makes sure action potentials are unidirectional
difference between action potentials in mylenated axons and non
much faster as can only take place at the nodes so will ‘jump’ from one node to another
other factors that affect the speed at which action potentials travel
- axon diameter - the bigger the diameter, the faster the impulse (less resistence to the flow of ions in the cytoplasm)
- temperature - the higher the temp, the faster the nerve impulse (ions diffuse faster)
all or nothing principle
if the threshold value is reached, the action potential will always be created no matter how large the stimulus is, the same sized action potential will always be triggered.
synaptic cleft
the gap which separates the axon of one neurone from the dendrite of the next neruone
synaptic knob
the swollen end of the presynaptic neurone - contains lots of mitochondria and large amounts of ER
excitatory neurotransmitters
result in the depolarisation of the post synaptic neurone
e.g acetylcholine
inhibitory neurotransmitters
neurotransmitters that result in the hyperpolarisation of the postsynaptic membrane
e.g GABA
synaptic transmission steps
- action potential enters presynaptic neurone
- depolarisation of the presynaptic membrane so calcium ion channels open
- calcium ion influx
- synaptic vesicle fuses with membrane, releasing neurotransmitter into synaptic cleft
- neurotransmitter diffuses across synaptic cleft and binds to recptors on post synaptic neurone
- sodium ion channels open, causing influx of sodium into postsynaptic neurone
- triggers an action. potential
how are the neurotransmitters removed after the action potential?
neurotransmitter is broken down by the enzyme, releasing it from the receptors, and the products are taken back to the presynaptic knob
acetylcholine is hydrolysed by acetylcholinesterase to form choline and ethanoic acid
why are the neurotransmitters removed?
so that the stimulus is not maintained and anoother stimulus can arrive and affect the synapse
role of the synapse in the nervous system
- ensure impulses are unidirectional
- allow an impulse from one neurone to be transmitted to a number of neurones at multiple synapses
how do synapses result in undirectional movement
receptors are only present in the postsynaptic membrane
summation
if the amount of neurotransmitter builds up sufficiently to reach the threshold, this will trigger an action potential
spatial summation
occurs when a number of presynaptic neurones connect to one postsynaptic neurone - each release neurotransmitter which builds up to a high enough level to trigger an action potential
temporal summation
occurs when a single presynaptic neurone releases neurotransmitter as a result of action pontial several times over a short period.
