5.3 neuronal communication Flashcards
chemoreceptors
detect chemicals
thermoreceptros
detect heat
mechanoreceptors (baroreceptors)
detect pressure
phtoreceptors
detect light
receptors are
SPECIFIC to one stimulus
transducer
a cell that can convert from x energy to electrical energy (eg light/chemical to electrical)
how can u become habituated (Desensetitsed) to something
- recpetors detect a CHANGE in the encironemnt, so if the stimulus is constant it wont continue t cause a response
- sodium channels remain open!!!!!!!
- limited amount of neurotransmitter, os eventually it stops being released across a synapse
how does a pacinian corpuscle work?
- baroreceptors
- layers of connective tissue around a sensory nerve fibre
- contain STRETCH MEDIATED Na+ channels
- typically, they are clsed. but when pressure applied, the channels are DEFORMED , and open. rapid influx of na+ ions, causing depolarisation, causing a generator potnetia and then action potential
resting potential
- approx -70
- maintained by SODIUM POTASSIUM PUMP
- 3Na+ out, 2 K+ in
motor neurones (direction)
CNS [RELAY] to effector (muscle/gland)
sensory neurones (direction)
sensory receptor to CNS
relay neurones (direction)
connect sensory to motor
specialisation of neurones
- myelin sheath => more efficient
- plasma membrane contains many ion channels
- plasma membrane contains many na+ k+ pump
- ## very long => transmit over a long distance
how to recognise sensory nuerone
- LONG dendron (before body)
- small cell body halfway down
- short axon (After body)
how to recognise motor neurone
- long axon
- cell body in the cns (At the end)
how to recodnise realy neruone
- short axon
- many dendrites
describe steps of action potential
- RESTING POTENTIAL: -70. 3na+ out, 2k+ in
- GENERATOR POTENTIAL (caused by a receptor) na+ channels open, and if past threshold potentia then causing
- DEPOLARISATION: na+ channels open, na+ facilitated diffusion down ECG into neuron, until reaches approx +40
- REPOLARISATION: na+ channels CLOSE, k+ channels OPEN. K+ move out of neruone FD down ecg. voltage is lowering
- HYPERPOLARISATION: voltage goes even more negative than resting. k+ channels too slow to close, so too many k+ out. sodium potassium pump kicks in to return
threshold potential
- minimum voltage needed to trigger an action potential
refractory period
- action potential cant occur
- ensures action potentials DONT OVERLAP
- and are UNIDIRECTIONAL
local current
- depolarisation: na+ mve through na+ channels into neruone down ECG
- open channels allow na+ to diffuse along sideways (local current)
- causes slight depolarisation further along neruone, causing POSITIVE FEEDBACK: causes more voltage gated na+ channels to open caysing FULL DEPOLARISATION
- unidirectional as only diffuses down CG, and due to refractory period
- OVERALL CALLED A WAVE OF DEPOLARISATION
myelin sheath
- insulating layer of fatty material , made of SCHWANN cells wrapped around neurone
- gaps in betwteen the scwhann cells are the NODES OF RANVIER
saltatory conduction
- in the myelinated parts of the nurone, as its an insulator, there can be NO MOVEMENT OF IONS
- So action potenitals can only occur at the NODES OF RANVIER; the AP will jump between them
- much faster than local current
Why are action potentials described as ‘all or nothing?’
- only if a threshold voltage is reached, an action potential occurs
- action potential is always of the same MAGNITUDE regardless of strengt
- stronger stimulus = more frequent action potentials
what efects the strength of the action potential
the FREQUENCY OF THE ACTION POTENTIALS
- stronger stimulus = more na+ channels opened, more generator potenntials, more frequenct action potentials
synapse
gap between neurones
why do u need neurotransmitters
electrical impulses cant pass through the gap
end of presynapctic nueron
synpatic KNOB
HOW DOES SYNAPTIC TRANSMISSION WORK
- action potential arrives at the synaptic knob, triggering opening of VOLTAGE GATED CA2+ CHANNELS
- they flood the tip of the knob by FACILITATED DIFFUSION, causing vesicles containing the NT to fuse with the presynaptic membrane
- NT released by exocytosis
- NT diffuse across synaptic cleft, bind to specific complementary receptors on the postsynaptic membrane
- triggesr na+ channels to open, na+ enters neurone, causing DEPOLARISATION and an action potenital is threshold voltage is reached
- enzyme eg actylcholine esterase hydrolyses ach into ethanoic acid and choline. STOPS SIGNALS so no more action potneitals
what happens to the hydrolysed choline and ethanoic acid
diffuse back to synaptic bulb and ATP is used to reform ach, which is stored in vesicles
which synapses use ach
cholinergic
summation
when the effects of several ESPS are added together
spatial summation
lots of presynaptic nuerones converge to one sungle postsynaptic nuerone
- several excitatory post synaptic potentials have to be added together in order to reach the threshold voltage
temporal summation
a single neuron fires a series of action potentials in succession until the threshold voltage is reached
Ipsp
inhibitory post synaptic potential
- prevent an action potential in the post synaptic neuron
how does the synapse ensure unidrectional?
- only the PRE synaptic membrane contains ach
- only the PRE synaptic membrane contains ca2+ channels
- and only the POST synaptic membrane has the speccific complmentary receptors
- POST has enzymes to break down nuerotransmitter
how does the synapce filter our low level stuff?
- several vesicles of NT must be released in order to create an action potential in the post synaptic
in the cell body there is lots of?
SER => synthesis neurotransmitters
MITOCHONDRIA => atp for active transport in the pumps
WHEN SAYING A GENERATOR POTENTIAL SAY THE MEMRBANE
depolarises
what exactly does hte myelin sheath insulate
axon
hy is transmission of action potentials along the axon slower in the absence of saltatory conduction?
- no nodes of ranvier
- whole axon has to be depolarised
na+ k+ pump is
always open during action potential
importance of a synapse (4)
- ensures unidirectional flow
- allows for SUMMATION (enough impulses arrive to trigger an AP in the next nuerone)
- filters out ‘low level’ stimuli
- can have excitatory and inhibitory
where is the thermoregulatory centre located in the brain
hypothalamus
differences in STRUCTURE of motor vs sensory neurones
MOTOR:
- longer axon
- cell body at end
- NO DENDRON
- cell body in CNS (sensory in PNS)
all action pitentials have the same…
MAGNITDUE
what produces myelin sheath
schwann cells
importance of myelin
- schwann cells produce
- insulated the axon
- speeds up rate of transmission of AP
- saltatory conduction as AP can only occur at nodes of ranvier
describe structure of myelin sheath
- schwann cells wrapped around axon
SIMILARITY motor and senosry
- dendrites
- axon
- myelinated
- cell body WITH NUCLEUS, SER
- sodium potassium pump, voltage gated chanels
How does sweat work
- cools body
- water has high LHV
- so heat energy from skin used to evaporate it
pressure receptors convert which type of energy to electrical
mechanical
all or nothing law
if the stimulus is not strong enough, an action potential wont be generated
local circuits in myelinated
- FEWER
- LONGER
explain why saltatory is faster?
- nodes of ranview are the ONLY parts with ion channels
- only parts where ions can flow
- only parts where depolarisation can occur
- so fewer local circuits
