Neuronal communication 5.3 Flashcards
what are transducers
convert the energy of the stimulus to electrical energy by creating an electrochemical gradient
what is the ‘all or nothing principle’
action potential only happens if the stimulus is strong, if its weak no action potential is produced.
what is the first step of generation and transmission of signal
stimulus
triggers opening of Na+ channels
Na+ diffuses INTO neurone
inside of neurone is less negative
(electrochemical gradient)
what is the second step of generation and transmission of a signal
depolarisation
if P.D reaches threshold value -50 mV
voltage gated sodium ion channels open
more sodium ions diffuse in
(positive feedback)
what is the third step of generation and transmission of a signal
repolarisation
at P.D of +30mV
sodium ion channels close
voltage gated potassium ion channels open
permeablity to K+ ions increase
K+ ion diffuse OUT
(negative feedback)
what is the fourth step of generation and transmission of signals
hyperpolarisation
P.D overshoots because K+ ion channels are slow to close
too many potassium ions diffuse out
at less than - 70 mV
what is the final step of generation and transmission of signals
resting potential
original P.D is restored
non-excited state
how does the pacinian corpuscle work
pressure deforms the membrane
sodium ion channels open
sodium ions diffuse into neuron
depolarisation creates generator potential
if there’s enough sodium ions it reaches threshold potential
what is the node of Ranvier?
gap in the myelin sheath in axon
what is a schwann cell
a cell wrapped around the axon forming the myelin sheath
where is the cell body of the motor/relay/sensory neuron at
cns/cns/pns
what does the motor neuron connect
CNS to effector
what does the relay neuron connect
sensory to motor
what does the sensory neuron connect
PNS to relay
what is the refractory period
the brief period immediately following the response before it recovers the capacity to make a second response
what is a synapse
junction between two or more neurons
what is the synaptic cleft
gap between neurons
what is the presynaptic bulb
axon end of first bulb
what is the presynaptic membrane
on next neuron has receptors and binds to neurotransmitter
describe the transmission across the synapse (6 marks)
1️⃣ Action potential arrives at pre-synaptic bulb → Ca²⁺ channels open
2️⃣ Ca²⁺ influx causes synaptic vesicles to release ACh into synaptic cleft
3️⃣ ACh binds to receptors on post-synaptic membrane
4️⃣ Na⁺ channels open → Depolarization → New action potential
5️⃣ ACh broken down by acetylcholinesterase (AChE) to stop signal
what is a cholinergic synapse
uses the neurotransmitter acetylcholine.
what are the advantages of myelinated neurons
transmit action potential quicker so can reach the end of the neuron faster
they can be longer too so carry impulses at longer distances
what is summation
when several EPSPs are added together
what happens if a neurone is subjected to both stimulation form IPSPs and EPSPs? (6 marks)
- if EPSPs > IPSPs → Membrane reaches threshold → Action potential fires
- If IPSPs > EPSPs → Membrane stays hyperpolarized → No action potential
- If EPSPs ≈ IPSPs → No significant change, neuron remains at resting potential
role of acetylcholinesterase
enzyme
hydrolyses acetylcholine into ethanoic acid
and choline
stops transmission of signals
why do impulses travel in one direction
- from receptors to effector
- cannot go the opposite way
types of sensory neurons and their function
- mechanoreceptors : pressure and movement e.g pacinian corpuscle
- chemoreceptors: chemical e.g olfactory receptors in nose
- thermoreceptors: temperature e.g hypothalamus
- photoreceptors: light e.g rods and cones
describe the sensory neurone
- Carry impulses from receptors to CNS
- Dendron → carries impulse to cell body
- Axon → carries impulse away from cell body
describe the relay neuron
- Found in CNS – connect sensory & motor neurons
- Short & highly branched for fast communication
describe the motor neuron
- Carry impulses from CNS to effectors
- Cell body at one end (in CNS)
- Long axon to transmit impulses to effectors
myelinated Vs unmyelinated
- myelinated = faster impulse - has myelin sheath - saltatory conduction
- vice versa
temporal Vs spatial summation
🔹 Temporal Summation → One neuron fires multiple times quickly
🔹 Spatial Summation → Multiple neurons release neurotransmitters simultaneously
excitatory Vs inhibitory
E:
- increase chance of action potential
- Acetylcholine (ACh) in cholinergic synapses
I:
- Reduce chance of action potential
- GABA
stronger stimulus means?
Higher frequency of action potentials (not higher voltage)
