the synapse- lecture 4

Question 1

who discovered the synapse

Answer 1

Ramon and Cajal

Question 2

what did ramon and cajal find

Answer 2

• neurons dont physically touch each other- theyre seperated by tiny gaps (synapses)
• synapses allow neurons to communicate
• recieving neruon is depolarisation- excitatory post synaptuc potential (EPSP)
• recieving neuron is hyperpolarisation- inhibitory post synaptic potential (IPSP)
• reflex arcs

Question 3

what is an reflex arc

Answer 3

automated (involuntary) response to stimulus e.g. muscle flexing reflex- a sensory neuron excites an interneuron which excites a motor neuron triggering the muscle to contract- sherrington (1906), Eccles (1963)
speed of a conduction (stimulus to response) significantly slower in a reflex arc compared to a conduction along a single axon, conduction is slower because delays at junctions (synapses)

Question 4

what happens when a single weak stimulus is applied

Answer 4

a reflex unlikely to occur BUT
if several weak stimuli are rapidly applied their cumulative strength can be sufficient to trigger a reflex- this is called temporal summation e.g. single pinch may not give response but a lot of quick pinches would- temporal summation

Question 5

what happens if a signal is sent when a single or uncoordinated stimuli is in one location

Answer 5

might not produce a reflex BUT
if several seperate stimuli are simultaneously recieved at different locations thier cumulative input strength can trigger a reflex- this is called spatial summation

Question 6

all or nothing principle

Answer 6

• an action potential is either produced or not produced
• if stimuli is of sufficient strength (exceeds excitary threshold)- there will be an action potential
• BUT the same sensory experiences and responses can be weak or intense

Question 7

rate law

Answer 7

• strength of stimulus affects the rate of firing
• a strong stimulus produces more action potentials than a weak stimulus
• the more the axon fires the greater the response

Question 8

post synaptic responses

Answer 8

the stimuli recieved will alter the charge (positive or negative) of the post synaptic membrane on the recieving neuron

Question 9

excitation

Answer 9

if recieved stimuli causes recieving neuron to become more positive (depolarisation) (EPSP)

Question 10

inhibition

Answer 10

if recieved stimuli causes recieving neuron to become more negative (hyperpolarisation) (IPSP)

refractory periods in action potentials

NO responses when axon is hyperpolarised (-ve)

IPSPs dont produce an action potential at next neuron

Question 11

what determines the nature of the post synaptic response?

Answer 11

all inputs are integrated in the recieiving neuron (neural integration)

the NET SUMMATION of these inputs determines the response

Question 12

net summation

Answer 12

• the more ESPSs received the greater the firing rate of recieving neuron
• if more ISPSs are recieved the firing rate of recieving neuron is reduced
• if only ISPSs are recieved (no EPSPs) the neuron will not fire

Question 13

who discovered chemical events at the synapse?

Answer 13

loewi (1920s)

Question 14

loweis (1920)

Answer 14

• stimulated the vegus of frog nerve causing the slowing of the heart- extracted the fluid from the heart then injected this to another frog and it slowed the other frogs heart
• discovered that nerves send messages through chemicals (neurotransmitters)- discovered acteylcholine

Question 15

parkinsons disease

Answer 15

progressive motor disorder

bradykinesis- slownes of movement, impairment dexterity, drooling, expressionless face

tremor at rest- involuntary shaking- typically starts in one hand

involves communication in midbrain

dopamine responsible for communication in brain that determines stability

in parkinsons- neurons responsible for secreting dopamine destroyed in the substantia nigra