Physiology 1

Question 1

what are the 5 regions of a neurone?

Answer 1

dendrites (receive inputs)
cell body/soma
axon hillock and initial segment (site of initiation of the all or none action potential)
axons (conducts output signal)
synapse (point of chemical communication)

Question 2

function of cell body/soma?

Answer 2

synthetic and metabolic centre
contains nucleus, ribosomes and ER
integrates incoming signals that are conducted passively to axon hillock

Question 3

what are the 4 types of neurone?

Answer 3

unipolar - e.g peripheral autonomic neurone
pseudounipolar - e.g dorsal root ganglion neurone
bipolar - e.g retinal bipolar neurone
multipolar - e.g lower motor neurone

Question 4

neurones are classified according to what?

Answer 4

shape

- number and conformation of processes (neurites) arising from the cell body

Question 5

what are the 4 functional regions of the neurone?

Answer 5

input (where input connects to dendrite)
integrative (cell body)
conductile (myelinated axon)
output (synapse)

Question 6

describe the process of an action potential occurring in a neurone?

Answer 6

resting membrane potential = -70mV
depolarizing stimulus occurs causing membrane potential to increase to threshold (-60mV)
once threshold is reached, membrane potential increases rapidly during upstroke via voltage activated Na+ channels
- upstroke temporarily overshoots where membrane potential becomes positive (+40mV)
downstroke then occurs where membrane potential decreases rapidly from +40mV via voltage activated K+ channels
- downstroke temporarily undershoots where membrane potential becomes even more negative than resting potential (-80mV)
membrane potential then increases back to resting potential

Question 7

what do action potentials allow?

Answer 7

allow electrical signals to be conducted over large distances without decaying
- nerve cell membrane is leaky, therefore passive signals do not spread far from site of origin due to current loss across membrane

Question 8

how does current leak across the nerve cell membrane?

Answer 8

current leaks back into the extracellular space across the membrane resistance generating a potential change across the membrane
for a given current, potential change across the membrane increases linearly with membrane resistance (Ohm’s Law)

Question 9

how does potential change across the membrane change in the absence of an AP?

Answer 9

passive process which decays exponentially with distance

- the distance a current can travel depends on membrane resistance and axial resistance of the axoplasm

Question 10

what is the length constant?

Answer 10

constant used to quantify the distance a current will travel passively along a neurite (longer length constant = current travels further)

• further spread of current = increased AP conduction
• increasing ratio of membrane resistance/axial resistance increases length constant

Question 11

how can distance of passive current spread be increased? (and therefore increased AP velocity)

Answer 11

decrease Ri (increase axon diameter)
increase Rm (add insulating material like myelin)
equation - length constant = (Rm/Ri) to power of 0.5

Question 12

what is saltatory conduction?

Answer 12

where action potential jumps from one node of ranvier to the next

• voltage activated Na+ channels cluster together at nodes
• affected by demyelinating disorders (MS, guillian barre)

Question 13

summarize chemical neurotransmission transmission?

Answer 13

1. uptake of precursor
2. synthesis of transmitter
3. storage of transmitter
4. depolarization by AP
5. Ca2+ influx through voltage activated Ca2+ channels
6. Ca2+ induced release of transmitter (exocytosis)
7. receptor activation
8. enzyme mediated inactivation of transmitter or reuptake of transmitter

Question 14

what are the 4 structural elements of the chemical synapse?

Answer 14

pre and post synaptic membranes separated by synaptic cleft
matrix of fibrous extracellular protein within cleft (holds membranes together)
vesicles within presynaptic terminal that store neurotransmitter
membrane differentiations
- presynaptically form active zones where vesicles cluster
- postsynaptically contain neurotransmitter receptors (postsynaptic density)

Question 15

what are the 3 morphological classifications of synapse?

Answer 15

axodendritic (axon of one neurone synapses on the dendrite of another)
axosomatic (axon of one neurone synapses on soma of another)
axoaxonic (axon of one neuron synapses on axon of another which then synapses on soma of another)

Question 16

what are the 2 functional classifications of synapse?

Answer 16

excitatory synapse
- transmitter usually glutamate
- depolarizes
inhibitory synapse
- transmitter usually GABA or glycine
- hyperpolarizes

Question 17

major amino acid neurotransmitters in the CNS?

Answer 17

glutamate
GABA
glycine

Question 18

which channels are involved in excitatory and inhibitory synapses?

Answer 18

excitatory = glutamate = Na+
inhibitory = GABA/glycine = Cl-

Question 19

what are the 2 types of synaptic integration?

Answer 19

spatial summation
- many inputs converge on a neurone to determine output (can be net excitation or inhibition)
temporal summation
- single input may modulate output by variation in AP frequency of that input