IC2

Question 1

phases of action potential generation

Answer 1

1) resting membrane potential at -60mV, determined by distribution of K+, Cl-, Na+
2) depolarisation stimulus: voltage gated calcium channels open in response to AP arriving at the axon terminal > excitatory neurotransmitter released at the neuromuscular junction (NMJ) and synapses within the CNS open ligand-gated channels
3) threshold membrane potential: as the cell depolarises, voltage-gated Na+ channels open.
4) rising phase: Na+ rapidly enters the cell through the voltage-gated Na+ channel.
5) overshoot phase: top of rising phase, inside of the cell becomes more positive, reversing the membrane potential polarity
6) falling phase: voltage-gated Na+ channels are inactivated and voltage-gated K+ channels open, increasing permeability to K+ and movement into the cell = membrane potential rapidly repolarises.
7) recovery phase: voltage-gated K+ channels close and membrane potential returns to normal

Question 2

electrical events at the neuromuscular junction

Answer 2

nerve impulse travel from brain > spinal cord > arrival of AP at pre synaptic cell > depolarisation > voltage gated ca2+ channels open > ca2+ influx > fusion of synaptic vesicle w pre-synaptic membrane > transmission of Act to synaptic cleft (NMJ) > ACh bind to post synaptic ligand-gated channels (NICOTINIC RECEPTORS) > ….

Question 3

what is sensory transduction?

Answer 3

transformation of external stimulus to action potential is called sensory transduction.

greater the stimulus strength, greater the frequency of action potentials (intensity = frequency)

Question 3

process of sensory transduction

Answer 3

application of stimulus > depolarisation of receptor membrane at the sensory nerve ending > AP travels to the trigger zone of associated primary afferent > AP moves through myelinated axon (not all are myelinated) > reaches axon terminal causing the release of transmitter

Question 4

nociceptors and their axons?

Answer 4

FOR PAIN

nociceptors are free nerve endings for which sensory transduction occurs.

nociceptor axons include C- and A-delta fibres

Question 5

sensory receptors and signal transduction

Answer 5

sensory receptors are sensory nerve endings that on stimulus > sensory transduction > AP in same cell/adjacent cell > primary afferent nerve fibres > CNS

Question 6

what are the different types of sensory receptors and their stimuli

Answer 6

mechanoreceptor
- mechanical energy (touch, pressure eg vibration, sound)
nociceptor
- tissue damage
chemoreceptor
- chemicals
photoreceptor
- light
thermoreceptor
- heat cold
proprioception
- sense position of body in space

Question 7

example of axon of mechanoreceptor and signal transduction process

Answer 7

A-beta myelinated receptor
has an ENCLOSED NERVE ENDING (not free nerve ending like nociceptors)

Question 8

what is the area of skin that will excite a receptor called

Answer 8

receptive field

Question 9

properties of C- and A-delta axons

Answer 9

C- axons are NOT myelinated

A-delta axons are only THINLY myelinated

nerve endings are FREE (NOT enclosed)

Question 10

TrpV1

Answer 10

protein molecule found on the membrane of nerve endings of NOCICEPTORS;

responds to high temps and certain chemicals eg capsaicin

gated channel that allows the permeation of calcium ions on stimulation.

Question 11

how does myelination affect sensory transduction?

Answer 11

thick myelination = faster conduction of signal.

no myelin eg in C = slowest conduction

Question 12

what happens in individuals with CIPA?

Answer 12

congenital insensitivity to pain with anhidrosis (CIPA)
- insensitivity to superficial and deep pain stimuli = decreased or loss of sensation WHILE RETAINING touch, vibration, position senses.

could be due to absence of nerve growth factor (NGF) dependent C/A-delta fibres due to loss of function mutation in NTRK1 gene on chromosome 1q21-22.

Question 13

what are the post-synaptic targets in a neuronal cell?

Answer 13

target for excitatory synapse is DENDRITE

for inhibitory synapse is SOMA

Question 14

movement of K+ in the neuronal cell?

Answer 14

movement OUT
- diffusion down gradient via leakage channels = negative charge on the inner plasma membrane face

movement INTO
- negative charged established attracts K+ back into the cell

electrochemical gradient

Question 15

how does hypokalemia affect signal transduction?

Answer 15

eg overuse of diuretics resulting in hypokalemia

concentration of k+ outside is decreased causing the gradient to favor movement out of cell = hyperpolarised = cells become less excitable = muscle paralysis?

Question 16

Broca’s area

damage

Answer 16

found in left hemisphere

damage = difficulty expressing language

Question 17

how do signals move in an axon during signal transduction?

Answer 17

the AP jumps from node to node (saltatory conduction)

between nodes of Ranvier, found between myelinated axons.

Question 18

Wernicke’s area
damge

Answer 18

found in left hemisphere

damage = difficulty comprehending language

Question 19

depression is marked by effect of which part of the brain

Answer 19

subgenual anterior cingulate cortex (ACC)
found anterior to the hypothalamus, at the frontal cortex region

increased activity of subgenual ACC associated with depression

brain stimulation of subgenual ACC may decrease activity = decrease depression symptoms.

Question 20

limbic structure

Answer 20

HIPPOCAMPUS
lesions of the medial temporal, more specifically hippocampus =
loss of memory for events (part of declarative memory) = eg Alzheimer’s

AMYGDALA
- also found in the limbic structure, involved in emotion and emotional memory = involved in mood changes

Question 21

Urbach wiethe disease

Answer 21

= amygdala

emotion and emotional memory
for mood changes

= cannot recognise facial expressions or emotions.

Question 22

what is equilibrium potential and how to calculate?

Answer 22

E = 58log(ECF/ICF)

equilibrium potential represents the potential at which the inward and outward gradients acting on the ion balance out and there is no net movement of ion across the membrane

ie electrochemical gradient of potassium in the neuron due to the leakage channels vs pull from negative charge

Question 23

E vs MP

Answer 23

membrane potential represents the concentration and permeability of the ions distributed across the membrane

Question 24

effect of E on MP

Answer 24

membrane potential will try to push towards the E value.

equilibrium between the movements = membrane potential remains at -80/60mV

if negative E = move out
if positive E = move in
size of E affects rate of movement

Question 25

absolute refractory period
VS
relative refractory period

Answer 25

absolute:
- during the rise and peak
- second AP cannot be initiated

relative:
- hyperpolarisation after the fall

Question 26

different types of synpases

Answer 26

electrical synapse:
- small synaptic cleft, current generated in the presynaptic neuron flows directly into the postsynaptic cell via gap-junction channels (specialised bridging channels)

chemical synapse:
- separated by synaptic cleft
consider NMJ

Question 27

what does frontal lobe play a part in?

Answer 27

involved in personality traits