Lecture 2

Question 1

Na/K pump

Answer 1

• integral protein that exchanges 3 sodium ions ( out) with two potassium ions ( in )
• energy dependent process

Question 2

Na/K pump process

Answer 2

1. 3 sodium ions bind to intracellular sites of the pump
2. phosphate group is transferred to the pump via hydrolysis of ATP
3. conformational change occurs, translocating sodium ions across membrane
4. conformational change exposes 2 potassium binding site on extracellular surface of pump
5. phosphate group is removed, pump returns to original conformation
6. this translocates potassium ions across membrane

Question 3

Resting membrane potential

Answer 3

• difference in charge across a membrane when a neuron is not firing
• value inside cell relative to extracellular environment ( -70mV )

Question 4

AP - depolarisation

Answer 4

• in response to a signal initiated by a dendrite, sodium channels open
• Na+ rushes into the cell down electrochemical gradient
• inside of cell becomes more positive
• outside the cell becomes more negative

Question 5

how does lidocaine work?

Answer 5

• lidocaine blocks fast voltage gated Na+ channels
• membrane of the post synaptic neuron can’t depolarise
• neuron will fail to transmit an action potential
• no pain signals propogate to the brain

Question 6

AP - repolarisation

Answer 6

• refers to restoration of membrane potential following depolarisation
• Na channels close
• K channels open
• K+ ions more concentrated inside cell
• causes passive efflux of K+ ions
• causes membrane potential to reurn to more negative internal differential

Question 7

AP - hyperpolarisation

Answer 7

• instead of going back to normal, extra K+ leaves the cell
• due to K+ channels being slow to close

Question 8

Absolute refractory period

Answer 8

• period of time where a 2nd AP cannot occur no matter how strong the stimulus is
• cause : inactivation of Na+ channels ( time taken for channels to rest )
• serves to limit frequency of APs and ensure undirectional APs

Question 9

Relative refractory period

Answer 9

• period of time where a 2nd AP can only occur with a stronger than normal stimulus
• cause : some Na+ channels open & can be activated

Question 10

AP - propogation

Answer 10

• axon surrounded by myelin
• acts as electrical insulation - less voltage loss - signal travels faster
• speed also depends on diameter
• large diameter - faster velocity

Question 11

why is propogation slower for unmyelinated fibres?

Answer 11

in unmyelinated fibres, every part of the axonal membrane needs to undergo depolarisation, propogation slower

Question 12

multiple sclerosis

Answer 12

• immune mediated
• demyelination of fibres
• causes slowing of AP propogation
• CNS disease

Question 13

Guillain Barre Syndrome

Answer 13

• autoimmune disease
• demyelination of axons
• causes slow propogation of AP
• causes immobility
• can recover

Question 14

Synapses

Answer 14

• junction b/w the nerve cell and its target tissue
• are chemical
• central synapse - b/w 2 neurons in CNS
• peripheral synapse - b/w neuron and muscle or gland

Question 15

Neurotransmitter termination

Answer 15

3 ways
* reuptake by astrocytes where the neurotransmitter is stored or destroyed by enzymes
* degradation by enzymes in synaptic cleft such as AChE
* diffusion of neurotransmitter as it moves away from synapse

Question 16

serotonin

Answer 16

• neurotransmitter that affects mood
• lack of it believed to be a cause of depression
• prozac prescribed as an antidepressant
• prozac block serotonin re-uptake (prolongs effect of serotonin)