Model Answers Flashcards
(8 cards)
Explain how the pacinian corpuscle works (pressure)
1- in resting state, stretch mediated Na+ channels too narrow to allow sodium ions to pass through therefore resting potential
2- when pressure applied it changes shape and causes membrane to stretch
3- when membrane stretches, Na+ channels widen which allows sodium ions to flow through
4- influx of sodium ions causes depolarisation which results in generator potential
5- the generator potential causes action potential which is passes along sensory neurone to CNS
How is a resting potential maintained
1- sodium potassium ion pump pumps Na+ ions actively pumped out of axon membrane whereas K+ pumped into
2- for every 3Na+ pumped out, 2K+ pumped in
3- therefore sodium ions diffuse back into by the electrochemical gradient while k+ diffuse out
4- most of the voltage gated Na+ ion channels are closed preventing Na+ movement however K+ open allowing them to diffuse out
5- more positively charged ions outside causing a -70mv
What happens during an action potential
1- neurone is at resting potential and not transmitting impulse
2- energy of stimulus triggers some sodium VGIC to open making membrane more permeable to sodium ions therefore diffuses into membrane down electrochemical gradient
3- change in charge causes more Na+ channels to open
4- when p.d reaches 40mv VGIC Na+ channels close and K+ open so they diffuse out of membrane down electrochemical gradient
5- inside of axon more negative than outside
6- lots of K+ diffuse out so now hyperpolarisation. VGIC now close and sodium potassium ion pump returns to normal
How is an impulse transmitted across a synapse?
1- action potential in presynaptic neurone causes Ca2+ channels to open so calcium ions enter synaptic knob
2- influx of calcium ions in pre neurone causes vesicles to fuse with the pre membrane release if acetylcholine into synaptic cleft
3- acetylcholine fuse with receptor sites on Na+ channels on post neurone causing the Na+ channels to open and the diffuse rapidly along conc gradient
4- influx of Na+ channels causes new action potential in post neurone
5- acetylcholine hydrolyses into ethanoic acid and choline which diffuses back into pre membrane to reuse. Also prevents creating more APs in post neurone
6- ATP is released by mitochondria to recombine ethanoic acid and choline into acetylcholine. Stored in vescicles for future use.
Describe a reflex arc
1- stimulus detected by sensory receptor such as heat or pressure
2- generation of electrical signals and The impulses then travel through the sensory neurone to the relay neurone to the cns.
3- The signal acts as a transducer as it is converted from and electrical impulses to a chemical impulse at synapse
4- the cns passes impulse to The motor neurone which carries out the electrical signal to an effector such as a limb muscle, the eye lid muscles or glands
5- causes the effector to carry out appropriate reaction in response to stimulus
Sliding filament model?
1- tropomyosin molecule prevents myosin head from attaching to actin molecule binding site
2- Ca2+ released from endoplasmic reticulum cause tropomyosin to pull away from binding site
3- myosin head attaches to actin binding site
4- myosin head changes angle moving actin filament forward along. ADP molecule is released
5- ATP molecule fixes to myosin head causing it to detach from actin
6- hydrolysis of ATP to ADP by myosin provides energy for myosin to go normal
7- myosin head reattaches to actin binding site and repeats
How is insulin secreted?
1- beta cells detect rise in blood glucose level and K+ channels are open so p.d is -70mv
2- glucose enters the cell by glucose transporter
3- glucose metabolised by mitochondria which causes ATP release
4- ATP binds to k+ channels so no more can no longer diffuse
5- causes depolarisation
6- depolarisation causes Ca2+ VGIC to open and release calcium ions which attach to secretory vesicles which release insulin by exocytosis
Action of adrenaline?
1- adrenaline hormone approaches receptor on cell surface membrane
2- adrenaline fuses to receptor site and then activates enzyme inside membrane
3- enzyme converts ATP to CAMP which acts as second messenger that activates other enzymes (cascade effect) 4- glycogen to glucose
