Action potentials

Question 1

explain how resting potential is maintained in a neurone

Answer 1

Sodium actively transported out of axon
potassium actively transported into the axon through sodium-potassium pump
sodium ions channels remains closed to prevent sodium movement
potassium ions channels remain open to allow diffusion out of the membrane

Question 2

Describe how the release of acetylcholine into a neuromuscular junction causes the cell membrane of a muscle fibre to depolarise

Answer 2

acetylcholine binds to receptor channels and causes sodium ions to enter muscle fibre
movement by diffusion
sodium ions to move in to muscle cell

Question 3

two advantages of simple reflexes

Answer 3

quicker transmission of impulses

rapid reactions

Question 4

explain what causes the conduction of impulses along a non-myelinated axon to be slower than along a myelinated axon

Answer 4

in a myelinated axon there is ion movement only at nodes and the impulse jumps from node to node
whereas in non-myelinated axons the impulse has to travel along the whole membrane

Question 5

describe how the resting potential is established in an axon by the movement of ions across the membrane

Answer 5

active transport/ pump of Na ion out of axon

diffusion of K ion out of axon/ little diffusion of na ion into the axon

Question 6

explain why sodium and potassium ion can only cross the axon membrane through proteins

Answer 6

can not pass through phospholipid bilayer because water soluble

Question 7

Describe the role of tropomyosin in muscle contraction

Answer 7

Ca2+ binds to tropomyosin forcing it change shape

binding site on actin exposed

Question 8

describe the role of ATP in muscle contraction

Answer 8

break actin-myosin bridge

Question 9

explain how muscles maintain posture

Answer 9

a muscle pulls in one direction at a joint and the other muscle pulls in the opposite direction
Antagonistic muscles are working at joints
both muscles contract to keep the body upright
only a few fibres contract to avoid fatigue

Question 10

a disease which produces less atp than healthy people are not able to maintain strong muscle contraction during exercise using sliding filament theory to suggest why

Answer 10

ATP is needed to form cross-bridges between actin and myosin. ATP is also needed during the power stroke when the myosin head moves pulling the actin filament towards the H-zone. ATP is also required for the myosin head to detach from the actin filament so that the rosin head returns back to its original position

Question 11

role of ATP in myofibril contraction

Answer 11

ATP needed to form a cross bridge between actin-myosin
ATP required for the myosin head to detach from actin filament so that the myosin head returns back to its original position

Question 12

slow twitch fibres contract… and respire….

Answer 12

slower aerobically

Question 13

fast twitch fibres contract…. and provide short or long burst of contractions

Answer 13

faster short burst

Question 14

the leg muscles of long distance cyclist are usually larger than the leg muscles of non-athletes
suggest why

Answer 14

increase in diameter of fibres due to trains and exercise
long distance cyclist have more slow twitch fibres
slow twitch fibres have wider diameter than fast twitch fibres
long distance cyclist have more mitochondria
long distance cyclist have more capillaries in muscles

Question 15

role of phosphocreatine in providing energy during muscle contraction

Answer 15

phosphocreatine provides phosphate to produce ATP

Question 16

glycogen granules are present in skeletal muscles

explain role in skeletal muscles

Answer 16

as a store of glucose

for respiration/to provide ATP

Question 17

during exercise the pH of skeletal muscles tissue falls. The fall in pH leads to a reduction in the ability of calcium ions to stimulate muscle contraction

Answer 17

low pH changes shape of calcium ion receptors 
fewer calcium ions bind to tropomyosin 
fewer tropomyosin molecules move away 
fewer binding sites on actin revealed 
fewer cross bridges can form 
fewer myosin heads bind

Question 18

explain the role of calcium ions and ATP in bringing about contraction of a muscle fibre

Answer 18

bind to tropomyosin
expose myosin bindin site
bind to the myosin head and cause it to change shape and causes actin to detach from actin-myosin cross bridge
release energy to ‘re-crack’

Question 19

An action potential is generated at the cell body of the motor neurone. Explain how this action potential passes along the motor neurone to the neuromuscular junction (3)

Answer 19

Depolarisation of axon membrane/influx of Na+ establishes local currents;
Change permeability to Na+ /open Na+ gates of adjoining region;
This process repeated along axon / self propagation

Question 20

When the action potential arrives at the neuromuscular junction, it results in the secretion of acetylcholine into the synaptic cleft. Explain how (3)

Answer 20

Depolarisation of presynaptic membrane;
Ca2+ channels open / increased permeability to Ca2+;
Influx of Ca2+;
Vesicles move towards presynaptic membrane;
Vesicles fuse with presynaptic membrane

Question 21

explain the importance of ATPase during muscle contraction

Answer 21

breaks down ATP yielding energy

used to form/ break actomyosin bridge

Question 22

describe the roles of calcium ions and ATP in the contraction of myofibril

Answer 22

hydrolysis of ATP provides energy for power stroke and breakage of actin-myosin cross bridge
calcium ions activate ATPase. Calcium ions cause tropomyosin molecules to move and expose myosin-binding sites on actin

Question 23

two ways in ATP is a suitable energy source for cells to use

Answer 23

produced in small quantities/ small amounts
energy readily available
immediate source of energy

Question 24

explain what leads to the differences in appearance between the relaxed myofibril and contracted myofibril

Answer 24

when contracted myosin and actin overlap more as myosin-actin cross bridge from actin moves along thick filament pulling Z-lines closer together.
Displacement of tropomyosin to allow interaction

Question 25

describe the role of calcium ions in the contraction of a sarcomere

Answer 25

they interact with tropomyosin molecule to reveal binding sites on actin
allowing myosin heads to bind to exposed sites on actin filament
energy released from ATP moves myosin head back to its original position

Question 26

calcium ions are involved in myofibril contraction describe how

Answer 26

Ca ion enter muscle cells from sarcoplasmic reticulum
this leads to the movement of tropomyosin exposing binding sites on actin
this allows for actin-myosin cross bridge formation
calcium ions also activate ATPase on myosin

Question 27

describe how calcium ions cause the myofibril to start contracting

Answer 27

calcium ions bind to troponin
tropomyosin becomes displaced
uncovers myosin binding site on actin
calcium ions activate ATPase

Question 28

describe the events that occur within a myofribil which enable it to contract

Answer 28

myosin heads bind to actin/ form cross bridge
myosin heads survival
actin slides relative to myosin
energy provided by hydrolysis of ATP