Action potentials Flashcards
explain how resting potential is maintained in a neurone
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
Describe how the release of acetylcholine into a neuromuscular junction causes the cell membrane of a muscle fibre to depolarise
acetylcholine binds to receptor channels and causes sodium ions to enter muscle fibre
movement by diffusion
sodium ions to move in to muscle cell
two advantages of simple reflexes
quicker transmission of impulses
rapid reactions
explain what causes the conduction of impulses along a non-myelinated axon to be slower than along a myelinated axon
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
describe how the resting potential is established in an axon by the movement of ions across the membrane
active transport/ pump of Na ion out of axon
diffusion of K ion out of axon/ little diffusion of na ion into the axon
explain why sodium and potassium ion can only cross the axon membrane through proteins
can not pass through phospholipid bilayer because water soluble
Describe the role of tropomyosin in muscle contraction
Ca2+ binds to tropomyosin forcing it change shape
binding site on actin exposed
describe the role of ATP in muscle contraction
break actin-myosin bridge
explain how muscles maintain posture
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
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
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
role of ATP in myofibril contraction
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
slow twitch fibres contract… and respire….
slower aerobically
fast twitch fibres contract…. and provide short or long burst of contractions
faster short burst
the leg muscles of long distance cyclist are usually larger than the leg muscles of non-athletes
suggest why
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
role of phosphocreatine in providing energy during muscle contraction
phosphocreatine provides phosphate to produce ATP
glycogen granules are present in skeletal muscles
explain role in skeletal muscles
as a store of glucose
for respiration/to provide ATP
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
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
explain the role of calcium ions and ATP in bringing about contraction of a muscle fibre
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’
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)
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
When the action potential arrives at the neuromuscular junction, it results in the secretion of acetylcholine into the synaptic cleft. Explain how (3)
Depolarisation of presynaptic membrane;
Ca2+ channels open / increased permeability to Ca2+;
Influx of Ca2+;
Vesicles move towards presynaptic membrane;
Vesicles fuse with presynaptic membrane
explain the importance of ATPase during muscle contraction
breaks down ATP yielding energy
used to form/ break actomyosin bridge
describe the roles of calcium ions and ATP in the contraction of myofibril
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
two ways in ATP is a suitable energy source for cells to use
produced in small quantities/ small amounts
energy readily available
immediate source of energy
explain what leads to the differences in appearance between the relaxed myofibril and contracted myofibril
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
describe the role of calcium ions in the contraction of a sarcomere
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
calcium ions are involved in myofibril contraction describe how
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
describe how calcium ions cause the myofibril to start contracting
calcium ions bind to troponin
tropomyosin becomes displaced
uncovers myosin binding site on actin
calcium ions activate ATPase
describe the events that occur within a myofribil which enable it to contract
myosin heads bind to actin/ form cross bridge
myosin heads survival
actin slides relative to myosin
energy provided by hydrolysis of ATP
