Muscles (5)

Question 1

Involuntary (smooth) muscle.

Answer 1

unstriated
controlled by autonomic nervous system
contracts slowly and fatigues slowly

functions: peristalsis, pupil dilatation and contraction, vasodilation and vasoconstriction.

Question 2

Cardiac muscle

Answer 2

striated
controlled by the autonomic nervous system (some under myogenic control)
contracts quickly, does not fatigue.

function: cause the heart to contract and relax.sk

Question 3

Skeletal muscle

Answer 3

striated
controlled by the somatic nervous system
contracts quickly, fatigues quickly

function: to move bones of the skeleton about the joints.

Question 4

Myogenic

Answer 4

generates their own electrical impulse to contract muscle (found in SAN)

Question 5

Structure of involuntary muscle

Answer 5

single, spindle - shaped cells each with its own nucleus.

Question 6

Structure of cardiac muscle

Answer 6

single, cylindrical branched cells, separated by intercalated disks, each with its own nucleus

Question 7

Structure of skeletal muscle.

Answer 7

multinucleate, cylindrical cells.`

Question 8

Fast twitch fibres

Answer 8

Used for short bursts of energy.
present in skeletal muscle.
contract rapidly but quickly fatigue.
gain energy from anaerobic respiration, stores creatine phosphate (can rapidly generate ATP from ADP in anaerobic conditions)

Question 9

slow twitch muscle fibres

Answer 9

contract less rapidly, fatigues very slowly.
gain energy from aerobic respiration
rich in myoglobin which creates a darker colour under the microscope

Question 10

Neuromuscular junctions

Answer 10

specialised synapses which occur at the end of a motor neurone where it meets a muscle fibre.

synaptic knob at the end of the motor neurone is the motor end plate.
when the action potential reaches the motor end plate, the end plate releases acetylcholine which causes muscle fibre to depolarise = muscle contraction

Question 11

Differences between NMJ and synapse

Answer 11

connects motor end plate (NMJ) connects 2 motor neurones (S)

sarcolemma depolarise (NMJ)
post synaptic neurone depolarise (N)

Depolarisation of muscle fibre membrane causes contraction (NMJ)
depolarisation sets up action potential which is a nerve impulse (S)

NMJ end plate has a flat surface known as a brush border (NMJ)
Synaptic knob is smooth and rounded (S)

Question 12

Motor units

Answer 12

muscle fibres are arranged in clusters known as motor units.

Question 13

Gradation of response

Answer 13

all muscle fibres in one motor unit are stimulated by a single motor neurone.
the brain controls the strength of contraction by altering the number of motor units that are stimulated.
the finer the function the fewer the number of muscle fibres.

Question 14

How a neuromuscular junction works

Answer 14

1. an impulse arrives at the neuromuscular junction, causing calcium ion channels to open, this causes the vesicles to fuse with the presynaptic membrane and release acetylcholine into the synaptic cleft by exocytosis.
2. acetylcholine binds to receptors on the muscle fibre membrane (sarcolemma) causing depolarisation
3. depolarisation wave travels down t-systems (tubules)
4. t-system depolarisation leads to calcium ions to be released from stores in the sarcoplasmic reticulum.
5. Ca2+ binds to proteins in the muscle, which leads to contraction.
6. acetylcholinesterase in the synapse rapidly breaks down acetylcholine so that the contraction only occurs when impulses arrive continuously.

Question 15

Sliding filament theory diagram of a myofibril.

Answer 15

[notes]

Question 16

How do the different regions of a myofibril change during contraction

Answer 16

sarcomere = shorter
H zone = shorter
I band = shorter
Z lines = closer together
A band = no change

Question 17

Structure of actin

Answer 17

each actin filament is made of 2 actin molecules.
protein made of globular beads
2 actin molecules coiled around eachother.
tropomyosin wraps around the actin filament
troponin forms balls along the length of the actin filament

Question 18

structure of myosin

Answer 18

each molecule of myosin has 2 protruding heads and a long tail.
heads contain ATPase (enzyme which hydrolyses ATP)
myosin heads can bind to actin filaments, but in relaxed muscles, the binding sites are blocked by tropomyosin

Question 19

Sliding filament theory movement

Answer 19

1. tropomyosin molecule prevents myosin head from attaching to the binding site on the actin molecule
2. calcium ions released from the sarcoplasmic reticulum causes the tropomyosin molecule to pull away from the binding sites on the actin molecule
3. myosin head now attaches to the binding site on the actin filament
4. head of myosin changes angle (45*) moving the actin molecule along as it does so. ADP molecule is released.
5. ATP molecule binds to myosin head causing it to detach from the actin filament.
6. hydrolysis of ATP to ADP by myosin provides the energy for the myosin head to resume its normal position
7. head of myosin reattaches to a binding site further along the actin filament and the cycle is repeated.

Question 20

What is the role of ATP in muscle contraction

Answer 20

ATP binding breaks the cross-bridge, which allows the myosin to reattach to the next binding site.

ATP is used to actively transport Ca2+ ions back into the sarcoplasmic reticulum when contraction stops.

in relaxed muscle, ATP reacts with creatine phosphate which is used to maintain ATP supply in contracting muscle.

ATP is used in protein synthesis to make actin and myosin

Question 21

How is the energy supply generated and maintained in muscle contraction using anaerobic respiration

Answer 21

Muscle cells quickly run out of O2 , anaerobic respiration in sarcoplasm releases some ATP (by glycolysis)
Also releases lactic acid (causes muscle fatigue)
Used for short periods of high intensity exercise

Question 21

How is the energy supply is generated and maintained in muscle contraction using aerobic respiration

Answer 21

Requires a good supply of oxygen and glucose, delivered by blood capillaries.
Some glucose comes from hydrolysis of glycogen
oxygen levels drop quickly during exercise therefore aerobic respiration is used for long periods of low intensity exercise

Question 22

How is the energy supply is generated and maintained in muscle contraction using creatine phosphate

Answer 22

Acts as a reserve supply of phosphate, which is available to combine with ADP.
Used for short bursts of vigorous exercise.
During muscle relaxation, creatine phosphate is replenished.