Skeletal Muscles

Question 1

gross muscle function

Answer 1

anatomy determines function/ action that it can contribute to
force (tension/pull) is produced by the muscle
force is transmitted to the skeleton via the tendon
movement occurs/ joint is stabilised/posture is maintained

muscle pull= moves insertion closer to origin

Question 2

muscle anatomy

Answer 2

muscle belly- cross section of muscle
epimysium wrapped around muscle belly
fascicules- bundle of inidvidual muscle fibres
perimysium- wraps around fascicules
endomysium- in between fibres
muscle fibres- many nuclei, membrane surrounding (sarcolemma)
bundles of myofibrils- bundles of sarcomeres

Question 3

sarcomere structure

Answer 3

each myofibril composed of thousands of sarcomeres
joined in series and parallel to one another
functional units of a muscle
made of myofilaments- thick and thin
structural proteins
titin- allows sarcomere to have elasticity
nebulin- structural stability
desmin- aids thin filaments

Question 4

actin (thin)

Answer 4

actin subunits in double helical strands
tropomyosin interacts with actin and covers binding sites where thick filament can bind
troponin controls positioning of tropomyosin

Question 5

myosin (thick)

Answer 5

around 300 myosin molecules per thick filament
myosin head= actin binding site + atp binding site
flexible hinge and tail which intertwines with other moleucles creating thick filament

Question 6

functions of muscle

Answer 6

producing movement
maintaining posture
storing and moving substances- protein, stores of carbs (glycogen), fat, myoglobin etc
moving substances= venous return; skeletal muscle pump
generating heat- shivering

Question 7

structural proteins in sarcomere

Answer 7

titin- allows sarcomere to have elasticity, return to original shape
nebulin- structural stability, acts like glue at Z line
desmin- aids in structure and shape of thin filaments

Question 8

sliding filament mechanism

Answer 8

during contraction filaments slide past each other
each of the two filaments remain relatively unchanged in length despite changes in gross muscle length
more overlap in sarcomere due to filaments gliding over eachother

Question 9

sarcoplasmic reticulum

Answer 9

interconnecting tubules surrounding myofibrils
regulates intracellular levels of calcium
change in charge in sarcolemma causes a release of calcium
stores calcium and releases on stimulation to allow contraction

Question 10

cross bridge cycle

Answer 10

action potential arrives at muscle
calcium released from SR
calcium binds to troponin
tropomyosin moves, uncovering binding site
hydrolysis of ATP (ADP+Pi) changes angle of myosin head, forming a cross bridge
Pi released from myosin head which changes angle of myosin head, powerstroke - ADP released (myosin pulls thin filament)
myosin head picks up another ATP and the bond with actin is released
repeats as action potentials arrive, until calcium or ATP levels drop

Question 11

length tension relationship

Answer 11

different amounts of tension/ pull depending on the position the muscle is in
muscle at shortest point (cant contract any more)- filaments overlapped, no further range to shorten, not able to generate tension

muscle in more lengthened position- some overlap of filaments but not against z line, can produce tension

muscle fully lengthened- less overlap between myosin and actin, less opportunity to form cross bridges and therefore develop tension

Question 12

force velocity relationship

Answer 12

force during shortening < isometric force (less force) faster the movement the less time myosin heads have to attach to binding site

force during lengthening> isometric force (greater force)

Question 13

fibre type characteristics

Answer 13

type 1- slow twitch- high mitochondrial density + endurance capacity
low max force and power
oxidative (fat source)

type 2a- fast twitch oxidative- intermediate mitchondrial density and endurance capctiy
inter. force and power
oxidative and glycolytic (fat and glycogen)

type 2x- low MD and EC
high force and power
glycolytic (glycogen and PCR)

Question 14

motor neuron

Answer 14

neuron- nerve cell
motor unit- single motor neuron and all of the fibres it innervates
gross movement would have 2- 3000 fibres per motor unit
fine movements would have 2-3 fibres per motor units

Question 15

transmission of nerve impulses

Answer 15

at rest= -70mV
when AP arrives at nerve cell, quick increase in membrane potential (30mV)

Question 16

depolarisation

Answer 16

at rest= more Na+ outside than inside (overall is negative)
AP= Na+ ion channels open, Na+ moves into cell from high conc to low conc (positive charge inside)
increased Na+ within the axon causes parts of axon to depolarise and Na+ gates close

Question 17

repolarisation

Answer 17

when potential reaches 30mV
K+ gates open and K+ leaves the axon and inside of the axon becomes less positive
K+ gates close (-90mV)

Question 18

return to rest

Answer 18

NaK+ pump reestablishes resting potential

Question 19

movement of action potential

Answer 19

as one part of the membrane is being depolarised, the part before is being repolarised and the depolarisation moves along the axon
signal is being passed along the membrane through depolarisation
depol regions (pos charge) move to neg charge regions on axon

Question 20

neuromuscular junction

Answer 20

where motor neuron meets muscle fibre
motor end plate- pocket formed around motor neuron by sarcolemma
synaptic cleft- short gap between neuron and motor end plate
acetylcholine- released from motor neuron resulting in depol of motor end plate

Question 21

synaptic tranmission at NM junction

Answer 21

when AP arrives, influx of Na+ into axon terminal, depol in end of axon terminal
triggers Ca+ VGIC to open and Ca+ enter
this triggers release of acl and is released into the synaptic cleft
acl interacts with Na+ channels on PSM, opens channels and Na+ enters muscle cell
sarcolemma membrane depolarised
triggers opening of Ca+ VGIC on muscle membrane and Ca+ enter muscle cell
stimulates Ca+ release from SR
acl reenters neruone as choline and acetic acid

Question 22

skeletal muscle control

Answer 22

efferent- neurons send impulses from CNS to limbs and organs eg muscles

aferent- neurones that carry nerve impulses from sensory receptors or sense organs toward the CNS

Question 23

afferent- golgi

Answer 23

golgi tendon organ- located at muscle tendon junction
senses tension in tendon when muscle contracts
has an inhibitive afferent neuron
increased tension/ large force generated = GTO relays message to efferent neuron, less stimulation/activation of muscle (protective)

Question 24

muscle spindles

Answer 24

in belly of muscle
have highly specialised encapsulated muscle fibres (intrafusal) which are parallel to normal muscle fibres
sensitive to changes in muscle length
efferent neuron causes muscle spindles to contract to maintain tension in middle of fibres
if muscle are stretching rapidly, quick contraction is needed to prevent overstretching