muscle and tendon

aperneurosis

flat sheet of dense connective tissue connecting muscle to bones/ fascia

epimysium

dense irregular connective tissue surrounding each muscle protecting it from friction

fasicle

a bundle of muscle fibers

perimysium

connective tissue surrounding a bundle of muscle fibres

endomysium

surrounds individual muscle fibres

muscle belly

fleshy, thickest part of the muscle, is encased in the epimysium

skeletal muscle structure

• multiple peripheral nuclei

• voluntary

• striated

• regular parallel bundles

• outermost layer surrounded by epimysium

cardiac muscle structure

• striated

• single central nucleus

• involuntary

• irregular arrangement

• intercalated disks

• intercalated disks have extensive gap junctions allowing cell to cell communication

smooth muscle contraction

• not striated

• single nucleus

• involuntary

• longer contractions

• overlapping sheets of spindle shaped cells

• microscopically appear homogenous

• connected through end to end junctions called gap junctions creating a watertight seal

function of skeletal muscle

• voluntary movement of skeleton controlled by somatic nervous system

• maintain body position and posture

• stabilise joints

• support underlying organs and soft tissue

• store nutrient reserves

• maintain correc body temperature

smooth muscle function

• involuntary contrction controlled by autonomic nervous system

• lines inner wall of vasculature, hollow visceral organs, major bodily tracts

• regulate blood pressure by altering systemic vascular resistance

• peristalsis

• regulate bodily secretion

• lines respiratory tract

• iris controls light entering

• hair follicles

what is muscle architecture

• the arrangement of muscle fibres relative to the axis of force

• maximum force developed by muscle is proportional to the number of sarcoeres hence fibre length

pennate muscle

• short fibres at an angle to internal tendon/aperneurosis

• increases PCSA

• PSCA is directly proportional to force

• short fibres mean less contraction distance so it is economical

• however trade off with speed

parallel muscles

• fibres run parallel to line of pull of muscle

• more sarcomeres in series mean more total muscle fibre shortening so more work

• work= force x distance

• moves joints through a large range of motion

• speed= distance/time

roles of tendon

• minimise distal limb mass

• join muscle to bone

• store elastic energy

• conserve energy

• power amplification: stretched tendons recoil faster than muscle shortens so more power. only a small amount of work is done but in a shorter time so power output is higher

• power= rate of doing work

tendon structure

• tenoblasts and tenocytes

• chondrocytes, synovial cells and vascular cells

• tendon collagen fibres are in a crimped pattern

• collagen fibrils- collagen fibres- fascicles (surrounded by endotenon) 

• fascicles are bound together by the endotenon a dense irregular connective tissue sheath to form the tendon

type i

• slow oxidative

• low myosin ATPase activity

• high oxidative capacity

• smaller diameter

• fatigue resistant

• less force production

• steady fatigue curve

type iia

• fast oxidative glycolytic

• high myosin ATPase activity

• high oxidative AND glycolytic capacity

type iib

• fast glycolytic

• high myosin ATPase activity

• high glycolytic capacity

• larger diameter (stronger) fatigue easily

what can fibre types be influenced by

• genetics

• training

• age

• lifestyle

• diet

isometric contraction

• muscle contracts but does not change length

• produces force but it is equal to resistance

• eg holding something

concentric contraction

• shortens as it generates force

• force greater than resistance

• movement

eccentric contraction

• muscle lengthens under tension

• lowering

• high force and low energy

• eg control or resist flexion of the elbow caused by the ground reaction force during landing impact

lactertus fibrosis

horse

Biceps stretches during stance when carpus locked in extension

– LF stores ELASTIC ENERGY

– When carpus buckles in late stance this rapidly releases the stored energy

– The leg swings forward

myosin

• thick filaments

• polypeptide chains

• 2 globular heads and a long tail

• heads are the site of myosin ATP enzyme

thin filaments

• 2 intertwned chains of actin molecules plus

• tropononin- small globular protein bound to actin and tropomyosin

• tropomyosin- rod shaped, located end to end along thin filament

sliding filament theory

• tropononin controls position of tropomyosin on the thin filament. myosin cant bind with tropomyosin on its binding site

• acetylcholine diffuses from neuron and ca ions are released into sarcoplasm and bind to troponin

• calcium acts on tropomyosin and the myosin binding site is exposed

• myosin head binds to actin at newly exposed site. pi and adp are released

• thin filament moves in the direction of its negative end because the myosin head is firmly attached to the thin filament during its power stroke

• the two heads of each myosin molecule work independently. only one head attaches to actin at a given time

• myosin head and atp bind. myosin head detaches from the thin filament

• atp is hhydrilysed

events during a muscle contraction

• resting state- troponin controls the position of tropomyosin on the thin filament- here tropomyosin blocks the myosin binding site on the actin molecules

• excitation contraction coupling- calcium ions bind to troponin which changes shape. this moves tropomyosin on the thin filament away from the myosin binding site

• myosin heeads bind to actin on the thin filament. causes detachment of adp and phosphate molecules

• power stroke: myosin heads move performin a power stroke which drags the thin filament towards the centre of the sarcomere

• detachment- ATP binds to myosin causing it to lose affinity for actin and to detach from the actin binding site

  • atp is hydrolysed into adp and phosphate which reenergises myosin head to return to prevous poition

    • no calcim- resting state

    • if calcium is oresent then return to stage 3

what are the 3 functions of ATP in skeletal muscle contraction

• energy released from atp hydrolysis re enrges the myosin head providing enery for cross bride movement and force generation

• binding of atp to myosin causes the release of the myosin head from actin allowing repeated contractions

• in the sacoplasmic reticulum ca-atpase hydrolyses atp in order to take ca ions back to the sr to end a muscle contraction