Muscular system Flashcards
Function of muscular sys (7)
- movement of the body
- maintain posture
- respiration
- produce body heat
- Communication
- constriction of organs & vessels e.g. digestive tract
- contraction of heart
4 properties of muscle
- Contractility: produce tension by shortening muscles
- excitability: respond to a stimulus - can transmit AP (nerves/hormones)
- Extensibility: stretched to its normal resting length
- Elasticity: able to recoil to resting length after stretched
Skeletal muscles
- attached to bone
- long, cylindrical, striated, multiple nuclei @ periphery (edges of cell)
- voluntary & involuntary (reflex)
- > > body movements
Smooth muscles
- walls of hollow organs, skin, glands, eyes
- spindle-shaped, elongated nuclei @ centre
- involuntary
- > > autonomic functions e.g. digestive tract
cardiac muscle
- heart
- cylindrical, branched, striated, intercalated discs, single nuclei @ centre
- Involuntary
- > > contract = generate pressure in <3 chambers
CT layers
- Epimysium: surrounds whole muscle
- Perimysium: surrounds fascicle (group of muscle fibres)
- Endomysium: surround individual muscle fibres
sacroplasmic reticulum function
store Ca2+
describe structure of muscle fibre (cell)
- sarcolemma (membrane)
- sarcoplasm (cytoplasm)
- multiple nuclei @ periphery
- lots of mitochondria
- myofibrils: contain myofilaments
- sarcoplasmic reticulum: stores Ca2+
- transverse (T) tubule: : fold into sarcolemma
function of T tubule
transmit AP from surface of cell into interior of cell => contraction
what’s a sarcomere
unit of contraction for skeletal muscles. ordered repeating units of myofilaments from z disk to z disk
Reason for striated appearance
- H zone: where actin (thin) & myosin (thick) don’t overlap
- A bands: dark band
- I band: light band (Z disks attach thin & thick myofilaments
what is tropomyosin & troponin
tropomyosin: protein covers binding site
troponin: small protein - changes shape when Ca2+ attach (exposes binding site by moving tropomyosin)
Sliding filament model
Myofilaments slide past each other bc actin dragged to midline => H zone disappears
Context: ATP attach to hinge region of myosin -> head cocks 90º, while Ca2+ attach to troponin exposing binding site -> head attach to binding site (cross-bridge). -> myosin relax (ADP realease) = moves actin to midline. -> ATP attach to head = release cross-bridge
neuromuscular junction function & structure
> > Contraction of muscle
- presynaptic terminal:
- Synaptic cleft
- Motor end-plate / Postsynaptic membrane: sarcolemma
excitiation-contraction coupling
mechanism where AP on sarcolemma => myosin & actin interaction.
AP travel along sarcolemma & T tubule-> initiates release of Ca2+ from sarcoplasmic ret. -> contraction of muscle cells. No more AP Ca2+ move back to sarcoplasmic ret. & tropomyosin closes binding sites & actin slides down
