muscular systems Flashcards
types of muscle
smooth
cardiac
skeletal
smooth muscle
fusiform shaped (tapering at both ends)
involuntary contraction (slow wave motions)
not striated, with only one centrally located nucleus
primary functions:
-digestion
- breathing
- circulation
cardiac muscle
cardiomyocytes
narrow and shorter than skeletal
one nucleus, many mitochondria
intercalated discs support synchronized contraction of cardiac tissue
intercalated discs
Z line of the sarcomere –observe the longitudinal section of the tissue
Desmosome – structural support
Fascia adherens – mechanical support
Gap junction – electrical synapses
skeletal muscle - organisation
elongated myocytes
multi nucleated
striated - banded pattern (proteins)
skeletal muscle - characteristics
excitability
-Capacity of muscle to respond to a stimulus
contractibility
-Ability to shorten in order to produce force
extensibility
-Can be stretched to a limited degree beyond normal length
elasticity
- Ability to recoil to original resting length following stretch
skeletal muscle - functions
movement/ locomotion
posture
stabilisation
generation of heat
- byproduct
- shivering
direct movement:
- indirect
tendons/ aponeurosis
immobile bone - origin
moveable bone - insertion
ligaments bone to bone
tendons muscle to bone
- direct
epimysium of muscle fused to periosteum of bone
epimysium of muscle fused to perichondrium of cartilage
anatomy of skeletal muscle
epimysium - dense fibrous connective tissue
fascicle - bundle of fibres
perimysium - dense fibrous connective tissue
endomysium - areolar connective tissue (covers each muscle fibre)
sarcolemma- plasma membrane (phospholipid bilayer)
connective tissue - contributes to elasticity
myofibril
protein
- thick filaments
- mainly myosin
thin filament
- actin
- troponin
- tropomyosin
thin filament
actin
tropomyosin
troponin complex - TnT -> tropomyosin
Tnc -> calcium
TnL -> actin
thick filament
titin
keep thick and thin filaments aligned, resist muscle from overstretching, and recoil muscle to resting length after stretching
nebulin
anchoring actin to z disc
dystrophin
anchoring protein
actin to membrane via protein complex
- sarcolemma
muscular dystrophy:
- weakening and breakdown of skeletal muscle
motor unit
two components
- alpha-motorneuron
- muscle fibres innervated by the AMN
three types of fibres
- slow
type I fibres
- fatigue resistant
type II a fibres
- fast fatiguing
type IIx fibres
Henneman’s size principle
motor units are activated in a preset sequence (I > IIa> IIx) which depends on the motor neuron size of the motor unit (from smallest to largest)
recruitment is based on the force require, not the velocity of movement
slow units are always recruited, regardless of velocity
type I muscle fibres
slow contraction speed
adapted for aerobic respiration:
-high capillary density
- high myoglobin content
- large aerobic metabolism capacity and blood supply
- high mitochondrial density and content/activity of oxidative enzymes
type II
fast contraction speed
adapted for anaerobic metabolism:
- less blood supply, myoglobin and mitochondria
- high content of glycogen and glycolytic enzymes
two types
- type II A : fast oxidative fibres
- type 11 X : fast glycolytic fibres
transverse tubules
Dihydropyridine receptor (DHP)
- voltage gated calcium channel
- L type calcium channel
ryanodine receptor
- releases calcium ions from sarcoplasmic reticulum
mechanism coupled
calsequestrin
glycoprotein
moderate affinity and high capacity for Ca 2+
allows large quantities of Ca 2+ to be stored in Sarcoplasmic reticulum
excitation contraction coupling
Ca 2+ binds to troponin (Tn- c ) on the thin filament
shifts tropomyosin off myosin binding sites
enables myosin to bind to actin
sliding filament mechanism
- at rest, ATP molecule binds to myosin head, and ATPase enzyme on myosin myosin hydrolyses ATP to ADP - reaction releases energy that ‘cocks’ myosin head (pointing away from M line) into an extended, high energy position (ADP and Pi remain attached)
- cocked myosin binds to active site on actin molecule (exposed by E-C coupling process)- called the ‘cross bridge’. Pi is released making bond stronger
- myosin releases ADP, bending myosin head and tugging actin along with it towards centre of sarcomere (power stroke)
- a new ATP molecule binds to myosin head to release myosin from actin
- ATP hydrolysis by ATPase cocks the myosin head again
- steps 3-5 are repeated (cross bridge cycling) at a new active actin site further down the actin filament to shorten the sarcomere
sarcomere - sliding filament mechanism
actin slides over
no change in myofilament length
pulls z lines together
A band stays same
I band decreases
H zone disappears
calmodulin
calcium modulated protein
- calcium binds to calmodulin
- Ca 2+ - calmodulin activates myosin light- chain kinase (MLCK)
- MLCK phosphorylates light chains in myosin heads and increases myosin ATPase activity
- active myosin cross bridges slide along actin and create muscle tension
relaxation
sarco(endo)plasmic Ca 2+ - ATPase
- membrane proteins
sodium/calcium exchanger
calcium kinetics influencers
K+ and Na+ - decrease activation of RER
increased Mg 2+
Pi
Ca2+
all three decreases activation of RER which cytosolic calcium influences activation
