muscle physiology Flashcards
Which muscle types are striated?
skeletal and cardiac
Skeletal muscles are innervated by the ____ nervous system
somatic
Cardiac and smooth muscles are innervated by the ____ nervous system
autonomic
What is the sole source of Calcium in skeletal muscles?
sarcoplasmic reticulum
What is the origin of Calcium in cardiac muscle?
Extra cellular fluid
and Sarcoplasmic reticulum (Ca-induced Ca release)
What is a motor unit?
A single Alpha Motor neurone and all the muscle fibres it innervates
What are the levels of organisation of skeletal muscle?
whole muscle -> muscle fibre -> myofibril -> sarcomere -> Actin (thin) / Myocin (thick)
What is the A-band of the sarcomere?
thick filaments with portions of overlapping thin filaments
What is the H-zone
the portion of the A-band (myosin/thick filament) where the thin filaments do not reach
What is the M-line?
It extends vertically down the middle of the H-zone
What is the I-Band?
The portion of the thin filaments which do not overlap with the thick filaments
What is the function of Calcium in muscle contraction?
induces cross bridge formation between myosin head and actin filament
What are T-tubules? How are they involved in contraction induction?
invaginations of the surface membrane that dip into the muscle fibre
Action potential in T-tubules induces Ca release from sarcoplasmic reticulum
How does Calcium enables cross bridge formation?
- Ca binding to troponin triggers the release of troponin-tropomyosin complex
- The cross bridge binding sites on actin are now exposed
What is the function of ATP in muscle contraction?
ATP phosphorylation energises the myosin heads
-once bound to actin, ADP+Pi are released, new ATP binds, inducing the power stroke
What factors define the gradation of skeletal muscle tension?
- number of muscle fibres
- frequency of stimulation and summation of contractions
- length of fibre at the onset of contraction
- thickness of muscle fibre
Skeletal muscle twitch is much _____ than the action potential.
longer
Restimulation of skeletal muscle before the end of contraction results in …
summation of contraction
What feature of the cardiac muscle AP prevents its tetanisation?
long refractory period
What muscle length is optimal for cross bridge formation?
resting muscle length
What are the 2 types of muscle contraction?
Isotonic contraction
Isometric contraction
What is isotonic contraction use for? What is happening to tension and muscle length?
- body movements
- moving objects
Tension is constant;
muscle length changes
What are isometric contractions used for?
- supporting objects in fixed position
- maintaining body posture
What happens to tension and muscle length during isometric contraction?
Muscle tension develops at constant muscle length
What are the 3 muscle fibre types?
Type I - Slow-oxidative
Type IIa - Fast-oxidative
Type IIx - Fast0glycolytic
What are Type I fibres used for?
Prolonged low work aerobic activity
Type IIa fibres use what metabolism?
both aerobic and anaerobic (walking)
What are Type IIa fibres used for?
prolonged moderate work (jogging)
What are the Type IIx fibres used for?
high intensity activities (jumping)
-use anaerobic metabolism
What is the receptor involved in the Stretch reflex?
Muscle spindle
Where and with what neurons do the afferent neurons activated by the muscle spindle synapse?
synapse at the spinal cord with alpha motor neurons
What are the efferent neurons that stimulate the contraction in stretch reflex?
Alpha motor neurons
