Physiology Flashcards
Which of the 3 types of muscles are striated?
Striated: skeletal and cardiac muscle
Unstriated: smooth muscle
Striation appears as alternating dark and light bands under the microscope. What makes up the light and dark bands?
Dark bands - myocin thick filaments
Light bands - actin thin filaments
Which ion links excitation and contraction?
Ca2+
Where does the Ca2+ involved in skeletal muscle vs cardiac muscle contraction come from?
Skeletal - entirely from the sarcoplasmic reticulum
Cardiac - ECF and sarcoplasmic reticulum
State what controls the strength of contraction in skeletal muscle (2) vs cardiac muscle (1)
Skeletal - motor unit recruitment and summation of contractions
Cardiac - preload
Skeletal muscles are arranged into…
Motor units
What are motor units?
A number of muscle fibres innervated by a single alpha motor neuron
What is the neurotransmitter at skeletal muscle neuromuscular junctions?
Acetylcholine
A muscle which requires precision more than power (e.g., the hand) has more/fewer muscle fibres per motor unit
Fewer (~10)
A muscle which requires power more than precision (e.g., the thigh) has more/fewer muscle fibres per motor unit
More (100s - 1000s)
Skeletal muscle fibres usually extend the entire length of muscle. T/F
True
Skeletal muscles are attached to bone by…
Tendons
A singular muscle fibre (cell) is made up of many…
Myofibrils
Myofibrils contain X and Y arranged into Z
X - actin
Y - myosin
Z - sarcomeres
The functional unit of skeletal muscle is…
the sarcomere
What are the 4 zones of the sarcomere called?
A-band
H-zone
M-line
I-band
Describe each sarcomere zone: A-band H-zone M-line I-band
A-band: area of actin and myosin overlap
H-zone: area in the middle of the A-band where thin filaments don’t reach
M-line: vertical line down the middle of the A-band and H-zone
I-band: initial portion of thin filaments that do not project into A-band i.e., do not overlap thich filaments
How is muscle tension produced?
The ATP-dependent sliding of actin filaments over myocin filaments
How does ATP aid skeletal muscle contraction and relaxation?
Contraction - broken down into ADP and Pi which energises myosin
Relaxation - releases the actin-myosin cross-bridge and pumps Ca2+ back into the sarcoplasmic reticulum
Why does rigor mortis occur when someone dies?
ATP is depleted to Ca2+ can no longer be pumped back into the sarcoplasmic reticulum and so the muscles stay contracted
Describe release of Ca2+ from the sarcoplasmic reticulum in skeletal muscle
The surface action potential spreads down the transverse (T)-tubules of the sarcoplasmic reticulum, causing it to release Ca2+ from its lateral sacs
Once myosin is energised by ATP, why is Ca2+ required to form the actin-myosin cross-bridge?
Ca2+ binds to troponin and moves the troponin-tropomyosin complex out of the myosin binding site on actin
Energised myosin can then bind to actin and form the cross-bridge
Summarise the process of excitation-contraction coupling in skeletal muscle (7)
- ACh released across neuromuscular junction
- ACh binds and causes an action potential to propegate along the surface membrane
- The action potential travels down the T-tubules of the sarcoplasmic reticulum and triggers Ca2+ release from the lateral sacs
- Ca2+ binds to troponin on actin filaments, pulling the troponin-tropomyosin complex out of the way to allow the actin-myosin cross bridge to form
- Myosin pulls actin towards the centre of the sarcomere using energy from ATP
- When there is no longer a local action potential, Ca2+ is actively taken back up by the sarcoplasmic reticulum
- With Ca2+ no longer bound to troponin, the troponin-tropomyosin complex blocks the binding site on actin again, and so actin slips back and contraction ends
What 2 factors influence the tension developed by skeletal muscle?
- The number of muscle fibres/motor units contracting within the muscle
- Tension developed by each contracting muscle fibre