3: Muscle Physiology II Flashcards
The degree of skeletal muscle tension depends on which two factors?
Number of muscle fibres contracting
Tension developed by each individual fibre
which itself depends on summation of contractions and optimal muscle length for contraction
Why do motor units allow the simultaneous contraction of a number of muscle fibres at the same time?
Alpha motor neuron is connected to several (hundred?) fibres
Stronger contractions can be achieved by the stimulation of (more / less) motor units.
more
During a submaximal contraction, motor unit recruitment is ___ which helps to prevent muscle fatigue.
asynchronus
In skeletal muscle, the duration of an action potential is (longer / shorter) than the resulting muscle contraction.
shorter
In cardiac muscle, is the duration of the action potential shorter than the resulting contraction?
No, longer
Refractory period
If a muscle fibre is restimulated after it has completely relaxed, the second contraction is of (smaller / greater / the same) magnitude compared to the first one.
the same
If a muscle fibre is restimulated before it has completely relaxed, the second contraction is added onto the magnitude of the first.
What is this called?
What is the main difference between the first and second contraction?
Summation of contractions
2nd contraction is stronger than the 1st
What is tetanus?
Why does it occur?
Maximal sustained contraction of muscle
Rapid stimulation, no opportunity to relax
Can cardiac muscle be tetanised?
Why / why not?
No
Refractory period
What is a single muscle contraction called?
Twitch
What name is given to the “strength” of a muscle contraction?
Tension
Every muscle fibre has an optimal ___ which allows it to achieve maximal tension during contraction.
length
What is the optimal length of muscle approximately equal to?
Its normal resting length
Which structures, attaching skeletal muscle to bone, allow for movement of the skeleton by muscles?
Tendons
If skeletal muscle is the contractile component contributing to movement of the skeleton, what type of component is connective tissue and tendons?
Elastic component
What are the two types of skeletal muscle contraction?
Isotonic contraction
Isometric contraction
What is isotonic contraction?
What is it used for?
Muscle tension remains constant
Muscle length changes
Body movements, moving objects
What is isometric contraction?
When is it used?
Muscle tension changes
Muscle length stays constant
Supporting objects in place, maintaining posture
Are all skeletal muscle fibres the same?
No
The main difference between muscle fibres involves the metabolism of which molecule?
ATP
A motor unit usually contains ___ type of muscle fibre.
one
Broadly, by which three means can skeletal muscle cells get their hands on ATP for use in contraction?
Glycolysis (anaerobically)
Oxidative phosphorylation (aerobic)
Creatine phosphate can give a Pi to ADP > ATP, immediate source but cells have limited supply
Why are Type I skeletal muscle fibres known as slow-oxidative fibres?
Don’t have a lot of myosin ATPase
Same capacity for oxidative phosphorylation as Type IIa, but less ADP available to them
What are Type I fibres also known as?
Are they anaerobic or aerobic?
What sort of activities are they used in?
Slow-oxidative or Slow-twitch fibres
Aerobic
Prolonged low intensity work - e.g posture, walking
What are Type IIa fibres also known as?
Are they anaerobic or aerobic?
What sort of activities are they used for?
Fast oxidative / Intermediate-twitch fibres
Both
Prolonged moderate work e.g jogging
What are Type IIx fibres also known as?
Are they anaerobic or aerobic?
What sort of activities are they used for?
Fast glycolytic / Fast-twitch fibres
Anaerobic
Short-term, high intensity work e.g jumping, doing a backflip etc.
Name two reflexes controlled by motor nerves receiving signals from the brain.
Withdrawal reflex
Stretch reflex as in knee jerk etc.
What is a reflex?
A rapid, predictable response to a specific stimulus
Why are testing reflexes important?
Allows you to localise lesions in the motor system
The stretch reflex is an example of which type of feedback mechanism?
Negative feedback
resists increase in muscle length
What is the receptor for the stretch reflex?
Muscle spindle
no need for a control centre as the reflex is monosynaptic
What activates the muscle spindle?
Muscle stretch
Stretching of the muscle spindle causes which type of neurons to fire?
Afferent neurons
Where do afferent neurons involved in the stretch reflex synapse?
What do they synapse with?
Spinal cord
Alpha motor neuron
Alpha motor neurons are (afferent / efferent).
efferent
What occurs at the end of the stretch reflex, once the efferent alpha motor neuron has been activated?
Contraction of stretched muscle
How is the stretch reflex elicited?
Tapping muscle tendon with a rubber hammer
What are muscle spindles also known as?
What are normal muscle fibres known as?
Intrafusal fibres
Extrafusal fibres
Do muscle spindles contract?
Yes, but doesn’t contribute to overall strength (they’re sensory receptors doing their own thing)
Where specifically in the muscle are muscle spindles found?
Belly
How do muscle spindles run compared to normal muscle fibres?
Parallel to them
What are the sensory nerve endings of muscle spindles called?
Annulospiral fibres
Muscle spindles have their own (efferent) motor nerve supply.
What are these neurons called?
Gamma motor neurons
Gamma motor neurons send signals to intrafusal fibres (muscle spindles) telling them to contract - if they don’t contribute to purposeful muscle contraction, why does this happen?
So muscle spindles maintain their sensitivity when muscle contracts
Pathology of what could cause impairment of skeletal muscle function?
1. Intrinsic disease of muscle itself
2. Disease of NMJ
3. Disease of motor neurons supplying the muscle
4. Disease of nerves further up the chain (neurology)
What is the general name for disease of muscle?
Myopathy
What are some common symptoms of muscle disease?
Muscle weakness / fatigue
Delayed relaxation
Muscle pain (myalgia)
Muscle stiffness
How can neuromuscular disease be investigated?
Electromyography (EMG)
Muscle enzymes (e.g creatine kinase)
Inflammatory markers (e.g CRPs, plasma viscosity)
Muscle biopsy
