Skeletal Muscle Physiology 2 Flashcards
what two factors does the gradation of skeletal muscle tension depend on
Number of muscle fibres contracting
Tension developed by each contracting muscle fibre
how can you achieve a stronger muscle contraction
by stimulating more motor units: motor unit recruitment
how is muscle fatigue prevented in sub maximal contractions
by asynchronous motor unit recruitment
what factors make up the tension developed by each contracting muscle fibre
frequency of stimulation
summation of contractions
length of muscle fibre
thickness of muscle fibre
why does a skeletal muscle twitch
the action potential is much shorter than the duration
how can twitches be used to give a stronger contraction
summate twitches give repetitive fast stimulation
twitch after twitch after twitch not allowing a break
what is tetanus
when the muscle fibre is stimulated so rapidly it is not allowed to rest it leads to a maximal sustained contraction
Cardiac and skeletal muscle can be tetanised true/false
false
cardiac muscle has long refractory periods to prevent tetanic contraction
what is it called when the skeletal muscle is stimulated once
twitch
how can you increase muscle tension without increasing frequency of stimulation
twitches overlap as there is not time for the muscle to rest, the second twitch adds to the first creating greater muscle tension
eventually produces a much stronger sustained contraction
what is an important mechanism for modulating the force of contraction in skeletal muscle
the frequency of stimulation
when is the muscle capable of achieving maximum contraction
when it is at its optimum length before the onset of contraction
RESTING LENGTH
how is muscle tension transmitted to bone
via the stretching and tightening of muscle connective tissue and tendon
what are the two types of skeletal muscle contraction
isotonic
isometric
what is isotonic contraction
used for body movements and moving objects
muscle tension remains constant ad the muscle length changes
what is isometric contraction
used for supporting objects and maintaining body posture
muscle tension develops at constant muscle length
what decreased the velocity of muscle shortening
the load eg. how heavy the object you’re picking up is
what are the main differences between skeletal muscle fibres
enzyme pathways
resistance to fatigue
activity of myosin ATPase
how many types of muscle fibre are in one muscle unit
two
muscle fibres with greater capacity to synthesise ATP are more resistant to fatigue true/fasle
true
what does the activity of myosin ATPase determine
the speed at which anergy is made available for cross bridge cycling
eg. speed of contraction
what does ATPase in muscle do
splits ATP to power power cross-bridge stroking
what is ATP needed in muscle relaxation
to pump calcium back into the lateral sacs of the sarcoplasmic reticulum
what are the metabolic pathways that produce ATP for skeletal muscle
Creatine phosphate
oxidative phosphorylation
Glycolysis
what does creatine phosphate do
transfers high energy phosphate from creatine phosphate to ADP to create an immediate source of ATP
what is the main source of ATP to muscles when O2 is present
oxidative phosphorylation
what is the main source of ATP to muscles when O2 isn’t present
Glycolysis
what are the three types of skeletal muscle fibre
slow-oxidative
fast-oxidative
fast- glyhcotic
what are type 1 muscle fibres
slow (slow twitch)
resistant to fatigue
used for prolonged relatively low work aerobic activities eg. posture maintenance
type 2 muscle fibres
(intermediate twitch)
fast oxidative
use aerobic and anaerobic
useful in prolonged moderate activities eg. jogging
type 2x muscle fibres
fast glycotic
(fast twitch fibres)
anaerobic metabolism
short term, high intensity activities eg. jumping
what inputs influence the motor units
brain inputs
inputs from a variety of receptors
what is a reflex
a stereotyped response to a specific stimulus
what makes reflexes important
they’re important for localising lesions in the motor system
what is the simplest monosynaptic spinal reflex
stretch reflex
what is the sense receptor in the stretch reflex
the muscle spindle
what does stretching of the muscle spindle cause
firing of afferent neurons
where do the afferent neurons fired in the stretch reflex go and what do they synapse with
synapse in spinal cord with the alpha motor neurons which innervate the stretched muscles
how do you elicit a stretch reflex
tapping a muscle tendon with a rubber hammer
what are muscle spindles
a collection of specialised muscle fibres
Intrafusal fibres
what are extrafusal fibres
normal muscle fibres
what are the sensory nerve endings of muscle spindles called
annulospiral
the discharge from muscle spindle sensory nerve endings decrease as the muscle is stretch true/false
false
increase
what are the efferent neurons that supply muscle spindles called
gamma motor neurons
what do gamma motor neurons do
adjust the level of tension in the muscle spindles to maintain their sensitivity when the muscles shorten during contraction
the contraction of intramural fibres doesn’t contribute to overall strength of muscle true/false
true
causes of intrinsic muscle disease
genetically determines myopathies
acquired myopathies eg.
inflammatory, non-inflammaroy, endocrine, toxic
symptoms of muscle disease
muscle weakness/tiredness
delayed relaxation after voluntary contraction (myotonia)
muscle pain (myalgia)
muscle stiffness
investigations in neuromuscular disease
EMG (electromyography) -electrodes detect the presence of muscular activity nerve conduction studies muscle enzymes (eg. creatine kinase) inflammatory markers (CRP) muscle biopsy
