Physiology 2 Flashcards
what does gradation of skeletal muscle tension depend on?
number of fibres contracting in the muscle
tension developed by each contracting fibre
what contributes to the number of muscle fibres contracting?
motor unit structure
motor unit recruitment
how is muscle fatigue prevented in submaximal contraction?
asynchronous motor unit recruitment
what contributes to the tension developed by each fibre?
frequency of stimulation
summation of contractions
length of fibre at onset of contraction
thickness of fibre
describe 3 types of twitching?
single twitch (not useful, weak)
twitch summation
Tetanus (smooth, sustained contraction)
how does twitching differ in cardiac muscle?
tetanus cannot occur in cardiac muscle due to the long refractory period, so another AP cannot act until muscle is relaxed
how does frequency of stimulation affect tension developed by skeletal muscle?
increased frequency = increased tension
when does maximal tetanic contraction occur?
when muscle is at optimum length (Lo)under resting conditions (not shortened or too stretched)
means optimum overlap between actin and myosin so most cross bridges can form
why is stretched muscle not effective?
actin and myosin don’t overlap so corss bridges cant form between them as they cant reach
is the resting length of a skeletal muscle the same as its optimal length?
yes
what are the 2 types of skeletal muscle contraction?
isotonic
isometric
what is isotonic contraction?
muscle tension remains constant as the muscle length changes
- body movements
- moving objects
what is isometric contraction?
muscle tension changes as muscle length stays constant
- supporting objects in fixed positions
- maintaining body posture
how is muscle tension transmitted to bone?
via elastic component of muscle
how does load affect velocity of muscle shortening?
larger load (heavier object) = slower velocity of shortening
what are the main differences between diiferent types of skeletal muscle fibres?
- enzymatic pathways for ATP synthesis (some produce more than others)
- the resistance to fatigue (amount of ATP synthesis dependant)
- activity of myosin ATPase (determines speed at which ATP is broken down and energy made available - speed of contraction)
are all muscle fibres in a whole muscle the same?
no
usually the same in one motor unit
what is the main method of ATP production in skeletal muscle?
oxidative phosphorylation - main source when oxygen present
anaerobic glycolysis - main source when lacking in oxygen
transfer of high energy phosphate from creatine phosphate to ADP (immediate source)
what are the 3 types of skeletal muscle fibres?
slow oxidative (type 1) fast oxidative (type 2a) fast glycolytic (type 2x)
type 1?
used for prolonged, low work aerobic activities (maintaining posture, walking)
- low myosin ATPase activity
- high oxidative phosphorylation
- low anaerobic glycolysis
type 2a?
use both aerobic and anaerobic metabolism
useful for prolonged relatively moderate work activities (jogging)
- high myosin ATPase activity
- high oxidative phosphorylation
- intermediate anaerobic glycolysis
type 2x?
use anaerobic metabolism and are mainly used for short term, high intensity activity (jumping)
- high myosin ATPase activity
- low oxidative phosphorylation
- high anaerobic glycolysis
what inputs motor neurons?
brain and variety of other receptors
- e.g withdrawal reflex
can be excitatory or inhibitory
what is a reflex?
stereotyped response to as specific stimulus
simplest form of coordinated movement
how can reflexes be used clinically?
can show where lesions/problems are in the motor system
what is the simplest monosynaptic spinal reflex?
stretch reflex
what is the stretch reflex?
negative feedback system that resists passive change in muscle length to maintain optimal resting length
what is activated in the stretch reflex?
muscle spindles (specialised sensory receptor muscle fibres)
how does a stretch reflex occur?
stretching of the muscle spindle increases firing in the afferent neurons
afferent neurons synapse in spinal cord with alpha motor neurons that innervate stretched muscle of efferent limb
results in contraction of stretched muscle
what are muscle spindles/ordinary fibres also known as?
spindles = intrafusal ordinary = extrafusal
where are muscle spindles found?
within belly of muscles and run parallel to ordinary fibres
have sensort nerve endings known as annulospiral fibres
what nerves supply muscle spindles and what do they do?
efferent motor neurons known as gamma motor neurons
adjust the level of tension in the muscle spindles to maintain their sensitivity to stretch when the muscle shortens during contraction
what can cause impairment of skeletal muscle function?
intrinsic disease of muscle
disease of NMJ
disease of lower motor neurons
disruption of input to motor nerves (upper motor neuron disease)
2 general types of intrinsic muscle disease?
genetic myopathies
acquired myopathies
describe 3 types of genetic myopathies
congenital myopathies chronic degredation (muscular dystrophy) abnormalities in muscle membrane ion channels (myotonia)
describe 4 acquired myopathies
inflammatory - polymyositis
non-inflammatory - fibromyalgia
endocrine - cushings, thyroid
toxic - alcohol, statins
what are 4 symptoms of muscle disease?
muscle weakness
delayed relaxation (myotonia)
muscle pain (myalgia)
muscle stiffness
give 4 investigations used for neuromuscular disease?
electromyography (EMG) Nerve conduction studies Muscle enzymes (CK) inflammatory markers (CRP) Muscle biopsy
what is single twitch?
muscle fibre is restimulated after it has completely relaxed
useless
what is a twitch summation?
muscle fibre is restimulated before it has completely relaxed
stronger than single
what is tetanus?
muscle fibre is stimulated so rapidly that is doesn’t have an opportunity to relax at all
maximal sustained contraction
how is the contractile component of skeletal muscle transmitted to bone?
via the stretching and tightening of muscle connective tissue and tendon (elastic component)
how can the stretch reflex be elicited?
tapping the muscle tendon with a hammer
this rapidly stretches the muscle resulting in contraction
- e.g knee jerk
what does knee jerk test?
femoral nerve
L3 and L4
what does ankle jerk test>
tibial nerve
S1 and S2
what does biceps jerk test?
musculocutaneous nerve
C5-C6
what does triceps jerk test?
radial nerve
C6-C7
what does brachioradialis test?
radial nerve
C5-C6
do muscle spindles contribute to overall strength of muscle contraction?
no
how does electromyography work?
records frequency and amplitude of muscle fibres action potentials
can differentiate between primary and secondary muscle disease
