Skeletal muscle physiology 2 Flashcards
What two things is the tension developed by a skeletal muscle influences by?
The number of muscle fibres contracting
The tension developed by each contracting muscle fibres
What 4 things might cause impairment to the skeletal muscle?
1- intrinsic muscle disease
2-neuromuscular junction disease
3-pathology of lower motor neurones
4-disruption of input to motor nerves
What is motor unit recruitment?
A stronger contraction could be achieved by stimulation of more motor units
What does asynchronous motor units recruitment during sub maximal contraction help to prevent
muscle fatigue
What does the tension developed by each individual contracting muscle fibre depend on?
- frequency of stimulation
- summation of contraction
- length of muscle fibre at onset of contraction
- thickness of muscle fibre
In skeletal muscle the duration of AP is the same as the duration of resulting twitch T/F
False- the duration of AP is much shorter than the duration of resulting twitch.
Is it possible to summate twitches to bring about a stronger contraction through a repetitive fast stimulation of skeletal /cardiac muscle- if so what is it called
YESfor SKELETAL- muscle tetanus. When no opportunity to relax between stimuli
no for cardiac- cannot be tetanised
What is a twitch
a single contraction caused by the skeletal muscle being stimulated once . It produces little tension
Maximal titanic contraction can be achieved when the muscle is at its optimal length before the onset of contraction t/f
t
The resting length of a skeletal muscle is approx its optimal length T/F
T
Skeletal muscle tension-
As a result cross bridge cycling ( _____ ____)- is transmitted to bone via the stretching and tightening of muscle connective tissue and tendon (_____ _____)
contractile component
elastic component
What is isotonic contraction used for?
Body movements and moving objects.
muscle tension remains constant as the muscle length changes
What is isometric contraction used for?
Supporting objects in fixed positions or for mainining body posture. Muscle tension develops at constant muscle length
the maximum the load the lower the velocity of shortening. Why is this?
The velocity of muscle shortening decreases as the load increases
What are the main differences between different types of skeletal muscle fibres
- enzymatic pathway for ATP synthesis
- the resistance to fatigue-muscle fibres with greater capacity to synthesise ATP are more resistant to fatigue
- Activity of myosin ATPase- this determines the speed at which energy is made available for cross bridge cycling i.e. the speed of contraction
Each motor unit contains many types of motor fibres T/F
F- each motor unit usually contains one type of muscle fibres
Metabolic pathways that supply ATP in muscle fibre inc
- transfer of high energy phosphate from creatine to ADP
- oxidative phosphorylation
- glycolysis
Describe type 1 skeletal fibres
Slow-twitch fibres- used for prolonged relatively low work aerobic activities
low myosin ATP activity- slow
Adundance of mitochondria so can do oxidative phosphorylation therefore resistance to fatigue
high myoglobin so can store oxygen
appear red in colour
e.g.walking
Describe type 11b skeletal fibres
Fast twitch fibres - use anaerobic metabolism nd are mainly used for short-term high intensity actvivity e.g. jumping
high levels of myosin ATPase activity- fast
abundance of enzymes that do anaerobic glycolysis
appear whitish in colour
Describe type 11a skeletal fibres
Fast oxidative fibres (intermediate-twitch fibres) use both aerobic and anaerobic metabolism. Useful in prolonged moderate work e.g. jogging
can be oxidative phosphorylation and glycolysis- mixture of the two
What is a reflex action?
A stereotypical response to a specific stimulus
The neural pathways for reflexes are important in ____ _____ in the motor system
localising lesions
What is the simplest monosynaptic spinal reflex?
Stretch reflex- serves as a negative feedback that resists passive change in muscle length to maintain optimal resting length of muscle
What is the sensory receptor in the stretch reflex?
Muscle spindle- stretching this increases firing in the affront neurons
Stretch reflex - where so the affront neurones synapse and what with?
spinal cord with the alpha motor neurones ( efferent limb of the stretch reflex) that innervate the stretched muscle
How can the stretch reflex be elicited?
Tapping the muscle tendons with a rubber hammer
What muscle is stretching in the knee jerk
quadriceps femoris
What fibres are muscle spindles known as
intrafusal
n.b. ordinary muscle fibres referred to as extrafusal vibres
What are muscle spindles
a collection of specialised muscle fibres. fOUND WITHIN BELLY OF MUSCLES AND RUN PARALLEL TO ORDINARY MUSCLE FIBRES
What are the sensory nerve endings on muscle spindles called
annulospiral fibres
Muscle spindles have their own efferent nerve supply T/F
T-Called gamma motor neurones. They adjust the level tension in the spindles to maintain their sensitivity when muscle shortens during contraction.
T/F
The discharge from he muscle spindles sensory endings decreases as the muscle is stretched
F the discharge from the muscle spindles sensory endings increases as the muscle ( and hence spindles) is stretched
The contraction of intrafusal fibres does not contribute to the overall strength of muscle contraction. T/F
T
What are some genetically determined myopathies that can cause intrinsic muscle disease?
Congenital myopathies
Chronic degeneration- e.g.muscular dystrophy
Abnormalities in muscle membrane ion channels e.g. myotonia
What are the 4 acquired myopathies that cause intrinsic muscle disease
Inflammatory e.g. polymyosititis, inclusion body myosititis
Non-inflamamtory e.g. fibromyalgia
Endocrine e.g. Cushing syndrome, thyroid disease
Toxic myopathies e.g. alcohol, statins
What are symptoms of muscle disease
muscle weakness/tiredness
delayed relaxation after contraction ( myotonia)
Muscle pain (myalgia)
muscle stiffness
What 5 investigations may be useful in neuromuscular disease
1 EMG
- Nerve conduction studies
- Muscle enzymes
- Infalmamtory markers
- Muscle biopsy
What are EMG helpful to differentiate
primary muscle disease from the muscle weakness caused by neurological disorders
What should be done at the same time as the EMG
Nerve conduction studies
