Skeletal Muscle Physiology 2 02/10/18 Flashcards
What do factors does the gradation of skeletal muscle tension depend on?
Number of muscle fibres contracting within the muscle
Tension developed by each contracting muscle fibre
What is motor unit recruitment?
A stronger contraction can be achieved by stimulation of more motor units
What helps to prevent muscle fatigue?
Asynchronus motor unit recruitment during submaximal contractions
What does the tension development of a muscle fibre depend on?
Frequency of stimulation
Summation of contractions
Length of muscle fibre
Thickness of muscle fibre
Which is longer, the duration of an action potential or the duration of the resulting twitch?
The muscle twitch
How can a stronger contraction be brought about?
Summating twitches through repetitive fast stimulation of skeletal muscle
What is tetanus and how is it brought about?
Maximal sustained contraction
When the muscle fibre is stimulated so rapidle that it does not have an opportunity to relax between stimuli
Can cardiac muscles be tetanised and why/why not?
No
The long refractory period prevents generation of tetanic contraction
What is the resulting action when a skeletal muscle is stimulated once?
Twitch
Tia/Tamera
Can a single twitch bring about meaningful muscle activity?
No
When the frequency of stimulation increases what happens to the tension?
Increases
When is skeletal muscle at its optimal length?
When it is resting
How is skeletal muscle tension transferred to bone?
Through tissue and tendons
What are the two types of skeletal muscle contraction?
Isotonic contraction
Isometric contraction
What is isotonic contraction?
Muscle tension remains the same as the muscle length changes
I.e. in body movements and moving objects
What is isometric contraction?
Muscle tension develops at constant muscle length
I.e. supporting objects in fixed position or maintaining body posture
What happens to the velocity of muscle shortening as the load increases?
It decreases
Are all skeletal muscle fibres the same?
No
What are the 3 differences in skeletal muscle fibres?
Enzymatic pathways for ATP synthesis
Resistance to fatigue
Activity of myosin ATPase
Which muscle fibres are more resistant to fatigue?
Muscle fibres with a greater capacity to synthesise ATP
What does the activity of myosin ATPase determine?
The speed at which energy is made available for cross bridge cycling
What are the three types of metabolic pathway that supplies ATP to muscle fibres?
Transfer of high energy phosphate from creatine phosphate to ADP
Oxidative phosphorylation (when O2 is present)
Glycolysis (When O2 is not present)
What are the three types of skeletal muscle fibre?
Slow-oxidative (Type 1)
Fast-oxidative (Type 2a)
Fast-glycolytic (Type 2x)
What are type 1 fibres mainy used for?
Prolonged, low work aerobic activities
What are Type 2a fibres used for?
Aerobic and anaerobic metabolism and prolonged moderate work
What are type 2x fibres used for?
Anaerobic metabolism and short term high intensity activities
What is the definition of a reflex?
Stereotyped response to a specific stimulus
What are the simplest form of coordinated movement?
Reflex actions
What are the neural pathways for reflexes important for localising?
Lesions in the motor system
What is the simplest monosynaptic spinal reflex?
The stretch reflex
Is the stretch reflex positive or negative feedback?
Negative
What is the sensory receptor in the stretch reflex and what is it activated by?
Muscle spindle activated by muscle stretch
What does stretching the muscle spindle do?
Increases firing in the afferent neurons
Where do the afferent neurons synapse and what with?
In the spinal cord with the alpha motor neurons
What does activation of the reflex result in?
Contraction of the stretched muscle
What coordinates the stretch reflex?
Simultaneous relaxation of antagonist muscle
How can the stretch reflex be elicited?
Tapping the muscle tendon with a rubber hammer
What nerve and spinal segment are responsible for the Knee jerk?
L3,L4
Femoral
What nerve and spinal segment are responsible for the Ankle jerk?
S1,S2
Tibial
What nerve and spinal segment are responsible for the Biceps Jerk?
C5, C6
Musculocutaneos
What nerve and spinal segment are responsible for the Brachioradialis Jerk?
C5,C6
Radial
What nerve and spinal segment are responsible for the Triceps Jerk?
C6-C7
Radial
What are muscle spindles?
Sensory receptors for stretch reflex
What are muscle spindles a collection of?
Specialised muscle fibres
What are muscle spindles known as?
Intrafusal fibres
What are ordinary muscle fibres known as?
Extrafusal fibres
What direction do muscle spindles and fibres run in?
Parallel
What are the sensory nerve endings on muscle spindles known as?
Annulospiral fibres
As the muscle is stretched, what happens to the discharge from muscle spindles?
It increases
Do muscle spindles have their own efferent motor nerve supply?
Yes
What are the efferent neurones that supple the muscle spindles called?
Gamma motor neurons
Does the contraction of intrafusal fibres contribute to the overall strength of the muscle?
no
What are 4 causes of impairment of skeletal muscle function?
Intrinsic muscle disease
Disease of the NMJ
Disease of lower motor neurons
Disruption of input to motor nerves
What are some causes of intrinsic muscle disease?
Genetic -Congenital -Muscular dystrophy -Myotonia Acquired -Inflammatory -Non-inflammatory (fibromyalgia) -Endocrine (cushings) -Toxic (alcohol)
What are 4 symptoms of muscle disease?
Muscle weakness
Delayed relaxation
Muscle pain
Muscle stiffness
What are some useful investigations for neuromuscular disease?
Electromyography Nerve conduction studies Muscle enzymes Inflammatory markers Muscle biopsy
