Skeletal Muscle Physiology 2 Flashcards
What are the 2 primary factors that lead to gradation of skeletal muscle tension?
- number of muscle fibres contracting within the muscle
- tension developed by each contracting muscle fibre
Explain how repetitive fast stimulation of skeletal muscle works?
Duration of AP is much shorter then the duration of the resulting muscle twitch –> possible to summate twitches to bring about a stronger contraction through repetitive fast stimulation of skeletal muscle
What is tetanus contraction?
Muscle fibre is stimulated so rapidly that it does not have an opportunity to relax at all between stimuli, a maximal sustained contraction known as tetanus occurs
Can cardiac muscle be tetanised?
No - only skeletal muscle
What is a twitch of a muscle?
A single contraction from one stimulation therefore it is not useful in bringing about meaningful skeletal muscle activity
The tension developed by skeletal muscle increases with increasing…?
frequency of stimulation
When can maximal tetanic contraction be achieved?
when the muscle is at it’s optimal length before the onset of contraction
When does the optimal length of a muscle occur?
The resting length of a muscle is approximately its optimal length
What are elastic components which transmit muscle tension?
Connective tissue
Tendon
What is isotonic contraction of muscles?
used for body movements and for moving objects.
Muscle tension remains constant as the muscle length changes
What is isometric contraction of muscles?
used for supporting objects in fixed positions and for maintaining body posture. Muscle tension develops at constant muscle length
What happens to the velocity of muscle shortening as the load increased?
Decreased
What can cause impairment of skeletal muscle function?
(1) Intrinsic disease of muscle
(2) Disease of NMJ
(3) Disease of lower motor neurons
which supply the muscle
(4) Disruption of inputs to motor unit
Give examples of genetically determined myopathies?
Congenital myopathies: characteristic microscopic changes leading to reduced contractile ability of muscles
Chronic Degeneration of contractile elements - muscular dystrophy
Abnormalities in muscle membrane ion channels e.g. myotonia
Give examples of acquired myopathies?
Inflammatory myopathies e.g. polymyosytis
Endocrine myopathies e.g. Cushing syndrome, thyroid disease
Toxic myopathies e.g. alcohol, statins
What is myotonia?
delayed relaxation (prolonged contraction) of theskeletal musclesafter voluntary contraction or electrical stimulation.[1]
Define reflex
A reflex action is a stereotyped response to a specific stimulus and are the simplest form of coordinated movement
What is the simplest monosynaptic spinal reflex?
Stretch reflex
What is the stretch reflex?
Stretch reflex serves as a negative feedback that resists passive change in muscle length to maintain optimal resting length of muscle
In the stretch reflex what is the sensory receptor?
Muscle spindle and is activated by muscle stretch
What happens after the muscle spindle is activated?
Stretching the muscle spindle increases firing in the afferent neurons
The afferent neurons synapse in the spinal cord with the alpha motor neurons (efferent limb of the stretch reflex) that innervate the stretched muscle
Activation of the reflex results in contraction of stretched muscle
How can the stretch reflex be elicited?
By tapping the muscle tendon with a rubber tendon hammer
Name some stretch reflexes?
Knee jerk, ankle jerk, biceps jerk, bracioradialis, triceps jerk
Name the peripheral nerve and spinal segment the knee jerk is involved in?
Femoral nerve
L3 L4
Name the peripheral nerve and spinal segment the ankle jerk is involved in?
Tibial nerve
S1, S2
Name the peripheral nerve and spinal segment the biceps jerk is involved in?
Musculocutaneous nerve
C5, C6
Name the peripheral nerve and spinal segment the brachioradialis is involved in?
Radial nerve
C5 C6
Name the peripheral nerve and spinal segment the triceps jerk is involved in?
Radial nerve
C6 C7
What are muscle spindles (intrafusal fibres) made of?
A collection of specialised muscle fibres
What are ordinary muscle fibres referred to as?
Extrafusal fibres
Why are the normal muscle fibres and muscle spindles different?
Intrafusal fibres (muscle spindles) keep extrafusal fibres (ordinary muscle) at their optimum
Where are muscle spindles found?
within the belly of muscles and run parallel to ordinary muscle fibres (extrafusal fibres)
What is the name for the muscle spindles sensory nerve endings?
annulospiral fibres
What kind of nerve supply do muscle spindles have? and what is their purpose?
- motor nerve supply in the form of gamma-motor neurons
- to adjust the level of tension in the muscle spindles to maintain their sensitivity when the muscle shortens during muscle contraction
What are the main differences between different types of skeletal muscle fibres?
- the enzymatic pathways for ATP synthesis
- the resistance to fatigue
- the activity of myosin ATPase
Does each motor unit usually carry one or more kinds of muscle fibres?
One
What metabolic pathways supply ATP for muscle fibres?
- transfer of high energy phosphate from creatine phosphate to ADP
- oxidative phosphorylation
- glycolysis
Which kin of muscle fibre is most resistant to fatigue?
Slow oxidative (type 1)
What are the difference between type 2a and type 2x muscle fibres?
speed of contraction and resistance to fatigue
2a - fast contraction and intermediate resistance to fatigue
2x - fast contraction but low resistance to fatigue
What are the 3 names of the main muscle fibre groups?
Slow oxidative - type 1
Fast oxidative - type 2a
Fast glycolytic - type 2x
What are type 1 (slow twitch fibres) muscle fibres used for?
prolonged relatively low work aerobic activities
What are type 2a (intermediate twitch fibres) muscle fibres used for?
prolonged relatively moderate work activities
What are type 2x (fast twitch fibres) muscle fibres used for?
short term high intensity activities
What investigations can be used for neuromuscular disease?
Electromyography
Nerve conduction studies
Muscle enzymes (creatine kinase)
