2. Skeletal muscle Flashcards
What is the structure of skeletal muscle?
Striated Multi-nucleated fused cells voluntary myoglobin present
What is fasciculation?
Small , local involuntary contraction of muscle
What is fibrillation?
Involuntary contraction of individual muscle fibres
What are the 3 categories of parallel muscles?
Strap
Fusiform
Fan-shaped
What is an example of a strap muscle?
Sartorius
What is an example of a fusiform muscle?
Biceps brachii
What is an example of a fan-shaped muscle?
Pectoralis major
What are the 3 types of pennate muscles?
Unipennate
Bipennate
Multipennate
What is an example of a unipennate muscle?
Extensor digitorum longus
What is an example of a bipennate muscle?
Rectus femoris
What is an example of a multipennate muscle?
Deltoid
What is compartment syndrome?
Limbs are divided into compartments by fascia. Trauma in one compartment could cause internal bleeding or swelling which increases pressure on blood vessels and nerves.
How is compartment syndrome treated?
Fasciotomy - cutting fascia to relieve pressure
What is a motor unit?
An alpha-motor neurone and the muscle fibres it innervates.
Each fibre is innervated by one neurone, but one neurone can innervate many fibres.
What is isometric contraction?
A muscular contraction in which the length of the muscle does not change despite being under tension.
What is isotonic contraction?
A muscular contraction in which the length of the muscle changes.
How is isotonic contraction categorised?
Concentric - muscle shortens e.g bicep in flexion
Eccentric - muscle lengthens e.g bicep in extension
What is an example of a first class lever?
Very few in body
Flexion and extension of the head at the neck
What is an example of second class lever?
Plantar flexion of foot
What is an example of a third class lever?
Biceps brachii
Most common in the body
What determines the power of a muscle?
Higher number of fibres per motor unit
What determines the fine control of a muscle?
Lower number of fibrils per motor unit
What are the 3 main types of muscle fibre, what is this based on?
Slow type 1 Fast type 2a Fast type 2x based on myosin heavy chain expression Each muscle has a different proportion of fibres depending on function.
What are the properties of type 1 muscle fibres?
- Slow oxidative
- aerobic
- high myoglobin
- many mitochondria
- rich capillary supply
- fatigue resistant
Which muscle fibres are the first to be recruited?
Type 1
What movements/actions utilise type 1 muscle fibres?
Standing
Walking
What are the properties of type 2a muscle fibres?
- fast oxidative
- aerobic
- high myoglobin
- many mitochondria
- moderate fatigue
What muscle fibres are the second to be recruited?
Type 2a
What actions utilise type 2a fibres?
Walking, running
What are the properties of type 2x muscle fibres?
- fast glycolytic
- anaerobic
- low myoglobin
- few mitochondria
- rapidly fatigue
What muscle fibres are the last to be recruited? During what type of exercise?
Type 2x
Running, sprinting, jumping
What are intrafusal muscle fibres?
Muscle spindles within the muscle belly that act as proprioceptors and sense stretch.
Separated form rest of muscle by collagen sheath.
Explain the innervation if intrafusal fibres.
Innervated by 2 sensory and 1 motor neurone:
- Gamma motor neurone keeps fibres taught
- Type 1a sensory neurones relay rate of change in muscle length to CNS
- Type 2 sensory neurones provide position sense.
What will patients with large fibre sensory neuropathy be unable to do?
Impeded output from muscle spindles, unable to perform accurate movement without visual input (e.g eyes closed)
What are the 2 main ways to control muscle force?
- Size principle
2. Rate code
Explain the size principle.
Small motor neurones are recruited before large motor neurones.Motor units with most fibre types: Slow type 1 (smallest) first Fast 2a Fast 2x (largest) last.
Explain the rate code.
More action potentials increase the force produced.
Subsequent AP produce summation up to a limit.
What is hypotonia?
Symptom of lack of normal basal skeletal muscle tone.
Most common in babies after birth (floppy baby syndrome)
Why is the resting membane potential of skeletal muscle more negative than other cells?
Also have a high concentration of Cl- leak channels (Cl- has negative equilibrium potential).
