Mechanics Of Skeletal Muscle Flashcards
What are the four main functions of skeletal muscle?
- Heat Generation
- Posture
- Movement
- Joint Stability
What are Fasciculations?
Name one condition where they are more frequent than usual
Small involuntary skeletal muscle contractions used to maintain muscle tone.
In motor neurone disease the number of fasciculations is much greater than normal
Give a brief description of compartment syndrome, and give three direct causes
A condition whereby a fascial compartment becomes filled with blood, leading to neuro and vascular compression and potential Volkmann’s contracture.
It can be caused by:
- Direct Trauma and subsequent haemorrhage
- Heavily Bruised Muscles
- Crush fractures
By what mechanism do circular muscles contract?
Give two examples of circular muscles
Concentric Contraction
- Orbicularis Occuli
- Orbicularis Oris
What are parallel muscles?
Muscles which contract parallel to the force generating axis
Give three types of parallel muscle and give at least one example of each type of parallel muscle
- Strap muscle eg Sartorius
- Fusiform Muscle eg Biceps Brachii
- Fan Muscle eg Pectoralis Major
What are pennate muscles and give one example of a multi-pennate muscle
Pennate muscles can be either unipennate, bipennate or multipennate. A good example of a multi-pennate muscle is the deltoid. In pennate muscles one or more aponeuroses run through the body of the muscle and the muscle fibres come off of it
What would be described as the Pennation angle of a muscle?
The angle the muscle fibres originate off of a aponeurosis in a pennate muscle
If a muscle is described as an agonist what is it?
The muscle which is the prime mover in the movement of a joint
If a muscle was described as an antagonist for a movement what would it be?
The direct opposition muscle to an agonist, which is the agonist for the opposite joint movement
What is the difference between a fixator muscle and a neutraliser muscle?
Fixator muscles during a movement prevent the joint doing any other movements than the one being performed by immobilising the joint.
Neutralisers prevent the unwanted movements during a certain muscle contraction, eg Pronator Teres preventing supination of the forearm during flexion
Finally what is the role of a synergist?
Aid the action of the agonist in the movement. Cannot perform the entire movement by themselves but assise
Describe Isotonic Muscle Contraction, and therefore explain concentric and eccentric skeletal muscle contraction
A variant of muscle contraction where the tension in the muscle remains constant but the size of the muscle changes. Concentric contraction is when the muscle is shortening and exerting a force.
Eccentric contraction is when a force is being exerted during muscle extension, such as walking down hill
What are the three main types of biomechanics in terms of muscle contraction? Give one example of each class
First Class (See-saw) - example is in neck extension Second Class (Wheelbarrow) - example gastrocnemius in Plantatflexion Third Class (Fishing Rod) - example is in forearm flexion
In what order are muscle fibres recruited to increase the force of muscle contraction?
- Small fibres before larger fibres (larger fibres lead to a larger increase in tension)
- Slow type 1 fibres, then Fast type IIa and finally fast type IIB
How does the Rate code affect muscle contraction?
Rate Codes are the rate of stimulus a muscle receives from the nervous system. A larger rate code leads to an increase in muscle tension up to the point of tetany by the process of SUMMATION.
When a muscle is in tetany what does this describe?
Tetany is a state of constant tension in the muscle, where the tension cannot get any higher and the muscle is described as fused
Describe the stages of muscle tension with an increasing rate code
- Twitch
- Wave Summation
- Unfused Tetany
- Fused Tetany
What is a motor unit? What would the effect on muscle control be if the motor unit has fewer innervated muscle fibres?
All the muscle fibres innervated by a single motor neurone. By having fewer muscle fibres per motor neurone there is greater control over the muscle contraction
What are the three main fibre types in skeletal muscle? List some of the properties for each….
-Slow Type 1 Aerobic Respiration Lots of mitochondria High myoglobin Highly vascularised - Fast Type IIa Same as the slow bar the fact it is only moderately resistant to fatigue - Fast Type IIX(B) Anaerobic Few mitochondria Grey/white in appearance Poorly vascularised Low myoglobin
What factor leads to the type of muscle fibre is present?
The expression of the heavy myosin light chain
What is an alternative name for intrafusal fibres and their main function?
Alternatively Intrafusal fibres are called Muscle spindles and they are used for proprioception within muscle
Where are intrafusal fibres located and how are they innervated?
Inside a collagen sheath within the muscle and are innervated by two sensory neurones and one gamma motor neurone. The motor neurone is used to keep the fibres taught.
Type 1 sensory neurone relay rate of change back to the CNS. Type 2 provides the position sense
Explain the injury to intrafusal fibres in large fibre sensory neuropathy
The type 2 sensory neurones in the intrafusal muscle fibre cannot relay sensory system about position to the CNS.
As a result the patient will make inaccurate movements.
