MSK: Skeletal Muscle Flashcards
Name the 3 arrangements of skeletal muscle.
- Parallel
- Pennate
- Circular
What are the 3 sub catalogues of parallel arranged skeletal muscle?
- Strap (fibres run longitudinally)
- Fusiform (cylindrical and wider in the centre with tapered off ends)
- Fan shaped (fibres converge at one end)
Describe the structure of pennate muscles.
They have one or more aponeuroses running through the muscle body from the tendon and the fascicles of the muscle fibres attach these to the aponeuroses at an angle.
What are the 3 subcategories of pennate muscles?
- Unipennate (fascicles are on the same side as the tendon)
- Bipennate (fascicles on both sides of the central tendon)
- Multipennate (central tendon branches)
Describe circular muscles.
The fibres form concentric rings around a sphincter or opening.
What are synergists?
Muscles that act to assist the primary mover. (Acting alone they cannot perform the movement of the agonist)
What are neutralisers?
They prevent unwanted actions that the agonist (muscle) can perform.
What are fixators? (Stabilisers)
They act to hold a body part (joint) immobile whilst another body part is moving.
What does the term contraction refer to?
The active cycling of cross bridges between the actin thin filaments and the Myosin thick filaments.
What is isotonic contraction?
Where the tension within the muscle remains constant and the length changes.
What are the 2 subtypes of isotonic contraction?
- Concentric (muscle shortens)
2. Eccentric (muscle lengthens)
What are the 3 types of muscle contraction?
- Isometric contraction (equal tension)
- Isotonic contraction (equal length)
- Passive stretch
What is isometric contraction?
It’s the contraction that occurs when the load against the muscle equals the contractile force being generated.
What is passive stretch?
When the muscle is being lengthened whilst in a passive state, I.e. Not being stimulated to contract.
What protein is important in muscle contraction?
Titin
What is the function of titin?
Connects the Z line to the M line in the sarcomere.
What type of motor neurones innervate skeletal muscle?
Alpha motor neurones
Where are the cell bodies of the neurones which innervate skeletal muscle found?
Ventral horn of the spiral chord (for the muscle of the limbs and trunk) or the motor nuclei of the brain stem (for the head and face)
What is the structure which connects individual muscle fibres and the alpha motor neurone?
Neuromuscular junction
Define a motor unit.
An alpha motor neurone and the group of individual muscle fibres that it innervates.
Which will have more muscle fibres in each motor unit?
Powerful muscles where fine control is less important e.g. Gastrocnemius
What are type 1 fibres also known as?
Slow muscle fibres
What are type 2 muscle fibres also known as?
Fast muscle fibres
What are the 2 types of fast muscle fibres present in humans?
- IIA
2. IIX
Which type of fast fibres are also known as intermediate fibres between fast and slow?
IIA
Why are type 1 fibres resistant to fatigue?
High mitochondria content and use of oxidative metabolism to produce ATP
Are IIA fibres classified as glycolytic or oxidative?
Both!
Are IIX fibres classified as glycolytic or oxidative?
Glycolytic
TRUE OR FLASE: most muscle are composed of a mixture of different types, it is the proportion of fast to slow fibres which determines the function
True
What 2 factors does the contractile force produced by a muscle depend on?
- Size principle
2. Rate code
What is he size principle?
Small motor neurones are recruited before large ones.
In general, what order does the size principle determine the motor unit will follow?
Type I first, then type IIA, then type IIX.
What is the rate code?
The frequency at which muscle fibres are stimulated by their alpha neurone.
What is the name of the term given to the phenomenon where no further force can be produced by a muscle?
Tetany
What is tone?
Degree of tension
What is the term given to a lack of muscle tone?
Hypotonia
Where is skeletal muscle tone controlled?
Locus coeruleus in the motor control centre of the brainstem
What are dihydropyrdine receptors also known as?
Voltage-gated L-type Calcium channels
What is malignant hyperthermia?
A condition triggered by some volatile anaesthetic agents which lead to uncontrolled increase in oxidative metabolism, and hence increase in body temperature.
What is the most common cause of malignant hyperthermia?
Polymorphism in ryanodine receptor
How much ATP is stored in muscle fibre?
Very little (sufficient for only a few seconds of contraction)
Name an additional short term store of ATP within muscle fibres.
Creatine phosphate
Name a disadvantage of using glycolysis under anaerobic conditions.
Lactate is produce from pyruvate by the action of lactate dehydrogenase.
For prolonged activity, what does the muscle do in order to be sufficiently supplied with ATP?
Switches to beta oxidation of fatty acids released from triglycerides stored in a diode tissue.