Week 2 - Skeletal Muscle Structure, Morphology and Function Flashcards
What is the most common shape of muscle? Give an example of a muscle which takes this shape.
Fusiform
Biceps brachii
List the shapes a muscle may be, and give examples of each.
Fusiform - biceps brachii Circular Convergent - pectoralis major Parallel - sartorius Unipennate - extensor digitorum longus Bipennate - rectus femoris Multipennate - deltoid
Describe a convergent muscle
Wide at origin but narrow at its insertion
Describe what a parallel muscle looks like
Straight up and down
What is the difference between unipennate, bipennate and multipennate muscles?
Unipennate - like half a feather
Bipennate - like a feather
Multipennate - like several feathers
What structure is every tendon continuous with?
The epimysium
What is fasciculation? Give an example of when it may occur.
Muscle twitching
In the eyes when tired
Which type of lever is most efficient?
1st class lever
Describe a first class lever
Pivot in the centre, with the force underneath to one side, and the load above on the other side
Describe a second class lever.
Like a wheelbarrow - force and load both on the left of the pivot.
Describe a 3rd class lever.
Like a fishing rod -
Force and load both on the right of the pivot
Briefly explain what happens in compartment syndrome.
Bleeding occurs within a compartment, which is bound by inextensible connective tissue. This raises the pressure inside the compartment, and as it cannot expand, leads to compression of the neurovasculature within the compartment.
Give the 4 muscle groups in terms of function.
Agonists
Antagonists
Synergists
Fixators
What is an agonist, in terms of muscles?
A “prime mover” - i.e. the main muscle performing a movement
What is a synergist?
A muscle aiding an agonist
What is an antagonist, with regards to muscles?
A muscle opposing the action of an agonist
What do fixator muscles do?
Stabilise the action of prime movers (agonists)
What are the two types of muscle contraction, and how do they differ?
Isotonic - tension constant, length variable
Isometric - length constant, tension variable
What are the two types of isotonic muscle?
Concentric - gets shorter
Eccentric - gets longer
What are the two major muscle fibre types?
Type I
Fast Twitch
What are type I muscle fibres?
Slow oxidative
How are fast twitch muscle fibres subdivided?
Type IIa - fast oxidative
Type IIb - fast glycolytic
Which muscle fibre type appear red, and why?
Slow oxidative
Due to the very high myoglobin content
Which are the palest muscle fibres?
Fast glycolytic
Which muscle fibre types are aerobic and which are anaerobic?
Slow and fast oxidative are aerobic
Fast glycolytic are anaerobic
Give 3 characteristics of both fast and slow oxidative muscle types.
High myoglobin (but more in slow)
Many mitochondria
Many capillaries
Which muscle fibre type(s) is/are fatigue resistant?
Slow and fast oxidative, although slow more so.
What functions may slow oxidative muscle fibres perform?
Posture
Endurance activity
Give an example of an activity facilitated by fast oxidative muscle fibres
Walking
Fast glycolytic muscle fibres rapidly fatigue. What sorts of activity do they therefore allow?
Short, intense activity
What are the major functions of skeletal muscle?
Movement
Posture
Stability of Joints
Heat generation (although only around 20% efficient)
What are proprioreceptors?
Muscle spindles that send signals to the brain telling it how much tension is being exerted.
What does proprioreception allow?
What might disrupt it?
Feedback control of movement
Alcohol
What is a motor unit?
A motor neurone and the muscle fibre(s) it innervates
What structure do motor neurones leave the brain via?
The ventral root
What is “crosstalk”?
Communication between neurones and muscle, via signalling molecules.
Why may atrophy of a muscle cause atrophy of the nerve that innervates it, and vice versa?
Lack of crosstalk due to fewer chemical signals being produced.
What two factors mean that baseline muscle tone is always present at rest?
Muscle activity
Motor neurone activity
How is muscle tone controlled?
Feedback via afferent fibres from the muscle to the motor control centres of the brain.
What is hypotonia?
Lack of muscle tone
What are the 3 possible causes of hypotonia?
- CNS problems
- PNS problems
- Muscle problems - myopathies (primary muscle degeneration)
What is an EMG and what is it used for?
An electromyogram
Used to measure electrical activity in the muscles; helps diagnose conditions such as MND.
How is the force of contraction of skeletal muscle controlled?
Spatial summation
Temporal summation
Explain spatial summation
More motor neurones are activated, and hence more muscle fibres contract, giving more forceful contraction
Explain temporal summation, including what it can lead to.
Increased frequency of action potentials in the muscle fibres.
In extremes, this can lead to tetany.
What is a contracture?
Continuous muscle contraction without relaxation
What are the possible sources of ATP within skeletal muscle?
ATP stores
Creatine phosphate
Glycolysis
Oxidative phosphorylation
Explain the pathophysiology behind muscle cramps.
Increased lactate causes the pH of the muscle to fall. This acts on nerve endings, causing pain.
If blood flow to a muscle is interrupted, how quickly are the glycogen stores depleted?
Within around 1 minute
