Flashcards in MSK Session 2 Deck (117):
What two types of muscle are there?
What type of muscle is the diaphragm?
Give an example of each type of skeletal muscle arrangement.
Circular: orbicularis oris
Convergent: pec. major
Unipennate: extensor digitorum longus
Fusiform: biceps brachii
Bipennate: rectus femoris
How are skeletal muscles attached to bones?
What does skeletal muscle continually contract?
To maintain posture
What is the mechanical efficiency of skeletal muscle?
~20%, rest dissipated as heat
What is the gross anatomy of skeletal muscle?
Epimysium --> perimysium --> endomysium
Muscle --> fascicle --> muscle fibre
What is fasciculation?
Low level muscle twitch often seen in the face when tired/nervous or more severely in motor neurone disease
What is a first class lever?
Where the force and load are on opposite sides of the fulcrum like a see-saw e.g. neck
What is a second class lever?
Where the force and load are to the left of the fulcrum like a wheelbarrow e.g. in the foot where the ball is the fulcrum
What is a third class lever?
Most common type of lever where the force and load are to the right of the fulcrum, like a fishing rod
What can be said about the length along which force acts in a third class lever?
What are agonists?
What are antagonists?
Oppose prime movers
What act together to allow fine, smooth movement?
Agonists and antagonists
What are synergists?
Muscles that assist prime movers by neutralising extra motion to keep motion in one direction
What are fixators?
Muscles that stabilise the action of prime movers by fixing non-moving joints when prime mover is acting over two joints
What are compartments?
Groups of muscles surrounded by connective tissue
What is compartment syndrome?
When pressure builds up inside a compartment due to the inability of the surrounding CT to undergo rapid expansion and causes nerve compression
What can cause compartment syndrome?
What effect can long-term training have on the connective tissue surrounding a compartment?
What is isotonic muscle contraction?
Constant tension with variable muscle length that changes to move a load
What happens in concentric isotonic muscle contraction?
What happens in eccentric isotonic muscle contraction?
Muscle exerts force whilst extended e.g. walking downhill
What is isometric muscle contraction?
Muscle remains a constant length but has variable tension
Describe isometric contraction in hand grip.
Forearm muscles do not change length but exert force
Small muscles also used which rapidly increase BP - risky for elderly and hypertensive
What are the three types of muscle fibre?
Type I - slow oxidative
Type IIa - fast oxidative
Type IIb - fast glycolytic
What is used to identify muscle type?
Mitochondrial staining on post mortem/needle biopsy sample
What characterises slow oxidative muscle?
High myoglobin levels
Lots of mitochondria
Rich capillary supply
Fatigue resistant - used in endurance activities and posture
What characterises fast oxidative muscle?
High myoglobin levels
Red to pink colour
Rich capillary supply
Moderate fatigue resistance - used for walking and sprinting
What characterises type IIb muscle?
Low myoglobin levels
White (pale) colour
Poorer capillary supply
Rapidly fatiguable - used for short intense movement
What is proprioception?
Awareness of self
How do specialised muscle fibres in the belly of a muscle allow proprioception to take place?
Sense stretch and send signals back to brain reporting tension and strain levels in the muscle
What can be considered as the feedback control of movement as well as feedback from the joints?
What is a motor unit?
Motor neurone and the muscle fibre it innervates
Where is the output of a motor neurone?
Through ventral root
How does the number of muscle fibres controlled by a motor neurone vary with control?
More control = fewer fibres innervated by a single neurone
What is cross talk?
Method of communication b/w neurones and muscle using signalling molecules
How does atrophy of a neurone or a muscle cause atrophy of its corresponding component?
Signals are either not released or not needed
Which signalling molecule maintains communication b/w motor neurone and muscle and is very important in the NMJ?
What causes baseline muscle tone in muscles at rest?
Motor neurone activity
Muscle elasticity due to protein content
What controls baseline muscle tone?
Motor control centres in the brain
Afferent fibre signals originating from the muscle
What is hypotonia?
Low level of muscle tone
What can cause hypotonia?
Primary degradation of the muscle
Lesions of cerebellum and cerebral/shock causing damage to motor cortex involved in feedback mechanism
Lesion of sensory afferents from the muscle spindles
Lesions of lower motor neurones e.g. polyneuritis
Spinal neural shock
What does polyneuritis affect?
Multiple motor neurones in body in different places
How is ACh exocytosed from the NMJ?
AP sweeps around membrane --> opens calcium channels --> calcium in
What happens when 2 ACh bind to the alpha-subunit of nicotinic receptors on the effector muscle?
Conformational change of ligand gated sodium --> sodium in --> depolarisation --> calcium release from SR
Why are anaesthetics used?
Less tissue damage is caused if the tissue is relaxed
What is given in addition to anaesthetics to counteract the initial contraction they cause by inhibiting AChE?
What is spatial summation?
Type of recruitment learned throughout life
How does spatial summation work?
More motor neurones are activated so more muscle fibres are recruited to develop more force
Where do reflex pathways in spatial summation come from?
Golgi tendon organs of muscle fibres
What do Golgi tendon organs sense?
Changes in muscle tension
What is temporal summation?
Recruitment where increased frequency of AP to muscle fibres causes summation
What is the difference between fused and infused tetanus?
Unfused = twitch
Fused = continuous force = no relaxation
What is present in all soil that interferes with feedback control of muscle tension to cause continual contraction?
What is electromyography?
Electrodes placed above/in muscles to record their electrical activity
Why is the amplitude in an electromyography equivalent to the force of contraction?
Increased recruitment of motor units
What is seen in an EMG that indicates MND?
Graph doesn't match up
How is relaxation of a muscle achieved by lower cytoplasm calcium content?
Pumping calcium back into SR via calcium pumps
Binding to calmodulin
What are sources of energy for muscle contraction?
Short term ATP stores in muscle fibre
Aerobic and anaerobic glycolysis
What energy source for muscle contraction can be measured for suspected muscle damage?
How does anaerobic glycolysis cause muscle cramp?
Conversion by LDH of pyruvate to lactate which acts on nerve endings coupled with a decrease in pH
When does peripheral fatigue occur?
Muscle glycogen stores are depleted
Within one minute of blood flow interruption
What is contracture?
State of continuous contraction when ATP is depleted
What causes rigor mortis?
Myosin X-bridges unable to detach from actin filaments
What is the time frame of rigor mortis?
Slow onset, peaks at 12-13 hours and can give v. exact time of death
What forms the anterior border of the axilla?
Pec. minor and major
What makes up the medial border of the axilla?
What forms the posterior border of the axilla?
What forms the lateral border of the axilla?
What forms the apex of the axilla?
Cervico-axillary canal bounded by the first rib, clavicle and superior edge of scapula a
What transverses the apex of the axilla?
What forms the base of the axilla?
Axillary fascia from 4th rib to axillary fossa
What enters and leaves the clavipectoral triangle?
Cephalic vein enters
Medial and lateral pectoral nerves leave
What is found in the quadrangular space?
Post-circumflex humeral artery
What is the main artery supplying the upper limb?
What are the parts of the axillary artery?
Medial, posterior and lateral to pec. minor
Describe the path of the axillary artery.
Lateral border of 1st rib --> medial border of pec. minor --> lateral border of pec. minor --> inferior border of teres major
What arteries branch off from the axillary artery?
Anterior and posterior circumflex humeral arteries
What is the collateral route enabling venous return if IVC is obstructed?
Brachial and basilic vein --> subclavian vein --> second part of axillary vein --> initial distal end
Describe the path of the axillary vein.
Which veins drain into the axillary vein?
Corresponding veins to the thoraco-acromial artery
Moving anteriorly to posteriorly in the axilla, how are the artery, nerve and vein arranged?
What 5 groups of lymph nodes are present in the axilla?
Where are the pectoral lymph nodes found and what area do they drain?
3-5 nodes on medial wall
Where are the subscapular lymph nodes located and what do they drain?
6-7 nodes on posterior axillary fold
Posterior wall and scapula
Where are the humeral lymph nodes found and what do they drain?
4-6 nodes on lateral wall
Where are central and apical lymph nodes found?
Central = 3-4 nodes deep to pec. minor
Apical = all other groups and lympahtics not already classified
What are the components of the brachial plexus?
Where do the roots of the brachial plexus arise?
Paired spinal nerves that leave the spinal cord via the intervertebral foramen of the vertebral column which divide into an anterior part
What is the fate of the posterior division of the spinal nerves that have left the spinal cord?
Innervate skin and musculature of the trunk
What do the roots of the brachial plexus pass between to enter the base of the neck?
Anterior and medial scalene muscles
What happens in the brachial plexus at the base of the neck?
Roots converge to form three trunks
What path do the trunks of the brachial plexus take?
Move laterally crossing the posterior triangle of the neck
What happens to the brachial plexus within the posterior triangle of the neck?
Each trunk divides into anterior and posterior branches
What path do the divisions of the brachial plexus take?
Pass into the axilla
What happens to the brachial plexus in the axilla?
Divisions combine to form three nerves which are the cross of the brachial plexus
What are the cords of the brachial plexus named relative to?
What do the cords of the brachial plexus give rise to?
What happens to the brachial plexus in the axilla and proximal part of the UL?
3 cords become 5 branches
What is the function of the five major branches of the brachial plexus?
Provide innervation to the muscle and skin they pass over
What are the five major branches of the brachial plexus?
What are the nerve roots of the ulnar nerve?
C8 and T1
What are the nerve roots of the radial nerve?
C5-8 and T1
What are the nerve roots of the median nerve?
C6-8 and T1
What are the nerve roots of the axillary nerve?
C5 and 6
What are the nerve roots of the musculocutaneous nerve?
What does the ulnar nerve innervate?
Muscles of hand
Flexor carpi ulnaris
Medial half of flexor digitorum profundus
Sense in anterior and posterior medial 1.5 fingers and palm area
What does the radial nerve innervate?
Extensor muscles in posterior compartment of forearm
Sense in posterior aspect of arm and forearm
Sense in posterior and lateral aspect of hand
What does the median nerve innervate?
Flexor muscles in forearm
2 lateral lumbricals that move index and middle fingers
Sense in lateral palm and lateral 3.5 fingers on palmar surface of hand
What branches does the median nerve give rise to?
Palmar cutaneous branch
Digital cutaneous branch
What does the axillary nerve innervate?
Long head of biceps brachii
Sense in regimental badge area
What branch does the axillary nerve give rise to?
Superior lateral cutaneous nerve of arm
What does the musculocutaneous nerve innervate?
Sense in lateral half of anterior forearm and small lateral portion of posterior forearm
What branch does the musculocutaneous nerve give rise to?
Lateral cutaneous branch of forearm