Muscles and movement
Macro  Micro
SK muscle  fascicles  fibres  myofibrils  actin/myosin (striations)
Strained/pulled muscle = tear of fibres
The longer the fibre the greater the range of contraction and movement at a joint
Muscle types:
1. Circular e.g. orbicularis oris
2. Pennate (=feather-shaped) e.g. deltoid
a. Uni/bi/multi = directionality
3. Fusiform (=spindle-shaped) e.g. biceps brachii
4. Quadrate (=4-sided) e.g. rectus abdominus
5. Flat + aponeurosis (=muscle attaches soft tissue/deep fascia by flattened tendon) e.g.
external oblique
Joint movement: requires that a muscle SPANS it and attaches bones via tendons on either side
of joint
Muscle attachment to bone: at least at 2 points – the origin and the insertion. During
contraction, SK muscle shortens along the long axis between the o and i, bringing them closer
together and decreasing the angle of the joint.
Type of movement:
Depends on:
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Which joint is spanned
Which aspect of the joint is spanned
The long axis of the fibres
The shapes of joint articular surfaces (do they limit movement in any direction?)
Biceps brachii spans:
1. Anterior shoulder joint  shoulder flexion
2. Anterior elbow joint  flexes elbow
3. Anterior proximal radioulnar joint  supination of the forearm
Deltoid movement:
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Anterior fibre originate at lateral 1/3rd of clavicle  flexion of shoulder
Middle fibres originate at acromion process of scapula  abduction of shoulder
Posterior fibres originate at spine of scapula  extension of the shoulder
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Insertion onto deltoid tuberosity of humerus
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Even though 1 joint is spanned, the deltoid has 3 origins  multidirectional movement
Articular surfaces & movement:
Shoulder joint: shallow socket (reduced stability) of glenoid fossa  circumduction of shoulder
Elbow joint: articulation of trochlea of distal humerus and the trochlear notch of the proximal
ulna allows only flexion/extension
Nomenclature: based on combination of…
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2.
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4.
5.
Shape (latin/greek)
Location
Size
Bony attachment
Main movement
a. e.g. biceps brachii (bi= 2, ceps= ‘cephalus’ i.e. head; brachii = arm region)
Reflexes: rapid, involuntary reactions that are protective against danger
Flexion withdrawal reflex: noxious touch stimulus (e.g. heat) causes sudden flexion to withdraw
Stretch reflexes: bicepts/triceps/knee/ankle
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tendon hammer used to apply a brief, sudden stretch to muscle tendon e..g before
quadriceps attachment onto proximal tibia
patient sits cross-legged- to produce tendon stretch.
Additional stretch from hammer poses ‘overstretching’ danger
Elicited brief contraction of muscle belly/extension of limb to prevent overstretching
The response is slight – i.e. a twitch – due to descending control
Reflex arc: sensory nerves detects stretch  synapses onto interneurons in SC  motor nerve
sends impulse to NMJ to elicit contraction of myofibrils
This requires:
1.
2.
3.
4.
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6.
Muscle
Sensory fibres
SC interneurons
Motor fibres
NMF
Descending control from brain
Pathology: Paralysis vs spasticity/atrophy vs hypertrophy:
Paralysis: muscle lacks motor supply and can’t contract (reduced resistance to stretch)
On examination: reduced tone (tonic contraction present during rest to allow the muscle
to readily contact when voluntarily required)
Spasticity: muscle lacks descending control from brain (increased resistance to stretch)
On examination: increased tone
Atrophy: reduced size of fibres as a result of inactivity (e.g. from immobilisation after fracture,
damage to motor supply or prolonged inactivity)
Hypertrophy: increased size of fibres  enlarged myself
NOTE: increased NUMBER of fibres = hyperplasia
Muscle location & compartments:
Epidermis  dermis (collagen/elastin)  superficial fascia (adipose)  deep fascia (tough,
fibrous CT)  SK muscle (covered by deep fascia)
Muscle compartments separated by deep fascia = muscle compartments/intermuscular septum
The IMS functionally splits muscles with each compartment receiving its own nerve supply
Why? Functional + stops infection spread BUT infection can spread upwards e.g.
necrotising fasciitis of quadriceps
Thigh compartments = 3 (anterior, medial, posterior); leg compartments = 3 (anterior, lateral,
posterior)
Arm compartments = 2 (anterior, posterior); forearm compartments = 2 (anterior, posterior)
Compartment syndrome (acute/chronic):
Tough deep fascia create enclosed space  haemorrhage or swelling increases pressure 
impedes muscle and nerve function
Fasciotomy: to relieve pressure, an incision is made longitudinally along compartment
to incise fascia. The wound is left open and packed for a few days + antibiotics
SK/SM border:
SK muscles line proximal respiratory and alimentary tracts (e.g. tongue, epiglottis)
Important for protective reflexes: sneezing, gagging, swallowing, vomiting
Transition to SM at trachea/middle 3rd of oesophagus
Other skeletal muscles: diaphragm, perineum (for micturition and defecation)
The rest of the GI/resp tract is SM
Need to know for each muscle:
Name/attachment/main actions/nerve supply/how to test it
e.g. biceps bracii attaches scapula to radius, producing flexion of the shoulder joint, elbow joint
and supination of radioulnar joints. BB is supplied by the musculocutaneous nerve and is tested
by the biceps jerk reflex