Musculoskeletal: Anatomy - Overview of the muscular system Flashcards
What characteristics are used to classify skeletal muscle?
Whether willfully controlled (voluntary vs involuntary)
Whether appearing striped under a microscope (striated vs smooth)
Whether located in the body wall and limbs or the hollow organs (somatic vs visceral/autonomic)
Compare and contrast the three different types of skeletal muscle in terms of their location, cell appearance, activity type, and stimulation
List the 7 different shape classifications of skeletal muscle and give an example of each
Flat: parallel fibres, often with an aponeurosis (flat sheet of tendons anchoring muscle to skeleton)
E.g. external oblique, sartorius
Pennate: feather-like; may be unipennate, bipennate, or multipennate
E.g. extensor digitorum longus (unipennate), rectus femoris (bipennate), and deltoid (multipennate)
Fusiform: spindle-shaped
E.g. biceps brachii
Convergent: arise from a broad area and converge to form a single tendon
E.g. pectoralis major
Quadrate: four equal sides
E.g. rectus abdominis
Circular or sphincteral: surround a body opening or orifice, constricting it when contracted
E.g. orbicularis oculi
Multi-headed or multi-bellied: more than one head of attachment or more than one contractile belly
E.g. biceps brachii (two heads), triceps brachii (three heads), digastric and gastrocnemius (two bellies)
Define origin
Usually the proximal end of muscle, which remains fixed during muscular contraction
Define insertion
Usually the distal end of muscle, which is mobile
What are the three functions of skeletal muscle?
- Automatic (reflexive) movements
(e. g. respiratory movements of the diaphragm, myotatic/stretch reflex) - Maintaining muscle tone (tonic contraction, even when “relaxed”)
- Phasic (active) contraction
What are the two types of phasic contraction? Define each
Isotonic: involves a change in muscle length
Isometric: muscle length remains the same, but muscle tension is increased above tonic levels to resist gravity or other antagonistic force
What are the two types of isotonic contraction?
Concentric: produces movement by muscle shortening
Eccentric: produces movement by controlled relaxation
Which type of isotonic contraction uses less metabolic load? Which is capable of generating higher tension?
Eccentric contraction requires less metabolic energy at the same load, but with maximal contraction can generate much higher tension levels than concentric contraction
What is a motor unit?
Functional unit of a muscle, consisting of a motor neuron and the muscle fibre it controls
How does the number of muscle fibres in a motor unit vary?
According to muscle size and function
E.g. large motor units in trunk and thighs, small motor units in eyes and hands where precision is needed
Define prime mover
Muscle primarily responsible for particular movement (can also be gravity)
Define fixator
Steadies part of a limb through isometric contraction while another part is moving
Define synergist in terms of muscle activity
Complements the action of prime movers
Define antagonist in terms of muscle activity. What is the difference between a primary and secondary antagonist?
Oppose the actions of another muscle (eccentrically contract as the active movers concentrically contract - to produce a smooth movement)
Primary antagonist: directly opposes the prime mover
Secondary antagonist: opposes synergists
Define shunt muscle
A muscle that’s pull is exerted along a line that parallels the axis of the bones to which it is attached - at a disadvantage for producing movement, but instead acts to maintain contact between the articular surfaces of the joint it crosses (i.e. resists dislocating forces; e.g. brachioradialis, brachialis)
Proximal attachment is nearer the joint it acts over and distal attachment is further away
Define spurt muscle
A muscle that’s pull is oriented obliquely relative to the bone it moves - capable of rapid and effective movement (e.g. biceps)
Proximal attachment further away from the joint and distal attachment closer
What causes DOMS?
Can be caused by eccentric contractions that are either excessive or associated with a novel task
Muscle lengthening is more likely to produce microtears and/or periosteal irritation (usually muscles cannot elongate beyond one third of their resting length without sustaining damage)
How can skeletal muscle fibres be replaced? How does the composition of new skeletal muscle compare with the original?
Skeletal muscle fibres cannot divide but can be replaced individually by new muscle fibres derived from satellite cells
Satellite cells are a potential source of myoblasts (muscle cell precursors), which are capable of fusing to form new skeletal muscle fibres if required
Number of new fibres that can be produced is insufficient to compensate for major muscle degeneration or trauma, and the new skeletal muscle is composed of disorganised mixture of muscle fibres and fibrous scar tissue
How do muscles increase in size with frequent strenuous activity?
Via hypertrophy of existing fibres
Can cardiac muscle be replaced?
No: cannot divide and there is no equivalent to the satellite cells of skeletal muscle to produce new fibres
What are pharyngeal arches?
Branchial arches in mammals
Primordia for a multitude of structures including face, jaw and pharynx (structurally same as skeletal muscle but usually covered by mucosa or near a mucosocutaneous junction; involved in superficial reflexes and glandular secretion)
What forms the vasculature of the pharyngeal arches?
Aortic arches
Describe the development of the branchial arches
Develop during fourth week as a series of mesodermal outpouchings on sides of developing pharynx
Pouches form on endodermal side, grooves or clefts form on ectodermal surface
Nerve supply is from cranial nerves and splanchnic mesoderm
Describe Hilton’s law
The nerves supplying a joint also supply the muscles moving the joint and the skin covering their distal attachments
