Topic 3.1: Musculoskeletal - Muscular systems and muscles

core functions of muscles (4)

produce movement

maintain posture and body position

stabilise joints

generate heat

special properties of muscular tissue that enable muscle to function - list (4)

1. Electrical excitability -> respond to stimuli to produce action potentials

2. Contractility -> contracts forcefully when stimulated

3. Extensibility -> ability to stretch without being damaged

4. Elasticity -> ability to return to original length and shape after contraction and extension

types of muscle - list (3)

skeletal muscle

cardiac muscle

smooth muscle

types of muscle - body location

skeletal: attached to bones or some facial muscles to skin

cardiac: on exists in heart

smooth: unitary muscle in walls of hollow visceral organs except for heart and multi-unit muscle in intrinsice eye muscles, airways and large arteries

types of muscle - cell morphology

skeletal: single, very long, cylindrical multincleate cells with obvious striations

cardiac: uni or bi-nucleate cells, striations, branching chains of cells

smooth: single, fusiform, uni-nucleate, no striations

types of muscle - voluntary or involuntary

skeletal: voluntary contraction for overall body motility

cardiac: involuntarily contracts with direct stimulation from nervous system

smooth: involuntary contractions via autonomic nervous system stimulation

structure of skeletal muscles - levels of categorisation (3)

1. Muscle = composed of individual muscle cells, blood vessels and nerves -> wrapped in epimysium

2. Fascicle = bundle of individual muscle cells -> wrapped in perimysium

3. Fibre = individual muscle cell -> wrapped in endomysium

approx number of muscles

700

differ by age, health, body biometriccs

layers of muscle connective tissue (3)

1. epimysium

2. perimysium

3. endomysium

often extend further than the muscle fibres themselves and are continuous with the connective tissue tendons

layers of muscle connective tissue - epimysium

outmost layer

wraps entire muscle

made of dense connective tissue

connects muscle to tendons

layers of muscle connective tissue - perimysium

middle layer

wraps bundles of fibres → fascicles

carries blood vessels and nerves

layers of muscle connective tissue - endomysium

innermost layer

wraps each single muscle fibre

supports capillaries and nerve endings

movement of bones at the joint due to contraction - summary

moveable bones move toward immovable/ loss movable bone which stays stationary

Typically, immovable bone at proximal end of muscle and the movable bone is at the distal end of muscle -> can have more than one of immovable and/or movable bone for the same muscle

movement of bones at the joint due to contraction - origin and insertion def

Origin (proximal) = attachment to immovable bone

Insertion (distal) = attachment to moveable bone

Eg. gastrocnemius forms bulk of calf -> contraction results in movement of heel bone towards femur

cause of muscles having different shapes

arrangement of their fascicles

Muscles generate power by contracting their fibres -> can only contract or length in the direction of their fascicles

what determines the power generated by a muscle

fascicle arrangement → not length of muscle fibre

muscle fascicle arrangements - list (4)

1. circular → arranged in concentric rings

2. convergent → triangular or fan shaped

3. parallel → either straplike or spindle shaped with expanded belly (fusiform)

4. pennate → fascicles are short and attach obliquely

muscle fascicle arrangements - circular summary and example

Usually found in muscles surrounding external body openings -> sphincters

Eg. orbicularis oris -> contraction closes the mouth

muscle fascicle arrangements - convergent summary and example

Muscle has broad origin with fascicles converging toward a single tendon of insertion -> indirect insertion

Strongest contraction

Eg. pectoralis major

muscle fascicle arrangements - parallel summary and examples (2)

Spindle shaped = narrow attachment points with broader belly

Length of fascicles runs parallel to the long axis of the muscle

Greatest shortening of length during contraction -> parallel arrangement typically seen in muscles that produce a lot of power or needed for body part to move a long way (eg. quads)

Eg. biceps brachii for fusiform and sartorius for parallel

muscle fascicle arrangements - pennate summary and example (3)

Unipennate -> fascicles insert onto only one side of the tendon

Eg. extensor digitorum longus

Bipennate -> fascicles insert onto the tendon from opposite sides of the muscles (looks like a feather)

Eg. rectus femoris

Multipennate -> fascicles insert onto tendon from many directions

Eg. deltoid

connective tissue associated with muscle - list (4)

• ligaments → fibrous connections between bones

• tendon → msucle belly to attachment site at bone

• aponeurosis → muscle belly to attachment site including bone

  • raphe → line of fibrous tissue where one muscle joins another

connective tissue associated with muscle - ligaments (2)

Composed of collagen fibres

Usually blends with periosteum of bones at the joint

connective tissue associated with muscle - tendon

Composed of fibrous tissue

connective tissue associated with muscle - aponeurosis (2)

Broad and flat connective tissue

Spread over a greater area than tendon

connective tissue associated with muscle - raphe (2)

Usually along an attachment point to bone

Not a separation of the same muscle but two separate muscles joining together

purpose of fascia

Wrap, package and insulate deep structures -> distinct from epimysium

whole groups of muscles with similar functions and usually sharing the same nerve supply are located in thesame fascial compartment

types of fascia (2)

superficial → loose subcutaneous tissue

deep → thin, rough sheet made primarily of collagen fibres

deep fascia - summary (3)

Strong, inelastic, usually present in a single layer

Not found in areas where expansion is required

Extends to invest individual bundles of investing fascia

intramuscular septa - def

compartments separated by thick sheets of deep fascia

retinaculum - def

where deep fascia thickens or condenses, forming a band -> typically holds tendons in place where they cross a joint

Eg. extensor retinaculum of foot prevents tendons connected to muscles more distal to it from bowstringing when joint is moved

antagonsit - def

muscle that opposes action of another muscle -> typically by excentric contraction

Sometimes regulates action of prime mover by providing resistance to slow or stop movement

Eg. triceps brachii opposes biceps during elbow flexion

prime mover - def

muscle that is responsible for producing a specific movement -> typically by concentration contraction

Eg. biceps brachii. = prime mover of elbow flexion

synergist - def

compliment action of prime mover by adding extra force to the same movement or reducing undesirable or unnecessary movements

Eg. brachialis = synergist of biceps in elbow flexion

fixator - def

muscle that steadies proximal parts of a limb while movements occur in distal parts -> typically by isometric contraction

Eg. rotator cuff muscles stabilise shoulder during elbow flexion

inferring action of muscle

Action of muscle can be inferred by position of the muscle relative to the joint it crosses

rule swaps for muscles that cross the knee and ankle due to limb rotation during development

muscle action - muscle that crosses on anterior side of a joint

produces flexion

(muscles that cross joints anteriorly produce extension)

pectoralis major crosses shoulder joint and allows flexion of arm

muscle action - muscle that crosses on posterior side of a joint

produces extension

(muscles that cross joints posterioly produce flexion)

latissimus dorsi crosses shoulder joint and allows extension of arm

muscle action - muscle that crosses on lateral side of a joint

produces abduction

deltoid crosses shoulder joint and allows abduction of arm

muscle action - muscle that crosses on medial side of a joint

produces adduction

teres major crosses shoulder joint and allows adduction of arm

naming of skeletal muscle - criteria (5)

• location

• shape

• size

• number of origins

• attachments

principle of neurovascular supply to skeletal muscle

one nerve, one artery, and one or more veins serve each muscle → all enter or exit near centre of muscle

principle of neurovascular supply to skeletal muscle - nerve

nerve ending controls activity → stimulates muscle fibres to contract

principle of neurovascular supply to skeletal muscle - arteries and veins

contracting muscles need a lot of energy, oxygen, and nutrients delivered by arteries

produce a large amount of metabolic wastes removed via veins

Individual muscle fibres are in close contact with capillaries

Major source artery and vein enter muscle belly via neurovascular hilum