Applied Clinical Anatomy Muscles

Types of Muscle Fibers

• skeletal muscle

• cardiac muscle

• smooth muscle

Skeletal Muscle

moves bones and other structures

• ex: eyes

cardiac muscle

forms most of the walls of the heart and adjacent parts of the great vessels

smooth muscle

• forms parts of the walls of most vessels and hollow organs

• moves substances through viscera like the intestines

• controls movement through blood vessels

Origin

fixed or proximal attachment

Insertion

mobile or distal attachment

Action

the action the muscle performs

Innervation

nervous supply to a muscle

One-Joint Muscle

crosses one point

• ex: brachialis

Two-Joint muscle

crosses two joints

• ex: bicep brachialis

Muscle architecture

• it is a way to categorize muscles

• this can help with understanding action and function of a muscle

• type of muscle

• fiber orientation

• origin and insertion

Muscle Shapes

• parallel

• convergent

• pennate

• fusiform

• circular

• digastric

Parellel

• the fascicles lie parellel to the long axis of the muscle

Convergent

a muscle with a broad attachment from which the fascicles converge to a single tendon

• ex: pectoralis major

Pennate

• muscle fascicles run obliquely attaching to the tendon

• feather-like in the arrangement

• three different types: unipennate, bipennate, multipennate

Fusiform

• wider in the middle, tapering to a tendon

• spindle-shaped

• round, thick belly, and tapered ends

• fascicles may be close to parallel in the center (belly) of the muscle but converge to a tendon at both ends

  • example: bicep brachii, brachioradialis

Circular

• surrounds a body opening or orifice

• constricts when contracted

  • example: orbicularis Occuli

Digastric

• features tow bellies in series, sharing a common intermediate tendon

  • example: digastric

Contractions of Muscles

skeletal muscles can undergo three types of contractions

• reflexive, tonic, phasic

reflexive contraction of muscles

automatic and NOT voluntarily controlled

• example: diaphragm, muscle stretch with reflex hammer

Tonic

slight contraction that does not produce movement or active resistance but gives the muscle firmness, assisting the stability of joints and maintenance of posture

• example: erector spinae when sitting

Phasic

there are two different types of contractions

• isometric: the muscle length does not change, and no movement occurs

• isotonic: the muscle changes length to move (concentric and eccentric)

Concentric

in which movement occurs by the muscle shortening

• this contraction would cause the biceps to create elbow flexion and would bring an object in the hand closer to the shoulder

Eccentric

in which the movement occurs by progressive relaxation of a contracted muscle creating a controlled lengthening of the muscle

• this contraction of the bicep would be bringing the object in the hand away from the shoulder as the elbow goes from flexion to extension

Structure of the skeletal muscle

made up of myofibrils which is made up of actin and myosin

• covered by a plasma membrane called sarcolemma

• connective tissue covering individual muscle fibers is called endomyosium

• a group of fibers (fascicles) is invested by perimysium

• and the entire muscle is surrounded by epimysium

Motor Unit

• the motor unit consists of a single motor neuron and all the muscle fibers innervated by it

• when a motor unit is activated, all of its muscle fibers contract

• small motor units - produce little force

• large motor units - produce lots of force

Agonist (prime mover)

the main muscle responsible for producing a specific movement of the body

Fixator

steady the proximal parts of a limb while movements are occurring in distal parts

synergist

steady the proximal parts of a limb while movements are occuring in distal parts

Antagonist

a muscle that opposes the action of a primer mover

Tendons

connect muscle to bone or may attach muscle to muscle

Tendon Composition

• 2/3 water

• dry weight

  • mostly type 1 collagen - cross linking

  • ground substance - proteins and polysaccharides

Tendon Function

• transmit tensile force from muscle to bone

• store elastic energy

• provide dynamic stability

• proprioception

Ligaments

run from one bony partner to another

Ligament composition

• 2/3 water

• dry weight:

  • type 1 collegen

  • ground substance - proteins and polysaccharides

• not all fibers run parallel

Ligaments Function

• static stabilization

• guide movement

• proprioception

Similarities of Ligaments and Tendons

• both have similar composition —> mostly water and type 1 collagen

• both provide stability and proprioception

Differences of Ligaments and Tendons

• static stability vs dynamic stability

  • static stability - ligaments, joint capsule, meniscus, labrum

  • dynamic stability - muscles and tendons

• tendons serve to assist in moving bone - ligaments do not

• overall, collagen makeup different

• sprain a ligament vs. strain a tendon

Sprain

• an injury to a ligament

• forces that stretch some or all the ligament fibers beyond their elastic limit will cause a sprain

• this stretching produces some degree of rupture of the fibers that make up the ligament

• ligament sprains can occur mid-substance, and/or at attachment sites

1st degree sprain

some fibers disruption or stretch with little or no loss of funciton (0-25%) mild sprain

2nd degree sprain

moderate: partial tearing with some loss of function/integrity. (25-75%) moderate sprain

3rd degree sprain

complete tear and loss of function/integrity. (>75%) severe sprain

Strain

• an injury to a muscle/tendon

• forces that stretch some or all the tendons fibers beyond their elastic limit will cause a strain

• this stretching produces some degree of rupture of the fibers that make up the tendons