Painting by Danny Quirk

Kaan Yücel M.D., Ph.D.

05.March.2014 Wednesday

interested in all the muscles in the body

Musculus (muscle) mus-mouse; musculus- little mouse.

So called because the shape and movement of some muscles (notably biceps) were thought to resemble mice. If you bend and straighten your arm at the elbow, you should see the front of the upper arm move under the skin. To the ancient Romans this movement resembled a little mouse scurrying beneath the skin.

Skeletal muscles move the skeleton, as a result the body.

Types of Muscles based on distinct characteristics

Functional voluntary vs. involuntary Histological striated vs. smooth or unstriated Anatomical (location) @ body wall (soma) and limbs @ hollow organs (viscera) or blood vessels

Skeletal striated muscle voluntary somatic muscle

gross skeletal muscles that compose the muscular system moving or stabilizing bones and other structures (e.g., the eyeballs).

Innervated by the somatic nervous system.

Cardiac striated muscle involuntary visceral muscle

forms the walls of the heart and adjacent parts of the great vessels. pumps blood.

Smooth muscle (unstriated muscle) involuntary visceral muscle

forms part of the walls of most vessels and hollow organs (viscera) moving substances through them

coordinated sequential contractions (pulsations or peristaltic contractions). Innervated by the autonomic nervous system.

FEATURES OF SKELETAL MUSCLES HEAD OR BELLY fleshy, reddish, contractile portions TENDON white non-contractile portions

composed mainly of organized collagen bundles, that provide a means of attachment.

Most skeletal muscles attach to Directly or indirectly to bones

Cartilages

Ligaments

Fascias

or combinations of the ones above

Some to organs (eyeball)/skin (facial muscles)/mucous membranes(intrinsic tongue muscles)

Muscles are organs of locomotion (movement) also:

provide static support give form to the body

provide heat

Some tendons form flat sheets aponeuroses anchor the muscle to the skeleton to deep fascia to aponeurosis of another muscle

Many terms provide information about a structure's Shape Size Location Function Resemblance of one structure to another

Basis of function Bones attached to

Abductor digiti minimi muscle abducts the little finger. Sternocleidomastoid muscle (G. kleidos, bolt or bar, clavicle) attaches inferiorly to the sternum and clavicle and superiorly to the mastoid process of the temporal bone of the cranium. Levator scapulae elevates the scapula (L. shoulder blade).

Descriptive names Deltoid muscle triangular, like the symbol for delta, the fourth letter of the Greek alphabet. -oid “like”; deltoid means like delta.

Position

medial, lateral, anterior, posterior

Length brevis, short; longus, long

Shape piriformis muscle pear shaped (L. pirum, pear + L. forma, shape or form).

Location

temporalis muscle in the temporal region (temple) of the cranium (skull).

according to their shapes

Flat muscles parallel fibers often with an aponeurosis

External oblique muscle broad flat muscle

Sartorius narrow flat muscle with parallel fibers longest muscle in the body

feather-like (L. pennatus, feather), arrangement of fasicles

Unipennate Extensor digitorum longus Bipennate Rectus femoris

Pennate muscles

Multi-pennate Deltoid

spindle shaped with a round, thick belly (or bellies) and tapered ends

Fusiform muscles

arise from a broad area converge to form a single tendon

four equal sides (L. quadratus, square) rectus abdominis between its tendinous intersections.

Convergent muscles

Quadrate muscles

orbicularis oculi closes the eyelids

Circular or sphincteral muscles surround a body opening or orifice, constricting it when contracted

more than one head of attachment or more than one contractile belly Biceps muscles two heads of attachment triceps muscles three heads Two bellies digastric muscle gastrocnemius muscle

Multi-headed or multi-bellied muscles

Skeletal muscles function by contracting they pull and never push.

When a muscle contracts and shortens one of its attachments usually remains fixed the other attachment (more mobile) pulled toward it

movement

Attachments of muscles origin & insertion

Origin proximal end of the muscle remains fixed during muscular contraction.

Insertion distal end of the muscle

movable

This is not always the case.

Some muscles can act in both directions under different

circumstances.

Reflexive Contraction automatic (reflexive) contraction, not voluntarily controlled

Respiratory movements of the diaphragm Myotatic reflex

Muscle tone (tonus) No movement, but

Certain firmness in muscles Assistance to the stability of joints Maintenance of posture Keeping the muscles ready to respond to stimuli

Absent only when? unconscious (during deep sleep or under general anesthesia) after a nerve lesion resulting in paralysis

Tonic Contraction slight contraction@ rest

Phasic Contraction: There are two main types of phasic (active) muscle contractions: (1) isotonic contractions, in which the muscle changes length in

relationship to the production of movement.

(2) isometric contractions, in which muscle length remains the same—no movement occurs, but the force (muscle tension) is increased above tonic levels to resist gravity or other antagonistic force.

When a muscle contracts its length decreases by 1/3 or ½.

Whereas the structural unit of a muscle is a skeletal striated muscle fiber, the functional unit of a muscle is a motor unit, consisting of a motor neuron and the muscle fibers it controls.

When a motor neuron in the spinal cord is stimulated, it initiates an impulse that causes all the muscle fibers supplied by that motor unit to contract simultaneously.

The number of fibers varies according to the size and function of the muscle. Large motor units, in which one neuron supplies several hundred muscle fibers, are in the large trunk and thigh muscles.

Functions of muscles Prime mover (agonist) main muscle responsible for producing a specific movement of the body. Does most of the work (expending most of the energy) required. In most movements, there is a single prime mover, but some movements involve two prime

movers working in equal measure.

Fixator steadies the proximal parts of a limb through isometric contraction while movements are occurring in distal parts. Synergist complements the action of a prime mover. Usual to have several synergists assisting a prime mover in a particular movement.

Antagonist a muscle that opposes the action of another muscle. A primary antagonist directly opposes the prime mover, synergists may also be opposed by secondary antagonists.

The same muscle may act as a prime mover, antagonist, synergist, or fixator under different conditions.

Nerves and arteries to muscles Variation in the nerve supply of muscles is rare; it is a nearly constant

relationship.

In the limb, muscles of similar actions are generally contained within a common fascial compartment and share innervation by the same nerves.

Nerves and arteries to muscles

Nerves supplying skeletal muscles (motor nerves) usually enter the fleshy portion of the muscle (vs. the tendon), almost always from the deep aspect (so the nerve is protected by the muscle it supplies). The blood supply of muscles is not as constant as the nerve supply and is usually multiple.

Fascia (L. fasciae)

wrapping, packing, and insulating materials of the deep structures of the body Underlying the subcutaneous tissue superficial fascia Deep fascia

dense, organized connective tissue layer, devoid of fat

covers most of the body deep to the skin and subcutaneous tissue

In the limbs, groups of muscles with similar functions sharing the same nerve supply are located in fascial compartments, separated by thick sheets of deep fascia, called intermuscular septa, that extend centrally from the surrounding fascial sleeve to attach to bones. These compartments may contain or direct the spread of an infection or a tumor.

Subserous fascia between the internal surfaces of the musculoskeletal walls and the serous membranes lining the body cavities. These are the endothoracic, endoabdominal, and endopelvic fascias; the latter two may be referred to collectively as extraperitoneal fascia.

lateral side of the abdomen

MUSCLE TONE

. Determination of the tone of a muscle is an important clinical examination. If a muscle is flaccid, then either the afferent, the efferent, or both neurons involved in the reflex arc necessary for the production of muscle tone have been interrupted. If, conversely, the muscle is found to be hypertonic, the possibility exists of a lesion involving higher motor neurons in the spinal cord or brain.

MUSCLE SHAPE AND FORM

. The general shape and form of muscles should also be noted, since a paralyzed muscle or one that is not used (such as occurs when a limb is immobilized in a cast) quickly atrophies and changes shape.

ELECTROMYOGRAPHY (EMG)

. a technique for evaluating & recording electrical activity produced by skeletal muscles A diagnostic procedure to assess the health of muscles and the nerve cells that control them (motor neurons). Can reveal nerve dysfunction, muscle dysfunction or problems with nerve-to-muscle signal transmission. Performed using an instrument called an electromyograph, to produce a record called an electromyogram.