Kaan Yücel M.D., Ph.D . 4.October.2013 Friday

The muscular system consists of all the muscles of the body.

The discipline related to the study of muscles is myology.

Musculus (muscle) is derived from the word 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.

All skeletal muscles are composed of one specific type of muscle tissue.

These muscles move the skeleton, therefore, move the body parts.

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.

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 muscle fibers in a motor unit varies from one to several hundred. 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.

Movement (phasic contraction) results from the activation of an increasing number of motor units, above the level required to maintain muscle tone.

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.

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.

Muscles of the Face and the Scalp The facial muscles (muscles of facial expression) move the skin and change facial expressions to convey mood. Most muscles attach to bone or fascia and produce their effects by pulling the skin.

The occipitofrontalis is a flat digastric muscle which elevates the eyebrows and produce transverse wrinkles across the forehead. This gives the face a surprised look.

The shape of the mouth and lips is controlled by a complex three-dimensional group of muscular slips, which include the following: Elevators, retractors, and evertors of the upper lip. Depressors, retractors, and evertors of the lower lip. The orbicularis oris, the sphincter around the mouth. The buccinator in the cheek

The platysma (G. flat plate) is a broad, thin sheet of muscle in the subcutaneous tissue of the neck. It helps depress the mandible and draw the corners of the mouth inferiorly. The orbicularis oculi closes the eyelids and wrinkles the forehead vertically. The muscles of the nose may provide evidence of breathing behaviors.

Cutaneous (sensory) innervation of the face and anterosuperior part of the scalp is provided primarily by the trigeminal nerve (CN V). Motor innervation to the facial muscles is provided by the facial nerve (CN VII).

Sternocleidomastoid (SCM) muscle broad, strap-like muscle with two heads

One head attaches to the sternum One head attaches to clavicle.

Bilateral contractions extension of the elevating the chin Unilateral contraction laterally flexes the neck

Trapezius muscle large, flat triangular muscle

Covers the posterior aspect of the neck & superior half of the trunk A direct attachment of the pectoral girdle to the trunk. A ssists in suspending the upper limb.

4 anterior axioappendicular muscles (pectoral muscles) move the pectoral girdle. Pectoralis major is the biggest of these four.

powerful adduction and medial rotation of the arm

Posterior shoulder muscles Superficial extrinsic shoulder muscles trapezius and latissimus dorsi Deep extrinsic shoulder muscles two muscles Intrinsic shoulder muscles deltoid, teres major, four rotator cuff muscles

latissimus dorsi (L. widest of back)

passes from the trunk to the humerus and acts directly on the shoulder joint and indirectly on the pectoral girdle. extends, retracts, and rotates the humerus medially

when folding the arms behind the back or scratching the skin over the opposite scapula

Deltoid thick, powerful, coarse-textured muscle covering the shoulder forms its rounded contour. As its name indicates, the deltoid is shaped like the inverted Greek letter delta (Δ).

Muscles of the Arm & the Hand Of the four major arm muscles: three flexors (biceps brachii, brachialis, and coracobrachialis) in the anterior (flexor) compartment supplied by the musculocutaneous nerve one extensor (triceps brachii) in the posterior compartment, supplied by the radial nerve.

The biceps brachii is the flexor of the arm.

The brachialis is the main flexor of the forearm.

The triceps brachii is the main extensor of the forearm.

flexor muscles of the forearm anterior (flexor-pronator) compartment of the forearm

extensor muscles of the forearm posterior (extensor-supinator) compartment of the forearm, innervated by branches of the radial nerve.

Muscles of the Gluteal Region, Back, Thigh Leg & the Foot gluteus maximus largest, heaviest, and most coarsely fibered muscle of the body. most superficial gluteal muscle extension and lateral rotation of the thigh

anterior thigh muscles flexors of the hip and extensors of the knee. sartorius, the “tailor's muscle” longest muscle in the body. quadriceps femoris (L., four-headed femoral muscle) It covers almost all the anterior aspect and sides of the femur. extensor of the leg.

The posterior thigh muscles include the hamstring muscles: (1) semitendinosus, (2) semimembranosus, and (3) biceps femoris (long head).

Four muscles in the anterior compartment of the leg

dorsiflexors of the ankle joint, elevating the forefoot and depressing the heel

lateral compartment of the leg smallest (narrowest) of the leg compartments

fibularis longus and brevis muscles Evertors of the foot

Posterior compartment of the leg plantarflexor compartment

is largest of the three leg compartments

inversion of the foot

superficial group of calf muscles gastrocnemius, soleus, and plantaris.

gastrocnemius and soleus share a common tendon calcaneal tendon (L. tendo calcaneus, Achilles tendon) most powerful (thickest and strongest) tendon in the body. triceps surae (L. sura, calf). raise heel during walking; flex the leg at the knee joint.

transverse abdominal internal obliques external obliques rectus abdominis

6 abdominal muscles