Myology (pages 35- 70)

Muscular system

is composed of contractile units of varied morphology energized by nerve impulses or humoral substances.

locomotion, respiration, circulation, alimentation, and indication of emotional states

muscular system provides power for:

muscles

the contractile organs responsible for movement in an animal.

Muscle cells (fibers)

the structural contractile elements of muscle enveloped by a connective tissue. They can contract resulting in sliding of the muscle-filament bundles which they contain in such a way to overlap one another.

Three types of muscles on the basis of their fine structure and physiological characteristics:

Striated (striped), Voluntary Skeletal (somatic) muscles

Striated, Involuntary Cardiac muscles

Nonstriated, Involuntary Smooth (visceral) muscles

STRIATED (striped), VOLUNTARY Skeletal (somatic) muscles

long, cylindrical, multinucleated cells; are the primary concern in this section.

They allow movement from one place to another (location), movement of one part of the body in relation to another, and the maintenance of body posture.

STRIATED, INVOLUNTARY Cardiac muscles

with intercalated discs between cell extremities; it is the working musculature of the heart and as the impulse conducting system for cardiac contraction.

NONSTRIATED, INVOLUNTARY Smooth (Visceral) muscles

spindle-shaped with a central nucleus, it is the musculature in the walls of hollow organs and blood vessels as well as in certain glands, the spleen, the eyeball and their follicles. This is responsible for breathing, peristaltic movements of the intestines, constriction of blood vessels and many other vital functions.

skeletal muscles color

reddish

cardiac muscles color

red-brown

smooth muscles color

yellow-gray

skeletal muscles cell length

up to 15 cm

cardiac muscles cell length

0.1 mm

smooth muscles cell length

0.1 mm

skeletal muscles cell diameter

0.1 mm

cardiac muscles cell diameter

0.5 mm

smooth muscles cell diameter

0.1 mm

skeletal muscles innervation

somatic NS

cardiac muscles innervation

autonomic NS

smooth muscles innervation

autonomic NS

form of the skeletal muscles

individual muscles variably shaped

form of the cardiac muscles

layers

form of the smooth muscles

layers

The Cross-Striated Skeletal Muscle

The muscle fiber is composed of myofibrils. The myofibrils, in turn, are composed of thick and thin myofilaments.

Each muscle fiber is bounded by plasmalemma (SARCOLEMMA), external to which is a basal lamina and fine collagen fibrils and reticular fibers.

The reticular fibers radiate into the surrounding tissue, between neighboring muscle cells, as ENDOMYSIUM.

Several neighboring muscle fibers form a PRIMARY MUSCLE FIBER BUNDLE—visible to the naked eye and is invested by internal PERIMYSIUM.

Several primary fiber bundles are united by external PERIMYSIUM to form a SECONDARY MUSCLE FIBER BUNDLE.

Finally, all secondary bundles, the entire muscle, are invested by a loose layer of collagenous fibers, the EPIMYSIUM.

The epimysium is followed by a FASCIA which is a latticework of collagenous fibers reinforced by elastic fibers.

Tendinous attachments

the dense connective tissue (tendon) connecting spindle-shaped or pennate muscles to bone.

Aponeurotic attachments

the flat, tendinous sheets (aponeurosis) associated with flat muscles such as those of the abdominal wall.

fleshy attachments

the apparent direct attachment of muscles to bone (e.g. scapular muscles).

1. Origin (head)- the less movable (more fixed point) of the two attachments. In the limbs, this is usually the more proximal attachment.

2. Insertion or Termination (tail)- the more movable of the two attachments. In the limbs, this is usually the more distal attachment.

3. Belly- the expanded fleshy portion of a muscle.

4. Slips- minor divisions of origin or termination.

Muscle contraction

shortening of a muscle, causing a change in the alignments of bones around a joint.

When a muscle fiber contracts it does so at its maximum power, and it is capable of contracting to about half of its stretched length.

Nerve impulse through MOTOR UNITS initiates contractions.

The number of motor units functioning at any one time determines the activity of the muscle.

Muscles are grouped into:

prime mover or agonist, antagonist, fixator/ articular muscles, and synergist

prime mover or agonist

produces the characteristic movement at a joint.

Antagonist

opposes the movement of a prime mover. It aids the prime mover by slowly relaxing so that the movement produced is smooth and controlled.

Fixator/Articular muscles

a muscle that stabilizes the proximal end of a limb while the distal end moves.

Synergist

(G. syn, together + ergon, work)

a fixation muscle that indirectly aids the action of a prime mover by stabilizing intermediate or proximal joints and enabling the force of the prime mover to be exerted on a more distal joint.

Muscular arrangements

The muscle fibers are grouped together into fascicles (bundles) that in turn are grouped together to form muscles.

Parallel muscle

the muscle bundles run parallel to each other the entire length of the muscle. This allows greatest shortening of the muscle, but less strength of contraction.

Pennate muscle (penna, feather)

the muscle having tendons all throughout its length.

This arrangement allows more bundles, thus, stronger contractions, but less shortening because of the shorter length of the muscle bundles.

types of pennate muscle

unipennate, bipennate, and multipennate muscles

unipennate muscle

a pennate muscle whose tendons run along one side.

bipennate muscle

a pennate muscle whose tendons branch on each side of the muscle.

multipennate muscle

a pennate muscle whose tendons invade in several places.

Sphincter

a muscle whose fibers encircle an opening.

The contraction of its fibers closes the opening.

This type of muscle is found at the entrance and exit of passageways.

muscle actions

extensors, flexors, adduction, abduction, rotation, circumduction, supination, and pronation

supination

the movement of the forearm so the palmar side is rotated upward or forward.

pronation

the movement of the palmar side of the paw or foot downward or backward.

sesamoid bones

located in certain tendons or joint capsules as small, rounded nodules. The three important functions include:

1. They protect tendons that pass over bony prominences.

2. They increase the surface area for attachment of tendons over certain joints.

3. They serve to redirect the pull of tendons so that greater effective force can be applied to the part being moved.

synovial bursa

is a simple connective tissue sac that is placed at a point of unusual pressure between a tendon or muscle and some underlying structure, commonly the prominence of a skeleton. It functions to protect the tendon.

1. Subcutaneous synovial bursa- if the bursa is located subcutaneously; usually acquired.

2. Submuscular synovial bursa- if the bursa is located in the tendinous insertion; usually inherited.

Synovial tendon sheath

a sac folded or wrapped around a tendon so that the two layers can be distinguished; the inner one is adherent to the tendon, while the outer one leaves the canal where the tendon lies. It improves the gliding of the tendon upon a bony prominence. The wall consists of: (1) the parietal part- which passes over the (2) tendinous part by way of mesotendon.

Areolar Tissue

a loose, irregularly connective tissue that often contains fat.

Fasciae

are connective tissue sheaths composed mainly of bundles of white fibers, with a greater or less admixture of elastic fibers in some cases; invest on individual muscles.

superficial fascia and deep fascia

types of fascia

superficial fascia

beneath the skin forming the deep portion of the subcutaneous tissue that covers the entire body.

deep fascia

is more firmly attached to the muscle that it encloses. It is composed of one or more layers of dense fibrous tissue. Its deep face may be attached to bones, ligaments and tendons; it may pass in between muscles as intermuscular septa.

Cutaneous muscles

are usually a pale variant of skeletal muscle with no direct attachment to the skeleton.

nerves and blood vessels

enter together at the hilus.

superficial structures

subcutaneous tissue, cutaneous trunci, and platysma

cutaneous trunci

Thin muscle sheet covering most of the dorsal, lateral and ventral walls of the thorax and abdomen.

It is more closely applied to the skin.

platysma

Can be seen extending from its origin on the dorsal midline to the border between the head and neck where it is continued by the cutaneous fasciae muscle.

muscles of thoracic limb is divided into the?

Muscles of the Pectoral Girdle (Extrinsic Muscles) and Intrinsic Muscles

Muscles of the Pectoral Girdle (Extrinsic Muscles)

Derived from the neck, thorax, and back regions and from the sides and ventral aspects of the chest.

Attached to the scapula and humerus and for this reason they are often referred to as TRUNK-LIMB MUSCLES.

The extrinsic muscles are:

1. Trapezius

2. Sternocephalicus

3. Brachiocephalicus

4. Omotransversarius

5. Latissimus dorsi

6. Superficial pectoral

7. Deep pectoral

8. Rhomboideus

9. Serratus ventralis

Trapezius

It is a broad, thin, triangular muscle lying under the skin and the cervical cutaneous muscle in the neck, and crosses the interscapular region of the shoulder.

It has two heads:

• Cervical part (Trapezius cervicales)

• Thoracic part (Trapezius thoracis)

Sternocephalicus

Arises from the sternum and inserts on the head.

The dorsal border is adjacent to brachiocephalicus.

The external jugular vein on its lateral surface.

It has two parts:

• The ventral part (Sternomastoideus) - represents the chief continuation of the muscle to the head.

• The dorsal part (Sternooccipitalis) – is thin but wide.

Brachiocephalicus

The wide muscle extends from the head and neck to the arm.

Clavicular intersection- a faint line at the shoulder, crossing the muscle on the deep surface of which the collar bone is connected.

It divides the muscle into:

• Cleidocephalicus- is further subdivided into superficial cleidocervicalis & deep cleidomastoideus

• Cleidobrachialis

Omotransversarius

Straplike and extends from the shoulder region to the cervical vertebrae.

Related to the deep cervical fascia, medially.

It is in a deeper plane than the brachiocephalicus; covered cranially by the cervical part.

Associated with superficial cervical lymph nodes.

Latissimus dorsi (widest of the back)

The broad, flat, triangular muscle extends from the dorsal thoracolumbar region to the medial side of the humerus.

It is located caudal to the scapula.

Superficial pectoral

The two muscles lie under the skin in the cranioventral part of the thorax between the cranial part of the sternum and the humerus.

The cranial border is thin, caudal border is thick and rounded forming the caudal borders of a triangle at the base of the neck.

Divided into two parts, based on fiber direction:

• Descending Pectoral- superficial

• Transverse Pectoral- deeper

Deep (ascending) pectoral

The broad muscle lying ventrally on the thorax; extends from the sternum to the humerus and is larger and longer than the superficial pectoral muscles.

It lies under the skin and the thoracic mammae.

Only the cranial part is covered by the superficial pectoral muscles.

Rhomboideus

It lies beneath the trapezius and holds the dorsal border of the scapula close to the body.

It is divided into:

• Cervical part (Rhomboideus cervicis)

• Thoracic part (Rhomboideus thoracis)

• Capital part (Rhomboideus capitis)

Serratus Ventralis

It is a powerful, serrated, fan-shaped muscle—the strongest and the most important—that acts as a sling to support the body between the limbs.

It covers the caudal half of the lateral surface of the neck and the cranial half of the lateral thoracic wall.

It has:

• Thoracic part (serratus ventralis thoracalis)

• Cervical part (serratus ventralis cervicis)

Summary for innervation of extrinsic muscles:

• Accessory nerve (XI)- Trapezius, Sternocephalicus, Brachiocephalicus, Omotransversarius

• Thoracodorsal nerve- Latissimus dorsi

• CRANIAL pectoral nerve- SUPERFICIAL pectoral

• CAUDAL pectoral nerve- DEEP pectoral

• Ventral branches of cervical nerves- Rhomboideus, Serratus Ventralis

Several important fasciae in the extrinsic muscles:

• Superficial fascia of the neck- superficial brachial and pectoral fasciae

• Deep fascia of the neck- wraps the sternocephalicus, cleidomastoideus, omotransversarius and cleidocervicalis

• Thoracolumbar fascia- deep fascia of the trunk.

Intrinsic Muscles of the Thoracic Limb

Confined mainly to the skeleton of the thoracic limb.

The main functions are flexors and extensors, although depending on their origin, course, and insertion, they can also cause moderate degrees of rotation, abduction, adduction, and supination.

Classifications of Intrinsic Muscles of the Thoracic Limb

1. Muscles of the Shoulder Joint

2. Muscles of the Elbow Joint

3. Muscles of the Radioulnar Joint

4. Muscles of the Carpal Joint

5. Muscles of the Digit

Muscles of the shoulder joint

Lateral: Deltoideus, Supraspinatus, Infraspinatus, and Teres minor

Medial: Teres major, Subscapularis, and Coracobrachialis

Deltoideus

It is composed of two portions that fuse and act in common across the shoulder.

Two parts:

• Scapular part (proximal) - covers the infraspinatus muscle.

• Acromial part (distal) - fusiform in shape.

Supraspinatus

Wider and larger than the infraspinatus, it is largely covered by the cervical part of the trapezius and the omotransversarius.

It lies on the supraspinous fossa and extends over the cranial border of the scapula so that a part of the muscle is closely united with the subscapularis.

Infraspinatus

A fusiform muscle lying deep to the aponeurosis of the deltoid muscle and filling the infraspinous fossa.

There is a bursa underneath its tendon of insertion and the greater tubercle of the humerus.

Teres Minor

A small wedge-shaped muscle ventral to the tendon of insertion of the infraspinatus muscle.

It crosses the lateral surface of the shoulder.

It is covered superficially by the deltoideus, caudally by the triceps and cranially by the infraspinatus.

Teres major

It is directly caudal to the subscapularis having three surfaces.

Fibers extend distally as its tendon of insertion usually unites with that of the latissimus dorsi.

Subscapularis

It acts as a medial collateral ligament of the shoulder joint.

It occupies the entire subscapular fossa, the boundaries of which it overlaps slightly.

Cranially is the supraspinatus; caudally is the teres major.

Coracobrachialis

It is a small, spindle-shaped muscle crossing the medial surface of the shoulder obliquely.

The conjoined tendon of the teres major and latissimus dorsi crosses its insertion.

The coracobrachialis tendon crosses the cranial to the center of the shoulder.

Summary of the muscle ACTIONS of the shoulder joint:

Lateral flexors- Deltoideus, Teres minor

Lateral extensor- Supraspinatus

Both lateral flexor and extensor- Infraspinatus

Medial flexor- Teres major

Medial extensors- Subscapularis, Coracobrachialis

Summary of the muscle INNERVATIONS of the shoulder joint:

Axillary nerve- Deltoideus, Teres minor, Teres major

Suprascapular nerve- Supraspinatus, Infraspinatus

Subscapular nerve- Subscapularis

Musculocutaneous nerve- Coracobrachialis

Muscles of elbow joint

o Cranial Arm Muscles- generally the FLEXORS

• Biceps brachii

• Brachialis

o Caudal Arm Muscles- generally the EXTENSORS

• Triceps brachii

• Anconeus

• Tensor fasciae antebrachii

Biceps brachii

It is a long, fusiform muscle lying on the cranial surface of the humerus and with only one head.

It is covered superficially by the pectoral muscles.

Transverse humeral retinaculum- fibrous tissue that holds the tendon of origin in the bicipital groove.

Brachialis

It is a long, thin muscle that lies in the brachialis groove of the humerus.

A large part of its lateral surface is covered by the lateral head of the triceps.

Distally it runs medial to the origin of the extensor carpi radialis.

Triceps brachii

The strongest muscle of the thoracic limb fills the space between the scapula and the humerus.

The triceps was originally known as the anconeus.

It has four heads:

• Long- completely bridges the humerus

• Lateral- distal to the long head, proximal to the elbow, and lateral to the accessory head.

• Accessory- between the lateral and medial heads.

• Medial- caudal to the humerus.

Anconeus

A small muscle located almost completely in the olecranon fossa.

The most distal fibers lie in a transverse plane.

Tensor fasciae antebrachii

It is a thin strap and insignificant muscle extending from the latissimus dorsi to the medial fascia of the forearm and olecranon.

It lies on the long head of the triceps.

Summary of the muscle ACTIONS of the elbow joint:

• Cranial Arm Flexors of the elbow- Biceps brachii, Brachialis

• Caudal Arm Extensors of the elbow- Triceps brachii, Anconeus, Triceps fasciae antebrachii

• Flexor of the Shoulder- Long Head of the Triceps brachii

Summary of the muscle INNERVATIONS of the elbow joint:

• Musculocutaneous nerve- Biceps brachii, Brachialis

• Radial nerve- Triceps brachii, Anconeus, Triceps fasciae antebrachii

Craniolateral Muscles of the Forearm- generally the EXTENSORS of the carpus

1. Brachioradialis

2. Extensor Carpi Radialis

3. Common Digital Extensor

4. Lateral Digital Extensor

5. Ulnaris Lateralis

6. Supinator

7. Abductor pollicis longus

8. Pronator teres

Caudomedial Muscles of the Forearm-generally the FLEXORS of the carpus

1. Flexor carpi radialis

2. Superficial Digital Flexor

3. Flexor Carpi Ulnaris

4. Deep Digital Flexor

5. Pronator Quadratus

Short Muscle of the Digits

1. Interossei

Brachioradialis

• A slender, inconstant muscle over the extensor carpi radialis.

• Frequently the muscle is removed with the skin.

• Can be mistaken for cephalic vein during venipuncture.

Extensor Carpi Radialis (E)

• It is the strongest extensor of the forearm.

• It is the largest of the craniolateral muscles, lying on the dorsal surface of the radius throughout most of its course.

• The tendon looks single but it is distinctly double throughout its distal third.

• Extensor retinaculum- holds these tendons in place.

Common Digital Extensor (C)

• It is a long muscle lying caudally to the extensor carpi radialis on the lateral side.

• Smaller than the radial extensor of the carpus and has multiple tendons of insertion.

• Its belly is divided into 4 and the 4 tendons are inserted into digits 2, 3, 4, and 5.

• Two heads:

  • Radial head (Muscle of Phillips)

  • Ulnar head (Muscle of Thiernesse)

Lateral Digital Extensor (L)

• It is about half the size of the common digital extensor.

• It lies between the common digital extensor and the ulnaris lateralis.

• The tendon divides into 3 and each inserts to digits 3, 4 and 5.

Ulnaris Lateralis (U)

• Lateral ulnar, Extensor carpi ulanris

• It is larger than the lateral digital extensor, behind which it lies.

• It is the most caudal, bounded deeply by the ulna and the large flexor group of muscles, which lie behind it.

• It is the only FLEXOR to arise on the lateral epicondyle.

Supinator

• It is short, broad, flat and obliquely placed across the lateral side of the flexor surface of the elbow joint.

• It is covered superficially by the extensor carpi radialis and common digital extensor.

• It lies principally on the proximal fourth of the radius.