MUSCULOSKELETAL ANATOMY.

INTRODUCTION

 

DEFINITION

These are the  contractile tissue which brings about all the movement in the body.


Types of muscle

The muscle are if three types:- skeletal, smooth, and cardiac.
Synonyms of skeletal muscle are
1) striped muscles
2) Striated muscles
3)Somatic muscles
4) Voluntary muscles.

Parts of a muscle

A) Two ends

1) ORIGIN
 
– It is one end of the muscle which mostly remains fixed during its contraction.
 
2) INSERTION
 
-It is the other end which mostly moves during its contraction.
-In the limb muscle, the origin is usually proximal to insertion.
-However, the origin and insertion sometimes are interchangeable, and at other situations difficult to define , as in the intercostal muscle.
– Muscles of pharynx, oesophagus, and the diaphragm act as involuntary muscles.


B) Two parts

1) FLESHY PART-: It is contractile, and is called the ‘belly’.
2) FIBROUS PART-: It is noncontractile and inelastic, when flattened ,it is called aponeurosis.
– The tendon receives Golgi tendon nerve endings.
– It is supplied by capillaries extending from the fleshy part and also from the periosteal arteries of the bone where the tendon terminates or gets inserted.


STRUCTURE OF STRIATED MUSCLE
.


A) CONTRACTILE TISSUE

-Each muscle is composed of numerous muscle fibers.
-The fiber of the muscles are multinucleated, cross-striated cylindrical cell (myocyte)  long.
-It is consist of sarcolemma (cell membrane) enclosing sarcoplasm (cytoplasm).
Embedded in the sarcoplasm there are
a)several hundred nuclei arranged at the periphery beneath the sarcolemma and
b) a number of evenly distributed longitudinal threads like structure are called myofibrils.
– each myofibril shows alternate dark and light bands as I bands.
Muscle -> fasciculi -> fibers -> myofibril ->myofilaments


B) SUPPORTING TISSUE

-Supporting tissue helps in organization of the muscle.
-Endomysium surrounds each muscle fiber separately.
-Perimysium surrounds bundles of muscle fibers of various sizes.
-Epimysium surrounds the entire muscle.
– The  tendon is the continuation of the connective tissue of the muscles.


C) TYPES OF FIBRES

1)TYPE 1 (SLOW) FIBRES.

-Show a slow ‘tonic’ contraction characteristic of postural muscle like gluteus maximus.
– These are red colour because of large amount of myoglobin.
-The fibers are rich in mitochondria and oxidative enzymes , but pair in phosphorylases.
–  Slow fibers are highly resistant to fatigue, Because of a well-developed aerobic metabolism.


2) TYPE 2 (FAST) FIBRES

-Show a fast ‘phasic’ contraction which is  required for the  large- scale muscular movements of the  body segments.
– These are paler ( white) in colour because of myoglobin.
-The fibers are  poor in mitro- chondria and oxidative enzymes , but rich in glycogen and phosphorylases.
– fast fiber are quite easily becomes fatigued, because of a  glycolytic respiration .


3) INTERMEDIATE FIBRES

.-Represent a variant of type 2 (fast) fibers which are relatively resistant to fatigue, although less than type1 (slow) fibers
– In man , most of the skeletal muscles show a mixture of fiber types ,but any one type may predominate.


FASCICULAR ARTITECTURE OF MUSCLES

– The arrangements of muscle fibers differs according to the direction, force and range of habitual movement at the particular joint.
– The force of movement is directly proportional to the size and number  of muscle fibers, and the range of movement is proportional to the length of fibers.
– According to the arrangement of their fasciculi , the muscles are classified  into the following group.


A) PARALLEL FASC ICULI

When these fasciculi are parallel mainly to the line of pull, the muscle  can resemble as
1) Quadrilateral ( thyrohyoid)
2) Strap- like with tendinous intersections ( rectus abdominis)
3) Strap -like (sternohyoid and sartorius)
4) Fusiform ( biceps brachii, digastric, etc)


B) OBLIQUE FASCICUL

-When the fasciculi are mostly oblique to the line of pull, the muscle may be triangular, or pennate (feather like) in the construction.
– This arrangement makes the muscle more powerful, although the range movement is reduced.
– Oblique arrangements are of the following-:
1) Triangular – temporalis
2) Unipennate- flexor pollicis longus, extensor digitorum longus.

3)Bipennate – rectus femoris, dorsal interossei, peroneus longus.

rectus femoris
4) Multipennate- subscapularuis, deltoid
5) Circumpennate – tibialis anterior.


C) SPIRAL OR TWISTED FASCICULI

-Spiral or twisted fibers are mainly found in trapezius, pectoralis major, latissimus dorsi, supinator, etc. -In certain muscle the fasciculi are crossed. These are called cruciate muscles, eg. Sternocleidomastoid, masseter and adductor magnus.

Naming of the muscle

Shape-:

 triangular- deltoid

Quadratus- quadratus femoris
Rhomboid – rhomboid major

Teres – teres major

Gracilis- gracilis.
Lumbrical – lumbricals of palm
Rectus- rectus abdominis

Size-:

Major- pectoralis major
Minor- pectoralis minor
Longus – adductor longus
Brevis – abductoe pollicis brevis
Latissimus – latisiimus dorsi
Longissimus- longissimus thoracis

Number of head:-

Biceps- biceps brachiu
Triceps- triceps brachii
Quadriceps – quadriceps femoris
Digastric – anterior and posterior bellies of digastric

Nerve supply of skeletal muscle.

-The nerve supply if a muscle is called motor nerve.

1) MOTOR FIBRES

a) Large myelinated alpha efferent which supply extrafusal muscle fibers.
b) Small myelinated gamma efferent which supply intrafusal fibers of the muscle spindles which refine and control muscle contraction.
c) The fine non- myelinated autonomic efferents which supply smooth muscle fibers of the blood vessels.

2) SENSORY FIBRES

-Myelinated fibers distribution to muscle spindles for proprioception, also tendons.

Muscle spindles

-These are spindle shaped sensory end organs of the skeletal muscle.
-Each spindle contains 6-14 intrafasal muscle fibers which are of two types, the larger nuclear bag fibers, and the smaller nuclear chain fibers.
-The spindle are innervated by both the sensory and motor nerves.
-The nerve supply of spindle is derived from gamma motor neuron of the spinal cord.
-Muscle spindles act as stretch receptors.
-The record and help regulate the degree and rate of contraction of the extrafusal fibers by influencing the alpha neurons, which act on ” motor end plate”.

Motor point

-It is a site where the motor nerve enters the muscle fibers supplied by it.
-Electrical stimulation is more effective at the motor point.

Motor unit

-It is define as the single alpha motor neuron together with the muscle fibers applied by it.

Nerve supply of smooth muscle

-Classified into

a)Single- unit type

Seen in intestine.
The nerve are classified into one muscle cell, is transmitted to other cells by the mechanical pull through the fused cell membrane.
The nerve supply us sparse.

b)Multi- unit type

Seen in the muscles of the ductus deferens.
Watch muscle cell receives a seperate nerve fiber. The contraction is simultaneous.
The nerve supply is rich.

Nerve supply if cardiac muscle.

The nerve supply of heart is sympathetic and parasympathetic nerve fibers.

Action of muscles

a)Prime movers

 -They bring about the desired movement .
-It is chief muscle for the movement
-When a prime mover  helps in  opposite movement of action by doing active controlled lengthening against gravity, it is know as action of paradox.
-Eg. Putting a glass back to the table is assisted by the gravity but controlled by a gradual active lengthening of biceps.

b)Antagonist

-they oppose the prime mover.
-They help the prime mover to actively controlled relaxation, so that the desired movement is smooth and precise.
-Thus the antagonist cooperate rather than oppose the prime movers.
-These is due to the reciprocal innervation of the opposite groups of muscles, regulated by the spinal cord through stretch reflex.

c) Fixators

-They are the group of muscles which stabilize the proximal joints of a limb, so that the desired movement at the distal joint may occur on a fixed base.
-Eg. Muscle acting on shoulder joint, e.g. trapezius, deltoid fix it for better movement of finger.

d) Synergists

-Two or more muscle causing one movement are synergist.
when the prime mover cross more than one joint ,the undesired action ar the proximal joints are prevented by certain muscles known as synergists.
-Eg. During making a tight fist by long digital flexors the wrist is kept fixed in extension by the synergists
-Thus, the synergists are special fixators

 -They are also called as partial antagonists to the prime movers.

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