Muscles

Description Of Human Muscles

Muscles : 

Muscle is the contractile tissue which produces movements. Derived from the mesodermal layer of embryonic germ cells.

  

Types of muscles : 

 

Classification of Muscles

Morphological classification (based on structure)

1.  Striated

v                    Skeletal muscle

v                    Cardiac muscle

2.  Non striated or smooth

v                    Smooth muscle

Functional classification

1.  Voluntary

v                    Skeletal muscle

2.  Involuntary

v                    Cardiac muscle

v                    Smooth muscle

 

CARDIAC MUSCLE :

Cardiac muscle consists of muscle cells with one centrally placed nucleus.
Nuclei are oval, and located centrally in the muscle cell.

Cardiac muscle is innervated by the autonomic nervous system.

Cardiac muscle exhibits cross-striations.

Cardiac muscle is also called involuntary striated muscle.

Cross-striations in cardiac muscle are less distinct than skeletal muscle.

In contrast to skeletal muscle cells, cardiac muscle cells often branch at acute angles

They are connected to each other by specializations of the cell membrane in the region of the intercalated discs.

Intercalated discs invariably occur at the ends of cardiac muscle cells.

   

Smooth Muscle :

Smooth muscle consists of spindle shaped cells of variable size.

The largest smooth muscle cells occur in the uterus during pregnancy. The smallest are found around small arterioles.

Smooth muscle cells contain one centrally placed nucleus.

The innervation of smooth muscle is provided by the autonomic nervous system.

Smooth muscle makes up the visceral or involuntary muscle.

Skeletal Muscle :

Most abundantly attached to Skeleton.

Showing cross striation under the microscope.

Supplied by somatic nerves, therefore under the voluntary control.

Respond quickly to stimuli, producing rapid contraction, that’s why fatigue quickly.

Skeletal muscle consists of very long tubular cells (also called muscle fibers).

Skeletal muscle fibers contain many peripherally placed nuclei.

Skeletal muscle fibers show in many preparations characteristic cross-striations. It is therefore also called striated muscle.

Skeletal muscle is innervated by the somatic nervous system.

Skeletal muscle makes up the voluntary muscle.

   

Coverings of muscle :

Epimysium

Entire muscle is surrounded by a connective tissue called the Epimysium.

Fascicles

Fascicles are actually bundles of individual muscle cells or muscle fibers.

Perimysium

Fascicles are surrounded by a connective tissue sheath called the perimysium.

Muscle fibers

Each fascicle is made up of several muscle cells known as muscle fibers.

Endomysium

Each muscle cell or muscle fiber is surrounded by a connective tissue sheath known as the endomysium.

  

Parts of Skeletal Muscle :

Origin

The one end of muscle which remains fixed during contraction (Proximal End)

Insertion

The other end which moves during contraction (Distal End)

Belly

Central contractile part.

Tendon or aponeurosis

Fibrous non-contractile part. When it is cord like called as tendon or when broad sheath like, aponeruosis

   

Structural Classification of Skeletal Muscle :

On the basis of arrangement of fibers

Parallel

1- Quadrilateral

2- Rhomboid

3- Strap like

4- Fusiform

Parallel Muscle :

The muscle fasciculi are parallel to the line of pull

Consists of parallel fibers all of equal size

The range of movement is maximum

The force of contraction is less

When muscle contracting all the muscle fibers are contacting with equal length

Structural Classification of Skeletal Muscle :

On the basis of arrangement of fibers

B- Oblique

1- Unipennate

2- Bipennate

3- Multipennate

4- Circumpennate

5- Triangular

6- Spiral or Twisted

Oblique Muscle :

The muscle fasciculi are oblique to the line of pull

Consists of oblique fibers (feather like) muscle fibers are variable size (some are shorter while other are loner) 

The range of movement is reduced

The force of contraction is powerful 

When muscle contracting all the muscle fibers are contacting with unequal length

Functional Classification of Muscle :

Agonist

Antagonist

Synergist

Fixator

Agonist

Agonist is kind of muscle that causes movement to occur. It creates the normal range of movement in a joint by contracting.

Agonists are also referred to as "prime movers" since they are the muscles that are primarily responsible for generating movement.

Antagonist

An antagonist is a kind of muscle that acts in opposition to the movement generated by the agonist and is responsible for returning a limb to its initial position.

Synergist

Synergist is a kind of muscle which perform, or assist in performing, the same set of joint motion as the agonists.

> Synergists are muscles that act on movable joints.

> Synergists are sometimes referred to as "neutralizers" because they help cancel out, or neutralize, extra motion from the agonists to make sure that the force generated works within the desired plane of motion

  

Fixator muscle

A muscle that acts as a stabilizer of one part of the body during movement of another part.

Fixator  

A fixator holds the origin of the agonist, stable. E.g., abducting arm deltoid is abductor, fixators are other flexors keeping the scapula in position e.g. rhomboids.

Blood supply and nerve supply of muscle :

Arteries supply the structure to which the muscles are in contact.

Nerve supply

Motor nerves enter the fleshy portion of muscle, almost always from the deep portion.

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