Muscles

Question 1

What are the types of muscles ?

Answer 1

1. Skeletal ( voluntary - striated ) muscles
2. Smooth ( involuntary - non striated ) muscles
3. Cardiac muscles ( involuntary - striated )

Question 2

What are the characteristics of the skeletal muscles ?

Answer 2

1. They are voluntary muscles that form the main bulk of the body.
2. They produce movements of the skeleton.
3. They are striated because microscopically they show alternating light and dark bands.
4. The proximal attachement of the muscles are called origin while the distal attachement of the muscles is called insertion.
5. They are characterized by rapid contractions like muscles of the limbs.

Question 3

What are the characteristics of the smooth muscles ?

Answer 3

1. They are involuntary muscles controlled by autonomic nervous system.
2. They form muscle layers of the walls of the viscera ( gastrointestinal tract , urinary tract , genital system , blood vessels.
3. They have no microscopic striations and are characterized by slow contractions.

Question 4

What are the characteristics of the cardiac muscles ?

Answer 4

1. They are striated.
2. They are involuntary controlled by autonomic nervous system.
3. They form myocardium of the heart.

Question 5

What are the ways of attachment of the muscles ?

Answer 5

1. By tendons : fibrous chord ( tendocalcaneus )
2. By aponeurosis : flat fibrous sheet ( external abdominal oblique aponeurosis )
3. By raphae : fibrous band separating fleshy muscles on either sides ( pharyngeal raphae )
4. By fleshy fibers ( popliteus muscles )

Question 6

What are the shapes of the skeletal muscles

Answer 6

Individual fibers of skeletal muscles are arranged either parallel or oblique to the long axis of the muscle. Other forms include : spiral , cruciate or circular arrangement.

A. Parallel fibers : produce wide range of movement but less force.

1. Quadrilateral : Quadratus laborum
2. Fusiform : Biceps brachii
3. Strap-like : sartorius
4. Strap-like with tendinous intersection : Rectus abdominis.

B. Oblique fibers : The range of movement is less but the force is more.

1. Pennate muscles :
   a. unipennate : fibers along one side of the tendon ( like half feather ) ex: flexor pollicis longus.
   b. bipennate : the tendon is in the middle and the fibers on both sides. Ex: dorsal interossei and rectus-femoris.
   c. multipennate : series of bipennates. Ex: deltoid
   d. circumpennate : the fibers converge on a tendon. Ex: tibialis anterior.
2. Triangular muscles : muscle fibers converge from a wide attachment to a narrow tendon. Ex: temporalis.

C. Spiral muscles : when such muscles contract ,they approximate their attachments and also bring then into the same plane and may be twisted. Ex: Trapezius.

D. Cruciate muscles : muscle fibers are made up of two or more planes in which they run in different directions. Ex : Sternocleidomastoid.

E. Circular muscles : muscle fibers for, a complete circle. ex: orbicularis oculi

Question 7

What is the mechanism of action of skeletal muscles

Answer 7

1. Prime mover : muscles that initiate the movement also called as agonist.
2. Antagonist : muscles that produce the opposite action of agonist.
3. Synergist : if the prime mover can move two joints and the movement is not wanted in one of the joints , the movement of the unwanted joint is prevented by synergist.
4. Fixator : muscles stabilize the origin of the prime mover so that it can act efficiently.

Question 8

What are the type of nerves supplying the skeletal muscles ?

Answer 8

Usually supplied by a mixed nerve : 40% sensory , 58% motor and 2% sympathetic. the nerve enters the muscles nearly at midpoint from its deep surface.

Question 9

https://www.youtube.com/watch?v=zfpVbJA-u2s