Anatomy and History of the Muscles 1: Classifications of Muscles

Question 1

What are the means of categorizing muscles?

Answer 1

Action
Direction of Fibers
Shape
Structure and Function
Innervation

Question 2

How can muscles be split into the key categories?

Answer 2

Question 3

Action
Prime Mover/Agonist

Answer 3

Chief muscle for primary action
E.g. biceps brachi

Question 4

Action
Synergist

Answer 4

Facilitates action of the prime mover
E.g. brachialis

Question 5

Action
Antagonist

Answer 5

Muscle that has opposite action to prime mover
E.g. triceps brachi

Question 6

Direction of fibers
Unipennate

Answer 6

Shaped like half a feather
Muscle fibers coming from one side of tendon
E.g. Extensor Digitorum Longus

Question 7

Direction of fibers
Bipennate

Answer 7

Shaped like a whole feather
Muscle fibers coming from both sides of the tendon
E.g. Rectus Femoris

Question 8

Direction of fibers
Multipennate

Answer 8

Collection of bipennate arrangement
E.g. Deltoid

Question 9

Direction of fibers
Circular

Answer 9

Have circular muscle fibers
E.g. Orbicularis Oris

Question 10

Direction of fibers
Strap

Answer 10

Have parallel running fibers
E.g. Sartorius

Question 11

Shape
Identify the shape of the muscle fibers

Answer 11

Question 12

Structure and Function
What is Striated Muscle?

Answer 12

Muscle made up of regularly arranged contractile units
Characterized by alternating light and dark bands

Question 13

Structure and Function
Striated Muscle
Structure of Skeletal Muscles

Answer 13

The cells are long, cylindrical (exhibit cross-striations) and multinucleated
The nuclei are peripherally placed
10-100mm in diameter
Up to 30cm in length

Question 14

Structure and Function
Striated Muscle
Skeletal Muscles
Action of Skeletal Muscle

Answer 14

Contraction is quick and strong and under voluntary control
Used for locomotion, mastication, and phonation

Question 15

Structure and Function
Striated Muscle
Skeletal Muscle
Nerve Supply

Answer 15

Supplied by somatic motor nerves
Site of contact between muscle and nerve endings are called motor end plates

Question 16

Structure and Function
Striated Muscle
Structure of Cardiac Muscle

Answer 16

Cardiac muscle fibers are short, cylindrical and branched (cross-striations)
Nucleus is centrally placed
Terminal ends of adjacent cardiac muscle fibers show dense-staining - junctional complexes called intercalated disks
They are located in the walls and septa of the heart
10-15mm in diameter
80-100mm in length

Question 17

Structure and Function
Striated Muscle
Cardiac Muscle
Action of Cardiac Muscle

Answer 17

Contraction is involuntary & rhythmic

Question 18

Structure and Function
Striated Muscle
Cardiac Muscle
Nerve Supply

Answer 18

Intercalated discs contain gap junctions allowing ionic communication between cells

Question 19

Structure and Function
Structure of Smooth Muscle

Answer 19

Cells contain irregularly arranged actin & myosin
Cells are fusiform with a central nucleus
0.2-2mm in diameter
20-200mm in length

Question 20

Structure and Function
Smooth Muscle
Action of Smooth Muscle

Answer 20

Involuntary
Slow
Long lasting

Question 21

Structure and Function
Smooth Muscle
Locations of Smooth Muscle

Answer 21

Blood vessels
Gastrointestinal tract (esophagus, stomach, small & large intestine)
Uro-genital organ walls (urinary bladder, ureter, urethra, uterine tube, uterus, vagina, vas deferens)