11 - Muscular System

Question 1

What is the byproduct of movement using muscles?

Answer 1

Heat

Question 2

What is the structure of a muscle?

Answer 2

A group of fascicles, which is a group of fibers, which are muscle cells.

Question 3

What are the CT components of a muscle?

Answer 3

1) Fascia = CT
a) Epimysium – surrounds entire muscle
b) Perimysium – surrounds fascicles
c) Endomysium – surrounds each muscle fiber
2) Tendons + Aponeuroses
 extensions of epi-, peri-, + endomysium
 anchors to bone (periosteum), cartilage, skin, or fascia
 tendon = rope-like
o e.g. Achilles tendon
 aponeurosis = sheet-like
o e.g. galea aponeurotica = epicranial aponeurosis

Question 4

What are the parts of a muscular fiber?

Answer 4

1) Sarcolemma = cell membrane
2) Sarcoplasm = cytoplasm
3) Myofibrils
4) T-tubules
5) Sarcoplasmic Reticulum

Question 5

How many myofibrils per fiber?

Answer 5

Hundreds to Thousands

Question 6

Describe the structure of a sarcomere.

Answer 6

• sarcomere structure (composed of proteins):
o made of 2 types of myofilaments:
a) thin filaments:
 composed of:
i. actin – functions in contraction
ii. tropomyosin + iii. troponin – regulate contraction (regulatory proteins)
b) thick filaments
 composed of:
i. myosin – functions in contraction
 attached to Z discs by titin
 has rod-like tail with 2 globular heads
o head extends toward actin and attaches to it – forming a crossbridge
o the myofilaments create dark + light bands (striations) of the sarcomere

Question 7

Descibe the bands of a sarcomere.

Answer 7

o banding pattern:
a) A band
 dark = length of thick filament – myosin + actin (with troponin + tropomysosin)
b) H zone
 lighter band at center of A band – myosin only
c) I band
 light = actin (with troponin + tropomyosin) + titin
d) Z discs (in center of I band)
 actin + titin attach
 connect sarcomeres: between 2 z-discs = 1 sarcomere
e) M line (middle line)
 where myosin tails (thick myofilaments) attach to each other (center of sarcomere)
o sarcomeres join end to end (at Z discs) to form myofibrils

Question 8

What are the T-tubules?

Answer 8

 continuations of sarcolemma that extend deep into fiber (cell)
 directly encircle myofilaments of myofibrils at junction of A & I bands (2/sarcomere)

Question 9

Describe the sarcoplasmic reticulum.

Answer 9

 = smooth ER

 triad = 2 enlarged areas of SR (terminal cisternae) & T-tubule

Question 10

What are the three mechanisms that muscles use to produce movement?

Answer 10

1) Pulling on bones when they contract
a) origin = attachment of tendon to stationary bone
b) insertion = attachment of tendon to movable bone (generally distal bone)
2) Using group action
a) agonist = major muscle producing the movement
b) synergists = help the agonist action and prevent undesirable motions caused by the agonist
c) antagonist = produces opposite action of agonist (contraction inhibited when agonist contracts)
3) Lever systems
 bone/muscle interaction at a joint
 parts:
a) levers = bone
b) fulcrum = joint
 effort = contraction of agonist
 resistance = opposes movement
 effort must be greater than resistance to get movement

Question 11

Describe the flexion and extension of the forearm according to muscle movement.

Answer 11

\: flexion of forearm
o	agonist = biceps brachii
o	antagonist = triceps brachii
o	synergists = brachialis, brachioradialis
o	lever = radius (insertion of agonist)
o	fulcrum = elbow joint
o	effort = muscle contraction
o	resistance = weight of forearm
	e.g.2: extension of forearm
o	agonist = triceps brachii
o	antagonist = biceps brachii

Question 12

How do we name skeletal muscles?

Answer 12

1) Action they perform (in anatomical position)
a) Flexors
 decrease angle between 2 bones
 e.g. biceps brachii
b) Extensors
 increase angle (back to anatomical position after flexion)
 e.g. triceps brachii
c) Abductors
 move limb away from midline
d) Adductors
 move limb toward midline
2) Shape of Muscle
 e.g.1: deltoid
o triangular shape
 e.g.2: trapezius
o trapezoid shape (no two sides parallel)
3) Origin + Insertion
 e.g.: sternocleidomastoid
o origin
• sterno = sternum
• cleido = clavicle
o insertion
• mastoid = mastoid process of temporal bone
4) Location
 e.g.: tibialis anterior
5) Relative size
 e.g.: gluteus
o maximus
o medius
o minimus
6) Direction of Fibers
 e.g.1: rectus abdominis
o rectus = straight ||
 e.g.1: external obliques \ //
7) Number of Origins
 e.g.1: biceps brachii
o 2 origins on scapula
 e.g.2: triceps brachii
o 3 origins on scapula and humerus
 e.g.3: quadriceps femoris
o 4 origins on os coxa and femur