Unit 11: Muscular System

Question 1

What is the muscular system?

Answer 1

• refers to skeletal muscle system
• primarily attached to bone
• produce movement by contracting

Question 2

What is skeletal muscle?

Answer 2

• cells called fibers
• fascicle = group fibres
• WHOLE muscle = group of fascicles

Question 3

What are the CT components of the skeletal muscle?

Answer 3

1) Fascia (CT surrounding muscles or other organs)
a) Epimysium - surrounds entire skeletal muscle
b) Perimysium - surrounds fascicles w/in skeletal muscle
c) Endomysium - surrounds each muscle fiber (cell) w/in
skeletal muscle
2) Tendons and Aponeuroses
- extension of epimysium, perimysium, and endomysium
- anchors muscle to bone (periosteum), cartilage, fascia
- tendon: a rope-like bundle of dense regular CT
- e.g. calcaneal (Achilles) tendon
- aponeurosis = a flat sheet of dense regular CT
- e.g. epicranial aponeurosis (scalp)

Question 4

What are the five parts of the skeletal muscle fiber structure?

Answer 4

• large cylindrical and multinucleate cells
• parts:
  1) Sarcolemma = cell membrane
  2) T-tubules (= continuations of sarcolemma that extend deep into fiber [cell])
  3) Sarcoplasm = cytoplasm
  4) Myofibrils (intracellular structures)
• w/in each fibre there are several hundreds to thousands
  5) Sarcoplasmic Reticulum
• is smooth endoplasmic reticulum
• triad is formed from 2 enlarged areas of sarcoplasmic reticulum (terminal cisternae), and a T-tubule that runs in btw. them

Question 5

More info on the structure of myofibrils (which is composed of sarcomeres)

Answer 5

Sarcomere structure (composed of proteins) is made of 2 types of myofilaments:
a) thin myofilaments: formed by 3 proteins involved in contraction: actin, tropomyosin, and troponin
b) thick myofilaments: formed by a protein called myosin, attached to Z discs by titin
- has rod-like tail w/ 2 globular heads - at rest, the heads extend toward actin and during contraction attaches to actin to shorten the sarcomere

• the myofilaments create dark and light bands (striations) of the sarcomere; banding pattern:
  a) A band = dark band that is length of thick myofilament
  b) H zone = lighter area at center of A band
  c) I band = light band consisting of thin myofilaments
  d) Z discs (in center of I band)
• connected to thick myofilaments (via titin) and thin myofilaments
• connection point btw. adjacent sarcomeres
  e) M line = where myosin tails (thick myofilaments) attach to each other (center of sarcomere)
• sarcomeres join end to end (at Z discs) to form a myofibril

Question 6

Biomechanics

Answer 6

1) Lever System
- 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

2) Pulling on bones when they contract
a) origin = attachment of tendon to stationary bone
b) insertion = attachment of tendon to movable bone

3) 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)

Question 7

Examples of biomechanics

Answer 7

1) flexion of forearm
- agonist = biceps brachii
- antagonist = triceps brachii
- synergists = brachialis, brachioradialis
- lever = radius (insertion of agonist)
- fulcrum = elbow joint
- effort = muscle contraction
- resistance = weight of object plus forearm

2) extension of forearm
- agonist = triceps brachii
- antagonist = biceps brachii