AP 1 M5 5.3: Physiology of the Muscular System

Question 1

Muscle tissue types

Answer 1

Muscle tissue is found in three distinct types in the body: skeletal, smooth, and cardiac.

Question 2

Voluntary control

Skeletal muscle

Answer 2

Skeletal muscle is under voluntary control. Voluntary control means a conscious decision is made to move this type of muscle.

Question 3

Skeletal muscle

Answer 3

Skeletal muscle tissue allows for conscious movement of the body and limbs.

Question 4

involuntary control

Muscle type

Answer 4

Smooth muscle and cardiac muscle are under involuntary control, meaning contraction of this muscle happens without a conscious decision

Question 4

Smooth muscle

Answer 4

Smooth muscle is found within the internal organs of the body, such as the digestive tract and blood vessels.

Question 5

Cardiac muscle

Answer 5

Cardiac muscle is only found within the heart.

Question 6

striated

Answer 6

Under the microscope, skeletal and cardiac muscle appear to be striated or striped in appearance, while smooth muscle is free of striations.

Question 7

Skeletal muscles make up

Answer 7

Skeletal muscles, which make up over 40% of the body’s weight, are attached to the skeleton by tendons, made of fibrous connective tissue.

Question 8

Tendons

Answer 8

Tendons connect muscle to bone

Question 9

muscles contract

Answer 9

When muscles contract, they become shorter. Muscles can only pull; they cannot push. Skeletal muscles must work in antagonistic pairs because muscles are only able to pull in the direction of their fiber orientation.

Question 10

ligaments

Answer 10

ligaments connect bone tissue to bone.

Question 11

antagonistic pair

Answer 11

If one muscle of an antagonistic pair bends the joint and brings the limb toward the body (the flexor), the other one straightens the joint and extends the limb (the extensor), as shown in the figure below.

Question 12

Flexion

Answer 12

Flexion - closing of a joint, “bending”

Question 13

Extension

Answer 13

Extension - opening of a joint, “straightening”

Question 13

Antagonistic pair example

Flexion and Extension

Answer 13

Flexor - biceps brachii
Extensor - triceps brachii

Question 14

Abduction

Answer 14

Abduction - movement away from midline

Question 15

Adduction

Answer 15

Adduction - movement towards midline

Question 16

Antagonistic pair example:

Abduction and Adduction

Answer 16

Abductor: TFL (of the hip)
Adductor: adductor longus, adductor magnus

Question 17

Dorsiflexion

Answer 17

Dorsiflexion - flexion superiorly occurring at the subtalar (ankle) joint (movement of the toes “up”)

Question 18

Plantarflexion

Answer 18

Plantarflexion - flexion inferiorly occurring at the subtalar (ankle) joint (movement of the toes “down”)

Question 19

Antagonistic pair example:

Dorsiflexor and Plantarflexion

Answer 19

Dorsiflexor: tibialis anterior
Plantarflexor: gastrocnemius

Question 20

Radial Deviation

Answer 20

lateral movement of the wrist towards the radius

Question 21

Ulnar Deviation

Answer 21

medial movement of the wrist towards the ulna

Question 22

Antagonistic pair example

Radial Deviation and Ulnar Deviation

Answer 22

Radial Deviator: flexor carpi radialis
Ulnar Deviator: extensor carpi ulnaris

Question 23

Pronation

Answer 23

rotation of the forearm so that the palm faces posteriorly

(or) rotation of the ankle so the sole of the foot faces laterally

Question 24

Supination

Answer 24

rotation of the forearm so that the palm faces anteriorly

(or) rotation of the ankle so the sole of the foot faces medially

Question 25

Antagonistic pair example

Pronation and Supination

Answer 25

Pronator: (of forearm) pronator teres
Supinator: (of forearm) biceps brachii

Question 26

Elevation

Answer 26

Elevation – upward movement of a structure

Question 27

Depression

Answer 27

Depression – downward movement of a structure

Question 28

Antagonistic pair example:

Elevation and Depression

Answer 28

Elevator: levator scapulae
Depressor: trapezius (lower fibers)

Question 29

Retraction

Answer 29

Retraction - movement of a structure to be drawn in the posterior direction (drawn backward)

Question 30

Protraction

Answer 30

Protraction - movement of a structure to be drawn in the anterior direction (drawn forward)

Question 30

Antagonistic pair example:

Retraction and Protraction

Answer 30

Retractor: rhomboids, trapezius
Protractor: serratus anterior

Question 30

A whole skeletal muscle

Answer 30

A whole skeletal muscle is composed of many muscle fibers in bundles

Question 31

muscle fiber

Answer 31

Each muscle fiber is a cell containing thousands of myofibrils, which are the contractile portions of the fibers

Question 32

Myofibrils

Answer 32

Myofibrils are cylindrical in shape and run the length of the muscle fiber. The light microscope shows that a myofibril has light and dark bands called striations.
It is these bands that cause skeletal muscle to appear striated. Striations of myofibrils are formed by protein myofilaments within contractile units called sarcomeres

Question 32

sarcomeres

Answer 32

It is these bands that cause skeletal muscle to appear striated. Striations of myofibrils are formed by protein myofilaments within contractile units called sarcomeres

Question 32

myofilaments

Answer 32

A sarcomere contains two types of protein myofilaments

Question 33

myosin

myofilaments

Answer 33

The thick filaments are made up of a protein called myosin,

Question 34

actin

myofilaments

Answer 34

the thin filaments are made up of a protein called actin

Question 35

As a muscle fiber contracts

Answer 35

As a muscle fiber contracts, the sarcomeres within the myofibrils shorten. When a sarcomere shortens, the actin (thin) filaments slide past the myosin (thick) filaments and approach one another. The movement of actin filaments in relation to myosin filaments causes the muscle to shorten.

Question 36

Z line

Various terms help to describe the components of a sarcomere

Answer 36

One sarcomere is from one Z line to one Z line. Z lines connect parallel bands of thin filaments.

Question 37

M line

Various terms help to describe the components of a sarcomere

Answer 37

The thick filaments are held together by the M line.

Question 38

I band

Various terms help to describe the components of a sarcomere

Answer 38

The I band (light band) appears light when stained because it only contains thin filaments.

Question 39

A band

Various terms help to describe the components of a sarcomere

Answer 39

The A band (dark band) contains thin and thick filaments; however, it stains darker because it contains the thick filaments. When a muscle contraction occurs, the Z lines move closer together towards the center of the sarcomere (M line).

Question 40

acetylcholine

For a muscle to contract

Answer 40

Once the nerve impulse reaches the muscle fiber (called a neuromuscular junction), acetylcholine (a special chemical called a neurotransmitter) is released from the motor nerve ending (Figure 5.40). Acetylcholine binds to receptors on the muscle cell, opening sodium channels and allowing sodium to flow inside the sarcoplasm (cytoplasm of a muscle cell).

Question 40

For a muscle to contract

Answer 40

For a muscle to contract, the nervous system must work together with the muscular system. First, a nerve impulse must be sent to the muscle.

Question 41

sarcoplasm

For a muscle to contract

Answer 41

Acetylcholine binds to receptors on the muscle cell, opening sodium channels and allowing sodium to flow inside the sarcoplasm (cytoplasm of a muscle cell).

Question 42

sarcolemma

For a muscle to contract

Answer 42

The presence of sodium ions causes an action potential to occur in the sarcolemma (cell membrane of a muscle fiber). The action potential causes calcium ions to be released from the sarcoplasmic reticulum

Question 42

sarcoplasmic reticulum

For a muscle to contract

Answer 42

The sarcoplasmic reticulum is a specialized type of smoother ER found within striated muscle tissue.

Question 42

movement of the many actin filaments together

For a muscle to contract

Answer 42

The movement of the many actin filaments together is what produces a muscle contraction. Muscle contraction ceases when the nerve impulses no longer stimulate the muscle fiber. With the cessation of a muscle action potential, calcium ions are pumped back into the sarcoplasmic reticulum by active transport. Once the calcium ions return to the sarcoplasmic reticulum, relaxation of the muscle occurs.

Question 43

cross-bridges

For a muscle to contract

Answer 43

In the presence of calcium ions, portions of the myosin filaments called cross-bridges bend backward and attach to actin filaments. After attaching to the actin filament, the cross-bridges bend forward and the actin filament is pulled along. The cross-bridges attach and detach some fifty to 100 times as the thin filaments are pulled to the center of a sarcomere. ATP is needed on a cellular level for the myosin cross-bridges to pull the actin filaments.