Chapter 8 - Skeletal Muscle and Electromyography

Question 1

Skeletal Muscle

Answer 1

• Makes movement, breathing, speech, and facial expression possible
• Almost completely under voluntary control
• Cells are very large and have visible stripes called striations (which are made up of organized units of contractile proteins)
• Cells are organized end-to-end and facilitate muscle shortening (or lengthening) to make movement possible

Question 2

All types of muscle have the following characteristics in common…

Answer 2

Excitability (muscle cells produce action potentials), contractility (muscle cells can shorten), extensibility (muscle cells can be stretched or lengthened), elasticity (muscle cells will return to their original length after being stretched)

Question 3

Muscle fibers

Answer 3

Individual muscle cells

Question 4

Fascicles

Answer 4

• The bundles of muscle fibers
• Many make up one whole muscle and are wrapped in an outer membrane called the fascia

Question 5

Fascia

Answer 5

• Holds the fascicles as well as blood and nerves together in one large unit
• Connect to the connective tissue making up tendons

Question 6

Tendons

Answer 6

Anchor muscle tissue to the bones they work to move during contraction

Question 7

Sarcolemma

Answer 7

The cell membrane that surrounds the muscle fiber (“sarco-“ = flesh)

Question 8

Sarcoplasm

Answer 8

Cytoplasm in the sarcolemma

Question 9

Myofibrils

Answer 9

Bundles of protein within the sarcoplasm

Question 10

Myofilaments

Answer 10

Many individual overlapping protein strands that make up each myofibril

Question 11

Sarcoplasmic Reticulum

Answer 11

The complex network of membranous sacs and tubes within the sarcoplasm that is full of calcium ions and surrounds each myofilament

Question 12

Terminal Cisternae

Answer 12

The large sacs formed by the ends of the sarcoplasmic reticulum

Question 13

Transverse Tubules (t-tubules)

Answer 13

The narrow tubes that the terminal cisternae of the sarcoplasmic reticulum

Question 14

Thick & Thin Filaments

Answer 14

• The two types of myofilaments contained within the myofibrils of the muscle fiber
• Slide past one another and shorten the muscle cell during contraction

Question 15

Sarcomere

Answer 15

The functional unit of a muscle cell and is formed by repeating units of thick and thin filaments that run end-to-end along the length of the muscle cell

Question 16

Actin, Tropomyosin & Troponin

Answer 16

The different proteins that make up the thin filaments of the sarcomere

Question 17

Actin (the thin filament)

Answer 17

A long string of globular proteins and looks like a strand of beads

Question 18

Myosin

Answer 18

• The protein that mostly makes up thick filaments
• The head of the molecule is hinged and can move back and forth during muscle contraction

Question 19

Active Site

Answer 19

In each molecule of actin and it allows the myosin to interact by attaching or binding to that specific site

Question 20

Tropomyosin

Answer 20

The long chains of a regulatory protein that cover the active sites on actin when the muscle is relaxed

Question 21

Troponin

Answer 21

Another smaller regulator protein that is attached along the lengths of the tropomyosin chains

Question 22

Cross-Bridge Formation

Answer 22

The myosin heads attach to the active site on actin

Question 23

Power Stroke

Answer 23

• The action that is caused by the myosin heads pivots immediately after cross-bridge formation
• Forces the actin filament to slide toward the the center of the sarcomere

Question 24

Attached Phase

Answer 24

The ADP and phosphate (P) left over from the original ATP molecule are released form the myosin

Question 25

Cross-Bridge Detachment

Answer 25

Allowed by the new ATP binding from the myosin remaining in a flexed attach position until a new ATP molecule binds to the myosin head

Question 26

Motor Unit

Answer 26

• Consists of one motor neuron and all of the individual muscle cells it controls
• Changing the number of these activated at a given time allows you to control how many muscle fibers contract within a single muscle

Question 27

2 reasons why not all motor units of a muscle are active at the same time

Answer 27

1. Motor units allow muscles to modulate the strength of a contraction
2. Motor units protect our muscles against fatigue

Question 28

Recruitment

Answer 28

The activation of additional motor units to increase muscle strength and force of contraction

Question 29

Fatigue

Answer 29

• Not being able to sustain an expected force from a muscle
• Fitness, age, psychology and physiology play a role in determining it

Question 30

Central Fatigue

Answer 30

• Caused by the CNS and psychological mechanisms
• Manifests as feeling “tired” or not wanting to go on

Question 31

Peripheral Fatigue

Answer 31

• Defined as problems with the neuromuscular junction between the motor nerve and muscle or problems within the muscle cell at the level of the sarcomere
• The calcium or ATP stores of the muscle cell may have been used up
• Physiologically you cannot go on

Question 32

Maximal Grip Force

Answer 32

• The amount of force that can be maintained by squeezing an object as hard as possible, can also be a useful diagnostic test
• Inability to muster strength often happens late in life and is a predictor for senescent decline (end of life)

Question 33

3 types of muscle contraction

Answer 33

Isometric, concentric, and eccentric

Question 34

Isometric Contraction

Answer 34

• A muscle may contract but not change length
• If you hold a load in your hand and do not raise or lower it, just hold it still, then your biceps brachii muscle is in a state of …
• The total force produced by the active sarcomeres is exactly balanced by the force of the load in the hand, and the length of the muscle does not change

Question 35

Concentric Contraction

Answer 35

• A muscle will shorten in length
• If you hold a load in your hand and raise it, then your biceps brachii muscle is in a state of …
• The thick and thin filaments will slide past one another and the muscle will shorten
• The total force produced by the active sarcomeres is greater than the force of the loaf in the hand, and the length of the muscle shortens

Question 36

Eccentric Contraction

Answer 36

• A muscle may contract and actually become longer
• If you hold a load in your hand and actively lower it (not just drop it), then your biceps brachii muscle is in a state of …
• The total force produced by the active sarcomeres is less than the force of the load in the hand, and the length of the muscle becomes greater

Question 37

Antagonistic Pairs

Answer 37

Pairs that muscles can be arranged in

Question 38

Agonist

Answer 38

Sometimes called the prime mover and can be thought of as the muscle performing the desired action

Question 39

Antagonist

Answer 39

Capable of the opposing action

Question 40

Coactivation

Answer 40

• When the motor units in both the agonist and antagonist are active at the same time
• Is a common phenomenon and usually must occur to perform a controlled movement or stabilize a joint

Question 41

Flexion

Answer 41

Describes a decrease in the angle between body parts

Question 42

Extension

Answer 42

Increases the angle between adjacent body parts

Question 43

Abduction

Answer 43

Describes the movement of a body part away from the midline

Question 44

Adduction

Answer 44

Movement of a body part toward the midline (“adding” the limb back to your trunk)

Question 45

Electromyography (EMG)

Answer 45

Used to examine electrical activity generated by muscles