Chapter 10: Muscle Tissue and Organization

Question 1

List and explain the 4 unique characteristics of muscle tissue.

Answer 1

1. Excitability - responsiveness; able to be stimulated by a nerve to move
2. Contractility - fibers shorten resulting in pull on bones or movement of body parts
3. Elasticity - ability to return to to original length when tension is released
4. Extensibility - capability to extend in length in response to contraction of opposing muscle fibers

Question 2

List and describe the 3 types of muscle tissue.

Answer 2

1. Skeletal Muscle
   - striated
   - voluntary
   - multinucleated
   i. e. muscles like biceps, quadriceps, etc
2. Smooth Muscle
   - NOT striated
   - involuntary
   - only 1 nucleus
   - fibers are short, fusiform shape
   - takes longer to contract and relax than skeletal muscle
   i. e. muscles in the digestive tract/intestines
3. Cardiac Muscle
   - striated
   - involuntary
   - typically 1-2 nuclei
   - fibers shorter and thicker than skeletal muscle and form Y-shaped branches
   - contain intercalated discs
   - autorythmic
   i. e. the heart wall

Question 3

List the functions of skeletal muscle (5)

Answer 3

1. Movement
2. Maintain posture
3. Temp regulation (ie shivering)
4. Storage and movement of materials
5. Support

Question 4

Describe these muscle attachments:
Tendon
Aponeuroses

Answer 4

Tendon - attaches muscle to: bone, skin, or another muscle; thick cordlike structure,

Aponeuroses - tendon that is a thin flat sheet

Question 5

Define origin and insertion.

Answer 5

Origin - the less movable attachment of a muscle; typically proximal to the insertion

Insertion - the more movable attachment of a muscle; the pull is toward the origin

Question 6

List and define the 4 parts of muscle cell anatomy

Answer 6

1. Sarcolemma - plasma membrane (right under the endomysium)
2. Sarcoplasm - cytoplasm
3. Sarcoplasmic reticulum - similar to smooth ER
4. Transverse tubules - invaginations of sarcolemma (they help spread nerve impulses for contraction)

Question 7

Define a motor unit.

Answer 7

A motor unit is composed of a

• single motor neuron
• the muscle fibers it controls
• the neuromuscular junctions between them

Question 8

Explain the all-or-none principle.

Answer 8

• A muscle fibers either completely contracts or it does not contract at all.
• When a motor unit is stimulated, all of it’s fibers contract at the same time
• Total force exerted by the muscle depends on the number of motor units that are activated
  ie. increase motor units = increase in force of contraction
  (think of lifting a box that you think will be heavier than it is)

Question 9

What is muscle tone?

Answer 9

Resting tension in a skeletal muscle.

• some motor units are active even when a muscle is at rest
• motor units cause the muscle to be tense but produce enough force to cause movement

Question 10

Define agonist.

Answer 10

muscle that contracts to produce a particular movement (also called “prime mover”)

Question 11

Define prime mover.

Answer 11

muscle that contracts to produce a particular movement (also called “agonist”)

Question 12

Define antagonist.

Answer 12

muscle action that opposes that of the agonist/prime mover

Question 13

Define synergist.

Answer 13

muscle action that assists the agonist/prime mover in performing an action;

contributes to tension near insertion or stabilizes origin;

may assist agonist by preventing movement at a joint; therefore stabilizing origin

Question 14

Define the 2 types of muscle contractions.

Answer 14

Isometric - length of the muscle does NOT change during the contraction; tension is generated but not enough to move the load

Isotonic - movement DOES occur; tension produced exceeds the load

Question 15

Define atrophy and what happens.

Answer 15

Muscles is reduced in size, tone, and power. (Fibers decrease in size and become weaker.)
Occurs due to reduced stimulation.

Question 16

Define hypertrophy and what happens.

Answer 16

• Muscle fibers increases in size.
• Caused by exercise; the muscle fibers are stimulated to produce more mitochondria.
• Muscle fibers develop more myofibrils and each contains a larger number of myofilaments.
• There’s an increase in glycogen stores and mitochondria

Question 17

Discuss the different types of skeletal muscle fibers. (3)

Answer 17

1. Fast (anaerobic, Type II X)
   - large size
   - large glycogen reserves
   - few mitochondria
   - majority of skeletal muscles
   - “white fibers” - lack myoglobin
2. Intermediate (aerobic, Type II A)
   - like Fast but more resistant to fatigue
   - more mitochondria
3. Slow (aerobic, Type I)
   - smaller size
   - endurance fibers (contract slowly and for a longer period of time)
   - “red fibers” - contain myoglobin

Question 18

List and describe the 4 organizational patterns in fascicles. Give examples of each.

Answer 18

1. Circular - sphincter; closes off an opening
   ie. orbicularis oris
2. Convergent - widespread fibers that converge on a common attachment site (often triangular)
   ie. pectoralis major
3. Parallel - fascicles run parallel to long axis (have central body called “belly”)
   ie. rectus abdominis
4. Pennate - one or more tendons extend through the body of the muscle; fascicles are arranged at oblique angle to the tendon
   (pull harder than parallel muscles of the same size)
   ie. rectus femoris

Question 19

List and describe the 3 types of pennate muscles. Give examples of each.

Answer 19

1. Unipennate - all muscles fibers are on the same side of the tendon
   (half feather)
   i.e. extensor digitorum
2. Bipennate - (most common) muscle fibers on both sides of the tendon
   (full feather)
   ie. rectus femoris (of the quads)
3. Multipennate - has branches of the tendon within the muscle
   ie. deltiod

Question 20

List the 3 actions of skeletal muscle.

Answer 20

1. Agonist/Prime mover
2. Antagonist
3. Synergist

Question 21

List and identify the 2 types of isotonic contractions.

Answer 21

Concentric contraction: muscle shortens

Eccentric contraction: muscle lengthens

Question 22

Define sarcomere.

Answer 22

The functional contractile unit of a skeletal muscle fiber.

Defined as the distance from one Z disc to the next Z disc.

Each shortens as the muscle fiber contracts.

Question 23

List the components of a sarcomere. (7)

Answer 23

Z discs
I bands
A band
H zone
M line
Thick filaments
Thin filaments

Question 24

Describe the components of a sarcomere. Be able to label them on a diagram.

(Diagram - Pg. 295-296)

Answer 24

Z disc - dark proteins in center of I band where thin filaments attach

I bands - light band containing thin filaments only and connectin proteins

A band - dark band in middle of sarcomere; entire thick filament us located here; part of thin filaments overlaps

H zone - lighter region in middle of A band containing thick filaments only

M line - dark protein disc in center of H zone

Thick filaments - myosin (protein)

Thin filaments - actin (protein)

Question 25

Describe sliding filament theory.

Answer 25

When a muscle contracts, thick and thin filaments slide past each other, and the sarcomere shortens.

• Width of A band remains constant.
• H zone disappears.
• Z discs of sarcomere more closer together; therefore sarcomere shortens in length.
• I bands shorten in length.

Question 26

Describe the structural organization of skeletal muscle from smallest to largest.

(Diagram - Pg. 289)

Answer 26

Thick and thin filaments found in sarcomeres = myofilaments.

Myofilaments bundled together = myofibril.

Bundles of myofibrils = muscle fiber and is incased in endomysium.

Bundles of muscle fibers = fascicle which is incased in perimysium

Bundles of fascicles = muscle which is incased in epimysium.

Question 27

Define superficial fascia.

Answer 27

Composed of aereolar connective tissue and adipose that separates muscle from skin.

Question 28

Define deep fascia.

Answer 28

Sheet of dense irregular connective tissue that separates individual muscles; binds muscles together; forms sheaths to help distribute nerves, blood vessels, and lymphatic vessels

Question 29

Smooth muscle is also known as what?

Answer 29

Visceral muscle

Question 30

Discuss the make up of thin and thick filaments.

Including actin, myosin, troponin, tropomyosin, and crossbridges

Answer 30

Thick filaments - bundles of proteins called myosin;
- these filaments have little projections extending out from them that look like the head of a golf club

Thin filaments - bundles of proteins called actin;
- looks like a twisted string of pearls

Crossbridges - formed when the myosin heads bind with the actin filaments during contraction

Tropomyosin and troponin - regulatory proteins that are part of the thin filaments

• tropomyosin: blocks the binding sites on the actin strands when needed
• troponin: assists with the binding process of the myosin to the actin

Question 31

Discuss the innervation of a muscle fiber.

Answer 31

• A single Motor Neuron typically controls numerous muscle fibers.
• Has a neuromuscular junction with each muscle fiber it controls.
• Initiates muscle contraction in the fibers it innervates.

Question 32

List the critical components of a neuromuscular junction including:
synaptic knob, synaptic vesicles, motor endplate, synaptic cleft, and ACh receptors.

Answer 32

Synaptic knob: expanded tip of the nerves axon;

Synaptic vesicles: small membrane sacs in the synaptic knob that contain ACh

ACh: “acetylcholine,” a neurotransmitter

Synaptic cleft: narrow space separating the synaptic knob with the motor end plate

Motor endplate: specialized region of the sarcolemma that is folded/indented to increase surface area covered by the synaptic knob

ACh receptors: located in the motor endplate; these receptors remain closed until ACh is released; the ACh causes the receptors to open and therefore the muscle becomes stimulated

AChE: enzyme located within the synaptic cleft that breaks down ACh so that the muscle is not continually stimulated

Question 33

Summarize the events that take place for a muscle contraction. (5 Steps)

Answer 33

1. Nerve impulse travels down the axon to the synaptic knob causing ACh to be released and bind with the ACh receptors on the motor endplate, initiating a muscle impulse.
2. Muscle impulse travels quickly along sarcolemma and into muscle fiber via T-tubules causing calcium to be released into the sarcoplasm.
3. Calcium then binds with the troponin causing tropomyosin to move and expose the active sites on the actin so that myosin can bind to them and form crossbridges
4. Myosin heads “attach, pivot, detach, return” (ATP is required for that process) causing the thin filaments to be pulled past the thick filaments. (This is the “contraction” of the sarcomere; where the I band disappears.) Since the sarcomere is shortening, the muscle contracts. This will continue as long as the calcium is still bound to the troponin.
5. Ion pumps move the calcium back into the sarcoplasmic reticulum which reduces the amount of calcium in the sarcoplasm, leading to relaxation. The sliding filaments (actin/myosin) passively slide back to their original state.

Question 34

Briefly discuss the effects of aging on skeletal muscle.

Answer 34

Decreased activity leads to:
- decreased muscle mass, muscle size, muscular power

Decreased elasticity
Decreased cardiovascular performance
Decreased exercises tolerance
Reduced capacity for recovery
Circulatory supply to muscles occurs more slowly

Question 35

What is a motor neuron?

Answer 35

A neuron that stimulates muscle contraction.