Lecture Exam 3

Question 1

Functional Characteristics of Muscle

Answer 1

Contractility, Excitability, Extensibility, Elasticity

* Major function: to be excited and generate force.

Question 2

Contractility

Answer 2

The ability to shorten and generate force.

Question 3

Excitability

Answer 3

The ability to receive and respond to stimuli (electrical currents).

Question 4

Extensibility

Answer 4

The ability to be stretched or extended.

Question 5

Elasticity

Answer 5

The ability to recoil and resume the original resting length.

Question 6

Types of Muscle Tissue

Answer 6

Skeletal, Smooth, and Cardiac

Question 7

Types of Muscle Tissue Differ In:

Answer 7

Structure, location, function, and how they are activate.d

Question 8

Skeletal Muscle

Answer 8

(Attached to skeleton): Voluntary; multiple nuclei along cell membrane; body movements
- Maintain posture, stabilize joints, and generate heat

Question 9

Smooth Muscle

Answer 9

Involuntary; walls of hollow organs: moves substances through them (ex: uterus, blood vessels)

• Help maintain blood pressure
• Squeezes or propels substances (food, feces) through organs

Question 10

Cardiac Muscle

Answer 10

Involuntary: single nucleus in middle; branched and striated: heart –> pumps blood

Question 11

Muscle as Organs

Answer 11

Each names muscle is a discrete organ: muscle, tissue, blood vessels, nerve fibers, and connective tissue.
(Ex: biceps is an organ)

Question 12

Muscle is covered by:

Answer 12

Connective tissue at various levels.

- Three layers at three levels: separate fibers, and compartmentalize individual muscles or groups of muscles

Question 13

Epimysium

Answer 13

(Outside muscle); dense tissue surrounds the entire muscle: made of collagen

Question 14

Perimysium

Answer 14

Fibrous tissue surrounds bundles of muscle fibers: each bundle is fascicle.

Question 15

Endomysium

Answer 15

Surrounding each muscle fiber: reticular connective tissue

Question 16

Fascia

Answer 16

General term for connective tissue sheets that surround muscle.

Question 17

Connective Tissue

Answer 17

• Provides a pathway for blood vessels and nerves to reach muscle fibers
• Continuous with tendon: forms tendons, which connect muscle to bone.

Question 18

Skeletal Muscle Fiber

Answer 18

• Skeletal muscle cells are ELONGATED and are often called skeletal muscle fibers.
• Each skeletal muscle cell contains SEVERAL NUCLEI located around the periphery of the fiber near the plasma membrane (sarcolemma).
• Fibers appear STRIATED due to the presence of actin and myosin myofilaments arranged in a specific order.
• A single fiber can be extended from one end of a muscle to the other ( from origin of insertion).
• Contracts rapidly but tires easily.
• Is controlled VOLUNTARILY (i.e., by conscious control)

Question 19

Sarcolemma (Muscle Fibers)

Answer 19

Muscle cell plasma membrane.
- Invaginations of the sarcolemma form T tubules, which wrap around the sarcomeres and penetrate into the cell’s interior at each A band-I band junction.

Question 20

Sarcoplasm (Muscle Fibers)

Answer 20

Cytoplasm of a muscle cell.

• Sarcoplasmic reticulum (SR) is an elaborate, smooth endoplasmic reticulum that mostly runs longitudinal and surrounds each myofibril.
• Paired terminal cisternal form perpendicular cross channels.
• Functions in the regulation of intracellular calcium levels.
• A triad is a T tubule and two terminal cisternae.

Question 21

Myo, mys, and sarco

Answer 21

Prefixes used to refer to muscle

Question 22

Myofibrils

Answer 22

Are densely packed, rod-like contractile elements.

- They make up most of the muscle volume.

Question 23

Muscle Contraction

Answer 23

Depends on two kinds of myofilaments: actin and myosin: thin and thick filaments in myofibrils.

Question 24

Microanatomy of Skeletal Muscle Fibers

Answer 24

Skeletal muscle cell = fiber or myofiber
- It is individually surround by sarcolemma and inside the muscle fiber we have sarcoplasm (there are structures called myofibrils, which are made of myofilaments or filaments) and sarcoplasmic reticulum (there are various other structures within SR).

Question 25

Myofiber

Answer 25

- Has thick and thin filaments running in sequence to give it a particular microscopic structure that gives rise to A and I bands and Z line. - A band: contains mostly thick filaments (appears darker). - I band: contains mostly thin filaments (appear lighter under microscope). - Thin filaments are held together by the Z line and thick filaments are held together by protein called M line. - Distance between Z discs in a myofibril is called sarcomere ( functional unit of muscle contraction). - Thick filaments are made up of myosin and thin filaments of actin tropomyosin. - Interaction of thick and thin filaments responsible for skeletal muscle fiber contraction.

Question 26

Thick Filaments

Answer 26

- Myosin molecules: hockey sticks - Each myosin molecule: 1. a head with an ATPase activity: breaks down ATP 2. a hinge region, which enables the head to move 3. a rod or shaft - A cross-bridge is myosin head that binds to the cross bridge binding site on Actin thin filaments. - Crossbridge on thick filament, binding site on thin filament.

Question 27

Thin Filaments

Answer 27

- Has three major proteins: actin (two strands), troponin, and tropomyosin - Crossbridge binding sites: present on actin (myosin heads (cross bridges) attached during contraction) - Tropomyosin and troponin hide the binding site. - When calcium binds to troponin: cross bridge binding site uncovered; ready for action.

Question 28

Sarcomeres in Myofibril

Answer 28

- The smallest contractile unit of a muscle: Z disk to Z disk: M line in middle. - Z disks anchors think filaments. - Six think filaments surround a thick filament: in relaxed muscle cross bridges do not bind thin filaments - Myofibrils appear striated because of A bands and I bands. - Thick filaments: extend the entire length of an A band. Think filaments: extend across the I band and partway into the A band. - Thin filaments do not overlap thick filaments in the lighter H zone. - M line anchors thick filaments. - The arrangement of myofibrils within a fiber is so organized a perfectly aligned repeating series of dark A bands and light I bands is evident.

Question 29

Sliding Filament Model

Answer 29

- Upon stimulation, myosin heads (crossbridges) bind to actin (at crossbridge binding sites) and sliding begins. - Each myosin head binds and detaches several times during contraction - (acting like a ratchet to generate tension and propel the thin filaments to the center of the sarcomere) - Thin filaments slide past the thick ones so that the actin and myosin filaments overlap to a greater degree. - As this event occurs throughout the sarcomeres, the muscle shortens - Actin and myosin myofilaments do not change in length during contraction - In the relaxed state, thin and thick filaments overlap only slightly

Question 30

Sliding Filament Model | Contraction

Answer 30

- Actin filaments slide past the myosin filaments toward each other. - Z disks are brought closer together, and the sarcomere shortens. - The H zones (yellow) and the I bands (blue) narrow. - The ends of the actin filaments overlap at the center of the sarcomere and the H zone disappears (when muscle fully contracted). - Actin and Myosin filaments do not change length during muscle contraction. - Actin and myosin filaments in a relaxed muscle and a contracted muscle are the same length. _ Sarcomere length is what shortens.

Question 31

Membrane Potentials

Answer 31

- Plasma membranes are polarized: electrical charge difference (resting membrane potential) across the plasma membrane - Resting potential: The inside of the plasma membrane is negative (presence of K+) and outside of the membrane is positive (presence of Na+) in a resting cell - - most of sodium outside of cell, most potassium inside cell

Question 32

Ion Channels

Answer 32

- Assist with the production of electrical potentials - Ligand-gated channels: open only when a small molecule binds a large molecule in cell membrane: sodium channels - Voltage-gated channels: open only when electrical current is applied: calcium channels - In our body electrical current is provided by action potentials - The nervous system stimulates muscles to contract through electric signals called action potentials - Action Potential: a large changes in electrical current that is all or none - Local potential: it is small change in electrical activity

Question 33

Local Potential

Answer 33

Stimulus small, depolarization is small: the electrical charge does not spread.

Question 34

Action Potential

Answer 34

Stimulus larger: equal to threshold or larger. Depolarization larger: electrical activity spreads. - Occur in an all-or-none fashion - A stimulus below threshold produces no action potential - A stimulus at threshold or stronger will produce an action potential - Propagate (travel) across plasma membranes