Chapter 9

Question 1

Types of muscle tissues

Answer 1

Skeletal, cardiac, and smooth

Question 2

Skeletal muscle tissue

Answer 2

Longest muscle cells and have striations. It is called voluntary muscle because it’s the only one that has conscious control.

Question 3

Cardiac muscle tissue

Answer 3

Occurs only in the heart and is striated. It is not voluntary but is contracts without being stimulated by the nervous system.

Question 4

Smooth muscle tissue

Answer 4

Found in the walls of hollow organs. It forces fluids and other substances through body channels. Also forms valves, dilates the pupils, and forms arrector pili muscles. It has elongated cells but no striations. No voluntary control and its contractions are slow and sustained. It’s visceral.

Question 5

Characteristics of muscle tissue

Answer 5

Excitability (ability of cell to receive and respond to a stimulus by changing membrane potential), contractibility (shorten when stimulated), extensibility (ability to extend or stretch, elasticity (ability of muscle cell to recoil and resume its resting length after stretching)

Question 6

Muscle functions

Answer 6

Produce movement, maintain posture and body position, stabilize joints, and generate heat

Question 7

Skeletal muscle nerve and blood supply

Answer 7

One nerve, one artery, and one or more veins serve each muscle. They enter or exit near the central part of the muscle and branch to connective tissue sheaths. Skeletal muscle has a rich blood supply. Capillaries take a long path through muscle and have cross-links the accommodate changes in muscle length.

Question 8

Connective tissue sheaths

Answer 8

Epimysium (overcoat of dense irregular connective tissue thy surrounds the whole muscle), perimysium and fascicles (muscle fibers are grouped into fascicles, each fascicles is a layer of dense irregular connective tissue called perimysium), endomysium (wispy sheath of connective tissue that surrounds each individual muscle fiber consisting of a rolar connective tissue)

Question 9

Attachments

Answer 9

Direct or fleshy attachments (epimysium is fused to the periosteum of a bone or perichondrium of a cartilage), indirect attachments (the muscles connective tissue wrappings extend beyond the muscle either as a tendon or a sheet like aponeurosis. These anchor the muscle to the connective tissue covering of a skeletal element (bone or cartilage) or to the fascia of other muscles)

Question 10

Sarcoplasm

Answer 10

The cytoplasm of the muscle cell that contains large amounts of glycosomes (granules of stored glycogen that provide glucose during muscle cell activity for ATP production) and myoglobin (red pigment that stores oxygen)

Question 11

Specialized structures of the muscle cell

Answer 11

Myofibrils, sarcoplasmic reticulum, and T tubules

Question 12

Myofibrils

Answer 12

A single muscle fiber contains thousands of rodlike Myofibrils that run parallel to its length. Account for 80% of cellular volume. They are made up of a chain of sarcomeres linked end to end. Sarcomeres contain even smaller structures called myofilaments.

Question 13

Striations

Answer 13

Dark A bands and light I bands are aligned. Each dark A band has a lighter midsection called the H zone. Each H zone is bisected vertically by a dark line called the M line formed by molecules of the protein myomesin. Each light I band has a midline interruption, a darker area called the Z disc.

Question 14

Sarcomeres

Answer 14

Region of a myofibril between two successive Z discs. Smallest contractile unit of muscle fiber, the functional unit of skeletal muscle. It contains an A band flanked by half an I band at each end. Sarcomeres align end to end.

Question 15

Myofilments

Answer 15

Muscle equivalent of the actin-containing micro filaments and myosin motor proteins. Two types of contractile myofilaments thick filaments (contains myosin (red) extend the entire length of the A band and connected in the middle of the sarcomere at the M line) and thin filaments (containing actin (blue) extend across the I band and partway into the A band. The Z disc, a protein sheet, anchors the thin filaments)

Question 16

Myofibril arrangements and band patterns

Answer 16

A hexagonal arrangement of six thin filaments surrounds each thick filament, and three thick filaments enclose each thin filament. The H zone of the A band appears less dense bc the thin filaments do not extend into this region. The M line in the center of the H zone is slightly darker bc of the fine protein strands there that hold adjacent thick filaments together. The myofilaments are held in alignment at the Z discs and the M lines, and are anchored to the sarcolemma at the Z discs.

Question 17

Molecular composition of myofilaments

Answer 17

Consists of six polypeptide chains: two heavy chains and four light chains. The heavy chains form the tail and each one has a globular head that attaches to the tail via a hinge. During contraction, the heads link thick and thin filaments together, forming cross bridges, and swivel around to generate force. Myosin splits ATP and uses released energy to drive movement.

Question 18

Actin

Answer 18

Has polypeptide units, called globular actin or G actin that has a myosin binding site (active site) to which the myosin heads attach during contraction. They polymerize into long actin filaments called filamentous or F actin.

Question 19

Tropomyosin

Answer 19

Rod shaped protein that spirals about the actin core and help stiffen and stabilize it. Arranged end to end along actin filaments and block myosin binding sites on actin so myosin heads on the thick filaments can’t bind to the thin filaments.

Question 20

Troponin

Answer 20

Globular protein with three polypeptide subunits. One attaches troponin to actin and another binds tropomyosin and helps position it on actin. The third subunit binds calcium ions.

Question 21

Elastic filament

Answer 21

Composed of titin. Titan goes form the Z disc to the thick filament and run to attach to the M line. It holds up the thick filament and organizes the A band, and helps muscle go back to its shape after stretching. It stiffens as it uncoils, helping the muscle revisit excessive stretching that might pull sarcomeres apart

Question 22

Dystrophin

Answer 22

Links the thin filaments to the integral proteins of the sarcolemma (which are anchored to the extracellular matrix)

Question 23

Other proteins that bind filaments

Answer 23

Nebulin, myomesin, and C proteins. Intermediate (desmin) filaments extend from the Z disc and connect each myofibril to the next throughout the muscle cell.

Question 24

Sarcoplasmic reticulum

Answer 24

Smooth endoplasmic reticulum that regulates intracellular levels of ionic calcium. It stores calcium and releases it in demand when the muscle fiber is stimulated to contract. SR tubules communicate in the H zone. Others called terminal cisterns (end sacs) form perpendicular cross channels at the A band-I band junctions. Also produce large numbers of mitochondria and glycogen granules.

Question 25

T tubules

Answer 25

At each A band-I band junction the sarcolemma protrudes into the cell and forms t tubules. The lumen (cavity) of the T tubules is continuous with extracellular space. As a result, they increase the muscle fibers surface area. They run between paired terminal cisterns forming triads (successive groupings of the 3 membranous structures. They conduct impulses that trigger the release of calcium from adjacent terminal cisterns.

Question 26

Sliding filament model of contraction

Answer 26

During contraction, the thin filaments slide past thick ones so that actin and myosin filaments overlap to a greater degree. Nervous system stimulates muscle fibers, the myosin heads on the thick filaments latch onto myosin-binding sites on actin in thin filaments, and the sliding begins. These cross bridge attachments form and break several times during contraction to propel thin filaments toward the center of the sarcomere.

Question 27

What occurs as a muscle cell shortens?

Answer 27

The I band shortens, the distance between Z discs shortens, the Z discs are pulled toward the M line, the H zones disappear, the A bands move closer but their lengths don’t change.

Question 28

Action potential

Answer 28

Electrical signal (nerve impulse) that is a large change in membrane potential that spreads rapidly over long distances within a cell. They don’t spread cell to cell, so it has to be converted to a chemical signal called a neurotransmitter that diffuses across the small gap between excitable cells.

Question 29

Acetylcholine

Answer 29

The neurotransmitter that motor neurons use to tell skeletal muscle to contract

Question 30

Chemically gated ion channels

Answer 30

Opened by chemical messengers (neurotransmitters) and creates small changes in membrane potential

Question 31

ACh receptor

Answer 31

Single protein in the plasma membrane that is both the receptor and an ion channel

Question 32

Voltage-gated ion channel

Answer 32

Open or close in response in response to changes in membrane potential. They underlie all action potentials. Chemically gated ion channels cause a small local depolarization (decrease in membrane potential) that triggers the voltage-gated ion channels to create action potential.

Question 33

Somatic motor neurons

Answer 33

Motor neurons that activate skeletal muscle fibers. They are in the spinal cord. Each neuron has an axon that extends from the cell body in the spinal cord to the muscle fiber it serves. The axons exit the spinal cord and pass throughout the body bundled together as nerves.

Question 34

Oval neuromuscular junction (motor end plate)

Answer 34

The axon of each neuron branches as it enters muscle so it can activate multiple muscle fibers. When it gets to the muscle fiber it divides again giving off branches that form the oval neuromuscular junction

Question 35

Axon terminal

Answer 35

Then end of an axon

Question 36

Synaptic cleft

Answer 36

Space between the muscle fiber and the end of the axon filled with a gel-like extracellular substance rich in glycoproteins and collagen fibers

Question 37

Synaptic vesicles

Answer 37

Within the axon terminal that are small membranous sacs containing acetylcholine

Question 38

Junctional folds

Answer 38

Part of the muscle fibers sarcolemma that helps form the neuromuscular junction is highly folded and provide a large surface area for the thousands of ACh receptors

Question 39

4 steps of skeletal muscle contraction

Answer 39

STEP 1: events at the neuromuscular junction-motor neuron releases ACh that stimulates muscle fiber causing depolarization called end plate potential (EPP) STEP 2: muscle fiber excitation-the EPP triggers an action potential that travels across the entire sarcolemma STEP 3: excitation contraction coupling-the AP in the sarcolemma propagates along the T tubules and causes release of Ca2+ from the terminal cisterns of the SR. Ca2+ is the final trigger. It binds to troponin and causes myosin binding sites on actin to be exposed so that myosin heads can bind to actin STEP 4: cross bridge cycling-muscle contracts as a result of a repeating cycle of steps that use myofilaments to slide relative to each other

Question 40

3 steps of AP across the sarcolemma

Answer 40

1. An end plate potential (EPP) is generated at the neuromuscular junction 2. Depolarization: generating and propagating an action potential 3. Repolarization: restoring the sarcolemma to its initial polarized state (negative inside, positive outside)

Question 41

Acetylcholinesterase

Answer 41

After ACh binds to the ACh receptors it’s effects are quickly terminated by acetylcholinesterase, am enzyme locate fin the synaptic cleft. It breaks down to ACh building blocks, acetic acid and choline.

Question 42

Excitation-contraction (E-C) coupling

Answer 42

Transmission of an AP along the sarcolemma causes myofilaments to slide. It causes a rise in intracellular levels of calcium ions that leads to sliding of the filaments