CH. 10 study guide

Where is smooth muscle found?

in the walls of hollow organs like your intestines and stomach

What does "excitation-contraction coupling" mean?

is the process by which an electrical stimulus triggers the release of calcium by the sarcoplasmic reticulum, initiating the mechanism of muscle contraction by sarcomere shortening

what is a skeletal muscle motor unit?

is the term applied to a single motor neuron and all of the muscle fibers that it stimulates

What is skeletal muscle tone? What is the function of skeletal muscle tone?

it is contracted a small amount to maintain its contractile proteins and produce muscle tone. The tension produced by muscle tone allows muscles to continually stabilize joints and maintain posture

how many motor neurons can innervate each skeletal muscle fiber?

its motor units will tend to have small innervation ratios. motor neuron will innervate a small number of muscle fibers enabling movement of the entire muscle

How does smooth muscle differ from skeletal muscle?

smooth muscle is not striated, it is involuntary, and is not under conscious control

Epimysium

surrounds entire muscle

What is the sarcoplasmic reticulum?

the endoplasmic reticulum of a muscle cell

What is meant by Ca2+-induced Ca2+ release in cardiac muscle?

the initial depolarization of the sarcolemmal membrane triggers Ca2+ influx by opening voltage-gated Ca2+ channels

What is a myofilament?

threadlike structures found in myofibrils which aid in contraction, composed of myosin (thick) and actin (thin)

What are T-tubules?

Tunnel-like structures that run deep into the cell. The AP spreads along the membrane and into the t tubules. They allow for rapid delivery of the AP deep inside the cell to the SR.

Why do cardiac muscle fibers have gap junctions?

are protein-lined tunnels, allow direct transmission of the depolarizing current from cell to cell, across the chambers of the heart, so that the cells contract in unison

what is a muscle fiber?

are the cells or basic building block of the muscle

how is the myosin head involved in muscle contraction?

bind actin, forming cross-bridges between the thick and thin filaments. This movement slides the actin filaments from both sides of the sarcomere, shortening the sarcomere and resulting in muscle contraction.

What is a myosin head?

binds with an actin filament

What are fascicles?

bundles of muscle fibers

can a motor neuron innervate more than one skeletal muscle fiber?

can innervate many muscle fibers

What is multi-unit smooth muscle? Where is multi-unit smooth muscle found?

- are composed of cells that rarely possess gap junctions, and thus are not electrically coupled - found in airways to the lungs and large arteries

What happens to the membrane potential when Na+ channels open and Na+ flows down its concentration gradient into a cell? What happens to the membrane potential when K+ channels open, and K+ flows down its concentration gradient out of a cell?

- channels open and Na+ can move through them.At equilibrium: ... The Na+ ions have moved down their concentration gradient until their further movement is opposed by a countervailing electrical potential difference across the membrane

What is the neuromuscular junction?

- point of contact between a motor neuron and a skeletal muscle cell

How is most smooth muscle innervated? What are the neurotransmitters that are used to innervate smooth muscle?

- primarily by the sympathetic nervous system through adrenergic receptors (adrenoceptors) - norepinephrine (NE) and acetylcholine (ACh)

Why is striated muscle striated? what types of muscle are striated?

- result of repeating bands of the proteins actin and myosin that are present along the length of myofibrils - cardiac and skeletal muscle

What is single-unit (or visceral) smooth muscle? What are some characteristics of single-unit smooth muscle?

- type of smooth muscle found in the uterus, gastro-intestinal tract, and the bladder - resistant to fatigue, a rapid onset of contractions, cannot exhibit tetanus, primarily use anaerobic metabolism

How is unfused tetanus different from a muscle twitch? Which generates more tension? Why?

- unfused tetanus is when the muscle fibers do not completely relax before the next stimulus because they are being stimulated at a fast rate; however there is a partial relaxation of the muscle fibers between the twitches - A fused tetanic contraction is the strongest single-unit twitch in contraction.

What is rigor mortis and what causes it?

A fixed muscular contraction after death its caused when ion pumps cease to function (ran out of ATP) and calcium builds up in sarcoplasm

Why is cardiac muscle highly oxidative?

Cardiac muscle cells generate most ATP from the β-oxidation of fatty acids. They are highly dependent on aerobic respiration and do not function well when oxygen supply from coronary arteries is critical

Why doesn't cardiac muscle have wave summation?

Cardiac muscle cells have a long refractory period, this ensures that cardiac muscle tissue can neither summary nor go into tetanus

how do cardiac muscles differ from skeletal muscle cells?

Cardiac muscle is involuntary and found only in the heart. Cardiac muscle is striated, but the bundles are connected at branching, irregular angles called intercalated discs. Skeletal muscle is striated in regular, parallel bundles of sarcomeres.

How is action potential generated?

Caused by an ionic imbalance between the axoplasm and extracellular fluid. Ionic imbalance is d/t the active Na-K-pump.

Perimysium

Connective tissue surrounding a fascicle

Endomysium

Connective tissue surrounding a muscle fiber

What is an isometric muscle contraction?

Contracting and no length change. Stabilizes muscles

muscle fiber

E

What is tropomyosin and what does it do?

It is a double stranded protein that covers active sites on actin, preventing myosin from binding to actin when muscle fibers rest

Fasicle

R

How do skeletal muscle motor units for fine control differ from those used for gross motor skills?

Small α motor neurons innervate relatively few muscle fibers and form motor units that generate small forces, whereas large motor neurons innervate larger, more powerful motor units

Endomysium

T

What are dense bodies in smooth muscle?

The actin filaments of contractile units are attached to dense bodies.

Ca2+ for contraction of smooth muscle comes from the extracellular fluid. Why is this possible?

The calcium that enters the cell from extracellular sources also diffuses into the cytoplasm of the cell and participates in smooth muscle contraction

What is a cross bridge?

The connection of a myosin head group to an actin filament during muscle contraction (the sliding filament theory).

how does the release of Ca2+ from the sarcoplasmic reticulum result in muscle contraction?

The depolarization of the sarcolemma stimulates the sarcoplasmic reticulum to release Ca2+, which causes the muscle to contract

What is wave summation?

When a muscle receives a 2nd stimulus before the 1st is complete, the contraction will be stronger.

Perimysium

X

What is troponin?

a regulatory protein that moves tropomyosin aside & exposes myosin binding sites when Ca+ is released during muscle contraction

Cardiac muscle has a relatively long action potential? Explain.

a sustained depolarization "plateau." This sustained depolarization provides for a longer contraction

skeletal muscle a) where is it found? b) what it looks like? c) whether it is under voluntary or involuntary control?

a) found between bones, and uses tendons to connect the epimysium to the periosteum, or outer covering, of bone b) arranged in bundles surrounded by connective tissue. appear striated with many nuclei squeezed along the membranes c) voluntary

smooth muscle a) where is it found? b) what it looks like? c) whether it is under voluntary or involuntary control?

a) in the gut and other internal organs b) are spindle-shaped (wide in the middle and tapered at both ends, somewhat like a football) c) involuntary

cardiac muscle a) where is it found? b) what it looks like? c) whether it is under voluntary or involuntary control?

a) located in the walls of the heart b) appear striated, appear spindle-shaped c) involuntary

Briefly describe excitation- contraction coupling in smooth muscle. a)What is calmodulin and what role does it play in excitation- contraction coupling in smooth muscle? b) What is caldesmon? c) What is myosin light-chain kinase?

a) smooth muscle cell does not contain enough calcium to maintain contraction for long periods of time. Once four Ca++ ions bind to the calmodulin, the Ca-calmodulin complex binds to the myosin light chain kinase and activates it b) a protein that in humans is encoded by the CALD1 gene. Caldesmon is a calmodulin binding protein. Like calponin, caldesmon tonically inhibits the ATPase activity of myosin in smooth muscle c) a calcium/calmodulin-dependent serine/threonine kinase, in order to facilitate myosin binding to *actin and therefore aid contractility

A skeletal muscle twitch is composed of a) a latent period, b) a period of contraction, and c) a period of relaxation. What happens during each of these periods?

a) the very short period of time between when the muscle receives the electrical impulse from the nerve b) the time during which tension develops in the muscle c) is the time during which tension is removed from the muscle

Briefly list and describe several local factors that are responsible for regulation of smooth muscle contraction.

action potentials are unique in that membrane potential acts to initiate or modulate contraction. As such graded membrane response can be stimulated by multiple factors including local humoral factors, circulating hormones, or mechanical stimulation like stretching of the cells

What is a sarcomere?

contractile unit of a muscle fiber

What is the sarcoplasm?

cytoplasm of a muscle cell

what is the difference between direct attachment and indirect attachment?

direct: takes place when muscle undergoes contraction. the epimysium of muscle is attaches to perimysium of the bone indirect: the connective tissue of the muscle extends as a tendon. These tendons anchor the muscle to bones

What is an eccentric muscle contraction?

lengthening of muscle

What are intercalated discs?

microscopic identifying features of cardiac muscle. support synchronized contraction of cardiac tissue

Functions of skeletal muscle

movement, posture, heat production

What is an concentric contraction?

muscle shortens

where are myosin binding sites located?

on the myosin head

How are precise, smooth movements attained?

place electrons around the target nerve instead of penetrating them

What is the sarcolemma?

plasma membrane of a muscle cell

Where does the action potential travel after it reaches the muscle from the neuron?

reaches the end of an axon, the axon releases chemicals called neurotransmitters. Neurotransmitters travel across the synapse between the axon and the dendrite of the next neuron. The binding allows the nerve impulse to travel through the receiving neuron

what triggers contraction in a skeletal muscle fiber?

release of calcium ions

Muscle origin and insertion

skeletal muscles begin at the origin (doesn't move) and end at the origin (which moves)