Unit 3 exam:

A band

("a" in dark, mnemonic) contains the zone of overlap, the region where we find thick and thin filaments and where tension is generated during contraction. In the middle of the A band where only thick filaments exist is the H zone (Ha!, mnemonic, H is in the A band). The M line (M is in the middle, mnemonic) is a dark line in the middle of the A band made up of structural proteins

Agonists

(prime movers) provide most force for given muscle action

A lever system includes 3 components:

1) load or resistance, 2) applied force that moves load, 3) pivot point (fulcrum); Changing configuration of these variables leads to lever classes

Actin

Actin is a contractile protein that has active sites that bind with the myosin heads of the thick filament. Two intertwining strands, each of which is composed of actin subunits that bind together like beads on a string.

Ca 2+ channels

Allow ions that trigger neurotransmitter release to diffuse into the axon terminal

How are muscles named?

Based on specific muscle's appearance, size, or position Some muscles have retained historical names that are unrelated to previous ways of deriving name The following highlights some examples of how muscles have been named - Muscles can be named based on their location using the directional terms introduced in Chapter 1 in combination with Greek and Latin word roots. - Muscles can be named based on the anatomical structures where they are attached. - Muscles can be named by the actions that they perform when contracted, which includes flexors, extensors, adductors, abductors, and levators.

Inadequate calcium in the neuromuscular junction would directly affect which of the following processes?

Calcium ions enter the axon terminal when voltage-gated calcium channels open in response to the arrival of an action potential. The presence of calcium causes synaptic vesicles to release acetylcholine into the synaptic cleft.

ACh receptors

Chemically-gated ion channel on the junctional folds to which the neurotransmitter binds

Curare can be used as a skeletal muscle relaxant with general anesthesia for certain types of surgeries. Curare has also been used by South American native peoples as an arrow poison for hunting wild game. How does it work

Curare is a plant extract that can bind to acetylcholine receptors, but in a way that does not cause the chemically-gated channels to open.

Myosin

Each myosin has globular heads at each end linked by intertwining tails. Myosin heads are connected to the tails by a hinge-like neck. Each myosin head has an active site that binds with actin

Which of the following is NOT a role of ATP in muscle contraction? Detaching the cross bridge from actin Energizing the power stroke of the cross bridge Transporting calcium ions into the sarcoplasmic reticulum Exposing myosin binding sites on actin

Exposure of myosin binding sites does not utilize ATP. During excitation-contraction coupling, calcium ions released from the terminal cisterns of the sarcoplasmic reticulum flood into the sarcoplasm. Calcium ions bind to troponin, which changes its conformation to slide tropomyosin away from the myosin binding sites. Therefore, calcium ions, not ATP, are responsible for exposure of the myosin binding sites on actin.

T or F: Myofilaments shorten to produce muscle contractions according to the sliding filament mechanism.

FALSE it is the sarcomere that shortens

synaptic cleft

Gap between the axon terminal and junctional folds

Which of these most likely occurred to change a muscle fiber's membrane potential from -90 mV to -95 mV?

In order for a muscle fiber's membrane potential to change from -90 mV to -95 mV, more positively charged ions left the cell than entered.

The poison ouabain, or arrow poison, blocks the Na+/K+ ATPase pump, preventing proper movement of ions across the membrane. A patient with hypotension (low blood pressure) is being treated with low doses of this poison to help increase blood pressure. How will this help the patient?

It will increase intracellular sodium and increase blood pressure.

Botulinum toxin is used in a clinical setting to weaken muscle for treating spasms and neurological movement disorders. It is also used in cosmetic procedures to prevent wrinkles by paralyzing facial muscles. It is a powerful neurotoxin produced by the bacterium Clostridium botulinum and related species. How does it work?

It works by preventing the release of acetylcholine from the axon terminal.

synpatic vesicles

Membranous sacs in the axon terminal that contain the neurotransmitter acetylcholine

Which ion diffuses into the muscle fiber through the open acetylcholine receptor?

Na+

Neostigmine helps to improve muscle tone and strength. It is sometimes used after surgery to help reverse the effects of muscle relaxants. What does it do

Neostigmine and related drugs prevent the breakdown of acetylcholine by acetylcholinesterase

Which structure of the neuromuscular junction the definition is a chemically-gated ion channel the definition the definition that the neurotransmitter the definition binds to?

Once released from the motor neuron, the neurotransmitter acetylcholine diffuses across the synaptic cleft and binds to an acetylcholine receptors on the junctional folds.

The following are the different arrangements in which fascicles are found in the human body

Parallel, convergent, pennate (unipennate, bipennate, multipennate)

Which of the following is responsible for muscle relaxation?

Relaxation occurs when stimulation of the nerve stops. Calcium is then pumped back into the sarcoplasmic reticulum by active transport breaking the link between actin and myosin. Actin and myosin return to their unbound state causing the muscle to relax. Removal of calcium ions lowers the calcium ion concentration below the threshold for muscle contraction.

Muscle contractions are involved in more than just movement of bones at joint; other functions of muscle contraction include:

Skeletal muscle contractions generate heat as by-product Contraction of diaphragm muscle is vital function associated with respiratory system Skeletal muscles attached to facial skin allow for facial expression and muscles in throat assist with swallowing Sphincters composed of skeletal muscle allow conscious control over opening and closing of body openings

concentration gradient in muscle cells

Sodium and potassium ions move through the sarcolemma using protein channels and carriers. These ions only move by diffusion if a gradient exists between the two regions on either side of the plasma membrane. It is maintained by the sodium potassium pump The pump moves 3 Na+ out and and 2 K+ ions into the cell The activity of the pump creates a high concentration of Na+ in the extracellular fluid, while the concentration in the cytosol remains lower.c. This creates a high concentration of K+ in the cytoplasm, while the concentration in the extracellular fluid remains lower.

What happens when botulinum toxin prevents the release of acetylcholine from the axon terminal? Make a prediction!

The botulinum toxin prevents the release of acetylcholine. Therefore, the junctional folds are not stimulated, the membrane potential remains unchanged, and the muscle fiber will not contract.

Z disc

The disc is found in the middle of the I band and is composed of structural proteins.

axon terminal

The endpoint of a neuron where neurotransmitters are stored

Neostigmine and related drugs prevent the breakdown of acetylcholine by acetylcholinesterase. What happens when neostigmine and related drugs prevent the breakdown of acetylcholine by acetylcholinesterase? Make a prediction!

The junctional folds will remain depolarized and the muscle fiber will remain contracted. The released acetylcholine stays around the junctional folds longer and can activate the acetylcholine receptors multiple times, initiating several action potentials. As a result, the muscle fiber will remain contracted for a longer time.

The pufferfish produces a deadly poison known as tetrodotoxin. Tetrodotoxin blocks the voltage-gated sodium ion channels, preventing sodium ions from entering the sarcolemma. If you consumed pufferfish that was not prepared correctly, in turn digesting tetrodotoxin, what effect would it have on your muscle fibers?

The poison would prevent action potentials from occurring along the sarcolemma. The poison blocks the voltage-gated sodium ion channels, preventing sodium from entering the cytosol, and in turn not allowing the sarcolemma to be depolarized. If the sarcolemma is not depolarized, an action potential will not occur, and the muscle will not contract.

sliding filament mechanism of contraction

The sarcomere extends from one z disc to the next. It is the functional unit where contraction occurs. The sliding filament mechanism explains how tension is generated during muscle contraction. During a contraction, both the I band and the H band narrow, while the A band remains unchanged. Myosin heads attach to actin to pull the thin filaments towards the M line, which brings Z disc closer together, shortening the sarcomere. Sarcomeres are arranged end to end within each myofibril and when simultaneously contracted, contract the whole muscle fiber.

Structure of skeletal muscle

The shape, size, placement, and arrangement of fibers in a skeletal muscle contribute to the function of that muscle. Form follows function

What effect does the diffusion of sodium ions through the chemically-gated ion channels have on the membrane potential across the junctional folds?

The voltage becomes smaller (less negative on the inner surface). (Diffusion of sodium ions into the muscle fiber causes partial depolarization of the junctional folds.)

Stages of creating an action potential

To begin, the membrane is at the resting membrane potential of -85 mV and the sodium and potassium voltage-gated channels are closed. Next, the sodium voltage-gated channel opens in response to a stimulus allowing sodium ions to enter the cell, making the membrane potential more positive. Repolarization of the cell membrane occurs when sodium voltage-gated channels close and potassium voltage-gated channels open, allowing potassium ions to leave the cell. The membrane potential is now negative again.

Tropomyosin

Tropomyosin is a long rope-like regulatory protein that twists around actin, covering up its active sites.

bipennate arrangement of fascicles

a pennate variation, features fascicles that are attached to both sides of the associated tendon.

unipennate arrangement of fascicles

a pennate variation, features fascicles that are only attached to one side of the associated tendon

thin filaments

actin, troponin , tropomyosin

Synergists

aid agonists by supplying supplemental force, minimizing unwanted movement; help stabilize joints

Fixators

also provide stabilizing force that anchors bone

striations in muscle

alternating light (I bands) where only thin filaments are found and dark (A bands) where both thick and thin filaments are found.

sphincters

are circular fascicle arrangements that surround body openings

elastic filaments

are composed of a single massive, spring-like structural protein called titin that stabilizes the myofibril structure and resists excessive stretching force.

Thick filaments

are composed of bundles of myosi

spiral

arrangement is found in muscles that wrap around another structure, such as a bone

fascicles and muscle shapes

bundles of muscle cells; specific arrangement affects both appearance and function of whole skeletal muscle

he myofibril is made of hundreds to thousands of myofilaments. What 3 types of proteins that exist in myofilaments

contractile proteins that generate tension regulatory proteins that dictate when a fiber may contract structural proteins that maintain proper alignment and fiber stability

electrical gradient

difference in electrical charges between the inside and outside of the cell Separation will create kinetic energy

electrical energy

discussed in terms of electrical potentials. The membrane potential of a cell is the electrical potential that exists across the plasma membrane.

Membrane potential

due to an unequal distribution of ions near the plasma membrane resulting in a polarized resting state. Cells are polarized (charged): A thin layer of negatively charged ions exists in the cytosol on the inside of the cell, while a thin layer of positively charged ions exists on the outside of the cell. This separation of charges creates an electrical gradient

resting membrane potential in muscle cell

electrical potential across the sarcolemma of a resting muscle fiber and measures -85 mV. (85 mV more negative than the outside) Resting membrane potentials change when the barrier to ion movement is removed from the plasma membrane.

kinetic energy

flow of electrical charges

Convergent arrangement of fascicles

forms a broad triangular- shaped muscle that tapers down into a single tendon

Pennate arrangement of fascicles

forms a muscle where the fascicles attach to the tendon at an angle giving it a feather-like appearance

Parallel arrangement of fascicles

forms a strap-like muscle with evenly spaced fascicles where muscle and tendon are the same width

first class lever

fulcrum sits between load and applied force; load moved in opposite direction than applied force

multipennate arrangement of fascicles

has several regions of fascicles joined by connective tissue where each section contributes to form a single tendon.

junctional folds of sarcolemma

increases surface area for ACh receptors contains acetylcholinesterase synaptic cleft separates junctional folds and the axon terminal

fusiform

is a muscular shape where the muscle midsection or belly is thicker than each tapered end

tropinin

is a small globular regulatory protein that holds tropomyosin in place and assists with turning contractions on and off.

Which one of the following components stimulates contraction of a skeletal muscle? Select Answer: - synaptic cleft - muscle fiber - motor neuron - acetylcholinesterase

motor neuron

Which of the following proteins is a component of thick filaments?

myosin (Myosin is a contractile protein with a "tail," "neck," and "head" region. Clusters of myosin form thick filaments.)

Binding of acetylcholine to the acetylcholine receptors causes these chemically-gated ion channels to

open

Does the depolarization of the junctional folds cause the voltage-gated sodium channels to open or close? Select the correct answer.

open

What is the functional contractile unit of the myofibril where muscle tension is produced?

sarcomere

Muscle origin and insertion

skeletal muscles begin and end at distinct anatomical locations a. Origin - anchoring point on bone, where skeletal muscle "originates from" b. Insertion-moving end of muscle whose tendon attaches to bone or other structures; usually on far side of joint

Functional groups of muscles

take cooperation of several individual muscles working as group to perform movement (action); roles of different muscles in group (Figure 9.3) agonist, antagonist, synergists, fixators

What will happen when Curare does not cause the chemically-gated channels to open?

the membrane potential remains unchanged and the muscle is prevented from contracting.

3 types of myofilaments

thick, thin, elastic

Antagonists

usually on opposite side of bones and joint where they meet; opposite action of agonist

Na +

voltage gated ion channel on the sarcolemma