exam 3

Place a single word into each sentence to correctly describe the length-tension relationship of skeletal muscles.

In a resting muscle fiber, a sarcomere is normally 2.0 to 2.5 micrometers long. This is the optimum length for producing maximum tension when the muscle contracts. If a muscle fiber is overly contracted, the thick filaments butt against the Z discs. Conversely, if the muscle fiber is overly stretched, there is not enough overlap between the thick and thin myofilaments. Therefore, if the thick and thin filaments do not overlap, very few cross-bridges are formed.

Why is myelin important? Check all that apply.

It speeds up signal conduction in the nerve fiber. It is formed to assist in the regeneration of damaged fibers. It insulates the nerve fiber.

Complete each sentence with the correct word or phrase, then click and drag the sentences to arrange them in the order that explains excitation.

1. An action potential reaches the axon terminal causing voltage-gated Ca²⁺ channels to open. 2. Stimulated by calcium ions, acetylcholine is released into the synaptic cleft via exocytosis. 3. Acetylcholine diffuses across the synaptic cleft before binding to its receptor, which is located on the motor end plate. 4. Acetylcholine receptors function as ligand-gated ion channels. 5. In response to acetylcholine binding, sodium ions move into the muscle fiber causing the membrane potential to rise. 6. When the membrane potential reaches threshold an action potential spreads across the sarcolemma due to the opening of voltage-gated Na⁺ channels.

Complete each statement by using the appropriate word or phrase from the list. Then place the statements in the order of an action potential repolarization event.

1. As the membrane potential rises toward zero, the voltage-regulated sodium channels begin closing which in turn reduces the sodium movement to the ICF. 2. With membrane potentials approaching +35 mV, the voltage-regulated potassium channels become fully activated. 3. Through the activated channels, potassium now flows outwards causing the membrane to repolarize back towards RMP. 4. With a larger duration of activation than sodium channels, the potassium channels allow for a greater movement of potassium to the ECF causing a short period of hyperpolarization.

Place a single word or phrase into each sentence to correctly describe the stages of muscle twitch.

1. Caused by a single stimulus, a quick cycle of contraction and relaxation is called a twitch. 2. The short delay between the stimulus and the onset of the twitch is called the latent period. 3. This is the time required for excitation, excitation-contraction coupling, and tensing of the elastic components of the muscle. 4. The force generated during this time is called internal tension. 5. Once elastic components are taut, the muscle produces external tension. 6. When the external tension moves a load, this is called the contraction phase.

The bond between the active site on actin and the myosin head is broken when an __________.

ATP molecules bind to the myosin head

Myosin heads directly use ______________ to transition to their _____________________ conformation, which enables them ready to bind to actin.

ATP; energized

Complete each sentence with the correct word, then drag the sentences into the correct order to accurately describe the steps of excitation-contraction coupling.

1. Voltage sensitive proteins respond to the action potential that spreads down the T tubule. 2. Voltage-gated calcium ion channels in the terminal cisterns open and release ions into the sarcoplasm. 3. These ions bind to troponin, which forms a complex with tropomyosin. 4. A conformational change in the troponin-tropomyosin complex occurs, revealing active sites on the actin filaments. 5. The myosin heads bind to the active sites and form cross-bridges between the thick and thin filaments.

Place the following structures in the order that an electrical impulse would travel beginning with the post-synaptic membrane.

1. dendrites 2. soma 3. axon hillock 4. internode 5. node of ranvier 6. terminal arborization 7. axon terminals

Place the following excitation-contraction coupling events in the order that they occur.

1. end plate potential reaches threshold 2. action potential sent throughout sarcolemma 3. voltage sensitive DPH receptors are activated 4. comformational changes open RyRI channels 5. release of calcium into sarcoplasm

the sequence of events associated with muscle fiber relaxation

1. exocytosis of neurotransmitter into synaptic cleft ceases. 2. ion channels in the sarcolemma stop opening 3. calcium ions are returned to storage within the muscle fiber 4. the myosin binding sites found on actin are again covered up by tropomyosin

Place these events into the order in which they occur during a single action potential.

1. local potential depolarizes membrane 2. threshold is reached 3. depolarization spike 4. repolarization 5. hyperpolarization

Place the following labels in the proper position to designate what effect each condition would have on membrane physiology.

Makes RMP Less Negative: ATP stores are declining through mitochondrial poisoning (arsenic), increased concentration of leaky sodium channels in membrane, decreased concentration of leaky potassium channels in membrane influences the ability to repolarize: voltage-regulated potassium channels are blocked, Ach esterase concentration is decreased influences the ability to depolarize: release of excitatory neurotransmitter by presynaptic input is blocked, size of synaptic cleft is increased, low ECF sodium, high ECF water concentration, neurotransmitter synthesis is compromised due to Golgi dysfunction in the presynaptic neuron

What is(are) the fundamental physiological properties that enable nerve cells to communicate with other cell

The ability to respond to environmental changes, the ability to produce electrical signals that are quickly conducted to other cells at distant locations, and the ability to secrete a chemical that will stimulate the next cell when an electrical signal reaches the end of a nerve fiber.

Thin filaments connect to and extend from either side of a ___________. These thin filaments are composed largely of the myofilament ____________.

Z disc; actin

Which term describes all neurons that carry signals towards the CNS?

afferent

Muscle contractions are initiated by the binding of __________ to __________.

calcium ions; troponin

If there was a high concentration of acetylcholine within the synaptic cleft, but little to no response at the motor end-plate, you would expect ________________ to be the responsible neuromuscular-blocking agent.

curare

Rigor mortis occurs after death because ____________________.

detachment of crossbridges does not occur due to the lack of ATP Correct

I band

distance between two adjacent A bands

Which of the following is true of interneurons? They cannot process, store, and retrieve information and "make decisions" that determine how the body responds to stimuli. They are contained entirely within the CNS and carry signals from one neuron to another. They carry signals to the central nervous system. They carry signals from the CNS to muscles and glands. They are specialized to detect stimuli such as light, heat, pressure, and chemicals.

They are contained entirely within the CNS and carry signals from one neuron to another.

The presence of calcium in the sarcoplasm is directly responsible for ____________________.

exposing the binding sites on actin

An action potential introduced at the neuromuscular junction is propagated along the sarcoplasmic reticulum. Group starts

false

In response to an action potential entering the neuron, calcium ions diffuse from the sarcolemma into the sarcoplasm.

false

In the brain, neurons are more abundant than neuroglia.

false

The binding of ATP Immediately initiates the sliding of muscle filaments past one another.

false

sarcomere

functional unit of muscle 1 sarcomere length from Z disc to Z disc

Which of the following are effectors? Sense organs Receptors Stimuli Reflexes GlandsCorrect

glands

An inhibitory local potential causes which of the following?

hyperpolarization of the plasma membrane

If it were possible to move the terminal cisternae further away from the T-tubules, it would

interfere with the signal required for the release of calcium from the sarcoplasmic reticulum

Some antidepressant drugs act by inhibiting monoamine oxidase (MAO). What is the function of this enzyme?

it breaks down monoamines

Position the following items in order of decreasing size.

largest-smallest: fascicle, fibers, myofibril, sarcomere, myofilament, f-actin, tropomyosin, troponin, Ca2+

A band

length of a thick filament (myosin)

The antidote that holds the most promise to counteract the effects of tubocurarine is one that _________________________.

modifies acetylcholine receptors so that they bind acetylcholine stronger than tubocurarine

Which of the following is the site of ATP binding and hydrolysis?

myosin

Which of the following happens as actin and myosin filaments slide past each other during muscle contraction?

neither actin nor myosin filaments shorten

Botulinum toxin causes muscle paralysis because ____________________.

no acetylcholine enters the synaptic cleft

Acetylcholine causes an end-plate potential by triggering the ______________________.

opening of sodium channels

Which connective tissue layer bundles muscle fibers together into fascicles?

perimysium

Facial wrinkles, such as glabellar or "frown" lines, appear with aging as a result of natural, repetitive muscle contractions. Botox® helps alleviate the appearance of these wrinkles by _________________.

relaxing the facial muscles that cause the wrinkles

Acetylcholine (ACh) is released from motor neurons and enters the __________________.

synaptic cleft

An action potential enters the depths of a muscle fiber by way of __________.

the t-tubules

Which of the following statements about the "heads" of the myosin molecules is true?

they can attach to different sites on the actin filament

Match each protein with the appropriate filament.

thick filament: myosin, myosin heads thin filament: actin, tropomyosin, troponin, active sites neither: dystrophin

Match each band or line with the type of filament with which it's associated.

thick: M line, H band thin: I band both: A band

The __________ is described as two strands of actin molecules wrapped together.

thin filament

After cross-bridges form, phosphate is released, followed by ADP. Group starts

true

Each myosin protein has a globular head that extends outward from the myosin filament. Group starts

true

In the PNS, unmyelinated fibers are enveloped in Schwann cells.

true

The nerve impulse is an electrical current that travels along dendrites or axons.

true

The sequence of cross-bridge formation and myofilament movement will be repeated as long as calcium ions and ATP are present.

true

The sodium-potassium pump is involved in establishing the resting membrane potential.

true

Unmyelinated nerve fibers (axons) in the PNS are enveloped in Schwann cells.

true

When cross-bridges form, and the muscle fibers contract, the actin myofilament slides past the myosin myofilament.

true

The __________ division carries signals to the smooth muscle in the large intestine.

visceral motor

Place a single word into each sentence to make it correct, then arrange the sentences into a logical paragraph order to describe the process of contraction of a sarcomere.

1. The step in which the muscle fiber develops tension and may shorten is called contraction. It begins after the active site on actin is exposed. 2. The myosin head must have an ATP molecule bound to it to initiate the process. 3. The head extends toward the exposed active site on the thin filament. 4. A cross-bridge is formed by the attachment of the myosin head to the thin filament. 5. The myosin head pushes forward, moving the thin filament toward the M line. This is called the power stroke. 6. Once more ATP binds, myosin will release from the actin and hydrolyze another ATP. This is called the recovery stroke.

Match each neurotransmitter with its action.

Acetylcholine: excites skeletal muscle and inhibits cardiac muscle GABA: most common inhibitory neurotransmitter in the bran Norepinephrine: involved in dreaming, waking, mood. Excites cardiac muscle Dopamine: mood elevation and skeletal muscle control Serotonin: sleepiness, alertness, thermoregulation, mood

Acetylcholine has which effect on the postsynaptic neuron?

Ligand-gated sodium ion channels open and sodium diffuses in.

During depolarization, which of the following statements about voltage-gated ion channels is true?

Na+ gates open before K+ gates.

Which types of glial cells are found in the central nervous system? Check all that apply. Oligodendrocytes Ependymal cells Microglia Astrocytes Schwann cells Satellite cells

Oligodendrocytes Ependymal cells Microglia Astrocytes

Place each label in the proper position to designate the appropriate glial cell.

Oligodendrocytes: form myelin sheath in CNS Ependymal Cells: ciliated cells resembling epithelium, produce and circulate CSF Microglia: macrophages of CNS Astrocytes: most abundant CNS glial cell, multi-functioning cells involved with neurogenesis, scar formation, etc Schwann Cells: form myelin sheath in PNS, insulate neurons and enhance rate of transmission in PNS Satellite Cells: surround and insulate cells of PNS and found around somas

Neurons are classified structurally according to the number of processes extending from the soma. Match each classification to its description.

One axon; multiple dendrites: multipolar neuron One axon; one dendrite: bipolar neurons A single process: unipolar neurons No axon; multiple dendrites: anaxonic neurons

Place a single word or phrase into each sentence to correctly explain the relationship between stimulus intensity and muscle tension.

Subthreshold stimuli produce no muscle contraction. When stimuli reach or exceed threshold, they excite more motor units. The more motor units excited, the stronger the contraction. When multiple motor units are excited, it is termed motor unit summation. When all nerve fibers are stimulated, an increase in stimulus strength will produce no increase in muscle tension.

What happens as a result of ion flow at a presynaptic terminal?

Synaptic vesicles migrate to the plasma membrane and release acetylcholine.

Which of the following statements about the resting membrane potential is true?

The exterior of the cell has a net positive charge and the interior has a net negative charge.

An action potential arriving at the presynaptic terminal causes what to occur?

Voltage-gated calcium ion channels open, and calcium ions diffuse into the cell.

Place a single word or phrase into each sentence to correctly explain the relationship between stimulus frequency and muscle tension.

With low-frequency stimulation, muscle relaxes fully between contractions, resulting in identical twitches per stimulus. As the frequency gets progressively higher, the muscle does not have time to relax in between twitches. Each twitch rides "piggyback" on the previous one, and generates higher tension. This pattern of stimuli causes a sustained fluttering contraction called incomplete tetanus. In a laboratory setting, an even higher stimulus frequency can cause the muscle to exhibit a state of continual contraction, called complete tetanus . Despite this pattern, the whole muscle contracts very smoothly because motor units function asynchronously, allowing some to relax while others contract.

The term "nerve fiber" refers to a(n) __________.

axon