Anatomy Lab 6

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Which of the following is an example of a presynaptic cell?

neuron

What separates the presynaptic and postsynaptic cells at a chemical synapse?

synaptic cleft

Which of the following best describes the role of calcium in synaptic activity?

calcium influx into the synaptic terminal causes vesicle fusion with the plasma membrane and the release of neurotransmitter

What is the role of neurotransmitter at a chemical synapse?

Neurotransmitter binds to receptors on the postsynaptic cell membrane

What mechanism releases neurotransmitter from presynaptic neurons?

exocytosis

What type of channel in the postsynaptic membrane binds neurotransmitter?

chemically gated

What is the primary role of the enzyme acetylcholinesterase (AChE) at a cholinergic synapse?

AChE degrades ACh in the synaptic cleft

Events that occur at cholinergic synapse...

-action potential depolarizes the synaptic terminal
-Ca influx triggers exocytosis of ACh
-ACh binds to receptors on the post synaptic membrane
-ACh is removed by AChE

Action potential propagation in a skeletal muscle fiber ceases when acetylcholine is removed from the synaptic cleft. Which of the following mechanisms ensures a rapid and efficient removal of acetylcholine?

ACh is degraded by acetylcholinesterase (AChE)

The neuromuscular junction is a well-studied example of a chemical synapse. Which of the following statements describes a critical event that occurs at the neuromuscular junction?

ACh is released by axon terminals of the motor neuron

Action potentials travel the length of the axons of motor neurons to the axon terminals. These motor neurons __________.

extend from the brain or spinal cord to the sarcolemma of a skeletal muscle fiber

Calcium entry into the axon terminal triggers which of the following events?

synaptic vesicles fuse to the plasma membrane of the axon terminal and release of ACh

Acetylcholine binds to its receptor in the sarcolemma and triggers __________.

the opening of ligand-gated CATION channels

Sodium and potassium ions do not diffuse in equal numbers through ligand-gated cation channels. Why?

The inside surface of the sarcolemma is NEGATIVELY charged compared to the outside. SODIUM ions diffuse inward along favorable CHEMICAL AND ELECTRICAL GRADIENTS

Excitation-contraction coupling is a series of events that occur after the events of the neuromuscular junction have transpired. The term excitation refers to which step in the process?

Excitation refers to the propagation of action potentials along the sarcolemma

Excitation of the sarcolemma is coupled or linked to the contraction of a skeletal muscle fiber. What specific event initiates the contraction?

Calcium release from the sarcoplasmic reticulum initiates the contraction

A triad is composed of a T-tubule and two adjacent terminal cisternae of the sarcoplasmic reticulum. How are these components connected?

a series of proteins that control calcium release

What is name given to the regularly spaced infoldings of the sarcolemma?

transverse or T tubules

Which of the following is most directly responsible for the coupling of excitation to contraction of skeletal muscle fibers?

calcium ions

What is the relationship between the number of motor neurons recruited and the number of skeletal muscle fibers innervated?

Hundreds of skeletal muscle fibers are innervated by a SINGLE motor neuron

The cross bridge cycle is a series of molecular events that occur after excitation of the sarcolemma. What is a cross bridge?

myosin head bound to actin

What structure is the functional unit of contraction in a skeletal muscle fiber?

sarcomere

Calcium ions couple excitation of a skeletal muscle fiber to contraction of the fiber. Where are calcium ions stored within the fiber?

sarcoplasmic reticulum

After a power stroke, the myosin head must detach from actin before another power stroke can occur. What causes cross bridge detachment?

ATP binds to the myosin head

How does the myosin head obtain the energy required for activation?

hydrolysis of ATP

What specific event triggers the uncovering of the myosin binding site on actin?

Ca ions bind to troponin and change its shape

When does cross bridge cycling end?

when sufficient calcium has been actively transported back into the SR to allow calcium to unbind from troponin

The neuromuscular junction is a connection between a neuron and a __________.

muscle fiber

The end of a neuron, where acetylcholine-filled vesicles are located, is called the __________.

synaptic terminal

synaptic cleft

the space between the synaptic terminal and the motor end plate

Inside a neuron, acetylcholine is contained within __________.

vesicles

What causes the vesicles inside a neuron to fuse with the plasma membrane?

action potential in the neuron

Acetylcholine receptors are primarily located __________.

motor end plate

An action potential in the muscle fiber causes __________.

the muscle fiber to contract

The role of acetylcholinesterase in the neuromuscular junction is to __________.

remove ACh from the synaptic cleft

Inside a muscle, bundles of single muscle fibers form __________.

fascicles

The muscle action potentials that initiate contraction are transmitted from the sarcolemma into the interior of the muscle fiber by __________.

T tubules

T tubules and the terminal cisternae are clustered into structures called __________.

triads

The sarcoplasmic reticulum contains __________.

calcium

Which organelle completely surrounds each myofibril inside a muscle fiber?

sarcoplasmic reticulum

To what regulatory protein does calcium bind during the initiation of the contraction cycle in skeletal muscle fibers?

troponin

Which of the following causes the active site on actin to be exposed or uncovered?

the generation of an action potential in the sarcolemma

Which of the following phrases best describes how excitation is coupled to contraction in skeletal muscle fibers?

through calcium release from the sarcoplasmic reticulum

Malignant hyperthermia (MH) is a rare genetic disease in which the sarcoplasmic reticulum leaks calcium when the patient is put under general anesthesia. Which of the following best describes how anesthesia would affect the skeletal muscles of a patient with MH?

the muscles would contract because of Ca binding to troponin

Myofibrils are __________.

made of a series of sarcomeres

define the edges of which of the following?

sarcomeres

Myosin molecules form what part of the sarcomere?

thick filaments

Which of the following is involved in the power stroke?

myosin

Which of the following proteins contains the active site involved in cross-bridge formation?

actin

When the sarcomere is at rest, what is covering the active sites on actin?

tropomyosin

When calcium is released inside a muscle cell, what does it bind to?

troponin

Myosin molecules form cross-bridges when they attach to __________.

actin

What happens immediately after the myosin head binds to the active site on actin?

the myosin head pivots, moving the actin strand

ATP binding leads to which of the following actions?

detaching and resetting cross-bridges

Which of the following terms are NOT used interchangeably

motor unit- motor neuron

Which of the following is NOT a phase of a muscle twitch?

shortening phase

Where does the acetylcholine that stimulates muscle contraction bind?

receptors in the motor end plate

When acetylcholine binds to its receptors, it results in __________.

the end plate potential, a grade polarization, and a change in ion permeability

Which of the following occurs during the latent period of muscle contraction?

calcium is released from the sarcoplasmic reticulum

As the stimulus voltage was increased in this activity, which of the following occurred?

the muscle force generated increased

Which of the following describes the relaxation phase?

the sarcomeres are increasing in length, and the force generated decreases

Which of the following can trigger a muscle twitch?

release of ACh or electrical stimulation

Which of the following is proportional to the amount of tension produced by a skeletal muscle?

the number of motor units activated

NO force is generated during which of the following?

latent period

What is the minimum voltage needed to generate active force in the skeletal muscle?

threshold voltage

A motor unit is defined as _______.

the axon terminals of a single motor neuron and all of the muscle fibers that it stimulates

In the lab, a researcher finds that the threshold stimulus to induce an action potential in a muscle fiber's sarcolemma was 3.0 volts. Which of the following would result in muscle tension?

3.0 volts and 4.0 volts

Increasing the applied voltage in the simulation corresponds to which in vivo event?

motor unit recruitment

As the stimulus voltage increased, the resulting muscle tension _______.

increased to a point until it reached a plateau

Which of the following occurs during the contraction phase?

cross-bridge cycling is taking place

Treppe is the phenomenon that results in _______.

a progressive increase in the force generated with repetitive stimulation

When the frequency of stimulation of a muscle is great enough, _______.

wave summation results and muscle twitches overlap

When wave summation occurs,

the muscle force generated increases

Why does wave summation occur?

muscle fibers are partially contracted when the next stimulus arrives

Which of the following produced an increase in stimulus intensity?

increasing the voltage applied

Which of the following produced an increase in stimulus frequency?

clicking the mouse in rapid succession

Which of the following does NOT describe treppe?

an increase in stimulus intensity is required to see the effect

tetanus

maximum forced produced has reached a plate, it can be fused, it can be unfused

Which of the following is true of the maximum stimulus frequency?

no greater muscle force can be generated and the muscle has reached maximal tetanic tension

Muscle twitches overlap with _______.

both fused and unfused tetanus

Which of the following would result in fused or unfused tetanus?

increasing the stimulus frequency

To transition from unfused tetanus to fused tetanus, ___________.

stimulus frequency increased

Which of the following describes the relationship between stimulus frequency and muscle tension?

When stimulus frequency increases, muscle tension increases to a maximum value

At what stimulus frequency was maximal tetanic tension developed

146 stimuli/sec

Which of the following occurs if the load attempted is equal to or greater than the force generated by a muscle?

isometric muscle contraction occurs

The resting length of the muscle ________.

Occurs when the muscle is relaxed

The graph of the length-tension relationship illustrates _______.

the optimal sarcomere length for muscle contraction and the amount of overlap between the thick and thin filaments in the resting muscle

Which of the following is generated when cross-bridges form between actin and myosin?

active force can increase or decrease, depending on the stating resting length of the muscle

Why does the active force of skeletal muscle change with the muscle's resting length?

the number of cross bridges between actin and myosin varies

Which starting length of the muscle provided the maximum total force?

the longest starting length

At which muscle length was the passive force the greatest?

100 mm

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