A & P I muscle physiology lab
Neuromuscular junction at rest
-No Na+ diffusion, chemically-gated channels closed, calcium channels closed, more negative charges inside sarcolemma, Ach in synaptic vesicles
Rank the sequence of events at the NMJ that initiate an action potential in the muscular fiber, from first to last.
1. Action potential arrives at the axon terminal 2. Calcium ions enter the axon terminal 3. Synaptic vesicles fuse to membrane of axon terminal 4. Acetylcholine is released into the synaptic cleft 5. Acetylcholine binds to its receptors on the junctionAl folds 6. Junctional folds become depolarized 7. Action potential is initiated on the sarcolemma
Acetylcholine
A neurotransmitter that enables learning and memory and also triggers muscle contraction
In a neuromuscular junction, synaptic vesicles in the motor neuron contain which neurotransmitter?
Acetylcholine (ACh)
Neuromuscular junction active
Ach in synpatic cleft, chemically-gated channels open, less negative charges inside sarcolemma, Na+ diffusion, calcium channels open
What causes the release of calcium ions into the sarcoplasm from the terminal cisterns?
An action potential traveling along the t tubule
The binding of the neurotransmitter to receptors on the motor end plate causes which of the following to occur?
Binding of the neurotransmitter causes chemically gated sodium channels to open in the motor end plate (junctional folds of the sarcolemma) and sodium enters the cell.
The sarcoplasmic reticulum contains
Calcium
Which of the following is responsible for preventing a muscle from contracting?
Calcium ions are removed from the sarcoplasm by active transport
Which of the following is NOT a role of ATP in muscle contraction?
Exposing myosin binding sites on actin
Inadequate calcium in the neuromuscular junction would directly affect which of the following processes?
Release of acetylcholine from the synaptic vesicles
The muscle action potentials that initiate contraction are transmitted from the sarcolemma into the interior of the muscle fiber by ___.
T tubules
conduct(s) action potentials throughout the interior of the muscle fiber.
T-tubule
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 calcium binding to troponin.
What happens immediately after the myosin head binds to the active site on actin?
The myosin head pivots, moving the actin strand.
Synaptic cleft
The narrow gap that separates the presynaptic neuron from the postsynaptic cell.
acetylcholine receptor
a type of chemically-gated ion channel located on the junctional folds of the muscle fiber.
Calcium channel
a type of voltage-gated ion channel located on the axon terminal.
Sodium channel
a type of voltage-gated ion channel located on the sarcolemma of the muscle fiber.
A myosin head binds to which molecule to form a cross bridge?
actin
Myosin molecules form cross-bridges when they attach to
actin
Which of the following proteins contains the active site involved in cross-bridge formation?
actin
What causes the release of calcium from the terminal cisternae of the sarcoplasmic reticulum within a muscle cell?
arrival of an action potential
What causes the myosin head to disconnect from actin?
binding of ATP
ATP binding leads to which of the following actions?
detaching and resetting cross-bridges
Conduction of an action potential along the sarcolemma depends upon ___________.
diffusion of sodium ions through voltage-gated channels
Acetylcholinesterase
enzyme that breaks down acetylcholine
What means of membrane transport is used to release the neurotransmitter into the synaptic cleft?
exocytosis
Inside a muscle, bundles of single muscle fibers form __________.
fascicles
receive(s) stimulus from the motor neuron.
junctional folds
Myofibrils are
made of a series of sarcomeres
What structure most directly stimulates a skeletal muscle fiber to contract?
motor neuron
Which of the following is involved in the power stroke?
myosin
What causes the power stroke?
release of ADP and Pi
Z lines define the edges of which of the following?
sarcomeres
Which organelle completely surrounds each myofibril inside a muscle fiber?
sarcoplasmic reticulum
How is acetylcholine (ACh) removed from the synaptic cleft?
simple diffusion away from the synaptic cleft and acetylcholinesterase (AChE; an enzyme)
synaptic vesicle
storage site for neurotransmitters
release(s) calcium ions into the sarcoplasm.
terminal cistern
The action potential on the muscle cell leads to contraction due to the release of calcium ions. Where are calcium ions stored in the muscle cell?
terminal cisterns (cisternae) of the sarcoplasmic reticulum
Which of the following most correctly describes excitation in the context of excitation-contraction coupling in skeletal muscle?
the generation of an action potential in the sarcolemma
Myosin molecules form what part of the sarcomere?
thick filament
Which of the following phrases best describes how excitation is coupled to contraction in skeletal muscle fibers
through calcium release from the sarcoplasmic reticulum
T tubules and the terminal cisternae are clustered into structures called __________.
triads
When the sarcomere is at rest, what is covering the active sites on actin?
tropomyosin
blocks binding sites on actin
tropomyosin
Which of the following causes the active site on actin to be exposed or uncovered
tropomyosin shifting position
The binding of calcium to which molecule causes the myosin binding sites to be exposed?
troponin
To what regulatory protein does calcium bind during the initiation of the contraction cycle in skeletal muscle fibers?
troponin
When calcium is released inside a muscle cell, what does it bind to?
troponin
change(s) shape upon binding with calcium ions.
troponin
When an action potential arrives at the axon terminal of a motor neuron, which ion channels open?
voltage-gated calcium channels