Neuromuscular Synapse & Muscle Physiology Flashcards
The points of contact between neurons where information is passed from one neuron to the next.
SYNAPSE
An action potential in the presynaptic cell causes __________ of the presynaptic terminal
depolarization
As a result of the depolarization, Ca 2+ enters the presynaptic terminal, causing release of
_______________ into the synaptic cleft
neurotransmitter
Neurotransmitter diffuses across the synaptic cleft and combines with receptors on the postsynaptic cell membrane, causing a change in its permeability to ions and, consequently, a change in its ________________
membrane potential
____________ neurotransmitters hyperpolarize the postsynaptic membrane: ____________ neurotransmitters depolarize the postsynaptic membrane.
INHIBITORY; EXCITATORY
It is the synapse between axons of motoneurons and
skeletal muscle.
NEUROMUSCULAR JUNCTION
(In Neuromuscular transmission) The neurotransmitter released from the presynaptic terminal is ____, and the postsynaptic membrane contains a ____________ receptor.
ACh, nicotinic
(In Neuromuscular transmission) ________________ catalyzes the formation of ACh from acetyl coenzyme A (CoA) and choline in the presynaptic terminal.
Choline acetyltransferase
(In Neuromuscular transmission) In the synthesis of ACh in the presynaptic terminal, ACh is stored in ______________ with ATP and proteoglycan for later release.
synaptic vesicles
(In Neuromuscular transmission) When action potentials are conducted down the motoneuron, depolarization of the presynaptic terminal opens ______ channels.
Ca 2+
(In Neuromuscular transmission) Ca 2+ uptake causes release of ACh into the___________
synaptic cleft.
(In Neuromuscular transmission) Diffusion of ACh to the _____________ (muscle end plate) allows binding of ACh to nicotinic receptors.
postsynaptic membrane
What is EPP (that is not an action potential, but simply a depolarization of the specialized muscle end plate)?
End plate potential
(In Neuromuscular transmission) The EPP is transient because ACh is ____________ to acetyl CoA and choline by ____________ (AChE) on the muscle end plate.
degrade, acetylcholinesterase
It is the most potent of neurotoxins that blocks presynaptic release of the neurotransmitter (acetylcholine) at the neuromuscular junction.
Botulinum toxin
It is a neurotoxin that competes with Ach for receptors on motor end plate, decreasing the size of the EPP
Curare
Acetylcholine (ACh) is made from ______ and _________
choline, acetyl COA
Type of synaptic transmission that is found at the neuromuscular junction
One-to-one synapse
As an example, many cells synapse on the postsynaptic cell to depolarize it to threshold, producing an action potential. What ty[e of synaptic transmission is this?
Many-to-one synapses
The postsynaptic cell integrates excitatory and inhibitory inputs. When the sum of the input brings the membrane potential of the postsynaptic cell to
threshold, it fires an ______________.
action potential
It is a postsynaptic potential that depolarize the postsynaptic cell, bringing it closer to threshold and closer to firing an action potential.
Excitatory postsynaptic potentials (EPSPs)
It is a postsynaptic potential that hyperpolarize the postsynaptic cell, moving it away from threshold and farther from firing an action potential; caused by opening Cl- channels.
Inhibitory postsynaptic potentials (IPSPs)
It is a chemical messenger, transmitting messages between neurons, or from neurons to muscles.
Neurotransmitters
A neurotransmitter that PROMOTES the generation of an electrical signal called an action potential in the
receiving neuron
Excitatory neurotransmitter
A neurotransmitter that PREVENTS the generation of action potential
Inhibitory neurotransmitter
What are the adrenergic receptors?
alpha-1, alpha-2, beta-1, and beta-2 receptors
Give some examples of EXCITATORY neurotransmitters
Glutamate
Aspartate
Nitric Oxide
Give some examples of INHIBITORY neurotransmitters
Glycine
GABA
Serotonin
Give some examples of neurotransmitters that act BOTH as excitatory and inhibitory
Acetylcholine
Norepinephrine
Dopamine
It is an inhibitory neurotransmitter that is present in high concentrations in the BRAIN STEM, being converted to melatonin in the pineal gland.
SEROTONIN
A neurotransmitter present in the neurons of the HYPOTHALAMUS (involved in allergic reactions)
HISTAMINE
A neurotransmitter prominent in MIDBRAIN neurons (correlated with Parkinson’s disease and schizophrenia)
DOPAMINE
The loss of dopaminergic neurons cause this disease
Parkinson’s disease
Increased levels of dopamine receptors is correlated to this disease
Schizophrenia
The primary transmitter released from postganglionic sympathetic neurons, which binds with α or β receptors on the postsynaptic membrane
NOREPINEPHRINE
It is synthesized from norepinephrine that binds with α or β receptors on the postsynaptic membrane
EPINEPHRINE
The most prevalent excitatory neurotransmitter in the brain, which binds to ionotropic receptors (ligand-gated ion channels) including the NMDA (N-methyl-D-aspartate) receptor.
GLUTAMATE
It is an inhibitory neurotransmitter that is synthesized from glutamate
GABA (Gamma-aminobutyric acid)
An inhibitory neurotransmitter found primarily in the SPINAL CORD and BRAIN STEM, which increases Cl− conductance.
GLYCINE
A primarily INHIBITORY neurotransmitter (and excitatory as well) in the GI tract, blood vessels, and the central nervous system; a PERMEANT GAS that diffuses from the presynaptic terminal to its target cell
NITRIC OXIDE
These are the three types of muscle tissue in the body.
Skeletal muscle
Smooth muscle
Cardiac muscle
It is striated, multi-nucleated, and usually attached to skeleton (voluntary).
SKELETAL MUSCLE
It is non-striated, spindle-shaped, uninucleated, and usually covering wall of internal organs (like GI tract, kidney, etc.) (Involuntary).
SMOOTH MUSCLE
It is striated, branched, uninucleated, and only covering walls of heart (Involuntary).
CARDIAC MUSCLE
The contractile proteins (that enable muscle contraction) are arranged in repeating subunits known as _____________. They give the skeletal muscle cells their striated appearance when viewed with a light microscope.
sarcomeres
A skeletal muscle is a group of muscle _________, which then consist of muscle _______ (that also consist of _________).
fascicles, fibers, myofibrils
Each muscle fiber is multinucleate and behaves as a single unit. It contains bundles of myofibrils, surrounded by _________ and invaginated by
____________.
sarcoplasmic reticulum (SR), transverse tubules (T tubules)
______ filaments: present in the A band in the center of the sarcomere. They contain myosin.
Thick
The myosin heads bind ______ and _____ and are involved in cross-bridge formation.
ATP, actin
It is a filament anchored at the Z lines and present in the I bands, containing actin, tropomyosin, and troponin.
Thin
It is a regulatory protein that permits cross-bridge formation when it binds Ca 2+.
Troponin
It is a troponin molecule that attaches the troponin complex to tropomyosin.
Troponin T
It is a troponin molecule that inhibits the interaction of actin and myosin.
Troponin I
It is a troponin molecule that binds with Ca 2+, permitting the interaction of actin and myosin.
Troponin C
It is an extensive tubular network, open to the extracellular space, that carries the depolarization from the sarcolemmal membrane to the cell interior.
Transverse tubules (T tubules)
The depolarization carried by T tubules cause a conformational change in the ____________ receptor, a voltage-sensitive protein.
dihydropyridine
It is an internal tubular structure that is the site of Ca 2+ storage and release for excitation–contraction coupling. It has terminal cisternae that make intimate contact with the T tubules in a triad arrangement.
Sarcoplasmic reticulum (SR)
The sarcolemmal membrane contains Ca2+ -ATPase (_________), which transports Ca 2+ from intracellular fluid into the SR interior, keeping intracellular [Ca 2+ low.].
Ca 2+ pump
It is is an essential process in muscle physiology, responsible for linking electrical signals from the somatic nervous system (action potentials) to mechanical muscle contractions
Excitation-contraction coupling (ECC)
[Steps in excitation–contraction coupling in skeletal muscle]
___________ in the muscle cell membrane initiate depolarization of the T tubules.
Action potential
[Steps in excitation–contraction coupling in skeletal muscle]
Depolarization of the T tubules causes a ____________ in its dihydropyridine receptor, which opens Ca 2+ release channels (ryanodine receptors) in the nearby SR, causing release of Ca 2+ from the SR into the _____________.
conformational change, intracellular fluid
[Steps in excitation–contraction coupling in skeletal muscle]
Ca 2+ binds to __________ on the thin filaments, causing a conformational change in troponin
that moves _________ out of the way.
troponin C, tropomyosin
The cross-bridge cycle repeats as long as ______ is bound to __________. Each cross-bridge cycle “walks” myosin further along the actin filament.
Ca2+, troponin C
As long as intracellular Ca 2+ concentration is low, cross-bridge cycling _________ (can, cannot) occur.
cannot
When intracellular Ca 2+ concentration decreases, Ca 2+ is released from troponin C, and tropomyosin again ________ the myosin-binding site on actin.
blocks
What mechanism does it explain when muscles do not relax and are stimulated repeatedly, releasing more Ca2+ from the SR, producing a cumulative increase in intracellular [Ca 2+], and extending the time for cross-bridge cycling?
Mechanism of tetanus
This is a type of muscle tissue that has thick and thin filaments that are not arranged in sarcomeres; therefore, it appears homogeneous rather than striated.
Smooth muscle
The most common type of smooth muscle that is present in the uterus, gastrointestinal tract, ureter, and bladder. It has a high degree of electrical coupling between cells and, therefore, permits coordinated
contraction of the organ (e.g., bladder)
Unitary (single-unit) smooth muscle
The type of smooth muscle that behaves as separate motor units and has little or no electrical coupling between cells. It is densely innervated; contraction is controlled by neural innervation (autonomic nervous
system) and is present in the iris, ciliary muscle of the lens, and vas deferens.
Multiunit smooth muscle
It is a type of smooth muscle that has properties of both multiunit and single-unit smooth muscle.
Vascular smooth muscle
[Steps in excitation–contraction coupling in smooth muscle]
There is no troponin; instead, ______ regulates myosin on the thick filaments.
Ca 2+
[Steps in excitation–contraction coupling in smooth muscle]
Ca 2+ binds to calmodulin. The Ca 2+–calmodulin complex binds to and activates _________________. When activated, myosin light chain kinase ____________ myosin and allows it to bind to actin, thus initiating cross-bridge cycling.
myosin light chain kinase, phosphorylates
Which characteristic or component is shared by skeletal muscle and smooth muscle?
(A) Thick and thin filaments arranged in sarcomeres
(B) Troponin
(C) Elevation of intracellular [Ca 2+ ] for excitation–contraction coupling
(D) Spontaneous depolarization of the membrane potential
C
Which of the following causes rigor in skeletal muscle?
(A) Lack of action potentials in motoneurons
(B) An increase in intracellular Ca 2+ level
(C) A decrease in intracellular Ca 2+ level
(D) An increase in adenosine triphosphate (ATP) level
(E) A decrease in ATP level
E
Where can you find multi-unit type of smooth muscles?
A. Duodenum
B. Sperm Duct
C. Aorta
D. Kidney
B
Choose the purely excitatory neurotransmitter:
A. Glycine
B. GABA
C. Glutamate
D. Acetylcholine
C
