38 Questions
What is the enzyme responsible for degrading/hydrolysing Ach at the neuromuscular junction?
Acetylcholinesterase
Which venom causes an explosive release of Ach leading to constant muscle contraction and potential respiratory failure?
Black widow spider venom
What effect does Botulinum toxin have on the neuromuscular junction?
Blocks the release of Ach
In comparison to EPSP, why is the end-plate potential (EPP) much larger in magnitude?
Release of more neurotransmitter from a single terminal button
What happens when Ach is not degraded at the NMJ?
Constant muscle contraction leading to respiratory failure
Which compound blocks the action of Ach at receptor channels?
Curare
What is released from the axon terminals at the neuromuscular junction to stimulate muscle contraction?
Acetylcholine
What structure forms when the terminal button of the motor neuron ends on the skeletal muscle fibers?
Motor end plate
Which division of the nervous system controls skeletal muscles and is responsible for conscious movements?
Somatic nervous system
What is the final common pathway for influencing muscle activity by areas like the primary motor cortex and basal nuclei?
Motor neurons
At the neuromuscular junction, what does each skeletal muscle fiber receive from one single motor neuron?
Innervation
Which neurotransmitter is involved in stimulating muscle contraction at the neuromuscular junction?
Acetylcholine
What type of potential is sent down the myelinated axon from the motor neuron to the skeletal muscle?
Action potential
Which component of the neuromuscular junction forms a direct connection with the skeletal muscle fibers?
Muscular component
What specific type of receptor responds to acetylcholine at the neuromuscular junction?
Nicotinic receptor
What is the role of acetylcholine at the neuromuscular junction?
Causing depolarization at the motor end plate
What happens when an axon fiber of a motor neuron loses its myelin sheath and reaches the muscle fiber?
It releases acetylcholine via exocytosis
What is the purpose of voltage-gated calcium channels opening at the neuromuscular junction?
To allow influx of calcium ions leading to Ach release
What effect does acetylcholine have on the motor end plate of skeletal muscle fibers?
Causes depolarization by moving Na+ into the cell and K+ out
Which channel proteins are present at the motor end plate of skeletal muscle fibers for Ach binding?
Nicotinic receptors
What is the main function of Action potentials at the neuromuscular junction?
Triggering exocytosis of vesicles containing Ach
What occurs as a result of an end plate potential (EPP) at the motor end plate?
Opening of voltage-gated sodium channels in adjacent areas of the membrane
What happens when an action potential reaches the axon terminal of a motor neuron?
Voltage-gated calcium channels open, leading to Ach release
What is the primary function of the somatic nervous system?
Control skeletal muscle in conscious movements
Explain the significance of motor neurons being the final common pathway.
Upper brain areas influence muscle activity through motor neurons.
Describe the innervation pattern of motor neurons on skeletal muscle fibers.
One motor neuron can innervate multiple muscle fibers, but each muscle fiber is innervated by only one motor neuron.
What is the structure formed when the axon terminal of a motor neuron connects with a skeletal muscle fiber?
Motor end plate
Explain the role of the neural component at the neuromuscular junction.
The neural component is represented by the terminal button of the motor neuron.
What is the function of the muscular component at the neuromuscular junction?
The muscular component is the motor end plate, where the motor neuron connects to the muscle fiber.
Why can't a single muscle fiber have connections with two neuromuscular junctions?
To ensure coordinated muscle contractions and prevent conflicting signals.
What is the significance of the myelinated axon of a motor neuron in transmitting action potentials?
Fast conduction of action potentials to skeletal muscle fibers.
Explain the role of acetylcholine in muscle contraction at the neuromuscular junction.
Acetylcholine stimulates muscle contraction by binding to receptors on the motor end plate.
What differentiates the function of the somatic nervous system from the autonomic nervous system in muscle control?
The somatic nervous system only causes excitation of muscle fibers, while the autonomic nervous system can cause both excitation and inhibition.
Each skeletal muscle fiber can be innervated by multiple motor neurons.
False
The motor end plate is a structure formed when the axon terminal of a motor neuron connects with a skeletal muscle fiber.
True
Neuromuscular junctions have only a neural component and no muscular component.
False
The myelinated axon of a motor neuron sends action potentials down to smooth muscles.
False
In the neuromuscular junction, one single motor neuron can innervate more than one skeletal muscle fiber.
True
Study Notes
Neuromuscular Junctions (NMJ)
- NMJ consists of multiple terminal buttons, each containing thousands of vesicles to store Ach
- Each terminal button releases more neurotransmitter than a pre-synaptic bulb in response to an action potential
- Motor end plate has a higher surface area and more density of receptors than a post-synaptic membrane, resulting in greater influx of positive ions and larger depolarization
- EPP (end plate potential) is larger than EPSP (excitatory post-synaptic potential)
Somatic Nervous System
- Somatic nervous system is the efferent division that controls skeletal muscle
- 1 motor neuron localized in the ventral horn of the spinal cord
- Myelinated axon sends action potential down to the skeletal muscle
- Axon terminals release Ach to stimulate muscle contraction
- Exception: muscles that control the head are localized in the brain, not spinal cord
- Motor neurons are the final common pathway, influenced by upper areas in the brain such as primary motor cortex and basal nuclei
- Somatic nervous system only produces excitation, whereas autonomic nervous system can produce excitation or inhibition
Chemicals/Agents that Act on NMJ's
- Black widow spider venom causes explosive release of Ach, leading to constant muscle contraction and respiratory failure
- Botulinum toxin blocks release of Ach, preventing muscle contraction and leading to respiratory failure
- Curare blocks action of Ach at receptor channels
- Organophosphates prevent inactivation of Ach, resulting in constant muscle contraction
- Myasthenia gravis inactivates Ach receptor-channels
Motor Units
- Motor unit = 1 motor neuron + all skeletal muscle fibers it innervates
- Process of how information is carried from nerve to muscle fiber:
- Action potential travels along axon fiber of motor neuron
- Axon loses myelin sheath and ends in a terminal button near muscle fiber
- Action potential causes voltage-gated Ca2+ channels to open, releasing Ach via exocytosis
- Ach enables communication between axon terminal and skeletal muscle fiber
- Receptors at motor end plate are nicotinic receptors, causing depolarization and muscle contraction
Explore the process of neurotransmission at the neuromuscular junction, including the influx of Na+ leading to action potential formation and the role of acetylcholinesterase. Learn about the differences between end plate potentials (EPP) and excitatory post-synaptic potentials (EPSP) in neuronal communication.
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