Neuroscience & Muscle Physiology: Core Concepts Explained

Mutated Acetylcholine Receptors and Muscle Function

If a child is born with a mutated acetylcholine receptor in a muscle cell, the depolarization of the muscle cell membrane will not be initiated, resulting in no intracellular calcium release.

Excitation-Contraction Coupling Mechanism

Excitation-contraction coupling occurs because intracellular calcium is released, allowing myosin to bind to actin, which in turn permits the shortening of myofibrils.

Impact of Spinal Cord Ventral Horn Damage

Damage to the medial ganglion of the ventral horns of the spinal cord primarily affects the movement of the limbs.

Effect of Intracellular Calcium Depletion in Muscle

If intracellular calcium is removed from a muscle fiber, it blocks the excitation-contraction coupling, preventing myosin from binding to actin.

Defining the Homunculus

A homunculus is a somatotopic representation of body parts, often depicted in the brain's sensory and motor cortices.

Understanding Rigor Mortis

If a student finds their deceased hamster cold and stiff, you should explain that its muscles remain contracted due to the absence of ATP. ATP is essential for muscle relaxation, as it allows myosin to detach from actin. Muscle relaxation is not primarily inhibited by a lack of calcium in this context; rather, the sustained contraction is due to the inability to break the actin-myosin cross-bridges without ATP.

Pain Sensitivity Loss After Burns

If a person who suffered a burn asks why they lost sensitivity to pain, you would explain that their free nerve endings, which are responsible for pain perception, have been damaged.

Reflex Response to Stepping on Glass

If you are walking barefoot through the grass and inadvertently step on a piece of glass, the system that reacts is the flexion reflex.

T-Tubules and Calcium Storage

While T-tubules are crucial for conducting action potentials into muscle fibers, the primary reservoir of intracellular calcium in both skeletal and cardiac muscle cells is the sarcoplasmic reticulum. T-tubules facilitate the release of calcium from the sarcoplasmic reticulum.

Aspirin's Analgesic Mechanism

The analgesic action of aspirin is primarily due to the decreased synthesis of proinflammatory molecules, specifically prostaglandins, through the inhibition of cyclooxygenase (COX) enzymes. It does not inhibit the synthesis of capsaicin.

Key Events in Excitation-Contraction Coupling

In excitation-contraction coupling, the following events occur in sequence:

• Neuromuscular transmission (at the neuromuscular synapse)
• Intracellular calcium release from the sarcoplasmic reticulum
• Subsequent events leading to muscle contraction, including myosin binding to actin and the hydrolysis of ATP to power the cross-bridge cycle.

Pain Relief Through Rubbing

If a child asks why rubbing an injured area relieves pain, you can explain that it activates sensory nerve fibers that stimulate inhibitory interneurons in the spinal cord. This mechanism, part of the Gate Control Theory of Pain, effectively "closes the gate" to pain signals, reducing their transmission to the brain.

Components of the Sarcomere

Among the structures forming the sarcomere, key components include thin filaments (actin), thick filaments (myosin), Z-discs, M-lines, and titin, all arranged in a highly organized manner to facilitate muscle contraction.

Morphine's Action on Pain Pathways

The direct action of morphine in the pain pathway is to stimulate the activity of inhibitory interneurons in the spinal cord, thereby reducing the transmission of pain signals.

Function of the Muscle Spindle

The muscle spindle, found within muscles, is a sensory organ that provides feedback to the central nervous system about changes in muscle length and the rate of change of length. It plays a crucial role in proprioception and reflex activity.

Slow Fiber Percentage in Paraplegia

A likely explanation for a paraplegic presenting a minimum percentage of slow-twitch muscle fibers is the lack of sustained muscle movement and weight-bearing activity. Slow fibers are adapted for endurance and are maintained through regular use.

Belgian Blue Bull Muscle Development

The exacerbated muscle development in a Belgian Blue bull is due to a natural genetic mutation that inactivates the myostatin gene. Myostatin is a protein that normally inhibits muscle growth, so its absence leads to increased muscle mass.

NMDA Receptor Activation and Hebb's Theory

NMDA receptor activation aligns with Hebb's theory of synaptic plasticity because it leads to a strengthening of the synapse, a process often associated with learning and memory.

Fight-or-Flight Response and Cardiac Activity

In relation to the fight-or-flight response, there is predominantly sympathetic nervous system activity. This typically leads to an increase in heart rate and contractility, primarily through the release of norepinephrine, not an increase in acetylcholine release in the heart. Acetylcholine is the primary neurotransmitter of the parasympathetic nervous system, which slows heart rate.

Role of the Basal Ganglia

The basal ganglia are involved in the initiation and coordination of movements, as well as the selection and refinement of motor programs.

The Morris Water Maze Test

The Morris water maze is a widely used behavioral task in neuroscience, primarily employed in memory studies. In this test, rodents (typically mice or rats) must learn to find a hidden escape platform submerged in opaque water, assessing spatial learning and memory.

Key Concepts in Synaptic Plasticity

Key concepts related to synaptic plasticity and memory formation include long-term potentiation (LTP), the role of the hippocampus, and the involvement of NMDA receptors.