BI2231 - Physiology: Neuromuscular System

Comprehensive flashcards derived from the BI2231 Neuromuscular System lecture, covering reflex arcs, synaptic transmission, movement types, and motor control pathways.

In a somatic reflex, which axons act as afferents and which act as efferents?

Afferents are Ia axons and efferents are eta axons.

What is the function of the Golgi tendon organ in the somatic reflex?

It uses Ib axons to detect active shortening and transmit information to the spinal cord to inhibit motor neurons of the extensor and stimulate motor neurons of the flexor muscle.

Which specific axons are involved as afferents in the flexion-withdrawal reflex?

The afferents are Aeta axons originating from nociceptors/cutaneous receptors for sharp pain.

What is the role of Perisynaptic Schwann cells (Teloglia) at the Neuromuscular Junction (NMJ)?

They play a role in NMJ synaptogenesis, maintenance, and transmission.

How is the "innervation ratio" defined in the neuromuscular system?

The total number of muscle fibers innervated by a single motor neuron, which typically ranges from $5$ to $2000$.

What happens when Acetylcholine (ACh) binds to nicotinic receptors in the muscle?

Activation of the AChR depolarizes the muscle plasma membrane and activates Na+ channels.

Describe the basic structure of the muscle nicotinic ACh receptor (nAChR).

It is an ionotropic ligand-gated sodium channel composed of subunits where alpha is considered the principal subunit.

What are the six steps of excitation-contraction coupling at the nerve presynapse?

1. Action potential-driven depolarization, 2. Ca2+ influx to presynapse, 3. Vesicle-fusion with the plasma membrane, 4. ACh release from vesicles, 5. ACh binding to nAChRs in muscle, 6. Na+ influx at motor end plate.

What role does the ryanodine receptor (RyR) play in motor end-plate excitation-contraction coupling?

The RyR induces the release of Ca2+ from the Sarcoplasmic Reticulum (SR) following a local release (Ca2+ spark), which sums to create a signal for contraction.

What are the three classifications of body movement based on neuronal control?

1. Postural reflex movement, 2. Voluntary movement, 3. Rhythmic movement.

Why are postural reflexes considered "higher-order" than autonomic reflexes?

Because they involve the midbrain, integrating peripheral and central nervous systems for righting reflexes and equilibrium reactions.

Which parts of the vestibular apparatus estimate head angular velocity versus linear acceleration?

The semicircular ducts (Anterior, Posterior, Lateral) estimate head angular velocity, while the Otoliths (Utricle and Saccule) estimate head linear acceleration (gravity and translational).

Which cranial nerve transmits head movement information to the Vestibular Nuclei (VN) and Vestibular Cerebellum?

The CNVIII (Vestibulocochlear nerve).

Identify the three major phases of voluntary movement and the structures associated with them.

1. Planning (Basal ganglia, Association cortex, Cerebellum), 2. Initiating (Cerebellum, Motor cortex), 3. Executing (Motor cortex).

What are the four primary functions of the Basal ganglia?

1) Planning and programming of movement, 2) Selection and suppression of movement, 3) Execution of automatic patterns, 4) Scaling of motor output.

What is the anatomical composition of the Basal ganglia?

It consists of the Striatum (Caudate Nucl. and Putamen), Lenticular Nucl. (Gl. Pallidus and Putamen), Substantia Nigra (midbrain), and Subthalamic Nucl. (diencephalon).

Identify the three functional divisions of the Cerebellum and their roles.

1. Vestibulocerebellum (Equilibrium and eye movement), 2. Spinocerebellum (Motor execution and limb movement), 3. Cerebrocerebellum (Preparation, initiation, and refinement of voluntary output).

Compare the functions of the lateral and anterior corticospinal tracts.

The lateral corticospinal tract controls fine, non-postural movement (e.g., fingers), whereas the anterior corticospinal tract controls movement involving core muscles.

What is the difference between the Vestibulospinal and Rubrospinal extra-pyramidal pathways?

The Vestibulospinal tract is a medial brainstem pathway controlling axial and proximal muscles; the Rubrospinal tract is a lateral brainstem pathway controlling distal muscles.

How is proprioception information transmitted to the somatosensory cortex?

Via muscle, joint, and skin receptor afferents (Ia , III) traveling through ipsilateral white columns, the medial lemniscus, and the thalamus to Brodmann a

What are the three anatomical levels in the nervous system that control voluntary movement?

The Cerebrum, Cerebellum, and Brain stem.

Define a Central Pattern Generator (CPG) in rhythmic movement.

Neural centres that generate pattern locomotion; while individual neurons fire non-rhythmically, rhythmic patterns arise from their coupling via reciprocal inhibition.

What do the acronyms MLR and PMRF stand for in the context of motor command regions?

MLR stands for Mesencephalic motor region and PMRF stands for Pontomedullary reticular formation.