Download PDF – RRB PM-UT04 – Anatomy & Physiology Practice Test 4: Nervous & Endocrine Systems

RRB PM-UT04 – Anatomy & Physiology Practice Test 4: Nervous & Endocrine Systems

Q1. Which glial cells form the myelin sheath around axonal projections within the Central Nervous System (CNS)?

A) Schwann cells

B) Oligodendrocytes

C) Microglia

D) Astrocytes

Answer: (B)

Oligodendrocytes are the neuroglial cells responsible for synthesizing and maintaining the myelin sheath around multiple axons within the central nervous system (CNS). In contrast, Schwann cells myelinate solitary axonal internodes within the peripheral nervous system (PNS). Astrocytes provide metabolic support and maintain the blood-brain barrier, while microglia function as resident macrophages.

Q2. What primary physiological event initiates the rapid depolarization phase (Phase 0) of a neuronal action potential?

A) Efflux of potassium ions through delayed rectifier channels

B) Influx of sodium ions through voltage-gated Nav channels

C) Influx of chloride ions through GABA-A receptor channels

D) Active extrusion of calcium ions via PMCA pumps

Answer: (B)

The rapid depolarizing upstroke of a neuronal action potential occurs when the membrane potential reaches threshold (approx. -55 mV), triggering the conformational opening of voltage-gated sodium channels (Nav). The inward drive of Na+ down both its concentration and electrical gradients rapidly shifts the intracellular potential toward +30 mV. Potassium efflux mediates subsequent repolarization.

Q3. Which cranial nerve provides parasympathetic innervation to the thoracic and abdominal viscera up to the splenic flexure of the colon?

A) Glossopharyngeal nerve (CN IX)

B) Facial nerve (CN VII)

C) Vagus nerve (CN X)

D) Oculomotor nerve (CN III)

Answer: (C)

The vagus nerve (cranial nerve X) provides extensive parasympathetic innervation to the thoracic viscera and much of the gastrointestinal tract, extending to approximately the proximal two-thirds of the transverse colon. Parasympathetic supply to the distal colon is mainly from pelvic splanchnic nerves (S2–S4).

Q4. A lesion of Cranial Nerve VII (Facial nerve) at the stylomastoid foramen results in which clinical manifestation?

A) Loss of cutaneous sensation over the forehead and cheek

B) Complete ipsilateral paralysis of the muscles of facial expression

C) Inability to elevate the upper eyelid (ptosis)

D) Deviation of the protruded tongue to the affected side

Answer: (B)

The facial nerve (CN VII) exits the skull through the stylomastoid foramen and supplies the muscles of facial expression through its terminal branches. A lesion at or distal to this region can cause ipsilateral lower motor neuron paralysis of facial-expression muscles, including impaired forehead wrinkling and eye closure. Bell palsy is the term for an acute idiopathic peripheral facial nerve palsy, so a known structural lesion is more precisely described as peripheral facial paralysis.

Q5. Which cranial nerve traverses the cribriform plate of the ethmoid bone to mediate the special sense of olfaction?

A) Optic nerve (CN II)

B) Olfactory nerve (CN I)

C) Trochlear nerve (CN IV)

D) Abducens nerve (CN VI)

Answer: (B)

The olfactory nerve (CN I) comprises unmyelinated primary bipolar sensory axons originating in the olfactory neuroepithelium of the superior nasal vault. These delicate nerve fascicles pass through the tiny foramina of the cribriform plate of the ethmoid bone to synapse directly within the olfactory bulb.

Q6. In a classical monosynaptic deep tendon stretch reflex (such as the patellar tap), what sensory receptor detects the initial muscle stretch?

A) Golgi tendon organ

B) Pacinian corpuscle

C) Muscle spindle (intrafusal fibers)

D) Ruffini ending

Answer: (C)

Muscle spindles are proprioceptive receptors located within skeletal muscles, arranged in parallel with the ordinary extrafusal muscle fibres. They contain intrafusal fibres and detect muscle length and changes in length. A patellar tendon tap stretches the quadriceps muscle spindle, activating group Ia afferents that excite alpha motor neurons in the spinal cord. Golgi tendon organs primarily detect muscle tension.

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