Neuroanatomy Practice Questions

Q: Which of the following is NOT a component of the lower motor neuron pathway?

Peripheral ganglia. The **Lower Motor Neuron (LMN)** is the final common pathway for motor control, consisting of the motor neurons that directly innervate skeletal muscle [1]. The LMN pathway begins in the central nervous system and ends at the neuromuscular junction. ### **Explanation of Options** * **Peripheral Ganglia (Correct Answer):** These are collections of nerve cell bodies located outside the CNS. However, they are primarily associated with the **sensory system** (e.g., Dorsal Root Ganglia) or the **Autonomic Nervous System** (e.g., Sympathetic chain) [2]. They do not carry somatic motor impulses to skeletal muscles and are therefore not part of the LMN pathway. * **Anterior Horn Cell (AHC):** These are the cell bodies of the LMNs located in the ventral gray matter of the spinal cord [2]. They represent the "starting point" of the LMN. * **Anterior Nerve Root:** This is formed by the axons exiting the AHCs [2]. It carries motor fibers before they join with sensory fibers to form a spinal nerve. * **Peripheral Nerve:** This is the continuation of the motor axons as they travel toward their target muscles. Damage at any point along this nerve results in LMN signs. ### **High-Yield Clinical Pearls for NEET-PG** * **LMN Lesion Signs:** Flaccid paralysis, significant muscle atrophy (denervation), fasciculations, and **hyporeflexia/areflexia** (loss of the efferent limb of the reflex arc) [1]. * **Components of LMN:** AHC, cranial nerve motor nuclei, ventral roots, peripheral nerves, and the neuromuscular junction. * **Poliomyelitis:** Specifically targets the **Anterior Horn Cells**, leading to pure LMN paralysis. * **Final Common Pathway:** A term coined by Sherrington to describe the LMN, as all CNS influences on muscle contraction must converge on these cells.

Q: The basal ganglia include all of the following structures, EXCEPT?

Fornix. Explanation: The **Basal Ganglia** (or Basal Nuclei) are a group of subcortical nuclei situated deep within the cerebral hemispheres, primarily involved in the control of posture and voluntary motor movements [1]. **Why Fornix is the Correct Answer:** The **Fornix** is a C-shaped bundle of nerve fibers that acts as the major output pathway of the **limbic system**, connecting the hippocampus to the mammillary bodies. It is involved in memory formation and emotional response, not motor control. Therefore, it is anatomically and functionally distinct from the basal ganglia. **Analysis of Incorrect Options:** * **Caudate Nucleus:** A large, C-shaped mass of grey matter that forms part of the **Striatum** (along with the Putamen). It is a core component of the basal ganglia [1]. * **Globus Pallidus:** Located medial to the putamen, it is divided into internal (GPi) and external (GPe) segments [1]. Together with the putamen, it forms the **Lentiform nucleus** [1]. * **Claustrum:** A thin sheet of grey matter situated between the insula and the putamen. While its exact function is debated, it is embryologically and anatomically classified as part of the basal ganglia. **High-Yield NEET-PG Pearls:** 1. **Corpus Striatum:** Comprises the Caudate nucleus and the Lentiform nucleus [1]. 2. **Functional Basal Ganglia:** Includes the Subthalamic Nucleus (Diencephalon) and Substantia Nigra (Midbrain) [1]. 3. **Blood Supply:** Primarily via the **Charcot’s artery** (Lenticulostriate branches of the Middle Cerebral Artery), which is a common site for hypertensive hemorrhage [1]. 4. **Clinical Correlation:** Degeneration of dopaminergic neurons in the Substantia Nigra pars compacta leads to **Parkinson’s Disease** [1].

Q: The genu of the internal capsule contains which of the following tracts?

Corticonuclear tract. The **internal capsule** is a compact band of white matter fibers situated between the thalamus and caudate nucleus medially, and the lentiform nucleus laterally. It is divided into five parts: anterior limb, genu, posterior limb, retrolentiform, and sublifentiform parts. ### **Explanation of the Correct Answer** The **genu** (meaning "knee") is the bend between the anterior and posterior limbs. It primarily contains the **corticonuclear (corticobulbar) tract** [1]. These fibers originate in the motor cortex and descend to synapse on the motor nuclei of cranial nerves in the brainstem, controlling the muscles of the head and neck [1]. ### **Analysis of Incorrect Options** * **A. Optic radiation:** These fibers carry visual information from the lateral geniculate body to the visual cortex. They are located in the **retrolentiform part** (behind the lentiform nucleus). * **B. Corticospinal tract:** These motor fibers for the limbs are located in the **anterior two-thirds of the posterior limb** [3]. They are organized somatotopically (Upper limb → Trunk → Lower limb) [2]. * **C. Corticorubral tract:** These fibers project from the cortex to the red nucleus and are also located in the **posterior limb**. ### **High-Yield Clinical Pearls for NEET-PG** * **Blood Supply:** The genu is primarily supplied by the **Lenticulostriate arteries** (branches of the Middle Cerebral Artery) and sometimes the **Recurrent artery of Heubner** (branch of the Anterior Cerebral Artery). * **Charcot’s Artery of Cerebral Hemorrhage:** One of the lenticulostriate arteries is prone to rupture in hypertensive patients, often leading to contralateral hemiplegia [4]. * **Posterior Limb Contents:** Contains sensory fibers (thalamocortical), corticospinal fibers, and auditory/visual radiations in its distal parts.

Q: Which of the following cells are not seen in the cerebellar cortex?

Magnocellular cells. The cerebellar cortex is organized into three distinct layers: the **Molecular layer** (outer), the **Purkinje cell layer** (middle), and the **Granular layer** (inner) [1]. ### Why Magnocellular cells is the correct answer: **Magnocellular cells** are not found in the cerebellar cortex. These are large neurons located in the **Red Nucleus** (of the midbrain) and the **Lateral Geniculate Nucleus (LGN)** of the thalamus. In the red nucleus, they give rise to the rubrospinal tract, while in the LGN, they form the magnocellular pathway responsible for detecting motion and depth. ### Why the other options are incorrect: * **Purkinje cells (Option A):** These are the hallmark cells of the cerebellum, located in the middle layer [1]. They are the only cells that provide **inhibitory output** (via GABA) from the cerebellar cortex to the deep cerebellar nuclei [1]. * **Stellate cells (Option B):** These are inhibitory interneurons located in the outer **Molecular layer** [1]. * **Basket cells (Option C):** Also located in the **Molecular layer**, these cells provide powerful inhibitory input to the cell bodies of Purkinje cells [1]. ### High-Yield Facts for NEET-PG: * **Layers of Cerebellar Cortex (Outer to Inner):** Molecular $\rightarrow$ Purkinje $\rightarrow$ Granular. * **Five Cell Types:** Purkinje, Granule, Stellate, Basket, and Golgi cells [1]. * **Excitatory vs. Inhibitory:** All cells in the cerebellar cortex are **inhibitory** EXCEPT for **Granule cells**, which are excitatory (using Glutamate) [1]. * **Afferent Fibers:** **Climbing fibers** (from inferior olivary nucleus) and **Mossy fibers** (from all other sources) are both excitatory [1]. * **Clinical Correlation:** Damage to the cerebellum results in **ipsilateral** symptoms (Ataxia, Hypotonia, Nystagmus, Intention tremor) [1].

Q: What are the findings of trigeminal nerve injury?

Loss of blinking reflex of eye. **Explanation:** The **Trigeminal nerve (CN V)** is the largest cranial nerve and provides sensory innervation to the face and motor innervation to the muscles of mastication. **1. Why Option B is Correct:** The **Blinking (Corneal) Reflex** consists of an afferent and an efferent limb. The **Ophthalmic division (V1)** of the trigeminal nerve carries the afferent (sensory) impulse from the cornea to the brainstem. The **Facial nerve (CN VII)** provides the efferent (motor) limb to the orbicularis oculi muscle. An injury to the trigeminal nerve disrupts the sensory input, resulting in a loss of the blinking reflex when the cornea is touched. **2. Why Incorrect Options are Wrong:** * **A & D (Pupillary dilation and Ptosis):** These are associated with the **Oculomotor nerve (CN III)** or sympathetic chain injury (Horner’s Syndrome). CN III controls the sphincter pupillae (constriction) and levator palpebrae superioris (eyelid elevation). * **C (Normal jaw reflex):** The **Jaw-jerk reflex** is a monosynaptic stretch reflex where both the afferent and efferent limbs are mediated by the **Mandibular division (V3)** of the trigeminal nerve. In a trigeminal nerve injury (specifically the motor root or V3), this reflex would be **absent or diminished**, not normal. **Clinical Pearls for NEET-PG:** * **Trigeminal Neuralgia (Tic Douloureux):** Characterized by stabbing, lancinating pain in the V2 or V3 distribution. * **Muscle Deviation:** In a lower motor neuron lesion of CN V, the jaw deviates **towards the side of the lesion** when opened due to the action of the contralateral lateral pterygoid muscle. * **Mesencephalic Nucleus:** This is the only site in the CNS that contains cell bodies of primary sensory neurons (proprioception for the jaw reflex).

Q: The retina is embryologically and functionally considered a part of which system?

Central Nervous System (CNS). ### Explanation **Why Option A (Central Nervous System) is Correct:** The retina is unique because it is not a peripheral sense organ but an **outgrowth of the forebrain (diencephalon)**. Embryologically, it develops from the **optic vesicle**, which invaginates to form the optic cup. Because it originates from the neural tube, it shares the same structural and functional characteristics as the brain: 1. **Myelination:** The axons of the retinal ganglion cells (which form the optic nerve) are myelinated by **oligodendrocytes**, not Schwann cells [1]. 2. **Meningeal Coverings:** The optic nerve is encased in all three layers of the meninges (dura, arachnoid, and pia mater) [2]. 3. **Blood-Brain Barrier:** The retina possesses a blood-retinal barrier, analogous to the blood-brain barrier [1]. **Why Other Options are Incorrect:** * **Option B (PNS):** Most cranial nerves are part of the PNS. However, the Optic Nerve (CN II) and Olfactory Nerve (CN I) are considered extensions of the CNS [3]. Unlike the PNS, the optic nerve cannot regenerate after significant injury. * **Option C (ANS):** While the ANS (sympathetic and parasympathetic fibers) regulates pupillary size and accommodation, the retina itself is the sensory neural tissue responsible for phototransduction and signal processing, which are CNS functions. **NEET-PG High-Yield Pearls:** * **The Optic Nerve is a Tract:** Because it is part of the CNS, the optic nerve is technically a white matter tract, not a true peripheral nerve [3]. * **Clinical Correlation:** Since the subarachnoid space extends around the optic nerve up to the back of the eye, increased intracranial pressure (ICP) is transmitted directly to the optic disc, leading to **papilledema**. * **Demyelination:** In Multiple Sclerosis (a CNS demyelinating disease), the optic nerve is frequently involved (**Optic Neuritis**), whereas it is spared in Guillain-Barré Syndrome (a PNS disease).

Q: Which of the following nuclei is responsible for upwards gaze?

Nucleus of Cajal. The control of ocular movements is a high-yield topic in Neuro-ophthalmology. To answer this question, one must distinguish between the centers for horizontal and vertical gaze. ### **Explanation of the Correct Answer** **D. Nucleus of Cajal (Interstitial Nucleus of Cajal):** Vertical gaze and torsional eye movements are controlled by centers located in the **midbrain**. The **Interstitial Nucleus of Cajal (INC)** and the **Rostral Interstitial Nucleus of the Medial Longitudinal Fasciculus (riMLF)** are the primary structures responsible. Specifically, the INC plays a crucial role in vertical gaze holding and coordinating upward eye movements. ### **Analysis of Incorrect Options** * **A. Paramedian Pontine Reticular Formation (PPRF):** This is the "horizontal gaze center" located in the **pons**. Lesions here result in the inability to look toward the side of the lesion. * **B. Nucleus Raphe Magnus:** This nucleus is located in the medulla and is primarily involved in the endogenous pain inhibitory pathway (serotonergic system), not ocular motility. * **C. Cuneiform Nucleus:** Located in the mesencephalic reticular formation, it is involved in locomotion and cardiovascular control, but has no direct role in vertical gaze. ### **NEET-PG High-Yield Pearls** * **Horizontal Gaze Center:** PPRF (Pons). * **Vertical Gaze Center:** riMLF and Nucleus of Cajal (Midbrain). * **Parinaud’s Syndrome (Dorsal Midbrain Syndrome):** Characterized by upward gaze palsy, lid retraction (Collier’s sign), and convergence-retraction nystagmus. It often occurs due to pineal gland tumors compressing the superior colliculus and pretectal area. * **MLF (Medial Longitudinal Fasciculus):** Connects the VI nucleus to the contralateral III nucleus; a lesion here causes **Internuclear Ophthalmoplegia (INO)**.

Question 1

Which of the following is NOT a component of the lower motor neuron pathway?

Accepted Answer

Peripheral ganglia

Answer

Anterior nerve root

Answer

Peripheral nerve

Answer

Anterior horn cell

Question 2

The basal ganglia include all of the following structures, EXCEPT?

Accepted Answer

Fornix

Answer

Claustrum

Answer

Globus pallidus

Answer

Caudate

Question 3

The genu of the internal capsule contains which of the following tracts?

Accepted Answer

Corticonuclear tract

Answer

Optic radiation

Answer

Corticospinal tract

Answer

Corticorubral tract

Question 4

Where is the nucleus of the trigeminal nerve located?

Accepted Answer

Pons

Answer

Midbrain

Answer

Medulla

Answer

Cerebellum

Question 5

An unconscious 48-year-old woman is admitted to the hospital. CT scan reveals a tumor in her brain. When she regains consciousness, her right eye is directed laterally and downward, with complete ptosis of her upper eyelid, and her pupil is dilated. Which of the following structures was most likely affected by the tumor to result in these symptoms?

Accepted Answer

Oculomotor nerve

Answer

Optic nerve

Answer

Facial nerve

Answer

Ciliary ganglion

Question 6

Which of the following cells are not seen in the cerebellar cortex?

Accepted Answer

Magnocellular cells

Answer

Purkinje cells

Answer

Stellate cells

Answer

Basket cells

Question 7

What are the findings of trigeminal nerve injury?

Accepted Answer

Loss of blinking reflex of eye

Answer

Pupillary dilation

Answer

Normal jaw reflex

Answer

Ptosis

Question 8

The retina is embryologically and functionally considered a part of which system?

Accepted Answer

Central Nervous System (CNS)

Answer

Peripheral Nervous System (PNS)

Answer

Autonomic Nervous System (ANS)

Answer

None of the above

Question 9

The floor of the fourth ventricle is NOT formed by which of the following structures?

Accepted Answer

Posterior surface of pons

Answer

Sulcus limitans

Answer

Anterior medullary velum

Answer

Posterior surface of medulla

Question 10

Which of the following nuclei is responsible for upwards gaze?

Accepted Answer

Nucleus of Cajal

Answer

Paramedian Pontine Reticular Formation

Answer

Nucleus Raphe Magnus

Answer

Cuneiform nucleus

Neuroanatomy — MCQs

Neuroanatomy — MCQs

On this page

Practice by Chapter

Want unlimited practice?