From exams ANAT flashcards

Sensory deficits produced by a left spinal cord hemisection

• Ipsilateral (left-sided) loss: Vibration, proprioception, and discriminative touch below the lesion.

• Contralateral loss: Pain and temperature sensation below the lesion.

Anterolateral (spinothalamic) pathway trajectory for pain transmission

Spinal cord entry via dorsal root → synapse in the dorsal horn → decussation across the anterior white commissure → ascent through the anterolateral funiculus to the thalamus → termination in the postcentral gyrus.

Cortical region responsible for tactile object recognition (stereognosis)

Somatosensory association cortex in the parietal lobe (integrates raw sensory features initially registered by the primary somatosensory cortex / postcentral gyrus).

Visual field defect caused by a right optic tract lesion

Left homonymous hemianopia (loss of the left visual field in both eyes).

Lesion causing selective loss of the right eye's nasal visual field

Damage to the right lateral optic chiasm, typically caused by extrinsic compression from an expanding right internal carotid artery aneurysm.

Arterial supply to key components of the visual pathway

• Retina and optic nerve: Ophthalmic artery
• Optic tract and lateral geniculate nucleus (LGN): Anterior choroidal artery
• Primary visual cortex: Posterior cerebral artery (PCA)

Pattern of retinal fiber decussation at the optic chiasm

• Nasal retinal fibers: Cross the midline to the contralateral optic tract.
• Temporal retinal fibers: Remain uncrossed and proceed into the ipsilateral optic tract.

Corticospinal tract origin and levels of decussation

• Origin: Primary motor cortex (precentral gyrus).
• Lateral corticospinal tract: Decussates at the pyramidal decussation in the caudal medulla.
• Anterior corticospinal tract: Descends uncrossed and decussates near the segmental level of termination.

Corticonuclear (corticobulbar) tract function and target

Connects the primary motor cortex to brainstem cranial nerve motor nuclei to coordinate voluntary movement of the head, face, and neck (does not descend to cervical spinal levels).

Betz cells

Giant pyramidal output neurons situated within layer V of the primary motor cortex (precentral gyrus) that project into the corticospinal tract.

Functional distinction: Premotor cortex vs. Prefrontal cortex

• Premotor cortex: Prepares and organizes movement sequences, often in response to external sensory cues.
• Prefrontal cortex: Governs goal setting, executive planning, working memory, and decision-making.

Embryological and anatomical localization of basal ganglia structures

• Telencephalon: Caudate nucleus, putamen, and globus pallidus
• Diencephalon: Subthalamic nucleus (STN)
• Midbrain: Substantia nigra (pars compacta and pars reticulata)

Basal ganglia indirect pathway mechanism

Striatum inhibits the external globus pallidus (GPe) → subthalamic nucleus (STN) is disinhibited → STN excites the internal globus pallidus/substantia nigra reticulata (GPi/SNr) → GPi/SNr inhibit the thalamus → thalamocortical drive and movement are suppressed.

Substantia nigra pars compacta (SNc) dopamine modulation of movement

Promotes movement by exciting striatal projection neurons in the direct pathway via $D_1$ receptors and inhibiting striatal projection neurons in the indirect pathway via $D_2$ receptors.

Hyperkinetic movement disorders: Chorea, Ballism, and Athetosis

• Chorea: Continuous, rapid, irregular, dance-like involuntary movements.
• Ballism: High-amplitude, violent, flinging limb movements (typically following subthalamic nucleus damage).
• Athetosis: Slow, continuous, writhing involuntary movements, primarily involving the distal extremities.

Cerebellar outflow pathways for vermal and intermediate zones

• Fastigial nucleus (vermis): Projects efferents primarily via the inferior cerebellar peduncle.
• Interposed nuclei (intermediate hemisphere): Project efferents primarily via the superior cerebellar peduncle.

Upper-limb unconscious proprioceptive pathway to the cerebellum

Primary afferents ascend in the fasciculus cuneatus → synapse in the accessory cuneate nucleus → project through the inferior cerebellar peduncle as the cuneocerebellar tract.

Red nucleus function and rubrospinal decussation

Modulates upper-limb motor control (primarily flexor tone). Its rubrospinal efferents cross the midline immediately within the midbrain at the ventral tegmental decussation.

Pupillary light reflex pathway

Retina → optic nerve ($\text{CN II}$) → pretectal area (midbrain) → bilateral Edinger–Westphal nuclei → oculomotor nerve ($\text{CN III}$) → ciliary ganglia → pupillary sphincter constriction (producing consensual response).

Right paramedian pontine reticular formation (PPRF) lesion deficit

Right horizontal conjugate gaze palsy (inability of both eyes to perform conjugate saccades toward the right).

Vestibulo-ocular reflex (VOR) circuit and physiological role

Angular acceleration detected by semicircular canals → vestibular nerve ($\text{CN VIII}$) → vestibular nuclei → medial longitudinal fasciculus (MLF) → abducens/oculomotor nuclei; rotates the eyes opposite head movement to preserve retinal image stability.

Lateral vs. medial vestibulospinal tract functions

• Lateral vestibulospinal tract (LVST): Descends ipsilaterally to activate antigravity extensor muscles for upright balance and posture.
• Medial vestibulospinal tract (MVST): Descends bilaterally through cervical and upper thoracic levels to stabilize head and neck posture.

Semantic memory vs. Episodic memory

• Semantic memory: General conceptual knowledge, vocabulary, and facts independent of personal context.
• Episodic memory: Autobiographical recall of personally experienced events localized to a specific time and place. (Both constitute declarative / conscious memory).

Procedural memory classification and examples

A subtype of non-declarative (implicit), non-conscious memory governing motor performance, habits, and automated motor skills (e.g., riding a bicycle).

Hippocampal declarative memory role and primary efferent path

Consolidates new declarative memories before storage across the cerebral cortex; sends primary output through the fornix to the mammillary bodies, which relay to the anterior thalamus.

Entorhinal cortex function and Wernicke–Korsakoff syndrome pathology

• Entorhinal cortex: Serves as the primary input gateway to the hippocampus and contains grid cells for spatial representation.
• Wernicke–Korsakoff syndrome: Nutritional deficit of thiamine ($\text{vitamin B}_1$) causing hemorrhagic necrosis of the mammillary bodies and medial thalamus.

Anatomical differentiation: Caudate nucleus vs. Lentiform nucleus

• Caudate nucleus: C-shaped mass positioned medially, directly adjacent to the lateral ventricle wall.
• Lentiform nucleus (putamen and globus pallidus): Wedge-shaped structure situated laterally, separated from the caudate by the internal capsule.

Fluid-filled ventricular channels: Midbrain vs. Hindbrain

• Midbrain: Contains the cerebral aqueduct (aqueduct of Sylvius).
• Hindbrain: Contains the fourth ventricle, positioned dorsal to the pons and upper medulla, and ventral to the cerebellum.