Exam Number 3 Nervous system and Special Senses

Comprehensive vocabulary flashcards covering the cranial nerves, autonomic nervous system divisions, sensory and motor pathways, reflex arcs, eye anatomy, visual circuits, and lacrimal apparatus.

Olfactory Nerve (CN I)

Sensory cranial nerve attached to the olfactory bulb; mediates smell and the afferent salivary reflex to smell.

Optic Nerve (CN II)

Sensory cranial nerve attached to the diencephalon; mediates vision and the afferent pupillary light reflex.

Oculomotor Nerve (CN III)

Motor cranial nerve originating in the midbrain; governs pupillary constriction, accommodation, and the efferent pupillary light reflex.

Trochlear Nerve (CN IV)

Motor cranial nerve originating in the midbrain; innervates the superior oblique muscle of the eye to direct ocular movement.

Trigeminal Nerve (CN V)

Mixed cranial nerve originating in the pons; provides sensory innervation to the face, drives chewing, and conducts the afferent corneal blink reflex as well as afferent and efferent jaw jerk reflexes.

Abducens Nerve (CN VI)

Motor cranial nerve originating at the junction of the pons and midbrain; controls lateral abduction of the eye.

Facial Nerve (CN VII)

Mixed cranial nerve originating at the junction of the pons and midbrain; controls muscles of facial expression, tear production, efferent corneal blink reflex, and salivary reflexes to taste or smell.

Vestibulocochlear Nerve (CN VIII)

Sensory cranial nerve originating at the junction of the pons and midbrain; transmits sensory information for hearing, balance, and equilibrium.

Glossopharyngeal Nerve (CN IX)

Mixed cranial nerve originating in the medulla; conveys taste from the posterior 1/3 of the tongue, conducts afferent gag reflexes, and mediates afferent and efferent salivary reflexes.

Vagus Nerve (CN X)

Mixed cranial nerve originating in the medulla; provides extensive parasympathetic supply to thoracic and abdominal organs, and controls swallowing, voice production, and the efferent gag reflex.

Accessory Nerve (CN XI)

Motor cranial nerve originating in the medulla; directs the motor movement of the shoulders.

Hypoglossal Nerve (CN XII)

Motor cranial nerve originating in the medulla; innervates the intrinsic and extrinsic muscles governing movement of the tongue.

Cranial Nerve Facial Mnemonic Diagram

A visual schematic mapping cranial nerve numbers to the face: 1 forms the nose (olfaction), 2, 3, 4, and 6 map around the eyes/eyebrows (vision and eye muscles), 5 forms the outline of the face (facial sensation/chewing), 7 forms the facial expression outline, 8 forms the ears (hearing/equilibrium), and 9, 10, and 12 map to the tongue and throat (taste, swallowing, and tongue movement).

Somatic Nervous System

Voluntary motor system utilizing a single motor neuron pathway connecting the CNS directly to skeletal muscle effectors, receiving input from proprioceptors and exteroceptors in joints, skin, and bones.

Autonomic Nervous System

Involuntary motor system utilizing a two-neuron efferent pathway (preganglionic and postganglionic) divided into sympathetic and parasympathetic divisions to regulate smooth muscle, cardiac muscle, and glands.

Preganglionic Neurons

Autonomic neurons whose cell bodies always reside within the central nervous system (brainstem or spinal cord) and whose axons terminate within autonomic ganglia.

Postganglionic Neurons

Autonomic neurons whose cell bodies are always situated inside peripheral autonomic ganglia and whose axons terminate at visceral effector tissues.

Sympathetic Division Anatomy

Thoracolumbar outflow characterized by preganglionic cell bodies in the lateral gray horn ($T_1-L_2/L_3$) with short preganglionic axons, and long postganglionic axons projecting from sympathetic chain or prevertebral ganglia to distant effectors.

Parasympathetic Division Anatomy

Craniosacral outflow characterized by preganglionic cell bodies in brainstem nuclei (cranial nerves III, VII, IX, and X) and sacral lateral gray matter ($S_2-S_4$) with long preganglionic axons, and short postganglionic axons emerging from terminal ganglia near or within target organs.

White Communicating Rami

Structures containing myelinated preganglionic sympathetic axons that exit spinal nerves to enter the sympathetic trunk; present exclusively at spinal levels $T_1-L_3$.

Gray Communicating Rami

Structures containing unmyelinated postganglionic sympathetic axons exiting the sympathetic chain to re-enter spinal nerves; found at all levels of the spinal cord.

Prevertebral (Collateral) Ganglia

Sympathetic ganglia located anterior to the abdominal aorta—including the celiac trunk, superior mesenteric, inferior mesenteric, and renal ganglia—where splanchnic preganglionic fibers synapse.

Greater Splanchnic Nerve

Sympathetic nerve composed of preganglionic axons originating from spinal cord segments $T_6-T_9$ that passes through the chain without synapsing to reach collateral ganglia.

Lesser Splanchnic Nerve

Sympathetic nerve composed of preganglionic axons originating from spinal cord segments $T_{10}-T_{11}$ that bypasses chain ganglia to synapse in prevertebral ganglia.

Least Splanchnic Nerve

Sympathetic nerve composed of preganglionic axons originating from spinal cord segment $T_{12}$ that travels to prevertebral ganglia.

Cholinergic Neurons

Neurons that synthesize and release acetylcholine; encompasses all sympathetic and parasympathetic preganglionic neurons, all parasympathetic postganglionic neurons, and sympathetic postganglionic neurons innervating sweat glands.

Adrenergic Neurons

Neurons that release norepinephrine (and epinephrine); primarily comprises the postganglionic neurons of the sympathetic nervous system innervating visceral effectors.

Nicotinic Receptors

Cholinergic receptors located on the cell bodies of all sympathetic and parasympathetic postganglionic neurons that bind acetylcholine.

Muscarinic Receptors

Cholinergic receptors located on the effector cells of all parasympathetic target organs and on sympathetic effectors of sweat glands.

Adrenergic Receptors

Receptors responding to norepinephrine and epinephrine on sympathetic effector tissues, classified into alpha ($\alpha$) and beta ($\beta$); activation of $\alpha_1$ and $\beta_1$ generally causes excitation, while $\alpha_2$ and $\beta_2$ generally cause inhibition.

Enteric Nervous System

Independent neuronal network embedded in the walls of the gastrointestinal tract that senses luminal chemical changes, regulates motility and enzyme secretion, and receives modulatory sympathetic and parasympathetic inputs.

Process of Sensation

A 4-step sequence: 1) Stimulation of a sensory receptor by specific mechanical or chemical energy, 2) Transduction of the stimulus into a graded potential, 3) Generation of an action potential reaching the CNS, and 4) Integration of sensory information by the CNS.

Free Nerve Endings

Unencapsulated sensory receptors including warm receptors, cold receptors, nociceptors, Merkel corpuscles (type I cutaneous), and hair root plexuses.

Encapsulated Nerve Endings

Sensory receptors enclosed in connective tissue capsules, including Meissner's corpuscles, lamellated (Pacinian) corpuscles, Ruffini's corpuscles (type II cutaneous), muscle spindles, and tendon organs.

Spinothalamic Tract

Anterolateral sensory pathway transmitting pain, temperature, crude touch, itch, and tickle; first-order neurons reside in dorsal root ganglia, second-order neurons in the spinal cord dorsal horn decussate at the spinal level, and third-order neurons relay from the thalamus to the primary somatosensory cortex.

Posterior White Column-Medial Lemniscus Pathway

Ascending pathway conveying discriminative fine touch, two-point discrimination, conscious proprioception, and vibration; first-order fibers ascend to the medulla oblongata, where second-order neurons decussate before projecting to the thalamus and somatosensory cortex.

Upper Motor Neuron (UMN) Lesion

Damage to motor neurons within the brain or spinal cord tracts resulting in spastic paralysis, hyperreflexia, rigidity, and abnormal reflexes.

Lower Motor Neuron (LMN) Lesion

Damage to motor neurons extending from the spinal cord or brainstem to skeletal muscle effectors, producing flaccid paralysis, hyporeflexia or areflexia, and severe muscle wasting.

Lateral Corticospinal Tract

Direct pyramidal motor pathway originating in the primary motor cortex whose axons decussate in the medullary pyramids and descend contralaterally in the lateral spinal cord to control skeletal muscles of distal limbs.

Anterior Corticospinal Tract

Direct motor pathway whose axons descend uncrossed in the anterior white column of the spinal cord and decussate locally at target spinal levels via the anterior white commissure to innervate axial and proximal limb muscles.

Corticobulbar Tract

Direct motor pathway originating in the head and face cortical areas that descends to synapse on lower motor neurons within brainstem cranial nerve nuclei governing muscles of the head, face, jaw, pharynx, larynx, and eyes.

Rubrospinal Tract

Indirect extrapyramidal motor pathway originating in the red nucleus of the midbrain that serves as a functional backup to corticospinal tracts for voluntary upper limb control.

Tectospinal Tract

Indirect motor pathway mediating visual and auditory reflexes that trigger involuntary turning of the head, neck, and eyes toward sudden stimuli.

Vestibulospinal Tract

Indirect motor pathway originating from vestibular nuclei that coordinates balance, equilibrium, and postural muscle tone.

Reticulospinal Tract

Indirect motor pathway coordinating stereotypical, repetitive motor activities such as walking, swimming, and running.

Fibrous Tunic

The outermost mechanical layer of the eye wall consisting of the posterior opaque sclera and the anterior clear cornea.

Vascular Tunic

The middle layer of the eye wall (uvea) composed of the choroid (supplying blood), ciliary body (altering lens curvature and producing aqueous humor), and iris (controlling pupillary diameter).

Iris Pupillary Muscles

Two smooth muscle layers of the iris: the radial muscles, which dilate the pupil under sympathetic control, and the circular muscles, which contract and constrict the pupil under parasympathetic control.

Retina

The sensory inner tunic of the eye housing photoreceptors (rods and cones), central retinal blood vessels, macula lutea, and the fovea centralis.

Fovea Centralis

A central depression within the retinal macula lutea containing a high density of cones, serving as the area of highest visual acuity.

Optic Disc

The anatomical site on the retina where ganglion cell axons converge and exit as the optic nerve, devoid of photoreceptors and known as the blind spot.

Anterior Cavity

The anterior segment of the eye located in front of the lens, subdivided into an anterior chamber and posterior chamber, both filled with aqueous humor.

Posterior Cavity

The vitreous chamber located between the lens and the retina, filled with gelatinous vitreous humor (vitreous body).

Lens Accommodation

The active physiological change in lens curvature governed by ciliary muscle contraction, increasing refractive power to focus diverging light rays from nearby objects sharply onto the retina.

Myopia

Nearsightedness resulting from an eyeball that is too long or a lens that is too thick, causing light rays to focus in front of the retina; corrected using concave lenses.

Hyperopia

Farsightedness resulting from an eyeball that is too short or a lens that is too thin, causing light rays to focus behind the retina; corrected using convex lenses.

Visual Pathway

The neurological route of visual transmission: Visual Field $\rightarrow$ Retina $\rightarrow$ Optic Nerve $\rightarrow$ Optic Chiasm $\rightarrow$ Optic Tract $\rightarrow$ Thalamus (Lateral Geniculate Nucleus) $\rightarrow$ Optic Radiations $\rightarrow$ Primary Visual Cortex in the occipital lobe.

Optic Chiasm

The crossroads of the visual pathway where nasal retinal fibers cross over to the contralateral side while temporal retinal fibers stay on the same side; a lesion here produces bitemporal hemianopia (loss of outer peripheral visual fields).

Lacrimal Fluid Drainage Pathway

The sequential transit of tears: 1. Lacrimal Gland $\rightarrow$ 2. Excretory Ducts $\rightarrow$ 3. Ocular Surface (Tear Film) $\rightarrow$ 4. Lacrimal Puncta $\rightarrow$ 5. Lacrimal Canaliculi $\rightarrow$ 6. Lacrimal Sac $\rightarrow$ 7. Nasolacrimal Duct $\rightarrow$ 8. Inferior Nasal Meatus.

Corneal Blink Reflex Arc

A somatic reflex arc wherein sensory mechanical stimuli on the cornea travel afferently via the ophthalmic branch of the trigeminal nerve (CN V), and motor efferents travel through the facial nerve (CN VII) to contract the orbicularis oculi muscle.

Pupillary Light Reflex Arc

An autonomic cranial reflex wherein light entering the eye activates afferent sensory fibers of the optic nerve (CN II) projecting to midbrain pretectal nuclei, which send efferent parasympathetic fibers through the oculomotor nerve (CN III) to constrict both pupils.

Gag Reflex Arc

A protective brainstem reflex triggered by somatic stimulation of the posterior pharyngeal wall, conducted afferently by the glossopharyngeal nerve (CN IX) and executed efferently by motor fibers of the vagus nerve (CN X).

Jaw Jerk Reflex

A monosynaptic stretch reflex mediated entirely by the trigeminal nerve (CN V), in which both sensory afferents and motor efferents traverse the mandibular division to elicit bilateral masseter contraction upon tapping the chin.

Ciliary Ganglion

A parasympathetic terminal ganglion situated in the posterior orbit receiving preganglionic fibers from the oculomotor nerve (CN III) that synapses to project short postganglionic fibers to the ciliary muscle and pupillary sphincter.

Pterygopalatine Ganglion

A parasympathetic ganglion receiving preganglionic fibers from the facial nerve (CN VII) via the greater petrosal nerve that sends postganglionic fibers to innervate the lacrimal glands, nasal cavity mucosa, and palatine glands.

Submandibular Ganglion

A parasympathetic ganglion receiving preganglionic fibers from the facial nerve (CN VII) via the chorda tympani that innervates the submandibular and sublingual salivary glands.

Otic Ganglion

A parasympathetic ganglion located just inferior to the foramen ovale receiving preganglionic fibers from the glossopharyngeal nerve (CN IX) via the lesser petrosal nerve to stimulate secretion from the parotid salivary gland.

Pelvic Splanchnic Nerves

Parasympathetic preganglionic fibers originating from sacral lateral gray matter segments ($S_2-S_4$) that travel directly to terminal and intramural ganglia in pelvic organs to innervate the distal colon, rectum, bladder, and reproductive tissues.

Sympathetic Pathway to the Heart

Autonomic circuit originating in spinal segments $T_1-T_5$ where preganglionic fibers ascend the sympathetic trunk to synapse in cervical and upper thoracic paravertebral ganglia, sending postganglionic cardiopulmonary splanchnic nerves to increase heart rate and force of contraction.

Sympathetic Pathway to the Lungs

Autonomic circuit originating in spinal segments $T_2-T_6$ that synapses in paravertebral ganglia and projects postganglionic cardiopulmonary splanchnic nerves through the pulmonary plexus to elicit bronchodilation and pulmonary vasoconstriction.

Monocular Blindness

Complete blindness isolated to a single eye resulting from an ipsilateral lesion or transection of the optic nerve prior to the optic chiasm.

Homonymous Hemianopia

Loss of the same contralateral visual half-field in both eyes (such as losing the entire left field in both eyes) caused by a complete unilateral lesion to the optic tract or optic radiations.

Somatosensory Homunculus

A distorted topographical map on the postcentral gyrus reflecting somatosensory input from the opposite side of the body, where surface areas with high receptor density (such as lips, fingertips, and tongue) occupy disproportionately large cortical regions.

Motor Homunculus

A functional mapping along the precentral gyrus depicting upper motor neuron organization, where muscles executing intricate, fine voluntary movements (such as the hands, fingers, face, and vocal cords) occupy the largest cortical areas.

Primary Somatosensory Cortex

The cerebral cortex region located in the postcentral gyrus of the parietal lobe (Brodmann areas 1, 2, and 3) that integrates incoming tactile, thermal, pain, and conscious proprioceptive sensations.

Primary Visual Cortex

The cortical processing center located in the occipital lobe around the calcarine fissure (Brodmann area 17) responsible for the initial conscious perception of basic visual inputs such as edges, orientation, and luminance.

Primary Auditory Cortex

The cortical region located in the superior temporal gyrus (Brodmann areas 41 and 42) dedicated to the initial conscious processing and frequency mapping of auditory signals.

Auditory Ossicles

A chain of three miniature bones in the middle ear cavity—the malleus, incus, and stapes—that mechanically amplify sound waves and transfer tympanic membrane vibrations to the oval window.

Pharyngotympanic (Auditory) Tube

A mucosa-lined conduit connecting the middle ear cavity with the nasopharynx that opens during swallowing and yawning to equalize air pressure across the tympanic membrane.

Cochlea and Spiral Organ (Organ of Corti)

A fluid-filled inner ear labyrinth housing mechanoreceptive hair cells resting on the basilar membrane that transduce fluid sound waves into nerve impulses along the cochlear nerve.

Vestibule (Utricle and Saccule)

The central bony inner ear cavity housing the maculae of the utricle and saccule, which employ otolith-weighted hair cells to detect static head position and linear acceleration.

Semicircular Canals

Three fluid-filled bony rings positioned at right angles to each other containing ampullary cristae with cupula-embedded hair cells that detect rotational or angular acceleration of the head.

Mechanoreceptors vs. Chemoreceptors

Sensory receptors distinguished by stimulus modality: mechanoreceptors detect physical deformation, pressure, stretch, or vibration, whereas chemoreceptors bind specific chemical molecules to signal taste, smell, and internal chemical levels.

Which part of the central nervous system is the seat of intelligence

Cerebrum, the largest part of the brain responsible for higher brain functions such as thought, memory, and learning.

Which of the following cranial nerves contains motor and sensory axons (mixed)

Facial (CNVII)

Which cranial nerve conducts sensations for smell?

Olfactory nerve (CN I)

The hypoglossal nerve innervates which of the following

muscles of the tongue, primarily responsible for its movement.

Which of the following cranial nerves emerge from the midbrain

Oculomotor nerve (CN III) and the trochlear nerve (CN IV).

Which of the following structures comprise the corpus striatum?

The caudate nucleus and the lentiform nucleus

Function of the basal ganglia

Initiation and Termination of movements

Which of the following is/are functions of the limbic system?

Emotions, olfaction, and short term memory storage

Parkinson’s disease is caused by damage to which part of the cerebrum?

The basal ganglia

What is the main function of the primary sensory areas of the brain?

Conscious perception of sensation

Where is the primary somatosensory area located

The postcentral gyrus

Where is Broca’s motor speech area located

Typically, the left frontal lobe close to the lateral fissure

Damage to Wernicke’s speech area causes which of the following problems with speech?

fluent aphasia

Visceral Effectors

Smooth muscle, cardiac muscle, glands

Autonomic motor innervation of smooth muscle, cardiac muscle and glands

Motor neuron cell bodies can be located in the spinal cord gray matter, receive motor innervation through a series of at least two motor neurons, not under voluntary control

What is true of the sympathetic nervous system?

No cranial nerves contain sympathetic axons, all sympathetic preganglionic neuron cell bodies located in lateral gray horn of sc, lateral gray horns are present only from T1-L2

Ganglions of sympathetic nervous system

Sympathetic chain ganglion, preaortic ganglion, superior mesenteric ganglion