Cranial Nerves Quiz

Cranial Nerves

• Cranial nerves are a set of twelve paired nerves in the vertebrate brain, connecting to various parts of the body.
• They transmit sensory information from the body to the central nervous system (CNS), as well as motor commands from the CNS to the muscles
• They vary in function and some nerves contain both sensory and motor fibres
• The 12 cranial nerves are numbered and named based on their location in the brain, and the areas they control.

Functional Types of Cranial Nerves

• There are different types of functions for cranial nerves, each with a specific role.
• General Somatic Efferent (GSE): Controls muscles from somites, including skeletal and extraocular muscles, as well as some in the tongue
• General Visceral Efferent (GVE) - Activates visceral organs
• Special Visceral Efferent (SVE): Activates muscles derived from the pharyngeal arches, face, palate pharynx and larynx(excluding eye & tongue).
• General Somatic Afferent (GSA) - Mediates information from muscles, skin, ligaments and joints
• General Visceral Afferent (GVA) - Mediates sensory innervation from the visceral organs
• Special Visceral Afferent (SVA) - Mediates visceral sensations such as taste (tongue) and smell from the nose
• Special Somatic Afferent (SSA) - Mediates special sensory sensations such as vision (retina) and hearing & equilibrium (inner ear).

Classification of Cranial Nerves

• Sensory cranial nerves contain only afferent (sensory) fibers. Example: Olfactory nerve, Optic nerve, Vestibulocochlear nerve
• Motor cranial nerves contain only efferent (motor) fibers. Example: Oculomotor nerve, Trochlear nerve, Abducent nerve, Accessory nerve, Hypoglossal nerve
• Mixed nerves contain both sensory and motor fibers. Example: Trigeminal nerve, Facial nerve, Glossopharyngeal nerve, Vagus nerve.

Olfactory Nerve (CN I)

• Special Sensory for smell
• Olfactory mucosa (SVA) sends signals to the cribriform foramina to the olfactory bulb
• Signals then travel to the olfactory nerve.
• Olfactory signals go to the ipsilateral olfactory cortex without synapsing in the thalamus.

Optic Nerve (CN II)

• Special Somatic for vision
• Optic nerve fibers carry information from the retina to the lateral geniculate body to the visual cortex in the occipital lobe,
• About 80-90% of optic nerve fibers cross at the optic chiasm
• Small number of fibers leave the chiasm to the suprachiasmatic nucleus of the hypothalamus influencing circadian rhythm.
• Damage to the optic nerve can result in visual loss

Oculomotor Nerve (CN III)

• Includes both somatic and parasympathetic fibers
• Supplies several extrinsic eye muscles (superior, inferior, medial rectus, inferior oblique and levator palpebrae superioris).
• Innervates the constrictor pupillae (sphincter pupillae) muscle in the iris.
• Innervates the ciliary muscle that controls the lens accommodation
• Edinger-Westphal nucleus, the parasympathetic nucleus, is located within the midbrain near the superior colliculus.

Trochlear Nerve (CN IV)

• Somatic Motor
• Innervates the superior oblique muscle
• Efferent fibers cross over and go to the contralateral superior oblique muscle.
• The trochlear nerve is the only cranial nerve that exits from the posterior/dorsal portion of the brainstem.

Abducens Nerve (CN VI)

• Somatic Motor
• Innervates the lateral rectus muscle
• Emerges from the pontomedullary junction
• Runs in subarachnoid space of the posterior cranial fossa
• Pierces dura at the point lateral to dorsum sellae
• Passes through the superior orbital fissure in tendinous ring
• Fibers coordinate lateral eye gaze

Trigeminal Nerve (CN V)

• Mixed nerve (sensory and motor)
• Three major divisions: ophthalmic (V1), maxillary (V2), and mandibular (V3)
• Three sensory nuclei: Mesencephalic, pontine (primary sensory), & spinal
• Sensory functions mediate pain, temperature, proprioception, and touch
• Motor functions control muscles involved in mastication (chewing), speech among others

Additional Information

• Many other cranial nerves and their functions exist, some involving different types of functions (general somatic efferent, general visceral efferent, special visceral efferent, general somatic afferent, general visceral afferent, special visceral afferent, special somatic afferent).
• These cranial nerves have specific origins and distributions and perform various functions relevant to several body parts with the brain.
• The structures and functions of cranial nerves are vital for understanding the overall function and integration of the nervous system.
• Clinical information provided for each cranial nerve highlights various conditions regarding each nerve.