Cranial nerves beginning

Cranial Nerves: Overview

• Cranial nerves are nerves that originate directly from the brain, not the spinal cord.
• They are responsible for various functions, including sensory perception, motor control, and autonomic functions.
• Olfactory, optic, oculomotor, trochlear, trigeminal, abducens, facial, intermediate, vestibulocochlear, glossopharyngeal, vagus, accessory, and hypoglossal nerves are the 12 pairs.

Olfactory Nerve (I)

• Sensory nerve, part of the olfactory pathway.
• Develops as a process of the telencephalon during fetal development.
• Originates from special olfactory cells (the first neurons).
• Dendrites have olfactory receptors in the nasal cavity, specifically the regio olfactoria.
• Axons gather into 15-20 fila olfactoria, passing through the lamina cribrosa to the olfactory bulb.
• Olfactory bulb contains the second neurons of the pathway.
• Axons from the second neurons form the olfactory tract, leading to the olfactory trigone.
• Olfactory trigone relays signals to subcortical areas for smell and eventually to the uncus – the main cortical center for smell. Subcortical centers include thalamic neurons, mamillary bodies, substantia perforata anterior, and amygdala.

Optic Nerve (II)

• Sensory nerve, part of the visual pathway.
• Develops as a process of the diencephalon during fetal development.
• Photoreceptors (rods and cones) are the first neurons in the pathway.
• Bipolar cells are the second neurons.
• Ganglionar cells are the third neurons, their axons forming the optic nerve.
• Passes through the optic canal with the ophthalmic artery.
• Forms the optic chiasm in the middle cranial fossa, where fibres cross and uncrossed, corresponding to the medial and lateral retina respectively.
• Optic tract continues, carrying input from both eyes.
• Subcortical visual centers include lateral geniculate nucleus and superior colliculus' gray matter.
• Optic radiations transmit signals through the internal capsule to the visual cortex in the calcarine sulcus region (cuneus and medial occipitotemporal gyrus).

Oculomotor Nerve (III)

• Mixed nerve (motor and parasympathetic).
• Contains two nuclei in the midbrain (tegmentum mesencephali): motor and parasympathetic nuclei.
• Emerges near superior colliculi.
• Enters the orbit via the superior orbital fissure, dividing into superior and inferior branches.
• Superior branch supplies superior rectus muscle and levator palpebrae superioris muscle .
• Inferior branch supplies inferior, medial rectus muscles and inferior oblique muscles.
• Parasympathetic fibres supply the sphincter pupillae and ciliary muscles of the eye via the ciliary ganglion.

Trochlear Nerve (IV)

• Motor nerve.
• Has a nucleus in the midbrain (tegmentum mesencephali) near the inferior colliculi.
• Emerges on the dorsal side of the midbrain, looping around the cerebral peduncles.
• Enters the orbit via the superior orbital fissure.
• Supplies the superior oblique muscle.

Trigeminal Nerve (V)

• Mixed nerve (motor and sensory).
• Contains four nuclei in the brainstem (upper pons): principal, mesencephalic, spinal, and motor nuclei.
• Has two roots: sensory and motor.
• Sensory root forms the trigeminal ganglion, which is surrounded by dura mater.
• Divides into three major branches: ophthalmic, maxillary, and mandibular nerves.

Abducens Nerve (VI)

• Motor nerve.
• Has a nucleus in the brainstem (lower pons).
• Emerges from the medulla between the pons and the pyramid.
• Enters the orbit via the superior orbital fissure.
• Supplies the lateral rectus muscle.

Facial Nerve (VII)

• Mixed nerve (motor and sensory via intermediate nerve).
• Motor fibres supply facial muscles (e.g., those for facial expression).
• Has a nucleus in the brainstem (pons).
• Emerges between the pons and the inferior olive, enters the internal acoustic meatus, and exits the skull via the stylomastoid foramen.
• Forms the parotid plexus and branches to supply muscles associated with facial expression and the stapedius muscle and posterior auricular nerve .

Intermediate Nerve

• Part of the facial nerve.
• Has two nuclei: superior salivatory (parasympathetic) and tractus solitarius (sensory).
• Sensory ganglion = geniculate ganglion.
• Two branches: greater petrosal (parasympathetic root for pterygopalatine ganglion) and chorda tympani (sensory and parasympathetic for submandibular ganglion for taste).

Vestibulocochlear Nerve (VIII)

• Sensory nerve with two parts: cochlear and vestibular.
• Cochlear nerve relays auditory information from the inner ear. First neurons are in the spiral ganglion and dendrites start from organ of corti (hearing receptors).
• Vestibular nerve relays balance information and both pass through the internal acoustic meatus.

Glossopharyngeal Nerve (IX)

• Mixed nerve (sensory, motor, and parasympathetic).
• Has three nuclei in the medulla: ambiguous (motor), tractus solitarius (sensory), and inferior salivatory (parasympathetic).
• Emerges from the medulla and exits via the jugular foramen.
• Two sensory ganglia (superior and inferior).

Vagus Nerve (X)

• Mixed nerve (sensory, motor, and parasympathetic).
• Has three nuclei in the medulla: ambiguous (motor), tractus solitarius (sensory), and dorsal vagal (parasympathetic).
• Emerges from medulla, exits via jugular foramen, and has superior and inferior ganglia.

Accessory Nerve (XI)

• Motor nerve.
• Has two nuclei (spinal accessory and ambiguous).
• Spinal nucleus originates in upper cervical spinal cord segments.
• Ambiguous nucleus is in the medulla.

Hypoglossal Nerve (XII)

• Motor nerve with a nucleus in the medulla.
• Emerges from the medulla and exits via the hypoglossal canal.
• Supplies the muscles of the tongue.

This quiz explores key concepts related to the neuroanatomy of the olfactory and optic pathways. Participants will answer questions about the functions of various neural structures and their connections in the brain. Test your knowledge on the roles of the olfactory receptors, Nn.olfactorii, and related pathways.