Head and Neck Anatomy: Cranial Nerves

Overview of the Nervous System

• Components:
  • Central Nervous System (CNS)
    • Brain: processes sensory information, initiates responses, stores memories, thoughts, and emotions.
      • Forebrain: cerebrum, thalamus, hypothalamus (controls body temperature, reproduction, eating, sleeping, emotions)
      • Midbrain: vision, hearing, motor control, sleep, alertness, temperature regulation.
      • Hindbrain: medulla, pons, cerebellum (vital bodily functions like breathing)
    • Spinal Cord: conducts signals to/from the brain, controls reflexes.
  • Peripheral Nervous System (PNS)
    • Sensory Division (Afferent): carries info from sensory organs to CNS.
      • Somatic: touch, pain, pressure, vibration, temperature, proprioception.
      • Visceral: stretch, pain, temperature, irritation, hunger.
    • Motor Division (Efferent): sends info from CNS to muscles/glands.
      • Somatic: voluntary skeletal muscle movements.
      • Visceral: autonomic nervous system (involuntary, fight/flight, rest/digest).

Cranial Nerves Overview

• Cranial Nerve I (Olfactory): Responsible for smell, processed in the temporal lobe.
• Cranial Nerve II (Optic): Vision, involves optic chiasma for visual field processing.
• Cranial Nerve III (Oculomotor): Motor to extraocular muscles, parasympathetic control of pupil constriction.
• Cranial Nerve IV (Trochlear): Motor to superior oblique muscle.
• Cranial Nerve V (Trigeminal): Sensory from orofacial region, somatic motor to muscles of mastication.
  • Divisions:
    • V1 (Ophthalmic): Forehead, eye.
    • V2 (Maxillary): Sensory from maxillary region.
    • V3 (Mandibular): Sensory and motor to mandibular region.
• Cranial Nerve VI (Abducens): Motor to lateral rectus muscle.
• Cranial Nerve VII (Facial): Motor to facial expression muscles, taste from anterior 2/3 of the tongue, parasympathetic to glands.
• Cranial Nerve VIII (Vestibulocochlear): Hearing and balance.
• Cranial Nerve IX (Glossopharyngeal): Taste/touch from posterior third of the tongue, gag reflex.
• Cranial Nerve X (Vagus): Visceral sensory/motor to organs, somatic motor to larynx/soft palate.
• Cranial Nerve XI (Accessory): Motor to sternocleidomastoid and trapezius.
• Cranial Nerve XII (Hypoglossal): Motor to tongue muscles.

Key Anatomy and Functions

• Olfactory Nerve (CN I): Nasal cavity to temporal lobe.
• Optic Nerve (CN II): Retina to occipital lobe, optic chiasma processes visual fields.
• Oculomotor Nerve (CN III): Eye muscle movement, pupil constriction (Edinger-Westphal nucleus).
• Trochlear Nerve (CN IV): Superior oblique muscle.
• Trigeminal Nerve (CN V): Facial sensation, chewing.
  • V1: Forehead and eye (frontal, lacrimal nerves).
  • V2: Maxillary region.
  • V3: Mandibular region.
• Abducens Nerve (CN VI): Lateral rectus muscle of eye.
• Facial Nerve (CN VII): Taste, facial expressions, salivation (chorda tympani, greater petrosal nerve).
• Vestibulocochlear Nerve (CN VIII): Inner ear balance (utricle and saccule) and hearing.
• Glossopharyngeal Nerve (CN IX): Taste, gag reflex, carotid body and sinus reflexes.
• Vagus Nerve (CN X): Heart, lungs, digestive tract functions.
• Accessory Nerve (CN XI): Neck and shoulder muscles.
• Hypoglossal Nerve (CN XII): Tongue movements.

Additional Notes

• Optic Chiasma: Crosses visual field information for processing in opposite brain hemispheres.
• Bell's Palsy: Facial nerve dysfunction resulting in temporary facial paralysis.
• Baroreflex/Chemoreceptors: Regulate blood pressure and composition via cranial nerves IX and X.