Head and Neck Anatomy Series: Cranial Nerves

Overview of the Nervous System

Central Nervous System (CNS)
- Composed of the Brain and Spinal Cord
- Brain:
  - Receives and processes sensory information
  - Initiates responses, stores memories, generates thoughts and emotions
  - Forebrain: Cerebrum, Thalamus, Hypothalamus (controls body temp, reproductive functions, eating, sleeping, emotions)
  - Midbrain: Top part of brain stem (vision, hearing, motor control, sleep, alertness, temperature regulation)
  - Hindbrain: Medulla, Pons, Cerebellum (supports breathing, heart rate)
- Spinal Cord:
  - Conducts signals to/from brain (neuronal highway)
  - Controls reflexes
Peripheral Nervous System (PNS)
- Sensory Division: (Afferent - towards CNS)
  - Somatic Sensory
    - General: Touch, pain, pressure, vibration, temperature, proprioception
    - Special: Vision, hearing, balance
  - Visceral Sensory
    - General: Stretch, pain, temperature, irritation in viscera, sensation of hunger
    - Special: Taste, smell
- Motor Division: (Efferent - away from CNS)
  - Somatic: Voluntary movements of skeletal muscles
  - Visceral Motor (Autonomic Nervous System)
    - Sympathetic: Fight or flight
    - Parasympathetic: Rest and digest

Each cranial nerve with its functions primarily categorized into sensory (afferent) and motor (efferent) divisions.

Function: Special visceral sensory (smell, olfaction)
Pathway: Nasal cavity -> Olfactory bulb & tract -> Temporal lobe (primary olfactory cortex of forebrain)
Component: PNS, sensory- visceral

Function: Special somatic sensory (vision)
Pathway: Retina -> Optic nerve -> Optic chiasma -> Optic tract -> Thalamus (lateral geniculate body) -> Occipital lobe (primary visual cortex)
Chiasma Function: Right visual field processed on the left brain side, left visual field on the right brain side

Function: Somatic motor (extraocular muscles), parasympathetic to smooth muscle (pupil constriction)
Muscles Innervated: Superior rectus, inferior rectus, medial rectus, inferior oblique, levator palpebrae superioris
Pathway: Edinger-Westphal nucleus -> Ciliary ganglion -> Iris/pupillary sphincter muscle

Function: Sensory (orofacial region), motor (mastication muscles)
Divisions:
- Ophthalmic (V1): Forehead, eye
  - Branches: Frontal (superorbital, supratrochlear), lacrimal, nasociliary
- Maxillary (V2): Pterygopalatine fossa region
  - Branches: Sphenopalatine, pharyngeal, greater and lesser palatine, PSA, infraorbital
- Mandibular (V3): Muscles of mastication
  - Branches: Auriculotemporal (TMJ), long buccal, lingual, inferior alveolar (mental, incisive, mylohyoid), medial pterygoid

Function:
- Sensory: Ear, tongue, palate
  - Posterior auricular (ear), chordae tympani (taste, anterior 2/3 of tongue)
- Motor: Muscles of facial expression
- Parasympathetic: Salivary glands
- Branches Mnemonic: Two Zanzibar By Motor Car (Temporal, Zygomatic, Buccal, Mandibular, Cervical)
- Condition: Bell's palsy - temporary paralysis

Function: Touch and taste from posterior 1/3 of the tongue, gag reflex, motor
Pathway:
- Sensory: Posterior 1/3 of the tongue
- Motor: Stylopharyngeus muscle
- Autonomic: Carotid sinus (baroreceptor), Carotid body (chemoreceptor), lesser petrosal (parotid gland)

Function: Sensory & motor from/to laryngeal mucosa below vocal cords, major body organs (heart, lungs, digestive tract), pharynx, larynx and soft palate muscles
Dual Function: Gag reflex motor end
Autonomic: Aortic bodies (baroreceptor and chemoreceptor)

Function: Somatic motor (sternocleidomastoid, trapezius)
Facts: Originates from C1 to C5, ascends via foramen magnum, exits through jugular foramen

Function: Somatic motor (tongue muscles), exception of palatoglossus (innervated by Vagus nerve)

Recap of cranial nerves and their major functions.
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