Lecture 4 (Cranial nerves, special senses)

What type of nerve do cranial nerves NOT have?

Cranial nerve do NOT carry sympathetic nerves

What are cranial nerves?

- 12 paired cranial nerves: 10 associated anatomically with the brainstem, 2 associated anatomically with forebrain

- Individually named and numbered by roman numerals

- May contain sensory or motor or both information (Mixed)

- Provide afferent and efferent supply (both somatic and autonomic) to head and neck and to a lesser extent thoracic and abdominal viscera

What are sensory functions of cranial nerves?

- Somatic: Touch, pain and temperature from the head and neck

- Special senses: Smell, vision, hearing, taste and balance

- Visceral: Visceral sensation (organ filling, bloating, distention, nausea, dysnea), blood pressure information from baroreceptors, chemoreceptors that monitor arterial oxygen (O2) and carbon dioxide (CO2) levels.

What are some motor functions of the cranial nerves?

- Somatic/voluntary: Skeletal muscles of head and neck (eye, jaw, tongue, face, larynx, some muscles of the neck)

- Visceral/involuntary: Autonomic supply to salivary glands and smooth muscles of pupil, lens, pharynx, thoracic organs and most of the abdominal organs.

What are the names of the cranial nerves?

1. Olfactory

2. Optic

3. Oculomotor

4. Trochlear

5. Trigeminal

6. Abducent

7. Facial

8. Vestibulocochlear

9. Glossopharyngeal

10. Vagus

11. Accessory

12. Hypoglossal

Describe the olfactory nerve?

- Modality = sensory (special sense)

- Function = smell/olfaction

- Olfactory receptors in the nasal cavity

- Location = forebrain

- Foramen = Cribiform plate of ethmoid bone

Describe the optic nerve?

- Modality= Sensory (special sense)

- Function = vision

- Cell bodies in the retina

- Location = forebrain

- Foramen = optic foramen

- Optic nerve is technically part of the central nervous sytem (unlike the other cranial nerves), as it is derived from an outpouching of the diencephalon during embryological development

- So, the myelin surrounding the optic nerve is not made of schwann cells but of oligodendrocytes

Describe the oculomotor nerve?

- Modality = motor (Two components - voluntary and involuntary)

- Function = movement of the eyeball (voluntary), constricts the pupil (involuntary)

- Location = midbrain, interpeduncular fossa

- Target muscles innervated ~5 extraocular muscles (voluntary) that move the eye ball. ~ sphincter pupillae (involuntary) constricts the pupil

- Foramen = superior orbital fussure

- target muscles innervated (voluntary)

Describe the trochlear nerve?

- Modality: Motor

- Function: Movement of eyeball

- Location: Midbrain

- Only nerve found on the dorsal surface of the brainstem (All others on the ventral)

- Foramen: Superior orbital fissure

- Target muscle innervated: Superior oblique

Describe the trigeminal nerve?

- Modality: Both sensory and motor

- Sensory (touch, pain, temperature) from face (Any face sensation)

- Motor -> Muscles of mastication

- Level of mid pons

- Is a big nerve that sits on the middle cereballar peduncle, looks like two nerves, bigger one is the sensory root and the smaller is the motor root

What are the trigeminal nerve divisions?

- Trigeminal nerve has got a sensory root and a motor root. Sensory root is divideed into the following 3 divisions.

- V1: Ophthalmic (exits superior orbital fissure)

- V2: Maxillary (exits foramen rotundum)

- V3: Mandibular (exits foramen ovale)

- The motor root joins the V3 (supplies the muscles of mastication)

describe the Abducens nerve?

- Modality: Motor

- Function: Moves the eyeball

- Location: Brainstem (hindbrain, between pons and medulla)

- Medial most nerve in the groove between the pons and the medulla

- Foramen: Superior orbital fissure

- Target muscle innervated: Lateral rectus

Describe the facial nerve

- Modality: Both sensory and motor

- Sensory information carried: Taste from anterior 2/3 tongue

- Motor information carried: Muscles of facial expression (skeletal) - 5 divisions. Salivary, lacrimal, nasal glands (autonomic)

- Location: Brainstem (hindbrain), in between VI and VIII. It has an intermediate nerve

- Foramen: Internal auditory meatus (inner aspect of the skull), travels in channel within the skull, exits the stylomastoid foramen (temporal bone), travels through Parotid salivary gland, divide into 5 groups to supply facial muscles.

- Lesion would cause facial paralysis

Describe the vestibulocochlear nerve?

- Modality: Sensory

- Function: balance/equilibrium and hearing (vestibular functions)

- Location: Brainstem (hindbrain), lateral to VII

- Goes to the vestibula aparatus

- Foramen: Internal auditory meatus

Describe the glossopharyngeal nerve?

- Modality: Both, sensory and motor

- Sensory information carried: Pain, touch, temperature from posterior 1/3 of tongue, and oro-pharynx. Taste from posterior 1/3 tongue. and pressure from carotid body/sinus (regulate BP)

- Motor information carried: Pharynx (swallowing), parotid salivary gland (autonomic). Facial nerve travels through but doesn't supply it.

- Exits lateral to olive

- Foramen: Jugular foramen

Describe the vagus nerve?

- Modality: both sensory and motor

- Sensory information carried: Larynx, pharynx, thoracic and abdominal viscera, Taste (most posterior taste buds). Pressure receptors in carotid and aortic bodies and carotid sinus

- Motor information carried: Pharynx and larynx (swallowing and speech), Heart, lungs, abdominal viscera (autonomic)

- Exits lateral to olive

- Foramen: Jugular foramen (w/IX)

Describe the accessory nerve?

- Modality: motor

- Two divisions

- Cranial: Originates from the brainstem at lateral medulla. Function - innervates parts of the pharynx and larynx

- Spinal: Originates outside skull (C1-C5) and enters via foramen magnum. Function: Innervates sternocleidomastoid & trapezius --> moves the head and neck

- Exits via jugular foramen with IX and X

Describe the Hypoglossal nerve?

- Modality: Motor

- Function: Moves the tongue (speech and eating)

- Exits medulla laterally between pyramid and olive

- Foramen: Hypoglossal canal (lateral walls of foramen magnum)

What are the special senses?

- Olfaction (I)

- Vision (II)

- Taste (VII and IX)

- Hearing and vestibular function (VIII)

What is the organisation of the retina and optic nerve?

- Retina divided into two halves: 1. Nasal (half closest to nose, medial), 2. Temporal (Lateral half)

- Visual world divided into two halves (R&L)

- For each eye: nasal half sees lateral visual field on the same side and the temporal half sees medial visual field on the same side

- All optic nerve axons from nasal retina (either side) cross at the optic chiasm (vision on the pheripheries cross over)

Describe the hearing and balance?

Hearing:

- Sound transmitted to cochlea via movement of three small bones in middle ear

- Move viscous fluid inside the cochlea, movement of fluid depends on frequency of sound, "waves" of movement stimulate auditory receptor "hair" cells. Nerve impulse in VIII nerve

Balance:

- Movement of head = movement of fluid in semicircular canals (vesitular apparatus). Stimulation of vestibular receptor "hair" cells. Nerve impulse in VIII nerve