Cranial Nerves - Lecture 3 (Neurophysiology)

Which Cranial Nerves are Sensory only?

Motor only?

Motor and Sensory?

Motor + Sensory + Parasympathetic?

Sensory only — CN I, II, VIII

Motor only — CN XI, XII

Motor + Sensory — CN IV, V, VI

Motor + Sensory + PSNS — CN III, VII, IX, X

What is Cranial Nerve I?

What is it mainly responsible for?

Which direction does the information flow (S, M, or PSNS)?

Cranial Nerve I is the Olfactory Nerve

Mainly responsible for Sense of Smell

Direction only flows Sensory (Afferent)

What is Cranial Nerve II?

What is it mainly responsible for?

Which direction does the information flow (S, M, or PSNS)?

Cranial Nerve II is the Optic Nerve

Mainly responsible for Sense of Sight

Direction only flows Sensory (Afferent)

What is the Olfactory Bulb?

What important purpose does it serve?

How is this affected when we remove the Brain?

Contains cell bodies of Secondary Sensory Neurons, who axons comprise the Olfactory Tract and travel to many Cortical and Subcortical regions

Connects the Olfactory Nerve to the Inferior Surface of the Brain; when the Brain is removed, you do not see the Olfactory Nerve because it is torn off the Olfactory Bulb

What is the main function of the Olfactory Tract?

Conveys olfactory information to Olfactory Cortical areas

What is the main pathway of Cranial Nerve I?

CN I = Olfactory Nerve

Olfactory Receptor Neurons of the Olfactory Epithelium (Mucosa) send smell information to the Olfactory Bulb (and thereby the Olfactory Nerve)

Where is the Olfactory Epithelium located?

How many Olfactory Receptor Neurons do we have?

Olfactory Epithelium (Mucosa) is located in the roof of the nasal cavity

We have 10 million Olfactory Receptor Neurons

What are the Secondary Sensory Neurons in the Cranial Nerve II Pathway?

Where are their cell bodies located?

Where do Bipolar Cells synapse in this pathway?

Secondary sensory neurons in CNII Pathway are Ganglion Cells

Their cell bodies are located in the Retina

Bipolar Cells synapse with Ganglion Cells

What forms the Optic Nerve?

Axons of Ganglion Cells that leave the eyeball

What is the Optic Chiasm?

Optic Nerve?

Optic Tract?

Optic Chiasm — x-shaped formation made by the crossing of the Ganglionic Cells

Optic Nerve — fiber bundle that connects the Eyeball to the Optic Chiasm

Optic Tract — fiber bundle that connects the Optic Chiasm to the Lateral Geniculate Body

Where does the Optic Tract enter the Brain?

What does it form?

Optic Tract enters the Brain at the level of the Posterior Diencephalon

Forms synapses on Neurons of the Lateral Geniculate Nucleus (LGN) of the Thalamus

What is the main pathway of Cranial Nerve II?

CN II = Optic Nerve

1. Photoreceptors in the Retina transmit visual information to Bipolar Cells of the Retina (primary sensory neurons)

2. Bipolar Cells do NOT fire impulses; instead, the pass information via Graded Signal Changes

What are the Primary Sensory Neurons of the Optic Nerve?

While heavily debated, we are choosing Bipolar Cells of the Retina to be the Primary Sensory Neuron

What is Cranial Nerve III?

What is it mainly responsible for?

Which direction does the information flow (S, M, or PSNS)?

Where does the Nerve exit from?

Oculomotor Nerve

Mainly responsible for Innervation of Eye Muscles

Information flows in the Motor, Sensory, and PSNS directions

Nerve exits from the Midbrain

Which eye muscles does the Oculomotor Nerve innervate?

Which direction do each of these muscles move the eye?

1. Superior Rectus (up)

2. Medial Rectus (toward nose / midline of the body; ADDUCTION)

3. Inferior Rectus (down)

4. Inferior Oblique (up and inward)

What is the Motor Component of CN III?

Sensory Component?

Parasympathetic Component?

CN III = Oculomotor Nerve

Motor — innervation of 4/6 eye muscles; innervation of the muscle responsible for elevating the upper eyelid

Sensory — transmission of sensory information for the muscle sensory receptors of the 5 innervated eye muscles

Parasympathetic — constriction of pupil via constriction of the circular muscle in the iris; change of lens shape via the ciliary muscle

What is Adduction?

Which eye muscle is responsible?

Movement of the eye towards the nose by Medial Rectus

Which eye muscle is responsible for moving the eye down?

Up?

Down — Inferior Rectus, with help from Superior Oblique (CN IV)

Up — Superior Rectus and Inferior Oblique

Which muscle is responsible for elevating the upper eyelid?

Which cranial nerve and its component is responsible for innervating this muscle?

Levator Palpebrae Superioris muscle

Innervated by the Somatic (Motor) Component of CN III (Oculomotor Nerve)

What does the Parasympathetic Component of the CN III do?

CN III = Oculomotor Nerve

1. Preganglionic neurons project to Ciliary Ganglion

2. Postganglionic fibers innervate the Circular Muscles of the Iris, causing constriction of the Pupil

3. They also innervate the Ciliary Muscle, causing the change in shape of the Lens

What is Cranial Nerve IV?

What is it mainly responsible for?

Which direction does the information flow (S, M, or PSNS)?

Where does the Nerve exit from?

Trochlear Nerve

Mainly responsible for innervation of the Superior Oblique eye muscle

Information flows in the Motor and Sensory directions

Nerve exits from the Caudal Midbrain

What is the Somatic (Motor) Component of CN IV?

CN IV = Trochlear Nerve

Helps the Oculomotor Nerve (CN III) move the eyeball downward and also causes inward rotation of the eyeball

Why is the Trochlear Nerve (CN IV) special?

Only CN that exits Dorsally and also the only one to cross the Midline before emerging from the Brainstem

How is a Lesion of the CN IV different than other lesions?

CN IV = Trochlear Nerve

Lesion of this nucleus affects the Contralateral Eye (other CNs affect the Ipsilateral Side)

What is the Sensory (Afferent) Component of CN IV?

Information from Superior Oblique muscle receptors (similar to CN III)

What is Cranial Nerve V?

What is it mainly responsible for?

Which direction does the information flow (S, M, or PSNS)?

Where does the Nerve exit from?

Trigeminal Nerve

Mainly responsible for sensory information from the Face and motor control of Chewing Muscles

Information flows in the Sensory and Motor directions

Nerve exits from the Pons

What are the three major divisions of the Trigeminal Nerve?

1. Ophthalmic (V1) — Sensory input from the Upper Face

2. Maxillary (V2) — Sensory Input from the Mid Face

3. Mandibular (V3) — Sensory Input from the Lower Face (including the anterior 2/3 of the tongue), Motor Outflow to the Chewing Muscles

What is the Spinal Trigeminal Nucleus?

Where is it located?

Secondary Sensory Neurons in the Brainstem responsible for pain and temperature from the face area

Located in the Medulla: Middle

What is the Trigeminal Main Sensory Nucleus?

Where is it located?

Secondary Sensory Neurons in the Brainstem responsible for touch sensation from the face area

Located in the Pons: Middle

What is the Trigeminal Mesencephalic Nucleus?

Where is it located?

Cell bodies of Primary Sensory Neurons that transmit information from chewing muscles

Located in the Midbrain: Rostral and the Pons: Middle

Why is the Trigeminal Mesencephalic Nucleus + Tract special?

Only structure in the CNS to:

1. Contain first order sensory neurons

2. Use electrical synapses, instead of chemical

What is the Trigeminal Motor Nucleus?

Where is it located?

Cell bodies of motor neurons that innervate chewing muscles and are involved (alongside TGM Nucleus + Tract) in the Monosynaptic Jaw Jerk Reflex

Located in the Pons: Middle

What is Cranial Nerve VI?

What is it mainly responsible for?

Which direction does the information flow (S, M, or PSNS)?

Where does the Nerve exit from?

Where is the majority of the nerve located?

CN VI = Abducens Nerve

Mainly responsible for Innervation of the Lateral Rectus Eye Muscle

Information flows in the Sensory and Motor directions

Nerve exits from the Pontomedullary Junction

Located in the Pons: Caudal

What is the Sensory Component of CN VI?

Motor Component?

Sensory — sensory signals from Muscle receptors (similar to CN III)

Motor — innervation of the Lateral Rectus eye muscle, which moves the eyeball laterally (Abduction)

What is Cranial Nerve VII?

What is it mainly responsible for?

Which direction does the information flow (S, M, or PSNS)?

Where does the Nerve exit from?

Where is the majority of the nerve located?

CN VII = Facial Nerve

Mainly responsible for the muscles that control Facial Expression

Information flows in the Motor, Sensory, and PSNS directions

Nerve exits at the Pontomedullary Junction

Majority of the nerve is located in the Pons: Caudal

What is the Sensory Component of CN VII?

Motor Component?

PSNS Component?

CN VII = Facial Nerve

Sensory — Pain, Temperature, and Touch information from part of the ear; sensory input from Taste Buds (w/CN IX and CN X)

Motor — somatic motor control of Facial Expression muscles

PSNS — control of Salivary Glands (EXCEPT Parotid) and Lacrimal Glands (produce tears)

What is Cranial Nerve VIII?

What is it mainly responsible for?

Which direction does the information flow (S, M, or PSNS)?

Where does the Nerve exit from?

Where is the majority of the nerve located?

CN VIII = Vestibulocochlear Nerve

Mainly responsible for Hearing and Balance (auditory and vestibular information)

Information flows only in the Sensory direction

Nerve exits at the Pontomedullary Junction (laterally to the Facial Nerve)

Majority of the nerve is located in the Medulla: Rostral

What controls the Auditory Component of CN VIII?

What is the general pathway of this component?

CN VIII = Vestibulocochlear Nerve

Controlled by the Cochlear Nuclei

General Pathway:

1. Hair cells in the Cochlea transmit information onto Primary Sensory Neurons

2. Primary Sensory Neurons exit the Cochlea, forming CN VIII, then terminate at the Cochlear Nuclei in the Brainstem

What controls the Vestibular Component of CN VIII?

What is the general pathway of this component?

CN VIII = Vestibulocochlear Nerve

Controlled by the Vestibular Nuclei

General Pathway:

1. Hair Cells in the Semicircular Canals, Saccule, and the Utricle transmit information onto Primary Sensory Neurons

2. Primary Sensory Neurons exit the structures, form CN VIII, and terminate at the Vestibular Nuclei in the Brainstem

What is Cranial Nerve IX?

What is it mainly responsible for?

Which direction does the information flow (S, M, or PSNS)?

Where does the Nerve exit from?

Where is the majority of the nerve located?

CN IX = Glossopharyngeal Nerve

Mainly responsible for taste and eating

Information flows in the Sensory, Motor, and PSNS directions

Nerve exits from the Upper Rostral Medulla

Majority of the nerve is located in the Medulla: Rostral

What is the Motor Component of CN IX?

Sensory Component?

PSNS Component?

CN IX = Glossopharyngeal Nerve

Motor — Innervates the muscle responsible for elevating the Pharynx during swallowing and speech (prevents choking)

Sensory — input from the Carotid Sinus (monitors BP) and the Carotid Bodies (monitors blood O2 levels); Pain, temp, and touch signals from part of the ear; signals from Posterior Tongue and Upper Pharynx (AFFERENT limb for Gag Reflex); Taste Buds

PSNS — control of the Parotid Salivary Glands

What two nuclei are responsible for the majority of CN IX?

What do they do?

CN IX = Glossopharyngeal Nerve

1. Rostral Part of the Nucleus Ambiguus

   • gives rise to the Somatic (Motor) and PSNS fibers

2. Spinal Trigeminal Nucleus

   • receives Pain, Temp, and Touch sensory signals

Which CNs are responsible for Taste Buds sensory signals?

Signals for Parts of the Ear?

Taste Buds — CN VII (Facial), CN IX (Glossopharyngeal), and CN X (Vagus)

Parts of the Ear — CN VII (Facial) and CN IX (Glossopharyngeal)

What does the Carotid Sinus do?

Carotid Bodies?

Which CN do they send input to?

Carotid Sinus — monitor BP with Baroreceptors

Carotid Bodies — monitor blood O2 levels with Chemoreceptors

CN IX (Glossopharyngeal)

What is Cranial Nerve X?

What is it mainly responsible for?

Which direction does the information flow (S, M, or PSNS)?

Where does the Nerve exit from?

Where is the majority of the nerve located?

CN X = Vagus Nerve

Mainly responsible for controlling the heart and many visceral organs

Information flows in the Sensory, Motor, and PSNS directions

Nerve exits from the Medulla

Majority of the nerve is located in the Medulla: Middle

What is the Motor Component of CN X?

Sensory Component?

PSNS Component?

CN X = Vagus Nerve

Motor — controls skeletal muscles in the Pharynx, Larynx, and tongue (only some, not all); EFFERENT limb for Gag Reflex

Sensory — from visceral structures; from BP receptors and chemoreceptors in the Aortic Arch; pain, temp, and touch from part of the ear, Larynx, and Pharynx; taste buds

PSNS — comprises most of the PSNS; control of heart and visceral organs (incl. pharynx, larynx, thorax, and abdomen)

What is Cranial Nerve XI?

What is it mainly responsible for?

Which direction does the information flow (S, M, or PSNS)?

Where does the Nerve exit from?

Where is the majority of the nerve located?

CN XI = Spinal Accessory Nerve

Mainly responsible for motor control of the two skeletal neck muscles (Sternomastoid and Trapezius)

Information flows only in the Motor direction

Nerve exits from the Medulla and then from the Skull (with CN X)

Majority of nerve is located in the Upper Cervical SC (cell bodies), then ascend to the Medulla

What are the two skeletal neck muscles?

Which CN are they innervated by?

1. Sternomastoid Muscle

2. Trapezius Muscle

Innervated by CN XI (Spinal Accessory Nerve)

What is Cranial Nerve XII?

What is it mainly responsible for?

Which direction does the information flow (S, M, or PSNS)?

Where does the Nerve exit from?

Where is the majority of the nerve located?

CN XII = Hypoglossal Nerve

Mainly responsible for somatic motor control of Tongue Muscles (except one)

Information flows only in the Motor direction

Nerve exits from the Medulla

Majority of the nerve is located in the Medulla: Middle