Clinical Anatomy of Sensory Pathways II

Lecture 6

What is the question of the chapter ?

How is sensory info transmitted from the face basically to the brain ?

What do the cranial nerves do ?

Innervate brain + brainstem origin is the brain

Main nerve ? Branches ?

Trigeminal Nerve

1. Opthalmic

2. Maxillary

3. Mandibular

Trigeminal Neuralgia ?

Disease of Trigeminal nerve

TRigeminal Nuclei ?

Where is the info processed ?

Cranial nerves: How much ? Where do they arise from ? Exit ? Names ? Numbers ?

• The cranial nerves are a set of 12 paired nerves that arise directly from the brain.

• The first two nerves (optic and olfactory) arise from the cerebrum, whereas the remaining 10 emerge from the brainstem (not from the brain directly)

• Exit the cranial cavity via the foramina

• Each nerve has a name that reflects its function and a number according to its location in the brain

• They are numerically identified in roman numerals (I-XII)

Functions of cranial nerves (3) ?

• The functions of the cranial nerves are sensory (carry sensory info) and motor or both

• Sensory cranial nerves help a person see, smell and hear, touching face, temperature change to face

• Motor cranial nerves help control muscle movements in the head and neck. For eg. Facial expressions or tongue

Cranial nerves: How much ? Names and corresponding numbers ? Involved in speech and swallowing ?

I olfactory nerve

II optic nerve

III oculomotor nerve

IV trochlear nerve

V Trigeminal nerve

VI ABducens nerve

VII Facial nerve

VIII Vestibulocochlear nerve

IX glossopharyngeal nerve

X Vagus nerve

XI accessory nerve

XII hypoglossal nerve

Involved in speech and swallowing: V, VII, IX, X, XI, XII

When you want to see how the nerves arise in the brain ? Numbers correspond to what ?

You look from the bottom.

Number corresponds to where they appear.

List of the cranial nerves, fibres and the functions ?

I olfactory (sensory) - olfaction

II optic (sensory) - vision

III oculomotor (oculo is latin word for eye) motor - movemnet of eyeball, parasympathetic - pupillary constriction + accomodation

IV trochlear (motor) - movement of eyeball

V trigeminal (associated with a lot of diaseases, sensory - general sensation, motor - opening/closing mouth (speech production), tension of typanic membrane

VI abducens (motor) - movement of eyeball

VII Facial: sensory - taste, motor- facial movement tension of ossicles, parasympathetic - salivation and lacrimation (production of tears)

VIII vestibulocochlear (sensory) proprioception of head, balance, hearing

IX Glossopharyngeal (sensory) general sensation, chemo/baroreceptors, taste (motor) swallowing, (parasympathetic) salivation

X Vagus (sensory) general sensation, chemo/baroreceptors, visceral sensation (info from gut to brain), (motor) speech/swallowing, (parasympathetic (control of these symptoms)

XI Acessory (motor) movement of head + shoulders

XII HYpoglossal (motor) movement of tonguw (speeach and language production)

Trigeminal Nerve: Associated with what ? Sensory or Motor ? Divided into what ? Function ?

Associated with a lot of pain and a lot of disorders

MIxed sensory and motor nerve

Divided into 3 main branches

• Opthalmic nerve (V1) sensory info from face/ upper scalp

• Maxillary nerve (V2) sensory info from eyes and upper face

• Mandibular nerve (V3) gets often irritated from tooth pain, innervates mandible.

Function

• Transmission of sensory info from the face / oronasal region/ teeth (e.g. pain, temperature, vibration, fine and crude touch, proprioception)

• Transmission of motor info to muscles of mastication (chewing)

V1 Opthalmic Nerve: General Function: Gives rise to what ?

General Function - Sensory innervation to the following structures: scalp, eye, nose, forehead

Gives rise to 3 main branches:

Frontal: sensory innervation for upper eyelid / forehead

Lacrimal: sensory innervation of lacrimal gland of eye. Important for crying

Nasociliary: Sensory innervation of mucous membranes of nasal cavity sensory innervation of eye (cornea, ciliary bodies, iris, upper eyelid and conjunctive)

V2 Maxillary Nerve: General Function ? Gives rise to what ?

General Function: sensory innervation to the following strcutures: palate, nasal cavity, teeth of the upper jaw, skin on the side of the nose, cheek, upper lip (important for speech production)

Gives rise to numerous sensory branches.

• superior alveolar nerve (anterior, middle, posterior)

• Zygomatic nerve

• Posterior superior alveolar nerve: supplies the maxillary sinus and roots of maxillary molars

• Middle superior alveolar nerve: supplies the roots of maxillary premolars

• Zygomatic nerve: supplies the skin of zygomatic arch and anterior temple

• Anterior superior alveolar nerve: supplies the maxillary central, lateral and canine teeth

V3 Mandibular Nerve: Sensory or MOtor ? General Function ? Divides inrto what ?

Contains both sensory and motor branches

General function: Innervates structures of

• lower jaw and face (tongue, lower lip and chin)

• Muscles of mastication (chewing)

Branches into 4 branches:

1. BUccal Nerve: conveys sensory info from the skin of the cheek and mandibular gingiva

2. Lingual Nerev: supplies the tongue, mandibular lingual gingiva

3. Inferior alveolar nerve: supplies the skin of chin/ skin of lower lip (another branch supplies the mylohoid)

4. Auriculo temporal nerve: sensory innervation to parts of the external ear, scalp and temporomandibular joint

What is the trigeminal nerve associated with ?

TRigeminal nerve associated with migraine. You have a pain in the left or right side of face due to trigeminal nerve gets inflamed. Severe pain.

Trigeminal Neuralgia: pain ? SYmptoms ? Cause ? Treatment ?

Very painful.

symptoms:

• Epsiodes of severe facial pain along the trigeminal nerve divisions (by eye down to jaw)

• Individual attack from few seconds / minutes / hours

• Regarded as one of the most painful disorders known in medicine

• Can be triggered by everyday sensory stimuli (tocuh to the face, eating, talking, shaving, brushing teeth)

Cause:

exact cause unknown (loss of myelin trigeminal nerve)

• Compression of blood vessel nerve brainstem

• Often seen in multiple sclerosis, stroke, trauma.

• Middle aged or later, 0.3% of people, female over-representation (females have a higher rate of migraine. might be connected)

Treatment:

• Antiepileptics: reduces activation of nerve. Loads of side effects

• Microvascular decompression

• Electrocoagulation: complete nerve is paralysed by surgery because pain is so bad. They cannot carry out facial expressions

Do spinal cord patients have facial expression ? Why ?

They have complete facial expression because the trigeminal nerve is not injured.

Sensory Info from the face does not enter the spinal cord: Where do they enter instead and what happens ?

• Sensory input (proprioception, touch, pain and temperature) from the face do not enter the spinal cord

• Why ? Because they enter the brainstem via the trigeminal nerve (does not originate in the spinal cord)

• ONce the pathways synapse in the brainstem, they join the pathways from the body on their way up to the thalamus and somatosensory cortex » consequently, spinal cord lesion do not produce sensory or motor losses involving the face.

How is sensory info from the head transmitted to the brain ?

somatosensory pathways:

1. Posterior / dorsal column-medial lemniscus pathway: (lecture 3) carries somatic information about fine touch, vibration, proprioception from upper and lower body, posterior third of the head)

2. Spinothalamic tract (lecture 3): carries sensory info about crude tocuh, pain, temperature from back of the head and muscle of the external ear

However all remaining general sensation from head (face, scalp, mouth cavity, meninges, sinuses, teeth, tongue, cornea and eyeball, outer surface of eardrum) are all conveyes via the trigeminal nerve (V) to brain.

» TRigeminal nerve pathways

Trigeminal nerve pathways ??

1. Mechanosensory information (face)

2. Temperature, pain (face)

TRigeminal pathway (Mechanosensory info): Function, and orders ??

Function: convey mechanosensory info from the face to the brain.

1st order neuron: Trigeminal nerve (opthalmic, maxillary, mandibular) enters the brainstem at the level of the pons ancd terminate on neurons in the principle nucleus of trigeminal complex

2nd order neuron: The second order neurons of the trigeminal nucleus complex give off axons that cross the midline (the medial lemniscus) and ascend to the ventral posterior medial (VPM) nucleus of the thalamus by way of the trigeminothalamic tract( also called the trigeminal lemniscus)

Third order neuron: Transmit the sensory signals from the VPM of the thalamus to the primary sensory cortex of the brain.

Trigeminal pathway (pain + temperature) Function ?? Orders ??

Function: convey pain and temperature info from the face to the brain.

First order neuron: First order neuron originating from the trigeminal ganglion cells and from ganglia associated with nerves VII (facial), IX (glossopharyngeal) and X (vagus) carry information from facial nociceptotors and thermoreceptors into the pons. Descend into the medulla, forming the spinal trigmeninal tract. Terminate in the spinal nucelus of trigemninal complex.

Second order neuron: Second order neurons in the spinal trigeminal nuclei cross the midline and ascend to the thalamus in the trigeminothalamic tract.

Third order neuron: transmit the sensory signals ventral posterior medial nucelus of the thalamus to the primary sensory cortex of the brain.

TRigeminal Pathways ??

1. Sensory receptors

2. Trigeminal nuclei

3. Thalamus

4. Somato-sensory Cortex

Ganglion = collection of neuronal cell bodies outside CNS

Nucelus = collection of neuronal cell bodies within the CNS

TRigeminal Nerve NUclei ?

LOcated in the midbrain, pons, medulla. CAn be divided into:

• Mesencephalic nucelus

• Pontine (sensory or principal) nucleus

• Spinal nucleus

• MOtor nucelus

Mesencephalic nucelus: (4)

• Receives proprioceptive sensory info from the muscles of mastication, head and neck

• Regulates tooth pain perception

• mediate the jaw jerk reflex

• Project to motor nucelus of the trigeminal nerve

Pontine (sensory or principal) nucleus: (3)

• Receives sensory info about discriminative sensation

• Light touch of the face, conscious perception of jaw

• Project directly to VPM (thalamus)

Spinal nucleus (3)

• receives info about deep / crude touch, pain and temperature

• Receives pain input from trigeminal nerve (V), facial (VII) and glossopharyngeal (IX) and vagus nerve (X)

• Project to VPM (thalamus)

MOtor nucleus (2)

• Located in the upper pons

• Contains motor neuron that innervate the muscles of mastication (important for regulation of chewing)

Refreed pain: WHat is it ? Example ? Reason ?

Referred pain / Reflective pain: Pain perceives at a location other than the site of the painful stimuklus location

Example: heart attack(NB most frequent)

» pain is often felt in the left side of neck, left shoulder and back rather than in the thorax (chest)

ReasonL sensory pain neurons from heart and arm / left shoulder converge onto some nerve pathways in the spinal cord.

» dorsal root ganglion and second order neuron (T1-T5) in spinal cord.

» CNS cannot clearly discern whether pain comes from the heart or from arm.

Another example, why it occurs, examples

Earache (Ear pain)

Most commonly occurs due acute infection of outer ear canal or middle ear canal

» however, pain that feels as if it is in the ear may actually originate in another structure in the head or neck

Ear shares nerves with other nearby structures (face, eyes, jaw, teeth, upper neck)

• Mandibular nerve (V3)

• Lesser Occipital Nerve (C2)

• Vagus Nerve (X)

• Facial nerve (VII)

• Greater auricular nerve

» pain that feels as if its in the ear may actually originate in another structure in the head or neck.

E.g. Wisdom teeth, Temporomandibular disorders (TMJ)

Other example: causes what ?? Pain where ??

Gallstones

• Causes inflammation of the gallbladder

• Usually pain is felt in the epigastric region

» However, if the inflammation irriates the peritonium around the diaphragmn, the pain and travel through the nerve, to its origin at C3 and C5, which is also the origin of the nerves that innervate the skin of the roght shoulder

» gallstones can cause pain in thew right shoulder

Other example

Eosaphagus pain

» local pain stimulated in the esophagus

Referred pain in the abdomen the oblique muscles and the throat

Other example

Kidney stones

» Can cause visceral pain in the ureter as the stone is slowly passes ionto the excretory system

» can cause refferd pain in the lower abdominal wall