Lecture 3: Neuroanatomy and physiology

Question 1

What is the general motor pathway to induce a contraction?

Answer 1

A motor impulse arises from the Primary motor area neuron cells to execute a desired movement. The impulse travels down along the axon of the UPPER MOTOR neuron. The target destination is a muscle to induce a contraction.

Question 2

Describe the pathway in more detail during the motor pathway.

Answer 2

the Axons converge from the cerebral hemisphere at the internal capsule and descend to the brainstem.

Question 3

What is the internal capsule?

Answer 3

The internal capsule is a location of many converged fibers. An injury to the internal capsule would have a massive effect.

Question 4

The axon in the brainstem carries the impulse to the

Answer 4

contralateral side of the body. Also called the pyramidal tract.

Question 5

Describe the corticospinal tract

Answer 5

The pathway of the axon of the upper motor neuron of the cortex to the nerve cell of a spinal nerve

Question 6

Describe the corticobulbar tract

Answer 6

The pathway of the axon of the upper motor neuron of the cortex to the nerve cell of a cranial nerve

Question 7

What are some details about the corticospinal tract?

Answer 7

-The grey matter of the spinal cord is on the inside surrounded by white matter
- The grey matter assumes the shape of the letter H with Dorsal and Ventral Horns
- The axons descend lateral to the grey matter, their name is anatomically assigned :The lateral corticospinal tract.

Question 8

The dorsal horn is

Answer 8

the relay center for sensory information, both Dorsal and ventral roots combine to form the nerve trunk

Question 9

What are some more details of the dorsal horn

Answer 9

-The dorsal horn of the spine is the main relay site for sensory information

-There is a need for many synapses to transmit a variety of sensations

Question 10

What is the ganglion?

Answer 10

• a structure that is used by the nervous system to provide a location for synapses.
• Due to the amount of synapses there is a need for more surface area to transmit neuron signals

Question 11

What is an important fact about the Corticobulbar tract?

Answer 11

All the cell bodies of the lower motor neurons of cranial nerves receive bilateral corticobulbar input except , lower ½ of VII and all of XII, both receive contra-lateral input only

Question 12

Cranial Nerve I

Answer 12

The olfactory nerve:

Olfactory receptor nerve cells { first order neuron} are in the nasal mucosa

Their axons go through Cribriform plate of ethmoid bone

They relay impulses to the olfactory bulb nerve cells { second order neuron} at the Orbitofrontal cortex.

The axons emerge from the olfactory bulb as the olfactory tract , and transmits impulses bilaterally to the Uncus

Damage could result in : Loss of smell or Olfactory hallucinations

Question 13

Cranial Nerve II

Answer 13

The optic nerve : Vision

-The first order neuron cells for vision reception are those of the retina

The retina on the nasal side sees the lateral visual field { temporal}

fibers on the same side collectively form an optic nerve that travels through the optic canal to the cranial cavity

The second order neuron cell is at the Thalamus Lateral geniculate body

Question 14

Cranial Nerve III

Answer 14

The Oculomotor nerve:

motor nucleus in the Midbrain , receives bilateral cerebral input

Reaches the orbit through the superior orbital fissure

Responsible for :
70 % of upper eyelid elevation
Movement of the eye ball in all directions except inward-downward, and lateral

Has an autonomic effect

Question 15

Describe Autonomic function of the Oculomotor nerve

Answer 15

an autonomic effect : ciliary muscle for the lens of the eye { accommodation} , and constrictor papillae , the autonomic fibers are superficial to the motor fibers on the nerve trunk .

If the lesion is external compression the autonomic function is lost , if the lesion is loss of intraneural blood supply , the motor function is lost

Testing for motor function: Ask the patient to move the eye in all directions .

Testing for autonomic function : Shine a torch light into one eye , there should be a pupillary constriction on both sides . This implies that the sensory input is resulting in simultaneous motor nucleus stimulation.

Question 16

Cranial Nerve IV

Answer 16

The trochlear
Purely motor , motor nucleus in Midbrain , supplies muscle responsible for inward- downward eye movement . Receives bilateral cerebral Input. Reaches the orbit through the superior orbital fissure

Question 17

Cranial Nerve VI

Answer 17

The Abducent

Purely motor , motor nucleus in Pons , supplies muscle responsible for lateral eye movement. Receives bilateral cerebral Input. Reaches the orbit through the superior orbital fissure.

Testing for movement and , asking about diplopia ;
Double vision of the same object.
Input from both eyes no longer synchronized

Question 18

Cranial Nerve V

Answer 18

Trigeminal

Motor and Sensory. Motor nucleus in Pons . Three Divisions. Bilateral cerebral motor input.
{Ophthalmic, Maxillary, Mandibular }

Question 19

Describe the sensory portion of the Trigeminal Nerve

Answer 19

Sensory: All the face except angle of mandible , general sensation from anterior 2/3 of the tongue & the buccal cavity

First order neurons : The nerve cells of those neurons are bipolar and are located in the trigeminal ganglion {two long axonal processes} .
The peripheral axons collect the sensations from the periphery

Question 20

Explain how the fibers of the Trigeminal enter the Cranium

Answer 20

The Ophthalmic fibers enter the Cranium through the superior orbital fissure of the sphenoid bone

The Maxillary fibers enter the Cranium through the Foramen Rotundum of the sphenoid bone

The Mandibular fibers enter the Cranium through Foramen Oval and foramen Spinosum
of the sphenoid bone,

Question 21

Motor V

Answer 21

motor fibers arise from the Trigeminal nucleus in the pons receiving the upper motor neuron cortico-bulbar input from both hemispheres

The lower motor neuron fibers emerge from the Pons through the Trigeminal ganglion along the mandibular division and supply innervation to the muscles of mastication

Testing : Motor decline in masticatory power
Sensory loss of corneal reflex , ( see later)

Question 22

Cranial Nerve VII

Answer 22

The facial Nerve

Motor, Sensory, & Autonomic

The Motor nucleus is in the Pons, The sensory nucleus is in the Medulla . It innervates the muscles of facial expression, Platysma, posterior belly of Digastric, Stapedius, Stylohyoid.

The upper half of the motor nucleus of the Facial nerve receives corticobulbar fibers from both cerebral hemispheres; the lower half of the motor nucleus receives corticobulbar fibers only from the contralateral side

The upper half of the nucleus supplies the upper half of the face , and the lower half of the nucleus supplies the lower half of the face

Question 23

Sensory and Autonomic properties of Cranial Nerve VII

Answer 23

There is a Ganglion {Geniculate ganglion} within the facial canal. The nerve cell axon splits into 2 directions.

The peripheral branch is Sensory and Autonomic, it divides into two branches

1- The Greater Superficial petrosal. This relays in the Sphenopalatine ganglion before supplying autonomic fibers to the lacrimal gland

2- The Chorda Tympani exits from the Facial canal before the Stylomastoid Foramen , it supplies the submandibular and sublingual salivary glands. The fibers of the chorda tympani also act as first order neurons for taste for the anterior 2/ 3 of the tongue. The fibers relay in the solitary nucleus of the upper medulla

3- The second order neurons cross, and ascend to the Cortical sensory area of the other side

Question 24

Describe the corneal reflex

Answer 24

When the surface of the eye ball is touched with a cotton or tissue gently, there is bilateral blinking

The afferent sensory information flows through the ophthalmic branch of trigeminal . The motor component is through the facial fibers exiting from the parotid gland to the muscles of facial expression

Question 25

What happens when there is a loss of facial expression

Answer 25

1- Injury to the upper motor neuron / motor cortical area: because of the bilateral innervation of the upper half of the nucleus, only the lower half of the face will be affected.

2- Injury to the lower motor neuron : the effect will be on the full half face of the affected side .

Question 26

Cranial Nerve VIII

Answer 26

The vestibulocochlear nerve

Responsible for Hearing and Equilibrium

Innervations from one side are directed to both hemispheres but predominantly to the contralateral side

Question 27

Cranial IX

Answer 27

The Glossopharyngeal Nerve

Motor { bilateral corticobulbar input} , Sensory & Autonomic, nucleus in Medulla

Motor to Stylopharyngeus and Pharyngeal constrictors

Sensory : general sensations and taste from the posterior 1/3 of the tongue general sensations from the pharynx

Gag reflex : Afferent IX , efferent X , Gag { elevate the palate, and contract the pharynx} on touching the posterior end of the soft palate and the pharyngeal wall with a tongue depressor

Autonomic to the Parotid gland

Question 28

Cranial X

Answer 28

The Vagus Nerve

Motor { bilateral corticobulbar input }, sensory , and Autonomic, nucleus in Medulla

Motor to soft palate , pharynx , and larynx

Sensory to thoracic and abdominal viscera { internal pain }

Autonomic : Heart, Gastrointestinal tract { the gut}, bronchial tree

Question 29

Cranial XI

Answer 29

The Accessory nerve:

Nucleus in Medulla , Nerve exiting from medulla binds with nerves fibers { also lower motor neuron fibers } from 1st 5 cervical segments .

The cervical fibers ascend into the cranium through the Foramen Magnum

Cranial fibers contribute to pharyngeal plexus supplying the pharynx , and larynx

Cervical fibers Supply two muscles: Trapezius and Sternomastoid

Exits cranium from jugular foramen

Question 30

Trapezius muscle:

Answer 30

Elevates the shoulder and tilts the head to the same side

Question 31

Sternomastoid Muscle

Answer 31

Unilateral contraction flexes the cervical vertebrae to the same side and rotates the head to the opposite side / Bilateral contraction: no rotation , only neck flexion

Question 32

Cranial Nerve XII

Answer 32

The hypoglossal

Purely Motor
Nucleus in Medulla
Supplies all Intrinsic and Extrinsic muscles of the tongue { except the Palatoglossal ( from Vagus)
Unilateral Corticobulbar supply from contralateral hemisphere { opposite side}
Bilateral UMNL / LMNL : inability to protrude the tongue
Unilateral UMNL : Deviated to the opposite side of the lesion
Unilateral LMNL : To the side of the lesion

Question 33

Intrinsic Muscle:

Answer 33

Both origin and insertion within the structure . Eg. Intrinsic muscles of the tongue and intrinsic muscles of the Larynx

Question 34

Extrinsic Muscles :

Answer 34

origin in one structure , insertion in another

Question 35

Palatoglossus

Answer 35

Origin: In the palate, insertion in the tongue { an extrinsic muscle of the tongue} ,

Action : elevates the back of the tongue towards the palate

Nerve supply : Vagus { pharyngeal plexus}