4th L

Question 1

explain the brainstem gross anatomy

Answer 1

-The brainstem (brain stem) is the distal part of the brain that is made up of the midbrain, pons, and medulla oblongata. Each of the three components has its own unique structure and function. Together, they help to regulate breathing, heart rate, blood pressure, and several other important functions. All of these brainstem functions are enabled because of its unique anatomy; since the brainstem houses cranial nerve nuclei
-the midbrain is the smallest of the three regions of the brainstem, measuring around 2cm in length. As it ascends, the midbrain travels through the opening in the tentorium cerebelli.
It can be divided into two main parts:
1-Tectum – located posterior to the cerebral aqueduct
2-Paired cerebral peduncles – located anteriorly and laterally.
Internally, the cerebral peduncles are further separated by the substania nigra into the crus cerebri (anterior) and the tegmentum (posterior).
-parts :\
Medulla oblongata
Pons
Midbrain
Fourth ventricle and the foramina of Luschka and Magendie
Interpeduncular, Quadrigeminal, Pontine, and Cerebellomedullary cisterns

Question 2

explain t he tracts of brainstem

Answer 2

The anteriolateral surface of the midbrain houses the paired crus cerebri. Four fibre tracts run within the crus:

1-Frontopontine fibres – located most medially. : The frontopontine fibers are situated in the medial fifth of the base of the cerebral peduncles; they arise from the cells of the frontal lobe and then pass through the anterior limb of internal capsule at last end in the nuclei of the pons. Coronal section through mid-brain.

2-Corticospinal fibres – motor fibres from the primary motor cortex. : [1] As the corticospinal tract travels down the brain stem, a majority of its fibers decussate to the contralateral side within the medulla then continues to travel down the spinal cord to provide innervation to the distal extremities and muscle groups

3-Corticobulbar tracts – motor fibres from the primary motor cortex. :The corticobulbar tract is a two-neuron path which unites the cerebral cortex with the cranial nerve nuclei in the brainstem involved in motor functions (apart from the oculomotor nerve).

4-Temporopontine fibres – located posterolaterally. : they originate in the temporal lobe and end in the nuclei pontis. Coronal section through mid-brain

Question 3

explain the nucleus of :
1-midbrain
2-pons
3- M.O

Answer 3

1-Notable( midbrain )nuclei include the superior and inferior colliculus nuclei, red nucleus, substantia nigra, oculomotor nuclear complex, and trochlear nucleus.

2-Pons :Cranial nerve nuclei: Sensory nuclei of trigeminal nerve, motor nucleus of trigeminal nerve; nucleus of the abducens nerve; nucleus of facial nerve; superior salivatory (salivary) nucleus; inferior salivatory (salivary) nucleus; vestibular nuclei; cochlear nuclei; solitary nucleus
Other nuclei: pontine nuclei, nucleus of lateral lemniscus, nuclei of pontine reticular formation, pedunculopontine nucleus, laterodorsal tegmental nucleus, locus coeruleus

3-M.O :Cranial nerve nuclei (IX-XII): inferior salivatory nucleus, spinal nucleus of trigeminal nerve, solitary nucleus, nucleus ambiguus, dorsal nucleus of vagus nerve, nucleus of accessory nerve, nucleus of hypoglossal nerve
Relay nuclei: gracile, cuneate, arcuate, and olivary nuclei
Reticular nuclei: raphe nuclei, gigantocellular (magnocellular) nucleus, perihypoglossal (Roller’s) nucleus, lateral reticular nucleus and many other small clusters of neurons distributed throughout the base of the medulla

Question 4

explain the CN 3

Answer 4

-It has two major components:
(1) a medially situated parasympathetic nucleus, ( Edinger Westphal nucleus or accessory autonomic nucleus), which innervates the intraocular muscles (the sphincter pupillae muscle and the ciliary muscle);
(2) more laterally situated nuclear complex for four extraocular muscles (the superior, inferior, and medial rectus muscles and the inferior oblique muscle).
-The combined motor and parasympathetic fibers traverse the red nucleus and exit the brainstem in the interpeduncular fossa as the oculomotor nerve.

Question 5

explain the Trochlear (CN IV)

Answer 5

-CN IV arises from the trochlear nucleus at the level of the inferior colliculus and then exits the dorsal surface of the brainstem (it is the only cranial nerve that does this), emerging from the midbrain tectum into the quadrigeminal cistern.
-The nerve winds around the brainstem, then runs forward, passes through the cavernous sinus in proximity to CN III, traverses the superior orbital fissure, and enters the orbit to supply the superior oblique.
-disorder :
Trochlear Nerve Palsy
Clinical:
diplopia,when the patient looks downward and inward
The affected eye deviates upward and slightly inward (medially, toward the side of the normal eye)

Question 6

explain Abducens (CN VI)

Answer 6

-The nucleus of the VI cranial nerve lies in the caudal pontine tegmentum, just beneath the floor of the fourth ventricle. Axons pass forward through the substance of the pons, weaving among descending corticospinal fi bers, and exit anteriorly. CN VI ascends the clivus, traverses the cavernous sinus in company with the CNs III, IV, and V, and then passes through the superior orbital fi ssure and enters the orbit to innervate the lateral rectus.
Clinical:
convergent strabismus, when looking toward the nose
diplopia