From My Biochemistry

THREE THINGS TEACHERS WISH STUDENTS KNEW

June 03, 2007
Queena Lee-Chua
Inquirer

MANILA, Philippine - When I ask my students: "How can you make the most of school?" they dutifully recite stock answers: Study hard. Come to school prepared. Do not cram. Avoid cheating. Better behave in class, or else.

I agree with everything, except the last one. I would rather have a class of lively students who challenge everyone with insights, rather than a group of silent automatons who regurgitate everything I say.

That said, my students have missed important points. Study hard, yes, but study wisely, too. Come to school prepared, not just with materials, but also with SMART goals. Do not cram, so make sure to master the basics beforehand. Avoid cheating, certainly, but outside of exams, never be afraid to ask for help.

Set SMART goals

Companies expend a lot of effort on five- or 10-year plans. Bankers help us save for retirement. Learners also need to set goals— SMART goals.

A goal is Specific. What do you want to accomplish? Instead of saying: "I want to be a good student," which is vague, state the goal clearly: "I want to get an average of 90 percent in History by the end of the quarter."

A goal is Measurable. You need to keep track of your progress. For example, "So far, I have received good scores on three quizzes. I need to practice my oral presentation, so I can maintain my average."

A goal is Action-Oriented. Merely dreaming about a good grade is not enough. You need to take action to achieve your goal. "To do well in History, I need to do my assignments and read the textbook regularly."

A goal is Realistic. Decide if a goal is attainable in the first place, and then think about how much effort, time and resources you can expend to reach your goal.

When I was a freshman in college, my goal was to learn as much math and English as I could, and do my best in other subjects. However, advanced placement classes meant solving math problems and writing compositions every day, on top of homework and term papers in other subjects. I was a class officer and a member of the Math Club, with frequent meetings and activities. To top it off, I yearned to be part of the swim team, which entailed frequent lengthy practice sessions.

I managed time pretty well, but there was no way I could do everything. Something had to give. I did not want to lose sight of my goal, which, after all, was mainly academic. There was no way I could sacrifice my studies. So with great reluctance, I dropped the swim team. In this lifetime, I would never be Christine Jacobs, but I could be a mathematician.

A goal is Time-Bound. How much have you achieved at a certain point? "If I want a good grade in History at the end of the quarter, which is a month away, do I focus more on the textbook, or do I revise my term paper? If both, how much time do I spend on each task?"

Ask for help

Seek help at the first sign of trouble. Students dread report card time, but I will tell you a secret: so do teachers. Parents, tutors and the rest of the extended family descend en masse to threaten or plead with teachers to "reconsider" failing marks. By then, it is too late.

When we fall ill, we go to the doctor at once. When we are hungry, we look for something to eat. Why then do students delay seeking help when they don't understand a lesson?

On the first day of class, I tell my students: "When you do not understand something, please seek help at once. Turn to a classmate, do research in the library or on the Net, ask your parents or consult me. If you let the little problems pile up, then you will be over whelmed later on."

In a class of 40 students, it is impossible for teachers to meet the learning needs of everyone. One-on-one tutorials may be essential for slower or faster learners. I inform students of my regular consultation hours, and I am happy that many of them use this opportunity to enhance learning. For students who need to brush up on the basics, I go through exercises with them in detail. For those who prefer a challenge, I discuss advanced topics or pose more complex problems.

Teachers, good teachers, at least, welcome questions. Last year, when my son was in Grade 2, his Science teacher told me: "I like the fact that Scott is not afraid to ask questions if he wants to clarify things. I especially admire him for doing the asking himself. Mostly, parents are the ones who call me up, and sometimes I wonder if they or their sons are the ones with the questions. I hope they are not doing the homework for their kids."

When the teacher discusses a lesson, review the details later in the day, even if the test is still far away. If a point is not clear, reflect on it for a while. If you really cannot understand it, then seek help as soon as possible. Do not close your eyes and pray that you will never see the topic again. According to Murphy's Law, the topics you don't know are most likely the ones you will meet in the test.

Master the basics

My friend was frantic. "Can you help my daughter? She does not know division and she has a test next week. I have been sitting beside her for four hours, and we have not made progress. Now I am yelling at her, and she is crying. I don't know what to do."

Sure enough, her daughter, whom I will call Riza, could not do division. But what my friend neglected to mention was that Riza could barely do multiplication either. Four hours, even four times four hours, of hard work was not the best strategy here. If Riza did not know that 4 times 6 is 24, then how could she tackle 24 divided by 4?

Rizas problem was not so much division itself, but lack of mastery of the skills required for division. I was not surprised to learn that Riza had also flunked a previous test for multiplication.

"Can't we just do division now, and go back to multiplication next time," she pleaded, "since the coming test will be on division anyway?"

Sorry, no way. New knowledge builds on prior learning and, for a subject like math, where one concept leads to another, mastery of the basics is essential. For the next four days, we did nothing but multiplication. I introduced songs, pointed out number patterns and advised Riza to eat memory-boosting foods.

We studied division only during the last two days, but by then, spurred by freshly learned multiplication facts and a giant fear of failure, Riza was able to grasp the concepts. She got 80 percent on the test, and would have gotten higher if she had finished the 50 items.Of course, to totally master a topic, how could a week, however intensive it had been, ever be enough?

Once, when I asked a student why he failed a test, he admitted: "I did not understand Chapter Two, so I skipped the pages and went to Chapter Three. But I got lost. I was hoping to catch up in the next chapter, but things got worse."

Studying hard is important, but it is also essential to study wisely. If you cannot comprehend a complex topic, chances are you have not understood the concepts leading up to it. Instead of banging your head on the proverbial wall, or worse, giving up, why don't you go back to earlier lessons? Again, seek help if needed.

Learning is not easy, but then, things worth doing seldom are. But with the right mindset, proper support and good habits, learning can not only be endured, but even enjoyed as well. Have a great school year!

Queena N. Lee-Chua is a professor of mathematics and psychology at the Ateneo de Manila University.

Neuroanatomy Transcriptions - Brainstem

Brainstem is made up of:

1. Medulla Oblongata
2. Pons
3. Midbrain

Occupies the: Posterior Cranial Fossa of the Skull

* Stalklike in shape

* Connects the narrow spinal cord with the expanded forebrain

Broad Functions:

1. Serves as a conduit for the ascending tracts and descending tracts connecting the spinal cord to the different parts of the higher centers in the forebrain

2. Contains important reflex centers associated with the control of respiration and the cardiovascular system; also associated with the control of consciousness

3. Contains important nuclei of cranial nerves III through XII

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GROSS APPEARANCE OF THE MEDULLA OBLONGATA

* Medulla Oblongata connects the pons superiorly with the spinal cord interiorly

* Junction of the medulla and spinal cord

° located at the origin of the anterior and posterior roots of the first cervical spinal nerve corresponding to the level of foramen magnum

* Conical in shape

* Broad extremity being directed superiorly

* Central Canal

° Continues upward into the lower half of the medulla

° In upper half it expands as the cavity of the 4^th ventricle

* Anterior Median Fissure

° Located at the anterior surface if the medulla

° Continuous inferiorly with the anterior median fissure of the spinal cord

* Pyramid

° Swelling located on each side of the median fissure

° Composed of bundles of nerve fibers, corticospinal fibers, which originate in large nerve cells in the precentral gyrus of the cerebral cortex

° Taper inferiorly

° It is here that majority of the descending fibers cross over the opposite side, forming the decussation of the pyramids

* Anterior external arcuate fibers

° Few nerve fibers that emerge from anterior medial fissure above the decussation and pass laterally over the surface of the medulla oblongata to enter the cerebellum

* Olives

° Posterolateral to the pyramids

° Oval elevations produced by the underlying inferior olivary nuclei

* Rootlets of the hypoglossal nerve

° Emerge in the groove between the pyramid and the olive

* Inferior Cerebellar Peduncles

° Posterior to the olives

° Connect the medulla to the cerebellum

* Roots of the glossopharyngeal and vagus nerves and cranial roots of accessory nerve

° Emerge in the groove between the olive and the inferior cerebellar peduncle

* Floor of the fourth ventricle

° Lower part is formed by the posterior surface of the superior half of the medulla oblongata

* Posterior Medial Sulcus

° Possessed by the posterior surface of the inferior half of the medulla which is continuous with the posterior aspect of the spinal cord

* Gracile Tubercle

° Elongated swelling on each side of median sulcus

° Produced by the underlying gracile nucleus

* Cuneate Tubercle

° Lateral to the gracile tubercle

° Similar swelling as the gracile tubercle

° Produced by the underlying cuneate nucleus

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INTERNAL STRUCTURE

Medulla Oblongata consists of white and gray matter but have been extensively rearranged

Explanation:

1. This rearrangement is due to the expansion of the neural tube to form the hindbrain vesicle
2. This hindbrain vesicle becomes the 4^th ventricle
3. The extensive lateral spread of the 4^th ventricle results in alteration in the position of the derivatives of the alar and basal plates of the embryo

To assist in understanding this concept:

Remember!

In the Spinal cord In Medulla Oblongata

derivatives Posterior to sulcus limitans lateral to sulcus limitans

of alar plates

derivatives anterior to sulcus limitans medial to sulcus limitans

of basal plates

4 Levels of the internal structure of the medulla oblongata

1. Level of decussation of pyramids
2. Level of decussation of lemnisci
3. Level of the olives
4. Level just inferior to the pons

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LEVEL OF DECUSSATION OF PYRAMIDS

* Great Motor Decussation

* Where a transverse section through the inferior half of the medulla oblongata passes through

* In superior part of the medulla: corticospinal fibers occupy and form the pyramid

* Inferiorly: about ¾ of the fibers cross the medial plane and continue down the spinal cord in the lateral white column as the lateral corticospinal tract

° As these fibers cross the midline, they sever the continuity between the anterior column of the gray matter of the spinal cord and the gray matter that surrounds the central canal

* Fasciculus gracilis and the fasciculus cuneatus

° Continue to ascend superiorly posterior to the central gray matter

* Nucleus gracilis and nucleus cuneatus

°Appear as posterior extensions of the central gray matter

* Substantia gelatinosa in posterior gray column of the spinal cord

° Becomes continuous with the inferior end of the nucleus of the spinal tract of the trigeminal nerve

* The fibers of the tract of the nucleus

° Situated between the nucleus and the surface of the medulla oblongata

° The lateral and anterior white columns of the spinal cord are easily identified in these sections and their fiber arrangement is unchanged

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LEVEL OF DECUSSATION OF LEMNISCI

* The Great Sensory Decussation

* Where a transverse section through the inferior half of the medulla oblongata, a short distance above the level of the decussation of the pyramids passes through

* Takes place anterior to the central gray matter and posterior to the pyramids

* The lemnisci have been formed from the internal arcuate fibers

* Internal arcuate fibers

° Emerged from the anterior aspects of the nucleus gracilis and nucleus cuneatus

° First travel anteriorly and laterally around the central gray matter

° They then curve medially toward the midline, where they decussate with the corresponding fibers of the opposite side.

* Nucleus of the spinal tract of the trigeminal nerve

° Lies lateral to the internal arcuate fibers

° Spinal tract of the trigeminal nerve lies lateral to the nucleus

* Lateral and Spinothalamic tracts and Spinotectal tracts

° Occupy an area lateral to the decussation of the lemnisci

° They are very close to one another and collectively known as the spinal lemniscus

* Situated in the anterolateral region of medulla oblongata:

° Spinocerebellar, vestibulospinal, rubrospinal tracts

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LEVEL OF OLIVES

* A transverse section through the olives passes across the inferior part of the 4^th ventricle

* The amount of gray matter has increased owing to the presence of the olivary nuclear complex:

° Nuclei of vestibulocochlear

° Glossopharyngeal

° Vagus

° Accessory

° Hypoglossal nerves

° Arcuate nuclei

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OLIVARY NUCLEAR COMPLEX

Inferior Olivary nucleus – Largest nucleus of this complex

* Gray matter – shaped like a crumpled bag with its mouth directed medially

- Responsible for the elevation on the surface of the medulla called, olive

* Smaller dorsal and medial accessory olivary nuclei are also present

* Cells of the inferior olivary nucleus send fibers medially across the midline to enter the cerebellum through the inferior cerebellar peduncle

* Afferent fibers reach the inferior olivary nuclei from the spinal cord (spino-olivary tracts) and from the cerebellum and cerebral cortex

* Function of the olivary nuclei: Associated with voluntary muscle movement

VESTIBULOCOCHLEAR NUCLEI

Made up of the following nuclei:

1. Medial vestibular nucleus
2. Inferior vestibular nucleus
3. Lateral vestibular nucleus
4. Superior vestibular nucleus

Cochlear nuclei - two in number

Anterior Cochlear nucleus - situated on the anterolateral aspect of the inferior cerebellar peduncle

Posterior Cochlear nucleus - situated on the posterior aspect of the peduncle lateral to the floor of the 4^th ventricle

NUCLEUS AMBIGUUS

* Consists of large motor neurons

* Situated deep within the reticular formation

* The emerging nerve fibers join the glossopharyngeal vagus, and cranial part of the accessory nerve and are distributed to voluntary skeletal muscle

* Deeply placed within the reticular formation

CENTRAL GRAY MATTER

* Lies beneath the floor of the 4^th ventricle

* Passes from medial to lateral

* The following important structures may be recognized:

1. Hypoglossal nucleus

2. Dorsal nucleus of the vagus

3. Nucleus of the tractus solitarius

4. Medial and inferior vestibular nuclei

* Arcuate nuclei

° Thought to be inferiorly displaced pontine nuclei

° Situated on the anterior surface of the pyramids

° They receive nerve fibers from the cerebral cortex

° Send efferent fibers to the cerebellum through the anterior external arcuate fibers

* Pyramids containing the corticospinal and some corticosnuclear fibers

° Situated in the anterior part of the medulla

° Separated by the anterior median fissure

° Corticospinal fibers descend to the spinal cord

° Corticonuclear fibers are distributed to the motor nuclei of the cranial nerves situated within the medulla

* Medial Lemniscus

° Forms a flattened tract on each side of the midline posterior the pyramid

° These fibers emerge from the decussation of the lemnisci and convey sensory information to the thalamus

* Medial Longitudinal Fasciculus

° Forms a small tract of nerve fibers situated on each side of the midline posterior to medial lemniscus and anterior to hypoglossal nucleus

° Consists of ascending and descending fibers

* Inferior Cerebellar Peduncle

° Situated in posterolateral corner of the section on lateral side of 4^th ventricle

* Spinal tract of trigeminal nerve and its nucleus

° Situated on the anteromedial aspect of the inferior cerebellar peduncle

* Anterior Spinocerebllar Tract

° Near the surface in the interval between the inferior olivary nucleus and the nucleus of the spinal tract of the trigeminal nerve

* Spinal Lemniscus

° Deeply placed

° Consists of:

Anterior Spinothalamic

Lateral Spinothalamic

Spinotectal tracts

Reticular formation

° Consists of a diffuse mixture of nerve fibers and small groups of nerve cells

° Deeply placed posterior to the olivary nucleus

° Represents, at this level, only a small part of this system, which is also present in the pons and midbrain

Glossopharyngeal

Vagus can be seen running forward and

Cranial part of the accessor nerves laterally through the reticular formation

* The nerve fibers emerge between the olives and the inferior cerebellar peduncles

Hypoglossal nerves

° Run anteriorly and laterally through the reticular formation and emerge between the pyramids and the olives

LEVEL JUST INFERIOR TO THE PONS

° No major changes

° Lateral vestibular nucleus has replaced the inferior vestibular nucleus

° Cochlear nuclei now are visible on the anterior and posterior surfaces of the inferior cerebellar peduncle

GROSS APPEARANCE OF THE PONS

* Pons is anterior to the cerebellum

* Connects the medulla oblongata to the midbrain

* About 1 inch (2.5 cm) long

* Owes its name to the appearance presented on the anterior surface, which is that of a bridge connecting the right and left cerebellar hemispheres

* Anterior surface

° Convex from side to side

° Shows many transverse fibers that converge on each side to form the middle cerebellar peduncle

* Basilar groove

° Shallow groove in the midline

° Lodges the basilar artery

* Anterolateral surface of the pons

° trigeminal nerve emerges on each side

° Each nerve consist of:

Smaller, medial part – the motor root

Larger, lateral part – sensory root

* In the groove between the pons and medulla oblongata

° There emerge from medial to lateral:

abducent, facial, and vestibulocochlear nerves

* the Posterior surface of the pons

° hidden from view

° Forms the upper half of the floor of the 4^th ventricle

° Triangular in shape

° Limited laterally by the superior cerebellar peduncles

° Divided into symmetrical halves by a median sulcus

° Lateral to this sulcus is an elongated elevation, the medial eminence

° Medial eminence is bounded laterally by the sulcus limitans and its inferior end is slightly expanded to form the facial colliculus

° Facial colliculus is produced by the root of the facial nerve winding around the nucleus of the abducent nerve

° The floor of the superior part of the sulcus limitans is bluish gray in color and is called the substantia ferruginea (it owes its color to a group of deeply pigmented nerve cells)

° Lateral to the sulcus limitans is the area vestibuli produced by the underlying vestibular nuclei

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INTERNAL STRUCTURE OF THE PONS

Divisions of the pons:

1. Tegmentum - posterior part

2. Basal part – anterior part by the transversely running fibers of the trapezoid body

The structure of the pons may be studied at two levels:

1. Transverse section through the caudal part
1. Passing through the facial colliculus
2. Transverse section through the cranial part
1. Passing through the trigeminal nuclei

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TRANSVERSE SECTION THROUGH THE CAUDAL PART

Medial lemniscus

• Rotates as it passes from the medulla into the pons
• Situated in the most anterior part of the tegmentum with its long axis running transversely
• Accompanied by the spinal and lateral lemnisci

Facial nucleus

• Lies posterior to the lateral part of the medial lemniscus
• The fibers of the facial nerve wind around the nucleus of the abducent nerve, producing the facial colliculus
• Fibers of the facial nerve pass anteriorly between the facial nucleus and the superior end of the nucleus of the spinal tract of the trigeminal nerve

Medial longitudinal fasciculus

• Situated beneath the floor of the 4^th ventricle on either side of the midline
• Main pathway that connects the vestibular and cochlear nuclei with the nuclei controlling the extraocular muscles (oculomotor, trochlear, and abducent nuclei)

Medial Vestibular nucleus

• Situated lateral to the abducent nucleus
• In close relationship to the inferior cerebellar peduncle
• Where the superior part of the lateral and the inferior part of the superior vestibular nucleus are located
• Posterior and anterior cochlear nuclei are also found at this level

Spinal Nucleus of the trigeminal nerve

• Lie on the anteromedial aspect of the inferior cerebellar peduncle

Trapezoid body

• Made up of fibers derived from the cochlear nuclei and the nuclei of the trapezoid body
• Run transversely in the anterior part of the tegmentum

Pontine Nuclei

• Small masses of nerve cells contained in the basilar part of the pons

Corticopontine fibers of the crus cerebri of the midbrain

• Terminate in the pontine nuclei
• Axons of these cells gives origin to the transverse fibers of the pons

Transverse fibers of the pons

• Cross the midline and intersect the corticospinal and corticonuclear tracts, breaking them up into small bundles
• Enter the middle cerebellar peduncle
• Distributed to the cerebellar hemisphere
• This connection forms the main pathway linking the cerebral cortex to the cerebellum

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TRANSVERSE SECTION THROUGH THE CRANIAL PART

* Internal structure is similar to that seen at the caudal levels

* But it now contains the motor and principal sensory nuclei of the trigeminal nerve

Motor nucleus of the trigeminal nerve

• Situated beneath the lateral part of the 4^th ventricle within the reticular formation
• Emerging motor fibers travel anteriorly through the substance of the pons and exit on its anterior surface

Principal sensory nucleus of the trigeminal nerve

• Situated on the lateral side of the motor nucleus
• Continuous inferiorly with the nucleus of the spinal tract
• Entering sensory fibers travel through the substance of the pons and lie lateral to the motor fibers

Superior Cerebellar peduncle

• Situated posterolateral to the motor nucleus of the trigeminal nerve
• Joined by the anterior spinocerebellar tract

Trapezoid body and medial lemniscus

• Situated in the same position as they were in the previous section

Lateral and spinal lemnisci

• Lies at the lateral extremity of the medial lemniscus

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GROSS APPEARANCE OF THE MIDBRAIN

* 0.8 inch (2 cm) in length

* Connects the pons an dcerebellum with the forebrain

* Its long axis inclines anteriorly as it ascends through the opening in the tentorium cerebelli

Cerebral Aqueduct

• narrow channel traversing the midbrain
• filled with CSF

Four colliculi

• Corpora quadrigemina
• Found on the posterior surface
• Rounded eminences that are divided into superior and inferior pairs by a vertical and a transverse groove

Superior Colliculi Inferior Colliculi

• Centers for visual reflexes Lower auditory centers

Trochlear nerves

• Emerging from the midline below the inferior colliculi
• Small diameter nerves that wind around the lateral aspect of the midbrain to enter the lateral wall of the cavernous sinus

* The superior and inferior brachia ascend in an anterolateral direction on the lateral aspect of the midbrain

Superior brachium

• Passes from the superior colliculus to the lateral geniculate body and the optic tract

Inferior brachium

• Connects the inferior colliculus to the medial geniculate body

* On anterior aspect of midbrain

• There’s a deep depression in the midline the interpeduncular fossa
• interpeduncular fossa
• Bounded on either side by the crus cerebri
• Floors are perforated by many blood vessels and this region is termed the posterior perforated substance
• Oculomotor nerve
• Emerges from a groove on the medial side of the crus cerebri
• Passes forward in the lateral wall of the cavernous sinus

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INTERNAL STRUCTURE OF THE MIDBRAIN

2 lateral halves of midbrain: Cerebral peduncles

Each divided into

- an anterior part: the Crus cerebri

- posterior part: Tegmentum

Division is made possible by substantia nigra, pigmented band of gray matter

Cerebral aqueduct

• Narrow cavity of the midbrain
• Connects the 3^rd and 4^th ventricle

Tectum

• Part of the midbrain posterior to the cerebral aqueduct
• Has four small surface swellings referred to previously
• 2 superior and 2 inferior colliculi

Central gray matter

• Surrounds the cerebral aqueduct (lined by ependyma)

Interpeduncular fossa on transverse sections of the midbrain

• Can be seen to separate the crura cerebri
• Whereas the tegmentum is continuous across the median plane

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TRANSVERSE SECTION OF THE MIDBRAIN AT THE LEVEL OF THE INFERIOR COLLICULI

Inferior colliculus

• Consists of a large nucleus of gray matter
• Lies beneath the corresponding surface elevation
• Forms part of the auditory pathway
• Receives many of the terminal fibers of the lateral lemniscus
• Pathway then continues through the inferior brachium to the medial genicualte body

Trochlear nucleus

• Situated in the central gray matter close to the median plane
• Posterior to the medial longitudinal fasciculus

1. Emerging fibers pass laterally and posteriorly around the central gray matter
2. Leave the midbrain just below the inferior colliculi
3. Fibers of the trochlear nerve now decussate completely in the superior medullary velum

* Mesencephalic nuclei of the trigeminal nerve

° Lateral to the cerebral aqueduct

* The Decussation of the superior cerebellar peduncles

° Occupies the central part of the tegmentum anterior to the cerebral aqueduct

*Reticular formation

° Smaller than that of the pons

° Situated lateral to the decussation

Medial lemniscus – ascends posterior to the substantia nigra

Spinal and trigeminal lemnisci – situated lateral to the medial lemniscus

Lateral Lemniscus – located posterior to the trigeminal lemniscus

Substantia Nigra

° Large motor nucleus

° Situated between the tegmentum and the crus cerebri

° Found throughout the midbrain

° Nucleus is composed of medium sized multipolar neurons that possess inclusion granules of melanin pigment within their cytoplasm

° Concerned with muscle tone

° Connected to the cerebral cortex, spinal cord, hypothalamus and basal nuclei

Crus cerebri

° Contains important descending tracts

° Separated from the tegmentum by the substantia nigra

° Middle 2/3 is occupied by the corticospinal and corticonulcear fibers

° Medial part is occupied by the frontopontine fibers

° Lateral part occupied by the temporopontine fibers

* These descending tracts connect the cerebral cortex to the anterior gray column cells of the spinal cord, cranial nerve nuclei, pons, and cerebellum

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TRANSVERSE SECTION OF THE MIDBRAIN AT THE LEVEL OF THE SUPERIOR COLLICULI

Superior colliculus

• Large nucleus of gray matter that lies beneath the corresponding surface elevation
• Forms part of the visual reflexes
• Connected to the lateral geniculate body by the superior brachium
• It receives afferent fibers from the optic nerve, the visual cortex and the spinotectal tract
• Efferent fibers
• Form the tectospinal and tectobulbar tracts,
• Responsible for the reflex movements of the eyes, head, and neck in response to visual stimuli
• Afferent pathway for the light reflex ends in the pretectal nucleus
• This is small group of neurons situated close to the lateral part of the superior colliculus
• After relaying in the pretectal nucleus, the fibers pass to the parasympathetic nucleus of the oculomotor nerve (Edinger-Westphal nucleus)

• The emerging fibers then pass to the oculomotor nerve.

Oculomotor nucleus

• Situated in the central gray matter close to the median plane, just posterior to the medial longitudinal fasciculus
• The fibers pass anteriorly through the red nucleus to emerge on the medial side of the crus cerebri in the interpeduncular fossa
• Nucleus of the oculomotor nerve is divisible into a number of cells group

* Medial, spinal, and trigeminal lemnisci

• Form a curved band posterior to the substantia nigra

* Lateral lemniscus

• Does not extend superiorly to this level

Red nucleus

• Rounded mass of gray matter
• Situated between the cerebral aqueduct and the substantia nigra
• Reddish hue seen in fresh specimen
• Due to its vascularity and the presence of an iron-containing pigment in the cytoplasm of many its neurons

• Afferent fibers reach the red nucleus from

1. Cerebral cortex through the corticospinal fibers
2. Cerebellum through the superior cerebellar peduncle
3. Lentiform nucleus, subthalamic and hypothalamic nuclei, substantia nigra, and spinal cord

• Efferent fibers leave the red nucleus and pass to

1. Spinal cord through the rubrospinal tract (as this tract descends, it decussates)
2. Reticular formation through the rubroreticular tract
3. Thalamus
4. Substantia nigra

Reticular formation

• Situated in the tegmentum lateral and posterior to the red nucleus

Crus cerebri

• Contains the identical important descending tracts,
• The corticospinal, corticonuclear and corticopontine fibers
• Present at the level of the inferior colliculus