Neuroscience 1A LC5 The Brainstem PDF

THE BRAINSTEM I. THE BRAINSTEM - It is important for rigidly programmed autonomic behavior necessary for I. BRAINSTEM...

THE BRAINSTEM I. THE BRAINSTEM - It is important for rigidly programmed autonomic behavior necessary for I. BRAINSTEM survival(Respiratory and Consciousness). A. Function - Passageway for ascending and descending fiber tracts running between the II. MIDBRAIN cerebrum and spinal cord. A. Surrounding Structures a. Rostrally - Heavily involved with innervation of head and face 1 of the 12 cranial b. Caudally nerves nucleus are found within the brainstem with their nerves emerging B. Structures found in Midbrain from them CNIII to CNXII. a. Tectum i. Quadrigeminal Plate - The brainstem is made up of the medulla oblongata, the pons, and the - Superior Colliculi midbrain and occupies the posterior cranial fossa of the skull. - inferior Colliculi ii. Cerebral Aqueduct - The brainstem has three broad functions: - Periaqueductal Gray 1. It serves as a conduit for the ascending tracts and descending tracts b. Tegmentum connecting the spinal cord to the different parts of the higher centers in the i. Red Nucleus forebrain. ii. Substantia Nigra 2. It contains important reflex centers associated with the control of iii. Ventral Tegmental Area respiration and the cardiovascular system and with the control iv. Reticular Formation consciousness. - Ascending Reticular Formation (ARS) 3. It contains the important nuclei of CNs III through XII. - Descending Reticulospinal Tract - There’s an exception: the only two cranial nerves that don't c. Cerebral Peduncles emerge from the brainstem are Olfactory Nerve (CN I) & Optic i. Corticobulbar Tract Nerve (CNII). ii. Corticospinal Tract - Ventral (front) part of the brainstem: Midbrain, Pons and d. Dorsal Column Medial Lemniscus Tract Medulla/ Medulla Oblongata e. Spinothalamic Tract - Dorsal (Back) Brainstem: Midbrain, Pons & Medulla oblongata f. Cranial Nerve Nuclei and the Emerging Nerve C. Pre-requisites for Coma a. Pathologic Positioning i. Decorticate Rigidity ii. Decerebrate Rigidity D. Respiratory Control E. Summary III. PONS A. Structures found in the Pons a. Corticospinal Tract b. Middle Cerebellar Peduncle c. 4th Ventricle d. Reticular Formation (Pontine Reticular Formation) e. Spinothalamic Tract f. Dorsal Column Medial Lemniscus Tract g. Cranial Nerves Figure 1. Midbrain, Pons, and Medulla Oblongata IV. MEDULLA OBLONGATA A. Structures found in the Medulla a. Pyramid b. Olive c. 4th Ventricle d. Reticular Formation e. Spinothalamic Tract (Pathway) f. Dorsal Column Medial Lemniscus Tract (Pathway) g. Cranial Nerves and their Nuclei B. Medulla in Summary V. BRAINSTEM CROSS SECTION SUMMARY Figure 2. Midsagittal Brainstem Midsagittal Brain: Midbrain, Pons & Medulla at top is the diencephalon and at the back is cerebellum Page 1 of 18 II. MIDBRAIN - Most rostral (Highest, essential for life) - middle of the brain - AKA: Mesencephalon (embryonic vesicle) mesen: middle cephalon: brain - It begins as a neural tube, the mesencephalon becoming the midbrain. - The midbrain measures about 0.8 in (2 cm) in length and connects the pons and cerebellum with the forebrain. - The midbrain connects the pons and the cerebellum with the forebrain. - The lateral halves, called the cerebral peduncles, are composed of the crus cerebri, which contain corticospinal fibers, and the substantia nigra, a pigmented band of gray matter. - The midbrain contains multiple nuclei including inferior and superior colliculi, substantia nigra. trochlear, mesencephalic (trigeminal), oculomotor, Edinger-Westphal, and the red nucleus. B. STRUCTURES FOUND IN THE MIDBRAIN a. Tectum - Latin “Roof” - Dorsal Side The tectum consists of four swellings. two superior and two Inferior colliculi, that are associated with vision and hearing, respectively. i. Quadrigeminal plate o “Hills” o Singular: Colliculus o Superior Colliculi (paired) Rostral bumps Visual information- receive visual input from the retina and from frontal (area 8) and occipital (area 19) eye fields Aids in decussation of several fibers of optic nerve Conjugate vertical gaze center. Saccadic eye movement (simultaneous movement of both eyes between two or more phases of fixation in the Figure 3. The Midbrain same Direction) - Example: When you are studying, your eyes are fixated on your book A. SURROUNDING STRUCTURES then suddenly someone when inside your room, your eyes will follow a. Rostrally that person then that fixation, then while the person is walking your - Diencephalon eyes follow them and that includes your neck following that person - Thalamus walking around the room. So that is known as Saccadic eye movement. - Hypothalamus Connects with Tectospinal tract- cervical nerves connections-head - Pineal body movement (while fixating on an object) b. Caudally - it’s directly connected also to the lateral geniculate nucleus. - Hindbrain - Pons, Medulla and Cerebellum Retina (Right and Left) -----> Optic nerve (Right and Left) ----> Optic Chiasm —-> Optic Tract —-> Lateral Geniculate nucleus —--> Optic Radiation (Right and Left) -----> Visual cortex o Inferior Colliculi (paired) Caudal bumps Processes auditory information Directly connected to medial geniculate nucleus Lateral Lemniscus- projects binaural auditory information to the inferior collicular nucleus Page 2 of 18  Figure 6. Cerebral Aqueducts o Periaqueductal (Periaqueductal gray) Figure 4. Midbrain, Pons, and Medulla Oblongata: Nerves (A), Parts (B) ii. Cerebral Aqueduct “Aqueduct of Sylvius” - Connects the 3rd to 4th ventricles Figure 7. Periaqueductal Gray - The cerebral aqueduct, which connects the third and fourth ventricles. passes through the midbrain and divides the Gray matter surrounding the cerebral aqueduct anterior (tegmentum) from the posterior (tectum). Role in autonomic function motivated behavior and behavioral response - The lateral ventricle is surrounded by cerebral hemispheres to threatening stimuli while the 3rd ventricle is surrounded by diencephalon, so Final common pathway mediating defensive reaction to fear the cerebral aqueduct is surrounded by midbrain, so the control center for descending pain modulation (Analgesia, Quinscence, cerebral aqueduct will connect the 3rd and 4th ventricles Bonding) that serves a “cana”. In hydrocephalus patients there is Coordination behavior essential to survival (changes in movement and accumulation of CSF at 3rd ventricle. posture) - CSF secretion in adults varies between 400 to 600 ml per - Spinocerebellar pathways (dec. nociceptive signals while enhancing day, depending on the subject and the method used to proprioceptive signals) study CSF secretion. - Alteration in cerebellar nuclear outputs - Narrow channel between tectum and tegmentum. - Regulation of spinal reflex circuits by inc alpha motor neuron activity Enkephalin cells that suppress pain Target for brain stimulation implants in patients with chronic pain - For surgeons, this is the target for brain stimulation implants in patients with chronic pain, in order to control pain, target the periaqueductal gray in order to suppress pain. e.g. cancer patients. b. Tegmentum “Floor Known as the “floor” of midbrain. Regions between the cerebral aqueduct and the cerebral peduncles Central core of the midbrain and the pons, and the anterior are the basilar areas i. Red Nucleus - Pink due to iron in Hg and ferrin - Motor coordination (extrapyramidal system - Tract: Rubrospinal tract ii. Substantia Nigra - Dark due to neuromelanin Dopaminergic neurons Figure 5. Lateral and Medial Aperture - Extra pyramidal systems: motor planning and learning Page 3 of 18  - Degeneration of Dopaminergic neurons Parkinsons disease Major enabling factor in state of - Neural reward system (Addiction) consciousness - Related to motor function Regulating wakefulness via cortical and behavioral - Functionally associated with the basal nuclei and is commonly arousal(sleep-wake transitions) divided into pars compacta and pars reticulata Damage:coma or death - If there’s degeneration of dopaminergic neurons that are found in substantia nigra that will result in “parkinson’s disease” thus, o Descending Reticulospinal Tract this serves the importance of substantia nigra. o Descending pathway to spinal cord o Extrapyramidal motor tract iii. Ventral Tegmental Area o Locomotion and postural control - Largest Dopamine area of the brain (Neural Reward System) o Act on the motor neurons supplying the trunk and - NEURAL REWARD SYSTEM proximal limb flexors and extensors e.g. positive reinforcement: tutor will give a project, the student will o Damage in descending reticulospinal tract at the mid do something very good that will impress the tutor so that he/she collicular level would lead to: decorticate and your the will get a good grade. In order for the student to have a good grade, cerebrate posture the tutor will give a good grade if he/she will give a good project. - Mummy (flexion of upper extremity and - Incentive Salience (wanting/craving for reward) extension of lower) - Associative Learning (Positive reinforcement) - Damage is above midbrain or mid collicular level - Pleasure (Joy, Euphoria and ecstasy) which is in the diencephalon - You still save your patient decerebrate posturing iv. Reticular Formation - extension of both extremities - The reticular formation extends through the central core of the - Damage is irreversible (ominous sign of medulla oblongata, pons and midbrain impending death. - It is an intricate system composed of loosely clustered neurons in - Damage is below mid collicular level white matter. - It's found all throughout the brainstem: medulla, pons and midbrain. Reticular formation- is actually bilateral, both sides are loosely ill They are the central core. defined nuclei or neurons that are scattered throughout the brainstem and other part of the brain and they are actually found in the white matter. and they are found in the central core of the brainstem : the midbrain, pons and medulla. Figure 8. Reticular Formations in the brainstem - Central core of the brainstem - Intermingling axons/ cluster of nerve cell bodies in the white matter - They are ill defined, cannot identify the nerve cell bodies by itself because they are interspersed within the white matter. And the intermingling of axons is the reason why it's called reticular formation. - Includes neurons in different parts of the brain - There are different areas in which the nerve cell bodies are located. - Major subsystem - Set of interconnected nuclei located throughout the brainstem - State of consciousness Figure 9. Cross section of midbrain, pons and medulla. - Cardiovascular and respiratory systems c. Cerebral Peduncles "Crus Cerebri/Basis Pedunculi" o Ascending Reticular Formation (ARAS) - They are found in the antero-lateral side of midbrain, and they are Ascending pathway to the cortex contained with motor fibers that run from cerebrum. “Extrathalamic” control modulatory system (outside the - Known as “crus cerebri/ basis pedunculi” thalamus) Page 4 of 18  - Innervate the ipsilateral spinal nucleus of CN XI that supplies the sternocleidomastoid and the - Contralateral spinal nucleus of CN XI that innervates the trapezius - The orbicularis oculi receive a variable number of crossed and uncrossed fibers; the paresis therefore varies from patient to patient ii. Corticospinal Tract (Motor Tract) - Left side of brain will control right side of body (and vice versa) because of decussation - A major tract that carries movement-related information from the motor cortex to the spinal cord. - The neurons that travel in the corticospinal tract are called upper motor neurons. Figure 10. Cross-section of midbrain showing cerebral peduncles. Figure 12. The Corticospinal Tract. Figure 11. The ventral view of cerebral peduncles. - The corticospinal tract starts (is located) at the precentral gyrus (central for motor) motor cortex 🡪goes in between the - Latin for "Foot " thalamus and ganglia known as the internal capsule --> enters - Made up of tracts anterolaterally, Axonal Fibers crossing vertically in the midbrain as large fiber bundles called the cerebral - A stalk of nervous tissue connecting the Cerebral cortex with the Brainstem peduncles 🡪 down to the medullary pyramids (pyramids of - Pons Nuclei - Spinal Cord medulla) 🡪 90% of the corticospinal fibers decussate, or cross to - Relays long motor tracts to contralateral side of the body the other side of the brainstem in a bundle called pyramidal - Central and medial portions: decussation (this is the reason why the right part of the brain Corticobulbar (Cranial Nerves: Head and face)- it is ipsilateral and do not will control the left side of the body via the lateral corticospinal decussate tract and vice versa, because of the decussation from this area) Corticospinal tracts (Spinal Nerves: Neck and Body)- contralateral and it 🡪 to the lateral side of spinal cord 🡪 goes to ventral horn/ decussates ventral column of spinal cord 🡪 emerges into the ventral root 🡪 now part of the lower motor neuron 🡪 goes out combined with i. Corticobulbar Tract the sensory root 🡪 innervates the distal skeletal muscles like - Corticobulbar do not decussate, remains ipsilateral those of the hands. - That means the right facial nerve will only control the muscle of the right face and will not decussate into the other side. - The tract for cranial nerves are always ipsilateral, they always innervate the same side in contrast with Corticospinal tract: which innervates the contralateral side of the body. Corticobulbar (Corticonuclear) Fibers - Arise from precentral and postcentral gyri - May synapse directly on motor neurons or indirectly via interneurons (corticoreticular fibers) - Innervate sensory nuclei (gracile, cuneate, solitary, and trigeminal) - Innervate cranial nerve motor nuclei bilaterally, with the exception of part of the facial nucleus - (CN VII). The upper face division of the facial nucleus receives bilateral input; the lower face - Division of the facial nucleus receives only contralateral input Figure 13. Pathway of Corticospinal Tract Page 5 of 18  CORTICOSPINAL TRACT PATHWAY Pre-central gyrus (motor neurons) Axon goes in between thalamus & basal ganglia Cerebral peduncle of midbrain Medullary pyramids (where decussation happens at spinomedullary junction) Figure14. The Cortical Homunculus representation. Lateral side of spinal cord (lateral corticospinal tract) - Damage to the corticospinal tract can lead to a collection of symptoms known as upper motor neuron syndrome - Symptoms: weakness or paralysis, hyperactive reflexes, decreased motor control, and either increased or decreased muscle tone Ventral horn/ventral column of spinal cord - Over time, patients may regain the ability to make crude movements but fine finger movements like writing or typing may remain impaired, suggesting the corticospinal tract is especially important for these types of movements. Emerges into ventral root (it becomes now part of lower motor neuron) SENSORY TRACTS: Spinothalamic Tract - Carry info for pain & temperature (from contralateral side of body) Dorsal column medial lemniscus tract - Carries info for fine touch, proprioception & vibration (from contralateral side of body) Goes out and combines with sensory root to innervate skeletal muscles d. Spinothalamic Tract (Antero-Lateral Tract) - There’s another tract coming out from it and its anterior - Referred to as anterolateral tract corticospinal tract (10% of the fibers; the straight part of the - Carries information for pain and temp from the contralateral side tract) are responsible for innervating/controlling the movement - Enters via dorsal root ganglia and decussates immediately of the muscles of the trunk (chest and abdomen). - Goes up the spinal cord as the lateral spinothalamic tract - Goes up to the midbrain then thalamus and relays the information to the o Anterior-Corticospinal Tract somatosensory cortex - Straight tract - Responsible for controlling trunk (chest, abdomen & back), (e.g. SPINOTHALAMIC TRACT PATHWAY Dwayne Johnson moving his chest) Information enters dorsal root then dorsal root ganglion ❖ Homunculus - Is the representation of your body in the cortex, the lower extremity is in the medial side of the brain, then on the top most is the upper extremities, and going lateral wise is the face, more lateral area is the tongue and pharynx. Spinal root at dorsal column (where it immediately decussates) - In the same manner for the sensory, the precentral gyrus: genitalia and upper limbs at the medial side. If there is damage here either the precentral gyrus or post central gyrus there will be weakness and some sensory disturbance at the lower Goes up to lateral spinothalamic tract (white matter) extremities. Midbrain Page 6 of 18  Thalamus (relay station) Somatosensory cortex (postcentral gyrus) e. Dorsal Column Medial Lemniscus Tract - Carries information for fine touch, proprioception, vibration from the contralateral section of the body - 3 order neuron o First order neuron are dorsal root ganglia o Second order neuron is where there is decussation o Third order neuron begin at the thalamus towards somatosensory cortex DORSAL COLUMN MEDIAL LEMNISCUS PATHWAY Fine touch enters dorsal root then goes to dorsal root ganglion Enters spinal cord at dorsal column Ascends spinal cord through fascilus cuneatus (carry info from upper half) or fascilus gacilis (carry info from lower half) Figure 15. The Dorsal Column Medial Lemniscus Pathway (left), and the Spinothalamic Tract Pathway (right). f. Cranial Nerve Nuclei within the Midbrain and Nerves EMerging From It Medulla - Cranial Nerve III (Oculomotor nerve) - Cranial Nerve IV (Trochlear nerve) Decussates at medial lemniscus Goes up to midbrain in medial lemniscus tract Goes up to thalamus (relay station) Figure 16. The cranial nerves. Somatosensory cortex (postcentral gyrus) o Oculomotor nerve (CN III) - Motor to the extraocular muscles (Medial rectus, Inferior rectus and Inferior oblique), ciliary muscle and pupillary constrictors - Emerges ventrally from the oculomotor nucleus and courses between the Posterior Cerebral Artery (PCA) and Superior Cerebral Artery (SCA) - Synapse with the Edinger Westphal nucleus (Accessory oculomotor nucleus) Page 7 of 18  Figure 19. Trochlear Nerve C. PREREQUISITES FOR COMA/ LOSS OF CONSCIOUSNESS (ROSTRO -CAUDAL) Figure 17. Oculomotor Nerve Mild Coma- Bilateral hemispheric dysfunction, Diffuse lesion of both Cerebral hemisphere (Cortical or subcortical White Matter) Functions: Moderate Coma- Bilateral Diencephalic Dysfunction (Thalamus/Subthalamus/ o Supplies parasympathetic pre- ganglionic fiber to the eye Hypothalamus/ Epithalamus) leading to “decorticate posture/ rigidity” o Pupillary constriction (pupillary sphincter muscle) Severe Coma- Damage on the mild collicular level of the brainstem (RAS - - If you put a light on the eye, pupils will constricts, known as Reticular activating system) leading to “decerebrate posture/ rigidity” “consensual eye reflex” o Lens accommodation (ciliary muscle) - remember that cerebellum is not involved here. - If you put a ballpen in front of the face and move it closer to - e.g. There is brain herniation: it will damage first both of the cerebral your eyes, there will be accommodation to the lens, ciliary hemisphere- mildly comatose but once there is herniation and muscle will contract and it will make the lens wider diencephalon will enter now the tentorium this will damage now both of o Convergence (Medial rectus) diencephalon and will result to moderately comatose. But once this - If you put a ballpen closer to the nose, the eyes will converge, herniation will progress down to the brainstem then it is now severely known as “convergial reflex” because of the contraction of the comatose- impending death. medial rectus - CN III emerges ventrally and courses between and courses between the Posterior cerebral artery (PCA) and Superior Cerebellar artery (SCA) - So there are two pairs (right and left oculomotor nerve, it occupies an area in between the posterior cerebral artery and superior cerebral artery. importance: like for example if there is an aneurysm there, and then the nerves merges in between of those arteries, so if it happens that there is a tumor/aneurysm -Posterior communicating artery (PCOM) so that oculomotor will be compressed by aneurysm and that will produce oculomotor nerve palsy. Some functions of the oculomotor nerve will be disrupted. Figure 20. Decorticate and Decerebrate Posturing a. Pathologic posturing: i. Decorticate rigidity- Is a flexion of upper extremity and extension of the lower extremity ii. Decerebate rigidity- Extension of both upper and lower extremity because the damage now has reached the brainstem. * This means, you can still save a patient that is in decorticate rigidity because the damage is still above the mid collicular level, mainly the Figure 18. The Oculomotor Nerve. damage here is in diencephalon but once the damage has reached the mid collicular level and below, it will now go into decerebate rigidity. Once the o Trochlear Nerve (CN IV) patient is in that condition then that is already irreversible and that is now - Exits dorsally wraps around cerebral peduncle an ominous sign of the impending death. - Innervate the Superior oblique muscles of the eye (makes your eye go downwards and laterally) D. RESPIRATORY CONTROL - Smallest CN and very thin, yet has the longest intracranial course. - If there is a lesion in diencephalon: cheyne-stokes respiration that means there are alternating tachypnea- bradypnea-tachypnea-bradypnea. But Page 8 of 18  once the damage reaches the midbrain it will be in sustained hyperventilation / sustained tachypnea. but once the damage reaches the pons, it's either Apneusis o Ataxic breathing, so breathing becomes irregular. And then when the damage reaches the medulla, it will be in respiratory arrest. Figure 21. Respiratory Control Cheyne- Stoke Respiration - Exits dorsally wraps around cerebral peduncle - Lesion on diencephalon - There is still an alternating tachypnea- bradypnea- tachypnea- Figure 23. Lateral, anterior, and lateral view of the brainstem bradypnea Sustained Hyperventilation - Lesion on midbrain III. PONS - Sustained tachypnea Apneusis/ Ataxic Breathing - Lesion on pons causing irregular breathing - Pons of Varolli (Bridge of Varolius) Respiratory Arrest - Named after italian anatomist Constanzo Varolio - Lesion on medulla - Latin for “bridge” (connects between two points) - Reflex control of the respiratory system - Surrounding structure o Inferior to midbrain o Superior to the medulla o Anterior to cerebellum Figure 22.. Dorsal view of the brainstem Figure 24. Brainstem showing the Pons Page 9 of 18  a. Corticospinal Tract Level Cavity Nuclei Motor Tracts Sensory Tracts Facial Fourth Facial Corticospinal Spinal colliculus ventricle nucleus, and tract of medial corticonuclea CN V; vestibular r tracts, lateral, nucleus, transverse spinal spinal pontine and nucleus of fibers, medial medial CN V, longitudinal lemnisci pronucle, fasciculus trapezoid nuclei Trigemin Fourth Main Corticospinal Lateral, al nuclei ventricle sensory and and spinal motor corticonuclea and nucleus of r tracts, medial CN V, transverse lemnisci pontine pontine nuclei, fibers, medial trapezoid longitudinal nuclei fasciculus Table 3. Levels of the Pons and their Major Structures A. STRUCTURES FOUND IN THE PONS a. Corticospinal tract b. Middle cerebellar peduncle c. 4th ventricle d. Reticular formation e. Spinothalamic tract f. Dorsal column medial lemniscus tract g. Cranial Nerves and their nuclei: i. V-Trigeminal Nerve ii. VI-Abducens Nerve iii. VII-Facial Nerve iv. VIII-Vestibulocochlear Nerve Figure 26. Anterior Corticospinal tract - Originates in multiple cortical areas o Primary motor cortex o Pre-motor cortex - Internal capsule o Between thalamus & o Basal ganglia - Cerebral Peduncles - Predominantly contralateral crossing at the pyramid - The pons is anterior to the cerebellum and connects the medulla oblongata to the midbrain. The anterior surface is convex, and the trigeminal nerve emerges anterolaterally. b. Middle Cerebellar Peduncle - Largest cerebellar peduncle - Connects cerebellum to the pons (contains fibers from the contralateral pontine nuclei and course to the cerebellum - Since there is a connection between the cerebellum and the pons; damage to your pons will make you lose your balance and coordination (which is the main function of your cerebellum). Figure 25. Structures in the Pons (midsection) Page 10 of 18  Figure 27. The Brain Stem - Pons Figure 30. Lesion resulting to enlarged ventricles c. 4th Ventricle - Cerebrospinal Fluid (CSF) Pathway Hydrocephalus - roughly pyramid-shaped space that forms the cavity of the metencephalon and myelencephalon * Concept on Hydrocephalus - If there will be an obstruction in the 4th ventricle, CSF will accumulate in the aqueduct of Sylvius and 3rd ventricle. - If the obstruction is in the aqueduct of Sylvius, CSF will not accumulate in the 4th ventricle since it is proximal to the aqueduct of Sylvius. Figure 31. Patient with Hydrocephalus - Hydrocephalus is a condition that involves the build-up of CSF (a fluid that is Figure 28. Cerebrospinal Fluid in the Brain produced in the cavities of the brain called ventricles). - CSF flows through the brain and the spinal cord and eventually is absorbed into the bloodstream. It serves a lot of functions: acting as a cushion, delivering nutrients, and removing harmful substances. - Involves accumulation of cerebrospinal fluid - Impaired reabsorption of the CFS in the bloodstream - Blockage in the ventricular system causes the CSF to accumulate can be congenital or acquired Communicating hydrocephalus - No blockage in the ventricular system Non-communicating (most common cause of hydrocephalus) - Blockage in the ventricular system Obstructive hydrocephalus - hemorrhage in the brainstem that leads to hydrocephalus. Aqueductal stenosis - 3rd and lateral ventricle - Can be acquired at birth or later on in life Figure 29. Cerebrospinal Fluid Pathway in the 4th Ventricle - Enlargement of the ventricles can lead to increased intracranial pressure Page 11 of 18  - When the CSF accumulates in the ventricles this causes the brain to be g. Cranial Nerve Nuclei within the Pons enlarged. - When hydrocephalus occurs in infants, their skull is more capable of expanding so their heads become more enlarged. In adults, their skulls don't expand and symptoms appear more quickly. - Treatment involves attempted draining of the CSF (using a cerebral shunt- plastic tube connecting to the catheter) to the abdominal cavity. - Early shunting (at least 3 months old), the better. Shunting beyond 3 months old, the possibility of permanent damage to the brain of the child is very high. - Third ventriculostomy - opening the interpeduncular cisterns to drain CSF (used for both hydrocephalus and aqueductal stenosis) d. Pontine Reticular formation - Purely defined as scattered clusters of nerve cell bodies and their axons. e. Spinothalamic Tract (Anterolateral tract/system) Figure 33. Cranial Nerves location in the Pons - Pain and temperature i. CN V (Trigeminal Nerve) f. Dorsal Column Medial Lemniscus tract Supply sensation to the face - Sensory tracts – (ascending unlike the motor tracts that are descending) Largest nerve - Carries sensory information for vibration, fine or light touch and 3 major branches proprioception. Ophthalmic (sensory nerve) - supply the forehead Maxillary (sensory nerve) - supply the maxillary area o Mandibular (mixed sensory-motor nerve) - supply muscles of mastication Figure 34. Trigeminal nerve highlighted with blue color ii. CN VI (Abducens Nerve) Supplies the lateral rectus muscle of the eye (abducts the eye laterally) Coordinated movements of the eyes and head Found in the junction of pons and medulla Figure 32. Dorsal Column Medial Lemniscus tract Figure 35. Abducens nerve highlighted with light blue color Page 12 of 18 iii. CN VII (Facial Nerve) Efferent Lateral to pons Innervates the muscle of facial expressions Important in corneal reflex Contains Right and Left facial nerve Figure 38. Basal Pons and Pontine Tegmentum - The basal pons doesn't form a direct connection between the cerebellar hemispheres but the pons is attached to the cerebellum by the middle cerebellar peduncles - A major pathway between the brainstem and cerebellum - The inferior cerebellar peduncles also travel through the pons to carry information to the cerebellum - The superior cerebellar peduncles enter the brainstem at the level of the Figure 36. Facial nerve highlighted with blue color pons and carry information from the cerebellum to the brain stem iv. CN VIII (Vestibulocochlear Nerve) Two nerves in one Connected to the cerebellum Vestibular - important in balance Cochlear - important in hearing Figure 39. Posterior view of the Brainstem - The pons forms most of the floor of the fourth ventricle and is home to several cranial nerve nuclei including - Trigeminal nuclei which are involved with sensory and motor functions - Abducens nucleus which controls lateral movements of the eye - Facial motor nucleus which controls muscles of facial expression - Vestibular nuclei which process vestibular information Figure 37. Vestibulocochlear nerve highlighted with light blue color SUMMARY Reflex control of the respiratory system Eye movement (CN VI - Lateral rectus), coordinated movements of eyes and head Tear and lacrimation (CN VII) Corneal Reflex o CN VII (Ophthalmic Nerve) – (Afferent Sensory Part) o CN VII (Facial Nerve) – Efferent (Motor Part) 2-MINUTE OF NEUROSCIENCE - Pons is a major division of the brainstem. found above the medulla and below the midbrain. Figure 40. Cross-Sections of the Pons - Pons is called the “bridge” because its anterior part (basal pons) causes the pons to connect the hemispheres of the cerebellum. - The pons also contains the locus coeruleus the largest collection of - Pontine tegmentum/ Dorsal Pons is the region behind the basal pons. norepinephrine-containing neurons in the brain and some of the rafi nuclei the major serotonin-producing neurons of the brain - The pons also serves as a conduit for many tracks passing up and down Page 13 of 18  through the brainstem like the corticospinal tract for voluntary movement medial lemniscus for tactile and proprioceptive sensations and spinothalamic tract for pain and temperature sensations Figure 43. Structure of Medulla (midsection) Figure 41. Cross-Section of the Pons and location of tracts IV. MEDULLA OBLONGATA Most caudal Continues as the spinal cord once it emerges at the Foramen Magnum (largest opening of the skull) Myelencephalon (origin) Bulbar - reference to medical condition in the nerves and tracts connected to medulla and muscles innervated (tongue, pharynx, larynx) (e.g. Bulbar palsy) The medulla oblongata connects the pons superiorly with the spinal cord inferiorly. The junction of the medulla and spinal cord is at the origin of the anterior and posterior roots of the first cervical spinal nerve, which corresponds approximately to the level of the foramen magnum. The medulla oblongata is conical in shape, its broad extremity being directed superiorly The medulla oblongata connects the pons superiorly and spinal cord Inferiorly. On either side of the anterior median sulcus are the two pyramids that taper Inferiorly, whereas most fibers cross at the decussation of the pyramids. Figure 44. Section of the brain containing the medulla The medulla oblongata contains multiple CN and cerebellar nuclei, the olivary nuclear complex, nucleus ambiguus, hypoglossal nucleus, A. STRUCTURES FOUND IN MEDULLA vestibulocochlear nuclei, dorsal nucleus of the vagus, and nucleus of the a. Pyramid tractus solltartus, and spinal nucleus of the trigeminal nerve. - Paired Ventral midline bulges - Contains the Corticospinal tract - The pyramids are composed of bundles of nerve fibers, called corticospinal fibers, which originate in large nerve cells in the precentral gyrus of the cerebral cortex. i. Corticospinal tract (pathway) - The corticospinal tract is also known as the ‘pyramidal tract’. - The lower leg, the trunk at the top and the arm on the lateral side. - The head and face are on the lateral side, just above the lateral sulcus. It will pass through the white matter and pass through the internal capsule. - The internal capsule is in between the thalamus and the basal ganglia. - The corticospinal tract also passes through the midbrain, the pons and the medulla. - In the medulla, it passes only through the pyramids. - In the midbrain, it passes through the cerebral peduncle. - At the medullary pyramids (spinomedullary junction), it will now decussate on the other side towards the lateral corticospinal tract, white matter of the spinal cord down to the muscles. Figure 42. Section of the brain containing the medulla - It also contains the anterior corticospinal tract that controls the muscle of the trunk (axial muscles): chest, abdomen and the back. Page 14 of 18  Figure 45. Medullary Pyramid - The upper motor neurons coming from the motor cortex will enter the Figure 48. Cross section of the olive medullary pyramids and decussate to the other side then go down as the corticospinal tract down to the spinal cord. i. Inferior olivary nucleus - Part of olivo-cerebellar system b. Olive - Cerebellar motor learning and function - Paired anterolateral bulges - Found in medulla - Lateral to pyramids 3 main nuclei - Contains inferior olivary nucleus - Primary olivary nucleus - Medial accessory olivary nucleus - Dorsal accessory olivary nucleus ii. Superior olivary nucleus - Part of auditory system - Perception of sound - Olivary nucleus looks like an intestine c. 4th ventricle - Contains CSF - Communicates with the Subarachnoid space via medial and lateral apertures i. Foramina of Luschka (Lateral aperture) ii. Foramina of Magendie (Medial aperture) Figure 46. Illustration of the Olive Figure 47. Actual image of a section of the brain containing the olive Figure 49. Lateral and medial aperture Page 15 of 18  d. Reticular formation ii. CN X (Vagus Nerve) - Is a set of interconnected nuclei located throughout the BS - Mixed motor-sensory nerve - Not anatomically defined - Autonomic Innervations to the heart, lungs, bronchi, trachea, - Includes neurons in different parts of brain larynx, pharynx and also sensation to external ear. - Cardiovascular and Respiratory system - Longest cranial nerve - The reticular formation,consisting of a diffuse mixture of nerve fibers - Associated with many and small groups of nerve cells,is deeply placed posterior to the olivary nucleus. e. Spinothalamic tract (pathway) Figure 52. Vagus Nerve (highlighted in blue, encircled in red) iii. CN XI (Accessory Nerve) - Goes along the side of medulla - Supplies the muscle of your neck (Sternocleidomastoid and trapezius muscle) - Used when turning neck from side to side or shrugging your Figure 50. Spinothalamic tract shoulders f. Dorsal column medial lemniscus tract (pathway) Nucleus Gracilis and Cuneatus o Dorsal column Nuclei - Synapse with the fasciculus gracilis and fasciculus cuneatus from the spinal cord Nucleus Gracilis - Carries sensory information from the lower half of the body entering the Lumbar level of spinal cord - Medial part Nucleus Cuneatus - Sensory from upper half (Upper limbs, trunk and neck) entering at the Cervical level of Spinal cord. - Lateral part Second Order Neurons (point of decussation for DCML tract) ○ First Order Neuron - Dorsal root ganglia ○ Third Order Neuron – Thalamus towards somatosensory cortex g. Cranial Nerves and their nuclei : Figure 53. Accessory Nerve (highlighted in blue, encircled in red) i. CN IX (Glossopharyngeal Nerve) iv. CN XII (Hypoglossal Nerve) - Down the medulla, this can be noticed first - Supplies the muscle of your tongue - Mixed motor-sensory nerve - Anterior ⅓ of the tongue is supplied by the Facial nerve. - tonsils, pharynx, tongue Posterior ⅓ is supplied by the glossopharyngeal nerve. Figure 51. Glossopharyngeal nerve (highlighted in blue, encircled in red) Figure 54. Hypoglossal Nerve (highlighted in blue, encircled in red) Page 16 of 18  B. MEDULLA IN SUMMARY - If the damage is only the right side of the spinal cord, there will only be lateral hemisection. There will only be weak paralysis on the right side. - Reflex control of cardiovascular and respiratory systems - Reflex control for swallowing and vomiting (CN IX / X) LOCALIZATION - Important in Phonation: Control of tongue (CN XII), Larynx and A. Localization of lesion in the Dorsal Lemniscus Medial Lemniscus Tract Pharynx (CN IX / X) - If the damage is from the dorsal root ganglion to the nucleus gracilis and nucleus cuneatus, there will be an ipsilateral loss of VENTRICLES OF THE BRAIN fine touch, vibration and position sense below the level of the lesion. - If the damage is from the decussation, to the thalamus, to the somatosensory cortex, there will be a contralateral loss of fine touch, vibration and position sense below the level of the lesion. B. Localization of lesion in the Spinothalamic Tract - If the damage is just before the decussation, there will be ipsilateral loss of pain, temperature and crude touch at the level of the lesion. - If the damage is from the decussation up to the thalamus and to the somatosensory cortex, there will be contralateral loss of pain, temperature and crude touch below the level of the lesion because the spinothalamic tract will decussate almost immediately towards the other side. UPPER AND LOWER MOTOR NEURON A. UPPER MOTOR NEURON - From the precentral gyrus, down to the spinal cord, just before the frontal horn, this will be the upper motor neuron. B. LOWER MOTOR NEURON - This will consist of the ventral horn cells. The spinal cord has Figure 55. Anterior view (left) and left lateral view (right) of the ventricles of the three horns: ventral, posterior and lateral horn. The ventral horn brain will contain motor neuron cells. The ventral horn cell to the - The cerebral hemisphere will house the lateral ventricle. The lateral neuromuscular junction will be the lower motor neuron. ventricle has a frontal horn, posterior horn and the lateral horn. Most of - The anterior horn cell will contain the neuronal cell bodies that the CSF is produced by the choroid plexus that is located at the lateral are motor in function. ventricles. It will drain at the foramen of monro towards the third - ventricle. The third ventricle is housed within the diencephalon. From the third ventricle, it will pass through the cerebral aqueduct (Aquaduct of Sylvius). From there, it will now drain to the fourth ventricle. From the fourth ventricle (housed between the pons and the upper medulla), it will now drain to the foramina of Luschka and Magendie and it will recirculate to the subarachnoid space. From the subarachnoid space, it will now drain to the venous circulation of the brain (venous system). Then, it will produce another CSF. CSF is constantly being produced whether there is an obstruction. - In the case of meningitis, the CSF will accumulate to the arachnoid space. The subarachnoid space is the main drainage of the CSF. If there is an inflammation to the subarachnoid space, it will no longer absorb CSF. There will be a communicating hydrocephalus which involves all the ventricles and the canals because it can no longer drain the CSF. - If the damage is from the precentral gyrus, before the decussation, What will be the presentation? What will be the part of the body? Ex. If the damage (tumor, trauma or stroke) is on the left, anywhere from the cerebral cortex to the internal capsule to the left midbrain, to the left medulla. There will be damage to the right side of the body (contralateral weakness or paralysis) If the damage is on the spinal cord, there will be an ipsilateral weakness or paralysis below the lesion. Table 4. Levels of the Medulla Oblongata and their major structures Ex. If the corticospinal tract is cut at the thoracic level, If the lesion is in T1, everything below T1 will be paralyzed on the same side. If the spinal cord is transected, there will be complete paralysis (paraplegic) below the level of the lesion on both sides. Page 17 of 18 INDEX Figure 57. The cranial nerves. Figure 56. Cross section of the Medulla. V. BRAINSTEM CROSS SECTION SUMMARY Page 18 of 18