Brain Stem Anatomy (005) PDF

(005) THE BRAINSTEM DR. ALLAN VIADO | 10/21/2020 OUTLINE I. BRAINSTEM I. BRAINSTEM -I...

(005) THE BRAINSTEM DR. ALLAN VIADO | 10/21/2020 OUTLINE I. BRAINSTEM I. BRAINSTEM -It is important for rigidly programmed autonomic behaviour necessary A.Function for survival(Respiratory and Consciousness II. MIDBRAIN A. Definition -Passageway for ascending and descending fiber tracts running B. Surrounding Structures between the cerebrum and spinal cord a. Rostrally b. Caudally -Heavily involved with innervation of head and face 1 of the 12 cranial C. Structures found in Midbrain nerves nucleus are found within the brainstem with their nerves a. Tectum emerging from them- CNIII to CNXII 1. Quadrigeminal Plate -The brainstem is made up of the medulla oblongata,the pons, and the i. Superior Culliculi midbrain and occupies the posterior cranial fossa of the skull. ii. Inferior Culliculi 2. Cerebral Aqueduct -The brainstem has three broad functions: i. Periaquaductal Gray b. Tegmentum 1. It serves as a conduit for the ascending tracts and descending tracts 1. Red Nucleus connecting the spinal cord to the different parts of the higher centers in 2. Substantia Nigra the forebrain; 3. Ventral Tegmental Area 4. Reticular Formation 2. it contains important reflex centers associated with the control of i. Ascending Reticular Formation respiration and the cardiovascular system and with the control of (ARS) consciousness;and ii. Descending Reticulospinal Tract c. Cerebral Peduncles 3. It contains the important nuclei of CNs III through XII. 1. Corticobulbar Tract - There’s an exception: the only two cranial nerves that doesn’t 2. Corticospinal Tract emerged from brainstem are Optic nerve d. Spinothalamic Tract (CN I) & Olfactory nerve. e. Dorsal Column Medial Lemniscus Tract f. Cranial Nerve Nucleis and the emerging nerve - Ventral (front) part of the brainstem: Midbrain, Pons and Medulla/ 1. Cranial Nerve III Medulla Oblongata 2. Cranial Nerve IV - Dorsal (Back) Brainstem: Midbrain, Pons & Medulla oblongata D. Pre-requisites for Coma also. a. Pathologic Positioning 1. Decorticate Rigidity 2. Decerebrate Rigidity E. Respiratory Control F. Summary III. PONS A. Definition B. Structures found in 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 C. Summary IV. MEDULLA OBLANGATA A. Definition B. Structures found in Medulla a. Pyramid i. Corticospinal Tract (Pathway) b. Olive i. Inferior olivary nucleus c. 4th Ventricle d. Reticular Formation e. Spinothalamic Tract (Pathway) f. Dorsal Column Medial Lemniscus Tract (Pathway) g. Cranial Nerves and their nuclei C. Medulla in Summary D. Brainstem cross section Summary V. BRAINSTEM CROSS SECTION SUMMARY VI. INDEX PREPARED AND EDITED BY: TRANS GROUP 3  (005) THE BRAINSTEM DR. ALLAN VIADO | 10/21/2020 - Midsagittal Brain: Midbrain, Pons & Medulla b. Caudally - at top is the diencephalon and at the back is cerebellum. Hindbrain II. MIDBRAIN Pons, Medulla and Cerebellum A. DEFINITION C. STRUCTURES FOUND IN THE MIDBRAIN -Most rostral a. Tectum -middle of the brain -latin “Roof” -AKA: Mesencephalon(embryonic vessicle) -Dorsal Side mesen: middle The tectum consists of four swellings. two superior cephalon : brain and two Inferior colliculi, that are associated with vision and hearing, respectively. - it begins as a neural tube, the mesencephalon becoming the midbrain. 1. Quadrigeminal plate - “Hills” - The midbrain measures about 0.8 in (2 cm) in length and - Singular: Colliculus connects the pons and cerebellum with the forebrain. - The midbrain connects the pons and the cerebellum with the i. Superior Colliculi(paired) forebrain. Rostral bumps - The lateral halves, called the cerebral peduncles, are Visual information composed of the crus cerebri, which contain corticospinal Aids in decussation of several fibers of fibers, and the substantia nigra, a pigmented band of gray optic nerve matter. Conjugate vertical gaze centre. - The midbrain contains multiple nuclei including, inferior and Saccadic eye Movement superior colliculi, substantia nigra. trochlear, mesencephalic (simultaneous movement of both eyes (trigeminal), oculomotor, Edinger-Westphal, and the red between two or more phases of fixation nucleus. in the same Direction) - Example: When you are studying, your eyes are fixated on your book then suddenly someone when inside your room, your eyes will follow that person then that fixation, then while the person is walking your eyes follow them and that includes your neck following that person walking around the room. So that is known as Saccaidic eye movement. connects with Tectospinal tract- cervical nerves connections-head movement(while fixating on an object - it’s directly connected also to the lateral geniculate nucleus. ii. Inferior Colliculi(paired) Caudal bumps Processes auditory information Directly connected to medial geniculate nucleus B. SURROUNDING STRUCTURES a. Rostrally Diencephalon Thalamus Hypothalamus Pineal body PREPARED AND EDITED BY: TRANS GROUP 3  (005) THE BRAINSTEM DR. ALLAN VIADO | 10/21/2020 2. Cerebral aqueduct i. Periaquaduct (Periaquaductal grey)- surrounding the aqueduct. - connects the 3rd to 4th ventricles - The cerebral aqueduct, which connects the third and fourth ventricles. passes through the midbrain and divides the anterior (tegmentum) from the posterior (tectum). - The lateral ventricle is surrounded by cerebral hemispheres while the 3rd ventricle is surrounded by diencephalon, so the cerebral aqueduct is surrounded by midbrain, so the cerebral aqueduct will connect now the 3rd and 4th ventricles that serves a “cana”. - Narrow channel between tectum and tegmentum. o gray matter surrounding the cerebral aqueduct o role in autonomic function motivated behaviour and behavioural response to threatening stimuli o control centre for descending pain modulation(analgesia, quinscence , bonding o enkephalin cell that suppress pain o target for brain stimulation implants in patients with chronic pain - for surgeons, this is the target for brain stimulation implants in patient with chronic pain, in order to control pain, target the periqueductal gray in order to suppress pain. e.g. cancer patients. b. Tegmentum - 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 basiliar areas 1. Red nucleus Pink due to iron in hg and ferrin Motor coordination(extrapyramidal system Tract: Rubrospinal tract 2. Substantia Nigra Dark due to neuromelanin Dopaminergic neurons Extra pyramidal systems: motor planning and learning Degeneration of Dopaminergic neurons Parkinsons disease Related to motor function Functionally associated with the basal nuclei and is commonly divided into pars compacta and pars reticulata Neural rewards system(addiction) If there’s degeneration of dopaminergic neurons that are found in substantia nigra, PREPARED AND EDITED BY: TRANS GROUP 3  (005) THE BRAINSTEM DR. ALLAN VIADO | 10/21/2020 that will result in “parkinson’s disease” State of consciousness thus, this serves the importance of Cardiovascular and respiratory systems substantia nigra. 3. Ventral Tegmental Area largest dopanmine producing area of the brain(neural reward system ❖ Neural reward system e.g. positive reinforcement: tutor will give a project, the student will do something very good that will impress the tutor so that he/she will get a good grade. In order for the student to have a good grade, the tutor will give a good grade if he/she will give a good project. Incentive salience(wanting or craving for reward Associative learning(positive reinforcement Pleasure like joy, euphoria and ecstasy. 4. Reticular formation The reticular formation extends through the central core of the medulla oblongata, pons and midbrain It is an intricate system composed of loosely clustered neurons in what is otherwise white matter. It's found all throughout the brainstem: medulla, pons and midbrain. they are the central core. i. Ascending Reticular Formation (ARS) o Ascending pathway to the cortex o Extrathalamic control modulatory system (outside the thalamus) o Major enabling factor in state of consciousness o Regulating wakefulness via cortical and behavioural arousal(sleep-wake transitions o Damage:coma or death ii. Descending Reticulospinal Tract o Descending pathway to spinal cord o Extrapyramidal motor tract o Locomotion and postural control o Act on the motor neurons supplying the trunk and proximal limb flexors and extensors Central core of the brainstem o Damage in descending reticulo spinal tract Intermingling axons/ cluster of nerve cell bodies in at the mid collicular level would lead to: the white matter decerebrate posturing(ominous sign of -They are ill defined, cannot identify the nerve cell impending death. bodies by itself because they are interspersed within the white matter. And the intermingling of axons is Reticular formation- is actually bilateral, the reason why it's called reticular formation. both sides are loosely ill defined nucleis or Includes neurons in different parts of the brain neurons that are scattered throughout the -There are different areas in which the nerve cell brainstem and other part of the brain and bodies are located. they are actually find in the white matter. Major subsystem and they are found in the central core of Set of interconnected nuclei located throughout the the brainstem : the midbrain, pons and BS medulla. PREPARED AND EDITED BY: TRANS GROUP 3  (005) THE BRAINSTEM DR. ALLAN VIADO | 10/21/2020 c. Cerebral Peduncles versa). Because of the decussation form this area. - they are found in the antero-lateral side of midbrain, and they are contained with motor fibers that run ❖ Homonculus from cerebrum. - is the representation of your body in the - known as “crus cerebri/ basis pedunculi” cortex, the lower extremity is in the medial side of 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. - in the same manner for the sensory, the precentral gyrus : genitalia and upper limbs at medial side. If there is a damage here either the precentral gyrus or post central gyrus there will be weakness and some sensory disturbance at the lower extremities. d. Spinothalamic Tract (antero-lateral tract) -Referred to as anterolateral tract - Latin for foot -Carries information for pain and temp from the contralateral side - Made up of tracts anterolaterally axonal fibers coursing vertically -Enters via dorsal root ganglia and decussates - Contains axonal fibers crossing vertically. immediately - The stalk of the nervous tissue connecting the cerebral cortex with the brainstem- Pons nuclei - spinal cord. -Goes up the spinal cord as the lateral spinothalamic - Relays motor tract to the contralateral side of the body tract Central and medial portions -Goes up to the midbrain then thalamus and relays the Corticobulbar (cranial nerve head and neck} and information to the somatosensory cortex corticospinal tracts(spinal nerves(neck and body} 1. Corticobulbar tract e. Dorsal Column Medial Lemniscus Tract - corticobulbar do not decussate, remains ipsilateral - that means the right facial nerve will only control - carries information for fine touch, proprioception, the muscle of right face and will not decussate into vibration from the contralateral section of the the other side. body - which are the tract for cranial nerves are always - 3 order neuron ipsilateral, they always innervate the same side in first order neuron are dorsal root ganglia contrast with Corticospinal tract: which innervates second order neuron is where there is the contralateral side of the body. decussation 2. Corticospinal tract (motor tract) third order neuron begin at the thalamus - starts at the precentral gyrus (central for motor) towards somatosensory cortex motor cortex is located in the precentral gyrus so the motor neurons there will send the axons, goes in between the thalamus and ganglia known as the internal capsule and then have the cerebral peduncle in the midbrain then it goes down to the medullary pyramids (the pyramids of medulla) and decussation at the pyramidal goes to the other side and then goes to the lateral side of spinal cord and goes to the ventral horn/ ventral column of spinal cord and it emerges into the ventral root. It is now part of the motor neuron and goes out combined with the sensory root to innervate now the skeletal muscles. * there’s another tract coming out from it and its anterior corticospinal tract (straight tract) they are responsible for controlling the movement of the trunk (chest and abdomen)- innervates the muscle of the trunk. This is the reason why the right part of the brain will control the left side of the body (vice PREPARED AND EDITED BY: TRANS GROUP 3  (005) THE BRAINSTEM DR. ALLAN VIADO | 10/21/2020 as the lateral spinothalamic tract and then goes now to the midbrain. And communicates now with the thalamus and that information will be relayed to the somatosensory cortex/post central gyrus. f. Cranial Nerves Nuclei within the Midbrain and Nerves emerging from it. i. Oculomotor Nerve (CN III) - Motor to the extraocular muscles: (Medial rectus, Inferior rectus, Inferior oblique) , ciliary muscles and pupillary constrictors. - Emerges ventrally from the oculomotor nucleus - Synapses with the Edninger Westphal nucleus (Accessory oculomotor nucleus) - directly connected to the occulomotor nerve. - Sensory tracts the conduction is towards the cns. How do they go out form cns? - Dorsal column medial lemniscus carries information for fine touch, proprioception and vibration from the contralateral side of the body. e.g. the fine touch proprioception and vibration enters dorsal root ganglion then enters the spinal cord at the dorsal column and ascends the spinal cord through fasciculus gracilis and fasciculus cuneatus. The fasciculus gracilis carries the information coming from the lower half the body while the fasciculus cuneatus will carry information from the upper half of the body, goes now to the medulla and communicates now to nucleus gracilis medially and nucleus cuneatus laterally. And will now decussate at the level of the medulla to the medial lemniscus. And goes up again in the midbrain, there is the dorsal column medial lemniscus tract there goes up to the thalamus, the synapse with the other group of neurons there. - Thalamus is the relay station, it will now relay that information in conduct that information towards the somatosensory cortex or post central gyrus. Spinothalamic tract: -Will carry the information for pain and temperature from the contralateral side of the body. So at the right side here also enters dorsal root ganglia, the dorsal column but immediately as it enters the spinal cord, it will go/decussate to the other side. Almost immediate decussation towards the either side as the lateral spinothalamic tract, that means it's now going up the spinal cord in the white matter PREPARED AND EDITED BY: TRANS GROUP 3  (005) THE BRAINSTEM DR. ALLAN VIADO | 10/21/2020 Functions: o Supplies parasympathetic pre- ganglionic fiber to the eye o Pupillary constriction (pupillary sphicter muscle) - if you put a light on the eye, pupils will constricts, known as “consensual eye reflex” o Lens accommodation (ciliary muscle) - if you put a ballpen in front of the face and move it closer to your eyes, there will be accommodation to the lens, ciliary muscle will contract and it will make the lens wider o Convergence (Medial rectus) - if you put a ballpen closer to the nose, the eyes will converge, known as “convergial reflex” because of the contraction of the 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. D. PREQUISITES FOR COMA diffuse lesion of both cerebral hemispheres (cortical or subcortical white matter) ○ mild coma bilateral diencephalic dysfunction(thalamus, subthalamus, epithalamus) ○ moderate(decorticate posturing) ii. Trochlear Nerve (CN IV) brainstem(RAS reticular activating system - Exits dorsally wraps around cerebral ○ severe coma(decerebrate posturing) peduncle - Innervate the Superior oblique muscles of the eye (makes your eye go downwards and laterally) - Smallest CN and very thin, yet has the longest intracranial course. PREPARED AND EDITED BY: TRANS GROUP 3  (005) THE BRAINSTEM DR. ALLAN VIADO | 10/21/2020 ❖ Prerequisites for Coma / loss of consciousness (Rostro- caudal) - bilateral hemispheric dysfunction= mildly comatose. - bilateral diencephalic dysfunction= moderate coma -dysfunction in the brainstem = severely comatose. * remember that cerebellum is not involved here. e.g. there is brain herniation: it will damage first both of the cerebral hemisphere- mildly comatose but once there is herniation and diencephalon will enter now the tentorium this will damage now both of diencephalon and will result to moderately comatose. But once this herniation will progress down to the brainstem then it is now severely comatose- impending death. F. SUMMARY Coordinated eye movements (CN III and IV) Pupillary light reflex, accommodation and convergence (CN III) Consciousness and arousal (Reticular formation) Movement and sensory (Tracts) Descending Tract -Corticospinal tract Ascending Tracts -Dorsal Column Medial Lemniscus a. 2 pathologic posturing: Pathway & Spinothalamic Tract 2 MINUTE NEUROSCIENCE i. Decorticate rigidity - is a flexion of upper extremity and extension of the Midbrain is one of the three divisions of the brainstem. At the lower extremity level of the midbrain, the fourth ventricle is narrowed to form the cerebral aqueduct which connects the 3rd and 4th ventricles. Bridging the Midbrain behind the cerebral aqueduct is called a tectum. In front of ii. Decerebate rigidity - extension of both the cerebral aqueduct is calle a tegmentum. The antero-lateral portion upper and lower extremity because the is called the basis peduncle. The tectum primarily consists of Superior damage now has reached the brainstem. Colliculi and Inferior Colliculi Posterior view of the tectum shows the 4 * this means, you can still save a patient bumps of the brainstem. that is in decorticate rigidity because the damage is still above the mid collicular The tegmentum contains the variety of Ascending and level, mainly the damage here is in Descending Tracts, Medial Lemniscus and Anterolateral Tracts. diencephalon but once the damage has Superior cerebellar peduncles, red nucleus (for motor coordination). reached the mid collicular level and Tegmentum contains nuclei for the cranial nerve 3 and 4 as well as below, it will now go into decerebate rigidity. Once the patient is in that Raphe nuclei. Ventral Tegmental Area largest collection of dopamine condition then that is already irreversible producing neurons in midbrain. Crura cerebri that contain fibers from and that is now ominous sign of the motor pathways in the corticobulbar and corticospinal tract. Substantia impending death. nigra other dopamine producing structure in the brain. The area surrounding the cerebral aqueduct is called the Periaqueductal Gray E. Respiratory Control (for pain modulation). - if there is a lesion in diencephalon: cheyne-stokes respiration that means there are alternating tachypnea- bradypnea-tachypnea-bradypnea. But once the damage reaches the midbrain it will be in sustained III. PONS hyperventilation / sustained tachypnea. but once the A. Definition damage reaches now the pons, its either Apneusis o Ataxic - Pons of Varolli (Bridge of Varolius) breathing, so breathing now becomes irregular. And then - Named after italian anatomist Constanzo Varolio when the damage no reaches medulla, it will be in - Latin for “bridge” (connects between two points) respiratory arrest. - Reflex control of the respiratory system - Surrounding structures PREPARED AND EDITED BY: TRANS GROUP 3  (005) THE BRAINSTEM DR. ALLAN VIADO | 10/21/2020 Inferior to midbrain Superior to the medulla B. Related structures found in the Pons Anterior to cerebellum - Corticospinal tract - The pons is anterior to the cerebellum and connects the - Middle cerebellar peduncle medulla oblongata to the midbrain. The anterior surface is - 4th ventricle convex, and the trigeminal nerve emerges anterolaterally. - Reticular formation - The anterior or basal part of the pons consists of transversely - Spinothalamic tract running fibers, called the trapezoid body, and descending - Dorsal column medial lemniscus tract bundles of the corticospinal tract. - Cranial Nerves and their nucleis: - The posterior part, or tegmentum, contains multiple ❏ V-Trigeminal Nerve nuclei, including facial, abducens, vestibular, ❏ VI-Abduscens Nerve pontine. trapezoid, and trigeminal (main sensory, ❏ VII-Facial Nerve spinal, and motor). ❏ VIII-Vestibulocochlear Nerve a. Corticospinal Tract - Originates in multiple cortical areas Primary motor cortex Pre-motor cortex - Internal capsule Between thalamus & Basal ganglia - Cerebral Peduncles - Predominantly contralateral crossing at the pyramids - Levels of the Pons and their major Level Cavity Nuclei Motor Tracts Sensory Tracts Facial Fourth Facial Corticospinal Spinal tract colliculus ventricle nucleus, and of CN V; medial corticonuclear lateral, vestibular tracts, spinal and nucleus, transverse medial spinal pontine fibers, lemnisci nucleus of medial CN V, longitudinal pronuclei, fasciculus trapezoid nuclei Trigeminal Fourth Main Corticospinal Lateral, nuclei ventricle sensory and and spinal and motor corticonuclear medial nucleus of tracts, lemnisci CN V, transverse pontine pontine fibers, nuclei, medial trapezoid longitudinal nuclei fasciculus PREPARED AND EDITED BY: TRANS GROUP 3  (005) THE BRAINSTEM DR. ALLAN VIADO | 10/21/2020 c. 4th Ventricle - Cerebrospinal Fluid (CSF) Pathway - roughly pyramid-shaped space that forms the cavity of the metencephalon and myelenephalon Produced mostly in the lateral ventricle 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 lose your balance and coordination (which is the main function of your cerebellum). ❖ Hydrocephalus Hydrocephalus is a condition that involves the build-up of CSF (a fluid that is 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 function: acting as a cushion, delivering PREPARED AND EDITED BY: TRANS GROUP 3  (005) THE BRAINSTEM DR. ALLAN VIADO | 10/21/2020 nutrients and removing harmful substances. o Involves accumulation of cerebrospinal fluid o Impaired reabsorption of the cfs in the bloodstream o Blockage in the ventricular system that causes the CSF to accumulate o can be congenital or acquired - Communicating hydrocephalus o No blockage in ventricular system - Non-communicating (most common cause of hydrocephalus) o Blockage in ventricular system - Enlargement of the ventricles can lead to increased intracranial pressure - When the CSF accumulates in the ventricles this causes the brain to be enlarged. - When hydrocephalus occurs in infants, their skull is more capable in 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 - It goes from the dorsal root ganglion to the dorsal beyond 3 months old, the possibility of permanent damage to column of the spinal cord up to the nucleus gracilis the brain of the child is very high. and nucleus cuneatus of the medulla then it decussates to the other side of the medulla through ❖ If there will be an obstruction in the 4th ventricle, CSF will the medial lemniscus pathway. It goes to accumulate in the aqueduct of Sylvius and 3rd ventricle. contralateral side up to the thalamus (third order neuron). The third order neuron will synapse with ❖ If the obstruction is in the aqueduct of Sylvius, CSF will not the sensory neuron at the sensory motor cortex. accumulate in the 4th ventricle since it is proximal to the aqueduct of Sylvius. - This is different to the pain and temperature which is the anterolateral or the spinothalamic tract. The anterolateral spinothalamic tract will decussate d. Pontine Reticular formation almost immediately as it enters the spinal cord Purely defined scattered clusters of nerve cells body through the substantia gelatinosa of the spinal cord and their axons. towards the other side. Then, it ascends at the white matter fiber tracts of the spinal cord towards the thalamus. From the thalamus, it gies to the somatosensory cortex. g. CRANIAL NERVE NUCLEIS WITHIN THE PONS e. Spinothalamic Tract (Anterolateral tract/system) f. Dorsal Culumn Medial Lumniscus tract - Sensory tracts – (ascending unlike the motor tracts that are descending) - Carries sensory information for vibration, fine or light touch and proprioception. PREPARED AND EDITED BY: TRANS GROUP 3  (005) THE BRAINSTEM DR. ALLAN VIADO | 10/21/2020 1. CN V (Trigeminal Nerve) Supply sensation to the face Largest nerve 3 major branches o Mandibular (mixed sensory-motor nerve) -supply muscles of mastication o Ophthalmic (sensory nerve) -supply the forehead o Maxillary (sensory nerve) -supply the maxillary area *facial nerve highlighted with blue color 4. CN VIII (Vestibulocochlear Nerve) Two nerve in one Connected to cerebellum Vestibular - important in balance Cochlear - important in hearing * trigeminal nerve highlighted with light blue color 2. CN VI (Abduscens 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 *Vestibulocochlear nerve highlighted with light blue color D. 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 CN V (Ophthalmic Nerve) - Afferent Sensory Part CN VII (Facial Nerve) - Efferent *abduscens nerve highlighted with light blue color Motor Part 3. CN VII (Facial Nerve) Efferent 2 MINUTE OF NEUROSCIENCE Lateral to pons Pons is a major division of the brainstem. found above the Innervates the muscle of facial expressions medulla and below the midbrain. Pons is called the “bridge” because its Important in corneal reflex anterior part (basal pons) causes the pons to connect the 2 hemisphere Contains Right and Left facial nerve of the cerebellum. Pontine tegmentum/ Dorsal Pons is the region behind the basal pons. PREPARED AND EDITED BY: TRANS GROUP 3  (005) THE BRAINSTEM DR. ALLAN VIADO | 10/21/2020 The pons is attached to the cerebellum by the middle cerebellar peduncles (a major pathway between brainstem and cerebellum. Inferior cerebellar peduncles also travel through pons to carry information to the cerebellum. Superior cerebellar peduncle enters the brainstem at the carry information from the cerebellum to the brainstem. IV. MEDULLA OBLONGATA A. Definition 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) - eg. 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. The medulla oblongata contains multiple CN and cerebellar nuclei, the olivary nuclear complex, nucleus ambiguus, hypoglossal nucleus, vestibulocochlear nuclei, dorsal nucleus of the vagus, and nucleus of the tractus solltartus, and spinal nucleus of the trigeminal nerve. B. STRUCTURES FOUND IN MEDULLA a. Pyramid - 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. PREPARED AND EDITED BY: TRANS GROUP 3  (005) THE BRAINSTEM DR. ALLAN VIADO | 10/21/2020 i. Corticospinal tract (pathway) - The corticospinal tract is also known as the ‘pyramidal tract.’ -The upper motor neurons will descend and crosses the other side towards the white matter of the spinal cord on the lateral side. b. Olive - Paired anterolateral bulges - Lateral to pyramids - Contains inferior olivary nucleus 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 passes through the internal capsule. The internal capsule is in between the thalamus and the basal ganglia. The corticospinal tract passes also 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. It also contains the anterior corticospinal tract that controls the muscle of the trunk (axial muscles): chest, abdomen and the back. i. Inferior olivary nucleus - Part of olivo-cerebellar system - Cerebellar motor learning and function PREPARED AND EDITED BY: TRANS GROUP 3  (005) THE BRAINSTEM DR. ALLAN VIADO | 10/21/2020 - Found in medulla 3 main nuclei - 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) e. Spinothalamic tract (pathway) d. Reticular formation - Is a set of interconnected nuclei located throughout the BS - Not anatomically defined - Includes neurons in different parts of brain - Cardiovascular and Respiratory system - The reticular formation,consisting of a diffuse mixture of nerve fibers and small groups of nerve cells,is deeply placed posterior to the olivary nucleus. PREPARED AND EDITED BY: TRANS GROUP 3  (005) THE BRAINSTEM DR. ALLAN VIADO | 10/21/2020 f. Dorsal column medial lemniscus tract (pathway) Nucleus Gracilis and Cuneatus Dorsal column Nucleus: - 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 g. Cranial Nerves and their nuclei : Second Order Neurons (point of 1. CN IX (Glossopharyngeal Nerve) decussation for DCML tract) ○ First Order Neuron - Dorsal -Down the medulla, this can be noticed root ganglia first ○ Third Order Neuron -- Thalamus towards -Mixed motor-sensory nerve somatosensory cortex -tonsils, pharynx, tongue PREPARED AND EDITED BY: TRANS GROUP 3  (005) THE BRAINSTEM DR. ALLAN VIADO | 10/21/2020 2. CN X (Vagus Nerve) 4. CN XII (Hypoglossal Nerve) -Mixed motor-sensory nerve -Supplies the muscle of your tongue -Autonomic Innervations to the heart, lungs, bronchi, trachea, larynx, pharynx Anterior ⅓ of the tongue is supplied by the and also sensation to inner ear. Facial nerve. Posterior ⅓ is supplied by the -Longest cranial nerve glossopharyngeal nerve. -Associated with many ganglias 3. CN XI (Accessory Nerve) C. MEDULLA IN SUMMARY -Goes along the side of medulla Reflex control of cardiovascular and respiratory systems - Supplies the muscle of your neck Reflex control for swallowing and vomiting (Sternocleidomastoid and trapezius muscle) (CN IX / X) - Used when turning neck from side to side Important in Phonation: Control of tongue or shrugging your shoulders (CN XII), Larynx and Pharynx (CN IX / X) PREPARED AND EDITED BY: TRANS GROUP 3  (005) THE BRAINSTEM DR. ALLAN VIADO | 10/21/2020 VENTRICLES LOCALIZATION - The cerebral hemisphere will house the lateral ventricle. The lateral ventricle has a frontal horn, posterior horn and the lateral horn. Most of the CSF is produced by the choroid plexus that is located at the lateral 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 If the damage is from the precentral gyrus, before the there is an obstruction. decussation, What will be the presentation? What will be the - In the case of meningitis, the CSF will accumulate to the part of the body? arachnoid space. The subarachnoid space is the main drainage of Ex. If the damage (tumor, trauma or stroke) is in the left, the CSF. If there is an inflammation to the subarachnoid space, it anywhere from the cerebral cortex to the internal capsule to will no longer absorb CSF. There will be a communicating the left midbrain, to the left medulla. There will be damage to hydrocephalus which involves all the ventricles and the canals the right side of the body (contralateral weakness or paralysis) because it can no longer drain the CSF. If the damage is on the spinal cord, there will be an ipsilateral weakness or paralysis below the lesion. 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. 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. A. Localization of lesion in the Dorsal Lemniscus Medial Lemniscus Tract -If the damage is from the dorsal root ganglion to the nucleus gracilis and nucleus cuneatus, there will be an ipsilateral loss of fine touch, vibration and position sense below the level of the lesion. PREPARED AND EDITED BY: TRANS GROUP 3  (005) THE BRAINSTEM DR. ALLAN VIADO | 10/21/2020 - 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 the ventral horn cells. The spinal cord has three horns: ventral, posterior and lateral horn. The ventral horn will contain motor neuron cells. The ventral horn cell to the neuromuscular junction will be the lower motor neuron. The anterior horn cell will contain the neuronal cell bodies that are motor in function. PREPARED AND EDITED BY: TRANS GROUP 3  (005) THE BRAINSTEM DR. ALLAN VIADO | 10/21/2020 BRAINSTEM CROSS SECTION SUMMARY PREPARED AND EDITED BY: TRANS GROUP 3  (005) THE BRAINSTEM DR. ALLAN VIADO | 10/21/2020 INDEX Fig. 1 The medulla cross section. Fig. 2 The cranial nerves PREPARED AND EDITED BY: TRANS GROUP 3  (005) THE BRAINSTEM DR. ALLAN VIADO | 10/21/2020 TEST YOURSELF 1. Damage to substantia nigra will cause what disease? 2. What type of nerve is colored yellow in the image? 10. What is the function of the encircled nerve 3. The cranial nerve in item 2 innervates what muscle? ANSWERS 4. Connects the 3rd and 4th ventricles. 1. Parkinson’s disease 5. If there is obstruction in the foramen of monro, where will the 2. Trochlear nerve CSF accumulate? 3. Superior oblique muscle 6. Will there be dilation of the third ventricle if there is an 4. Cerebral aqueduct/Aquaduct of Sylvius obstruction in the foramen of monro? 7. What structure is encircled in the image below? 5. Lateral ventricle (proximal part) 6. The third ventricle will not dilate. 7. Pyramid 8. Vagus Nerve 9. Cerebral Peduncle/Crus Cerebri 10. Shrugging of shoulders/innervates the sternocleidomastoid and trapezius. REFERENCES Haines, Duane E. & Mihailoff, Gregory A. (2018). Fundamental neuroscience for basic and clinical applications (5th ed.). Philadelphia: Elsevier, Inc. Snell, Richard S. (2018). Clinical neuroanatomy (8th ed.).Philadelphia: Lippincott Williams and Wilkins. 8. The longest cranial nerve that innervates the heart, bronchi and trachea. 9. Structure labeled no. 4 in this image. PREPARED AND EDITED BY: TRANS GROUP 3