NEUROSCIENCE_LC5_BRAINSTEM.pdf

COURSE OUTLINE I. THE BRAINSTEM A. Functions B. General Structures C. Importance D. MRI Axial Comparisons II. MIDBRAIN A. Surrounding Structures B. Opening C....

COURSE OUTLINE I. THE BRAINSTEM A. Functions B. General Structures C. Importance D. MRI Axial Comparisons II. MIDBRAIN A. Surrounding Structures B. Opening C. Axial Dimensions D. Structures of the Midbrain E. Summary III. PONS A. Surrounding Structures B. Related Structures C. Summary IV. MEDULLA OBLONGATA A. Structures B. Bulbar Palsy C. Brainstem Respiratory Center D. Clinical Significance E. Summary V. REFERENCES I. THE BRAINSTEM Rigidly programmed automatic behavior necessary for survival ( Respiration and Consciousness) Reflex center (eg: Corneal reflex, gag reflex, pupillary light reflex,etc) Figure 1. The Brainstem Brainstem are important for respiration, consciousness, cardiovascular control, and reflex center of face. They are passageways or B. GENERAL STRUCTURES conduits of ascending or descending tracts. Sensory tracts will begin in the spinal cord and VISIBLE STRUCTURES OF THE DORSAL ascend towards the thalamus then to the (BACK) BRAINSTEM somatosensory cortex. For the descending tract (corticospinal tract, corticobulbar tract), it will descend to the brainstem then to the spinal cord. Midbrain ○ Superior colliculus ○ Inferior colliculus A. FUNCTIONS ○ Superior brachium ○ Inferior brachium Pons Passageway or conduit for ascending (eg. ○ Fourth ventricle DCML) and descending (Corticospinal tract) ○ Facial colliculus fiber tracts running between cerebrum and ○ Cerebellar peduncles (middle, superior, and spinal cord. inferior) Passageway to and from cerebellum via ○ Sulcus limitans cerebellar peduncles. ○ Medial eminence Heavily involved with innervation of the Head and Face. Middle cerebellar peduncle is the largest CN III to XII - cranial nerves nuclei are found among the three peduncles. within the brainstem with their nerves emerging from them. Medulla Oblongata Exceptions: ○ Cuneate tubercle ○ CN I- Telencephalon ○ Gracile tubercle ○ CN II- Diencephalon ○ Striae medullares ○ Vagal triangle Cerebellar peduncle - bridge between ○ Hypoglossal triangle cerebellum and brainstem Medulla is characterized by the endpoint of the CN I and CN II are not actually cranial nerves. fourth ventricle. BATCH 2028 1F 1 NEUROSCIENCE LC_5 C. IMPORTANCE What are the primary internal and external features of the midbrain, pons, and medulla? What are their significance and their functions? Health and disease correlation D. MRI AXIAL COMPARISONS Midbrain - “2 feet” Ponds - “big belly” Medulla- “2 pyramids” Figure 2. Dorsal (Back) Brainstem VISIBLE STRUCTURES OF THE MID-SAGITTAL BRAINSTEM Midbrain ○ Tectum Figure 4. Corticospinal tract and MRI axial comparisons of the midbrain ○ Tegmentum ○ Cerebral aqueduct ○ Crus Cerebri Pons II. MIDBRAIN ○ Basal area ○ Fourth ventricle Most Rostral/Most superior/ smallest about 2 ○ Medial Longitudinal Fasciculus cm. ○ Pregnant-like appearance "Middle of the Brain" Medulla Oblongata Aka: Mesensephalon (Embryonic Vesicle) ○ Foramen of Magendie ○ Mesen - Middle ○ Choroid plexus of fourth ventricle ○ Cephalon - Brain ○ Inferior medullary velum ○ Decussation of pyramids ○ Central canal of spinal cord Once the medulla oblongata exits the foramen magnum, it will now be the spinal cord. Figure 5. Midbrain This is an illustration of the ventricles Above the midbrain is diencephalon; it has the third ventricle. 1. Rostrally Diencephalon ○ Thalamus ○ Hypothalamus ○ Pineal body 2. Caudally Hindbrain ○ Pons ○ Medulla Figure 3. Mid-Sagittal Brainstem ○ Cerebellum BATCH 2028 1F 2  NEUROSCIENCE LC_5 TENTORIAL NOTCH/OPENING Aka: the tentorial incisure or incisura tentori. Refers to the anterior opening between the free edge of the tentorium cerebelli and the clivus for the passage of the brainstem. Figure 8. Tentorial notch/opening Midbrain, characteristically, has two feet-like Figure 6. Midbrain surrounding structures structures, and dark melanin called substantia nigra. Two openings: tentorial notch and foramen B. OPENING magnum Any mass lesion in the brain will try to push Midbrain ascends through the opening of the everything towards the foramen magnum tentorium cerebelli. because the skull is a closed structure and there Tentorium cerebelli is a fold of dura that is no opening. Most of the time, it is divides the brain into two halves. First half is the rostrocaudal herniation. cerebellum and brainstem. The second half is the cerebrum and diencephalon. CLINICAL NOTE: HERNIATION Figure 7. Midbrain ascends through the opening of the tentorium cerebelli Figure 9. Herniation BATCH 2028 1F 3 NEUROSCIENCE LC_5 Example: Epidural hematoma will expand or try to push the cerebrum down towards the tentorial notch/ tentorial opening. This is called tentorial herniation. From that opening, it will compress other structures like pons or brainstem then always towards the foramen magnum. This will result in comatose. C. AXIAL DIMENSIONS Table 1. Two Levels in Axial Dimension Two Levels of the Midbrain and their Major Structure LEVEL CAVITY NUCLEI MOTOR TRACT SENSORY TRACT Inferior Cerebral Inferior colliculus, substantia nigra, Corticospinal and corticonuclear tracts, Lateral, trigeminal, spinal, and colliculi aqueduct trochlear nucleus, mesencephalic nuclei temporopontine, frontopontine, medial medial lemniscus; decussation of of CN V longitudinal fasciculus superior cerebellar peduncles Superior Cerebral Superior colliculus, substantia nigra, Corticospinal and corticonuclear tracts, Trigeminal, spinal, and medial colliculi aqueduct oculomotor nucleus, Edinger-Westphal temporopontine, frontopontine, medial lemniscus nucleus, red nucleus, mesencephalic longitudinal fasciculus, decussation of nucleus of CN V rubrospinal tract ○ Superior colliculi ○ Inferior colliculi Pineal gland is just above the superior colliculi. It is also part of the epithalamus included in diencephalon. Roof of the midbrain is tectum, housing the canal called the cerebral aqueduct or aqueduct of Sylvius. Cerebral Aqueduct - surrounded by the Periaquaductal Grey TEGMENTUM (MIDBRAIN DIMENSION) Red Nucleus Reticular formation Substantia nigra Floor of the midbrain is tegmentum. It also contains the ventral tegmental area which is the largest dopamine-producing area. Tegmentum is not only part of the midbrain but also an extension of the pons and medulla (called pontine tegmentum and medullary Figure 10. Parts of midbrain axial dimension tegmentum, respective Parts of the Axial Dimension of Midbrain: CEREBRAL PEDUNCLES 1. Superior colliculi 2. Cerebral aqueduct - surrounded by Corticospinal Tract - limbs and trunk periaqueductal gray Corticobulbar Tract - facial expression (VIl), 3. Red nucleus mastication (V3), neck Movements (XI), larynx 4. Substantia nigra and pharynx (IX/X), Tongue (X) 5. Cerebral peduncle - bridge between In the cerebral peduncle, only the descending cerebrum and brainstem tract can be seen. Three divisions: tectum found at the back; Cranial Nerve V3 is called mandibular nerve; anterior part is tegmentum including substantia third portion of trigeminal nerve nigra; two feet called cerebral peduncle Accessory nerve (CN XI) for neck movements Hypoglossal nerve (CN XII) for tongue D. STRUCTURES OF THE MIDBRAIN Pharynx is the passageway of food VS. larynx as the passageway of air. These are controlled TECTUM by CN IX and X Quadrigeminal Plate - directly inferior to SENSORY TRACTS - going towards the thalamus Pineal Gland (third-order neuron) BATCH 2028 1F 4 NEUROSCIENCE LC_5 Spinothalamic/Anterolateral tract - sensory TECTUM tract for pain and temperature Dorsal Column medial lemniscus (DCML) Latin "roof“ tract - sensory tract for conscious Dorsal side proprioception, discriminative touch, and vibration Main feature: Sensory tracts are ascending tracts. Quadrigeminal plate (Corpora Spinothalamic and DCML are the two tracts Quadrigemina) that ascend to the brainstem, from the medulla ○ "Hills" towards thalamus. ○ Singular: Colliculus Spinothalamic tract is for pain and temperature. ○ Superior colliculi (paired) DCML is for conscious proprioception and ○ Inferior colliculi (paired) vibration because it reaches the ○ Separated by Cruciform Sulcus somatosensory cortex. CRANIAL NERVE NUCLEI and their NERVES emerging from the midbrain: III (Oculomotor N.) IV (Trochlear N.) Only two cranial nerves (CN III or oculomotor and CN IV or trochlear nerve) are found inside the midbrain. Figure 13. The tectum SUPERIOR COLLICULI Rostral bumps Visual information Aid in decussation of several fibers of optic nerve Conjugate Vertical Gaze center. Saccadic eye movement (simultaneous movement of both eves between two or more phases of fixation in the same direction) Directly connected to lateral geniculate nucleus (Relay center in Thalamus for the visual pathway, Figure 11. Structures found in the midbrain receiving sensory input from the retina) Connects with Tectospinal tract - Cervical nerves connection - Head movement (while visually fixating on an object) Both eyes will always follow the same direction. Saccadic eye movement: For example, you are reading something and someone suddenly entered the room. The point of fixation will be changed suddenly from the cellphone towards the person who suddenly entered. You are fixated in two phases in the same direction. This is controlled by the superior colliculus. Most of the sensory pathways will travel first to the thalamus before entering the somatosensory cortex. It will also connect to the tectospinal tract which is an extrapyramidal tract. Figure 12. The tectum and tegmentum BATCH 2028 1F 5  NEUROSCIENCE LC_5 Figure 15. Course of the optic nerve Figure 14. Quadrigeminal plate - Superior colliculi OPTIC PATHWAY For example, if you are fixating on something, Optic pathway from the left and right retina will be then biglang may dumating at napatingin ka, carried by the optic nerve. This nerve functions your neck will also follow because of the for the sense of sight. Optic nerve will decussate tectospinal tract. The superior colliculi will on both sides to the optic chiasm (right and left). control your gaze as well as the movement of There will be fibers coming from the left going the muscles of your neck. Neck will always towards the right, and fibers coming from the right follow the direction of your gaze because of the going to the left. The optic tract coming from the chiasm will relay tectospinal tract which is an extrapyramidal tract, information to the lateral geniculate nucleus of the that is, an unconscious tract. thalamus From the lateral geniculate nucleus, that The only conscious tract that goes towards the nuclei will either talk also to the oculomotor muscle are the corticospinal and corticobulbar nucleus to function as reflexes such as tract. Example of the corticospinal tract is the accommodation reflex, convergence reflex through movement of limbs consciously. the visceral oculomotor nucleus or accessory Any problem with the extrapyramidal tract, you oculomotor nucleus or the Edinger Westphal nucleus will have extrapyramidal symptoms. Examples are Parkinson’s disease, dystonia, Most of the signals or impulses. coming from the hemiballismus, in which you cannot control them lateral geniculate nuclei will travel towards the from moving because the signal is coming from optic radiation and end up in Brodmann Area 17 somewhere else aside from the cortex. from the occipital lobe which is the final common Note that you can only control something if it's pathway for vision where you can see, process, coming from the cortex. and identify the color and size of the image. All of these will be consciously managed by the occipital lobe. Unconscious reflexes include pupillary reflex, cornea of accommodation reflex (near response reflex), convergence reflex which are all taken care of by the brainstem. Accommodation reflex - when someone goes towards you and points his fingers in front of you, your eyes will converge and constrict along with the change of size of lens. Figure 16. Location of Medial and Lateral geniculate nucleus BATCH 2028 1F 6  NEUROSCIENCE LC_5 Lateral geniculate nucleus is for the functioning of INFERIOR COLLICULI oculomotor nerve inside midbrain Most of the fibers coming from the lateral Caudal bumps geniculate nuclei will proceed as optic radiation Processes auditory information and head movement in response to auditory stimulus TECTOSPINAL TRACT Directly connected to Medial geniculate nucleus (Thalamic relay between the inferior colliculus and Part of the extrapyramidal tracts. Tectospinal the auditory cortex of the temporal lobe) fibers arise from the superior colliculus of the midbrain. NOTE: Process auditory information in response Axons pass ventromedially around the to auditory stimulus and head movement. periaqueductal grey matter and cross in the dorsal Example: pag may pumutok na firecracker sa tabi tegmental decussation. mo, your neck will also follow the direction of the In the spinal cord, descending tectospinal fibers lie sound. near the ventral median fissure and terminate predominantly in cervical segments. The superior colliculus receives visual input and the tectospinal tract is thought to mediate reflex movements of the neck in response to visual stimuli. Figure 18. Quadrigeminal plate - Inferior colliculi Fiber of inferior colliculus will travel towards the medial geniculate nucleus of the thalamus then will send the information to the temporal cortex. Note that hearing is located in the temporal cortex. Conscious processing of hearing is processed within the temporal cortex. Then it will send information towards the limbic system for remembering. Figure 17. Tectospinal tract Figure 19. Auditory pathway BATCH 2028 1F 7 NEUROSCIENCE LC_5 CEREBRAL AQUEDUCT CSF Pathway: (AQUEDUCT OF SYLVIUS) CSF is produced by the choroid plexus from the Connects 3rd and 4th Ventricle lateral ventricles. It will travel to the foramen of Narrow channel between tectum and tegmentum Monroe to the third ventricle and then will travel Since this is a narrow channel, so it is prone to to the cerebral aqueduct/ aqueduct of Sylvius. obstruction Then, it will go to the fourth ventricle going to the lateral and medial aperture of the foramen of Luschka and Magiendie then towards the subarachnoid space. Then it goes back to the arachnoid villi and then to the venous drainage system. Around fifty percent (50%) of CSF will go towards the central canal of the spinal cord. The other component will go to the arachnoid granulation then will go towards the sinuses. From the sinuses, they will go back towards the choroid plexus and will produce CSF again. Function of CSF: cushion of brain so if you accidentally hurt your head (or pag nauntog ka), the brain will just bounce. Note: Lateral ventricle is housed by cerebrum. Third ventricle is housed by diencephalon. CLINICAL NOTE: CONGENITAL AQUEDUCTAL STENOSIS Figure 20. Lateral ventricle with Cerebral aqueduct Obstruction leads to triventricular “Aqueduct of Sylvius” hydrocephalus 2 lateral ventricles 3rd ventricle Triventricular hydrocephalus because you have two lateral ventricles (right and left) and one third ventricle. It will result in a hydrocephalic patient and it is very common. Figure 22. Aqueductal stenosis Figure 21. Cerebrospinal fluid pathway BATCH 2028 1F 8  NEUROSCIENCE LC_5 CLINICAL NOTE: PEDIATRIC HYDROCEPHALUS Pediatric hydrocephalus happens inside the uterus Hydrocephalic patients should be operated within two to three months because beyond that, greater damage in the brain will be expected. It will lead to mental retardation, enlarged head. In adults, obstruction, hemorrhage, or trauma that will obstruct the ventricular pathway will result in hydrocephalus in just a few hours because of the accumulation of CSF where its production is constant (approximately 300cc to 700cc of CSF production per day). This will lead to comatose within 24hrs. Figure 24. Ventriculoperitoneal shunting LATERAL VENTRICLE has three horns namely frontal, occipital, and lateral horn main site of the production of CSF CSF will go towards the foramen of Monroe towards third ventricle THIRD VENTRICLE Figure 23. Pediatric hydrocephalus; VP shunting Surrounded by diencephalon CLINICAL NOTE: FOURTH VENTRICLE VENTRICULOPERITONEAL SHUNTING Has the foramen of Luschka and foramen of Ventriculoperitoneal shunting is the Magiendie shunting of ventricles towards the abdominal cavity. It includes the shunting of CSF from CENTRAL CANAL one point to another. Insertion of catheter in Most of CSF will travel in the central canal of the the abdomen will be lifetime. spinal cord Example: If there is a tumor inside the third ventricle, the lateral ventricle will dilate including the foramen of Monro. Anything that is proximal will dilate from the site of obstruction. Another is obstruction in the cerebral aqueduct. This is triventricular hydrocephalus because you have two lateral ventricles (R and L) and third ventricle to dilate including the foramen of Monro. Figure 25. Aqueduct obstruction “Mickey Mouse sign” BATCH 2028 1F 9  NEUROSCIENCE LC_5 PERIAQUEDUCTAL GRAY GATE CONTROL THEORY OF PAIN Grey matter surrounding the cerebral aqueduct Stimulation of Periaqueductal grey activates ○ Control center for descending pain Enkephalin releasing Neurons modulation (Analgesia, Quiescence, Raphae nuclei (Reticular formation) release Bonding). serotonin (5-HT) ○ Pain and temperature fibers of the Dorsal horn of Spinal cord spinothalamic tract send information to the ○ Excitatory synapse with inhibitory PAG via spinomesencephalic tract. interneurons in laminae ll (Substancia Target for brain stimulation implants in patients Gelatinosa) releasing enkephalin or with Chronic pain dynorphin (opioid NT). Enkephalin (opiod peptide) produces cells that ○ Enkephalin binds to mu and Dynorphin suppress pain. binds Kappa opiod receptors from the C Projection to the raphe nucleus (part of ARAS) - and A delta fibers (carries pain signals Serotonin pathway. from nociceptors). Role in Autonomic function, motivated behavior, ○ Mu opiod receptor activation - inhibits and behavioral response to threatening stimuli. substance P from the 1st and 2nd order Final common pathway mediating defensive neurons thereby halting the signal from reaction to fear. reaching the VPL nucleus of the thalamus Coordinates behaviour essential to survival ○ This produces immediate and profound (changes in movement and posture) analgesia ○ Spinocerebellar pathways (dec. nociceptive/Pain signals while enhancing proprioceptive signals) ○ Alteration in cerebellar nuclear outputs ○ Regulation of spinal reflex circuits by inc Alpha motor neuron activity NOTE: Role of periaqueductal gray in autonomic, motivated behavior, and behavioral response to threatening stimuli. For example in an oncoming train, you do not freeze but instead you run. That reaction is stimulated by the periaqueductal gray, creating a defensive mechanism and increases the autonomic sympathetic function and proprioceptive signals so you can immediately move your body. It also activates the cerebellum (responsible for movement) so it will have coordinated movements by running away from threatening objects and form your reflexes. Figure 27. Pain modulating system CLINICAL NOTE: DBS SURGERY Deep brain stimulation involves the implantation of a neurostimulator device that sends electrical impulses to definite targets inside the brain, i.e. the different brain nuclei & stimulates neurons located in it through implanted electrodes. TEGMENTUM The "Floor" Region between the cerebral aqueduct and the cerebral peduncles Contents: Figure 26. Periaqueductal grey (Central grey) ○ Red nucleus ○ Substantia Nigra ○ Reticular Formation BATCH 2028 1F 10 NEUROSCIENCE LC_5 Figure 28. Tegmentum in the brainstem RED NUCLEUS Pink due to iron (Fe) in hg and Ferrin. Extrapyramidal motor nucleus (part of the Extrapyramidal system). Facilitates flexor movements in the contralateral limbs (Coordination/planning/learning). It relays motor impulses from the cerebral cortex and cerebellum to the thalamus & the spinal Figure 29. Red Nucleus cord (cortico-rubro-spinal and dentatorubro-spinal). RUBROSPINAL TRACT Input: Extrapyramidal tract ○ Corticorubral tract: from the motor and Fiber tract cross the midline and descend thru premotor areas of the cerebral cortex. pons and medulla ○ Dentatorubral tract: from the opposite Terminate in the ventral horn (Anterior Grey dentate nucleus of the cerebellum. Column ) of the Spinal Cord. Output: Facilitate/modulate the activity of Flexor ○ Rubrospinal tract: to the spinal cord Muscles ○ Rubrothalamic tract: to the motor nuclei of the thalamus (VA and VL thalamic nuclei) Lesion: ○ results in signs of cerebellar damage (contralateral tremor, ataxia, dysdiadochokinesia, dysmetria, overshooting, etc). Figure 30. Rubrospinal tract BATCH 2028 1F 11 NEUROSCIENCE LC_5 SUBSTANTIA NIGRA CLINICAL NOTE: PARKINSON’S DISEASE Progressive disorder due to degeneration of the Dopamine production substantia nigra. ○ Neurotransmitter/Neurohormone affects Loss of NT Dopamine - neuromodulator for motor many systems of the central nervous system planning and learning ranging from movement control, cognitive Dopamine - produced by the following: executive functions, and emotional limbic ○ Ventral Tegmental Area activity ○ Hypothalamus Dark due to Neuromelanin in Dopaminergic neurons Since dopamine is also connected with the corpus Considered a Part of the Basal Ganglia as it is a striatum of the basal ganglia, it is also involved part of the Corpus Striatum with motor, planning, and learning. Lack of Extrapyramidal system - Motor planning and dopamine will cause uncoordinated movements, learning such as tremors. ○ Degeneration of dopaminergic neurons - Parkinson’s disease. Corpus Striatum ○ Caudate Head ○ Lenticular nuclei Putamen Globus pallidus Subthalamic Nucleus Substantia Nigra Intricate synapses to promote or antagonize movement (Extrapyramidal) Substantial Nigra is part of the tegmentum not the crus cerebri Figure 32. Substantia nigra and Parkinson’s disease VENTRAL TEGMENTAL AREA Largest Dopamine producing area of the brain Dopamine also takes part in the Neural Reward system aside from its extrapyramidal NT functions Incentive salience (motivation/wanting/Craving for reward) Associative learning (Positive reinforcement/acquire info about relationships between events or entities in the environment) Pleasure (Joy, euphoria and ecstasy) Figure 31. Substantia nigra Figure 33. Dopamine and serotonin pathways BATCH 2028 1F 12  NEUROSCIENCE LC_5 RETICULAR FORMATION ASCENDING RETICULAR ACTIVATING SYSTEM (ARAS) Is a set of interconnected nuclei located Regulates wakefulness throughout the Brainstem Loosely clustered neurons in the white matter Not anatomically defined originating from brainstem towards the State of behavioural arousal and Diencephalon, Limbic system to the Sensory consciousness Cortex. Inputs for Cardiovascular and Respiratory systems Interplay of Neurotransmitter systems Central core of the brainstem (interconnected (produce cortical activity and alertness when nucleis in Midbrain/pons to Medulla). Not stimulated). anatomically well defined ○ Noradrenergic system Intermingling of axons/Cluster of nerve cell bodies ○ Acetylcholine system in white matter ○ Dopaminergic system Includes neurons in different parts of brain ○ Serotonergic system Major subsystems for wakefulness: ○ Histaminergic system ○ Ascending reticular formation (ARAS) Damage: Coma or death ○ Descending Thalamic Ventrolateral Damage of ARAS, in the cerebrum, will result in preoptic area (VPA) coma. But damage to its origin (brainstem) will result in immediate death. Brainstem: center of consciousness and respiration. Figure 35. Ascending reticular activating system (ARAS) VENTROLATERAL PREOPTIC AREA (THALAMIC VPA) Descending (arousal) Pathway Release GABA reuptake inhibitors Interrupts wakefulness/arousal ARAS inhibit the VPA to maintain wakefulness Figure 34. 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. Figure 36. Descending pathway BATCH 2028 1F 13  NEUROSCIENCE LC_5 CLINICAL NOTE: CENTRAL AND MEDIAL PORTIONS PREREQUISITE FOR COMA/LOSS OF CONSCIOUSNESS 1. Corticobulbar (Corticonuclear) tract Cranial Nerves: Head and face Diffuse lesion of both Cerebral hemisphere Motor CN V3,VIl,IX,X,XI,XIl (Cortical or subcortical White Matter) ○ Mild Coma 2. Corticospinal tracts Bilateral Diencephalic Dysfunction Spinal Nerves: Neck and Body (Thalamus/Subthalamus/ Hypothalamus) ○ Moderate Coma (Decorticate posturing) Brainstem (ARAS - Ascending Reticular activating system) ○ Severe Coma (Decerebrate posturing) ARAS or consciousness per se involves the cerebrum, diencephalon, and brainstem. Cerebellum has nothing to do with consciousness. It can only affect consciousness if there’s a cerebellar hematoma that enlarges and compresses the brainstem. In that way, you will lose consciousness in cases of cerebellar hematoma. If there's damage in the cerebrum, the patient will be in a mild coma, and a damage to diencephalon will produce moderate coma. But if the brain stem is damaged or being compressed, there will be a loss of ARAS and the patient will be severely comatose. Because the rubrospinal tract resides in the brainstem, the patient will lose control of his flexor muscles and thereby extend. He will be in a vegetative state and will no longer be functional. CEREBRAL PEDUNCLES Crus cerebri/Basis pedunculi/Basis pontis Latin for "Foot" Made up of tracts anterolaterally (Axonal Fibers coursing vertically). A stalk of nervous tissue connecting the Figure 37. Cerebral peduncles Cerebral cortex with the Brainstem. Relays long motor tracts to the contralateral side of the body. THE HOMUNCULUS NOTE: The cerebellar peduncles would be a pathway for the cortex to communicate with the cerebellum through the middle cerebellar peduncles making the cortico-ponto-cerebellar pathway. The cerebellum is linked to other parts of the central nervous system (CNS) by numerous efferent and afferent fibers that are grouped together on each side into three large bundles, or peduncles. The superior cerebellar peduncles connect the cerebellum to the midbrain, the middle cerebellar peduncles connect the cerebellum to the pons, and the inferior cerebellar peduncles connect the cerebellum to Figure 38. The homonculus the medulla oblongata. BATCH 2028 1F 14 NEUROSCIENCE LC_5 CORTICOBULBAR (CORTICONUCLEAR) TRACT V3, VII, IX, X,XI, XI|l 50% decussate (in contrast, Most Corticospinal tract decussate, some do not decussate as the anterior corticospinal tract which innervates the trunk muscles). CN nuclei innervating skeletal muscles thereby generally receive bilateral first order neuron innervation (ie. From both (L & R) cerebral motor cortex). Figure 41. Facial muscle innervation CORTICOSPINAL TRACT Originates in multiple cortical areas ○ Primary motor cortex ○ Premotor cortex Internal capsule ○ Between Thalamus & Basal Ganglia Cerebral peduncles Predominantly contralateral crossing at the pyramids Note: Most decussate as the lateral corticospinal tract at the spinomedullary junction to innervate the contralateral limb muscles, some do not decussate as the anterior (Ventral) Corticospinal tract to innervate the Trunk muscles Figure 39. Corticobulbar tract Bilateral cortical innervation ○ Facial muscle innervation Figure 40. Bilateral cortical innervation Figure 42. Corticospinal tract BATCH 2028 1F 15 NEUROSCIENCE LC_5 SPINOTHALAMIC (ANTEROLATERAL) TRACT AND DORSAL COLUMN MEDIAL LEMNISCUS (DCML) TRACT Figure 44. Cranial nerves location Ill nuclei and nerve (Oculomotor nerve) IV nuclei and nerve (Trochlear nerve) OCULOMOTOR NERVE (CN III) Figure 43. Spinothalamic tract (Anterolateral tract) and Dorsal column medial lemniscus tract CRANIAL NUCLEI AND NERVES Figure 45. Oculomotor nerve (CN III) and associated arteries Motor to the extraocular muscles (Medial rectus, Inferior rectus and inferior oblique), ciliary muscle and pupillary constrictors Emerges ventrally from the oculomotor nucleus Synapse with the Edinger Westphal nucleus (Accessory oculomotor nucleus) Supplies Parasympathetic preganglionic fiber to the eye: ○ pupillary constriction (pupillary sphincter Figure 44. Cranial nerves location muscle) ○ Lens accommodation (Ciliary muscle) ○ Convergence (Medial rectus) Damage to your cranial nerve III will dilate your pupils. Adducts the eyeball. BATCH 2028 1F 16  NEUROSCIENCE LC_5 E. SUMMARY Coordinated eye movements (CN IIl and IV) Pupillary light reflex, accommodation and Econvergence (CN III) Consciousness and arousal (Reticular formation) Movement and sensory (Tracts) Dopamine effects (Substancia nigra and the Ventral Tegmental Area) Figure 46. Oculomotor nerve (CN III) Note: CN IIl emerges ventrally and courses between the Posterior cerebral artery (PCA) and Superior Cerebellar artery (SCA) PCOM aneurysms may compress on CN III producing Pupillary dilation. TROCHLEAR NERVE (CN IV) Exits dorsally wraps around cerebral peduncle Purely motor nerve Innervate the Superior oblique muscle of the eye Smallest CN, yet has the longest intracranial Figure 48. Superior dorsal view of the brainstem with course cerebellum The only nerve which originates from the back of the brainstem. III. PONS Pons Varolii (Bridge of Varolius) - Italian anatomist Constanzo Varolio Latin for “bridge” Figure 47. Trochlear nerve (CN IV) passage in the brainstem The cranial nerve with the longest extracranial Figure 49. Parts of the brainstem and midbrain course is the vagus nerve. BATCH 2028 1F 17 NEUROSCIENCE LC_5 A. SURROUNDING STRUCTURES Inferior to midbrain Superior to the medulla Anterior to the cerebellum Figure 51. Location of pons in the brainstem Figure 50. Parts of the brain Figure 52. Parts of the pons TABLE 2. Levels of the Pons Levels of the Pons and their Major Structures LEVEL CAVITY NUCLEI MOTOR TRACTS SENSORY TRACT Facial Fourth Facial nucleus, abducens nucleus, Corticospinal and Spinal tract of CN V; lateral, colliculus ventricle medial vestibular nucleus, spinal corticonuclear tracts, spinal, and medial lemnisci nucleus of CN V, pontine nuclei, transverse pontine fibers, trapezoid nuclei medial longitudinal fasciculus Trigemin Fourth Main sensory and motor nucleus Corticospinal and Lateral, spinal, and medial al nuclei ventricle of CN V, pontine nuclei, trapezoid corticonuclear tracts, lemnisci nuclei transverse pontine fibers, medial longitudinal fasciculus The only cranial nerve that originates within B. RELATED STRUCTURES the body of the pons is the trigeminal nerve CNV the other cranial nerves would originate Corticospinal tract at the junction between the pons and the Middle cerebellar peduncle medulla (CN VI, CN VII, CNVIII). 4th ventricle Reticular formation Spinothalamic tract Dorsal column medial lemniscus tract Cranial Nerve Nuclei and their nerves: V, VI, VII, VIII On the anterolateral surface of the pons, the trigeminal nerve emerges on each side. Each nerve consists of a smaller, medial part, known as the motor root, and a larger, lateral part, known as the sensory root. In the groove between the pons and the medulla oblongata, from medial to lateral, the abducens, facial and Figure 53. Ventral pons vestibulocochlear nerves emerge. BATCH 2028 1F 18 NEUROSCIENCE LC_5 Figure 57. Location of cerebral peduncle Figure 54. Cross-section of the Pons MIDDLE CEREBELLAR PEDUNCLE Largest cerebellar peduncle Connects cerebellum to the pons (contains fibers from the contralateral pontine nuclei and course to the cerebellum) Figure 55. Transverse section of the pons at the level of the trigeminal nerve CORTICOSPINAL TRACT Figure 58. Cross-section and parts of the Pons CORTICO-PONTO-CEREBELLAR PATHWAYS Figure 56. Corticospinal tract Figure 59. Cortico-ponto-cerebellar pathways BATCH 2028 1F 19  NEUROSCIENCE LC_5 4TH VENTRICLE lies at the back of the pons. An obstruction or blockage to 4th ventricle would result in dilation of the cerebral aqueduct, third ventricle and the two lateral ventricles. 4th ventricle occupies both the pons and the upper medulla, lower to the medulla it will become the central canal. Figure 61. Sensory tracts: Spinothalamic tract and Dorsal column medial lemniscus tract (DCML) CRANIAL NUCLEI AND NERVES CN V (Trigeminal Nerve) - The trigeminal nerve will give rise to three branches, two purely sensory (ophthalmic and maxillary nerves) and one mixed sensory and motor (mandibular nerve) CN VI (Abducens Nerve) - The abducens nerve abducts the eyes. While the oculomotor nerve CNIII would adduct the eyes. CN VII (Facial Nerve) - The facial nerve innervates the muscles of facial expression and salivation. CN VIII (Vestibulocochlear Nerve) C. SUMMARY Reflex control of the respiratory system Figure 60. Normal brain vs. Enlarged ventricles ○ apneustic center ○ pneumotaxic center Eye Movement (CN VI - Lateral rectus) PONTINE RETICULAR FORMATION Hearing and balance (CN VIll) Facial expression, Taste, Tear and Lacrimation (CN VII) Sensory tracts Corneal Reflex Spinothalamic tract (Anterolateral tract) ○ CN V-I (Ophthalmic) - Afferent Dorsal Column Medial lemniscus tract ○ CN VII (Facial Nerve) - Efferent (DCML) Figure 62. View of the brainstem from the back (through the cerebellum) BATCH 2028 1F 20 NEUROSCIENCE LC_5 Figure 63. Cross-sections of the pons IV. MEDULLA OBLONGATA Most caudal part of brainstem Continues as the spinal cord once it emerges at the Foramen Magnum Roughly 3 cms in length and 2 cms in diameter Myelencephalon Superiorly - Pons Caudally - First Cervical spinal nerve TABLE 3. Levels of Medulla Oblongata Levels of Medulla Oblongata and their Major Structures LEVEL CAVITY NUCLEI MOTOR TRACT SENSORY TRACT Decussation of Spinal tract of CN V, posterior Decussation of Central Nucleus gracilis, nucleus cuneatus, corticospinal spinocerebellar tract, lateral pyramids canal spinal nucleus of CN V, accessory tracts, pyramids spinothalamic tract, anterior nucleus spinocerebellar tract Decussation of medial lemnisci, Nucleus gracilis, nucleus cuneatus, fasciculus gracilis, fasciculus Decussation of Central spinal nucleus of CN V, accessory Pyramids cuneatus, spinal tract of CN V, medial lemniscus canal nucleus, hypoglossal nucleus posterior spinocerebellar tract, lateral spinothalamic tract, anterior spinocerebellar tract Inferior olivary nucleus, spinal nucleus of CN V, vestibular Medial longitudinal fasciculus, Olives, inferior Fourth nucleus, glossopharyngeal tectospinal tract, medial lemniscus, cerebellar ventricle nucleus, vagal nucleus, Pyramids spinal tract of CN V, lateral peduncle hypoglossal nucleus, nucleus spinothalamic tract, anterior ambiguuus, nucleus of tractus spinocerebellar tract solitarius Just inferior to Fourth Lateral vestibular nucleus, cochlear No major changes in distribution of pons ventricle nuclei gray and white matter BATCH 2028 1F 21 NEUROSCIENCE LC_5 Figure 64. Transverse section of the brainstem along the rostral-caudal axis A. STRUCTURES Pyramid ○ Corticospinal tract (pathway) Olive ○ Inferior-olivary nucleus 4th Ventricle Reticular formation Spinothalamic tract (Anterolateral tract) Dorsal Column Medial Leminiscus Tract (DCML) Cranial nerves and their nuclei: IX, X, XI,XII Nucleus Gracilis and Cuneatus MEDULLARY PYRAMIDS Paired ventral midline bulges Contains the corticospinal trac Figure 66. Corticospinal tract - Pyramidal tract Figure 65. Location of pyramids within the brainstem BATCH 2028 1F 22 NEUROSCIENCE LC_5 INFERIOR OLIVARY NUCLEUS Part of olivo-cerebellar system Cerebellar motor learning and function 3 main nuclei: ○ Primary olivary nucleus ○ Medial accessory olivary nucleus ○ Dorsal accessory olivary nucleus SUPERIOR OLIVARY NUCLEUS Considered part of the pons Part of auditory system Aids in Perception of sound Related to the vestibulocochlear nerve (CN VIII) - cochlear nerve carries hearing. Figure 67. Corticospinal pathway and Localization of lesion/injury Figure 68. Upper vs. Lower motor neuron OLIVES Paired anterolateral bulges Lateral to pyramids separated by the Figure 69. Locations of Olives antero (ventro)-lateral sulcus Posterior lateral to the pyramids are the olives 4TH VENTRICLE In the sections the olives appear as an intestinal structure. There are two olivary nucleus (the superior and inferior olivary nuclei) only the Communicates with the subarachnoid space inferior olivary nucleus is mainly seen in the via medial and lateral apertures medulla ○ Foramina of Luschka (Lateral aperture) ○ Foramina of Magendie (Median aperture) BATCH 2028 1F 23  NEUROSCIENCE LC_5 NUCLEUS GRACILIS & NUCLEUS CUNEATUS Dorsal column Nuclei ○ Synapse with the fasciculus gracilis and fasciculus cuneatus from the spinal cord ○ Fine discriminative touch, vibration, conscious proprioception ○ Nucleus Gracilis: receives sensory information from the lower half (T6 and Below) of the body entering the lumbar level of spinal cord ○ Nucleus Cuneatus: receives sensory information from upper half (Above T6 - upper limbs, trunk, and neck) entering at the Cervical level of Spinal cord Second order neurons (point of decussation for DCML tract) Note: ○ First order neuron - Dorsal root ganglia Figure 70. 4th ventricle ○ Third order neuron - Thalamus to somatosensory cortex RETICULAR FORMATION Is a set of interconnected nuclei located throughout the BS The reticular formation is a complex network of neuron pathways located in the white matter of the BS, running through the midbrain, pons, and medulla. It is responsible for consciousness and balance. Not anatomically defined Includes neurons in different parts of brain Cardiovascular and Respiratory systems Figure 72. Dorsal column system containing Nucleus gracilis and Nucleus Cuneatus Figure 73. Spinothalamic tract localization of Figure 71. Reticular formation lesion/injury BATCH 2028 1F 24 NEUROSCIENCE LC_5 If the damage is from the first order neuron to nucleus gracilis or nucleus cuneatus, it would lead to ipsilateral loss of fine touch, vibration, and position sense. Figure 74. Dorsal column-medial lemniscus (DCML) localization of lesion/injury If the damage is in the postcentral gyrus or Figure 75. Bulbar palsy midbrain, there would be a contralateral hemisensory loss or fine touch, vibration, and position sense. BULBAR PALSY VS. PSEUDOBULBAR PALSY CRANIAL NUCLEI AND NERVES Bulbar palsy is a lower motor neuron lesion (Nuclei to nerves) of cranial nerves IX, X, and XII. CN IX (Glossopharyngeal Nerve) Pseudobulbar palsy is an upper motor neuron - CN X (Vagus Nerve) corticobulbar tract lesion of cranial nerves IX, X, CN XI (Accessory Nerve) and XII. CN XII (Hypoglossal Nerve) TABLE 4. Bulbar vs. Pseudobulbar Palsy B. BULBAR PALSY Pseudobulbar Bulbar (LMN CN (UMB CN IX, CN X, IX, CN X, CN Due to palsy coming from the lower cranial CN XII) XII) nerves. Gag Increased Absent Reference to medical condition in the nerves and tracts connected to medulla and muscles Tongue Spastic Wasted, Fasciculations innervated by the lower cranial nerves (tongue, pharynx, larynx tongue, etc) Jaw jerk Increased Absent/Normal Bilateral impairment of function of the lower cranial nerves IX, X, and XII, which occurs due Speach Spastic dysarthria Nasal to lower motor neuron lesion either at nuclear or Limbs UMN signs LMN signs fascicular level in the medulla or from bilateral lesions of the said cranial nerves outside the Emotions Labile Normal brainstem. Motor neuron Bilateral CVA disease Causes Multiple sclerosis GB syndrome Motor neuron Poliomyelitis disease Brainstem infarction C. BRAIN STEM RESPIRATORY CENTER Respiratory center ○ Pontine respiratory group Pneumotaxic center Apneustic center ○ Medullary respiratory group Dorsal Ventral BATCH 2028 1F 25 NEUROSCIENCE LC_5 MEDULLARY RESPIRATORY GROUP DORSAL Most fundamental role - inspiration (inhalation) Integrating center of respiration Set and maintain rate of inspiration via the Fr neurons; ○ Mostly Nucleus of the solitary tract Endpoint of sensory information from pontine respiratory group, CN X and IX Sends signals to the respiratory center from chemoreceptors, baroreceptors, and lung stretch receptors ○ Reticular formation of the medulla VENTRAL Contains both inspiratory and expiratory neurons Expiratory area of respiratory control ○ Nucleus ambiguus ○ Nucleus retroambiguus ○ Interneurons in the pre-botzinger complex Active during forceful breathing and inactive during quiet restful respirations Sends inhibitory impulses to the apneustic center PONTINE RESPIRATORY GROUP Connected via Solitary nucleus PNEUMOTAXIC CENTER Figure 76. Brainstem respiratory center upper pons Nuclei ○ Suprabranchial nucleus BRAINSTEM RESPIRATORY CONTROL ○ Medial parabrachial nucleus Controls rate and pattern of breathing Antagonist to the apneustic center Receives input Inspiratory "Switch off" ○ chemoreceptors, mechanoreceptors, the ○ Limits impulses to the Phrenic nerve cerebral cortex, and the hypothalamus in decreasing tidal volume order to regulate the rate and depth of ○ Absence or damage - increase depth breathing of respiration and decrease Stimulated by altered levels of: respiratory rate. Breathing almost ○ oxygen, carbon dioxide, and blood pH, by impossible hormonal changes relating to stress and Regulates the amount of air each breath anxiety from the hypothalamus, and also by signals from the cerebral cortex to give APNEUSTIC CENTER a conscious control of respiration. Injury to respiratory groups can cause various lower pons breathing disorders that may require Sends signal to the dorsal group mechanical ventilation, and is usually promoting inhalation associated with a poor prognosis. Delay the inspiratory "switch off” Controls the intensity of breathing Note: the most powerful stimulant for breathing is Inhibited by pulmonary stretch receptors the accumulation of carbon dioxide in the blood. and pneumotaxic center BATCH 2028 1F 26 NEUROSCIENCE LC_5 D. CLINICAL SIGNIFICANCE Depression of the respiratory center ○ Brainstem damage: TBI, stroke, tumor, etc ○ Drugs: opioids and sedatives Stimulated by Amphetamines Note: The absence of function in the brainstem is one of the criteria for diagnosing brain dead, not the absence of cerebral function. In the absence of function of the brainstem, there should be an absence of the function of respiration. Figure 77. Depression of the respiratory center E. SUMMARY Reflex control of cardiovascular and respiratory systems Reflex control of swallowing and Vomiting (CN IX/X) Important in Phonation: control of tongue (CN XII), Larynx and Pharynx (CN IX/X) Extensive role of the vagus nerve V. REFERENCES Viado, A. (September 10-11, 2024). Brainstem. Splittgerber (2019). Snell's Clinical Neuroanatomy (8th edition). Philadelphia: Wolters Kluwer BATCH 2028 1F 27