Brain stem lecture @mbbs.pptx

Neurophysiology and Central nervous system

1. Neurophysiology by ADEDAYO, Lawrence D. ( PhD) Physiology Program College of Health Sciences Bowen University Iwo Second Semester 2022/2023 session

2. Topic: The brainstem ( Midbrain, Pons and the medulla ) Lecture III

3. Introduction The brain stem is the region between the diencephalons and the spinal cord. It consists of three parts: midbrain, pons, and medulla oblongata. The midbrain is the most superior portion of the brain stem. The pons is the bulging middle portion of the brain stem. This region primarily consists of nerve fibers that form conduction tracts between the higher brain centers and spinal cord. The medulla oblongata, or simply medulla, extends inferiorly from the pons. It is continuous with the spinal cord at the foramen magnum. All the ascending (sensory) and descending (motor) nerve fibers connecting the brain and spinal cord pass through the medulla. Each part of brain stem is connected to cerebellum by cerebellar peduncles (superior, middle & inferior).

4. General functions of the Brainstem Pathway of tracts between cerebral cortex & spinal cord. Site of origin of nuclei of cranial nerves (from 3 rd to 12 th ). Site of emergence of cranial nerves (from 3 rd to 12 th ). Contains groups of nuclei & related fibers known as reticular formation responsible for: control of level of consciousness, perception of pain, regulation of cardiovascular & respiratory systems BRAINSTEM STR UC TURE

5. The Midbrain (mesencephalon) The mesencephalon is the most superior part of the brainstem. It is divided into an anterior and a posterior section by the Aqueduct of Sylvius which connects the third and fourth ventricles. Motor tracts, including the fibers of the pyramidal system, pass downward on the midbrain's anterior surface. Sensory axons, including those of the spinothalamic tract also ascend, along the front of the midbrain behind the motor tracts.

6. On each side, the midbrain contains a red nucleus and a substantia nigra. The red nucleus contains numerous blood vessels and receives information from the cerebrum and cerebellum and directs subconscious motor commands concerned with muscle tone and posture. Lateral to the red nucleus is the melanin- containing substantia nigra which secretes dopamine to inhibit the excitatory neurons of the basal nuclei.

7. The midbrain connections

8. The midbrain connections (cont’d) The corpora quadrigemina , which is located on the posterior surface of the midbrain, is composed of two superior colliculi and two inferior colliculi . The superior colliculi are part of the visual system, relaying input from the optic tract t o the lateral geniculate bodies of the thalamus (control reflex movements of the eyes, head and neck in response to visual stimuli). The inferior colliculi are part of the auditory pathway and send information to the medial geniculate bodies of the thalamus, (control reflex movements of the head, neck and trunk in response to auditory stimuli).

9. Nuclei in the midbrain Several important nuclei are located in the midbrain, including the red nuclei , the substantia nigra , and the nuclei of cranial nerves III (oculomotor nerve) and IV (trochlear nerve). The red nuclei connect the midbrain to the cerebellum and to the inner ear. It is also an important part of the extra pyramidal tract. The cerebellum compares input from muscles and joints with motor output from the cortex and relays subsequent adjustments to the cortex through the red nucleus and thalamus. The substantia nigra is a group of dark-colored, dopaminergic cells. Lesions here cause Parkinson's disease. Both of these cranial nerves provide innervation for motor movements of the eyes

10. Dorsal Mesencephalic syndromes   Mainly neuroophthalmologic abnormalities Commonly seen in: Hydrocephalus Consists of : Pupillary abnormality Paralysis of conjunctiva Upward gaze (downward occlusion)……ophthalmoplegia. Convergence retraction (Nystagmus): eyes make repetitive uncontrolled movement. Pathologic lid retraction (Collier‘s sign)

11. The Hindbrain The rhombencephalon , or hindbrain, is composed of two regions: the metencephalon and the myelencephalon . Metencephalon The metencephalon is composed of the pons and the cerebellum. The pons can be seen as a rounded bulge on the underside of the brain, between the midbrain and the medulla oblongata Surface fibers in the pons connect to the cerebellum, and deeper fibers are part of motor and sensory tracts that pass from the medulla oblongata, through the pons, and on to the midbrain.

12. Within the pons are several nuclei associated with specific cranial nerves—the trigeminal (V), abducens (VI), facial (VII), and vestibulocochlear (VIII). Other nuclei of the pons cooperate with nuclei in the medulla oblongata to regulate breathing. The two respiratory control centers in the pons are known as the apneustic and the pneumotaxic centers. Damage to the ventral pons can produce a rare condition called locked-in syndrome. Which is characterized by paralysis of almost all voluntary muscles so that communication by the aware, awake person is possible only by eye blinks.

13. The Pons Literally means “bridge” Wedged between the midbrain & medulla. Contains: Sensory and motor nuclei for 4 cranial nerves Trigeminal (5), Abducens (6), Facial (7), and Auditory/Vestibular (8) Respiratory nuclei: Apneustic & pneumotaxic centers work with the medulla to maintain respiratory rhythm Nuclei & tracts that process and relay info to/from the cerebellum Ascending, descending, and transverse tracts that interconnect other portions of the CNS

14. Associated functions with the pons Arousal Assists in Controlling Autonomic Functions Relays Sensory Information between the Cerebrum and Cerebellum Sleep

15. Myelencephalon The myelencephalon is composed of only one structure, the medulla oblongata, simply called the medulla. About 3 cm (1 in.) long, the medulla is continuous with the pons superiorly and the spinal cord inferiorly. All of the descending and ascending fiber tracts that provide communication between the spinal cord and the brain must pass through the medulla. Many of these fiber tracts cross to the contralateral side in elevated triangular structures in the medulla called the pyramids. Thus, the left side of the brain receives sensory information from the right side of the body and vice versa. Similarly, because of the decussation of fibers, the right side of the brain controls motor activity in the left side of the body and vice versa .

16. Many important nuclei are contained within the medulla. Several nuclei are involved in motor control, giving rise to axons within cranial nerves VIII, IX, X, XI, and XII. The vagus nuclei (there is one on each lateral side of the medulla), for example, give rise to the highly important vagus (X) nerves. Other nuclei relay sensory information to the thalamus and then to the cerebral cortex. The medulla contains groupings of neurons required for the regulation of breathing and of cardiovascular responses; hence, they are known as the vital centres. The vasomotor centre controls the autonomic innervation of blood vessels; the cardiac control centre, closely associated with the vasomotor centre, regulates the autonomic nerve control of the heart; and the respiratory centre of the medulla acts together with centers in the pons to control breathing .

17. Other Medullary Autonomic Reflexes Swallowing, coughing, sneezing, gagging, and vomiting are also reflex responses integrated in the medulla oblongata. Swallowing is controlled by a central program generator in the medulla. It is initiated by the voluntary act of propelling what is in the mouth toward the back of the pharynx and involves carefully timed responses of the respiratory as well as the gastrointestinal system. Coughing is initiated by irritation of the lining of the trachea and extrapulmonary bronchi. The glottis closes, and strong contraction of the respiratory muscles builds up intrapulmonary pressure, whereupon the glottis suddenly opens, causing an explosive discharge of air. Sneezing is a somewhat similar response to irritation of the nasal epithelium. It is initiated by stimulation of pain fibers in the trigeminal nerves.

18. Role of medulla in Vomiting Vomiting is an example of the way visceral reflexes integrated in the medulla including coordinated and carefully timed somatic as well as visceral components. Vomiting starts with salivation and the sensation of nausea. Reverse peristalsis empties material from the upper part of the small intestine into the stomach. The glottis closes, preventing aspiration of vomitus into the trachea. The breath is held in mid inspiration. The muscles of the abdominal wall contract, and because the chest is held in a fixed position, the contraction increases intra-abdominal pressure. The lower esophageal sphincter and the esophagus relax, and the gastric contents are ejected. The "vomiting center" in the reticular formation of the medulla really consists of various scattered groups of neurons in this region that control the different components of the vomiting act.

19. Roles of medulla oblongata in control of respiration, heart rate, and blood pressure The medullary areas for the autonomic reflex control of the circulation, heart, and lungs are called the vital centers because damage to them is usually fatal. The afferent fibers to these centers originate in a number of instances in specialized visceral receptors. The specialized receptors include not only those of the carotid and aortic sinuses and bodies but also receptor cells that are located in the medulla itself. The motor responses are graded and delicately adjusted and include somatic as well as visceral components .

20. Medulla oblongata Autonomic nuclei: Cardiovascular centers Alter the rate and force of cardiac contractions Alter the tone of vascular smooth muscle Respiratory rhythmicity centers Receive input from the pons Additional Centers Emesis, deglutition, coughing, hiccupping, and sneezing Most inferior region of the brain stem. Becomes the spinal cord at the level of the foramen magnum. Ventrally, 2 ridges (the medullary pyramids) are visible. These are formed by the large motor corticospinal tracts. Right above the medulla-SC junction, most of these fibers cross-over (decussate)

21. Sensory & motor nuclei of 5 cranial nerves: Auditory/Vestibular (8), Glossopharyngeal (9), Vagus (10), Accessory (11), and Hypoglossal (12) Relay nuclei Nucleus gracilis and nucleus cuneatus pass somatic sensory information to the thalamus Olivary nuclei relay infomation from the spinal cord, cerebral cortex, and the brainstem to the cerebellar cortex .

22. Clinical significance of the pons Central pontine myelinosis is a demyelination disease that causes difficulty with sense of balance, walking, sense of touch, swallowing and speaking. In a clinical setting, it is often associated with transplant or rapid correction of blood sodium. Undiagnosed, it can lead to death or Locked-in syndrome. Dorsal Mesencephalic syndromes

23. We survive by work, but we impact by hardwork ……don’t be slothful in all your dealings…. Adedayo

24. Thanks for listening

25. This challenging time in national life, is a period to ruminate on how Africans will liberate Africa from neocolonialism. The youth of this generation which I believe you and I belongs to can fight this course and restore the glory of Nigeria and Africa . Starting from us with our faith in God is a task achievable. Words for the moment