Brain Stem and Cerebrospinal fluid- L4 Faisal I. Mohammed, MD, PhD University of Jordan

Objectives List the functions of the brain stem (Medulla oblongata, Pons, and Midbrain) Explain the cranial nerves and their functions Delineate the functions of the cerebellum Distinguish the functions of diencephalon (thalamus and Hypothalamus) Describe the functions of the basal ganglia Identify the cerebral cortex lobes and explain their functions and dissect it functional areas Differentiate primary from associations areas of the cerebral cortex University of Jordan

Major Parts of the Brain Brain stem- continuation of the spinal cord; consists of the medulla oblongata, pons and midbrain. Cerebellum- second largest part of the brain. Diencephalon- gives rise to thalamus, hypothalamus and epithalamus. Cerebrum- largest part of the brain. University of Jordan

The Brain University of Jordan

Protective Coverings of the Brain The cranium The cranial meninges: dura mater, arachnoid mater and pia mater. University of Jordan

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Brain Blood Flow and the Blood-Brain Barrier Brain receives approximately 20% of the total blood supply. Internal carotid and vertebral arteries carry blood to the brain. Internal jugular veins return blood from the brain. Blood-brain barrier (BBB) protects brain from harmful substances. University of Jordan

Cerebrospinal Fluid (CSF) Clear fluid (plasma without its proteins) Circulates through cavities in the brain (ventricles) and the spinal cord (central canal) and also in the subarachnoid space. Absorbs shock and protects the brain and the spinal cord. Helps transport nutrients and wastes from the blood and the nervous tissue. Has almost half the concentration of blood glucose Has no RBC very few WBC University of Jordan

Ventricles CSF-filled cavities within the brain. Lateral ventricles: cerebral hemispheres. Third ventricle: diencephalon. Cerebral aqueduct: midbrain. Fourth ventricle: brain stem and the cerebellum. University of Jordan

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Formation and Circulation of CSF in the Ventricles Choroid plexuses- networks of capillaries in the walls of the ventricles. Ventricles are lined by ependymal cells. Plasma is drawn from the choroid plexuses through ependymal cells into the ventricles to produce CSF. University of Jordan

Formation and Circulation of CSF in the Ventricles University of Jordan

Circulation of CSF CSF from the lateral ventricles → interventricular foramina → third ventricle → cerebral aqueduct → fourth ventricle → subarachnoid space or central canal. CSF is reabsorbed into the blood by arachnoid villi. University of Jordan

Medulla Oblongata Pyramids- Bulges on the anterior aspect of the medulla. Formed by the large corticospinal tracts that pass from the cerebrum to the spinal cord. A common site for decussation of ascending and descending tracts. University of Jordan

Centers of the Medulla Oblongata Vital centers: Cardiovascular center- Respiratory center- Also includes centers for vomiting, swallowing, sneezing, coughing and hiccupping. Houses five pairs of cranial nerves, VIII-XII. Portion of the ventricle found here is the fourth ventricle. University of Jordan

Pons University of Jordan

Pons Origin of cranial nerves V (trigeminal), VI (abducens), and VII (facial) Contains nuclei of the reticular formation Reticular formation is origin of reticulospinal University of Jordan

Midbrain or Mesencephalon Extends from the pons to the diencephalon. Part of the ventricle found here- cerebral aqueduct. Cerebral peduncles: axons of the corticospinal, corticopontine and corticobulbar tracts. Tectum- situated posteriorly and contains four rounded elevations: two superior ones called superior colliculi and two inferior ones called inferior colliculi. University of Jordan

Midbrain or Mesencephalon University of Jordan

Midbrain Nuclei Nuclei that control cranial nerves III (oculomotor) and IV (trochlear) Corpora quadrigemina – four domelike protrusions of the dorsal midbrain Superior colliculi – visual reflex centers (Tectospinal) moves head Inferior colliculi – auditory relay centers (Tectospinal) moves head Substantia nigra –large area with dark pigments. Help control subconscious muscle activities. Loss of neurons here is associated with Parkinson disease. functionally linked to basal nuclei Red nucleus – largest nucleus of the reticular formation; red nuclei are relay nuclei for some descending motor pathways University of Jordan

Midbrain University of Jordan

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Cranial Nerves CN I is the olfactory nerve (sense of smell).

Cranial Nerves CN II is the optic nerve (sense of sight).

Cranial Nerves CN III, IV, and VI innervate the extraocular muscles that allow us to move our eyes. CN III also supplies motor input to our eyelid muscles and facilitates pupillary constriction.

Cranial Nerves CN V is the trigeminal nerve (the major sensory nerve of the face). It has three large branches, each of which supplies an area of the face: ophthalmic maxillary mandibular

Cranial Nerves CN VII is the facial nerve. It has 5 large somatic branches which innervate the muscle of facial expression. It also carries some taste sensations (anterior 2/3 of tongue). Paralysis of CN VII is called Bell’s Palsy and leads to loss of ability to close the eyes and impairment of taste and salivation.

Cranial Nerves CN VIII is the vestibulocochlear nerve. From the inner ear, the vestibular component carries information on balance, while the cochlear component enables hearing. Damage of CN VIII causes vertigo, ringing in the ears, and/or deafness.

Cranial Nerves CN IX is the glossopharyngeal nerve. This nerve carries some taste sensations as well as ANS impulses to salivary glands and the mechanoreceptors of the carotid body and carotid sinus (senses changes in BP).

Cranial Nerves CN X is the vagus nerve (“the wanderer”), which carries most of the parasympathetic motor efferents to the organs of the thorax and abdomen.

Cranial Nerves CN XI is the spinal accessory nerve. This nerve supplies somatic motor innervation to the Trapezius and Sternocleidomastoid muscles.

Cranial Nerves CN XII is the glossopharyngeal nerve. This is a very large nerve (a lot of resources) to be devoted solely to the tongue – it takes a lot more coordination than you might guess to chew, talk, and swallow without injuring our tongue.

Reticular formation Extends from the upper part of the spinal cord, throughout the brain stem, and into the lower part of the diencephalon. Part of the reticular formation called the reticular activating system (RAS) consists of sensory axons that project to the cerebral cortex. The RAS helps maintain consciousness. Inhibition of RAS causes sleep University of Jordan

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