Class grades 3 Quizzes Clinical Notebooks Due: 2 Exams 9/27: Ventricular System 11/20: Brainstem and Basal Ganglia 12/6: Cranial Nerves Clinical Notebooks Due: 11/13----no late submissions accepted 2 Exams 11/1: Somatosensory System, Visual System, Central Auditory System, and Vestibular System 11/27: Motor System: Cortical Level, Cerebellum, Brainstem, Basal Ganglia and Spinal Cord

The Meninges and the Ventricular System

Learning Objectives 1. Describe the meninges, their locations, and their functions. 2. Identify parts of the ventricular cavities. 3. Discuss functions of cerebrospinal fluid. 4. Describe the mechanism of cerebrospinal fluid production. 5. Describe the circulation of cerebrospinal fluid. 6. Explain the diagnostic significance of the cerebrospinal fluid. Learning Objectives 1. Describe the meninges, their locations, and their functions. 2. Identify parts of the ventricular cavities. 3. Discuss functions of cerebrospinal fluid. 4. Describe the mechanism of cerebrospinal fluid production. 5. Describe the circulation of cerebrospinal fluid. 6. Explain the diagnostic significance of the cerebrospinal fluid.

Protection of the CNS Function: CNS is fairly soft and gelatinous in nature Basic protection Protection of the CNS Function: CNS is fairly soft and gelatinous in nature Make the brain and spinal cord susceptible to traumatic injuries Basic protection 1. Three meningeal layers 2. Cushioning cerebrospinal fluid 3. Bony wall of the skull and the vertebral column

Meninges of the Brain

Meninges of the Brain Three Meninges: Meninges of the Brain Consist of concentric fibrous tissue membranes that encase the CNS 1. Dura mater 2. Arachnoid membrane 3. Pia mater

The Meninges Bhatnagar & Andy, 1995, Figure 2.45A The Meninges

Meningeal Layers: Dura Mater Location: Function: Meningeal Layers: Dura Mater Location: Gray outermost membrane Attached to inner surface of the skull Overlies the arachnoid membrane Function: Provides the maximum meningeal protection of the CNS

Meningeal Layers: Dura Mater Structure: Two spaces Two fibrous layers of the dura Meningeal Layers: Dura Mater Structure: Consists of dense, fibrous, connective tissues Two spaces 1. Epidural The potential space between the dura and the bone 2. Subdural The potential space between the dura mater and the arachnoid Two fibrous layers of the dura Attached to each other Except to form sinuses That absorb blood from veins and the circulated cerebrospinal fluid 1. Periosteal: External layer Attached to the inner surface of the cranium 2. Meningeal: Internal layer Forms various septa (dural extensions) Forms two lateral compartments for the cerebral hemispheres And one posterior compartment for the cerebellum

The Meninges Bhatnagar & Andy, 1995, Figure 2.45A The Meninges

The Meninges Love & Webb, 1996, Figure 3-3 The Meninges

Dural Extensions Falx Cerebri Location: Cavity Formations: The largest dural reflection Location: Extends longitudinally in the interhemispheric fissure Between the two hemispheres Forms a vertical partition in the cranial cavity between two cerebral hemispheres Cavity Formations: Dorsal edge of the interhemispheric fissure Forms the cavity for the Superior Sagittal Sinus Inferiorly within this fissure above the corpus callosum Inferior Sagittal Sinus is along the free inferior margin of the falx cerebri

Dural Extensions on Midsagittal Section Bhatnagar & Andy, 1995, Figure 2.43 Dural Extensions on Midsagittal Section Bhatnagar & Andy, 1995, Figure 2.43

Dural Extensions on Coronal View Bhatnagar & Andy, 1995, Figure 2.44A Dural Extensions on Coronal View Bhatnagar & Andy, 1995, Figure 2.44A

Dural Extensions Tentorium Cerebelli Location: Tentorial Notch Arises from the petrous portion of the temporal bone Margins are inserted between the cerebellum and the basal surface of the temporal and occipital lobes Occipital lobes lie over it Cerebellum located below it Tentorial Notch Anteriorly, free borders of the tentorium cerebelli Constitute the Tentorial notch Opening Where the brainstem descends through the tentorial notch toward the foramen magnum

Dural Extensions on Midsagittal Section Bhatnagar & Andy, 1995, Figure 2.43 Dural Extensions on Midsagittal Section Bhatnagar & Andy, 1995, Figure 2.43

Dural Extensions on Coronal View Bhatnagar & Andy, 1995, Figure 2.44A Dural Extensions on Coronal View Bhatnagar & Andy, 1995, Figure 2.44A

Dural Extensions Falx Cerebelli Location: Dural Extensions Extension from the tentorial cerebelli Separates the two cerebellar hemispheres

Dural Extensions on Midsagittal Section Bhatnagar & Andy, 1995, Figure 2.43 Dural Extensions on Midsagittal Section Bhatnagar & Andy, 1995, Figure 2.43

Dural Extensions on Coronal View Bhatnagar & Andy, 1995, Figure 2.44A Dural Extensions on Coronal View Bhatnagar & Andy, 1995, Figure 2.44A

Meningeal Layers: Arachnoid Membrane Structure: Location: Meningeal Layers: Arachnoid Membrane Structure: Thin, nonvascular membrane Location: Between the internal pia mater and the external dura mater Does not adhere to the cortical surfaces like the pia mater

Meningeal Layers: Arachnoid Membrane Spaces: 1. Subarachnoid space 2. Subdural space: Meningeal Layers: Arachnoid Membrane Spaces: Space between the pia and the arachnoid Traversed by Arachnoid Trabeculae Consist of fibrous and elastic connective tissue 1. Subarachnoid space Between the arachnoid and the pia Filled with cerebrospinal fluid Produced in the ventricular system Enters the subarachnoid space through openings in the fourth ventricle Subarachnoid space envelopes the entire nervous system 2. Subdural space: Space between the dura mater and the arachnoid Arachnoid granulations (villi) Push through the dura Cerebrospinal fluid drains through villi into the vascular system

The Meninges Bhatnagar & Andy, 1995, Figure 2.45A The Meninges

Arachnoid Villi or Granulations Bhatnagar & Andy, 1995, Figure 2.41 Arachnoid Villi or Granulations Bhatnagar & Andy, 1995, Figure 2.41

Meningeal Layers: Pia Mater Location: Structure: Meningeal Layers: Pia Mater Location: Closely attached to the surface of the brain Follows the contours of the gyri and sulci Structure: Thin, transparent, collagenous (connective tissue) membrane Contains a network of blood vessels That penetrates the pia before entering the cortical substance Pia also surrounds the blood vessels Forms a perivascular space

The Meninges and the Spinal Cord Similar Structures The Meninges and the Spinal Cord Similar structure as the meninges in the brain With a few exceptions Dura is single-layered instead of two layers

The Spinal Cord and Its Meninges Bhatnagar & Andy, 1995, Figure 2.46 The Spinal Cord and Its Meninges Bhatnagar & Andy, 1995, Figure 2.46

The Ventricles

The Ventricular System Three Parts: Function: Three Parts: 1. The Lateral Ventricles 2. The Third Ventricle 3. The Fourth Ventricle Function: Serves as a pathway for the circulation of the CSF Each ventricle contains a tuft-like structure called the Choroid Plexus *Which is concerned mainly with the production of CSF

Ventricular System in Relation to Brain: Lateral View Bhatnagar & Andy, 1995, Figure 2.37 Ventricular System in Relation to Brain: Lateral View Bhatnagar & Andy, 1995, Figure 2.37

Ventricular System: Lateral View Bhatnagar & Andy, 1995, Figure 2.35A Ventricular System: Lateral View Bhatnagar & Andy, 1995, Figure 2.35A

Ventricular System: Dorsal View Bhatnagar & Andy, 1995, Figure 2.35B Ventricular System: Dorsal View Bhatnagar & Andy, 1995, Figure 2.35B

The Lateral Ventricles Structure and Shape: Location: Connection: Choroid Plexus: The Lateral Ventricles Structure and Shape: Paired, one in each hemisphere C-shaped cavity Location: In the parietal lobe, and anterior, posterior and inferior horns, extending into the frontal, occipital, and temporal lobes, respectively Connection: Connected to the third ventricle by an opening called the intraventricular foramen or the foramen of Munro Choroid Plexus: Projects into the cavity on its medial aspect

Ventricular System in Relation to Brain: Lateral View Bhatnagar & Andy, 1995, Figure 2.37 Ventricular System in Relation to Brain: Lateral View Bhatnagar & Andy, 1995, Figure 2.37

The Third Ventricle Location and Shape: Connection: Choroid Plexus: Small slit between the thalami Connection: Connected to the third ventricle by an opening called the intraventricular foramen or the foramen of Munro Connected also to the fourth ventricle, through the cerebral aqueduct of the aqueduct of Sylvius Choroid Plexus: Situated above the roof of the ventricle

Ventricular System in Relation to Brain: Lateral View Bhatnagar & Andy, 1995, Figure 2.37 Ventricular System in Relation to Brain: Lateral View Bhatnagar & Andy, 1995, Figure 2.37

The Fourth Ventricle Location: Shape: Structure: Function: Location: Anterior to the cerebellum and posterior to the pons and the superior half of the medulla Continuous superiorly with the cerebral aqueduct and the central canal below Shape: Tent-shaped roof, two lateral walls, and a floor Structure: Three small openings The two lateral foramina of Luschkea The median foramen of Magendie Function: CSF enters the subarachnoid through these openings

Ventricular System in Relation to Brain: Lateral View Bhatnagar & Andy, 1995, Figure 2.37 Ventricular System in Relation to Brain: Lateral View Bhatnagar & Andy, 1995, Figure 2.37

Subarachnoid Space Location: Arachnoid Trabeculae Subarachnoid Space Located around the entire CNS Between the arachnoid membrane and the pia mater Arachnoid Trabeculae Extend from the arachnoid to pia mater Contribute to the maintenance of the subarachnoid space Which is filled with CSF

The Meninges Bhatnagar & Andy, 1995, Figure 2.45A The Meninges

Ventricles Inner Walls Ventricles Inner Walls Lined with a layer of the Ependymal Cells Glia cells Prevent infusion of external substances into the cerebrospinal fluid

Cerebrospinal Fluid Structure: Circulation Function: Structure: Clear, colorless fluid that suspends the brain and the spinal cord Circulation Circulates from the ventricles to the subarachnoid space Function: Serves as a cushion between the CNS and the surrounding bones *Thereby protecting the brain and spinal cord against direct trauma Fluid aids in: Regulation of intracranial pressure Nourishment of the nervous tissue Removal of waste products

Choroid Plexus Function: Location: Function: Produces CSF Location: Primarily in the center of the lateral and fourth ventricles

Path of CSF Circulation Pathway: Flows from the lateral ventricles into the third ventricle Via Monro’s foramen Then flows from the third ventricle to the fourth ventricle through the cerebral aqueduct Then flows from the fourth ventricle into the subarachnoid space through three apertures Two lateral Foramina of Luschka One mediodorsal Magendie’s foramen Then travels to reach the inferior surface of the cerebrum and moves superiorly over the lateral aspect of each hemisphere Some of it moves into the subarachnoid space around the spinal cord Pathway: Flows from the lateral ventricles into the third ventricle Via Monro’s foramen Then flows from the third ventricle to the fourth ventricle through the cerebral aqueduct Then flows from the fourth ventricle into the subarachnoid space through three apertures Two lateral Foramina of Luschka One mediodorsal Magendie’s foramen Then travels to reach the inferior surface of the cerebrum and moves superiorly over the lateral aspect of each hemisphere Some of it moves into the subarachnoid space around the spinal cord

The Ventricular System: Midsagittal View Bhatnagar & Andy, 1995, Figure 18.2 The Ventricular System: Midsagittal View Bhatnagar & Andy, 1995, Figure 18.2

Circulation of the CSF Love & Webb, 1996, Figure 3-6

Clinical Considerations Drainage of the CSF Inadequate Drainage of the CSF Clinical Considerations Drainage of the CSF Draining of the CSF from the subarachnoid space Is a pressure sensitive process Emptying of CSF into the Superior Sagittal Sinus Requires a pressure differential between the subarachnoid space and the venous-sinus system *At least 30-60 mmH20 regulates normal CSF drainage from the arachnoid villi Inadequate Drainage of the CSF If for any reason, this pressure differential is altered And the sinus pressure exceeds the ventricular pressure The one-way openings of the arachnoid villi close Ending the draining and elevating intracranial pressure

Clinical Considerations Rate of CSF Production Disassociation between Production and Absorption Rate of the CSF Clinical Considerations Rate of CSF Production Is independent of its absorption and interventricular pressure CSF continues to be produced Even after an interruption in its drainage into the sinus system Disassociation between Production and Absorption Rate of the CSF Results in hydrocephalus Three contributing etiologies: 1. Increased production of CSF 2. Blocking of draining passage Through which the CSF reaches the subarachnoid space 3. Impaired absorption of the CSF

Clinical Considerations Hydrocephalus Increased Pressure in the Brain Sustained Pressure Clinical Considerations Hydrocephalus Increased Pressure in the Brain Regardless of the underlying cause An excessive amount of CSF pressure Results in an increased pressure in the brain Sustained Pressure Causes enlargement of the ventricles Compresses the surrounding white and gray matters Results in damage to the surrounding vital cortical tissues If hydrocephalus occurs in infancy The increased CSF pressure Also causes an enlargement of the cranial vault

MRI of Enlarged Lateral Ventricles Secondary to Hydrocephalus Bhatnagar & Andy, 1995, Figure 18.3 MRI of Enlarged Lateral Ventricles Secondary to Hydrocephalus Bhatnagar & Andy, 1995, Figure 18.3

Medical Diagnostic Procedures Measurement of the pressure of the fluid If abnormally high, may suspect: Intracranial tumor Intracranial hemorrhage Hydrocephalus Meningitis Encephalitis Measurement of the pressure of the fluid If abnormally high, may suspect: Intracranial tumor Intracranial hemorrhage Hydrocephalus Meningitis Encephalitis *Sustained pressure causes enlargement of the ventricles and damage to the surrounding vital cortical tissues Due to compression of the surrounding white and gray matters

Treatment Hydrocephalus No longer a fatal condition If diagnosed early Can be surgically treated Treatment Involves diverting the blocked ventricular CSF To another cavity for absorption Procedure Tube is surgically inserted in the ventricular cavity And use to divert CSF flow to the peritoneal cavity in the abdomen Treatment Hydrocephalus No longer a fatal condition If diagnosed early Can be surgically treated Involves diverting the blocked ventricular CSF To another cavity for absorption Procedure: Tube is surgically inserted in the ventricular cavity And used to divert CSF flow to the peritoneal cavity in the abdomen

Medical Diagnostic Procedures Lumbar Puncture or Spinal Tap Needle inserted into the lumbar subarachnoid space Between the fourth and fifth lumbar vertebrae Because spinal penetration at this point does not cause any injury to nerve fibers Attach needle hub to a manometer or other pressure sensitive device A pressure level higher than normal suggests that a pathologic process exists Medical Diagnostic Procedures Lumbar Puncture or Spinal Tap Needle inserted into the lumbar subarachnoid space Between the fourth and fifth lumbar vertebrae Because spinal penetration at this point does not cause any injury to nerve fibers Attach needle hub to a manometer or other pressure sensitive device A pressure level higher than normal suggests that a pathologic process exists

Medical Diagnostic Procedures Catheter Insertion into the Lateral Ventricles Measure Ventricular pressure Increased intracranial pressure occurs in response to: 1. Increased amounts of CSF 2. Brain swelling 3. And brain tumors Medical Diagnostic Procedures Catheter Insertion into the Lateral Ventricles Measure Ventricular pressure Increased intracranial pressure occurs in response to: 1. Increased amounts of CSF 2. Brain swelling 3. And brain tumors

Medical Diagnostic Procedures Additional Procedures Associated with Spinal Puncture Procedure also used to draw out CSF for chemical or cell studies Diseases of the CNS change the constituent composition of the CSF An alteration serves as a diagnostic tool for identifying pathologic changes that occur in the brain and spinal cord May suggest acute bacterial meningitis Route used to inject drugs to combat infection or to induce anesthesia Anesthesia prevents nerve impulses from being conducted through the spinal nerves From the lower body up to the level of the spinal injection Medical Diagnostic Procedures Additional Procedures Associated with Spinal Puncture Procedure also used to draw out CSF for chemical or cell studies *Diseases of the CNS change the constituent composition of the CSF An alteration serves as a diagnostic tool for identifying pathologic changes that occur in the brain and spinal cord May suggest acute bacterial meningitis Route used to inject drugs to combat infection or to induce anesthesia *Anesthesia prevents nerve impulses from being conducted through the spinal nerves From the lower body up to the level of the spinal injection

Define the Following Technical Terms: Arachnoid granulations Arachnoid trabecula Cerebrospinal fluid Choroid plexus Ependymal cells Intracranial pressure Lumbar Puncture Meninges Meningitis Septum Subarachnoid space Subdural space Ventricles Define the Following Technical Terms: Arachnoid granulations Arachnoid trabecula Cerebrospinal fluid Choroid plexus Ependymal cells Intracranial pressure Lumbar Puncture Meninges Meningitis Septum Subarachnoid space Subdural space Ventricles

Review Questions 1. Discuss the function of the meningeal membranes of the brain and spinal cord. 2. Describe the location of epidural, subdural, and arachnoid spaces. 3. Name the dural extensions of the brain and describe their relationship to the brain. 4. With a labeled diagram, identify major parts of the ventricular system. 5. Discuss the functions of the cerebrospinal fluid. 6. Discuss the production, circulation, and absorption of the cerebrospinal fluid. 7. Describe the mechanism, clinical implications, and treatment of hydrocephalus. Review Questions 1. Discuss the function of the meningeal membranes of the brain and spinal cord. 2. Describe the location of epidural, subdural, and arachnoid spaces. 3. Name the dural extensions of the brain and describe their relationship to the brain. 4. With a labeled diagram, identify major parts of the ventricular system. 5. Discuss the functions of the cerebrospinal fluid. 6. Discuss the production, circulation, and absorption of the cerebrospinal fluid. 7. Describe the mechanism, clinical implications, and treatment of hydrocephalus.

The Meninges and the Ventricular System Graphics Graphics: 57,30,31,29,23,12,13,9,26,44,49,10,45

THINGS TO DO BEFORE LECTURE