Brain Sinuses Venous channels found between layers of dura mater They carry oxygen-depleted blood They are not real veins – possess no muscular coat but lined with endothelium

Venous Blood Flow Veins of brain  Sinuses  Internal Jugular Vein  Brachiocephalic Vein  Superior Vena Cava  Right Atrium See Figure 21.24

Not real veins – tunnels through membranes Dural venous sinuses. Sagittal section of the skull, showing the sinuses of the dura. The dural venous sinuses (also called dural sinuses, cerebral sinuses, or cranial sinuses) are venous channels found between layers of dura mater in the brain.  in human anatomy, any of the channels of a branching complex sinus network that lies between layers of the dura mater, the outermost covering of the brain, and functions to collect oxygen-depleted blood. Unlike veins, these sinuses possess no muscular coat. Their lining is endothelium, a layer of cells like that which forms the surface of the innermost coat of the veins. The sinuses receive blood from the veins of the brain and connect directly or ultimately with the internal jugular vein. Blood from the sinuses, after it leaves the internal jugular vein, flows through the brachiocephalic vein and the superior vena cava to the upper right chamber (atrium) of the heart.

Blood-Brain Barrier Metabolically active Ischemia Diabetes Protection 2% weight 20% O2 & Glucose Ischemia Diabetes Protection Cilia – CSF Semi-permeable

Blood-Brain Barrier Can Pass Cannot Pass Glucose (via transport proteins) Lipid-soluble substances  O2, CO2, alcohol, anesthetics Large molecules ex. Proteins Most antibiotic drugs Trauma, inflammation and certain toxins can break down the BBB

Cerebrospinal Fluid Produced from arterial blood 80-150 mL Circulates in subarachnoid space, ventricles, sulci and spinal cord

Fig 14.3 Brain Ventricles

Functions of CSF The brain “floats” in the cranial cavity. Mechanical protection – cushion / shock absorbing medium Homeostatic function –pulmonary ventilation and cerebral blood flow affected by pH of CSF. Circulation – minor exchange of nutrients & waste Blood-CSF barrier

Formation of CSF Ventricles Choroid Plexuses Ependymal cells Figure 14.3

Choroid (Arachnoid) Villi Fig 14.4

Choroid (Arachnoid) Villi

Circulation of CSF Refer to Figure 14.4

Anatomy of the brain: The Cerebrospinal Fluid CSF https://www.youtube.com/watch?annotation_id=annotati on_1491644747&feature=iv&src_vid=K9BYEO9725k&v =7B1w6lDw-yM AWFUL commentary but good visual. Talk over the video

Brainstem

Medulla Oblongata Most inf  foramen magnum  pons Medial Leminscal Spinothalamic tracts Corticospinal tracts Pyramids Decussation of pyramids Nuclei

Sensory Pathways

Medulla Oblongata

Medulla Oblongata Nucleus  collection of neuronal cell bodies in CNS Nuclei of origin for cranial nerves VIII, IX, X, XI, XII

Reticular Formation (RAS) Network of nerves  monitors ingoing / outgoing sensory/motor impulses. Level of consciousness Reticular Formation (RAS) Most influential part RAS = reticular activating system

Pons Nuclei of origin for cranial nerves V, VI, VII and VIII

Pons Apneustic – promotes inspiration by stimulating nerves in M.O. Controls intensity. Pneumotaxic – Antagonistic. Inhibits inhalation. Regulates rate of respiration.