Encephalon – Brain

Brain Components Fig 14.1 Brain Stem Cerebellum Diencephalon Cerebrum Midbrain, Pons, Medulla Oblongata Cerebellum “Little Brain” Diencephalon Thalamus, Hypothalamus, Epithalamus Cerebrum

Protective Coverings of the Brain Cranial bones Meninges Dura mater Arachnoid mater Pia mater

Cranial Bones Cranial vault formed by 8 cranial bones Encloses and protects brain Floor divided into 3 fossa: Anterior – front lobes Middle – temporal lobes and base of diencephalon Posterior - cerebellum

Meninges Surround and protect the brain and spinal cord Three membranes: 1. Dura mater 2. Arachnoid mater 3. Pia mater

Dura Mater Tough outermost meninx. Composed of two layers: Periosteal Meningeal Venous sinuses between the layers.

Dura Mater Falx cerebri Falx cerebelli Tentorium cerebelli Separates cerebrum from cerebellum Separates 2 hemispheres of cerebrum Separates 2 hemispheres of cerebellum

Arachnoid Mater Middlemost meninx Characterized by its filmy, weblike structure Loosely follows contours of cerebral structures but lies over sulci

Pia Mater Thin, delicate innermost meninx Closely adheres to surface of brain and follows sulci and fissures Provides support for blood vessels serving brain tissue Sheath of pia mater

Note periosteal and meningeal layers with venous dural sinus between them

Meningeal Spaces Real or potential spaces between meningeal layers: Epidural Space = potential space Between Skull and Dura Subdural Space = Real space Between dura and arachnoid Small bridging veins (little support) cross the space Subdural hematoma Subarachnoid space is a real space Lies between the arachnoid and pia mater Contains cerebrospinal fluid Subarachnoid hemorrhage Epidural space is a potential space The blood supply to the meninges consists of blood vessels that lie within grooves in the skull As a result of trauma, the skull can be fractured and the blood vessels disrupted. The ruptured vessels can lead to an accumulation of blood within the epidural space, called an epidural hematoma.

Subarachnoid space is a real space Lies between the arachnoid and pia mater Contains cerebrospinal fluid - partially protects brain from jolts and blows Damage to blood vessels within pia can lead to subarachnoid hemorrhage

Brain Injuries Hemorrhage – active or ongoing bleeding. Hematoma – accumulation of blood within one of the meningeal spaces or surrounding tissues. Contusion – Type of hematoma. Blood escapes ruptured capillaries and enters surrounding tissue.

Brain Blood Flow Internal carotid arteries Vertebral arteries Internal jugular veins The brain is very metabolically active and depends on continuous oxygen and glucose supply from blood - amount of oxygen and glucose it uses varies with degree of mental activity Ischemia quickly results in loss of brain function

Arterial Brain Blood Flow ANTERIOR: Common Carotid Arteries  Internal Carotid Arteries  Base of skull  Cranium  Branch to anterior and middle cerebral arteries

Arterial Brain Blood Flow POSTERIOR: Subclavian arteries  Vertebral arteries Transverse foramina of cervical vertebrae  foramen magnum Join at junction of pons and medulla  Basilar artery  Pontine branches Posterior inferior cerebellar arteries (off the vertebral artery) Basilar divides at midbrain  anterior inferior cerebellar and superior cerebellar arteries

Arterial Brain Blood Flow Vertebral arteries Subclavian Cervical vertebrae transverse foramina Basilar artery Cerebellum, brainstem and occipital lobes. Pontine arteries Cerebellar arteries: Cerebellum Cerebral arteries Internal Carotid Artery Posterior communicating artery Anterior communicating artery The brain derives its arterial supply from two systems: the internal carotid arteries and the vertebral arteries The internal carotid arteries, anteriorly, supply a proportionately greater amount of blood flow They originate from the common carotid arteries, and enter the cranium through the base of the skull After giving off some small branches, they divide into the anterior and middle cerebral arteries The vertebral arteries, posteriorly, originate as branches off the subclavian arteries, pass through the transverse foramina of the cervical vertebrae and enter the cranium through the foramen magnum They join at the junction of the pons and medulla to form the basilar artery The basilar artery divides at the level of the midbrain to form paired posterior cerebral arteries Three major paired arteries perfuse the cerebella and brainstem and originate from the posterior arterial supply: the posterior inferior cerebellar artery, off the vertebral artery anterior inferior cerebellar and superior cerebellar arteries, off the basilar artery The basilar artery also gives rise to small pontine arteries

Arterial Brain Blood Flow Terminal branches of Carotid and Vertebral arteries = circle of Willis Circulatory anastomosis (connection between 2 blood vessels) Backup route in case of blockage Branch into various cerebral arteries to supply brain with blood

Brain Blood Flow Animation https://www.youtube.com/watch?v=MPcO2ibO75o