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BRAIN STRUCTURE ANDFUNCTION
THE CENTRAL NERVOUS SYSTEM•The Central Nervous System (CNS) is the major control center for thebody.•In about 3 pounds of tissue, the CNS has 100 billion neurons.•The brain collects sensory information, evaluates it, and sendsinstructions to effectors via motor neurons to direct appropriateresponses.•The spinal cord serves two major roles:–Serves as a pathway for information to and from the brain–It controls rapid reactions (reflexes) to specific stimuli
CNS OVERVIEW:THE MAIN PARTS OF THE CNS•The CNS consists of–The brain•Cerebrum•Diencephelon•Brainstem•Cerebellum•The spinal cord
STRUCTURE OF A NEURON
CNS OVERVIEW:PROTECTION OF THE CNS•The CNS is protected by:–Bone•Cranial bones protect the brain•Vertebrate protects the spinal cord–Three meninges(layers of connective tissue surrounding the CNS) Cranialand spinal meninges•Dura mater (outermost) composed of dense irregular connective tissue.•Arachnoid mater (middle) avascular covering, composed of collagen andelastic fibers. Surrounds the brain and spinal cord.•Inner pia mater (inner) thin, transparent connective tissue layer,composed of interlacing collagen and fine elastic fibers.–Cerebrospinal fluid(CSF) - the CNS is cushioned by a thin layer of fluid
CNS OVERVIEW:PROTECTION OF THE CNS
MENINGESThree meninges:1.Dura mater: most superficial2.Arachnoid mater: a thin and wispy membrane3.Pia mater: attached tightly to the surface of brain
MENINGESDURAL VENUS SINUSEScollect the blood that returns from the brain,as well as cerebrospinal fluid (CSF) from around the brain.The sinuses then empty into the veins that exit the skull
CNS OVERVIEW:BLOOD FLOW TO THE BRAIN•Blood supply to the brain is a crucial source of O2andnutrients•The brain receives 20% of blood supply but composes only2% of the body weight.•Blood flow to active areas of the brain increases during higherlevels of metabolic activity•Interruptions in blood flow have very serious consequences(unconsciousness, stroke, death)
CNS OVERVIEW:THE BLOOD-BRAIN BARRIER•Theblood-brain barrier (BBB)prevents pathogens and harmfulchemicals from entering the brain•The BBB is composed of 3 components–Tight junctions between capillary endothelial cells. At these junctionsyou have proteins that selectively transport molecules across thebarrier. Ex: glucose, Oxygen, Hormones etc.–A thick basement membrane underlying the endothelium–A layer of astrocytes that cover the capillaries, this prevents directcontact of blood with the brain extracellular fluid.