Chapter 9 The Nervous System CNS and PNS Where are we going Today Overview of the anatomy of the CNS and PNS Autonomic Nervous System Sympathe c Autonomic Nervous System Parasympathe c Soma c Nervous System Skeletal Muscle Structure Muscle Contrac on Synap c Communica on General Anatomy of the CNS The CNS is ul mately responsible for everything perceive do feel and think Coordinates the ac vity of all our organ systems Contains about 100 billion neurons and about 100 trillion synapses all contained within the brain and spinal cord Cells of the Brain Glial Cells Make up 75 90 of the brain Cri cal to maintenance of the normal extracellular environment surrounding neurons and synapses Remove certain NTs Synthesize and store molecules used by neurons Phagocy ze pathogens and dead or injured cells Provide myelina on The Importance of Myelina on General Anatomy of the CNS The bony cranium and vertebral column act as a rigid set of armor surrounding the delicate nervous ssue Between the bone and brain ssue are three membranes called the meninges and a layer of cerebral spinal uid They provide protec on to prevent soU brain ssue from crashing into the hard surface of the skull Protec ve Structures of the CNS Cerebral Spinal Fluid CSF Clear watery uid that bathes the CNS Produced by the choroid plexus 500 ml day Circulates through the ventricles and enters the subarachnoid space Cerebral Spinal Fluid CSF Has several func ons Acts as a chock absorber to protect the soU nervous ssue which essen ally oats in CSF Provides essen al nutrients and removes waste products Maintains a normal ionic composi on around neurons Blood Supply to the Brain CNS receives about 15 of the blood that the hearts pumps and consumes 50 of the glucose due to its high rate of metabolic ac vity Brain has a constant and essen al need of blood glucose because Neurons have very li le glycogen Do not have access to fa y acids for energy Cannot use anaerobic metabolism Stroke CNS is so dependent on blood supply that disrup on of blood ow for even a few minutes can result in irreversible damage Stroke is an event where blood ow is interrupted because of a blocked or ruptured blood vessel in the brain Stroke symptoms vary with the loca on and extent of the a ected area such as muscle paralysis loss of sight in a part of visual eld ngling or other sensory disturbances disturbances of language disorienta on etc Stroke Blood Brain Barrier Blood Brain Barrier Grey and White Ma er The Brain The brain consists of three main parts Forebrain Cerebrum Diencephalon Cerebellum Brainstem Midbrain Pons Medulla Oblengota Cerebral Cortex Spinal Cord and PNS Is a cylinder of nervous ssue that is con nuous with the lower end of the brain and surrounded by the vertebral column Branching o the spinal cord at regular intervals are 31 pairs of spinal nerves The numerous axons that travel within a single spinal nerve generally travel to adjacent regions of the body Dermatomes As a result it is possible to map out the body s surface into di erent sensory regions called dermatomes each of which is served by a par cular spinal nerve This enables clinicians to determine the loca on of damage to the spinal cord or spinal nerves Peripheral Nervous System PNS Two func onal halves of the spinal cord gray ma er dorsal and ventral A erent axons enter through the dorsal root and terminate in the dorsal horn Info to the brain E erent axons originate in ventral horn and exit through ventral root Info from the brain Spinal Cord White Ma er Similarly there are two major types of tracts that make up the white ma er of the spinal cord Ascending tracts transmit informa on from the spinal cord to the brain Descending tracts transmit informa on from the brain to the spinal cord Pathways of Ascending and Descending Tracts
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