HP_C13Notes_Antomy of the Nervous System

HP_C13Notes_Antomy of the Nervous System - Human Physiology...

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Human Physiology Notes Chapter 13 – Anatomy of the Nervous System Overview CNS includes the brain and spinal cord PNS includes the cranial and spinal nerves CNS receives messages from (sensory), and communicates with (motor) the body via the PNS Protection for the CNS Cranium and Meninges Bone and membranes surrounding the brain provide physical protection The CNS Floats in Cerebrospinal Fluid CSF bathes brain and spinal cord via the ventricles (lateral ventricles, third and fourth) the subarachnoid space and central canal CSF is secreted by ependymal cells of the choroid plexus, a region located in the walls of the ventricles CSF functions o Physical protection – buoyancy within the CSF protects brain from trauma o Chemical protection – CSF composition provides optimum cellular environment Similar to plasma, but lower K + concentration, higher H + concentration, Na + concentrations comparable o Circulation – exchange of nutrients, waste products The Blood-Brain Barrier CNS protected from toxins, hormones, and some neurotransmitters Substances that can pass include gasses (O 2 and CO 2 ), lipid soluble substances (steroids, alcohol), water Tight junctions between endothelial cells regulate movement of substances from blood to brain Brain capillaries are surrounded by foot processes created by astrocytes; these “feet” are highly selective Regions of the CNS (Spinal Cord to Cortex) The Spinal Cord Each region of spinal cord (8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal) divided into: o Segments that give rise to pairs of spinal nerves o Spinal nerves branch just before joining spinal cord Branches = roots Dorsal root = sensory fibers, info into the CNS; dorsal root ganglion houses cell bodies of sensory neurons Ventral root = motor fibers, info out of the CNS Spinal cord transmits info between body and brain o Sensory info from body to brain travels through ascending spinal tracts Ascending tracts typically decussate (cross); each hemisphere receives info from opposite side of body o Motor info from brain to body travels descending tracts
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