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Chapter 3

2NF3 Chapter 3- Organization of the Nervous System

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Andrew Wade

03/06/2014 03/06/2014 Chapter 3- Organization of the Nervous System Stroke-R.S Definition- an interruption of blood to the brain that kills brain cells and causes the sudden appearance of neurological symptoms Ischemia –a deficiency in blood flow to the brain due to functional constriction or to the actual obstruction of a blood vessel, such as a clot Treated by a drug called tissue plasminogen activator (t-PA)- breaks up clots and allows the return of normal blood flow to the affected region Neurons receives as many as 15 thousand connections from other cells Neurons in brain are organized in layers as well as groups called nuclei (groups of cells forming clusters▯ some are folded and others have distinctive shapes and colours Neuroanatomy: finding your way around the brain Describing locations in the brain Rostrum/Rostral= beak Caudum/Caudal=tail Dosum/Dorsal-back Ventrum/Ventral=stomach Superior/ inferior are used to refer to structures that are located dorsally or ventrally Anterior= front Posterior=behind Lateral=side Medial=center or in between 03/06/2014 Coronal section is cut in a vertical plane from crown of head Horizontal section viewed looking down on brain Sagittal section cut lengthwise front to back and viewed from the side Nervous system = symmetrical Structures that lie on same side are ipsilateral, if they lie on opposite side, they are contralateral . bilateral if one of them lies in each hemi Any movement toward a brain structure is afferent (body’s sensory pathways that carry messages to brain) and movement away is efferent (motor pathways leading to the body from the brain and spine) Awonderland of nomenclature Precentral gyrus- also called gyrus precentralis or motor strip –PRIMARY MOTOR CORTEX M1 An overview of nervous system structure and function CNS- brain and spine PNS- somatic nervous system and automatic nervous system SNS- spinal and cranial nerves to and from the sensory organs and the muscles, joints and skin Prod movement and transmits incoming sensory info to CNS including vision, hearing, pain, temp ,touch and the position and movement of body parts ANS- balances body’s internal organs to rest and digest through parasympathetic(calming) nerves or to flight and flee OR engage in vigorous activity through the sympathetic (arousing) nerves Support and Protection The brain and spine are supported and protected from injury and infection in 4 ways 1:CNS lies within bony encasements, PNS lies outside them 03/06/2014 the PNS can renew itself after injury by growing new axons and dendrites, whereas self-repair is much more limited within the CNS within bony case enclosing CNS is a triple-layered set of membranes- meninges the outer dura mater is a double layer of tissue enclosing the brain in a kind of loose sack the middle arachnoid membrane= think sheet of delicate tissue that follows the contour of the brain the inner pia mater- moderately tough tissue that clings to the surface of the brain brain and spin are cushioned from shock and sudden changes of pressure by cerebrospinal fluid that circulates in the 4 ventricles inside the brain, in the spinal column, and within the subarachnoid space in the brains enclosing membranes if outflow is blocked, as occurs in a congenital condition called hydrocephalus, severe mental retardation and even death can result brain and spin protected from many chemical substances circulating in the rest of the body by the blood-brain barrier. To for this, the cells of capillaries form tight junctions with one another, preventing many blood-borne sub from crossing from capillaries into CNS tissues Blood Supply Brain receives blood supply from 2 internal carotid arteries and 2 ventral arteries that course up each side of the neck Anterior cerebral artery (ACA)- irrigates the medial and dorsal part Middle cerebral artery (MCA) irrigates the lateral Posterior cerebral artery (PCA) irrigates ventral and posterior surfaces Neurons and Glia Stem cell has great capacity for self renewal Adult stem cells are located in brains ventricular zone In developing embryo- stem calls give rise to progenitor cells that migrate and act as precursor cells giving rise to non dividing, primitive types of nervous system cells called blasts▯ some differentiate into neurons others into glia The simplest sensory neuron, a bipolar neuron consists of cell body with a dendrite on one side and an axon on the other Somatosensory neurons, project from bodys sensory receptors into spinal cord, are modified so that the dendrite and axon are connected, which speeds info conduction▯bring info to CNS 03/06/2014 Interneurons, within brain and spin link up sensory and motor neuron act in CNS Stellate cell- thalamus Pyramidal cell- cortex Purkinje cell- cerebellum Motor neurons- locate din brainstem project to facial muscles and motor neurons in the spin project to other muscles of the body Called final common path Architecture of neurons differ from region to region in nervous system TYPES of glial cells –page 58 Ependymal Astrocyte Microglial Oligodendroglia Schwann Gray, white and reticular matter Gray matter- colour from capillary blood vessels and neuronal cell bodies that predominate there White matter- consists of axons that extend from these cell bodies to form connections with neurons in other brain areas- covered with layer of glial cells Reticular matter-contains a mix of cell bodies and axons from which it acquires its mottled gray and white appearance Layers, nuclei, nerves and tracts Tract= a large collection of axons projecting to or away from a nucleus or layer in CNS 03/06/2014 They carry info fro one place to another within CNS Nerves-= fibers and fiber pathways that enter and leave the CNS (ex.Auditory nerve) After they enter the CNS, they are then called tracts Origin and Dev of the CNS 3 regions of the developing brain Vertebrate Prosencephalon-front brain (olfaction) Mesencephalon –middle brain (vision and hearing) Rhombencephalon- hindbrain( movement and balance)- Spinal cord considered part of hindbrain mammals prosencephalon divides into telecephalon- endbrain and diencephalon-hindbrain ( including the thalamus) metencephalon- across brain▯ including enlarged cerebellum and myelencephalon-spinal brain▯lower region of brainstem brain begins as a tube and even after it fold and matures, its interior remains hollow the 4 pockets created by the folding of this hollow interior in the brain are called ventricles and are numbered 1-4. Lateral ventricles (1-2) form C-shaped lakes underlying cerebral cortex (3-4) extend into the brainstem and spinal cord all are filled with cerebrospinal fluid- prod by ependymal glial cells located adjacent to ventricles 03/06/2014 The spinal cord Spinal cord structure and spinal nerves 5 regions from top to tail 30 spinal cord segments 8 cervical 12 thoracic 5 lumbar 5 sacral coccygeal dermatomes- skin cutes, encircle the spinal column as a stack of rings 6 segments can be represented on the arm each spinal segment is connected by SNS spinal nerve fibers to the body dermatome of the same number, including the organs and musculature that lie within the dermatome afferent fibers entering dorsal part of spinal cord (posterior in humans) bring info from sensory receptors of body. These converge as they enter spinal cord- forming dorsal root efferent info leaving ventral (anterior in humans) part of spinal cord, carry info from spine to muscles from ventral root inner part of cord consists of gray matter- composed largely of neural cell bodies outer part- white matter. White matter fiber tracts carry info to and from brain Spinal cord function and spinal nerves Francois magendie, by cutting dorsal roots caused loss of sensation and cutting ventral roots caused loss of movement Charles bell suggested the opposite functions for each of the roots 03/06/2014 Bell-magendie law- stating that dorsal part of spine is sensory and ventral is motor Charles Sherrington- showed spinal cord retains many functions even after its separated from brain Paraplegic- person who’s spinal cords are cut so that they no longer have control over legs Quadriplegic- if cut is higher on cord, makes them unable to use arms Movements dependent only on spinal-cord function= reflexes Size of spinal nerve fiber coming from each kind of receptor is distinctive Pain and temp fibers =small The stimulation of pain and temp in a limp prod flexion movements tat bring limb inward toward body Muscle and touch=large Stimulation of muscle and touch receptors in a limb produces extension movements Connections between CNS and SNS Cranial nerves- 12 pairs, have different functions Some are afferent and others are efferent Some have both sensory and motor functions Mnemonic for memorizing the 12 nerves On old Olympus’s towering top, a Finn and German view some hops 1-olfactory 2-optic 3-oculomotor 4-trochlear 03/06/2014 5-trigeminal 6-abducens 7-facial 8-auditory vestibular 9-glossopharyngeal 10-vagus 11-spinal accessory 12-hypoglossal ANS connection Even without conscious awareness, it stays on the job to keep heart beating and liver releasing glucose etc WithoutANS, which regulates internal organs and glands by connections through SNS to CNS, life would not exist ANS must k
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