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Chapter 3

PSYC 271 Chapter 3: PSYC 271 Chapter 3 Textbook Notes

9 Pages

Course Code
PSYC 271
Amanda Maracle

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WEEK 2 - Chapter 3: Anatomy of the Nervous System 3.1 General Layout of the Nervous System Divisions of the Nervous System - Central nervous system (CNS) located within the skull and the spine - Peripheral nervous system (PNS) located outside the skull and spine o Somatic Nervous System interacts with the external environment ▪ Afferent Nerves: carry sensory signals from the skin, skeletal muscles, joints, eyes, ears and so on to the CNS ▪ Efferent Nerves: carry motor signals from the CNS to the skeletal muscles o Autonomic Nervous System regulates the body’s internal environment ▪ Afferent Nerves: carry sensory signals from internal organs to the CNS ▪ Efferent Nerves: carry motor signals from CNS to internal organs including sympathetic and parasympathetic nerves • Sympathetic Nerves: autonomic motor nerves that project from the CNS in the lumbar (small of the back) and the thoracic (chest area) regions of the spinal cord • Parasympathetic Nerves: autonomic motor nerves that project from the brain and sacral (lower back) region of the spinal cord **remember the difference by afferent (a=arrive, approach) & efferent (e=exit, escape)** - The sympathetic and parasympathetic nerves synapse on other second-stage neurons that carry the signal the rest of the way o Sympathetic synapse at a substantial distance from their target organs o Parasympathetic synapse on very short second-stage neurons - Important to remember that sympathetic NS is activated in threatening situations; changes indicative of psychological arousal - Parasympathetic goal is to conserve energy and indicative of psychological relaxation - Each autonomic target is regulated by opposing sympathetic and parasympathetic input - Most PNS nerves come from spinal cord, but there are 12 cranial nerves from the brain that include purely sensory nerves Meninges, Ventricles and Cerebrospinal Fluid - The meninges are protective membranes of the brain and spinal cord 1. Dura mater, the outer meninx 2. Arachnoid membrane, immediately inside dura mater 3. Subarachnoid space, that contains many blood vessels and cerebrospinal fluid (CSF) 4. Pia mater, adheres to surface of CNS - The central canal is a channel that runs length of spinal cord - The cerebral ventricles (4) include the two lateral, third ventricle and fourth ventricle - CSF is produced by choroid plexus, capillary network that protrude into the ventricles from the pia mater o Excess is absorbed by the subarachnoid space into blood-filled spaces, which run through dura mater and drain into jugular veins WEEK 2 - Chapter 3: Anatomy of the Nervous System The cerebral ventricles and the absorption of CSF from subarachnoid space(blue) into a major sinus. Note the three meninges Blood-Brain Barrier - Impedes passage of many toxic substances from blood into brain - Cells of the blood vessel walls are tightly packed, forming a barrier to the passage of many molecules, such as proteins and some other large molecules, unlike other blood vessels in the body o Glucose, for example, is critical for brain function and so, is not blocked and is actively transported o Associated with many CNS disorders - Degree of effect from drugs on the brain depends on the ease at which they penetrate the blood-brain barrier Difference between normal blood capillaries and those in the brain (less dense) WEEK 2 - Chapter 3: Anatomy of the Nervous System 3.2 Cells of the Nervous System Anatomy of Neurons - External & Internal Anatomy of Neurons is depicted in the picture - Neuron Cell Membrane o Composed of lipid bilayer with embedded protein molecules o Includes channel proteins, signal proteins (transfer signal inside the neuron when certain molecules bind to them on the outside of the membrane) - Classes of Neurons o Multipolar (most neurons), unipolar (one process extending), bipolar (two processes extending) and interneuron (short/no axon) - Neurons and Neuroanatomical Structure o Either composed primarily of cell bodies (nuclei in the CNS and ganglia in the PNS) OR those composed primarily of axons (tracts in the CNS and nerves in PNS) WEEK 2 - Chapter 3: Anatomy of the Nervous System Glia: The Forgotten Cells - Oligodendrocytes (CNS) o Glia cells with extensions that wrap around the axons of some neurons of the central nervous system o Rich in myelin, fatty insulating substance, that form myelin sheaths that increase the speed and efficiency of axonal conduction o More than one myelin segment on more than one axon - Schwann Cells (PNS) o Similar function as myelin sheath o Constitutes one myelin segment o only these can guide axonal regeneration after damage - Microglia o Smaller than other glial cells o Respond to injury or disease by multiplying, engulfing cellular debris, and triggering inflammatory responses - Astrocytes o Largest glial cells that are shaped like a star o Some cover outer surface of blood vessels in brain and make contact with neuronal cell bodies o Allow passage and deny passage of chemicals from blood to CNS neurons o Exchange chemical signals with neurons and other astrocytes to control/establish synapses between neurons o Control blood-brain barrier Classification of glia in the CNS and PNS; picture showing red astrocytes, blue neurons and green oligodendrocytes. WEEK 2 - Chapter 3: Anatomy of the Nervous System 3.3 Neuroanatomical Techniques and Directions Neuroanatomical Techniques - Must prepare neural tissue in a variety of ways, each of which permits a clear view of a different aspect of neuronal structure - Golgi Stain o Discovered when trying to stain meninges o Exposing silver chromate to neural tissue block, but chemical reaction invaded a few neurons in each slice of tissue and stained each invaded neuro entirely black o See individual neurons, only in silhouette o To see individual neuron shape - Nissl Stain o Provides gross indication of brain structure by selectively staining groups of neural bodies o Can distinguish individual neural cell bodies, this count number of neurons in various areas o Most commonly used dye is cresyl violet - Electron Microscopy o Limit of magnification is 1500X that cannot reveal fine anatomical details of neurons o To get an electron micrograph to achieve greater detail, coat slices of neural tissue with electron-absorbing substance that is taken up by different parts of neurons to different degrees; then pass electron beam onto photographic film o Scanning electron microscope provides spectacular electron micrographs in 3D, but not as much magnification - Neuroanatomical Tracing Techniques o Anterograde tracing methods: trace paths of axons projecting away from cell bodies in a particular area ▪ Done by injecting chemicals that can be taken up by cell bodies and then transported forward along axon to terminal buttons ▪ Brain is removed and sliced to reveal injected chemical o Retrograde tracing methods: work in reverse to trace axon paths projecting into a particular area ▪ Done by injecting chemical normally taken up by terminal buttons then transported backwards along axon to cell bodies Directions in the Vertebrate Nervous System - Described in orientation of the spinal cord - Has three axes: anterior-posterior, dorsal-ventral and medial-lateral o Anterior: toward the nose end o Posterior: toward the tail end o Dorsal: toward surface of the back/top of head o Ventral: toward surface
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