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Chapter 3

Psychology 46-256 Chapter 3: Notes on Anatomy of the Nervous System

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Chapter 3: Anatomy of the Nervous System General Layout of the Nervous System Divisions of the Nervous System  Vertebrate nervous system is composed of two divisions: central nervous system and peripheral nervous system  Central Nervous System (CNS)  located within the skull and spine o Composed of two divisions: brain and spinal cord  Peripheral Nervous System (PNS)  located outside the skull and spine o Composed of two divisions: somatic nervous system and autonomic nervous system o Somatic nervous system (SNS)  interacts with the external environment  Composed of afferent nerves that carry sensory signals from the external sensory (ex. skin, eyes, ears) to CNS  And efferent nerves that carry motor signals from CNS to the skeletal muscles o Autonomic nervous system (ANS)  regulates the body's internal environment  Composed of affect nerves that carry sensory signals from internal organs to the CNS  And efferent nerves that carry motor signals from CNS to internal organs  Has two kinds of efferent nerves: sympathetic nerves and parasympathetic nerves  Sympathetic nerves  autonomic motor nerves that project from CNS in the lumbar (back) and thoracic (chest) regions of spinal cord  Parasympathetic nerves  motor nerves that project from the brain and sacral (lower back) region of spinal cord Meninges, Ventricles, and Cerebrospinal Fluid  3 Meninges  three membranes protecting the brain and spinal cord (singular: meninx) o outer meninx called dura mater o Inside dura mater: arachnoid membrane o Beneath the arachnoid membrane is a space called the subarachnoid space (contains many large blood vessels and cerebrospinal fluid) o Then the innermost meninx: pia mater (adheres to the surface of CNS)  Protecting the CNS is the cerebrospinal fluid (CSF)  fills the subaracbonoid space, central canal of spinal cord, and the cerebral ventricles of the brain o Continuously produced by the choroid plexuses (networks of capillaries, small blood vessels, that protrude into the ventricles from the pia mater)  Central canal  a small central channel that runs the length of the spinal cord  Cerebral ventricles  four large internal chambers of the brain (the two lateral ventricles, the third ventricle, and the fourth ventricle) Blood-Brain Barrier  Blood-brain barrier  mechanism that keeps certain toxic substances in the blood from passing into brain tissue Cells of the Nervous System  Two fundamentally types of cells in the nervous system: neurons and glial cells Anatomy of Neurons  Neurons  cells that are specialized for the reception, conduction, and transmission of electrochemical signals (P. 55) o Cell body  centre of the neuron o Cell membrane  membrane that encloses the neuron o Dendrites  short processes emerging from the cell body, which receive most of the synaptic contacts from other neurons o Axon hillock  the cone-shaped region at the junction between the axon and the cell body o Axon  long, narrow process that projects from the cell body o Myelin  fatty insulation around many axons o Nodes  gaps between sections of myelin o Buttons  buttonlike ending of the axon branches, which release chemicals into synapses o Synapses  gaps between adjacent neurons across which chemical signals are transmitted  Neuron cell membrane is composed of a lipid bilayer (two layers of fat molecules)  Classes of Neurons o Multipolar neuron  a neuron with more than two processes extending from its cell body o Unipolar neuron  a neuron with one process extending from its cell body o Bipolar neuron  a neuron with two processes extending from its cell body o Interneurons  neurons with a short axon or no axon at all  Function: to integrate the neural activity within a single brain structure, not to conduct signals from one structure to another Glial Cells: The Forgotten Cells  Glial cells  non-neural cells that are found throughout the nervous system o Oligodendrocytes  glial cells with extensions that wrap around the axons of some neurons of the central nervous system o Schwann cells  (second class) similar function in peripheral nervous system o Each Schwann cell constitutes ONE myelin segment, whereas each oligodendrocyte provides several myelin segments on more than one axon o Difference  Schwann cells can re-grow after damage (that's why Schwann cells are restrict to PNS) o Microglia  (third class) respond to injury or disease by multiplying, engulfing cellular debris, and triggering inflammatory responses o Astrocytes  (fourth class) extensions cover the outer surfaces of blood vessels that course through the brain, make contact with neuron cell bodies  Allows some chemicals from the blood into CNS neurons and blocking others Neuroanatomical Techniques and Directions  Golgi Stain  a neural stain that completely darkens a few of the neurons in each slice of tissue, thus revealing their silhouettes o Accidental discovery by Camillo Golgi in early 1870s o Made it possible to see individual neurons for the first time  Nissl stain  Golgi stain provides no indication of the number of neurons in an a
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