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Chapter 3

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PSYC 271
Richard Beninger

Cindy Zhu, PSYC271 Fall 2011 Page 1 of 7 Chapter 3: Anatomy of the Nervous System 3.1 General Layout of the Nervous System Division of the Nervous System • Central nervous system (CNS): brain and spinal cord, encased in bone • Peripheral nervous system (PNS): located outside skull and spine, including the somatic nervous system and the autonomic nervous system • Afferent: “sensory” neurons, carry sensory signals from receptors to CNS. • Efferent: “motor” neurons, carry motor signals from CNS to muscles or glands. • Spinal nerves: 31 pairs of nerves that project from spine, all have both sensory and motor fibres. • Cranial nerves: 12 pairs of nerves that project from the brain, most have both sensory and motor fibres except I (olfactory) and II (optic) which are purely sensory. o The longest are the vagus nerves (X) that have fibres to and from the gut. Autonomic Nervous System Somatic Nervous System (ANS) (SNS) What about? Internal environment External environment * Afferent: sensory signals from * Afferent: sensory signals from internal organs skin, muscles, eyes, ears about environment and your position in it * Goal is to maintain homeostasis Do we control it? Unconscious, involuntary Voluntary Effector organs Smooth muscle (gut, blood vessels), Skeletal muscles only cardiac muscle, glands Effect on targets Excitatory or inhibitory Excitatory only (e.g. muscle contraction) Neuron structure Two neurons to get to target Single neuron straight from CNS to (preganglionic and postganglionic target neurons) Cindy Zhu, PSYC271 Fall 2011 Page 2 of7 The AUTONOMIC NERVOUS SYSTEM (ANS) can be further subdivided: Parasympathetic Nervous Sympathetic Nervous System System Where from? Brain and sacral spinal cord (at base, Thoracic and lumbar spinal cord (back near vestigial tail) and lower back) Postganglionic Second-stage neuron is close to target Second stage neuron is far from target neuron Ganglion Ganglia are close to target organs Ganglia are far from target organs, lying close to spinal cord Effect Conserve energy, psychological Stimulate, organize, mobilize energy in relaxation: rest and digest threatening situations; arousal: fight or flight A target organ can receive opposing sympathetic and parasympathetic input, and is thus controlled by the relative levels. Meninges, Ventricles, and Cerebrospinal Fluid Cindy Zhu, PSYC271 Fall 2011 Page 3 of7 • Meninges: 3 protective membranes for the brain and spinal cord: from outside in: o Dura mater (“tough mother”): 2 inflexible, tough membrane layers anchored to skull. Areas where the 2 layers separate are dural sinuses. o Arachnoid mater (“spider-like mother”): attached to inferior surface of dura mater. o Subarachnoid space: filaments look like spider web, filled with cerebrospinal fluid (CSF) to support and protect brain. o Pia mater: innermost, firmly attached to brain/spinal cord • Cerebrospinal fluid: fills subarachnoid space, central canal of spinal cord and cerebral ventricles. Functions: buoyancy (1.4kg to 50grams with CSF, prevents drooping under its own weight), circulation (provides nutrients, removes waste), and protection (cushion against skull, without it would have serious headaches). Subarachoid • CSF is produced by the choroid plexuses, Space capillaries that protrude into the ventricles from the pia mater and filter blood to produce CSF. • CSF flows through subarachoid space and subarachoid granulations before being absorbed into blood-filled dural sinuses (in the dura mater) and draining into the large jugular veins of the neck. o If flow is CSF is blocked, the resulting buildup cause walls of ventricles to expand, causing hydrocephalus (water head). • Ventricles: four large internal chambers of the brain, which are all connected and filled with CSF. • Cerebral aqueduct: connects third and fourth ventricles. • Central canal: small CSF-filled central channel that runs the length of the spinal cord. Blood-Brain Barrier • Blood-brain barrier: impedes passage of toxic substances to prevent disturbance of the brain by introduction of unwanted chemicals. This is due to the special tightly packing structure of cerebral blood vessels, which form a barrier to the passage of proteins and other large molecules. • The degree to which drugs can influence brain activity depends on ability to penetrate the blood-brain barrier. Some necessary molecules, like glucose, are actively transported in. 3.2 Cells of the Nervous System Anatomy of Neurons Cindy Zhu, PSYC271 Fall 2011 Page 4 of7 • Neurons: cells specialized for reception, conduction and transmission of electrochemical signals. • Internal anatomy: endoplasmic reticulum (rough with ribosomes do protein synthesis, smooth do lipid synthesis); golgi complex (packages molecules in vesicles), microtubules (rapid transport of material throughout neuron), mitochondria (aerobic energy release),
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