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Chapter 3

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Psychology 2220A/B
Scott Mac Dougall- Shackleton

Afferent = towards something (A=approach, arrive) Anatomyof the Nervous System- DRAW OUT DIAGRAMS January-12-12 Efferent = away (E=exit, escape) 12:00 PM GENERAL LAYOUT OF THE NERVOUS SYSTEM - DIVISIONSOF THE NERVOUS SYSTEMS - Centralnervous system (CNS) - division of the nervous system located within the skulland spine ○ Brain - located in skull ○ Spinalcord - located in spine - Peripheralnervous system (PNS) - division located outside the skull and spine ○ Somaticnervous system (SNS) - part of the PNS that interacts with the external environment  Afferent nerves - carry sensory signals from the skin, skeletal muscles, joints, eyes, ears, etc, to the CNS  Efferent nerves - carry motor signals from the CNS tothe skeletal muscles ○ Autonomicnervous system (ANS) - part of the PNS that regulates the body's internal environment  Afferent nerves - carry sensory signals from internal organs to the CNS  Efferent nerves - carry motor signals from the CNS to internal organs □ Sympatheticnerves - those autonomic motor nerves that project from the CNS in the lumbar (small of back) and thoracic (chest area) regions of the spinal cord - The sympathetic neurons that project from the CNS synapse on second-stage neurons at a substantial distance from their target organs □ Parasympatheticnerves - those autonomic motor nerves that project from the brain and sacral (lower back) region of the spinal cord - The parasympathetic neurons synapse near their target organs on very short second-stage neurons - Three important principles of the functions of the sympathetic and parasympathetic systems: 1. Sympathetic nerves stimulate, organize, and mobilize energy resources in threatening situations; whereas parasympathetic nerves act to conserve energy 2. Each autonomic target organ receives opposing sympathetic and parasympathetic input, and its activity is thus controlled by relative levels of sympathetic and parasympathetic activity 3. Sympathetic changes are indicative of psychological arousal, whereas parasympathetic changes are indicative of psychological relaxation - Cranialnerves - 12 pairs which project from the brain - parasympathetic ○ Include the olfactory nerves and the optic nerves ○ Longest nerve - vagus nerves - MENINGES, VENTRICLES, AND CEREBROSPINAL FLUID - The brain and spinal cord (CNS) are protected by the three meninges: ○ Dura mater - the outer meninx; tough membrane ○ Arachnoid membrane - immediately inside the dura matter; fine membrane  Subarachnoid space - the space beneath the arachnoid memb; contains many large blood vessels and cerebrospinal fluid ○ Pia mater - innermost meninx; delicate; adheres to the surface of the CNS - The CNS are also protected by the cerebrospinal fluid which fills the: ○ Subarachnoid space ○ Centralcanal - a small central channel that runs the length of the spinal cord ○ Cerebralventricles - the four large internal chambers of the brain: the two lateral ventricles, the third ventricle, and the fourth ventricle - Cerebrospinal fluid supports and cushions the brain ○ Choroid plexuses - networks of capillaries that protrude into the ventricles from the pia mater  Continuously produce cerebrospinal fluid  Excess CSF is absorbed from the subarachnoid space into large blood-filled spaces (dural sinuses) which run through the dura mater anddrain into the large jugular veins of the neck - Hydrocephalus -when the walls of the ventricles, and thus the brain, begin to expand b/c CSF cannot drain due to a tumour blocking its path - BLOOD-BRAINBARRIER - Blood-brain barrier - a mechanism that impedes the passage of many toxic substances from the blood into the brain ○ The cells of the blood vessel walls are tightly packed - thus forming a barrier to the passage of many molecules - some molecules get actively transported through if important CELLS OF THE NERVOUS SYSTEM - Two 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 - External anatomy of neurons - Cellbody - the metabolic center of the neuron - aka soma - Cellmembrane - the semipermeable membrane that encloses the neuron - Dendrites - the short processes emanating from the cell body, which receive most of the synaptic contacts from other neurons - Axon hillock - the cone-shaped region at the junction between the axon and the cell body - Axon - the long, narrow process that projects from the cell body - Myelin - the fatty insulation around many axons - Nodes of ranvier - the gaps between sections of myelin - Buttons - the button-like endings of the axon branches, which release chemicals into synapses - Synapses -the gaps between adjacent neurons across which chemical signals are transmitted - Internal anatomy of neurons - Nucleus - the spherical DNA-containing structure of the cell body - Mitochondria -sites of aerobic (oxygen-consuming) energy release - Endoplasmicreticulum - a system of folded membranes in the cell body; rough portions (those with ribosomes) play a role in the synthesis of proteins; smooth portions (those without ribosomes) play a role in the synthesis of fats - Cytoplasm- the clear internal fluid of the cell Ribosomes - internal cellular structures on which proteins are synthesized; they are located on the endoplasmic reticulum - Ribosomes - internal cellular structures on which proteins are synthesized; they are located on the endoplasmic reticulum - Golgicomplex - a connected system of membranes that packages molecules in vesicles - Microtubules -tubules responsible for the rapid transport of material throughout neurons - Synapticvesicles - spherical membrane packages that store neurotransmitter molecules ready for release near synapses - Neurotransmitters - molecules that are released from active neurons and influence the activity of other cells - Neuron cell membrane - Composed of a lipid bilayer - Has channel proteins and signal proteins embedded within it - Classes of neurons - Multipolar neuron - a neuron with more than two processes extending from its cell body ○ Most neurons - Unipolar neuron - a neuron with one process extending from its cell body - Bipolar neuron - a neuron with two processes extending from its cell body - Interneurons - with a short axon or no axon ○ Function is to integrate the neural activity within a single brain structure, not to conduct signals from one structure to an other - Neurons and neuroanatomical structure - CNS - clusters of cell bodies = nuclei ○ Bundles of axons = tracts - PNS - clusters of cell bodies = ganglia ○ Bundles of axons = nerves - GLIAL CELLS: THE FORGOTTEN CELLS - Overall, the numbers of glial cells and neural cells are approximately equal - Different types: 1. Oligodendrocytes - glial cells with extensions that wrap around the axons of some neurons of the CNS  These extensions are rich in myelin  The myelin sheaths they form increase the speed and efficiency of anoxal conduction  Each oligodendrocyte provides several myelin segments, often on more than one segment 2. Schwann cells - PNS glial cells with similar function  Each schwann cell constitutes one myelin segment  Only schwann cells can guide axonal regeneration after damage - which is why effective axonal regeneration in the mammalian nervous system is restricted to the PNS 3. Microglia - smallthan the other glial cells - they respond to injury or disease by multiplying, engulfing cellular debris, and triggering inflammatory responses 4. Astrocytes -the largest glial cells, and star shaped  The extensions of some astrocytes cover the outer surfaces of blood vessels that course through the brain  Make contact with neuron cell bodies  Play a role in allowing the passage of some chemicals from the blood into CNS neurons and in blocking other chemicals  Havebeen shown to send and receive signals from neurons and other glial cells, to control the establishment and maintenance of synapses between neurons, to modulate neural activity, to maintain the function of axons, and to participate in glial circuits NEUROANATOMICAL TECHNIQUES AND DIRECTIONS - NEUROANATOMICAL TECHNIQUES - Neurons are so tightly packed which is why it is difficult to see their structure with a microscope - Golgi stain - The silver chromate created by the chemical reaction of the two substances Golgi was using invaded a dew neurons in each slice of tissue and stained each invaded neuron entirely black - This made it possible to see individual neurons for the first time, although only in silhouette - Commonly used when the overall shape of neurons is of interest - Nissl stain - Unlike the Golgi stain, the Nisslstain is able to provide an indication of the number of neurons in an area or the nature of their inner structure - Most common dye used is cresyl violet - able to penetrate all cells on a slide, but they bind effectively only to structures in neuron cell bodies - Thus by counting the number of nissl stained dots, you can estimate the number of cell bodies in an area - Electron microscopy - Provides information about the details of neuronal structure - Light microscopy is inefficient bc the limit of its magnification is 1500x - so it can't reveal the fine details of neurons - Usea beam of electrons through tissue onto photographic film - electron micrograph - Scanning electron microscope = 3D, but not as much magnification - The strength of the electron microscope is also a weakness: because the images are so detailed, they can make it difficult to visualize general aspects of neuroanatomical structure - Neuroanatomical tracing techniques - Two types: 1. Anterogradetracing methods - used when an investigator wants totrace the paths of axons projecting away from cell bodes located in a particular area - Forward - Usechemicals that move forward along their axons to their terminal buttons 2. Retrogradetracing methods - used when an investigator wants to trace the paths of axons projecting into a particular area - Backward - Usechemicals that move backward along their axons to their cell bodies - DIRECTIONSIN THE VERTEBRATE NERVOUS SYSTEM - Directions in the vertebrate nervous system are described in relation to the orientation of the spinal cord DRAW OUT FIGURE 3.14/3.15/3.16 - DRAW OUT FIGURE 3.14/3.15/3.16 - The vertebrate nervous system has three axes - straightforward for most vertebrates: 1. Anterior-posterior - Anterior - toward the nose end (rostral) - Posterior - toward the tail end (caudal) 2. Dorsal-ventral - Dorsal - toward the surface of the back or the top of the head - Ventral - toward the surface of the chest or the bottom of the head 3. Medial-lateral - Medial - toward the midline of the body - Lateral - away from the midline toward the body's lateral surfaces - Humans complicate this simple three-axis system b/c we walk on our hind legs ○ Dorsal - top of the human head and back of the human body ○ Ventral - bottom of our head, front of our body ○ Superior - top of primate head ○ Inferior - bottom of primate head ○ Proximal - closer to the CNS, with regard to the PNS ○ Distal - farther from the CNS, with regard to the PNS - Midsagittalsection - a section of the brain cut down between the two hemispheres - Cross section - a section cut at a right angle to any long, narrow structure, such as the spinal cord or a nerve SPINAL CORD - The spinal cord comprises two different areas: 1. Grey matter - an inner H-shaped core composed largely of cell bodies and unmyelinated interneurons 2. Whitematter - an area surrounding the grey matter composed largely of myelinated axons - Dorsalhorns - the two dorsal arms of the spinal
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