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The Nervous System Mary ET Boyle, Ph.D. Department of Cognitive Science UCSD
What’s the big deal?
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Detect Evaluate Decide Respond
Analysis of the nervous system to understand the biological basis for behavior. Modern studies ◦ Neuroanatomists ◦ Neurochemists ◦ Neurophysiologists ◦ Neuropsychologists Neuroscience – term introduced in mid-1960s
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The brain must know what is happening outside in the environment.
•perceive •remember •decide •act
sensory neurons motor neurons interneurons
Peripheral Nervous System (PNS)
Central Nervous System ( CNS)
Organization
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Detects/processes environmental stimuli:
Somatic Nervous System Regulates internal organs:
Autonomic Nervous System
Organization of PNS
Detects environmental stimuli:
Somatic Nervous System Regulates internal organs:
Autonomic Nervous System
Decision! Central nervous system
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Brain
Spinal Cord
Components of the CNS
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Anterior
Posterior Dl Left Dorsal
Right Ventral
Anatomical directions
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Horizontal section— Shows structures viewed from above/below
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Sagittal section— Divides structures into right and left parts
Coronal section (frontal section)— Shows views from the front/back
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Review of Anatomical Directions
Anterior—toward the front (e.g., dog’ s nose) Posterior—toward the rear (e.g., dog’s tail) Ventral—toward the belly Dorsal—toward the back Rostral—toward the head Caudal—toward the tail Medial—toward the midline Lateral—away from the midline Superior—above a structure Inferior—below a structure
Fundamental cellular unit Purpose of neurons: ◦ receive ◦ process ◦ transfer
Information is made up of chemical or electrical signals Unidirectional
Neurons
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Neurobiology of Cognition COGS 17
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Four major types of synapses
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Three types of neurons
Some multipolar neurons
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Support Staff: Glia
More than just glue?
Glia, short for neuroglial cells.
Their purpose is to provide metabolic support, insulate, protect, reinforce, repair, and cleanup damaged areas.
Mounting evidence suggests that glial cells may be nearly as critical to thinking and learning as neurons are. Glia
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are much more numerous than neurons. outnumber neurons 2:1. are found in both the CNS and PNS. Neuroglia means “ nerve glue. ”
Researchers have found that the average human cerebral cortex has approximately two glial cells for every neuron (other brain regions have up to 10 times as many). That’s a glia index of 2.0. The index in comparable regions in rodents is 0.4, in worms 0.17. There is work that supports the theory that a high concentration of glia may actually boost the ability to think. So here’s something to think about: the glia index in the cerebral cortex of dolphins is 3.0. Glia …
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protoplasmic astrocytes
fibrous astrocytes
Basic classification of glial cells
microglial cells
Spanish anatomist Pío del Río Hortega classified these cells. Hortega made these drawings in 1920 with the help of a microscope’s camera lucida.
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Multiple sclerosis (MS) is a progressive central nervous system disorder.
Localized oligodendrocyte demyelination prevents affected nerve cells from functioning properly.
In some cases, the demyelinated axons completely fail to work.
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Glia and neurons work together
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Neurobiology of Cognition Zlokovic & Apuzzo: Neurosurgery 43(4):877-878, 1998. COGS 17
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(PNS) Peripheral Nervous System
The Autonomic The Somatic Nervous System Nervous System
Enables one to The Somatic interact with the Nervous System physical environment.
Two types of nerves:
Efferent Afferent Cranial Spinal neurons take neurons bring messages from messages from the CNS to the sensory skeletal muscles receptors to the CNS
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Table 2.1: Klein/Thorne: Biological Psychology © 2007 by Worth Publishers
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Efferent neurons The Autonomic control glandular Nervous System activityy and internal organ functioning.
Two divisions:
Sympathetic Parasympathetic
ShiSympathetic
Prepares the organism to respond to challenging or dangerous conditions.
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CNS protection
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Ventricular System
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CNS: spinal cord
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Three main functions: ◦ Recognizing detected stimuli ◦ Analyzing the information ◦ Executing the appropriate response
The Central Nervous System: The Brain
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Myelencephalon—contains the medulla oblongata, which controls basic life functions (e.g., respiration, heart rate, vomiting, salivation Reticular formation (reticular activating system)—begins in the medulla, extends to other areas of the brain and is involved in arousal Metencephalon consists of two major structures: ◦ Pons—a “bridge” for many fibers passing from one side of the brain to the other. Sensory fibers, fibers from the cortex to cerebellum, and fibers that relay information on sleep, arousal and dreaming pass through it. ◦ Cerebellum—involved in the development and coordination of movement Raphé system—plays a role in sleep and arousal
Hindbrain
Midbrain - mesencephalon
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Tectum (“roof”) relays visual and auditory information and controls simple reflexes, eye and ear orientation movements superior colliculi (“little hills”)—relays visual information inferior colliculi—relays auditory information
Tegmentum (“floor covering”) substantia nigra—integration of voluntary movements red nucleus —controls basic body movements reticular formation —controls arousal and consciousness brain stem—midbrain + hindbrain (minus the cerebellum)
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Thalamus—major relay station for sensory information Medial geniculate nucleus (MGN)—relays auditory information Lateral geniculate nucleus (LGN)—relays visual information Other nuclei connect to areas not involved in sensation, e.g., the ventrolateral nucleus receives information from the cerebellum and relays it to the motor cortex.
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Hypothalamus—detects need states (e.g., hunger and thirst), controls the autonomic nervous system, and controls pituitary hormone production and release The suprachiasmatic nucleus of the hypothalamus also is involved in the control of biological rhythms.
Pituitary gland (hypophysis)—regulates other glandular activity of the body (often called the “master gland”) Anterior pituitary gland (adenohypophysis)—produces several hormones including somatotropin, thyrotropin, adrenocorticotropin, and the gonadotropins Posterior pituitary (neurohypophysis)—releases oxytocin and antidiuretichormone (ADH) which are produced in the hypothalamus
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Limbic System The limbic system governs emotions such as anger, happiness, and fear and is involved in the storage and retrieval of memories. The limbic system is a group of structures surrounding the brain stem. The limbic system structures include the amygdala, cingulate gyrus, and hippocampus.
Basal Ganglia— have widespread connections to the cortex and forebrain and are involved in the initiation of voluntary movements, maintaining muscle tone and posture Parts of the basal ganglia include: The caudate nucleus, the putamen, and the globus pallidus
The caudate nucleus and the putamen are referred to as the corpus striatum due to their appearance.
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Somatosensory cortex —anterior portion of the parietal lobe. Motor cortex —area of the frontal lobe anterior to the central sulcus. The face and hands have a large amount of representation in these areas. This representation allows for great sensitivity and motor control for these areas of the body.
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Neurons—Perform information processing and communications functions of the nervous system ◦ Consist of three major parts: 1. Soma (cell body)—contains nucleus, mitochondria, and ribosomes 2. Dendrites—portions of the neuron that transmit information toward the cell body (typically) 3. Axon—a structure on the neuron which transmits information away from the cell body
Terms review
sensory neuron ◦ A neuron that detects changes in the external or internal environment and sends information about these changes to the central nervous system. ◦ Sensory neurons carry information to the CNS
motor neuron ◦ A neuron locat ed withi n the cent ral nervous syst em that cont rol s the contraction of a muscle or the secretion of a gland. ◦ They carry information from CNS to muscles to control their functioning.
interneuron ◦ A neuron located entirely within the central nervous system. ◦ Interneurons connect sensory and motor neurons or communicate with other interneurons.
central nervous syy()stem (CNS) ◦ The brain and the spinal cord.
peripheral nervous system (PNS) ◦ The part of the nervous system outside the brain and spinal cord, including the nerves attached to the brain and the spinal cord.
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Peripheral NS Central NS ◦ Nerve—a collection of ◦ Tract—a collection axons outside the of axons within the CNS CNS
◦ Ganglion (plural, ◦ Nucleus (plural, ganglia)—a collection nuclei)—a collection of cell bodies outside of cell bodies within the CNS the CNS
Cells of the Nervous System: Terminology
Presynaptic terminal—a swelling at the end of the axon or telodendron ◦ Synaptic vesicles (contain neurotransmitter substance) ◦ Synapse—point of functional contact between a neuron and its target ◦ Synaptic cleft—small space which separates the presynaptic terminal from its target
Cells of the Nervous System: Terminology
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Axodendritic—the axon synapses with dendrites of another neuron Axosomatic—the axon syypnapses with the cell body of another neuron Dendrodendritic synapse—occurs when the dendrites of one neuron synapses with the dendrites of another neuron Axoaxonic synapse—the axon of one neuron synapses with the axon of another neuron Neuromuscular junction—the axon synapses with a muscle
Cells of the Nervous System: Types of Synapses
Pituitary gland (hypophysis)—regulates other glandular activity of the body (often called the “master gland”)
Anterior pituitary gland (adenohypophysis)— produces several hormones including somatotropin, thyrotropin, adrenocorticotropin, and the gonadotropins
Posterior pituitary (neurohypophysis)—releases oxytocin and antidiuretic hormone (ADH) which are produced in the hypothalamus
CNSCNS——TheThe Brain, Forebrain: The Diencephalon
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CNS—The Brain, Forebrain: The Telencephalon
The telencephalon (end brain) consists of three parts: ◦ Limbic system ◦ Basal ganglia ◦ Cerebral cortex
CNS—The Brain, Forebrain: The Telencephalon
Limbic System ◦ The limbic system governs emotions such as anger, happiness, and fear and is involved in the storage and retrieval of memories. ◦ The limbic system is a group of structures surrou nd ing t he b ra in ste m. ◦ The limbic system structures include the amygdala, cingulate gyrus, and hippocampus.
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Basal Ganglia—have widespread connections to the cortex and forebrain and are involved in the initiation of voluntary movements, maintaining muscle tone and posture Parts of the basal gangli lia incl ud e: ◦ The caudate nucleus, the putamen, and the globus pallidus The caudate nucleus and the putamen are referred to as the corpus striatum due to their appearance.
CNSCNS——TheThe Brain, Forebrain: The Telencephalon
Cerebral Cortex—the convoluted outer layer of the forebrain that processes sensory information, controls thinking, decision making, stores and retrieves memory, and initiates motor responses
The cortex is divided into two hemispheres (connected by the corpus callosum) and each hemisphere has four lobes.
CNSCNS——TheThe Brain, Forebrain: The Telencephalon
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soma ◦ The cell body of a neuron, which contains the nucleus.
dendrite ◦ The branched, treelike structure attached to the soma of a neuron; receives information from the terminal buttons of other neurons.
synapse ◦ A junction between the terminal button of an axon and the membrane of another neuron.
axon ◦ The long, thin, cylindrical structure that conveys information from the soma of a neuron to its terminal buttons.
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multipolar neuron ◦ A neuron with one axon and many dendrites attached to its soma.
bipolar neuron ◦ A neuron with one axon and one dendrite attached to its soma.
pseudounipolar neuron ◦ A neuron with one process attached to its soma; the process divides, with one branch receiving sensory information and the other sending the information into the central nervous system.
terminal button ◦ The bud at the end of a branch of an axon; forms synapses with another neuron; sends information to that neuron.
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neurotransmitter ◦ A chemical that is released by a terminal button; has excitatory or inhibitory effect on another neuron.
membrane ◦ A structure consisting principally of lipid molecules that defines the outer boundaries of a cell and also constitutes many of the cell organelles, such as he Golgi apparatus.
nucleus ◦ A structure in the central region of a cell, containing the nucleolus and chromosomes.
nucleolus ◦ A structure within the nucleus of a cell that produces the ribosomes.
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ribosome ◦ A cytoplasmic structure, made of protein, that serves as the site of production of proteins translated from mRNA.
chromosome ◦ A strand of DNA, with associated proteins, found in the nucleus; carries genetic information.
deoxyribonucleic acid (DNA) ◦ A long, complex macromolecule consisting of two interconnected helical strands; along with associated proteins, strands of DNA constitute the chromosomes.
gene ◦ The functional unit of the chromosome, which directs synthesis of one or more proteins.
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messenger ribonucleic acid (mRNA) ◦ A macromolecule that delivers genetic information concerning the synthesis of protein from a portion of a chromosome to a ribosome.
enzyme ◦ A molecule that controls a chemical reaction, combining two substances or breaking a substance into two parts.
non-coding RNA (ncRNA) ◦ A form of RNA that does not encode for protein, but has functions of its own.
cyyptoplasm ◦ The viscous, semiliquid substance contained in the interior of a cell.
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mitochondrion ◦ An organelle that is responsible for extracting energy from nutrients.
adenosine triphosphate (ATP) ◦ A molecule of prime importance to cellular energy metabolism; its breakdown liberates energy.
endoplasmic reticulum ◦ Parallel layers of membrane found within the cytoplasm of a cell. Rough endoplasmic reticulum contains ribosomes and is involved with production of proteins that are secreted by the cell. Smooth endoplasmic reticulum is the site of synthesis of lipids and provides channels for the segregation of molecules involved in various cellular processes.
Golgi apparatus ◦ A complex of parallel membranes in the cytoplasm that wraps the products of a secretory cell.
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exocytosis ◦ The secretion of a substance by a cell through means of vesicles; the process by which neurotransmitters are secreted.
lysosome ◦ An organelle surrounded by membrane; contains enzymes that break down waste products.
cytoskeleton ◦ Formed of microtubules and other protein fibers, linked to each other and forming a cohesive mass that gives a cell its shape.
microtubule ◦ A long strand of bundles of protein filaments arranged around a hollow core; part of the cytoskeleton and involved in transporting substances from place to place within that cell.
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Glial cells ◦ One-tenth the size of neurons ◦ Ten times as numerous as neurons Types of Glial cells ◦ Astrocytes—provide physical support to neurons, nourishment and other functions. New evidence suggests that astrocytes also integrate neuronal messages and release neurotransmitters that affect the sensitivity of synapses.
Cells of the Nervous System: Glial cells
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Types of Glial cells (cont.) ◦ Microglial cells—remove debris ◦ Oligodendrocytes—produce myelin which covers the axons of neurons in CNS ◦ Schwann cells—produce myelin which covers the axons of neurons in PNS Multiple sclerosis—destroys oligodendrocytes
axoplasmic transport ◦ An active process by which substances are propelled along microtubules that run the length of the axon.
anterograde ◦ In a direction along an axon from the cell body toward the terminal buttons.
retrograde ◦ In a direction along an axon from the terminal buttons toward the cell body.
glilia ◦ The supporting cells of the central nervous system.
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astrocyte ◦ A glial cell that provides support for neurons of the central nervous system, provides nutrients and other substances, and regulates the chemical composition of the extracellular fluid.
phagocytosis ◦ The process by which cells engulf and digest other cells or debris caused by cellular degeneration.
oligodendrocyte ◦ A type of glial cell in the central nervous system that forms myelin sheaths.
myelin sheath ◦ A sheath that surrounds axons and insulated them, preventing messages from spreading between adjacent axons.
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node of Ranvier ◦ A naked portion of a myelinated axon, between adjacent oligodendroglia or Schwann cells.
miccogaroglia ◦ The smallest of glial cells; act as phagocytes and protect the brain from invading microorganisms.
Schwann cell ◦ A cell in the peripheral nervous system that is wrapped around myelinated axon, providing one segment of its myelin sheath.
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Skull—outer bony covering that encases the brain Vertebral Column—outer bony covering that encases the spinal cord Meninges ◦ Dura matter ◦ Arachnoid matter ◦ Pia mater Ventricular system
The Protective Features of the CNS
blood-brain barrier ◦ A semipermeable barrier between the blood and the brain produced by the cells in the walls of the brain’s capillaries.
area postrema ◦ A region of the medulla where the blood-brain barrier is weak; poisons can be detected there and can initiate vomiting.
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