Outline Of Functional Organization Of Nervous System 1c122u

Outline of Functional Organization of Nervous System Overview of the Nervous System -

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One of the body’s homeostatic control systems Contains sensors, integrating centers, and output pathways More interneurons in a pathway = greater number of interconnections and ability to integrate info 2/48!!!!!!

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Cnidarians -

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Most nervous systems are organized into 3 functional divisions: o Afferent sensory o Integrating o Efferent motor Cnidarians are an exception o Nervous system is interconnected web or nerve net o Neurons are not specialized into diff. divisions o Neurons carry AP in both directions  Neurons not specific sensory/motor

Nervous Systems Across Animal Groups -

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Nervous System : -

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Bilaterally symmetrical o Right and left side are mirror images Cephalization o Sense organs are concentrated at anterior end Ganglia o Groups of neuronal cell bodies Nuclei o Groups of neuronal cell bodies within the brain Brain o Integrating center made up of clusters of nuclei Tracts o Bunds of many axons within the CNS Nerve o Bundle of many axons outside of CNS

Structure of a Nerve

Bundles of myelinated and unmyelinated axons Enclosed in several layers of connective tissue o Endoneurium  Wraps each axon o Perineurium  Wraps a bundle (fascicle) of axon o Epineurium  Wraps the entire nerve Mixed Nerves o Contain both afferent and efferent neurons  Each neuron is either afferent (sensory) or efferent (motor)

Cephalization Occurs in most animals o Cnidarians and echinoderms lack cephalization Organisms with more complex nervous systems have more neurons = more synapses o Increased # of synapses allow for more integration of info, and more complex behaviors o Memories are stored in synapses, a complex nervous system also allows for a greater potential for learning

FIGURE 8.4!!!!!!!!!!!!!! The Vertebrate CNS -

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High degree of cephalization Uniqe in having a hollow dorsal nerve cord (spinal cord) Part of Nervous system is encased within cartilage or bone o CNS = brain + spinal cord) Part of Nervous system extends to periphery of body o PNS = nerves outside CNS

Cranial & Spinal Nerves Cranial Nerves -

Exit directly from skull 13 pairs Some afferent, some motor, some mixed

Spinal Nerves -

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Branch from spinal cord Enter and exit between adjacent vertebrae Named based on region of vertebral column from which they emerge o Cervical, thoracic, lumbar, sacral and coccygeal Mixed nerves

Gray and White Matter -

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Brain and spinal cord contain 2 types of tissues: o Gray Matter (neuronal cell bodies) o White Matter (tracts of axons and myelin sheaths) Spinal cord white matter on surface, gray matter inside Cerebral Cortex gray matter on surface, white matter inside

CNS is isolated and protected -

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Meninges o Layers of CT surrounding brain + Spinal Cord o # of meninges vary across taxa (mammals have 3; fishes have 1) Cerebral Spinal Fluid (CSF) o Fills spaces within the CNS and acts as shock absorber Blood – brain barrier o Tight junctions in brain capillary endothelium limit age of solutes from bloodstream into CSF

The Vertebrate Brain -

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Brain is an extension of SC o Nerve tracts extend between brain and SC Several cavities called ventricles containing CSF 3 regions o Rhombencephalon (hindbrain)  Reflexes and involuntary behaviors o Mesencephalon (midbrain)  Coordination of sensory info  Relay center in mammals o Prosencephalon (forebrain)  Integration of olfactory info with other senses

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Regulate body temp, reproduction, eating, emotion Learning and memory in mammals

Brain Size and Morphology -

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Most groups of verts have the same major brain structures although these structure vary in relative size Much of variation due to body size Birds and mammals have larger brains than other verts Animals with large brains have more neurons o More complex integ centers and more behaviors

Parts of Mammalian Brain -

TABLE 8.2!!!!!!!!!!!!!!!!!!!!!

Cerebrum -

Outer layer is cortex Divided into 2 cerebral hemispheres o Left side = controls right side of body o Right side = controls left side of body  **neurons between the 2 sides via corpus callosum

Hypothalamus -

Located at base of forebrain o Under thalamus Helps maintain homeostasis o Body temp, thirst, hunger, reproduction o Interaction with autonomic nervous system o Regulates secretion of pituitary hormones

Limbic System -

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A network of connected structures that lie between the cortex and the rest of the brain Influences emotions, motivation, memory Sometimes called the emotional brain Includes hypothalamus and other parts o Amygdala

Aggression and fear responses Hippocampus  Converts Short- term memory to long – term memory Olfactory bulbs  Sense of smell 

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o Thalamus -

Large grouping of gray matter above hypothalamus Part of the reticular formation Receives input from limbic system and all senses EXCEPT olfaction Relays info to cortex Acts as a filter by blocking some afferent signals

Epithalamus -

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Located above the thalamus Habenular nuclei o Communicates with the tegmentation of the midbrain Pineal Complex o Establishes circadian rhythms o Secretes melatonin Cortex o Integrates and interprets sensory info o Initiates voluntary movements o Takes over midbrain fxn of lower verts o Isocortex (outer layer  For cognition and higher brain fxn  More folded in advanced mammals  Gyri  Folds  Sulcus  Grooves

Topology of the Cerebral Cortex -

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Association Areas of Cerebrum -

Autonomic Nervous System – Involuntary Nervous System -

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6 Layers Differs in shape and density of neurons Variable number of connections within each layer

Lobes named according to their function or overlying bones of the skull

Involved in Homeostasis Branches of ANS o Sympathetic  Most active during periods of stress/ physical activity  Fight or flight system o Parasympathetic  Most active during rest  Rest and digesting system o Enteric  Independent of 2 other systems  Affects digestion by innervating the organs of the alimentary canal

Maintaining Homeostasis

Cortical Lobes -

Receives info from adjacent areas and further process and integrate info Size of areas is larger in animals with more complex behaviors

PNS DIVISONS!!! FIGURE 7.16!!!!!!!!!!!!!!

Cortical Layers -

Each region of cortex corresponds to a specific part of the body that it controls by motor output or from which it receives sensory input Size of brain region devoted to diff. parts of body varies widely

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Balancing of sympathetic and parasympathetic systems 3 mechanisms for regulating autonomic function o Dual innervations  Most organs receive input from bothsystems o Antagonistic Action  One system stimulates while the other inhibits o Basal Tone  Under resting conditions Autonomic neurons carry APs FIGURE 8.17!!!!!!!!!!!

Antagonistic Action Table 8.3!!!!!!!!!!!!!!!!

Similarities in Autonomic Pathways -

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Pathways contain 2 neurons in series o Preganglionic  May synapse with many postganglionic neurons and instrinsic neurons o Postganglionic  Neurotransmitter is released at effector organ from varicosities Pre & post neurons synapse with each other in the autonomic ganglia

Autonomic Reflex Arcs -

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Somatic Motor Pathways – Voluntary Nervous System -

Differences in Autonomic Pathways -

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Differences between the Sympathetic (S) and Parasympathetic (PS) branches o Preganglionic Cell body Locations  S – thoracic and lumbar regions of spinal cord  PS – hind brain and sacral region of spinal cord o Ganglia location  S – chain that runs close to spinal cord  PS – close to effector Number of postganglionic neurons that synapse with a single preganglionic neuron

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Some effectors receive only sympathetic innervations o Adrenal medulla  Collection of modified postganglionic neurons o Sweat Glands o Arrector pili muscles in the skin o Kidneys o Blood vessels o FIGURE 8.20

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Regulation of the Autonomic System Figure 8.21!!!!!

3 Categories o Reflex behaviors  Involuntary and simple o Rhythmic behaviors  Underlie locomotion, breathing and the fxn of the heart o Voluntary behaviors  Most complex and diverse

Reflex Arcs -

Sympathetic vs Parasympathetic Systems TABLE 8.4!!!!!!!!!!!!!!

Control only 1 type of effector  skeletal muscles Usually under conscious control o Cerebrum Cell bodies of motor neurons are located in the CNS Monosynaptic o Axons are very long, and extend all the way muscle Axon splits into a cluster of axon terminals at the NMJ release acetylcholine Synaptic cleft between motor neuron and the muscle is very narrow Effect on the muscle cell always excitatory o Eg. Causes depolarization and contraction Some pathways are not under conscious control o Eg. Knee – jerk reflex

Animal Behaviors

Only Sympathetic Innervation -

Most autonomic changes occur via simple neural circuits that do not involve conscious centers of the brain Figure 8.22!!!!!!!!!!!!!!!!!!

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Least complex integrated responses Can involve as few as 2 neurons (monosynaptic) or more than 2 (polysynaptic) Figure 8.23!!!!

Convergence and Divergence in Reflex Arcs -

Neurons in reflex arcs arranged in 2 ways:

Convergence  Allows spatial summation o Divergence  Amplify signals Some reflex arcs have both convergence and divergence FIGURE 8.24!!!!!!!!!! o

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Rhythmic Behaviors -

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Governed by pattern generators o Groups of neurons that produce self – sustaining rhtymic depolarizations 2 types of pattern generators o Pace maker cell  A cell generates spontaneous depolarizations that control the firing of all the cells in the network o

Emergent property of the network  Rhythmic depolarization occurs because of the organization of neurons in the network

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Invertebrate Learning and Memory -

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Swimming Behavior of Leech -

Involves pattern generators and reflexes o Brainstem initiates the process and regulates speed o The spinal cord acts as a pattern generator o Afferent signals are sent back to CNS o Cortex is involved with guiding locomotion in complex envi o Cerebellum coordinates locomotion

Voluntary movements!!!!! FIGURE 8.28 Learning and Memory -

Most animals can learn and form memories due to the plasticity of the nervous system o Learning  Process of acquiring new info o Memory

Well studied in sea slug (Aplysia) Habituation o Decline in response to a stimulus after repeated exposure o Allows animal to ignore unimiportant stimuli and focus on novel stimuli o Caused by changes in presynaptic axon terminal  Inactivation of Ca2+ channels  Neurotransmitter release Sensitization o Increase in response to gentle stimulus after exposure to a strong stimulus o Caused by changes in presynaptic axon terminal 

FIGURE 8.26!!!!!!!!!!!!

Tetrapod Locomotion -

Retention and retrieval of info Plasticity  Changes in synaptic and neuronal function in response to stimuli 

Involves a secondary circuit  Serotonin released by facilitating interneuron binds to receptors  Activation of G proteins  Inactivation of K channels, AP duration  Ca2+ influx neurotransmitter release by sensory neuron

Mechanism of Serotonin’s effects -

FIGURE 8.31!!!!!!!!

Memory in Mammals -

Hippocampus involved in Long – term memory, but memories are stored in cerebrum o Memories are stored by increasing the efficiency of the synapse between 2 neurons

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Long term potentiation (LTP) o Repetitive stimulation of hippocampal tissue leads to an

increase in the response of the postsynaptic neuron