Chapter 12 Book Notes
Chapter 12 Book Notes CBIO 2200
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This 7 page Class Notes was uploaded by Rholonda Pruitt on Thursday March 24, 2016. The Class Notes belongs to CBIO 2200 at University of Georgia taught by Leslie Pryor in Fall 2016. Since its upload, it has received 36 views. For similar materials see Anatomy & Physiology I in Anatomy at University of Georgia.
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Date Created: 03/24/16
Chapter 12 Notes 03/01/2016 ▯ 12.1 Basic Structure and Function of the Nervous System brain – nervous tissue contained within cranium spinal cord – extension of the nervous tissue within the vertebral column The Central and Peripheral Nervous System o Central nervous system (CNS) – brain and spinal cord o Peripheral nervous system (PNS) – everything else o Cells in CNS and PNS: glial cells – provide a framework of tissue that supports the neurons and their activities neurons – more functionally important tan glial cells in terms of the communicative function of the nervous system soma – cell body process – extensions of the soma axon – fiber that connects a neuron with its target dendrite – responsible for receiving most of the input from the other neurons gray matter – has many cell bodies and dendrites white matter – has many axons; has myelin (lipid-rich substance that insulates axons) o In the CNS Nucleus – localized collection of neuronal cell bodies Tract – bundle of axons o In the PNS Ganglion – localized collection of neuronal cell bodies Nerve – bundle of axons Functional Divisions of the Nervous System o Basic Functions Sensation – sensory functions; involved in receiving information about the environment around us Stimulus – particular event in the environment that changes from homeostasis Response – motor functions; involved in generating responses to sensory information Integration/association areas – involved in integrating sensory information with other sensations as well as memories, emotional state, or learning (cognition) o Controlling the Body Somatic nervous system (SNS) Responsible for conscious perception and voluntary motor responses Autonomic nervous system (ANS) Responsible for involuntary control of the body, ususally for sake of homeostasis Regulates organ systems of the body Enteric nervous system (ENS) Controls smooth muscle and glandular tissue in digestive system Not dependent on CNS ▯ 12.2 Nervous Tissue Nervous tissue composed of neurons and glial cells Neurons o Considered to be the bases of nervous tissue o Responsible fore electrical signals o Parts of the Neuron Synapses – where neurons connect with other neurons or target cell Axon hillock/initial segment – where axon emerges from soma Axoplasm – where cytoplasm changes to a solution of limited components in axon hillock Node of Ranvier – gap in the myelin covering the axon Axon segment – length of the axon between the gaps Axon terminal – the end of the axon Synaptic end bulb – make connection with target cell at the synapse o Types of Neurons Unipolar – have only one process emerging from the cell; only found in invertebrates; exclusive sensory cells; cell bodies found in ganglia Bipolar – have two processes that extend from each end of the soma (1 axon and 1 dendrite); not common; found in olfactory epithelium and retina Multipolar – have one axon and two or more dendrites; majority of neurons Glial Cells o Supporting cells o Glial cells of the CNS Astrocyte – star-shaped; maintain concentration of chemicals in extracellular space, remove excess signaling molecules, react to tissue damage, and contribute to blood brain barrier (BBB) (physiological barrier that keeps substances that circulate in the rest of the body from the cns Oligodendrocyte – insulates axons Microglia – may originate as macrophages; ingest and digest diseased/damaged cells and pathogens Ependymal – filters blood to make cerebrospinal fluid (CSF) (fluid that circulates through the CNS); part of BBB Line ventricles (one of four central cavities that are remnants of the hollow center of the neural tube formed during the embryonic development of the brain) Choroid plexus – specialized structure in the ventricles where ependymal cells come in contact with blood vessels and filter and absorb components of the blood to make CSF o Glial Cells of the PNS Satellite cell – found in sensory and autonomic ganglia and surround the cell bodies of the neurons; provide support and does what astrocytes do (except for participating in BBB) Schwann cell – insulate axons with myelin; wrap around a portion of only one axon segment and no others unlike oligodendrocyte o Myelin lipid-rich sheath that surrounds the axon creating the myelin sheath (facilitates transmission of electrical signals along axon) ▯ 12.3 The Function of Nervous Tissue thermoreceptor – sensory receptor that is sensitive to temperature graded potential – amount of change in electrical state depending on the strength of the stimulus threshold – voltage at which a signal is generated action potential – resulting signal of threshold propagation – traveling of action potential neurotransmitter – signaling molecule released at synaptic end bulbs thalamus – part of the CNS that acts as a relay for sensory information cerebral cortex – where conscious perception occurs and integration occurs; sends signals down to the spinal cord for movement o precentral gyrus of the frontal cortex – has axon that extends all the way down the spinal cord upper motor neuron located here lower motor neuron – causes muscle fibers to contract ▯ 12.4 The Action Potential Electrically Active Cell Membranes o Concentration of Na+ higher outside of the cell o Concentration of K+ higher inside of the cell o Electrochemical exclusion – channel pore is charge-specific o Size exclusion – channel pore is size-specific o Nonspecific channel – channel selective for charge but not size; exclude anions o Gated – channels that do not allow for ions to freely diffuse across the membrane and are opened by certain events o Ligand-gated channel/ionotropic receptor – opens when signaling molecule (ligand) bind to the extracellular region of the channel o Voltage-gated channel – responds to changes in the electrical properties of the membrane in which it is embedded o Leakage channel – randomly gated (opens and closes at random) The Membrane Potential o Membrane potential – distribution of charge across the cell membrane o Concentration of ions in extracellular and intracellular fluid is pretty balanced (net neutral charge) o Slight difference occurs on membrane surface o Resting membrane potential - -70 mV o The Action Potential Depolarization – membrane potential moves toward zero Repolarization – membrane voltage moves back toward resting membrane potential; generally overshoots that value If threshold not met, no action potential occurs Activation gate – opens when the membrane crosses -55 mV (Na+) Inactivation gate – closes after a specific period of time (Na+) Another action potential cannot be generated while one is already in progress (refractory period) two types of refractory periods: absolute refractory period – another action potential will not start relative refractory period o Propagation of the Action Potential Continuous conduction – propagation along unmyelinated axon; slow Salutatory conduction – propagation along myelinated axon; fast (jumps from node to node) Resistance – when sodium ion based depolarization spreads faster down a wide axon than a narrow one ▯ 12.5 Communication Between Neurons Graded Potentials o Local changes in membrane potential are called graded potentials o Can be depolarizing or hyperpolarizing Depolarizing usually involves Na+ and Ca2+ entering cell Hyperpolarizing usually involves K+ leaving cell or Cl- entering o Types of Graded Potentials Generator potential – when graded potentials develop in the dendrites that influence the generation of an action potential in the axon of the same cell Receptor potential – graded potentials result in release of neurotransmitters at synapses with sensory neurons Postsynaptic potential (PSP) – graded potential in the dendrites of a neuron that is receiving synapses from other cells Excitatory postsynaptic potential (EPSP) – depolarization in a postsynaptic potential Inhibitory postsynaptic potential (IPSP) – hyperpolarization of a postsynaptic potential o Summation Summate – changes due to graded potentials adding together to reach the threshold Spatial summation – associating the activity of multiple inputs to a neuron with each other Temporal summation – relationship of multiple action potentials from a single cell resulting in a significant change in the membrane potential Synapses o Chemical synapse – neurotransmitter is released from one cell and it affects the other cell o Electrical synapse – direct connection between two cells so that ions can pass directly from one cell to the next o Characteristics of all synapses: Presynaptic element Neurotransmitter Synaptic cleft Receptor proteins Postsynaptic element Neurotransmitter elimination/re-uptake o Neurotransmitter Release Neurotransmitter released from vesicle via exocytosis into synaptic cleft (small gap between cells) o Neurotransmitter Systems Cholinergic system – system based on acetylcholine Have two types of receptors: Nicotinic receptor – binds to nicotine Muscarinic receptor – binds to muscarine (product of some mushrooms) Biogenic amine – group of neurotransmitters that are enzymatically made from amino acids; include tyrosine, dopamine, norepinephrine, epinephrine, serotonin, etc. Neuropeptide – neurotransmitter molecule made up of chains of amino acids connected by peptide bonds Metabotrophic receptor – involves complex of protein on the extracellular surface of the cell and the intracellular side of the protein initiates activity of the G protein (guanosine triphosphate hydrolase that physically moves from the receptor protein to the effector protein to activate the latter) Effector protein – enzyme that catalyzes the generation of a new molecule, which acts as the intracellular mediator of the signal that binds to the receptor ▯ ▯
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