Ch12 Nerv System
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| Peripheral Nervous System | Consists of all nervous tissue outside the CNS.
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| Nerve | bundle of hundreds to thousands of axons plus associated connective tussue and blood vessels
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| Ganglia | Small masses of nervous tissue, consisting primarily of neuron cell bodies.
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| Enteric plexuses | Extensive networks of neurons locatesd in the walls of organs of the gastrointestinal tract.
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| Sensory receptor | A structure of the nervous system that monitors changes in the external or internal environment.
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| Parts of the PNS | Somatic nervous system and autonomic nervous system and enteric nervous system.
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| Somatic nervous system | Sensory neurons convey info from somatic receptors to the CNS. Motor neurons conduct impulses from the CNS to skeletal muscles. VOLUNTARY
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| Autonomic Nervous System | Motor neurons conduct nerve impulses from the CNS to smooth muscle, cardiac muscle, and glands. INVOLUNTARY
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| Two divisions of the ANS | Sympathetic division and parasympathetic division
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| Enteric Nervous System | Brain of the gut. Involuntary.
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| Functions of the Nervous System | Sensory function, Integrative function, Motor Function
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| Effectors | Muscles and glands
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| Electrical Excitability | The ability to respond to a stimulus and convert it into an action potential.
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| Stimulus | Any change in the environment that is strong enough to initiate an action potential.
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| Action Potential (Nerve Impulse) | An electrical signal that travels along the surface of the membrane of a neuron. Travels due to the movement of ions between interstitial fluid and the inside of a neuron.
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| Nissl Bodies | Produces proteins that are used to replace cellular components.
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| Neurofibrils | Bundles of intermediate filaments that provide the call shape and support.
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| Microtubles | Assist in moving materials between the cell body and axon.
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| Lipofuscin. | Contained in aging neurons. Pigment.
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| Nerve Fiber | Any neuronal process that emerges from the cell body of a neuron.
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| Dendrites | Receiving or input portions of a neuron.
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| Axon | Propagates nerve impulses toward another neuron, a muscle fiber, or a gland cell.
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| Axon Hillock | Cone-shaped elevation where the axon joins to the cell body.
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| Initial Segment | The part of the axom closest to the axon hillock.
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| Trigger Zone | Where nerve impulses arise. The junction of the axon hillock and the initial segment.
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| Axoplasm | The cytoplasm of an axon.
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| Axolemma | Plasma membrane of the axon.
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| Synapse | The site of communication between two neurons or between a neuron and an effector cell.
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| Synaptic Vesicles | Tiny membrane-enclosed sacs that store neurotransmitters.
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| Neurotransmitter | A molecule released from a synaptic vesicle that excites or inhibits another neuron, muscle fiber, or gland cell.
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| Slow Axonal Transport | Moves materials about 15 mm per day. Conveys axoplasm from the cell body toward the axon terminals. Supplies new axoplasm to developing or regenerating axons.
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| Fast Axonal Transport | Move materials 200-400 mm per day. Uses proteins as motors. Moves in both directions.
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| Multipolar Neurons | Usually have several dendrites and one axon. Most neurons in the brain and spinal cord, and all motor neurons.
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| Bipolar Neurons | Have one main dendrite and one axon. Found in the retina, the inner ear, and olfactory area of the brain.
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| Unipolar Neurons | Dendrites and one axon are fused to form a continuous process. Most function as sensory receptors
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| Sensory or Afferent Neurons | Most are unipolar. Contain sensory receptors at the distal ends or are located just after sensory receptors that are separate cells.
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| Motor of Efferent Neurons | Convey action potentials away from the CNS to effectors through cranial or spinal nerves.
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| Interneurons or Association Neurons | Mainly located in the CNS between sensory and motor neurons. Integrate incoming sensory info and elicit a motor response.
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| Neuroglia | Astrocytes, oligodendrocytes, microglia, ependymal cells, Schwann cells and setellite cells.
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| Astrocytes | Contain microfilaments that give them strength and enable thm to support neurons. Processes of astrocytes wrap around capillaries to isolate neurons of the CNS from harmful subs in blood. Blood/Brain Barrier
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| Oligodendrocytes | Form and maintain the myelin sheath around CNS axons.
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| Myelin Sheath | A multilayered lipid and protein covering around some axons that insulates them and increases the speed of nerve impulse conduction.
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| Microglia | Function as phagocytes. Remove cellular debris and phagocytize microbes and damaged tissue.
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| Ependymal Cells | Cuboidal to columnar cells arranged in a single layer that possess microvilli and cilia. Produce, monitor, and assist in the circulation of cerebrospinal fluid.
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| Schwann Cells | Encircle PNS axons. Form myelin sheath. Each myelinates a single axon. Participates in axon regeneration.
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| Satellite Cells | Regulate the exchanges of materials between neuronal cell bodies and interstitial fluid in the PNS
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| Neurolemma | The outer nucleated cytoplasmic layer of the Schwann cell. Found only around axons in the PNS
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| Nodes of Ranvier | Gaps in the myelin sheath.
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| Ganglion | A cluster of neuronal cell bodies located in the PNS.
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| Nucleus | Cluster of neuronal cell bodies located in the CNS.
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| Nerve | A bundle of axons lcated in the PNS.
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| Tract | A bundle of axons that is located in the CNS
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| White matter | Composed primarily of myelinated axons
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| Gray matter | Contains neuronal cell bodies, dendrites, unmyelinated axons, axon terminals, and neuroglia.
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| Graded Potentials | Used for short distance communication only.
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| Action Potentials | Allow communication over long distancse within the body.
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| Resting Membrane Potential | In excitable cells, an electrical potential difference across the membrane.
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| Electrochemical Gradient | A concentration difference plus an elctrical difference. As iions move,they create a flow of electrical current that can change the membrane potential.
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| Leak channels | Randomly alternate between open and closed positions. Typically are more K leak channels than Na leak channels. Membranes permeability to K is higher. Found in nearly all celss.
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| Ligand-gated Channel | Opens and closes in response to the binding of a ligand stimulus. Neurotransmitters, hormones, and particular ions can open or close these. Located in some sensory neurons, and in interneurons and motor neurons.
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| Mechanically Gated Channel | Opens or closes in response to vibration, touch, pressure, or tissue stretching. Found in auditory receptors in the ears, in receptors that monitor stretching of internal organs, and in touch receptors and pressure receptors in the skin.
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| Voltage-Gated Channel | Opens in response to a change in membrane potential (voltage). Participate in the generation and conductin of action potentials in the axons of all types of neurons.
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| Resting Membrane Potential | Exists because of buildup of negative ions along the inside of the membrane and positive ions outside. Such a separation is a form of potential energy.
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| Graded Potential | A small deviation from the membrane potential that makes the membrane either more polarized or less polarized. Mechanically gated or ligand gated channels open or close. The electrical signals vary depending on the strength of the stimulus.
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| Hyperpolarizing Graded Potential | When the response makes the membrane more polarized
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| Depolarizing Graded Potential | When the response makes the membrane less polarized.
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| Decremental Conduction | The mode of travel by which graded potentials die out as they spread along the membrane. Useful for short distance communication only.
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| Summation | The process by which graded potentials add together. It can become stronger and last longer.
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| Depolarizing Phase of an Action Potential | The negative membrane potential becomes less negative, reaches zero, and then becomes positive. The voltage-gated Na+ channels open, and Na+ rushes into the cell. The inside of the membrane becomes more positive than the outside.
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| Repolarizing Phase of an Action Potential | The membrane potential is restored to the resting state of -70 mV. Caused by the voltage-gated K+ channels opening and allowing K+ to flow out. Slowing of Na+ inflow and acceleration of K+ outflow cause the membrane potential to go negative again.
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| After-Hyperpolarizing Phase | The membrane potential temporarily becomes more negative than the resting level. Occurs when the voltage-gated K+ channels remain open after the repolarizing phase ends.
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| Threshold | An action potential occurs in the membrane of the axon of a neuron when depolarization reaches this level. The generation of an action potential depends on whether a particular stimulus reaches this level.
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| Subthreshold Stimulus | A stimulus that is a weak depolarization that cannot bring the membrane potential to threshold.
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| Threshold Stimulus | A stimulus that is just strong enough to depolarize the membrane to threshold.
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| Suprathreshold Stimulus | A stimulus that is strong enough to depolarize the membrane above threshold.
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| All-or-None Principle | Characteristic of action potentials: it either occurs completely or it does not occur at all.
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| Refractory Period | The period of time after an action potential begins during which an excitable cell cannot generate another action potential in ersponse to a normal threshold stimulus.
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| Absolute Refractory Period | Even a very strong stimulus cannot initiate a second action potential. Coincides with the period of Na+ channel activation and inactivation. Graded potientials do not exhibit a refractory period.
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| Relative Refractory Period | The period of time during which a second action potential can be initiated, but only by a larger-than-normal stimulus.
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| Propagation | How information is communicated through action potentials. Not decremental. Depends on positive feedback. The action potential regenerates over and over at adjacent regions of membrane from the trigger zone to the axon terminals.
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| Continuous Conduction | Involves step-by-step depolarization and repolarization of each adjacent segment of the plasma membrane. Occurs in unmyelinated axons and in muscle fibers.
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| Saltatory Conduction | Special mode of action potential propagation that occurs along myelinated axons. Occurs because of uneven distribution of voltage-gated channels. The action potential appears to leap from node to node. Travels faster. Uses less ATP.
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| Factors that Affect the Speed of Propagation | Amount of myelination, Axon diameter (larger axons propagate faster because of larger surface area), and Temperature (propagate slower when cooled).
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| A fibers | Largest diameter axons, mylinated. Conduct at speeds of 12-130 m/sec. Axons associated with touch, pressure, position, thermal and pain sensations, motor neurons that conduct to skeletal muscles.
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| B fibers | Axons that are smaller than A fibers. Myelinated. 15m/sec. Conduct impulses from the viscera to the brain and spinal cord. Constitute all the axons of the autonomuc motor neurons that extend from the brain and spinal cord to the ANS relay stations.
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| C fibers | The smallest axons. Unmyelinated. 0.5-2m/sec. Longest absolute refractory periods. Conduct some sensory impulses for pain, touch, pressure, heat, and cold, and pain from the viscera. Constrict and dilate pupils, increase and decrease heart rate.
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| Frequency of Action Potentials | A light touch generates a low frequency of action potentials. A firmer pressure elicits action potentials that pass down the axon at a higher frequency. Also, a firm pressure stimulates a larger number of pressure-sensitive neurons than does a light touch
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| Graded Potential Characteristics | Arise in dendrites and cell body. Ligand-gated or mech gated channels. Decremental. Amplitude depends on stimulus. Duration is longer. No refractory period; summation can occur.
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| Characteristics of Action Potentials | Arise at trigger zpnes and propagate along axon. Voltage-gated channels. Permit comm over ong distance. Amplitude is all or none. Duration is short. Consists of depolarizing followed by repolarizing. Refractory period present; no summation.
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| Presynaptic Neuron | Refers to a nerve cell that carries a nerve impulse toward a synapse.
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| Postsynaptic Cell | The cell that receies a signal. May be a postsynaptic neuron or an effector cell.
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| Electrical Synapse | Action potentials conduct directly between the plasma membranes of adjacent neurons through structures called gap junctions. Tunnels connect the cytosol of the two cells directly. Common in smooth muscle, cardiac muscle, and in the embryo. Fast, synched.
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| Chemical Synapse | The splasma membranes of presynaptic and postsynaptic neurons are close but do not touch. The presynaptic neuron releases a neurotransmitter that diffuses through the fluid and binds to the postsynaptic neuron.
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| Synaptic Cleft | Space in chemical synapses.
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| Postsynaptic Potential | A type of graded potential produced by the postsynaptic neuron when it receives the chemical signal. The ions change the voltage across the membrane. It may be depolarizing or hyperpolarizing. When a depol potential reaches threshold, action pot triggers.
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| Synaptic Delay | The time required for the processes at a chemical synapse.
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| Voltage-Gated Ca Channels | Open in the synaptic end bulbs of the presynaptic axon. Ca flow inward and triggers the synaptic vesicles to release neurotransmitters.
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| Neurotransmitter Receptors | After the neurotransmitter molecules diffuse across the synaptic cleft, they bind to these receptors on ligand-gated channels, which open and allow particular ions to flow across.
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| Excitatory Postsynaptic Potential | A depolarizing postsynaptic potential.
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| Inhibitory Postsynaptic Potential | A hyperpolarizing postsynaptic potential.
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| Ionotropic Neurotransmitter Receptor | A type of neurotransmitter receptor that contains a neurotransmitter binding site and the ion channel are components of the same protein.
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| Metabotropic Receptor | A type of neurotransmitter receptor that contains a neurotransmitter binding site but lacks an ion channel as part of its structure. A G protein opens or closes an ion channel.
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| Removal of Neurotransmitter | Diffusion (moves away), Enzymatic degradation, Uptake by cells (transported back into the neuron that released them)
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| Spatial Summation | A summation of postsynaptic potentials in response to stimuli thata occur at different locations in the membrane of a postsynaptic cell at the same time.
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| Temporal Summation | Summation of postsynaptic potentials in response to stimuli that occur at the same location in the membrane of the postsynaptic cell but at defferent times.
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| Acetylcholine (ACh) | Neurotransmitter which is released by many PNS neurons and by some CNS neurons. Excitatory or inhibitory.
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| Amino Acids | Serve as neurotransmitters in the CNS. Glutamate and asparate are excitatory. Glutamate works in the brain. GABA and glycine are inhibitory.
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| Biogenic Amines | Norepinephrine, epinephrine, dopamine, and serotonin.
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| Norepinephrine | Plays roles in arousal, dreaming, and regulating mood.
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| Dopamine | Plays roles in emotional responses, addictive behaviors, and pleasurable experiences. Help regulate skeletal muscle tone and movement.
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| Serotonin | Involved in sensory perception, temperature regulation, control of mood, appetite, and the induction of sleep.
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| Neuropeptides | Neurotransmitters consisting of 3-40 aino acids linked by peptide bonds.
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| Enkephalins, Endorphins, Dynorphins. | Opioid peptides. Neuropeptides that relieve pain.
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| Substance P | Neuropeptide released by neurons that transmit pain-related input from peripheral pain receptors into the CNS, enhancing the perception of pain.
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| Neural Circuits | Neurons trhat process specific types of information organized into complicated networks
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| Simple Series Circuit | A presynaptic neuron stimulates a single postsynaptic neuron. The second stimulates another, and so on.
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| Divergence | When a single presynaptic neuron synapses with several postsynaptic neurons.
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| Diverging Ciruit | The nerve impulse from a single prsynaptic neuron causes the stimulation of increasing numbers of cells along the circuit. Sensory signals are arranged this way, allowing a sensory impulse to be relayed to several regions of the brain.
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| Convergence | Several presynaptic neurons synapse with a single postsynaptic neuron. Permits more efective stimulation or inhibition of the postsynaptic neuron.
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| Converging Circuit | The postsynaptic neuron receives nerve impulses from several different sources.
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| Reverberating Circuit | The incoming impulse stimulates the first neuron, which stimulates the second, and so on. Branches from later neurons synapse with the earlier ones, so the impulses are sent back through the circuit again and again.
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| Plasticity | The capability of the nervous system to change based on experience. The sprouting of new dendrites, synthesis of new proteins, and changes in synaptic contacts with other neurons.
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| Regeneration | The capability of the nervous system to repliate or repair themselves. Limited; in the CNS, little to none occurs.
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| Neurogenesis | The birth of new neurons from undifferentiated stem cells. Appears in animals. Happens in the adult human hippocampus, an area crucial for learning.
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| Damage and Repair in the PNS | Axons and dendrites associated with a neurolemma may undergo repair if the cell body is intact, if the Schwann cells are functional, and if scar tissue formation does not occur too rapidly.
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| Chromatolysis | About 24-48 hours after an injury to a process of a peripheral neuron, the Nissl bodies bread up into fine granular masses.
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| Wallerian Degeneration | Degeneration of the distal portion of the axon and myelin sheath. The neurolemma remains. After this Macrophages phagocytize the debris and the axon is regenerated.
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| Regeneration Tube | The Schwann cells on either side of an injured site multiply, grow toward each other and form this. It guides growth of a new axon.
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| The Brain | The center for registering sensations, correlating them with one another and with stored information, making decision, taking action, directing behavior towards others, intellect, emotions, behavior, and memory.
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| Neural Tube | Hollow tube in the ectoderm of the embryological tissue from which the brain and spinal cord arise.
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| The Parts of the Brain | The brain stem, diencephalon, cerebrum, and cerebellum.
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| Protective Covering of the Brain | The brain is protected by the cranial bones and the cranial meninges.
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| The Cranial Meninges | Dura mater, arachnoid, and pia mater. Three extensions of the dura mater separate parts of the brain: the falx cerebri, falx cerebelli, and the tentorium cerebelli.
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| Circle of Willis | Cerebral arterial circle at the base of the brain from which blood flows.
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| Oxyegn in the Brain | Utilizes about 20% of the O2 in the body. One of the most metabolically active organs.
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| Glucose in the Brain | Because carb storage in the brain is limited, the supply of glucose to the brain must be continuous. Deficiency may produce mental confusion, dizziness, convulsions, and unconsciousness.
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| Blood Brain Barrier | Protects brain cells from harmful substances and pathogens by serving as a selective barrier to prevent passage of many substances from the blood to the brain.
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| Blood Brain Barrier Composition | Consists of tight junctions between capillary endothelial cells, thick basement membrane surrounding the capillaries and astrocyte processes that secrete chemicals to maintain permeability.
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| Cerebrospinal Fluid | A clear, colorless liquid that protects the brain and spinal cord against chemical and physical injuries and carries oxygen, glucose, and other needed chemicals from the blood to neurons and neuroglia.
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| CSF Contribution to Homeostasis | Provides mechanical protection, chemical protection, and circulation.
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| How CSF is formed | By filtration of blood plasma from networks of capillaries called choroid plexuses found in the 4 ventricles and circulates through the suarachnoid space, ventricles, and central canal.
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| Blood-Cerebrospinal Fluid Barrier | Materials entering CSF from the choroid capillaries cannot leak between the surrounding ependymal cells, which permit certain substances to enter the fluid but exclude others and protect the brain and spinal cord from harmful elements.
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| Reabsorbtion of the CSF | Reabsorbed into the blood by the arachnoid villi of the superior sagittal blodd sinus. Occurs at the same rate at which CSF is produced in the choroid plexuses, thereby maintaining a relatively constant CSF volume and pressure.
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