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Definition
- Nerve cells that transmit nerve impulses between parts of the nervous system.
- Components: cell body, axon, dendrite
- Dendrites bring electrical impulses to the cell body, axons send electrical impulses away from the cell body.
- Neurons have an all or none response; nerves may have a graded response, depending on how many individual neurons within the nerve fiber.
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| Take nerve signals away from sensory receptors to the CNS |
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| Lie in the CNS and carry nerve impulses within the CNS |
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| take nerve impulses away from the CNS and take them to an effector (i.e. muscles & glands) |
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- Cells that service the neurons in some way, nutritive or supportive functions.
- Schwann cells are a specialized neuroglial cell that form so-called myelinated nerves.
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Definition
- Many axons are covered by a type o neuroglia classed Schwann cells. Schwann cells contain myelin (a lipid substance) that forms an 'onion skin' wrapping around nerve axons or dendrites. They electrically insulate them from the exterior except for at gaps called Nodes of Ranvier in the PNS.
- Surrounding th emyelin layer is a neurilemma or cellular sheath.
- If nerve cells are damaged, the neurilemma acts as a pathway for neuron regeneration.
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Term
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Definition
- A resting neuron has potential energy (like an unused cell phone) called resting potential when a neuron is not conducting a nerve impulse. -65 mV
- The energy exists b/c the cell membrane is polarized, positively charged ions are stashed outside the cell and negatively charged ions are in the inside of the cell.
- Positively charged Na+ ions are on the outside of the axons cell membrane
- Positively charged K+ diffuse out of the cell contributing to the positive charge.
- The inside of the cell is negative because of the presence of large negatively charged proteins and other molecules stuck inside the cell because of their size (selective permeability)
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Term
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Definition
- Polarity change in the axons of neurons
- During action potential a stimulus (i.e. being pricked by a pin) causes the neuron to reach its threshold, increase from -65 to -40 mV.
- The stimulus must be strong enough to cause the cell to reach threshold.
- Action potential is an all-or-nothing event. Once threshold is reached, the action potential happens automatically and completely.
- Increasing the strength of a stimulus (pressing harder with the pin) won't change the strength of an action potential. However it may cause more action potentials to occur in a given period (i.e. the person will perceive that pain has increased)
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Term
| Depolarization: Sodium Gates Open |
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Definition
- Called depolarization because the charge inside the axon (its polarity) changes from negative to positive, +40 mV.
- Protein channel specific for sodium ions are located in the cell membrane of the axon.
- When an action potential begins these protein channels open and Na+ ions rush into the cell.
- Adding these positively charged Na+ causes the inside of the axon to become positive compared to the outside.
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Definition
- Called repolarization because the inside of the axon resumes a negative charge.
- Potassium gates open due to depolarization and sodium gates close almost immediately after.
- Potassium flows rapidly from the inside of the neuron to the outside. As positively charged K+ exit the axon the inside of the cell becomes negative again (due to the large negatively charged ions trapped inside the cell) and the outside positive.
- When the sodium-potassium pump completes the action potential potassium is returned to the inside of the axon and sodium to the outside, resting potential is restored.
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Term
| propagation of an action potential |
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Definition
- Saltatory conduction: In myelinated nerve fibers, an action potential at one Node of Ranvier causes an action potential at the next node, jumping over the enter myelin-coated portion of the axon. This action is much faster.
- If an axon is completely unmyelinated, an action potential at one local stimulates an adjacent part part of the axon membrane to produce an action potential. Conduction along the entire axon in this fashion can by rather slow b/c each section of the axon must be stimulated.
- Regardless of whether an axon is myelinated or not, its action potentials are self-propagating. Each action potential generates another along the entire length of the axon.
- Like the action potential itself, conduction of an action potential is an all-or-none event--either an axon conducts its action potential or it doesn't. The intensity of a message is determined by how many action potentials are generated within a given time.
- The volley of action potential are very quick b/c only a small number of ions are exchanged with each action potential.
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Definition
- The short period of time as soon as the action potential has passed by each successive portion of an axon, during which nerve conduction is not possible.
- This ensure the one-way direction of a signal from the cell body down the length of the axon to the axon terminal.
- During this period the Na+ and K+ pump restores ionic balances to resting value.
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Term
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Definition
- Passing a nerve signal from one neuron to another.
- Axons branch into many small ending each tipped with an axon terminal.
- Axon terminals come in very close contact with either the dendrite or cell body of another neuron.
- The region of close proximity between them is called a synapse.
- At the synapse is a small gap called the synaptic cleft which separates the sending neuron from the receiving neuron.
- Neurotransmitters carries out transmisson across a synapse.
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Term
| Release of Neurotransmitter |
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Definition
- Nerve signals traveling along an axon reach an axon terminal.
- Ca2+ ions enter the terminal and stimulate synaptic vesicles to merge with the plasma membrane of the sending neuron.
- Neurotransmitter molecules, acetylcholine (ACh) and norepinephrine (NE), release into the synaptic cleft and diffuse across the cleft to the receiving membrane. There neurotransmitter molecules bind with specific receptor proteins.
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| Neurotransmitters Bind to Receptors |
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Definition
- Can have either an excitatory or inhibitory response.
- Excitation occurs because the neurotransmitter has caused the Na+ gate to open and Na+ to diffuse into the receiving neuron. Thus causing membrane potential to move in a positive direction (possible leading to action potential).
- Inhibition occurs when a neurotransmitter causes K+ to enter the receiving neuron. It causes the membrane potential to become more negative and decrease the likelihood of an action potential.
- In sufficient neurotransmitter binding, a threshold for an action potential is exceeded and an action potential occurs.
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Term
| Removal of Neurotransmitters |
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Definition
- Once a neurotransmitter has been released into a synaptic cleft and has initiated a response, it is removed from the cleft.
- In some synapses the receiving membrane contains enzymes that rapidly inactivate the neurotransmitter. For example ACh is rapidly broken down by Acetylcholinesterase (AChe).
- In other synapses the sending membrane rapidly reabsorbs the neurotransmitter, possibly for repackaging in synaptic vesicles or for molecular breakdown.
- THe short existence of neurotransmitters at a synapse prevents continuous stimulation (or inhibition) of receiving membranes. The receiving cell needs to be able to respond quickly to changing conditions. If the neurotransmitter were to linger in the cleft, the receiving cell would be unable to respond to a new signal from a sending cell.
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Term
| Integration of Signals at Synapses |
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Definition
- Whether or not a neuron will fire depends on the sum of excitatory and inhibitory signals.
- A given neuron may synapse with many other neurons through its dendrites.
- Each synapse can be either excitatory or inhibitory.
- If total excitatory if greater than inhibitory at any given moment and exceed threshold, the neuron will fire action potential.
- Integration is the summing up of excitatory and inhibitory signals.
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Term
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Definition
- Drugs interfere with the action of neurotransmitters.
- A local anesthetic may block the release of an excitatory neurotransmitter.
- Anti-depressants might alter the reuptake or prevent breakdown of an excitatory neurotransmitter.
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Term
| Peripheral nervous System (PNS) |
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Definition
- Contains the nerves that carry signals to and from the CNS.
- Nerves consist of long axons, projecting from the CNS, or long dendrites of many neurons bundled together.
- Cell bodies and the dendrites of neurons are usually found in the CNS or in ganglia (local clusters of nerve cell bodies in the PNS).
- Includes the Somatic System & Autonomic System
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Term
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Definition
- Cranial nerves (12 pairs)
- Nerves that originate in the brain.
- Nerves for head, neck, and facial regions
- Vagus nerve is an exception, serves many internal organs as well as the pharynx & larynx.
- Include sensory and motor nerves as well as mixed nerves that contain both.
- Spinal nerves (31 pairs)
- Originate in spinal column
- Roots on a spinal nerve physically separate the axons of sensory neurons from the axons of mother neurons.
- Dorsal root of spinal nerves contain dendrites of sensory neurons bringing impulses to the spine.
- Ventral roots of a spinal nerve contain axons of motor neurons carrying impulses away from the spine.
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Term
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Definition
- Reflexes are automatic responses to things in the environment that do not necessarily involve the brain (i.e. eye blinking, knee reflex)
- If your hand touches a sharp pin sensory receptors in the skin generate nerve signals that move along sensory receptors in the skin, generate nerve signals that move along sensory fibers through the dorsal-root ganglia toward the spinal cord.
- Sensory neurons that enter the cord dorsally pass signals to many interneurons in the spinal cord. Some of these interneurons synapse with motor neurons whose shot dendrites and cell bodies are in the spinal cord.
- Nerve signals travel along these motor fibers to an effector which brings a/b a response to the stimulus. (i.e. In this case the effector is a muscle which contracts so that you withdraw your hand from the pin)
- This whole series of responses occurs because some of the interneurons involved carry nerve signals to the brain. The brain makes you aware of the stimulus and directs these other reactions to it. One doesn’t feel pain until the brain receives the information and interprets it.
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Term
| Autonomic System (think automatic) |
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Definition
- Occurs in the PNS
- Regulates the activity of cardiac and smooth muscles, organs, and glands.
- Center for integration is the hypothalamus.
- Divided into the sympathetic and parasympathetic divisions.
- Activation of these two systems generally causes opposite responses.
- They both function automatically and usually in an involuntary manner, innervate all internal organs, and use two neurons and one ganglion for each impulse
- The first neuron has a cell body within the CNS and a preganglionic fiber that enters the ganglion.
- The second neuron has a cell body within a ganglion and a postganglionic fiber that leaves the ganglion
- Motor neurons are responsible for automatically controlling internal organs
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Term
| Sympathetic System (Fight or Flight) |
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Definition
- Preganglionic fibers arise from the middle, or thoracolumbar, portion of the spinal cord. They terminate almost immediately in ganglia that lie near the cord.
- Therefore in this division the preganglionic fiber is short but the postganglionic fiber that contacts an organ is long.
- Accelerates the heartbeat and increases the breathing rate by dilating the bronchi—active muscles, after all, require ready supply of glucose and oxygen
- Inhibit the digestive organs as well.
- Neurotransmitter in sympathetic system is primarily norepinephrine (NE) which similar to the drug epinephrine a.k.a. adrenaline
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Term
| Parasympathetic System (Rest & Digest) |
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Definition
- Includes some cranial nerves (i.e. the vagus) as well as fibers that arrive from the sacral (bottom) portion of the spinal cord.
- Preganglionic fibers are long and the postganglionic fiber short because the ganglia lie near or within the organ
- Promotes all the internal responses associated with a relaxed state.
- Pupils contract
- Heartbeat slows down
- Digestion promoted
- Neurotransmitter is primarily acetylcholine
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Term
| Central Nervous System (CNS) |
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Definition
- The spinal cord and brain make up the CNS where sensory information is received and motor control is initiated.
- Nerves in the CNS are protected by three layers of membranes called meninges (hence meningitis)
- Spaces between the meninges are filled with cerebrospinal fluid which protects neurons in the CNS from physical shocks.
- Spaces in brain called ventricles also contain cerebrospinal fluid
- The CNS is composed of two types of nervous tissue—gray matter (contains nonmyelinated fibers) bodies and short, and white matter (contains myelinated axons that run together in bundles called tracts)
- The spinal cord transmits messages to and from the brain and coordinates reflex responses.
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Term
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Definition
- Central Canal
- Contains Cerebrospinal fluid
- Gray matter:
- Consists of unmyelinated fibers and cell bodies
- Centrally located
- Contains portions of sensory neurons and motor neurons
- White matter consists of
- Long fibers of myelinated interneurons running up and down the spinal cord connecting the spinal cord to the brain.
- Dorsal tracts carry information to the brain.
- Ventral tracts carry information from the brain.
- Center for many reflex arcs
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