Term
| Describe the concept of the channel as a gate or door. |
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Definition
| Part of the integral protein that forms such a channel may act as a gate or door, opening and closing on demand, to alter the flow of ions along their diffusion gradient. |
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Term
| A cell that exhibits a membrane potential is called |
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Definition
| a polarized cell or has a polarized membrane. |
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Term
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Definition
| a general term for any nerve process (sensory dendrite or motor axon). |
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Term
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Definition
| a bundle of many nerve fibers, both sensory and motor, that course along the same path in the PNS. |
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Term
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Definition
| a bundle of related nerve fibers in the CNS that connects different areas of the CNS. |
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Term
Association neurons (interneurons)
(Major Neuron Type) |
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Definition
| The cell bodies and dendritic zones of association neurons are always located within the gray matter of the CNS. Their dendrites receive input from the sensory neurons and their axons carry that information to other locations within the CNS. They “associate” sensory input with integration, interpretation, and motor functions. |
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Term
| Assuming that there is a diffusion gradient, what happens when a channel opens? |
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Definition
| When the channels are open, specific ions in the intracellular fluid or the extracellular fluid flow through them, according to their diffusion gradients. |
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Term
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Definition
| attach blood vessels to neurons, helping to form the blood-brain barrier. They help maintain the proper balance of K+ for the neurons and participate in the metabolism of neurotransmitters. They are responsible for forming scars in the CNS after injury. |
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Term
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Definition
| a single, long, thin, cylindrical projection from the cell body that moves toward an effector or another neuron. It ALWAYS carries the nervous message away from the cell body. |
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Term
Axon collateral
(Axonal Structure) |
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Definition
| Along the axon’s length, side branches called axon collaterals may depart from the main axon to innervate other structures. |
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Term
Axon hillock
(Axonal Structure) |
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Definition
| The axon hillock, a cone-shaped elevation, is that region of the neuronal cell body from which the axon arises. |
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Term
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Definition
| have a single dendrite and a single axon extending from the cell body; associated with the special senses. |
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Term
Cell body
(Cell Structure) |
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Definition
| contains typical cellular organelles surrounded by cytoplasm. There is a large nucleus with a very prominent nucleolus and neurofibrils, elements of the cytoskeleon that give the neuron structure and shape. |
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Term
| Communication by neurons depends upon two basic properties of their cell membranes. List them. |
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Definition
1. There is an electrical voltage, called the resting membrane potential (RMP), across the cell membrane.
2. Their cell membranes contain a variety of ion channels (pores) that may be open or closed. |
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Term
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Definition
| The dendrite is usually a short, tapering, and highly branched process extending from the cell body; usually unmyelinated (sensory dendrites are the exception). It is ALWAYS a process that carries the nervous message towards the cell body. |
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Term
| Describe the central nervous system. |
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Definition
| The CNS consists of the brain and the spinal cord, within which incoming sensory information is processed, thoughts and emotions are generated, and memories are stored. Most nerve impulses that stimulate muscle contraction and glandular secretion originate in the CNS. |
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Term
| Describe the peripheral nervous system. |
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Definition
| The PNS consists of 12 pairs of cranial nerves associated with the brain and 31 pairs of spinal nerves associated with the spinal cord. |
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Term
| Describe the somatic nervous system. |
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Definition
| The somatic nervous system is concerned with sensory information from the skin, skeletal muscles, and special senses, and motor information to the skeletal muscle only. |
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Term
End bulbs
(Axonal Structure) |
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Definition
| The tips of the axon terminals swell into bulb-shaped synaptic end-bulbs that contain synaptic vesicles filled with a chemical known as a neurotransmitter. Most neurons utilize a single type of neurotransmitter. |
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Term
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Definition
| form a continuous epithelial lining for the ventricles of the brain and the central canal of the spinal cord. They probably assist in the circulation of cerebrospinal fluid, but their role is mostly unknown. |
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Term
| How does the nervous system accomplish its homeostatic role? |
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Definition
| These reactions, carried out by electrical messages called nerve impulses (action potentials), allow for second-to-second adjustments in homeostasis. |
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Term
| How does the role of the endocrine system compare with that of the nervous system? |
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Definition
| The endocrine system, using blood-borne chemical messengers called hormones, controls long-term homeostasis. Rather than making second-to-second adjustments, the endocrine system controls processes over days, weeks, months, and years. |
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Term
| How is it formed in the PNS? |
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Definition
| Schwann cells form the myelin sheath around motor axons and sensory dendrites during fetal life and the first postnatal year. In this process, Schwann cells line up along the length of the nerve fiber, attach to it, then begin to spiral around it, leaving behind multiple layers of glial cell membrane. |
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Term
| How is the resting membrane potential related to the formation of a polarized membrane? |
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Definition
| The greater the difference in charge across the membrane, the larger the membrane potential (voltage). |
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Term
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Definition
| small phagocytic cells that engulf and destroy microbes and cellular debris in the CNS. They migrate to areas of injured nervous tissue and help to clean the area. |
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Term
Motor (efferent) neurons
(Major Neuron Type) |
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Definition
| he cell bodies of motor neurons are located in the gray matter of the CNS. Their axons pass out of the CNS into either spinal or cranial nerves to innervate skeletal muscles, cardiac muscle, smooth muscle, or glands. |
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Term
Multipolar
(Neuronal Type) |
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Definition
| usually have several dendrites and a single axon; most neurons are of this type. (motor neurons and association neurons) |
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Term
| Name the autonomic subdivisions. |
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Definition
| The motor portion of the autonomic nervous system is divided into two portions: the sympathetic nervous system and the parasympathetic nervous system. |
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Term
| Name the two principal divisions of the nervous system. |
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Definition
central nervous system (CNS)
peripheral nervous system (PNS) |
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Term
Nissl substance
(Cell Structure) |
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Definition
| Scattered throughout the cytoplasm of the cell body are structures called Nissl bodies (chromatophilic substance), orderly arrays of rough endoplasmic reticulum used for protein synthesis. |
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Term
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Definition
| give support to neurons of the CNS. They produce the myelin sheath found around axons of the CNS. Each oligodendrocyte uses its processes to wrap several axons. |
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Term
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Definition
| upport neurons found in ganglia in the PNS; function is obscure. |
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Term
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Definition
| also known as neurolemmocytes, produce the myelin sheath around the axons of motor neurons and the dendrites of sensory neurons in the PNS. |
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Term
Sensory (afferent) neurons
(Major Neuron Type) |
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Definition
| The dendrites are associated with receptors in the periphery of the body. They pass through either spinal or cranial nerves towards the CNS. Their cell bodies are located in ganglia just outside the CNS and their axons pass into the CNS where they synapse. |
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Term
Telodendrion
(Axonal Structure) |
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Definition
| At their terminations with effectors, the axon and axon collaterals end by dividing into many fine processes called axon terminals or telodendria. |
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Term
| The autonomic nervous system. |
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Definition
| The autonomic nervous system carries sensory information from the viscera to the CNS and motor information from the CNS to cardiac muscle, smooth muscles, and glands. |
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Term
| The nervous system is the body’s control center and communication network. What three functions does it serve? |
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Definition
1. senses changes in the environment, both internal and external
2. integrates and interprets the sensory input for understanding
3. responds by initiating muscular contractions or glandular secretions |
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Term
Trigger zone
(Axonal Structure) |
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Definition
| Just distal to the axon hillock is an area called the trigger zone where nerve impulses arise for propagation along the axon. This area of membrane is rich with voltage-gated sodium channels (to be described later). |
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Term
|
Definition
| have a single process extending from the cell body called the central process that divides into two parts. The axonal portion carries an impulse away from the cell body; the dendritic portion is attached to a receptor distally and carries an impulse to the cell body. |
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Term
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Definition
| The output component of the PNS consist of nerve cells called motor (efferent) neurons that originate in the CNS and conduct nerve impulses away from the CNS to the effectors. |
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Term
| What are neuroglial cells? |
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Definition
| Neuroglial cells are the supportive, nurturing, and protective cells for the neurons. They occupy only half of the CNS, are much smaller than neurons and outnumber them. They remain mitotic throughout life and tend to fill in spaces of injured neurons after disease and injury. |
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Term
| What are sensory neurons? |
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Definition
| The input component of the PNS consists of nerve cells called sensory (afferent) neurons that conduct nerve impulses from sensory receptors to the CNS and end within the CNS. |
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Term
| What are the nodes of Ranvier? |
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Definition
| At intervals along the length of a nerve process, between the individual Schwann cells (PNS) or pieces of oligodendrocytes (CNS), are gaps in the myelin sheath called the nodes of Ranvier (neurofibral nodes). |
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Term
| What is a membrane channel? |
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Definition
| A membrane channel (pore) allows a specific substance to move through a water-filled passageway to either enter or leave the cell. In neuronal membranes, sodium and potassium channels are of utmost importance. |
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Term
| What is current? What are the paths for ion flow through the neuronal membrane? |
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Definition
The resting membrane potential (RMP) serves as a type of battery. Flow of the electrical charges is called current.
In living cells, this current is created when the ions flow across the membrane.
Since the lipid bilayer is a good insulator, the main paths for current flow across the membrane are the ion channels.
Thus, when the ion channels are open in the membrane, current flows and this changes the membrane potential. |
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Term
| What is its function of the myelin sheath? |
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Definition
The sheath electrically insulates the nerve fiber, greatly increasing the speed of nerve impulse conduction.
Nerve processes with such a covering are said to be myelinated while those without are unmyelinated. Therefore, there are neurons with different speeds of transmission. |
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Term
| What is the function of neurons? |
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Definition
| Nerve cells, called neurons, are responsible for conducting impulses from one part of the body to another and are therefore the structural and functional units of the nervous system. |
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Term
| What is the myelin sheath |
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Definition
| Most nerve fibers are surrounded by a multilayered lipoprotein produced by the neuroglia (Schwann cells in the PNS and oligodendrocytes in the CNS) called the myelin sheath. |
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Term
|
Definition
| As the multiple layers of membrane are formed, the cytoplasm and organelles of the Schwann cells are pushed to the outside. This portion of the Schwann cell is known as the neurilemma. It is found only around neurons of the PNS; oligodendrocytes do not form a neurilemma. |
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Term
| What is the relationship between the two systems? |
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Definition
| Cranial and spinal nerves of the PNS carry sensory information from the CNS to effectors (muscles and glands) in the periphery. |
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Term
| What is the resting membrane potential? |
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Definition
| The resting membrane potential (RMP) occurs because there is a small build up of negative charges just inside the cell membrane of the neuron and an equal build up of positive charges outside. |
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Term
| gray matter vs. white matter |
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Definition
In a section of fresh brain and spinal cord, some regions appear white and glistening while others are grayish. The gray areas are the gray matter of the CNS, areas of nerve cell bodies, dendrites, axon terminals, and/or unmyelinated axons, and neuroglia.
The whitish areas are the white matter of the CNS; this refers to aggregations of the myelinated processes of many neurons, arranged into tracts. |
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Term
|
Definition
A nucleus is a collection of similar neuronal cell bodies and dendrites within the gray matter of the CNS that perform a specific function. These collections of neurons are often called centers.
A ganglion is a collection of similar neuronal cell bodies outside the CNS, lying in the periphery. Ganglia contain the cell bodies of sensory neurons or the second neuronal cell body of an autonomic pathway. |
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Term
|
Definition
| An ______ is a specific membrane protein structure that allows only a specific substance to pass through the membrane while excluding others. |
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Term
|
Definition
(non-gated) channels are always open
(glucose channels, for example) |
|
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Term
|
Definition
channels open and close in response to
some sort of stimulus: voltage, chemical, mechanical, light |
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Term
| Voltage-gated (or regulated) channels |
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Definition
| open in response to a direct change in the membrane potential (voltage). |
|
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Term
|
Definition
| the ability to respond to certain types of stimuli by producing impulses. |
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Term
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Definition
| The __________ for a particular neuron is the place where the voltage-gated ion channels are clustered most densely. |
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Term
| Chemically Gated Channels |
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Definition
| open and close in response to specific chemical stimuli, such as neurotransmitters and hormones. |
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Term
| Mechanically gated ion channels |
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Definition
| open or close in response to mechanical stimuli such as touch, pressure, or vibration (sensory receptors). |
|
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Term
|
Definition
| close in response to light energy (found only in the photoreceptors of the eyes). |
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Term
|
Definition
| The presence of chemical-,mechanical-, or light-gated channels allows for a graded response, an electrical response that varies in size, depending on how many channels are opened and for how long. This is ultimately translated into the number of action potentials created in the sensory neurons per unit time. |
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Term
| action potential (nerve impulse) |
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Definition
| During an _______________, two types of voltage-gated ion channels open and then close, first the channels for Na+, then those for K+. |
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Term
|
Definition
| Rapid opening of the voltage-gated Na+ channels results in _________, the loss and then reversal of the membrane polarization by the neuron. |
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Term
|
Definition
| The slower opening voltage-gated K+ channels and the closing of the previously open Na+ channels result in _________, the recovery of the resting membrane potential. |
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Term
|
Definition
| The period of time during which an excitable cell (muscle or neuron) cannot generate another action potential is called the |
|
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Term
| absolute refractory period |
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Definition
| The _______________ refers to the time period during which a second stimulus cannot initiate a second action potential. It coincides with Na+ channel activation and inactivation. |
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Term
|
Definition
| A single neuron, like a single muscle fiber, generates an action potential according to the |
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Term
|
Definition
| The point of communication between cells, either neuron-neuron or neuron-effector |
|
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Term
|
Definition
| the neuron sending the signal is the |
|
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Term
|
Definition
| the neuron receiving the message is the |
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Term
|
Definition
| When the summation is the result of several presynaptic neurons releasing their neurotransmitter into the trigger zone within the same time frame, it is called |
|
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Term
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Definition
| When summation results from buildup of neurotransmitter released by a single presynaptic neuron firing several times in rapid succession, the result is called |
|
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Term
|
Definition
| is in a chemical class by itself. It is the most common neurotransmitter and can be excitatory or inhibitory, depending upon the location in the body. |
|
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Term
|
Definition
| is used in 75% of the excitatory synapses of the brain. (Excitatory amino acids) |
|
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Term
|
Definition
| is an excitatory neurotransmitter of the spinal cord. (Excitatory amino acids) |
|
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Term
|
Definition
| is the most common inhibitory neurotransmitter in the spinal cord. (Inhibitory amino acids) |
|
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Term
| GABA (gamma amino butyric acid) |
|
Definition
| is the most common inhibitory neurotransmitter in the brain. (Inhibitory amino acids) |
|
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Term
|
Definition
| The neurotransmitter may diffuse through the extracellular fluid and away from the synapse. |
|
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Term
|
Definition
| There may be specific enzymes present in the synaptic cleft or on the postsynaptic membrane to degrade the neurotransmitter. |
|
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Term
|
Definition
| In some cases the neurotransmitter is actively transported back into the presynaptic neuron and reused. |
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Term
|
Definition
| In a diverging circuit, a single presynaptic neuron synapses with more than one postsynaptic neuron, in a process called |
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Term
|
Definition
| The simplest circuit is the ______ in which a single presynaptic neuron synapses with a single postsynaptic neuron, which stimulates another, which stimulates another, etc. |
|
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Term
|
Definition
| have a single synaptic neuron that diverges, then each neuron in the pathway synapses on a common postsynaptic neuron |
|
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Term
|
Definition
| branches from neurons later in a pathway synapse with neurons found earlier in the pathway |
|
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Term
|
Definition
| several presynaptic neurons with a single postsynaptic neuron, in a process known as |
|
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Term
|
Definition
| is used extensively by the sympathetic nervous system. It can be either excitatory or inhibitory, depending upon its location. |
|
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Term
|
Definition
| has actions similar to norepinephrine. |
|
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Term
|
Definition
| may be excitatory or inhibitory, depending upon its location. It is important in mood elevation and basal ganglia control of skeletal muscle function. |
|
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Term
|
Definition
| is involved in alertness, sleepiness, and mood control. |
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Term
|
Definition
| The functions of _______ as a neurotransmitter are obscure. |
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Term
|
Definition
|
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Term
| Enkephalins and endorphins |
|
Definition
| are endogenous opioids that function in relief of pain. |
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Term
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Definition
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