Term
| the nervous system is divided into two parts the 1) __________, composed of the brain and spinal cord, and 2)the __________, consisting of the nerves that connect the brain or spinal cord with the body's muscles, glands, and sense organs. |
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Definition
1) the central nervous system (CNS)
2) the peripheral nervous system |
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Term
| the basic unit of the nervous system is the individual nerve cell, or ________ |
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Definition
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Term
neurons operate by generating electrical signals that move from one part of the cell to another part of the same cell or the neighboring cells.
in most neurons, the electrical signal causes the release of chemical messengers ____________ to communicate with other cells or with effectors |
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Definition
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Term
| integrator (or integrating center) |
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Definition
cells that receive one or more signals and send out appropriate response
...
most neurons serve as integrators because their output reflects the balance of inputs they receive from thousands or hundreds of thousands of other neurons that impinge upon them |
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Term
| long extensions or __________ connect neurons to each other and perform the neuron's input and output functions. |
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Definition
1) processes
-most neurons contain a cell body and two types of processes -dendriteds and axons |
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Term
| a neuron's _________ contains the nucleus and ribosomes and thus has the genetic information and machinery necessary for protein synthesis. |
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Definition
| 1) cell body (a.k.a soma) |
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Term
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Definition
-highly branched extension of neuron cell body; receives synaptic input from other neurons
....they and the cell body receive most of the inputs from other neurons, with the dendrites taking a more important role in this regard than the cell body. |
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Term
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Definition
| -extension from neuron cell body; propagates (spreads) action potentials away from the cell body |
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Term
the "trigger zone" where, in most neurons, the electrical signals are generated
..it's also a region where the axon connects to the cell body |
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Definition
axon hillock (or initial segment)
...the signals they generate then propagate away from the cell body along the axon, or sometimes, back along the dendrites. |
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Term
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Definition
| end of axon; responsible for releasing neurotransmitters from the axon. these chemical messengers diffuse across an extracellular gap to the cell opposite the terminal --> (in other words, axon terminal forms synaptic or neuroeffector junction with postjunctional cell) |
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Term
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Definition
insulating material covering axons of many neurons; consists of layers of myelin-forming cell plasma membrane wrapped around axon
-the myelin sheath speeds up conduction of the electrical signals along the axon and conserves energy |
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Term
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Definition
| movement of a substance or action potential in the forward direction from a neuron's dendrites and/or cell body, toward the axon terminal |
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Term
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Definition
| movement of a substance or action potential backward along a neuron, from axon terminals toward the cell body and dendrites |
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Term
| neurons are divided into three functional classes, what are they? |
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Definition
1) afferent neurons
2) efferent neurons
3) interneurons |
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Term
| afferent neurons (sensory) |
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Definition
- transmit information INTO the CNS from receptors at their peripheral endings
-cell body and the long peripheral process of the axon are in the peripheral nervous system; only the short central process of the axon enters the CNS
-most have no dendrites (do not receive inputs from other neurons) |
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Term
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Definition
- transmit information OUT of the CNS to effector cells, particularly muscles, glands, or other neurons
-cell body, dendriteds, and a small segment of the axon are in the CNS; most of the axon is in the peripheral nervous system |
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Term
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Definition
-function as integrators and signal changers
-integrated groups of afferent and efferent neurons into reflex circuits
-connects neurons and lies entirely WITHIN the CNS
-account for 99% of all neurons |
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Term
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Definition
| a cell or portion of a cell that contains structures of chemical molecules sensitive to changes in an energy form in the outside world or internal environment; in response to activation by this energy, the sensory receptor initiates action potentials in that cell or an adjacent one |
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Term
| _________ neurons propagate electrical signals from their receptors into the brain or spinal cord |
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Definition
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Term
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Definition
-groups of afferent and efferent neurons of the peripheral nervous system.
(*a nerve fiber is a single axon, and a nerve is a bundle of axons (fibers) bound together by connective tissue)
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Term
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Definition
programmed cell death that typically occurs during differentiation and development
(as many as 50-70 percent of neurons undergo apoptosis) |
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Term
| neurotransmitters, which are released by a _________ neuron and combine with protein receptors on a _________ neuron, transmit information across a synapse |
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Definition
1) presynaptic
2) postsynaptic |
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Term
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Definition
knee-jerk reflex elicited by tapping below the kneecap requires no interneurons --the afferent neurons interact directly with efferent neurons...
..it does not reach the CNS |
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Term
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Definition
the anatomically specialized junction between two neurons where one neuron alters the electrical and chemical activity of another.
...most synapses occur between an axon terminal of one neuron and a dendrite or the cell body of a second neuron. (but sometimes synapses occur between two dendrites or between a dendrite and a cell body or between an axon terminal and a second axon terminal) |
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Term
| a neuron that conducts a signal TOWARD a synapse is called __________, whereas a neuron conducting signals AWAY from a synapse is _________ |
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Definition
1) presynaptic neuron
2) postsynaptic neuron |
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Term
| why does resting potential exists? |
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Definition
| ..because of a tiny excess of negative ions inside the cell and an excess of positive ions outside. |
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Term
the concentration differences for sodium and potassium are established by the action of the sodium-potassium pump (Na+/K+ -ATPase)
that pumps sodium out of the cell and potassium into it |
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Definition
the concentration differences for sodium and potassium are established by the action of the sodium-potassium pump (Na+/K+ -ATPase)
that pumps sodium out of the cell and potassium into it |
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Term
| the magnitude of the resting potential depends mainly on two factors: |
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Definition
1) differences in specific ion concentrations in the intracellular and extracellular fluids
2) differences in membrane permeabilities to the different ions, which reflect the number of open channels for the different ions in the plasma membrane. |
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Term
equilibrium potential
(*no net movement of the ion because the opposing fluxes are equal...the potential will undergo no further change). |
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Definition
| the voltage difference across a membrane that producess a flux of a given ion species that is equal but opposite to the flux due to the concentration gradient of that same ion species |
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Term
ion channels are voltage-gated...
and ligand-gated |
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Definition
-that is, it activates/inactivates depending on the voltage gradient of the plasma membrane
-that is, it activates/inactivates depending on the binding of ligands to the channel |
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Term
| when a pump moves net charge across the membrane and contributes directly to the membrane potential, it is known as _________ |
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Definition
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Term
| changes in the membrane potential from its resting level produce electrical signals. these signals are: |
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Definition
GRADED POTENTIALS and ACTION POTENTIALS
**these changes are the most important way that nerve cells process and transmit information
Graded potentials are important in signaling over SHORT distances, whereas Action potentials are the LONG-distance signals of nerve and muscle membranes |
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Term
| what are the three terms used to describe the direction of changes in the membrane potential relative to the resting potential? |
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Definition
| DEPOLARIZE, REPOLARIZE, and HYPERPOLARIZE |
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Term
| "polarized" simply means... |
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Definition
that the outside and inside of the cell have a different net charge..
e.g.: -70 mV, is polarized |
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Term
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Definition
| the membrane is depolarized when its potential becomes LESS NEGATIVE (closer to zero) than the resting level... so that the cell interior becomes LESS negative than the resting level |
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Term
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Definition
| overshoot refers to a reversal or the membrane potential polarity --that is, when the inside of a cell becomes positive relative to the outside |
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Term
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Definition
| return transmembrane potential to its resting level |
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Term
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Definition
| voltage difference between inside and outside of cell in absense of excitatory or inhibitory stimulation |
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Term
| when the potential is MORE NEGATIVE than the resting level, the membrane is __________ |
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Definition
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Term
| changes in membrane potential that the neuron uses as signals occur because.... |
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Definition
| ...of changes in the permeability of the cell membrane to ions. |
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Term
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Definition
| changes in membrane potential that are confined (limited) to a relatively small region of the plasma membrane |
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Term
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Definition
| increase in muscle tention or shortening in response to rapid, repetitive stimulation relative to single twitch |
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Term
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Definition
ability to generate action potentials
...only excitable membranes can conduct action potentials. the propagation of action potentials down the axon is the mechanism the nervous system uses to communicate over long distances |
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Term
| mechanically gated channels |
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Definition
| open in response to physical deformation (stretching) of the plasma membranes |
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Term
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Definition
| give a membrane the ability to undergo action potentials. |
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