Nerve cells that conduct messages are called (1) ____. (2) _____ cells, which support and nurture the activities of neurons, make up less than half the volume of the nervous system. (3) _______ neurons respond to specific kinds of environmental stimuli, (4) ______ connect different neurons in the spinal cord and brain, and (5) ______ neurons are linked with muscles or glands. All neurons have a (6) _______ ________ that contains the nucleus and the metabolic means to carry out protein synthesis. (7) _______ are short, slender extensions of the (6), and together these two neuronal parts are the neurons’ “input zone” for receiving (8) _____. The (9) _____ is a single long, cylindrical extension away form the (10) ______; in motor neurons, the (11) ______ has finely branched (12) ________ that erminate on muscle or gland cells and are “output zones,” where messages are sent on to other cells.
A neuron at rest establishes unequal electric charges across its plasma membrane, and a(n) (13) ____ ____ is maintained. Another name for (13) is the (14) _____ _____ _____; it represents an ability for the membrane to be disturbed. Weak disturbances of the neuronal membrane might set off only slight changes across a small patch, but strong disturbances can cause a(n) (15) _______ ______, which is an abrupt, short-lived reversal in the polarity of charge across the plasma membrane of the neuron. For a fraction of a second, the cytoplasmic side of a bit of membrane becomes positive with respect to the outside. The (16) ______ that travels along the neural membrane is nothing more than short-lived changes in the membrane potential.
D. cell body
K. signals (stimuli)
L. voltage differential
M. resting membrane potential
N. action potential
Complete the paragraph with the correct term listed below (some may be used more than once). *continued paragraphs from the above question #9*
How is the resting membrane potential established, and what restores it between action potentials? The concentrations of (1) ______ ions (K+), sodium ions (2) (_____+), and other charged substances are not the same on the inside and outside of the neuronal membrane. (3) _____ proteins that span the membrane affect the diffusion of specific types of ions across it.
(4) ____ proteins that span the membrane pump sodium and potassium ions against their concentration gradients across it by using energy stored in ATP. A neuronal membrane has many more positively charge (5) _____ ions inside than out and many more positively charged (6) ____ ions outside than inside. There are about (7) _____ times more potassium ions on the cytoplasmic side outside, and there are about (8) _____ times more sodium ions outside than inside. Some channel proteins leak ions through them all the time; others have (9) ______ that open only when stimulated. Transport proteins called (10) _____ – _____ _____ counter the leakage of ions across the neuronal membrane and maintain the resting membrane potential. In all neurons, stimulation at an input zone produces (11) ____ signals that do not spread very far (half a millimeter or less). (12) ______ means that signals can vary in magnitude – small or large- depending on the intensity and (13) ______ of the stimulus. When stimulation is intense or prolonged, graded signals can spread into an adjacent (14) ______ _______ of the membrane – the site where action potentials can be initiated.
A(n) (15) _______ _______ is an abrupt, brief reversal in voltage difference that moves along a neuron. Once an action potential has been achieved, it is an (16) _____ – _____ – ______ event; its amplitude will not change even if the strength of the stimulus changes. The minimum change in membrane potential needed to achieve an action potential is the (17) _____ value.
The cytoplasm next to the plasma membrane of a neuron at rest is more (18) ____ than the interstitial fluid just outside the membrane. During an action potential, the inside of a disturbed patch of membrane becomes more (19) _____ than the outside. After an action potential, (20)_______ conditions are restored at the membrane patch.
K. sodium-potassium pumps
O. action potential
P. trigger zone