| NAD | neutrophil actin dysfunction; new antigenic determinant; nicotinamide adenine dinucleotide; nicotini... |
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| NAMN | nicotinic acid mononucleotide |
| niacin | Nicotinic acid |
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| NAADP | Nicotinic acid adenine dinucleotide phosphate |
| nicotinic alcohol | <chemical> 3-pyridinemethanol. A direct-acting peripheral vasodilator that causes flushing and may decrease blood pressure. It is used in vasospasm and threatened gangrene. Pharmacological action: vasodilator agents. Chemical name: 3-Pyridinemethanol (12 Dec 1998) |
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| nicotinic antagonists | Drugs that bind to nicotinic cholinergic receptors (receptors, nicotinic) and block the actions of acetylcholine or cholinergic agonists. Nicotinic antagonists block synaptic transmission at autonomic ganglia, the skeletal neuromuscular junction, and at central nervous system nicotinic synapses. (12 Dec 1998) |
| nicotinic cholinergic receptor | A class of receptors responsive to acetylcholine that also are activated by nicotine; ganglionic (including the adrenal medulla) and neuromuscular receptors. Two classes exist: nicotinic-neuronal and nicotinic-muscular. (05 Mar 2000) |
| nicotinic receptors | A class of cholinergic receptors on skeletal muscle cells that are linked to ion channels in the cell membrane. (05 Mar 2000) |
| synapse | <physiology> A connection between excitable cells, by which an excitation is conveyed from one to the other. 1. Chemical synapse: one in which an action potential causes the exocytosis of neurotransmitter from the presynaptic cell, which diffuses across the synaptic cleft and binds to ligand gated ion channels on the post synaptic cell. These ion channels then affect the resting potential of the post synaptic cell. 2. Electrical synapse: one in which electrical connection is made directly through the cytoplasm, via gap junctions. 3. Rectifying synapse: one in which action potentials can only pass across the synapse in one direction (all chemical and some electrical synapses). 4. Excitatory synapse: one in which the firing of the presynaptic cell increases the probability of firing of the postsynaptic cell. 5. Inhibitory synapse: one in which the firing of the presynaptic cell reduces the probability of firing of the postsynaptic cell. (10 Jan 1998) |
| inhibitory synapse | A synapse in which an action potential in the presynaptic cell reduces the probability of an action potential occurring in the postsynaptic cell. The most common inhibitory neurotransmitter is GABA, this opens channels in the postsynaptic cell which tend to stabilise its resting potential, thus rendering it less likely to fire. See: excitatory synapse, presynaptic inhibition, postsynaptic inhibition. (18 Nov 1997) |
| electrical synapse | <physiology> A connection between two electrically excitable cells, such as neurons or muscle cells, via arrays of gap junctions. This allows the cells to be electrically coupled and so an action potential in one cell moves directly into the other, without the 1 ms delay inherent in chemical synapses. Electrical synapses do not allow modulation of their connection and so only occur in neuronal circuits where speed of conduction is paramount (e.g. The crayfish escape reflex). A few electrical synapses are rectifying, implying a more specialised property than a simple gap junction. (18 Nov 1997) |
| electrotonic synapse | <cell biology> A junction between two cells consisting of many pores that allow the passage of molecules up to about 900D. Each pore is formed by an hexagonal array (connexon) of six transmembrane proteins (connexins) in each plasma membrane: when mated together the pores open, allowing communication and the interchange of metabolites between cells. Electrical synapses are gap junctions and metabolic cooperation depends upon the formation of gap junctions. (18 Nov 1997) |
| excitatory synapse | <physiology> A synapse (either chemical or electrical) in which an action potential in the presynaptic cell increases the probability of an action potential occurring in the postsynaptic cell. See: inhibitory synapse. (18 Nov 1997) |