Wechat logo 50 41 d4bae92fc2b9067675bfee08d2b00834882415940f50456376420c2e77a679ac
返回

neuron

neuron
神经元【名词】【解剖学】神经原,神经细胞

Definitions

a highly specialized cell of the nervous system, having two characteristic properties: irritability (ability to be stimulated) and conductivity (ability to conduct impulses). They are composed of a cell body (called also neurosome or perikaryon), containing the nucleus and its surrounding cytoplasm, and one or more processes (nerve fibers) extending from the body. Called also nerve cell. adj., adj neuro´nal.  The nerve fibers are actually extensions of the cytoplasm surrounding the nucleus of the neuron. A nerve cell may have only one such slender fiber extending from its body, in which case it is classified as unipolar. A neuron having two processes is bipolar, and one with three or more processes is multipolar. Most neurons are multipolar; this type is widely distributed throughout the central nervous system and autonomic ganglia. The multipolar neurons have a single process called an axon and several branched extensions called dendrites. The dendrites receive stimuli from other nerves or from a receptor organ, such as the skin or ear, and transmit them through the neuron to the axon. The axon conducts the impulses to the dendrite of another neuron or to an effector organ that is thereby stimulated to action. Many processes are covered with a layer of lipid material called the myelin sheath. Peripheral nerve fibers have a thin outer covering called neurilemma.Types of Neurons. Neurons that receive stimuli from the outside environment and transmit them toward the brain are called afferent or sensory neurons. Those that carry impulses in the opposite direction, away from the brain and other nerve centers to muscles, are called efferent neurons, motor neurons, or motoneurons. Another type, the interneuron, found in the brain and spinal cord, conducts impulses from afferent to efferent neurons.Synapses. The point at which an impulse is transmitted from one neuron to another is called a synapse. The transmission is chemical in nature; that is, there is no direct contact between the axon of one neuron and the dendrites of another. The cholinergic nerves (parasympathetic nervous system) liberate at their axon endings a substance called acetylcholine, which acts as a stimulant to the dendrites of adjacent neurons. In a similar manner, the adrenergic nerves (sympathetic nervous system) liberate epinephrine or related substances. The synapse may involve one neuron in chemical contact with many adjacent neurons, or it may involve the axon terminals of one neuron and the dendrites of a succeeding neuron in a nerve pathway. There are many different patterns of synapses.Receptor End-Organs. The dendrites of the sensory neurons are designed to receive stimuli from various parts of the body. These dendrites are called receptor end-organs and are of three general types: exteroceptors, interoceptors, and proprioceptors. The exteroceptors are located near the external surface of the body, receive impulses from the skin, and transmit information about the senses of touch, heat, cold, and other factors in the external environment. The interoceptors are located in the internal organs and receive information from the viscera, e.g., pressure, tension, and pain. The proprioceptors are found in muscles, tendons, and joints and transmit "muscle sense," by which one is aware of the position of one's body in space.Neurons and Effectors. The axons of motor neurons form synapses with skeletal fibers to produce motion. These junctions are called motor end-plates or myoneural junctions. The axon of a motor neuron divides just before it enters the muscle fibers and forms synapses near the nuclei of muscle fibers. These motor neurons are called somatic efferent neurons. Visceral efferent neurons form synapses with smooth muscle, cardiac muscle, and glands.Upper and lower motor neurons. From Damjanov, 2000. Types of Neurons. Neurons that receive stimuli from the outside environment and transmit them toward the brain are called afferent or sensory neurons. Those that carry impulses in the opposite direction, away from the brain and other nerve centers to muscles, are called efferent neurons, motor neurons, or motoneurons. Another type, the interneuron, found in the brain and spinal cord, conducts impulses from afferent to efferent neurons. Synapses. The point at which an impulse is transmitted from one neuron to another is called a synapse. The transmission is chemical in nature; that is, there is no direct contact between the axon of one neuron and the dendrites of another. The cholinergic nerves (parasympathetic nervous system) liberate at their axon endings a substance called acetylcholine, which acts as a stimulant to the dendrites of adjacent neurons. In a similar manner, the adrenergic nerves (sympathetic nervous system) liberate epinephrine or related substances. The synapse may involve one neuron in chemical contact with many adjacent neurons, or it may involve the axon terminals of one neuron and the dendrites of a succeeding neuron in a nerve pathway. There are many different patterns of synapses. Receptor End-Organs. The dendrites of the sensory neurons are designed to receive stimuli from various parts of the body. These dendrites are called receptor end-organs and are of three general types: exteroceptors, interoceptors, and proprioceptors. The exteroceptors are located near the external surface of the body, receive impulses from the skin, and transmit information about the senses of touch, heat, cold, and other factors in the external environment. The interoceptors are located in the internal organs and receive information from the viscera, e.g., pressure, tension, and pain. The proprioceptors are found in muscles, tendons, and joints and transmit "muscle sense," by which one is aware of the position of one's body in space. Neurons and Effectors. The axons of motor neurons form synapses with skeletal fibers to produce motion. These junctions are called motor end-plates or myoneural junctions. The axon of a motor neuron divides just before it enters the muscle fibers and forms synapses near the nuclei of muscle fibers. These motor neurons are called somatic efferent neurons. Visceral efferent neurons form synapses with smooth muscle, cardiac muscle, and glands.





Sound e31a43d441998f862b764d17930467a5a23de45c433219259bed5eb42e3a7615