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There are 43 segments of nerves in the human body. [4] With each segment, there is a pair of sensory and motor nerves. 31 segments of nerves are in the spinal cord and 12 are in the brain stem. [4] Interneurons also known as association neurons are present throughout the central nervous system forming links between the sensory and motor fibres. [5]
A motor neuron (or motoneuron or efferent neuron [1]) is a neuron whose cell body is located in the motor cortex, brainstem or the spinal cord, and whose axon (fiber) projects to the spinal cord or outside of the spinal cord to directly or indirectly control effector organs, mainly muscles and glands. [2]
A 2-D model of cortical sensory homunculus. A cortical homunculus (from Latin homunculus 'little man, miniature human' [1] [2]) is a distorted representation of the human body, based on a neurological "map" of the areas and portions of the human brain dedicated to processing motor functions, and/or sensory functions, for different parts of the body.
Neuron cell body. The accepted view of the neuron attributes dedicated functions to its various anatomical components; however, dendrites and axons often act in ways contrary to their so-called main function. [9] Diagram of a typical myelinated vertebrate motor neuron Neurology video
The following diagram is provided as an overview of and topical guide to the human nervous system: Human nervous system. Human nervous system – the part of the human body that coordinates a person's voluntary and involuntary actions and transmits signals between different parts of the body.
The soma of a neuron (i.e., the main part of the neuron in which the dendrites branch off of) contains many organelles, including granules called Nissl granules, which are composed largely of rough endoplasmic reticulum and free polyribosomes. [5] The cell nucleus is a key feature of the soma.
The somatic part consists of the nerves that innervate the skin, joints, and muscles. The cell bodies of somatic sensory neurons lie in dorsal root ganglia of the spinal cord. The visceral part, also known as the autonomic nervous system, contains neurons that innervate the internal organs, blood vessels, and glands.
This neuron's ascending axons will cross to the opposite side either in the spinal cord or in the brainstem. In the case of touch and certain types of pain, the third-order neuron has its cell body in the ventral posterior nucleus of the thalamus and ends in the postcentral gyrus of the parietal lobe in the primary somatosensory cortex (or S1).