Most neurons receive signals via the dendrites and soma and send out signals down the axon. The term neurite is used to describe either a dendrite or an axon, particularly when the cell is undifferentiated. Neurons may lack dendrites or have no axon. At the farthest tip of the axon's branches are axon terminals, where the neuron can transmit a signal across the synapse to another cell. It branches but usually maintains a constant diameter. The axon leaves the soma at a swelling called the axon hillock and travels for as far as 1 meter in humans or more in other species. Dendrites typically branch profusely and extend a few hundred micrometers from the soma. The soma is a compact structure, and the axon and dendrites are filaments extruding from the soma. Additionally, neurons have other unique structures such as dendrites, and a single axon.
Neurons are special cells which are made up of some structures that are common to all other eukaryotic cells such as the cell body (soma), a nucleus, smooth and rough endoplasmic reticulum, Golgi apparatus, mitochondria, and other cellular components. When multiple neurons are functionally connected together, they form what is called a neural circuit. Interneurons connect neurons to other neurons within the same region of the brain or spinal cord. Motor neurons receive signals from the brain and spinal cord to control everything from muscle contractions to glandular output. Sensory neurons respond to stimuli such as touch, sound, or light that affect the cells of the sensory organs, and they send signals to the spinal cord or brain. Neurons are typically classified into three types based on their function.
Non-animals like plants and fungi do not have nerve cells. The neuron is the main component of nervous tissue in all animals except sponges and placozoa. Neurons communicate with other cells via synapses - specialized connections that commonly use minute amounts of chemical neurotransmitters to pass the electric signal from the presynaptic neuron to the target cell through the synaptic gap. For example, slow, thin, unmyelinated neurons conduct pain whereas faster, thicker, myelinated neurons conduct casual touch.Within a nervous system, a neuron, neurone, or nerve cell is an electrically excitable cell that fires electric signals called action potentials across a neural network. Generally, there is a correlation between the type of sensory modality detected and the type of afferent neuron involved. The sensory information (touch, pain, temperature, etc.,) is then conveyed to the central nervous system by afferent neurons, of which there are a number of different types with varying size, structure, and properties. In the periphery, the somatosensory system detects various stimuli by sensory receptors, such as by mechanoreceptors for tactile sensation and nociceptors for pain sensation. In the case of touch and certain types of pain, the third neuron has its cell body in the ventral posterior nucleus of the thalamus and ends in the postcentral gyrus of the parietal lobe. The axons of many of these neurons terminate in the thalamus, and others terminate in the reticular activating system or the cerebellum. The second has its cell body either in the spinal cord or in the brainstem this neuron’s ascending axons will cross to the opposite side either in the spinal cord or in the brainstem.
The first always has its cell body in the dorsal root ganglion of the spinal nerve.ĭorsal root ganglion: Sensory nerves of a dorsal root ganglion are depicted entering the spinal cord. thalamus: Either of two large, ovoid structures of gray matter within the forebrain that relay sensory impulses to the cerebral cortex.Ī somatosensory pathway will typically have three long neurons: primary, secondary, and tertiary.postcentral gyrus: A prominent structure in the parietal lobe of the human brain that is the location of the primary somatosensory cortex, the main sensory receptive area for the sense of touch.reticular activating system: A set of connected nuclei in the brain responsible for regulating wakefulness and sleep-to-wake transitions.parietal lobe: A part of the brain positioned superior to the occipital lobe and posterior to the frontal lobe that integrates sensory information from different modalities and is particularly important for determining spatial sense and navigation.
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