Atlas of plant and animal histology

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Glossary: N


Nectary: (in plants) it is a glandular structure that synthesizes and releases carbohydrates. Nectaries get the energy and substances from phloem.

♣ Plant tissues: Glandular.

Nerve: (in animals) it is bundle of axons. Nerves consist of axons, glial cells (Schwan's cells) and connective tissue. Axons are wrapped in the connective tissue called endoneurium. Groups of axons form small bundles inside the nerve surrounded by the perineurium, and the whole nerve is covered by the epineurium.

Nerve fascicle: it is a bundle of axons within a peripheral nerve that is surrounded by an envelope of connective tissue called perineurium.

♣ Animal organs: Nerve.

Nerve ganglion: it is a group of neurons, and other associated cells, found outside the central nervous system. Nerve ganglia contains very large neuronal somata surrounded by a capsule of connective tissue. There are motor ganglia that innervate muscle cells to produce movement, and sensory ganglia that gather information from different parts of the body (temperature, taste, proprioception, etcetera) and send this information to the central nervous system.

Nevous tissue: it is one of the four fundamental tissues in animals. The nervous tissue is composed of two main cell types: neurons and glia, with very little extracellular matrix. Neurons are specialized cells that receive and process inner and outer information of the body, and send the results to other organs of the body, mainly muscles. The nervous tissue forms the central nervous system (brain and spinal cord) and the peripheral nervous system. Both are in charge of the many functions that the animal body performs, included those considered superior, such as thinking and conscience.

♣ Animal tissues: Nervous tissue.
♣ Cell types: Neuron, Astrocyte.

Nervous tunic: it is the inner layer of the eye and contains the retina.

♣ Animal organs: Senses.

Neuroepithelial cell: (in taste buds) it is a type of sensory cell found in the taste buds of the animal oral cavity. There are about 10 to 14 neuroepithelial cells per taste bud. They work as chemoreceptors that recognize airborne taste molecules and send information to the nerve fibers that wrap the cell basal part.

♣ Animal organs: Senses.

Neuron: it is a cell type of the nervous tissue. Neurons are morphologically complex cells with three domains: soma, dendrites and axon. Dendrites and axons are filiform and branches cell processes. The nucleus and many organelles are found in the soma. Neurons are responsible for processing the information coming from the body sensory organs and give a response that is usually a muscular movement or hormone release. Neurons communicate between each other by molecules known as neurotransmitters, which are usually released in special cell structures called synapses.

♣ Cell types: The neuron .
♣ Animal tissues: Nervous tissue .

Neutrophil: it is a type of sensory neuron involved in olfaction. Olfactory receptor neurons are found in the olfactory epithelium, in the nasal cavity. They recognize the airborne olfactory molecules. This recognition is transformed in electric information, which is transmitted to the olfactory bulb via the olfactory nerve.

♣ Animal tissues: Blood, Blood cells .

Nissl bodies: are colored structures observed in the cytoplasm of neurons after staining with basic dyes, such as cresyl violet. Nissl bodies are dark purple or dark blue. They are thought to be cytoplasm aggregates of endoplasmic reticulum with many ribosomes and mRNA.

♣ Animal tissues: Nervous tissue, Spinal cord .

Nociceptor: it is a type of sensory receptor that encode noxious or damaging stimuli. Nociceptors may respond to chemical, mechanical and temperature stimuli.

♣ Animal organs: Senses.

Nucellus: (in plants) it is a part of the ovule, in the ovary of flowers. Nucellus surrounds the macrospore (the egg). In angiosperms, the nucellus is in turn wrapped by the integuments, whereas in gymnosperms is naked. Nucellus is a storing structure to feed and protect the egg. In angiosperms, the nucellus is also known as megasporangium.

♣ Plant organs: Seed, Flower, Flower section .

Node: (in plants) it is the point of the stem where flowers and branches are inserted.

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