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Neuron Basics

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Neuron Basics Cells of Neural Tissue Neurons: basic unit of the nervous system, these cells communicate with one another and with other cells Neuroglia: regulate the environment of neurons, provide supporting framework, act as phagocytes Structure of a Neuron Motor neuron Neuron from spinal cord Components of Neuron to Know Dendrites: receive incoming signals Axon: carries outgoing signals Synaptic terminal: where axon communicates with dendrites of another cell Mitochondrion: supply ATP Nucleus: houses DNA and nucleolus Nucleolus: makes ribosomes Nissl bodies: clusters of rough ER and free ribosomes - makes gray matter gray Components of Neuron to Know, continued Axon hillock: region of neuron where an action potential may arise due -to presence of specific chemicals, -mechanical pressure, -changes in temperature, or -shifts in extracellular ion concentrations Components of Neuron to Know, continued Collaterals: branches of axon Synapse: site where one neuron communicates with another neuron Schwann cells: glial cells in the PNS that myelinate the axons of neurons Node of Ranvier: part of the neuron that is NOT myelinated, in between the Schwann cells along the axon Cell Body Functional Classification of Neurons Sensory neurons: 10 million in afferent division of PNS Two kinds of receptors: Somatic sensory receptors External Proprioreceptors Visceral receptors (internal receptors) Functional Classification of Neurons, continued Motor neurons: 500,000 of efferent division of PNS carry instructions from CNS to other tissues Effectors: peripheral targets, two kinds: Somatic motor neurons: innervate skeletal muscles Visceral motor neurons of autonomic division (sympathetic and parasympathetic): cardiac, smooth muscle, glands, adipose tissue Functional Classification of Neurons, continued Interneurons (association neurons): 20 billion! -Located entirely within the brain and spinal cord -Connect other neurons -Distribute sensory information -Coordinate motor activity -Play a role in all higher functions: memory, planning, learning Structural Classification of Neurons Multipolar neuron: two or more dendrites and a single axon, most common in CNS Unipolar neuron: the dendrites and axon are continuous and the cell body is off to one side, mostly comprise sensory portion of PNS Bipolar neurons: one dendrite and one axon, with cell body in between, rare but occur in special sense organs and act as relays for sight, smell, hearing Neuroglia Glia means “glue” Found in both PNS and CNS, but great variety in CNS Four types of neuroglia in CNS: 1. Astrocytes 2. Oligodendrocytes 3. Microglia 4. Ependymal Astrocytes -Largest and most numerous -Secrete chemicals to maintain blood-brain barrier -Create structural framework for CNS neurons Repair damaged neural tissue Oligodendrocytes -Have fewer processes than astrocytes -Wrap around axons of neurons to form myelin sheaths -Each cell myelinates short segments of several axons Internodes: areas covered in myelin Microglial cells: microglia -Smallest and rarest of neuroglia -Phagocytic cells derived from white blood cells that migrated into CNS as it formed -Engulf cellular waste and pathogens Ependymal cells -Line central canal of spinal cord -Line ventricles of the brain (chambers filled with cerebrospinal fluid) -Ependyma: the lining of epithelial cells they form -Ependyma produces CSF in some regions Some ependyma have cilia to help circulate CSF Two Types of Neuroglial Cells in PNS 1. Satellite cells:surround and support cell bodies in PNS, much as astrocytes do in CNS 2. Schwann cells: cover every axon outside the CNS Neurilemma: outside of the Schwann cell on a neuron of the PNS *One Schwann cell can only myelinate the axon of a single neuron Be able to recognize each of the different kinds of cells based upon their structures and functions. Structures of Neuroglial Cells.
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