Histology of Nervous Tissue Ch. 12-2

Neurons vs. Neuroglia Neurons Neuroglia Provide unique functions Sensing, thinking, remembering, controlling muscle activity, regulating glandular secretions Support, nourish, and protect the neurons Maintain homeostasis in the interstitial fluid that bathes them

Neurons Vocabulary: Neuron – nerve cell Electrical excitability the ability to respond to a stimulus and convert it into an action potential Stimulus any change in the environment that is strong enough to initiate an action potential Action potential – nerve impulse An electrical signal that propogates (travels) along the surface of the membrane of a neuron Can travel up to 280 mph

Parts of a Neuron Three parts Cell body Dendrites Axon Main part of the cell Includes organelles, nucleus, and cytoplasm Dendrites Receiving parts of the neuron Short, tapered, and highly branched Axon Transmitting parts of the neuron Long, thin, cylindrical

Parts of a Neuron

Parts of a Neuron Synapse – site of communication between 2 neurons or a neuron and an effector cell Synaptic end bulb – swollen end of an axon where synaptic vesicles hold neurotransmitters

Neural Diversity Multipolar neurons Bipolar neurons Unipolar neurons Several dendrites, one axon Found in brain and spinal cord Bipolar neurons One main dendrite, one axon Eye, ear, olfactory of brain Unipolar neurons Axon and dendrite fuse at beginning and then branch Occurs as an embryo

Neural Diversity

Others Purkinje cells – cerebellum Pyramidal cells – cerebral cortex of brain

Neuroglia Actively participate in nervous tissue functioning Do not generate action potentials Can multiply and divide – neurons cannot

Types of Neuroglia CNS PNS Astrocytes – create blood-brain barrier, strength Oligodendrocytes – create myelin sheath around CNS axons Microglia – remove cellular debris during neural development Ependymal cells – assist with circulation of cerebrospinal fluid PNS Schwann cells – create myelin sheath around PNS axons Satellite cells – support, regulate exchange of materials

Types of Neuroglia

Types of Neuroglia

Myelination Myelin sheath – multilayered lipid and protein covering around some axons Provides insulation Increases speed of nerve impulse If a cell has myelin we say that it is myelinated Gaps in the myelin sheath are called nodes of Ranvier