Histology of Nervous Tissue

Ch. 12-2

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 vs. Neuroglia

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• 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– 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– 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

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