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Histology of Nervous Tissue
Exercise 15 Histology of Nervous Tissue
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(a) cell body (soma); (b) Nissl bodies; (c) dendrites; (d) axon; (e) axon hillock; (f) synaptic terminals (a.k.a., axon terminals). (a) Schwann cells; (b) neurilemma of a Schwann cell; (c) myelin sheath of a Schwann cell; (d) nucleus of a Schwann cell; (e) axon of a neuron; (f) node of Ranvier. (a) axon terminal; (b) synaptic cleft; (c) postsynaptic membrane; (d) synaptic vesicles (if shown)
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Two Cell Types in Neural Tissue
Neuron Neuroglia (glial) cell Fig. 12-1
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Neuroglia (glial) cell
Several types Old Edition: 12-6
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Figure Neuroglia. Capillary Neuron Astrocyte Astrocytes are the most abundant CNS neuroglia Myelin sheath Process of oligodendrocyte Neuron Microglial cell Nerve fibers Microglial cells are defensive cells in the CNS. Oligodendrocytes have processes that form myelin sheaths around CNS nerve fibers. Fluid-filled cavity Cilia Cell body of neuron Satellite cells Ependymal cells Schwann cells (forming myelin sheath) Brain or spinal cord tissue Nerve fiber Ependymal cells line cerebrospinal fluid-filled cavities. Satellite cells and Schwann cells (which form myelin) surround neurons in the PNS.
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CNS vs. PNS Central Nervous System Peripheral Nervous System
Brain & spinal cord Peripheral Nervous System Cranial nerves, spinal nerves, ganglia, and nerve plexuses
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Neurons classified by Function
Sensory (afferent) Motor (efferent)
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Figure 15.7 Classification of neurons on the basis of function.
Peripheral process (axon) Ganglion Cell body Sensory neuron Central process (axon) Spinal nerve Afferent transmission White matter Interneuron Receptive endings Gray matter Efferent transmission Motor neuron Spinal cord (central nervous system) To effectors (muscles) 10
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Neurons classified by Impulse Direction
Mixed Carries sensory & motor All spinal nerves, most cranial nerves Pure Carry only sensory or only motor Impulse toward CNS only (some cranial nerves) Impulse to an organ, muscle, etc. (some parts of spinal cord…)
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Neuron Terminology Ganglion Nuclei Tract Nerve
Cluster of cell bodies in the PNS “gray matter” Nuclei Clusters of cell bodies in the CNS Tract Neuron processes in the CNS “white matter” Nerve Neuron processes in the PNS
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Figure 15.2a Structure of a typical motor neuron.
Dendrites Cell body Nucleus Impulse direction Axon Myelin sheath gap (node of Ranvier) rough endoplasmic reticulum Axon terminals Axon hillock Schwann cell Terminal branches 13
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Figure 15.2b Structure of a typical motor neuron.
Nucleus of neuroglial cell Neurofibril Nucleus Nucleolus Dendrites Chromatophilic substance 14
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Myelinated Nerve Fibers of PNS
Schwann Cells: Neurilemma: peripheral part of cell Nucleus: within the neurilemma (superficial) Fig. 12-5
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rotates around the axon, wrapping its plasma membrane loosely around
Figure 15.3a Myelination of a nerve fiber (axon) by Schwann cells. (1 of 4) Schwann cell plasma membrane Schwann cell cytoplasm 1 A Schwann cell envelops an axon. Axon Schwann cell nucleus 2 The Schwann cell then rotates around the axon, wrapping its plasma membrane loosely around it in successive layers. 3 The Schwann cell cytoplasm is forced from between the membranes. The tight membrane wrappings surrounding the axon form the myelin sheath. Myelin sheath Schwann cell cytoplasm 16
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Myelinated Nerve Fibers of PNS
Myelin sheath Axon Node of Ranvier Fig. 12-5
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axon terminal & the next cell (presynaptic neuron) (postsynaptic
Synapse Connection between the axon terminal & the next cell (presynaptic neuron) (postsynaptic neuron or other cell) Fig. 12-5
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Figure 15.2c Structure of a typical motor neuron.
Presynaptic neuron Direction of action potential Mitochondrion Synaptic cleft Axon terminal Synaptic vesicles Postsynaptic neuron 19
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Synapse Synaptic vesicles In axon terminal Contain neurotransmitters
Acetylcholine most common 12-2 Fig. 12-5
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Nerve impulse travels 12-2 Fig. 12-5
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Structure of a Nerve 13-6
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Figure 15.8a Structure of a nerve showing connective tissue wrappings.
Axon Myelin sheath Endoneurium Perineurium Epineurium Fascicle Blood vessels 23
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Figure 15.6 Photomicrographs of neurons.
Dendrites Dendrites Cell body Cell body Nerve fibers Satellite cells Cell bodies 24
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Review Figure 15.1 25
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Review Figure 15.2 26
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