University:
Texas A&M University
Course:
BIOL 319 | Integrated Human Anatomy and Physiology I
Academic year:

2024
Views:

172

Pages:

30
Author:

imophulebf10

Histo 07 NERVOUS TISSUE Part 2 Objectives Part 1 • Describe the components of a neuron. • Distinguish between neurons and glial cells. • Identify the components of the meninges, grey and white matter. Part 2 • Recognize peripheral nerves and identity their structural components (in longitudinal and transverse sections); understand the structural and functional differences between myelinated and unmyelinated fibers with both light microscopy and electron micrographs. THE NERVOUS SYSTEM PERIPHERAL NERVOUS SYSTEM (PNS) ALL NERVOUS TISSUE (NEURONS, SUPPORT CELLS, AND AXONS) OUTSIDE THE BRAIN AND SPINAL CORD Auerbach’s Plexus (“Myenteric Plexus”) is sandwiched between the two layers of smooth muscle in the muscularis externa that controls gut peristalsis Ganglia - collections of nerve cell bodies in PNS Smooth muscle Smooth muscle Meissner’s plexus Rat small intestine Auerbach’s Plexus Ganglia -collections of nerve cell bodies in organs nerve cell bodies 29291 Human pancreas Cystic duct of monkey Peripheral ganglion, monkey Axons Satellite cells Nissl bodies Neuron Organization of Peripheral Nerves Nerve fibers - axons invested by connective tissue Epineurum - surrounding entire nerve Perineurum - surrounding fascicles – constitutes the PNS blood barrier via tight junctions between fibroblasts Endoneurum - between individual nerve axons Organization of Peripheral Nerves Nerve fibers - axons invested by connective tissue Epineurum - surrounding entire nerve Perineurum - surrounding fascicles – constitutes the PNS blood barrier via tight junctions between fibroblasts Endoneurum - between individual nerve axons Slide 6 Nerve (cross section; Bodian’s stain/lissamine red) Bodian’s stain/lissamine red stain – • axons and nuclei: black • myelin: pink-red • connective tissue: brown to black Fascicle: group of neurons surrounded by perineurium endneurium: surrounds each axon’s myelin sheath Nerve: group of fascicles bound by epineurium 19673 perineurium Myelinated axon Unmyelinated fibers (axons) do not have a myelin sheath covering, but they are still supported by simple folds of Schwann cells. unmyelinated axons EM 54 and 55: Nerve Function of Myelin Increase speed of condition • 1 meter/sec TO 120 meters/sec High-resistance low capacitance • Insulator Protection of axon Possible nutritional role Direct regenerating axons SCHWANN CELL STRUCTURE / FUNCTION MOST PERIPHERAL NERVES ARE MYELINATED 1 SCHWANN CELL/1 AXON FOR LOCATION SCHWANN CELL STRUCTURE / FUNCTION MOST PERIPHERAL NERVES ARE MYELINATED 1 SCHWANN CELL/1 AXON FOR LOCATION FORMATION OF MYELIN SHEATH • NODES OF RANVIER • SCHMIDT-LANTERMAN CLEFTS • NEUROKERATIN NETWORK NODE OF RANVIER Slide 5: Nerve (longitudinal section) H&E • Stains axons, Schwann cells (neurolemmocytes), and connective tissue • Myelin contains lipids, this is not stained and will have dissolved away during tissue preparation Longitudinal section Cross section Schwann cell nuclei Axons Neurolemma Node of Ranvier Fibroblast Nerve (longitudinal section) Schwann cells, the principle glia of the PNS, wraps around axons of motor and sensory neurons of the PNS to form their myelin sheath. Schwann cell nuclei Fibroblast Node of Ranvier Axons Neurolemma Peripheral nerve, monkey ut 193 Nerve (cross section) Fibroblasts of perineurium Capillaries Axons Neurolemma of Schwann cell 29297 Slide 7: Myoneural junction (gold chloride/formic acid) • Skeletal muscle fibers still stain purple to black. Skeletal muscle cells Slide 7: Myoneural junction (gold chloride/formic acid) • Skeletal muscle fibers still stain purple to black. Skeletal muscle cells Axons Slide 7: Myoneural junction (gold chloride/formic acid) • Skeletal muscle fibers still stain purple to black. Skeletal muscle cells Motor end plates Axons Slide 7: Myoneural junction (gold chloride/formic acid) • Skeletal muscle fibers still stain purple to black. Skeletal muscle cells Motor end plates Axons End feet (terminal buttons and end of presynaptic cell) NEURONAL STRUCTURE / FUNCTION Axonal transport Anterograde - toward terminal - kinesin Retrograde - toward cell body - dynein • Tetanus toxin • Neurotropic viruses (herpes and rabies) use path to get to cell body in CNS Summary of the Physiological Events at the Synapse • Arrival of action potential at axon terminal • Opening Ca++ channels • Influx of Ca++ into axon terminal Summary of the Physiological Events at the Synapse • Arrival of action potential • • • • • at axon terminal Opening Ca++ channels Influx of Ca++ into axon terminal Exocytosis of neurotransmitter Diffusion of neurotransmitter across synaptic cleft Binding of neurotransmitter to receptors on target cell Summary of the Physiological Events at the Synapse • Arrival of action potential • • • • • • • at axon terminal Opening Ca++ channels Influx of Ca++ into axon terminal Exocytosis of neurotransmitter Diffusion of neurotransmitter across synaptic cleft Binding of neurotransmitter to receptors on target cell Opening of Na+ channels causing depolarization of target cell Removal of neurotransmitter Neurotransmitter ACh vs NE Acetylcholine (ACh) is the neurotransmitter released in the synaptic cleft of the motor end plate innervating muscle. However, norepinephrine (NE) is the neurotransmitter released from most sympathetic postganglionic nerves. Histo 07 Clinical Correlation When a peripheral nerve is injured/severed, the segment of the axon distal to the injury and its myelin sheath completely degenerate and their remnants are removed by macrophages. However, Schwann cells proliferate and form cellular columns that act as guides for the regrowing axon back to the original muscle. Macrophages Schwann cells Figure 6. Astrocytes. Adapted from “Inducing Alignment in astrocyte tissue constructs by surface ligands patterned on biomaterials” -

Nervous Tissue Part 2

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