NeurohistologyLectI

NeurohistologyLectI - Lecture 1 Neurohistology I: Cells and...

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3 Lecture 1 Neurohistology I: Cells and General Features Overall Objectives: to understand the histological components of nervous tissue; to recognize the morphological features of neurons; and to differentiate myelinated from non-myelinated axons I. Basic Organization: A. Central Nervous System (CNS)—brain and spinal cord B. Peripheral Nervous System (PNS)—all cranial and spinal nerves and their associated roots and ganglia Functional PNS Divisions: A. Somatic Nervous System—a one neuron system that innervates (voluntary) skeletal muscle or somatosensory receptors of the skin, muscle & joints. B. Autonomic Nervous System—a two neuron visceral efferent system that innervates cardiac and smooth muscle and glands. It is involuntary and has two major subdivisions: 1) Sympathetic (thoracolumbar) 2) Parasympathetic (craniosacral) II. Histological Components: A. Supporting (non-neuronal) Cells Glial cells provide support and protection for neurons and outnumber neurons 10:1. The CNS has three types and the PNS has one: 1. Astrocytes —star-shaped cells that play an active role in brain function by influencing the activity of neurons. They are critical for 1) recycling neurotransmitters; 2) secreting neurotrophic factors (e.g., neural growth factor) that stimulate the growth and mainte- nance of neurons; 3) dictating the number of synapses formed on neuronal surfaces and modulating synapses in adult brain; and 4) maintaining the appropriate ionic composition of extracellular fluid surrounding neurons, by absorbing excess potassium and other larger molecules. 2. Oligodendrocytes — The oligodendrocyte is the analog of the Schwann cell in the central nervous system and is responsible for forming myelin sheaths around brain and spinal cord axons. Myelin is an electrical insulator. 3. Microglia —are the smallest of glial cells. They represent the intrinsic immune effector cells of the CNS and underlie the inflammation response that occurs following damage to the central nervous system and the invasion of microorganisms. 4. Lemmocytes (Schwann Cells)— Schwann cells are glia cells of the PNS. They wrap individually around the shaft of peripheral axons, forming a layer or myelin sheath along segments of the axon. The Schwann cell membrane, which forms the myelin sheath, is composed primarily of lipids; the lipid serves as an insulator thereby speeding the trans- mission rate of action potentials along the axon.
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4 dendritic zone (receives input) axon (conducts excitation) myelin node myelin internode telodendritic branches (with terminal bulbs) next neuron (dendrite) axon hillock (of cell body) input dendrite cell body (soma) initial segment (of axon) axon Multipolar Neuron 5. Ependyma — in addition to the above glial cells, the CNS has epithelial-like cells that line the ventricles of the brain and the central canal of the spinal cord.
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NeurohistologyLectI - Lecture 1 Neurohistology I: Cells and...

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