Nerve Tissue

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Nerve Tissue

Al-Maarefa College

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Objective• Understand the microscopic difference

between excitable and non-excitable cells present in the nervous system.

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Nerve Tissue• Cells have very high ability to – Respond to stimuli– Transmit impulses

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Nerve Tissue

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Nerve Tissue• NEURON is the main nerve cell)

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Nerve Tissue• NEURON is the main nerve cell– Cell Body(3)– Dendrites (5)– Axon(1)

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Motor Neurone

• Figure 9–2. Motor neuron. The myelin sheath is produced by oligodendrocytes in the central nervous system and by Schwann cells in the peripheral nervous system. The neuronal cell body has an unusually large, euchromatic nucleus with a well-developed nucleolus. The perikaryon contains Nissl bodies, which are also found in large dendrites. An axon from another neuron is shown at upper right. It has 3 end bulbs, one of which forms a synapse with the neuron. Note also the 3 motor end-plates, which transmit the nerve impulse to striated skeletal muscle fibers. Arrows show the direction of the nerve impulse.

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Motor Neurone• Cell body• Dendrites• Axon– Covered by Myelin

sheath

Figure 9–2. Motor neuron. The myelin sheath is produced by oligodendrocytes in the central nervous system and by Schwann cells in the peripheral nervous system. The neuronal cell body has an unusually large, euchromatic nucleus with a well-developed nucleolus. The perikaryon contains Nissl bodies, which are also found in large dendrites. An axon from another neuron is shown at upper right. It has 3 end bulbs, one of which forms a synapse with the neuron. Note also the 3 motor end-plates, which transmit the nerve impulse to striated skeletal muscle fibers. Arrows show the direction of the nerve impulse.

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Neurones

Figure 9–4. Simplified view of the three main types of neurons, according to their morphological characteristics.

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Neuron• Multipolar

Kuehnel, Color Atlas of Cytology, Histology, and Microscopic Anatomy

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Neuron's – cerebral cortex

Kuehnel, Color Atlas of Cytology, Histology, and Microscopic Anatomy

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Neuron's – spinal cord

Kuehnel, Color Atlas of Cytology, Histology, and Microscopic Anatomy

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Nerve and Reflex Arc

Figure 9–32. Schematic representation of a nerve and a reflex arc. In this example, the sensory stimulus starts in the skin and passes to the spinal cord via the dorsal root ganglion. The sensory stimulus is transmitted to an interneuron that activates a motor neuron that innervates skeletal muscle. Examples of the operation of this reflex are withdrawal of the finger from a hot surface and the knee-jerk reflex. (Modified, redrawn, and reproduced, with permission, from Ham AW: Histology, 6th ed. Lippincott, 1969.)

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Nerve Fiber (Axon)• Nerve fibers are long nerve cell processes (axon

cylinder, axon) with a surrounding membrane• Schwann cells (neurolemmocytes, peripheral glial

cells) enfold the axon and form an insulating cover known as Schwann’s sheath (neurolemma).

Kuehnel, Color Atlas of Cytology, Histology, and Microscopic Anatomy

Stain: osmium tetroxide; magnification: × 1000

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Nerve Fiber (Axon)• Myelinated nerve fiber, i.e., the axon is covered by a

myelin sheath, which is rich in lipids.• Every 0.8 to 1.0 mm, a node of Ranvier subdivides

the myelin sheath into segments or internodes.

Kuehnel, Color Atlas of Cytology, Histology, and Microscopic Anatomy

Stain: osmium tetroxide; magnification: × 1000

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Sciatic nerve – cross section• 1 Fascicle (nerve fiber bundle)• 2 Perineurium• 3 Epineurium• 4 Artery• 5 Vein• 6 Adipose

tissue

Stain: alum hematoxylin; magnification: × 10Kuehnel, Color Atlas of Cytology, Histology, and Microscopic Anatomy

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Glial Cells• Glial cells (Neuroglia) or (Glia)• (Greek "glue”• Non-neuronal cells that maintain homeostasis,

form myelin, and provide support and protection for the brain's neurons

• They occupy the entire space between neurons and separate nerve cells from blood vessels

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Glial Cells - Functions1. Surround neurons and hold them in place2. Supply nutrients and oxygen to neurons3. Insulate one neuron from another4. Destroy pathogens and remove dead neurons

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Glial Cells - Types• Astrocytes (macroglia)• Oligodendrocytes• Microgliocytes

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Astrocytes

Kuehnel, Color Atlas of Cytology, Histology, and Microscopic Anatomy

• Most abundant• Deal wit homeostasis – relate to vessels

Figure 9–13. Drawings of neuroglial cells as seen in slides stained by metallic impregnation. Note that only astrocytes exhibit vascular end-feet, which cover the walls of blood capillaries.

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Astrocytes and nerve cells

Kuehnel, Color Atlas of Cytology, Histology, and Microscopic Anatomy

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Microglia

• Figure 9–13. Drawings of neuroglial cells as seen in slides stained by metallic impregnation

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Microglia• Oligodendrocytes:– Closely related to

neurons– Provide myelin

protection for CNS neurons

Figure 9–13. Drawings of neuroglial cells as seen in slides stained by metallic impregnation

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Neurons and glial cells

Kuehnel, Color Atlas of Cytology, Histology, and Microscopic Anatomy

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Neuron and glial cells

Kuehnel, Color Atlas of Cytology, Histology, and Microscopic Anatomy

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Summary• Nerve Tissue Cells:– Neurons:• Myelinated• Non-myelinated

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Summary• Nerve Tissue Cells:– Neurons:• Myelinated• Non-myelintaed

– Neurolial cells:• Astrocytes • Microglia• Oligodendrocytes