Nervous Tissue 2

1. Nervous Tissue 2 Originally Given By: Dr.Ahmed Attayeb Written By: Dr.Divine, Edited & Made up 2 date: Abo Malik Thanks for: DR.I

2. NEUROGLIA • Neuroglia are the supporting cells of the nervous tissue in the CNS. They can never transmit impulses. • Types of Neuroglia:- 1-Astrocytes 2-Oligodendrocytes 3-Microglia 4-Ependymal cells (NOTE):In contrast to Schwann cells that are in the PNS, these neuroglia are found only in CNS.

3. 1-Astrocytes • The largest of all neuroglia with a large nucleus • Have cytoplasmic processes which support neurons & the blood vessels • Form the Blood-brain barrier • Can divide & fill the places of damaged parts of CNS

4. Types of Astrocytes • There are two types: • Protoplasmic astrocytes: Found in gray matter of CNS supporting the nerve cell bodies, the axons & the blood vessels. • Fibrous astrocytes: Found in white matter supporting the axons & the blood vessels.

6. 2-Microglial cell • Found in gray & white matter • Small cell with oval nucleus • Short cytoplasmic processes • Phagocytic cell • Originate from monocytes in bone marrow

7. 3-Oligodendrocytes • Found in gray & white matter of the CNS • Small cells with few cytoplasmic processes • Each cytoplasmic process forms a separate myelin segment (internode) • Each oligodendrocyte forms myelin sheath for many axons in CNS

8. Oligodendrocyte

9. 4-Ependymal cells • Columnar Ciliated cells • Lining the ventricles of the brain & central canal of spinal cord • In the ventricles they secrete the cerebrospinal fluid.

10. Synapse • Synapse is the point of contract between the end of the axon & another neuron, muscle or gland cell • Synapse transmits impulses from the axon to another cell

11. Types of synapses • Chemical synapse:- (in CNS & PNS) Needs a chemical (neurotransmitter) to transmit impulses • Electrical synapse:- (Only in the CNS) as gap junctions between axon & the other neuron in CNS.

12. Chemical Synapse • There chemical synapse consists of four components: • Presynaptic membrane is the membrane of the end of the axon • Postsynaptic membrane is the membrane of the other cell e.g. Neuron • Synaptic cleft is a space between the two membranes • Synaptic vesicles in the axon secrete the neurotransmitter into the synaptic cleft

14. Types of Chemical Synapses • Axosomatic synapse It occurs between axon & cell body. • Axodendritic synapse It occurs between axon & dendrite. • Axoaxonic Synapse It occurs between axon & another axon.

15. NERVE ENDINGS • Terminations of axons in epithelium, CT or muscle There are 2 types of nerve endings:- A) Motor nerve endings(somatic OR autonomic) B) Sensory nerve endings(somatic OR autonomic)

16. 1-Somatic motor nerve endingMotor end Plate (Neuromuscular junction) • Synapse of a motor axon with a skeletal muscle fiber • The axon of a single neuron divides to supply more than 100 muscle fibers • Neuron cell body is in the CNS • Neuron & muscle fibers it supplies is called a motor unit

18. 2-Autonomic motor nerve endings • Synapses of axons in cardiac muscle, smooth muscle, or gland. • The cell bodies of these axons are located in autonomic ganglia.

19. B) Sensory nerve endings • Terminations of axons in epithelium , CT or skeletal muscle • The neuron cell bodies of these axons are located in the spinal & cranial nerve ganglia. • E.g: • Pacinian corpuscle • Muscle Spindle

20. Sensory Nerve EndingsPacinian corpuscle • Pressure receptor found in the skin • Oval in shape, covered by a CT capsule • The end of the axon is umyelinated in the center of the corpuscle • Many layers of flattened cells surround axon & there is tissue fluid between the layers

22. Sensory Nerve Endings Muscle spindle • Stretch receptor found in skeletal muscle • Cylindrical in shape & covered by a CT capsule • Contains small muscle fibers called intrafusal fibers surrounded by sensory axons • The muscle fibers outside the muscle spindle are called extrafusal muscle fibers supplied by motor axons