L7: Nervous tissue Flashcards
What is the nervous system classified into?
The nervous system is classified into:
- Central nervous system (C.N.S): include brain and spinal cord.
- Peripheral nervous system (P.N.S):
Peripheral nerves: may be cranial or spinal nerves
Ganglia: may be spinal or autonomic ganglia.
What is the definition of neurons?
β Neurons are the structural& functional unit of the nervous system.
β It is a specialized cell that transmit impulses within the nervous system.
What is the structure of the neuron?
β The neuron or the nerve cell consists of:
Cell Body: It contains the nucleus and surrounding cytoplasm contain many organelles (Nissl granules, Golgi apparatus, Mitochondria)
Processes: axon and dendrites.
What is the shape of nissl granules under LM?
Basophilic granules scattered in the cytoplasm.
What is the distribution of Nissl granules?
All over the neuron except in:
ο² Around the nucleus.
ο² Axon
What is the stain of Nissl granules?
Stained basophilic by Hx
What is the function of Nissl granules?
Synthesis of protein
Compare between the processes of the nerve cell
What is the classification of New Orleans according to the number of processes (polarity)?
Unipolar nerve cells
Pseudounipolar nerve cells
Bipolar neurons
Multipolar neurons
Unipolar nerve cells
- Nerve cells are rounded with only one process.
- e.g. mesencephalic nucleus of trigeminal nerve.
Pseudounipolar nerve cells
- Nerve cells are rounded.
- single process which divides in inverted T-shaped manner into 2 branches, a dendrite and an axon.
- e.g. sensory ganglia or spinal ganglia
Bipolar neurons
- The cells are fusiform, with 2 processes, a dendrite and an axon.
- e.g. bipolar neurons of retina and olfactory epithelium
Multipolar neurons
- Have many dendrites and one axon.
- Have star-shaped body.
- e.g. neurons in sympathetic ganglia
What is the definition of nerve fibers?
It is the axon of the nerve cell with its surrounding membranes.
What is the structure of nerve fibers?
- The axon membrane named (axolemma) and its cytoplasm named βaxoplasmβ.
- Have no Nissl granules.
- It may be:
ο² Naked or ensheathed (with myelin sheath, neurolemma or both).
What is a histological appearance of myelin sheath?
- White tubular covering of the axon
- Interrupted at intervals called (nodes of Ranvier)
- Segment between two successive nodes is called (internodal segment)
- Appears in the form of concentric layers derived mainly from the cell membrane of Schwann cell
What is the function of myelin sheath?
Insulation of the nerve impulses.
What is the histological appearance of Neurolemmal Sheath (Schwann Cells)?
ο Chain of cells forming a tube around myelin sheath
ο Each cell has a flat oval nucleus
ο Corresponds to an internodal segment
What are the functions of Neurolemmal Sheath (Schwann Cells)?
ο Insulation in nonmyelinated nerve fibers.
ο Regeneration of peripheral nerve after injury.
ο Myelin formation
What are the types of nerve fibers according to its covering?
1) Naked Fibers:
ο² (Non-myelinated without neurolemma) e.g. gray matter.
2) Ensheathed fibers:
ο² Myelinated with neurolemma: e.g. peripheral nerves.
ο² Myelinated without neurolemma: e.g. nerve fibers in the white matter.
ο² Non-myelinated with neurolemma: e.g. sympathetic nerve fibers.
What is the structure of nerve trunk?
1) Nervous component:
ο² Groups of nerve fibers (myelinated axons with neurolemma) arranged in
bundles.
2) C. T. component:
ο² Epineurium: It is a dense C. T. surrounds the whole nerve trunk.
ο² Perineurium: It is a dense C. T. surrounds the bundles of nerve fibers.
ο² Endoneurium: It is a delicate loose C. T. lie between the individual nerve fibers.
What is neuroglia?
β It is the interstitial supporting tissue of the nervous system
β Non-neuronal cells present in the CNS& PNS.
What is the Neuroglia Of CNS?
ο Astrocytes
ο Oligodendroglia
ο Microglia
ο Ependymal cells
What is the neuroglia of PNS?
ο Satellite cells
ο Schwann cells
What is the shape and function of astrocytes?
Shape: It is star-shaped branching cells
Function: Nutrition by connecting neurons to blood vessels
What is the shape of Microglia?
It is small cells having spiny processes
What is the function of microglia?
- can transform into a macrophage that migrate to the site of infection or injury to phagocytose foreign bodies or bacteria.
- Hence, microglia are described as (police man of the brain).
What is the shape of oligodendroglia?
It is cells have few processes
What is the function of oligodendroglia?
Formation of myelin sheath of nerve fiber in the CNS.
What is the shape of ependymal cells?
It is cells Line the spinal cord and the ventricular system of the brain
What is the function of ependymal cells?
Secretion of cerebrospinal fluid (CSF).
What is the shape of satellite cells?
It is small cells that surround neurons in sensory, sympathetic, and parasympathetic ganglia
What is the function of satellite cells?
They are highly sensitive to injury and inflammation
What is the shape of Schwann cells?
It is Flat cells forming a tube around myelin sheath of nerve fiber
What is the function of Schwann cells?
Formation of myelin sheath of nerve fiber in the PNS.
Notes about neuroglia
β In CNS: Oligodendrocyte have processes that wrap around the axons. One oligodendrocyte forms myelin sheath for several neurons (3- 50 neurons).
β In PNS: only one Schwann cell provides myelination for one axon (only a segment of one axon).
What is the definition of nerve ganglia?
β Collection of nerve cells and nerve fibers, covered by a C. T. capsule, outside the C. N. S.
What are the types of nerve ganglia?
1) Spinal.
2) Autonomic: Sympathetic or Parasympathetic.
Compare between spinal (dorsal root) ganglion and sympathetic ganglion
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