Question
Question: The area where medullary sheath is present in the nerve fiber is A. Nissl granules B. Schwann c...
The area where medullary sheath is present in the nerve fiber is
A. Nissl granules
B. Schwann cells
C. Node of Ranvier
D. Schwann node
Solution
The axon is also surrounded by a membrane known as the myelin sheath or meninges, which is not present in all fibers. Myelinated fibers are called myelinated or nerve fibers, while other fibers without myelinated sheath are called unmyelinated fibers.
Complete answer:
Neurons are structural and functional units of the nervous tissue and nervous system. Some neurons can be about the same length as the body itself. So, neurons with a longer process (protrusion) are the longest cells in the body.
Neuron consists of following parts
Cell bodies - Cell bodies vary in size and shape. Its shape can be irregular, round, oval, round, star-shaped or pyramidal. Like normal cells, it consists of the cytoplasm, the cell nucleus, and the cell membrane.
Dendrites - Cell membranes are made up of a series of sticky structures known as dendrites. Length varies up to one meter (peripheral sensory nerve fibers). Each dendrite contains Nissan granules, mitochondria, and nerve fibers. Nissl granules-The cytoplasm of the perikarion shows the presence of a basophilic mass known as granules or Nissl bodies when examined with certain staining methods.
Axon -Axons or nerve fibers arise from the axonal tubercles of the perikaryon, which are rich in nerve fibers but lack granules. Axons also contain mitochondria, inferior granules, and nerve fibers parallel to the long axis of the axon. The axoplasm is surrounded by a cell membrane called the axolemma, which is connected to the cell membrane of the parent body.
There are two types of axons: myelinated and unmyelinated. In myelinated nerve fibers, the cells of the nerve sheath form the myelin sheath around the axon.
Node of Ranvier -The gap between two adjacent plants is known as the Ranvier knot.
Schwann cells - A special set of Schwann cells arranged linearly around the axolemma form the myelin sheath in a process known as myelinogenesis. Since Schwann cells grow around the axon and span its entire length.
However at the nodes of Ranvier myelin sheath is not present due to which the nodes of Ranvier do not pose any kind of insulation to the flow of electrical impulses.
Hence the correct option is (C).
Note: Myelinated nerve fibres are located in the skull and spinal nerves. In unmyelinated nerve fibers, Schwann cells do not form myelin sheaths and do not have Ranvier nodules. They are common in the autonomic and somatic nervous systems.
Myelin sheaths of many axons in the body separate these axons, with the exception of the Ranvier node. Since the impulse travels through myelinated neurons, depolarization occurs only in the nodes. Impulse Passes the myelin sheaths from one node to the next. This process of induction of conduction is named after saltere, the root meaning leap. Saltatory conduction is the reason why the pulse travels faster in myelinated neurons than in unmyelinated neurons.