Nervous System and Neurons

Schwann cells also called as neurolemmocytes are the principal glia of the peripheral nervous system (PNS). Myelinating Schwann cells wrap around axons of motor and sensory neurons to form the myelin sheath. 

Dendrites are the branched projections of a neuron, that act to propagate the electrochemical stimulation received from other neural cells to the cell body, or soma, of the neuron from which the dendrites project.

The node of Ranvier is a periodic gap in the insulating sheath on the axon of certain neurons that serves to facilitate the rapid conduction of nerve impulses. These interruptions in the myelin covering were first discovered in 1878 by French histologist and pathologist Louis Antoine Ranvier, who describes the nodes as constrictions. They are present in myelinated nerves.

The two main types of cells of the nervous system are neurons/nerve cells and neuroglia. The main function of neurons is to receive sensory inputs from the internal and external environment by sensory nerves and transmit it to CNS (brain and spinal cord) for processing and finally transmit the nerve impulses from CNS to effectors (muscles and glands).

The basic parts of a neuron are the dendrites, the cell body and the axon. However, all neurons vary somewhat in size, shape and characteristics depending on the function and role of the neuron. Some neurons have few dendritic branches, while others are highly branched in order to receive a great deal of information. Some neurons have short axons, while others can be quite long. The longest axon in the human body extends from the bottom of the spine to the big toe and averages a length of approximately three feet.

A neuron is an electrically excitable cell. It is the functional and structural unit of the nervous system. It processes and transmits information through electrical and chemical signals. These signals between neurons occur via synapses, specialized connections with other cells. Neurons can connect to each other to form neural networks. Neurons are the core components of the nervous system.

Sensory neurons receive sensory inputs from the internal and external environment by sensory nerves and transmit it to CNS (brain and spinal cord) for processing. This makes option A incorrect. 

A nerve is composed of nerve fiber bundles. A nerve fiber is a threadlike extension of a nerve cell and consists of an axon and myelin sheath (if present) in the nervous system. There are nerve fibers in the central nervous system and peripheral nervous system. A nerve fiber may be myelinated and/or unmyelinated. In the central nervous system (CNS), myelin is produced by oligodendroglia cells.
Muscle tissue is a soft tissue that composes muscles in animal bodies and gives rise to muscles ability to contract. This is opposed to other components or tissues in muscle such as tendons or perimysium.
Bundle sheath cells is a layer of cells in plant leaves and stem that forms a sheath surrounding the vascular bundles.

Dendrites are the small extension of nerve cells that receive signals from sensory receptors or other neurons. The nerve impulse is not conducted by them. The long extension of the cell body of the nerve cell is called as axon that serves to conduct the nerve impulse away from the cell body. The increased diameter of axon results in reduced resistance to local current flow which in turn causes the action potential at its one site to activate the adjacent site. Soma is the metabolic center of the nerve cell where the metabolic contents are manufactured. It is not involved in nerve impulse conduction. Thus, the correct answer is option B.

Schwann/Schwarm cells of peripheral nervous system form the myelin sheath around the myelinated fibers. Gaps between two Schwann cells form nodes of Ranvier which are the unmyelinated areas. Dendrites are the small extension of nerve cells that receive signals from sensory receptors or other neurons and brings them towards the cell body. The synaptic knob is the small button like structure present at the end of the axonal branch at the synapse and serves to store the neurotransmitters which are released in the synaptic cleft. The correct answer is A.

Dendrites are the small extension of nerve cells that receives signals from sensory receptors or other neurons through axon and brings them towards the cell body. Thus, the correct answer is option A.

Neurotransmitters are endogenous chemicals that enable the process of neurotransmission. They transmit signals across a chemical synapse from one neuron (nerve cell) to another "target" neuron, muscle cell, or gland cell. 

The axon can be defined as the long cytoplasmic process of the cell body, which transmits the impulse from the cell body to other neurons. The axon of the neuron is covered by a lipid-rich membrane, called myelin sheath. The myelin sheath is formed by Schwann cells and each Schwann cell covers a part of the axon.
Thus, the correct answer is the option D.

The dendrites of the neuron are called as 'afferent processes' because they transmit impulses to the neuron cell body.
Thus, the correct answer is the option (B), 'Dendrite'.

Cells of the nervous system are called nerve cells or neurons. Neurons have specialized cell parts, called dendrites and axons. A thin sheath covers the axon of the nerve cell. This sheath is called as neurilemma. The sarcolemma also called the myolemma, is the cell membrane of a striated muscle fiber cell. It is not present in the nerve cell.