Nervous system in animals - class-IX

Neurons are the structural and functional unit of the nervous system. Each neuron consists of dendrites, axon, and soma. Dendrites are the small extension of nerve cells that receive signals from sensory receptors or other neurons. 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. Cyton /soma is the metabolic center of the nerve cell where the metabolic contents are manufactured. It is not involved in nerve impulse conduction. A nephron is the anatomical and functional unit of kidney and thus is the part of the excretory system. Thus, the correct answer is option C.

The nervous system is a collection of cells, tissues, and organs ( brain, spinal cord, nerves ) through which an organism receives information from its surroundings and then directs the organism to respond to the stimulus.

The brain regulates an array of functions necessary for survival. The brain houses our mind and our memories. Most available evidence suggests that the functions of memory are carried out by the hippocampus and other related structures in the temporal lobe of the brain. The brain also helps in the analysis of various body functions.

The primary components of the neuron are the soma (cell body), the axon (a long slender projection that conducts electrical impulses away from the cell body), dendrites (tree-like structures that receive messages from other neurons), and synapses (specialized junctions between neurons).

A. Synaptic vesicle store various neurotransmitters that are released at the synapse.

B. Synaptic knob-The bulbous structure present at the terminal end of an axon.

c. Dendrites-also dendrons, are branched protoplasmic extensions of a nerve cell that propagate the electrochemical stimulation received from other neural cells to the cell body, or soma, of the neuron from which the dendrites project.

D. Schwann cell -also called neurilemma cell, any of the cells in the peripheral nervous system that produce the myelin sheath around neuronal axons.

So, the correct option is 'Synaptic Knob'.

Neurilemma is the outermost covering of Schwann cells that surrounds the axon of the neuron. It is also known as neurolemma.

The vacuole is membrane bound organelle present in all plant and fungal cells and some protist, animal and bacterial cells. The flagellum is an appendage, that protrudes from the cell body of certain prokaryotic and some eukaryotic cells. Nucleus and mitochondria are membrane bound organelles present in almost all cells. Perikaryon, also called cyton is the bulbous end of a neuron containing cell nucleus. Dendrites are the short cytoplasmic processes of the cell body of the neuron, which receives stimulus from other neurons. 
So, the correct answer is option D.

Nerves are made up of bundles of the axons of nerve cells. A nerve is an enclosed, cable-like bundle of axons (long, slender projections of neurons) in the peripheral nervous system.

Nodes of Ranvier are periodic gaps in the insulating sheath (myelin) on the axon of certain neurons, that serves to facilitate the rapid conduction of nerve impulses. 

An axon is also known as a nerve fiber. It is a long, slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neuron's cell body. The function of the axon is to transmit information to different neurons, muscles and glands.

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. 

A Nissl granule is a large granular body found in neurons. These granules are rough endoplasmic reticulum (RER) with rosettes of free ribosomes and are the site of protein synthesis.

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.

A Nissl granule is a large granular body found in neurons. These granules are rough endoplasmic reticulum (RER) with rosettes of free ribosomes and are the site of protein synthesis.

A Nissl body is also known as Nissl or tigroid substance. It is a large granular body found in neurons. These granules are rough endoplasmic reticulum (RER) with rosettes of free ribosomes and are the sites of protein synthesis.

A Nissl body is also known as Nissl or tigroid substance. It is a large granular body found in neurons. These granules are rough endoplasmic reticulum (RER) with rosettes of free ribosomes and are the site of protein synthesis.

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 brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. In a typical human, the cerebral cortex is estimated to contain 15-33 billion neurons, each connected by synapses to several thousand other neurons. These  neurons communicate with one another by means of long protoplasmic fibers called axons, which carry trains of signal pulses called action potentials to distant parts of the brain or body targeting specific recipient cells. These brain cells are the only cells which do not have the ability to regenerate.

A neuron is an electrically excitable cell. 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, which includes the brain, spinal cord which together comprise the central nervous system (CNS) and the ganglia of the peripheral nervous system (PNS). Specialized types of neurons include: sensory neurons which respond to touch, sound, light and all other stimuli affecting the cells of the sensory organs that then send signals to the spinal cord and brain, motor neurons that receive signals from the brain and spinal cord to cause muscle contractions and affect glandular outputs and interneurons which connect neurons to other neurons within the same region of the brain or spinal cord in neural networks.
Therefore, the correct answer is option C.

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.

A centriole is a small set of microtubules arranged in a specific way. There are nine groups of microtubules. When two centrioles are found next to each other, they are usually at right angles. The centrioles are found in pairs and move towards the poles (opposite ends) of the nucleus when it is time for cell division. Neurons cannot divide because they lack centrioles.
Because centrioles function in cell division, the fact that neurons lack these organelles is consistent with the amitotic nature of the cell.

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 different cells in the body can regenerate in order to replace the damaged or the worn-out cells. 
• The neurons are one of the brain cells. The cells divide during the embryonal stage. After the birth of a child, the cells lose their capacity to divide. 
• These cells have the least capacity of regeneration. 
• Thus, the correct answer is option C. 

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. 

Unlike unmyelinated axons in periphary nerves which an embedded in neurilemma of Schwann cells, those of central nerves lie free in neuropil(nertwork of glial cells and nerve cell components).

Nissl granules are specialized structures found in the cell body (cyton) and dendrites of neurons, but they are notably absent from the axon and the axon hillock.

Nodes of Ranvier are periodic gaps in the myelin sheath of medullated (myelinated) nerve fibers where the axonal membrane is exposed.

Nissl granules are composed of rough endoplasmic reticulum (RER) and free ribosomes, which are rich in RNA, giving them a strong affinity for basic dyes.

In medullated nerve fibers, the nodes of Ranvier are the specific points where the myelin sheath is interrupted and the axonal membrane comes into direct contact with the extracellular environment.

Nissl granules are essentially clusters of rough endoplasmic reticulum and ribosomes, which are the machinery responsible for protein synthesis within the neuron.

Nissl granules are characteristic cytoplasmic inclusions found specifically in the cell bodies and dendrites of nerve cells (neurons).

Nodes of Ranvier are the periodic gaps in the myelin sheath of medullated (myelinated) nerve fibers. They allow for saltatory conduction of nerve impulses.

The perikaryon (cell body) and dendrites are characteristic structures of a neuron that distinguish it from other typical animal cells. While other cells have nuclei and mitochondria, these specific extensions and the cell body structure are unique to neurons.

Schwann cells are specialized glial cells that wrap around the axons of neurons in the peripheral nervous system to form the myelin sheath.

The axon is the long projection of a neuron that is typically covered by the myelin sheath, which is a fatty insulating layer that speeds up impulse transmission.

The medullary sheath is composed of a shinning, white, fatty substance called myelin. This sheath perhaps serves as an insulating layer, preventing loss of energy of the nerve impulse during its passage along the fibre. The medullary sheath is continuous around the fibres in the central nervous system, but in the fibres of the peripheral nerves, it is absent at certain points known as the Node of Ranvier. The part of a nerve fibre between two successive nodes is termed the internode.

Areolar tissue contains collagen, epithelium contains keratin, and muscle fibers contain actin. Melanin is a pigment found in skin and hair, not a structural protein characteristic of neurons.

Myelin is an insulating layer, or sheath, that forms around nerves. It is made up of protein and fatty substances. The fat helps to insulate the axons from electrically charged atoms and molecules. The purpose of the myelin sheath is to allow electrical impulses to transmit quickly and efficiently along the nerve cells.

Certain neurons or nerve cells may almost equal the length of body itself. The axon of a motor neuron in the spinal cord, that innervates a muscle in the foot can be about 1 meter (3 feet) in length.

Sareolemma appears to be a misspelling of sarcolemma, which is the cell membrane of muscle fibres, NOT neurons. Neurons DO have neurilemma (Schwann cell membrane), axon, dendrites. The spelling error makes option C the correct answer as the absent structure.

In a resting neuron, the exterior of the cell membrane is positively charged relative to the interior due to the higher concentration of sodium ions outside.

The generation and propagation of an action potential in an axon are primarily driven by the rapid influx of sodium ions and the subsequent efflux of potassium ions.

Due to the decussation (crossing over) of nerve pathways in the central nervous system, sensory information from the right side of the body is processed in the left somatic sensory area of the brain.

• Myelin sheath is formed by oligodendrocytes in the CNS and by Schwann cells in the peripheral nervous system. 
• These cells wrap layer upon layer of their own plasma membrane in a tight spiral around axon. 
• The insulating layer checks the leakage of charge and lesser stoppage points (nodes of Ranvier) leading to acceleration of the conduction and conservation of the metabolic energy.
  

1. Myelin sheath is formed by oligodendrocytes in the central nervous system and by Schwann cells in the peripheral nervous system. 
2. These cells wrap layer upon layer of their own plasma membrane in a tight spiral around axon. 
3. The insulating layer checks the leakage of charge and lesser stoppage points (nodes of Ranvier) leading to acceleration of the conduction and conservation of the metabolic energy.

During depolarization, voltage-gated sodium channels open, allowing sodium ions to rush into the neuron, which makes the interior less negative.

Calcium influx into the synaptic terminal is essential for the exocytosis of neurotransmitter vesicles. Without extracellular calcium, the neurotransmitter cannot be released even if the action potential reaches the terminal.

Grey matter is a major component of the central nervous system, consisting of neuronal cell bodies, neuropil, glial cells, synapses, and capillaries.

In a neuron, synaptic vesicles store various neurotransmitter that is released at the synapse. The release is regulated by a voltage-dependent calcium channel. Vesicles are essential for propagation nerve impulses between neurons and are constantly recreated by the cell.

The myelinated nerve fibers contain a myelin sheath surrounding the axons of nerve cells. While in unmyelinated nerve fibre is not enclosed by a Schwann cell and hence does not form a myelin sheath around the axon.

The axon of the neuron secretes the substance named neurotransmitter to communicate with next dendrite.

Irritability or excitability is the ability of nerve cells to respond to environmental stimulus. Primary function of nerve cells is to generate sensory input in response to external and internal stimuli followed by integration of sensory information to generate motor output. Thus, nerve cells exhibit higher rate of irritability as compared to other cell types. 

Cyton is the cell body of the neuron. It contains the nucleus.

Each mammalian neuron consists of a cell body, dendrites, and an axon. The cell body contains the nucleus and cytoplasm. The axon extends from the cell body and often gives rise to many smaller branches before ending at nerve terminals. Dendrites extend from the neuron cell body and receive messages from other neurons. 

A Nissl body is a large granular body found in neurons. These granules are rough endoplasmic reticulum (RER) with rosettes of free ribosomes and are the site of protein synthesis. These are present in cyton of the nerve cell.