Neuron as Structural and Functional Unit of Neural System Questions in English

(D) . Multipolar neurons have several dendrites and one axon.
Most neurons in the brain and spinal cord of our body are of this type.

(D) By observing the provided diagram of the neuron:
$1$. $A$ points to the main body of the neuron,which is the Cell body (Cyton).
$2$. $B$ points to the granular structures within the cytoplasm,known as Nissl bodies.
$3$. $C$ points to the branched processes extending from the cell body,which are Dendrites.
$4$. $D$ points to the central spherical structure,the Nucleus.
$5$. $E$ points to the initial segment of the axon that lacks a myelin sheath,the Naked portion of axon.
$6$. $F$ points to the insulating layer surrounding the axon,the Myelin sheath.
$7$. $G$ points to the gap between two myelin sheaths,the Node of Ranvier.
Therefore,the correct matching is $A$ = Cell body,$B$ = Nissl bodies,$C$ = Dendrites,$D$ = Nucleus,$E$ = Naked portion of axon,$F$ = Myelin sheath,$G$ = Node of Ranvier.

(D) Nerve fibres are specialized structures of neurons,consisting of axons or dendrites.
Muscle fibres are characterized by the presence of myofibrils,which are contractile elements,and a specialized plasma membrane called the sarcolemma.
In contrast,nerve fibres possess dendrites,which are branched projections that receive signals and carry them toward the cell body,a feature absent in muscle fibres.
Therefore,the presence of dendrites is a distinguishing feature of nerve fibres.

(A) Neurons are derived from the ectodermal germ layer during embryonic development. The specific precursor cells that differentiate into neurons are known as neuroblasts. These cells undergo division and migration to form the mature nervous system.

(A) Neurons are classified into two types based on the length of their axons: Golgi type-$I$ and Golgi type-$II$.
Golgi type-$I$ neurons possess very long axons that extend far from the cell body.
Golgi type-$II$ neurons have short axons that do not extend far from the cell body.

(D) The myelin sheath is a lipid-rich insulating layer that surrounds the axons of many neurons in the vertebrate nervous system.
It is formed by Schwann cells in the peripheral nervous system and by oligodendrocytes in the central nervous system.
This sheath increases the speed of electrical impulses along the nerve fibre.
Therefore,it is a characteristic feature of vertebrate nerve fibres.

(A) Neuroglia cells are the supporting cells of the nervous system that provide protection and structural support to neurons.
Unlike neurons,neuroglia cells do not possess Nissl's granules,which are specialized rough endoplasmic reticulum involved in protein synthesis.
Therefore,the correct distinction is that they lack Nissl's granules.

(B) In myelinated nerve fibers,the myelin sheath is not continuous but is interrupted at regular intervals by gaps known as the Nodes of Ranvier.
These nodes represent the junction or space between two adjacent Schwann cells.
Therefore,the correct option is $(b)$.

(A) Nerve cells (neurons) are the longest cells in the human body. Some nerve cells,such as those that extend from the spinal cord to the feet,can reach lengths of over a foot $(30 \ cm)$ or more. They are specialized for the transmission of electrical impulses throughout the body.

(C) Nissl's granules,also known as Nissl bodies,are basophilic structures of various shapes such as angular,conical,or rhomboidal.
They consist of rough endoplasmic reticulum with free polyribosomes.
These granules are characteristically found in the cell body (cyton) and dendrites of neurons,but they are most prominently located in the cyton.

(D) Nissl's granules are characteristic features of the nerve cell body (cyton) and dendrites.
They are composed of rough endoplasmic reticulum $(RER)$ and free ribosomes.
Because they contain a high concentration of ribosomal $RNA$ $(rRNA)$,which is acidic,they show a strong affinity for basic dyes (basophilic).
Therefore,the correct answer is Ribosomes.

(B) The correct answer is $B$.
Neurons consist of three main parts: the cell body (cyton),dendrites,and the axon.
Dendrites are short,branched extensions that act as the afferent processes,meaning they receive electrical impulses from other neurons or sensory receptors and transmit them toward the cell body.
In contrast,the axon is the efferent process that carries impulses away from the cell body.

(D) The cell body,also known as the cyton or soma,is the metabolic center of a neuron.
In the central nervous system $(CNS)$,cell bodies are concentrated in the grey matter of the brain and the spinal cord.
In the peripheral nervous system $(PNS)$,cell bodies are found in clusters known as ganglia.
Therefore,cell bodies are present in the brain,spinal cord,and ganglia.

(B) Neurons are classified on the basis of the number and nature of their processes (dendrites and axons) arising from the cell body (cyton).
Based on this,neurons are classified into four types:
$(i)$ Apolar or non-polar neurons: These lack any processes.
$(ii)$ Unipolar neurons: These have a single process arising from the cell body.
$(iii)$ Bipolar neurons: These have two processes,one axon and one dendrite.
$(iv)$ Multipolar neurons: These have one axon and multiple dendrites.

(D) Neuroglial cells (or glia) are non-neuronal cells in the central and peripheral nervous systems that do not produce electrical impulses.
They perform several critical functions:
$1$. They act as packing cells that support and protect neurons.
$2$. They provide metabolic support and nutrition to neurons.
$3$. Some theories suggest they play a role in memory storage by modulating synaptic plasticity and potentially storing information via $RNA$ codes.
Therefore,all the given statements are correct.

(D) The $Node$ of $Ranvier$ is a gap in the myelin sheath of a nerve cell.
These nodes are found along the $Axon$ of myelinated neurons.
They facilitate the rapid conduction of nerve impulses through saltatory conduction.
Therefore,the correct option is $D$.

(C) The $Axon$ $hillock$ is a specialized region of the cell body $(cyton)$ of a neuron. It is the conical-shaped area from which the axon originates. This region is significant because it is typically the site where action potentials are initiated.

(B) Nerve cells,or neurons,are the structural and functional units of the neural system.
They are specialized cells designed to transmit electrical impulses.
The defining structural features that distinguish neurons from other cell types are the $Axon$ and $Dendrites$.
$Dendrites$ receive signals from other neurons,while the $Axon$ conducts impulses away from the cell body to other neurons or effector organs.

(C) The axon is the long,slender projection of a nerve cell (neuron) that conducts electrical impulses away from the cell body.
Inside the axon,the cytoplasm is referred to as the axoplasm,and the central core is known as the axis cylinder.
The axoplasm contains fine,thread-like structures known as neurofibrils.
These neurofibrils are proteinaceous filaments,typically about $90 \ \mathring{A}$ in diameter,which provide structural support and assist in the transport of materials along the axon.

(C) The $neurilemma$ (or $neurolemma$) is the outermost nucleated cytoplasmic layer of $Schwann$ cells that surrounds the axon of the neuron.
In peripheral nerve fibers,$Schwann$ cells wrap around the axon to form the $myelin$ $sheath$.
After the formation of the $myelin$ $sheath$,the remaining cytoplasm and the nucleus of the $Schwann$ cell are pushed to the periphery,forming the $neurilemma$.
Therefore,the $neurilemma$ surrounds the $myelin$ $sheath$.

(B) The myelin sheath is an electrically insulating layer that surrounds the axons of many neurons.
It is formed by glial cells,specifically Schwann cells in the peripheral nervous system and oligodendrocytes in the central nervous system.
This sheath increases the speed at which electrical impulses propagate along the myelinated fiber.

(D) . Bipolar neurons are typically spindle-shaped,having the axon at one pole and a dendron at the other.
They are found in the retina,spiral ganglion of the cochlea,vestibular ganglion,and olfactory neuroepithelium.

(D) neuron consists of three main parts: the cell body (cyton),dendrites,and the axon.
$1$. Dendrites are the afferent processes that receive signals and conduct them towards the cell body.
$2$. The axon is the single,long,efferent process that conducts nerve impulses away from the cell body to another neuron or effector organ.
Therefore,the efferent process of the neuron is called the axon.

(C) . Neurons are the structural and functional units of nervous tissue.
They are specialized cells responsible for receiving,processing,and transmitting information through electrical and chemical signals.
Their number is quite high,exceeding $1 \times 10^{12}$ in the human brain alone.

(D) The nervous system is composed of neurons,which consist of a cell body $(Cyton)$,an axon $(Axon)$,and often a protective covering called the $Myelin$ $sheath$.
$Intermedin$,also known as $Melanocyte-Stimulating$ $Hormone$ $(MSH)$,is a hormone secreted by the intermediate lobe of the pituitary gland,which is part of the endocrine system,not the nervous system.

(A) Nissl's granules are characteristic granular bodies found in the cell body (cyton) and dendrites of neurons. They are composed of rough endoplasmic reticulum and ribosomes,which are involved in protein synthesis. These granules are absent in the axon and the axon hillock.

(A) Neuroglial cells,also known as glial cells or glia,are non-neuronal cells in the central nervous system and peripheral nervous system.
They do not produce electrical impulses like neurons.
Their primary function is to provide structural support,protection,insulation,and nourishment to neurons.
Therefore,they are best defined as nonsensory supporting cells.

(C) The nervous tissue is composed of neurons and neuroglial cells. Neurons are excitable cells,whereas neuroglial cells (which include Schwann's cells) are non-excitable,supporting cells that protect and support the neurons. Therefore,the correct answer is $C$.

(D) The myelin sheath is a lipid-rich insulating layer that surrounds the axons of neurons.
Phosphorus is a critical component of phospholipids,which are the primary structural lipids forming the myelin sheath.
Therefore,phosphorus is essential for the synthesis and maintenance of the myelin sheath.

(A) neuron consists of a cell body (cyton),dendrites,and an axon.
$1$. Dendrites are the afferent processes that receive signals and conduct them towards the cell body.
$2$. The axon is the single,long,efferent process that conducts nerve impulses away from the cell body to a synapse or effector organ.
Therefore,the efferent process is the axon.

(D) In a nerve,nerve fibres are organized into bundles known as fascicles. Each fascicle is surrounded by a connective tissue sheath called the perineurium. The entire nerve is then enclosed by the epineurium,while individual nerve fibres are wrapped in the endoneurium.

(B) The weakest current strength that can excite a tissue is known as the $Rheobase$.
$Chronaxia$ is the minimum time required for a current of twice the $Rheobase$ strength to excite a tissue.
$Saltatory$ conduction refers to the jumping of nerve impulses along myelinated axons.
$Reflex$ $arc$ is the neural pathway that controls a reflex action.

(D) Nissl's granules are characteristic structures found in the cell body (cyton) and dendrites of neurons.
These granules are composed of rough endoplasmic reticulum $(RER)$ and free ribosomes.
Since ribosomes are primarily composed of ribosomal $RNA$ $(rRNA)$ and proteins,they are essentially sites of protein synthesis.
Therefore,Nissl's granules are present in neurons and are made up of $RNA$ and proteins.

(D) nerve fibre is surrounded by three layers of connective tissue.
$1$. The $Endoneurium$ is the innermost layer that directly covers individual nerve fibres (axons).
$2$. The $Perineurium$ surrounds a bundle of nerve fibres known as a fascicle.
$3$. The $Epineurium$ is the outermost layer that encloses the entire nerve.
Therefore,the immediate covering of a nerve fibre is the $Endoneurium$.

(C) The correct answer is $C$.
The neuron (nerve cell) is considered the largest cell in the human body in terms of length.
Some neurons,such as those extending from the spinal cord to the feet,can reach a length of nearly $1 \ m$ or more,which is significantly longer than any other cell type in the body.

(C) The dorsal root ganglion contains the cell bodies of sensory neurons. These neurons carry sensory information from the peripheral receptors toward the central nervous system. Therefore,the dorsal root ganglion is classified as sensory.

(C) Nissl granules are specialized rough endoplasmic reticulum found in the cell body (cyton) of neurons. They are highly active in protein synthesis,which is essential for maintaining the structural and functional integrity of the nerve cell. During the early stages of nerve cell degeneration (chromatolysis),the Nissl granules are the first to undergo dissolution or fragmentation,making them the most sensitive indicators of neuronal injury.

(A) The ventricles of the brain and the central canal of the spinal cord are lined by a specialized type of epithelial tissue known as ependymal cells.
These cells are a type of glial cell that plays a crucial role in the production,circulation,and monitoring of cerebrospinal fluid $(CSF)$.

(D) The neural system is composed of neurons,which are classified based on the presence or absence of a myelin sheath.
$1$. Myelinated nerve fibres are found in spinal and cranial nerves.
$2$. Non-myelinated nerve fibres are enclosed by a Schwann cell that does not form a myelin sheath around the axon and is commonly found in autonomous and the somatic neural systems.
Therefore,autonomic nerves contain non-myelinated nerve fibres.

(B) The myelin sheath,also known as the medullary sheath,is a lipid-rich layer that surrounds the axons of many neurons.
It acts as an insulating layer that increases the speed of electrical impulses along the nerve fibres.
In the $CNS$ (Central Nervous System),myelin is produced by oligodendrocytes,while in the $PNS$ (Peripheral Nervous System),it is produced by Schwann cells.
Therefore,the correct answer is $B$.

(A) Nodes of Ranvier are the periodic gaps in the myelin sheath of an axon.
These gaps allow for saltatory conduction,which increases the speed of nerve impulse transmission.
Therefore,they are specifically located along the axon of a neuron.

(A) The $Axon$ is a single,long process of uniform thickness that extends from the cell body.
It contains neurofibrils and neurotubules but lacks $Nissl's$ granules,the $Golgi$ complex,and ribosomes.
$Nissl's$ granules are typically found in the $Cyton$ (cell body) and $Dendrites$ (dendrons) of the neuron,where they are involved in protein synthesis.

(A) The correct answer is $A$.
Myelinated or medullated nerve fibers $(Axon)$ are surrounded by an inner thick medullary sheath composed of a fatty substance called myelin.
This myelin sheath acts as an electrical insulator and increases the speed of nerve impulse conduction.

(B) $Nissl's$ granules are specialized structures found in the cell body $(cyton)$ and dendrites of neurons.
They are composed of rough endoplasmic reticulum $(RER)$ with free ribosomes and are responsible for protein synthesis within the nerve cell.

(D) . Neurons are the specialized cells of the nervous system.
Neurons in the central nervous system lack the ability to divide or regenerate once they have reached maturity. Therefore,if they are damaged or die,they are not replaced by new cells,unlike skin cells,liver cells,or osteocytes,which possess varying degrees of regenerative capacity.

(B) Nerve cells (neurons) consist of a cell body,dendrites,and an axon. Neurilemma is the outermost nucleated cytoplasmic layer of Schwann cells that surrounds the axon of the neuron.
Sarcolemma is the fine transparent tubular sheath which envelops the fibers of skeletal muscles. Therefore,nerve cells do not possess sarcolemma.

(C) The junction between a motor neuron and a muscle fiber is called the neuromuscular junction. The terminal part of the motor neuron that contacts the muscle fiber is specifically referred to as the motor end plate or simply the end plate. This structure contains receptors for neurotransmitters like acetylcholine,which facilitate the transmission of nerve impulses to the muscle,triggering contraction.

(A) The dendrites are short,branched processes that project from the cell body $(cyton)$.
They contain neurofibrils,neurotubules,and $Nissl$ granules.
Their primary function is to receive nerve impulses and conduct them towards the cell body $(cyton)$.

(C) The correct answer is $C$.
Nerve cells,also known as neurons,are the longest cells in the human body.
Some neurons,such as those extending from the spinal cord to the feet,can reach lengths of over a foot ($30 \ cm$ or more).
These cells are specialized for transmitting electrical impulses over long distances throughout the body.

(B) The medullary sheath (myelin sheath) is not continuous along the entire length of the nerve fibre.
It is interrupted at regular intervals by gaps known as $Nodes \text{ of } Ranvier$.
In these regions, the $Schwann$ cells are absent, which results in the discontinuity of the myelin sheath.