Neural tissues - class-IX

• Spinal cord and brain control all activities of our body. Spinal cord possesses nerves, which carry messages between the brain and the body.
•  The brain sends commands for the functioning of different organs of the body via nerves. 
• Therefore, they are made of nervous tissue. Hence, option B is correct.  

Cyton or cell body of a neuron possesses cytoplasm and nucleus. It contains many organelles, including granules called Nissl granules, which are composed largely of rough endoplasmic reticulum and free polyribosomes. Therefore, option D is correct. 

• The densely packed nerve cells present in the brain, spinal cord, and sense organs are called neurons. They are specialized for the conduction of nerve impulses and they are mainly of two types, sensory neurons, and motor neurons.

• The neurons are specialized for the conduction of nerve impulses. Conduction of nerve impulses is aided by synapse. 
• Synapse is a structure that allows a neuron to pass the electrical signal or chemical signal to another neuron. Therefore, option A is correct.  

• Dendrons are short, branched parts arising from cell body or cyton. Dendrons are many in number. 
• Neurolemma is the outermost nucleated cytoplasmic layer of Schwann cells. It surrounds the axon of the nerve cell. 
• Neurofibrils are long, thin, microscopic fibrils that run in every direction in the cell body and also extend in axon and dendrites. 
• Axon is a long, thin hair-like processes coming out of the cyton of a nerve cell. 

Cyton is a cell body of the neuron containing a nucleus, cytoplasm.   
Synapse is a structure that allows a neuron to pass an electrical signal or chemical signal to another neuron. 
Axon is a long, thin, hair-like process arising from the cell body of the neuron. 
A neuron is the functional unit of nervous tissue. It contains cyton or cell body, long, thin hair like the process called axon and many short branches called dendrites. Therefore, option C is correct. 

The longest cells in the human body are neurons. Neurons are cells within the nervous system and carry messages throughout the body. Although they range in size, some neurons are 3 feet long. These include the neurons that go from the skin into the spinal cord and up into the brain stem. Their impressive length makes neurons the longest cells in the body. 

The length of the muscle cell is 1-40 micrometers.
Nerve cells possess a cell body and one to many thin, fiber-like axons.
Some nerve cells possess axons as long as 1 meter. Therefore, option B is correct. 

Dendrite is a short branched extension of a nerve cell, along which impulses received from other cells at synapses are transmitted to the cell body. A neuron is an electrically excitable cell that processes and transmits information through electrical and chemical signals. These signals between neurons occur via synapses, specialized connections with other cells. An axon is a long, slender projection of a nerve cell, or neuron, that typically conducts electrical impulses away from the neuron's cell body. Myelinated axons are known as nerve fibers. The function of the axon is to transmit information to different neurons, muscles and glands. A neutrophil is a type of white blood cell, a type of granulocyte, and a type of phagocyte. 

The nerve cells stop dividing after the birth of the child. There are no centrosomes in the neurons. Since there are no centrosomes the formation of the spindle apparatus cannot take place. The spindle fibres are necessary for the cell division to take place because they help in the attachment of the chromosomes

The neurotransmitter substance found between a motor neuron and a muscle cell is acetylcholine. In the autonomic nervous system, acetylcholine (ACh) is the neurotransmitter in the preganglionic sympathetic and parasympathetic neurons. ACh is also the neurotransmitter at the adrenal medulla and serves as the neurotransmitter at all the parasympathetic innervated organs. ACh is also the neurotransmitter at the sweat glands, and at the piloerector muscle of the sympathetic ANS. 

The average length of muscle fibers is of a few centimeters. 
The average size of epithelial cells is of few microns. 
Nerve cells possess a cell body and one to many thin, fiber-like axons.

• The axon terminals are the end of axon fiber and located close to the dendrites of another neuron, forming a connection known as a synapse and allowing them to send messages from neuron to neuron with the help of neurotransmitter. 
• So, a nerve cell transmits it's impulse to another through its axons. 

In the nervous system, a synapse is a structure that permits a neuron (or nerve cell) to pass an electrical or chemical signal to another neuron. Synapsis is the fusion of chromosome pairs at the start of meiosis. A cell junction (or intercellular bridge) is a type of structure that exists within the tissue of some multicellular organisms, such as animals. Cell junctions consist of multiprotein complexes that provide contact between neighbouring cells or between a cell and the extracellular matrix. Synapticula is one of the numerous calcareous processes which extend between, and unite, the adjacent septa of certain corals.

The myelin sheath of neurons provides them with an insulating covering. It allows rapid transmission of signals from the nervous system to the body and vice-versa. Any damage to the myelin sheath will cause hindrance and slowing down of the transmission of signals to the axons.

So, the correct answer is 'Action potentials would be conducted too slowly along the neurons'.

The four segments of the spinal cord, going from top to bottom, these are the cervical, thoracic, lumbar and sacral segments. Injury to a certain segment of the cord will generally affect the parts of the body below the point of injury. Depending upon the severity and extent of the injury, there will be varying loss of movement and sensation. Damage to the spinal cord can also affect bodily functions such as breathing, bowel and bladder function, hormone release, temperature control, and movement of food through the stomach and intestines. It bears repeating that no two spinal cord injuries behave exactly alike. 

A unipolar neuron is a type of neuron, in which only one neurite or protoplasmic process extends from the cell body. Bipolar neuron is a type of neuron, which has two processes extending from the cell body. Pseudounipolar contains an axon, that has split into two branches, one branch runs to the periphery and the other to the spinal cord. A multipolar neuron is a type of neuron that possesses a single, long axon and many dendrites. The majority of the neurons are multipolar.

The dendrites are the short, cytoplasmic extension which is present in the sensory organs and are responsible for the reception of the electric impulse. The dendrite passes the electric impulse to the cell body which passes the impulse to the axon. The axon is the long cytoplasmic extension of the neuron. There are telodendrons which are present at the tail of the axons. These regions can release neurotransmitters which can help in the transmission of the impulse through the synapse to the next neuron.

In the nervous system, afferent neurons (otherwise known as sensory neurons), carry nerve impulses from receptors or sense organs toward the central nervous system.

Neurons are the structural and functional units of the nervous system, responsible for transmitting electrical and chemical signals.

The neuroglia or glial cells are defined as supportive cells of the central nervous and peripheral nervous system that primarily support, protect and nourish the neurons. There are basically four types of neuroglial cells:-

Bone, Blood and Lymph are all types of specialized connective tissue. But, nerve cells belong to a different set of tissues named nervous tissue. Nervous Tissues are the primary tissue of the nervous system that allows communication between various organs and tissues. It is composed of glial cells and neurons.

Cyton, axon, and myelin are all components of a neuron. Intermedin is a hormone produced by the intermediate lobe of the pituitary gland, not a part of nervous tissue.

• The multipolar neuron is the neuron which has many dendrons and one axon.
• Multipolar neurons are the most common type of neuron. They are located in the central nervous system (brain and spinal cord) and in autonomic ganglia.
• Hence Multipolar neuron means The neurons which have many dendrons and one axon.
• So, the correct answer is 'with many dendrons and one axon'.

Answer is option A i.e. "Axo-axonic"
Axo-axonic is a type of neural structure synapse between two axons. In case case, the axon of one neuron makes synapse with axon of the other neuron (i.e both, site of neurotransmitter release and site of receptor binding, are axons). It is essential for the transmission of nerve impulses. Axoaxonic junction modulate neuronal transmission by either inhibiting or facilitating depolarization at the presynaptic membrane.

Neurons feature many thin projecting fibres called axons, which penetrate deep into tissues. They are able to communicate with other cells by chemical or electrical means at synapses. Neuronal function is supported by neuroglia, specialized cells which provide nutrition, mechanical support, and protection.

Nerve cells carry out different function as, to receive the message from within or outside of the body, to transfer the messages from body part to the brain, to carry the signal from the brain to different parts of the body. Thus nerve cell helps the brain in control and coordination of the body.
Therefore, option D is correct. 

a) Multipolar neurons have more than two processes emanating from the neuron cell body. They are mainly located in central nervous system and are most common type of human neurons.

• Unipolar nerve cell means Nerve cell without dendron. They have only one structure extending from the soma(cell body).
• Unipolar neurons are common in insects, where the cell body is often located at the periphery of the brain and is electrically inactive.
  
• Hence Unipolar nerve cell means Nerve cell without dendron.
• So, the correct answer is 'Nerve cell without dendron'.

A complex network of nerve cells or neurons forms the nervous system. This system is responsible for transmitting electrical impulses throughout the body.

The nature of nerve impulse is electrochemical(with in neuron it is electrical and between neuron it is chemical).

• The human body is made up of trillions of cells. Cells of the nervous system called nerve cells or neurons, are specialized to carry "messages" through an electrochemical process. Neurons carry out basic cellular processes such as protein synthesis and energy production.
• Protein synthesis in the extensions of nerve cells, called dendrites, Local protein synthesis in dendrites, not in the cell body of nerves, provides the ability to respond rapidly and selectively to external stimuli. 

Calcium is involved in muscle contraction, Iodine is essential for thyroid function, and Cobalt is part of Vitamin B12 (energy metabolism). Chlorine is an electrolyte, but the pairing 'Cl - nerve conduction' is less specific or standard compared to the other biological roles listed.

• Myelin is a layered substance made of phospholipid, cholesterol and protein that covers the axons of the neurons.
• It insulates the nerve impulses from the surrounding nerve fibres. 
• It also increases the speed of impulses through nerve axons.
  
• It is formed in the central nervous system by glial cells called the oligodendrocytes.
• Whereas, in the peripheral nervous system they are produced by Schwann cells.
  
• So, the correct answer is 'Schwann cells'.

• Myelin is an insulating layer or sheath that forms around nerves, including those in the brain and spinal cord.
•  It is made up of protein and fatty substances. 
• This myelin sheath allows electrical impulses to transmit quickly and efficiently along the nerve cells.
•  If myelin is damaged, these impulses slow down. Hence, the Myelin sheath has layers of fat and protein up to 100.

The long extensions of a nerve cell (axons and dendrites) are essential for its function of transmitting signals over long distances within the body.

Bipolar neurons are specialised neurons that have two cytoplasmic extensions. Out of which one serves as an axon and other serves as a dendrite both having similar branches. They function in sight, hearing, tasting, etc. They are located in the retina of the eyes, the roof of the nasal cavity, inner ear.