Neural Control And Coordination - Class 11 Medical Biology - Extra Questions

• The second cranial nerve i.e cranial nerve || is also called an optic nerve. It is located in the back of the eye.
• The area, where the optic nerve leaves the eye, is called a blind spot.
• REASON: Because it is characterized by the absence of specialized photosensitive (light-sensitive) cells or photoreceptors(rods and cones). therefore, there is no image detection in this area.

• We can pay our concern by not making any discriminatory judgment and taking measures to prevent injuries and abuse. By helping them and caring for them and if possible helping in the detection and treatment of impairments and helping them access the mainstream humanitarian services.

• (A) The transparent part of the sclera is cornea.
• The external layer of the eye is composed of dense connective tissue and is called the sclera. The anterior portion of the sclera is called the cornea.
• The cornea is the transparent front part of the sclera that covers the iris, pupil, and anterior chamber. The remaining part of sclera except cornea region is white in color.
  
• (B)The spot on the retina where cones are most abundant is fovea.
• Fovea a small depression in the retina of the eye where visual acuity is highest. The center of the field of vision is focused in this region because cones are more abundant in this region.

• -Function of B (Pupil)- It regulates the amount of light entering the eye.
• -Function of C (Retina)- It is the site for the formation of image of the objects leading to vision.
• -Function of D (Vitreous Chamber)-The vitreous chamber is the largest cavity in the eye. It helps to maintain the shape of the eyeball.

• Eyelashes are an important part of the eye that protects the eye from various particles present within the air such as dust and other foreign particles.
• It helps to keep moisture like sweat or rain out of your eyes.
• Eyelashes have the ability to sense and alert a possible danger to the eyelids to protect the eyes from it, by blinking of the eyes.
• It also shields your eyes from the bright light of the sun.
  
• Therefore, if eyelashes are not present it will cause a damage to our eyes.

The tissue of the nervous system consists of two types of cells, those are the Nerve cells and Glial cell. The nerve cells are called Neuron and the glial cells are called neuralgia. Among these, the neurons performed the function of the nervous system by transmitting information from one part of the body to another and the glial cells are supporting elements.

The Neurons are the structural and functional units of the nervous system.

A typical structure of neuron consists of a cell body and two processes, those are Dendron and Axon. The cell body of a neuron is like other cells of the body, consisting of a nucleus and cytoplasm covered by a plasma membrane. The cytoplasm contains various organelles and inclusions. In adult nerve cells, the centrosome is absent or inactive so their division does not occur. Specialized cytoplasmic organelles called Nissl granules or Nissl body made up of ribonucleoprotein are found in the cell body except in the axon hillock region from where the axon arises. These granules are also present in dendrons but absent in axon.

 In general, a neuron has many dendrons. However, in some neurons, the Dendron may be only single or may be absent in case. The single long efferent process of a neuron is called axon which carries impulses away from the cell body to the next neuron or the target organ, such as muscle or gland.

Axons are usually unbranched. However, they give a few small terminal branches called telodendria having swollen ends known as terminal buttons. An axon is also called nerve fiber. A neuron possesses only one axon and the variable number of dendrons. If there is only one process, it is usually the axon. In such type of neurons, the cell body receives stimulation. In some specialized neurons, the axon may be absent, such as adrenal medullary cells and amacrine cells of a retina of an eye.

1. Fovea centralis -is a small depression which is located in the eye in the center of the macula (where eyesight is sharpest) which is composed of closely packed cones in the eye and it does not have any rods in it, it is necessary for sharp vision in conditions of bright light.
   
2. Choroid - it is also known as choroidea or choroid coat. It is the thin erectile vascular layer of the eye. It has connective tissues and blood vessels which lie between the retina and the sclera. It contains the retinal pigmented epithelial cells and provides oxygen and nourishment to the outer retina, i.e., the inner portion of the retina.

1. The autonomic nervous system is divided into two main divisions: Sympathetic nervous system 
   
2. Parasympathetic nervous system
   

• Sympathetic preganglionic fibres tend to be shorter than parasympathetic preganglionic fibres because sympathetic ganglia are often closer to the spinal cord that are the parasympathetic ganglia. 
• This is due to the number of synapses formed by the preganglionic fibres with ganglionic neurons. 
• Hence, the parasympathetic division of the autonomic nervous system has longer preganglionic fibres.

• The structure responsible for protecting the eye from sweat is eyelids.
  
• It is a thin fold of skin that covers as well as protects the human eye from dust, foreign debris and sweat.

• The internal layer of the eye which prevents reflection of light is known as choroid layer.
  
• It is a black pigmented layer under the sclera.
• This layer is rich in blood supply that brings oxygen and nutrients to nourish the eyeball.

• The autonomic nervous system controls the internal organs and glands of the body. 
• There are three divisions of the autonomic nervous system- the sympathetic nervous system, the parasympathetic nervous system, and the enteric nervous system. 
• In the sympathetic nervous system, the cell bodies of the preganglionic neurons are located in the lateral horns of the grey matter of the 12th thoracic and first 2 lumbar segments of the spinal cord.
• Therefore, the sympathetic system is also called the thoracolumbar division.
  

• The ear performs two sensory functions, hearing and maintenance of body balance.
• Anatomically, the ear can be divided into three major sections called the outer ear, the middle ear, and the inner ear. 

 The autonomic nervous system of the body is the part of the nervous system that controls involuntary actions. It controls the body functions that cannot be acted on by will, for example, breathing, the beating of the heart, digestion, etc. the autonomic nervous system is further of two types- the sympathetic nervous system and the parasympathetic nervous system.

The sympathetic nervous system functions in flight or fight or emergency situations. It increases the heart rate and increases the muscular strength. It slows the body functions like urination that are less important during emergencies.

The parasympathetic nervous system has actions antagonistic to those of the sympathetic nervous system. It lowers the heart rate and decreases the blood pressure. It stimulates the removal of wastes from the body via excretion and urination.

• Eyes are paired sense organs located in the sockets of the skull called orbits.
• Eyes are supplied with a second cranial nerve called optic nerve. 
• The wall of the eyeball consists of three layers -

• When the light enters the human eye through the cornea, it then passes through the aqueous humor, the lens and the vitreous humor. Then the image is formed on the retina of the eye.

• Cornea: The cornea is the dome-shaped outer layer of the eye that helps in focusing light by refracting or bending light and thereby helps in vision.
  
• Iris: The iris is a circular structure present behind the cornea and regulates the amount of light that enters the eye by changing the size of the pupil.

• The retina is the innermost tunic of the eyeball. It is a thin, delicate and transparent membrane. It appears purplish red in colour.
  
• The retina is composed of three distinct regions. They are Optic disc, macula lutea and peripheral retina.
• It's composed of several layers, including one that contains specialized cells called photoreceptors.
• There are two types of photoreceptor cells in the human eye : rods and cones. Rods are located throughout the retina; cones are concentrated in a small central area of the retina called the macula.
• At the center of the macula is a small depression called the fovea. The fovea contains only cone photoreceptors and is the point in the retina responsible for maximum visual acuity and color vision.
• Rod photoreceptors detect motion, provide black-and-white vision and function well in low light. 
• Cones are responsible for central vision and color vision and perform best in medium and bright light.
• Light rays are focused by the cornea and lens onto the retina, where vision begins. Photoreceptor cells take light focused by the cornea and lens and convert it into chemical and nervous signals which are transported to visual centers in the brain by way of the optic nerve.
  

• Sympathetic division controls involuntary and automatic physical reactions) that responds to emergency situations by mobilizing and controlling the energy necessary to cope with the situation.

• The sympathetic nervous system can accelerate heart rate, widen bronchial passages, decrease motility of the large intestine, constrict blood vessels, increase peristalsis in the esophagus, cause pupillary dilation, piloerection (goose bumps) and perspiration (sweating), and raise blood pressure.
• The sympathetic division is also called the thoracolumbar division because the preganglionic neurons are located along the spinal cord from segments T1 to L 2, basically in the middle section of the length of the spinal cord.

• A unipolar neuron is a type of neuron in which only one protoplasmic process (neurite) extends from the cell body.
• A bipolar neuron or bipolar cell is a type of neuron which has two extensions (one axon and one dendrite).
  

$$\textbf{Solution:}$$ 

$$\bullet$$ Myelin sheath covers the axon of the myelinated neurons. It acts as the insulator covering the axon. The white matter contains myelinated neurons. 

$$\bullet$$ Parts of the brain given here which are composed of white matter include the thalamus, hypothalamus, pons and medulla oblongata. 

$$\bullet$$ Neuronal cell bodies and the unmyelinated neurons form the grey matter.

$$\bullet$$ The cerebral cortex and cerebellar medulla are the structures that are composed of grey matter.