CBSE Questions for Class 11 Medical Biology Neural Control And Coordination Quiz 11 - MCQExams.com

1. The first thing light encounters when it enters the eye is the cornea, a protective clear covering over the pupil and iris. The cornea bends the light and begins to form an image.
2. Light passes from the cornea to the pupil, the dark circle in the centre of the iris, which is the coloured portion of the eye. The pupil regulates the amount of light that will enter the inner eye based on environmental conditions: It dilates, growing bigger to receive more light under dim lighting conditions, and shrinks in response to bright light. This response is quicker in young individuals and tends to slow with increasing age.
3. From the pupil, light waves travel to the lens of the eye. The lens is a clear, flexible structure that focuses an upside-down image onto the retina. It is flexible so that it can focus on images that are close or far away. Eye injuries, normal variations in the eye and age can distort the lens, making it difficult to focus on nearby or faraway objects -- you see the objects, but details are hazy. Late in life, the lens can also become clouded and form cataracts that make images seem hazy and dim.
4. The lens focuses light and images on the retina, a layer of light-sensitive cells at the back of the eye. It is made up of two kinds of photoreceptor cells: cones and rods. The cones transmit colour and sharp images. The concentration of cones is low on the sides of the retina and increases as the cones approach the centre of the retina or the macula. The rods are more sensitive to light and are more numerous than cones; They let you see when lighting is dim, although what you see lacks colour and clear details.
5. Once the retina senses the image, it sends impulses to the optic nerve at the back of the eye. The optic nerve then transmits them to special areas in the brain, which automatically flips the upside-down image so that it becomes upright again. Disease or injury can damage the optic nerve, resulting in varying degrees of blindness.

• The choroid is a thin layer tissue that is part of the middle layer of the wall of the eye, between the sclera and the retina.
  
• The choroid is filled with blood vessels that bring oxygen and nutrients to the eye.

• The retina is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs. 
• The primary light-sensing cells in the retina are the photoreceptor cells, which are of two types: rods and cones. 
• Rods function mainly in dim light and provide black-and-white vision. Cones function in well-lit conditions and are responsible for the perception of colour.
• Rhodopsin is a biological pigment found in the rods of the retina.
•  Rhodopsin is extremely sensitive to light, and thus enables vision in low-light conditions. Hence, retinal is sensitive to light energy, a part of rhodopsin and found in both rods and cones.

• The nervous system is divided into two major subdivisions. They are the Central nervous system(brain and spinal cord) and peripheral nervous system.
• The peripheral nervous system is in turn divided into two divisions. They are a somatic and autonomic nervous system.
• The main function of the PNS is to connect the CNS to the limbs and organs, essentially serving as a relay between the brain and spinal cord and the rest of the body.
  
• The autonomous nervous system is completely independent of the central nervous system is a false statement because, within the brain, the autonomic nervous system is regulated by the hypothalamus(part of CNS).
  

• The autonomic nervous system is divided into two subdivisions. They are the sympathetic and parasympathetic nervous system.
• The sympathetic nervous system (SNS) controls the body's responses to a perceived threat and is responsible for the "fight or flight" response while The parasympathetic nervous system (PNS) controls homeostasis and the body at rest and is responsible for the body's "rest and digest" function.
  
• Hence Sympathetic and parasympathetic nervous systems are often antagonistic(opposing) in their functions.
• So, the given statement is false.

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

B. Synaptic knob are the bulbous structures present at the terminal end of an axon.

C. Dendrites, also called 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 cells, also called neurilemma cells are any of the cells in the peripheral nervous system that produce the myelin sheath around neuronal axons.

So, the correct option is 'B'.

Correct answer: A

Explanation:

The gaps approx. 1 mm wide formed between the two adjacent myelin sheath cells, along the axons are called as the nodes of Ranvier.

Nodes of Ranvier are the uncovered part of axons.

Also they are the periodic gaps in axon that propagate the action potential down an axon.

Hence, the proper answer is 'Axon'.

• 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.