NCERT Solutions for Class 11 Science Biology Chapter 21 - Neural Control And Coordination

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Chemical which are released at the synaptic junction are called neurotransmitters. They are involved in the transmission of impulses at the synapse. A synapse consists of nerve terminal called pre-synaptic knob that contains synaptic vesicles in which neurotransmitters are present.

Hence, the correct answer is option B.

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The ion-gated channels control the movement of Na⁺ and K⁺ ions on both sides of the neuron. Other ions given in the options have different function and are not involved in nerve excitation. Ca²⁺ ions are related to muscle contraction, Mg²⁺ ions act as a cofactor in some reactions, Cl^– ions are important for setting cell membrane potential.

Hence, the correct answer is option A.

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Resting membrane potential is maintained by the active transport of ions by the sodium-potassium pump or ion-pumps that transport 3Na⁺ outward for every 2K⁺ into the cell.

Hence, the correct answer is option C.

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The autonomic neural system consists of two parts:-
Sympathetic and parasympathetic neural systems that control the functions of our visceral organs of the body. Somatic neural system is a part of peripheral nervous system which is not related to function of visceral organs. Also, CNS is not related to it.

​Hence, the correct answer is option B.

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Brain is not involved in any kind of reflex action. However, muscle spindle, inter-neuron, and motor neuron are involved in the reflex arc.

Hence, the correct answer is option C.

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Emotions such as excitement, pleasure, rage and fear are controlled by limbic lobe or limbic system along with the hypothalamus.

Hence, the correct answer is option C.

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Rod cells of the retina contain a purplish red coloured pigment called rhodopsin. This pigment consists of opsin and retinal. The photosensitive compound in the eye is composed of opsin protein and retinal which is the aldehyde of vitamin A.
Other vitamins B, C and D are not related with vision.

Hence, the correct answer is option A.

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Human eyeball consists of three layers and it encloses lens, aqueous humor and vitreous humor.

Hence, the correct answer is option B.

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Wax secreting glands present in the ear canal is called sebaceous gland or ceruminous gland. 
On the other hand, sweat gland produces sweat, prostate gland secretes fluid that nourishes sperm, and Cowper's gland is one of glands present in males that helps in lubricating urethra for sperms to pass through it.

Hence, the correct answer is option D.

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The part of internal ear responsible for hearing is cochlea. It is a spirally coiled structure which is connected with saccule. It resembles a snail shell in appearance.

Hence, the correct answer is option A.

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The organ of corti is a structure that is present in cochlea. Cochlea consists of the three fluid filled chambers:- the upper scala vestibuli, the middle scala media and the lower scala tympani. Scala media has two membranes- upper membrane called reissners membrane and a lower membrane called basilar membrane. This basilar membrane bears the organ of corti.

Hence, the correct answer is option D.

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The correct order of involvement in electrical impulse movement.
(i) Dendrites → (ii) Cell body → (iii) Axon → (iv) Axon terminal → (v) Synaptic knob

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Vestibular apparatus is present in the inner ear that helps the body in maintaining posture and equilibrium. There are two sets of organs in the inner-ear, semi circular canals and otolith. The semi-circular canals are in three different planes. Relative orientation of these canals send signals to the brain which help to maintain balance and posture of the body.

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Cone cells of the retina enable us to see coloured objects around us. There are three types of cone cells that have their own characteristic pigments which respond to red, green and blue light.

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The reception and transmission of sound waves occur in the following order:-
$\mathrm{External} \mathrm{auditory} \mathrm{canal} \to \mathrm{Ear} \mathrm{drum} \to \mathrm{Malleus} \to \mathrm{Incus} \to \mathrm{Stapes} \to \mathrm{Cochlea} \to \mathrm{Cochlear} \mathrm{nerve}$

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Structures which are involved in the protection of brain are:-
(i) Cranium/Skull - The skull consists of 8 cranial bones that form hard protective covering of the brain.
(ii) Meninges - The brain is covered with three membranes called meninges. These three membranes are pia mater, arachnoid and dura mater.
(iii) Cerebrospinal fluid (CSF) - It is present in the spaces between meninges which functions as shock absorbing pads.

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Extreme emotions such as aggressive behaviour, restlesssness etc. are regulated by the limbic system (i.e. the inner part of the cerebral hemisphere and a group of associated deep structures) and hypothalamus.

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The cerebral cortex consists of many neuron cell bodies, dendrite, glial cells, and capillaries. This gives cerebral cortex a greyish appearance and hence called grey matter.
White matter is also a component of CNS that consists of fibres of tracts covered with myelin sheath that constitute the inner part of cerebral hemisphere. This gives an opaque white appearance to the layer, Thus called white matter.

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The human brain, the urge for eating or hunger is controlled by hypothalamus.

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The semi-circular canals of the vestibular apparatus in the inner-ear are involved in the sense of vertigo.

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While travelling at a higher altitude, symptoms of dizziness and vomiting is faced by a person due to following reasons:-
(i) Eustachian tube faces disturbance in maintaining the pressure on either sides of the ear drum.
(ii) The orientation and adjustments in semi circular canals of the inner ear gets disturbed causing dizziness.

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Just like the input devices, sense organs function to sense the environment and send message to the brain. So, sensory neurons are equivalent to input devices of the computers.
Brain is the control centre that interprets the message and send commands to the concerned organ. Thus, it acts as a CPU (Central Processing Unit) of the computer.
The message or the responses of the body are conveyed by motor neurons which act as output devices.

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A blow on the back of the neck can be very dangerous for a person. It may lead to an impairment of cognitive abilities or physical functioning of a person. A person's behavioural or emotional functioning can also be disturbed. Quadriplegia (paralysis from the neck down including the trunk and limbs) is a consequence of cervical injuries.

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The middle ear cavity is connected with pharynx by the eustachian tube. It equalizes the pressure on either sides of the ear drum. In normal condition the eustachian tube remain collapsed but during swallowing, yawning, chewing it gets open due to a sudden change in the pressure. The eustachian tube also drains the mucus of the middle ear. It also helps in proper reception and transmission of sound waves to the internal ear.

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Colour the image as given in question accordingly.

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A neuron consists of three main parts: cell body, axon and dendrites. Any stimulus/nerve impulse passes from one neuron to another via axon. A nerve impulse is referred to as electrochemical disturbance that passes along neuron during conduction of an excitation. Neurotransmitters are released and transported at a synapse. At a chemical synapse, the membranes of the pre- and post synaptic neurons are separated by a synaptic cleft. The axon terminals have vesicles filled with neurotransmitters that are involved in the transmission of impulses at these synapses. The movement of synaptic vesicles is stimulated when the impulse or action potential arrives at the axon terminal. These synaptic vesicles then fuse with the plasma membrane and release neurotransmitters in the synaptic cleft. Neurotransmitters which are released, binds to their specific receptors that are present on post synaptic membrane. This binding opens ion channels that allow the entry of ions which can generate a new action potential in the post-synaptic neuron.

Answer:

The forebrain consists of cerebrum, thalamus and hypothalamus. Cerebrum forms the major part of the brain. Limbic system is also a part of fore brain.
Cerebrum is divided into two cerebral hemispheres connected by a tract of nerve fibres called corpus callosum.
Various structures of forebrain are as follows:-
(1) Thalamus: Its function include processing and relaying sensory information. It translates signals to the cerebral cortex and also regulates sleep and wake up cycle. It also regulates arousal activities and consciousness.
(2) Hypothalamus: Its function is to regulate endocrine system and closely related to the pituitary gland. It also controls our body temperature, urge of eating and drinking.
(3) Pituitary: Its function is to produce hormones as part of the endocrine system.
(4) Cerebral cortex: It is responsible for memory, attention, awareness, thought, language and consciousness.
(5) Limbic system: It is responsible for controlling emotions that can affect the activity of autonomic nervous system facilitated by the hypothalamus.

Answer:

Ears are a pair of statoacoustic organ meant for both balancing and hearing.
Middle Ear
The middle ear contains three bones (ossicles)
(i) The malleus (hammer)
(ii) Incus (Anvil)
(iii) Stapes (Stir-up)
These bones are attached to each other in a chain like fashion. Tympanic membrane is attached to malleus. Oval window is attached to stapes. Ossciles increase the frequency of transmission of sound waves to the inner ear.
Middle ear opens into eustachian tube as well that connects with the pharynx and maintains the pressure between the middle ear and outside atmosphere.

Internal Ear
Inner ear consists of labyrinth of fluid-filled chambers within temporal bone of the skull.
Labyrinth consist of two parts:- bony and membranous. The bony labyrinth is a series of channels. Inside the channels, membranous labyrinth lies which has fluid called endolymph. Channels are surrounded by a fluid called perilymph.
The coiled portion of labyrinth is called cochlea.
The cochlea has two large canals:-
(1) an upper vestibular canal (scala vestibuli)
(2) a lower tympanic canal (scala tympani)
These two are separated by cochlea duct.
Scala vestibuli and scala tympani are filled with perilymph and cochlea duct is filled with endolymph.