Chapter – 18
Neural Control and Coordination
Q1. Briefly describe the structure of the following:
Ear
Answer
:Ear: Ear is the sense organ for hearing and equilibrium. It consists of three portions external ear, middle ear, and internal ear.
1. External ear: It consists of the pinna, external auditory meatus, and a tympanic membrane. Pinna is a sensitive structure that collects and directs the vibrations into the ear to produce sound. External auditory meatus is a tubular passage supported by cartilage in the external ear. The tympanic membrane is a thin membrane that lies close to the auditory canal. It separates the middle ear from the external ear.
2. Middle ear: It is an air-filled tympanic cavity that is connected with pharynx through the eustachian tube. The eustachian tube helps to equalize air pressure in both sides of the tympanic membrane. The middle ear contains a flexible chain of three middle bones called ear ossicles. The three ear ossicles are malleus, incus, and stapes that are attached to each other.3. Internal ear: It is also known as the labyrinth. The labyrinth is divided into the bony labyrinth and a membranous labyrinth. The bony labyrinth is filled with perilymph while a membranous labyrinth is filled with endolymph.The membranous labyrinth is divided into 2 parts.Vestibular apparatus: It is a central sac-like part that is divided into utriculus and sacculus. A special group of sensory cells called macula are present in sacculus and utriculus. Vestibular apparatus also contains three semi-circular canals. The lower end of each semi-circular canal contains a projecting ridge called crista ampularis. Each ampulla has a group of sensory cells called crista. Crista and macula are responsible for maintaining the balance of body and posture.Cochlea: Cochlea is a long and coiled outgrowth of the sacculus. It is the main hearing organ. Cochlea consists of three membranes. The organ of Corti, a hearing organ, is located on the basilar membrane that has hair cells.
Q3. Explain the following processes:
(a) Polarisation of the membrane of a nerve fibreAnswer:Polarisation of the membrane of a nerve fibre:
When the nerve fibre is at the resting phase, it is said to be in the polarised state.In a polarised state, the membrane of the nerve fibre experiences resting potential.The following steps take place during the process of polarisation of the membrane of a nerve fibre:When a depolarised region of a nerve fibre starts becoming polarised initially, there are more K + ions outside the nerve fibre and the axon membrane contains large amount of Na + ions.As the region of the membrane starts attaining the polarised state, the membrane becomes more permeable to K + ions and impermeable to Na + ions and negatively charged proteins.3 Na + ions are sent outside the axon and 2 K + ions are sent into the axon by a sodium-potassium pump by active transport.The inner side of the membrane becomes electronegative (negatively charged) and the outer side becomes electropositive (positively charged) because of the movement of sodium and potassium ions. This makes the nerve fibre polarised.
Q5. Write short notes on the following:
(a) Neural coordination
Answer:
Coordination is a characteristic feature of living organisms. It is the process through which two or more organs interact and complement the functions of one another.Coordination is achieved by two ways in humans and other higher order animals—neural coordination and chemical coordination.Neural coordination is carried out by highly specialised cells called neurons.The neural system is a network of point-to-point connections between the neurons and the organs and it operates through nerve impulses.Neural coordination is always between the stimulus and the response—receptors and effectors.All body functions are carried out and controlled by neural coordination.The stimulus is received from organs such as the skin and a response is generated which is sent to the muscles or glands.The previous stimulus is always stored in memory by the neural system.Neural coordination helps in controlling and harmonising voluntary actions such as running, walking, writing and talking.It helps us to remember, analyse, think and reason because the brain, a part of the neural system, is the site of intelligence.All vital functions such as breathing, working of the heart and digestion are controlled by neural coordination.It helps maintain homeostasis by coordinating between various metabolic activities of the body.
Q6. Give a brief account of:
(a) Mechanism of synaptic transmission
Answer:
The mechanism of synaptic transmission at the electrical synapse:In this case, the pre-synaptic and post-synaptic membranes are in proximity.Impulse in the form of electric current directly flows from the pre-synaptic neuron to the post-synaptic neuron.Transmission is faster than the chemical synapse.
Q7. Answer briefly:
(a) How do you perceive the colour of an object?
Answer:
Cone cells present in the retina of the eye are responsible for colour vision. There are three kinds of cone cells which respond to red, green and blue light. Different cone cells get stimulated at different wavelengths of light. The other colours are detected by the simultaneous stimulation of more than one kind of cone cells. When all the three types of cells are stimulated simultaneously, a sensation of white light is produced
Q8. Explain the following:
(a) Role of Na+ in the generation of action potential.
Answer:
Sodium ions diffuse from the outside to the intracellular fluid because of the electrochemical gradient. The potassium ions move out, and the membrane becomes negatively charged from outside and positively charged from inside. This sudden change in the membrane potential is called the action potential, and the membrane is said to be depolarised.
Q10. Answer the following:
(a) Which part of the ear determines the pitch of a sound?
Answer:
The cochlea determines the pitch of a sound.
b) Which part of the human brain is the most developed?
Answer:
The cerebrum is the most developed.
c) Which part of our central neural system acts as a master clock?
Answer:
The hypothalamus of the central neural system acts as a master clock.
Q11. The region of the vertebrate eye, where the optic nerve passes out of the retina, is called the
(a) fovea
(b) iris
(c) blind spot
(d) optic chaisma
Answer:
(c) Blind spot The region of the vertebrate eye, where the optic nerve passes out of the retina, is called the blind spot. Photoreceptors are absent in this region.