NCERT Class 11-Biology: Chapter –21 Neural Control and Coordination Part 5

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Question 2:

Name the parts of human forebrain indicating their respective functions.

Answer:

Human Forebrain consists of 3 parts – Cerebrum (makes the major part of the human brain), Thalamus and Hypothalamus.

Cerebrum

It is further divided into 4 lobes:

a. Frontal lobe: associated with parts of speech, reasoning, planning, problem-solving and movement.

b. Parietal lobe: Helps in movement, perception of stimuli and orientation.

c. Occipital lobe: Visual processing

d. Temporal lobe -> perception and recognition of memory, auditory smell, speech.

The cerebrum also includes:

a. Sensory areas: receive messages

b. Association areas: Associate information with the previous and other sensory information.

c. Motor areas: Responsible for the action of voluntary muscles.

The cerebrum is also responsible for thinking, intelligence, consciousness and memory.

Thalamus-

It is a small structure located right above the brain stem.

a. It responsible for relaying sensory information from the sense organs, relaying motor information for movement and coordination.

b. Thalamus is found in the limbic system within the cerebrum. The limbic system is mainly responsible for the formation of new memories and storing past experiences.

Hypothalamus - The hypothalamus is a small and important part of the brain, located exactly below the thalamus.

a. It Controls the mood and emotions.

b. It coordinates the messages from the autonomous nervous system.

c. It synthesises of body’s essential hormones.

d. It receives the impulses, sense of taste and smell

e. It is involved in controlling body temperature, peristalsis, the rate of heartbeat, and blood pressure.

f. It is involved in forming an axis with the pituitary which is the main link between the nervous and the endocrine systems.

Question 3:

Explain the structure of middle and internal ear with the help of diagram.

Answer:

Structure of middle and internal ear

Structure of Middle and Internal Ear

Structure of middle and internal ear

Middle ear

a. It contains three ossicles called malleus (hammer), incus (anvil) and stapes (stirrup) which are attached to one another in a chain-like fashion.

b. The malleus is attached to the tympanic membrane and the stapes is attached to the oval window of the cochlea.

c. A Eustachian tube connects the middle ear cavity with the pharynx and helps in equalising the pressures on either sides of the ear drum.

Inner Ear

a. It is also called Labyrinth.

b. It is fluid-filled.

c. It has two parts – the bony and the membranous labyrinth.

d. The bony labyrinth is a series of channels.

e. Inside these channels lies the membranous labyrinth. It is surrounded by a fluid called perilymph.

f. The membranous labyrinth is filled with a fluid called end lymph.

g. The coiled portion of the labyrinth is called cochlea.

h. The space within cochlea called scala media is filled with end lymph.

i. At the base of the cochlea, the scala vestibuli ends at the oval window, while the scala tympani terminate at the round window which opens to the middle ear.

j. The inner ear also contains a complex system called vestibular apparatus composed of three semi-circular canals and the eolith and is located above the cochlea.

k. Each semi-circular canal lies in a different plane at right angles to each other. The base of canals is swollen and is called ampulla

l. Ampulla contains a projecting ridge called crista ampullary which has hair cells. The saccule and utricle contain a projecting ridge called macula.

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