CBSE Class 11 Biology Neural Control and Coordination Assignments

NEURAL CONTROL AND COORDINATION

POINTS TO REMEMBER

Action potential: A sudden change in the electrical charges in the plasma membrane of a nerve fibre.

Aqueous humour: The thin watery fluid that occupy space between lens and cornea in eye.

Blind spot: A spot on retina which is free from rods and cones and lack the ability for vision.

Cerebrospinal fluid: An alkaline fluid present in between inner two layer of meninges.

Cerebellum: A part of hind brain that controls the balance and posture of the body.

Cochlea: A spirally coiled part of internal ear which is responsible for hearing.

Corpus callosum: A curved thick bundle of nerve fibres that joins two cerebral hemisphere.

Depolarisation: A condition when polarity of the plasma membrane of nerve fibre is reversed.

Endolymph: The fluid filled within membranous labyrinth.

Eustachian tube: A tube which connect ear cavity with the pharynx.

Fovea: A area of highest vision on the ratina which contain only cones.

Meninges: Three sheets of covering of connective tissue wrapping the brain.

Grey Matter: This shows many convolutions which increase the amount of vital nerve tissue.

Medulla oblongata: Posterior most part of the brain which is continuous with spinal cord and control respiration, heart rate, swallowing, vomiting.

Pons: Thick bundles of fibres on the ventral side of brain below cerebellum.

Foramen magnum: A big aperture in the skull posteriorly through which spinal cord emerges out.

Spinal cord: A tubular structure connected with medulla oblongata of brain and situated in the neural canal of the vertebral column, covered by meninges.

Synaptic cleft: A narrow fluid filled space which separates two membranes of the two neurons at the synapse.

Synaptic vesicles: These are membrane bound vesicles in the axoplasm of the axon terminal and these store neurotransmitter.

Neurotransmitter: These are chemicals stored in synaptic vesicles, diffuse to reach the membrane of next neuron for its stimulation.

Synapse: A physiological junction between axon of one neuron and dendrite of next neuron.

CNS: Central neural system

PNS: Peripheral neural system

ANS: Autonomic neural system

Cell body: Cytoplasm with nucleus, cell organelles and Nissl's granules

Dendrites: Short fibres which branch rapidly and project out of cell

Axon: Single, long fibre, branched at distal end

Multi polar: One axon and two or more dendrites. Found in cerebral Cortex

Bipolar: One axon and one dendrite. Found in retina of eye

Unipolar: Cell body with axon only. Found usually in the embryonic stage

Conduction of nerve impulse along axon

Polarised membrane/Resting Potential: In resting phase when neuron is not conducting an impulse, the axonal membrane is called polarised. This is due to difference in concentration of ions across the axonal membrane.

At Rest:

- Axoplasm inside the axon contain high concentration of \(\text{K}^+\) and low concentration of \(\text{Na}^+\).

- The fluid outside the axon contain low concentration of \(\text{K}^+\) and high concentration of \(\text{Na}^+\).

As a result the outer surface of axonal membrane is positively charged and inner surface is negatively charged. The electric potential difference across the resting plasma membrane is called resting potential.

Action Potential: When a nerve fibre is stimulated, the permeability of membrane to \(\text{Na}^+\) is greatly increased at the point of stimulus (rapid influx of \(\text{Na}^+\)) and hence polarity of membrane is reversed and now membrane is said to be depolarised. The electric potential difference across the plasma membrane at that site is called action potential, which in fact termed as nerve impulse.

Depolarisation is very rapid, so that conduction of nerve impulse along the entire length of axon occurs in fractions of second.

Transmission of Impulses at Synapse

(i) At electrical synapses: Here the membrane of pre and post-synaptic neuron are in very close proximity. Electric current can flow directly from one neuron into other across these synapses, like impulse conduction along a single axon.

(ii) At chemical synapses: Here the membrane of pre and post-synaptic neuron are separated by fluid filled space called synaptic cleft. Neurotransmitter are involved here.

When an impulse arrives at the axon terminal, it stimulates the movement of the synaptic vesicles towards membrane and they fuse with the plasma membrane and release their neurotransmitter in the synaptic cleft. These chemicals bind to specific receptors, present on the post-synaptic membrane. Their binding opens ion channels and allow the entry of ion which generate new potential in post synaptic neuron.

Human brain: Human brain is the major portion of central neural system. Which is well protected by the skull.

The brain is surrounded by three cranial meninges:

i) Duramater - outer layer

ii) Arachnoid - middle layer

iii) Piamater - inner layer-remain in contact with brain

Parts of Brain:

Fore brain: (a) Cerebrum, (b) Thalamus, (c) Hypothalamus

Mid brain

Hind brain: (a) Cerebellum, (b) Pons, (c) Medulla oblongata

Functions of parts of brain:

Cerebrum: Centre of intelligence, memory and imagination, reasoning, judgement, expression of will power.

Thalamus: Acts as relay centre to receive and transmit general sensation of pain, touch and temperature.

Hypothalamus: Centre for regulation of body temperature, urge for eating and drinking.

Mid brain: Responsible to coordinate visual reflexes and auditory reflexes.

Cerebellum: Maintains posture and equilibrium of the body as well as coordinates voluntary movements.

Pons varoli: Relays impulses between medulla oblongata and cerebral hemisphere and between the hemisphere of cerebrum and cerebellum.

Medulla oblongata: Centre that control heart beat, breathing, swallowing, salivation, sneezing, vomiting and coughing.

Reflex action: It is a spontaneous, autonomic and mechanical response to a stimulus that occurs at the level of spinal cord, with involvement of brain.

Reflex arc: The flow of nerve impulse along the specific pathway during reflex action. It consist of:

a) A receptor

b) An Afferent neuron (sensory neuron)

c) An interneuron

d) An efferent neuron (motor neuron)

e) An effector organ

Organ of Sight - Eye

Organ of Hearing - Ear

QUESTIONS

Very Short Answer Questions (1 mark each)

Question 1. Name the fluid present in membranous labyrinth.
Answer: Endolymph
In simple words: Endolymph is the fluid found inside the membranous labyrinth of the inner ear.

Exam Tip: Remember that perilymph fills the bony labyrinth, while endolymph fills the membranous labyrinth.

Question 2. Name the area of retina where only cones are densely packed.
Answer: Fovea
In simple words: The fovea is the central pit in the retina responsible for sharpest daylight and colour vision.

Exam Tip: Fovea contains only cones and lacks rods entirely, providing high visual acuity.

Question 3. Name the inner most meninges of the brain.
Answer: Piamater
In simple words: Piamater is the delicate innermost protective layer covering the brain directly.

Exam Tip: Recall the sequence from outside to inside: Duramater -> Arachnoid -> Piamater.

Question 4. To which part of the brain communication and memory are associated?
Answer: Cerebrum
In simple words: The cerebrum handles higher mental functions like memory, intelligence, and communication.

Exam Tip: Cerebrum is the main thinking part of the forebrain.

Question 5. Name the bundle of fibres that connect two cerebral hemisphere in human being.
Answer: Corpus callosum
In simple words: Corpus callosum is a thick tract of nerve fibres linking the left and right cerebral hemispheres.

Exam Tip: This is a frequent one-mark question in board examinations.

Question 6. Name the photo pigment present in the rod cells.
Answer: Rhodopsin (Visual purple)
In simple words: Rhodopsin is the light-sensitive pigment found in rods used for dim-light vision.

Exam Tip: Do not confuse rhodopsin (rods) with iodopsin (cones).

Question 7. Why can impulses flow only in one direction?
Answer: Because neurotransmitters are released only from the axon terminals into the synaptic cleft to bind with receptors on the post-synaptic membrane.
In simple words: Synapses act as one-way valves because chemical signals travel solely from presynaptic to postsynaptic neurons.

Exam Tip: Mention synaptic vesicles and neurotransmitters for complete credit.

Question 8. Where is hypothalamus located in the brain?
Answer: At the base of the thalamus.
In simple words: The hypothalamus sits right below the thalamus in the forebrain.

Question 9. Distinguish between electrical synapses and chemical synapses.
Answer: 1. At electrical synapses, pre- and post-synaptic neurons are in very close proximity allowing direct electric current flow. At chemical synapses, membranes are separated by a fluid-filled space called the synaptic cleft.
2. Electrical transmission is faster than chemical transmission, which requires neurotransmitters.
In simple words: Electrical synapses use direct current flow, while chemical synapses use chemical messengers across a gap.

Exam Tip: Present the differences in tabular form or clear points to score full marks.

Question 10. What is iris? Give the function of iris.
Answer: The pigmented, opaque continuation of the choroid that forms a visible colored portion of the eye is called the iris.
Function: It controls the amount of light entering the eye by adjusting the size of the pupil.
In simple words: The iris is the colored part of the eye that regulates how much light gets inside.

Exam Tip: Clearly mention the regulation of the pupil aperture.

Question 11. What is organ of corti? Where is it located?
Answer: The organ of Corti is a structure containing hair cells that act as auditory receptors.
Location: It is located on the basilar membrane within the cochlea of the inner ear.
In simple words: The organ of Corti is our hearing organ situated inside the cochlea.

Exam Tip: Mention both its definition and exact anatomical location.

Question 12. Differentiate between cerebrum and cerebellum.
Answer: 1. Cerebrum is the main part of the forebrain controlling intelligence, memory, and reasoning. Cerebellum is part of the hindbrain controlling posture, equilibrium, and muscle coordination.
2. Cerebrum consists of two cerebral hemispheres joined by corpus callosum. Cerebellum has a highly convoluted surface to provide additional space for neurons.
In simple words: Cerebrum handles thinking and memory, while cerebellum coordinates balance and movement.

Exam Tip: Contrast their major locations and primary physiological functions.

Question 13. Fill in the blanks in the different columns A to D:
Answer:
(A) To collect sound waves
(B) Eustachian tube
(C) Colour vision (or vision in bright light)
(D) Iris
In simple words: Matching ear and eye anatomical components with their correct physiological functions.

Exam Tip: Write the corresponding alphabet clearly along with the filled term.

Question 14. Why are grey matter and white matter contained in human nervous system named so?
Answer: Grey matter appears grey because it contains cell bodies, dendrites, and synapses of neurons which lack myelin sheaths. White matter appears white due to the abundant presence of myelinated axons reflecting light.
In simple words: Unmyelinated cell bodies look grey, while myelinated nerve fibers look white.

Exam Tip: The key differentiator is the presence or absence of myelin sheaths.

Short Answer Questions (3 marks each)

Question 15. Observe the diagram given right and answer the following questions: (i) Label the parts A and B. (ii) Give the function of C and D. (iii) Name the layers which wrap this organ.
Answer:
(i) A: Cerebrum, B: Corpus callosum
(ii) C: Balancing of body and maintenance of posture; D: Control of involuntary actions like vomiting, coughing, breathing, and heart rate (Medulla oblongata).
(iii) Meninges (Duramater, Arachnoid, and Piamater).
In simple words: Identifying brain regions, their functions, and protective membranes.

Exam Tip: Label each sub-part explicitly as (i), (ii), and (iii).

Question 16. What is a synapse? How does the nerve impulse cross the chemical synapse?
Answer: Synapse: A junction between the axon terminal of one neuron and the dendrite of the next neuron.
Mechanism: When an impulse reaches the axon terminal, synaptic vesicles fuse with the plasma membrane and release neurotransmitters into the synaptic cleft. These chemicals bind to specific receptors on the post-synaptic membrane, opening ion channels and generating a new action potential.
In simple words: A synapse is the junction where chemical messengers transmit nerve signals between neurons.

Exam Tip: Use keywords: synaptic cleft, neurotransmitters, receptors, and post-synaptic membrane.

Question 17. Give the function of the following: (i) Cerebrum (ii) Hypothalamus (iii) Mid brain
Answer:
(i) Cerebrum: Centre of intelligence, memory, imagination, reasoning, and judgment.
(ii) Hypothalamus: Regulates body temperature, urge for eating and drinking, and controls pituitary hormone secretion.
(iii) Mid brain: Coordinates visual and auditory reflexes.
In simple words: Summary of functions for cerebrum, hypothalamus, and midbrain.

Question 18. What is meant by reflex action? Name the components of a reflex arc in correct sequence from receptor upto effector. Support your answer by a diagram.
Answer: Reflex action: A spontaneous, involuntary, and mechanical response to a peripheral stimulus that occurs without conscious thought, usually mediated by the spinal cord.
Sequence of Reflex Arc:
Receptor -> Sensory neuron (Afferent neuron) -> Interneuron (spinal cord) -> Motor neuron (Efferent neuron) -> Effector organ (muscle/gland).
In simple words: A reflex action is an instant automatic response routed through a specific pathway called a reflex arc.

Exam Tip: Always write components in the exact directional sequence from receptor to effector.

Question 19. Draw a diagram of V. S. of human eye and label the following: Iris, Retina, Cornea, Blind spot, Ciliary body and Vitreous chamber.
Answer: 1. Draw a spherical outline representing the eyeball with anterior bulging for the cornea.
2. Label Cornea at the transparent front window.
3. Label Iris just in front of the crystalline lens.
4. Label Ciliary body holding the lens in place.
5. Label Retina lining the inner posterior wall.
6. Label Blind spot where the optic nerve leaves the retina.
7. Label Vitreous chamber as the large cavity behind the lens filled with vitreous humor.
In simple words: Sketch a vertical section of the human eye and clearly indicate all requested anatomical parts.

Exam Tip: Use clear, uncrossed lines for labeling diagram components.

Long Answer Questions (5 marks each)

Question 20. Describe in detail, how conduction of nerve impulse takes place through a nerve fibre.
Answer: 1. Resting Potential (Polarized State): When a neuron is not conducting an impulse, the axonal membrane is polarized. Axoplasm contains high \(\text{K}^+\) and low \(\text{Na}^+\), while extracellular fluid has high \(\text{Na}^+\) and low \(\text{K}^+\). The outer surface is positively charged and the inner surface is negatively charged.
2. Action Potential (Depolarization): When a stimulus is applied, membrane permeability to \(\text{Na}^+\) increases rapidly, causing a massive influx of sodium ions. This reverses the polarity (outer surface becomes negative, inner becomes positive), creating an action potential or nerve impulse.
3. Repolarization: Shortly after, permeability to \(\text{Na}^+\) declines and \(\text{K}^+\) efflux increases, restoring the resting negative charge inside the membrane.
In simple words: Nerve conduction involves resting polarization, stimulus-induced sodium influx (depolarization), and potassium outflow (repolarization).

Exam Tip: Mention ion distribution (\(\text{Na}^+\) and \(\text{K}^+\)), resting potential, and depolarization steps clearly to score full marks.