NCERT Solutions for Class 11 Biology Chapter 21
NCERT Solutions Class 11 Biology Chapter 21 by Extramarks are one of the most crucial study materials that students can refer to, and prepare well for their exams. Subject matter experts with a considerable amount of experience have researched and prepared these solutions. The solutions comprise accurate answers, examples, and diagrams to ensure that students understand everything comprehensively.
NCERT Solutions for Class 11 Biology Chapter 21 – Neural Control and Coordination
Access NCERT Solutions for Biology Class 12 Chapter 21 – Neural Control and Coordination
NCERT Biology Class 11 Neural Control and Coordination
Chapter 21 of Class 11 Biology covers different aspects of the human neural system. There are practice questions at the end of the chapter to help students revise and gauge their understanding of the concepts. The NCERT Solutions for Class 11 Biology Chapter 21 by Extramarks will help students solve these practice questions with a high level of accuracy. Prepared by subject matter experts, the NCERT Solutions for Chapter 21 Biology have simple language and good use of examples so that students understand each and everything without any confusion.
Class 11 Neural Control and Coordination NCERT Solutions
NCERT Class 11 Biology Chapter 21 talks about the neural system of a human body with absolute clarity. Mechanisms of neural coordination such as the physiology of reflex action, the transmission of nerve impulses, impulse conduction across a synapse, reflex arc, and central neuron system are covered in the chapter.
The Forebrain, Hindbrain, Midbrain, spinal cord, peripheral nervous system, and autonomic nervous system which are all part of the central nervous system are discussed in this chapter. Sense organs like ears and eyes are one of the important topics of this chapter as well. This chapter talks about the mechanisms of impulse conduction, vision, and hearing in great detail.
All possible questions that can be asked from this chapter are covered in Biology Class 11 NCERT Solutions Chapter 21, which is why referring to these solutions will surely help students in scoring well.
CBSE Class 11 Biology Chapter 21 NCERT Solutions – Marks Distribution
NCERT Solutions Class 11 Biology Chapter 21 by Extramarks serve as an excellent reference material for Class 11 students. It helps them in understanding the format to answer these questions. Chapter 21 – Neural Control and Coordination comes under Unit V – Human Physiology. Students can expect a total of 18 marks from Unit V. Therefore, they must refer to NCERT Solutions by Extramarks to score better in the subject.
Benefits of NCERT Biology Class 11 Chapter 21
Here are some of the reasons to refer to NCERT Solutions for Biology Class 11 Chapter 21:
- The solutions have answers to all the questions in the NCERT Class 11 Biology textbook.
- The solutions are prepared by subject-matter experts.
- The solutions are prepared as per CBSE guidelines.
- Solutions can be accessed online and offline.
Excess secretion of growth hormone in adults leads to__________.
- A) Acromegaly
- B) Goitre
- C) Gigantism
- D) Dwarfism
Answer: A) Acromegaly
Explanation: Excessive growth occurs due to the overproduction of growth hormone. This condition in children is known as gigantism while in adults it is known as acromegaly. A noncancerous (benign) pituitary tumour is generally the cause of the overproduction of growth hormone.
Lathyrism is caused by excessive consumption of
- A) Khesari dal
- B) Mustard oil
- C) Polished rice
- D) Mushrooms
Answer: A) Khesari dal
Explanation: Lathyrism is a neuronal disorder. This disease leads to lower-limb paralysis. Excessive consumption of Khesari dal can cause Lathyrism. The disease has been named on the scientific name of the Khesari dal, i.e. Lathyrus sativus. This Khesari dal had been banned for years in India due to its link to this disorder.
Which is an example of positive feedback?
- A) Seasonal growth
- B) Vessel diameter and blood pressure
- C) Allosteric inhibition of enzymes
- D) Both A and B.
Answer: A) Seasonal Growth
Explanation: The positive feedback mechanism is one that involves the enhancement of the original stimulus by the end product. Seasonal growth is an example of positive feedback in the control of population.
A poisonous lizard is ___________________.
- A) Heloderma
- B) Agkistrodon
- C) Chamaeleon
- D) Varanus
Answer: A) Heloderma
Explanation: Venomous lizards are a part of the genus Heloderma which is the only genus of the family Helodermatidae. The family’s members are venomous. Their venom glands are not located in their upper jaws like snakes, instead, their venom glands can be found in their lower jaws. Heloderma do not have the musculature that enables them to inject venom like snakes. The venom in them is generally utilised for defence and is not of much use in capturing prey as getting the venom into the flesh of the prey would require chewing it.
A person who shows unpredictable moods, outbursts of emotions, quarrelsome behaviour, and conflicts with others is suffering from
- A) Borderline Personality Disorder (BPD)
- B) Mood disorder
- C) Addiction disorder
- D) Schizophrenia
Answer: A) Borderline Personality disorder (BPD)
Explanation: Borderline personality disorder is a disorder that causes an individual to have an emotionally unstable personality. It is a serious mental illness that influences the functioning of a person’s everyday life. Self-image issues, instability in relationships, and issues in dealing with behaviour and emotions are BPD’s main features. A person who has BPD suffers from quarrelsome behaviour, mood swings or unpredictable moods, and conflicts.
All cranial nerves are related to parasympathetic nerve fibres except
- A) Oculomotor
- B) Facial
- C) Accessory spinal
- D) Vagus
Answer: C) Accessory Spinal
Explanation: Parasympathetic nervous system’s nerve fibres emerge from the central nervous system. Several cranial nerves, especially the facial nerve, vagus nerve, oculomotor nerve, and the glossopharyngeal nerve, are a part of specific nerves. The parasympathetic system is normally said to have craniosacral outflow due to its location. The central nervous system provides motor innervation to the two neck muscles – the trapezius muscle and the sternocleidomastoid muscle – through the spinal accessory nerve. Lower motor neurons which are located in the spinal cord’s upper segment form the fibres by which the spinal accessory nerve is formed. The cluster of neurons is referred to as the spinal accessory nucleus. The spinal accessory nucleus is located in the anterior horn’s (found in the spinal cord) posterolateral aspect. In contrast to this, most other motor neuron cell bodies are found in the anterior horn of the spinal cord.
Name the primary and secondary lymphoid organs.
Bone marrow and Thymus form the primary lymphoid organs. These are the organs where immature lymphocytes mature into antigen-sensitive lymphocytes. Lymph nodes, spleen, tonsils, Peyer’s patches, Mucosa-associated Lymphoid Tissue (MALT), and other specialised zones are a part of the secondary lymphoid organs.
Which signals will get interrupted in case of a spinal cord injury?
Signals coming from the nerves along with signals coming to the receptors will be interrupted if one suffers a spinal cord injury.
Q.1 Briefly describe the structure of the following:
(a) Brain: Brain is the main coordinating centre of nervous system in all vertebrates and most invertebrates. It is most complex organ of the body. Brain consists of neurons, glial cells and blood vessels. Brain is made up of three main parts:
Following diagram shows the structure and location of various parts of human brain.
Forebrain: Forebrain consists of cerebrum, thalamus, and hypothalamus.
- The cerebrum or cortex is the largest part of the human brain and is a highly folded structure. This is also known as grey matter due to the presence of a large number of neuron cell bodies giving it a greyish appearance. Cerebrum is divided into two halves (hemispheres) by a deep furrow. Two hemispheres are joined to each other with nerve fibres, known as the corpus callosum. The cerebrum is further divided into four lobes: the frontal lobe, parietal lobe, occipital lobe, and temporal lobe. The motor areas, sensory areas and large regions that are neither sensory nor motor in function are known as association areas. These areas are involved in complex functions like inter-sensory associations, memory and communication. The inner part of cerebral hemisphere consists of fibres which are covered with myelin sheath and thus; gives an opaque white appearance, hence it is called white matter.
- Thalamus is a major coordination centre for sensory and motor signalling. It is involved in functions like thoughts and actions. It is covered by cerebrum.
- Below thalamus, hypothalamus is present which controls body temperature, hunger and thirst.
Midbrain: The midbrain is located between the thalamus/hypothalamus of the forebrain and pons of the hindbrain. A canal called the cerebral aqueduct passes through the midbrain. Four round swellings or lobes constitute the dorsal portion of the midbrain and are known as corpora quadrigemina. It consists of the tectum and tegmentum. It is associated with vision, hearing, motor control, sleep/wake, alertness and temperature regulation.
Hindbrain: The hindbrain is made of the cerebellum, pons and medulla. Cerebellum is a highly convoluted structure and thus; provides extra space for a large number of neurons. Like cerebrum, cerebellum is also divided into two hemispheres. Cerebellum is associated with regulation and coordination of movement, posture, and balance. Pons is made up of fibre tracts interconnecting various regions of the brain. The medulla is connected to the spinal cord and contains regulatory centres for respiration, cardiovascular reflexes and gastric secretions.
(b) Eye: Eyes are organs for the perception of light and colours. The pair of eyes are located in sockets of the skull known as orbits. They are nearly spherical in shape. The wall of the eyeball consists of the following three layers: the outer-most sclera, middle choroid and inner-most retina.
Sclera: It is the outer most layer and consists of dense connective tissues. The anterior portion of this layer is called cornea.
Choroid: it is the middle layer and contains blood vessels. It is bluish in appearance. It thickens at the anterior portion of the eye and forms a ciliary body that holds the lens with the help of other ligaments. The ciliary body further extends to form iris, which gives characteristic colour to the eyes. There is an aperture in the front part of the eyes, called pupil. Pupil is surrounded by iris. Muscles of iris regulate the diameter of pupil.
Retina: Retina is the innermost layer and it contains three layers of cells – from inside to outside – ganglion cells, bipolar cells and photoreceptor cells. Photoreceptor cells are of two types-rods and cones.
Eye is divided into two chambers-
Aqueous chamber: It is the space between the cornea and the lens, and contains a thin watery fluid called aqueous humour.
Vitreous chamber: It is the space between the lens and the retina and is filled with a transparent gel, called the vitreous humour. The place where blood vessels enter and optic nerves leave the eyeball is called blind spot because no photoreceptors are present in this region, so no image is formed at this place. There is another place on the retina where only cones are present and it is fovea. Fovea is the region of highest visual resolution.
(c) Ear: Ears are organ of hearing and maintaining balance. Anatomically an ear is divided into three parts- outer, middle and inner ear.
- Outer ear: Outer ear consists of the pinna and external auditory meatus (canal). External auditory meatus extends up to the tympanic membrane (eardrum). Pinna and meatus contain sebaceous glands.
- Middle ear: Middle ear contains three small bones (ossicles) called malleus, incus and stapes. They are attached to each other like a chain. Malleus is attached to tympanic membrane and stapes is connected to inner ear. Middle ear is connected to pharynx by a tube called Eustachian tube. Eustachian tube helps in balancing air pressure at both sides of tympanic membrane.
- Inner ear: Inner ear is a fluid-filled structure called labyrinth. Labyrinth is divided into two parts- bony and membranous labyrinth. The bony labyrinth is filled with perilymph, while membranous labyrinth is filled with endolymph. Membranous labyrinth is further divided into following parts:
- Vestibular apparatus: It is a sac-like structure and is composed of three semi-circular canals and otolith organ (otolith consists of utricule and saccule). Base of the canals are swollen and is called ampulla (ampulla contains crista ampullaris). Otolith contains a projecting ridge called macula. Macula and crista are responsible for maintaining posture and the balance of the body.
- Cochlea: Cochlea is a coiled structure and extension of succulus. It contains organ of Corti which acts as the auditory receptor. It is the main organ for hearing.
Q.2 Compare the following:
(a) Central neural system (CNS) and Peripheral neural system (PNS)
(b) Resting potential and action potential
(c) Choroid and retina
|Central Nervous System (CNS)||Peripheral Nervous System (PNS)|
|CNS mainly consists of brain and spinal cord.||PNS consists of all the nerves (spinal and cranial nerves) associated with CNS.|
|It has bony protective covering.||It is not protected by any bony covering.|
|It is the main centre for coordination and processing of information.||It is not the main coordination centre. It is involved in the conduction of voluntary and involuntary impulses across the body.|
|Resting potential||Action potential|
|Resting potential is the potential difference across the membrane of neurons under the resting stage. The membrane at this stage is said to be polarised||Action potential is the potential difference across the membrane of neurons when there is the conduction of nerve impulse. The membrane at this stage is said to be depolarised|
|Membrane becomes more permeable to potassium ions and less permeable to sodium ions. It results in a high concentration of sodium ions outside the membrane.||Membrane becomes more permeable to sodium ions resulting in inward movement of sodium ions and outward movement of potassium ions.|
|The membrane becomes positively charged on the outer side and negatively charge inside.||The membrane becomes negatively charged on the outer side and positively charge inside.|
|Choroid is the middle layer of eyeball.||Retina is the innermost layer of eyeball.|
|It contains numerous blood vessels that supply nutrients and oxygen to retina and other tissues.||It contains photoreceptor cells namely cones and rods and is involved in the perception of light and colour.|
Q.3 Explain the following processes:
(a) Polarisation of the membrane of a nerve fibre
(b) Depolarisation of the membrane of a nerve fibre
(c) Conduction of a nerve impulse along a nerve fibre
(d) Transmission of a nerve impulse across a chemical synapse
(a) Polarisation of the membrane of a nerve fibre: Polarisation of the membrane of neuron occurs during resting phase when there is no conduction of nerve impulse. There are different types of ion channels present on the neural membranes. During the resting phase, membrane is relatively more permeable for potassium ions (K+) and nearly impermeable to sodium ions (Na+). The membrane is also impermeable to negatively charged proteins present inside the cell. As a result, concentration of sodium ions is higher on the outer side of membrane as compared to the inner side. These gradients across the resting membranes are maintained by the active transport of ions by the sodium-potassium pump which transports three Na+ outwards for two K+ into the cell. The outer side of the membrane becomes positively charged and the inner side becomes negatively charged due to a difference in the concentration of ions. This is known as polarisation of the membrane of a nerve fibre.
(b) Depolarisation of the membrane of a nerve fibre: When there is a nerve impulse at the site of a polarised membrane, permeability of membrane towards sodium ion changes. The membrane at the site of impulse becomes freely permeable to sodium ions. This causes a rapid influx of sodium ions resulting in increased sodium ion concentration at the inner side of the membrane. The inner side of the membrane becomes positively charged and the outer side becomes negatively charged. This reversal in polarity of the membrane is called depolarisation.
(c) Conduction of a nerve impulse along a nerve fibre: Conduction of nerve impulse is carried out by depolarisation of plasma membrane of nerve cell. Whenever there is a nerve impulse, it opens the sodium ion channel present on the membrane of nerve fibres resulting in the rapid influx of sodium ions to the inside of the nerve fibre. This generates a positive charge at the inner side of the membrane and a negative charge on outer side. This potential difference is called action potential and the state of nerve fibre is said to be in depolarised state. Just ahead of this point, the polarity of the axon membrane is opposite i.e. the outer side is positive and inner side is negative. This results in flowing of current from site of action potential to further down the axon. On the outer surface, current flows in reverse order completing the circuit. The polarity at the site of origin of impulse is reversed and action potential is generated further ahead. As the nerve impulse moves forward, the membrane becomes depolarised that causes the nerve impulse to travel forward.
(d) Transmission of a nerve impulse across a chemical synapse: Junction between two neurons is called synapse. Nerve impulse travels from one neuron to another through these synapses. At a chemical synapse, the membranes of the two neurons (pre-synaptic and post-synaptic neurons) are separated by a synaptic cleft, which is filled with a fluid. The nerve impulse is transmitted from presynaptic neuron to post-synaptic neuron with the help of neuro-transmitters in the following manner:
- Axon terminal of a presynaptic neuron contains neurotransmitters in vesicles.
- When there is nerve impulse, vesicles filled with neurotransmitters fuse with the membrane and release neurotransmitters in the synaptic cleft.
- At synaptic cleft, neurotransmitters bind to their specific receptors present on the membrane of the post-synaptic neurons.
- This opens ion channels in post-synaptic neurons resulting in the generation of potential difference.
- The potential difference leads to the transmission of nerve impulse which may be excitatory or inhibitory from pre-synaptic neurons to post-synaptic neurons.
Q.4 Draw labelled diagrams of the following:
Q.5 Write short notes on the following:
(a) Neural coordination
(f) Ear ossicles
(h) Organ of Corti
(a) Neural coordination: Coordination by the neural system is done through electric impulses that send signals to target organs/tissues to act coordinately with other organs or tissues. Neural coordination is performed mainly by brain and neurons in the body. Brain receives the stimulus with the help of nerves and sends signals in the form of an electric impulse to the effector organs.
(b) Forebrain: Forebrain consists of the cerebrum, thalamus, and hypothalamus.
- The cerebrum or cortex is the largest part of the human brain and is highly folded structure. The cerebrum is divided into two halves (hemispheres) by a deep furrow. Two hemispheres are joined to each other with nerve fibres known as the corpus callosum. The cerebrum is further divided into four lobes: the frontal lobe, parietal lobe, occipital lobe, and temporal lobe. The cerebrum is involved in complex functions like intersensory associations, memory and communication.
- Thalamus is a major coordination centre for sensory and motor signalling. It is involved in functions like thoughts and actions. It is covered by the cerebrum.
- Below thalamus, the hypothalamus is present which controls body temperature, hunger and thirst.
(c) Midbrain: It is located between the thalamus of forebrain and pons of the hindbrain. Midbrain consists of the tectum and tegmentum. It is associated with vision, hearing, motor control, sleep/wake, alertness and temperature regulation.
(d) Hindbrain: The hindbrain consists of the cerebellum, pons and medulla oblongata. Like cerebrum, cerebellum is also divided into two hemispheres and is a highly convoluted structure. Cerebellum is associated with regulation and coordination of movement, posture, and balance. Pons connects two hemispheres of the cerebellum. The medulla oblongata is the posterior part of the brain. It is associated with the maintenance of balance and posture of body.
(e) Retina: Retina is the innermost layer of the eyeball and it contains three layers of cells from inside to outside – ganglion cells, bipolar cells and photoreceptor cells. Photoreceptor cells are of two types- rods and cones. Cone cells contain iodopsin pigment that is highly sensitive to bright light. Cone cells are involved in the perception of bright light and colour. Rod cells of retina contain pigment rhodopsin which is highly sensitive to dim light.
(f) Ear ossicles: The middle ear contains three very small bones called ossicles. They are as follows.
- Malleus: Malleus is attached to the eardrum (tympanic membrane) at one side and to the incus at another side.
- Incus: Incus is connected with stapes.
- Stapes: It is attached to the internal ear.
They together transmit sound waves from the external ear to the internal ear.
(g) Cochlea: Cochlea is a coiled structure and extension of the succubus. It contains the organ of Corti which acts as an auditory receptor. It is the main organ for hearing. Cochlea forms three chambers- upper scala vestibule, middle scala media and lower scala tympani.
(h) Organ of Corti: Organ of Corti is the part of cochlea, the internal ear. It is located in cochlear duct between the scala vestibuli and the scala tympani. It is found in mammals only. It contains hair cells and auditory receptors. It is the main site for hearing.
(i) Synapse: In a nervous system, synapse is a gap between the two neurons through which nerve impulse gets transferred from one neuron to another. There are two types of synapse-
(a) If the two neurons are in very close proximity, nerve impulse is transferred directly from one neuron to another like the transfer of nerve impulse within a single neuron. This kind of synapse is called electrical synapse.
(b) If the two neurons are separated by a synaptic cleft, then transfer of nerve impulse is mediated by neurotransmitters and the synapse is called as chemical synapse.
Q.6 Give a brief account of:
(a) Mechanism of synaptic transmission
(b) Mechanism of vision
(c) Mechanism of hearing
(a) Mechanism of synaptic transmission: Synaptic transmission is the transfer of nerve impulse from one neuron to another. Synaptic transmission is of two types:
Direct transmission, like at electrical synapse
- At electrical synapse, the membranes of pre- and post-synaptical neurons have hardly any gap (synaptic cleft is absent).
- Thus electrical current or the nerve impulse is transferred directly from one neuron to another.
- This type of transmission is very fast.
Indirect transmission mediated by neurotransmitters, like at chemical synapse
- At chemical synapse, axon of first neuron (presynaptic neuron) releases neurotransmitters (Acetylcholine) in synaptic cleft (synaptic cleft is a fluid filled gap between axon of first neuron and dendrite of the second neuron).
- Neurotransmitters then activate the ion channels present on the dendrite of next neuron (called as post-synaptic neuron)
- This causes the depolarisation resulting in transmission of nerve impulse.
- This type of transmission is slower as compared to electric transmission.
(b) Mechanism of vision: Retina in the eye balls is the site of light and colour perception. Retina contains photoreceptor cells- rod cells and cone cells.
- Photoreceptor cells contain light sensitive photopigments that are composed of opsin (a protein) and retinal (an aldehyde of vitamin A).
- As the light falls on retina passing through pupil, it causes dissociation of retinal from opsin.
- This causes the change in conformation of opsin resulting in change in membrane permeability in photoreceptor cells and generation of action potential.
- These action potentials (impulses) are transmitted to the visual cortex area of the brain by the optic nerves,
- The neural impulses are analysed and image formed on retina is perceived.
(c) Mechanism of hearing
- External ear receives sound waves and transfers them to the tympanic membrane (eardrum).
- Sound waves generate vibrations in tympanic membrane which are transferred to the oval window of internal ear through ear ossicles (malleus, incus and stapes).
- Vibrations are then passed-on to cochlea where they generate waves in lymph.
- The waves in the lymph induce a ripple in the basilar membrane.
- It causes the hair cells to bend and press them against the tectorial membrane.
- As a result, nerve impulses are generated in the associated afferent neuron.
- These are transmitted by the afferent fibres via auditory nerves to the auditory cortex of the brain, where the impulses are analysed and the sound is recognised.
Q.7 Answer briefly:
(a) How do you perceive the colour of an object?
(b) Which part of our body helps us in maintaining the body balance?
(c) How does the eye regulate the amount of light that falls on the retina?
(a) The retina in the eyeballs is the site of colour perception. Cone cells present in retina recognise colours. There are three types of cone cells which are responsible for the recognition of different wavelength of light (different colours). Cone cells contain light sensitive photo-pigments that are composed of opsin (a protein) and retinal (an aldehyde of vitamin A). As the light falls on cone cells passing through the pupil, it causes dissociation of retinal from opsin. It causes the change in conformation of opsin that results in a change in membrane permeability in photoreceptor cells and generation of an action potential. These action potentials (impulses) are transmitted by the optic nerves to the visual cortex area of the brain, where the neural impulses are analyzed and coloured image formed on the retina is perceived.
(b) Vestibular apparatus present in the internal ear is responsible for maintaining the body balance. It is a sac-like structure and is composed of three semicircular canals. Canals contain endolymph (a fluid) and sensors (crista ampullar, present at the base of canals, and macula, present in otolith).
(c) Eyes regulate the amount of light falling on the retina with the help of a pupil. The pupil is an aperture at the front of the eyeballs. It is surrounded by iris that is made up of contractile muscles. Iris contracts or expands to constrict or dilate the pupil which in turn regulates the amount of light passing through it.
Q.8 Explain the following:
(a) Role of Na+ in the generation of action potential.
(b) Mechanism of generation of light-induced impulse in the retina.
(c) Mechanism through which a sound produces a nerve impulse in the inner ear.
(a) The sodium (Na+) ion plays an important role in generating and maintaining the potential difference necessary for the conduction of nerve impulse. When the outer side of the membrane of the nerve fibre is positively charged and the inner side is negatively charged, it is in resting state. At this state, there is a high concentration of sodium ions at the outer side of the membrane of nerve fibres. To generate an action potential, polarity should be reversed i.e. outer side should be negative and inner side of the membrane should be positive. When a neuron gets a nerve impulse, sodium ions cross the membrane of nerve fibres through sodium ion channels. This reverses the charge distribution across the membrane. The outer side of membrane becomes negatively charged, while the inner side becomes positively charged. Potential difference generated by this charge redistribution is called an action potential.
(b) Photoreceptor cells contain light-sensitive photo-pigments that are composed of opsin (a protein) and retinal (an aldehyde of vitamin A). As the light falls on retina passing through the pupil, it causes dissociation of retinal from opsin. It changes the conformation of opsin that results in change in membrane permeability of photoreceptor cells and generates an action potential. These impulses are transmitted by the optic nerves to the visual cortex area of the brain, where the neural impulses are analyzed and the image formed on retina is perceived.
(c) The external ear receives sound waves and transfers them to the tympanic membrane (eardrum). Sound waves generate vibrations in the tympanic membrane which are transferred to the oval window of the internal ear through ear ossicles (malleus, incus and stapes). Vibrations are then passed on to cochlea where they generate waves in the lymph. The waves in the lymph induce a ripple in the basilar membrane. It causes the hair cells to bend and presses them against the tectorial membrane. As a result, nerve impulses are generated in the associated afferent neuron that is transmitted via auditory nerves to the temporal lobe of the cerebral cortex of the brain, where the impulses are analysed and the sound is recognised.
Q.9 Differentiate between:
(a) Myelinated and non-myelinated axons
(b) Dendrites and axons
(c) Rods and cones
(d) Thalamus and Hypothalamus
(e) Cerebrum and Cerebellum
|Myelinated axons||Non-myelinated axons|
|These are covered with a myelin sheath.||These are not covered with a myelin sheath.|
|Schwan cells are present in the myelin sheath.||Schwan cells are absent.|
|Node of Ranvier is present.||Node of Ranvier is absent.|
|Conduction of nerve impulse is faster.||Conduction of nerve impulse is slower.|
|Chances of loss of impulse during conduction are less.||Chances of loss of impulse during conduction are high.|
|Dendrites may be branched or unbranched.||Axons are branched structures.|
|They carry impulse towards the cell body (neuron).||They carry impulse away from the cell body.|
|Myelin sheath is absent.||They may or may not have a myelin sheath.|
|Dendrites are small.||They are long and big.|
|Nissl’s granules are present.||They are absent in axons.|
|Rods help to see in dim light.||They help to see in bright light.|
|They are not involved in visualisation of a colour.||They help in visualisation of colours.|
|They contain purple photo-pigment called rhodopsin.||They have violet photo-pigment called iodopsin.|
|Thalamus is the part of forebrain. It is a major coordination centre for sensory and motor signalling.||Hypothalamus is the part of forebrain that controls body temperature and urge for eating and drinking.|
|It is part of the forebrain.||It is part of hindbrain.|
|It is the centre for controlling activities like intelligence, communication, memory, movement, etc.||It controls involuntary activities like balance, body equilibrium, fine movement coordination, sneezing, coughing, etc.|
|It is located in the anterior portion of the forebrain.||It is located just above the brain stem.|
|It is the largest part of the brain.||It is the second-largest part of the brain.|
Q.10 Answer the following:
(a) Which part of the ear determines the pitch of a sound?
(b) Which part of the human brain is the most developed?
(c) Which part of our central neural system acts as a master clock?
(a) Cochlea determines the pitch of sound.
(b) Forebrain is the most developed part of brain.
(c) Hypothalamus acts as a master clock of body.
Q.11 The region of the vertebrate eye, where the optic nerve passes out of the retina, is called the
(c) blind spot
(d) optic chaisma
(c) blind spot
[Explanation: Region of the retina where optic nerves pass is called blind spot because this region does not contain any photo-receptors.]
Q.12 Distinguish between:
(a) Afferent neurons and efferent neurons
(b) Impulse conduction in a myelinated nerve fibre and unmyelinated nerve fibre
(c) Aqueous humor and vitreous humor
(d) Blind spot and yellow spot
(e) Cranial nerves and spinal nerves
|Afferent neurons||Efferent neurons|
|Afferent neurons transmit nerve impulse towards brain or spinal cord.||Efferent neurons transmit nerve impulse from brain to effector organs.|
|Impulse conduction in a myelinated nerve fibre||Impulse conduction in an unmyelinated nerve fibre|
|In myelinated nerve fibres, Schwann cells form the myelin sheath around the axon. The gaps between two adjacent myelin sheaths are called nodes of Ranvier.||In unmyelinated nerve fibres, a single Schwann cell encloses the axon and there is no myelin sheath.|
|The nerve impulse is transmitted from one node to another. This type of impulse transmission is fast.||The nerve impulse is transmitted in a continuous manner along the entire length of the nerve fibre. This type of impulse transmission is slow.|
|Aqueous humor||Vitreous humor|
|It is a thin and watery fluid that is present between cornea and lens.||It is a transparent gel that is present between the lens and retina.|
|Blind spot||Yellow spot|
|Blind spot is the region of retina where optic nerves pass.||It is small area on retina that is present at the posterior pole of the eye.|
|Photoreceptors are absent in this region.||Cone cells are present.|
|It does not sense light due to the absence of photoreceptors.||It perceives bright light.|
|Cranial nerves||Spinal nerves|
|Nerves arising from brain are called as cranial nerves. There are 12 pairs of cranial nerves.||Nerves arising from spinal cord are called as spinal nerves. There are 31 pairs of spinal nerves.|
FAQs (Frequently Asked Questions)
1. What is Neural coordination?
The various organs in the body interacting and complementing each other’s functions implies the coordination of organs. Organs work in a synchronised manner, i.e. they do not work independently. The neural system and endocrine system of the human body are what jointly integrate and coordinate all the activities of the organs in the human body in order to make them function in a synchronised manner. This is known as neural coordination. This coordination is fast and short-spanned. An organised network of point-to-point connections is provided by the neural system for quick coordination. A network of nerves in the body aids in this connection.
2. Define the Brain.
The central processing organ of the body that acts as the ‘control and command system’ is called the brain. The skull guards it and three membranes called cranial meninges cover it. The three membranes include the outer layer which is called the dura mater, the middle layer called arachnoid, and the inner layer called the pia mater. The dura mater is a tough and fibrous membrane, the arachnoid is fragile and light, and the pia mater is an expansion of the brain tissue. The pia mater is a vascular membrane of the brain and is richly supplied by the blood. The Forebrain, the Hindbrain, and the Midbrain are the three sections of the brain.
3. What are the parts of the human neural system?
The human neural system consists of two parts, namely the central neural system and the peripheral neural system. The brain and the spinal cord make up the central neural system, therefore, control of the body and mind are this system’s main function. The peripheral neural system is a kind of nervous system. It executes the task of providing information to the entire body. This system plays a role outside the spinal cord and brain.
4. What are the benefits of NCERT solutions for Class 11 Biology Chapter 21 Neural Control And Coordination?
Extramarks has NCERT Solutions Class 11 Biology Chapter 21 – Neural Control and Coordination available on its site. The solutions can also be accessed through its app. These are a reliable source of reference that one can avail The multiple benefits offered by Biology Class 11 NCERT Solutions Chapter 21 are:
- The solutions have answers to all the questions that are given in the NCERT textbook.
- Students can refer to the solutions online and offline.
- The solutions have answers written in simple language and explained with the help of examples and diagrams.
Give a brief about the structure of the human ear.
The outer ear, the middle ear, and the inner ear are the three parts that form the structure of the human ear. The outer ear consists of an auricle or a pinna (which is a visible portion). The middle ear has three tiny bones known as malleus, incus, and stapes while the inner ear encompasses vestibular apparatus and snail-shell-like cochlea which are two distinct functional units.
Write a short note on reflex action.
A sudden and involuntary response to stimuli is known as a reflex action. Immediate action is taken in response to a stimulus without much thought of the outcome. The immediate withdrawal of your hand from a pan that is too hot is an example of this. Reflex action kicks in to minimise the damage that can be caused to the body.