(a) Afferent neurons and Efferent neurons Afferent Neurons:- Afferent neuron conducts nerve impulses toward the brain or the spinal cord. Efferent Neurons:- Efferent neuron conducts nerve impulses from the brain or spinal cord to the effector organs such as muscles or glands. (b) Impulse conductionRead more
(a) Afferent neurons and Efferent neurons
Afferent Neurons:- Afferent neuron conducts nerve impulses toward the brain or the spinal cord.
Efferent Neurons:- Efferent neuron conducts nerve impulses from the brain or spinal cord to the effector organs such as muscles or glands.
(b) Impulse conduction in a myelinated nerve fibre and unmyelinated nerve fibre
Impulse Conduction in a Myelinated Nerve Fibre:-
1. Myelinated nerve fibre, the action potential is conducted from one node to another.
2. Conduction of impulses is faster.
Impulse Conduction in an Unmyelinated Nerve Fibre:-
1. Unmyelinated nerve fibre, the action potential is not conducted from node to node. It is carried along the whole length of the nerve fibre.
2. Conduction of impulses is slower.
(c) Aqueous humor and vitreous humor:-
Aqueous Humour:- Thin, watery fluid present between the cornea and the lens.
Vitreous Humour:- Transparent gel present between the lens and the retina.
(c) Blind spot and yellow spot:-
Blind Spot:-
1. Blind spot is a spot on the retina present at the point of origin of the optic nerve.
2. Photoreceptor cells are absent from this region.
3. Insensitive to light as both rods and cones are absent.
Yellow Spot:-
1. Yellow spot is a small area on the retina present at the posterior pole of the eye, lateral to the blind spot.
2. Only cones are present in this region.
3. Sensitive to bright light as cones are present.
(f) Cranial nerves and spinal nerves.
Cranial Nerves:-
1. Cranial nerves arise from the brain.
2. 12 pairs of cranial nerves.
Spinal Nerves:-
1. Spinal nerves arise from the spinal cord.
2. 31 pairs of spinal nerves
(c) Blind spot Blind spot is the part where the optic nerve passes out of the retina. Photoreceptors are absent from this region. For more answers visit to website: https://www.tiwariacademy.com/ncert-solutions/class-11/biology/chapter-21/
(c) Blind spot
Blind spot is the part where the optic nerve passes out of the retina. Photoreceptors are absent from this region.
(a) Cochlea determines the pitch of a sound. (b) Forebrain is largest and the most developed part of the human brain. (c) Hypothalamus acts as a master clock of the human body. For more answers visit to website: https://www.tiwariacademy.com/ncert-solutions/class-11/biology/chapter-21/
(a) Cochlea determines the pitch of a sound.
(b) Forebrain is largest and the most developed part of the human brain.
(c) Hypothalamus acts as a master clock of the human body.
(a) Myelinated and non-myelinated axons:- Myelinated Axons:- 1. Transmission of nerve impulse is faster 2. Myelinated axon has a myelin sheath. 3. Node of Ranvier is present between adjacent myelin sheaths. 4. Found in the brain, the spinal cord, the cranial and spinal nerves 5. Schwann cells are obRead more
(a) Myelinated and non-myelinated axons:-
Myelinated Axons:-
1. Transmission of nerve impulse is faster
2. Myelinated axon has a myelin sheath.
3. Node of Ranvier is present between adjacent myelin sheaths.
4. Found in the brain, the spinal cord, the cranial and spinal nerves
5. Schwann cells are observed inside the myelin sheath
Non-myelinated Axons:-
1. Transmission of nerve impulse is slower
2. Myelin sheath is absent
3. Node of Ranvier is absent
4. Found in autonomous and somatic neural systems
5. Schwann cells are not observed inside the myelin sheath
(b) Dendrites and axons:-
Dendrites:-
1. Dendrite is a small projection arising from the neuron. It conducts the nerve impulse toward the cell body.
2. Nissl’s granules are present in dendrites.
3. Dendrites are always non-myelinated.
Axons:-
1. Axon is a single, long projection that conducts the nerve impulse away from cell body to the next neuron.
2. Nissl’s granules are absent from axons.
3. Axons can be myelinated or non-myelinated.
(c) Rods and cones:-
Rods:-
1. Rods help in twilight vision.
2. They have visual purple pigment called rhodopsin.
3. Rods are the photoreceptor cells of the retina that are sensitive to dim light.
Cones:-
1. Cones help in colour vision.
2. They have visual violet pigment called iodopsin.
3. Cones are the photoreceptor cells of the retina are sensitive to bright light.
(d) Thalamus and Hypothalamus
Thalamus:- Thalamus is the part of the forebrain that receives nerve impulses of pain, temperature, touch, etc., and conducts them to the cerebral hemisphere.
Hypothalamus:- Hypothalamus is the part of the forebrain that controls involuntary functions such as hunger, thirst, sweating, sleep, fatigue, sexual desire, temperature regulation, etc.
(e) Cerebrum and Cerebellum:-
Cerebrum:- Part of the forebrain that controls voluntary functions. It is the place where intelligence, will power, memory, etc.
Cerebellum:- Part of the hindbrain that controls voluntary functions and controls the equilibrium.
(a) Sodium ions play an important role in the generation of action potential. When a nerve fibre is stimulated, the membrane potential decreases. The membrane becomes more permeable to Na+ ions than to K+ ions. As a result, Na+ diffuses from the outside to the inside of the membrane. This causes theRead more
(a) Sodium ions play an important role in the generation of action potential. When a nerve fibre is stimulated, the membrane potential decreases. The membrane becomes more permeable to Na+ ions than to K+ ions. As a result, Na+ diffuses from the outside to the inside of the membrane. This causes the inside of the membrane to become positively-charged, while the outer membrane gains a negatively charge. This reversal of polarity across the membrane is known as depolarisation. The rapid inflow of Na+ ions causes the membrane potential to increase, thereby generating an action potential.
(b) Retina is the innermost layer of the eye. It contains three layers of cells – inner ganglion cells, middle bipolar cells, and outermost photoreceptor cells. Photoreceptor cells are composed of a protein called opsin and an aldehyde of vitamin A called retinal. When light rays are focused on the retina through the cornea, retinal gets dissociated from opsin. As a result, the structure of opsin gets changed. This in turn causes the permeability of the membrane to change, thereby generating a potential difference in the cells. Consequently, an action potential is generated in the ganglion cells and is transmitted to the visual cortex of the brain via the optic nerves. In the cortex region of the brain, the impulses are analysed and the image is formed on the retina.
(c) The pinna of the external ear collects the sound waves and directs them to the tympanic membrane (ear drum) via the external auditory canal. The ear drum then vibrates the sound waves and conducts them to the internal ear through the ear ossicles. The ear ossicles increase the intensity of the sound waves. These vibrating sound waves are conducted through the oval window to the fluid in the cochlea. Consequently, a movement is created in the lymph. This movement produces vibrations in the basilar membrane, which in turn stimulate the auditory hair cells. These cells generate a nerve impulse, conducting it to the auditory cortex of the brain via afferent fibres. The auditory cortex region interprets the nerve impulse and sound is recognised.
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 (f) cranial nerves and spinal nerves.
(a) Afferent neurons and Efferent neurons Afferent Neurons:- Afferent neuron conducts nerve impulses toward the brain or the spinal cord. Efferent Neurons:- Efferent neuron conducts nerve impulses from the brain or spinal cord to the effector organs such as muscles or glands. (b) Impulse conductionRead more
(a) Afferent neurons and Efferent neurons
Afferent Neurons:- Afferent neuron conducts nerve impulses toward the brain or the spinal cord.
Efferent Neurons:- Efferent neuron conducts nerve impulses from the brain or spinal cord to the effector organs such as muscles or glands.
(b) Impulse conduction in a myelinated nerve fibre and unmyelinated nerve fibre
Impulse Conduction in a Myelinated Nerve Fibre:-
1. Myelinated nerve fibre, the action potential is conducted from one node to another.
2. Conduction of impulses is faster.
Impulse Conduction in an Unmyelinated Nerve Fibre:-
1. Unmyelinated nerve fibre, the action potential is not conducted from node to node. It is carried along the whole length of the nerve fibre.
2. Conduction of impulses is slower.
(c) Aqueous humor and vitreous humor:-
Aqueous Humour:- Thin, watery fluid present between the cornea and the lens.
Vitreous Humour:- Transparent gel present between the lens and the retina.
(c) Blind spot and yellow spot:-
Blind Spot:-
1. Blind spot is a spot on the retina present at the point of origin of the optic nerve.
2. Photoreceptor cells are absent from this region.
3. Insensitive to light as both rods and cones are absent.
Yellow Spot:-
1. Yellow spot is a small area on the retina present at the posterior pole of the eye, lateral to the blind spot.
2. Only cones are present in this region.
3. Sensitive to bright light as cones are present.
(f) Cranial nerves and spinal nerves.
Cranial Nerves:-
1. Cranial nerves arise from the brain.
2. 12 pairs of cranial nerves.
Spinal Nerves:-
1. Spinal nerves arise from the spinal cord.
2. 31 pairs of spinal nerves
For more answers visit to website:
See lesshttps://www.tiwariacademy.com/ncert-solutions/class-11/biology/chapter-21/
The region of the vertebrate eye, where the optic nerve passes out of the retina, is called the
(c) Blind spot Blind spot is the part where the optic nerve passes out of the retina. Photoreceptors are absent from this region. For more answers visit to website: https://www.tiwariacademy.com/ncert-solutions/class-11/biology/chapter-21/
(c) Blind spot
Blind spot is the part where the optic nerve passes out of the retina. Photoreceptors are absent from this region.
For more answers visit to website:
See lesshttps://www.tiwariacademy.com/ncert-solutions/class-11/biology/chapter-21/
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 a sound. (b) Forebrain is largest and the most developed part of the human brain. (c) Hypothalamus acts as a master clock of the human body. For more answers visit to website: https://www.tiwariacademy.com/ncert-solutions/class-11/biology/chapter-21/
(a) Cochlea determines the pitch of a sound.
(b) Forebrain is largest and the most developed part of the human brain.
(c) Hypothalamus acts as a master clock of the human body.
For more answers visit to website:
See lesshttps://www.tiwariacademy.com/ncert-solutions/class-11/biology/chapter-21/
Differentiate between: (a) Myelinated and non-myelinated axons (b) Dendrites and axons (c) Rods and cones (d) Thalamus and Hypothalamus (e) Cerebrum and Cerebellum
(a) Myelinated and non-myelinated axons:- Myelinated Axons:- 1. Transmission of nerve impulse is faster 2. Myelinated axon has a myelin sheath. 3. Node of Ranvier is present between adjacent myelin sheaths. 4. Found in the brain, the spinal cord, the cranial and spinal nerves 5. Schwann cells are obRead more
(a) Myelinated and non-myelinated axons:-
Myelinated Axons:-
1. Transmission of nerve impulse is faster
2. Myelinated axon has a myelin sheath.
3. Node of Ranvier is present between adjacent myelin sheaths.
4. Found in the brain, the spinal cord, the cranial and spinal nerves
5. Schwann cells are observed inside the myelin sheath
Non-myelinated Axons:-
1. Transmission of nerve impulse is slower
2. Myelin sheath is absent
3. Node of Ranvier is absent
4. Found in autonomous and somatic neural systems
5. Schwann cells are not observed inside the myelin sheath
(b) Dendrites and axons:-
Dendrites:-
1. Dendrite is a small projection arising from the neuron. It conducts the nerve impulse toward the cell body.
2. Nissl’s granules are present in dendrites.
3. Dendrites are always non-myelinated.
Axons:-
1. Axon is a single, long projection that conducts the nerve impulse away from cell body to the next neuron.
2. Nissl’s granules are absent from axons.
3. Axons can be myelinated or non-myelinated.
(c) Rods and cones:-
Rods:-
1. Rods help in twilight vision.
2. They have visual purple pigment called rhodopsin.
3. Rods are the photoreceptor cells of the retina that are sensitive to dim light.
Cones:-
1. Cones help in colour vision.
2. They have visual violet pigment called iodopsin.
3. Cones are the photoreceptor cells of the retina are sensitive to bright light.
(d) Thalamus and Hypothalamus
Thalamus:- Thalamus is the part of the forebrain that receives nerve impulses of pain, temperature, touch, etc., and conducts them to the cerebral hemisphere.
Hypothalamus:- Hypothalamus is the part of the forebrain that controls involuntary functions such as hunger, thirst, sweating, sleep, fatigue, sexual desire, temperature regulation, etc.
(e) Cerebrum and Cerebellum:-
Cerebrum:- Part of the forebrain that controls voluntary functions. It is the place where intelligence, will power, memory, etc.
Cerebellum:- Part of the hindbrain that controls voluntary functions and controls the equilibrium.
For more answers visit to website:
See lesshttps://www.tiwariacademy.com/ncert-solutions/class-11/biology/chapter-21/
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) Sodium ions play an important role in the generation of action potential. When a nerve fibre is stimulated, the membrane potential decreases. The membrane becomes more permeable to Na+ ions than to K+ ions. As a result, Na+ diffuses from the outside to the inside of the membrane. This causes theRead more
(a) Sodium ions play an important role in the generation of action potential. When a nerve fibre is stimulated, the membrane potential decreases. The membrane becomes more permeable to Na+ ions than to K+ ions. As a result, Na+ diffuses from the outside to the inside of the membrane. This causes the inside of the membrane to become positively-charged, while the outer membrane gains a negatively charge. This reversal of polarity across the membrane is known as depolarisation. The rapid inflow of Na+ ions causes the membrane potential to increase, thereby generating an action potential.
(b) Retina is the innermost layer of the eye. It contains three layers of cells – inner ganglion cells, middle bipolar cells, and outermost photoreceptor cells. Photoreceptor cells are composed of a protein called opsin and an aldehyde of vitamin A called retinal. When light rays are focused on the retina through the cornea, retinal gets dissociated from opsin. As a result, the structure of opsin gets changed. This in turn causes the permeability of the membrane to change, thereby generating a potential difference in the cells. Consequently, an action potential is generated in the ganglion cells and is transmitted to the visual cortex of the brain via the optic nerves. In the cortex region of the brain, the impulses are analysed and the image is formed on the retina.
(c) The pinna of the external ear collects the sound waves and directs them to the tympanic membrane (ear drum) via the external auditory canal. The ear drum then vibrates the sound waves and conducts them to the internal ear through the ear ossicles. The ear ossicles increase the intensity of the sound waves. These vibrating sound waves are conducted through the oval window to the fluid in the cochlea. Consequently, a movement is created in the lymph. This movement produces vibrations in the basilar membrane, which in turn stimulate the auditory hair cells. These cells generate a nerve impulse, conducting it to the auditory cortex of the brain via afferent fibres. The auditory cortex region interprets the nerve impulse and sound is recognised.
For more answers visit to website:
See lesshttps://www.tiwariacademy.com/ncert-solutions/class-11/biology/chapter-21/