RBSE Solutions Class 12 Biology Chapter 26 Man-Nervous System

 

RBSE Solutions for Class 12 Biology Chapter 26 Man-Nervous System

 

RBSE Class 12 Biology Chapter 26 Multiple Choice Questions

 

Question 1. What is the unit of the nervous system?
(a) Nephron
(b) Neuron
(c) Brain
(d) Spinal cord
Answer: (b) Neuron
In simple words: The neuron is the basic building block and functional unit of the nervous system. It helps to transmit messages throughout the body.

🎯 Exam Tip: Remember that the neuron is the structural and functional unit of the nervous system, distinct from a nephron, which is the unit of the kidney.

 

Question 2. Temperature controlling centre in the brain of man is:
(a) Pituitary gland
(b) Diencephalon
(c) Loading [MathJax]/extensions/MathMenu.js
Answer: [Answer missing in source]
In simple words: The brain has a specific part that helps to keep our body temperature steady, like a thermostat.

🎯 Exam Tip: For questions about specific brain functions, recall the major parts of the brain and their primary roles, like the hypothalamus for temperature regulation.

 

Question 3. A function of the parasympathetic nervous system is:
(a) Dilation of pupil
(b) Secretion of sugar in the liver
(c) Increase heartbeat
(d) Stimulate secretion of saliva
Answer: (d) Stimulate secretion of saliva
In simple words: The parasympathetic nervous system helps our body "rest and digest," so it makes us produce more saliva when we eat.

🎯 Exam Tip: Differentiate between the "rest and digest" (parasympathetic) and "fight or flight" (sympathetic) functions of the autonomic nervous system to correctly identify their effects.

 

Question 4. The scientist who worked on conditioned reflex action:
(a) Mendel
(b) Pavlov
(c) Darwin
(d) Evan Wilmut
Answer: (b) Pavlov
In simple words: Pavlov was a famous scientist who studied how animals learn to respond to things, like dogs salivating when they hear a bell.

🎯 Exam Tip: Associate key scientists with their groundbreaking experiments or theories, such as Pavlov with conditioned reflexes, Mendel with genetics, and Darwin with evolution.

 

Question 5. Number of cranial nerves present in Man are:
(a) 10 Pairs
(b) 10
(c) 12 Pairs
(d) 12
Answer: (c) 12 Pairs
In simple words: Humans have 12 pairs of special nerves that come directly from the brain, helping with things like sight, smell, and facial movements.

🎯 Exam Tip: Remember that cranial nerves come in pairs and are usually counted as such (e.g., 12 pairs, not 12 individual nerves).

 

RBSE Class 12 Biology Chapter 26 Very Short Answer Type Questions

 

Question 3. Which is the longest cell?
Answer: The longest cell in the human body is the nerve cell, also known as a neuron.
In simple words: The nerve cell is the longest cell.

🎯 Exam Tip: When asked about the longest cell, always specify "nerve cell" or "neuron" for accuracy.

 

RBSE Class 12 Biology Chapter 26 Short Answer Type Questions

 

Question 1. Which are two parts of the autonomous nervous system?
Answer: The two main parts of the autonomous nervous system are:
• Sympathetic Nervous System
• Parasympathetic Nervous System
In simple words: The two parts are the sympathetic and parasympathetic nervous systems.

🎯 Exam Tip: Clearly list both the sympathetic and parasympathetic systems as the two divisions of the autonomous nervous system.

 

Question 2. Why the name peripheral nervous system is given?
Answer: The peripheral nervous system gets its name because it consists of nerves that extend from the central nervous system (brain and spinal cord) to all other parts of the body, or the 'periphery'. These nerves connect the central nervous system to the organs, muscles, and skin.
In simple words: It's called peripheral because it connects the brain and spinal cord to all the outer parts of the body.

🎯 Exam Tip: Define the peripheral nervous system by explaining its origin (from CNS) and its function (connecting to all body organs), linking it to the meaning of 'peripheral'.

 

Question 3. Write one function of the following:
1. Cerebrum
2. Cerebellum
3. Medulla oblongata
4. Hypothalamus
Answer: [Answer missing in source]
In simple words: The functions of these brain parts are important for many body actions.

🎯 Exam Tip: When listing functions of brain parts, provide clear and concise actions for each to score well.

 

Question 4. Write the main parts of the brain.
Answer: The main parts of the brain are:
1. Forebrain: This includes the Cerebrum and Diencephalon.
2. Midbrain: This part has 4 optic lobes.
3. Hindbrain: This includes the Cerebellum, Pons, and Medulla oblongata.
In simple words: The brain is divided into three main parts: the forebrain, midbrain, and hindbrain.

🎯 Exam Tip: For main parts of the brain, a simple three-division classification (forebrain, midbrain, hindbrain) is usually sufficient, with a brief mention of their components.

 

Question 5. Write the name of the fluid-filled in the cavities of the brain.
Answer: The fluid that fills the cavities of the brain is called Cerebrospinal Fluid (CSF). This fluid helps to protect the brain and spinal cord.
In simple words: Cerebrospinal Fluid (CSF) fills the brain cavities.

🎯 Exam Tip: Clearly state "Cerebrospinal Fluid" and its abbreviation "CSF" when identifying the fluid in brain cavities.

 

RBSE Class 12 Biology Chapter 26 Essay Type Questions

 

Question 1. Explain simple reflex action (arch) with the help of well-labelled diagram depicting a transverse section of the spinal cord and nervous pathway of reflex action.
Answer: A reflex arch is the nerve pathway involved in a reflex action. It allows a rapid, involuntary response to a stimulus. It consists of the following five parts:
1. Sensory organ: These are receptors on the body that detect external or internal stimuli, like heat or pain.
2. Sensory Nerve: This nerve carries the impulse from the sensory organ to the spinal cord.
3. The nerve centre (Interneurons): Located in the spinal cord, this center processes the impulse.
4. Motor nerve: This nerve transmits the impulse away from the spinal cord to the effector organs.
5. Effector organs: These organs, like muscles or glands, perform the action or response to the impulses received through the motor nerve.
In simple words: A reflex arc is the path a nerve signal takes to cause a quick, automatic reaction. It has five parts: sensory organ, sensory nerve, nerve center, motor nerve, and effector organ.

🎯 Exam Tip: When explaining the reflex arc, list the five components in sequence and briefly describe their role in transmitting the impulse and executing the response.

 

Question 2. Describe the structure of the brain of a man with a diagram.
Answer: The human brain is a complex organ divided into three main parts:
Structure of Brain:
1. Forebrain
2. Cerebellum
3. Brain Stem

1. Forebrain:
In humans, the forebrain includes two main parts:
• Cerebral hemispheres (Cerebrum)
• Diencephalon

Cerebrum:
• It makes up two-thirds of the brain and is divided into two hemispheres by a longitudinal fissure.
• Both hemispheres are connected internally by the corpus callosum.
• Each cerebral hemisphere has five lobes:
1. Frontal lobe
2. Parietal lobe
3. Temporal lobe
4. Occipital lobe
5. Insula lobe (not visible from outside)
• The brain's outer layer, the cortex, has distinct ridges (gyri) and grooves (sulci).
• These gyri and sulci increase the cortex's surface area by three times.
• The inner part of the cerebrum is known as white matter.

Functions of the Cerebrum:
1. Frontal lobes: These control memory, thinking, reasoning, emotions, judgment, planning, willpower, and personality. They also manage voluntary muscles and many sensations.
2. Parietal lobes: These interpret sensory perceptions like touch, pain, cold, and heat. They also help with speech, handicrafts, and understanding thoughts.
3. Temporal lobes: These interpret and decode sounds, helping with language comprehension, smell, and auditory sensations.
4. Occipital lobes: These interpret and decode visual sensations, especially concerning colors and shapes. They also control eye movements.
5. Insula lobes: These coordinate memory and other parts of the cerebrum.

2. Diencephalon:
• It is clearly divided into the epithalamus, thalamus, and hypothalamus.
• The thalamus forms 80% of the diencephalon and acts as a relay center for sensory perceptions like taste, touch, hearing, vision, pain, and heat. It interprets these sensations and sends motor commands for voluntary movements.
• The hypothalamus contains about 12 large nuclei and is divided into four main parts:
1. Supraoptic part: Located above the optic chiasma, its axons enter the pars nervosa of the pituitary gland.
2. Tuberal part: This is the broadest middle part, attached to the pituitary by a stalk called the infundibulum.
3. It includes a projection, the tuber cinerarium, around the infundibulum.
4. Mammillary part: This is the posterior-most part with two small, round projections (mammillary bodies). It controls reflex actions related to smell.
5. Preoptic part: This small part is anterior to the supraoptic part and controls some autonomic reflex actions.
• It also helps regulate diurnal rhythms and sleep.

Midbrain:
It is the middle part of the brain, also called the mesencephalon. It consists of two parts:
1. Corpora Quadrigemina:
• It contains four optic lobes, collectively known as Corpora Quadrigemina.
• Two superior optic lobes and two inferior optic lobes are present.
• These optic lobes connect to the dorsal surface of the midbrain via the Tatum.
• They receive stimuli related to vision and hearing.
2. Cerebral peduncle:
• Also called Crura Cerebri.
• It is a bundle of nerve fibers that connect the cerebral cortex to the spinal cord and other brain parts.

Cerebellum:
The cerebellum is the second-largest part of the brain and consists of two lobes. Its dorsal side is well-developed, and its two main functions are:
• Maintaining body posture and equilibrium.
• Coordinating muscular activities.

Pons Varolii:
It lies just above the medulla oblongata and below the cerebral peduncle. It connects both lobes of the cerebellum and other parts of the brain.
• It is made of white matter.
• It contains the Pneumotaxic center, which regulates breathing. It also controls chewing, saliva secretion, tear release, and eye movements.

Medulla Oblongata:
This is the posterior-most part of the brain, triangular in shape, and located between the pons and spinal cord. Its cavity is called metacoel, and the medulla continues into the spinal cord. Its functions include:
• Controlling centers for breathing, coughing, and swallowing.
• Controlling centers for heartbeats, blood pressure, peristalsis in the alimentary canal, and other involuntary activities.

Brain Ventricles:
• The mammalian brain has hollow cavities called ventricles, which are lined by ependymal epithelium and filled with cerebrospinal fluid (CSF).
• The brain has four ventricles: I, II, III, and IV.
• Ventricles I and II (paracoels) are found in the cerebral hemispheres.
• Each paracoel forms a rhinocoel in the olfactory lobe, also known as zero ventricles.
• Both paracoels open into the third ventricle through the foramen of Monro.
• The third ventricle (dioctyl) is found in the roof of the diencephalon.
• Posterior choroid plexus: Located in the roof of the metacoel, it consists of pia mater and a network of blood capillaries. The anterior choroid plexus produces CSF, while the posterior choroid plexus absorbs CSF and secretes it into the subarachnoid space.
• There are three openings in the posterior choroid plexus for CSF absorption:
1. Foramen of Magendie (one)
2. Foramen of Luschka (two)
• Arachnoid villi in the subarachnoid space absorb CSF and return it to the venous blood.
In simple words: The brain has three main parts: forebrain, midbrain, and hindbrain. The forebrain includes the cerebrum (for thinking, memory) and diencephalon (for relaying signals and controlling body functions). The midbrain connects these parts. The hindbrain includes the cerebellum (for balance), pons, and medulla oblongata (for vital functions like breathing and heart rate). The brain also has fluid-filled spaces called ventricles with CSF for protection.

🎯 Exam Tip: Structure your answer by clearly outlining the main parts of the brain and then detailing each part's sub-components, structure, and functions. A well-organized response makes it easier to score full marks.

 

Question 3. Describe the cranial nerves of mammals.
Answer: The vital activities of the body are controlled and coordinated by two main systems:
1. Nervous System: This includes the central nervous system (brain and spinal cord) and the peripheral nervous system.
2. Endocrine System: This involves hormones.

The nervous system is further divided into:
• Central nervous system: This consists of the brain and spinal cord.
• Peripheral nervous system: This includes cranial nerves and spinal nerves.
• Autonomous nervous system: This includes the sympathetic and parasympathetic nervous systems.

A nerve cell or neuron is the basic structural and functional unit of the nervous system. The spaces between neurons are filled by neuroglial cells.

The structure of a neuron can be compared by its parts:
The cyton (cell body) has a large, round nucleus, tiny neurofibrils, cytoplasmic organelles, and many Nissl's granules. Nissl's granules are ribosomes made of RNA and proteins. The centrosome is absent, meaning nerve cells do not divide. Nissl's granules are groups of lamellae attached to ribosomes, which help synthesize proteins.

Types of neurons based on structure of axon:
• Bipolar: Has one axon and one dendron. Found in eyes, cochlea, and olfactory epithelium.
• Multipolar: Has one axon and many dendrites. Most vertebrates have multipolar neurons.
• Myelinated or Medullated: The axon is surrounded by a myelin sheath.
• Non-myelinated or Non-medullated: The axon is not surrounded by a myelin sheath.
In simple words: Cranial nerves are part of the peripheral nervous system, which works with the central nervous system. Nerves are made of neurons, which are cells with a main body (cyton), branches that receive signals (dendrons), and a long part that sends signals (axon). Axons can have a protective covering (myelin) or not.

🎯 Exam Tip: When describing cranial nerves, include their classification within the broader nervous system, key neuron structures (dendron, axon, cyton), and a comparison of their features, along with neuron types.

 

Question 4. Describe reflex action.
Answer: A reflex action is a rapid, automatic response to a stimulus that occurs without conscious thought. This response is quick and involuntary, and the brain typically has no direct control over it.

For example:
1. Withdrawing your hand instantly when touching a sharp pin or hot object.
2. Salivating when you smell or think about tasty food.

Reflex actions are divided into two main types:
1. Simple or unconditioned reflex action
2. Acquired or conditioned reflex action

1. Unconditioned Reflex action:
• These are natural or inborn actions.
• No learning is needed for these reflexes.
• Examples include blinking when an object comes close to the eye.

2. Conditioned Reflex action:
• These reflexes require learning, training, or experience.
• The Russian physiologist Ivan Pavlov famously explained this through his experiment with a dog.
• Pavlov's experiment: He rang a bell just before feeding a dog. Over time, the dog began to salivate when it heard the bell, even without food.
• Examples:
1. Instantly braking your vehicle if something suddenly appears in front of it.
2. Tying shoelaces while talking to someone else.
3. A dog running away if you pretend to pick up a stone to throw.
4. A student standing up when a teacher enters the class.

Mechanism of Reflex Action:
• Nerve fibers from the spinal cord and motor fibers from the ventral root play a crucial role.
• For instance, a pinprick on the skin stimulates sensory nerve endings.
• These sensory fibers transmit the stimulus to neurons in the dorsal ganglia of the spinal nerve.
• The nerve signal then goes to dendrites of nearby motor nerves.
• Axons of motor cells (which are fibers of the ventral root) carry the stimulus to leg muscles, causing them to contract and move the leg away.
• These actions are very fast and are collectively known as reflex action.

Spinal Reflex Arch:
• The nerve pathway involved in a reflex action is known as a reflex arch.
• It consists of the following five parts:
1. Sensory organ: Receptors on the body that receive external or internal stimuli.
2. Sensory Nerve: Carries impulses from sensory organs to the spinal cord.
3. The nerve center: Interneurons in the spinal cord that process the actions.
4. Motor nerve: Transmits impulses away from the spinal cord to the effector organs.
5. Effector organs: These organs complete their actions by responding to impulses from the motor nerve.
In simple words: Reflex action is a fast, automatic body response that doesn't need thinking. There are unconditioned reflexes (natural, like blinking) and conditioned reflexes (learned, like Pavlov's dog). The reflex arc is the pathway of nerve signals, involving sensory input, processing in the spinal cord, and motor output to cause a quick reaction.

🎯 Exam Tip: When describing reflex action, clearly define it, distinguish between unconditioned and conditioned reflexes with examples, and explain the step-by-step mechanism of the reflex arc.

 

Question 5. Describe spinal nerves in detail.
Answer: Spinal nerves are a crucial part of the peripheral nervous system. Here are their details:
• These nerves originate from the spinal cord.
• There are 31 pairs of spinal nerves in total.
• All spinal nerves are mixed, meaning they contain both sensory and motor neurons.
• Each spinal nerve exits through an intervertebral foramen between two vertebrae of the vertebral column.
• Based on their origin point, spinal nerves are named as follows:

In simple words: Spinal nerves come from the spinal cord and are found in 31 pairs. They are 'mixed' nerves, carrying both sensory and motor signals. Each pair exits between vertebrae and is named according to its region, like cervical or thoracic.

🎯 Exam Tip: When detailing spinal nerves, remember to mention their origin, number of pairs, mixed nature, exit points, and be able to list the different types with their respective numbers and locations, potentially using a table for clarity.