The nervous system functions as the body’s rapid and intricate communication and control system. Its basic units are nerve cells called neurons, which transmit information via electrochemical signals known as nerve impulses. These signals travel along neurons and are relayed across junctions called synapses to other neurons, muscles, or glands. The peripheral nervous system (PNS) encompasses all the nerves extending outside the CNS, forming a network that connects the CNS to sensory organs and effector organs throughout the body. Reflex actions are swift, involuntary responses to stimuli that occur without conscious thought. Specialized sensory organs, such as the eyes, ears, nose, tongue, and skin, are responsible for detecting various stimuli from the external world and relaying this sensory information to the nervous system for processing and response.
Review Questions
Multiple Choice Questions:
1. Put a tick mark (✓) against the correct alternative in the following statements:
(a) Medulla oblongata controls
(i) Smelling
(ii) Beating of heart and respiratory movement
(iii) Intelligence and will power
(iv) Balancing the body
(b) Spinal cord is an extention of:
(i) Cerebellum
(ii) Cerebrum
(iii) Vertebral column
(iv) Medulla oblongata
(c) Body posture is mantained by:
(i) Cerebellum
(ii) Cerebrum
(iii) Medulla oblongata
(iv) Spinal cord
Short Answer Questions:
1. Write one word in the space provided to complete the second pair of the related words pertaining to nervous system.
Memory: cerebrum:: breathing:
Balance: cerebellum:: reasoning:
Ans:
Memory: cerebrum:: breathing: brainstem
Balance: cerebellum:: reasoning: cerebrum
2. (a) Name three major divisions of the human nervous system.
Ans:
- Central Nervous System (CNS): Encompassing the brain and the spinal cord, this division functions as the primary command center for processing information and orchestrating bodily functions.
- Peripheral Nervous System (PNS): This division is composed of all neural elements situated outside the CNS, including nerves and ganglia. Its role is to establish a communication network between the CNS and the body’s extremities and internal organs, enabling the central control system to interact with the rest of the organism.
- Autonomic Nervous System (ANS): Often regarded as a component of the PNS, the ANS governs involuntary physiological processes such as heart rate, digestion, breathing rhythm, pupil dilation, urination, and sexual response. Operating largely without conscious input, it is characterized by two primary branches: the sympathetic nervous system (associated with responses to stress or danger) and the parasympathetic nervous system (associated with relaxation and energy conservation). Certain classifications also acknowledge the enteric nervous system (which controls the digestive system) as a third branch within the ANS.
(b) Name the three main parts of human brain.
Ans:
Cerebrum: As the largest part of the brain, the cerebrum is the seat of higher-level intellectual functions, encompassing thinking, learning, memory consolidation, emotional processing, language comprehension and production, and conscious command over voluntary movements. Its defining feature is its division into two distinct cerebral hemispheres.
Cerebellum: Positioned inferiorly to the cerebrum and dorsally within the cranial cavity, the cerebellum’s primary role involves the coordination of motor actions, the maintenance of equilibrium and body posture, and the precise control of fine motor skills. It also participates in certain aspects of cognition.
Brainstem: Located at the base of the brain, the brainstem acts as a crucial relay center, connecting the cerebrum and cerebellum to the spinal cord. It governs numerous involuntary and life-sustaining functions, including breathing, heart rate regulation, blood pressure control, sleep-wake cycles, and essential reflexes such as swallowing and vomiting. The brainstem is composed of three main subdivisions: the midbrain, the pons, and the medulla oblongata.
3. Given here is the diagram of a neuron. Name the parts numbered 1-6.
Ans:
- dendrite
- dendrite (Terminal Arborization)
- nucleus
- axon (Nerve fibre)
- cell Body (cyton)
- node of ranvier
- sheath
Long answer questions
Question 1.
With the help of a suitable diagram describe the structure of a neuron.
Answer:
The neuron, the fundamental unit of the nervous system, is structurally adapted for rapid communication. It consists of a central cell body housing the nucleus, numerous branching dendrites that serve as primary sites for receiving signals from adjacent neurons, and a single,In many neurons, the axon is encased by a myelin sheath, an insulating layer that significantly accelerates signal conduction along the axon with periodic gaps called Nodes of Ranvier. The axon terminates in multiple axon terminals, each ending in a synaptic knob. These knobs contain and release chemical messengers called neurotransmitters into the synaptic cleft, enabling communication across synapses with other neurons or effector cells such as muscle fibers or glands.
Question 2.
Briefly describe the structure of the cerebrum in human brain, and mention its functions.
Ans:
The cerebrum, the most substantial component of the human brain, is distinctly separated into two cerebral hemispheres, which are linked by a robust band of nerve fibers called the corpus callosum. Its outermost layer, the cerebral cortex, displays a complex, folded architecture and is regionally organized into four primary lobes: the frontal lobe, which oversees sophisticated thinking and deliberate muscle control; the parietal lobe, responsible for interpreting sensory inputs and spatial orientation; the temporal lobe, involved in processing sounds, forming memories, and understanding language; and the occipital lobe, dedicated to deciphering visual information. Together, these lobes and the entire cerebrum orchestrate a vast array of high-level functions, encompassing conscious thought, intellect, memory, the processing of sensory data, and the initiation of voluntary actions.
Question 3.
Mention the three functions of spinal cord.
Ans:
The spinal cord serves three primary roles: it acts as the main communication pathway, relaying sensory information to the brain and motor commands to the body; it independently coordinates quick, involuntary reflex actions to protect the body; and it contains neural circuits that help regulate repetitive movements such as walking.
Question 4.
Describe three kinds of nerves, giving example of each.
Ans:
Nerves are categorized by the direction of signal transmission. Sensory nerves (afferent) relay information from sensory receptors throughout the body to the central nervous system (CNS). An example is the optic nerve, which transmits visual data from the eyes to the brain. Motor nerves (efferent) carry commands from the CNS to effector organs, such as muscles and glands, to initiate actions. Nerves controlling arm movements are an example. Mixed nerves, the most common type in the peripheral nervous system, contain both sensory and motor fibers, enabling bidirectional communication. The vagus nerve, involved in sensory feedback from organs and motor control of the throat and abdomen, exemplifies a mixed nerve.
Question 5.
What are voluntary and involuntary actions ? Which part of the nervous system controls them ?
Ans:
Voluntary actions are deliberate movements initiated and controlled by conscious thought, primarily governed by the motor cortex located within the cerebrum. We consciously decide to perform these actions, and the signals travel from the brain to the skeletal muscles. In contrast, involuntary actions are automatic bodily processes that occur without conscious control, essential for maintaining life. These are primarily regulated by the autonomic nervous system (ANS), which controls functions like heart rate, digestion, and breathing. Specific regions of the brainstem, including the medulla and pons, also oversee many involuntary functions, while the spinal cord plays a crucial role in coordinating rapid, automatic reflex responses.
Additional Questions
I. Multiple choice questions. Tick (✓) the correct choice:
I. Nervous system in humans consists of
(a) brain and nerves
(b) brain and spinal cord
(c) brain, spinal cord and nerves
(d) none of the above.
II. Fill in the blanks:
- The basic structural unit of the nervous system is the neuron.
- The central nervous system consists of brain and spinal cord.
- A neuron consists of cell body, dendrite and axon.
- The neurons carrying impulses from the brain to the muscles are called motor or efferent neurons.
- The peripheral nervous system consists of nerves.
- The three main parts of the brain are cerebrum, cerebellum and medulla oblongata (brain stem).
III. State whether the following statements are true (T) or false (F):
1. Each neuron consists of three parts called cell body, cyton and axon.
False. Each neuron consists of three parts called cell body, dendrite and axon.
2. The largest part of the brain is the cerebrum.
True.
3. Cerebellum maintains balance of the body.
True.
4. There are 31 pairs of cranial nerves.
False. There are 12 pairs of cranial nerves.
IV. Find the odd-one out, giving reasons:
Axon, cell body, dendrite, cerebellum
Ans.
Cerebellum is the odd one out as it is a part of brain while rest three are parts of a neuron.
V. Define the following:
1. Reflex arc
2. Sensory neuron
3. Motor neuron
4. Neuron
Ans:
- Reflex arc: The neural circuit underlying swift, involuntary reactions.
- Sensory neuron: A nerve cell conveying sensory information to the central nervous system.
- Motor neuron: A nerve cell transmitting instructions from the central nervous system to muscles or glands.
- Neuron: The basic signaling unit of the nervous system.
VI. Answer the following:
Question 1.
Describe the two parts of the nervous system.
Ans:
The nervous system is divided into the Central Nervous System (CNS), comprising the brain and spinal cord (the main processing unit), and the Peripheral Nervous System (PNS), which includes all nerves extending outside the CNS, forming a communication network with the rest of the body. The PNS has components for conscious actions (somatic) and automatic bodily functions (autonomic).
Question 2.
What are nerves? Mention the types of nerves found in humans.
Ans:
Nerves are elongated cords of nerve fibers that conduct signals throughout the body. Humans have three primary types: sensory nerves (afferent) that relay sensory information from the body’s receptors to the central nervous system (CNS), exemplified by the optic nerve transmitting visual data. Motor nerves (efferent) carry commands from the CNS to muscles and glands, such as the nerves controlling limb movement. The most prevalent type is mixed nerves, which contain both sensory and motor fibers, enabling bidirectional communication. Spinal nerves, carrying both sensory input and motor output, are a prime example of mixed nerves.
Question 3.
Explain the structure of brain.
Ans:
The human brain, the central processing unit of the nervous system, exhibits a hierarchical structure organized into distinct regions with specialized functions. The most prominent division is the cerebrum, the largest part of the brain, responsible for higher-level cognitive abilities. It is characterized by its division into two cerebral hemispheres, the left and right, interconnected by the corpus callosum, a substantial bundle of nerve fibers facilitating interhemispheric communication. The outer layer of the cerebrum is the cerebral cortex, composed of gray matter and exhibiting a highly convoluted surface with ridges (gyri) and grooves (sulci) that significantly increase its surface area, thereby accommodating a greater number of neurons. Each cerebral hemisphere is further partitioned into four principal lobes: the frontal lobe, crucial for planning, decision-making, voluntary movement, and language production; the parietal lobe, involved in processing sensory information and spatial awareness; the temporal lobe, responsible for auditory processing, memory formation, and language comprehension; and the occipital lobe, dedicated to the interpretation of visual stimuli.
Question 4.
Compare the nervous system and the endocrine system.
Ans:
The nervous system employs swift electrical and chemical signals via nerve cells for rapid, localized, and short-duration responses. The endocrine system utilizes slower chemical messengers (hormones) transported in the bloodstream for gradual, widespread, and longer-lasting effects on processes such as growth and energy regulation. Both systems contribute to maintaining the body’s internal equilibrium and can interact with each other.
