Nervous System Online Test 10th Science Lesson 15 Questions in English

One of the characteristic features of all living organisms is responding to stimuli. Stimulus refers to the changes in the environmental condition, that are detected by receptors present in the body

Relevant changes in the activities of organisms to a particular- stimuli are called their reactions or responses. Living organisms show their response to different kinds of stimuli like light, heat, cold, sound, smell, taste, touch, pressure, pain or the force of gravity etc.

To provide the correct response to a stimulus, it is necessary that all the organs work together in a proper coordinated manner. This working together of various organs in a systematic, controlled and efficient way to produce proper response to various stimuli is called coordination.

In animals including human the coordination between the various cells and organs is essential for their diverse activities to maintain physiological balance called homeostasis.

The nervous system is made up of nervous tissues. It is formed of three distinct components namely the neurons, neuroglia and nerve fibres.

A neuron or nerve cell is the structural and functional unit of the nervous system. Information is conducted through neurons in the form of electrical impulses from one part of the body to another.

Neuron or nerve cell is the longest cell of the human body with a length of over 100µm. These cells are highly specialised to detect, receive and transmit different kinds of stimuli.

Neuroglia is also called as glial cells. They are non-exciting, supporting cell of the nervous system. They do not initiate or conduct nerve impulses.

The nerve fibres are the long slender processes of neurons. A number of nerve fibres are bundled up together to form nerves.

A neuron typically consists of three basic parts: Cyton, Dendrites and Axon. A neuron or nerve cell is the structural and functional unit of the nervous system.

Cyton is also called cell body or perikaryon. It has a central nucleus with abundant cytoplasm called Neuroplasm.

The cytoplasm has large granular body called Nissl’s granules and the other cell organelles like mitochondria, ribosomes, lysosomes, and endoplasmic reticulum. Neurons do not have the ability to divide. Several neurofibrils are present in the cytoplasm that help in transmission of nerve impulses to and from the cell body.

Dendrites are the numerous branched cytoplasmic processes that project from the surface of the cell body. They conduct nerve impulses towards the cyton.

The axon is a single, elongated, slender projection. The end of axon terminates as fine branches which terminate into knob like swellings called synaptic knob. The plasma membrane of axon is called axolemma, while the cytoplasm is called axoplasm. It carries impulses away from the cyton. The axons may be covered by a protective sheath called myelin sheath which is further covered by a layer of Schwann cells called neurilemma.

The axons may be covered by a protective sheath called myelin sheath which is further covered by a layer of Schwann cells called neurilemma. Myelin sheath breaks at intervals by depressions called Nodes of Ranvier. The region between the nodes is called as internode. Myelin sheath acts as insulator and ensures rapid transmission of nerve impulses.

A junction between synaptic knob of axon of one neuron and dendron of next neuron is called synaptic junction. Information from one neuron can pass to another neuron through these junctions with the release of chemicals known as neurotransmitters from the synaptic knob.

Structurally the neurons may be of the following types: Unipolar neurons: Only one nerve process arises from the cyton which acts as both axon and dendron. Bipolar neurons: The cyton gives rise to two nerve processes of which one acts as an axon while another as a dendron Multipolar neurons: The cyton gives rise to many dendrons and an axon

Explanation Unipolar Neurons- Found in early embryos but not in adult Bipolar Neurons- Found in retina of eye and olfactory epithelium of nasal chambers Multipolar Neurons- Found in cerebral cortex of brain

Sensory or afferent neurons which carry impulses from the sense organ to the central nervous system. Motor or efferent neurons which carry impulses from the central nervous system to effector organ such as the muscle fibre or the gland. Association neurons conduct impulses between sensory and motor neurons.

Nerve fibres are of two types based on the presence or absence of myelin sheath. Myelinated and non-myelinated nerve fibres form the white matter and grey matter of the brain.

Myelinated nerve fibre: The axon is covered with myelin sheath Non-myelinated nerve fibre: The axon is not covered by myelin sheath.

All the information from the environment are detected by the receptors located in our sense organs such as the eyes, the nose, the skin, etc.

Information from the receptors is transmitted as electrical impulse and is received by the dendritic tips of the neuron. This impulse travels from the dendrite to the cell body and then along the axon to its terminal end. On reaching the axonal end, it causes the nerve endings to release a chemical (neurotransmitter) which diffuses across a synapse and starts a similar electrical impulse in the dendrites of the next neuron, then to their cell body to be carried along the axon.

The flow of nerve impulses from axonal end of one neuron to dendrite of another neuron through a synapse is called synaptic transmission.

Each neuron can transmit 1000 nerve impulses per second and make as many as ten thousand of synaptic contacts with other neurons.

Neurotransmitters are the chemicals which allow the transmission of nerve impulse from the axon terminal of one neuron to the dendron of another neuron or to an effector organ. The important neurotransmitter released by neurons is called Acetylcholine.

The complexity of nervous system can be observed during the course of evolution. We the human beings differ from other animals in our ability to think and take actions, which is due to the well-developed nervous system.

Human nervous system is differentiated into three: central nervous system (CNS), peripheral nervous system (PNS) and autonomic nervous system (ANS).

The CNS acts as centre for information processing and control. It consists of the brain and the spinal cord. The PNS is made up of the nerves which connect the brain and spinal cord to all parts of the body. The ANS is formed of sympathetic and parasympathetic nerves.

The brain and the spinal cord being delicate vital structures are well protected in bony cavities of the skull and the vertebral column respectively. CNS is formed of two types of matter such as white matter or grey matter with respect to the presence or absence of myelin sheath which we have discussed earlier.

The brain is the controlling centre of all the body activities. It is covered by three connective tissue membrane or meninges.

Duramater (dura: tough; mater: membrane) is the outermost thick fibrous membrane Arachnoid membrane (arachnoid: spider) is the middle, thin vascular membrane providing web like cushion Piamater (Pia: soft or tender) is the innermost, thin delicate membrane richly supplied with blood.

Meningitis is an inflammation of the meninges. It can occur when fluid surrounding the meninges becomes infected. The most common causes of meningitis are viral and bacterial infections.

Meningeal membranes protect the brain from mechanical injury. A human brain is formed of three main parts: (a) forebrain (b) midbrain and (c) hindbrain.

The forebrain is formed of cerebrum and diencephalon. The latter consists of dorsal thalamus and ventral hypothalamus.

Cerebrum is the largest portion forming nearly two third of the brain. The cerebrum is longitudinally divided into two halves as right and left cerebral hemispheres by a deep cleft called median cleft.

Two cerebral hemispheres are interconnected by thick band of nerve fibres called corpus callosum. The outer portion of each cerebral hemisphere is formed of grey matter and is called cerebral cortex.

The inner or deeper part is formed of white matter and is called cerebral medulla. The cortex is extremely folded forming elevations called gyri with depressions between them termed as sulci that increase its surface area.

Each cerebral hemisphere is divisible into four lobes: a frontal lobe, a parietal lobe, a temporal lobe and an occipital lobe. These lobes are also known as cerebral lobes and are associated with specific functions. Any damage in specific lobe in-turn affects its function.

The cerebrum is responsible for the thinking, intelligence, consciousness, memory, imagination, reasoning and willpower.

Thalamus present in cerebral medulla is a major conducting centre for sensory and motor signalling. It acts as a relay centre.

Hypothalamus lies at the base of the thalamus. It controls involuntary functions like hunger, thirst, sleep, sweating, sexual desire, anger, fear, water balance, blood pressure etc.

Hypothalamus acts as a thermoregulatory (temperature control) centre of the body. It controls the secretion of hormones from anterior pituitary gland and is an important link between nervous system and endocrine system.

Midbrain is located between thalamus and hind brain. The dorsal portion of the mid brain consists of four rounded bodies called corpora quadrigemina that control visual and auditory (hearing) reflexes.

A human brain is formed of three main parts: (a) forebrain (b) midbrain and (c) hindbrain. Hindbrain is formed of three parts cerebellum, pons and medulla oblongata.

The human brain constitutes nearly 60 percent of fat. The most crucial molecules that determine our brain’s integrity and the ability are Essential Fatty Acids (EFAs). EFAs cannot be synthesised and must be obtained from food. Fish, green leafy vegetables, almond, walnut are rich sources of EFAs.

Cerebellum is second largest part of the brain formed of two large sized hemispheres and middle vermis. It coordinates voluntary movements and also maintains body balance.

‘Pons’ a latin word meaning bridge. It is a bridge of nerve fibre that connects the lobes of cerebellum. It relays signals between the cerebellum, spinal cord, midbrain and cerebrum. It controls respiration and sleep cycle.

Medulla oblongata is the posterior most part of the brain that connects spinal cord and various parts of brain. It has cardiac centres, respiratory centres, vasomotor centres to control heart-beat, respiration and contractions of blood vessels respectively. It also regulates vomiting and salivation.

Electroencephalogram (EEG) is an instrument which records the electrical impulses of brain. An EEG can detect abnormalities in the brain waves and help in diagnoses of seizures, epilepsy, brain tumor, head injuries, etc.

Spinal cord is a cylindrical structure lying in the neural canal of the vertebral column. It is also covered by meninges.

Spinal cord extends from the lower end of medulla oblongata to the first lumbar vertebra. The posterior most region of spinal cord tapers into a thin fibrous thread like structure called filum terminal.

Internally, the spinal cord contains a cerebrospinal fluid filled cavity known as the central canal. The grey matter of spinal cord is ‘H’ shaped. The upper end of letter ‘H” forms posterior horns and lower end forms anterior horns.

The upper end of letter ‘H” forms posterior horns and lower end forms anterior horns. A bundle of fibre pass into the posterior horn forming dorsal or afferent root. Fibres pass outward from the anterior horn forming ventral or efferent root. These two root joins to form spinal nerves. The white matter is external and have bundle of nerve tracts

Spinal cord conducts sensory and motor impulses to and from the brain. It controls reflex actions of the body.

The brain is suspended in a special fluid environment called cerebrospinal fluid (CSF). It is lymph like, watery fluid that surrounds and protects the brain within the skull. It also fills the central canal of the spinal cord.

Functions of Cerebrospinal fluid: It acts as shock absorbing fluid and protects the brain from damage when it is subjected to sudden jerk. It supplies nutrients to the brain It collects and removes wastes from the brain. It is also responsible for maintaining a constant pressure inside the cranium.

A reflex is any response that occurs automatically without consciousness. There are two types of reflexes. Simple or basic reflexes Acquired or conditioned reflexes

Simple or basic reflexes These reflexes are inbuilt and unlearned responses. Many of the actions we perform in our day to day life are simple reflexes. e.g., winking of eyes when any dust particles enter, sneezing, coughing, yawning, etc. We perform these actions without thinking

Acquired or conditioned reflexes are the result of practice and learning. Playing harmonium by striking a particular key on seeing a music note is an example of conditioned reflexes which required conscious training effort.

Peripheral nervous system is formed by the nerves arising from the brain and the spinal cord. The nerves arising from the brain are called cranial nerves. Nerves arising from spinal cord are called spinal nerves.

In man, there are 12 pairs of cranial nerves. Some of the cranial nerves are sensory e.g. optic nerve which innervates the eye. Some are motor nerves which helps in rotation of eyeball. It also innervates the eye muscles, muscles of iris and tear gland.

There are 31 pairs of spinal nerves. Each spinal nerve has a dorsal sensory root and the ventral motor root. The direction of impulses in dorsal spinal root is towards the spinal cord and in ventral spinal root away from the spinal cord.

Autonomic nervous system (ANS) is also called as visceral nervous system as it regulates the function of internal visceral organs of our body through its two antagonistic (opposite) components sympathetic and parasympathetic systems.

Autonomic nervous system (ANS) enables the body to perform rapid and specific visceral activities in order to maintain steady state. It controls the involuntary functions of the visceral organs.