Nervous System In Human

Control And Coordination of Class 10

NERVOUS SYSTEM IN HUMAN:

Human nervous system is one of the most highly developed nervous systems among living organisms on this planet.

The human nervous system can be further divided.

Nervous System In Human

Central Nervous System:

The central nervous system (CNS) is the processing center for the nervous system. It receives information from and sends information to theperipheral nervous system. The two main organs of the CNS are the brain and spinal cord. The brain processes and interprets sensory information sent from the spinal cord. Both the brain and spinal cord are protected by three layers ofconnective tissuecalled the meninges.

Within the central nervous system is a system of hollow cavities called ventricles. The network of linked cavities in the brain (cerebral ventricles) is continuous with the central canal of the spinal cord. The ventricles are filled with cerebrospinal fluid which is produced by specializedepitheliumlocated within the ventricles called the choroid plexus. Cerebrospinal fluid surrounds, cushions, and protects the brain and spinal cord from trauma. It also assists in the circulation of nutrients to the brain.

BRAIN:

The brain is the control center of the body. It consists of three main components: the forebrain, the brainstem, and the hindbrain. It is soft, whitish, large sized structure present inside cranial cavity of cranium of the skull. In man, it is about 1200-1400 gm in weight and has about 10,000 million neutrons.

Cranium protects brain from external injuries. The brain is also protected by the meninges and the cerebrospinal fluid. Meninges are made up of three layers i.e., duramater, arachnoid and piamater from outside to the inside.

Theforebrain

The Fore brain receives impulses from the eyes. Wherever the hind brain receives impulses from the ears and the skin. Fore brain includes cerebrum and olfactory lobes.

Cerebrum is the dome shaped roof of the brain. It is the largest part of the brain. It is most important, complex and specialised part of the brain.

It consists of two cerebral hemispheres joined together by a broad curved thick band of nerve fibres called corpus callosum. It has an outer thick layer of grey matter, called cerebral cortex, made of cell bodies of billions of nerve cells.

Cerebral cortex is highly folded and convoluted. The elevations are known as gyri whereas depressions are known a sulci. They increase the surface area of cerebrum. Cerebral cortex has distinct sensory, motor and association areas.

Olfactory lobes: A pair of bodies covered by cerebrum. It is not so developed in humans. It is concerned with olfaction (smell).

Cerebrum: It forms about two-third of the brain. Different areas of cerebrum perform different functions. Association areas control learning, reasoning, intelligence, personality, thinking, memory, etc. Sensory areas give us sensation by receiving information from eyes, ears, nose, tongue, skin. Motor areas give instructions to muscles for various voluntary actions. However, certain sensations are distinct from seeing or hearing, for example, how do we know that we have eaten enough? The sensation of feeling full is because of a centre associated with hunger, which is in a separate part of the fore brain.

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Cerebrum is further divided into two equal halves – the two cerebral hemispheres. Each hemisphere has fissures which further divides it into lobes – frontal (region for speech, facial muscular activities and higher mental activities), temporal (region of hearing or auditory reception), parietal (region for taste, smell, touch, temperature and conscious association) and occipital (region for sight or visual reception).

Themidbrainand the hindbrain together make up thebrainstem. The midbrain is the portion of the brainstem that connects the hindbrain and the forebrain. This region of the brain is involved in auditory and visual responses as well as motor function.

Thehindbrainextends from the spinal cord and contains structures such as theponsandcerebellum. These regions assist in maintaining balance and equilibrium, movement coordination, and the conduction of sensory information. The hindbrain also contains themedulla oblongatawhich is responsible for controlling such autonomic functions as breathing, heart rate, and digestion.

  •  Pons: It takes part in regulating respiration.
  •  Cerebellum: It helps in maintaining posture and balance. It also coordinates smooth body movements like walking in a straight line, riding a bicycle, picking up a pencil etc.
  • Medulla Oblongata: It controls various involuntary actions such as heart beat, blood pressure, salivation, breathing, peristaltic movements, etc. Medulla also controls reflex actions like, swallowing, sneezing, vomiting, etc.

Nervous System In Human

Human brain

Spinal Cord:

The spinal cord is a cylindrical shaped bundle of nerve fibers that is connected to the brain. The spinal cord runs down the center of the protective spinal column extending from the neck to the lower back. Spinal cord nerves transmit information from body organs and external stimuli to the brain and send information from the brain to other areas of the body. The nerves of the spinal cord are grouped into bundles of nerve fibers that travel in two pathways. Ascending nerve tracts carry sensory information from the body to the brain. Descending nerve tracts send information pertaining to motor function from the brain to the rest of the body.

Neurons:

Neuronsare the basic unit of the nervous system. All cells of the nervous system are comprised of neurons. Neurons contain nerve processes which are "finger-like" projections that extend from the nerve cell body. The nerve processes consist of axons and dendrites which are able to conduct and transmit signals. Axons typically carry signals away from the cell body. They are long nerve processes that may branch out to convey signals to various areas. Dendrites typically carry signals toward the cell body. They are usually more numerous, shorter and more branched than axons. Axons and dendrites are bundled together into what are called nerves. These nerves send signals between the brain, spinal cord, and other body organs via nerve impulses. Neurons are classified as either motor, sensory, or interneurons. Motor neurons carry information from the central nervous system to organs, glands, and muscles. Sensory neurons send information to the central nervous system from internal organs or from external stimuli. Interneurons relay signals between motor and sensory neurons.

Reflex Action and Reflex Arc

Reflex action: A reflex action may be defined as a spontaneous, involuntary and unconscious (without will) response of the effectors to a stimulus.

Reflex action is a spontaneous, automatic, mechanical response to a stimulus without the will the animal. Reflex action is controlled by spinal cord. It is a stereo typed response to a stimulus.

Reflex action was first discovered by Marshall Hall in 1833.

Best and Taylor defined action as an automatic involuntary and often unconscious action.

Reflex action is a elementary function discharged by the nervous system. It is important in protective behaviour such as the withdraw also of the limbs from pain and in locomotion and is standing.

MECHANISM OF REFLEX ACTION

”A reflex action works in the following ways :

lReceptor organ : It receives the stimulus and initiates a sensory nerve impulse.

lSensory nerve fibre : It conducts impulses from receptor to the spinal cord.

lSpinal cord : It acts as modulator and changes sensory impulses into the motor impulse.

lMotor nerve firbe : It conducts motor nerve impulse from spinal cord to the effectors.

lEffector organ : It gives the response. This produces either the movement of some muscles or secretion from a gland.

” Reflex arc : Path followed by an impule in reflex action is known as reflex arc. Reflex always travels in one direction.The direction taken by nerve impulse and responses in a reflex action is from the receptor organs like skin to the spinal cord and from the spinal cord to the effector organs like muscles.

” Reflex travels in the following sequence :

Stimulus Receptor organ Sensory nerve Spinal cord

Motor nerve Effector organ Response to stimulus

Peripheral Nervous System:

Peripheral nervous sytem comparises the nerves that connect the central nervous system with different parts of body. The neurons of peripheral nervous system include both motor neurons and sensory neurons. The fibres of motor and sensory neurons are bundled together into nerves, which are of two types :

  • Cranial nerves connected directly to the brain, such as the optic nerve
  • Spinal nerves connected to the spinal cord.

Motor nerves are divided into two groups–somatic nervous system and autonomic nervous system.

The somatic nervous system regulates voluntary activities while the autonomic nervous system performs a variety of functions which are not under the control of an individual.

Autonomic Nervous System

It controls involuntary activities of internal organs such as heart, blood vessels, glands & smooth muscles of alimentary canal & uterus. It is subdivided into

  •  Sympathetic
  •  Parasympathetic system.

Organs receive nerves from both sympathetic and parasympathetic nerve fibres. They have opposite effects on the organs if one is stimulatory, the other is inhibitory.

Effects of Sympathetic and Parasympathetic System :

Organ

Sympathetic System

Para-sympathetic system

Heart

Increases heart beat

Decreases heart beat

Blood vessels

Constricts arteries & raises blood pressure.

Dilates arteries & lowers blood pressure

Bronchi

Dilates bronchi making breathing easier

Constricts bronchi

Eye

Dilates pupil

Constricts Pupil

Gastric secretion

Inhibits secretion

Stimulates secretion

Salivary glands

Inhibits secretion of saliva

Stimulates secretion

Urinary bladder

Relaxes urinary bladder

Contracts urinary bladder.

Liver

Reduces bilei secretion

Promotes bile secretion.

Nervous System In Human

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