NERVOUS SYSTEM IN HUMANS

 NERVOUS SYSTEM IN HUMANS:

Introduction:

·         Control and coordination of an organism are the results of the units of various organs, organ systems and chemicals produced is the organism.

·         Proper coordination gives the best response. All living organisms are made up of different types of cells which help them to control and coordinate with their surroundings.

·         Endocrine glands constitute the endocrine system which coordinates and control the body metabolism.

·         Nervous system is a complex network of nerves and cells that carry message to and from the brain and spinal cord to various parts of the body. The nervous system includes both the CNS and PNS. The CNS made up of brain and spinal cord and the PNS is made up of somatic and the ANS.

·         Nervous system is the body’s electrical wiring, is a complex collection of nerves and specialized cells known as neurons that transmit signals between different parts of the body.

·         Neuron signal to other cells through fibres called axons. Chemicals called neurotransmitter are released at gaps called synapses. These communications take only a fraction of milliseconds.

·         Sensory neurons respond to stimuli such as light and sound. Motor neurons carry activation signals to muscles and glands.

·         Neurons are supported and fed by glial cells. Glial derives from the Greek word for “glue”.

·         Vertebrates, animals with backbone and spinal columns, have central and peripheral nervous system.

·         The CNS is the integration and command centre of the body. It consists of the brain, spinal cord and retina of eye.

·         The PNS consists of sensory neurons ganglia (clusters of neurons) and nerves that connect the CNS to arms, hands, legs and feet.

·         The cranial nervous system connects the brain to the eyes, mouth, ear and other parts of head.

·         The ANS connects the CNS to the lungs, heart, stomach, intestine, and bladder and sex organ.

·         The branch of medicine that studies the nervous system is called neurology. Doctors who treat the nervous system are neurologists.

·         The cranial nervous system connects the brain to the eyes, mouth, ear and other parts of heart.

·         The ANS connects the CNS to the lungs, heart, stomach, intestine, and bladder and sex organs.

·         The branch of medicine that studies the nervous system is called neurology. Doctors who treat the nervous system are neurologists.

Nervous System:

Nervous system or the neural is a complex network of nerve cells or neurons specialized to carry messages. The complexity of the nervous system increases as we move towards higher animals. In simple organisms, especially in the invertebrates neural system is a network of neuron which is known as nerve net while in vertebrates nervous system is much organized and developed which involves the brain. In the human body, the neural system integrates the activities of organs based on the stimuli which is detected and transmitted by neurons. They transmit messages in the form of electrical impulses and convey messages to and from the sense organs. Thus, the neurons coordination involves the participation of the sense organs, nerves, spinal cord and brain.

Human Nervous system:

·         Human nervous system is a complex network of neurons which organized to form CNS and PNS.

·         Central nervous system together with the Peripheral nervous system together constitutes the human neural system.

                         

Types of Nervous System:

There are two types of nervous system:

·         Central nervous system

·         Peripheral nervous system

 

        I.            Central Nervous System:

·         CNS controls thought processes, guides movement and registers sensation throughout the body.

·         CNS consists of the control and information processing units, the brain and spinal cord.

Classification of CNS:

CNS can be classified into two types:

         i.            Brain:

·         Brain is central information processing organ of our body which controls all the function of body.

·         It acts as the command and control system.

Structure of brain:

·         Human brain is well protected by the skull.

·         Brain is covered by cranial meninges consisting of an outer layer called Duramater, a very thin middle layer called arachnoid and an inner layer called piamater (which is in contact with the brain tissue).

·         Brain can be divided into three parts:

a)      Forebrain:  It consists of cerebrum, thalamus and hypothalamus. Cerebrum forms the major part of the brain. Cerebrum wrapped around a structure called thalamus, which is a major coordinating centre for sensory and motor signalling. Hypothalamus lies at the base of the thalamus. It controls body temperature, urge for eating and drinking.

b)      Midbrain: It is located between the thalamus of the forebrain and pons of the hindbrain.

c)       Hindbrain: It comprises of pons, cerebellum and medulla.

                  

Functions of Brain:

·         Brain controls the voluntary movements, balance of the body, functioning of vital involuntary organs, thermoregulation, hunger and thirst, circadian rhythms of our body, activities of several endocrine glands of body.

·         It also controls the human behaviour.

·         It is also the site for processing of vision, hearing, speech, memory, intelligence, emotions and thoughts.

      ii.            Spinal cord:

·         Spinal cord is a long, fragile, single continuous structure that goes from the brain passes through the base of the skull and ends down a spinal column.

·         It consists of nerves that carry incoming and outgoing messages between the brain and rest of the body.

·         It is also the centre of refluxes such as knee jerk reflexes.

            

      II.            Peripheral Nervous System:

·         PNS consists of the nerves that connect peripheral parts to the brain and spinal cord.

·         PNS includes two types of nerve fibre; one which transmits messages from tissues and organs to the CNS is called afferent nerve fibres, while the nerve fibres convey messages from CNS to the corresponding peripheral organ are called efferent nerve fibres.

        

Classification of PNS:

·         The peripheral neural system is classified into two types:

         i.            Somatic nervous system: It is the neural system that controls the voluntary actions in the body by transmitting impulses from CNS to skeletal muscle cells. It consists of the somatic nerve.

       ii.            Autonomic nervous system: The autonomic neural system is involved in the involuntary actions of the body like regulation of physiological functions which involves digestion, respiration, salivation etc. It is a self regulating system that conveys the impulses from the CNS to the smooth muscles and involuntary organs. ANS is further subdivided into two categories:

a)      Sympathetic Nervous system:

b)      Parasympathetic nervous system

Nerves:

Nerves are thread like structures which emerges from the brain and spinal cord. Nerves are responsible for carrying messages to all parts of the body. There are three types of nerves:

         i.            Sensory nervessend messages from all the senses to brain.

       ii.            Motor nervescarry messages from the brain to all the muscles.

      iii.            Mixed nervescarry both sensory and motor neurons.

There are two other types of nerves:

a)      Cranial nerves: These nerves begin from the brain as these nerves carry impulses from the CNS.  There are 12 pairs of cranial nerves in humans. Certain cranial nerves belong to the group of mixed nerve while certain ones fall under sensory nerves.

b)      Spinal nerves: It begins from the brain as these nerves carry impulses to start from the CNS. Spinal nerves originate from the spinal cord. There are 31 pairs of spinal nerves in human body.

The nerve fibres of PNS are of two types:

         i.            Afferent fibres: The afferent nerve fibres transmit impulses from tissues/ organs to the CNS.

       ii.            Efferent fibres: It transmits regulatory impulses from the CNS to the concerned peripheral tissues/ organs.

Functions of Nervous System:

        I.            Control all body function: Nervous system is the master system of human body. It controls all the activities of body in such a way that all the systems collectively make a human being. Nervous system controls all the voluntary functions of human body that are directed by human. It also control those function that are below the level of consciousness of human beings. Control of a function means that the intensity of the function can be increase or decrease according to the demands of human body.

      II.            Coordination of different body organs: Nervous system not only establishes coordination between different systems but also between different organs of a system. To form an organ system role of the component organs must also be coordinated. So nervous system is not only important for formation of an organism by different organ systems but also for formation of a system by different organs of human body.

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