Human Nervous System

The 2 types are: • Nervous • Chemical

this is brought about by the nervous system, which is made up of the brain, spinal cord, nerves and sense organs. ex- when you feel hungry you eat

this type of coordination is brought about by the chemical messengers called hormones. ex- when you see a bull on the street your instinct is to run. chemicals release extra energy in the blood to help you run

• nervous system is made up of cells called nerve cells or neurons • it is made up of a cyton and an axon • it contains of a nucleus • dendrites receive impulses from organs and transmit them to axon • end of axon has a number of branches called axon terminals or terminal branches

• nervous system is made up of cells called nerve cells or neurons • it is made up of a cyton and an axon • it contains of a nucleus • dendrites receive impulses from organs and transmit them to axon • end of axon has a number of branches called axon terminals or terminal branches

the axon terminals of a neuron lie very close to the dendrites of another. their point of contact is called synapse it is at this place where the message is transmitted .

• sensory neurons • motor neurons • association neurons

• SENSORY: these carry impulses from the sense organs to the spinal cord or brain • MOTOR: these carry impulses from brain or spinal cord to the source [ muscle ] • ASSOCIATION: these are present in the spinal cord and transmit impulses from one neuron to another

a nerve is formed of a bundle of axons enclosed in a tubular medullary sheath. its types - sensory nerve - motor nerve - mixed nerve

- SENSORY: consists of sensory neuron ex- optic nerve - MOTOR: contains only motor neurons ex- muscle of the eye -MIXED: carries both, sensory and motor neurons ex- nerve going to the tounge

• The central nervous system 2. The peripheral nervous system

• This consists of the braina and spinal cord. Brain lies within the skull and the spial cord lies within the vertebral column. • It consists of nerves that pass to and from the central nervous system. Its 2 parts are: ~ somatic nervous system ~ autonomic nervous system

• it is the complex and important part of our body • on an average an adult brain weighs 1.5kg • it is protected by a bony structure called skull or cranium • brain is further divided into 3 membranes called meninges which are separated by the fluid floating around in our brain

• cerebrum • cerebellum • medulla oblongata

• it is the largest portion of the brain • it is divided into 2 hemispheres called the cerebral hemispheres • each of these are hollow • outer surface is covered with bridges and grooves to accommodate many neurons • human cerebrum contains about 9B neurons • this controls all the voluntary actions ex- intelligence , will power , consciousness

• it is smaller and is under the cerebrum • its main function is to balance the body and coordinate muscular activities • cerebellum implements the action that the cerebrum decides • a drunk person cannot coordinate his movements properly as alcohol affects the cerebellum

• it is the lowest part • it controls the activities of internal organs ex- beating of heart , breathing • if this is seriously injured it may cause immediate death of a person

it extends from the medulla through the whole backbone

• control reflexes below the neck • carry messages from skin , muscle to brain • conduct commands from brain to muscle of the trunk limbs

its divided into somatic and autonomic nervous system.

• they consist of 2 types of nerves: ~cranial nerves which arise from the brain ~spinal nerves which arise from the spinal cord • it is responsible for relaying sensations like smell , taste , etc • and also for sending commands from central nervous system to skeletal muscles

• it consists of a pair of chains of ganglia • it regulates involuntary actions and works unconsciously ex- blood pressure , respiratory rate • it operates through 2 systems: ~ sympathetic system ~ parasympathetic system

• this produces immediate flight or fight responses

• this re-establishes normal conditions ex- if sympathetic system increases heart rate then parasympathetic will relax it