Understanding the Nervous and Endocrine Systems

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Nerve Impulse

A stimulus occurs, sensory receptors detect the stimulus, sensory neurons receive the information and transmit it to the central nervous system (CNS). The CNS receives the information and a response is decided. Motor neurons transmit the response to the effectors, which carry out the response. The response is given through motor responses carried out by muscles and secretory responses carried out by glands.

Nervous System

The nervous system receives and transmits information rapidly through electrical impulses. Information is transmitted through sensory neurons and processed in the CNS.

Endocrine System

The endocrine system consists of glands that secrete hormones. These hormones are carried in the blood to the cells of the target tissue or organ.

Sensory Receptors

Sensory receptors capture information from external and internal environments. There are two types: interoceptors, which are sensitive to general body conditions and sensations like thirst, and exteroceptors, which are located in sense organs and are sensitive to external stimuli.

The Eye

Light rays reflected off objects pass through the cornea, aqueous humor, pupil, and lens. The lens adjusts to focus on objects nearby or far away through a process called accommodation. The image formed on the retina is inverted and smaller than the object viewed. Photoreceptors in the retina convert the image into nerve impulses carried by the optic nerve to the cerebral cortex for interpretation.

The Sense of Touch

The epidermis, the outer layer, is made up of several layers of cells, with the surface ones being dead. The dermis, the inner layer, contains touch receptors.

The Sense of Smell

The sense of smell enables the body to detect chemical molecules in the air. There are two types of receptors: respiratory mucous membrane and olfactory mucous membrane.

The Sense of Taste

The sense of taste enables the body to detect flavors. There are four basic tastes: sweet, salty, sour, bitter, and umami. Chemoreceptors respond to chemicals dissolved in saliva and are located mainly on the tongue, palate, pharynx, and larynx.


Hearing involves sound waves traveling through six parts of the ear to reach the brain.


The three semicircular canals inside the inner ear contain hair cells and endolymph. When you move, the endolymph stimulates mechanoreceptors hair cells that detect movements.

The Nervous System

The nervous system detects and interprets external and internal stimuli, producing necessary responses for the body to function and transmitting them to the effectors. Sensory neurons send information from receptors to the CNS for interpretation and responses. Motor neurons send responses from the CNS to effectors, causing muscle contractions or gland secretions. Relay neurons connect sensory and motor neurons.

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