Sensory System: Introduction, Organs and Functions

Sensory System: Introduction, Organs and Functions

The sensory system represents an integration of the functions of the PNS and CNS. The Sensory Division of the Peripheral Nervous System gathers information about the Body’s Internal Conditions and External Environment.

The human experience is affected by both internal and external stimuli. Humans are able to distinguish among many different types of stimuli by means of a highly developed system of a sense organ.

The sensory system translates light, sound, temperature, and other aspects of the environment to electrical signals and transmits these signals, in the form of Action Potentials, to the Central Nervous System, where they are Interpreted.

The overview of sensation

There are millions of neurons in the body that do not receive impulses from other neurons. Instead, these neurons which are called sensory receptors, react directly to stimulation from the environment.

Many Receptors that enable the Body to receive information from the environment are located in highly specialized Organs called sense.
Examples of stimulation include light, sound, motion, chemical, pressure, pain or changes in the temperature.

Once these Sensory Receptors are Stimulated, they transform one form of energy from the Environment (LIGHT, SOUND) into another form of energy (ACTION POTENTIAL) that can be transmitted to other neurons. These Action Potentials (IMPULSES) reach the Central Nervous System (CNS).

In the sensory system, a Sensory Receptor is a Neuron that is Specialized to detect a Stimulus. There are many kinds of Sensory Receptors, and they can be categorized on the basis of the type of stimuli they respond to:

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Types of Sensory Neurons

• Mechanoreceptors – respond to Movement, Pressure, and Tension.
• Photoreceptors (RODS AND CONES) – Respond to Variations in Light.
• Chemoreceptors- respond. to Chemicals.
• Thermoreceptors – Respond to Changes in Temperature.
• Pain receptors – Respond to Tissue Damage – PAIN!
6. The sensory receptors are contained in the sense organs.
7. Each of the five senses (sight, hearing, smell, taste, and touch) has a specific sense organ associated with it.
8. The most familiar Sense Organs are the eyes, ears, nose, skin and taste bud. These Organs have a receptor that can respond to Stimuli by producing nerve impulses in a Sensory Neuron.
9. The Receptors convert the energy of a Stimulus into electrical energy that can travel in the nervous system.
10. Receptors inside the body inform the CNS about the conditions of the body.
11. Temperature receptors throughout the body detect Changes in Temperature. This information travels to the hypothalamus, which helps control body temperature.
12. Specialized cells (Receptors) within each sense organ enable it to respond to particular stimuli.
13. Messages from Sense Organs to the CNS are all in the form of Nerve Impulses. How does our brain know whether incoming impulse is sound or light?
14. This information is built into the “WIRING” in the Pathways of Neurons that Synapse with each other, and into the location in the Brain where the information arrives.
15. The Brain knows if the information received is from a Sensory Neuron that comes from light receptors cells when it gets the message.

Classification of sensory organs:-

• Taste – The ability to detect chemicals in food, minerals and harmful substances such as poison and it is also known as gestation. The taste bud on the tongue acts as a sensory organ for these detections. A taste bud is divided into five basic tastes: sweet, bitter, salty, sour and umami.
• Smell – The ability to detect the smell which is close to related to the sense of taste and it is also known as olfaction. The olfactory receptors in the nose act as the sensory organ to sense the smell of chemicals from food or floating in the air.
• Touch – Touch or somatosensory perception is perceived by activation in neural receptors in the skin.

The main sensation comes from pressure applied to these receptors, called mechanoreceptors. The skin has multiple receptors that sense levels of pressure from gentle brushing to firm as well as the time of application from a brief touch to sustained.

There are also receptors for pain, known as nociceptors, and for temperature, called thermoreceptors. Impulses from all three types of receptors travel through the peripheral nervous system to the central nervous system and the brain.
• Hearing- It is also called an audition, which is the perception of sound. Sound is comprised of vibrations that are perceived by organs inside the ear through mechanoreceptors.
• Sight- It is also called vision, which is the ability of the eyes to perceive images of visible light.

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