Sensory Pathways and Sensations

Humans can distinguish among many different types of internal and external stimuli because we have highly developed sensory systems. Examples: the taste of spoiled food, the pain of a headache.

Our sensory systems translate aspects of the environment into electrical signals and transmit the information to our central nervous system.

The purpose of sensations is to enable the body to respond appropriately to changing situations in order to maintain homeostasis.

Sensations follow very precise pathways that have the following parts: 1.Receptors - detect changes and generate impulses 2.Sensory neurons – transmit impulses from receptors to the CNS, found in spinal nerves and cranial nerves.

Sensations follow very precise pathways that have the following parts: 3. Sensory tracts – white matter in the brain or spinal cord that transmits impulses to the brain. 4. Sensory area – areas in the cerebral cortex that feel and interpret the sensations.

Receptors: *Sense Receptor – a neuron that is specialized to detect a stimulus. There are many types, classified by the type of stimuli they respond to.

Types of Sense Receptors: Photoreceptors – respond to light Mechanoreceptors – respond to movement, pressure, and tension

Types of Sense Receptors: Pain receptors – respond to tissue damage. Chemoreceptors – respond to chemicals Thermoreceptors – respond to temperature

Sensory receptors are found all over the body, but they are most concentrated in the sense organs.

The Sense Organs

*Sense organ – an organ that contains sensory neurons which detect external stimuli. The eyes, ears, nose, tongue, and skin are our sense organs.

When a sense organ receives the appropriate stimulation, its sensory receptors convert the stimulus into an electrical signal.

This action potential goes to the specific region of the brain where it can be interpreted.

The nose controls your sense of smell or olfaction. There may be a thousand or more basic scents.

Chemicals in the environment are perceived by olfactory receptors in the mucous membranes of our nasal passages.

The molecules in the air bind to these specialized chemoreceptors and stimulate them to send a signal through the ethmoid bone to the olfactory bulbs.

From there the signal goes to the olfactory areas in the temporal lobe of the cerebral cortex.

Adaptation to odors occurs quickly. Both pleasant and unpleasant scents may be very distinct at first but rapidly seem to fade.