Sensation, Synesthesia, and Touch

• Sensory receptors are what allow us to collect information about the outside world.

• We are limited by what stimuli we can transduce.• Transduction is the process of converting

environmental stimulus into nerve impulses.

We only see a SMALL part of the electromagnetic spectrum as “light” because we have receptors for it.

If we had a receptor for infrared light we would experience a different world entirely.

Classes of Receptors

• Chemoreceptors: detects chemical stimuli• Nociceptors: stimulated by tissue damage• Thermoreceptors: sense temperature (hot or cold)• Mechanoreceptors: sense mechanical forces • (i.e. touch, stretch, pressure)

• Photoreceptors: respond to light

Receptors, Sensation, and PerceptionSensation:

-The low-level biochemical and neurological events initiated by a stimulus acting upon the receptor cells of a sensory organ.

Perception:-The mental process involved with awareness and

interpretation of the stimulus

Projection: -Process in which the brain projects the sensation back

to the apparent source. Allows pinpoint the region of stimulation.

• All senses can be classified as either general or special.

• A general sense is one that is distributed throughout the body and has receptor cells within the structures of other organs.

• General senses often contribute to the sense of touch, or to proprioception (body movement) and kinesthesia (body movement), or to a visceral sense, which monitor internal organs.

General Vs. Special

• A special sense is one that has a specific organ devoted to it, namely the eye, inner ear, tongue, or nose.

• Each type of information or stimuli you can sense is referred to as a sensory modality.

• Listing all the different sensory modalities, which can number as many as 17, involves separating the five major senses into more specific categories, or submodalities, of the larger sense.

• The general sense of touch, which is known as somatosensation, can be separated into submodalities of light pressure, deep pressure, vibration, itch, pain, temperature, or hair movement

• Simply stimulating the receptors will cause you to experience the sensation.

• For example, the sensation of heat associated with spicy foods involves capsaicin, the active molecule in hot peppers.

• Capsaicin molecules binds to receptors that are sensitive to temperatures above 37°C.

Synesthesia• Synesthesia is a condition in which one sense (for

example, hearing) is simultaneously perceived as if by one or more additional senses such as sight.

• Cross stimulation of sensory modalities.

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HEARING

•Sound waves are mechanical pressure waves that must travel through a medium and cannot exist in a vacuum.•There are two main characteristics of a sound wave: frequency, and amplitude.

•Frequency is the number of waves per unit of time and is heard as pitch; high-frequency sounds are high-pitched, and low-frequency sounds are low-pitched.•Most humans can perceive sounds with frequencies between 30 and 20,000 Hz; other animals, such as dolphins, can detect sounds at far higher frequencies.

• Amplitude, the dimension of a wave from peak to trough, is heard as volume; louder sounds have greater amplitudes than those of softer sounds.

Structures of the ear

Outer ear• The outer ear consists of the visible part of the ear

(or pinna), the external auditory canal (meatus), and the tympanic membrane (tympanum) or eardrum.

Tympanum•Sound waves are collected by the pinna, travel through the auditory canal, and cause vibration of the tympanum (ear drum).

Auditory OssiclesThe 3 bones of the middle ear, that transfer energy from the vibrating ear drum to the inner ear.

Incus (anvil) Malleus (hammer) Stapes (stirrup)

•The incus connects the malleus to the stapes, which allows vibrations to reach the inner ear.

Middle Ear• Oval Window= membrane covered opening to inner

ear; vibrations of stapes cause motion of a fluid in the inner ear

• Auditory Tube (Eustachian tube) connects middle ear to the throat; maintains equal air pressure on both sides of the eardrum

• The middle ear cavity is air-filled while the inner ear is fluid-filled; if sound waves were to impinge directly on the oval window, the membrane would barely move.

Inner Ear

Major structures of inner Ear• Semicircular Canals= Provide sense of equilibrium

(Balance)• Cochlea= snail shell shaped structure which

functions houses the organ of corti

Inner Ear• Organ of Corti= contains hearing receptors; rows of

hair-like processes which sheer back and forth as sound vibrations pass through the fluid of the inner ear

Humans can only hear a range of frequencies.~30 Hz - 20,000 Hz

Demo Link: http://www.ece.ncsu.edu/virtuallab/JAVA/applets/osc.html

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STRUCTURES OF THE EYE

The eye itself is a hollow sphere composed of three layers of tissue.

Tunics (layers) of the eye

• Fiberous Tunic (outer layer)– Cornea– Sclera

• Vascular Tunic (blood supply)– Choroid layer– Iris– Ciliary body

• Neural Tunic– Retina– Optic Disc

Conjunctiva• Is a thin protective covering of epithelial cells. It

protects the cornea against damage by friction (tears from the tear glands help this process by lubricating the surface of the conjunctiva)

Cornea• Is the transparent, curved front of the eye which

helps to converge the light rays which enter the eye

Sclera• Is an opaque, fibrous, protective outer structure. It

is soft connective tissue, and the spherical shape of the eye is maintained by the pressure of the liquid inside. It provides attachment surfaces for eye muscles

Choroid• Has a network of blood vessels to supply nutrients

to the cells and remove waste products. It is pigmented that makes the retina appear black, thus preventing reflection of light within the eyeball.

Ciliary body• Has suspensory ligaments that hold the lens in

place. It secretes the aqueous humour, and contains ciliary muscles that enable the lens to change shape, during accommodation (focusing on near and distant objects)

Iris• Is a pigmented muscular structure consisting of an

inner ring of circular muscle and an outer layer of radial muscle. Its function is to help control the amount of light entering the eye so that: – too much light does not enter the eye which would

damage the retina – enough light enters to allow a person to see

Pupil• Is a hole in the middle of the iris where light is

allowed to continue its passage. In bright light it is constricted and in dim light it is dilated

Lens• Is a transparent, flexible, curved structure. Its

function is to focus incoming light rays onto the retina using its refractive properties

Retina• Is a layer of sensory neurons, the key structures

being photoreceptors (rod and cone cells) which respond to light. Contains relay neurons and sensory neurons that pass impulses along the optic nerve to the part of the brain that controls vision

Photoreceptors (not on handout)

Rods• Provide vision in dim

light• Produce colorless vision

(black and white)

Cones• Provide vision in bright

light• Produce color vision

Fovea (yellow spot) • A part of the retina that is directly opposite the

pupil and contains only cone cells. It is responsible for good visual acuity (good resolution)

Blind spot • Is where the bundle of sensory fibers form the optic

nerve; it contains no light-sensitive receptors

Vitreous humour• Is a transparent, jelly-like mass located behind the

lens. It acts as a ‘suspension’ for the lens so that the delicate lens is not damaged. It helps to maintain the shape of the posterior chamber of the eyeball

Aqueous humour • Helps to maintain the shape of the anterior

chamber of the eyeball

Chambers of The Eye (not on handout)

Chambers of The Eye(not on handout)

Lens

Anterior chamber

Vitreous Chamber

Posteriorchamber

Anterior Chamber: Behind cornea, in front of irisPosterior Chamber : Behind iris, in front of lensVitreous Chamber: Between lens and retina

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