lesson overview 31.4 the senses

Lesson Overview The Senses

Lesson Overview31.4 The Senses


• Sensory receptors are categorized by the type of stimuli to which they respond. Sensory Receptors

Type Responds to LocationsChemoreceptor Chemicals Mouth & nosePhotoreceptor Light Eyes

Mechanoreceptor Touch, pressure, & vibration

Skin & ears

Thermoreceptor Temperature SkinPain receptor Tissue injury Skin


Touch • Human skin contains at least seven types of

mechanoreceptors that respond to different levels of pressure and creates the sensation of touch.

• Not all parts of the body are equally sensitive to touch. For example, the skin on your fingers has a much higher density of touch receptors than the skin on your back.


Temperature • Thermoreceptors respond to heat and cold

and are found throughout the skin • The hypothalamus is part of the brain that

senses blood temperature


Pain • Pain receptors in the skin respond to physical

injuries like cutting or tearing. • Many tissues also have pain receptors that respond

to chemicals released during infection or inflammation.

• The brain does not have pain receptors. o For this reason, patients are often kept

conscious during brain surgery, enabling them to tell surgeons what sensations are produced when parts of the brain are stimulated.


Smell and Taste• Your senses of taste and smell

involve the ability to detect chemicals.

• Chemoreceptors = chemical-sensing cells o Taste buds = the sense organs in the mouth

that detect taste o Olfactory receptors = the sense organs in

the nose that detect smell


Hearing and Balance• The human ear has two sensory functions—

hearing and detecting movement• Mechanoreceptors found in parts of the ear

transmit impulses to the brain. o The brain translates the impulses into

sound and information about balance.

o Hearing = cochlea (see the notes below)

o Balance = semicircular canals


Hearing 1. Sound is a result of vibrations moving

through the air around us. 2. Vibrations enter the ear cause the eardrum

to vibrate.


Hearing 3. Three tiny bones, called the hammer, anvil,

and stirrup, transmit these vibrations to a membrane that creates pressure waves in the fluid-filled cochlea of the inner ear.


Hearing 4. The cochlea is lined with tiny hair cells that are

pushed back and forth by these pressure waves. 5. The motion of these sensitive hair cells produces

nerve impulses that travel to the brain which processes these nerve impulses as sound.


Balance • Semicircular canals = Three tiny canals

within the inner ear that monitor the position of your body, especially your head, in relation to gravity.


1.The semicircular canals are filled with fluid and lined with hair cells.

2.As the head changes position, the fluid in the canals also changes position, causing the hair on the hair cells to bend.


Balance 3.This bending sends impulses to the brain that

enable it to determine body motion and position.


Vision• How do the eyes and brain produce vision?• Vision occurs when photoreceptors in the

eyes transmit impulses to the brain, which translates these impulses into images.


Order that light passes through the eye:

1. Cornea = a tough transparent layer of cells.


2. Iris = colored part of the eye • Pupil = small opening in

the middle of the iris


3.Lens = focuses the eyes to see near or distant objects clearly• Small muscles attached to

the lens change its shape helping to adjust the eyes’ focus


4.Retina = inner layer of the eye where the lens focuses• Photoreceptors arranged

in a layer in the retina convert light energy into nerve impulses that are carried to the brain


oThere are two types of photoreceptors: rods and cones.

oRods = only sense in black and white oCones = respond to different colors,

producing color vision


Label the eye:

lesson overview 31.4 the senses

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