The Chemical Context of Life

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Thermoreceptors & Pain Receptors

Thermoreceptors, which respond to heat or cold, help regulate body temperature by signaling both surface and body core temperature.

In humans, pain receptors, or nociceptors, are a class of naked dendrites in the epidermis.

They respond to excess heat, pressure, or chemicals released from damaged or inflamed tissues.

Slide 19

The mechanoreceptors responsible for hearing and equilibrium detect moving fluid or settling particles

Hearing and perception of body equilibrium are related in most animals.

Settling particles or moving fluid are detected by mechanoreceptors.

Slide 20

Sensing Gravity and Sound in Invertebrates

Most invertebrates maintain equilibrium using sensory organs called statocysts.

Statocysts contain mechanoreceptors that detect the movement of granules called statoliths.

Slide 21

The statocyst of an invertebrate

Sensory axons

Statolith

Cilia

Ciliated receptor cells

Slide 22

Many arthropods sense sounds with body hairs that vibrate or with localized “ears” consisting of a tympanic membrane and receptor cells

1 mm

Tympanic membrane

Slide 23

Hearing and Equilibrium in Mammals

In most terrestrial vertebrates, sensory organs for hearing and equilibrium are closely associated in the ear.

Slide 24

Human Ear

Hair cell bundle from a bullfrog; the longest cilia shown are about 8 µm (SEM).

Auditory canal

Eustachian tube

Pinna

Tympanic membrane

Oval window

Round window

Stapes

Cochlea

Tectorial membrane

Incus

Malleus

Semicircular canals

Auditory nerve to brain

Skull bone

Outer ear

Middle ear

Inner ear

Cochlear duct

Vestibular canal

Bone

Tympanic canal

Auditory nerve

Organ of Corti

To auditory nerve

Axons of sensory neurons

Basilar membrane

Hair cells

Slide 25

Hearing

Vibrating objects create percussion waves in the air that cause the tympanic membrane to vibrate.

Hearing is the perception of sound in the brain from the vibration of air waves.

The three bones of the middle ear transmit the vibrations of moving air to the oval window on the cochlea.