Transcript A View of Life

Chapter 13
Senses
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Outline
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Types of Sensory Receptors
Sense of Taste
Sense of Smell
Sense of Vision
– Focusing
– Integration of Visual Signals
– Abnormalities of the Eye
Sense of Hearing
Sense of Equilibrium
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Sensory Receptors and Sensations
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Sensory receptors are specialized to detect
certain types of stimuli.
– Exteroceptors detect stimuli outside the
body.
 Taste, smell, vision.
– Interoceptors detect stimuli inside the
body.
 Blood pressure, blood volume, pH.
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Types of Sensory Receptors
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Chemoreceptors.
– Respond to chemical substances in the
immediate vicinity.
Pain Receptors.
– Respond to chemicals released by
damaged tissue.
Mechanoreceptors.
– Stimulated by mechanical forces.
Thermoreceptors.
– Stimulated by changes in temperature.
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How Sensation Occurs
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Sensation occurs when nerve impulses
arrive at the cerebral cortex of the brain.
Perception occurs when the cerebral cortex
interprets the meaning of sensations.
– All sensory receptors initiate nerve
impulses; the sensation that results
depends on the part of the brain receiving
the nerve impulses.
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Sensation
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Proprioceptors
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Proprioceptors are mechanoreceptors that
help determine limb position in space by
detecting the degree of muscle relaxation,
stretch of tendons, and movement of
ligaments.
– Muscle spindles act to increase the
degree of muscle contraction, while Golgi
tendon organs act to decrease it.
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Muscle Spindle
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Cutaneous Receptors
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The dermis contains cutaneous receptors,
which include:
– Mechanoreceptors.
 Sensitive to touch.
– Nociceptors.
 Sensitive to pain.
– Thermoreceptors.
 Sensitive to temperature.
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Sensory Receptors in Human Skin
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Chemical Senses
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Sense of Taste.
– Receptors for taste are found in taste
buds located primarily embedded in
tongue epithelium.
 Four primary tastes.
 Sweet.
 Sour.
 Salty.
 Bitter.
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Taste Buds
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Sense of Smell
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Sense of smell is dependent on olfactory
cells located within olfactory epithelium high
in the roof of the nasal cavity.
– Olfactory bulbs have direct connections
with the limbic system and its centers for
emotions and memory.
– Sense of taste and smell work together to
create a combined effect.
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Olfactory Cell Location and Anatomy
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Sense of Vision
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The eyeball has three layers.
– Sclera.
– Choroid.
– Retina.
The retina contains two types of
photoreceptors.
– Rods.
– Cones.
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Anatomy of the Human Eye
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Focusing
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When looking at an object, light rays pass
through the pupil and are focused on the
retina.
– Focusing starts with the cornea and
continues as the rays pass through the
lens and the humors.
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Focusing
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Photoreceptors
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Vision begins once light has been focused
on the photoreceptors in the retina.
– Rods are very sensitive to light and
therefore are suited to night vision.
– Cones allow detection of fine detail and
color.
 Color vision depends on three different
kinds of cones which contain blue,
green, and red pigments.
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Photoreceptors in the Eye
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Integration of Visual Signals in the Retina
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The retina has three layers.
– Layer closest to choroid contains rod cells
and cone cells.
– Middle layer contains bipolar cells.
– Innermost layer contains ganglion cells.
Only rod and cone cells are light-sensitive,
thus light must penetrate to the back of the
retina before they are stimulated.
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Structure and Function of the Retina
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Integration of Visual Signals in the Brain
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The visual pathway begins in the retina and
passes through the thalamus before
reaching the cerebral cortex.
– The pathway and visual cortex take the
visual field apart, and the cortex rebuilds it
so we correctly perceive the field.
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Optic Chiasma
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Abnormalities of the Eye
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Color blindness.
– Particular type of cone is lacking.
Distance Vision
– Nearsighted.
 Elongated eyeball.
– Farsighted.
 Shortened eyeball.
Astigmatism.
– Uneven cornea.
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Eye Abnormalities and Corrective Lenses
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Sense of Hearing
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Anatomy of the Ear.
– Outer ear consists of the pinna and the
auditory canal.
– Middle ear begins at tympanic membrane
and ends at bony wall with a round
window and oval window.
 Ossicles found between tympanic
membrane and the oval window.
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Sense of Hearing
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Anatomy of the Ear.
– Inner ear consists of semicircular canals,
vestibule, and cochlea.
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Human Ear
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Process of Hearing
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When the basilar membrane (spiral organ)
vibrates, stereocilia of the hair cells bend,
and nerve impulses are transmitted to the
brain.
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Mechanoreceptors for Hearing
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Sense of Equilibrium
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Cupula movement within the semicircular
canals detects rotation and/or angular
movement of the head.
– Rotational Equilibrium.
Movement of the otolithic membrane within
the utricle and the saccule detects
movement of the head in the vertical and
horizontal planes.
– Gravitational Equilibrium.
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Review
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Types of Sensory Receptors
Sense of Taste
Sense of Smell
Sense of Vision
– Focusing
– Integration of Visual Signals
– Abnormalities of the Eye
Sense of Hearing
Sense of Equilibrium
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