Transcript Chapter 18 - Austin Community College

Lecture PowerPoint to accompany
Inquiry into Life
Twelfth Edition
Sylvia S. Mader
Chapter 18
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
18.1 Sensory Receptors and
Sensations
• Sensory Receptors
– Specialized to detect specific stimuli
– Interoreceptors - detect stimuli inside body
• Includes receptors for blood pressure, blood volume, and pH
of the blood.
• Directly involved in homeostasis, regulated by negative
feedback
– Exteroreceptors - detect stimuli outside body
• Includes receptors for taste, smell, vision, hearing, and
equilibrium.
• They function to inform the CNS about environmental
conditions
18.1 Sensory Receptors and
Sensations
• Types of Sensory Receptors
– Chemoreceptors
• Taste, smell, blood pH
– Photoreceptors
• Vision (light)
– Mechanoreceptors
• Hearing, gravity, motion, body position
– Thermoreceptors
• Temperature
– Located in the hypothalamus and skin
18.1 Sensory Receptors and
Sensations
Detection
Sensation
18.1 Sensory Receptors and
Sensations
• How Sensation Occurs
– Sensory Transduction
• Energy from a chemical or physical stimulus is converted into
an electrical signal (nerve impulse)
– The stronger the stimulus, the more frequent the action
potentials
• The sensation that results depends on the part of the part of
the brain receiving the nerve impulses
18.1 Sensory Receptors and
Sensations
• How Sensation Occurs
– Integration:
the summing up of environmental
signals by sensory receptors
– Sensory Adaptation: a decrease in response to a
stimulus (not being consciously
aware of a stimulus)
18.2 Somatic Senses
• Three Types of Somatic Sensory Receptors
– Proprioceptors
– Cutaneous Receptors
– Pain Receptors
18.2 Somatic Senses
• Three Types of Somatic Sensory Receptors
– Proprioceptors
• Mechanoreceptors involved in reflex action
– Help maintain muscle tone
– Muscle spindles increase the degree of muscle
contraction
– Golgi tendon organs decrease the degree of muscle
contraction
– The result is proper muscle length and tension (tone)
Muscle Spindle
18.2 Somatic Senses
• Three Types of Somatic Sensory Receptors
– Cutaneous Receptors
– In the dermis of the skin
– Fine touch receptors
• Meissner corpuscles and Krause end bulbs - fingertips, lips, palms,
penis, clitoris
• Merkel disks - junction of epidermis and dermis
• Root hair plexus - free nerve endings at base of follicles
– Allows sensation when hair is touched
– Pressure receptors
• Pacinian corpuscles - onion-shaped, deep in dermis
• Ruffini endings - encapsulated receptors with complex nerve
networks
– Temperature receptors - free nerve endings
Cutaneous Receptors in the
Human Skin
18.2 Somatic Senses
• Three Types of Somatic Sensory Receptors
– Pain Receptors
• Free nerve endings
• Damaged tissues release chemicals that stimulate pain
receptors
• Alert us to possible danger
– Referred Pain
• In some areas stimulation of internal pain receptors is also
perceived as pain from the skin
• Most likely explanation- impulses from internal pain receptors
also synapse in cord with neurons receiving pain impulses
from skin
– Ex: pain originating in heart is also referred to left arm and
shoulder
18.3 Senses of Taste and Smell
• Sense of Taste
– Taste buds contain chemoreceptors and are located in the
tongue, hard palate, pharynx, epiglottis
– There are different receptors for salty, sour, bitter, and sweet
tastes
– Taste bud structure
• Each has a pore surrounded by supporting cells and taste cells
• Taste cells have microvilli with receptors
– How the brain receives taste information
• Chemicals bind to receptors on microvilli-impulses generated
• Gustatory (taste) cortex surveys incoming pattern of impulses
• “Weighted average” is the perceived taste
Taste Buds in Humans
18.3 Senses of Taste and Smell
• Sense of Smell
– 80-90% of what we perceive as taste is actually smell
– Olfactory Cells
• Chemoreceptors (modified neurons) located high in nasal
cavity
• Olfactory cells have a tuft of olfactory cilia with receptors for
odor molecules
– How the Brain Receives Odor Information
• Nerve fibers lead to olfactory bulb, an extension of the brain,
• A single odor is composed of many different molecules which
activates a characteristic combination of receptor proteins
• Odor’s “signature” is interpreted by brain
Olfactory Cell Location and Anatomy
18.4 Sense of Vision
Anatomy of the Human Eye
Anatomy and Physiology of the Eye
18.4 Sense of Vision
• Anatomy and Physiology of the Eye
– Function of the Lens
• Focuses light rays onto the retina
– Image is inverted and upside down on the retina
– If eyeball is too long or too short corrective lenses are needed
to bring image into focus on the retina
• Visual accommodation
– For viewing close objects
» Lens rounds up to bring the image into focus on the lens
» Lens shape is controlled by the ciliary muscle
» Elasticity of the lens may decrease with age
Focusing the Human Eye
18.4 Sense of Vision
18.4 Sense of Vision
• Visual Pathway to the Brain
– Function of Photoreceptors (Rods and Cones)
• Rods
– Very sensitive to light, important for night vision
– Visual pigment is rhodopsin
– Also provide us with peripheral vision and the perception
of motion
• Cones
– Activated by bright light
– Allow for color perception
Photoreceptors in the Eye
18.4 Sense of Vision
• Visual Pathway to the Brain
– Function of the Retina
• Three Layers of Cells
– Layer closest to choroid contains rods and cones
– Middle layer composed of bipolar cells
– Inner layer composed of ganglion cells
» Sensory fibers become the optic nerve
• Rod and cone cells synapse with bipolar cells which synapse with
ganglion cells
• Integration occurs as signals pass to bipolar and ganglion cells
• Considerable processing occurs in the retina before ganglion cells
generate impulses
• Impulses from the ganglion cells travel in the optic nerve to the visual
cortex where further integration occurs
Structure and Function of the Retina
18.4 Sense of Vision
• Visual Pathway to the Brain
– From the Retina to the Visual Cortex
• Optic nerves from each eye travel to the optic chiasma
• Some of the axons cross over at the optic chiasma
– Fibers from the right half of each retina join together to form the
right optic tract
– Fibers from the left half of each retina join together to form the
left optic tract
• Optic tracts travel around the hypothalamus and most fibers
synapse with nuclei in the thalamus
– Axons from the thalamic nuclei form optic radiations that carry
impulses to the visual area
– Right and left visual areas must communicate for us to see
entire visual field
Optic Chiasma
18.5 Sense of Hearing
• The Ear Has Two Sensory Functions
– Hearing and Balance
• Mechanoreceptors (hair cells) located in the inner
ear associated with both functions
Anatomy of the Human Ear
18.5 Sense of Hearing
• Auditory Pathway to the Brain
–
–
–
–
–
Sound waves enter the auditory canal
Tympanic membrane (ear drum) begins to vibrate
Vibrations are amplified across the middle ear bones
The stapes is attached to the oval window
Oval window vibrates and transmits vibrations to fluid
inside the cochlea
Mechanoreceptors for Hearing
18.5 Sense of Hearing
• Auditory Pathway to the Brain Continued . . .
– Stapes causes the oval window to vibrate
– Vibrations move from the vestibular canal to the
tympanic canal across the basilar membrane
– Basilar membrane moves up and down and the
stereocilia of the hair cells bend
– This generates nerve impulses in the cochlear nerve
– The nerve impulses travel to the brain
– The auditory cortex interprets them as sound
18.6 Sense of Equilibrium
• Rotational Equilibrium Pathway
– Three semicircular canals arranged so that one is in
each plane of motion
– Each semicircular canal has an enlarged base called
an ampulla
• Each ampulla contains hair cells with stereocilia embedded in
a cupula
– As fluid within a canal flows and bends a cupula, the
stereocilia are bent and this changes the pattern of
impulses carried in the vestibular nerve to cerebellum
and cerebrum
• Brain uses this information to make postural corrections
18.6 Sense of Equilibrium
• Gravitational Equilibrium Pathway
– Depends on utricle and saccule
• Utricle is sensitive to horizontal movements of the head
• Saccule is sensitive to vertical movements of the head
– Both contain hair cells with stereocilia embedded in an
otolithic membrane
• Large central cilium called the kinetocilium
• Calcium carbonate granules (otoliths) rest on otolithic
membrane
– When head or body moves in horizontal or vertical
plane the otoliths are displaced and the otolithic
membrane sags
Mechanoreceptors for Equilibrium
18.7 Disorders that Affect the Senses
• Disorders of Taste and Smell
– Sense of smell begins to decline after age 60
– Some people are born without a sense of smell
– Other factors that contribute to a decrease in the
ability to taste and/or smell include:
• Upper respiratory infections
• Allergies
• Exposure to certain drugs or chemicals (including tobacco
smoke)
• Brain trauma
18.7 Disorders that Affect the Senses
• Disorders of the Eye
– Color Blindness
• Complete colorblindness is rare
• Most common types involve deficiency in one type of cone
• Red-green colorblindness
– Most common type
– X-linked recessive trait
– 5-8% of the male population
Testing for Colorblindness
18.7 Disorders that Affect the Senses
– Distance Vision
• Nearsighted
– Can see close objects better than distant ones
– Eyeball is elongated so image is brought to point focus in
front of the retina
– Corrected by concave lenses which diverge light rays so
point focus is farther back
• Farsighted
– Can see distant objects better than close ones
– Eyeball is shortened so image is brought to point focus
behind the lens
– Corrected by convex lenses to increase bending of light
rays so point focus is farther forward
Corrective Abnormalities of the Eye and
Possible Corrective Lenses
18.7 Disorders that Affect the Senses
• Common Causes of Blindness
– Retinal Disorders
• Capillaries to the retina may become damaged
• Macular Degeneration
– Cones are destroyed
• Detached retina
– Glaucoma
• Fluid builds up in the eye destroying nerve fibers associated
with peripheral vision
– Cataracts
• Cloudy spots on the lens
• Exposure to UV light, diabetes, heavy alcohol
consumption,and smoking are all risk factors
18.7 Disorders that Affect the Senses
• Disorders of Hearing and Equilibrium
– Hearing Loss
• Mobility of the middle ear bones decreases with age
• The ability to hear high-pitched sounds is affected first.
– Sudden Deafness
• Usually occurs in only one ear
• Causes include infections, trauma, and side effects of some
drugs
• Sometimes resolves itself
– Deafness at Birth
• Genetic and/or environmental causes (pathogens)
18.7 Disorders that Affect the Senses
• Disorders of Hearing and Equilibrium
– Vertigo (dizziness)
• Can be caused by problems in the brain or inner ear
– Meniere’s Disease
• Caused by an increased fluid volume in the inner ear
• Hearing loss and vertigo are both characteristics of this
condition