Inquiry into Life Twelfth Edition Chapter 18 Lecture PowerPoint to accompany Sylvia S. Mader Copyright © The McGraw-Hill Companies, Inc. Permission required.

Inquiry into LifeTwelfth Edition

Chapter 18

Lecture PowerPoint to accompany

Sylvia S. Mader

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


• 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


Detection

Sensation


• 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


• 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


– 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


– 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


• 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



• 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


• 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


• 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


• 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


– 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


• 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


• 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)


• 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

Inquiry into Life Twelfth Edition Chapter 18 Lecture PowerPoint to accompany Sylvia S. Mader Copyright © The McGraw-Hill Companies, Inc. Permission required.

Documents