Chapter 44 Flashcards
What are exteroceptors?
receptors that sense stimuli that arise in the external environment
Evolutionarily speaking, where did vertebrate sense evolve?
first in water before the invasion of land
What are the consequences of the fact that vertebrate sensory systems evolved in water before land?
may senses of terrestrial vertebrates emphasize stimuli that travel well in water
What are interoceptors?
receptors that sense stimuli that raise from within the body
Which are typically more complex, exteroceptors or interoceptors?
exteroceptors
Which bear more of a resemblance to primitive sensory receptors, exteroceptors or interoceptors?
interoceptors?
What are the three broad classes of receptors?
mechanoreceptors, chemoreceptors, electromagnetic receptors
What are mechanoreceptors? (2)
stimulated by mechanical forces such as pressure; include receptors for touch, hearing, and balance
What are chemoreceptors? (2)
detect chemicals or chemical changes; includes receptors for smell and taste
What are electromagnetic receptors? (2)
react to heat and light energy; includes eye photoreceptors
What is the four-step process for the conveying of sensory information?
stimulation, transduction, transmission, interpretation
Describe stimulation in the four-step process for the conveying of sensory information.
a physical stimulus impinges on a sensory neuron or associated/separate sensory receptor
Describe transduction in the four-step process for the conveying of sensory information.
stimulus energy is transformed into graded potentials in the dendrites of the sensory neuron
Describe transmission in the four-step process for the conveying of sensory information.
action potentials develop in the axon of the sensory neuron and are conducted to the CNS along an afferent nerve pathway
Describe interpretation in the four-step process for the conveying of sensory information.
brain creates sensory perception from the electrochemical events produced by afferent stimulation.
Why do sensory cells respond to stimuli?
because they possess stimulus-gated ion channels in their membranes
In most causes, the sensory stimulus causes what event in the receptor cell?
causes a depolarization f the receptor cell, analogous to an EPSP
What is a receptor potential?
a depolarization that occurs in a sensory receptor on stimulation
What type of potential is a receptor potential?
a graded potential
What is the relationship between the size of the sensory stimulus and the degree of polarization?
the larger the sensory stimulus, the greater the degree of polarization
What is responsible for conveying the intensity of a stimulus?
the frequency of action potentials, NOT their summation
What is the relationship between stimulus intensity and action potential frequency?
a logarithmic relationship
What is the name for the receptors of the skin?
cutaneous receptor
Cutaneous receptors are classified as
interoceptors
What are nociceptors?
the receptors that transmit impulses perceived as pain
Most nociceptors consist of
free nerve endings located throughout the body, especially near surfaces where damage is most likely to occur
What is transient receptor potential (TRP) ion channel?
a class of ion channel proteins found in nociceptors
The TRP ion channel is stimulated by
temperature to produce an inward flow of cations of Na+ and Ca2+
The inward flow of Na+ and Ca2+ through the TRP ion channel causes
a depolarizing current which further causes the sensor neuron to fire, leading to the release of glutamate and an EPSP in neurons in the spinal cord, ultimately producing the pain response.
The first identified TRP channel responds to
the chemical capsaicin, which is found in chili peppers, and also responds to heat
A cold-responsive TRP receptor responds to
the chemical menthol
How do TRP channels reduce the body’s pain response?
chemical stimulation of the TRP channels reduces the body’s pain response by desensitizing the sensory neurons
What are thermoreceptors?
naked dendritic endings of sensory neurons that are sensitive to changes in temperature
How are nociceptors and thermoreceptors similar?
nociceptors also contain free nerve endings
Thermoreceptors contain
TRP ion channels that are responsive to both hot and cold
Where are cold receptors located?
immediately below the epidermis
Which are more numerous, cold or warm receptors?
cold receptors are 3-4 x more numerous than warm receptors
Where are warm receptors located?
slightly deeper in the dermis, below the cold receptors
Where are thermoreceptors found in the brain?
in the hypothalamus, where they monitor the temperature of circulating blood and provide the CNS with info on the body’s core temp
What are four main types of mechanoreceptors in the skin?
merkle cell, meissner corpuscle, ruffini corpuscle, pacinian corpuscle
What are Merkle cells?
tonic receptors located near the surface of the skin that are sensitive to touch pressure and duration
What are Meissner corpuscles?
phasic receptors sensitive to fine touch, concentrated in hairless skin
What are Ruffini corpuscles?
tonic receptors located near the surface of the skin that are sensitive to touch pressure and duration
What are Pacinian corpuscles?
pressure-sensitive phasic receptors deep below the skin and in the subcutaneous tissue
What are the two tonic receptors?
Merkle cells and Ruffini corpuscles
What are the three phasic receptors?
Meissner corpuscles, hair follicle receptors, and Pacinian corpuscles
The four mechanoreceptors in the skin contain
sensory cells with ion channels that open in response to mechanical distortion of the membrane
What does it mean to be phasic?
intermittently activated
What does it mean to be tonic?
continuously activated
Phasic receptors are found on surfaces
that do not contain hair, like fingers/palms/nipples
Pacinian corpuscles consist of
the end of an afferent axon surrounded by a capsule of alternating layers of connective tissue cells and extracellular fluid
What happens when sustained pressure is applied to a Pacinian corpuscle?
the elastic capsule absorbs much of the pressure and axon ceases to produce impulses
Muscle length and tension are monitored by
proprioceptors
What are muscle spindles?
sensory stretch receptors that lie in parallel with the rest of the fibers in the muscle
Each muscle spliced consists of
several thin muscle fibers wrapped together and innervated by a sensory neuron, which becomes activated when the muscle/spindle is stretched
What are proprioceptors?
sensory receptors that provide information about the relative position or movement of the animal’s body parts
What are Golgi tendon organs?
a proprioceptor that monitors the tension exerted on tendons when an associated muscle contracts
What do baroreceptors do?
detect blood pressure
Blood pressure is monitored at what two main sites in the body?
the carotid sinus and the aortic arch
What is the carotid sinus?
an enlargement of the left and right internal carotid arteries that supply blood to the brain
What is the aortic arch?
the portion of the aorta very close to its emergence from the heart
What exactly do baroreceptors detect?
they detect tension or a stretch in the walls
Describe what happens when blood pressure decreases. (2)
the frequency of impulses produced by the baroreceptors decreases; CNS responds by stimulating sympathetic division which increases heart rate and causes vasoconstriction
Describe what happens when blood pressure increases. (2)
baroreceptor impulses increase; reduces sympathetic activity and instead stimulates parasympathetic division which lowers heart rate
What is hearing?
the detection of sound waves
Why does hearing work better in water than in air?
because water transmits pressure waves more efficiently
What system in fish provides a sense of “distant touch?”
lateral line system
The lateral line system enables fish to
sense objects that reflect pressure waves and low-frequency vibrations
Is the lateral line system found in amphibians?
found in amphibian larvae but is lost at metamorphosis
Is the lateral line system found in terrestrial vertebrates?
no
How does the lateral line system interact with the fish’s hearing?
the lateral line system supplements the fish’s sense of hearing
What does the lateral line system consist of?
hair cells within a longitudinal canal in the fish’s skin that extends along each side of the body and within several canals in the head
(lateral line system) The hair cells’ surface processes project into
a gelatinous membrane called a cupula
(lateral line system) hair cells have hairlike processes called
stereocilia
What is a kinocilium?
longer hairlike process present on hair cells in the lateral line system
Describe sterecilia. (2)
actually microvilli; contain actin fibers
Describe a kinocilium. (2)
true cilium; contains microtubules
If the stereocilia are bent in the direction of the kinocilium, what happens?
associated sensory neurons are stimulated and generate a receptor potential
If the stereocilia are bent in the opposite direction of the kinocilium, what happens?
activity of the sensory neuron is inhibited
Otoliths are composed of
calcium carbonate crystals
Where are otoliths located?
otolith organs of the membranous labyrinth, a system of fluid-filled chambers and tubes also present in other vertebrates
What structure in the fish is primarily responsible for detecting sound?
otoliths
What structures make up the outer ear? (2)
ear canal; ear drum (tympanic membrane)
Vibrations of the tympanic membrane cause movement of
one or more small bones that are located in a bony cavity known as the middle ear
Amphibians/reptiles have what single middle ear bone?
stapes (stirrup)
Mammals have what three middle ear bones?
stapes (stirrup); malleus (hammer); incus (anvil)
What connects the middle ear to the throat?
Eustachian tube
What is another name for the Eustachian tube?
auditory tube
The stapes vibrates against
a flexible membrane called the oval window
The oval window leads to
the inner ear
What transmits sound into the inner ear?
the oval window, because it’s smaller in diameter than the tympanic membrane and thus vibrations against it produce more force per unit area
What does the inner ear consist of?
cochlea
What is the cochlea?
bony structure containing part of the membranous labyrinth called the cochlear duct
Where is the cochlear duct located?
center of the cochlea
The area above the cochlear duct is called the
vestibular canal
The area below the cochlear duct is called the
tympanic canal
The cochlear duct, vestibular canal, and tympanic canal are all
filled with fluid
The oval window opens into the
upper vestibular canal, so that when the stapes causes it to vibrate, it produces pressure waves of fluid
The pressure waves produced by the upper vestibular canal travel to
the tympanic canal, which pushes the round window and transmits the pressure back into the middle ear cavity
As pressure waves are transmitted through the cochlea to the round window, what happens?
the cochlear duct vibrates, which causes the basilar membrane (bottom of cochlear duct) to vibrate
The surface of the cochlear duct’s basilar membrane contains
sensory hair cells
What is the tectorial membrane?
gelatinous membrane into which stereocilia from hair cells from the cochlear duct’s basilar membrane project
What is the organ of Corti? (3)
apparatus consisting of basilar membrane, hair cells + sensory neurons, tectorial membrane
The basilar membrane of the cochlea is made up of
elastic fibers of varying length and stiffness
Describe the basilar membrane fibers at the far end of the cochlea and at the base of the cochlea.
At the base of the cochlea, the fibers are short and stiff; at the far end, they’re 5 times longer and 100 times more flexible
Which parts of the cochlea respond to higher and lower pitches?
base responds to higher pitches, apex responds to lower pitches
When a wave of sound energy enters the cochlea from the oval window, what happens?
it initiates an up-and-down motion that travels the length of the basilar membrane
What causes hair cell depolarization in the basilar membrane?
bending of stereocilia
The hair cell depolarization in the basilar membrane results in
action potentials sent to the brain
What is the frequency range of human hearing?
20 to 20,000 Hz in children
What is echolocation?
when mammals emit sounds and determine the time it takes for the sounds to bounce back
What is a statocyst?
sensory structure that consists of ciliated hair cells with the cilia embedded in a gelatinous membrane containing crystals of calcium carbonate
Give four examples of animals that make use of echolocation.
bats, shrews, whales, dolphins
What is another name for the calcium carbonate crystals in the statocyst?
statoliths
What do statoliths do?
increase the mass of the gelatinous membrane so that it can bend the cilia when the animal’s position changes
Perilymph fluid is similar in composition to
interstitial fluid
Endolymph fluid is similar in composition to
intracellular fluid
The receptors for gravity in most vertebrates consist of
two chambers of the membranous labyrinth called the utricle and the saccule
What is contained with the utricle and saccule?
stereocilia and a kinocilium
The hairlike processes in the utricle and saccule are embedded within
the otolith membrane which contains calcium carbonate crystals
The utricle is more sensitive to
horizontal acceleration
The saccule is more sensitive to
vertical acceleration
The membranous labyrinth of the utricle and saccule is continuous with
three semicircular canals which are oriented in different directions so as to pick up any angle of acceleration
Accelerations of the utricle and saccule cause
cilia to bend, which produces an action potential in an associated sensory neuron
What are ampullae?
swollen ends of the semicircular canals into which protrude the cilia of another group of hair cells
The cilia that protrude into the ampullae are embedded within
a sail-like wedge of gelatinous material called a cupula
The cupula that contain the cilia that protrude into the ampullae itself protrudes into
the endolymph fluid of each semicircular canal
When the head rotates, what happens inside the cupula?
fluid inside semicircular canals pushes against the cupula and causes cilia to bend
What is the vestibular apparatus?
term that collectively refers to the saccule, utricle, and semicircular canals
What is another name for taste?
gustation
What are the five tastes?
sweet, sour, salty, bitter, umami
What are taste buds?
collections of chemosensitive epithelial cells associated with afferent neurons
In fish, where are taste buds located?
scattered over the surface of the body
The most sensitive vertebrate chemoreceptors can be found in
fish
The taste buds of all terrestrial vertebrates occur in the
epithelium of the tongue and oral cavity, within raised areas called papillae
Taste buds are shaped like
onions
How many taste cells does each taste bud have?
between 50 and 100
What are taste pores?
the top of the taste bud through which microvilli poke through
The prototypical salty taste is due to (2)
Na+ ions which diffuse through Na+ channels into cells in receptor cells in the taste bud; Na+ influx depolarizes membrane and causes receptor cell to release neurotransmitter and activate sensory neuron that sends impulse to brain
The prototypical sour taste is due to (2)
H+ ions; increased concentration of H+ ions depolarize the membrane when they diffuse through ion channels
Sweet, bitter, and umami substances bind to
G-protein coupled receptors specific for each category
What is another name for smell?
olfaction
Where are olfaction chemoreceptors located?
upper portion of the nasal passages
The olfaction chemoreceptors project into
the nasal mucosa
The axons of olfaction chemoreceptors project
directly into the cerebral cortex
What needs to happen to an odorant particle before it can be detected?
particle must dissolve in extracellular fluid before they can activate the olfactory receptor
What are peripheral chemoreceptors? (2)
located in the aortic and carotid bodies; sensitive to plasma pH
What are the central chemoreceptors?
located in the medulla oblongata; sensitive to the pH of cerebrospinal fluid
Which two chemoreceptors monitor pH?
peripheral chemoreceptors and central chemoreceptors
What happens to the pH when the breathing rate is too low?
concentration of plasma CO2 increases which lowers both blood pH and cerebrospinal fluid pH
What do photoreceptors do?
capture light energy
Invertebrates have what kind of vision systems?
simple visual systems with photoreceptors clustered in eyespots
What is a limitation of eyespots?
eyespots can perceive the direction of light, but cannot be used to construct a visual image
What are the four phyla?
annelids, mollusks, arthropods, chordates
How did the visual systems of the four phyla evolve?
evolved independently - an example of convergent evolution
What is the sclera?
the “white of the eye”; formed of tough connective tissue
Light enters the eye through
a transparent cornea, which begins to focus the light
Why does light focusing occur?
light is refracted when it travels into a medium of different density
What is the iris?
colored portion of the eye
The contraction of iris muscles in bright light results in
the decreasing of the size of its opening, the pupil
What is the opening of the iris?
pupil
What is the lens?
transparent structure that completes the focusing of light onto the retina @ back of eye
How is the lens attached to ciliary muscles?
lens is attached by the suspensory ligament to the ciliary muscle
The shape of the lens is influenced by
the amount of tension in the suspensory ligament
What is the fovea? (2)
center of retina; point where eye forms sharpest image
The suspensory ligament surrounds the lens and connects it to which ciliary muscle?
the circular ciliary muscle
What happens when the ciliary muscle contracts?
pulls slack in the suspensory ligament which makes the lens more rounded and bends light more strongly (close vision)
What happens when the ciliary muscle relaxes?
ciliary muscle moves away from lens and tightens the suspensory ligament; lens becomes more flattened and bends light less (distance vision)
People who are nearsighted or farsighted
do not properly focus the image on the retina
The lens in amphibians and fish
does not change; they focus images by zooming in and out
Rods are
visual photoreceptors responsible for black-and-white vision
Cones are (2)
response for high visual acuity (sharpness) and color vision
How many rods and cones are in each retina?
100 million rods + 3 millian cones
Where are most cones concentrated?
in the fovea
Are rods in the fovea?
No, rods are almost completely absent from the fovea
What is the basic common cellular structure of rods and cones?
inner segment rich in mitochondria contains numerous vesicles filled with neurotransmitter molecules; connected by narrow stalk to outer segment, which is packed photopigments
What is rhodopsin?
photopigment in rods
Rhodopsin consists of
opsin bound to a molecule of cis-retinal (derived from vitamin A)
Where is Vitamin A derived from?
carotene, a photosynthetic pigment in plants
What is photopsin?
photopigment of cones
How many different types of cones do humans have?
3
Photopsin consists of
cis-retinal bound to a different protein
How many layers are in the retina?
3 layers of cells
The layer closest to the external surface of the eyeball consists of
rods and cones
The next layer after the one containing rods and cones contains
bipolar cells
The layer closest to the cavity of the eye contains
ganglion cells
In order to reach the photoreceptors, light must first
pass through the ganglion cells and bipolar cels
The ganglion cells in the eye function as
neurons that send action potentials to the brain
The ganglion sends information to the brain via what structure?
optic nerve
The retina contains two additional types of neurons called
horizontal cells and amacrine cels
In the dark, photoreceptor cells (2)
release an inhibitory neurotransmitter that hyper polarizes the bipolar neurons; this prevents the bipolar neurons from releasing excitatory neurotransmitters to the ganglion cells that signal to the brain
In the light, photoreceptor cells
stop releasing inhibitory neurotransmitters which stimulates bipolar neurons; bipolar cells in turn stimulate ganglion cells which sends info to the brain
What are lateral geniculate nuclei?
structures of the thalamus that project into the occipital lobe and transmit action potentials from ganglion cells
What is the relationship between cones and bipolar cells in the fovea?
in the fovea, each cone makes a one-to-one connection with a bipolar cell
What is the relationship between bipolar cells and ganglion cells in the fovea?
in the fovea, each bipolar cell synapses with one ganglion cell
Why is the point-to-point relationship important in the fovea?
responsible for the high acuity of foveal vision
Outside of the fovea, what is the relationship between rods, bipolar cells, and ganglion cells? (2)
many rods can converge on a single bipolar cell, many bipolar cells can converge on a single ganglion cell
What is the consequence of the multiple relationships outside the fovea?
permits the summation of neural activity, making the area of the retina outside the fovea more sensitive to dim light than the fovea, but at the expense of acuity and color vision
Color blindness results from
the inherited lack of one or more types of cones
People with normal color vision are called
trichromats (have all three cones)
People with only two types of cones are called
dichromats
What is parallax?
slight displacement of images because of binocular vision
What is binocular vision?
the ability to perceive 3D images and to sense depth
Most birds have what placement of eyes?
laterally placed eyes
How many foveas do birds have in each retina?
2; one fovea provides sharp frontal vision; the other provides sharper lateral vision
What are the only vertebrates that can sense infrared radiation?
snakes
Pit vipers have what specialized structure to detect heat? (2)
pit organs located on either side of the head; each pit organ is composed of 2 chambers separated by a membrane
All aquatic animals generate
electrical currents from contractions of their muscles
Give three examples of elasmobranchs.
sharks, rays, and skates
Elasmobranchs have electroreceptors calle
the ampullae of Lorenzini
Where are Lorenzini receptors located?
in sacs that open through the jelly-filled canals to pores on the body surface
Why are ampullae of Lorenzini useful?
can sense electrical currents generated by the muscle contractions of their prey
Give four examples of animals that navigate along the magnetic field lines of the earth.
eels, sharks, bees, some birds
