Chapter 44: Sensory Systems (Part 1, Week 10)

Question 1

WHat is a system in an animal that consists of specialized cells that respond to a specific type of chemical or physical stimulus and send signals to the central nervous system, where the signals are received and interpreted?

Answer 1

A sense

Question 2

[Start 44.1 An Intro to Sensation]

What do sensory systems convert?

Answer 2

Chemical or physical stimuli from an animal’sbody or the external environment into a signal that causes a change in the membrane potential of sensory neurons.

Question 3

What is the process by which incoming stimuli are converted into neural signals?

Answer 3

Sensory transduction

Question 4

What is an awareness of the sensations that are experienced?

Answer 4

Perception

Question 5

What, in animals, is a specialized cell whose function is to receive sensory inputs?

Answer 5

Sensory receptor

This could be a neuron, or maybe an epithelial cell that synapses with a neuron referred as a sensory neuron.

Question 6

How do sensory receptors transmit the intensity of a stimulus? In the case of strong or weak stimuli to the sense of touch.

Answer 6

Sensory transduction begins when thespecialized endings of a sensory receptor respond to a stimulus.

This stimulus opens ion channels that allow sodium ions (Na+) to diffuse down their electrochemical gradient into the cell, depolarizing the sensory receptor.

The amount of depolarization is directly related to the intensity of the stimulus, because a stronger stimulus opens more ion channels.

With this, if it is a light tough, the ion channels will be few and will not create an action potential. Otherwise, this touch, could cause a response if more ion channels opened and an action potential occured.

Question 7

What is the first response of a sensory receptor to stimuli?

Answer 7

A graded change in the membrane potential of the cell body that is proportional to the intensityof the stimulus

Question 8

What becomes less and less negative as the strength of the stimulus increases?

Answer 8

The membrane potential, or in this case, the receptor potential. (The membrane potential in a sensory receptor cell of an animal)

When a stimulus is strong enough, it depolarizes the membrane to the threshold potential at the axon hillock and produces an action potential in a sensory neuron.

Question 9

How, then, can action potentials provide information about the intensity of a stimulus?

Remember, when an action potential starts regardless of intensity of the stimulus, they proceed in an all or none manner.

Answer 9

The answer is that the strength of the stimulus determines the frequency of action potentials generated.

Question 10

How does the strong stimulus create multiple action potentials?

Answer 10

It can overcome the membrane’s relative refractory period.

Question 11

Why do different stimuli produce different sensations?

Answer 11

They activate specific neural pathways that are dedicated to processing only that type of stimulus.

The brain can separate and identify each sense because each one uses its own dedicated pathway.

Question 12

How are sensory receptors divided into general classes?

Answer 12

Based on the type of stimulus, or modality, to which they respond.

Each class of receptor uses a different mechanism to detect stimuli and to transmit the information to different regions of the CNS.

Question 13

What are the 6 different sensory receptors and briefly state their function.

Answer 13

Mechanoreceptors - transduce mechanical energy such as touch, pressure, stretch, movement, and sound.

Thermoreceptors - detect cold and heat.

Nociceptors - or pain receptors, detect extreme heat, cold, and pressure, as well as certain potentially damaging molecules such as acids.

Electromagnetic receptors - sense radiation within a portion of the electromagnetic spectrum, including visible, UV, and infrared light,as well as electrical and magnetic fi elds in some animals.

Photoreceptors - are a type of electromagnetic receptor that detect visible light.

Chemoreceptors - recognize specifi c chemical compounds in the air,water, body fluids, or food.

Question 14

[Start 44.2 Mechanoreception]

What do some skin receptors consist of?

Answer 14

Some of these specialized receptors consist of neuronal dendrites covered in dense connective tissue.

Question 15

How are skin receptors suitable for responding to different types of stimuli?

Answer 15

In mammals, these receptors are located at different depths.

Question 16

What is a specialized receptor that senses touch and light pressure and lies just beneath the skin surface of an animal?

Answer 16

Meissner corpuscles

They are found throughout the skin but are concentrated in areas sensitive to light touch, such as the fingertips, lips, eyelids, and genitals.

Question 17

What is in contrast of Meissner corpuscles, and are located much deeper beneath the surface of the skin, and are particularily in the soles of the feet and palms of the hands?

These corpuscles respond best to deep pressure or vibration.

Answer 17

Pacinian corpuscles and Ruffini corpuscles

Question 18

T/F All skin corpuscles contain sensory receptor neurons that generate action potentials when the structure of the corpuscle is deformed.

Answer 18

True.

Even hair follicles have sensory receptors that detect movement of hair and whiskers.

Question 19

What is a type of mechanoreceptor found widely in an animal’s organs and muscle tissues that can be distended?

Answer 19

Stretch receptors

In decapod crustaceans such as crabs and lobsters, for example, stretch receptors in muscles of the tail, abdomen, and thorax relay signals to the brain regarding the positions in space of the different body parts. This information allows the animal to coordinate complex motor functions, such as walking backward or sideways.

In another example, when the mammalian stomach stretches after a meal, the stretch receptors in the stomach are deformed, causing them to become depolarized and send action potentials to the brain.

The brain interprets the signals as fullness, which inhibits appetite.

Question 20

What is a mechanoreceptor in animals that is a specialized epithelial cell with deformable stereocilia?

Answer 20

A hair cell.

The stereocilia are deformable projections from epithelial cells called hair cells that are bent by movements of fluid or other stimuli?

Question 21

How are stereocilia different from true cilia?

Answer 21

They do not have motor proteins for movement.

Question 22

What does the stereocilia allow hair cells to detect?

Answer 22

Since they are displaced by movements of fluid or other physical stimuli, it allows animals to detect movements and sound waves.

Question 23

What happens to the ion channels in hair cells when stereocilia bend?

Go through the motion and explain the process.

Answer 23

• Hair cells contain ion channels that open or close when the stereocilia bend. This leads to a change in the cell’s membrane potential.
• When the plasma membrane depolarizes, voltage-gated Ca2+ channels open, resulting in the release of neurotransmitter molecules from the hair cells.
• The neurotransmitters then bind to protein receptors in adjacent sensory neurons and may initiate action potentials that are sent to the CNS.

Question 24

T/F At rest, the neurotransmitter of a hair cell is released in small amounts at all times which results in a steady number of action potentials being generated to another sensory neuron.

Answer 24

True.

Question 25

Since there is a consistent release of neurotransmitter from the hair cell, what does the change in the flow of fluid across the receptor?

Answer 25

It either inhibits the release of the neurotransmitter or excites the release of the neurotransmitter.

Ultimately, this either greatly reduces or greatly increases the FREQUENCY of action potentials.

Question 26

What is the ability to detect and interpret sound waves; present in vertebrates and arthropods?

Answer 26

Audition

Question 27

What is the human hearing range and how do we percieve lower and higher wavelengths?

Answer 27

20-2000 Hz

Short wave lengths have higher frequencies making them seem high pitched while longer wavelengths have lower freqs and sound deeper.

Question 28

What are the three compartments of a mammalian ear?

Answer 28

THe outer, middle and inner ear.

Question 29

What does the outer compartment consist of? (2)

Answer 29

External ear or the pinna (plural, pinnae)

Auditory canal

Question 30

What separates the outer compartment of the ear from the middle compartment? (1)

Answer 30

The tympanic membrane (the eardrum)

Question 31

What are the three bones within the middle compartment?

Answer 31

Ossicles (named malleus, incus, and stapes)

Question 32

What do the three bones in the middle compartment link?

Answer 32

Movement of the ear drum to the oval window.

The oval window is similar to the eardrum and separates the middle of the ear from the inner compartment.

Question 33

What is the inner compartment composed of where one part (means snail) and is a coiled chamber of bone containing hair cells, and also the membrane-like round window which functions for balance?

Answer 33

The coiled chamber is called cochlea

And the membrane-like round window is called the vestibular system.

Question 34

Where does the cochlea and vestibular system send their generated signals?

Answer 34

They send them to the auditory nerve to the auditory cortex of the brain.

Question 35

What are the steps of generating electrical signals in the mammalian ear?

Answer 35

1. Sound waves cause the trympanic membrane (ear drum) to vibrate back and forth.
2. The three bones, the ossicles behind the ear drum, transfer the vibrations to the cochlea.
3. The vibration then moves pressure waves through a fluid called the perilymph which is found in two passages in the cochlea called the vestibular and tympanic canals, which are separated by a tube called the cochlear duct.
4. The waves travel from the vestibular canal to the tympanic canal and eventually strike the round window, where they dissipate.

Question 36

Where do longer-wavelength and shorter-wavelength vibrations travel within the vestibular and tympanic canals?

Answer 36

Shorter wavelengths travel THROUGH the cochlear duct vibrating while the longer wavelengths travel AROUND the cochlear duct.

Question 37

What is a component of the mammalian ear that vibrates back and forth in response to sound and bends the stereocilia in one direction and then the other? This also coats the cochlear duct where wavelengths travel through and around it.

Answer 37

Basilar membrane - formed from elastic fibers tensed across the cochlear duct.

Question 38

What is the coiled structure in the vertebrate ear responsible for detecting sound and is where mechanical virbrations are transduced into electrical signals?

Answer 38

Organ of Corti - this rests on top of the basilar membrane which coats the cochlear duct.

Question 39

What does the organ of Corti contain?

Answer 39

Supporting cells and rows of hair cells.

The stereocilia of the hair cells are embedded in a gelatinous tectorial membrane. The vibration of the basilar membrane bends the stereocilia in one direction and then the other.

When bent in one direction, the hair cells depolarize and release neurotransmitter, which activates adjacent sensory neurons that then send action potentials to the CNS via the auditory nerve.

When bent in the other direction, the hair cells hyperpolarize and stop releasing neurotransmitter. In this way, the frequency of action potentials generated by the sensory neurons is determined by the up-and-down vibration of the basilar membrane.

Question 40

Hearing Facts

The basilar membrane is lined with protein fibers that span its width. These fibers function much like the strings of a guitar. The fibers near the oval and round windows at the base of the cochlea are short and rigid, and they vibrate in response to high-frequency waves. Longer and more resilient fibers are near the other end of the cochlea and vibrate to lower-frequency waves.

For this reason, hair cells closer to the oval and round windows respond to high-pitched sounds, whereas those at the opposite end are triggered by lower-pitched sounds. When we hear a great number of sound frequencies at once, such as at a musical concert, the waves traveling through the cochlea activate hair cells all along the basilar membrane in a physical representation of the music!

These cells stimulate sensory neurons, which send multiple action potentials to the auditory areas of the brain for processing. The most incredible feature of this process, however, is that the mammalian ear and brain can “tune in” to all of these frequencies simultaneously.

Answer 40

N/A

Question 41

What is a vital feature of hearing?

Answer 41

The ability to determine the direction fromwhich a sound originates.

Question 42

How doesan animal locate a sound?

Answer 42

Under most circumstances, sound does not arrive at both ears simultaneously. Sound waves coming from the right, for example, excite the sensory receptors in an animal’s right ear first and the left ear some milliseconds later, and therefore the brain receives action potentials from the auditory nerves of each ear at slightlydiff erent times. The brain interprets the time difference to determine the direction from which a sound came.

Question 43

What is the phenomenon in which certain species listen for echoes of high-frequency sound waves in order to determine the distance and location of an object.?

Answer 43

echolocation

Question 44

What is the sense of balance called, which is another form of mechanoreception?

Answer 44

Equilibrium

Question 45

What is a part of balance in which is an animal’s ability to sense the position, orientation, and movement of its body?

Answer 45

Proprioception

Question 46

What is an organ of equilibrium found in many invertebrate species especially aquatic organisms?

Answer 46

Statocysts

Statocysts are small round structures consisting of an outer sphere of hair cells and one or more
statoliths, which are tinygranules of sand or other dense objects.

When the animal moves, gravity alters the statoliths’ position. If the animal turns on its side, for example, the movement of statoliths stimulates a new set of hair cells to release neurotransmitter, generating action potentials in sensory neurons that inform the brain of the change in body position.

Question 47

What is the organ of balance in vertebrates and is located in the inner ear next to the cochlea?

Answer 47

The vestibular system

The vestibular system is composed of a series of fluid-filled sacs and tubules, which provide information about either linear or rotational movements. The utricle and saccule, the two sacs nearest the cochlea, detect linear movements of the head, such as those that occur when an animal runs, jumps, or changes its posture.

The hair cells within these structures are embedded in a gelatinous substance that contains granules of calcium carbonate called otoliths (from the Latin, meaning ear stones), which are analogous to statoliths.

When the head moves forward, the heavy otoliths are temporarily left behind as they are dragged forward more slowly, and the weight of the otoliths bends the stereocilia of the hair cells in the direction opposite to that of the linear movement.

This bending changes the membrane potential of the hair cells and alters the electrical responses of nearby sensory neurons.These signals are sent to the brain, which uses them to interpret how the head has moved.

Question 48

MOre hearing Facts/Information

Three semicircular canals connect to the utricle at bulbous regions called the ampullae (singular, ampulla).

The function of the semicircular canals is to detect rotational motions of the head. The hair cells in the semicircular canals are embedded in the ampullae in a gelatinous cone called the cupula.

When the head moves, the fluid in the canal shifts in the opposite direction. This movement of fluid pushes on the cupula and bends the stereocilia of the hair cells in the direction of the fluid flow, which is opposite to that of the motion of the head.

The three canals are oriented at right angles to each other, and each canal is maximally sensitive to motion in its own plane.

For example, in humans the canal that is oriented horizontally would respond most to rotations such as shaking the head “no,” whereas the other canals respond to“yes” motions or to tipping the ear to the shoulder. Overall, by comparing the signals from the three canals, the brain can interpret the motion of the head in three dimensions.

Answer 48

N/A

Question 49

What is the microscopic sensory organs in fishes and some toads that allows them to detect movement in surrounding water?

Answer 49

Lateral line system

This sensory system has hair cells that detect changes in water currents brought about by waves, nearby moving objects, and low-frequency sounds traveling through the water.

The lateral line system runs along both sides of the body and the head of the animal.

Small pores let water enter into a lateral line canal. The stereocilia of hair cells of each lateral line organ protrude into a gelatinous structure called a cupula (similar to the cupula of thevertebrate vestibular system).

When the cupula is moved by the water, the stereocilia bend, causing the release of neurotransmitter from the hair cell. This stimulates a response in sensory neurons at the base of the hair cells. The response provides information to the brain about changes in water movement, such as the approach of a predator.

Question 50

[Start 44.3 Thermoreception and Nociception]

What are the two types of thermoreceptors?

Answer 50

Those that respond to hot and those that respond to cold.

Question 51

What are sensory neurons with free peripheral endings in the skin and internal organs?

Answer 51

Nociceptors or pain receptors

Not only do they respond to external stimuli but also internal stimuli such as molecules released into the extracellular fluid from injured cells.

Question 52

What are the signaling molecules that damaged cells release that cause inflammation and make pain receptors more sensitve to painful stimuli?

Answer 52

Prostaglandins.

Anti-inflammatory drugs such as aspirin and ibuprofen reduce pain by preventing the production of prostaglandins.

Question 53

When nociceptors, or pain receptors, send the signals to the CNS for interpretation, where are the signals also sent which holds memories and emotions that will become associated with the nerve signals?

Answer 53

The limbic system in the brain.

And the reticular formation of the brainstem which increases alertness and arousal.

This is an important response to a painful stimulus.

Question 54

[Start 44.4 Electromagnetic Reception]

What do electromagnetic receptors detect?

Answer 54

Radiation within a wide range of the electromagnetic spectrum, including those wavelengths that correspond to visible light, UV light, and infrared light, as well as electrical and magnetic stimuli.

Question 55

What is the mechanism, found in many fish, that is a specialized sensory structure for detecting electric fields in the environment?

Answer 55

Electroreception

Question 56

What are the two types of electroreception?

More explanatory than just two terms.

Answer 56

1. First, many fishes living in dark waters can detect the weak electric field generated by the activity of excitable tissues such as the muscles and nerves of other animals.

To do this, they use exquisitely sensitive electroreceptors located in pores in the head region. These sensory receptors are as heavily innervated as the eyes of these fishes, suggesting the importance of this sense for their survival.

Sharks and rays in particular can detect even the tiny electrical signals generated by the beating hearts of prey hiding beneath a layer of sand on the ocean floor.

2. In a second type of electroreception, some fishes generate their own electric fields with a special organ derived from excitable tissue.

As a fish swims through its environment, nearby objects will disturb this field and this disturbance can be sensed by the fish. This might happen, for example, if a potential prey or predator moved close to the animal. Although electroreception is primarily found in fishes, it is not unique to them.

The platypus, a mammal that lives in the murky waters of streams and ponds, has electroreceptors on the skin of its bill that can detectvery small electric currents produced by its prey.

Question 57

Fun Facts about Infrared radiation and Snakes

Venomous snakes known as pit vipers (a group that includes copperheads and rattlesnakes) can localize prey in the dark with detectors that sense the heat emitted from animals as infrared radiation.

These detectors are located in pits on each side of the head between the eyes and nostrils. Within the pit, a thin, nerve-rich, temperature-sensitive membrane becomes activated in response to infrared waves emitted by live animals.

When the snake detects the heat of the animal, it localizes its prey by moving its head back and forth until both pits detect the same intensity of radiation. This indicates that the prey is centered in front of the snake.

Answer 57

N/A