Sensory Physiology - Textbook Flashcards

Question

Pacinian corpuscles?

Answer 1

Pacinian corpuscles are specialized mechanoreceptors that detect transient pressure and high-frequency vibration. They are located deep in the skin, in joint capsules, and around some organs. Each Pacinian corpuscle consists of a nerve ending surrounded by concentric layers of collagen, resembling the layers of an onion. These layers are highly responsive to rapid changes in pressure, enabling the detection of vibrations and touch stimuli that quickly come and go. When pressure is applied and then changes or moves, it causes deformation of the corpuscle’s layers, mechanically gating the ion channels of the neuron, leading to depolarization and the initiation of an action potential. This makes Pacinian corpuscles one of the fastest-adapting receptors in the sensory system, capable of detecting sudden disturbances transmitted through soft tissues.

Answer 2

1. _Muscle spindles_ on the surface of skeletal muscles monitor the length of the muscle. Each muscle spindle consists of modified muscle fibers called intrafusal fibers enclosed in a connective tissue capsule. 2. _Golgi tendon organs_ are located at the junction between a skeletal muscle and a tendon. These receptors are stimulated by changes in the tension in the tendon. 3. _Joint capsule receptors_ are located in the capsules that enclose the joints. Several types of receptors are in this category, including receptors similar to free nerve endings, Pacinian corpuscles, and Golgi tendon organs. These receptors detect pressure, tension, and movement in the joint.

Answer 3

Tonic receptors provide continuous feedback about the presence of stimuli. They adapt slowly to a stimulus, which means they can signal the duration and steady presence of pressure or touch. This is essential for tasks that require sustained grip or continuous monitoring of object placement, such as holding a tool or maintaining balance. Phasic receptors, on the other hand, respond rapidly but briefly to changes in stimulation, quickly adapting to a constant stimulus. They are particularly useful for detecting changes in our environment, such as the initial contact or release of an object. This helps in tasks requiring fine motor skills, like typing or manipulating small objects, where the onset and cessation of touch need to be precisely registered. Together, these receptors allow vertebrates to integrate detailed information about both static and dynamic changes in their surroundings. This combination enhances sensory perception, providing a comprehensive understanding of tactile stimuli that aids in complex behaviors, improves spatial awareness, and heightens overall survival capabilities.

Answer 4

Insects have complex touch organs because their exoskeletal structure necessitates specialized adaptations for sensing their environment. Unlike mammals, which have their sensory neurons spread across the soft and flexible skin, insects possess a hard, rigid exoskeleton that does not itself have sensory capabilities. As a result, insects require specialized structures like setae (hair-like structures) and campaniform sensilla (dome-shaped structures) which are embedded in the exoskeleton but connected to sensory neurons. These organs amplify mechanical stimuli from the environment and transmit these signals to the nervous system, allowing the insect to detect touch, pressure, vibrations, and even air currents, crucial for navigation, predator avoidance, and communication. This setup enables insects to maintain acute sensory perception despite their protective, non-flexible outer layer.

Answer 5

Many invertebrates have organs called statocysts that they use to detect the orientation of their bodies with respect to gravity. Statocysts are hollow, fluid-filled cavities that are lined with mechanosensory neurons, and contain dense particles of calcium carbonate called statoliths. When the orientation of the animal changes, the statolith moves across the sheet of mechanoreceptors. Each statocyst is composed of a globelike structure called the macula, and three cristae, each oriented in a different plane. The cristae and macula contain statoliths that move in response to mechanical stimuli.

Answer 6

The most sensitive insect ears are called tympanal organs. A tympanal organ consists of a very thin region of the cuticle, called the tympanum, located over an air space similar to the air space in a drum. Sound waves cause the thin tympanum to vibrate, causing the air within the air space to vibrate. A chordotonal organ in this air space detects these vibrations, and sends signals in the form of action potentials to the nervous system. (Tympanal organs are found on many locations on the insect body, including the legs, abdomen, thorax, and wing base!)

Answer 7

Most vertebrate hair cells have a single long cilium, the kinocilium, and many shorter projections, called stereocilia.

Answer 8

The stereocilia are connected to each other and the kinocilium by a series of small fibers that cause the bundle of hair cells to act as a single unit. One particular type of these fibers, called a **tip link**, connects the top of each shorter stereocilium to the side of the adjacent taller one.

Answer 9

Neuromasts are sensory organs found primarily in aquatic vertebrates, including fish and some amphibians, as part of their lateral line system. These organs are key for detecting water currents and vibrations, which helps these animals navigate, orient themselves, hunt prey, and avoid predators in their environment. Neuromasts can be located both externally on the skin and internally in canals within the body. Each neuromast consists of a cluster of hair cells, similar to those found in the inner ear of vertebrates, surrounded by support cells and gelatinous structures called cupulae. The hair cells contain hair-like projections (stereocilia and kinocilia) that extend into the cupula. When water motion or pressure changes displace the cupula, it causes the stereocilia to bend, thereby converting mechanical stimulus into electrical signals that are transmitted to the brain via sensory nerves. This allows the fish to detect and respond to changes in their aquatic environment effectively.

Answer 10

The external structures are called the *outer ear* and in mammals consist of the pinna, which forms the distinctive shapes of mammalian ears, and the auditory canal. The auditory canal leads to the *middle ear*, which contains a series of small bones that transfer sound waves to the *inner ear*. The inner ear is embedded within the skull and consists of a series of fluid-filled membranous sacs and canals.

Answer 11

The *vestibular apparatus* of the inner ear detects movements or changes in body position.

Answer 12

The utricle and saccule are two of the major components of the vestibular system located in the inner ear, primarily responsible for detecting linear accelerations and head position relative to gravity. These structures help with balance and spatial orientation in vertebrates. Utricle: This is slightly larger than the saccule and is oriented horizontally when the head is in an upright position. The utricle is sensitive primarily to horizontal movements and the effect of gravity when the head tilts. It plays a crucial role in detecting acceleration and deceleration movements, such as when starting or stopping walking. Saccule: Located vertically when the head is upright, the saccule responds to vertical movements and contributes to the perception of verticality and vertical acceleration, such as when going up or down in an elevator.

Answer 13

In most vertebrates, the saccule also contains a small extension called the _lagena_. In birds and mammals, the lagena is greatly extended and is called the cochlear duct (in birds), or the _cochlea_ (in mammals)

Answer 14

The utricle and saccule contain a series of mineralized _otoliths_.

Answer 15

The tympanic membrane, also known as the eardrum, is a thin, cone-shaped membrane that separates the external ear from the middle ear and vibrates in response to sound waves.

Answer 16

The oval window is a membrane-covered opening that leads from the middle ear to the inner ear. It receives vibrations from the last of the three small bones in the middle ear—the stapes—and transmits these vibrations to the fluid of the cochlea in the inner ear.

Answer 17

The malleus, incus, and stapes, commonly known as the hammer, anvil, and stirrup, respectively, are the three tiny bones of the middle ear. They form a connected chain that transmits and amplifies sound from the tympanic membrane to the oval window. The malleus attaches to the tympanic membrane, receives vibrations from it, transfers these vibrations to the incus, which in turn passes them to the stapes, and finally, the stapes pushes against the oval window to transmit sounds into the inner ear.

Answer 18

Cetacean outer ears do not perform the sound collecting and amplifying function that is typical of the ears of land mammals. Cetacean ears do not have pinnae, the ear canal is small and plugged with debris and wax, and it does not connect to the tympanic membrane.

Answer 19

Perilymph is the fluid that fills the space within the bony labyrinth, which houses the cochlea, semicircular canals, utricle, and saccule of the inner ear. This fluid is similar in composition to cerebrospinal fluid and is located in the scala tympani and scala vestibuli of the cochlea. Perilymph facilitates the transmission of sound vibrations from the oval window to the cochlear duct and helps to cushion the inner ear's delicate structures.

Answer 20

Endolymph is the fluid within the membranous labyrinth, which is enclosed by the bony labyrinth. It fills the cochlear duct (scala media), the central part of the cochlea, and the membranous portions of the vestibular system. Endolymph is unique in that it has a high potassium ion concentration, contrasting with the high sodium ion concentration of perilymph. This ionic difference is crucial for the electrochemical processes that enable hearing and balance.

Answer 21

The Organ of Corti is the sensory organ of hearing, located within the cochlear duct (scala media) of the cochlea on the basilar membrane. It contains hair cells, which are the actual sensory receptors. These hair cells are mechanically stimulated by the vibration of the basilar membrane caused by sound waves, and they convert these mechanical vibrations into electrical signals that are sent to the brain via the auditory nerve.

Answer 22

The Basilar Membrane is a narrow, flexible membrane that runs the length of the cochlea, separating the scala tympani from the scala media. It supports the Organ of Corti and plays a key role in the auditory process. Its mechanical properties vary along its length (being stiffer at the base and more flexible at the apex), which allows it to resonate at different frequencies along its length. This mechanical property helps in the tonotopic mapping of sound frequencies, where higher frequencies cause peak vibrations closer to the base and lower frequencies peak towards the apex. This differential movement is critical for the perception of pitch.

Answer 23

These two hair cells line the vertebrate inner ear. Inner hair cells detect sounds, and outer hair cells help to amplify sounds.

Answer 24

The round window of the cochlea is a flexible, membrane-covered opening in the bone of the cochlea in the inner ear. It serves as a secondary boundary for the perilymphatic fluid that fills the cochlea. Located just below the oval window, the round window plays a critical role in the functioning of the inner ear by allowing the fluid inside the cochlea to move. When sound waves travel through the cochlea and cause the oval window to move inwards, the round window bulges outward. This complementary movement helps to relieve pressure within the cochlea, enabling the fluid to transmit the sound vibration effectively throughout the inner ear structures for proper auditory processing. The round window thus acts as a pressure release valve, ensuring that the fluid vibrations caused by incoming sounds can propagate along the basilar membrane without any back pressure that would otherwise dampen the sensory response.

Answer 25

Place coding is a mechanism in the auditory system where different frequencies of sound waves are detected by specific regions of the cochlea in the inner ear. This coding occurs on the basilar membrane within the cochlea, which is structured to be more responsive to high frequencies at its base and to low frequencies at its apex. As sound waves enter the cochlea, they generate traveling waves along the basilar membrane, peaking at locations specific to each frequency due to variations in the membrane's stiffness and width. Hair cells located at these peak points convert the mechanical wave into nerve impulses, which are then transmitted to the brain. The brain interprets these signals based on where they originated along the cochlea, allowing it to distinguish different sound frequencies through this tonotopic organization.

Answer 26

If the endolymph of the vertebrate inner ear had high Na+ and low K+, it would significantly disrupt sound transduction. Normally, the endolymph has an unusually high concentration of K+ and a very low concentration of Na+, which is critical for the normal functioning of hair cells within the cochlea. In the typical scenario, when sound waves cause the basilar membrane to move, the hair cells' stereocilia deflect, leading to the opening of mechanically-gated ion channels at their tips. These channels are selectively permeable to K+, allowing K+ ions from the high-K+ endolymph to flow into the relatively low-K+ cytoplasm of the hair cells. This influx of K+ causes depolarization of the hair cell, leading to neurotransmitter release at the base of the hair cell, which then stimulates the auditory nerve fibers. If the ionic composition of the endolymph were reversed to high Na+ and low K+, the usual ion gradient needed for hair cell depolarization would be altered. Na+ ions might enter the cells instead of K+, but because hair cells are specifically adapted to use K+ for depolarization, the normal depolarization process would be inefficient or might not occur at all. This could lead to a failure in neurotransmitter release and, consequently, no transmission of auditory signals to the brain. Essentially, hearing would likely be impaired or completely lost if the ionic gradients were reversed in this manner.

Answer 27

The basilar membrane of the mammalian ear plays a crucial role in the ability to discriminate different sound frequencies due to its unique structure and mechanical properties. It stretches from the base to the apex of the cochlea, varying in width and stiffness along its length. This gradient in physical characteristics is key to its function in frequency discrimination. At the base of the cochlea, the basilar membrane is narrower and stiffer, which makes it responsive to high-frequency sounds. As you move towards the apex of the cochlea, the membrane becomes wider and more flexible, making it more responsive to lower frequencies. This structural variation allows the basilar membrane to act as a frequency analyzer. When sound waves enter the cochlea, they create waves within the cochlear fluid that travel along the basilar membrane. The point at which these waves peak and subsequently cause the greatest displacement of the membrane varies depending on the frequency of the sound. High-frequency sounds cause peak displacements closer to the base of the cochlea, while lower-frequency sounds peak closer to the apex. This spatial variation in vibration along the basilar membrane means that different frequencies of sound stimulate different sets of hair cells located along its length. Each set of hair cells is connected to nerve fibers that transmit these specific frequency signals to the brain, where they are interpreted as sounds of varying pitches. This finely tuned structure allows for the precise discrimination of a wide range of sound frequencies, which is essential for tasks such as understanding speech and appreciating music.

Answer 28

Ciliary photoreceptors have a single cilium protruding from the cell, often with a highly folded ciliary membrane that forms lamellae or disks that contain photopigments, the molecules specialized for absorbing the energy coming from incoming photons. In contrast, in rhabdomeric photoreceptors (also called microvillus photoreceptors) the apical surface that contains the photopigments is elaborated into multiple outfoldings called microvillar projections. Ciliary Photoreceptors: These are primarily found in vertebrates. The light-detecting part of a ciliary photoreceptor, known as the outer segment, is formed from the membrane of a modified cilium. The outer segment contains stacks of membranous discs which house photopigments like rhodopsin. When light hits these pigments, it triggers a signal transduction cascade that ultimately leads to changes in the cell's membrane potential. Ciliary receptors typically participate in image-forming vision and are highly efficient in detecting light due to their intricate organization and concentration of photopigments. Rhabdomeric Photoreceptors: Commonly found in invertebrates such as insects and mollusks, these photoreceptors have a different structure. Their light-sensing part consists of microvilli – tiny, finger-like projections that extend from the cell body. These microvilli contain the photopigments responsible for light detection. Rhabdomeric photoreceptors are part of a larger structure called a rhabdom, where several photoreceptors aggregate their microvilli to increase light absorption. Unlike ciliary receptors, rhabdomeric ones often function more directly through modulation of ion channels by the light-activated photopigments, leading to a change in the cell’s membrane potential.

Answer 29

Rods are highly sensitive to light and function best in low-light conditions, making them crucial for night vision. They do not mediate color vision and have a relatively low spatial resolution, which means they are better at detecting motion and general shapes rather than detailed images. Rods are more numerous than cones in the human retina, with about 120 million rod cells concentrated mainly around the periphery. Cones, on the other hand, require more light to function and are vital for color vision and seeing fine detail. Humans typically have three types of cones, each sensitive to different wavelengths of light (red, green, and blue), which allows for the perception of a wide range of colors. Cones also contribute to high visual acuity, enabling the detection of fine details. There are about 6 million cones in the human retina, mostly concentrated in the central fovea, the area of the retina responsible for sharp central vision.

Answer 30

The retina and the fovea are integral parts of the eye, each serving distinct roles in vision. The retina is a thin layer of tissue that lines the back inside wall of the eye and is responsible for receiving and processing light. This sensory membrane contains millions of photoreceptor cells (rods and cones) that detect light and convert it into electrical signals. These signals are then transmitted to the brain via the optic nerve. The retina is crucial for all aspects of vision, including color perception, low-light vision, and detail resolution. The fovea is a small, specialized region within the retina that is essential for sharp central vision, which is important for activities like reading, driving, and any task where visual detail is of primary importance. The fovea is densely packed with cones, the photoreceptors needed for detecting color and fine detail. This area lacks rods and is structured in such a way that other layers of the retina are displaced, allowing light to directly strike the cones without any dispersion, providing the clearest and most detailed visual input. The foveal region is surrounded by the macula, which also plays a key role in high-resolution vision.

Answer 31

A chromophore is a molecule, or part of a molecule, that is responsible for its color. This component of a molecule absorbs certain wavelengths of light and reflects or transmits others, which is what makes it visible to the human eye as colored. Chromophores play a crucial role in various biological, chemical, and technological applications. In biological contexts, chromophores are key components of visual pigments in the photoreceptor cells of the eye. For example, the chromophore in the rods and cones of the retina is called retinal, a derivative of vitamin A. This particular chromophore undergoes a change in its structure when it absorbs light, triggering a series of biochemical reactions that eventually convert the light signal into a neural signal, a process central to vision.

Answer 32

Opsins are G protein–coupled receptors that are covalently linked to the chromophore. All of these photopigments, however, consist of a vitamin A–derived chromophore bound to a G protein in the opsin gene family (rhodopsin, iodopsin, porphyropsin, melanopsin... etc)

Answer 33

Phototransduction in rhabdomeric and ciliary photoreceptors involves converting light into neural signals, but the mechanisms and structural components of these receptors differ significantly, reflecting their adaptation to different evolutionary paths and functional requirements. Rhabdomeric photoreceptors, primarily found in invertebrates like mollusks and arthropods, use microvillar structures that increase their surface area, where the phototransductive machinery is located. These receptors typically employ a phosphoinositide signaling cascade. The activation of this pathway leads to the opening of ion channels that depolarize the cell, a mechanism that contrasts with how signals are processed in ciliary types. Ciliary photoreceptors, on the other hand, are typical in vertebrates and are characterized by their ciliary structure, which originates from a modified cilium. These photoreceptors utilize a cyclic nucleotide (cGMP) cascade, where light exposure leads to a reduction in cGMP levels, causing ion channels to close and the cell to hyperpolarize. This difference in response to light (hyperpolarization versus depolarization) is a fundamental contrast between the two types. Furthermore, ciliary receptors are often more directly involved in image-forming vision, with their structural setup allowing for a high degree of spatial resolution. Rhabdomeric receptors are sometimes linked to non-image-forming vision, like circadian photoentrainment, although they too can contribute to image-forming vision in some species.

Answer 34

Rods are slender and elongated cells, optimized for high sensitivity to light. They contain a stack of membrane discs that house the photopigment rhodopsin, which is extremely sensitive to light. Rods are highly sensitive to light and are thus responsible for vision under low light conditions (scotopic vision). They do not mediate color vision and have low spatial acuity, but are very effective at detecting motion. Cones are shorter and tapered, and they contain fewer membranous discs than rods. The discs in cones are embedded in the outer membrane rather than being detached, which may facilitate rapid recovery and recycling of photopigments. Cones contain photopigments known as cone opsins, which are less sensitive to light but provide color sensitivity and higher spatial resolution. Cones require more light to function and thus contribute to daytime (photopic) and color vision. There are typically three types of cones in humans, each sensitive to different wavelengths of light (red, green, and blue), which allows for detailed color discrimination and high visual acuity.

Answer 35

1. Flat sheet 2. Cup shaped 3. Vesicular 4. convex

Answer 36

Flat-sheet eyes contain a layer of photoreceptor cells that form a primitive retina lined with a pigmented epithelium. These eyes provide some sense of light direction, and may allow the detection of contrasts between light and dark. Many animal groups have eyes of this type, although they are most often seen in larval forms or as accessory eyes in adults. However, the limpet Patella has a simple patch of pigmented cells that serve as its primary eyes.

Answer 37

Cup-shaped eyes are similar to flat-sheet eyes, except that the retinal sheet is folded to form a narrow aperture. These eyes provide much better discrimination of light direction and intensity, and allow improved detection of contrasts between light and dark. The most advanced cup-shaped eyes, such as those of the Nautilus, a cephalopod, have extremely small, pinhole-sized openings. The pinhole blocks most of the light from entering the eye so that an incoming point light source illuminates a single point on the retina, forming an image. This design is similar to a primitive type of camera called a pinhole camera. Pinhole camera eyes can form images, although the resolution is poor and the image is dim. In order to form a crisp image, the aperture (pinhole) must be small, but a small aperture lets in only a small amount of light, resulting in a dim image. Thus, there is a compromise between image clarity and image intensity.

Answer 38

Vesicular eyes and modern cameras solve this conflict by inserting a lens into the pinhole aperture. A lens takes multiple sources of light and refracts them, focusing the light from a single source onto a single point on the retina. The challenge in developing a good vesicular eye is that the lens must fit precise specifications in order to provide a clear image. However, even a bad lens is better than no lens at all, and provides an improvement over a pinhole camera–type eye. Vesicular eyes are found in some mollusks, but only the cephalopod mollusks have the capacity to alter the shape or position of the lens to focus the image. Like cephalopods, vertebrates have complex vesicular eyes with a lens that can be used to generate a sharp, focused image.

Answer 39

Convex eyes are present in many annelids, mollusks, and arthropods. In these eyes, the individual photoreceptors radiate outward from the base, forming a convex, rather than a concave, light-gathering surface. The most complex convex eyes are the compound eyes of the arthropods.

Answer 40

Ommatidia are the individual units of compound eyes found in arthropods, such as insects and crustaceans. Each ommatidium is a miniature eye itself, complete with a cornea, a lens-like crystalline cone, light-sensitive photoreceptor cells forming a structure called the rhabdom, and pigment cells that isolate each ommatidium to minimize optical interference. This arrangement allows each ommatidium to capture light from a specific part of the visual field, contributing to a pixelated, mosaic view of the environment. Compound eyes excel in detecting motion and have a wide field of view, though they typically offer lower resolution than the camera-type eyes seen in vertebrates. This type of vision is particularly advantageous for navigation, predator avoidance, and prey capture among arthropods. (like the eyes of flies!)

Answer 41

The sclera is the opaque, fibrous, protective outer layer of the human eye that is commonly referred to as the "white of the eye." It forms the supporting wall of the eyeball and is continuous with the clear cornea at the front of the eye. The sclera provides structural integrity and protection for the delicate components of the eye, maintaining its shape and safeguarding it from external injuries or shocks. It is composed mainly of collagen and elastic fiber, which give it both toughness and flexibility. The sclera also serves as an attachment point for the muscles that control eye movement, enabling the eye to look in different directions.

Answer 42

Aqueous Humor: This is a clear, watery fluid that fills the space between the cornea and the lens, known as the anterior chamber of the eye. The aqueous humor is produced by the ciliary body, a structure located behind the iris. This fluid helps to maintain intraocular pressure, provides nutrients to the avascular structures of the eye (like the lens and cornea), and removes metabolic wastes. The aqueous humor flows through the pupil and drains out of the eye via the trabecular meshwork at the angle where the iris and cornea meet. Vitreous Humor: This is a transparent, gel-like substance that fills the much larger space behind the lens, making up the bulk of the eye's volume, known as the vitreous chamber. The vitreous humor is composed mostly of water mixed with collagen fibers and hyaluronic acid, giving it a jelly-like consistency. This structure helps to stabilize the eye and provide physical support to the retina. The vitreous humor also plays a role in maintaining the shape of the eye and, unlike aqueous humor, does not continually regenerate but stays relatively stable throughout life.

Answer 43

The vesicular eye, equipped with a lens, excels in light gathering and image formation, allowing for high visual acuity and the ability to focus on objects at different distances. This type of eye adjusts its aperture to accommodate varying light conditions, enhancing vision in both bright and dim environments. In contrast, the pinhole-type eye, simpler in structure without a lens, provides a greater depth of field and lacks chromatic aberration, meaning all distances are moderately focused without color distortion. However, it cannot match the vesicular eye in terms of image detail and light sensitivity, making the latter more suitable for animals requiring precise visual abilities.

Answer 44

In order to produce focused images of objects at various distances, the eye must ensure that the focal point falls on the retina, a process termed _accommodation_. Because the location and shape of the cornea are fixed, the cornea does not participate in accommodation. Instead, the lens must either change position relative to the retina, or change shape.

Answer 45

Laser eye surgery, which reshapes the cornea to correct refractive errors, would likely be ineffective in aquatic vertebrates. This is because water has a similar refractive index to the cornea, which minimizes the cornea's role in focusing light in aquatic environments. Instead, the lens plays a more critical role in the vision of aquatic vertebrates by providing the necessary refraction to focus light onto the retina. Consequently, altering the cornea's shape would not significantly impact vision for these animals as it does for terrestrial vertebrates, where the cornea substantially contributes to focusing light.

Answer 46

Passive and active electroreception are two distinct methods used by aquatic animals to perceive electrical signals in their environment. Passive electroreception involves detecting the natural electrical fields generated by other organisms, such as muscle contractions or bioelectric fields, which help predators locate prey or enable navigation and communication. This mode is common in sharks, rays, and some bony fish. In contrast, active electroreception is characterized by the emission of electrical pulses by an animal, which then detects the changes in these pulses caused by the presence and properties of objects in the environment, effectively allowing them to "see" through electrical images. This method is used by electric fishes like the electric eel and knifefish, which can control the frequency and amplitude of their electric discharges to obtain detailed information about their surroundings, even in murky waters where other senses might be less effective.

Answer 47

When two wave-type electric fish encounter each other, their electrical signals interact and produce beats. The fish detect the beats, and the beat frequency helps them to interpret the signals coming from other electric fish. The high sensitivity of electric fish to the beats generated by interacting electrical signals explains why these electric fish must be producing an EOD in order to easily detect signals from other electric fish.

Answer 48

Magnetoreception, or the ability to detect magnetic fields (also called magnetoception), is widely distributed throughout the animal kingdom. Migratory birds, homing salmon, and many other organisms use Earth’s magnetic field to help them navigate.

Answer 49

Magnetite is a natural mineral that responds to magnetic fields, and thus could be the basis for magnetoreception in animals. Particles resembling it have been found in the sensory neurons of these animals.

Answer 50

The pit organs of a pit viper, despite using the same type of receptor (TRPA1) as nociceptors (pain receptors in mammals), are specialized to detect infrared radiation (heat) rather than pain. This specificity arises from the adaptation of these receptors in the pit organ to respond primarily to thermal stimuli rather than mechanical or chemical signals that typically induce pain. When a pit viper tracks its prey, the TRPA1 receptors in its pit organs detect the heat emitted by the prey’s body, allowing the snake to effectively locate and target it, especially in low-light conditions. The differentiation in function, despite the similarity in receptor type, highlights a remarkable example of evolutionary adaptation where the same type of receptor is used for different purposes across species.

Answer 51

Although human retinas contain functional cryptochromes, which are capable of restoring magnetoreception in cryptochrome-deficient Drosophila, humans do not exhibit magnetoreceptive behavior. This discrepancy likely arises because the presence of cryptochrome alone is insufficient to confer magnetoreception. In species with known magnetoreception, such as birds, these cryptochromes are part of a more complex sensory system that includes neuronal wiring and brain structures specifically dedicated to processing magnetic field information. Humans lack this specialized neural architecture. Thus, while our cryptochromes can perform similar molecular functions as those in species with magnetoreception, the absence of an integrated system to interpret and use the information derived from magnetic fields results in the lack of magnetoreceptive abilities. This underscores the importance of both molecular components and specific neural circuitries in the development of sensory capabilities.

Answer 52

A sense organ is a specialized structure consisting of multiple tissues that work together to perceive specific types of external stimuli, such as light, sound, or touch, and translate them into signals that can be processed by the nervous system. Examples include the eye, ear, and skin. In contrast, a sensory receptor is a specific cell or cell component, often located within a sense organ, that is specialized to respond to a particular type of stimulus. These receptors can be individual cells or distinct cellular structures that detect mechanical forces, chemicals, temperature, and other physical phenomena. While sense organs contain and support sensory receptors, sensory receptors are the specific sites where stimulus detection occurs.

Answer 53

Labeled-line coding is a sensory encoding system where specific neurons or pathways are dedicated to conveying information about one type of stimulus. In this model, each sensory receptor is "labeled" for a specific modality (e.g., taste, sound, light), and the brain interprets the input from each receptor along a direct, unambiguous line, assuming that any activation signals the presence of its specific stimulus. An example of labeled-line coding can be seen in the gustatory system (taste). Taste receptors on the tongue are specialized to detect one of the basic tastes: sweet, sour, salty, bitter, and umami. Each type of taste receptor responds to particular chemical components in food. For instance, sweet receptors respond to sugars like glucose and fructose. When these receptors are activated, they send signals through specific neural pathways to the brain, which interprets these signals as the taste "sweet." This direct pathway from a specific type of receptor through a dedicated set of neurons to a brain region that interprets the signal as a specific taste demonstrates the labeled-line coding model.

Answer 54

Mechanoreception: Detection of mechanical changes or disturbances such as touch, sound, pressure, and vibration. Examples include tactile receptors in the skin and hair cells in the auditory and vestibular systems. Chemoreception: Sensing chemical stimuli, which includes taste (gustation) and smell (olfaction). Chemoreceptors also detect internal body chemicals, like CO2 levels in the blood. Photoreception: Sensing light, involved in vision. Photoreceptors in the eyes, such as rods and cones in vertebrates, detect light intensity and color. Thermoreception: Detecting changes in temperature, enabling the sensation of heat and cold. Certain receptors respond to external temperature changes, while others monitor the internal temperature of the body. Electroreception: Sensing electrical fields, which is especially prominent in aquatic animals like sharks and rays, helping them to navigate and locate prey by detecting the electrical impulses emitted by other organisms. Magnetoreception: Sensing magnetic fields, which is thought to aid in navigation, particularly in migratory species like birds, turtles, and some fishes. Nociception: Detecting harmful stimuli that could cause injury, leading to the sensation of pain. Nociceptors are present in skin, joints, and organs across various animal groups.

Answer 55

The relationship between the intensity of a stimulus and the response of primary afferent neurons is characterized by an increase in the frequency of action potentials as stimulus intensity increases. This is known as rate coding. Primary afferent neurons encode changes in stimulus intensity by varying the rate at which they fire action potentials. A more intense stimulus triggers the neuron to fire more rapidly, which is interpreted by the central nervous system as a stronger stimulus. This modulation allows the nervous system to detect and respond to changes in the environment by translating physical stimulus intensity into a neural code that reflects different levels of stimulus strength.

Answer 56

Mammalian odorant and pheromone receptors both function as G Protein-Coupled Receptors (GPCRs) and are located in the nasal tissues, playing critical roles in the detection of airborne chemicals. However, they differ significantly in their specific functions and locations. Odorant receptors are found in the olfactory epithelium and detect a wide range of volatile chemicals, contributing broadly to the sense of smell. In contrast, pheromone receptors are typically located in the vomeronasal organ (VNO) and are specialized to detect pheromones, which are specific chemicals released by other individuals of the same species to trigger particular behavioral or hormonal responses. This specialization allows mammals to respond to environmental odors and social signals distinctly, ensuring both survival and reproductive success.

Answer 57

In both mammals and insects, the receptors involved in odorant detection are protein structures embedded in the membranes of olfactory sensory neurons, which bind specific molecules from the environment and initiate a signal transduction pathway leading to a neural response. However, there are key differences in their molecular structure and diversity. Mammalian olfactory receptors are primarily G-protein-coupled receptors, comprising a large gene family with about 1,000 different receptors in humans, allowing a broad and nuanced perception of smells. Insects, on the other hand, utilize not only G-protein-coupled receptors but also ionotropic receptors (e.g., the insect olfactory receptors and ionotropic glutamate receptors), which are typically more direct in converting chemical binding into electrical signals. Insects tend to have fewer types of olfactory receptors than mammals but achieve specificity and diversity in odor detection through various combinations of these receptors and their unique patterns of expression.

Answer 58

Gustatory receptors in the taste system detect five primary types of tastants: sweet, umami, bitter, salty, and sour, each using distinct signal transduction mechanisms. Sweet, umami, and bitter tastes are detected through G-protein-coupled receptors (GPCRs). For sweet and umami tastes, activation of these GPCRs leads to a signaling cascade involving the release of second messengers that ultimately result in neurotransmitter release. Bitter taste utilizes a similar GPCR system but often involves a larger family of receptors, allowing detection of a wide variety of potentially toxic substances. In contrast, salty and sour tastes generally involve ion channels rather than GPCRs. Salt taste is primarily detected through sodium channels that directly allow sodium ions to enter the cell, generating an action potential. Sour taste detection is mediated by ion channels that detect the presence of protons (H+), which can block specific potassium channels or activate proton-specific channels, leading to depolarization of the taste cell. Thus, while sweet, umami, and bitter rely on metabotropic mechanisms, salty and sour are governed by ionotropic mechanisms, reflecting their direct chemical nature.

Answer 59

The gustatory systems of mammals and insects are distinct both structurally and functionally, tailored to their specific ecological needs. Mammalian taste receptors are localized in taste buds on the tongue, responding to five basic tastes through mechanisms like G-protein-coupled receptors for sweet, umami, and bitter, and ion channels for salty and sour. In contrast, insects have gustatory receptors on various body parts, such as mouthparts, legs, and antennae, which detect a range of chemical cues using gustatory receptor proteins that often directly influence ion channels. While mammalian taste primarily aids in food selection, insect gustation is integral not only to feeding but also to behaviors such as oviposition and pheromone detection, demonstrating a broader ecological application.

Answer 60

The major families of mechanoreceptor proteins involved in touch, proprioception, and hearing in various organisms include the Piezo, TREK/TRAAK, and DEG/ENaC protein families. Piezo proteins are critical for detecting mechanical forces on the skin and internal organs, playing a pivotal role in touch and proprioception. The TREK/TRAAK family, part of the larger group of potassium channels, is involved in responding to mechanical stretch and temperature changes, influencing both proprioceptive and nociceptive pathways. DEG/ENaC proteins, sodium channels, are essential for mechanosensation in both vertebrates and invertebrates, crucial for tasks ranging from touch sensation to hearing. These diverse families allow organisms to detect and respond to a wide range of mechanical stimuli, from gentle touch to the vibrations associated with sound.

Answer 61

Merkel cells: Slowly adapting; respond to light touch, detail about object shapes and textures. Meissner's corpuscles: Rapidly adapting; sensitive to changes in texture and low-frequency vibrations. Ruffini endings: Slowly adapting; detect skin stretch, important for finger position and object manipulation. Pacinian corpuscles: Rapidly adapting; respond to high-frequency vibrations and deep pressure.

Answer 62

Outer hair cells in the cochlea play a crucial role in hearing not by transmitting sound information to the brain, but by enhancing auditory sensitivity and frequency resolution. These cells act as mechanical amplifiers; when they detect sound, they change their length and stiffness in response to the vibrations. This action increases the motion of the basilar membrane, selectively amplifying specific frequencies of sound. By doing so, outer hair cells fine-tune the vibrations within the cochlea, making it possible for inner hair cells to transmit more precise signals through afferent neurons to the brain. This amplification is essential for normal hearing sensitivity and for the ability to discern different sound frequencies, contributing significantly to our detailed and nuanced perception of sound.

Answer 63

In the vertebrate ear, several mechanisms amplify environmental sound stimuli to enhance hearing. The outer ear captures sound waves and funnels them toward the tympanic membrane (eardrum), which vibrates in response. These vibrations are then mechanically amplified by the ossicles (malleus, incus, and stapes) in the middle ear, effectively increasing the force of the sound waves as they are transferred to the oval window of the cochlea. Inside the cochlea, the movement of fluid within the cochlear duct displaces the basilar membrane, translating these mechanical forces into neural signals. Additionally, outer hair cells in the organ of Corti dynamically respond to the fluid motion by changing length, which serves to selectively amplify specific frequencies by enhancing the movement of the basilar membrane, thereby providing a finer auditory sensitivity and selectivity. These mechanisms collectively enable the ear to convert minute variations in air pressure into detailed auditory information.

Answer 64

Ciliary Photoreceptors Evolution: This theory suggests that photoreceptors evolved from a common ancestral ciliary cell type that originally functioned in light detection. Over time, these cells specialized and adapted to more complex vision tasks in animals such as vertebrates. The ciliary photoreceptors, like those found in human rods and cones, utilize a single cilium that extends from the cell body and is embedded with photopigments, which are crucial for capturing light. Rhabdomeric Photoreceptors Evolution: Alternatively, rhabdomeric photoreceptors, primarily found in invertebrates like mollusks and arthropods, might have evolved from a distinct lineage of light-sensitive cells. These photoreceptors are characterized by their microvillar structures, which are densely packed with photopigments. They likely arose from an ancestral cell that used microvilli for light absorption, diversifying later into the more complex rhabdomeric organs seen in many invertebrates today.

Answer 65

First, rods contain a high concentration of the photopigment rhodopsin, which is extremely sensitive to low light levels. This allows rods to respond to even a few photons of light, making them much more sensitive than cones, which require brighter light. Additionally, rods have a structure that maximizes their light-absorbing capability; they feature a long, cylindrical outer segment packed with stacks of membrane discs where rhodopsin is embedded. This design increases the surface area available for light capture. Moreover, rods benefit from a phenomenon called spatial summation, where signals from multiple rods converge onto a single neuron, amplifying the light signal and enhancing sensitivity in low-light conditions. This makes rods particularly well-suited for night vision and seeing in poorly lit environments.

Answer 66

Rods: Specialized for low-light vision, rods are highly sensitive to light and allow for night vision but do not support color discrimination. Cones: Responsible for color vision and high-acuity vision in well-lit conditions, cones are less sensitive to low light but crucial for detecting fine detail and different colors. Horizontal cells: These cells integrate and regulate input from multiple photoreceptor cells, aiding in contrast enhancement and spatial resolution by modulating the output of rods and cones. Bipolar cells: Acting as a relay between photoreceptors (rods and cones) and ganglion cells, bipolar cells transmit signals from the photoreceptors to the ganglion cells, with different types either enhancing or inhibiting the signal based on the visual information received. Amacrine cells: These cells interact at the level of the inner synaptic layer, influencing the bipolar cell-ganglion cell synapses, and are involved in complex processing tasks like image refinement and motion sensitivity. Retinal ganglion cells: The final output neurons of the retina, ganglion cells receive inputs from bipolar and amacrine cells and send visual information to the brain via the optic nerve, encoding and transmitting image details critical for further visual processing.

Answer 67

In mammals, the ability to focus on objects at varying distances, known as accommodation, is achieved by changing the shape of the lens. The lens is a flexible, transparent structure situated behind the iris and is controlled by the ciliary muscles surrounding it. When viewing objects that are close, the ciliary muscles contract, which reduces the tension on the zonule fibers connected to the lens, allowing the lens to become thicker and more curved. This increased curvature enhances the lens's refractive power, enabling it to focus light from near objects onto the retina. Conversely, when viewing distant objects, the ciliary muscles relax, the zonule fibers tighten, and the lens becomes flatter, decreasing its curvature and refractive power to focus light from far away onto the retina. This dynamic adjustment of the lens shape is crucial for maintaining clear vision across different visual distances.

Answer 68

The pit organs in snakes, such as pit vipers, and the thermoreceptors found in other vertebrates both serve the function of detecting temperature changes but differ significantly in their sensitivity and ecological roles. Pit organs are highly specialized infrared sensory receptors that enable snakes to detect very slight changes in ambient temperature, allowing them to "see" the heat radiated by warm-blooded prey, even in total darkness. This organ contains a membrane that can detect temperature changes as minute as 0.003°C, which is much more sensitive than the general thermoreceptors found in other vertebrates. In contrast, typical vertebrate thermoreceptors are distributed throughout the skin and internal organs and help regulate body temperature by responding to external and internal temperature changes, but with less precision compared to the specialized pit organs of snakes. Thus, while both serve thermoreceptive functions, the pit organs are adapted for precise hunting and navigation, whereas general thermoreceptors are crucial for overall thermoregulation.

Answer 69

Active electrolocation and echolocation are sensory modalities used by different animal species to navigate and locate objects in their environment, but they function through distinct mechanisms and are adapted to different ecological niches. Active electrolocation, utilized by certain fish species such as the elephant nose fish, involves the generation of electrical fields and the detection of distortions in these fields caused by objects or other living organisms. This method is particularly effective in murky or dark waters where visual cues are limited. In contrast, echolocation, employed by bats and some marine mammals like dolphins, involves emitting sound waves and detecting the echoes that bounce back from objects. This method is highly effective in air or clear water environments, enabling precise localization and identification of objects over greater distances. While both systems process environmental information to create a perceptual map of the surroundings, they utilize different physical phenomena—electric fields versus sound waves—to achieve this.

Answer 70

Mechanoreceptors and photoreceptors in the eye are specialized to respond to different types of stimuli due to their distinct structures and activation mechanisms. Mechanoreceptors, such as those in the skin and other tissues, are sensitive to mechanical forces like pressure or stretch, but they lack the molecular machinery necessary to respond to light, which requires a photopigment that changes structure when struck by photons. Conversely, the retina's photoreceptors, rods, and cones contain these photopigments specifically tuned to detect light. However, a sufficiently large mechanical stimulus, such as pressing on the eyeball, can indirectly affect the retina and photoreceptors, creating a sensation of light (known as phosphenes), not because the mechanoreceptors are responding to light, but because the mechanical pressure is indirectly stimulating the photoreceptors. This phenomenon illustrates how sensory systems are finely tuned to their specific types of stimuli yet can sometimes cross-activate under abnormal conditions.

Answer 71

Taste receptors primarily use labeled-line coding to convey specific taste information from the tongue to the brain. In this system, each receptor is tuned to a particular type of tastant (sweet, sour, salty, bitter, or umami) and sends its signal along a dedicated neural pathway. This allows the brain to recognize distinct tastes based on which neurons are activated. For example, cells that respond to sweet stimuli connect to specific brain regions associated with the perception of sweetness, ensuring that taste signals are not mixed up, allowing for clear and distinct taste perceptions. This system illustrates how labeled-line coding provides specificity and accuracy in sensory processing, essential for the discernment of different tastes.

Answer 72

Receptors for fine touch, such as Merkel cells and Meissner's corpuscles, are typically found in the shallow layers of the skin because these layers are more sensitive to light touch and slight pressure, allowing for greater precision in sensing textures and fine details. These receptors are adapted to detect subtle deformations of the skin's surface, making them well-suited for tasks like reading Braille or feeling the texture of an object. Conversely, receptors for stronger touch stimuli, such as Pacinian corpuscles, are located deeper in the dermis or in subcutaneous tissue. These deeper receptors are adapted to respond to more significant pressures and vibrations, which travel further into the body. Their deeper location helps in buffering against damage and provides a robust response to high-pressure stimuli, important for proprioception and awareness of our body's interactions with the environment.

Answer 73

Hair cells in sensory systems such as the inner ear possess prominent cilia called stereocilia on their apical surface, which significantly enhance their sensitivity to mechanical stimuli. These cilia amplify minute movements through leverage, transforming small vibrations into larger motions that effectively open ion channels linked by tip links. This mechanism allows the stereocilia to convert mechanical energy into electrical signals in a highly sensitive and directional manner. The extensive array and organization of these cilia increase the surface area, capturing more stimuli and providing precise detection of the direction and magnitude of mechanical forces. Thus, these cilia are fundamental in translating physical motion into neural information, crucial for hearing and balance.

Answer 74

The inner ears of most vertebrates contain three semicircular canals, each oriented roughly perpendicular to the other two. This arrangement allows for the detection of rotational movements across all three dimensions of space. The canals are filled with fluid, and each canal responds to rotations in a different plane: horizontal, vertical, and oblique. As the head moves, the fluid inside the respective canal lags behind due to inertia, and this movement relative to the canal walls bends hair cells embedded in a gel-like structure called the cupula located at one end of each canal. The bending of these hair cells generates nerve impulses that inform the brain about the direction and speed of the rotation. Having three canals provides a full spatial representation necessary for maintaining balance and coordinating movement accurately in a three-dimensional world.

Answer 75

Animals with excellent peripheral vision, such as many prey species, tend to have a retina that is more uniformly populated with photoreceptor cells across a wider area, allowing them to detect movements and threats from a broader range of angles. This includes a larger distribution of rods, which are more sensitive to light and motion than cones, enhancing their ability to see in lower light conditions which often characterize peripheral regions of the visual field. In contrast, animals with poor peripheral vision, like predators that focus on detail and color in the center of their visual field, often have a denser concentration of cones in a central area known as the fovea, enabling sharp central vision but reducing the scope and sensitivity of their peripheral vision. This specialization allows them to better capture and focus on specific targets directly ahead of them.

Answer 76

Humans can distinguish thousands of colors despite having only three types of cone photoreceptors (red, green, and blue) through a process known as color mixing and the phenomenon of color opponency. Each type of cone responds to different wavelengths of light, and the brain combines the input from these cones in various proportions to perceive a wide spectrum of colors. This trichromatic theory of color vision explains how various combinations and intensities of the red, green, and blue signals can create the perception of virtually any color. Additionally, the color opponency mechanism, which involves the processing of colors in opposing pairs (red-green, blue-yellow), enhances color discrimination and helps in distinguishing subtle differences in color despite the limited types of cone receptors.

Answer 77

If an individual had a degenerative disease that destroyed the horizontal cells of the retina, several significant changes in visual perception could be predicted. Horizontal cells are crucial for integrating and regulating the input from multiple photoreceptors, particularly influencing contrast enhancement and color perception by inhibiting nearby photoreceptors and bipolar cells. Without horizontal cells, the individual would likely experience a decrease in visual contrast, making it harder to distinguish edges and contours. Additionally, there might be a reduction in the ability to perceive fine detail and a decrease in the dynamic range of vision, leading to difficulties in adapting to different lighting conditions. Overall, the visual system's ability to process complex visual scenes effectively would be significantly impaired.

Sensory Physiology - Textbook Flashcards

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