AP Bio Chapter 38: Sense Organs

Golgi tendon spindles

-A type of proprioceptors buried in the tendons that attach muscle to bone -When the muscles are stretched too much, they generate nerve impulses that cause the muscles to relax

Muscle spindles

-A type of proprioceptors embedded in muscle fibers -If a muscle relaxes too much, they stretch, generating nerve impulses, causing the muscle to contract slightly

Olfactory bulbs

-An extension of the brain -Have direct connections with the limbic system and its centers for emotions and memories

How odor works

-An odor contains many odor molecules that activate a characteristic combination of receptor proteins -The neurons communicate this information via the olfactory tract to the olfactory areas of the cerebral cortex

Image forming eyes are found in 4 invertebrate groups:

-Annelids -Cnidarians -Molluscs -Arthropods (have compound eyes)

Farsightedness or hyperopia

-Cannot easily focus on nearby objects but are able to focus on distant objects -Often have a shortened eyeball and when they try to focus on close objects, the image is focused behind the retina

Sensory Receptors

-Capable of detecting changes in internal or external conditions, and can communicate that information to the central nervous system -Participate in Sensory Transduction -Some are modified neurons, while some are specialized cells closely associated with neurons

Compound eyes

-Composed of many individual units called ommatidia, each possessing all the elements needed for light reception -The cornea and crystalline cone function as lenses to direct light rays toward the photoreceptors, which generate nerve impulses that pass to the brain via optic nerve fibers. -Outer pigment cells absorb stray light rays to prevent the rays from passing to one visual unit to another.

Cochlear implant

-Consists of an external device that sits behind the ear and an internal device that has been surgically implanted under the skin -‎The external part picks up noises and sounds from the surrounding environment and converts them into electrical impulses ‎-These impulses are directly sent to different regions of the auditory nerve and then to the brain

Outer Ear

-Consists of the pinna and the auditory canal -The opening of the auditory canal is lined with fine hair and glands -Glands that secrete earwax, or cerumen, are located in the upper wall of the auditory canal

Ciliary muscle

-Controls the shape of the lens -Found within the ciliary body -When viewing a distance object, it is relaxed, causing the suspensory ligaments attached to the ciliary body to be taut; the lens remains flat -When viewing a nearby object, visual accomodation occurs; it contracts, releasing tension of the suspensory ligaments and the lens becomes rounder due to natural elasticity

Gravitational Equilibrium

-Depends on the utricle and saccule, which are two membranous sacs located in the vestibule -‎These sacs contain little hair cells whose stereocilia are embedded within a gelatinous material called an otolithic membrane -‎Calcium carbonate molecules, or otoliths, rest on this membrane -‎The utricle is sensitive to horizontal movements while the saccule responds to vertical movements

Human Eye

-Elongated sphere about 2.5 cm in diameter -‎Has three layers: the sclera, the choroid, and the retina

Panoramic vision

-Found in animals with eyes facing sideways -Their visual field is very wide -Mainly seen in prey in order for them to spot predators

Lateral line system

-Found in fish; guides them in movement and in locating fellow fish, predators, prey and mates -Usually runs along the fish on both sides from the gills to the tail; detects water currents and pressure waves from nearby objects. -Water from the environment enters tiny canals that contain hair cells with cilia embedded in a gelatinous cupula. -When the cupula bends due to pressure waves the hair cells initiate nerve impulses

Cutaneous receptors

-Found in the dermis, making the skin sensitive to touch, pressure, pain and temperature -‎At least two types of free nerve endings in the epidermis are thermoreceptors: both warm and cold receptors contain ion channels with activities that are affected by temperature -Cold receptors generate nerve impulses at an increased frequency as the temperature drops -Warm receptors increase activity as temperature rises

Nociceptors

-Free nerve endings which act as pain receptors -Found in the skin and many internal organs -Can be sensitive to extreme temperatures or excessive pressure -Evolutionary advantageous b/c they alert us to potential danger

Two sensory functions of the ear

-Hearing -Balance (Equilibrium) *The mechanoreceptors for both of these functions are located in the inner ear consisting of hair cells with stereocilia (long microvilli) that are sensitive to mechanical stimulation

Tympanum

-Helps insects to hear; a thin membrane that stretches across an air space of some sort, such as the tracheae -The membrane is stimulated to vibrate by sound waves which directly activate nerve impulses in attached receptor cells

Taste buds

-In adult humans: 3,000 Located primarily on the tongue -Lie along the wall of the papillae -Isolated ones are present on the hard palate, the pharynx, and the epiglottis -Have supporting cells and a number of elongated taste cells that end in microvilli; these microvilli bear receptor proteins for certain molecules

Olfactory cells

-In humans, there are approx. 10 ~ 20 million of these cells -Located within the olfactory epithelium in the roof the nasal cavity -They are modified neurons -Each cells ends in a tuft of 5 olfactory cilia that bear receptors proteins for odor molecules -Each olfactory cell only has 0.1% different types of receptor proteins -Nerve fibers from similar olfactory cells lead to the same neuron in the olfactory bulb

Rotational Equilibrium

-Involves the semicircular canals which are arranged so that there is one in each dimension of space -‎the base of each of the three canals, called the ampulla, is slightly enlarged -‎Inside the ampullae: little hair cells whose stereocilia are embedded within a gelatinous material called a cupula -Each ampulla responds to head movements in a different plane of space -‎As endolymph within a semicircular canal flows over and displaces a cupula, the stereocilia of the hairs bend and the pattern of impulses which carried by the vestibular nerve to the brain changes -The brain uses this information to maintain equilibrium through appropriate motor output to various skeletal muscles that can right our position in space as needed

Gravitational equilibrium organs

-Known as statocysts -Found in cnidarians, molluscs, and crustaceans, which are arthropods -When the head stops moving, the statolith stimulates the cilia of the closest hair cells, which generate impulses that are interpreted as the position of the head.

Central region of the retina

-Known as the fovea centralis -Cone cells are densely packed -Light is normally focused here when we look at an object directly -Vision is most acute here

Macular degeneration

-Leading cause of blindness for people in the U.S. under the age of 65 -Capillaries supplying the retinas become damaged -Hemorrhages and blocked vessels can occur

Retina

-Located in the posterior compartment -Contains photoreceptors called rod cells and cone cells : the rods are very sensitive to light and are distributed in the peripheral region of the retina and provide us with peripheral vision and perception of motion : the cones are found mainly in the fovea centralis and require bright light, are sensitive to different wavelengths of light, allowing humans to view color and fine details -The rod and cone cells synapse with the bipolar cells, which further synapse with the ganglion cells that initiate nerve impulses

Sense of balance in humans

-Mechanoreceptors in the semicircular canals detect rotational/angular movement of the head (rotational equilibrium) -Mechanoreceptors in the utricle and saccule detect straight-line movement of the head in any direction. (gravitational equilibrium)

Four types of cutaneous receptors that are sensitive to touch

-Meissner corpuscles and Krause end bulbs: concentrated in the fingertips, lips, palms, tongue, nipples, penis, and clitoris -Merkel disks: found where the epidermis meets the dermis -Root hair plexus: a free nerve ending which winds around the base of a hair follicle and fires if a hair is touched

Three distinct divisions of the ear

-Outer -Inner -Middle

Two types of cutaneous receptors which are sensitive to pressure

-Pacianian corpuscles: onion shaped sensory receptors that lie deep within the dermis -Ruffini endings: encapsulated by sheaths of connective tissue and contain lacy networks of nerve fibers

Location of chemo-receptors in different creatures

-Planarians: Concentrated in the auricles located on the sides of their heads -Insects: Taste receptors in their mouth -Housefly: Feet -Crustaceans: Appendages and antennae -Fish: Scattered over surface of skin -Snakes: Jacobson's organs on roof of the mouth

Somatic senses

-Senses whose receptors are associated with the skin, muscles, joints, and viscera -‎Three types of receptors: proprioceptors, cutaneous receptors, and pain receptors -‎Send nerve impulses via the spinal cord to the primary somatosensory areas of the cerebral cortex

Mechanoreception

-Sensing physical contact on the surface of the skin or movement of the surrounding environment -The simplest mechanoreceptors are free nerve endings found in the skin -Most complex mechanoreceptors are found in the middle and inner ear of vertebrates

5 main types of taste receptors

-Sweet -Sour -Salty -Bitter -Umami (savory)

How taste buds work

-Taste buds open at a taste pore -Microvilli project into the taste pore -When molecules bind to the receptor proteins on the microvilli, nerve impulses are generated in associated nerve fibers -These nerve impulses travel to the brain, where they get interpreted as taste

Kinocilium

-The largest stereocilium -If stereocilia move towards it, nerve impulses increase in the vestibular nerve -‎If stereocilia move away from it, nerve impulses decrease in the vestibular nerve

Three layers of neurons found in the retina

-The layer closest to the choroid contains rod and cone cells -The middle layer contains bipolar cells -Innermost layer has ganglion cells whose sensory fibers become the optic nerve

Echolocation

-The production of very high frequency sounds -Used for learning about objects in the environment by listening for echoes

Choroid

-Thin, dark brown layer containing many blood vessels and a brown pigment that absorbs stray light rays -Towards the front of the eye, it thickens and forms the ring shaped ciliary body and a thin circular muscular diaphragm, the iris.

Stereoscopic vision

-Three dimensional vision, found in animals with two front-facing eyes -The visual fields overlap and each eye is able to see an object from a different angle -Mainly seen in predators

Proprioceptors

-mechanoreceptors involved in reflex actions that maintain muscle tone, the body's equilibrium, and posture

Evolutionary advantage of hearing

-receive information from a distance and from any direction -‎avoiding danger, finding mates, detecting prey, and communication

Process of hearing: the pressure is passed to the fluid within the cochlea

1. Sound waves enter the auditory canal 2. ‎ When a large number of sound waves strike the tympanic membrane, it vibrates slightly 3. ‎The malleus takes the pressure from the inner surface of the tympanic membrane and passes it by means of the incus to the stapes in such a way that the pressure is multiplied about 20 times as it moves 4. ‎The stapes strikes the membrane of the oval window, causing it to vibrate

Aqueous humor

A basic, watery solution that fills the anterior compartment between the cornea and the lens; provides a fluid cushion and nutrient/waste transport for the eye

Rhodopsin

A complex molecule made up of the protein opsin and a light-absorbing molecule known as retinal (a derivative of Vitamin A) -When a rod absorbs light, it splits into the two parts, leading to a cascade of reactions and the closure of ion channels in the rod cell's plasma membrane; the release of inhibitory transmitter molecules from the rod's synaptic vesicles stops

Volume

A function of the amplitude of sound waves. -Louder noises cause the fluid in the vestibular canal to exert more pressure and the basilar membrane to vibrate to a greater extent. This increased stimulation is interpreted by our brains as volume. -The brain interprets the tone of a sound based on the distribution of the stimulation of hair cells

Tapetum lucidum

A membrane found in the back of the eye in many vertebrates -Reflects light back into the photoreceptor cells of the retina to increase sensitivity to light

Conjunctiva

A thin layer of epithelial cells forms a mucous membrane called ____ that covers the surface of the sclera and keeps the eyes moist

Nearsightedness or myopia

Able to focus on close objects but cannot focus on objects far away -Often have an elongated eyeball, and when they attempt to look at a distant object, the image is brought to focus in front of the retina

Diurnal

Active during the day

Perceptions

Any sensory stimuli which humans, and possibly other animals, become aware of *Many sensory impulses are not received at the conscious level of the brain

Lens

Attached to the ciliary body by ligaments; divides the cavity of the eye into 2 portions and helps form images

Middle Ear

Begins at the tympanic membrane (eardrum) and ends at a bony wall with two small openings (the oval window and the round window) covered by membranes. -Three small bones (collectively called the ossicles) are found between the tympanic membrane and the oval window. -Individually, they are called the: -Malleus (hammer) -Incus (anvil) -Stapes (stirrup) because their shapes resemble said objects -The malleus adheres to the tympanic membrane, while the stapes touches the oval window

Diabetic retinopathy

Capillaries to the retina become damaged secondary to diabetes

Most frequently performed surgery in the US

Cataract surgery

Pheromones

Chemical messages passed between individuals

The most common cause of blindness in adults

Diseases of the retina

Auditory tube aka eustachian tube

Extends from each middle ear to the nasopharynx, permits equalization to air pressure

Three areas of the inner ear

Filled with fluids Composed of three areas: -semicircular canals and vestibule: concerned with equilibrium -cochlea: concerned with hearing; spirals

Tympanal organs

Found in the thorax of grasshoppers and front legs of crickets

Camera-type eye

Found in vertebrates and certain molluscs (squids, octopi) -A single lens focuses an image of the visual field on photoreceptors, which are closely packed together -In vertebrates: the lens changes shape to help focusIn molluscs: the lens moves back and forth to focus

Function of earwax

Helps to guard the ear against the entrance of foreign materials

LASIK

Laser assisted in situ keratomileusis -A laser removes part of the cornea to flatten it in order to achieve optimum vision

Blind spot

No vision is possible in this area because there are no cones or rods present

Sclera

Opaque, white fibrous layer that covers most of the eye -In front of the eye, it becomes the transparent cornea, the window of the eye

Carotenoids

Pigments that can be easily converted into Vitamin A in the body

Three different types of cones in the retina

Red Green Blue -Each pigment is made up of opsin and retinal, but a slight difference is present in the opsin structure of each, giving them different absorption patterns

Pupil

Regulates light entering the eye

Chemoreceptors

Respond to a diverse range of chemical substances, such as: -Oxygen in the blood -Molecules of food in the mouth or nasal passages -Most primitive sense; found almost universally in animals

Photoreceptors

Respond to light energy -Found in human retinas

Retinal detachment

Retina peels away from the supportive choroid layer

Glaucoma

Second most common cause of blindness in the US -Drainage system of the eyes fails and aqueous humor builds up and increases intraocular pressure

Photoreceptors

Sensory receptors that are sensitive to light; not all of them form images like our eyes do (such as a planarias eye spots)

Papillae of the tongue

Small elevations that are visible to the unaided eye

Thermoreceptors

Stimulated by changes in temperature -Located in the hypothalamus and skin

Mechanoreceptors

Stimulated by mechanical forces, usually pressure -Responsible for detecting changes that are perceived, such as sound/touch -Maintain equilibrium, balance, and proper tone in muscles and joints

Iris

The colored portion of the eye that regulates the size of the pupil

Sensory Transduction

The conversion of a stimulus into a nerve impulse -The plasma membrane of a sensory receptor contains proteins that react to a stimulus; if the stimulus is sufficient, nerve impulses begin, which are carried by a sensory nerve fiber within the PNS to the CNS -Occurs once light has been focused on the photoreceptors in the retina

Vertigo

The feeling that a person or their environment is moving when no motion is occurring

Cataracts

The lens becomes opaque and incapable of transmitting light rays

In the most basic sense, hearing is caused by _______

The vibration in a surrounding medium to resonate some part of the animal's body; this resonance is converted into electrical signals through some means that can be interpreted by the animal's brain

Inner Ear

When a cochlea cross-section is examined, the vestibular canal, cochlear canal, and the tympanic canal become visible. The vestibular and tympanic canals are filled with perilymph (continuous with the cerebrospinal fluid) The cochlear canal contains endolymph, which is similar in composition to tissue fluid -Along the length of the basilar membrane, which forms the lower wall of the cochlear canal, are little hair cells whose stereocilia are embedded within a gelatinous membrane known as the tectorial membrane The hair cells of the cochlear canal, called the organ of Corti or spiral organ, synapse with nerve fibers of the cochlear nerve (auditory nerve) When the stapes strikes the membrane of the oval window, pressure waves move from the vestibular canal to the tympanic canal across the basilar membrane, causing the round window to bulge. The basilar membrane moves up and down, causing the stereocilia of the hair cells embedded in the tectorial membrane to bend. Nerve impulses begin in the cochlear nerve and travel to the brain stem. When they reach the auditory areas of the cerebral cortex, they are interpreted as sounds.

Astigmatism

When the cornea or lens is uneven and the image appears fuzzy