Senseory Organs Flashcards
What is the function of sensory receptors?
“Detect changes in the environment and trigger appropriate responses. “
What kind of changes can sensory receptors detect?
“Mechanical
What are the four main groups of sensory receptors?
“Mechanoreceptors
What is the key function of any sensory receptor?
“To convert the stimulus they detect into electrical impulses. “
What does the brain do with the electrical impulses from sensory receptors?
“Translates them into sensations like pictures
How do photoreceptors work to produce vision?
“Light is converted into electrical impulses
What is the simplest form of sensory structure?
“Free dendritic endings (nerve endings) of sensory neurones (primary sense cells). “
Where are touch receptors located?
“In mammalian skin. “
What is a more complex form of sensory structure?
“Groups of cells that are not neurones but are specialized to detect stimuli (secondary sense cells) and synapse with sensory neurones. “
Where are taste receptors located?
“An example of the more complex sensory receptor. “
What is the most complex form of sensory structure?
“A sense organ
What are examples of sense organs?
“Ears and eyes. “
What do sensory receptors in the skin and sense organs detect?
“External stimuli. “
What do sensory receptors within the body detect?
“Internal stimuli. “
What sensations does mammalian skin detect?
“Touch
Why is skin considered a sense organ?
“Because it has a rich supply of sensory receptors and detects many types of stimuli. “
What kind of cells are sensory receptors in the skin?
“Mainly dendritic endings of sensory neurones (primary sense cells). “
What are the two types of dendrites in the skin?
“Finely branched with free ends and dendrites enclosed within capsules. “
Are sensory receptors evenly distributed in the skin?
“No. Each type is concentrated in certain regions. “
How do touch and pressure sensations differ?
“Touch receptors are sensitive to small pressures
Where are touch receptors with free ends located?
“Close to the surface of the skin
What stimulates touch receptors with free ends?
“Slightest pressure or movement of hairs. “
Where are Meissner’s corpuscles located and what do they detect?
“Just below the epidermis and are sensitive to touch. “
What is the structure of a Meissner’s corpuscle?
“A single coiled dendrite of a sensory neurone enclosed in a fluid-filled capsule. “
Where are touch receptors concentrated?
“Fingertips
What can we identify by touching with our fingertips?
“Shape and texture of an object. “
What do blind people use to read?
“Braille characters
Where are pressure receptors (Pacinian corpuscles) located?
“Deeper parts of the dermis
What is the structure of a Pacinian corpuscle?
“A single dendrite surrounded by layers of connective tissue. “
What is the function of touch and pressure sensations?
“To warn and prevent us from injuring ourselves. “
What happens to people with leprosy?
“They hurt themselves because they cannot feel touch
What do thermoreceptors detect?
“Changes in temperature. “
Where are most thermoreceptors located?
“Free dendritic endings in the epidermis and dermis. “
What are the special thermoreceptors?
“Cold receptors and heat receptors (dendrites enclosed in capsules). “
What is the role of thermoreceptors?
“Regulating body temperature in warm-blooded animals. “
What is the function of pain receptors?
“Provide acute warning of damage to body tissues. “
What are special pain receptors called?
“Nociceptors. “
What is the structure of nociceptors?
“Small
Where are nociceptors located?
“Near the surface of the skin (epidermis) and in many internal organs. “
Where is pain sensitivity the highest?
“Surface of the eyes and skin of the abdomen. “
What is the pain pathway?
“Pain stimulus -> electrical impulse -> sensory neurone -> spinal cord -> neurochemicals -> second neurone -> brain. “
Where do pain-relieving drugs act?
“Spinal cord level. “
What are stretch receptors?
“Sensory nerve fibres wrapped around specialized muscle fibres (spindle fibres). “
Where are stretch receptors located?
“Buried deep within skeletal muscles. “
What is the function of stretch receptors?
“Monitor the position and movements of the body and so maintain balance. “
What kind of information do smell and taste provide?
“Information about our external environment. “
What kind of receptors detect smell and taste?
“Chemoreceptors. “
Where are smell chemoreceptors located in mammals?
“Epithelial lining of the upper portion of the nasal cavity (olfactory organs). “
What is the structure of smell chemoreceptors?
“Sensory neurones (primary sense cells) with fine processes extending into the mucus film. “
How are smell chemoreceptors stimulated?
“Chemicals dissolve in the mucus film and stimulate the chemoreceptors. “
How do the impulses travel from smell chemoreceptors to the brain?
“Via the olfactory nerves. “
How do we detect different smells?
“One theory proposes that each smell is a mixture of basic odours
Where are taste chemoreceptors located in mammals?
“Upper surface of the tongue
Where are taste receptors found on the tongue?
“In taste buds. “
Where are taste buds located?
“In grooves on the surface of the tongue. “
What kind of cells are taste receptors?
“Specialized sense cells that synapse with sensory neurones. “
How are taste receptors stimulated?
“Taste chemicals have to be in a dissolved form. “
What are the four types of basic tastes?
“Sweet
Where are sweet and salty tastes registered on the tongue?
“At the front. “
Where is sour taste registered on the tongue?
“At the sides. “
Where is bitter taste registered on the tongue?
“At the back. “
What does the sense of sight (vision) enable us to do?
“See our external environment. “
What kind of information does sight provide?
“Details about location
What is the stimulus for sight?
“Light (400-700 nm wavelength). “
What kind of receptors detect light?
“Photoreceptors. “
What are the specialized sense organs for sight?
“Eyes. “
Where are eyes located in mammals?
“Anteriorly in the head. “
What is the shape of the eye?
“Spherical (eyeball). “
Where is the eyeball located?
“In a bony socket in the skull. “
What protects the front part of the eyeball?
“Upper and lower eyelid. “
What kind of fluid do tear glands produce?
“Saline tear fluid (sodium chloride and hydrogen-carbonate). “
How often do we blink?
“Every two to ten seconds. “
What are the functions of tear fluid?
“Cleans and keeps the eye surfaces moist
Where does tear fluid drain?
“Into the nasal cavity via tear ducts. “
How many muscles are attached to each eyeball?
“Six sets. “
What is the function of the eye muscles?
“Enable the eye to move in many directions. “
What nerve connects the eye to the brain?
“Optic nerve. “
What are the most important functional structures of the eye?
“Lens and retina. “
What are the three layers of the eyeball wall?
“Sclera
What is the sclera?
“Outermost
What are the functions of the sclera?
“Protects and maintains the shape of the eyeball. “
What is the cornea?
“Transparent part of the sclera at the front. “
What is the conjunctiva?
“Thin transparent membrane lining the eyelids and covering the cornea. “
What is the choroid?
“Middle layer with black pigmented cells and a rich supply of blood capillaries. “
What does the choroid form?
“Ciliary body and iris. “
What holds the lens in place?
“Suspensory ligaments from the ciliary body. “
What is the lens?
“Transparent
What fills the space in front of the lens?
“Watery aqueous humour. “
What fills the space behind the lens?
“Jelly-like vitreous humour. “
What is the function of the vitreous humor?
“Maintains the spherical shape of the eyeball. “
What is the iris?
“Coloured opaque disc of muscular tissue in front of the lens. “
What is the pupil?
“Hole in the centre of the iris. “
How does light enter the eye?
“Through the pupil. “
What is the retina?
“Light-sensitive inside layer at the back of the eyeball. “
Where does the retina get its nourishment?
“From the capillaries in the choroid. “
What are the two types of photoreceptors in the retina?
“Rods and cones. “
What are rods responsible for?
“Black and white vision (and night vision). “
What are cones responsible for?
“Colour vision. “
What other cells do photoreceptors synapse with?
“Bipolar neurones
How many rods and cones are in the human retina?
“About 125 million rods and 7 million cones. “
Where are cones most concentrated?
“Yellow spot or fovea centralis. “
Where is the fovea centralis located?
“At the back of the eye
What is the function of the fovea centralis?
“Most sensitive area to light on the retina. “
What is the blind spot?
“Area where the optic nerve leaves the eye
What kind of objects give off light?
“Luminous objects. “
How do we see non-luminous objects?
“They reflect light. “
What determines the color of an object?
“The color of light it reflects. “
What is white light composed of?
“Seven different colors: red
What is a light ray?
“The path along which light energy flows. “
What is a light beam?
“A collection of light rays. “
How is an image formed in a pinhole camera?
“Light from an object passing through a tiny hole forms an inverted image on the screen. “
How does the size of the image in a pinhole camera relate to the object’s distance?
“The size of the image varies and is related to the distance. “
What is refraction?
“The bending of light when it travels from one medium to another. “
What is a lens?
“Any transparent material with at least one curved face. “
What does a convex lens do to light rays?
“Bends them towards each other (converges) to a focus. “
What is the effect of a thick convex lens on the focal point?
“Bends light more
What does a concave lens do to light rays?
“Bends them away from each other (diverges). “
What does a simple lens camera use to focus images?
“A convex lens to focus images on a light-sensitive screen (film). “
How is a sharp image obtained in most cameras?
“By moving the lens nearer or further from the film. “
What is the focal length of a lens?
“The distance between the centre of the lens and its principal focus (focal point). “
How do we see an object?
“Light rays from the object enter our eyes
What are the characteristics of the image formed on the retina?
“Real
Where is most of the light bending in the eye?
“At the air/cornea surface. “
What is the role of the lens in focusing light?
“Makes final fine bending adjustments. “
What prevents reflection of light inside the eyeball?
“The pigmented (black) choroid layer. “
What do rods and cones do when light falls on them?
“They are stimulated and send electrical impulses to the brain. “
How does the brain interpret the electrical impulses from the eye?
“Draws on past experience to perceive the object’s orientation
When is vision most clear?
“When the image falls on the fovea centralis. “
Why is there a blind spot?
“Because there are no sensory cells where the optic nerve leaves the retina. “
What happens in the eye in bright light?
“More photoreceptors are stimulated
What does the brain do to the iris in bright light?
“Sends motor impulses to contract circular muscles and relax radial muscles
Why does the pupil constrict in bright light?
“To protect the retina from damage. “
What happens in the eye in dim light?
“The brain sends motor impulses to relax circular muscles and contract radial muscles
What is accommodation?
“The ability of the eye to see nearby and far-away objects clearly. “
How is accommodation achieved?
“By changing the shape of the lens to alter its focal length. “
What is the lens made of?
“Many layers of transparent
How is the lens attached?
“To the ciliary body by suspensory ligaments. “
What happens to the lens and muscles when viewing a far-away object?
“Ciliary body muscles relax
What happens to the lens and muscles when viewing a nearby object?
“Ciliary body muscles contract
What are the near and far points of vision?
“The nearest and furthest points at which the eye can see an object clearly. “
What is the near point distance for a normal eye?
“About 25 cm. “
What is happening to the eye muscles at the near point?
“They are contracted to the maximum
What happens if an object is closer than the near point?
“The image is formed behind the retina and appears blurred. “
What is the far point distance for a normal eye?
“At infinity. “
What is happening to the eye muscles at the far point?
“They are most relaxed
What is binocular vision?
“Vision using both eyes. “
How does the brain process images from both eyes?
“Combines the two slightly different images into one. “
What is the result of binocular vision?
“Accurate perception of depth and 3D vision. “
What are the photoreceptors in the retina?
“Rods and cones. “
Where are rods and cones located within the cell?
“In the outer segments
What is rhodopsin?
“A light-sensitive pigment-protein complex in rods. “
What happens to rhodopsin when light falls on it?
“It undergoes a molecular shape change
What vitamin is essential for rhodopsin production?
“Vitamin A. “
What happens if there is a lack of vitamin A?
“Night-blindness. “
What are rods sensitive to and what kind of vision do they provide?
“They are extremely sensitive to light and provide black and white vision (dim light vision). “
What are cones responsible for and what kind of vision do they provide?
“They function in bright light and are responsible for color vision. “
Where are cones concentrated in the retina?
“In and around the fovea centralis. “
Where are rods concentrated in the retina?
“Outside the fovea centralis. “
When are cones most stimulated?
“When we look directly at an object in bright light. “
When are rods most stimulated?
“When we look at an object out of the corner of our eyes (peripheral vision). “
What are the three types of cone cells?
“Red light-sensitive
How do we see other colors?
“By combinations of stimulation of the three basic cone types. “
Why can’t we see colors well in dim light?
“Because cones function best in bright light. “
What happens in color-blindness?
“One or more types of cones are absent or defective. “
What is a common type of color-blindness?
“Red-green color-blindness. “
