Exam 7 Senses #1-107 Flashcards
is the conscious or subconscious awareness of external or internal stimuli
Sensation
Components of the central nervous system receive sensory impulses from receptors throughout the body
Impulses to lower parts of the CNS elicit simple responses, such as __ __
various reflexes
Impulses that reach the ___ provide a crude awareness of the location and type of sensation
Thalamus
Impulses that reach the ___ ___ enable the precise location of the stimulus, as well as the type of stimulus
cerebral cortex
is the conscious awareness and interpretation of the meaning of sensations
Perception
There is no ____ of sensory impulses that do not reach the thalamus and cerebral cortex: blood pressure and carbon dioxide concentration, for example
perception
Whereas nerve impulses do provide the sensation of such stimuli as blood pressure and CO2 concentration, there is no perception of them since they do not reach the ___ ___
Cerebral cortex
A __ __ is a unique type of sensation: touch, pain, vision, hearing
sensory modality
An individual sensory neuron carries information for only one type of modality
Sensory modalities are grouped into two classes
- General senses
2. Special senses
Somatic senses
Visceral senses
are included as what type of senses?
General Senses
Tactile sensations: touch, pressure, vibration, itch, tickle
Thermal sensations: warm, cold
Pain sensations
Proprioceptive sensations
Dynamic sensations (movements of limbs and head)
Modalities of the general senses include
____ sensations provide information about conditions within internal organs. ____ sensation is usually not appreciated at the conscious level of awareness other than as “feeling good” or “feeling bad.”
Visceral
Someone who is in the initial stages of a heart attack will often vaguely “not feel good.” They will not feel actual pain until later when the ____ pain becomes so intense that it rises to the level of consciousness
Visceral
Special senses comprises the modalities of:
Smell Taste Vision Hearing Equilibrium
The first step in the process of sensation is activation of a sensory receptor by a stimulus
Sensory receptors comprise either
specialized cells or the dendrites of a sensory neuron
Each sensory receptor monitors one (and only one) type of stimulus to which it is sensitive, and responds weakly, if at all, to other kinds of stimuli
This is selectivity
Stimulation of the sensory receptor
Transduction of the stimulus
Generation of impulses
Integration of sensory input
Events required for sensation
Events required for sensation:
Stimulation of the sensory receptor
Transduction of the stimulus
Generation of impulses
Integration of sensory input
The stimulus must occur within the receptive field of the ___, which is the body region where stimulation elicits a response
receptor
____ is the conversion of stimulus energy into electrical energy
Transduction
The sensory receptor transduces energy in a stimulus into a ___ ___
graded potential
Graded potentials vary in amplitude depending on the strength of the stimulus
Graded potentials are not ___
propagated
Because of ____, each type of sensory receptor transduces only one kind of stimulus
selectivity
Graded potentials that ___ __ ___ in a sensory neuron trigger one or more nerve impulses that propagate toward the central nervous system
sum to threshold
Sensory neurons that conduct impulses from the PNS into the CNS are termed __ __ __
first-order neurons
Specific regions of the CNS receive and integrate sensory nerve impulses
Conscious sensations or perceptions are integrated in the ___ __
cerebral cortex
Microscopic appearance
Origin of stimuli, and consequent location of the receptor
Type of stimulus detected
sensory receptor classification
Bare dendrites
No structural specialization microscopically
Pain, thermal, tickle, itch, some touch
Free nerve endings
Dendrites are enclosed in a connective tissue capsule
Capsule enhances sensitivity or specificity of the receptor
Pressure & vibration (lamellated), some touch (Meisner)
Encapsulated nerve endings
Sensory receptors for certain special senses are specialized, separate cells
The specialized cell synapses with first-order sensory neuron
Hearing and equilibrium hair cells (inner ear), photoreceptors (retina), gustatory receptors (taste buds)
Separate cells
Two different kinds of graded potentials are produced by sensory receptors
- generator potentials
2. receptor potentials
Amplitude of both types of potentials varies directly with the ____ of the stimulus
intensity
Generator potentials are produced by dendrites of
Free nerve endings
Encapsulated nerve endings
Receptive part of olfactory receptors
The sensory receptor is the first-order neuron; they are one and the same
A sufficiently large generator potential will generate an __ __
action potential
Free nerve endings are bare dendrites of_____. They have no apparent structural specialization. This example shows a cold-sensitive receptor.
first-order neurons
slide 18 pic
____ nerve endings have dendrites of first-order neurons surrounded by a specialized capsule. This example shows a lamellated corpuscle.
encapsulated
slide 19 pic
Receptor potentials are produced by
Hair cells of the inner ear (both equilibrium and hearing)
Gustatory receptors (taste)
Photoreceptors (sight)
The receptor potential triggers release of ______, which diffuses across the synaptic cleft and produces a postsynaptic potential (PSP) in the first-order neuron
The sensory receptor is not the first-order neuron
The PSP may in turn trigger one or more nerve impulses
neurotransmitter
Specialized receptor cells are separate and distinct from the first-order neuron. There is a ____ between the receptor and the first-order neuron. This example shows a taste receptor.
synapse
slide 21 pic
Located at or near body surface
Provide information about external environment
Sight, odor, taste, touch, pressure, vibration, thermal, pain
Exteroceptors
Interoceptors AKA:
AKA visceroceptors
or is it velociraptor..
Located in blood vessels, visceral organs, muscles, & nervous system
Provide information about internal environment
Impulses usually not consciously perceived
Interoceptors
Located in muscles, tendons, joints, inner ear
Provide information about body position, muscle length and tension, position and motion of joints, and equilibrium
Proprioceptors
proprio = one’s own
mechanical pressure, touch sensations, pressure, vibration, proprioception, hearing, equilibrium, stretching of blood vessels and internal organs
Mechanoreceptors
changes in temperature
Thermoreceptors
physical or chemical damage to tissue (pain)
Nociceptors
detect light that strikes the retina
Photoreceptors
chemicals in mouth (taste), nose (smell) and body fluids
Chemoreceptors
osmotic pressure of body fluids
Osmoreceptors
Most sensory receptors exhibit ____, which is a decrease in the generator potential or receptor potential amplitude when exposed to a stimulus that is applied at a constant level over a reasonably long term
adaptation
Because of _____, the perception of a sensation may fade or disappear, even though the true magnitude of the stimulus has not changed
adaptation
Receptors vary in how quickly they adapt
Rapidly adapting receptors
Adapt very quickly
Are specialized for signaling changes in a stimulus
Examples:
touch, pressure, smell
Slowly adapting receptors
Adapt slowly
Continue to trigger nerve impulses as long as the stimulus persists
Examples:
pain receptors, proprioception, chemical composition of the blood
____ sensations arise from stimulation of sensory receptors embedded in the skin or subcutaneous layer, in mucous membranes, muscles, tendons, joints, and inner ear
Those ____ sensations that arise from stimulating the surface of the skin are termed cutaneous sensations
Somatic
Somatic sensations have four modalities:
Tactile
Thermal
Pain
Proprioceptive
Tactile sensations comprise:
Touch Pressure Vibration Itch Tickle
____ sensations arise to a great degree by activation of the same structural type of receptor
Free nerve endings: itch, tickle
Encapsulated nerve endings: touch, pressure, vibration
Tactile
____ are usually due to stimulation of tactile receptors in the skin or subcutaneous layer
Touch sensations
is the ability to perceive that something has contacted the skin, but its location, shape, size, and texture can not be ascertained
Crude touch
provides specific information about the location that is touched, and the shape, size, and texture of the source of stimulation
Fine touch
____ is a sustained sensation that is felt over a larger area than touch
It occurs with deformation of deeper tissues than does touch, hence some of the receptors for pressure are deeper
Pressure
Sensations of _____ result from rapid and repetitive sensory signals from tactile receptors
vibration
Corpuscles of touch (___ ___), which detect lower-frequency vibrations
Meissner’s corpuscles
Lamellated corpuscles (___ ___), which detect higher-frequency vibrations
Pacinian corpuscles
___ sensations result from stimulation of free nerve endings by certain chemicals
May be associated with a local inflammatory response
Itch
____ sensations are thought to arise from free nerve endings and lamellated corpuscles
Tickle
Thermal sensations comprise
Coldness
Warmth
____ are unspecialized free nerve endings that respond to absolute and relative changes of temperature, primarily within the innocuous range
They are located in the skin, cornea, tongue, and bladder
Each sensation is mediated by different specific receptors
Thermoreceptors
Pain receptors are free nerve endings found in every tissue of the body except the ____
brain
Pain receptors are termed _____, they exhibit very little adaptation
Nociceptors
Nociceptors can be activated by intense thermal, mechanical, or chemical stimuli
Tissue irritation or injury releases chemicals that stimulate nociceptors
Kinins
Prostaglandins
Potassium ions
___ are polypeptides that induce vasodilation and increased blood vessel permeability, and serve as chemotactic agents for phagocytes. They are formed in blood from inactive precursors called kininogens
Kinins
____ are lipids that intensify the effects of histamine and kinins, and stimulate the emigration of phagocytes through capillary walls. They are released by damaged cells.
Prostaglandins
Kinins affect some nerve endings, causing much of the pain associated with inflammation, and ____ intensify and prolong the pain.
Persistence of pain after the stimulus is removed occurs because the pain-mediating chemicals linger
Prostaglandins
Two types of pain:
Fast
Slow
Types of pain differentiated based on:
Types of nerve fibers that propagate the impulses (hence the speed of propagation)
Where in the body the particular type of pain can occur
Perception of pain occurs very rapidly
Propagated along medium-diameter, _____ __ __
Also termed acute, sharp, or pricking pain
Not felt in deeper tissues of the body
Examples:
Needle puncture
Knife cut
myelinated A fibers
Perception of pain occurs more slowly—a second or more after the stimulus is applied
Propagated along small-diameter, ___ __ __
Also termed chronic, burning, aching, or throbbing pain, it may be excruciating
Felt in both the skin, deeper tissues of the body, and internal organs
Example: toothache
Unmyelinated C fibers
is pain that arises from stimulation of receptors in the skin
Superficial somatic pain
is due to stimulation of receptors in skeletal muscles, joints, tendons, and fascia
Deep somatic pain
results from stimulation of nociceptors in visceral organs
Visceral pain
Visceral pain may seem to arise in or just deep to the skin that overlies the stimulated organ
The phenomenon is called ?
referred pain
___ __ occurs when nerve fibers from regions of high sensory input (such as the skin) and nerve fibers from regions of normally low sensory input (such as the internal organs) happen to converge on the same levels of the spinal cord
Referred pain
Pain of a heart attack may be felt in the skin over the heart and along the left arm because sensory fibers from the heart, the skin over the heart, and the skin along the medial aspect of the left arm enter the same spinal cord segments
slide 40
___ is relief from pain
Analgesia
Some analgesic drugs block formation of ____, which stimulate nociceptors (aspirin, ibuprofen)
prostaglandins
Local anesthetics block conduction of nerve impulses by preventing opening of ________ (Novocain™)
voltage-gated Na+ channels
Morphine and other opiate drugs alter the quality of pain perception in the brain; pain is still sensed, but it no longer is ____
noxious
Amputees may still experience sensations such as itching, pressure, tingling, or pain as if the limb were still there
This is termed ?
Phantom limb sensation
Possible explanations:
Cerebral cortex interprets impulses arising in the proximal portions of sensory neurons that previously carried impulses from the limb as still coming from the nonexistent limb
Neurons in the brain generate sensations of body awareness, including those neurons that previously received sensory impulses from the missing limb, thereby giving rise to false sensory perceptions
Phantom limb sensation
Proprioceptive sensations arise in receptors termed ____, allowing us to know where our head and limbs are located and how they are moving even without looking at them
_____ adapt slowly, and then only slightly, so they provide continuous information to the brain
Proprioceptors
Proprioceptors embedded in muscles (especially postural muscles) and tendons provide information regarding:
degree of muscle contraction amount of tension on tendons position of joints relative rates of movement of body parts weights of objects
Hair cells of the vestibular apparatus in the inner ear are ____ that monitor the orientation and position of the head
proprioceptors
Types of proprioceptors discussed:
Muscle spindles
Tendon organs
Joint kinesthetic receptors
are proprioceptors in skeletal muscles that participate in stretch reflexes
Their function is to measure muscle length—how much a muscle is being stretched
They are slowly adapting
Muscle spindles
Either sudden or prolonged stretching of the muscle will stimulate the muscle spindle
By adjusting how vigorously a muscle spindle responds to stretching, the brain sets an overall level of ___ __ (the small degree of contraction that is present when a muscle is at rest)
muscle tone
Muscle spindles are interspersed among ordinary skeletal muscle fibers, and aligned parallel to them
The concentration of muscle spindles varies with the particular muscle
Muscles requiring finely controlled movements have numerous muscle spindles (greater density)
Muscles involved in coarser movements have fewer (lesser density)
The small skeletal muscles of the middle ear have very few muscle spindles (at one time, it was thought they had none)
____ are located at the junction of a tendon and a muscle
They provide information about changes in muscle force
They are slowly adapting
____ protect tendons and their associated muscles from damage due to excessive tension
Tendon organs
The term ____ does not refer to a particular kind of receptor, but rather to a particular function, which is providing information about parameters associated with the movement (kinesis) of synovial joints
joint kinesthetic receptor
joint kinesthetic receptor
The parameters include:
Pressure Changes in velocity -acceleration -deceleration Tension
The receptors are located in and around the articular capsule of synovial joints
____ (sense of smell) and ____ (sense of taste) are called the chemical senses since they are stimulated by chemicals, the molecules of which interact with receptors to produce a generator potential (___) or receptor potential (___)
Olfaction
Gustation
These two senses work together—when you have a cold, so that you cannot smell anything, food does not taste as good because the sense of smell enhances the sense of taste
In both senses, the stimulating molecules must be dissolved to be perceived
___ is much more sensitive than taste to the same chemical
Olfaction
Millions of olfactory receptors are present in a little less than 1 in^2 of olfactory epithelium, which is in the ____ part of the nasal cavity
superior
The olfactory epithelium is a pseudostratified ciliated columnar epithelium consisting of three kinds of cells:
Olfactory receptors
Supporting cells (AKA sustentacular cells)
Basal stem cells
Olfactory receptors are ____ neurons that are the first-order neurons of the olfactory pathway
bipolar
Each olfactory receptor has a/an
axon ending in the olfactory bulb
knob-shaped dendrite
cilia projecting from the dendrite
chemical slide 5 pic
The cilia projecting from the dendrites of the olfactory receptor cells are termed _____
They are the sites of olfactory transduction (conversion of stimulus energy into a graded potential in a sensory receptor)
olfactory hairs
chemical slide 6 pic
Odorants are chemicals that can stimulate the olfactory hairs, which means that odorants are chemicals that have an odor
Olfactory receptors respond to the chemical stimulation of an odorant molecule by producing a ___ ___, thereby initiating the olfactory response
Only slight molecular alterations may distinguish different odorants
generator potential
Concentration differences of the same substance can result in different odorants
Indole is a substance found in both coal tar and perfumes. Concentrated indole just plain stinks. When sufficiently diluted, indole gives off a fragrance like ___
Jasmine…
yep, that was the slide.
___ are columnar epithelial cells of the mucous membrane lining the nose
They provide physical support, nourishment, and electrical insulation for the olfactory receptors
Supporting cells
chem slide 9 pic
___ are interspersed among the supporting cells
They undergo continuous cell division producing new olfactory receptors, which live only about a month
Olfactory receptors are neurons, so their replacement is unusual since mature neurons are not generally replaced
Basal Stem cells
chem slide 10 pic
Olfactory glands within the supporting connective tissue produce mucus
These ducted glands are also called ___ ___
The mucus moistens the olfactory epithelium surface, and dissolves odorants
Bowman’s glands
slide 11 pic
Both supporting cells of the nasal epithelium and olfactory glands are innervated by branches of the ____ CN__?. Certain chemicals stimulate the nerve, causing tears and runny nose due to consequent action of the lacrimal glands and nasal mucous glands
Facial nerve (CN VII)
The broad overall general mechanism whereby olfactory receptors react to odorant molecules is the same as most sensory reactors react to their specific stimuli
The stimulus (an odorant molecule) encounters the receptor
A generator potential develops and triggers one or more nerve impulses
Olfaction has a low threshold (as do all the special senses)
Methyl mercaptan is added to natural gas because its threshold is extremely low, and because it is a recognizable, but not “usual” odor
Odor thresholds
Adaptation to odors initially occurs rapidly—about 50% in the first few seconds after stimulation
After the first few seconds adaptation continues, but at a slower rate
Virtually complete insensitivity to some odors can occur in about a minute, even if the odors are strong
Adaptation to odors
Bundles of slender, unmyelinated axons of olfactory receptors extend through olfactory foramina in the cribriform plate of the ethmoid bone
All the bundles taken together comprise the ___ nerve?
olfactory nerves (cranial nerve I)
The olfactory nerves terminate in the ___ __ (paired masses of gray matter in the brain) within which the axon terminals of the first-order neurons (olfactory receptors) form synapses with dendrites and cell bodies of second-order neurons
olfactory bulbs
Axons of olfactory bulb neurons extend posteriorly to form the ___ ___
The axons subsequently project into the lateral olfactory area, which is probably the primary olfactory area where conscious awareness of smells begins, as well as to other parts of the brain
olfactory tract
Olfactory sensations are the only sensations that reach the cerebral cortex without first synapsing in the ____
thalamus
Other axons of the olfactory tract project to the ___ ___ and hypothalamus, which accounts for emotional and memory-evoked responses to odors
Limbic system
There are about 1,000 different kinds of receptor cells
Each receptor recognizes multiple odorants, and a single odorant can be recognized by multiple receptors
Different smells come from different combinations of receptors, so that 1,000 different types of sensors can identify 10,000 odors (similar to 26 letters of the alphabet being used in various combinations to form thousands of words)
many kinds of receptor cells
Each different kind of receptor cell is scattered throughout the olfactory epithelium
The olfactory nerve for a given receptor type connects to just ## spots in the olfactory bulb
The second order neurons project from these spots on the olfactory bulb to the brain, forming a sensory map that is probably the same for each person (different mice are known to have the same sensory map)
Two
New nerve cells formed from __ __ __ send out axons that find their way to the same spots in the olfactory bulb where their predecessors connected
Thus, roads on the odor map are constantly renewed so that destinations in the brain remain unchanged
basal stem cells
reduced ability to smell
Hyposmia
May be associated with age, since ability to smell decreases with age
May also be due to head injury, Alzheimer disease, Parkinson disease, smoking, and some drugs such as antihistamines, analgesics and steroids
Hyposmia
total lack of sense of smell
anosmia
Most result from…
Head injuries that tear the olfactory nerves, or from the
Aftereffects of nasal cavity inflammation (due to a cold, allergy, or smoking),
Physical obstruction of the nasal cavity (such as polyps)
Aging
Anosmia
Zinc deficiency is the cause in many cases (one-third), so the cure is rapid once the correct form of zinc supplement is prescribed (zinc is a growth factor for the receptors of chemical senses)
Some (but not many) cases are due to genetic factors
Anosmia
Receptors for taste sensations are located in the?
taste buds
Most taste buds are on the ___, but some are also on the . . .
Soft palate (posterior portion of the roof of the mouth)
Pharynx (throat)
Epiglottis (cartilaginous flap over the voice box)
The number of taste buds declines with age
tongue
Each taste bud is an oval body consisting of an aggregation of three kinds of neuroepithelial cells (a subtype of stem cell).
?
Gustatory receptor cells
Supporting cells (AKA sustentacular cells)
Basal cells
At the apex of the taste bud is a small opening called the ______
Each gustatory receptor cell has a single, long microvillus, called a gustatory hair, which projects through the ____
Taste pore
Basal cells produce supporting cells
Supporting cells then differentiate into ___ receptor cells
___ receptor cells have a life span of about ten days
Gustatory
A ___ is a chemical that stimulates gustatory receptor cells
___ must be dissolved before they can be tasted (a substance that is not water-soluble can not be tasted)
After being dissolved (in saliva) the ___ contacts the plasma membrane of the gustatory hairs. The gustatory hairs are the sites of taste transduction
Tastant
Physiology of gustation:
The gustatory hairs are the sites of taste ____
transduction
The result of transduction is a receptor potential that stimulates ___ of synaptic vesicles from the gustatory receptor cell
The neurotransmitter molecules trigger nerve impulses in the first-order sensory neurons that synapse with the gustatory receptor cell
exocytosis
Primary tastes are the fundamental tastes from which all other flavors of taste are composed
The five modern-day primary tastes are:
Sweet Sour Bitter Salty Umami
Some also advocate adding fats to the list of primary tastes; others want to add calcium
There may be an ___ advantage conferred by each of the tastes
Receptors for taste are distributed over the tongue, but sensitivity for sweet, sour, bitter, and salty is acute at various positions on the tongue
Evolutionary
Classic taste map of the tongue shown
slide 33
____ tastes are associated with safe foods: we have an absolute requirement for carbohydrates
Acute sensitivity (conventional receptor location): tip of tongue
Sweet
____ tastes are associated with spoiled foods: many foods become bitter or acidic when they spoil
Acute sensitivity (conventional receptor location): back sides of tongue
Sour
___ tastes are associated with poisonous foods (many natural poisons and spoiled foods are bitter)
Acute sensitivity (conventional receptor location): back middle of tongue
Bitter
___ tastes are associated with sodium chloride, something we need in our diet
Acute sensitivity (conventional receptor location): front sides of tongue (just back and to the side of sweet, perhaps somewhat overlapping sweet)
Salty
___ is the taste of certain amino acids, which are the building blocks of protein
___ is a Japanese word for the taste imparted by glutamate in foods, and though there is no direct English translation it is often described as meaty, savory, or broth-like
Receptor location: diffuse (there is no conventional location)
Umami
check out this guy on slide 36
MSG!
Taste buds occur in elevations on the tongue called ___
Papillae
There are three types of papillae that contain taste buds:
Vallate Papillae Fungiform papillae (mushroom-shaped) Foliate papillae (mostly lost during childhood)
___ papillae contain tactile receptors to discern the texture of food, but not taste buds
Filiform
Each primary taste has a different threshold
The threshold for ____ substances is the lowest
The threshold for sour substances is somewhat higher than for ___ substances
The threshold for the remaining primary tastes are higher than for sour substances
bitter
Complete adaptation to a specific taste can occur in #-# minutes (a relatively brief period of time) of continuous stimulation
1-5 minutes
___ is the combination of taste (tongue) plus odor (olfactory epithelium).
Flavor
Volatile food chemicals are carried into the nasal cavity from behind as we eat (____ ___).
Even though the same receptors in the olfactory epithelium act in ___ ___ and orthonasal olfaction (from the nostrils), the brain distinguishes between the two because it keeps track of breathing out and breathing in
retronasal olfaction
The brain combines taste and __ __, creating flavor.
retronasal olfaction
Taste receptor cells do not have an axon (the graded potentials they produce are called ___ ___, rather than generator potentials)
receptor potentials
Gustatory receptor cells synapse with ___ of the first-order neurons that comprise the initial portion of the gustatory pathway
Each first-order neuron synapses with many gustatory receptor cells in several taste buds
dendrites
Three cranial nerves include axons of first-order gustatory neurons from taste buds:
Facial nerve (cranial nerve VII), anterior two-thirds of the tongue
Glossopharyngeal nerve (cranial nerve IX), posterior one-third of the tongue
Vagus nerve (cranial nerve X), throat and epiglottis
From the taste buds, impulses propagate along the appropriate cranial nerve to the gustatory nucleus in the ___ ___
medulla oblongata
From the medulla some axons project to the limbic system and hypothalamus, others project to the thalamus and on to the primary gustatory area in the ___ __ of the cerebral cortex to give rise to the conscious perception of taste
parietal lobe
The accessory structures of the eye are the . . .
Eyelids Eyelashes Eyebrows Lacrimal (tearing) apparatus Extrinsic eye muscles
The upper and lower eyelids . . .
Termed?
Palpebrae
Eyelids: Shade the eyes during sleep Protect eyes from: \_\_ \_\_ Spread lubrication secretions over the eyes
Excessive light
Foreign objects
The upper eyelid is more movable than the lower
The ___ ___ ___ muscle moves the upper eyelid
levator palpebrae superioris
The ___ ___ is the space between the upper and lower eyelids
palpebral fissure
The angles of the palpebral fissure are termed _____:
commissures
The medial commissure is nearer the ___ bone
The lateral commissure is closer to the ___ bone
nasal
temporal
The __ ___ is in the medial commissure, and contains
Sebaceous (oil) glands
Sudoriferous (sweat) glands
lacrimal caruncle
Structures of the eyelid from superficial to deep: (7)
Epidermis Dermis Subcutaneous tissue Fibers of orbicularis oculi muscle Tarsal plate Tarsal glands Conjunctiva
The ___ __ is a thick fold of connective tissue that gives form and support to the eyelids
tarsal plate
Tarsal glands (___ __) in each tarsal plate are modified sebaceous glands that secrete a fluid that helps keep the eyelids from adhering to each other
Meibomian glands
The conjunctiva:
Thin, protective mucous membrane
Composed of ___ ___ __ with many goblet cells
stratified columnar epithelium
___ conjunctiva lines inner aspect of the eyelids
Palpebral
Bulbar conjunctiva is on the anterior surface of the eyeball
*covers sclera but not the ___
cornea
The ___ ___ is a group of structures that produces and drains lacrimal fluid, or tears
lacrimal apparatus
Lacrimal fluid is a watery solution containing salts, some mucus, and ___ (a bactericidal enzyme)
lysozome
Lacrimal glands secrete lacrimal fluid
It then drains into the excretory lacrimal duct onto the surface of the ____ of the upper lid
The tears then pass medially over the eyeball
conjunctiva
Tears next enter two small openings called ___ ___
lacrimal puncta
Tears next enter two small openings called lacrimal puncta
Then the tears pass into two ducts called the ___ ___ (superior and inferior)
lacrimal canals
The lacrimal canals lead to the lacrimal sac
Then to the ___ __
The __ ___ carries the lacrimal fluid into the nasal cavity
nasolacrimal duct
Tears are normally carried away as fast as they are produced, either by evaporation or by passing into the lacrimal canals, then into the nasal cavity
___ is a protective mechanism: the tears dilute and wash away irritating substances
A buildup of tears can also occur when an inflammation of the nasal mucosa obstructs the nasolacrimal ducts
Lacrimation
