Nervous System- Sensation Flashcards
Sensation
the conscious or subconscious awareness of changes in the external or internal environment
Special sense
olfaction, gustation, vision, audition, and equilibrium
Complex sensory organs such as the eyes and ears
Allow us to detect changes in our environment
general senses
somatic
visceral
somatic sense
tactile sensations, thermal sensations, pain sensations, proprioceptive sensation
visceral sense
info about conditions within internal organs
4 conditions for a sensation to occur
A stimulus must activate a sensory receptor
-light, heat, pressure, mechanical energy, or
chemical energy
A sensory receptor converts the stimulus into an electrical signal which produces nerve impulses if the stimulus was sufficient
The nerve impulses are conducted along a neural pathway from the sensory receptor to the brain
A region of the brain must receive and integrate the nerve impulses into a sensation
perception
the conscious awareness and interpretation of sensations; primarily a function of cerebral
cortex
A given sensory neuron carries info for one type of sensation only
adaptation
a decrease in the strength of a sensation during a prolonged stimulus; a characteristic of most sensory receptors
Rapidly adapting receptors (phasic receptors) – adapt very quickly; specialized for signaling changes in stimuli; pressure, touch, and olfaction
Slowly adapting receptors (tonic receptors) – adapt slowly and continue to trigger nerve impulses as long as the stimulus persists; pain, body position, and chemical composition of the blood
structural classifications of nerve receptors
free nerve endings
encapsulated nerve endings
separate cells
free nerve endings
simplest; bare dendrites that lack any structural specializations; pain, temperature, tickle, itch, and some touch sensations
encapsulated nerve endings
dendrites are enclosed in a connective tissue capsule with a distinctive microscopic structure; some touch, pressure, and vibration
separate cells
specialized cells that synapse with sensory neurons; hair cells in the inner ear
functional classifications of nerve receptors (types of stimuli they detect)
mechanoreceptors thermoreceptors nocieptors photoreceptors chemoreceptors osmoreceptors
machanoreceptors
sensitive to mechanical stimuli including deformation, stretching, bending
of cells; touch, pressure, vibration, proprioception, audition, and equilibrium; stretching of blood vessels and internal organs
thermoreceptors
detect changes in temperature
free nerve endings; rapidly adapting, but continue to generate nerve
impulses more slowly throughout a prolonged stimulus
cold receptors
warm receptors
Above and below these ranges stimulate mainly nociceptors
nociceptors
respond to painful stimuli resulting from physical or chemical damage to tissue
sensory receptors for pain; free nerve endings; in practically every tissue of
the body except the brain
Respond to several types of stimuli: excessive stimulation of sensory receptors, excessive stretching of a structure, prolonged muscular contractions, inadequate blood flow, presence of certain chemical substances
Pain may persist even after the stimulus is removed because pain-causing chemicals
linger and because nociceptors exhibit very little adaptation
fast pain
photoreceptors
detect light that strikes the retina of the eye
chemoreceptors
detect chemicals in the mouth (gustation), nose (olfaction), and body fluids
osmoreceptors
detect the osmotic pressure of body fluids
somatic senses
arise from stimulation of sensory receptors in the skin, mucous membranes, muscles, tendons, and joints
areas with largest numbers: tip of the tongue, the lips, and fingertips
tactile
touch
receptors in the skin or subcutaneous layer
meissner corpuscles
hair root plexuses
merkel discs
ruffini corpuscles
meissner corpuscles ( corpuscles of touch)
rapidly adapting touch receptors; located in the dermal papillae of hairless skin; fingertips, hands, eyelids, tip of the
tongue, lips, nipples, soles, clitoris, and tip of the penis
hair root plexuses
rapidly adapting touch receptors; found in hairy skin; free nerve endings wrapped around hair follicles; detect movements on the skin surface that disturb hairs
merkel discs ( type I cutaneous mechanoreceptors)
slowly adapting touch receptors; saucer-shaped, flattened free nerve endings; plentiful in fingertips, hands, lips, and external genitalia
ruffini corpuscles ( type II cutaneous mechanoreceptors)
slowly adapting touch
receptors; elongated encapsulated receptors deep in the dermis, ligaments, and tendons; hands and soles; most sensitive to stretching that occurs as digits or limbs are moved
pressure
sustained sensation that is felt over a larger area and occurs in deeper tissues
than touch; deformation of deeper tissues
Meissner corpuscles and Merkel discs contribute to sensation of pressure
Pacinian corpuscle (lamellated corpuscle)
rapidly adapting; large oval structure
composed of a multilayered connective tissue capsule that encloses a dendrite;
widely distributed in the body
vibration
result from rapidly repetitive sensory signals from tactile receptors
Meissner corpuscles – detect lower-frequency vibrations
Pacinian corpuscles – detect higher-frequency vibrations
itch
stimulation of free nerve endings by certain chemicals often because of local
inflammatory response
tickle
probably mediated by free nerve endings; cannot tickle oneself, probably because of action in the cerebellum when you are moving your own fingers
thermal
thermoreceptors
cold receptors
located in epidermis; activated by temperatures between 10-40 C
(50-105 F)
warm receptors
located in the dermis; activated by temperatures between 32-48
C (90-118 F)
pain
noicieptors
fast pain
perception occurs very rapidly; acute, sharp, or pricking; not felt in deeper tissues of the body; precisely localized
Needle puncture or knife cut to the skin
slow pain
perception begins a second or more after a stimulus is applied, then gradually
increases in intensity over a period of several seconds or minutes; chronic, burnings, aching, or throbbing; in the skin and in deeper tissues or internal organs; well localized but more diffuse
toothache
referred pain
when pain is felt in areas removed from the stimulus; usually served by the same segment of the spinal cord
Proprioceptive sensations
allow us to know where our head and limbs are located and how they are moving even if we are not looking at them, so that we can walk, type, or dress without using our eyes
kinesthesia
the perception of body movements
propioceptors
receptors located in skeletal muscles and tendons, in and around synovial joints, and in the inner ear that
Inform us of the degree to which muscles are contracted, the amount of tension on
tendons, and the positions of joints
Allow one to estimate the weight of objects and determine the muscular effort necessary to perform a task
Adapt slowly and only slightly to ensure coordination
opthalmology
the science that deals with the eye and its disorders
Otorhinolaryngology
the science that deals with the ears, nose, and throat and their disorders
olfaction
smell
Nose contains 10-100 million receptors for olfaction
Some nerve impulses for olfaction and gustation propagate to the limbic system which can evoke strong emotional responses and memories
olfactory epithelium
upper portion of the nasal cavity
olfactory receptors
first-order neurons of the olfactory pathway; live for only a month or so
Olfactory receptors adapt by about 50% in the first second or so after stimulation and very slowly thereafter
olfactory hairs
cilia that project from a knob-shaped tip on each olfactory receptor; respond to
inhaled chemicals
odorants
chemicals that have an odor and can therefore stimulate the olfactory hairs
supporting cells
columnar epithelial cells of the mucous membrane lining the nose; provide
physical support, nourishment, and electrical insulation for the olfactory receptors; help detoxify chemicals that come in contact with the olfactory epithelium
basal stem cells
stem cells located between the bases of the supporting cells and continually undergo cell division to produce new olfactory receptors
olfactory glands
produce mucus that moistens the surface of the olfactory epithelium and
serves as a solvent for inhaled odorants
The brain has the ability to recognize about 10,000 different odors (different combinations of primary odors)
Olfactory receptors adapt by about 50% in the first second or so after stimulation and very slowly thereafter
how many primary odors
100s, brain has the ability to recognize 10,000 different odors ( different combinations of primary odors)
olfactory ( I) nerve
about 40 bundles of slender unmyelinated axons of olfactory receptors that
extend through about 20 holes in the cribriform plate of the ethmoid bone; terminate in the brain in olfactory bulbs
olfactory bulbs
paired masses of gray matter located below the frontal lobes of the cerebrum; here, first order neurons synapse with second order neurons
olfactory tract
second order neurons leaving the olfactory bulbs form the olfactory tract; project to the primary olfactory area, the limbic system, and hypothalamus
primary olfactory area
temporal lobe where conscious awareness of olfaction begins
gustation
taste
only 5: sour, sweet, bitter, salty, and unami( meaty or savory)
flavors are combinations of the five primary tastes, plus olfactory and tactile sensations
Complete adaptation to a specific taste can occur in 1-5 minutes of continuous stimulation
Different tastes arise from activation of different groups of gustatory neurons
Facial (VII) nerve, glossopharyngeal (IX) nerve, vagus (X) nerve – propagate impulses to the medulla oblongata
From thalamus to the primary gustatory area – parietal lobe of the cerebral cortex; gives rise to
the conscious perception of gustation
From medulla, to limbic system and hypothalamus, and thalamus
taste buds
where receptors for taste are located; nearly 10,000 in a young adult on the tongue,
roof of the mouth, pharynx, and epiglottis; number declines with age
Each one consists of 3 types of epithelial cells: supporting cells, gustatory receptor cells (10 days), and basal cells
papillae
elevations on the tongue where taste buds are found; provide a rough texture to the
upper surface of the tongue
vallate papillae
form an inverted V shaped row at the back of the tongue
fungiform papillae
mushroom shaped elevations scattered over the entire surface of the tongue
filiform papillae
on the entire surface of the tongue; contain touch receptors but no taste buds
tastant
a chemical that stimulates gustatory receptor cells; dissolves in saliva and enters taste
pores resulting in an electrical signal
vision
More than half the sensory receptors in the human body are located in the eyes
accessory structures
eyebrows and eyelashes
eyelids ( upper and lower_
extrinsic muscles
eyebrows and eyelashes
protect the eyeballs from foreign objects, perspiration, and direct rays of the sun
eyelids ( upper and lower)
shade the eyes during sleep, protect the eyes from excessive light and foreign objects, spread lubricating secretions over the eyeballs
extrinsic muscles
cooperate to move each eyeball right, left, up, down, and diagonally
Superior rectus, inferior rectus, lateral rectus, medial rectus, superior oblique, and
inferior oblique
lacrimal appartus
a group of glands, ducts, canals, and sacs that produce and drain lacrimal fluid (tears)
lacrimal glands ( right and left)
each about the size and shape of an almond; secrete tears through lacrimal ducts onto the surface of the upper eyelid
lacrimal canals and nasolacrimal duct
allow the tears to drain into the nasal cavity
lysozyme
a bacteria-killing enzyme in tears
lacrimation
only humans express emotions by crying; parasympathetic stimulation,
lacrimal glands produce excessive tears that spill over the edges of the eyelids and fill the
nasal cavity with fluid
layers of the eyeball
fibrous tunic
vascular tunic
retina
fibrous tunic
the outer coat of the eyeball; consists of an anterior cornea and a posterior
sclera
cornera
sclera
conjunctiva
vascular tunic
middle layer of the eyeball composed of the choroid, ciliary body, and iris
choroid ciliary body lens iris pupil
choroid
a thin membrane that lines most of the internal surface of the sclera; contains many blood vessels that help nourish the retina and melanocytes that produce melanin which causes this layer to appear dark brown in color
ciliary body
consists of the ciliary processes (folds on the inner surface), ciliary muscle (smooth muscle that alters the shape of the lens for near or far vision)
lens
a transparent structure that focuses light rays onto the retina; constructed of many layers of elastic protein fibers
iris
the colored part of the eyeball including the circular and radial smooth muscle fibers
pupil
the hole in the center of the iris through which light enters the eyeball
retina
third and inner coat of the eyeball; lines the posterior ¾ of the eyeball and is the
beginning of the visual pathway
neural layer
pigmented layer
photoreceptors
neural layer
multilayered outgrowth of the brain; photoreceptor layer, bipolar cell layer, and ganglion cell layer with inner and outer synaptic layers where synapses occur
pigmented layer
a sheet of melanin-containing epithelial cells located between the choroid and the neural part of the retina; helps to absorb stray light rays
photoreceptors
specialized cells that begin the process by which light rays are ultimately converted to nerve impulses
rods
cones
rods
allow us to see shades of gray in dim light
cones
stimulated by brighter light, giving rise to highly acute color vision; blue cones, green cones, and red cones
optic (II) nerve
where the axons of the ganglion cells exit the retina
interior of the eyeball
divided into two cavities by the lens
anterior cavity
vitreous chamber
anterior cavity
anterior to the lens and filled with aqueous humor
aqueous humor
aqueous humor
a watery fluid similar to cerebrospinal fluid that helps maintain the shape of the eye and nourishes the lens and cornea; completely replaced every 90 min
vitreous chamber
larger cavity behind the lens; contains vitreous body
vitreous body
a clear, jellylike substance which forms during embryonic life and is not replaced thereafter; helps prevent the eyeball from collapsing and holds the retina flush against the choroid
intraocular pressure
pressure in the eye produced mainly by the aqueous humor; maintains the shape of the eyeball and keeps the retina smoothly pressed against the choroid so the retina is well nourished and forms clear images
image formation
3 processes for the eye to form clear images on the retina
refraction or bending of light
change in shape of the lens
refraction or bending of light by the lens and cornea
75% takes place at the cornea, the
rest is handled by the lens; images focused on the retina are inverted and reversed
refraction
the bending that takes place at the junction between two substances
as light passes through it
accommodation
increase in the curvature of the lens for near vision
emmetropic eye
normal eye
myopia
nearsightedness; eyeball is too long relative to focusing power, can only see near
hyperopia
farsightedness; eyeball is too short relative to focusing power, can aonly see far
astigmatism
either the cornea or the lens has an irregular curvature
constriction or narrowing of the pupil
narrowing of the diameter of the hole through which light enters the eye
binocular vision
a characteristic of human eyes that allows both eyes to focus on only one set of objects; allows perception of depth and 3D nature of objects
convergence
the automatic movement of the two eyeballs toward the midline to focus on an object
vision pathway
After the rods and cones are stimulated by light, electrical signals are triggered in bipolar cells, then transmitted to ganglion cells
Ganglion cells become depolarized and generate nerve impulses
Optic (II) nerve
the axons of the ganglion cells exit the eyeball and extend posteriorly to the optic chiasm (where they cross over), then to the thalamus
In the thalamus they synapse with neurons whose axons project to the primary visual
areas
saccades
rapid movements that shift the fovea to an object of interest
fovea
portion of the retina with the greatest visual acuity, where only cone receptors are located; center of the macula
smooth pursuit movements
slow and are used for tracking a moving object
vergence movements
(convergent or divergent) ensure that the image of an object of interest falls on the same place on the retina of each eye
vestibuloocular reflexes
use information from the semicircular canals to compensate for head motion by adjusting eye position to maintain the direction of gaze
optokinetic reflexes
use visual information to supplement the effects of the vestibuloocular reflex
3 main regions of the ear
external ear
middle ear
internal ear
external ear
collects sound waves and channels them inward
auricle external auditory canal cerminous glands tympanic membrane perforated eadruym
auricle
the part of the ear that you can see; skin-covered flap of elastic cartilage shaped
like the flared end of a trumpet
external auditory canal
a curved tube that extends from the auricle and directs sound waves toward the tympanic membrane; contains a few hairs and ceruminous glands that help prevent foreign objects from entering the ear
cerminous glands
secrete cerumen (earwax)
tympanic membrane ( eardrum)
a thin semitransparent partition between the externalauditory canal and the middle ear; sound waves cause the eardrum to vibrate
perforated eardrum
tearing of the tympanic membrane due to trauma or infection
middle ear
a small, air-filled cavity between the eardrum and the inner ear
divides inner from outer
auditory tube
auditory ossicles
oval window
conveys sound vibrations to the oval window
auditory tube (eustachian tube)
connects the middle ear with the upper part of thethroat; when open, air pressure can equalize on both sides of the eardrum; when closed, if air pressure changes abruptly there may be a rupture
auditory ossicles
3 tiny bones extending across the middle ear and attached to it by ligaments: malleus (hammer), incus (anvil), and stapes (stirrup)
oval window
thin bony partition between the middle and internal ear, where the inner
ear begins
internal (inner) ear
divided into the outer bony labyrinth and inner membranous labyrinth
houses the receptors for hearing and equilibrium
bony labrinth
a series of cavities in the temporal bone including the cochlea (audition) and the vestibule and semicircular canals (equilibrium); contains perilymph
perilymph
a fluid that surrounds the inner membranous labyrinth
cochlea
a bony spiral canal that resembles a snail’s shell; organ of audition
vestibule
the oval-shaped middle part of the bony labyrinth
semicircular canals
3; anterior and posterior are vertical, lateral is horizontal
membranous labyrinth
a series of sacs and tubes with the same general shape as the bony labyrinth; contains endolymph fluid
physiology of audition
The auricle directs sound waves into the external auditory canal
Sound waves strike the eardrum and cause it to vibrate
The eardrum connects to the malleus which also starts to vibrate, then transmitted from the malleus to the incus and then to the stapes
The stapes moves back and forth and pushes the oval window in and out
The movement of the oval window creates waves in the perilymph of the cochlea, then in the endolymph inside the cochlear duct
The waves in the endolyph cause the basilar membrane to vibrate which stimulate the
vestibulocochlear (VIII) nerve where a nerve impulse is generated
The vestibulocochlear (VIII) nerve terminates in the medulla on the same side of the brain; axons ascend to the midbrain, then to the thalamus, and finally to the primary auditory area in the temporal lobe
vestibular apparatus
the receptor organs for equilibrium including the saccule, utricle, and membranous semicircular ducts
static
dynamic
static
maintenance of the position of the body relative to the force of gravity; tilting the
head or linear acceleration/deceleration (elevator or car)
uricle and saccule
two sacs inside the membranous labyrinth in the vestibule;these trigger nerve impulses in the vestibular branch of the vestibulocochlear
(VIII) nerve
macula
macula
a small thickened region of the walls of both the utricle and the saccule that are perpendicular to one another; receptors for static equilibrium; provide sensory info on the position of the head in space and help maintain appropriate posture and balance
dynamic
the maintenance of body position in response to rotational acceleration
or deceleration; shaking the head “no”
Detects rotational acceleration and deceleration
Trigger nerve impulses in the vestibular branch of the vestibulocochlear
(VIII) nerve
semicircular ducts
3 portions inside the membranous labyrinth inside the bony semicircular canals; lie at right angles to one another in 3 planes
equilibrium pathways
The vestibular branch axons of the vestibulocochlear (VIII) nerve enter the brain stem, then extend to the medulla or cerebellum where they synapse with the next neurons in the equilibrium pathways
Some axons conduct from the medulla along the cranial nerves that control eye movements and head and neck movements
Other axons form a spinal cord tract that conveys impulses for regulation of muscle tone in response to head movements
Various pathways enable the cerebellum to play a key role in maintaining equilibrium
anosmia
total lack of the sense of olfaction
detached retina
detachment of the neural portion of the retina from the pigment epithelium due to
trauma, disease, or age-related degeneration; the result is distorted vision and blindness
nystagmus
a rapid involuntary movement of the eyeballs, possibly caused by a disease of the central nervous system; associated with conditions that cause vertigo
otalgia
Earache
tinnitus
a ringing, roaring, or clicking in the ears
vertigo
A sensation of spinning or movement in which the world seems to revolve or the person seems to revolve in space
