Chapter 9 Flashcards
Process of Sensation: involves what 4 steps?
- Stimulation of the sensory receptor (graded=receptor potential)
- Transduction of the stimulus
- Generation of action potentials
- Integration of sensory input
Process of sensation in a sentence.
During the process of sensation, sensory information is transformed into electrical signals (graded potentials and action potentials), conveyed into the CNS, and then integrated.
What are the 5 types of resort receptors?
- Mechanoreceptors
- Thermoreceptors
- Photoreceptors
- Chemoreceptors
- Nociceptors
Mechanoreceptor
Sensitive to mechanical stimuli such as the deformation, stretching, or bending of cells
Thermoreceptors
Detect changes in temperature
Photoreceptors
Detect light that strikes the retina of the eye
Chemoreceptor
Detect chemicals in the mouth (taste), nose (smell), and body fluids
Nociceptors
Respond to painful stimuli resulting from physical or chemical damage to tissues. Light, dull pain is often perceived as itch.
Sensory receptors are either
Peripheral endings of sensory neurons or separate cells that synapse with sensory neurons
Sensory receptors that are peripheral endings of sensory neurons
Stimulus ——> receptor potential (nerve endings are either encapsulated or free (dendrites) —triggers—> action potentials ——> propagate into CNS
Sensory receptor that is a separate cell
Stimulus ——> receptor potential (separate cell) —triggers—> release of neurotransmitter from sensory receptor —triggers—> postsynaptic potential —triggers—> action potentials ——> propagate into CNS
Receptive field of a neuron are the
Stimulated physical area
Receptive field of a somatic sensory neuron
Space on skin
Receptive field of a visual neuron in eye
The visual space/area you see
Serve as receptive field of an olfactory receptor cell in nose
Select group of odorants entering the nose
Serve as a receptive field of an auditory neuron in inner ear
A particular set of sound frequencies
Serves as receptive field of a taste neuron in tongue
Specific type of tastings on tongue
sensory neurons with separate receptive fields
if sensory neurons have separate receptive fields, then a given neuron will respond only if there is a stimulus present in the receptive field associated with that neuron
sensory neurons with overlapping receptive fields
if sensory neurons have overlapping receptive fields, then al participating neurons will respond to a stimulus that extends into the region of overlap, but the response of each neuron is proportional to the relative position of the stimulus
sensory coding (4, stimulus…)
- stimulus modality
- stimulus location
- stimulus intensity
- stimulus duration
modality
each unique type of sensation: pain, touch, vision, taste, hearing
labeled lines
the neural pathways that convey information about modality from peripheral receptors to specific regions of the cerebral cortex
touch receptor in the skin
primary somatosensory cortex
gustatory receptor cell
gustatory cortex
olfactory receptor cell
olfactory cortex
hair cell (sound receptor) in cochlea of the inner ear
primary auditory cortex
photoreceptor
primary visual cortex
the size of the cortical region that represents a body part may expand or shrink somewhat, depending on
the quantity of sensory input received from the body part
the primary somatosensory area (postcentral gyrus) contains
primary somatosensory cortex
the primary somatosensory area (postcentral gyrus) exhibits
somatotopy (a body map
precentral gyrus is
primary motor cortex
the primary motor area (precentral gyrus) contains
upper motor neurons that control contralateral muscles
sensory homunculus
human body scaled for sensory receptors
stimulus location
two-point discrimination can be demonstrated by applying the two points of a caliper to the skin
if the two caliper points stimulate the same receptive field, then
only one point of touch is perceived
if the two caliper points stimulate different receptive fields and this input is conveyed into the CNS along separate pathways, then
two points of touch are perceived
least to greatest two point discrimination thresholds for different parts of the body
index finger, lip, big toe, palm, forehead, sole of foot, back, thigh, arm, calf
lateral inhibition
the phenomenon by which input from sensory receptors along the border of a stimulus is substantially inhibited compared to input from sensory receptors at the center of the stimulus
lateral inhibition produces
a central area of excitation surrounded by an area in which the afferent information is inhibited (in other words, better “resolution” or acuity
stimulus intensity is encoded by these two things
- the frequency of action potentials generated in response to the stimulus
- the number of sensory receptors activated by the stimulus
the nervous system interprets the increase in sensory receptor activation as
an increase in stimulus intensity
slowly adapting receptors produce
a significant response as long as the stimulus persist
rapidly adapting receptors responds when
the stimulus is first applied, cease, and may also produce a second response when the stimulus is removed
example of slowly adapting receptor
the brain must be continuously informed about the level of arterial blood pressure in order to maintain the driving force for movement of blood through body tissues.
example of rapidly adapting receptor
you normally notice your clothes touching your body when you first put them on and then are aware of them after that because of rapidly adapting touch receptors present in the skin; also, like sitting on a chair
a sensory pathway
a group of parallel chains of neurons that convey sensory receptors in the periphery to the cerebral cortex
touch, pressure, vibration and proprioception travel via the
dorsal columns in the spinal cord
skin: pain, temperature, itch, and tickle travel through the
spinothalamic tract
most sensory pathways decussate (cross over to the opposite side) as they course through the
spinal cord or brain stem
tactile sensations
encompass a variety of sensations including touch, pressure, vibration, itch, tickle
Pacinian corpuscle =
lamellated corpuscle
Meissner’s corpuscle
rapidly adapting mechanoreceptor, touch and pressure (fluttering and stroking)
Merkel’s corpuscle
slowly adapting mechanoreceptor, touch and pressure (steady pressure, texture)
free neuron ending
slowly adapting, including nociceptors, itch receptors, thermoreceptors, and mechanoreceptors (temperature, noxious stimuli, hair movement)
Pacinian (lamellated) corpuscles
rapidly adapting mechanoreceptors, vibration and deep pressure
Ruffini corpuscle
slowly adapting mechanoreceptor, skin stretch
Krause end bulbs
touch
root hair plexus
touch
sample question: the receptors responsible for detecting deep pressure and high-frequency vibration are __________?
A. arrector pili corpuscles
B. lamellated (Pacinian) corpuscles
C. Ruffini corpuscles
D. Krause bulbs
E. tactile corpuscles
B. lamellated (Pacinian) corpuscles
a Pacinian corpuscle at rest
mechanically-gated cation channel closed
transduction in a Pacinian corpuscle
- mechanically-gated cation channel open
- influx of Na+ and Ca2+ causes a depolarizing receptor potential
thermal sensations are detected by
thermoreceptors
there are two thermoreceptors
cold receptors and warm receptors
cold receptors are activated by temperatures between
10C - 35C (50F - 59F)
there are fewer than cold receptors
warm receptors
warm receptors are activated by temperatures between
30C - 45C (86F - 113F)
pain sensations
protect the body from stimuli that can cause tissue damage (all tissue EXCEPT brain and spinal cord!!)
pain sensation: types of nociceptors
- mechanical
- thermal
- polymodal
mechanical nociceptor
pinch or puncture
thermal nociceptor
extremes <10C or >45C
polymodal nociceptor
intense mechanical, thermal, and chemical
fast pain (A-delta fibers)
e.g. needle puncture or paper cut
slow pain (C fibers, small unmyelinated)
e.g. dull tooth ache, stubbing toe = it takes seconds till it starts throbbing
transduction in warm and cold receptors involves
cation channels that open in response to warm temperatures or cool temperatures, respectively
transient receptor potential (TRP) channel two types
V3 and M8
transduction in warm receptors uses
TRPV3 and camphor
transduction in cold receptors uses
TRPM8 and menthol
transduction in nociceptors involves cation channels that open in response to
noxious stimuli
transduction in extreme heat receptors
transient receptor potential (TRP) channels type V1 (TRPV1) and capsaicin`
a spinal reflex pathway that is activated by a nociceptor
provide unconscious protective responses when a noxious stimulus begins to damage the body
examples of spinal reflex pathways
stepping on a tack or touching a hot burner on the stove elicits the flexor reflex, which quickly withdraws the affected limb away from the painful stimulus
ascending pathways to the brain that are activated by nociceptors
allow pain information to be processed by higher centers
the two main neurotransmitters released from first-order pain neurons are
glutamate and the neuropeptide substance P
referred pain is caused by
convergence on the same second-order neuron
referred pain occurs because both somatic sensory and visceral sensory neurons often
converge on second-order neurons of the ascending pathway to the brain
pain felt in the left arm caused by lack of blood to the heart muscle during a myocardial infarction (MI) is a type of __________ pain
a. imaginary
b. psychological
c. referred
d. generalized
e. phantom limb pain
c. referred
endogenous analgesia system
another way that pain sensations can be suppressed
two components of the brain involved in the endogenous analgesia system
periaqueductal gray matter and nucleus raphe magnus
periaqueductal gray matter
a region of gray matter located in the midbrain
nucleus raphe magnus
a region of gray matter located in the reticular formation of the medulla oblongata
endogenous opioids
three types of neuropeptides that have morphine-like actions: enkephalins, endorphins, and dynorphins
enkephalins
neuropeptide that inhibits pain impulses by suppressing release of substance P; may have a role in memory and learning, control of body temperature, sexual activity, and mental illness
endorphins
neuropeptide that inhibits pain by blocking release of substance P; may have a role in memory and learning, sexual activity, control of body temperature, and mental illness
dynorphins
neuropeptide that may be related to controlling pain and registering emotions
proprioceptive sensations
- provide information about the position of the body in space and the relative location of body parts to one another
- provide information about muscle length, joint position, and tendon tension (kinesthesia)
kinesthesia
- motion perception
- the perception of the extent and direction of movement of body parts; this sense is possible due to action potentials generated by proprioceptors
the two types of proprioceptors
muscle spindle and tendon organ
transduction in a muscle spindle
spindle activity involves mechanically-gated cation channels that open when the sensory nerve ending around an intrafusal fiber is stretched
the two major pathways convey somatic sensory input to the primary somatosensory cortex
dorsal column pathway and anterolateral (spinothalamic) pathway
dorsal column pathway
- sensory pathways that conveys information for touch, pressure, vibration, and proprioception
dorsal column pathway process
First order neuron:
- receptors detect touch, pressure, vibration, and proprioception on the LEFT SIDE, these neurons travel from the receptors to the nuclei of the medulla still on the LEFT SIDE
Second order neuron:
- in the nuclei of the medulla, these neurons cross to the RIGH SIDE of the body (decussation) and ascend through the midbrain and eventually reach the thalamus still on the RIGHT SIDE
Third order neuron:
- in the thalamus, these neurons then project to the primary somatosensory cortex on the RIGHT SIDE
anterolateral (spinothalamic) pathway
conveys action potentials for pain, temperature, itch, and tickle to the cerebral cortex
anterolateral (spinothalamic) pathway process
First order neuron:
- receptors detect pain, temperature, and crude touch on the LEFT SIDE, these neurons travel from the receptors and enter the dorsal horn of the spinal cord
Second order neuron:
- in the dorsal horn of the spinal cord, these neurons cross to the RIGHT SIDE of the spinal cord (decussation) and ascend into the anterolateral pathway, making their way through the medulla on the RIGHT SIDE, the midbrain on the RIGHT SIDE, until they reach the thalamus on the RIGHT SIDE
Third order neuron:
- in the thalamus, these neurons then project to the primary somatosensory cortex on the RIGHT SIDE
olfactory epithelium
5-cm^2 patch where the receptors for olfaction, the sense of small, are located
the olfactory epithelium consists of three types of cell
olfactory receptor cells, supporting cells, and basal cells
olfactory receptor cells
a sensory neuron that detect olfactory stimuli
supporting cells
provide physical support to the olfactory receptor cells and help detoxify chemicals that come in contact with the olfactory epithelium
basal cells
stem cells that continually undergo cell division to produce new olfactory receptor cells, which live for only about two months before being replaced
olfactory transduction
Binding of an odorant molecule to an olfactory receptor protein activates a G protein ad adenylyl cyclase, resulting in the production of cAMP. Cyclic AMP opens a cation channel that allows Na+ and Ca2+ ions to enter the olfactory receptor. The resulting depolarization may generate an action potential, which propagates along the axon of the olfactory receptor cell.
the olfactory pathway
conveys olfactory information from olfactory receptor cells in the nose to the olfactory areas of the brain
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 limbic system
the neural connections of the olfactory pathway account for
our emotional responses to odors
gustatory system
the taste system
tastants
chemicals that stimulate gustatory receptor cells
taste buds contain the receptors for five primary tastes
sweet, sour, salty bitter, and umami
levels of the tongue?
cells –> tastebuds –> papilla
each taste bud consists of three types of cells
supporting cels, gustatory receptor cells, and basal cells
the supporting cells surround about
50 gustatory receptor cells in each taste bud
several microvilli project from each gustatory receptor cell to
the tongue’s surface through the taste pore
basal cells are
stem cells that give rise to supporting cells and gustatory receptor cells
unlike olfactory receptor cells, gustatory receptors cells are not neurons. instead, they are
modified epithelial cells that synapse with first-order taste neurons of the gustatory pathway
filiform papillae
not associated with taste, seen in cats tongue for grooming
transduction of salty and sour tastants
involves the passage of these stimuli directly into the gustatory receptor cell through ion channels present in the plasma membrane
salty and sour transductions steps
- The Na+ ions in a salty tastant or the H+ ions in a sour tastant enter a gustatory receptor cell through Na+ channels or H+ channels, respectively.
- The movement of Na+ or H+ ions into the cell causes a depolarizing receptor potential to form.
- The depolarization in turn causes voltage-gated Ca2+ channels in the plasma membrane to open, allowing Ca2+ ions to flow into the cell.
- The increase in intracellular Ca2+ stimulates the release of neurotransmitter. Once released, the neurotransmitter molecules excite the first-order taste neuron that synapses with the gustatory receptor cell
unlike salty or sour tastants, sweet, bitter, and umami tastants do not themselves enter gustatory receptor cells. Instead, they bind to
G protein-coupled receptors located in the plasma membrane of the
sweet, bitter, umami transduction steps
- A sweet, bitter, or umami tastant binds to a specific receptor that is coupled to a G protein known as gustducin. Gustducin then activates the enzyme phospholipase C to produce the second messenger inositol trisphosphate (IP3).
- IP3 binds to and opens transient receptor potential (TRP) channels (TRPM5) that are present in the plasma membrane
- opening the TRP channels mainly allows Na+ ions to enter the cell, resulting in the formation of a depolarizing receptor potential.
- The depolarization in turn causes voltage-gated Ca2+ channels in the plasma membrane to open, allowing Ca2+ ions to enter the cell.
- IP3 also binds to and opens Ca2+ channels in the membrane of the endoplasmic reticulum (ER). The ER is a membranous organelle that stores calcium ions (Ca2+). So, opening these IP3-gated Ca2+ channels cause the release of Ca2+ from the lumen of the ER into the cytosol
- The increase in intracellular Ca2+ due to the opening of voltage-gated Ca2+ channels and IP3-gated Ca2+ channels triggers the release of neurotransmitters from the gustatory receptor cell. Then the liberated neurotransmitter molecules excite the first-order taste neuron that synapses with the gustatory receptor cell.
think: if sweet, bitter, umami invoke the same transmitter, how does our brain tell the difference between different foods?
neurotransmitters: salt = unclear; sour = ATP + serotonin; sweet, bitter, umami = ATP
the gustatory pathway extends from
taste receptors to the gustatory cortex
the gustatory pathway
conveys taste information from gustatory receptor cells in the tongue to the gustatory cortex of the brain
three cranial nerves contain axons of the first order taste neurons that innervate the taste buds:
the facial (VII) and glossopharyngeal (IX) nerves serve the tongue, and the vagus (X) nerve serves the pharynx and epiglottis
the gustatory pathway steps
- detection by taste buds: when you eat or drink, chemicals in your food dissolve in saliva and come into contact with taste buds on your tongue and other parts of your mouth
- activation of sensory cells: these chemicals activate gustatory (taste) receptor cells within the taste buds
- signal transmission: activated gustatory cells send signals through gustatory nerves. The main nerves involved are the facial nerve (VII), glossopharyngeal nerve (IX), and vagus nerve (X)
- relay in the brainstem: the signals travel to the medulla oblongata in the brainstem, where they synapse in the nucleus of the solitary tract
- thalamus relay: from the brainstem, the signals are relayed to the thalamus, specifically the ventral posteromedial nucleus
- processing in the cerebral cortex: finally, the thalamus sends the taste information to the gustatory cortex, located in the insula and frontal operculum, where the sensation of taste is consciously perceived
the accessory structures of the eye include
eyebrows, eyelashes, eyelids, lacrimal apparatus, and extrinsic eye
the eyebrows and eyelashes help
protect the eyes from foreign objects, perspiration, and direct rays of the sun
the upper and lower eyelids
shade the eyes during sleep and protect the eyes from excessive light and foreign objects
the lacrimial apparatus is
a group of glands, canals, and ducts that produce and drain lacrimal fluid or tears
lacrimal glands are the
components of the lacrimal apparatus that secrete tears. after being secreted, tears pass over the surface of the eyeball toward the nose into two lacrimal canals and a nasolacrimal duct, which allow the tears to drain into the nasal cavity
tears
lubricate and cleanse the eye, they also contain a bacteria-killing enzyme called lysozyme that helps protect the eye from onfection
other important structures of the eye are the extrinsic eye muscles, which
attach to the outer surface of the eyeball, these skeletal muscles are responsible for moving the eye in various directions
the eye is a sphere composed of three layers
a lens and two cavities
the outer layer of the eye consists of an
anterior and posterior sclera
the cornea is a
transparent structure that admits light into the eye; it also refracts (bends) the incoming light rays (refraction of light by the cornea and lens helps fucus light onto the retina, the part that detects light)
the sclera, the white of the eye, is a
tough coat of connective tissue that covers the entire eyeball except the cornea; gives shape to the eye and protects its internal parts
the middle layer of the eye consists of the
choroid, ciliary body, and iris
the choroid
lines most of the inner surface of the sclera; it contains the pigment melanin, which causes this layer to appear dark in color
melanin in the choroid absorbs stray light rays, which prevents reflection and scattering of light within the eye. as a result,
the image cast on the retina by the cornea and lens remains sharp and clear
at the front end of the eye, choroid becomes the
capillary body
the ciliary body is responsible for
secreting fluid called aqueous humor
extending from the ciliary body are
zonular fibers (suspensory ligaments) that attach to the lens
contraction or relaxation of smooth muscle present in the ciliary body changes the tightness of the zonular fibers, which
alters the shape of the lens for viewing object up close or at a distance
the iris is the part of the eye that is responsible for
eye color
in the center of the iris is a hole known as the
pupil
the iris regulates
the amount of light that enters the eye by adjusting the diameter of the pupil
changes in pupil diameter involve two types of smooth muscles present in the iris:
circular muscle (sphincter pupillae) and radial muscles (dilator pupillae)
when the eye is stimulated by bright light
the circular muscle contracts, which decreases the size of the pupil (constriction)
when the eye must adjust to dim light,
the radial muscles contract, which increase the size of the pupil (dilation)
the smooth muscles of the iris are under control of
the autonomic nervous system
parasympathetic fibers of the oculomotor nerve (III) nerve cause contraction of the
circular muscles
sympathetic nerve fibers cause contraction of the
radial muscles
the inner layer of the eye is the
retina
the retina is responsible for
converting light into action potentials
the retina is further subdivided into
a pigmented layer and a neural later
the pigmented layer consists of
epithelial cells that contain melanin
the melanin in the pigmented layer of the retina, like in the choroid, helps
to absorb stray light rays
the neural layer of the retina is a
multilayered outgrowth of the brain
the neural layer of the retina consists of three distinct layers of cells that sequentially process visual signals
the photoreceptor layer, bipolar cell layer, and ganglion cell layer
photoreceptors, which include rods and cones, are
sensory receptors that detect light and convert it into receptor potentials
bipolar cells are
neurons that convey signals from photoreceptors to ganglion cells
ganglion cells are
neurons that generate action potentials in response to signals from bipolar cells
the axons of the ganglion cells give rise to the optic (II) nerve, which
carries sensory information about light in the form of action potentials from the eye to the brain
not that when light enters the eye, it passes through the
ganglion and bipolar cell layers before it enters the photoreceptor layer
the two other types of cells present in the bipolar layer of the retina are
horizontal cells and amacrine cell
horizontal and amacrine cells form
laterally directed neural circuits that modify the signals being transmitted along the pathway from photoreceptors to bipolar cells to ganglion cells
the macula lutea is
an oval area located in the center of the posterior retina, it is yellowish in color due to the presence of yellow pigment, it is responsible for central vision (the ability to see straight ahead)
the fovea is
a small depression in the center of the macula lutea; the area of highest visual acuity or resolution
the optic disc is the site where
the optic (II) nerve exists the eyeball
because photoreceptors are not present in the optic disc, it is also known as the
blind spot
the fovea centralis has
no rods and light rays land perpendicular to the retina and light reaches the cones most effictively
behind the pupil and iris of the eye is the lens, an
elastic structure that refracts light rays; normally is perfectly transparent because its cells lose their nuclei and other organelles and gradually become filled with a special group of clear organelles called crystallin
rods are
highly sensitive to light
cones have
low sensitivity to light
rods and cones are necessary for
normal vision
three types of cones
blue, green, red
blue cones
420nm
green cones
530nm
red cones
560nm
the photopigments present in rods and cones contain two parts
a derivative of vitamin A called retinal and a protein known as opsin
retinal is the
light-absorbing part of all visual photopigments
the human retina contains for different opsins
one present in rods and one in each of the three different cones
small variations in the amino acid sequences of the different opsins permit
the rods and cones to maximally absorb different wavelengths of light
red 700nm waves
- long wavelength
- low frequency
- low energy
blue 450nm waves
- short wavelength
- high frequency
- high energy
ratio of ganglion cells to photoreceptors
1 million ganglion cells: 126 million photoreceptors
the high degree of convergence in rod pathways increases the
light sensitivity of rod vision, but slightly blurs the image that is perceived
cones in the fovea are
densely packed and have smaller diameter than in the periphery
the photopigments of rods and cones respond to light via the following cyclic process
- Isomerization. In darkness, retinal has a bent shape, called cis-retinal, which fits snugly into the opsin portion of the photopigment. When cis-retinal absorbs a photon of light, it straightens out to a shape called trans-retinal. This cis-to-trans conversion is called isomerization and is the first step in visual transduction. After retinal isomerizes, chemical changes occur in the outer segment of the photoreceptor. These chemical changes lead to the production of a receptor potential.
- Bleaching. In about a minute, trans-retinal completely separates from opsin. Retinal is responsible for the color of the photopigment, so the separation of trans-retinal from opsin causes opsin to look colorless. Because of the color change, this part of the cycle is termed bleaching of photopigment.
- Conversion. An enzyme called retinal isomerase converts trans-retinal back to cis-retinal.
- Regeneration. The cis-retinal then can bind to opsin, reforming a functional photopigment. This part of the cycle—resynthesis of a photopigment—is called regeneration.
ishihara test
testing for red-green color blindness
B-carotene in plant juices is
typically mixed with milk in smoothies to enhance absorption; body changes that into vitamin A
night blindness is caused by
a below normal amount of rhodopsin, usually due to prolonged vitamin A deficiency
phototransduction
converting light to receptor potential
operation of a rod in darkness
- In darkness, cis-retinal is the form of retinal associated with the photopigment of the photoreceptor. Photopigment molecules are present in the disc membranes of the photoreceptor outer segment.
- Another important occurrence during darkness is that there is a high concentration of the second messenger cyclic GMP (cGMP) in the cytosol of the photoreceptor outer segment. This is due to the continuous production of cGMP by the enzyme guanylyl cyclase in the disc membrane.
- After it is produced, cGMP binds to and opens nonselective cation channels in the outer segment membrane. These cGMP-gated channels mainly allow Na+ ions to enter the cell.
- The inflow of Na+, called the dark current, depolarizes the photoreceptor. As a result, in darkness, the membrane potential of a photoreceptor is about −40 mV. This is much closer to zero than a typical neuron’s resting membrane potential of −70 mV.
- The depolarization during darkness spreads from the outer segment to the synaptic terminal, which contains voltage-gated Ca2+ channels in its membrane. The depolarization keeps these channels open, allowing Ca2+ to enter the cell. The entry of Ca2+ in turn triggers exocytosis of synaptic vesicles, resulting in tonic release of large amounts of neurotransmitter from the synaptic terminal.
operation of a rod in light
- When light strikes the retina, cis-retinal undergoes isomerization to trans-retinal.
- Isomerization of retinal causes activation of a G protein known as transducin that is located in the disc membrane.
- Transducin in turn activates an enzyme called cGMP phosphodiesterase, which is also present in the disc membrane.
- Once activated, cGMP phosphodiesterase breaks down cGMP. The breakdown of cGMP lowers the concentration of cGMP in the cytosol of the outer segment.
- As a result, the number of open cGMP-gated channels in the outer segment membrane is reduced and Na+ inflow decreases.
- The decreased Na+ inflow causes the membrane potential to drop to about −65 mV, thereby producing a hyperpolarizing receptor potential.
- The hyperpolarization spreads from the outer segment to the synaptic terminal, causing a decrease in the number of open voltage-gated Ca2+ channels. Ca2+ entry into the cell is reduced, which decreases the release of neurotransmitter from the synaptic terminal. Dim lights cause small and brief receptor potentials that partially turn off neurotransmitter release; brighter lights elicit larger and longer receptor potentials that more completely shut down neurotransmitter release.
retinal ON pathway in response to darkness
cone is depolarized –> increased release of inhibitory glutamate molecules -graded potential-> bipolar cell is hyperpolarized –> decreased release of excitatory glutamate molecules -action potential-> ganglion cell is hyperpolarized –> fewer action potentials are generated
retinal ON pathway in response to light
cone is hyperpolarized –> decreased release of inhibitory glutamate molecules –> bipolar cell is depolarized –> increased release of excitatory glutamate molecules –> ganglion cell is depolarized –> more action potentials are generated
retinal OFF pathway in response to darkness
cone is depolarized –> increased release of excitatory glutamate molecules –> bipolar cell is depolarized –> increased release of excitatory glutamate molecules –> ganglion cell is depolarized –> more action potentials are generated
retinal OFF pathway in response to light
cone is hyperpolarized –> decreased release of excitatory glutamate molecules –> bipolar cell is hyperpolarized –> decreased release of excitatory glutamate molecules –> ganglion cell is hyperpolarized –> fewer action potentials are generated
in an ON-center/OFF-surround field
the ganglion cell is excited when light is present in the center and inhibited when light is present in the surround
in an OFF-center/ON-surround field
the ganglion cell is inhibited when light is present in the center and excited when light is present in the surround
neural circuitry responsible for an ON-center/OFF-surround field
increased firing rate of action potential
neural circuitry responsible for an OFF-center/ON-surround field
decreased firing rate of action potential
what is the correct sequence that visual information travels in the retina?
A. bipolar cells, ganglion cells, photoreceptors
B. ganglion cells, bipolar cells, photoreceptors
C. photoreceptors, ganglion cells, bipolar cells
D. photoreceptors, bipolar cells, ganglion cells
D. photoreceptors, bipolar cells, ganglion cells
within the eye, electrical impulses pass from
A. photoreceptors to bipolar cells to ganglion cells
B. bipolar cells to photoreceptors to ganglion cells
C. photoreceptors to ganglion cells to bipolar cells
D. ganglion cells to bipolar cells to photoreceptors
A. photoreceptors to bipolar cells to ganglion cells
the optic nerve is formed from fibers of
A. bipolar cells
B. ganglion cells
C. rods and cones
D. amacrine
B. ganglion cells
the visual pathway
- extends from photoreceptors to the visual areas of the brain
- conveys visual information from the retina to the visual areas of the brain
the primary visual cortex has a map of visual space
each region within the cortex receives input from a different part of the retina, which in turn receives input from a particular part of the visual field
both eyes receive input from the left and right visual fields to
allow depth perception
optic chiasm (crossing) allows
binocular vision and depth perception
depth perception
enables us to judge distance
Gibson and Walk (1960) suggested that
human infants (crawling age) have depth perceptions, even newborn animals show depth perception
damage to the right optic nerve
complete loss of vision in right eye
damage to the optic chiasm
loss of peripheral (temporal) vision in both the left and right eye
damage to the right optic tract
loss of left visual field in both eyes
the ear is divided into three main regions
the external ear, the middle ear, and the inner ear
the external ear collects
sound waves and channels them inward
the middle ear conveys
sound vibrations to the oval window
the inner ear houses the
receptors for hearing and equilibrium
the external ear consists of the
pinna, external auditory canal, and tympanic membrane
the pinna is a
skin-covered flap of cartilage located on each side of the head; it collects sound waves and directs them into the external auditory canal
the external auditory canal is a
curved tube that conveys sound waves from the pinna to the tympanic membrane
cerumen (earwax)
the external auditory canal contains this sticky substance which helps prevent foreign objects from entering the ear
the tympanic membrane or eardrum is
a thin, semitransparent structure between the external auditory canal and the middle ear
when sound waves strike the tympanic membrane, it
vibrates and then transmits the vibrations to the middle ear
the middle ear is a
small, air-filled cavity located between the tympanic membrane and inner ear
within the partition separating the middle and inner ears are two membrane covered openings:
an upper oval window and a lower round window
upper oval window
a small, membrane-covered opening between the middle ear and inner ear into which the footplate of the stapes fits
lower round window
a small opening between the middle and internal ear, directly below the oval window, covered by membrane
three tiny bones called auditory ossicles extend across the middle ear
malleus, incus, and stapes (commonly known as the hammer, anvil, and stirrup)
one end of the malleus is attached to the
tympanic membrane, and the footplate od the stapes fits into the oval window
the main function of the auditory ossicles is to
transmit and amplify vibrations from the tympanic membrane to the oval window
the middle ear also contains two skeletal muscles that
contract reflexively to protect the structures of the inner ear from damage by loud noises
the tensor tympani muscle
is attached to the malleus, protects the inner ear from loud sounds by limiting the movements of the tympanic membrane
the stapedius muscle
is attached to the stapes, protects the inner ear from loud noises by dampening the movements of the stapes in the oval window
because it takes a fraction of a second for the tensor tympani and stapedius muscles to contract, they can
protect the inner ear from prolonged loud noises but not from brief ones such as gunshot
the middle ear is connected to the pharynx (throat) by the
eustachian tube or auditory tube
the eustachian tube is normally closed at the
end closest to the pharynx
during swallowing and yawning, the eustachian tube opens, allowing
air to enter or leave the middle ear until the pressure in the middle ear equals the atmospheric pressure
the inner ear, also known as the labyrinth is
a complicated series of canals
the inner ear consists of two main divisions
an outer bony labyrinth that encloses an inner membranous labyrinth
the bony labyrinth is a
series of cavities in the temporal bone of the cranium; it includes the cochlea, vestibule, and semicircular canals
the cochlea is the
sense organ for hearin
the vestibule and semicircular canals are the
sense organs for equilibrium
the bony labyrinth contains a fluid called
perilymph (chemically similar to cerebrospinal fluid) that surrounds the membranous labyrinth
membranous labyrinth
a series of sacs and tubes that have the same general shape as the bony labyrinth
the membranous labyrinth contains fluid calles
endolymph
the level of potassium ions (K+) in endolymph is
unusually high and potassium ions play a role in the generation of auditory signals
the vestibule is the
middle part of the bony labyrinth
the membranous labyrinth in the vestibule consists of two sacs called the
utricle and the saccule
behind the vestibule are three bony
semicircular canals, each of which lies at approximately right angles to the other two
the portions of the membranous labyrinth that lie inside the bony semicircular canals are called the
semicircular ducts
cochlea
a winding, cone-shaped tube forming a portion of the inner ear and containing the organ or Corti
cochlea is divided into three channels
cochlear duct, scala vestibuli, and scala tympani
the cochlear duct or scala media is a
continuation of the membranous labyrinth into the cochlea; it is filled with endolymph
the channel above the cochlear duct is the scala tympani, which
ends at the round window
both the scala vestibuli and scala tympani are part of the bony labyrinth of the cochlea and are filled with
perilymph
the scala vestibuli is connected to the scala tympani at a region at the apex of the cochlea known as the
helicotrema
the vestibular membrane separates the
scala vestibuli from the cochlear duct
the basilar membrane separates the
cochlear duct from the scala tympani
resting on the basilar membrane is the
organ of Corti or spiral organ
the organ of Corti consists of
supporting cells and hair cells
there are two groups of hair cells
a single row of inner hair cells and three rows of outer hair cells
at the apical tip of each hair are stereocilia, which are actually
microvilli arranged in several rows of graded height
the stereocilia are embedded in a flexible, gelatinous covering called the
tectorial membrane
most of the sensory neurons, which are first-order auditory neurons, synapse
with the inner hair cells; the motor neurons synapse mainly with the outer hair cells
at their basal ends, hair cells receive innervation from sensory and motor neurons of
the cochear branch of the vestibulochoclear (VII) nerve
inner hair cells are
the receptors for hearing, they convert the mechanical vibrations of sound into electrical signals
sound waves are generated from
a vibrating object
outer hair cells do not serve as hearing receptors, instead, they
increase the sensitivity of the inner hair cells
pitch
determined by frequency of sound waves
intensity
determined by the amplitude of the sound waves, which is the difference in pressure between areas of compression and rarefaction; measured in decibels
transmission of sound waves through the ear
- The pinna directs sound waves into the external auditory canal.
- When sound waves strike the tympanic membrane, the alternating high and low pressure of the air causes the tympanic membrane to vibrate back and forth. The distance it moves, which is very small, depends on the intensity and frequency of the sound waves. The tympanic membrane vibrates slowly in response to low-frequency (low-pitched) sounds and rapidly in response to high-frequency (high-pitched) sounds.
- The central area of the tympanic membrane connects to the malleus, which also starts to vibrate. The vibration is transmitted from the malleus to the incus and then to the stapes.
- As the stapes moves back and forth, it pushes the membrane of the oval window in and out. The oval window vibrates about 20 times more vigorously than the tympanic membrane because the auditory ossicles efficiently transmit small vibrations spread over a large surface area (tympanic membrane) into larger vibrations of a smaller surface (oval window).
- The movement of the stapes at the oval window sets up fluid pressure waves in the perilymph of the cochlea. As the oval window bulges inward, it pushes on the perilymph of the scala vestibuli.
- Pressure waves are transmitted from the scala vestibuli to the scala tympani and eventually to the round window, causing it to bulge outward into the middle ear. (See step 9 in the figure.)
- As the pressure waves deform the walls of the scala vestibuli and scala tympani, they also push the vestibular membrane back and forth, creating pressure waves in the endolymph inside the cochlear duct.
- The pressure waves in the endolymph cause the basilar membrane to vibrate, which moves the hair cells of the organ of Corti against the tectorial membrane. This leads to bending of the hair cell stereocilia, resulting in the production of receptor potentials that ultimately lead to the generation of action potentials.
sound transduction
transmitted by the hair cells inner hair cells (responsible of sound transduction) and outer hair cells (enhance the sensitivity of inner hair cells)
sound transduction for resting hair cell (weakly depolarized)
At rest, hair cells have a slight positive charge inside due to a steady influx of potassium ions. They are weakly depolarized and ready to respond to sound vibrations.
sound transduction for strongly depolarized hair cell
When sound waves cause the hair cell’s stereocilia (tiny hair-like projections) to bend towards the tallest stereocilium, potassium and calcium ions rush into the cell. This causes the cell to become strongly depolarized, releasing neurotransmitters that send a signal to the auditory nerve.
sound transduction for hyperpolarized hair cell
When the stereocilia bend in the opposite direction (away from the tallest stereocilium), potassium channels close, reducing the influx of potassium ions and increasing the cell’s negative charge. This hyperpolarizes the cell, decreasing neurotransmitter release and reducing the signal to the auditory nerve.
sound discrimination on the basilar membrane
pitch depends on which basilar membrane region vibrates and loudness depends on how much the basilar membrane vibrates
from hair cells of the cochlea, auditory information is conveyed along the
cochlear branch of the vestibulocochlear (VIII) nerve and then to the brain stem, thalamus, and cerebral cortex
otolithic organs: in the utricle and saccule
- perpendicular to each other
- detect linear acceleration or deceleration
- detect head tilt
- saccule vertical acceleration/deceleration (elevator)
semicircular ducts detect
rotational acceleration/deceleration
Meniere’s disease
results from an abnormal buildup of endolymph that enlarges the membranous labyrinth
a layer of dense calcium carbonate crystals called
otoliths help move the membrane
treating positional vertigo
the Epley Maneuver of moving the head in certain direction to return dislodged otoliths
as head rotates in one direction, the drag of the endolymph causes
capula and its embedded hairs to bend in opposite direction
