Unit 7 Flashcards
Sensation
The first stage in the functioning of the senses, starting with information at the peripheral sensory receptors
Perception
The process of recognizing, organizing, and interpreting sensory information
Sensory receptor
may be a specialized structure at the end of a peripheral neuron or a separate cell that communicates with an afferent neuron by means of a chemical synapse.
Afferent neuron
Afferent neuron is taking info from the sensory receptor into the cortex
Receptor specialization
may be part of afferent sensory neuron or may be a separate, specialized cell adjacent to afferent sensory neuron.
Sensory unit
is defined as a single nerve axon and all the sensory receptors which transmit information to it.
Primary afferent and the receptors that define its receptive field
Receptive field
is the spatial region where application of a stimulus causes a sensory neuron to respond. Receptive fields can overlap, and the definition also applies to higher order neurons, as well as to primary afferents. No differentiation of information occurs within the receptive field.
Sensory receptive field: spatial resolution
Receptor fields are like pixels, the more receptor fields equal more detail
Smaller RFs tiling an area = higher spatial resolution
Discrimination
is the ability to perceive two or more stimuli as separate. High discrimination implies a low ratio of receptors to nerve fibers: the sensory unit is small and the receptive field is small. High discrimination, however, usually carries the penalty of low sensitivity unless the receptor density is very high.
Sensitivity
is the ability to measure small changes in stimulus intensity: for this purpose a high ratio of receptors to nerve fibers is preferable. The intensity of stimulus is coded by single receptors but the more receptors there are involved the more effectively changes in intensity can be detected. The bigger the stimulus, the more receptors will be stimulated. Size of receptor field and density of receptor distribution are both important factors in sensitivity of a sensory unit.
Transduction
is the conversion of one form of energy into another. Sensory transduction converts the energy of the stimulus into a receptor or generator potential. Transduction couples stimulus detection (i.e., activation of a receptor protein) to the opening or closing of an ion channel. The type of receptor proteins, and how they are coupled to ion channels, is different in each sensory system: e.g., compare the transduction channels in somatosensation (mechanical) to the vision (light-based).
Transduction channels are often non selective
Typically results in the transduction current being carried by Na+, but can be by other ions
Transduction in Sensory system
The conversion of stimulus energy into electrical potentials in neurons
Unique physiological process that is common to all sensory systems
Multi step process
Stimulus > accessory structures
Receptor: conformational change in transducer protein
2nd messenger systems
ion channel activation/inactivation (conductance change)
Receptor potential
Neurotransmitter release
Action potential in primary afferent neuron
Graded response
the amplitude of the receptor potential is proportional to the size of the stimulus: the larger the stimulus, the larger the graded response at the receptor. A graded response can be depolarizing or hyperpolarizing.
Stimulus energy
A stimulus is an energy change (e.g., light, sound) which is registered by the senses (e.g., vision, hearing, taste, etc.) and constitutes the basis for perception. The term ‘stimulus energy’ refers to the type of environmental change (e.g., light, sound, mechanical pressure, etc.).
Stimulus intensity
Threshold
The minimun intensity of a stimulus that is required to produce a response from a sensory system
Can be defined in terms of
Receptor threshold
AP threshold
Perception threshold
The adequate stimulus will produce the response with the lowest threshold
Stimulus duration
For most receptors, a supra-threshold stimulus depolarizes the receptor membrane which leads to AP generation in the primary afferent neuron
However the typical response to a constant stimulus is not constant with time
The CNS is generally much more interested in changing stimuli than static ones
The process is called adaption
Stimulus duration: receptor adaptation
Very few receptors exhibit no change in receptor potential in response to a constant stimuli (otoliths)
If the change in receptor potential occurs slowly, the response is called tonic (olfactory sys)
If it occurs rapidly it is called phasic (auditory sys)
Different from the concept of selective attention which is a CNS process
Stimulus modality Specificity
means that receptors respond to one form of energy more than any other, and that receptors respond to only a narrow range of stimulus energy. The principle of specificity does NOT mean that a receptor cannot respond to other forms of energy (e.g., photoreceptors responding to intense pressure). However, due to the segregation of sensory pathways (think of the organization of sensory cortices, with each system in a different physical location), any stimulus is perceived as if it was the adequate stimulus (e.g., pressure on photoreceptors is perceived as “seeing stars”).
Stimulus modality adequate stimulus
The type of energy that a receptor responds to under normal conditions (ie. the type of energy that has the lowest threshold for receptor activation and size)
This pathway-specific segregation of sensory information is termed the “labelled line” theroy of modality coding
Photoreceptors
transduce light energy to neural signals. Absorption of photon changes protein channel configuration to open ion channel. Photoreceptors are found in humans primarily in the retina, for vision and circadian rhythms via pineal gland.
Chemoreceptors
transduce chemical energy/info to neural signals. A chemical in the environment acts as ligand to open the receptor’s ion channel. Chemoreceptors are found in olfaction, taste, GI tract, breathing control.
Mechanoreceptors
transduce mechanical energy/distortion into neural signals. They are frequently specialized receptors, including somatosensory receptors; auditory and vestibular hair cells; and internal receptors in ligaments (bone-to-bone connective tissue). Free nerve endings involved in pain sensation (nociception) may also contain less specialized mechanoreceptors.
Vestibular hair cells
Very similar to hair cells in auditory system
High concentration of K+ in endolymph
K+ in Ca++ in, NT released
But they have spontaneous firing in absence of input, so when there is no rotation, hair cells release a base rate of NT
Bend cilia one way and more/less NT is released
Mechanotransduction: hair cells
Transduction in hair cells is K+ based
When cilia are bent K+ gates are pulled open and K+ enters, changing the polarity opening Ca++ gate
Ca++ enters and NT exists (graded response)
Nociceptors
transduce pain info from chemical, mechanical, and/or thermal damage into neural signals. Nociceptors can be unimodal (only be activated by one stimulus) or polymodal/multimodal; that is, they can have more than one adequate stimulus. Most nociceptors respond to heat and cold, mechanical stimuli, and chemicals associated with tissue damage or disease (both external and internal). Polymodal nociceptors are more commonly known as unmyelinated free nerve endings. They also may be silent; that is, they are dormant until tissue damage or disease activates their sensitivity.
Thermoreceptors
transduce thermal energy (temperature info) into neural signals. codes absolute and relative changes in temperature, primarily within the innocuous range. In the mammalian peripheral nervous system, warmth receptors are thought to be unmyelinated C-fibers (low conduction velocity), while those responding to cold have both C-fibers and thinly myelinated A delta fibers (faster conduction velocity). The adequate stimulus for a warm receptor is warming, which results in an increase in their action potential discharge rate. Cooling results in a decrease in warm receptor discharge rate. For cold receptors their firing rate increases during cooling and decreases during warming. Some cold receptors also respond with a brief action potential discharge to high temperatures, i.e. typically above 45 °C, and this is known as a paradoxical response to heat. It causes us to perceive the cold object as hot. The mechanism responsible for this behavior has not been determined. Certain chemicals can also act as ligands that bind thermoreceptors, and therefore can be perceived as hot or cold (e.g., capsaicin/chili powder can fill hot).
Receptor threshold
is the intensity of the stimulus that will drive a change in receptor potential
Action potential threshold
is the intensity of the stimulus with will drive changes in enough receptor potentials to cause an action potential to fire in the afferent neuron
Perception threshold
is the intensity of the stimulus that will produce a conscious perception – also relies on higher-order aspects like attention
Saturation
is the maximum intensity of a stimulus that produces a response from a sensory system.
Dynamic Range
is the range of intensities that will produce a response from a receptor or sensory system (i.e., the difference between threshold and saturation). Even within a modality, individual receptors will have different thresholds and dynamic ranges. As a result, the sensory system as a whole will have a wider dynamic range than an individual receptor.
Frequency coding
is the encoding of stimulus intensity by the frequency of action potentials induced by the stimulus.
Population coding
is the encoding of stimulus intensity by the number of receptors activated by the stimulus.
Stimulation of a single sensory unit is dependent on how many parts in the cell are being activated (more=stronger stim)
Stimulation of multiple sensory units (How many neighboring cells are being activated)
Sensory adaptation
is a phenomenon that occurs when the sensory receptors become exposed to stimuli for a prolonged period. Most receptors decrease their ability to respond and will develop a diminished sensitivity to the stimulus. A few types of stimuli, like pain, may cause the sensory receptors to become more sensitive to the stimulus with a prolonged response.
tonic response
is a change in receptor potential that occurs slowly.
Slowly adapting fibers (SA) – fire continuously as long as pressure is applied (e.g., found in somatosensory Merkel and Ruffini receptors). Code for stimulus intensity over the duration of the stimulus.
phasic response
is a change in receptor potential that occurs rapidly.
Rapidly adapting fibers (RA) – fire at onset and offset of stimulation (e.g., found in somatosensory Meissner receptors and Pacinian corpuscles). Code for stimulus onset and offset.
Acuity
Stimulus location: is the ability to precisely localize a stimulus. Acuity is increased with smaller receptive field sizes and increased density of receptors within the region of the stimulus. Receptors generally are concentrated in the center of the receptive field.
Convergence
is a pattern of connectivity in which information from multiple neurons (typically at one level of processing, like the photoreceptors) joins together in their inputs onto a single neuron (typically at the next level of processing, like the retinal ganglion cells). Convergence creates larger receptive fields in this way. The larger receptive field of the second, single neuron encompasses all the receptive fields of the input neurons at the first level. As no differentiation of information can occur within a receptive field, there is no way to separate out the information from the first group of neurons once it all is combined at the second neuron. Cones have low convergence, rods have high convergence.
Two point discrimination
The ability to perceive two fine points as two points and not one
Divergence
is a pattern of connectivity in which information from one neuron is divided into multiple neural pathways. This is a mechanism for spreading the same stimulation to multiple neurons or neuronal pools in the CNS, and is seen in such regions as the spreading of information from primary visual cortex (V1) to various distinct higher-order visual pathways (e.g., visual motion, visual form, color).
Labeled line
is a specific pathway that transmits information about a specific sensory modality. Stimulation of a labeled line only produces a sensation of its primary sensory modality no matter what type of stimulus energy produces the action potentials. Pathways for different modalities terminate on different places of the cerebral cortex, and thus lead to different types of perception based on their different cortical connectivity patterns. Such a pathway begins with a sensory unit.
First-, second-, and third-order neurons
The afferent neuron in a sensory pathway is the first order neuron. It synapses with a second order neuron (either in the spinal cord or brain stem, depending on the specific somatosensory tract: tactile vs. pain/temperature), which in turn synapses with a third order neuron in the thalamus. The third order neuron guides the impulse to primary sensory cortex (S1), and then on to create conscious perception.
Retina
The back of the eyeball, considered a part of the brain, where light hits the photoreceptive cells and visual information begins being processed.
Fovea
the part of the retina, where vision is most acute and color vision is best. Cone photoreceptors are most prevalent here.
Photoreceptor cells
Cells that line the back of the retina and have parts that change shape when they are hit with a photon, allowing them to detect light in a certain part of the visual field. Humans have two main types, rods and cones, and there are three different subtypes of cones. Photoreceptor cells are composed of an outer segment, which has stacked cell membranes that contain the photoreceptor proteins, and a cell body at the base
Rods
Photoreceptor cells that are located outside the fovea. They are responsible for low-light vision (highly sensitive to light) and useful for detecting movement, but at the cost of visual acuity. They do not differentiate between colors.
Cones
Photoreceptor cells that are located primarily in the fovea. They are responsible for high acuity vision, but take more photons of light to activate (good for daytime vision). There are three types, each most responsive to different wavelengths of light (corresponding to red, green, and blue), which, when combined, allow for color vision.
Rods vs cones similarities
Same layer in retina
Molecules of photo pigment embedded in outer segments
Outer segments embedded in pigment epithelium
Graded potentials
Release inhibitory NT
Photoreceptor proteins
light-sensitive protein molecules involved in the sensing and response to light in a variety of organisms by undergoing a structural change when they absorb light. This structural change opens ion channels, which causes a change in the graded potential (ion flow) of the photoreceptor (in other words, causes the photoreceptor cell to signal that light has been detected).
Rods and Cones differences
Rods have 1 type of photopigment, cones have 3
Rods don’t code for color, cones do
Rods are excellent for motion detection, cones are poor for motion detection
Rods have poor acuity, cones have excellent acuity (high resolution vision)
Rods have high sensitivity (operate in dim light), cones have low sensitivity (require bright light)
Opsins
a type of photosensitive pigment proteins found in photoreceptors: e.g., rhodopsin in rods and photopsin in cones (3 types are in cones, making up the L,M, and S cone types), and melanopsin in the melanopsin-containing retinal ganglion cells (also called intrinsically photosensitive retinal ganglion cells – see below).
Light absorption by an opsin molecule causes protein structure change
If the eyes are stabilized, photoreceptors and retinal ganglion cells become desensitized/adapt to the current stimulus
Photoreceptor transduction
In inactive cell there is more K+ inside and Na+/Ca++ outside and the ion gates are closed. On the bottom of the cell body vesicles of NT are waiting to be released to signal the rest of the retinal circuitry
In the “Dark Current” (the dark turn photoreceptors on) cGMP holds Na+ gates open (signals inhibitory response to turn everything down resulting in nothing happening) and Na+ enters the cell
Na+ accumulates in the cell and the change in polarity opens the Ca++ gate
Ca++ enters and NT are released and visual receptors fire in the dark
As positive charges accumulate in the cell, Na+ exists via electrostatic pressure (b/c there are too many positive charges in the cell causing ionic flow to slow down)
Ca++ pump ejects Ca++ out of the cell (requires ATP)
Ejection of Ca++ ends NT release and the cycle begins again (if still in the dark)
Ca++ and Na+ enters and NT is repeatedly released as long as there is no light
Isomerization (in the light. Light enters causing change in shape of opsins)
Photo-pigment (opsin) absorbs light, get’s “bleached” and turns from visual purple to pink (meaning it’s now inactive, the molecule has now changed shape)
Isomerization initiates a metabolic chain reaction changing cGMP into 5’GMP which keeps Na+ gates closed
With no influx of Na+, Ca++ gates remain shut so the “Dark Current” is shut down (no NT released)
Light adapted
When much of our photo-pigment has been isomerized
Come inside on a sunny day, at first the indoor light seems very dim
In the snowy artic, so much bright light at once can temp blind you, if all your photopigment is isomerized at once
Eventually you can see well again because in time your photopigments will regen
Dark adapted
When we spent a lot of time in the dark
At first when you turn out the light you can’t see anything
But in time as your photo-pigment regens you can see faint shapes in the dark
How do receptor cells signal that light is present if they are turned off by light
They are able to signal that light is present because turning off photoreceptors is an inhibitory response. It matters not what the cell does but how they are connected.
Dark current
refers to the entry of Na+ and Ca2+ into the photoreceptor cell when light is not hitting the cell. Photon absorption in the light turns the dark current off; thus, photoreceptors become less active in the light.
Isomers
are molecules or polyatomic ions with identical molecular formulas — that is, same number of atoms of each element — but distinct arrangements of atoms in space. Isomerization is the process in which a molecule, ion, or molecular fragment is transformed into an isomer with a different chemical structure.
Photoisomerization
is the conversion of 11-cis retinal to its isomer, all-trans retinal, when 11-cis retinal absorbs light. The structural change of the retinal created by the added energy from the photon drives an overall structural change in the opsin molecule in which the retinal is embedded. This is called activation of opsin.
Regeneration
is the conversion from the all-trans retinal back to the 11-cis-configuration via several enzymatic steps in photoreceptor and retinal pigment epithelial cells.
Retinal
is a chromophore that is bound to the rest of the opsin protein. A chromophore is a region in the molecule where the energy difference between two separate molecular orbitals falls within the range of the visible spectrum. Visible light that hits the chromophore can thus be absorbed by exciting an electron from its ground state into an excited state. In biological molecules that serve to capture or detect light energy, the chromophore of the retina – retinal – causes a conformational change of the molecule when hit by light.
Retinal ganglion cells
Cells in the retina that receive input from modulatory neurons (which get input from photoreceptor cells) and transmit the information down the optic nerve to the brain.
Odorant molecule
any substance capable of stimulating the sense of smell by binding to an olfactory receptor
Olfactory epithelium
(also known as olfactory neuroepithelium) - a sheet of cells that contains the olfactory receptors and that lines the upper part of the nasal passages. The epithelium is covered by a mucous layer through which odorants must be absorbed before activating the olfactory receptors.
Olfactory receptors
(also known as odorant receptors) - are expressed in the dendrites of the olfactory receptor neurons and are responsible for the detection of odorant molecules. Rather than binding only one specific odorant, olfactory receptors can bind to a range of odorant molecules with different degrees of activation, and, conversely, a single odorant molecule may bind to a number of olfactory receptors with varying affinities.
Olfactory receptor neurons
(also known as olfactory receptor cells or olfactory sensory neurons) - bipolar neurons with dendrites facing the nasal cavity (in the olfactory epithelium) and axons that pass through the openings in the cribriform plate (bone) to synapse in the olfactory bulb. Olfactory receptors are located along the dendrites. These neurons make up the ‘olfactory nerve’ – the first cranial nerve.
Basal stem cells
continually undergo cell division to produce new olfactory receptors, which live for only a month or so before being replaced. They are located between the bases of the supporting cells
Olfactory mucus
Many small Bowman’s glands secrete mucus onto the surface of the olfactory membrane. Mucus is carried to the surface of the epithelium by ducts. The secretion moistens the surface of the olfactory epithelium and dissolves odorants so that they can bind to olfactory receptors.
Olfactory nerve
the first cranial nerve (CN I) is actually the many small nerve fascicles of the olfactory receptor neurons. The olfactory nerve is unique among cranial nerves, because it is capable of some regeneration if damaged (see olfactory bulb below).
Olfactory bulb
is a multi-layered structure located on the ventral surface of the brain that receives inputs from olfactory receptor neurons and sends output to cortex via mitral cell axons. The olfactory bulb is one of only three structures in the brain that has been found to undergo continuing neurogenesis in adult mammals. The olfactory-receptor-neuron axons that form synapses in olfactory bulb glomeruli are also capable of regeneration following regrowth of an olfactory receptor neuron in the olfactory epithelium.
Tastant molecule
any substance capable of stimulating the sense of taste
Taste receptor cells
provide taste information. They are located throughout the tongue in the taste buds, have areas of higher sensitivity, and have a very short life span (i.e., they are replaced frequently with new taste cells).
Taste bud
structure on the tongue that contains several taste receptor cells. A young tongue contains ~10,000 taste buds. Taste bud cells can be organized into three main types, in part according to their function: types I-IV. In general, bitter, sweet and umami stimuli are detected by type II cells, sour stimuli are detected by type III cells, and salty (NaCl) stimuli are detected by as-yet-undefined taste bud cells. Note that sweet and bitter, for example, are sensory perceptions of flavor, which is strongly modulated by other sensory inputs and cognitive processes; the compounds that elicit them are often labelled with these same names as shorthand.
Type I cells
support cells in the taste bud that are similar to glial cells.
Type II cells
detect bitter, sweet and umami stimuli. These are ligand-gated receptors that pick up different things depending on what type of ligand they’re binding. They are metabotropic (2nd messenger systems). Type II cells release ATP molecules through gap junctions to the afferent gustatory nerve fibers (like in an electrical synapse), rather than releasing neurotransmitters across a chemical synapse.
Type III cells
detect sour stimuli and possibly salty stimuli (although this is not confirmed for salty). Sour foods are acidic, which means that they release H+ ions. The H+ ions block leaky K+ channels, leading to a depolarization of the type III cell, changes in Ca++, and the ultimate release of serotonin across a chemical synapse to the afferent gustatory nerve fiber. As salty foods contain Na (NaCl), the extra Na+ ions from the food are thought to depolarize the salt receptor by directly entering through a Na+ receptor which opens voltage gated Ca++ channels and the influx of Ca++ causes NT release
Type IV cells
are also called basal cells. They are stem cells that differentiate into type I, II, and III taste cells during rapid cell turnover in taste buds.
Microvilli
microscopic cellular membrane protrusions that increase the surface area of cells and minimize any increase in volume and are involved in a wide variety of functions
Taste pore
any of numerous spherical clusters of receptor cells found mainly in the epithelium of the tongue and constituting the end organs of the sense of taste.
Gustatory nerves
nerve fibers at each taste bud that receive information from the taste receptor cells. Their axons join three different cranial nerves to carry taste information to cortex (which cranial nerve depends on location in tongue and pharynx/throat).
Cutaneous senses
perception of touch and pain from stimulation of the skin
Proprioception
ability to sense position of the body and limbs
Epidermis
The outermost layer of the skin, composed mostly of dead cells
Dermis
The middle layer of the skin, which contains the nerves and blood vessels
Subcutaneous tissue
The deepest layer of the skin, made up of vessels, fat, and connective tissue
Glabrous skin
hairless skin (e.g., on palms, soles, lips, labia, penis)
Mechanoreceptor
sensory receptor that responds and transduces mechanical pressure or distortion (stretching, vibration) into neural signals. There are specialized somatosensory receptors; auditory and vestibular hair cells; ligament (bone to bone connective tissue). Normally there are four main types in glabrous mammalian skin: Pacinian corpuscles, Meissner’s corpuscles, Merkel’s discs, and Ruffini cylinders.
Mechanotransduction
physical deformation of the cell membrane causes the opening of a mechanotransduction channel
Pacinian corpuscles
are one of the four major types of mechanoreceptor in glabrous (hairless) mammalian skin. They are nerve endings in the skin responsible for sensitivity to vibration and pressure. They respond only to sudden disturbances and are especially sensitive to vibration. The vibrational role may be used to detect surface texture, e.g., rough vs. smooth. Lamellar corpuscles are also found in the pancreas, where they detect vibration and possibly very low frequency sounds. Lamellar corpuscles act as very rapidly adapting mechanoreceptors. Groups of corpuscles respond to pressure changes, e.g. on grasping or releasing an object.
located deep in dermis
Is a pressure receptor where external pressure causes the corpuscle to deform, sodium ion channels open and sodium ions diffuse into the neurone down the concentration gradient
The greater the pressure the more deformation
The membrane is depolarized (generator potential) and the greater the pressure, the more sodium channels open causing a bigger generator potential that is limited by the refractory period
If threshold of the neurone is reached an AP devleops and is transmitted along the sensory neurone
Free nerve endings
Unspecialized, afferent nerve ending
Unencapsulated with no complex sensory structures
Located: skin, muscle, bone, connective tissue
Different rates of adaption, stimulus modalities and fiber types
o Aδ fibers are fast-adapting
o C fibers are slowly adapting
Can detect temp, pain (nociception), mechanical stimuli (touch, pressure, stretch)
Encapsulated nerve endings
For touch and proprioception (internal muscle and organ movements)
Acute nociceptive pain
Part of a rapid warning relay instructing the motor neurons of the central nervous system to minimize detected physical harm. It is mediated by nociceptors, on A-δ and C fibers.
These nociceptors are free nerve endings that terminate just below the skin, in tendons, joints, and in body organs. They serve to detect cutaneous pain, somatic pain and visceral pain.
When a noxious stimuli is detected it synapses the excitatory inter neuron in spinal cord, exciting the motor neuron which contracts a flexor muscle to pull sensor away.
Nociceptors (pain sensors) are specialized for heat, chemicals, severe pressure, and cold. Hot and cold sensations are carried via thermoreceptors.
Threshold of eliciting receptor response must be balanced to warn of damage but not be affected by normal activity
Sound pressure wave
Sound is a mechanical wave that results from the back and forth vibration of the particles of the medium through which the sound wave is moving. If a sound wave is moving from left to right through air, then particles of air will be displaced both rightward and leftward as the energy of the sound wave passes through it. The motion of the particles is parallel (and anti-parallel) to the direction of the energy transport. A sine wave can be used to encode information about the compression and rarefaction (expansion) of a sound pressure wave.
Inner ear
from oval window to auditory nerve; includes oval window, round window, cochlea, auditory nerve fibers, and the semicircular canals of the vestibular system.
Cochlea
The coiled and channeled main structure of the inner ear, which contains three fluid filled canals that run along its entire convoluted length; the fluid-filled canals are separated by membranes, one of which is the basilar membrane, on which thousands of hair cells (auditory receptors) are arranged and are stimulated by the vibration of the stapes.
Basilar membrane
The basilar membrane within the cochlea of the inner ear is a stiff structural element that separates two liquid-filled tubes (the scala – you don’t need to know these) that run along the coil of the cochlea, forming a base for the hair cells to transduce the sound waves in the cochlear fluid to electrochemical signals in the brain. The base is narrow and stiff resonating to high frequencies while the apex is wide and floppy resonating with low frequencies.
Place coding
The more the basilar membrane resonates, the farther it moves
The more the cilia of the hair cells bend against the tectorial membrane the more NT the hair cells release
The distribution of NT releases along the basilar membrane that codes for frequency
Temporal rate coding
The whole basilar membrane vibrates at rate of input
The tissues can only resonate so fast, so the hair cells accommodate this with graded response responding to relative amounts of vibration along basilar membrane
Group of ganglion cells working together
But hair cells communicate to spiral ganglions (ANF) which fire AP/produces volleys of activity at rate of input
Refractory period for AP limit how frequency spiral ganglions can fire
They only fire when they are ready/reach peak (locked to phase of input)
Tonotopic organization
map of tones: Each section of the basilar membrane responds to a preferential frequency and the sections are organized from high to low. Tonotopic organization is also seen in the cortex as tonotopic gradients (cortical representations of tones).
Inner hair cells
the sensory receptors of the auditory system located on the basilar membrane in the cochlea that convert sound waves to nerve signals by having their hair-like stereocilia being physically moved by sound waves in the cochlear fluid. Hair cells are columnar cells, each with a bundle of 100-200 specialized stereocilia at the top, for which they are named. These cilia are the mechanosensors for hearing. Lightly resting atop the longest cilia is the tectorial membrane, which moves back and forth with each cycle of sound, tilting the cilia and allowing electric current into the hair cell. Hair cells, like the photoreceptors of the eye, show a graded response, instead of the spikes typical of other neurons. Loud noise can damage and destroy hair cells, which do not regrow. Continued exposure to loud noise causes progressive damage, eventually resulting in hearing loss and sometimes ringing in the ears (tinnitus).
Stereocilia and kinocilium
stereocilia are projections at the top of the hair cell that are attached to one another by structures which link the tips of one cilium to another. Stretching and compressing the tip links may open an ion channel and produce the receptor potential in the hair cell. The kinocilium is one larger, more stable cilium to which the stereocilium attach at the tips.
Vestibular system
the part of the inner ear that is responsible for encoding information about equilibrium, the sense of balance. The vestibular system relies on hair cells with stereocilia (mechanoreceptors) in specialized structures that sense head position, head movement, and whether our bodies are in motion. Components include: Vestibule, Utricle and saccule, Semicircular canals, Membranous ampullae
Vestibule
the central part of the bony labyrinth of the inner ear, which is situated medial to the eardrum (tympanic membrane), posterior to the cochlea, and anterior to the semicircular canals. It serves as an entrance to the other sections of the vestibular system. (Latin = ‘entrance hall”)
Utricle and saccule:
structures that sense head position. They are composed of macula tissue (hair cells surrounded by support cells). The stereocilia of the hair cells extend into a viscous gel called the otolith. The otolith contains calcium carbonate crystals, making it denser and giving it greater inertia than the macula. Head tilt is interpreted by the brain on the basis of the pattern of hair-cell depolarization.
Otoliths organs
The macula is made of the utricle and saccule with hair cells lining the walls of these endolymph filled chambers.
Otoliths are “ear stones” made of calcium carbonate crystals sitting in gelatinous material where hair cells are embedded. When the head is upright, there is a base rate of firing and whatever angle you tilt your head some otoliths will weight down the cilia of some hair cells controlling the rate of firing.
Semicircular canals
three ring-like extensions of the vestibule. One is oriented in the horizontal plane, whereas the other two are oriented in the vertical plane. Rotational movement of the head is encoded by the hair cells in the ampullae at the base of the semicircular canals. As one of the canals moves in an arc with the head, the internal fluid (endolymph) moves in the opposite direction, causing the cupula and stereocilia within each ampulla at the bases of the canals to bend. As the fluid pushes against the crista one way or the other, hair cells fire more or less. They are tubes filled with K+ rich endolymph
Membranous ampullae
The base of each semicircular canal, where it meets with the vestibule, connects to an enlarged region known as the ampulla. The ampulla contains the hair cells that respond to rotational movement, such as turning the head while saying “no.” The stereocilia of these hair cells extend into the cupula, a membrane that attaches to the top of the ampulla. As the head rotates in a plane parallel to the semicircular canal, the fluid lags, deflecting the cupula in the direction opposite to the head movement. There are anterior, posterior and lateral ampullae, corresponding to the semicircular canals. By comparing the relative movements of both the horizontal and vertical ampullae, the vestibular system can detect the direction of most head movements within three-dimensional (3-D) space (can only detect change).
Cochlear nucleus
a group of cell bodies in the lower section (medulla) of the brainstem that receives the inputs from all the auditory nerve fibers coming from the cochlea
Skeletal muscle (or striate muscle)
is one of three major muscle types, the others being cardiac muscle and smooth muscle. It is a form of striated muscle tissue which is under the voluntary control of the somatic nervous system. Most skeletal muscles are attached to bones by bundles of collagen fibers known as tendons. The term ‘striate’ comes from its striped appearance of the muscle created by the various bands of myofilaments (e.g., Z-line).
Cardiac (heart) muscle
Has endogenous rhythm of activity, modified by neurons
Smooth (organ) muscle
Can sustain contraction, mostly autonomically controlled
Flexor muscle
one that moves a body part towards your body (e.g., biceps muscle that flexes upper arm)
Extensor muscle
one that move a body part away from your body (e.g., triceps muscle that extends upper arm)
Groups of antagonistic pairs of flexor and extensor muscles work in sync to control body movements
Neuromuscular junction (or myoneural junction) –
is a chemical synapse between a motor neuron and a muscle fiber. It allows the alpha motor neuron to transmit a signal via the release of acetylcholine (Ach) to the muscle fiber, causing muscle contraction (Na+ gates open, enters cell, changes polarity opens Ca++ gates, enters cells, but instead of releasing NT it releases sarcomeres to contract muscles). Muscles require innervation to function—and even just to maintain muscle tone, avoiding atrophy.
Sarcomere
is the unit of striated muscle tissue between two Z-lines (also called Z-disks). Skeletal muscles are composed of tubular muscle cells (myocytes called muscle fibers or myofibers) which are formed in a process known as myogenesis. Sarcomeres are composed of long, fibrous proteins as filaments that slide past each other when a muscle contracts or relaxes.
Myofibrils
are composed of repeating sections of sarcomeres, which appear under the microscope as alternating dark and light bands. Muscle fibers contain numerous tubular myofibrils.
Z-line
is the point of connection between the lateral boundaries of two sarcomeres and serves as a filament anchor. Because of these anchoring properties, Z-lines are responsible for force transmission, generated by the actin–myosin cross-bridge cycling during a muscle contraction. Recent research points to additional functions of Z-lines, such as signal transduction and associated nuclear translocation with the cell. Z-lines are also called Z-disks, since in reality the ‘line’ is a 3-D point of attachment.
Myosin
is the protein which forms the thick filament within a sarcomere. Myosin has a long, fibrous tail and a globular head, which binds to actin. The myosin head also binds to ATP, which is the source of energy for muscle movement. Myosin can only bind to actin when the binding sites on actin are exposed by calcium ions. When Ca++ enters muscle cells, cross bridges activate and row actin and myosin in pairs pulling them closer together.
Actin
is the protein which forms the thin filament within a sarcomere. Actin molecules are bound to the Z line, which forms the borders of the sarcomere.
Spinal reflex pathway
is a neural pathway that controls a reflex action (e.g., withdrawal reflex). As most sensory neurons synapse in the spinal cord before going to cortex, spinal motor neurons can be rapidly activated without waiting for signals to go to/come from the brain first. Sensory input is sent to the brain while the reflex is being carried out.
Dorsal root ganglion
The sensory nerves of the peripheral nervous system have their cell bodies in the dorsal root ganglion (ganglion means a group of cell bodies) .These cells have projections (really like dendrites) that carry information from the peripheral sensory receptors via a peripheral nerve, and they also have projections (think of like axons) that carry information into the spinal cord, forming the dorsal root.
Ventral root
is the motor nerve exiting the spinal cord to innervate the muscle
Interneuron
is a neuron which transmits impulses between other neurons, especially as part of a reflex arc.
Stretch reflex (or myotatic reflex)
refers to the contraction of a muscle in response to its passive stretching. When a muscle is stretched, the stretch reflex regulates the length of the muscle automatically by increasing its contractility as long as the stretch is within the physiological limits. It is a one synapse reflex meaning it goes directly from incoming somatosensory info to outgoing muscle contraction.
Muscle spindle
A proprioceptor in muscle detects passive stretch of muscle. The muscle spindle excites motor neuron in spinal cord.
Golgi tendon reflex (also called inverse stretch reflex, autogenic inhibition, tendon reflex)
Over contracting muscle pulls so hard on tendon, the golgi tendon organ signals spinal cord.
Activates an inhibitory inter neuron in spinal cord that inhibits motor neuron to origional muscle, reducing contraction
Golgi tendon organ also activates an excitatory inter neuron in spinal cord
Excites motor neuron to antagonistic muscle, increasing its contraction, which decreases origional’s contraction
Golgi tendon organ
is a proprioceptive sensory receptor organ that senses changes in muscle tension. It lies at the origins and insertion of skeletal muscle fibers into the tendons of skeletal muscle. It provides the sensory component of the Golgi tendon reflex. The Golgi organ is not to be confused with the Golgi apparatus, which is an organelle in the eukaryotic cell, or the Golgi stain, which is a histologic stain for neuron cell bodies. All of these are named after the Italian physician Camillo Golgi.
Pain withdrawal reflex
is defined as the automatic withdrawal of a limb from a painful stimulus. This reflex protects humans against tissue necrosis from contact with noxious stimuli such as pain or heat. It can occur in either the upper or lower limbs. Specifically, the withdrawal reflex mediates the flexion of the limb that comes into contact with the noxious stimuli; it also inhibits the extensors of that same limb. This reflex also promotes the extensors and inhibits the flexors of the contralateral arm or leg, virtually ensuring that the opposite limb provides stabilization. Hence, some signals can cross the midline of the spinal cord to mediate the movement of the opposite limb. This response is a polysynaptic reflex, which means that interneurons are involved in mediating the reflex between the afferent (sensory) and efferent (motor) signals. Also, it is also an intersegmental reflex arc, meaning that the outcomes of the reflex get mediated by the stimulation or inhibition of motor neurons from multiple levels of the same spinal cord. In evolution, this withdrawal response is critical in avoiding the significant dangers.
Afferent neuron
refers to a neuron that carries information (usually sensory) from the periphery TO the spinal cord and/or brain. The term comes from the Latin ad (to) + ferre (carry).
Efferent neuron
refers to a neuron that carries information (usually motor) FROM the brain/spinal cord to a peripheral target (e.g., muscle). The term comes from the Latin ex (away, out of) + ferre (carry).
