Unit 7

Question 1

Sensation

Answer 1

The first stage in the functioning of the senses, starting with information at the peripheral sensory receptors

Question 2

Perception

Answer 2

The process of recognizing, organizing, and interpreting sensory information

Question 3

Sensory receptor

Answer 3

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.

Question 4

Afferent neuron

Answer 4

 Afferent neuron is taking info from the sensory receptor into the cortex

Question 5

Receptor specialization

Answer 5

may be part of afferent sensory neuron or may be a separate, specialized cell adjacent to afferent sensory neuron.

Question 6

Sensory unit

Answer 6

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

Question 7

Receptive field

Answer 7

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.

Question 8

Sensory receptive field: spatial resolution

Answer 8

Receptor fields are like pixels, the more receptor fields equal more detail
Smaller RFs tiling an area = higher spatial resolution

Question 9

Discrimination

Answer 9

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.

Question 10

Sensitivity

Answer 10

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.

Question 11

Transduction

Answer 11

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

Question 12

Transduction in Sensory system

Answer 12

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

Question 13

Graded response

Answer 13

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.

Question 14

Stimulus energy

Answer 14

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.).

Question 15

Stimulus intensity

Answer 15

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

Question 16

Stimulus duration

Answer 16

 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

Question 17

Stimulus duration: receptor adaptation

Answer 17

 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

Question 18

Stimulus modality Specificity

Answer 18

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”).

Question 19

Stimulus modality adequate stimulus

Answer 19

 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

Question 20

Photoreceptors

Answer 20

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.

Question 21

Chemoreceptors

Answer 21

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.

Question 22

Mechanoreceptors

Answer 22

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.

Question 23

Vestibular hair cells

Answer 23

 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

Question 24

Mechanotransduction: hair cells

Answer 24

 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)

Question 25

Nociceptors

Answer 25

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.

Question 26

Thermoreceptors

Answer 26

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).

Question 27

Receptor threshold

Answer 27

is the intensity of the stimulus that will drive a change in receptor potential

Question 28

Action potential threshold

Answer 28

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

Question 29

Perception threshold

Answer 29

is the intensity of the stimulus that will produce a conscious perception – also relies on higher-order aspects like attention

Question 30

Saturation

Answer 30

is the maximum intensity of a stimulus that produces a response from a sensory system.

Question 31

Dynamic Range

Answer 31

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.

Question 32

Frequency coding

Answer 32

is the encoding of stimulus intensity by the frequency of action potentials induced by the stimulus.

Question 33

Population coding

Answer 33

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)

Question 34

Sensory adaptation

Answer 34

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.

Question 35

tonic response

Answer 35

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.

Question 36

phasic response

Answer 36

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.

Question 37

Acuity

Answer 37

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.

Question 38

Convergence

Answer 38

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.

Question 39

Two point discrimination

Answer 39

The ability to perceive two fine points as two points and not one

Question 40

Divergence

Answer 40

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).

Question 41

Labeled line

Answer 41

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.

Question 42

First-, second-, and third-order neurons

Answer 42

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.

Question 43

Retina

Answer 43

The back of the eyeball, considered a part of the brain, where light hits the photoreceptive cells and visual information begins being processed.

Question 44

Fovea

Answer 44

the part of the retina, where vision is most acute and color vision is best. Cone photoreceptors are most prevalent here.

Question 45

Photoreceptor cells

Answer 45

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

Question 46

Rods

Answer 46

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.

Question 47

Cones

Answer 47

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.

Question 48

Rods vs cones similarities

Answer 48

 Same layer in retina
 Molecules of photo pigment embedded in outer segments
 Outer segments embedded in pigment epithelium
 Graded potentials
 Release inhibitory NT

Question 49

Photoreceptor proteins

Answer 49

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).

Question 50

Rods and Cones differences

Answer 50

 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)

Question 51

Opsins

Answer 51

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

Question 52

Photoreceptor transduction

Answer 52

 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)

Question 53

Light adapted

Answer 53

 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

Question 54

Dark adapted

Answer 54

 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

Question 55

How do receptor cells signal that light is present if they are turned off by light

Answer 55

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.

Question 56

Dark current

Answer 56

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.

Question 57

Isomers

Answer 57

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.

Question 58

Photoisomerization

Answer 58

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.

Question 59

Regeneration

Answer 59

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.

Question 60

Retinal

Answer 60

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.

Question 61

Retinal ganglion cells

Answer 61

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.

Question 62

Odorant molecule

Answer 62

any substance capable of stimulating the sense of smell by binding to an olfactory receptor

Question 63

Olfactory epithelium

Answer 63

(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.

Question 64

Olfactory receptors

Answer 64

(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.

Question 65

Olfactory receptor neurons

Answer 65

(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.

Question 66

Basal stem cells

Answer 66

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

Question 67

Olfactory mucus

Answer 67

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.

Question 68

Olfactory nerve

Answer 68

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).

Question 69

Olfactory bulb

Answer 69

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.

Question 70

Tastant molecule

Answer 70

any substance capable of stimulating the sense of taste

Question 71

Taste receptor cells

Answer 71

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).

Question 72

Taste bud

Answer 72

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.

Question 73

Type I cells

Answer 73

support cells in the taste bud that are similar to glial cells.

Question 74

Type II cells

Answer 74

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.

Question 75

Type III cells

Answer 75

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

Question 76

Type IV cells

Answer 76

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.

Question 77

Microvilli

Answer 77

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

Question 78

Taste pore

Answer 78

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.

Question 79

Gustatory nerves

Answer 79

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).

Question 80

Cutaneous senses

Answer 80

perception of touch and pain from stimulation of the skin

Question 81

Proprioception

Answer 81

ability to sense position of the body and limbs

Question 82

Epidermis

Answer 82

The outermost layer of the skin, composed mostly of dead cells

Question 83

Dermis

Answer 83

The middle layer of the skin, which contains the nerves and blood vessels

Question 84

Subcutaneous tissue

Answer 84

The deepest layer of the skin, made up of vessels, fat, and connective tissue

Question 85

Glabrous skin

Answer 85

hairless skin (e.g., on palms, soles, lips, labia, penis)

Question 86

Mechanoreceptor

Answer 86

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.

Question 87

Mechanotransduction

Answer 87

physical deformation of the cell membrane causes the opening of a mechanotransduction channel

Question 88

Pacinian corpuscles

Answer 88

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

Question 89

Free nerve endings

Answer 89

 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)

Question 90

Encapsulated nerve endings

Answer 90

For touch and proprioception (internal muscle and organ movements)

Question 91

Acute nociceptive pain

Answer 91

 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

Question 92

Sound pressure wave

Answer 92

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.

Question 93

Inner ear

Answer 93

from oval window to auditory nerve; includes oval window, round window, cochlea, auditory nerve fibers, and the semicircular canals of the vestibular system.

Question 94

Cochlea

Answer 94

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.

Question 95

Basilar membrane

Answer 95

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.

Question 96

Place coding

Answer 96

 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

Question 97

Temporal rate coding

Answer 97

 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)

Question 98

Tonotopic organization

Answer 98

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).

Question 99

Inner hair cells

Answer 99

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).

Question 100

Stereocilia and kinocilium

Answer 100

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.

Question 101

Vestibular system

Answer 101

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

Question 102

Vestibule

Answer 102

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”)

Question 103

Utricle and saccule:

Answer 103

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.

Question 104

Otoliths organs

Answer 104

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.

Question 105

Semicircular canals

Answer 105

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

Question 106

Membranous ampullae

Answer 106

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).

Question 107

Cochlear nucleus

Answer 107

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

Question 108

Skeletal muscle (or striate muscle)

Answer 108

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).

Question 109

Cardiac (heart) muscle

Answer 109

Has endogenous rhythm of activity, modified by neurons

Question 110

Smooth (organ) muscle

Answer 110

Can sustain contraction, mostly autonomically controlled

Question 111

Flexor muscle

Answer 111

one that moves a body part towards your body (e.g., biceps muscle that flexes upper arm)

Question 112

Extensor muscle

Answer 112

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

Question 113

Neuromuscular junction (or myoneural junction) –

Answer 113

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.

Question 114

Sarcomere

Answer 114

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.

Question 115

Myofibrils

Answer 115

are composed of repeating sections of sarcomeres, which appear under the microscope as alternating dark and light bands. Muscle fibers contain numerous tubular myofibrils.

Question 116

Z-line

Answer 116

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.

Question 117

Myosin

Answer 117

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.

Question 118

Actin

Answer 118

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.

Question 119

Spinal reflex pathway

Answer 119

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.

Question 120

Dorsal root ganglion

Answer 120

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.

Question 121

Ventral root

Answer 121

is the motor nerve exiting the spinal cord to innervate the muscle

Question 122

Interneuron

Answer 122

is a neuron which transmits impulses between other neurons, especially as part of a reflex arc.

Question 123

Stretch reflex (or myotatic reflex)

Answer 123

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.

Question 124

Muscle spindle

Answer 124

A proprioceptor in muscle detects passive stretch of muscle. The muscle spindle excites motor neuron in spinal cord.

Question 125

Golgi tendon reflex (also called inverse stretch reflex, autogenic inhibition, tendon reflex)

Answer 125

 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

Question 126

Golgi tendon organ

Answer 126

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.

Question 127

Pain withdrawal reflex

Answer 127

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.

Question 128

Afferent neuron

Answer 128

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).

Question 129

Efferent neuron

Answer 129

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).