Mechanisms of sensory-Allard Flashcards

Question

Labeled Line Coding: Law of Specific Nerve Energies

Answer 1

- this is how the brain knows the AP it is receiving is coming from something that touched you rather than some sound or line frequency - the lines coding the pathway that those AP are traveling will only lead to one area in the cortex and that one area of the cortex is dedicated to that specific modality - any AP that reach that area of the cortex will give the sensation of that modality; so if those AP reach your somatosensory cortex which is dedicated to processing info from touch then what you will feel is touch even if that pathway was accidentally or intentionally stimulated by some other form of energy that pathways is dedicated to sensing signals for a specific type of sensation The 3 neuron pathway that leads to the cortex is dedicated to sending signals about a specific form of energy a specific sensation so anytime signals are passing along that pathway, those signals can only end up giving you one type of sensation so if that pathway is stimulated electrically in the somatosensory cortex that is dedicated to feeling vibration in your finger, then that's what you will feel, even though you stimulated not by putting something vibrating against your finger; you just activated that pathway -allows our brains to know the meaning of those AP - allows for localization (in case of somatosensation) of where the stimulus is - these pathways are hardwired, coded in your DNA Excitation of a sensory receptor and sensory neuron elicits only one sub-modality of sensation. This is the labeled line principle. Localizes the stimulus Identifies the type of stimulus Premises: individual receptors preferentially transduce information about an adequate stimulus individual primary afferent fibers carry information from a single type of receptor

Answer 2

Each sense has its specialized area of cortex which when activated produces the experience associated with that sense. if you stimulate anywhere along this pathway either with adequate stimulus or some other mode electrically you will get nothing but touch in that area that is dedicated to that pathway

Answer 3

it will not give anything else but the sense of light if the visual cortex is stimulated Evidence: the brain associates a specific modality (adequate stimulus) with a signal coming from a specific receptor "light" is the sensation generated by stimulation of the photoreceptors, even if the actual stimulus is pressure on the eye. Stimulation anywhere along the sensory pathways from a sensory receptor to the specialized sensory cortex will only result in one particular sensation

Answer 4

I touch you very lightly or very hard you can feel the difference but how do those AP convey whether it was a light or heavy touch? - with increased intensity, more receptors for that modality are activated - so with heavy touch, that pressure will spread to adjacent receptors that will end up activating more receptors in that area - whatever receptor that is activated by the light touch will also activate the heavy touch but the AP that are generated will be more frequency; so higher intensity= higher frequency of AP going towards that region of the brain Intensity is coded by: # of receptors activated -Receptors have variable thresholds frequency of APs -directly related to the receptor potential -modified by inhibitory or stimulatory inputs -modified by adaptation

Answer 5

an example of a touch receptor change in membrane potential (MP) is smaller with light touch; change in MP is correlated to strength of stimulus and correlated to frequency of AP when the touch is light the change in MP is smaller than when the touch is heavy thus change in MP is higher the change in MP is correlated to the strength of stimulus which is correlated to the frequency of AP

Answer 6

but what if the receptor can adapt; that means that even though the stimulus is staying at the same intensity the frequency of the AP ends up decreasing overtime which gives you a lower sensation so you don't really feel the intensity the way that you did in the beginning -all of our receptors adapt to some extent Adaptation: Decreased Sensitivity to a Sustained Stimulus Receptor membranes become less responsive Receptor potential decreases Inactivation of Na+ or Ca2+ channels Activation of K+ channels Action potentials decline in frequency Dictated by the receptor structure

Answer 7

- weak stimulus only activates a few of the terminal nerve endings - strong stimulus activating many more primary afferent neurons

Answer 8

- relates to how much NT is released - moderate frequency of AP = a moderate amount of NT released at the terminal of the neuron (calcium is what allows the release of NT released from vesicles) 1. Receptor potential strength and duration vary with the stimulus. 2. Receptor potential is integrated at the trigger zone. 3. FREQUENCY of AP is proportional to stimulus INTENSITY. Duration of a series of AP is proportional to stimulus duration. 4. NT release varies with the pattern of AP arriving at the axon terminal.

Answer 9

- how long the stimulus is applied or how long you feel the stimulus is modulated by adaptation - the sensation of the duration of the AP can change based on whether the receptor is highly or lowly adaptive Frequency of APs is… - directly related to the receptor potential - modified by inhibitory or stimulatory inputs - modified by adaptation

Answer 10

tonic receptors adapt very slowly: -pain fibers show very little adaptive quality phasic receptors adapt fast: - can see the generator potential go down even though the stimulus has not changed; our sensation of the stimulus is decreased - occurs with fine touch receptors A is tonic B is slowly adaptive as C C is phasic and very adaptive (put on clothes but then don't feel the clothes anymore) Few receptors lack adaptive ability (otoliths: head position) Tonic receptors (adapt slowly or not at all) - nociceptors, proprioceptors, thermoreceptors, crude touch - Usually coupled to small diameter, unmyelinated fibers Phasic receptors (fast-adapting) signal at beginning and end of stimulus - pressure, fine touch, smell - Usually coupled to large, myelinated fibers

Answer 11

go in the cold water and swim but then don't feel the cold anymore sensory adaptation: loss of responsiveness in receptor cells after stimulation has remained unchanged for a while, as when a swimmer becomes adapted to the temperature of the water absolute threshold: minimum stimulation needed to detect a particular stimulus; usually defined as the stimulus needed for detection 50% of the time difference threshold: minimum difference between two stimuli that a subject can detect 50% of the time; just noticeable difference (JND); increases with magnitude

Answer 12

this graph shows that when the stimulus intensity is increased, the MP is increased there is a point in which that even though the stimulus is increased the receptors potential won't increase

Answer 13

absolute refractory period

Answer 14

- how much of a difference between two intensities can we tell - this depends on the initial intensity - the amount of change necessary to detect difference is related to the INITIAL intensity - the higher the initial intensity the higher the change needs to be to be detected -The larger the magnitude of the stimulus (I) the larger the change in magnitude (ΔI) must be to be detected.

Answer 15

Thermoreceptors - Respond to temperature changes - Heat, cold Nociceptors (thermo-, chemo-, mechano-) -Respond to potentially damaging stimuli Mechanoreceptors - Respond to mechanical forces - Touch, pressure, vibration, stretch

Answer 16

Hair follicle receptor Light touch Moving touch Pacinian corpuscles Deep pressure Vibration Meissner’s corpuscles Fine touch Merkel receptors Pressure and texture Ruffini endings Skin stretch Deep pressure

Answer 17

-the hair bulb is surrounded by primary afferent neuron; when the hair follicle is deflected the pressure or the movement of the hair follicle is transmitted down to the bulb and the primary afferent neuron and hair bulb rub against each other; there are mechanically gated channels on this primary afferent neuron; these channels are then opened up by the friction btw the bulb and primary afferent nerve ending; that friction opens up the mechanically gated channels allowing the influx of Na for depolarization of membrane to generate AP at the initial segment - located deep in the dermis - they show rapid/high adaption: once the hair follicle is deflected you get AP even though the hair follicle stays deflected the channels close very rapidly and you get no AP even though that pressure deflecting hair follicle may still be there - these hair follicle receptors most keen to something moving across your skin (like a bug) - myelinated neuron - axon diameter relatively large; are Abeta or Agamma Location: deep dermis Accessory organ: Hair follicle Receptor: Free nerve endings tightly coiled around hair follicle Receptive Field: small Transduction Mechanism: 1. Hair is deflected 2. Motion of hair follicle against nerve endings triggers opening of mechanosensitive ion channels. 3. Ion channels are opened 4. Ion channels are quickly blocked by collagen fibers Adaptation: Rapid Fiber Type: Aβ & Aδ

Answer 18

touch receptor - located in the deep dermis and glabrous (hairless) skin - they are also proprioceptors; found in the joints capsule so laso give info about how our joints are interacting with each other - have an accessory organ structure with concentric layers of flattened lamina; in btw the layers are fluid filled sacs; the structure of these layers are supported by collagenous tissue - inside the concentric layers are the nerve terminals - spaces between lamellae are filled with fluid pressure is applied to concentric layers which causes a deflection in the tip of the neuron so a physical interaction opens mechanically gated channels on the top of the sensory ending --> influx of Na -->depolarization--> AP - so even though I keep the pressure here; because there is a lot of fluid, the fluid disperses moves around so that the tip of the nerve is no longer deflected even though the stimulus of the pressure is still there; this neuron is no longer being stimulated; AP stops - this is a very good example of a phasic response; when the stimulus is first applied it goes away rapidly and then you get APs when the stimulus is removed - large myelinated fibers type: Aalpha - receptive field is large so you don't need a lot of them - they are structured very well to detect vibration 9its pressure coming and going) rapidly adapting ``` Location: deep dermis hairy and glabrous skin joint capsules (proprioceptor) Accessory Organ Structure: concentric lamellae of flattened cells supported by collagenous tissue spaces between lamellae are filled with fluid Receptor structure: bare nerve terminals occupies center of corpuscle Receptive field: large Fiber type: Aβ ``` Transduction Mechanism: Applied pressure is transmitted to the nerve terminal deforming it Mechanically gated Na+ ion channels are opened, depolarizing the membrane. AP are generated along the fiber . Fluid between lamellae is quickly dispersed, relieving the pressure on the terminal. Membrane potential returns to resting level Removal of the probe again deforms nerve terminal resulting in depolarization.

Answer 19

- structured to give sensation of light tough - allows to feel texture - gives a sensation of vibration but as of high frequency like the pacinian corpuscle - located beneath the epidermis on the plantar surface of hands and feet - have stacks of epithelial cells that are intertwined with the neuron terminal; allows disks to slide against each other when light touch is felt; activating mechanically gated channels on these terminal endings leading to depolarization - these like the pacinian are rapidly adaptive but have smaller receptive field - Abeta Location: Beneath the epidermis fingers, palm of the hand, plantar surface of the foot toes (glabrous skin) Accessory Organ Structure: Stacks of horizontally flattened epithelial cells enclosed in a connective tissue sheath. Receptor structure: bare nerve terminals arborizes among the epithelial cells Receptive field: small Adaptation: Rapid Fiber type: Aβ

Answer 20

- another fine touch receptors - allows us to feel the shape of things (edges, corners) - the sensation of light touch is detected by this Merkel cell that is in the superficial layer of the epidermis -now this is DIFFERENT; there is a separate structure= the primary afferent neuron and the Merkel's cell; the actual sensory receptor is an element that is separate from the primary afferent neuron but they are very closely aligned with each so the sensation of light touch is detected by the Merkel's cells that is in the superficial layers of our epidermis -you use this along with Meissner's to read braille - when there is pressure applied to the skin; mechanically gated channels are opened in the Merkel's cells - this Merkel's cell produces NT which is then released onto the primary afferent neuron which has receptors for those NT allowing you to get an AP after neuron terminal is depolarized - receptive field is small - slowly adapting Location: below the epidermis, lips, finger tips (glabrous skin) Receptor: Large epithelial cell in close contact with a sensory neuron terminal Transduction: Merkel’s cell releases neurotransmitter Receptive Field: Small Adaptation: slowly adapting

Answer 21

- are specialized to detect stretch - spread fingers very widely and get tightening sensation that is Ruffini's endings - located in the deep dermis layer in both types of skin - embedded in collagenous capsule - large receptive field - Abeta - slowly adapting Located: Deep dermis layer of both hairy and glabrous skin Receptor: Endings of sensory neuron encapsulated within bundles of collagen fibrils that are connected with similar fibrils of the dermis Receptive Field: large Fiber type: Aβ Adaptation: Slow

Answer 22

Pacinian Corpuscle: - deep touch - vibration - large, vague borders receptive field - fast adapting Meissner's Corpuscle: - fine touch - small, sharp borders receptive field - fast adapting Merkel's disc: - texture/touch - small, sharp borders receptive field - slow adapting Ruffini's ending: - stretch - large vague borders receptive field - slow adapting