Lecture 9 & 10

Why can different members of the TRP channels family, detect warm, cold, and extreme temperatures>

Different TRP channels change their protein conformation and open upon exposure to different temperatures

What is a difference between a regular thermoreceptor and a nociceptive thermoreceptor?

Regular thermoreceptors respond to mild temperature range, while nociceptive thermoreceptors are activated only by extreme temperatures

A temperature stimulus can activate a thermoreceptive sensory neuron by causing the opening of

Gated sodium channels

Which statements below are true for nociceptive sensory neurons? Choose ALL that apply

Some nociceptive neurons can respond to harmful chemicals as well as extreme pressure

Nociceptive neurons can respond to extreme temperature and pressures

Nociceptive neurons can be both low-threshold or high-threshold neurons

Nociceptive neurons can be mechanoreceptive, thermoreceptive, and chemoreceptive sensory neurons.

Which choice below shows the correct order of sensory neurons ranking from the fastest conducting to the slowest conducting neuron?

A alpha, A beta, A delta, and C fibers

When we are injured, we feel a sharp pain first because the _____ is transmitted by the faster _____ sensory fiber. We feel an ensuing throbbing pain later because the _____ is transmitted via a slower unmyelinated _____ sensory fiber

First pain, A delta, second pain, C

Warm temperature stimuli are detected by ____ and transmitted to the brain via the ____ pathway. Extreme temperature stimuli, on the other hand, are detected by ____ and are transmitted to the brain via the ____.

A delta, anterolateral, A delta and C, anterolateral

Which choices below correctly describe the differences between the dorsal column medial-lemniscal and the anterolateral pathways? Choose ALL that apply

Extreme pressure and temperature sensation are relayed to the brain via the anterolateral pathway

Mechanoreceptive and proprioceptive signals are transmitted to the brain via the dorsal column pathway, while the temperature and pain signals are relayed to the brain through the anterolateral pathway

Pain sensations in the head region can be transmitted to the brain via the trigeminothalamic pathway

Mild temperature and pressure sensation in the hard region can be relayed to the brain via the trigeminothalamic pathway

First pain signals are relayed to the ____, while slower second pain signals that can keep us awake are relayed to ____.

Primary somatosensory cortex, associated pain areas in the pain matrix

____ can decrease pain signal transmission to the brain by secreting ____ to decrease first- and second-order pain sensory neuron activities

Periaqueductal grey area, endorphins

The itch sensation can also be transmitted by C sensory neurons. Based on what you know about the spinal cord getting theory, how you do think scratching your skin can alleviate your itch sensation?

A-beta mechanoreceptor neuron activated by scratching can result inthe inhibition of the second-order spinal cord neuron involved in transmitting the itch signals to the brain

The placebo effect cna be abolished if a person is administered with a

Endorphin antagonist

A patient has been diagnosed to have functional impairment in large receptive field and slow-adapting somato-sensation on skin. Which cutaneous mechanoreceptor is likely not functioning properly in this patient?

Ruffini receptor

Somatosensation is detected by multiple specialized receptors: ___ detect cutaneous tissue stretch, ___ detect internal tissue stretch, ___ detect temperature, and ___ detect extreme stimuli that can injure tissues

Mechanoreceptors, proprioceptors, thermoreceptors, nociceptors

Exteroceptor

A sensory receptor that receives sensory stimuli from outside of the body

Example: skin receptors that can sense pressure applied on the surface of the skin

Interoceptor

A sensory receptor that receives sensory stimuli from within the body

Example: muscle spindle in the muscle that can sense muscle stretch

Mechanoreceptor

A sensory receptor that detect mechanical stimuli, such as pressure on the skin. 4 major types of ___ include Merkel, Meissner, Pacinian and Ruffini receptors

Example: ruffini receptor in the skin can detect pressure-induced skin stretch

Proprioceptor

A sensory receptor that receives proprioceptive stimuli within the body, such as changes in limb position

Example: Golgi tendon organi in the tendon that can sense tendon stretch

Thermoreceptor

A sensory receptor that can detect relative changes in temperature

Example: ___ on the skin can detect hot or cold temperatures

Nociceptor

A sensory receptor that can detect extreme pressure, extreme temperature or chemicals that can harm the body or warn the body of potential damage. The brain interprets these detected signals as pain sensation

Example: pain receptors on the skin can detect scalding temperature as pain sensation

Spatial sensation

The ability to detect the separation of two points

Example: Merkel receptors on the skin has the higher ___ resolution than Ruffini receptors because they can detect closed touch sensation on the skin (via a two-point touch test)

Receptive field

The area in which stimuli can activate a sensory receptor. A sensory receptor with smaller receptive field has better spatial resolution than a sensory receptor with large receptive field

Example: Merkel receptors have smaller ___ than Ruffini receptor, so they can have better spatial resolution than Ruffini receptors

Slow-adapting neuron

A neuron that continues to fire action potentials throughout the entire duration of ta stimulus

Example: A merkel and Ruffini mechanoreceptor neurons will continue to fire action potentials during the entire time a pressure is applied on the skin

Fast-adapting neuron

A neuron which will fire only when there is a change in the stimulus condition, such as the beginning and at the end of a stimulus

Example: a Meissner and Pacinian mechanoreceptor neurons will only fire when a pressure is applied to or removed from the skin

Dorsal column medial lemniscal pathway

A 3-neuron chain that transmits somsatosensory signals (pressure and proprioceptive signals) from the body (except the head region) to the somatosensory cortex. Pain and temperature somatosensory signals from the body are transmitted via the anterolateral pathway (lecture 10)

Example: touch sensation from the arm is transmitted from the cervical spinal sensory neuron to the somatosensory cortex via the ___

Trigeminothalamic pathway

A 3-neuron chain that transmits somatosensory signals (pressure, proprioceptive, pain and temperature signals) from the head region via the trigeminal nerve to the somatosensory cortex

Example: the trigeminal nerve (5th cranial nerve) transmits facial sensory signals to the somatosensory cortex via the pons and the thalamus

Somatotopy

A somatosensory cortical organization in which all parts of the body have cortical representation in the somatosensory cortex. The size of cortical representation is proportional to the number of somatosensory receptors in a particular body part

Cortical homunculus

Distorted cortical representations of body parts results from the fact that the size of cortical representation is proportional to the number of somatosensory receptor in a particular body part, not to the total surface area of that body part

Example: close to 50% of the somatosensory cortex is devoted to the head region even through the head represents only about 9% of the total body surface area in adults

Agonist

A chemical compound that can mimic the function of a receptor’s physiological ligand

Example: nicotine is an ___of the acetylcholine receptor because it can activate the acetylcholine receptor, just like the function of the ligand acetylcholine

Antagonist

A chemical compound that inhibits the function of a receptor

Example: tetrodotoxin is an ___ of the voltage-gated sodium channel because it prevents the opening of the channel when it binds to the channel

Chemoreceptor

A sensory receptor that can be activated by chemical ligands

Example: some nociceptors are ___, as they can be activated by chemicals that harm the body or chemicals that warn the body of potential harm

Polymodal receptor

A sensory receptor that can detect multiple stimuli

Example: a pain receptor that can detect both extreme pressure and extreme temperature

Generator potential (receptor potential)

A graded potential generated due to the opening of gated ion channels on a sensory receptor neuron/cell

Example: pressure on the skin can activate the pressure-sensitive sodium channels on the Merkel mechanoreceptor neuron, initiating generator or receptor potentials which can be summed up to generate action potentials

Superficial pain

Pain originating from the surface of the skin or of the mucous membrane

Example: pain from a ___ scratch on the skin

Somatic pain

Pain originating from deeper tissues, such as the deeper layer of the skin or the muscle/tendon/bone

Example: pain from torn ligament

Visceral pain

Pain originating from internal organs

Example: pain from a bloated stomach

Parallel pain processing

There are two distinct responses to a pain stimulus, as pain sensation are transmitted and processed as two types of pain signals: first pain signals (processes for sensory discrimination/localization in the somatosensory cortex) and second pain (processed for affective/emotions in other areas in the pain matrix). These two pain signals are processed in parallel by two anatomically distinct neural circuits

Pain matrix

Brain areas involved in processing and integration of pain signals

First pain

Sharp, well-localized pain sensation transmitted by the faster A-delta pain fiber neurons to the somatosensory cortex for pain quality assessment and localization

Second pain

Dull, throbbing and diffuse pain sensation transmitted by the slower non-myelinated C fiber neurons to the pain matrix outside of the somatosensory cortex for emotion and motivation aspected of pain

Anterolateral pathway

A 3-neuron chain that transmits pain and temperature signals from tehe body (except the head) contralaterally through the spinal cord to the somatosensory cortex and the associated areas in the brain

PAG (periaqueductal grey area)

A region in the mid brain that has multiple nuclei and involved in multiple functions, including pain modulation. I can secrete endorphins to mitigate pain signals transmission to the brain, thus lessening the pain sensation

Spinal cord gate theory of pain control

A model that explains why strong tactile stimulation can mitigate pain sensation at the same skin area. This theory proposes that the A-beta mechanoreceptor neurons, upon activation by pressure stimuli, can disinhibit spinal interneurons which can then inhibit pain signals transmission by neighboring C fiber neurons

Placebo effect

A phenomenon in which a pharmacological inert drug can elicit beneficial physiological response, such as pain sensation mitigation. A potential mechanism underlying this phenomenon is endorphin secretion by the brain to inhibit pain signal transmission to the brain

Dissociate of pain and touch sensation

Loss of pressure/tactile and pain/temperature sensation at opposite sides of the body, such as in the case of spinal cord hemisection. This dissociation of somatosensation is due to the fact that pressure/tactile signals are transmitted ipsilaterally up the spinal cord until they cross over at the medulla. Pain/temperature signals, on the other hand, cross over as soon as they enter the spinal cord so they are transmitted contralaterally up the spinal cord

Referred pain

A phenomenon in which visceral pain in perceived as superficial pain at a different location in the body. A possible mechanism underlying this phenomenon could be the convergence of sensory neurons from a skin area and from a vsiceral organ onto the same spinal interneuron to relay their sensory signals to the brain. The brain thus misinteprets that pain signals from the visceral sensory neuron came from the superficial sensory neuron

Phantom pain

The perception of pain coming from a missing body part. This phenomenon has been proposed to possibly originate from cortical mis-organization after body part removal, from aberrant spinal neuron activation after injury or from pain stimuli derived from peripheral neuronmas at the site of limb severance.

Which choice below shows the correct order of events in the sensory process

Detection, transduction, transmission, and processing in brain

Based on what you have learned abotu the 4 major types of mechanoreceptors, which receptor do you think would give you the highest spatial resolution for skin sensation? Clue: smaller receptive field = greater spatial resolution

Merkel receptor

You are rummaging through your backpack to find your cell phone in the bark. Which cutaneous receptor would be mot helpful in enabling you to find your cell phone by touch alone?

Merkel receptor

Merkel and Meissner

Near skin surface

Sensitive to fine pressure

High spatial resolution

Ruffini and Pacinian

Deeper in the skin

Respond to higher pressure

Low spatial resolution

Merkel and Ruffini

Detects duration of pressure (object texture and shape)

Meissner and Pacinian

Detects changes in pressure (object movement)

___ mechanoreceptors enable us to carry out motor movements. ___ mechanoreceptors, on the other hand, allow us to detect objects touching us

Proprioceptive, Cutaneous

A small pressure applied to the skin will activate a Ruffini receptor by opening its ___. A larger pressure applied to the skin will activate a Ruffini receptor even more by opening ___.

Sodium channels, more sodium channels

When your leg touches the. corner of a chair, you are aware of this sensation because a ___ neuron transmits this sensation via the ___ pathway to the brain

Lumbar cutaneous mechanoreceptor, dorsal column

A lesion in the left somatosensory cortex will ___ touch sensation at the ___

Decrease, right leg & Decrease, right arm

In human, about 40% of the somatosensory cortex is devoted to the head region/ This means that

About 40% of somatosensory receptors are located in the head region

True statements for the organization of the somatosensory cortex

Somatosensory cortex is somatotopically organized, with the size of the cortical area devoted to each body region proportional to the number of somatosensory receptors in that body part

Information from each somatosensory modality is represented in its own functional column in the somatosensory cortex

The somatosensory cortex has 6 layers of neurons, with each layer of neuron carrying out a specific function

What is the mechanism that allows us to remember our somatosensory experience?

The somatosensory information is relayed from the primary somatosensory cortex to other associated brain areas to generate learning and memory of the somatosensory experience

Following an injury, a patient lost touch sensation in his/her left arm, which injury condition listed below can produce this somatosensory deficit?

Left cervical sensory neuron, right somatosensory cortex

A person lost his/her second toe in an accident, what possible consequences of this injury?

Somatosensory cortical area for the first toe will expand over time

Somatosensory cortical area for the second toe will shrink and disappear over time

Somatosensory cortical area for the third toe will expand over time

Based on what you have learned about the sensory system so far, a right cervical spinal nerve will innervate ___, and transmits its sensory signals to the ___

Right arm, left somatosensory cortex