Somatosensory - 2.28.17

Question 1

A ___ ___ _____ is an unspecialized, afferentnerve ending, meaning it brings information from the body’s periphery toward the brain. They function as cutaneous receptors and are essentially used by vertebrates to detect pain. They are the same as a ____ nerve.

Answer 1

A free nerve ending (FNE) is an unspecialized, afferentnerve ending, meaning it brings information from the body’s periphery toward the brain. They function as cutaneous receptors and are essentially used by vertebrates to detect pain. They are the same as a cuteanous nerve.

Question 2

Conduction velocity is proportional to fiber ___.

Answer 2

conduction velocity is proportional to fiber diameter (myelinization)

Question 3

Alpha-beta fibers are myelinated/unmyelinated? What are they useful for?

What would happen if it was blocked?

Answer 3

Myelinated

They are important for sharp, prickling pain and temperature. They are fast!

You have pain relief and a loss of temperature sensation.

Question 4

C fiber’s function is:

Are they myelinated or unmyelinated?

Answer 4

C fiber’s function is slow pain, autonomic, postganglionic sympathetic, polymodal nociceptors.

They are unmyelinated.

If it is blocked, there is pain relief and a loss of temperature sensation.

Question 5

Where are free nerve endings found?

Answer 5

All skin, epidermis and some viscera

Question 6

Where are Meissner’s corpuscles found?

Answer 6

Glabrous skin (hairless skin)

Question 7

What is the function of Meissner’s Corpuscles

Answer 7

Dynamic, fine/light touch.

Question 8

Pacinian corpuscles are found where? What is their function?

Answer 8

Pacinian corpuscles are found in deep skin layers, ligaments and joints.

They sense vibration and pressure.

Question 9

Merkel Disc’s are large myelinated fibers found where?

Function?

Answer 9

They are found in fingertips and superficial skin.

They sense pressure, deep static touch (e.g. sharp edges), and position sense.

Question 10

Ruffini Corpuscles are located where and function how?

Answer 10

They are located in finger tips and joints

They sense pressure, slippage of objects along surface of skin, and joint angle change.

Question 11

Dermatomes:

C2

C3

C4

C6

T4

T7

T10

L1

L4

L5

S2,3,4

Answer 11

Dermatomes:

C2 - posterior half of the skull “cap”

C3 - high turtleneck shirt

C4 - lower collared shirt

C6 - includes thumbs

T4 - nipples

T7 - Xiphoid process

T10 - at the umbilicus (improtant for early appendicitis pain referral)

L1 - inguinal ligament

L4 - includes kneecaps, medial ankle

L5 - big toe

S2,3,4 - perianal area and genitals

Question 12

A-beta fibers carry ___ and ___ information. A delta and c fibers carry __ and __ information.

Answer 12

A beta fibers carry touch and pressure information. A delta and c fibers carry pain and temperature information.

Question 13

List from largest to smallest

A-beta

A-delta

C fiber

Answer 13

A-beta > A-delta > C fiber (unmyelinated so slowest)

Question 14

The more myleinated you are, the __ you are and the __ you are

Answer 14

Thicker and faster

Question 15

Selective activation or inactivation depends on ___. For example, when you are injecting a local anesthetic into a part in the skin, you should know which fibers are inactivated. The ___ diameter fibers get inactivated first. So, the __ fibers which carry pain info will be the first to go. The next fibers to go will be the __ fibers.

Answer 15

Selective activation or inactivation depends on size. For example, when you are injecting a local anesthetic into a part in the skin, you should know which fibers are inactivated. The smallest diameter fibers get inactivated first. So, the C fibers which carry pain info will be the first to go. The next fibers to go will be the A-delta fibers.

Question 16

If you get compression on your limb, which fibers are first to get inactivated? The ___ diameter fibers get inactivated first, and the ___ diameter fibers remain active for a longer time.

If you are doing electrical stimulation, then again, the ___ diameter fibers get activated at the lowest stimualation threshold.

Answer 16

If you get compression on your limb, which fibers are first to get inactivated? The larger diameter fibers get inactivated first, and the smallest diameter fibers remain active for a longer time.

If you are doing electrical stimulation, then again, the larger diameter fibers get activated at the lowest stimualation threshold.

Question 17

Externally applied pressure, such as compression of the skin above a nerve, first blocks the myelinated ___ fibers, while ___ fibers continue to conduct action potentials and allow the slow conducting pain to be carried.

A low dose of local anesthesia applied to peripheral nerves blocks the unmyelinated __ fibers before the myelinated ___ fibers. Under this condition, the slow conducting pain information is blocked, and only the fast conducting pain information by A delta fibers is carried to the CNS. This experiment provides additional evidence that two different types of nerve fibers carry noxious information.

Answer 17

Externally applied pressure, such as compression of the skin above a nerve, first blocks the myelinated A delta fibers, while C fibers continue to conduct action potentials and allow the slow conducting pain to be carried.

A low dose of local anesthesia applied to peripheral nerves blocks the unmyelinated C fibers before the myelinated A delta fibers. Under this condition, the slow conducting pain information is blocked, and only the fast conducting pain information by A delta fibers is carried to the CNS. This experiment provides additional evidence that two different types of nerve fibers carry noxious information.

Question 18

Most of touch information is relayed by what fibers?

Answer 18

A-beta fibers, which are large myelinated fibers.

Question 19

All of the sensory fibers in the skin get turned on by special ion channels called ___ ___ ___ channels. All touch and pain fibers have these, and their channels that are repsonsive to particular kinds of stimulation.

Answer 19

All of the sensory fibers in the skin get turned on by these special ion channels called transient receptor potential channels. All touch and pain fibers have these, and their channels that are repsonsive to particular kinds of stimulation.

Question 20

Four kinds of sensory receptors of skin:

2 that are relatively superficial are the __ and ___.

2 that are relatively deep in the skin and are the __ and __.

___ cells are slowly adapting, whereas the ___ are rapidly adapting.

Answer 20

Four kinds of sensory receptors of skin:

2 that are relatively superficial are the Meissner corpuscle and Merkel cell.

2 that are relatively deep in the skin and are the Pacinian corpuscles and Ruffini endings.

Merkel cells are slowly adapting, whereas the Meissner’s corpuscles are rapidly adapting.

Question 21

The ___ corpuscles and ___ cells, since they are located more sperficially have small, relatively well-defined receptive fields, whereas the ___ corpuscles and __ ___, which are located deeper in the skin, have a broad, not-well defined receptive field.

Answer 21

The Meissners and Merkels, since they are located more sperficially have small, relatively well-defined receptive fields, whereas the Pacinian and Ruffini endings, which are located deeper in the skin, have a broad, not-well defined receptive field.

Question 22

The ___ corpuscles are really good at detecting vibration. They have rapid on and off ability.

Answer 22

Pacinian

Question 23

Two point discrimination:

On the _____, you can distinguish two different stimuli that are really close together. Whereas when you get to the arm, back or belly or thigh, you can only detect stimuli that are ___ ___. This is because of the ___ ___.

____ are highly innervated (lots of little receptors), so you have an ability to detect things that are close together.

Things like your back, are areas that are not highly innervated so you cannot detect things that are close together because there aren’t enough receptors to do it.

Answer 23

Two point discrimination:

On the fingers, you can distinguish two different stimuli that are really close together. Whereas when you get to the arm, back or belly or thigh, you can only detect stimuli that are far apart. This is because of the innervation density.

Fingers are highly innervated (lots of little receptors), so you have an ability to detect things that are close together.

Things like your back, are areas that are not highly innervated so you cannot detect things that are close together because there aren’t enough receptors to do it.

Question 24

______: our ability to know where our limbs are in space.

There are three sets of receptors which allow us to do this:

What are they?

Answer 24

Proprioception: our ability to know where out limbs are in space.

1. Muscle spindles - length detectors embedded in muscle. They contain specialized fibers called intrafusal muscle fibers which shorten and lengthen with the whole muscle (innervated by A-alpha fibers). Muscle spindles supply the input that drives the stretch reflex.
2. Joint receptors - Golgi tendon organs and free nerve endings which detect muscle tension and give negative feedback.
3. Cutaneous receptors - Pacinian corpuscles and Ruffini’s corpuscles, but they also reside in skin and joints.

In addition, the brain knows where it told the limb to go. So we hae the motor command as part of the information about where the limb is supposed to be.

Question 25

Muscle spindles are a specialized receptors that are embedded in muscles. Each muscle has many many muscle spindles which detect the ____ of the muscle. They can also detect the ___ with which the muscle is changing ___

They consist of specialized muscle fibers inside a little fibrous capsule and the capsule is spindle shaped which is why it is called a muscle spindle. The muscle fibers inside the capsule are called ___ ___ fibers and are in a capsule. These fibers have _____ contractile ends. The middle of the fiber does not have any muscular element and so it can ___, like a rubber band. So, if the muscle lengthens and shortens, it is the ___ part of the intrafusal muscle fiber that is lengthening and shortening.

Alternatively, if the ends of the fibers contract, they can pull on the middle and lengthen it, which is important for adjusting the guage or sensitivity of the fiber. This is controlled by the __ neurons. And finally, the sensory endings (the____, the fastest conducting fibers we have) will conduct quickly back to the ___. Regular muscle fibers are called ____.

Intrafusal muscle fibers are innervated by large myelinated axons (____). ____ relay into the CNS information about the ___ of the muscle. When the muscle is long, the fibers are ___. When the muscle shortens, the fiber becomes ____. This is the basis of the ___ reflex.

When you take a reflex hammer and knock on a tendon, you stretch the muscle. When you stretch the muscle, the muscle spindle is ____, and sends a signal to the CNS, and the motor neuron shortens (contracts).

Answer 25

Muscle spindles are a specialized receptors that are embedded in muscles. Each muscle has many many muscle spindles which detect the length of the muscle. They can also detect the speed with which the muscle is changing length

They consist of specialized muscle fibers inside a little fibrous capsule and the capsule is spindle shaped which is why it is called a muscle spindle. The muscle fibers inside the capsule are called intradusal muscle fibers and are in a capsule. These fibers have striated contractile ends. The middle of the fiber does not have any muscular element and so it can stretch, like a rubber band. So, if the muscle lengthens and shortens, it is the middle (stretchy) part of the intrafusal muscle fiber that is lengthening and shortening.

Alternatively, if the ends of the fibers contract, they can pull on the middle and lengthen it, which is important for adjusting the guage or sensitivity of the fiber. This is controlled by the gamma neurons. And finally, the sensory endings (the A-alpha fibers, the fastest conducting fibers we have) will conduct quickly back to the CNS. Regular muscle fibers are called extrafusal.

Intrafusal muscle fibers are innervated by large myelinated axons (A-alpha fibers). A-alppha fibers relay into the CNS information about the length of the muscle. When the muscle is long, the fibers are active. When the muscle shortens, the fiber becomes inactive. This is the basis of the stretch reflex (knee jerk).

When you take a reflex hammer and knock on a tendon, you stretch the muscle. When you stretch the muscle, the muscle spindle is active, and sends a signal to the CNS, and the motor neuron shortens (contracts).

Question 26

Muscle spindles are __ detectors, and the __ motor neurons can adjust the sensitivity of the muscle spindle.

___ motor neurons can reset the sensitivity of the spindle to measure length even when the muscle is contracting.

This figure illustrates the important role of gamma motor neuron activity in regulating the responses of muscle spindles.

The figure on the left illustrates that when muscles contract the spindle is no longer able to measure ____. The spindle afferent falls silent.

The figure on the right shows how the ____ motoneuron resets or retightens the spindle so it can again report stretch even when the muscle is contracting. The gamma motor neurons can regulate the gain of muscle spindles so that they can operate efficiently at any length of the parent muscle.

Alpha and Gamma motoneurons are typically __-____ so the that while the muscle contracts, the ends of the intrafusal fibers also contract. This keeps enough tension on the middle of the fiber, so that there is constant feedback from the spindle on muscle length.

If the Gamma motoneurons are activated alone (in some pathological states), the spindle becomes abnormally ____ even at the normal resting length of the muscle. The spinal cord interprets this as muscle ____ and sends commands to the muscle to ___ (this is the stretch reflex). This constant contraction is called ___.

Activation of gamma motoneurons is thought to be one of the mechanisms for the ____ seen after upper motoneuron damage

Answer 26

Muscle spindles are length detectors, and the gamma motor neurons can adjust the sensitivity of the muscle spindle.

Gamma motor neurons can reset the sensitivity of the spindle to measure length even when the muscle is contracting

This figure illustrates the important role of gamma motor neuron activity in regulating the responses of muscle spindles.

The figure on the left illustrates that when muscles contract the spindle is no longer able to measure length. The spindle afferent falls silent.

The figure on the right shows how the gamma motoneuron resets or retightens the spindle so it can again report stretch even when the muscle is contracting. The gamma motor neurons can regulate the gain of muscle spindles so that they can operate efficiently at any length of the parent muscle.

Alpha and Gamma motoneurons are typically co-activated so the that while the muscle contracts, the ends of the intrafusal fibers also contract. This keeps enough tension on the middle of the fiber, so that there is constant feedback from the spindle on muscle length.

If the Gamma motoneurons are activated alone (in some pathological states), the spindle becomes abnormally sensitive even at the normal resting length of the muscle. The spinal cord interprets this as muscle stretch and sends commands to the muscle to contract (this is the stretch reflex). This constant contraction is called spasticity.

Activation of gamma motoneurons is thought to be one of the mechanisms for the spasticity seen after upper motoneuron damage

.

Question 27

Golgi tendon organs detect muscle ____ (force of contraction). It provides ___ feedback to motor neurons. It is embedded in tendons that attach the muscle to bone. The tendon is not stretchable, so it cannot detect length, but it can detect ____. The muscle spindle gives posititve feedback, whereas the golgi tendon organ gives negative feedback. When muscle spindles get stretched, it tells the nervous system to become activated and contract the muscle to the normal length again.

The golgi tendon organ does the opposite. This creates a nice positive and negative feedback which is going to the spinal cord, telling it about the tension and length of muscle. This helps to create a ____ muscle contraction. GTO’s may prevent tissue damage by setting ____ on strength of muscle contraction.

It also has clinical significance in ___. In ___, the limbs become very stiff and you really cannot move them. You have to push really hard to move the limbs. It resists movement and until all of a sudden it collapses when you put enough pressure (this is the ___-___ response). It is not entirely clear what underlies this response but many people think it is the golgi tendon activity. It becomes so active because of the tension, that it finally overcomes everything and inhibits the motor neurons causing this response.

GTO is innervated by ____ –super fast report on muscle force.

Answer 27

Golgi tendon organs detect muscle tension (force of contraction). It provides negative feedback to motor neurons. It is embedded in tendons that attach the muscle to bone. The tendon is not stretchable, so it cannot detect length, but it can detect tension. The muscle spindle gives posititve feedback, whereas the golgi tendon organ gives negative feedback. When muscle spindles get stretched, it tells the nervous system to become activated and contract the muscle to the normal length again.

The golgi tendon organ does the opposite. This creates a nice positive and negative feedback which is going to the spinal cord, telling it about the tension and length of muscle. This helps to create a smooth muscle contraction. GTO’s may prevent tissue damage by setting limits on strength of muscle contraction.

It also has clinical significance in spasticity. In spacticitiy, the limbs become very stiff and you really cannot move them. You have to push really hard to move the limbs. It resists movement and until all of a sudden it collapses when you put enough pressure on it (clasp knife response). It is not entirely clear what underlies this response but many people think it is the golgi tendon activity. It becomes so active because of the tension, that it finally overcomes everything and inhibits the motor neurons causing the clasp-knife response.

GTO is innervated by A-alpha sensory axons –super fast report on muscle force.

Question 28

The dorsal column carries what kind of info?

___, light touch and vibration. Basically, all touch info. Since it also carries proprioceptive info, the muscle spindles send a collateral into the ____ column. Since the spindle also has direct control of ____ neurons, it sends another collateral into the ___ horn, where it makes a connection with an alpha motor neuron, which will project out to the periphery to innervate a ___. So the spindle goes both to the __ column and into the __ horn of the spinal cord. The GTO does the same thing.

Answer 28

The dorsal column carries what kind of info?

Propioception, light touch and vibration. Basically, all touch info. Since it also carries proprioceptive info, the muscle spindles send a collateral into the dorsal column. Since the spindle also has direct control of A motor neurons, it sends another collateral into the ventral horn, where it makes a connection with an alpha motor neuron, which will project out to the periphery to innervate a muscle.

So the spindle goes both to the dorsal column and into the ventral horn of the spinal cord. The GTO does the same thing.

Question 29

Dorsal column end in a set of nuclei called the __ __ __. The axons thar arise in this nuclei form a pathway called the ___ ___ ___ ___ pathway. This is the touch system.

If there is a stroke in the brain stem, you will get symptoms that include the medial lemniscus system and corticospinal tract system, so you will be ___ and you won’t be able to feel ____.

Answer 29

Dorsal column end in a set of nuclei called the dorsal column nuclei. The axons thar arise in this nuclei form a pathway called the dorsal column/medial lemniscus pathway. This is the touch system.

If there is a stroke in the brain stem, you will get symptoms that include the medial lemniscus system and corticospinal tract system, so you will be paralyzed and you won’t be able to feel fine touch.

Question 30

A lateral pontine syndrome is a lesion which is similar to the lateral medullary syndrome, but because it occurs in the pons, it also involves the cranial nerve nuclei of the pons. It can be caused by an interruption to the blood supply of the ___ ___ ____artery.

Which areas are affected?

Answer 30

A lateral pontine syndrome is a lesion which is similar to the lateral medullary syndrome, but because it occurs in the pons, it also involves the cranial nerve nuclei of the pons. It can be caused by an interruption to the blood supply of the anterior inferior cerebellar artery.

Lateral pons (vestibular nuclei, facial nucleus, trigeminal nucleus, cochlear nuclei, sympathetics), middle/inferior cerebellar peduncles

Question 31

The spinal thalamic tract is located next to the _____ nucleus (which is responsible for __ and ___. in the face). It receives fibers from the ipsilateral face, whereas in the brainstem the spinal thalamic tract are fibers from the contralateral body. So, when you see a person who has loss pain and temp. on one side of the face and opposite side of the body and they have hoarseness and dusphagia (can’t swallow), it is probably an ___ stroke because it includes the STT and the trigeminal nucleus of the spinal nerve and nucleus ambiguous.

Answer 31

The spinal thalamic tract is located next to the trigeminal nucleus (which is responsible for pain and temp. in the face). It receives fibers from the ipsilateral face, whereas in the brainstem the spinal thalamic tract are fibers from the contralateral body. So, when you see a person who has loss pain and temp. on one side of the face and opposite side of the body, hoarseness and dysphage (can’t swallow) it is probably an PICA stroke because it includes the STT and the trigeminal nucleus of the spinal nerve and nucleus ambiguous.

Question 32

VPM receives info from the ___ and VPL receives info from the ___ and they relay this info to the cerebral cortex to the first somatic sensory area which is the post central gyrus.

Answer 32

VPM receives info from the FACE and VPL receives info from the LIMBS and they relay this info to the cerebral cortex to the first somatic sensory area which is the post central gyrus.

Question 33

If you have a patient who cannot move their face or speak, what type of stroke do they have? MCA or ACA?

Answer 33

MCA

Question 34

Lesions of the _____ are impaired perception of light touch, severely impaired proprioception, severely impaired discriminative touch.

Answer 34

Lesions of the somatosensory area (S1) are impaired perception of light touch, severely impaired proprioception, severely impaired discriminative touch (two point discrimination thing).

The sensory loss is somatotopically appropriate.

Question 35

Higher order processing of body info ends up in one place which is the ____. Damage to this area causes people to completely neglect the opposite side of the world. It is called neglect, and they behave as if that part of the world does not exist.

Answer 35

Right parietal cortex.

Question 36

Pain fibers are called ___. They are simply afferent fibers that give us information about destruction or potential detruction. There are different types of receptors that detect different types of pain. In this case, the receptors are the TRP channels. All the nociceptors are very fine unmyelinated, undifferentiated axon terminals but they have different TRP receptors.

There are two kinds of nociceptor fibers:

___ fibers - rapidly adapting and relay info about sharp prickly pain

__ fibers - unmyelinated, slowly conducting, summating and late onset, which carry different types of information.

Answer 36

Pain fibers are called nociceptors. They are simply afferent fibers that give us information about destruction or potential detruction. There are different types of receptors that detect different types of pain. In this case, the receptors are the TRP channels. All the nociceptors are very fine, unmyelinated, undifferentiated axon terminals but they have different TRP receptors.

There are two kinds of nociceptor fibers:

A-delta fibers - rapidly adapting and relay info about sharp prickly pain

C fibers - unmyelinated, slowly conducting, summating and late onset, which carry different types of information.

Question 37

Pain is not well localized on the body the way touch is. The reason why, is because when pain fibers enter the dorsal horn, they travel in __ tracts, which is the most dorsal part of the dorsal horn. They then ascend or descend 1 or 2 levels within Lissau’s fasiculus, leaving off terminals as they go. This is why pain is not well localized. It then synapses onto a cell body in layers __, __ and __, of the __ ___ in the grey matter. The axons from layers __ and __ then decussates (anterior white commisure) and ascends via spinal thalamic fasiculus.

The STT is the pathway for pain and temperature (crude touch). Layer _ and layer _ are the origins of the spinal thalamic tract.

Layer 5 fibers are interesting because they receive convergent inputs from ____ (pain fibers) and from ___ (touch fibers).

If you bang your elbow, rubbing it helps the pain. How does this happen? Explain.

The ___ fibers and ___ fibers can both terminate on layer 5. But it turns out, that they also terminate on an ____ which gives them the ability to inhibit each other. The one that has the strongest input will win and inhibit the other one. Inititally, when pain info comes in, that is the strongest input, which is why you feel pain! Then, when you start rubbing that area, the rubbing becomes the strongest input. The reason why you don’t feel pain any more is because ____ fibers has activated the inhibtory neuron which inhbits the ____ fibers. So this system creates a kind of a balance between __ and __ fibers. When one of them wins, it will block out the other, preventing one from getting onto the spinal thalamic tract.

This is called the __ theory of pain.

Answer 37

Pain is not well localized on the body the way touch is. The reason why, is because when pain fibers enter the dorsal horn, they travel in Lissau’s tracts, which is the most dorsal part of the dorsal horn. They then ascend or descend 1 or 2 levels within Lissau’s fasiculus, leaving off terminals as they go. This is why pain is not well localized. It then synapses onto a cell body in layers 1 , 2, and 5 of the dorsal column in the grey matter. The axons from layers 1 and 5 then decussates (anterior white commisure) and ascends via spinal thalamic fasiculus.

The STT is the pathway for pain and temperature (crude touch). Layer 1 and layer 5 are the origins of the spinal thalamic tract.

Layer 5 fibers are interesting because they receive convergent inputs from A-delta(pain fibers) and fromA-beta (touch fibers).

If you bang your elbow, rubbing it helps the pain. How does this happen? Explain.

The A-beta fibers and A-delta fibers can both terminate on layer 5. But it turns out, that they also terminate on an interneuron which gives them the ability to inhibit each other. The one that has the strongest input will win and inhibit the other one. Inititally, when pain info comes in, that is the strongest input, which is why you feel pain! Then, when you start rubbing that area, the rubbing becomes the strongest input. The reason why you don’t feel pain any more is because A-beta fibers has activated the inhibtory neuron which inhbits the A-delta fibers. So, this system creates a kind of a balance between pain (A-delta) and touch (A-beta) fibers. When one of them wins, it will block out the other, preventing one from getting onto the spinal thalamic tract.

This is called the Gait theory of pain.

Question 38

Visceral afferents (like in stomach, gall bladder, etc.) will terminate on the same spinal thalamic neuron as the pain afferents (__ fibers) from the ___, which is why pain from the viscera is often reffered to locations on body the surface because they are both using the same spinal thalamic neuron to get to the brain.

Answer 38

Visceral afferents (like in stomach, gall bladder, etc.) will terminate on the same spinal thalamic neuron as pain afferents from the skin, which is why pain from the viscera is often reffered to locations on body the surface because they are both using the same spinal thalamic neuron to get to the brain.

Question 39

The spinothalamic system (aka ___) relays pain and temperature information to consciousness.

It plays a major role in localizing pain and discriminating among different types of pain. _____ and ______ projections feed into emotional responses to pain.

The _____ system plays a major role in eliciting arousal and attention. It has ascending projections to the limbic system and also feeds into the descending pain modulating pathways.

The ____ pathway is the most direct pathway to the limbic system and elicits the autonomic nervous system response to pain.

Answer 39

The spinothalamic system (aka spinal thalamic tract) relays pain and temperature information to consciousness. It plays a major role in localizing pain and discriminating among different types of pain. Thalamocortical and corticocortical projections feed into emotional responses to pain.

The spinoreticular system plays a major role in eliciting arousal and attention. It has ascending projections to the limbic system and also feeds into the descending pain modulating pathways.

The spinohypothalamic pathway is the most direct pathway to the limbic system and elicits the autonomic nervous system response to pain.

Question 40

The midbrain is also called the ___. The info coming from the face is weird. The info comes in and goes through a tube called the __ __ of the __ __. It is a long tube that extends from the mesencephalon down into the upper cervical spinal cord. Pain and temp axons come in the trigeminal nerve and go down this tube for some distance and then terminates on some axon which sends another axon across the midline to join the STT. This spinal nucleus at the trigeminal nerve travels right next to the spinal thalamic tract from a contralateral body. So, if you get an infarct that occludes this area, you will get loss of pain and temperature on the ___ side of the face and on the ___ side of body. Spinal thalamic tract and spinal nucleus are right next to each other. A lesion that gets them both gets trigeminal stuff before it hits the midline

Answer 40

The midbrain is also called the mesencephalon. The info coming from the face is weird. The info comes in and goes through a tube called the spinal nucleus of the trigeminal nerve. It is a long tube that extends from the mesencephalon down into the upper cervical spinal cord. Pain and temp axons come in the trigeminal nerve and go down this tube for some distance and then terminates on some axon which sends another axon across the midline to join the STT. This spinal nucleus at the trigeminal nerve travels right next to the spinal thalamic tract from a contralateral body. So, if you get an infarct that occludes this area, you will get loss of pain and temperature on the same side of the face and on the opposite side of body.

Question 41

What is circled in hot pink?

What happens if you get a stroke in PICA?

Answer 41

The spinal nucleus of trigeminal nerve and the STT. They are both included in the PICA. So you can lose pain and temp in one side of the face and the opposite side of the body. The medial leminscus is preserved so fine touch is preserved.

Question 42

Pain, Temperature and Crude Touch Summary Slide:

Primary afferents enter ___ tract

First synapse in layers __, __ and __.

Second order fibers cross midline and enter ____ tracts

Trace pathway to thalamus

Synapse in VPL

also intralaminar and other nuclei

Third order neurons project ___

Also SII, insula and other cortical areas

Answer 42

Primary afferents enter Lissauer’s tract

First synapse in layers I, II, V

Second order fibers cross midline and enter spinothalamic tracts

Trace pathway to thalamus

Synapse in VPL

also intralaminar and other nuclei

Third order neurons project primary somatosensory cortex

Also SII, insula and other cortical areas