6_Ascending Somatosensory Systems Flashcards
Pathways carrying somatosensation for the body, whether they are pain and temperature sensations, or the sensations of vibration, body position in space and discriminative touch, enter the _________________________________________________.
spinal cord in a segmental fashion over the dorsal root of each spinal nerve.
This segmental arrangement (from embryological origin) is reflected in the adult as the:
dermatomal map
In their simplest form, these pathways of somatosensation can be viewed as three neuron pathways, using just three neurons to carry the somatosensation from:
the peripheral receptors to the brain for perception of that somatosensory modality.
Throughout the transfer of information from the periphery to the brain, this segmental arrangement is _____________________________________________________. This arrangement is referred to as a somatotopic organization.
maintained as a topographic map within the pathways and nuclei carrying each sensation.
We see this representation in the homunculus positioned over both:
primary somatosensory cortex and primary motor cortex.
The modalities of conscious proprioception, discriminative touch (two-point discrimination; light touch), position sense (proprioception) and vibratory sensations for the body are carried via the:
dorsal column/medial lemniscus system.
The __________ nerve and related pathways carry these sensations for the face.
trigeminal
What is proprioception?
Modality that provides information concerning movement and position of body parts (in part, joint position in space).
What are two modalities of proprioception?
conscious and unconscious.
Conscious proprioception is:
involved in Kinesthesia, the sense of perception of movement of joints.
Unconscious proprioception is:
proprioception mediated or carried by the spinocerebellar tracts to be discussed later.
The sensations of proprioception and discriminative touch are necessary for _____________.
Stereognosis
What is stereognosis?
the ability to identify an object by feel.
Which modalities are carried by the dorsal column/medial lemniscus system?
proprioception and discriminative touch
The transfer of the sensations of these modalities to the cortex is organized in:
a three-neuron chain (disregarding any interneurons).
Where are primary or first order neuron cell bodies located?
cell body is in the dorsal root ganglia from S5 through C1.
Primary neurons are an example of ______________ neurons.
pseudounipolar
The peripheral processes (________________________________) are heavily myelinated (_____) and are in contact with __________ receptors; muscle spindles, golgi tendon organs, pacinian corpuscles, joint receptors, etc.
(axons up to the level of the dorsal root ganglion)
(Ia, Ib, II)
encapsulated
The central processes are _________________ and enter the spinal cord __________ and ascend (without synapsing) in either the fasciculus _______ or fasciculus _________.
heavily myelinated
segmentally
gracilis
cuneatus
The fasciculus gracilis fibers originate from :
S5-T7; lower trunk and the lower limb
The fasciculus cuneatus fibers originate from:
T6-C1; upper trunk and upper limb
The fasciculi gracilis and cuneatus comprise the dorsal or posterior columns. These fibers are added sequentially within the _____________in a topographic fashion from medial (__________) to lateral (____________).
dorsal columns
medial (lower extremities)
lateral (upper extremities).
Where are the secondary or second order neuron cell bodies?
Both nuclei are located at the level of the closed or _________.
cell bodies are located in the nucleus gracilis and nucleus cuneatus, respectively.
caudal medulla
The ascending fibers in the dorsal columns synapse on:
secondary order neurons
The axons of secondary neurons form the __________ fibers that cross the midline to form the ___________________.
internal arcuate
contralateral medial lemniscus
The medial lemniscus is somatotopically organized and projects to the:
ventral posterolateral nucleus of the thalamus (VPL).
Where are tertiary or third order neuron cell bodies located?
cell bodies are in the VPL.
The axons of these neurons project through the:
posterior limb of the internal capsule to the primary somatosensory cortex (Areas 3,1,2; postcentral gyrus in the parietal lobe).
The distribution of the projections to the postcentral gyrus is still organized in a ____________________ (the somatosensory homunculus).
somatotopic organization
Those areas of the body that are _______________ have the ____________ representation within this cortex; i.e., index finger, tongue.
most sensitive
greatest
EXCEPTION – (discriminative touch and conscious proprioception) Proprioception of the lower extremity includes _________ (part of Nucleus Gracilis) and ____________ (spinal cord levels T1-L2).
Nucleus Z
Clarke’s Nucleus
EXCEPTION - ). (discriminative touch and conscious proprioception) This alternative pathway carries some of the modality of conscious proprioception for the:
for the lower extremities.
EXCEPTION - (discriminative touch and conscious proprioception) An extra neuron is added between the dorsal root ganglion and the nucleus Gracilis. Some of the large diameter first order fibers end in the:
ipsilateral dorsal nucleus of Clarke.
EXCEPTION -(discriminative touch and conscious proprioception) A second neuron sends its axon out ipsilaterally to ascend in the ________________, adjacent to the dorsal __________ tract and then synapse in ______.
dorsolateral fasciculus
spinocerebellar
Nucleus Z
EXCEPTION - (discriminative touch and conscious proprioception) The nucleus Z is located at the:____________________________________.
Axons of nucleus Z join the internal arcuate fibers and cross to ascend as part of the contralateral medial lemniscus. The rest of the pathway is the same. Functionally, this system is similar to the others.
rostral end of nucleus Gracilis.
EXCEPTION - (discriminative touch and conscious proprioception) Axons of nucleus Z join the ______________ fibers and cross to ascend as part of the _______________________. The rest of the pathway is the same. Functionally, this system is similar to the others.
internal arcuate
contralateral medial lemniscus
The “alternative pathway” has been proposed as a possible neural pathway by which some conscious perception of proprioception for the lower extremities is:
maintained when the dorsal column system is damaged due to trauma or degenerative illnesses.
The sensory modalities of pain, temperature and non-discriminative touch for the body (trunk and extremities) are carried over a system termed the:
anterolateral system or spinothalamic system.
There are two primary pathways to the anterolateral system (or spinothalamic system):
1) the lateral spinothalamic pathway and
2) the anterior spinothalamic pathway.
These same sensory modalities for the anterior two thirds of the head/face, oral and nasal cavities utilize the ______________ and its central nuclei and tracts.
trigeminal nerve
The sensation of pain and temperature is carried by the ________________________________, it is named for the position of the fiber bundle of axons from the second neuron of the three-neuron chain. The sensation of pain is pervasive and very personal. It is also of tremendous clinical significance.
lateral spinothalamic system.
The lateral spinothalamic system is named for the:
position of the fiber bundle of axons from the second neuron of the three-neuron chain.
True or false: The sensation of pain is simple and very generic.
False: The sensation of pain is pervasive and very personal.
For pain, the First or primary neuron is a _______________ neuron with its cell body in __________________.
pseudounipolar
dorsal root ganglia.
Lateral Spinothalamic: The peripheral receptors are:
free nerve endings (non-encapsulated).
Lateral Spinothalamic: The fibers are smaller (________), ______ myelinated fibers (A-δ fibers).
2.0-5.0 μm
lightly
Lateral Spinothalamic: The A-δ fibers transmit their information _____ quickly (________) and carry the sensation of ________ pain that is fairly localizable.
more
6-36 M/sec
pricking
The central processes (of pain) enter the spinal cord ________ and bifurcate in the ___________.
laterally and
Lissauer’s tract
Lateral Spinothalamic: The central processes may ________ or ________ several segments, or enter the dorsal horn at that level and then synapse on neurons _________________________________.
ascend or descend
in substantia gelatinosa/nucleus Proprius (Lamina of Rexed II, III)
What level lamina is substantia gelatinosa and nucleus proprius?
Lamina of Rexed II, III
Lateral Spinothalamic: The neurotransmitter identified for this neuron is most likely:
glutamate (as is the neurotransmitter for the rest of the neurons in this pathway).
Lateral Spinothalamic:
The exact position of the cell body for the second order neuron is:
not known with any certainty. It is, however, probably located in substantia gelatinosa (some of them may also be in the nucleus proprius)
Lateral Spinothalamic: These second order neurons send their axons across the midline, through the ______________, in an ascending and ________ (1-2 segments) direction to form the ______________________on the contralateral side of the cord.
anterior white commissure
oblique
lateral spinothalamic tract
Lateral Spinothalamic: The second order neuron pathway has a somatotopic organization, the more laterally placed fibers carry pain and temperature sensations from ______________ and the more medially situated fibers from progressively______________________.
lower body segments
higher levels of the spinal cord
Lateral Spinothalamic: This sensory tract ascends through the spinal cord and brainstem to reach the ___________________ and intra laminar thalamic nuclei.
ventral posterolateral thalamic nucleus (VPL)
Lateral Spinothalamic: The third or tertiary neuron cell body is located in: _____.
VPL
Lateral Spinothalamic: The somatotopic distribution of this sensory pathway is maintained within this nucleus i.e., the neurons situated most laterally are:
used to transfer information concerning pain from the lower extremity (lumbar-sacral dermatomes).
Lateral Spinothalamic: The axons of these neurons leave VPL and ascend to:
primary somatosensory cortex, via the superior thalamic radiations (the medial part of the posterior limb of the internal capsule).
Lateral Spinothalamic: Primary somatosensory cortex is located in ___________, cortical areas 3, 1, and 2. Again, the somatotopic organization is represented along this cortex. The result is a ____________________ body called a homunculus (little man).
postcentral gyrus
representation of the contralateral
Lateral Spinothalamic: The homunculus is upside down, as if:
it is hanging by the lower limb with the leg representation in the midline cortex and the rest of the body on the lateral surface with the neck and head towards the lateral sulcus.
Lateral Spinothalamic: The homunculus representation allows for the precise localization of _________ pain; _______ pain is less localized.
pricking
burning
Lateral Spinothalamic: What will loss of 3rd order neurons will result in?
loss of localization of pain
**but not the affective emotional response to pain
Lateral Spinothalamic: The precision of this system makes it useful to:
define lesion sites.
Lateral Spinothalamic: By using the fact that the sensations cross in a relatively segmental manner, it is possible to identify the: ____________________ by the loss of painful stimulation.
level of a spinal cord lesion
Loss of painful stimulation =
anesthesia
Loss of pain over half of the body would =
hemi-anesthesia.
Lateral Spinothalamic: This “simple system” for the transfer of pain to the perceptive level is:
actually more complicated.
Lateral Spinothalamic: In addition to the lateral spinothalamic tract (substantia gelatinosa/nucleus proprius to VPL) there are at least three parallel systems:
1) spinocervicothalamic
2) spinoreticulothalamic
3) spinomesencephalic.
Parallel Systems: The spinocervicothalamic pathway contains an extra neuron that originates in the ________ and ascends _______ to a group of cells located at the level of the _____ dorsal horn. These fibers then join the ___________________.
dorsal horn
ipsilaterally
cervical
medial lemniscal system
Parallel Systems: This alternate pathway (spinocervicothalamic) carries modalities of _________________________________________________However, the information in this pathway is ______________.
conscious proprioception, discriminative touch, and pain and temperature.
non-localizable
Parallel Systems: Spinoreticulothalamic pathways have a _______ (synapse) in the:
relay
reticular formation of the brain stem.
Parallel Systems: This pathway (Spinoreticulothalamic) eventually reaches ___________________________ that project to widespread cortical areas including:
medial and intralaminar thalamic nuclei
the limbic system.
Parallel Systems: Limbic system connections involve the hypothalamus, which in turn activate ______________________. This pathway functions to help in analyzing the stimulus within the __________ domain. It also functions to activate:
or influence the autonomic nervous system.
emotional
the SNS response.
Parallel Systems: Spinomesencephalic (spinotectal) pathway projects to the _____________________ and ______________. This pathway can activate ________ pathways that are critical for modulating incoming painful stimuli.
superior colliculus and periaqueductal gray in the midbrain.
descending
Parallel Systems: The spinoreticulothalamic and spinomesencephalic pathways can activate __________ pathways originating from ______________ and ________________ of the reticular formation.
descending
Raphe’ nuclei and locus ceruleus
Raphe’ nuclei =
serotonin
locus ceruleus =
norepinephrine
Parallel Systems: These nuclei have _______ projections to the spinal cord that function in the proposed circuitry used in the __________ of the transmission of painful sensations
descending
modification
Anterior spinothalamic pathway: This pathway is also a _____ neuron pathway that carries the modality of:
three
light or non discriminative touch as well as pain sensation
Anterior spinothalamic pathway: The majority of the 1st order fibers of this pathway are_____ (0.1-1.3 μm), ____________ (C-fibers). The C fibers transmit their information ______ (0.5-1.0 M/sec.) and carry the sensation of _____________, as well as ___________________ impulses. The neurotransmitter of these neurons is thought to be _____________.
small unmyelinated slowly burning pain thermal nociceptive substance P
Anterior spinothalamic pathway: Each of the neuron cell bodies is located in the same structures as those for the:
lateral spinothalamic tract.
Anterior spinothalamic pathway: This sensation is demonstrated by brushing a piece of cotton across the skin. The patient is aware of being touched but is unable to:
identify texture or precise limits of the stimulation.
Anterior spinothalamic pathway: While this is a three neuron pathway, the trajectory of the axon of the second order neuron is:
very random, unlike that described for the previous system.
Anterior spinothalamic pathway: It may travel up or down 10 to 12 segments before:
it crosses through the anterior white commissure
Anterior spinothalamic pathway: Once the axons have crossed, they then form the:
anterior spinothalamic pathway.
Anterior spinothalamic pathway: This pathway also ascends to ____. This pathway also is thought to carry _____________________
VPL
non-specific temperature information.
Trigeminal nerve (CN V) is a ________ nerve and thus carries both sensory and motor fibers.
mixed
The modalities of pain, temperature, light touch, discriminative touch (two point discrimination), and conscious and unconscious proprioception for the _________ two-thirds of the face and head, are all carried by fibers in the_________ nerve.
anterior
trigeminal
Trigeminal nerve division: ophthalmic division; above the orbit=
V1
Trigeminal nerve division: maxillary division; below the orbit and above the mouth=
V2
Trigeminal nerve division: mandibular division; below the mouth=
V3
Components ___ and ___ are exclusively sensory, ___ is sensory, but also has a motor component.
V1 and V2
V3
Sensory components for the trigeminal system are organized in _______________ similar to the organization observed in the spinal cord as well as have parallel __________________ and ______________________ pathways.
a three-neuron system
trigeminoreticulothalamic
trigeminomesencephalic
Nociception and thermal sensation: Primary neuron (1st order neuron) - cell body is in the: _____________, located on the floor of the middle cranial fossa.
trigeminal ganglia
Nociception and thermal sensation: Myelinated and unmyelinated fibers (A-delta and C caliber) enter the ________________ at the level of the _________. The fibers then descend ________ in this tract to synapse in the Spinal trigeminal nucleus located in the _________.
Spinal tract of V
middle pons
ipsilaterally
medulla
Nociception and thermal sensation: Second order neuron cell body is in the: ______________. The Spinal trigeminal nucleus has _____ divisions, each organized in a topographical pattern with respect to the distribution of incoming sensory information.
Spinal Nucleus of V
three
Nociception and thermal sensation: NOTE: This nucleus is also receiving input of somatosensation from branches of other CN, i.e., VII, IX, and X from skin areas around the ear.
NOTE: This nucleus is also receiving input of somatosensation from branches of other CN, i.e., VII, IX, and X from skin areas around the ear.
Nociception and thermal sensation: The fibers of these second order neurons cross the midline and line up adjacent to the cervical component of the ________________ This tract then ascends ____________ as the ventral trigeminal thalamic tract to synapse in the ______________________________.
medial lemniscus
contralaterally
ventral posteromedial (VPM) thalamic nucleus
Nociception and thermal sensation: . Third order neuron located in the __________________ thalamic nucleus. [NOTE: this is the medial division of the same nucleus that is the site of the third order neurons of the somatosensory systems of the body, i.e., VPL]
ventral posteromedial (VPM)
Nociception and thermal sensation: Fibers of these VPM neurons leave the thalamus and ascend to the cortex in the ___________________________. They then terminate or synapse in face area of primary somatosensory cortex; Postcentral gyrus; Brodmann’s areas ____________.
posterior limb of the internal capsule
3, 1, and 2.
Nociception and thermal sensation: Pathological Conditions associated with the transmission of pain via the trigeminal nerve do occur. Trigeminal _______________________ is marked by excruciating pain. The pain is set off by only _______ stimulation. The cause is uncertain, but at times has been attributed to a ______________ of the nerve by _________________________.
neuralgia or Tic douloureux
mild
compression
swelling of the nerve sheath.
Nociception and thermal sensation: In Trigeminal neuralgia, drastic measures may need to be taken to relieve the pain such as __________________________________ in the spinal tract of V. This is possible due to the topographical distribution of the fibers carrying the pain sensation and the anatomical location on the lateral surface of the caudal medulla.
surgically cutting the descending fibers
The transfer of information concerned with discriminative touch and conscious proprioception is also organized in _______________, but travels via different pathways.
three neuron chains
Touch: Primary or first order neuron cell bodies for discriminative touch, as well as light touch, are in the:
trigeminal ganglion.
Touch: There is a topographic organization similar to that for pain and temperature over the _____________________ of this nerve.
three peripheral branches
Touch: Secondary or second order neurons cell bodies are in the:
main sensory nucleus (discriminative touch).
Touch: The main sensory nucleus is concerned with two-point discrimination over the entire distribution of the trigeminal nerve. The majority of the axons leaving this nucleus cross the midline and ascend in the_____________________________ However, there is an extra pathway that ascends ipsilaterally____________________________________ In either case, these second order axons ascend to end in the _________________________________________.
ventral trigeminothalamic tract (VTT). in a dorsal trigeminothalamic tract (DTT). ventral posteromedial (VPM) thalamic nucleus
Primary or first order neuron cell bodies for conscious proprioception are in the ________________________. This is a nucleus of cells similar to the pseudounipolar cells of a ganglion, however, they are positioned within the CNS. A descending component of this nucleus is involved in a ________________________.
mesencephalic nucleus of V.
myotatic reflex, the “jaw-jerk” reflex
Conscious Proprioception: Secondary or second order neuron cell bodies are located in the __________________. This system is not well understood at this point. The axons from these neurons may be crossed or uncrossed and ascend in either the VTT or DTT. They do, however, synapse in the ______.
reticular formation.
VPM
Conscious Proprioception: Tertiary or third order neuron cell bodies are located in ____. The axons of these neurons ascend with the other axons of the sensory modalities of the face through the ______________________________to terminate in the postcentral gyrus.
VPM
posterior limb of the internal capsule
What is a myotatic reflex?
A reflex having only one synapse, an afferent limb (incoming stretch information) and an efferent limb (lower motor neuron innervating muscle).
