Section 3, Part 1 Flashcards
What are somatosensory circuits?
FOur ascending networks that conduct sensory information from the body’s skin, muslces and joints
What are the three somatosensory circuits that serve the trunk and limbs?
1- Lemniscal
2- Anterolateral
3- spino-cerebellar
What somatosensory circuit carries info from the head and neck?
Trigeminal syste?m
What does the lemniscal system carry?
Epicritic sense
What are epicritic senses?
Vibration, tactile form, position sense, simple touch
What does the anterolateral system carry?
Protopathic sense
What are prothopatic senses?
Pain, temperature sense, simple touch
What doees the spino-cerebellar system carry?
Proprioception
What are proprioception senses?
Muscle, joint information
What type of senses does the trigeminal system carry?
Epicritic, protopathic, priopriocetive
Does the information in the lemniscal system come from dorsal or ventral root axons?
Large Diameter dorsal root axons
The neurons of which system are particularly vulnerable to ischemia, toxicity, bacteria….?
The lemniscal system
Lemniscal system lesions typically show protopathic or epicritic losses first?
Epicritic
Where do the lower limb lemniscal dorsal root axons enter the spinal cord?
Lower thoracic and lumbosacral levels
How do the lemniscal system dorsal root axons ascend the gray matter?
Gracile fasciculus (they cross the spinal cord to get to this)
Where do the upper limb lemniscal dorsal root axons enter the spinal cord?
Upper thoracic and cervical levels
How do the lemniscal system dorsal root axons ascend the gray matter?
Cuneate fasciculus (they cross the spinal cord to get to this)
Doe the fasciculi of the lemniscal system ascend the cord on the same side or opposite side of the body that they serve?
Same side (so symptoms of a lesion would be ipsilateral to the lesion)
Where do the lemniscal system fasiculi synapse?
Medulla
After the gracile and cuneate axons synapse in the medulla, what are the axons called?
Medial lemniscus
Where do the medial lemniscus axons ascend to?
Thalamus—-> synapses on the VPL
If there is a lesion in the medial lemniscus would the symptons be ipsilateral or contralateral to the lesion?
Contralateral
After the lemniscal system synapse at the VPL, where do the axons go?
Postcentral gyrus (via the internal capsule)
What is stereogenosis?
Recognizing tactile shapes placed in the hand
Will be lost in an epicritic lesion
What is two-point tactile sense?
Ability to separate the location of two simultaneous touches near each other on the skin
Will be lost in an epicritic lesion
What is position sense?
Ability to state the position of the limb, without visual cues (has some motor consequences, causing shuffling gait and reaching inaccuracies)
Will be lost in an epicritic lesion
What is vibration sense?
Sensitivity to high frequencysimulations, such as vibration from a tuning fork
Will be lost in an epicritic lesion
What is simple touch sensation?
Patient knows when they have been touched
largely intact in an epicritic lesion
In the anterolateral system, where does the information come from?
Information comes to the spinal cord via small-diameter dorsal root axons
Which tract is associated with the anterolateral system?
Lissauer’s tract (dorsolateral fasiculis
Do the neurons of the anterolateral system synapse early or late?
They synapse early, almost as soon as they enter the spinal cord
How do the axons of teh anterolateral system ascend in the white matter?
The anterolateral tract/ system
True or false:
Most of the anterolateral tract neurons first cross the midline before ascending to the brain
True
If there is a lesion in the anterolateral system, will symptoms be on the same side or opposite side of the lesion?
Opposite side
Where do anteriolateral neurons synapse/ terminate?
Reticular formation and the VPL mainly.
What are the three protopathic sensations associated with the anterolateral system?
Pain, temperature, simple-touch
If there is a lesion to the anterolateral system, which protopathic senses are affected?
Pain and temperature are reduced but simple touch is largely intact
Which system does this statement describe?
Signals from muscle spindle and joint receptors enter the CNS via the dorsal roots
Spino-cerebellar syste
True or false:
In the spino- cerebellar system, axons from the leg and lower trunk ascend as part of the gracile fasiculus.
True
Where is the dorsal nucleus of Clarke located?
In the thoracic cord
What terminates at the nucleus of clarke?
Spino-cerebellar system axons from the leg and lower trunk that ascend as part of the gracile fasciculus
True or false:
In the spino- cerebellar system, axons from the arms and upper trunk ascend as part of the cuneate nucleus
true
What terminates at the accessory cuneate nucleus?
Spino-cerebellar system axons from the arm and upper trunk that ascend as part of the cuneate nucleus
Where do the axons of the accessory cuneate nuclues terminate and what is the tract that they ascend?
cerebellum, via the cuneocerebellar tract
How does the majority of the somatosensory information from the head and neck enter the CNS?
Via CN5 axons whose cell bodies are in the trigeminal ganglion.
(There is also some input from CN 7, 9, 10)
How do axons of teh trigem nerve convey epicritic snesation?
They synapse immediately in the principal/ chief sensory nucleus of CN 5 and in the pntine part of the spinal sucleus of CN 5
Where do second order neurons of CN5 go?
They cross the midline and join the medial lemiscus to go to the thalamus and go on to the post central gyrus
Pathology of the pontine portion of the CN5 input causes what?
Epicritic losses of the head and neck. Symptoms are on the same side if the pathology lies before the crossing (at the medial lemniscus)
Pathology of the caudal portion of teh spinal trigeminal tract (in the medulla) and nucleus of CN5 causes ____________ losses on the __________ side of the head
Pathology of the caudal portion of teh spinal trigeminal tract (in the medulla) and nucleus of CN5 causes PROTOPATHIC losses on the SAME side of the head
What type of information does the mesencephalic tract of CN5 carry?
Proprioceptive input from the face (part of the trigem system)
Where doe mesencephalic nucleus neurons synapse?
Motor nucleus of CN5 (for jaw reflexes —> via the reticular formation before projecting to the cerebellum)
Where doe the mesencephalic neurons of CN5 ultimately project to?
cerebellum
Where does the motor component of the trigem nerve arise from?
Axons arise fro cellsin the motor nucleus of CN 5 in the pons
What does the motor component of the trigem nerve do?
Innervate the muscles of mastication on the same side
What are the two motor circuits?
Pyramial and brainstem-spinal
Are motor circuits ascending or descending?
Ascending
What are the component tracts of the Pyramidal system?
Cortico-bulbar
Cortico-pontine
Cortico-rubro-olivary
cortico- spinal
Which motor system is characterized by direct cortical input?
Pyramidal
What are the component tracts of the brainstem- spinal motor system?
Vestibulospinal
tectospinal
reticulospinal
rubrospinal
