Section 3 Flashcards
What is the function of the thalamus?
it is the gateway to the cerebral cortex, and specific systems end in particular regions of the thalamus (thalamic nuclei) prior to projecting to specific regions of the cortex.
Primary visual cortex is
area 17
Primary somatosensory cortex is
made up of areas 3, 1, and 2
Primary motor cortex is
area 4
Premotor is
area 6
Auditory cortices are
areas 41, and 42
What is the relationship between the basal ganglia, cerebellum and the thalamus?
Motor information from the basal ganglia and cerebellum also send projections to specific thalamic nuclei, which in turn project to motor areas of the cortex.
The lateral geniculate nucleus
receives input from the optic tract, and projects to the primary visual cortex (V1 or Brodmann area 17).
The medial geniculate nucleus
receives auditory input from the inferior colliculus, an auditory relay nucleus, via the brachium of the inferior colliculus, and projects to the auditory cortex (A1 or areas 41).
The anterior tubercle consists of what?
mainly of the anterior nucleus, which receives input from the mammillary bodies (hypothalamus) and projects to the cingulate gyrus.
Each area of cortex that receives a projection from a specific thalamic nucleus
also sends a projection back to that nucleus. Although only some of these nuclei have clinical significance (i.e., pathology is common and causes visible symptoms)
transmitting auditory information
vestibulocochlear nerve, primary auditory cortex, medial geniculate body, inferior colliculus and brachium of the inferior colliculus
What is the location of the anterior nucleus (A)?
anterior tubercle
What is the input for the anterior nucleus (A)?
mammillary bodies
What is the target for the anterior nucleus (A)?
cingulated gyrus
What is the function of the anterior nucleus (A)?
emotions
What is the location of the dorsomedial nucleus (DM) or mediodorsal nucleus?
Medial to internal medullary lamina
What is the input for the dorsomedial nucleus (DM) or mediodorsal nucleus?
1) amygdala 2) hypothalamus 3) spinal trigeminal nucleus 4) ALS
What is the target for the dorsomedial nucleus (DM) or mediodorsal nucleus?
Frontal lobe anterior to motor areas and to orbital cortex
What is the function of the dorsomedial nucleus (DM) or mediodorsal nucleus?
Emotions and non motor frontal lobe functions
What is the location of the ventral anterior (VA) nucleus?
Lateral to internal medullary lamina
What is the input for the ventral anterior (VA) nucleus?
1) globus pallidus 2) cerebellum
What is the target for the ventral anterior (VA) nucleus?
premotor cortex
What is the function of the ventral anterior (VA) nucleus?
motor
What is the location of the ventral lateral (VL) nucleus?
Posterior to ventral anterior (VA) nucleus
What is the input for the ventral lateral (VL) nucleus?
1) globus pallidus 2) cerebellum
What is the target for the ventral lateral (VL) nucleus?
1) precentral gyrus 2) premotor cortex
What is the function of the ventral lateral (VL) nucleus?
motor
What is the location of the ventral posterolateral nucleus (VPL)?
Posterior to VL nucleus
What is the input for the ventral posterolateral nucleus (VPL)?
Medial lemniscus (Dorsal Column Nuclei)
What is the target for the ventral posterolateral nucleus (VPL)?
Postcentral gyrus
What is the function of the ventral posterolateral nucleus (VPL)?
Somatic sensation, body
What is the location of the ventral posteromedial nucleus (VPM)?
Medial to VPL
What is the input for the ventral posteromedial nucleus (VPM)?
Medial lemniscus (Trigeminal Sensory Nuclei)
What is the target for the ventral posteromedial nucleus (VPM)?
Postcentral gyrus (near lateral fissure)
What is the function of the ventral posteromedial nucleus (VPM)?
Somatic sensation, head
What is the location of the pulvinar (P)?
posterior thalamus
What is the input for the pulvinar (P)?
1) superior colliculus 2) occipital lobe 3) temporal lobe 4) parietal lobe
What is the target for the pulvinar (P)?
occipital lobe, temporal lobe, parietal lobe
What is the function of the pulvinar (P)?
1) visual perception 2) language
What is the location of the medial geniculate nucleus (MGN)?
Posterior ventral surface of thalamus
What is the input for the medial geniculate nucleus (MGN)?
Inferior colliculus
What is the target for the medial geniculate nucleus (MGN)?
Auditory cortex
What is the function of the medial geniculate nucleus (MGN)?
audition
What is the location of the lateral geniculate nucleus (LGN)?
Posterior ventral surface of thalamus
What is the input for the lateral geniculate nucleus (LGN)?
Optic tract
What is the target for the lateral geniculate nucleus (LGN)?
Visual cortex
What is the function of the lateral geniculate nucleus (LGN)?
vision
What is the location of the intralaminar nucleus (ILN)?
Embedded in internal medullary lamina
What is the input for the intralaminar nucleus (ILN)?
1) Reticular formation 2) spinal cord 3) spinal trigeminal nucleus 4) ALS 5) globus pallidus
What is the target for the intralaminar nucleus (ILN)?
Basal ganglia, diffusely to cortex
What is the function of the intralaminar nucleus (ILN)?
Attention, arousal
What does the lemniscal system carry?
Epicritic sense (from trunk and limbs)
What does epicritic sense mean?
Vibration, tactile form (2 point discrimination) position sense simple touch
What does the anterolateral (spinothalamic) carry?
Protopathic sense (from trunk and limbs)
What does protopathic sense mean?
Pain, temperature sense and simple touch
What does spino-cerebellar carries?
Proprioceptive (from trunk & limbs)
What does proprioceptive mean?
Muscle, joint information
What does the trigeminal system carry?
All sensation (from head and neck)
What does it mean that the trigeminal system mean by carrying all sensation?
1) epicritic 2) protopathic 3) proprioceptive
In the lemniscal system information comes to the spinal cord via
large-diameter dorsal root axons.
In the lemniscal system large neurons are especially vulnerable to what?
insult from ischemia, toxicity, bacteria, etc,
In the lemniscal system early symptoms of peripheral nerve disease often first show as what?
“epicritic” rather than “protopathic” losses
In the lemniscal system dorsal root axons from the lower trunk and limbs enter where?
at lower thoracic and lumbosacral levels, send a segmental collateral to the dorsal gray matter, and ascend the cord as the gracile fasciculus.
In the lemniscal system gracile fasciculus
it’s a segmental collateral to the dorsal grey matter and ascends the cord from the lower thoracic and lumbosacral levels
In the lemniscal system upper trunk and limb axons enter where?
at upper thoracic and cervical levels and ascend as the cuneate fasciculus.
In the lemniscal system, what does the cuneate fasciculus do?
ascends the cord from the upper thoracic and cervical levels
What would damage to the cuneate or gracile fasciculus on one side cause and why?
Damage e.g. on the left, would cause epicritic losses on the same (left) side of the body because these fasciculi ascend the cord on the same side as the body they serve
In the lemniscal system where do the fasciculi (axons) synapse (end)?
in the medulla
In the lemniscal system what happens to the information after it synapses in the medulla?
it is picked up by second-order neurons whose cell bodies lie in the gracile & cuneate nuclei
In the lemniscal system what happens to the information from the fascicule after the gracile and cuneate nuclei?
Axons of these cells exit the nuclei, cross to the other side in the medulla (called “internal arcuate fibers”), at which time they are renamed the medial lemniscus
In the lemniscal system what happens to the information from the fascicule after the medial leminscus?
The medial lemniscus ascends to the thalamus
In the lemniscal system damage to the right medial lemniscus would produce what, and why would you see these symptoms?
epicritic symptoms on the patient’s left side of the body because of the crossing
In the lemniscal system the medial lemniscus synapses in the
ventral posterolateral nucleus of the thalamus (VPL)
In the lemniscal system what happens to the information from the fascicule after it gets to the VPL?
it is then picked up by the third-order neurons, which carry it to the postcentral gyrus (aka S1, Brodmann’s area 3,2,1) via the internal capsule
pathology on the right side of the brain at the level of the postcentral gyrus would cause what?
symptoms on the left side of the body
In the lemniscal system, epicritic symptoms include the loss of
1) stereognosis 2) two-point tactile 3) position sense 4) vibration 5) simple touch
stereognosis:
cannot recognize tactile shapes placed in the hand (called astereognosis).
two-point tactile:
cannot separate the location of two simultaneous touches near each other on the skin
position sense:
cannot state the position of the limb, without visual cues. This has some motor consequences, causing a shuffling gait, and reaching inaccuracies
vibration:
insensitivity to high frequency stimulation, such as vibrations from a tuning fork
simple touch:
largely intact. The patient knows when she has been touched, but with slightly less sensitivity
In the anterolateral (or spinothalamic) system information comes to the spinal cord via what?
small-diameter dorsal root axons.
In the anterolateral (or spinothalamic) system information travel in a tract on the dorsolateral aspect of the spinal cord called and where do they synapse?
Lissauer’s tract or dorsolateral fasciculus up or down one or two spinal segments only and then synapse immediately in the dorsal horn of the spinal cord, i.e. at or near the level they enter.
After one or more synapses within local networks of the dorsal horn, axons carrying this information ascend in the white matter of the cord as the
anterolateral (AL, or spinothalamic) tract or system.
Most of the AL tract neurons first do what?
cross the midline before ascending to the brain.
Damage to the AL tract on one side will cause what?
protopathic symptoms on the opposite side of the body
AL axons synapse where?
diffusely and at every level in the brainstem.
Where do most of the AL axons terminate?
in the reticular formation
A few of the AL axons make it where?
Some make it to the thalamus where they terminate in; 1) VPL as well as several other nuclei including the 2) dorsomedial (DM or MD) and 3) intralaminar nuclei.
What happens to ascending axons from areas of the reticular formation?
receiving anterolateral projections relay this information to the same regions of the thalamus.
In the AL system, signals pass via the internal capsule to where?
primary somatosensory cortex (postcentral g. or SI, areas 3,1,2 of Brodmann) as well as to more widespread areas related to pain perception and appreciation (anterior cingulate, frontal lobe).
In the AL system, at every level, the symptoms of pathology are?
reduced protopathic sensation of the trunk and limbs on the opposite side of the body.
What does reduced “protopathic” mean?
1) pain 2) temperature 3) simple touch
In the AL system, reduced protopathic; pain?
reduced or no sense of pain from a pinprick or from chronic internal pain
In the AL system, reduced protopathic; temperature?
reduced or lost sense of warming and cooling of the skin
In the AL system, reduced protopathic; simple touch?
largely intact, but reduced in sensitivity
In the Spino-cerebellar system, where do the signals come from and where do they go?
Signals from muscle spindles and joint receptors enter the CNS via the dorsal roots, and after one or more synapses, spino-cerebellar tracts carry this information to the same side of the cerebellum.
In the Spino-cerebellar system does the information go to the same side or the opposite side of the cerebellum?
Same side
In the Spino-cerebellar system axons from the leg and lower trunk do what?
ascend as part of the gracile fasciculus.
These axons from the leg and lower trunk that ascend as part of the gracile fasciculus terminate where?
in the dorsal nucleus of Clarke or Clarke’s nucleus in the thoracic cord.
In the Spino-cerebellar system what happens to the information from the leg and lower trunk after Clarke’s nucleus?
Second order neurons from Clarke’s nucleus ascend to the cerebellum along the lateral rim of the white matter as the dorsal spinocerebellar tract.
In the Spino-cerebellar system what happens to the component from the arm and upper torso?
it ascends with the cuneate fasciculus to the medulla
In the Spino-cerebellar system where do the component from the arm and upper torso synapse?
in the accessory (or lateral) cuneate nucleus.
In the Spino-cerebellar system where does the component from the arm and upper torse synapse?
They synapse in the accessory (or lateral) cuneate nucleus.
In the Spino-cerebellar system what happens to the information from the arm and upper torso after they synapse in the accessory or lateral cuneate nucleus?
Second-order neurons carry the signals to the cerebellum as the cuneocerebellar tract.
In the Spino-cerebellar system is there crossing to the opposite side as the incoming information?
Several other pathways also carry information to the cerebellum, ending PRIMARILY ON THE SAME SIDE of the cerebellum, even though the anterior or ventral spinocerebellar tract crosses, like the anterolateral system, but then the majority re-crosses prior
Pathology of the Spino-cerebellar system.
The clinical effects of pathology of these tracts are seldom seen, since they are rarely damaged in isolation
In the Trigeminal System most somatosensory information from the head and neck enters the CNS via
CN 5 axons whose cell bodies are in the trigeminal ganglion. Some information also arrives via CN 7, 9 and 10.
Axons of the trigeminal nerve convey epicritic sensation synapse immediately where?
in the principal or chief sensory nucleus of CN 5 and in the pontine part of the spinal nucleus of CN 5.
In the trigeminal system what happens after epicritic sensation synapses in the principle or chief sensory nucleus of CN 5 and in the pontine part of the spinal nucleus of CN 5?
Second-order neurons leave these nuclei, cross the midline, and join the medial lemniscus en route to the thalamus (ventral posteromedial nucleus, VPM)
In the Trigeminal System what happens after the VPM of the thalamus?
Subsequent neurons forward the signals to the postcentral gyrus