Neuroscience 3-1 Ascending Pathways Overview Amanda C. Conta Steencken Flashcards
Name the four somatosensory circuits.
- Dorsal Column-Medial Leminiscal System
- Anterolateral (spinothalamic) System
- Spinocerebellar system
- Trigeminal system
Anterolateral system carries what kind of information?
Protopathic sense from trunk and limbs
Dorsal Column-Medial Lemniscal System carries what kind of information?
Epicritic sense from trunk and limbs
What does protopathic mean?
Pain and temperature, and crude touch, nocioception
What does epicritic mean?
Mechanosensation
What does mechanosensation include?
Vibration, position, 2-point discrimination, simple touch
Where can you find the gracile and cuneate nuclei?
Medulla
Where do fibers from the dorsal column-medial lemniscal system decussate?
At the level of the medulla
What’s the pathway for vibration/light touch?
Skin –> DRG –> posterior (dorsal) columns –> primary sensory neuron –> sensory decussation in internal arcuate fibers –> Posterior (dorsal) column nuclei (cuneate/gracile) –> secondary sensory neuron (medial lemniscus) –> thalamus (ventral posterior lateral nucleus)
Where do mechanoreceptors from the lower body synapse?
The gracile nucleus in the caudal medulla
Where do mechanoreceptors from the upper body synapse?
The cuneate nucleus in the caudal medulla
Where do the mechanoreceptor neurons decussate?
In the caudal medulla, in the internal arcuate fibers, AFTER entering their respective dorsal column nuclei
Where do the anterolateral neurons decussate?
At the level of the spinal cord
What do anterolateral and dorsal column medial lemniscal systems have in common?
They both project from the thalamus to the primary somatosensory cortex.
What are the three things we are to associate with the spinocerebellar tract?
Ipsilateral
Proprioception
Cerebellum
What information does the trigeminal system carry?
All sensory information from the head and neck:
- -epicritic
- -protopathic
- -proprioceptive
The thalamus surrounds what ventricle?
3rd
Name this structure: relay center of the brain, conveying sensory and motor information to/from the cerebral cortex.
Thalamus
Sensory circuits are also known as __1__ circuits, while, motor circuits are also known as __2__ circuits.
- Ascending
2. Descending
Why are the descending tracts called the pyramidal system? Is this direct or indirect motor system?
Because the motor axons pass through the medullary pyramids, this is an example of direct cortical motor control
If the motor axons don’t go through the medullary pyramids, where do they go? Is this direct or indirect motor system?
They are extra-pyramidal, they are thus part of the brainstem-spinal system. This is an indirect motor system.
The pyramidal system includes what direct tracts?
Corticospinal tract (lateral and ventral) Corticobulbar tract
The brainstem-spinal system includes what indirect tracts?
Rubrospinal tract
Tectospinal
Reticulospinal
Vestibulospinal
What is the function of the lateral corticospinal tract?
Controls voluntary, fine, motor movements of distal/appendicular musculature
Where do the lateral corticospinal tract neurons synapse?
Within the spinal gray matter
What is the pattern of decussation in the lateral corticospinal tract?
85% of axons cross in the caudal medulla, called the “pyramidal decussation”
If the motor axons do not decussate in the caudal medulla, what happens to them and what do they become?
15% of the descending motor axons do not cross the midline; they descend in the anterior ventral white matter of the spinal cord as the anterior corticospinal tract
Cortical control of the hypoglossal nucleus is predominantly:
Controlateral
The facial nerve synapses in the motor nucleus of CN 7. Where do the lower nerves go?
The lower nerves primarily innervate the controlateral facial muscles (muscles of expression), and both the contralateral and ipsilateral upper face (forehead)
Name the 5 main upper motor neuron lesion signs:
- Hypperreflexia
- Hypertonia
- Positive Babinski
- No muscle atrophy
- No fasciculations
Name the 5 main lower motor neuron lesion signs:
- Hyporeflexia
- No Babinski
- Muscle atrophy
- Fasiculations
- Hypotonia
Axons of upper motor neurons project to:
another motor neuron in the brainstem or spinal cord
Axons of lower motor neurons project to:
muscles
From CN VIII to cochlear nucleus you can have __1__ hearing loss. After cochlear nuclei and second order neurons there is __2__. Therefore hearing loss can be __3__.
- unilateral
- crossing over, and bilateral hearing
- not be obvious
Where do the auditory neurons synapse of the vestibulocochlear nerve synapse? After that, how do the nerves proceed?
Dorsal and Ventral Cochlear Nuclei, proceeding ipsilaterally
2nd order neurons leave the cochlear nuclei and synapse:
Assorted pontine nuclei, bilaterally
What is the lateral lemniscus?
Neurons conveying auditory information from the pontine regions form the lateral lemniscus
Where does the lateral lemniscus terminate?
Inferior Colliculus
Axons from the inferior colliculus pass to the __1__ bilaterally in the __2__.
- Medial Geniculate Nucleus
2. Brachium of the inferior colliculus
MGN axons project to primary auditory cortex called __1__ via the auditory radiations.
Heschel’s gyrus
The auditory radiations are also known as:
Sublenticular portion of the internal capsule
Name the ways you can achieve total bilateral hearing loss.
- Damage to both vestibulocochlear nerves
- Damage both cochlear nuclei
- Lesions to both sides of the auditory pathway
- Damage to Both auditory cortices
- Damage to BOTH MGN
- Damage to both auditory radiations.
After the dorsal and ventral cochlear nuclei, all auditory information is:
bilateral
Wernicke’s area includes the:
- supramarginal gyrus
2. planum temporale
Deafness in one ear can only be caused by:
- damage to the vestibulocochlear nerve
2. damage to the cochlear nuclei
Each visual field is “seen” by the ___ visual cortex.
contralateral
Axons carrying information destined for V1 of the primary visual cortex synapse where?
In the LGN
Second order neurons project from the LGN to where?
They become the optical radiations and travel to V1.
Explain what happens in the optic radiations.
- Information from the upper half of the VF travels in the TEMPORAL lobe bundle - lower banks of the calcarine sulcus in the lingual gyrus
- Information in the lower half of the VF travels in the PARIETAL lobe bundle - upper banks of the calcarine sulcus in the cuneate gyrus
A right homonymous hemianopia is caused by a lesion where?
In the left optic tract
A left homonymous quadrantanopia is caused by a lesion where?
Upper or lower optic radiations on the right side
A right homonymous hemianopia with central sparing is caused by a lesion where?
Occipital lobe optic radiations
