Brainstem pathways Flashcards
Describe the pathway of the Anterolateral system starting in the hand.
Pain temp sensation in the hand–> travels to Lissauer’s fasciculus–> up/down a level or two –> deccusates in the anterior white commissure –> travels up the contralateral spinal column in the spinothalamic tract (anterolateral portion of the spinal cord) –>VPL of the thalamus
[Don’t forget: pain and temperature information reaches cells in the dorsal horn via the central processes of dorsal root ganglion cells (delta and C fibers; neuron #1). Dorsal horn cells (neuron #2) project to the contralateral VPL via the ALS. Finally, cells in VPL (neuron #3) project to areas 3, 1 and 2 (somatosensory cortex) for perception of the pain and temperature.]
Describe the location and connections of the inferior olive, as well as deficits resulting from damage.
Resides in the ventral medulla. Is the SOLE source of climbing fibers to the purkinje cells in the CONTRAlateral cerebellum. Climbing fibers run through the inferior cerebellar peduncle.
Deficits will manifest the same as destruction of the CONTRAlateral cerebellum (so a L sided ISO destruction would show a R sided ataxia).
Describe the “direct pathway” of the basal ganglia.
Neurons in the GP fire at a rate of 50x/sec. Neurons from the striatum fire at a rate of near zero.
Basal firing of GP neurons inhibits impulses from the thalamus reaching the motor cortex. Firing of the striatum inhibits the inhibitory output of the GP, allowing the thalamus to signal the cortex.
Where might DBS be placed in advanced parkinson’s?
Stimulation of the subthalamic nucleus (STN) or globus pallidus interna (GPi) often provides a state like the well-medicated state, but with stimulation (as opposed to medication), this state can be achieved over most of the day, and with significant reduction or even elimination of medications.
Chorea
(Greek for dance) means nearly continuous rapid movements of the face, tongue or limbs (usually distal portions).
Athetosis
indicates slow, writhing, ceaseless movements of hand, sometimes lips, tongue, neck and foot.
On what chromosome is the CAG repeat in Huntington’s chorea present?
Chromosome 4.
Describe the actions of dopamine and Ach in the basal ganglia. How will too much/too little of each manifest, clinically?
How does this relate to regulation of the direct/indirect pathways?
Dopamine = Grease.
Too little - Parkinsonian symptoms
Too much - Huntington-like symptoms (chorea).
Administration of anticholinergic worsens choreic symptoms. Ach and Dopamine are said to be “in balance”.
The direct pathway facilitates movement, while the indirect pathway inhibits movement. When activity in the direct pathway is reduced relative to the indirect pathway, the result is a paucity of movement (a “hypokinetic” disorder like Parkinson’s disease). When activity in the indirect pathway is relatively reduced, the result is a “hyperkinetic” disorder, like Huntington’s disease.
A stroke in a small ganglionic branch of the PCA that damages one side of the subthalamic nucleus can lead to what condition?
Hemiballismus. This is characterized by flailing movements of the arm and leg on one side. Loss of excitation by the subthalamic nucleus reduces inhibitory outflow of globus pallidus so motor programs are inappropriately initiated through the disinhibited thalamus.
Usually in the elderly.
What is the minimum number of synapses from a cerebellar Purkinje cell (output cell of the cerebellar cortex) to the cerebral cortex?
x
- What is the source of climbing fibers reaching the cerebellum?
(for example, the inferior olivary nucleus receives multimodal input and projects to the contralateral cerebellum and the axons of these neurons are the “climbing fiber” input to Purkinje cells
Describe the interlocking circuits of the basal ganglia including the caudate, putamen, globus pallidus, subthalamic nucleus and substantia nigra. Which of these contains dopaminergic cell bodies?
x
Pontine nuclei project to _____ as what fiber type?
They receive input from _____.
Contralateral cerebellum; mossy fiber inputs
Ipsilateral cerebral cortex.
