Corticobulbar tracts and Basal Ganglia Flashcards
Corticobulbar projections for facial expression above the eyes
Primary motor cortex- bilateral
cranial nerve nuclei- ipsilateral
Corticobulbar projections for muscles of facial expression below the eyes, tongue
Primary motor cortex- contralateral
Cranial nerve nuclei- ipsilateral
jaw jerk reflex assesses
CN V, its nucleus, and corticobulbar pathway
divisions of the facial motor nucleus
medial- bilateral above the eyes
lateral- contralateral below the eyes
Cranial nerve VII test shows
cortical lesion- relative preservation of brow and forehead mvmt
facial motor nucleus or nerve lesion: problem wrinkling on side of lesion
Cranial nerve XII test
stick out your tong.
Weakness on side of deviation is from primary motor cortex on contralateral side OR nerve on same side.
Basal ganglia is responsible for
repeated movement.
It’s called the “accessory motor circuit”
lentiform nucleus
putamen + globus pallidus
Direct excitation
depolarization –> actioin potential – neurotransmitter release
indirect excitation
“disinhibition”
constant hyperpolarization prevents action potentials in an otherwise active circuit
removing the inhibitory action –> “go” (riding the brakes)
What is the substantia nigra’s role?
Give that extra push via dopamine (D1 receptors on striatum)- caudate and putamen
W/out substantia nigra
bradykinesia, hallmark of parkinson’s
parts of substantia nigra
pars compacta
pars reticulata
Parts of the striatum
caudate nucleus
nucleus accumbens
putamen
Rules to remember for the BG pathways
Basal ganglia structures release GABA
Other structures release glutamate
SN pc releases dopamine
2 major pathways by which dopamine turns the basal ganglia ‘on’
Nigrostriatal pathway
Projections from the Substantia Nigra pars compacta to the caudate or putamen
Motor-related
Mesolimbic pathway
Projections form Ventral Tegmental Area to the nucleus accumbens
Limbic
2 major fiber pathways reach the thalamus from differnt origins, back to cortex
Ansa lenticularis
– Lens hook
Lenticular Fasciculus
— Lens-like bundle
Thalamic Fasciculus
- – aka Forel’s Field
- – Also carries cerebellar info
Parkinson’s Disease
involves a progressive loss of dopamine neurons
Parkinson’s Disease has characteristic motor triad phenotype
Resting tremor
Rigidity (lead pipe)
Bradykinesia (akinesia)
Long-term l-DOPA tx can lead to dyskinesia
A “hypokinetic” disorder eg. oculomotor hypokinesia
100% of men with REM behavior disorder will develop Parkinson’s Disease
Impulse control deficiencies present later in disease course
Cognitive effects dependent on laterality
Chronic drug abuse (cocaine, amphetamine) linked to higher rates of disease
Huntington’s Disease
is another common disorder that targets the Basal ganglia
Huntington’s Disease = genetic mutation of polyglutamine (CAG) repeats causes neuronal death
Targets the striatum
Chorea (random, involuntary, flicking mvmt.)
Considered a disorder of “hyperkinesia”
Indirect pathway is diminished relative to direct pathway
often begins with depression
basal ganglia
The basal ganglia connects and extends the function of our reptilian brain to many outputs. It has both motor and non-motor functions integral to carrying out stereotyped and adaptive behaviors.
