MOTOR SYSTEM : BASAL GANGLIA Flashcards
Basal ganglia major function is
provide a feedback mechanism to the cerebral cortex for the initiation and control of motor
responses.
basal ganglia consist
neostriatum (caudate nucleus and putamen)
paleostriatum (globus pallidus)
Two additional nuclei, the subthalamic nucleus and substantia nigra,
The primary regions of the basal ganglia that serve as afferents (receiving areas from the cortex) are the
caudate nucleus and putamen (neostriatum).
major outputs of the basal ganglia arise from neurons located
in the
medial pallidal segment.
These neurons give rise to two fiber
bundles, the ansa lenticularis and lenticular fasciculus, which supply
thalamic nuclei.
thalamic fasciculus
lenticular fasciculus and ansa
lenticularis
a tract connecting the globus pallidus (internus) to the
thalamus.
Lenticular fasciculus
principal inputs from the primary motor, secondary motor, and primary somatosensory regions of cortex are directed to
Putamen
caudate nucleus, receives inputs from
cortical association regions
frontal eye fields
limbic regions of cortex
BG receive inputs from
thalamus (centromedian nucleus), substantia nigra
subthalamic nucleus.
Dopamine is produced in the
Pars Compacta of the substantia nigra
D2 receptors in the neostriatum if activated
inhibit
GABA-neurons
D1 receptors if activated
stimulate GABA-neurons
two principal
components of substiantia nigra
pars compacta
pars reticulata : receives an inhibitory
(GABA)-ergic input from the neostriatum.
(which is excitatory when acting through D1 receptors and inhibitory when acting through D2 receptors).
movement control system of the basal ganglia
Indirect pathway
Direct pathway
Activation of the direct pathway
causes
excitation of the motor
cortex and thus facilitates
movements
Activation of the indirect pathway
inhibits cortical-induced
movements
pathway of direct pathway
cortex : Glutamate+ve {Neostriatum activation} ~ GABA -ve {inhibition of Globus pallidus medialis} ~. Disinhibition of thalamus which leads to excitation of motor cortex ~ stimuli is sent to spinal cord then to skeletal muscle
Pathway of indirect pathway
cortex : Glutamate+ve {Neostriatum activation} ~ GABA -ve {inhibition of Globus pallidus lateralis} ~. Disinhibition of subthalamic nucleus ~ leads to activation of Globus medialis i.e Glu +ve (increase inhibition of thalamus) ~ stimuli is sent to spinal cord then to skeletal muscle
Degenerative disease that affects the substantia nigra (depletion of dopamine) and it’s projections to the striatum
Parkinsons’s disease
Parkinsons’s disease symptoms
masked face (no facial expression)>stooped posture, bradykinesia, shuffling gait, pill rolling tremor
Lewy bodies in the melanin containing neurons of the substantia nigra
reduced red nucleus
Analog of meperidine (Damerol) - MPTP(Methylphenyltetrahyropyridine) can induce parkinsonism by
damaging dopaminergic neurons in the substantia nigra
Huntington’s disease involeves
ADID of chromosome 4 - degenration of cholinergic and GABA-ergic neurons of the striatum
gyral atrophy in the frontal and temporal lobes
choeriform dyskinesia often in girls after rheumatic fever
Sydenham’s chorea (St. Vitus dance )
movement disorder due to vascular lesion in the subthalamic nucleus - C/L violent flinging (ballistic movements of 1/both extremities)
Hemiballism (there is loss of excitatory neurons from the subthalamic nucleus) to the GP mediallis
ARID (chromosome 13) with a defect in copper metabolism leading to wing-beaiting tremor. Lesions in the lentiform nucleus (globbus pallidus and putamen)
Wilson’s disease
Tx; penicillamine ( a chelator)
brief involuntary movements in forms of motor and vocal tics: repition of words, repeating words of others anf offensive words
motor tics : eye blinking, shrugging
Tourette syndrome
