Which Brodmann’s area is associated with the primary motor cortex?
area 4
Neurons from which spinal tracts arise from the primary motor cortex and associated motor cortices?
Corticospinal tract (CST) and corticonucleus system
What type of neurons arise from the motor cortices?
UMNs
How is the motor homunculus organized?
Where do CST fibers cross?
pyramidal decussation in the medulla
What side of the body is innervated by the L primary & associated motor cortices?
The R side of the body
A lesion in the CST tract rostral/superior to the medulla pyramids results with hemiparesis or hemiplegia on what side of the body?
contralateral side of lesion b/c lesion is before decussation
A lesion of the CST caudal/inferior to the medulla pyramids results in hemiparesis on which side of the body?
ipsilateral side b/c lesion is after decussation
Fibers of the corticonuclear tract project where?
to the motor nuclei of CNs in the midbrain, pons & medulla
What are the only two groups of head/facial muscles to receive contralateral innervations instead of bilateral innervation by UMNs of the Corticonucleus system?
lower facial muscles & genioglossus muscle
The lateral corticospinal tract supplies what type of muscles?
appendicular muscles (muscles of extremities)
The anterior corticospinal tract supplies what type of muscles?
axial muscles (muscles of the trunk)
Which part of the corticospinal tract does not cross to the contralateral side?
The anterior CST
After leaving the motor cortices what structures do the UMNs axons of the CST pass through in the telencephalon?
corona radiata –> posterior limb of internal capsule
What do UMNs of the CST code for/ what is their effect on LMNs?
encode for required force & direction of movement
What brain systems/regions are important for the activation of the appropriate response to a stimulus?
Cerebellum, Basal nuclei, thalamus, and primary/supplemental sensory cortices
What is Brodmann area 6?
supplementary motor cortex
What cortical region plans the muscular movements and what executes the plan
- supplementary motor cortex (area 6) = plans
- primary motor cortex (area 4) = executes
UMNs from which motor cortex project to the reticular activating system to form the reticulospinal fiber/tract?
supplementary motor cortex
What structure is located at the anteromedially most part of the striatum
Nucleus accumbens
What structures lies superomedially to the internal capsule?
caudate nucleus
What structures lie lateral to the internal capsule?
Lentiform nucleus (globus pallidus and putamen) of the basal nucleus
What structure lies directly medial to the putamen?
globus pallidus
What structure lies directly lateral to the globus pallidus?
putamen
What is the function of the putamen?
subconscious muscular movement (i.e. posture)
What is the function of the caudate nucleus?
patterned movements associated w/ walking (remember cycle?)
What is the function of the globus pallidus?
- adjusts muscle tone
- (influences UMNs’ modulatory effects on LMNs)
What are the 5 major nuclei of the basal nuclei/ganglia?
- caudate nucleus
- nucleus accumbens
- globus pallidus
- putamen
- substantia nigra
What is the most ventral part of the midbrain?
substantia nigra (posterior to cerebellar peduncle but anterior to the tegmentum)
What are the 2 parts of the substantia nigra?
pars compacta and pars reticulate
What is the main site of input into the substantia nigra?
pars compacta
What part of the substantia nigra houses neurons that contain melanin and make dopamine?
pars compacta
What do the pars compacta due with the dopamine it makes?
projects to and supplies the caudate and putamen with dopamine
What is the function of the pars reticulate?
projects to other brain regions
What nucleus is the pars reticulate a functional homolog of?
globus pallidus (medial segment)
What are the 2 pathways of the basal nucleus?
direct and indirect pathways
What is the function of the direct basal nucleus pathway?
increases activity of the thalamus = increases cerebral activity
What is the function of the indirect pathway of the basal nucleus?
inhibits the direct pathways = decreases thalamic activity
Pallidothalamic fibers are GABAergic neurons that are apart of which basal nuclear pathway?
indirect pathway b/c that inhibit thalamic activity
GABAergic neurons typically do what?
act as inhibitory neurons = decreasing activity of target cells
What is the subthalamic fasciculus?
a bidirectional pathway between the subthalamus and globus pallidus
Function of the subthalamic fasciculus when the direct pathway is active?
pallidosubthalamic fiber (GABAergic) inhibit subthalamic cells = blocks inhibition of thalamus
Function of the subthalamic fasciculus when the indirect basal pathway is active?
pallidosubthalamic fibers are inhibited = activation of suthalamopallidal fibers (Glutamate) –> activation of pallidothalamic fiber (GABAergic fibers –> inhibits thalamus activity
What are nigro-thalamic fibers?
non-dopaminergic fibers from pars reticulars –> thalamus
Where do nigro-thalamic fibers terminate?
ventroanterior and ventrolateral thalamic nuclei
What are nigro-striatal fibers?
dopaminergic fibers from pars compacta
Name the fibers and part of the substantia nigra that are destroyed in Parkinson’s disease?
Nigro-striatal fibers from the pars compacta
What nuclei comprise the dorsal (corpus) striatum?
caudate nucleus & putamen
What type of fibers are striatonigral fibers?
GABAergric (inhibitory)
What is the path of striatonigral fibers?
putamen –> par compacta of substantia nigra & globus pallidus
What is the path of nigro-striatal fibers?
substantia nigra –> striatum (caudate & putamen)
What damage to what structure is most commonly associated with Parkinson’s disease?
pars compacta of substantia nigra w/in the basal nucleus
What would be some signs of Parkinson’s disease?
- shuffling gait
- tremoring limbs at rest
- akinesia
- bradykinesia
- disrupted eye movements
- loss of postural reflexes
When do Huntington’s Disease symptoms begin?
35-44yrs of age
Loss of what fibers are associated with Huntington’s disease?
striatonigral fibers (GABAergic) = inhibit pars compacta of substantia nigra
Why would the loss of striatonigral fibers lead to Huntington’s disease?
Loss of inhibition of substantia nigra –> overactivation of the corpus striatum = loss of cognitive coordination
What is Sydenham’s chorea?
Childhood autoimmune disease that disrupts the neuronal activity of basal nucleus
What is a major manifestation of rheumatic fever?
Sydenham’s chorea
What is ballismus?
uncontrolled flinging (ballistic movement) of limbs
How does ballismus typically present?
as hemiballismus
What is chorea?
rapid, irregular involuntary, dance-like movements that flow randomly from one body region to another
What diseases can chorea be seen with?
- Huntington disease
- tardive dyskinesia
- treatment of Parkinson’s disease
- rheumatic fever
What is athetosis?
the continuous writhing of distal portions of one or more extremities
What nuclei receive UMNs from corticonuclear fibers?
- motor nuclei of CN 5, 7, 12
- nucleus ambiguus (CNs 9 and 10)
- accessory nucleus (CN 11)
UMN lesions of CN 7 lead to what type of facial paralysis?
central facial paralysis (central 7) = drooping of contralateral lower lip
LMN lesions of CN 7 lead to what type of facial paralysis?
Bell (facial) palsy = flaccid paralysis of upper and lower facial muscles on the ipsilateral side
UMNs lesions of nucleus ambiguus leads to damage in motor neurons from what nerves?
CNs 9 and 10
Damage to UMN going to the CN 10 part of nucleus ambiguus leads to what?
- R UMNs –> L nucleus ambiguus –> ____
deviation of plate/uvula towards lesion/away from the damaged nerve
R UMNs –> L nucleus ambiguus –> weak uvula on L = deviation to R.
Damage of R UMNs to the L hypoglossus motor nucleus results in what?
loss of Left (contralateral) hypoglossus nerve = tongue protrudes to left
Damage to LMNs from the hypoglossus motor nucleus or root of the hypoglossus nerve results in what?
weakness and deviation of tongue to side of lesion
What other tract runs in close association to the corticonuclear tract?
corticospinal tract (CST)
occlusion or hemorrhage of what artery would result in a lesion to corticonuclear tract as it passes through the internal capsule?
lenticulostriate/thalamostriatal artery from the MCA.
