Basal Ganglia ( lecture 6)

what are the two functions of the basal ganglia

motor control and motor learning

the basal ganglia function to perform what type of actions

selection and initiation/ executing actions

the BG consist of several interconnected ____

nuclei

what are the 4 main nuclei of the basal ganglia?

striatum, globus pallidus, subthalamic nucleus, and substantial nigra

Which structures make up the striatum?

caudate nucleus, putamen, and nucleus accumbens - ventral striatum

what structures make up the globus pallidus?

external and internal segment

what structures make up the substantia nigra?

pars compacta and pars reticulata

out of all the basal ganglia nuclei, what is the main input nucleus?

striatum

what are the two output nuclei for the basal ganglia

globus pallidus internal segment and substantia nigra

where do the output nuclei project to

the thalamus or the brainstem

where is the substantia nigra located?

midbrain

what structures make up the basal ganglia intrinsic layer?

globus pallidus external segment, subthalamic nucleus, substantia nigra pars compacta

what structures provide input to the stiatum?

cerebral cortex and the substantia nigra pars compacta

a brain circuit that connects the cortex to the striatum

corticostriatal pathways

a brain circuit that connects the substantia nigra pars compacta to the striatum

nigrostriatal pathways

what neurotransmitter does the corticostriatal pathway use? is this inhibitory or excitatory?

glutamate ( excitatory)

what neurotransmitter does the nigrostriatal pathway utilize? Is this inhibatory or excitatory?

dopamine ( either excitatory or inhibitory)

list the steps of the direct pathway ( don't include neurotransmitters)

1. cortex or substantia nigra pars compacta send an excitatory signal to the striatum (caudate or putamen)

2. the caudate/ putamen sends and inhibitory signal to the globus pallidus internal segment

3. the globus pallidus internal segment sends an inhibitory signal to either the thalamus or the brainstem

list the steps of the indirect pathway ( don't include neurotransmitters)

1. cortex or substantia nigra pars compacta send an excitatory signal to the striatum (caudate or putamen)

2. the striatum ( putamen or caudate) send an inhibitory signal to the globus pallidus external segment

3. the globus pallidus external segment sends an inhibitory signal to the subthalamic nucleus

4. the subthalamic nucleus sends an excitatory signal to the globus pallidus internal segment

5. the globus pallidus internal segment sends an inhibitory signal to the thalamus or brainstem

what are the two most common neurotransmitters that can be utilized by the output systems?

GABA and glutamate

what neurotransmitter does the subthalamic nucleus release to excite the globus pallidus internal segment

Glutamate

what neurotransmitter does the putamen/caudate release to inhibit the GBi or GBe segments?

GABA

what neurotransmitter does the GBe use to inhibit the Subthalamic nucleus?

GABA

what is the main inhibitory neurons projecting from the striatum (caudate and putamen) ?

medium spiny neurons

where do the medium spiny neurons project to?

globus pallidus internal and external segment

input to the medium spiny neurons from the cortex and the substanstia nigra pars compacta is called what type of input?

extrinsic input

what does disinhibition mean?

removing the inhibition

list the order of the disinhibitory circuit

striatum (inhibitory) - GP- ( inhibitory) thalamus - (excitatory) M1

what kind of output does the globus pallidus prove the thalamus at rest

tonic inhibition output to the thalamus

At rest, how does the disinhibitory circuit work to inhibit movement?

at rest the cortex provides no stimulus to inhibit the striatum, striatum provides no stimulus to inhibit the globus pallidus, the Globus pallidus will have tonic inhibition to inhibit the thalamus, which inhibits the primary motor cortex

during movement, how does the disinhibitory circuit work to excite M1 and cause movement?

cortex provides excitatory stimulus to striatum, striatum inhibits the globus pallidus, which means it cannot inhibit the thalamus, the thalamus excites M1 and produces movement

what are the 4 major basal ganglia circuits?

motor, oculomotor, executive/associate, emotion, motivation

what areas does the motor circuit of the basal ganglia receive input from?

M1, SMA, PMC and CMA

what is the difference between the input that the globus pallidus internal segment provides and the cerebellum provide the thalamus at rest?

the globus pallidus provides the thalamus with tonic inhibition, the cerebellum provides the thalamus with tonic excitatory

what is the function of the motor circuit in the motor control?

voluntary muscle activity, via the motor thalamus and then to the cerebral cortex

what is the importance behind the cerebellum providing tonic excitatory inputs to the thalamus and the GPi prviding tonic inhibitory inputs to the thalamus simultaneously?

cerebellum helps with muscle tone while globus pallidus inhibits unnecessary movements

what structure in the striatum is associated with the motor circuit?

putamen

list the steps of the motor circuit ( simple)

M1- putamen- GPi- thalamus ( VL)

the ventrolateral nucleus of the thalamus is also known as what

the motor thalamus

what is the origin of the oculomotor circuit

frontal eye field and supplementary eye field

what is the function of the oculomotor circuit

helps in decisions about eye movements and spatial awareness

where does the executive/associate (prefrontal) circuit origniate?

dorsolateral prefrontal cortex and lateral orbitofrontal cortex

input to the executive/associate circuit that is related to executive functions

dorsolateral prefrontal cortex DLPFC

input to the executive/ associate circuit that is related to empathic and socially appropriate responses and behavior

lateral orbitofrontal cortex LOFC

where does the limbic circuit originate

anterior cingulate area and medial orbitofrontal cortex

what are the functions of the limbic circuit

limbic, cognitive, and motor systems, identifies value of stimuli , involved in reward guided behaviors, and concerned with seeking pleasure and novelty

the major outputs of the basal go where?

cortex

what are the three non-cortical structures that receive outputs from the basal ganglia

pedunculopontine nuclei, locomotor centers in the midbrain reticular formation, and superior colliculus

what type of signal does the GPi have on the pedunculopontine N

tonic inhibition

what tract does the pedunculopontine nN and midbrain locomotion area associate with

reticulospinal tract

what is the importance of the globus pallidus tonically inhibiting the pedunculopontine N at rest

the pedunculopontine nucleus wont be able to inhibit the reticulospinal tract meaning that you will have excitation of your postural and girdle muscles at rest

does the midbrain locomotor region excite or inhibit the reticulospinal tract

excite

what occurs during rest and there is tonic inhibition to the midbrain locomotor region sent from the GPi

the GPi will inhibit the midbrain locomotor region, this will in turn cause there not to be excitation of the reticulospinal tract and inturn no gait will occur

if the tonic inhibitory input to the midbrain locomotor region is stopped what will occur?

the midbrain locomotor region will excite the reticulospinal tract and that will cause gait to occur

what is the non-cortical structure that receives tonic inhibitory input that causes saccadic eye movements?

superior colliculi

does the direct or indirect pathway support movement?

direct pathway

does the direct or indirect pathway suppress movement?

indirect pathway

why is it important to integrate both the direct and indirect pathways

the direct pathway facilitates desired movements while the indirect pathway suppresses conflicting movements

what of input does the substantia nigra pars compacta give off to the basal ganglia

can be inhibitory or excitatory

what type neurons go from the substantia nigra pars compacta to the putamen

dopaminergic

what dopamine receptor is excitatory and facilitates the direct pathway

D1 receptors

what dopamine receptor is inhibitory and delivers inhibitory input to the indirect circuits

D2 receptors

does dopaminergic input to the striatum increase or decrease excitability to the cortex?

increases

dopaminergic input to the striatum ___ the direct pathway and ____ indirect patheays

facilitates the direct pathway and inhibits the indirect pathway

what are the 5 movement disorders of the basal ganglia

akinesia, bradykinesia, alterations in muscle tone, freezing and festinating gait, involuntary movement s

akinesia

failure to initiate movement or absence of movement

bradykinesia

slow movement

degeneration of what nuclei can cause parkinson's disease?

substantia nigra pars comptacta

what does degeneration of the substantia nigra do to the tonic inhibition sent to the motor thalamus, pedunculopontine nucleus, and midbrain locomotor region?

increases tonic inhibition to these non-cortical structures

what would an increase of the tonic inhibition of the GBi on the motor thalamus cause?

this will effect the corticospinal tracts and cause bradykinesia

what would an increase of tonic inhibition of the GBi on the peduncopontine nucleus cause?

an increase in the inhibition of the inhibitory effect of the peduncle pontine nucleus , meaning an increase in reticulospinal tract function, causing trunk and girdle rigidity

what would an increase of tonic inhibition of the GBi on the midbrain locomotor area nucleus cause?

inhibition of the midbrain locomotor region on the reticulospinal tract and cause freezing and festinating gait

the increase inhibition of the pedunculopontine nucleus causes an increase or decrease stimulus on the reticulospinal tract

increase

the increase inhibition of the midbrain locomotor region causes an increase or decrease stimulus on the reticulospinal tract

decrease

Parkinson's disease is a ____ of dopaminergic input, due to the degeneration of _____

decrease, substantia nigra compacta

which pathway is most likely involved in producing akinesia

indirect pathway

hypokinesia

reduced movement amplitude

both bradykinesia and hypokinesia are related to ____

increased tonic inhibition from BG to motor thalamus

rigidity is caused by:

increased tonic inhibition to the pedunculopontine nucleus

rigidity is often most pronounced where in the body?

proximal joints and trunk where there are large muscle masses

hypotonia of limb muscles are caused by:

increased tonic inhibition to motor thalamus

how would you describe freezing and festinating gait

difficulty in initiating walking and turning

what causes freezing/ festinating gait?

increased tonic inhibition to midbrain locomotor center

resting tremor

alternating to and from movement caused by alternating contractions in opposing muscles

rate of BG tremors

3-6 per second

what causes a resting tremor?

increases synchronization of oscillatory discharge

chorea

rapid, somewhat spasmodic involuntary movements- characteristic of huntington's disease

athetosis

slow, spreading contractions of closely related muscle groups