basal ganglia normal

basal ganglia function

• has indirect influence on movement

• is involved in Planning, Initiation, and Execution of movement (PIE)

• also involved in postural control, maintaining muscle tone, and production of automatic movements

• does NOT recieve sensory input (unlike the cerebellum)

basal ganglia is ..

an integration center for the cortex

Caudate and putamen (make up the striatum) - these are basal ganglia

• internal capsule separates them

• cellular bridges connects them

• they receive ALL inputs to the basal ganglia

putamen

• a large nucleus forming the lateral portion of the basal ganglia

  • sits between external capsule laterally & globus pallidus medially

  • fused with the head of caudate anteriorly and ventrally

Caudate nucleus

• long, C-shaped mass (has head, body, tail)

• runs alongside the lateral ventricle and thalamus the whole way

• amygdala sits anterior to the tip of its tail, in temporal lobe

globus pallidus

• major part of basal ganglia

• has internal + external parts (internus and externus)

• sits lateral to internal capsule

• comes from diencephalon

the amygdala (amygdaloid nuclear complex) is considered part of…

the limbic system

• controls emotion, fear, motivation, memory tied to emotion

Subthalamic nucleus

• sits below thalamus, right where the thalamus meets the midbrain

• comes from the midbrain

  • while thalamus comes from forebrain

substantia nigra

• sits in the ventral (front part) midbrain

• extends rostrally (upward) towards the ventral (bottom of) thalamus

• located right below (caudal to) subthalamic nucleus

substantia nigra: pars compacta

• Contains darkly pigmented cells → these make dopamine.

• Sits more dorsomedial to pars reticulata

• This is the part that degenerates in Parkinson’s disease

substantia nigra: pars reticulata

• the pale zone

• Functionally and structurally similar to the globus pallidus internus → both act as output nuclei.

• Located more ventrally

the striatum (caudate/putamen) AND globus pallidus blood supply

• lenticulostriate arteries = comes from the middle cerebral artery

• anterior choroidial artery = comes from internal carotid artery

  • “LArry” pneumonic

caudate head and anterior portions of putamen blood supply

• recurrent artery of heubner = comes from anterior cerebral artery

  • “laRRY” pneumonic

basal ganglia inputs: corticostriate fibers

• these are signals/inputs sent from the cortex to basal ganglia

• They use the neurotransmitter glutamate → EXCITATORY input to the basal ganglia

putamen receives input from…

primary motor cortex and somatosensory cortex

• heavily involved in motor control

caudate receives input from…

parietal, occipital, and temporal association areas

• including the frontal eye fields

  • cognition, eye movements, planning

Basal ganglia inputs: nigrostriatal fibers

• these signals/inputs come from substantial nigra

• uses dopamine

  • this neurotransmitter can excite some cells and inhibit other cells in the striatum

  • dopamine crucial for movement

Basal ganglia inputs: thalamostriate fibers

• these signals/inputs from intralaminar nuclei of the thalamus

• uses glutamate = excitatory input to striatum

  • helps keep striatum activated

basal ganglia inputs: bulbostriate fibers

• these signals/inputs from brainstem (raphe nucleus of reticular formation)

• uses serotonin = inhibitory to the striatum

  • helps modulate/calm down activity in basal ganglia

What neurotransmitter does the cortex use to activate the striatum in the direct and indirect pathways?

Glutamate

What does the striatum do to the GPi & GPe (after being activated by cortex) in the direct pathway?

Inhibits it (using GABA)

What is the baseline activity of the GPi?

always provides tonic inhibition of the thalamus (constant brake).

What happens to the thalamus when the GPi is inhibited?

The thalamus is disinhibited and becomes more active

What does an activated thalamus do in the direct pathway?

Excites the supplementary motor area (SMA) of the cortex

What neurotransmitter from the substantia nigra pars compacta strengthens the direct pathway and facilitates movement?

Dopamine

What is the baseline activity of the GPe?

Tonic inhibition of the subthalamic nucleus (STN)

• when this structure is inhibited, it disinhibts the subthalamic nucleus → becomes more active

What neurotransmitter does the subthalamic nucleus use to excite the GPi?

Glutamate

When the GPi becomes more active in the indirect pathway, what does it do to the thalamus?

Inhibits it more strongly

What happens to movement when the thalamus is more inhibited?

Movement is reduced (movement suppression)

• overall functional outcome of the indirect pathway = inhibits/fine tunes movement

Why does dopamine inhibition of the indirect pathway lead to increased movement?

Because inhibiting an inhibitory pathway → overall movement facilitation

where do the outputs leave the basal ganglia?

through

• globus pallidus internis

  • handles output for body except head and neck

• substantia nigra pars reticulata

  • handles head and neck

what type of output signals do GPi and substantially nigra send?

they’re tonically inhibitory

• They are always ON, always sending inhibitory GABA

• Their job is to keep the thalamus quiet unless a pathway (direct or indirect) changes that

where do basal ganglia outputs go?

• GPi and substantia nigra send inhibitory GABA to VL and VA of thalamus

• thalamus sends signal to entire frontal lobe

basal ganglia outputs also travel to…

• intralaminar nuclei = centromedian and parafascicular → projects back to the striatum

  • think attention and arousal loops

• mediodorsal nuclei = involved with limbic system

  • helps link movement with emotion and motivation

  • think emotion + cognition

substantia nigra pars reticulata and globus pallidus internis also project to…

• pontomedullary reticular formation

  • Think: posture & muscle tone control

    • Influences the descending reticulospinal tract

    • Helps regulate automatic posture + tone adjustments

substantia nigra pars reticulata also projects to…

• superior colliculus

  • Think: eye and head movements

    • Controls tectospinal pathways

    • Helps with reflexive orienting movements (turning head/eyes toward a stimulus)

What does the basal ganglia regulate in the oculomotor channel?

Eye movements

Where does input for eye-movement control enter the basal ganglia? (oculomotor channel)

From the posterior parietal cortex and prefrontal cortex → into the body of the caudate nucleus

in the oculomotor channel of basal ganglia, once the input goes to the body of caudate where does it go?

globus pallidus internus and substantia nigra pars reticulata

• output nuclei

Through which thalamic nuclei does the oculomotor channel send information from the output nuclei?

the MD (mediodorsal) and VA (ventral anterior) thalamus (in cortex)

Where does the oculomotor channel ultimately send output to initiate eye movements?

The frontal eye fields and supplementary eye fields

prefrontal channel/pathway of basal ganglia

• involved in cognitive processes involving frontal lobes (thinking, planning, decision-making)

  • input comes from posterior parietal cortex and premotor cortex → to head od caudate

  • signal passes through GPi and substantially nigra pars reticulata

  • signal travels through thalamus (mediodorsal + ventral anterior)

  • signals (output) is sent to the prefrontal cortex

limbic channel/pathway of basal ganglia (ventral striatal pathway)

• involved in limbic regulation of emotions and motivational drives

  • begins with emotional input from limbic structures (limbic cortex, hippocampus, amygdala)

  • signal goes to ventral striatum (specific: nucleus accumbens)

  • signal passes through output nuclei (GPi + substantia nigra pars reticulata, & ventral pallidum)

  • travels through mediodorsal + ventral anterior thalamus

  • output ends up at limbic cortex of the anterior cingulate gyrus and the medial orbital frontal gyri

    • these are emotional/motivational frontal areas