What do the basal ganglia and the cerebellum have in common?
Basal ganglia and cerebellum are both subcortical structures and are both involved in motor control and recieve input from cortex and direct output mainly through the thalamus. The function of both of them is to guide the body towards smooth, coordinated control of voluntary movements.
What embryological structures produces the basal ganglia?
Prosencephalon (forebrain) and mesencephalon (midbrain)
What embryological structure produce the cerebellum?
The rhombencephalon (hindbrain)
What are the structures of the basal ganglia called?
Caudate Putamen and globus pallidus (forebrain structures) Thalamus and subthalamus
What is the sequence of events that result in movements?
Pre-frontal cortex is activated to decide on an action. Pre-motor, primary motor, and supplementary motor cortex is activated. Ipsilateral (same side) projections to BG and Cerebellum conveying intended motor plan Central processing to modify plan Projects back to cortex via thalamus Upper motor neurons in primary motor cortex are activated. Corticospinal fibers descend through corona radiata and internal capsule to enter the midbrain Signal passes through pons to medulla to decussate in the pyramids. Descend contralaterally through ventral horn and then synapses with Lower Motor neurons Skeletal muscles are innervated at neuromuscular junction Muscle contracts
Which parts of the brain are important for coordination of movement?
Basal ganglia and cerebellum
Which part of the brain inhibits unwanted movements?
The basal ganglia
Which part of the brain mantains posture and balance?
Which part of the brain processes cortical information to plan, fine-tune and initiate movement?
Which part of the brain facilitates movements that are required to carry out an action?
The basal ganglia
Which part of the brain processes cortical, spinal and vestibular information?
Which part of the brain coordinates complex movements by comparinf the intended movement and current position?
Which part of the brain maintains tone and monitoring movement in real time?
What is the difference between the influence of the basal ganglia and the cerebellum on movement?
Basal ganglia process information by facilitating the movements needed for the action and inhibiting movements that are not needed. Cerebellum processes cortical, spinal (proprioception), and vestibular information to coordinate complex movements by comparing intended movement and current position while maintaining tone and monitoring movement in real time and maintaining posture and balance.
How are the right muscles for an action chosen and then processed for execution?
Motor plan is sent to basal ganglia and cerebeullum for consultation and processing. Information is then integrated at the thalamus. Adjusted plan is sent to motor cortex with appropriate timing and amplification. Appropriate motor plan for smooth voluntary movement is executed.
Are basal ganglia identical to ganglia in the PNS?
No, PNS contains ganglia and CNS ganglia are called nuclei. (Basal nuclei)
What does the structure of basal ganglia look like?
Collection of neuronal cell bodies in the CNS that are distinctly surrounded by white matter. All subcortical nuclei are involved in motor control.
The caudate nucleus and the putamen in 3 planes
Globus pallidus externus and internus
What structures do the basal ganglia surround?
The lateral ventricle
Where does the caudate nucleus sit relative to the lateral ventricle?
Caudate head sits on medial aspect of anterior horn of lateral ventricle. Body sits inferiorly to the body of the lateral ventricle. And the tail sits in the roof of the posterior horn of the lateral ventricle.
What is the nucleus inferior to the thalamus called?
The subthalamic nucleus
What structure is sandwiched between the caudate nucleus and the lentiform nucleus anteriorly and the caudate nucleus + the thalamus posteriorly?
The internal capsule (A sandwiched section of white matter tracts, containing motor and sensory projection fibers, that extends from the cortex and is also termed the corona radiata)
What part of the substantia niagra produces dopamine?
The Pars compacta
Where must coronal sections be taken for the ability to see the thalamus and the substantia niagra?
Posteriorly (if coronal section shows no thalamus its an anterior section)
What is the extreme capsule? What structure lies medially to it?
The extreme capsule is a long association fiber pathway of white matter in the brain that provides bidirectional communication between such areas as the claustrum and the insular cortex, and the inferior frontal gyrus (Broca’s area) and the middle-posterior portion of the superior temporal.
The claustrum lies medially to it.
What structure lies medially to the putamen?
Both external and internal globus pallidus
What is the lentiform nucleus?
The collective name for putamen and globus pallidus
What does GABA stand for?
What is the claustrum and where is it located?
Unknown yet (related to consciousness) it contains lots of connections to the cortex. Lateral to that there is extreme caspule and insula more laterally.
Where is the insula located?
Deep within the temporal and parietal lobes and can’t be seen from the outside of the brain.
Name the structures:
Under the lateral ventricles: Caudate nucleus
Internal capsule between the 2 parallel yellow lines
Between the green and red lines is the extreme capsule
What is the collective name of the caudate nucleus and putamen?
What is the collective name of the putamen and globus pallidus?
The lentiform nucleus
What is the paleostriatum?
Globus pallidus internus and externus
What is the collective name of the caudate nucleus, the putamen, and the globus pallidus?
What neurotransmitters are involved in the direct and indirect circuits of movement?
Excitatory neurotransmitters include glutamate (Na and Ca influx resulting in depolarization)
Inhibitory neutrotransmitters include GABA which results in Cl- influx and K+ efflux
What happens during the direct pathway?
Motor cortex sends excitatory signal to striatum.
Striatum sends inhibitory signal to globus pallidus internus
Globus pallidus stops sending as much inhibitory signals to the thalamus
Thalamus excites UMNs
What happens at rest in the direct pathway?
No inhibition of the globus pallidus taking place so there is constant inhibition of the thalamus
How does the indirect pathway work?
A detour is taken instead of going directly to the GPinternus the signal goes to the GPexternus and then to the subthalamus then to GPinternus and thalamus and then cortex/UMNs. This extra detour results in excitation of cortex/UMNs.
From the striatum to the GP externus there is an inhibitor signal and another inhibitory signal from the GPexternus to subthalamus and from the subthalamus to the GPinternus we have an excitatory signal synapsing with the inhibitory signal of the thalamus. Inhibiting the inhibition of the thalamus results in excitation of UMNs and actions take place.
What does the substantia niagra do?
Fine-tunes actions to prevent overshooting.
Where do neurons of the substantia niagra project to?
What happens when dopamine binds to D1 and D2 receptors?
D1: Stimulates striatal neurons on direct pathway via D1 receptors. (Direct pathway favoured)
D2: Inhibits indirect pathway neurons via D2 receptors. (Direct pathway favoured)
What does the action of dopamine do in general to the thalamus?
Loosens inhibition of thalamus slightly
What happens during Parkinson’s disease?
Degeneration of dopamine releasing neurons in the substantia niagra.
Loss of dopamine results in decreased motor activity.
Less movement and a difficulty initiating movement.
Can affect both the direct and indirect pathways
What happens during Huntington’s disease?
Hyperkinetic disorder characterised by flailing, uncontrolled and unwanted movements due to degeneration of inhibitory neurons in the caudate nucleus. This condition affects only the indirect pathway.
Why does huntington’s disease only affect the indirect pathway?
Neurons in the caudate (striatum) on the direct pathway release GABA and a bit of substance P. Neurons in the indirect pathway release GABA and encephalin. Huntington’s disease is specific only to those cells that also release encephalin so indirect pathway is affected.
What is the tentorium cerebella?
The fold of dura between cerebrum and cerebellum
What covers the posterior surface of the cerebellum?
Folia which are folds to increase surface area of cerebellum.
What are the divisions of the cerebellum?
2 lobes on posterior surface (anterior and posterior lobes)
What lobes does the primary fissure separate in the cerebellum?
The anterior and posterior lobes
What does the horizontal fissure of the cerebellum separate?
The rostral and caudal parts of the posterior lobe
What structure connects the 2 hemispheres of the cerebellum?
How is the floccular nodular lobe separated from the posterior lobe?
Floccular nodular lobe is separated from posterior lobe by posterolateral fissure.
What view is this of the cerebellum?
How is the cerebellum connected to the brain stem?
Via 3 peduncles:
Superior (to midbrain)
Middle (to pons)
Inferior (to Medulla)
What are the functional divisions of the cerebellum?
Vestibulocerebellum (contains the flocculonodular lobe and is concerned with balance and input from vestibular complex)
Spinocerebellum (Contains vermal and paravermal regions and is concerned with proprioception/tone and input from spinal cord)
Cerebrocerebellum (Contains lateral hemispheres and is important for coordination and planning with input from cerebral cortex)
Order the divisions of the cerebellum from phylogenetically oldest to newest:
Where does information from the trunk, shoulder girdle and hip girdle come in on the cerebellum?
Where does the output of the cerebellum come from?
The deep cerebellar nuclei
What are the 4 pairs of cerebellar nuclei?
Where do the dentate nuclei sit?
Near the lateral hemispheres.
What are the interposed nuclei?
Emboliform and globose nuclei
Does the cortex of the cerebellum contain grey matter or white matter?
Which nuclei does all information from the lateral hemispheres go?
Which nuclei are associated with the spinocerebellum?
The interposed nuclei
Which nuclei does information from the vestibulocerebellum go through?
The fastigial nuclei
How many layers does the cerebellar cortex have?
Molecular layer (outermost
Purkinje layer (middle)
Granular layer (innermost)
What are all input fibers to the cerebellum from cortex, spinal cord, and vestibular apparatus called?
What kind of signals (inhibitory or excitatory) enter the cerebellar cortex via the mossy fibers?
Excitatory signals containing glutamate
What are the input fibers of the cerebellar cortex that enter through inferior olivary nucleus called?
What structures do output fibers of the cerebellum pass through?
The deep nuclei of the cerebellum
What output fibers does the cerebellar cortex use?
Purkinje cells which inhibit deep cerebellar nuclei.
The layers of the cerebellar cortex:
How does processing and regulation of cerebellar output take place?
There are pathways for strong stimulation, weak stimulation, and inhibitory pathways which sharpen signal while alse auto-inhibiting to prevent overactivity.
Strong stimulation pathways stimulate the deep cerebellar nuclei increasing their activity.
Climbing fibers synapse onto purkinje dendrites which is a 1:1 ratio. This pathway strongly inhibits the deep cerebellar nuclei. Diffuse stimulation occurs via mossy fibers which produce glutamate and excite heaps of granule cells which excite purkinjes resulting in diffuse inhibition of deep cerebellar nuclei.
As soon as granule cells fire they stimulate golgi cells which then inhibit granule cells. Parallel fibers stimulate purkinje fibers while also stimulating basket cells and stellate cells which are inhibitory to surrounding purkinjes creating activity in only the desired purkinje fibers.
Which cerebellar fibers are important for strong stimulation?
Cerebellar fibers which produce aspartate and excite the deep cerebellar nuclei
What is dysmetria and how can we test for it?
Distance-related disorder resulting in overshooting or undershooting movements. This can be tested by trying to touch your nose.
What is dysdiadochokinesia and how can it be tested for?
It is a timin-related disorder resulting in an inability to switch on and switch off antagonising muscle groups in a coordinated fashio. This can be tested by trying to touch fingers in order.
What is dyssynergia?
A force-related dysorder resulting in uncoordinated and abrupt movements.
What is ataxia?
Poor condition with respect to distance timing and force.