How many neurons does the cerebellum have?
-almost as many as the rest of the brain =small brain
How do cerebellum and basal ganglia feed into the motor neurons?
-basal ganglia and cerebellum do not directly influence motor neurons, the influnce is on the motor cortex and brainstem integration
What are the 3 functions of the basal ganglia?
1. Allow the selection of complex patterns of voluntary movement 2. Evaluate the success of actions in achieving goals of those actions (involved in motor learning 3.Initiating movements (know from damage to basal ganglia =Parkinson's can't get movements going)
What is basal ganglia's primary function?
-to control and regulate activities of the motor and premotor cortical areas so that voluntary movements can be performed smoothly
What are the 5 interconnected nuclei that make up the basal ganglia?
4.Subthalamic nuclei (just below the thalamus)
5.Substantia nigra pars compacta and Substantia nigra pars reticulata
Which 3 nuclei of the basal ganglia are in the forebrain (telencephalon)?
1.Caudate 2.Putamen 3.Globus Pallidus
Where is the substantia nigra?
True or false: Are globus pallidus and Substantia nigra pars reticulata similar tissue?
Why is substantia nigra called that?
-black, presence of melanin
What cells are in the substantia nigra?
-dopamine secreting cells
True or false: Are caudate and putamen the same kind of tissue?
What are the 2 divisions of the globus pallidus?
-internal and external
Can you microscopically distinguish putamen and caudate?
no -functionally also the same, input areas of the basal ganglia
What is the function of caudate and putamen in the basal ganglia?
-input areas of basal ganglia
Where does the caudate get input from?
-substantia nigra pars compacta
Where does the putamen get input from?
-substantia nigra pars compacta
What does input to the basal ganglia excite?
-GABAergic neurons of the caudate and putamen
What are the two output region of basal ganglia?
-substantia nigra pars reticulata -internal division of the globus pallidus -GABAergic neurons
How can connections between the input and output areas of basal ganglia be made?
-direct or indirect pathway
What is striatum?
-input of basal ganglia -structure that is divided by white matter tract and is made up of caudate and putamen
What is corpus striatum?
striatum plus globus pallidus
What regions of the brain project to the corpus striatum (ie. putamen and caudate)?
What does the direct pathway ultimately lead to?
-when activated by cortical input leads to cortical excitation and therefore movement -important for initiating movement
What does the indirect pathway ultimately lead to?
-when activated inhibits cortical activity and therefore no movement
What is the direct pathway?
1. Get input from the cerebral cortex
2. That excited the caudate and putamen
3. That leads to inhibition of globus pallidus internal segment (the putamen caudate neurons when excited inhibit this region)
4.Globus pallidus tonically inhibits VA/VL complex, when the caudate and putamen inhibit this function then thalamus is more active as it is not being inhibited
5. VA/VL complex of thalamus excited the frontal cortex= movement!
----also remember substantia nigra pars compacta makes dopamine= that also excited the caudate/putamen, enhancing this pathway -D1 must be present for the indirect pathway to occur!
What is the indirect pathway?
1. Get input from cerebral cortex.
2.That excites the caudate/putamen
3. In this case the substantia nigra pars compacta is producing D2 (which is inhibitory) and the globus pallidus external segment will be inhibited
4. Globus pallidus external segment normally tonically inhibits the subthalamic nucleus and now g.p is inhibited by the caudate putamen so the subthalamic nucleus will be less inhibited and more active
4.b globus pallidus external segment normally also inhibits globus pallidus internal segment but now g.p.e is inhibited so it doesn't inhibit the internal segment
5.The subthalamic nucleus will excite the globus pallidus internal segment
6. The globus pallidus internal segment tonically inhibits VA/VL of the thalamus and this way it will increase its inhibition
7. VA/VL complex of thalamus then doesn't send excitation to frontal cortex= no movement!
What is the role of dopamine in the direct and indirect pathway?
-dopamine producing substantia nigra pars compacta, has two types of receptors D1 and D2, -D1 is excitatory and makes direct pathway happen -D2 is inhibitory and makes indirect pathway happen
Why does L-dopa work as a treatment for Parkinson's (for a while)?
-more dopamine in the brain -can initiate movement again
What is the center-surround organisation of the direct/indirect pathway?
What does this picture demonstrate?
-basal ganglia is involved in many more things that just motor control
What happens in Parkinson's disease?(in terms of basal ganglia)
-loss of substantia nigra
-so no dopamine, cannot get movement going
What happens in Huntingtin's disease in terms of basal ganglia?
-loss of cells in basal ganglia
What are the functions of the cerebellum? (4)
1. Coordinating the timing and sequence of muscle actions and movements
2. Maintenance of muscle tone
3. Motor learning
4.Planning sequences of muscle activation for complex movements
(like an optimizer -part of getting better at the movements all muscles at tone so ready to go= cerebellum does that-when damaged then not -lot of connection to motor cortex and brain stem) --tweaking the plan -adjust the movement motor plan going to the spinal cord, error detector
What is the overall division and organisation of the cerebellum?
-has thin layer of cortex and grey matter and white matter and then deep grey matter = deep cerebellar nuclei
What are the inputs of the cerebellum? (the info goes from there to cerebellum)
How does the information get to the cerebellum from its input areas?
1.-goes from frontal and parietal cortex to the pontine nuclei from there goes to the cerebellar cortex 2- from vestibular nuclei goes to the cerebellar cortex 3.from inferior olive goes to the cerebellar cortex 4.from external cuneate nucleus to the cerebellar cortex 5.from dorsal nucleus of Clarke goes to cerebellar cortex
What is the inferior olive (olivary nucleus) for?
- closely associated with the cerebellum, meaning that it is involved in control and coordination of movements, sensory processing and cognitive tasks likely by encoding the timing of sensory input independently of attention or awareness
What are the vestibular nuclei for?
-contributes to balance in most mammals and to the sense of spatial orientation, is the sensory system that provides the leading contribution about movement and sense of balance
What are the brain regions that project to the cerebellum?
-primary motor cortex
-primary somatosensory cortex
-motor association cortex
-sensory association cortex
What are the outputs of the cerebellum?ascending outputs
-motor cortex -inferior olive
How does the information from the cerebellum gets to its targets? ascending outputs
1. cerebellar cortex to deep cerebellar nuclei, from there to VL (ventral lateral) complex of thalamus, then from there to primary motor and premotor cortex
2. cerebellar cortex to deep cerebellar nuclei, from there to the red nucleus (parvocellular) and from there to inferior olive
What is the functional organisation of the major descending outputs of the cerebellum?
What are the descending outputs of the cerebellum?
-descending motor pathways of the brainstem -
1.Cerebellar cortex to vestibular nuclei
2.Deep cerebellar nuclei to reticular formation
3.Deep cerebellar nuclei to superior colliculus
-all those to lower motor neurons in medial ventral horn
What is ataxia?
-can't get the end point right -the precision of the movement is not right
The cerebellum is responsible for integrating a significant amount of neural information that is used to coordinate smoothly ongoing movements and to participate in motor planning.= if not working= ataxia