Unit 6

 Basal Ganglia and Cerebellum 

 

TOPICS COVERED

Basal Ganglia anatomy

Basal ganglia pathways

Basal ganglia function

Basal ganglia disorders

 

Cerebellum anatomy

Cerebellum pathways

Cerebellum function

Cerebellum disorders

 

 

UNIT CONTENT

 

History

It was as early as 1664 when the first clear identification of distinct subcortical structures was published by the English anatomist Thomas Willis (Parent, 1986). What is now functionally known as the basal ganglia was then referred to as the corpus striatum. It held such a central position, striped with a wide range of cortical and brainstem fibers, that at the time it was believed to be the "sensorium commune" as defined by Aristotle. It was a structure thought to both receive all sensory modalities and initiate all motor acts. This idea appeared to be anatomically reinforced by its central position and clearly visible ascending and descending fiber systems.

Two subsequent events relegated the corpus striatum to an obscure and less defined position. The attractiveness of the histological organization of the cortex, and the possibility of localizing higher mental functions drew many neurologists of both the 18th and 19th centuries to cortical research. Amongst those that continued studying the corpus striatum, there was a sudden realization that many of the functions originally assigned to it were in fact properties of neighbouring corticospinal paths (Wilson, 1914). As Wilson (page 428) describes, the corpus striatum "seemed to fall from its high estate and depreciate in physiological significance".

Ramón Cajal, 1890 At the beginning of the 20th century there were serious attempts to provide detailed comparative descriptions of the corpus striatum (Wilson 1914, Cajal 1911 - shown left). It began to gain importance once again with the discoveries that lesions of these areas would often result in disorders of motor functions in humans (Wilson 1914, Vogt 1911). The corpus striatum came to be viewed as the major components of the "extrapyramidal motor system" (Parent, 1986). This term loosely grouped the corpus striatum with an array of brain stem nuclei and reflected the assumption that this grouping constituted a complete and independent motor unit (Carpenter 1981). The term "basal ganglia" has been generally used to refer to these major anatomical telencephalic subcortical nuclei at the base of the forebrain.

 

 

Thanks to:  The Institute for Adaptive and Neural Computation (ANC) is part of the School of Informatics at the University of Edinburgh.

 

 

The basal ganglia - required reading

The term "basal ganglia" refers to a loosely grouped collection of large subcortical nuclear (gray) masses derived from the telencephalon and located deep within each cerebral hemisphere. The nuclear components include the claustrum, amygdaloid nuclear complex, nucleus accumbens, and the corpus striatum.

The term is now used to refer more specifically to the corpus striatum and two additionally related nuclei, the subthalamic nucleus and the substantia nigra; derivatives of the diencephalon and mesencephalon, respectively. Although not part of the telencephalic basal ganglia these nuclei are reciprocally connected with and functionally related to the corpus striatum. The focus of this tutorial will be entirely on the corpus striatum and those structures functionally related to it.

We know from our understanding of their organizaton, connections, and deficits that ensue from their pathology that the corpus striatum and related nuclei play an important role in motor control. Interestingly, the component nuclei themselves have no direct projections to spinal cord levels. They influence motor activity by interacting with areas of the cerebral cortex that give rise to descending motor pathways through a number of feedback loops.

The corpus striatum, related nuclei, and connections are sometimes described as forming the "extrapyramidal motor system." This is now an antiquated concept but was once conceived to represent a complete and independent motor system distinct from the phylogenetically newer corticospinal or "pyramidal motor system".

Sweet,sweet pictures - take a look, I suspect you will find them useful.

 

basal ganglia

  • They are functionally important, at a minimum, for controlling voluntary movements and establishing postures. When they are altered - say in disorders like Huntington disease or Wilson disease - the person has unwanted movements, such as involuntary jerking movements of an arm or leg or spasmodic movement of facial muscles.
  • The caudate nucleus and putamen along with the interposed anterior limb of the internal capsule are collectively known as the corpus striatum (i.e. striated body) because of their appearance.
  • Similarly, the shape of the putamen and globus pallidus resembles a lens, and they are collectively called the lenticular nucleus.

Thanks to:

WWAMI MEDICAL EDUCATION PROGRAM

                        Washington-Wyoming-Alaska-Montana-Idaho

Basal ganglia II - required reading

Special thanks to the Karolinska Institutet © for the material immediately below.

Basal ganglia sagittal view depiction

Basal ganglia dorsal plane view

 

MRI of the caudate nucleus

Disorders of the basal ganglia

Wilson's disease - required reading

Huntington disease - required reading

Tourette's syndrome -required reading

 

1st Required QUIZ

UNIT 6

Please take in : www.uh.edu/webct

You will have 22 minutes to complete the Required Quiz - use your time wisely!

 

Parkinson's disease - required reading - be sure to read the entire side (all segments listed in the left column)

 

 

2nd Required QUIZ

UNIT 6

Please take in : www.uh.edu/webct

You will have 8 minutes to complete the Required Quiz - use your time wisely!

 

 

 

The Cerebellum - required reading

·         Function: To enable smooth coordinated movement

·         plays an important role in the maintenance of posture and equilibrium.

·         Sends fibers via the cerebellar-spinal tract to modulate the activity of the alpha as well as the gamma motor neurons (Lower motor neurons).

o        The cerebellum receives information from a wide array of senses:

o        Pressure and touch

o        Positional receptors: Spindle and Golgi tendon organs

o        Eyes and ears

o        A copy of the command signal is sent from the cerebral cortex to the cerebellum, where it acts as a comparator.

 

Cerebellum II - required reading

 

cerebellum (sarah bell' um)

  • It is important for coordinating voluntary movements (e.g. walking, posture, speech) and for learning motor (skilled) behaviors.
  • The cerebellum, like the cerebrum, has a cortex or outer covering of gray matter. The types/names of neurons and layers in the two cortices differ.

Back to Dorsal Lateral View

Back to Midsagittal View

Back to Basal View

Cerebello-Olivary degeneration
of  Holmes

WWAMI MEDICAL EDUCATION PROGRAM

                        Washington-Wyoming-Alaska-Montana-Idaho

 

Special thanks to the Karolinska Institutet © for the pictures immediately below.

 

Basal ganglia sagittal view depiction

 

 

 

MRI of the cerebellum

 

 

Detailed MRI for those interested in the technology - NOT required reading

 

Cerebellum III - required reading - a special thanks to New Horizons for Learning for this material.

 

Cerebellum IV - required reading - a special thanks to the Society for Neuroscience for this material

Clinical deficits associated with cerebellar lesions: - REQUIRED READING - just know basic symptoms

  1. dysmetria or past pointing
  2. dysdiadochokinesia
  3. intention or movement tremor
  4. nystagmus
  5. dysarthria
  6. hypotonia

Just a great listing of all sorts of "neuro" stuff. - Not required but interesting (some links are dead)

2nd Required QUIZ

UNIT 6

Please take in : www.uh.edu/webct

 You will have 25 minutes to complete the Required Quiz - use your time wisely!