Nine Flashcards
What does basal ganglia refer to? What do they do functionally? What don’t they do? What happens if the interconnections are damaged?
The term “basal ganglia” refers to three pairs of large, strongly interconnected, nuclear masses deep within the cerebral hemispheres, diencephalon, and midbrain whose
abnormalities result in the movement disorders.
- Anatomically, Physiologically, and Functionally Related Nuclei In the Cerebral Hemispheres, Diencephalon and Midbrain that Control Voluntary Movements
- Functionally Enable Desired Movements to Occur and Competing Movements to be Inhibited
- When Interconnections are Damaged Results in (Movement Disorders (Dyskinesia) with Negative and Positive Clinical Signs
For many years the basal ganglia were thought to be the highest center for an extrapyramidal motor system. We now know that in humans the basal ganglia chiefly regulate voluntary movements throughout the pyramidal system.
What are the 4 nucleus of the basal ganglia? Where are they located? What are the sub/supra/interdivisions of the the basal ganglia?
In the cerebral hemisphere, there is the caudate nucleus and the lentiform nucleus (putamen, pallidum (lateral, medial)). They make up the corpus striatum. The putamen and the caudate nucleus are related and are called the striatum. In the diencephalon, there is the subthalamic nucleus. In the midbrain, there is the substantia nigra (pars reticula and pars compacta).
Where is the caudate nucleus located? What is its shape? What are its parts? Where is the lentiform nucleus located? What is its shape? What surrounds the lentiform nucleus?
It is a comma shaped nucleus with a head, body, and tail. The head is largest and protrudes into the anterior horn of the lateral ventricle. The body arches downward and forward and the tail ends in the temporal lobe.
The lentiform nucleus is wedgeshaped. There are fibers that connect the caudate nucleus with the putamen through the anterior limb of the internal capsule. The medial part of the pallidus is lateral to the internal capsule across from the thalamus. The putamen is medial to the external capsule.
Where is the subthalamic nucleus located? What is its shape?
The subthalamic nucleus is a large nuclear mass in the subthalamus and appears as a prominent biconvex-shaped structure nestled in the arm of the most rostral part of the cerebral crus (where the internal capsule is meeting the cerebral crus, ventral to the thalamus).
Where is the substantia nigra? How far does it extend? Where is the pars compact? What are the cells in the pars compacta like? Where is the par reticularis?
The substantia nigra is the largest nuclear mass of the midbrain, extending throughout its length and even overlapping with the subthalamus rostrally. It consists of two parts: the pars compacta and the pars reticularis. The pars compacta is more dorsal and its cells contain the pigment melanin that gives this structure the black color for which the nucleus was named. The cells of the pars compacta are rich in dopamine. The pars reticularis is more ventral and intermingles with the fiber bundles of the cerebral crus. It extends more rostrally than does the pars compacta.
Where does the basal ganglia receive its input from? Which part of the BG receives the input? What kind of input is received (which NT, exc or inh)?
Afferent input to the basal ganglia arises chiefly from the cerebral cortex and is directed to the striatum. Virtually all areas of the cerebral cortex project in a very orderly manner to the striatum. These corticostriate projections reach the caudate nucleus and putamen directly from the adjacent white matter, most via the anterior limb of the internal capsule and the external capsule. These are excitatory inputs and thus use glutamate.
Describe the indirect pathway (from which part to which part, exc. or inh, NT). Describe the direct pathway in the same way. Describe the pathway involving the SN.
In the indirect pathway, the striatum is excited by the cortex (corticostriatal), the striatum then inhibits (GABA) the lateral pallidus which inhibits the subthalamic nucleus (GABA) which in turn excites the medial pallidum (Glut). By inhibiting an inhibitory pathway, you’re essentially exciting the the medial pallidum (opposite of direct).
In the direct pathway, the striatum is excited by the cortex (Glut), the striatum then inhibits the medial pallidum (GABA).
In the pathway involving the SN, the pars compacta both inhibits and excites the striatum using dopamine.
In the same way, describe the output pathway from the BG. What is the ultimate effect of the indirect and direct pathways.
The medial pallidum is the chief output nucleus of the BG. It inhibits (GABA) the Ventral Anterior (VA) Nucleus which is located in the thalamus. The VA nucleus then excites the perimotor complex (Glut) which excites the pyrimidal system (glut).
Direct inhibits the inhibition of the VA. It enables desired movement.
The indirect excites the inhibition of the VA, thus inhibiting competing movements.
