4. Basal Ganglia
Part 4 of 4
James Knierim, Ph.D.
.
Disorders of the Basal Ganglia
A number of neurological disorders result from damage to the basal ganglia. Two of these disorders (Parkinson’s disease and Huntington’s disease) will be briefly discussed here to relate the concepts learned in this chapter to the symptoms of the disorders. More thorough treatment of these disorders will be given in the chapter on Disorders of the Nervous System.
Nigrostriatal pathway and Parkinson’s disease
Figure 4.10 Parkinson’s disease and Huntington’s disease. Click on disease names to see neural damage that produces the disorders. |
Parkinson’s disease is characterized by slowness or absence of movement (bradykinesia or akinesia), rigidity, and a resting tremor (especially in the hands and fingers). Patients have difficulty initiating movements, and once initiated the movements are abnormally slow. The cause of Parkinson’s disease is the loss of the dopaminergic neurons in the substantia nigra pars compacta (Figure 4.10). From one’s knowledge of the effects of the nigrostriatal pathway on the direct and indirect pathways, it becomes straightforward to see why the loss of this pathway results in the poverty of movement symptomatic of Parkinson’s disease. Because the nigrostriatal pathway excites the direct pathway and inhibits the indirect pathway, the loss of this input tips the balance in favor of activity in the indirect pathway. Thus, the GPint neurons are abnormally active, keeping the thalamic neurons inhibited. Without the thalamic input, the motor cortex neurons are not as excited, and therefore the motor system is less able to execute the motor plans in response to the patient’s volition.
Indirect pathway and Huntington’s disease
The symptoms of Huntington’s disease are in many respects the opposite of the symptoms of Parkinson’s disease. Huntington’s disease is characterized by choreiform movements: involuntary, continuous movement of the body, especially of the extremities and face. Often these movements resemble pieces of adaptive movements, but they occur involuntarily and without behavioral significance. Huntington’s disease results from the selective loss of striatal neurons in the indirect pathway (Figure 4.10). Thus, the balance between the direct and indirect pathways becomes tipped in favor of the direct pathway. Without the normal inhibitory influence on the thalamus that is provided by the indirect pathway, thalamic neurons can fire randomly and inappropriately, causing the motor cortex to execute motor programs with no control by the patient.
Test Your Knowledge
- Question 1
- A
- B
- C
- D
- E
Which of the basal ganglia nuclei receive direct cortical input?
A. Claustrum and amygdala.
B. Centromedian nucleus and subthalamic nucleus.
C. Substantia nigra pars compacta and globus pallidus external.
D. Globus pallidus internal and substantia nigra pars reticulata.
E. Caudate and putamen.
Which of the basal ganglia nuclei receive direct cortical input?
A. Claustrum and amygdala. This answer is INCORRECT. The claustrum and amygdale are not components of the basal ganglia.
B. Centromedian nucleus and subthalamic nucleus.
C. Substantia nigra pars compacta and globus pallidus external.
D. Globus pallidus internal and substantia nigra pars reticulata.
E. Caudate and putamen.
Which of the basal ganglia nuclei receive direct cortical input?
A. Claustrum and amygdala.
B. Centromedian nucleus and subthalamic nucleus. This answer is INCORRECT. These nuclei do not receive direct cortical input.
C. Substantia nigra pars compacta and globus pallidus external.
D. Globus pallidus internal and substantia nigra pars reticulata.
E. Caudate and putamen.
Which of the basal ganglia nuclei receive direct cortical input?
A. Claustrum and amygdala.
B. Centromedian nucleus and subthalamic nucleus.
C. Substantia nigra pars compacta and globus pallidus external. This answer is INCORRECT. These nuclei do not receive direct cortical input.
D. Globus pallidus internal and substantia nigra pars reticulata.
E. Caudate and putamen.
Which of the basal ganglia nuclei receive direct cortical input?
A. Claustrum and amygdala.
B. Centromedian nucleus and subthalamic nucleus.
C. Substantia nigra pars compacta and globus pallidus external.
D. Globus pallidus internal and substantia nigra pars reticulata. This answer is INCORRECT. These nuclei do not receive direct cortical input.
E. Caudate and putamen.
Which of the basal ganglia nuclei receive direct cortical input?
A. Claustrum and amygdala.
B. Centromedian nucleus and subthalamic nucleus.
C. Substantia nigra pars compacta and globus pallidus external.
D. Globus pallidus internal and substantia nigra pars reticulata.
E. Caudate and putamen. This answer is CORRECT! The caudate and putamen are the only parts of the basal ganglia that receive direct cortical input.
- Question 2
- A
- B
- C
- D
- E
All of the following statements about the basal ganglia are correct EXCEPT:
A. The net effect of excitation of the direct pathway is to inhibit cortex.
B. Dopaminergic neurons of the substantia nigra signal unexpected reward or unexpected absence of reward.
C. The basal ganglia have both motor and cognitive functions.
D. The subthalamic nucleus is the origin of the only purely excitatory pathway within the basal ganglia intrinsic circuitry.
E. Parkinson's disease results from damage to the basal ganglia.
All of the following statements about the basal ganglia are correct EXCEPT:
A. The net effect of excitation of the direct pathway is to inhibit cortex. This answer is CORRECT! This is a FALSE statement. The net effect of excitation of the direct pathway is to excite cortex.
B. Dopaminergic neurons of the substantia nigra signal unexpected reward or unexpected absence of reward.
C. The basal ganglia have both motor and cognitive functions.
D. The subthalamic nucleus is the origin of the only purely excitatory pathway within the basal ganglia intrinsic circuitry.
E. Parkinson's disease results from damage to the basal ganglia.
All of the following statements about the basal ganglia are correct EXCEPT:
A. The net effect of excitation of the direct pathway is to inhibit cortex.
B. Dopaminergic neurons of the substantia nigra signal unexpected reward or unexpected absence of reward. This answer is INCORRECT. This is a TRUE statement.
C. The basal ganglia have both motor and cognitive functions.
D. The subthalamic nucleus is the origin of the only purely excitatory pathway within the basal ganglia intrinsic circuitry.
E. Parkinson's disease results from damage to the basal ganglia.
All of the following statements about the basal ganglia are correct EXCEPT:
A. The net effect of excitation of the direct pathway is to inhibit cortex.
B. Dopaminergic neurons of the substantia nigra signal unexpected reward or unexpected absence of reward.
C. The basal ganglia have both motor and cognitive functions. This answer is INCORRECT. This is a TRUE statement.
D. The subthalamic nucleus is the origin of the only purely excitatory pathway within the basal ganglia intrinsic circuitry.
E. Parkinson's disease results from damage to the basal ganglia.
All of the following statements about the basal ganglia are correct EXCEPT:
A. The net effect of excitation of the direct pathway is to inhibit cortex.
B. Dopaminergic neurons of the substantia nigra signal unexpected reward or unexpected absence of reward.
C. The basal ganglia have both motor and cognitive functions.
D. The subthalamic nucleus is the origin of the only purely excitatory pathway within the basal ganglia intrinsic circuitry. This answer is INCORRECT. This is a TRUE statement.
E. Parkinson's disease results from damage to the basal ganglia.
All of the following statements about the basal ganglia are correct EXCEPT:
A. The net effect of excitation of the direct pathway is to inhibit cortex.
B. Dopaminergic neurons of the substantia nigra signal unexpected reward or unexpected absence of reward.
C. The basal ganglia have both motor and cognitive functions.
D. The subthalamic nucleus is the origin of the only purely excitatory pathway within the basal ganglia intrinsic circuitry.
E. Parkinson's disease results from damage to the basal ganglia. This answer is INCORRECT. This is a TRUE statement.
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