Basal Ganglia 2024 PDF

Neurophysiology BASAL GANGLIA University Of Fallujah College Of Medicine Lecture : 10 Stage : second Lecturer :Dr. Mohammed Abdulwahed Al Rawi Department: Physiology Date: 21-1-2025 The Basal Ganglia  OBJECTIVES Enumerate the functiona...

Neurophysiology BASAL GANGLIA University Of Fallujah College Of Medicine Lecture : 10 Stage : second Lecturer :Dr. Mohammed Abdulwahed Al Rawi Department: Physiology Date: 21-1-2025 The Basal Ganglia  OBJECTIVES Enumerate the functional parts of the basal ganglia. Explain the role of basal ganglia. Discuss the diseases resulted from basal ganglia abnormalities. List the functions of reticular activating system.  They are gray matter nuclei surrounded by the white matter of the brain. On each side of the brain, these ganglia consist of the caudate nucleus, putamen (both are called the straiatum), globus pallidus (internal& external parts), substantia nigra (pars compacta& pars reticulata), and subthalamic nucleus. They are located mainly lateral to and surrounding the thalamus, occupying a large portion of the interior regions of both cerebral hemispheres. almost all motor & sensory nerve fibers connecting the cerebral cortex and spinal cord pass through the space that lies between the major masses of the basal ganglia, the caudate nucleus and the putamen. This space is called the internal capsule of the brain. Function of the Basal Ganglia One of the principal roles of the basal ganglia in motor control is to function in association with the corticospinal system to control complex patterns of motor activity. An example is the writing of letters of the alphabet. When there is serious damage to the basal ganglia, the cortical system of motor control can no longer provide these patterns. Instead, one’s writing becomes crude, as if one were learning for the first time how to write. Neural Pathways of the Putamen Circuit They begin mainly in the premotor and supplementary areas of the motor cortex and in the somatosensory areas of the sensory cortex. Next they pass to the putamen (mainly bypassing the caudate nucleus), then to the globus pallidus, next to the nuclei of the thalamus, and finally return to the cerebral primary motor cortex. 1. The Putamen Circuit: For subconscious (automatic) execution of learned patterns of movement. Also motor planning, motor preparation, specifying amplitudes of movement and movement sequences. Some neurologists hypothesize that the putamen also plays a role in the selection of movement. Role in learning. Role in "hate circuit“. -Role of the Basal Ganglia for Cognitive Control 2. The Caudate Circuit function The term cognition means the thinking processes of the brain, using both sensory input to the brain plus information already stored in memory. A good example of this would be a person seeing a lion approaching. The caudate nucleus helps process visual information and control movement. It’s involved in working memory, learning, motivation and emotions (romantic exchange). Function of the Basal Ganglia to Change the Timing and to Scale the Intensity of Movements Two important capabilities of the BG in controlling movement are (1) to determine how rapidly the movement is to be performed and (2) to control how large the movement will be. For instance, a person may write the letter “a” slowly or rapidly. Also, he or she may write a small “a” on a piece of paper or a large “a” on a chalkboard. Movement modulation through disinhibition Movement modulation through disinhibition Output nuclei of the basal ganglia are inhibitory Output nuclei maintain a high tonic level of discharge, suppressing activity in target regions Firing under quiescent conditions (in the absence of movement) Movement modulation occurs through disinhibition of thalamocortical target regions  Neurotransmitter Substances in the Basal Ganglia System (1) Dopamine pathways (mostly inhibitory) (2) gamma-aminobutyric acid (GABA) pathways( always inhihitory) (3) acetylcholine pathways. (4) multiple general pathways from the brain stem that secrete norepinephrine, serotonin, enkephalin, and several other neurotransmitters in the basal ganglia as well as in other parts of the cerebrum. (5) multiple glutamate pathways that provide most of the excitatory signals that balance out the large numbers of inhibitory signals transmitted especially by the dopamine, GABA, and serotonin inhibitory transmitters.  Abnormal Function in the basal ganglia lesions in the globus pallidus frequently lead to spontaneous and often continuous repetitive involuntary, slow, writhing movements of a hand, an arm, the neck, or the face movements called athetosis. A lesion in the subthalamus often leads to sudden flailing movements of an entire limb, a condition called hemiballismus. Multiple small lesions in the caudate lead to flicking movements in the hands, face, and other parts of the body, called chorea. Lesions of the substantia nigra lead to the common and extremely severe disease of rigidity, akinesia, and tremors known as Parkinson’s disease. Clinical Syndromes Resulting from Damage to the Basal Ganglia 1. Parkinson’s Disease Parkinson’s disease results from widespread destruction of that portion of the substantia nigra that sends dopamine-secreting nerve fibers to the caudate nucleus and putamen. The disease is characterized by (1) rigidity of much of the musculature of the body, (2) involuntary tremor of the involved areas even when the person is resting, and (3) serious difficulty in initiating movement, called akinesia. 2. Huntington’s Disease (Huntington’s Chorea) Huntington’s disease is a hereditary disorder that usually begins causing symptoms at age 30 to 40 years. It is characterized at first by flicking movements in individual muscles and then progressive severe distortional movements of the entire body. In addition, severe dementia develops along with the motor dysfunctions. The abnormal movements of Huntington’s disease are believed to be caused by loss of most of the cell bodies of the GABA-secreting neurons in the caudate nucleus and putamen and of acetylcholine-secreting neurons in many parts of the brain. reticular activating system Signals are sent from the cortex to the brain stem excitatory area, which in turn sends still more excitatory signals to the cortex. This is a general mechanism of positive feedback leading to an “awake” mind. This helps to maintain the level of excitation of the cerebral cortex or even to enhance it. Pain signals in particular increase activity in this excitatory area and therefore strongly excite the brain to attention. Medullary reticular Inhibitory Area This area can inhibit the reticular faciliatory area of the upper brain stem and thereby decrease activity in the superior portions of the brain as well. One of the mechanisms for this is to excite serotonergic neurons; these in turn secrete the inhibitory neurohormone serotonin.  SUMMARY Basal ganglia consist of the caudate nucleus, putamen (both are called the striatum), globus pallidus (internal& external parts), substantia nigra (pars compacta& pars reticulata), and subthalamic nucleus. The main function of basal ganglia is movement modulation through disinhibition. Clinical Syndromes Resulting from Damage to the Basal Ganglia include Parkinson Disease and Huntington’s Chorea. The reticular activating system is composed of facilitatory and inhibitory areas