Direct pathway of movement
Encyclopedia
The direct pathway of movement is a neuronal circuit within the central nervous system
(CNS) through the basal ganglia
which facilitates the initiation and execution of voluntary movement. It works in conjunction with the indirect pathway of movement
.
The direct pathway passes through the caudate
, putamen
, and globus pallidus
, which are parts of the basal ganglia. It also involves the substantia nigra
, a part of the midbrain. In a resting individual, a specific region of the globus pallidus, known as the internus, and a portion of the substantia nigra, known as the pars reticulata, send spontaneous inhibitory signals to the ventral anterior nucleus of the thalamus
, through the release of GABA
, an inhibitory neurotransmitter. Inhibition of the excitatory neurons within VA, which project to the motor regions of the cerebral cortices of the telencephalon
, leads to a reduction of activity in the motor cortices and a lack of muscular action.
When the pre-frontal region of the cerebral cortex
, which is generally involved in decision making and planning, determines that a particular motor activity will be executed, it sends activating signals to the motor cortices. The motor cortices send signals through the basal ganglia to refine the choice of muscles that will participate in the movement and to amplify the activity in the motor cortices that will drive the muscle contractions.
In the direct pathway, the motor cortices send activating signals to the caudate and putamen. The cells of the direct pathway in the caudate and putamen that receive these signals are inhibitory and, once they become activated, send inhibitory signals to the globus pallidus internus and substantia nigra pars reticulata. Thus, activation of the direct pathway will stop activity in the globus pallidus internus and substantia nigra pars reticulata. Before activation of the direct pathway, these two nuclei were actively sending inhibitory signals to the ventrolateral nucleus of the thalamus, which prevented the development of significant activity in the motor cerebral cortices. This behavior ceases on activation of the direct pathway. The net effect is to allow the activation of the ventrolateral nucleus of the thalamus which, in turn, sends activating signals to the motor cortices. These events amplify motor cortical activity that will eventually drive muscle contractions.
...
Interruption or dysfunction of the direct pathway results in hypokinesia
, which is, in general terms, a disease which leads to a lack of motion.
Central nervous system
The central nervous system is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish...
(CNS) through the basal ganglia
Basal ganglia
The basal ganglia are a group of nuclei of varied origin in the brains of vertebrates that act as a cohesive functional unit. They are situated at the base of the forebrain and are strongly connected with the cerebral cortex, thalamus and other brain areas...
which facilitates the initiation and execution of voluntary movement. It works in conjunction with the indirect pathway of movement
Indirect pathway of movement
The indirect pathway of movement is a neuronal circuit through the basal ganglia and several associated nuclei within the central nervous system which helps to prevent unwanted muscle contractions from competing with voluntary movements...
.
Overview of Neuronal Connections and Normal Function
The direct pathway passes through the caudate
Caudate
Caudate can refer to:* Caudate nucleus* Caudate lobe of liver* Cauda equina* Members of the Caudata order....
, putamen
Putamen
The putamen is a round structure located at the base of the forebrain . The putamen and caudate nucleus together form the dorsal striatum. It is also one of the structures that comprises the basal ganglia. Through various pathways, the putamen is connected to the substantia nigra and globus pallidus...
, and globus pallidus
Globus pallidus
The globus pallidus also known as paleostriatum, is a sub-cortical structure of the brain. Topographically, it is part of the telencephalon, but retains close functional ties with the subthalamus - both of which are part of the extrapyramidal motor system...
, which are parts of the basal ganglia. It also involves the substantia nigra
Substantia nigra
The substantia nigra is a brain structure located in the mesencephalon that plays an important role in reward, addiction, and movement. Substantia nigra is Latin for "black substance", as parts of the substantia nigra appear darker than neighboring areas due to high levels of melanin in...
, a part of the midbrain. In a resting individual, a specific region of the globus pallidus, known as the internus, and a portion of the substantia nigra, known as the pars reticulata, send spontaneous inhibitory signals to the ventral anterior nucleus of the thalamus
Thalamus
The thalamus is a midline paired symmetrical structure within the brains of vertebrates, including humans. It is situated between the cerebral cortex and midbrain, both in terms of location and neurological connections...
, through the release of GABA
Gabâ
Gabâ or gabaa, for the people in many parts of the Philippines), is the concept of a non-human and non-divine, imminent retribution. A sort of negative karma, it is generally seen as an evil effect on a person because of their wrongdoings or transgressions...
, an inhibitory neurotransmitter. Inhibition of the excitatory neurons within VA, which project to the motor regions of the cerebral cortices of the telencephalon
Telencephalon
The cerebrum or telencephalon, together with the diencephalon, constitutes the forebrain. The cerebrum is the most anterior region of the vertebrate central nervous system. Telencephalon refers to the embryonic structure, from which the mature cerebrum develops...
, leads to a reduction of activity in the motor cortices and a lack of muscular action.
When the pre-frontal region of the cerebral cortex
Cerebral cortex
The cerebral cortex is a sheet of neural tissue that is outermost to the cerebrum of the mammalian brain. It plays a key role in memory, attention, perceptual awareness, thought, language, and consciousness. It is constituted of up to six horizontal layers, each of which has a different...
, which is generally involved in decision making and planning, determines that a particular motor activity will be executed, it sends activating signals to the motor cortices. The motor cortices send signals through the basal ganglia to refine the choice of muscles that will participate in the movement and to amplify the activity in the motor cortices that will drive the muscle contractions.
In the direct pathway, the motor cortices send activating signals to the caudate and putamen. The cells of the direct pathway in the caudate and putamen that receive these signals are inhibitory and, once they become activated, send inhibitory signals to the globus pallidus internus and substantia nigra pars reticulata. Thus, activation of the direct pathway will stop activity in the globus pallidus internus and substantia nigra pars reticulata. Before activation of the direct pathway, these two nuclei were actively sending inhibitory signals to the ventrolateral nucleus of the thalamus, which prevented the development of significant activity in the motor cerebral cortices. This behavior ceases on activation of the direct pathway. The net effect is to allow the activation of the ventrolateral nucleus of the thalamus which, in turn, sends activating signals to the motor cortices. These events amplify motor cortical activity that will eventually drive muscle contractions.
...
Diseases Involving the Direct Pathway
Interruption or dysfunction of the direct pathway results in hypokinesia
Hypokinesia
Hypokinesia refers to decreased bodily movement. It is associated with basal ganglia diseases , mental health disorders and prolonged inactivity due to illness, amongst other diseases.Hypokinesia describes a spectrum of disorders:...
, which is, in general terms, a disease which leads to a lack of motion.