Share Flipboard Email. Regina Bailey. Biology Expert. Regina Bailey is a board-certified registered nurse, science writer and educator. Featured Video. Cite this Article Format. Bailey, Regina. Basal Ganglia Function. Hypothalamus Activity and Hormone Production. Cingulate Gyrus and the Limbic System. Divisions of the Brain: Forebrain, Midbrain, Hindbrain.
Function and Layers of the Meninges in the Brain. Discover the Mysteries of Broca's Area and Speech. Your Privacy Rights. A diffuse region of gray matter throughout the brain stem, known as the reticular formation , is related to sleep and wakefulness, such as general brain activity and attention.
The general level of alertness is controlled by the reticular formation. The cerebellum is largely responsible for comparing information from the cerebrum with sensory feedback from the periphery through the spinal cord. It accounts for approximately 10 percent of the mass of the brain. The cerebellum consists of 2 cerebellular hemispheres separated by a worm-like structure called the vermis Figure Figure Cerebellar Hemispheres.
On the right is a posterior view of the cerebellum. The cerebellum has 2 cerebellar hemispheres separated by a middle structure called the vermis. Descending fibers from the cerebrum have branches that connect to neurons in the pons. Those neurons project into the cerebellum, providing a copy of motor commands sent to the spinal cord. Sensory information from the periphery, which enters through spinal or cranial nerves, is copied to a nucleus in the medulla known as the inferior olive.
Fibers from this nucleus enter the cerebellum and are compared with the descending commands from the cerebrum. If the primary motor cortex of the frontal lobe sends a command down to the spinal cord to initiate walking, a copy of that instruction is sent to the cerebellum.
Sensory feedback from the muscles and joints, proprioceptive information about the movements of walking, and sensations of balance are sent to the cerebellum through the inferior olive and the cerebellum compares them.
If walking is not coordinated, perhaps because the ground is uneven or a strong wind is blowing, then the cerebellum sends out a corrective command to compensate for the difference between the original cortical command and the sensory feedback. The output of the cerebellum is into the midbrain, which then sends a descending input to the spinal cord to correct the messages going to skeletal muscles. The description of the CNS is concentrated on the structures of the brain, but the spinal cord is another major organ of the system.
Whereas the brain develops out of expansions of the neural tube into primary and then secondary vesicles, the spinal cord maintains the tube structure and is only specialized into certain regions. As the spinal cord continues to develop in the newborn, anatomical features mark its surface.
The anterior midline is marked by the anterior median fissure , and the posterior midline is marked by the posterior median sulcus. Axons enter the posterior side through the dorsal posterior nerve root , which marks the posterolateral sulcus on either side.
The axons emerging from the anterior side do so through the ventral anterior nerve root. You should learn to be comfortable with both. On the whole, the posterior regions are responsible for sensory functions and the anterior regions are associated with motor functions.
This comes from the initial development of the spinal cord, which is divided into the basal plate and the alar plate. The basal plate is closest to the ventral midline of the neural tube, which will become the anterior face of the spinal cord and gives rise to motor neurons.
The alar plate is on the dorsal side of the neural tube and gives rise to neurons that will receive sensory input from the periphery. The length of the spinal cord is divided into regions that correspond to the regions of the vertebral column.
The name of a spinal cord region corresponds to the level at which spinal nerves pass through the intervertebral foramina. Immediately adjacent to the brain stem is the cervical region, followed by the thoracic, then the lumbar, and finally the sacral region.
The spinal cord is not the full length of the vertebral column because the spinal cord does not grow significantly longer after the first or second year, but the skeleton continues to grow. The nerves that emerge from the spinal cord pass through the intervertebral formina at the respective levels. The sacral spinal cord is at the level of the upper lumbar vertebral bones.
The spinal nerves extend from their various levels to the proper level of the vertebral column. The posterior horn is responsible for sensory processing. The anterior horn sends out motor signals to the skeletal muscles. The lateral horn , which is only found in the thoracic, upper lumbar, and sacral regions, is the central component of the sympathetic division of the autonomic nervous system. Some of the largest neurons of the spinal cord are the multipolar motor neurons in the anterior horn.
The fibers that cause contraction of skeletal muscles are the axons of these neurons. The motor neuron that causes contraction of the big toe, for example, is located in the sacral spinal cord.
The axon that has to reach all the way to the belly of that muscle may be a meter in length. The neuronal cell body that maintains that long fiber must be quite large, possibly several hundred micrometers in diameter, making it one of the largest cells in the body.
Just as the gray matter is separated into horns, the white matter of the spinal cord is separated into columns. Ascending tracts of nervous system fibers in these columns carry sensory information up to the brain, whereas descending tracts carry motor commands from the brain. Looking at the spinal cord longitudinally, the columns extend along its length as continuous bands of white matter. Between the two posterior horns of gray matter are the posterior columns.
Between the two anterior horns, and bounded by the axons of motor neurons emerging from that gray matter area, are the anterior columns. The white matter on either side of the spinal cord, between the posterior horn and the axons of the anterior horn neurons, are the lateral columns. The posterior columns are composed of axons of ascending tracts. The anterior and lateral columns are composed of many different groups of axons of both ascending and descending tracts—the latter carrying motor commands down from the brain to the spinal cord to control output to the periphery.
Watch this video to learn about the gray matter of the spinal cord that receives input from fibers of the dorsal posterior root and sends information out through the fibers of the ventral anterior root. As discussed in this video, these connections represent the interactions of the CNS with peripheral structures for both sensory and motor functions. The cervical and lumbar spinal cords have enlargements as a result of larger populations of neurons.
Unable to process the form. Check for errors and try again. Thank you for updating your details. Log In. Sign Up. Become a Gold Supporter and see no ads. Log in Sign up. Articles Cases Courses Quiz. About Recent Edits Go ad-free. Edit article. View revision history Report problem with Article. Recordings from these neurons in monkeys have shown that they tend to respond when the monkey receives an unexpected reward, and they tend to be inhibited when the monkey fails to receive an expected reward Figure 4.
In this way, motor habits can be constructed that tend to reward the animal. As mentioned earlier, there are a number of cortical loops through the basal ganglia that involve prefrontal association cortex and limbic cortex.
Through these loops, the basal ganglia are thought to play a role in cognitive function that is similar to their role in motor control. That is, the basal ganglia are involved in selecting and enabling various cognitive, executive, or emotional programs that are stored in these other cortical areas. Moreover, the basal ganglia appear to be involved in certain types of learning. For example, in rodents the striatum is necessary for the animal to learn certain stimulus-response tasks e.
Recordings from rat striatal neurons show that early in training, striatal neurons fire at many locations while a rat learns such a task on a T-shaped maze Figure 4. This suggests that initially the striatum is involved throughout the execution of the task. As the animal learns the task and becomes exceedingly good at its performance, the striatal neurons change their activity patterns, firing only at the beginning of the trial and at the end. A A rat is trained to run down a T-shaped maze and make a left turn for food reward if it hears a high-pitch tone or make a right turn for food reward if it hears a low-pitch tone.
B Early in training, as the rat is beginning to learn the task, striatal neurons fire at locations all over the maze, especially at the choice point. C Late in training, when the rat has mastered the task and performs very quickly and accurately, the striatal neurons now fire only at the start and ends of the maze. In humans, the basal ganglia appear to be necessary for certain forms of implicit memory tasks. Like motor habit learning discussed above, many types of cognitive learning require repeated trials and are often unconscious.
An example is probabilistic classification Figure 4. In this type of task, people have to learn to classify objects based on the probability of belonging to a class, rather than on any explicit rule. In one experiment, subjects were shown a deck of cards with different symbols. Each symbol was associated with a certain probability of predicting rain or sunshine, and the subjects had to say on each trial whether the symbol was a predictor of rain or sunshine.
Because the same symbol sometimes predicted sunshine and other times predicted rain, the subjects could not devise a simple rule, and they made many errors at first. Over time, however, they began to get better at classifying the symbols appropriately, although they still often claimed to be guessing.
Patients with basal ganglia disorders were impaired at this task, suggesting that the processing of the cognitive loops of the basal ganglia are somehow involved in our ability to subconsciously learn the probabilities of predicted outcomes associated with particular stimuli. A number of neurological disorders result from damage to the basal ganglia. More thorough treatment of these disorders will be given in the chapter on Disorders of the Nervous System. Click on disease names to see neural damage that produces the disorders.
Patients have difficulty initiating movements, and once initiated the movements are abnormally slow. 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. Often these movements resemble pieces of adaptive movements, but they occur involuntarily and without behavioral significance.
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.
Claustrum and amygdala. Substantia nigra pars compacta and globus pallidus external. Globus pallidus internal and substantia nigra pars reticulata. Centromedian nucleus and subthalamic nucleus.
The caudate and putamen are the only parts of the basal ganglia that receive direct cortical input. Dopaminergic neurons of the substantia nigra signal unexpected reward or unexpected absence of reward. The subthalamic nucleus is the origin of the only purely excitatory pathway within the basal ganglia intrinsic circuitry. The net effect of excitation of the direct pathway is to inhibit cortex.
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