Most of the axons of the anterior corticospinal tract will decussate in the spinal cord just before they synapse with lower motor neurons. The fibers of these two different branches of the corticospinal tract preferentially stimulate activity in different types of muscles. The lateral corticospinal tract primarily controls the movement of muscles in the limbs, while the anterior corticospinal tract is involved with movement of the muscles of the trunk, neck, and shoulders.
As they travel down to the spinal cord, corticospinal tract neurons send off many collateral fibers that make connections in a number of areas including the basal ganglia , thalamus , various sensory nuclei , etc.
Additionally, corticospinal tract fibers terminate in various places in the spinal cord, including the posterior horn which is normally involved in processing sensory information. These diverse connections suggest that the functions of the corticospinal tract are likely diverse as well, and that defining it as having movement as its sole function is an oversimplification.
When the upper motor neurons of the corticospinal tract are damaged, it can lead to a collection of deficits sometimes called upper motor neuron syndrome.
When such an injury occurs, it often results in a state of paralysis or severe weakness immediately following the event, usually on the side of the body opposite to the location of the injury. After several days, function begins to return, but some abnormalities persist.
The patient often displays spasticity, which involves increased muscle tone and hyperactive reflexes; motor control may also be decreased. As mentioned above, after damage to the corticospinal tract the ability to make crude movements generally returns but some deficit in fine finger movements may remain.
Also, patients may display other abnormal reflexes; the best known of these is the Babinski sign. When the sole of the foot is stroked it generally causes the toes in adults to curl inwards; in someone with damage to the corticospinal tract the toes fan outwards, an abnormal movement referred to as the Babinski sign after neurologist Joseph Babinski.
In infants, it is normal to observe the Babinski sign due to the fact that the corticospinal tract is not yet fully myelinated. Thus, the lack of a Babinski sign in infants is considered abnormal and potentially problematic, while the presence of a Babinski sign is adults is pathological and indicates possible corticospinal tract damage.
Nolte J. Philadelphia, PA. Elsevier; We experience these things every day, but how do our brains create them? The secondary neurons in the lateral spinothalamic tract cross over to the other side of the spinal cord and then ascend in the spinal cord, through the brainstem, and to the ventral posterolateral VPL nucleus in the thalamus. Because this pathway travels in the anterolateral portion of the spinal cord and brainstem, it is often referred to as the anterolateral system. In the thalamus, spinothalamic neurons synapse on cells that will carry the sensory information to the primary somatosensory cortex, which is the main processing area for sensations from the body.
The anterior spinothalamic tract aka ventral spinothalamic tract carries general touch or light touch sensations from the body. These sensations begin with sensory receptors in the skin, which pass a signal onto neurons that travel to the spinal cord.
In the spinal cord, these neurons give rise to ascending and descending branches that synapse on neurons in the dorsal horn of the spinal cord. Secondary neurons arise from the nucleus proprius in the dorsal horn, cross over to the other side of the spinal cord, and ascend to the thalamus near the lateral spinothalamic tract.
From there, the information is carried on to the somatosensory cortex. A spinal cord injury that involves the spinothalamic tract can lead to distinctive sensory deficits.
Because neurons in the tract cross over to the other side of the spinal cord before traveling up to the brain, they are carrying information from the opposite side of the body. Thus, if there is damage to one side of the spinal cord, it can cause a loss of pain, temperature, and light touch sensations on the side of the body opposite from where the damage occurred. Augustine JR. Human Neuroanatomy. We experience these things every day, but how do our brains create them?
Your Brain, Explained is a personal tour around your gray matter. Dingman weaves classic studies with modern research into easily digestible sections, to provide an excellent primer on the rapidly advancing field of neuroscience.
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