The lateral corticospinal tract is responsible for the motor pathway of the pronator quadratus. This tract begins in the precentral gyrus of the motor cortex where a signal is transmitted from the upper motor nerve through the progression tracts of the internal capsule and through the cerebral peduncles of the midbrain. It decussates in the medulla and travels down the lateral corticospinal tract in the lateral column of the spinal cord. It then decussates in the spinal cord and synapses at the anterior horn to the lower motor neurons of the skeletal muscles.
|
|
The lateral spinothalamic tract conveys pain and temperature. In the spinal cord, the spinothalamic tract has somatotopic organization. This is the segmental organization of its cervical, thoracic, lumbar, and sacral components, which is arranged from most medial to most lateral respectively. The pathway crosses over (decussates) at the level of the spinal cord, rather than in the brainstem like the dorsal column-medial lemniscus pathway and lateral corticospinal tract.
|
|
The styloglossus, the shortest and smallest of the three styloid muscles, arises from the anterior and lateral surfaces of the styloid process near its apex, and from the stylomandibular ligament. Passing inferiorly and anteriorly between the internal and external carotid arteries, it divides upon the side of the tongue near its dorsal surface, blending with the fibers of the longitudinalis inferior in front of the hyoglossus; the other, oblique, overlaps the Hyoglossus and decussates with its fibers.
|
|
The neurons for voluntary thigh contraction originate near the summit of the medial side of the precentral gyrus (the primary motor area of the brain). These neurons send a nerve signal that is carried by the corticospinal tract down the brainstem and spinal cord. The signal starts with the upper motor neurons carrying the signal from the precentral gyrus down through the internal capsule, through the cerebral peduncle, and into the medulla. In the medullary pyramid, the corticospinal tract decussates and becomes the lateral corticospinal tract.
|
|
Those from the lowest ribs pass nearly vertically downward, and are inserted into the anterior half of the outer lip of the iliac crest; the middle and upper fibers, directed downward (inferiorly) and forward (anteriorly), become aponeurotic at approximately the midclavicular line and form the anterior layer of the rectus sheath. This aponeurosis formed from fibres from either side of the external oblique decussates at the linea alba. The aponeurosis of the external oblique muscle forms the inguinal ligament. The muscle also contributes to the inguinal canal.
|
|
In the spinal cord, the axons synapse and the secondary neuronal axons decussates and then travel up to the superior cerebellar peduncle where they decussate again. From here, the information is brought to deep nuclei of the cerebellum including the fastigial and interposed nuclei. From the levels of L2 to T1, proprioceptive information enters the spinal cord and ascends ipsilaterally, where it synapses in Clarke's nucleus. The secondary neuronal axons continue to ascend ipsilaterally and then pass into the cerebellum via the inferior cerebellar peduncle.
|
|
The cuneate fasciculus tract is responsible for the sensation of the pronator quadratus position and movement, deep touch, visceral pain, and vibration. This tract begins in the dorsal nerve root where the signal is transmitted through the dorsal horn and up the posterior column of the spinal cord. It synapses with an interneuron in the gracile nucleus. It then decussates in the medial lemniscus of the medulla, travels through the cuneate nucleus and through the medial lemniscus of the midbrain to synapse in the thalamus.
|
|
The plan to use the gastrocnemius in running, jumping, knee and plantar flexing is created in the precentral gyrus in the cerebrum of the brain. Once a plan is produced, the signal is sent to and down an upper motor neuron. The signal is passed through the internal capsule and decussates, or crosses, in the medulla oblongata, specifically in the lateral corticospinal tract. The signal continues down through the anterior horn of the spinal cord where the upper motor neuron synapses with the lower motor neuron.
|
|
All of these sensations travel along the same general pathways towards the brain. One pathwaydorsal column-medial lemniscus pathwaybegins with sensation from the periphery being sent via afferent nerve fiber of the dorsal root ganglion (first order neuron) through the spinal cord to the dorsal column nuclei (second order neuron) in the brainstem. The second order neuron's projection decussates at the medulla through medial lemniscus to the third order neurons in the thalamus. The third order neuron's axon terminates at the primary somatosensory cortex of the parietal lobe.
|
|
In the medulla, at the dorsal column, nuclei of the first-order neuron synapse with the second- order neuron, which then decussates (crosses over to the other side of the central nervous system) into the medial lemniscus. The second-order neuron then carries the information to the ventral posterolateral nucleus of the thalamus and then the somatosensory cortex in the parietal lobe. Immediately, the posterior parietal lobe synthesizes the information into a recognizable pattern. The coded information is then sent to the prefrontal cortex to devise a motor response to the stimulation.
|
|
Descending motor pathways carry motor signals from the brain down the spinal cord and to the target muscle or organ. They typically consist of an upper motor neuron and a lower motor neuron. The lateral corticospinal tract is a descending motor pathway that begins in the cerebral cortex, decussates in the pyramids of the lower medulla (also known as the medulla oblongata or the cervicomedullary junction, which is the most posterior division of the brain) and proceeds down the contralateral side of the spinal cord. It is the largest part of the corticospinal tract.
|
|