Functions of the spinal cord

The spinal cord is responsible for two vital CNS functions. The cord  

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The spinal cord is the most anatomically inferior portion of the CNS and its functions are at the lowest level of sophistication (see Table 6.1). As mentioned earlier, the spinal cord receives sensory input from the periphery of the body and contains the cell bodies of motor neurons responsible for voluntary and involuntary movements. Once again, the involuntary and neurologically simple reflexes are processed entirely at the level of the spinal cord. Voluntary, deliberate movements are initiated and controlled by thought processes in the cerebrum. The second important function of the spinal cord is to transmit nerve impulses to and from the brain. Ascending pathways carry sensory input to higher levels of the CNS and descending pathways carry impulses from the brain to motor neurons in the spinal cord. 

Interneurons are found in all areas of the spinal cord gray matter. These neurons are quite numerous, small, and highly excitable they have many interconnections. They receive input from higher levels of the CNS as well as from sensory neurons entering the CNS through the spinal nerves. Many intemeurons in the spinal cord synapse with motor neurons in the ventral hom. These interconnections are responsible for the integrative functions of the spinal cord including reflexes. 

Methamphetamine, derived from ephedrine, and cocaine [1], and caffeine are known as CNS stimulants, though the strength of each activity is different. On the other hand, strychnine isolated from the seed of Strychnos nux-vomica (Loganiaceae) stimulates the reflex function of the spinal cord. That is to say, it is a stimulant of the spinal cord in the CNS. 

The spinal cord is classically divided into white and grey matter (Fig. 21.2). The grey matter can be organised into ten different laminae, which run continuously along the entire length of the spinal cord. Within a given section of a spinal cord, each lamina can be seen as a layer of functionally distinct cells. Laminae I to VI comprise the dorsal horn, laminae VII to IX the ventral horn, and lamina X is the substantia grisea centralis which surrounds the central canal. 

Explain the function of the gray matter of the spinal cord... 

Describe the location and function of each of the four types of neurons found in the gray matter of the spinal cord... 

All ascending tracts cross to the opposite side of the CNS. For example, sensory input entering the left side of the spinal cord ultimately terminates on the right side of the cerebral cortex. These tracts may cross — at the level of entry into the spinal cord a few segments above the level of entry or within the medulla of the brainstem. The locations of specific ascending tracts are illustrated in Figure 7.2 and a summary of their functions is found in Table 7.1. 

Signals are also transmitted to the reticular formation of the brainstem by way of the spinoreticular tract. The reticular formation plays an important role in the response to pain. First, it facilitates avoidance reflexes at all levels of the spinal cord and, second, it is responsible for the significant arousal effects of pain. Signals from the reticular formation cause an increase in the electrical activity of the cerebral cortex associated with increased alertness. Furthermore, it sends nerve impulses to the hypothalamus to influence its functions associated with sudden alertness, such as increased heart rate and... 

Even in the case of spinal cord injury where application of anti-Nogo antibodies results in regeneration of the cut axons, an additional important element for functional recovery is enhanced fiber growth from the unlesioned fibers, i.e. compensatory plasticity, as discussed above. After high corticospinal tract injury in the rat at the level of the medullary pyramid and treatment with anti-Nogo antibodies, rubrospinal pathways were shown to sprout into deafferented areas of the spinal cord, resulting in high levels of functional recovery, i.e. a functional switch in the remodeled pathway [42]. 

It is indicated in spasticity due to neurological disorders e.g., multiple sclerosis, chronic myelopathy, degenerative diseases of the spinal cord, cerebrovascular accidents and cerebral palsy painful muscle spasm associated with static and functional disorders of the spine (cervical and lumbar syndromes) painful muscle spasm following surgery e.g., for herniated intervertebral disc or for osteoarthritis of the hip. 

The 5-HT3 receptor is the only monoamine neurotransmitter receptor that functions as a lig-and-gated ion channel, controlling the flux of Na-i- and K+ ions. 5-HT3 receptors are located on parasympathetic nerve terminals in the gastrointestinal tract, and high densities are found in areas of the brain associated with the emetic response, such as the area postrema. The antiemetic effects of 5-HT3 antagonists, such as ondansetron, result from actions at these sites. 5-HT3 receptors in the dorsal horn of the spinal cord have been implicated in nociception and development of new 5-HT3 receptor-related compounds may have potential as non-opioid, non-addictive analgesics. 

The central nervous system (CNS) - the brain and spinal cord - is involved in the reception and interpretation of peripheral afferent nociceptive impulses. Reflexes mediated by spinal interneurons and the gating functions of the dorsal horn of the spinal cord are particularly crucial. However, our knowledge of brain mechanisms is still limited. 

Studies to elucidate the functional role of NO have used inhibitors of NO synthase such as L-NAME and L-NMMA (see below). Systemic and intrathecal injections of NO synthase inhibitors have been shown to reduce noxious responses to formalin and carrageenan-induced hyperalgesia (Sakurada et al., 2001). Furthermore, NO-induced mechanical hyperalgesia has been reported to be mediated by supraspinal centers and does not occur in in vitro preparations of the spinal cord. 

The human body consists of approximately 1015 cells. Cells can have a variety of shapes and sizes according to their specialized functions. A typical cell has a rounded shape and is about 10 pm in diameter. Nerve cells can be very long. The nerve cells that run all the way from the tips of one s toes to the base of the spinal cord are about 1 m in length. Epithelial cells that line capillaries are extremely flat to minimize flow resistance. Bone cells (osteocytes) have a star shape to better interlock with neighboring cells and impart strength and rigidity.3... 

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