Medical brain notes 24

  Internal Structure of the Spinal Cord The arrangement of white and grey matter and the division of grey matter into ventral, dorsal and lateral columns has been seen.         We have also noted that the white matter of the spinal cord is divisible into anterior, posterior, and lateral funiculi. These funiculi are made up of fibres running up and down the cord.         The relative amount of grey and white matter, and the shape and size of the grey columns, vary at different levels of the spinal cord (Fig. 5.1). The amount of grey matter to be seen at a particular level can be correlated with the mass of tissue to be supplied. It is, therefore, greatest in the region of the cervical and lumbar enlarge-ments which supply the limbs. The amount of white matter undergoes progressive increase as we proceed up the spinal cord. This is a result of the fact that: a.          ...

  Grey Matter of the Spinal Cord Subdivisions of Grey Matter The grey matter of the spinal cord may be subdivided in more than one manner.         Traditionally, the ventral grey column has been divided into a ventral part, the  head , and a dorsal part, the  base.  Similarly, the dorsal grey column has been subdivided (from anterior to posterior side) into a  base,  a  neck , and a  head . These subdivisions have, however, been found to have little importance. Nuclei in spinal grey matter         An attempt has been made to recognise discrete collections of neurons (or nuclei) in various regions of the spinal grey matter. These are illustrated in the left half of Fig. 5.2.          The neurons of the ventral grey column ( ventral horn cells ) are arranged in the form of several discrete and elongated groups. We can recognize a.  ...

  Subdivisions of Grey Matter The grey matter of the spinal cord may be subdivided in more than one manner.         Traditionally, the ventral grey column has been divided into a ventral part, the  head , and a dorsal part, the  base.  Similarly, the dorsal grey column has been subdivided (from anterior to posterior side) into a  base,  a  neck , and a  head . These subdivisions have, however, been found to have little importance. Nuclei in spinal grey matter         An attempt has been made to recognise discrete collections of neurons (or nuclei) in various regions of the spinal grey matter. These are illustrated in the left half of Fig. 5.2.          The neurons of the ventral grey column ( ventral horn cells ) are arranged in the form of several discrete and elongated groups. We can recognize a.       ...

  Significance of Neurons in Grey Matter of Spinal Cord The  ventral horn cells  of the spinal cord may be functionally divided into three major categories as follows. a.                The most prominent neurons with large cell bodies and prominent Nissl substance are designated  alpha neurons . These are somatic efferent neurons (Fig. 3.1). Their axons ( alpha efferents)  leave the spinal cord through the ventral nerve roots of spinal nerves and innervate skeletal muscle. They occupy lamina IX of the ventral grey column. b.                Some smaller neurons designated as  gamma neurons  are also located in lamina IX. They supply intrafusal fibres of muscle spindles (Fig. 4.2). Sensory impulses arising in the spindle travel to the spinal cord and reach the alpha neurons. The gamma neurons thus influence the acti...