In the ventral horn, Lamina VIII and IX contain motoneurones of different types.
Flexor and Extensor Motoneurones
The diagram shows that the medial column (IX) controls extensors amd the lateral column controls flexors.
Proximal and Distal Muscle Innervation
There is a further topographic arrangement in that within any segment, the most ventral motoneurones innervate distal muscles and the motoneurones that occupy a more dorsal position in the ventral horn innervate proximal muscles in the limb.
Rostral vs Distal Segmental Arrangements
In addition, the proximal muscles of each limb are controlled by the rostral segments and the distal muscles are connected to motoneurones in lower parts of the cord innervating the limb.
Motor neurons that innervate flexor muscles are located dorsal to motor neurons that innervate extensor muscles.
Motor neurons that innervate distal muscles are located lateral to motor neurons that innervate proximal and axial muscles.
The Lateral Horn (the autonomic nucleus in the lateral part of Lamina VII)
Autonomic Pre-ganglionic Neurones
The intermediolateral nucleus (IML) is found in the lateral horn of the spinal grey matter, which is part of Rexed lamina VII. The lateral horn exists only in certain segments of the spinal cord, viz the first thoracic to the second lumbar segments (the sympathetic outflow), and from the second to the fourth sacral segments (the parasympathetic outflow).
Autonomic preganglionic neurones have finely myelinated axons that enter the ventral roots, and proceed towards either the sympathetic or parasympathetic ganglia.
The slide opposite shows a pronounced lateral horn at the level of the central canal.
The diagram opposite shows the difference between the paths of the sympathetic preganglionic neurones, which enter the sympathetic chain, and the parasympathetic neurones that innervate the bladder.
These neurones innervate the lower urinary tract.
In addition the sacral cord has a specialised group of motoneurones that innervate the skeletal muscle of the external sphincters, and the cell bodies of these motoneurones are in a part of the ventral grey matter called "Onuf's nucleus". These neurones have close functional connections with the parasympathetic system, both of which are involved in the control of continence.