Ventral horn of the spinal cord

What is the Ventral Horn of the Spinal Cord?

The spinal cord is a vital part of the human body. Protected by a chain link of bones called vertebrae, it transmits messages to and from the brain and controls important autonomic functions such as blood pressure, breathing, bladder and bowel control and the beating of the human heart.

When we decide to pick up an object from a table, there’s a complex exchange of information between our brains and the muscles in our arms and hands. If we’re suddenly exposed to threat such as a hot object, our spinal cord works to ensure a rapid response that protects us from harm.

The spinal cord is essentially a long tube that runs from the medulla oblongata at the base of the skull down to the lumbar vertebra at the hips.

This is a very complex structure, and there are many vital components within the anatomy of the spine. One of the most interesting is the ventral horn of the spinal cord which helps send impulses to the skeletal muscles so that we can walk, run and pick up a coffee cup.

What is the function of the ventral horn of the spinal cord?

The ventral horn has a number of alternative names including:

  • Anterior grey column
  • Anterior cornu
  • Anterior horn of the spinal cord

If you cut the spinal cord across, it reveals two distinct areas of white and grey matter. The white matter, on the outside, is basically a collection of nerve fibres feeding up and down the cord. The grey matter is a collection of cell bodies, neuron fibres and interneurons at the centre of the spinal cord and is shaped like a butterfly.

Grey matter and white matter in the spinal cord

This grey matter is split into various horns (so called because of their shape), one of which is the ventral horn which contains motor neurons. It sends signals out to the skeletal muscles and works with the posterior grey column which receives signals regarding touch and sensation.

When it comes to spinal cord injuries, the ventral horn can play a significant part in spasticity where impulses are sent to muscles causing uncontrolled movement. There are also a number of different medical conditions and diseases that involve damage to the ventral horn.

These include:

  • Spinal muscular atrophy
  • Amyotrophic lateral sclerosis
  • Poliomyelitis
  • Spinal and bulbar muscular atrophy

Medications such as norepinephrine work by reducing the power of alpha neurons which are present in areas like the ventral horn and are responsible for sending out muscle impulses.

Which neuronal structures are located in the ventral horn?

The ventral horns are at their largest in the area of the cervical and lumbar regions where they control muscle movement in the arms and legs.

There are different types of motor neuron in the ventral horn:

  • Alpha cells: These are more numerous than gamma cells in the ventral horn and are involved in conducting rapid impulses to the skeletal muscles.
  • Gamma cells: There are about half as many of these types of cell which are involved in conducting slow muscle impulses.

More numerous than alpha and gamma cells, however, are what are known as associated neurons.

  • Interneurons provide a connection between the ventral and the posterior horns and can be involved in reflex responses (for example, when someone flinches from a hot object).
  • The internuncial neurons are used to connect different vertebrae and transmit and receive information up and down the spinal cord.

Apart from connecting different cells, these associated neurons also have an inhibitory control in the central nervous system. While many components of the spinal cord have separate functions they all work together to complete a range of highly complex tasks.

Why does the size of the ventral horns of the spinal cord vary along its length?

The spinal cord is about 45cm long and around 1cm wide. The amount of grey matter can change depending on where in the spinal cord it is located. Take a cross-section of the cervical vertebrae, for example, and there will be more grey matter than towards the bottom of the lumbar region.

Explaining the reason for this is fairly simple. The more muscles that a particular region of the spine serves, the greater number of neurons are needed and hence the bigger the size of the ventral horn. Damage to these larger areas of nerve activity are generally a lot more catastrophic when it comes to spinal cord injuries.

Summary

The ventral horn is a complex and important part of the spinal cord. It plays a large role in sending impulses to the skeletal muscles but is also connected to other parts of the spinal cord, including the posterior grey column. Damage to this area of the spine can cause major disruption to the transmission of signals to the muscles and extreme loss of mobility.