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You've Got a Nerve

Tuesday 4th Nov 2014, 01.30pm

Most of us take movement and balance for granted, and it’s only when something goes wrong that we realise how complicated it is.  In the early 1900s, an Oxford researcher called Charles Sherrington examined microscope slides of muscles, nerves, the spine and the brain and traced the connections between them.  Using this box of slides, he built up a picture of how muscles are controlled. Some diseases can damage nerve cells and affect muscle control.  Researchers today still use the basic principles established by Sherrington to investigate how to fix these problems.

Who was Charles Sherrington?

Sir Charles Sherrington (1857 – 1952) was the Waynflete Professor of Physiology at the University of Oxford.  He was one of the outstanding physiologists of his time. Sherrington demonstrated that an animal’s sensory system is linked to the part of the central nervous system involved with movement.  He explored how single nerve cells communicate between each other through electrical or chemical signals.  The structures that allow this communication he called ‘synapses’.

The microscope slides

A wooden box bearing Sherrington's name and containing 21 drawers of glass microscope slides was recently rediscovered in the Physiology Department at the University of Oxford.  The box had been kept on various shelves and under benches in several offices since Sherrington retired in 1936. The glass slides are of various tissues, including nerves and other parts of the nervous system, which have been stained to help show the cellular structures.  Some of the slides represent Sherrington’s own work, and some are from colleagues, students or from collaborators.

Examination of the slides shows that, even 100 years later, they can be linked to some of Sherrington’s original publications.  The slides show the breadth and depth of his work and allow us to interpret the original research materials that have provided the foundations of modern neuroscience.

Since its rediscovery, the entire contents of the box have been examined and related to original publications (see Nat Rev Neurosci. 2010 Jun;11(6):429-36) digitally scanned and can be seen on the University of Oxford website.

What are the parts of the nervous system?

The central nervous system includes the brain and spinal cord.  It is comprised of neurons (nerve cells), glia (cells which support and protect the neurons), cardiovasculature r (which carries the blood) and the meninges (membranes which cover the brain and spinal cord).

Neurons and nerves

Neurons are electrically excitable cells that process and transmit information through electrical and chemical signals.  They are the core component of the nervous system.  There are several specialised types of neurons, including:
Sensory neurons - these respond to touch, sound, light and all other stimuli, and send signals to the spinal cord and brain.
Motor neurons – these receive signals from the brain and spinal cord and bring about muscle contractions and affect the outputs of glands such as the salivary glands.
Interneurons – these connect neurons to other neurons within the same region of the brain or spinal cord, to create neural networks.

Synapses

Synapses are specialised structures that allow a nerve cell to pass signals (electrical or chemical) to another cell. As well as coining the term ‘synapse’, Sherrington realised that some synapses can inhibit how neurons function.

Muscle Spindle

Muscles are comprised of contractile fibres, amongst which there are small spindle-shaped structures that sense the amount the muscle has contracted.  Sherrington was one of the first people to emphasise the sensory role of the muscles in regulating tone and posture. The discovery of sensory fibres in muscle spindles provided Sherrington with evidence that when a muscle is stretched, it sends this information on the muscle length to the spinal cord, which allows the animal to regulate its motor movements.

Click on the image on the right to try your hand at being a neuroscientist like Charles Sherrington. See if you can find the muscle spindle pictured above using our virtual microscope.

Reflexes

A reflex action, also known as a reflex, is an involuntary and almost instantaneous movement in response to a stimulus.

The stretch reflex is the mechanism by which a muscle contracts in response to stretching within the muscle.  This reflex is essential for standing, through the postural muscles of the neck, back and lower limbs.

Reciprocal muscle movement

The concept of reciprocal muscle movement was one of Sherrington's most important discoveries.  It states that when a muscle contracts there is a simultaneous inhibition of its partner muscle.  For example, when you flex your biceps, your triceps are inhibited to stop the muscles pulling against each other.

In 1932, Sherrington was awarded a Nobel Prize in Physiology or Medicine for his work on reflexes and muscle inhibition.

In 1932, Sherrington was awarded a Nobel Prize in Physiology or Medicine for his work on reflexes and muscle inhibition.

Sherrington’s findings in today’s research

In medicine, reflexes are often used to assess the health of the nervous system.  This is what doctors are looking for when they check the patella, or ‘knee jerk’ reflex.

Sherrington noted that following injury to the lower motor neurons (eg due to direct spinal cord injury) there is a loss of muscle tone and reflexes, but after damage in the brain (e.g. after a stroke) there was rigidity of certain joints, including the elbow, knee and neck.

Current research is examining how to remodel existing connections, or use cell replacement therapy using stem cells, to restore movement.

How can healthy people experience Sherrington’s discoveries?

Our movements and balance all depend on intact reflexes.  Our movements not only rely on the muscle stretch reflexes, but are complemented with visual information from the eyes and from the vestibulocochlear (balance) sensory organ in the inner ear.  This is why it is easier to stand on one leg with your eyes open.  Our balance and coordination is badly affected by alcohol and we find it much more difficult to navigate without the visual input in the dark.

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