Nervous Circuits

Reverend Dr David C.M. TaylorSchool of Medicine

dcmt@liverpool.ac.ukhttp://www.liv.ac.uk/~dcmt

To use our understanding of the case to Be able to distinguish between upper and

lower motor neuron lesions To gain an understanding of the spinal reflexes To start to understand the control of

movement

Our objectives in this plenary

Experienced one-sided weakness in her arm and face In principle the problem could lie in the

periphery (spinal motor neurones etc.,) Or it could lie centrally (with the motor

neurones or pathways that control the spinal motor neurones)

Mrs Webster

We need to distinguish between upper and lower motor neurones.

Upper motor neurones are in the motor cortex

Lower motor neurones are in the spinal cord - think about the knee jerk reflex

So?

The descending fibres cross in the medulla en route to the spinal cord

Upper motor neurones

This image of an homunculus has been removed to avoid breach of copyright

Pathway

This image of descending motor pathways has been removed to avoid breaching copyright

Click on the black box to view video

Knee jerk reflex

stretch receptorin muscle

contraction of muscle

spinal motor neurone

Tap tendon just below patella

stretch muscle activate receptors

extensor contracts extensor mn

Renshaw cellinhibitory

interneuronesflexor relaxes flexor mn

Monosynaptic Reflex

Simple withdrawal reflex

More fully…

Full crossed extensor reflex

Simple scheme

Plan Execute

Cortical associationareas

MovementIdea Premotor andmotor cortex

Overview of control

Plan Execute

Basal ganglia

Cortical associationareas

Lateral cerebellum

intermediatecerebellum

MovementIdea Premotor andmotor cortex