Download Control of Muscular Contraction

Control of Muscular
Contraction
Methods of Control
There are 3 main mechanisms within the body to ensure that
smooth and safe movement occurs: 1. Proprioceptors – Sense organs located in joints, tendons and
muscles. They provide kinaesthetic feedback concerning the body’s
movement.
2. Muscle Spindle Apparatus – Sensitive receptors that exist between
skeletal muscle fibres. They relay information via Afferent neurones
concerning the state of muscle contraction and the length or
extension of the muscle.
3. Golgi Tendon Organs – Thin capsules of connective tissue which
exist where muscle fibre and tendon meet. They cause a muscle to
relax if high tensions within the muscle occur.
Muscle Spindle Apparatus
Changes in the length and
rate of change of the
muscles are sensed by
receptors in the muscle
fibre called Muscle
Spindles. These consist of
very specialized muscle
fibres called Intrafusal
Fibres. These are
surrounded by the normal
fibres known as Extrafusal
Fibres.
If the muscle is stretched
or shortened it is detected
by the intrafusal fibres of
the muscle.
Nervous Supply
There are different types of nerves that have different roles within
the muscle spindle apparatus and muscle contraction itself.
Afferent Neurones –
Carry messages away from muscle/sensory organ to the CNS.
Efferent Neurones –
Carry messages from the CNS to the muscle/sensory organ.
Alpha Motor Neurones – Nerves that
supply the ‘normal’ extrafusal muscle fibres.
Gamma Motor Neurones – Nerves
that supply the Intrafusal muscle fibres.
Biceps Example

Neural Input into the
Muscle

Extrafusal fibers are
input by alpha motor
neurons


These neurons are large
and fast.
Intrafusal Fibers are
input by gamma motor
neurons


These neurons are
relatively small and
slow.
They are involved in the
control of muscle tone.
a
g
Stretch Reflex
The activation of the muscle spindle is seen in the stretch reflex. This is
where a muscle is suddenly stretched, the muscle contracts to resist the
stretch and prevent the muscle from tearing.
PRACTICAL
Test the reflexes in a partners knee by tapping there patellar tendon. What
happens to their leg and what causes this?
Now look back at the picture on the previous slide and suggest what would
happen if a weight was placed in the hand?
This stretch is detected by the sensory neurons in the arm
and transferred to the interneuron in the spinal chord.
sensory neuron
interneuron
a motor neuron
A command to further contract the muscle is sent out the
alpha motor neuron.
sensory neuron
interneuron
a motor neuron
The arm is returned to its commanded position.
sensory neuron
interneuron
a motor neuron