Proprioception Flashcards
What is proprioception?
The sense of knowing what the orientation of the body is in space
What information does the brain use in proprioception?
Muscle length
Where does the information for the muscle length come from?
The spindle
Muscle spindles lie _____ to the muscle fibres
Parallel
Anything inside the spindle is…?
Intrafusal
Anything outside the spindle is…?
Extrafusal
Fluid around the spindle is called
Endolymph
What type of ending do type Ia fibres have?
Anulospiral
What type of ending do type II fibres have?
Flower spray
Pulling apart of anulospiral endings does what?
Activates action potentials in the axon
Where are group II endings embedded?
In the equatorial regions of the bag fibres
But have anulospiral endings largely confined to nuclear chain fibres
Group Ia sensory endings relay information on the _____ phase of muscle stretch
Dynamic
Group II endings relay information on the _____ phase of the muscle stretch
Static
Group Ia fibres give us information on what?
When the stretch is occurring
Group II fibres give us information on what?
When the muscle is at its final length
Muscle spindles are only useful when they are _____
Under tension
When the muscle contracts what is activated?
Gamma-motor neurones co-activated with alpha-motorneurones
Spindle shortens in register with extrafusal fibres
Why do you get alpha-gamma co-activation?
So that you don’t get unloading of the spindle and therefore tension is maintained
What happens to gamma-motorneurones in the presence of serotonin?
Increased activity
What happens to gamma-motorneurones in the presence of NA?
Decreased activity
By slightly stimulating the gamma-motorneurone with serotonin, what happens?
The intrafusal fibres can be made slightly stiffer
Stiffer materials transmit stretches _____
Better
By inhibiting the gamma-motorneurones with NA, what happens?
The intrafusal fibres can be made more elastic and floppy
Do elastic materials transmit stretches well and why?
No
Because they themselves stretch
Tendon Jerk Reflex
Only monosynaptic reflex
Primary sensory endings (Ia) are activated and send action potentials along the limb to the spinal cord
It has a single synapse with the homonymous muscle’s a-neurone and produces an action potential in it
The muscle contracts in opposition to the stretch and the limb jerks
Jendrassik’s manoeuvre
Causes excitation in upper segment of the spinal cord (C5)
Excitation spills over the rest of the spinal cord
Spill over effects the gamma-motorneurone pool, which makes the intrafusal fibres stiffer and more sensitive
Tonic vibration reflex
On flexion, group II afferents frequency decreases
Vibrator applied to tendon drives the Group II afferents in muscle so they discharge at much higher frequency
The Stretch Reflex
Opposes the lengthening of a muscle
Polysynaptic refelx
Spindle Ia makes excitatory connections on homonymous and synergistic muscle
Ia’s also act through inhibitory interneurones that innervate antagonistic muscles
When muscle stretched, Ia firing rate increases
Causes contraction of the homonymous and synergist muscles and relaxes antagonistic muscles
Reflex counteracts the stretch, enhancing the springiness of the muscle
Homonymous muscle
Muscle that the spindle is in
Synergistic muscle
Muscles that help the main muscle contraction
Where is proprioceptive information processed?
At the level of the spinal cord
What does the somatosensory cortex do?
Higher level processing such as touch information
What is the central pathway for proprioceptive information?
Dorsal Column - Meidal Lemniscal System
