Proptrioception Flashcards
What two things does muscle control require?
Excitation of alpha motor neurons
Continuous feedback from each muscle to the nervous system
Where does information on muscle length come from?
The muscle spindle
What is a golgi tendon organ?
It is a proprioceptive sensory receptor that senses changes in muscle tension of skeletal muscle fibres
It provides the sensory information of the golgi tendon reflex
The information is relayed to the spinal cord and cerebellum
What is proprioception?
Sense of knowing your orientation
Describe the structure of type 1a afferent fibres
They are anulospiral
They wrap around the equator of both bag and nuclear chain intrafusal muscle fibres
Describe the structure of group ii afferent fibre endings
They have a ‘flower spray’ terminal ending embedded in the equatorial regions of the nag fibres
Anulospiral afferent endings are confined to which nerve endings?
Nuclear chain fibres
What information do group 1a and group 2 sensory fibres relay?
1a = the dynamic phase of muscle stretch ie as the stretch is occuring 2 = information on the static phase of the stretch eg the muscles final length
When do muscle spindles not send action potentials?
When they are slack they stop sending action potentials so they lose proprioception
What happens when a muscle contracts?
Gamma motor neurons are co-activated with alpha motor neurons
The spindle shortens in register with the extrafusal fibres
Gamma motor neurons gather up the slack causing tension in the intrafusal spindle
What analagy can be used to decribe how gamma motor neurons work?
The fisherman - the line is slack until the fish swims towards the fisherman
This means he no longer can locate the fish due to the loss of tension
The tension has to be increased again to relocate the fish
What can increase gamma motor neuron activity?
Serotonin
What can decrease gamma motor neuron activity?
Noradrenaline (Na)
What is the effect of serotonin on the gamma motor neurons?
The intrafusal fibres become slightly stiffer in the presence of serotonin
The stiffer materials transmit stretches with greater fidelity
What is the effect of noradrenaline on gamma motor neurons?
Causes the intrafusal fibres to become elastic and floppy
Elastic materials do not transmit stretches well
What is the tendon jerk reflex?
It is the only monosynaptic reflex in the body
The muscle is stretched by a hammer blow to its tendon
This causes the primary sensory endings (group 1a) to be activated and they send action potentials along the limb to the spinal cord
The muscle contracts in opposition to the stretch and the limb jerks as a consequence
What is jendrassik’s manoevre?
The patient clenches the teeth , flexes both fingers and interlocks the fingers
The tendon below the patients knee is then hit to elicit the patellar reflex
What is the effect on the jerk reflex in the jendrassik’s manoevre?
The position of the hands causes excitation in the upper segments of the spinal cord
This excitation spins over to the rest of the spinal cortex so the alpha motorneurons which supply the quadriceps are bought more to threshold
The reflex response is therefore bigger
Describe the tonic vibration reflex
Group 2 afferents vibrate at around 50Hz when the arm is straight
Group 2 afferents fire about 20Hz when the arm is fully stretched
If a vibrator is applied to the tendon it drives the Group 2 afferents in muscle so they discharge at 100Hz
What did Sherrington show?
Showed that a reflex required sensory input from the muscle and a return pathway to the muscle
He used a the decerebrate cat to show this
Spindle 1a neurons make connections on what two types of muscles?
A homonymous muscle (a muscle that the spindle is in) Syngergistic muscles (those that help maintain contraction)
When a muscle stretches what happens to 1a firing rates?
They increase
How do 1a motor neurons cause the relaxation of the antagonists muscles?
They act through inhibitory interneurones that innervate antagonistic muscles
What is the central pathway called for the somatosensory system?
The Dorsal-Column-Medial Lemniscal system
What is the The Dorsal-Column-Medial Lemniscal system?
An ascending spinal tract carrying sensory information to the brain, mediatinf conscious proprioception
What are the three relays in the The Dorsal-Column-Medial Lemniscal system?
1) The central process of DRG cells synapse on to neurons in the gracile and cuneate nuclie in the lower medulla
2) These then ascend in to the medial lemniscus and synapse on neurons in the ventral posterior lateral nucleus of the thalamus
3) These send axons to the primary somatosensory cortex
Where are the primary and secondary somatosensory cortices located?
The anterior parietal lobe and the posterior parietal cortex
S2 is deep within the lateral sulcus
Lesioning in the primary somatosensory cortex causes what?
Produces proprioceptive deficits eg lost ability to discriminate size, texture and shape of objects
How many regions are there in the primary somatosensory cortex?
Four
