Muscle spindles, Golgi tendon organs and spinal reflexes Flashcards
What categories can intrafusal fibres be subdivided into on the basis of morphology and function?
Nuclear bag fibres (dynamic or static)
Chain fibres
What are dynamic nuclear bag fibres?
Sensitive to the rate of change of muscle length, innervated by dynamic, but not static y-MNs
What are static nuclear bag fibres?
More sensitive to the absolute length of the muscle. innervated by static y-MNs
What are chain fibres?
Sensitive to the absolute length of the muscle. innervated by static y-MNs.
Which two types of afferent fibres innervate the intrafusal fibres?
Ia (Aa) and II (AB)
Describe Ia fibres?
Form a primary annulospiral nerve ending winding around the centre of all intrafusal fibres
Describe II fibres?
More slowly conducting, form flower spray endings on all intrafusal fibres except the bag 1 dynamic type
In activities in which muscle length changes slowly and predictably only ______ ______ are active
In activities in which muscle length changes slowly and predictably only static y-MNs are active
_______ ______ are active during behaviours in which muscle length changes rapidly and unpredictably.
Dynamic y-MNs are active during behaviours in which muscle length changes rapidly and unpredictably.
Where are Golgi tendon organs located?
At the junction of muscle and tendon
What do Golgi tendon organs do?
Monitor changes in muscle tendon, they are in series with, rather than parallel to extrafusal fibres
What innervates Golgi tendon organs?
Group Ib sensory afferents (myelinated, slightly slower than Ia fibres)
What is the role of Golgi tendon organs?
Regulate muscle tension
- protect muscle from overload (weight lifting)
- regulate muscle tension to an optimal range
Group Ib afferents enter the spinal cord and synapse upon _________ ____________ which, in turn, synapse upon the ______ _______ neurones of the ___________ muscle forming the basis of the reverse myotactic reflex
Group Ib afferents enter the spinal cord and synapse upon inhibitory interneurones which, in turn, synapse upon the alpha motor neurones of the homonymous muscle forming the basis of the reverse myotactic reflex
Why is the reverse myotactic reflex important?
Proprioceptive feedback is thought to be important for the proper execution of fine motor acts
Proprioceptive axons are present in connective tissue of joints e.g.
Joint capsules and ligaments
Proprioceptive axons respond to changes in _____, ______ and ________ of movement of a joint. Also prevent excessive _______ or ________
Proprioceptive axons respond to changes in angle, direction and velocity of movement of a joint. Also prevent excessive flexion or extension
Mixture of ____ adapting and _______ adapting units that have either a ____ ________ or ___ ________ for activation (thus information concerning movement and the static, or resting position of a joint is transmitted to the CNS.)
Mixture of fast adapting and slowly adapting units that have either a high threshold or low threshold for activation (thus information concerning movement and the static, or resting position of a joint is transmitted to the CNS.)
Nocicepitve free nerve endings are found in capsule and connective tissue, __ and __ are most numerous
Nocicepitve free nerve endings are found in capsule and connective tissue, HT and SA are most numerous
Golgi-type endings are found only in _______ and __, __ are the most numerous
Golgi-type endings are found only in ligaments and HT, SA are the most numerous
Paciniform endings are found where and what is their function
Found in periosteum near the articular attachments and the fibrous part of the joint capsule
LT and SA acceleration detectors
Ruffini endings are found mainly where and what is their function
Found in joint capsule
LT and SA to detect static position and speed of movements
Proprioceptive information arises from (3)?
- muscle spindles
- Golgi tendon organs
- joint receptors
Spinal interneurones receive input from (4)
- primary sensory axons (Ia and Ib)
- Descending axons from the brain
- collaterals (branches) of LMNs
- other interneurones
Input to spinal interneurones may be _______ or _______. interneurones integrate incoming information to generate an _______
Input to spinal interneurones may be excitatory or inhibitory. interneurones integrate incoming information to generate an output
Inhibitory interneurones mediate (2)?
- inverse myotactic reflex
2. reciprocal inhibition between extensor and flexor muscles
At a joint voluntary contraction of an _______ will stretch an antagonist flexor, initiating the _______ reflex. However, _______ pathways that activate the a-MN controlling the extensor muscles also via ______ _________, inhibit the a-MNs supplying the antagonist muscles, in this case allowing extension.
At a joint voluntary contraction of an extensor will stretch an antagonist flexor, initiating the myotactic reflex. However, descending pathways that activate the a-MN controlling the extensor muscles also via inhibitory interneurones, inhibit the a-MNs supplying the antagonist muscles, in this case allowing extension.
Excitatory interneurones mediate (2)
The flexor reflex
The crossed extensor reflex
What is the crossed extensor reflex
Noxious stimulus cause slump to extend by;
- contraction of extensor muscles via excitatory interneurones
- relaxation of flexor muscles via excitatory and inibitory interneurones
Why is the crossed extensor reflex important?
Enhances postural support during withdrawal of a foot from a painful stimulus
What is the flexor reflex
Noxious stimulus cause limb to flex by;
- contraction of flexor muscles via excitatory interneurones
- relaxation of extensor muscle via excitatory and inhibitory interneurones
