Muscle stretch reflexes and proprioception Flashcards
Types of muscle receptors
Muscle spindles and Golgi tendon organs
Muscle spindles signal
Stretch
Golgi tendon organs signal
Tension produced by muscle contraction
Joint mechanoreceptors consist
Larger fibres signal joint position
Smaller Aδ fibres are most active at the extremes of movement and are protective.
Muscle spindles are situated
In the fleshy part of muscles
Golgi tendon organs are situated
In tendons at the ends of a muscle
Are muscle spindles encapsulated?
Yes
How do muscle spindles lie with extrafusal fibres?
Specialised intrafusal fibre in parallel with extrafusal fibres
Muscle spindle structure and innervation
Specialised intrafusal muscle fibers the central part of which is non-contractile and contains the nuclei.
Large diameter myelinated sensory nerve fibres wrapped around the noncontractile part of the muscle the ends of which are sensitive to stretch of the intrafusal fibre
Small diameter gamma motor nerve fibres that innervate the contractile ends of the intrafusal fibres
Two types structural types of intrafusal fibres
Nuclear chain fibres
Nuclear bag fibres
Nuclear chain fibres abundance and structure
Nuclear chain fibres (variable numbers per spindle), named because their nuclei are aligned in a single row
(chain) in the centre of the fibre
Nuclear bag fibres abundance and structure
Nuclear bag fibres (2-3 per spindle) - named because their nuclei are collected in a bundle in the middle of the fibre.
Two functional types of intrafusal fibers and their function
Static: Non-adapting (or very slowly adapting); these measure the length of the spindle at any instant.
Dynamic: Rapidly (though not completely adapting); these measure the rate of change of length
Nuclear bag fibre function
Nuclear bag fibres can be static
Only nuclear bag fibres are dynamic, the contractile ends of the dynamic bag fibres are more viscous so stretching occurs in the central nuclear part.
Nuclear chain fibre function
All nuclear chain fibres are static
Main sensory nerves sending afferents from stretch receptors in the muscle
Myelinated A-alpha and A-beta fibres.