CNS Motor control; Spinal Reflexes Flashcards
Describe components of a reflex arc?
- sense organ
- afferent neuron
- dorsal horn of spinal cord
- effector neurone
- ventral root
- relevant muscle
What are the levels of integration?
Spinal cord level - homeostasis and reflex actions - simplest level Subcortical level - primitive actions - securing food & reproduction Cortical level - highest level of neural activity - science & philosophy
What fibres sense changes in length of a muscle?
intrafusal fibres - lost contractile proteins and are wrapped in nerves
What organ is the length transducer in muscles and what fibres come from it?
spindle
- afferent fibres type 1a and II both myelinated but 1a faster
- efferent but fewer in order to maintain sensitivity of spindle in face of muscle shortening
What fibres are found within the spindle?
dynamic nucleus bag
Static nuclear bag fibres
Nuclear chain fibres
What are the properties and function of Dynamic nuclear bag fibres?
fibres to sense velocity
- contained in dynamic nucleus bag
- fast adapting (when stimulus changes firing rate changes quickly)
- innervated by Ia (fast)
- phasic response (senses acceleration)
What are the properties and function of Static
nuclear bag fibres?
- slowly adapting (reacts slowly to stimulus changes)
- innervated by type II (slow)
What are the properties and function of Nuclear chain fibres?
- signal absolute muscle length
- provide static response of muscle spindle
What is the function of the efferent nerves coming off the spindle?
- efferent gamma nerves are co-activated when the main alpha nerve of the muscle is activated
- when activated they help shorten the spindle too
- preventing spindle unloading and becoming neurally silent
- can also sensitise the spindle
Describe the stretch reflex?
- afferent nerves from bag and chain fibres innervate muscle when stretched
- causes contraction against stretch, damping rapid changes in muscle length
- reciprocal innervation of antagonistic muscle via inhibitory interneuron means inhibited to aiding damping
What organ can monitor force of the muscle?
Golgi tendon organ
Describe the structure/location of the Golgi tendon organ?
- Within the fascicles of a tendon (therefore in series with the muscle)
- constitutes of net of nerve endings
What will illicit firing from a Golgi tendon?
- contraction of a muscle (force)
- but not stretch
- too much force will illicit response which reduces muscle contraction
Through what pathway does the Golgi tendon feedback information and to where?
- innervates main Alpha nerve via an inhibitory interneurone
- supra-spinal system
What is clonus (symptom) and what causes it?
- Exaggerated tremor in response to small stimuli
- upper motor neurone lesion when descending inhibitory input to gamma fibres absent
What is a characteristic symptom of patients with lower motor neurone lesion and concomitant spastic paralysis?
- Inverse response to the stretch reflex
- resulting in resistance to movements to suddenly and rapidly give way
What is the Flexor reflex?
- Stimulation of flexor muscle inhibits antagonistic extensor muscle on same limb
- opposing limb (opposite side of body) will reflexively act the opposite way (extensors contract and flexors inhibited)
What is the positive supporting reflex?
- leg extends to push down on a finger touching sole of the foot
When is the positive supportive reflex useful to test?
- upper motor neurone lesions
- more evident in patients with lesions
Give examples of spinal level integrated reflexes?
- Positive supportive reflex
- Cord righting reflex
- walking
What is required to keep us standing (reflex)?
- proprioception
- sensation from soles of feet
- vestibular function
- leg muscles pressing against floor
- trunk muscles keeping gravity above base
- neck muscles hold head up
What reflexive processes are required for walking?
- pattern generators within spinal cord set alternate contractions of flexors and extensors
- precisely timed and rhythmically
