Standing Upright Flashcards
Proprioception
Afferent input about the position of the body and its parts
Input from: muscles, tendons, joints, skin
** rough surface, know where joints are etc
* Receptors monitor length and tension of muscles: golgi tendons and spindles…. they monitor movement of joints and effect of movements on overlying skin
How do you modify muscle contraction strength?
motor unit- not the entire muscle, just the fibres it innervates. As few as four fibres or as many as thousands.
“Recruitment of motor units and the sequence of the motor units that they are recruited”
The AP will reach and cause the smallest ones to contract first.
e.g. picking up a bucket and realizing it is filled with sand- suddenly recruit more motor units
Maximum strength out of the contraction
Optimal length (weight lifter jiggling their arms before they lift to get to the optimal length)
What do muscle spindles and golgi tendon organs do?
Provide afferent info essential for controlling muscle activity
Afferent info from muscle spindles and golgi tendon organs is used in what 2 ways?
- Appraisal of motor areas of the brain about muscle length and tension
- Control of muscle length and tension in a negative feedback fashion by means of local spinal reflexes
What are motor neurons influenced by?
- Local reflex circuitry
- Descending pathways from the brain stem and cerebral cortex
Components of a simple reflex
What do higher centres do?
What does the middle level do?
What does the local level do?
Where does most descending synaptic input go?
NOT directly to motor neurons- synapse with interneurons which synapse with motor neurons. 90% of spinal cord neurons. Integrate input from higher centres, peripheral receptors, and other interneurons.
Inputs to local interneurons
Afferent fibres carry information from sensory receptors in what three sources?
What is this? What does it do?
Muscle Spindle
Detect stretch. In the fleshy part of the muscle (belly). Run parallel- detect the rate of change in which muscle fibres are stretched. Is it too quick? Or does it need to increase the speed? And change the length of the muscle fibres.
Aids in coordination and efficiency of muscle contraction.
Muscle spindle types of fibres
* Nuclear bag fibres- sense the onset of stretch.
* Nuclear chain fibres- nuclei distributed along the length of the intrafusal fibre- sense sustained stretch.
BOTH are activated on RAPID STRETCH. (can be a protective mechanism– if both fire= rapid stretch)
What are gamma motor neurons?
Efferent neuron which innervates intrafusal fibres (nuclear chain fibres)
What are alpha motor neurons?
Extrafusal fibres (nuclear bag fibres)
The more intrafusal fibres are stretched…?
The quicker the firing rate (back to the spinal cord). (the less the stretch the slower the firing rate).
Why are gamma motor neurons there?
there will be a delay in detecting the stretch– they are there to keep them muscle spindle fibres under tension. Rubber band example.
Stretches the tendon = stretches the muscle (quadricep muscle) = signal up through the sensory neuron up through the spinal cord = directly with alpha motor neuron= signal back to the quadricep = contraction of leg
quick change in posture made –> lots of things happen but what is recriprocal innervation?
Opposite muscle needs to contract= simple reflex.
Reciprocal innervation is what causes the antagonism of muscle- one is excitatory and the other is inhibitory.
Golgi tendon organs
Sensors in the tendon. Still detecting something going on in the muscle though through tension applied to the tendon. The greater the force on the tendon, the more the sensors are squeezed between the collagen fibres (firing rate increases). Protects but also about responding.
Tendon Reflex
- Sensory neuron into spinal cord (always messages going up to the brain to the higher centres)
- Synapse with 2 interneurons- inhibitory and excitatory.
** these reflexes are one motor unit, the others might be doing something different
* Can be overridden by higher centres
Flexor reflex
aka withdrawal reflex
stim of sensory neuron to spinal cord– synapses with stimulatory interneuron– stimulating hamstring to pull it away (in this case)– one motor neuron– so if you need to pull it away quickly you need to synapse with either ascending or descending motor neurons. Stimulation of the entire muscle to pull it away.
** everything going up to the brain to detect pain or stimulus
Crossed Extensor Reflex
Interneurons going across the spinal cord to relax or contract the other muscles to take the weight.
* Allows you to take the weight
* Always information going to the brain to modulate the response (put hot plate on the table instead of dropping it straight away)
Maintenance of Posture and Balance
* Reflexes: stretch and crossed extensor
* Afferent pathways involved in postural reflexes: the eyes, vestibular apparatus, proprioceptors (joints, muscle, touch)
