Standing Upright

Question 1

Proprioception

Answer 1

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

Question 2

How do you modify muscle contraction strength?

Answer 2

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

Question 3

Maximum strength out of the contraction

Answer 3

Optimal length (weight lifter jiggling their arms before they lift to get to the optimal length)

Question 4

What do muscle spindles and golgi tendon organs do?

Answer 4

Provide afferent info essential for controlling muscle activity

Question 5

Afferent info from muscle spindles and golgi tendon organs is used in what 2 ways?

Answer 5

1. Appraisal of motor areas of the brain about muscle length and tension
2. Control of muscle length and tension in a negative feedback fashion by means of local spinal reflexes

Question 6

What are motor neurons influenced by?

Answer 6

1. Local reflex circuitry
2. Descending pathways from the brain stem and cerebral cortex

Question 7

Components of a simple reflex

Answer 7

Question 8

What do higher centres do?

Answer 8

Question 9

What does the middle level do?

Answer 9

Question 10

What does the local level do?

Answer 10

Question 11

Where does most descending synaptic input go?

Answer 11

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.

Question 12

Inputs to local interneurons

Answer 12

Question 13

Afferent fibres carry information from sensory receptors in what three sources?

Answer 13

Question 14

What is this? What does it do?

Answer 14

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.

Question 15

Muscle spindle types of fibres

Answer 15

* 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)

Question 16

What are gamma motor neurons?

Answer 16

Efferent neuron which innervates intrafusal fibres (nuclear chain fibres)

Question 17

What are alpha motor neurons?

Answer 17

Extrafusal fibres (nuclear bag fibres)

Question 18

The more intrafusal fibres are stretched…?

Answer 18

The quicker the firing rate (back to the spinal cord). (the less the stretch the slower the firing rate).

Question 19

Why are gamma motor neurons there?

Answer 19

there will be a delay in detecting the stretch– they are there to keep them muscle spindle fibres under tension. Rubber band example.

Question 20

Answer 20

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

Question 21

quick change in posture made –> lots of things happen but what is recriprocal innervation?

Answer 21

Opposite muscle needs to contract= simple reflex.

Reciprocal innervation is what causes the antagonism of muscle- one is excitatory and the other is inhibitory.

Question 22

Golgi tendon organs

Answer 22

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.

Question 23

Tendon Reflex

Answer 23

1. Sensory neuron into spinal cord (always messages going up to the brain to the higher centres)
2. 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

Question 24

Flexor reflex

Answer 24

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

Question 25

Crossed Extensor Reflex

Answer 25

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)

Question 26

Maintenance of Posture and Balance

Answer 26

* Reflexes: stretch and crossed extensor

* Afferent pathways involved in postural reflexes: the eyes, vestibular apparatus, proprioceptors (joints, muscle, touch)