What type of sensory fibres are found in muscle spindle?
Type Ia and Type II fibres
Describe the myotatic reflex
Stretching a muscle, and the muscle spindle, results in reflex contraction of the muscle via alpha motor neurones coming from the spinal cord
Give an example of how the myotatic reflex helps to maintain posture
The stifle joint is maintained by extensors i.e. quadriceps running across the joint. Gravity tends to flex the joint. The effect of this is to stretch the extensor muscles which leads to their contraction through the myotatic reflex and this maintains the joint.
The myotatic reflex is a fast/slow reflex?
Fast
Is the myotatic reflex adaptive or non-adaptive?
Non-adapting
Describe the spinal reflex seen due to pressure receptors in the paws of an animal (and the buttress reaction)
If an animal is held up with its eyes covered and pressure applied to their back paw this causes extension of the limb. The buttress reaction occurs when an animal doesn't want to move forward: if you pull them this applies extra pressure to their front paws, causing extension of the front limbs and makes it harder for you to move them.
What is the function of the positive supporting reaction? How does it do this?
This acts to bring the altitude of the body and head up to its normal supporting position. If an animal is standing on a slope and, for example, more pressure is applied on the back legs than the front then the back limbs will extend and the forelimbs will flex to correct the body and head position.
Describe the positive sway reaction
If you push an animal from the side more pressure is applied to the paws on the opposite side, causing extension of the limbs opposite to the side the force was applied on.
What are the postural reflexes?
The head-righting reflex, the tonic vestibular-ocular reflex, the dynamic vestibular ocular reflex and dynamic postural vestibular reflex
Where do postural reflexes come from?
The vestibular apparatus (otolith organs and semicircular canals)
What do the otolith organs and semicircular canals measure?
What set of reflexes do the otolith organs give rise to?
The tonic vestibular reflexes
Describe the head righting reflex
This tries to maintain the head at its normal altitude i.e. when you push an animals head down they will bring it up to normal position
Describe the tonic vestibule-ocular reflex
If you hold an animals head down their eyes will rotate up to try and keep the normal fixation point
Which reaction will support the tonic vestibular reflexes?
The positive supporting reaction
What set of reflexes do the semicircular canals give rise to?
The dynamic vestibular reflexes
Describe the dynamic vestibular ocular reflex
If an animal is being rotated the DVOR causes the eyes to slowly rotate in the direction opposite to that of rotation of the head. This rotation is limited by the eye socket and when the eyes reach the limit of rotation they flick very quickly back in the same direction of the head and then start to rotate slowly against the direction of the head, and so on.
What is the term for the quick flicking of the eyes during the dynamic vestibular ocular reflex?
Vestibular nystagmus
Describe the dynamic postural reflex
When you rotate an animal around eventually the semicircular canals will adapt to the movement. Then when the rotation stops the semicircular canals think the animal is moving in the opposite direction very quickly, so they predict you are about to fall over and make you move quickly in the same direction you were originally rotating in.
What happens if you get different information coming from the eyes and vestibular apparatus?
You get motion sickness, and it usually causes vomiting
Describe the neck reflex
The neck is the equal but opposite reaction to the tonic vestibular head righting reflex. It allows the animal to move its head down e.g. to eat.
... in the neck provide proprioceptive information about the position of our head relative to the body?
Mechanoreceptors
Why is using reflexes to correct our posture an advantage?
There is no need to have conscious input into every action by having these reflexes. This is a quicker and more reliable way of getting the correct posture and head position than using conscious thought.
What is the difference between tonic vestibular reflexes and dynamic vestibular reflexes?
Tonic vestibular reflexes measure what has happened to us and react to a situation that has already occurred. Whereas dynamic vestibular reflexes are not reactive reflexes - they try t predict what will happen and prevent it. They are also generally stronger than the tonic reflexes.
Describe how overall posture is regulated
The visual and vestibular system act on the vestibular nucleus and cerebellum. The vestibular nucleus and cerebellum then act through an integrating centre in the neck. Inputs going through the integrating centre cause postural adjustment. Acting on these postural adjustments are pressure receptors and other spinal reflexes, such as the myotatic reflex.
True or false: locomotion is caused by spinal reflexes?
False - it largely a spinal phenomenon but is not caused by spinal reflexes.
What causes locomotion?
Central pattern generators which lie within the spinal cord
What initiates and stops locomotion?
Higher centres in the brain
What type of nervous input goes into muscles?
Alpha and gamma neurones
How does the myotatic reflex help main the angle of a joint with a variable load?
If you have a variable force acting on the joint then if you act just using alpha input you have to constantly measure he angle of the joint and adjust alpha input appropriately. Gamma input allows contraction of the muscle through the myotatic reflex and so any variable load can by countered using the myotatic reflex. This is a simpler way of maintaining the angle of a joint.
What does an increase/decrease in the load of a joint do to the myotatic reflex?