Reflexes Flashcards
(29 cards)
What three classes of movement do we have?
- Voluntary
- Reflexes
- Rhythmic motor patterns
What is meant by voluntary movement?
complex actions (reading and writing), purposeful goal orientated (directed, learned)
What is meant by reflex movement?
involuntary, rapid and stereotyped - knee jerk, eye blink
What is meant by rhythmic motor pattern movement?
combines voluntary and reflexive acts such as chewing and walking. the initiation and termination are voluntary but the rest is generally reflexive. To do these, we need a centre pattern generator element.
What are the components of the monosynaptic reflex arc?
- A detectable change in environment
- A receptor detects change and this sends a signal along the afferent pathway
- Signal is received by integrating centre along with those from other stimuli
- These signals reach the effector and mediate a response
- Sometimes the response gives negative feedback
[ in the integrating centre this is compared to a ‘set point’ and then the integrating centre sends another signal along the efferent pathway ]
Why do we have muscle spindles innervated by motor neurons?
If we weren’t able to change the length of muscle spindle, we would lose information about its change in length.
Where does locomotion occur?
in the spinal cord
How is movement coordinated?
Propriospinal tracts they allow limbs to communicate with each other allowing for coordinated movement and balance maintenance. Locomotion occurs within the spinal cord and so we need communication between different levels. Reflexes bring about this rhythmic action.
Where are centre pattern generators located and why?
In the spinal cord. Capable of autonomous signals and are modulated by proprioception input.
What are CPGs initiated by?
mesencephalic locomotor region.
Where is output from CPG through?
reticular nuclei and reticulospinal tracts.
What can CPGs be modelled by?
inhibitory Ia interneurons and Renshaw cells (RCs)
Where do inhibitory interneurons receive their information?
They have information coming in from muscle spindle fibres and GTOs but also from the cross-extensor withdrawal reflex aswell.
Where are alpha-motor neurons found?
They lie in clumps within the ventral horn or spinal cord (LMNs).
Explain the relationship between alpha motor neurons and muscle fibres
Some axons branch back into the spinal cord and synpase with interneurons called Renshaw cells..
This suppresses weakly firing motor neurons and produced economical movement.
When are alpha motor neurons and muscle fibres important?
Importance reflected in Strychnine positioning - disables Renshaw inhibition leading to convulsions.
What is meant by a polysynaptic reflex?
Synapse with interneurons before synapsing with alpha motor neurons. Stimulation of alpha motor neurons allows AP to travel down the motor neuron.
What is the main function of the alpha motor neurons and Renshaw cells?
They allow dampening down of very active firing activity. If you experience great pain, there are a lot of signals travelling down alpha motor neuron meaning that the muscle will move very quickly and also very forcefully. Renshaw cells have the ability to make this a smooth movement. This is because strychnine specifically disables Renshaw cells in the spinal cord leading to very forceful contractions and convulsions.
What is meant by a withdrawal reflex?
protective reflex of rapidly moving limb away from a dangerous stimulus. Stimulation of limb elicits extension of contralateral limb helping to maintain balance and posture.
What must you be able to do to move away from a stimulus/
Move your weight and centre of balance.
Describe the step cycle
STEP 1: stance phase - foot touching the ground
STEP 2: swing phase - flexion of hip, knee and ankle followed by extension.
Stance and swing phase are out of sync.
What is the purpose of the Inverse Myotactic reflex (GTO reflex)?
It is protective in preventing tearing of muscle detachment on tendon.
Also contributes to the maintenance of posture.
What is the Myotactic reflex (GTO reflex) stimulated by?
stimulated by an increase in muscle tension. Signals are transmitted to the spinal cord and the reflex is completely inhibitory.
What is the effect of negative feedback in the myotactic (GTO) reflex?
negative feedback mechanism prevents excess muscle tension. Inhibitory effect can be so great that is leads to unloading of the muscle suddenly.
