ms Lecture 7

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ms Lecture 7
2014-08-24 10:37:27

Lecture 7 of Motor Systems
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  1. What are the properties of spinal interneurones? Where is it thought that these are found?
    • Usually small
    • Multi-polar(have a number of dendrites)
    • Local projection (although some extend over much longer distances from side to side across the spinal cord or up and down over a number of segments)
    • Many inhibitory (GABA, glycine)
    • Some excitatory (glutamate)
    • Interneurones are found between one neural input and an output cell.
  2. How is grey matter organised? And what are the categories?
    • Grey matter is organised into nine layers
    • Rexed’s Laminae (LI - LIX)
    • Dorsal horn: LI-LVI  = Sensory
    • Intermediate: LVII-VIII = Interneurones
    • Ventral horn: LIX = Motor
  3. How does the classical view of interneurones differ from the modern view?
    • The Classical view, was that interneurones simply took part of very simple reflex arch actions.
    • The modern view says that interneurones is the site where there are many inputs and outputs so they can act on many different neuroneses well as motor neurons, interneurones help connect different neurones to the spinal cord.
  4. What are the different inputs that converge on interneurones? And give examples
    • Descending Inputs (Cortico-spinal, Reticulo-spinal, Rubro-spinal etc)
    • Sensory Inputs (Skin, Joint, Muscle)
    • Inputs from other INs (Proprio-spinal INs, Crossed INs, IaINs, IbINs, II INs etc)
  5. What is gating by interneurones? And give an example.
    Interneurones can act as control mechanisms to interrupt a pathway via inhibition, this is called gating. A typical example of this is the “pain gate theory” = after an injury, sensory neurones transmit the sensation of pain to the CNS, however if you rub the affected area you manage to slightly reduce the pain because this action activates mechanoreceptors that act via interneurones to inhibit the pathways transmitting the pain signal i.e. “close the pain gate" ( explained in greater detail in D&B lecture on opioid analgesics).
  6. Give examples of spinal interneurones.
    • Ia inhibitory interneurones (IaINs)
    • Ib interneurones (IbINs)
    • II interneurones (II INs) 
    • Renshaw cells LVIII crossed interneurones
    • Interneurones mediating presynaptic inhibition
    • Propriospinal interneurones
  7. Define reflex. (EASY)
    An involuntary coordinated pattern of muscle contraction and relaxation elicited by a peripheral stimulus.
  8. What happens when dorsal roots are cut? What is the stimulus and response?
    • Dorsal roots supply sensory input. By cutting it, sensory input is eliminated and there is no longer a contraction which proves that the contraction of the muscle in response to the stretch is a reflex.
    • stimulus= stretch
    • response= contraction
  9. Explain the tendon jerk reflex.
    • Primary muscle spindle detects stretch on muscle
    • Ia afferent transmits the signal (as an excitatory signal to the CNS)
    • Alpha motor neurone is excited
    • Excitation via A-alpha efferent causes the muscle to contract resulting in what we know as the tenon jerk reflex
  10. What are the functions of stretch reflexes? Give an example of what stretch reflexes can overcome.
    • Act to resist unwanted lengthening – postural role (sort of a negative feedback to control posture)
    • Coordination between opposing muscles – reciprocal inhibition (contraction agonist, relaxation antagonist) 
    • Form basis of rhythmic patterns e.g. locomotion, mastication
    • Negative feedback control of contraction
    • Natural instability.
  11. If the reflexes in the lower limb were to reduce, what would that include?
    If reflexes were reduced in the lower limb that could indicate the presence of a lesion at a lower level of the cord.
  12. How is the Ib interneurone reflex different from Ia?
  13. How is the Ib interneurone reflex different from Ia?
    • Opposite effect to that of muscle spindle receptors.  this is kind of a negative feedback control. It is possible that it has a role in limiting damagingly powerful contractions.
  14. Explain the process of a Flexion reflex.
    • 1. Reciprocal innervation - contraction of flexors, relaxation of extensors
    • 2. Crossed-extension -opposite pattern in contralateral limb.
    • 3. Withdrawal of foot from painful stimulus and postural support in opposite leg