Lecture 12- Lower Motorneuron Flashcards
What are the 3 classes of input to lower motorneurons?
- direct sensory input 2.lot of the signals from spinal cord,indirect and local interneuron input to lower motorneurons 3.and descending inputs
What is the overall organisation of neural structures that control movement?
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What do the skeletal muscles do?
-do the moving -receive excitation from the spinal cord or brain stem
What is a motor neuron pool?
pools= has many nerves innervating a muscle lower motor neuron= sends its axon out and excites muscle
In what way are motorneurons a final common pathway?
- if you’re going to have any effect on movement, must be from signals that come through the lower motorneuron
How are the cerebellum and basal ganglia involved in motor control?
-major role in motor control, but they don’t project directly
What are reflexes?
-the simplest motor behaviours
Where are the motorneurons located?
- in ventral part of the spinal cord
- then interneurons are nearby, some projecting to the motor neurons pools and some get descending input
With what experiment did they figure out the spatial distribution of motor neurons in the ventral horn of the spinal cord?
- inject dye in muscles on the calf and see what dye is where in the spinal cord, can tell by this what nerves innervate what bits
- see constellations (motor pools of that muscle
What are muscles and how are they innervates?
-excitatory contractile tissue -excitatory motor neurons-exist in constellations /clusters in relation to the muscles they innervate
What is the somatotopic organisation of lower motor neurons?
- neurons that are medial= closer to the midline = innervate muscle that is medial
- the lateral muscles (further from the midline, like fingers etc,) innervated by more lateral nerves
- somatotopy, mapping
- also ventral and dorsal mapping, neurons in the ventral part innervate ventral -dorsal neurones supply dorsally located muscles
What are the interneurons connecting the medial motor neurons?
- tend to be long, link up big spans, connect medial motor neurons
- medial motor neurons usually connect axial muscle (close to the spine) versus the pectoral girdle
- the midline muscle= used to balance oneself= so want to do more things at the same time(more interconnected)
- those interneurons are much more interconnected than the interneurons connecting laterally that innervate the digits = those don’t have that much interconnection
- in the picture the long distance local circuit neurons
What does midline muscle tend to do?
- tends to be for postural control
What does distal muscle tend to do?
-lateral neurons) tends to be for more dextrous voluntary movement
Why are the medial motor neurons connected by the long local circuits?
-innervate midline muscle -the midline muscle= used to balance oneself= so want to do more things at the same time (more interconnected)
What is a motor unit?
- element of muscle control
- for each of the neuron= how many muscle fibres does it activate
- size differs with muscle
Why are the muscle fibres one neuron innervates distributed in the muscle?
-the force of a muscle is so great that if you activated just one area you could tear the muscle, this way you don’t