BMS 300 1st Edition Lecture 26Outline of Last Lecture I. Ascending and descending pathways -DCML-anterolateral system1. spinothalamic tract >pain, crude touch, pressure 2. three neuron pathway II. Brown seguard -spinal cord hemisection >what sensations get through III. The post central gyrus and the somato sensory cortex -somotrophy on the somato sensory cortex IV. The pre-central gyrus -the motor cortex >upper motor neurons >corticospinal tract >lower motor neurons V. Motor unit -the lower motor neuron and the muscle fibers it innervates These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.-functional significance of the motor unit >all or none response of the skeletal muscle cells Outline of Current Lecture VI. Motor cortex and descending pathways -somatotopy on the precentral gyrus 1. motor cortex-internal capsule -decussation of the pyramids-lateral cortico spinal tract -innervation of lower motor neurons VII. The motor unit-refination -the neuromuscular synapse -nicotinc acetycholine receptors -E.P.S.P-action potentialsVIII. Membrane systems of skeletal muscle cells -sarcolemma -T-tubule -S.R. (sarcoplasmic reticulum) IX. The T-SR junction -DHP receptors-T-tubule charge sensitive-RYR receptors-SRCurrent LectureSomatotropy in the pre-central gyrus: motor cortex -the motor cortex is bilaterally symmetrical -there are 6 layers of neuronal cell bodies -layer 5 contains the cell body of the upper motor neuron -if we would take a “walk” on this cell body we would leave the motor cortex and go intothe white matter (myelinated axons) of the internal capsule -we have white matter regions that are characterized by conductile processes that orginate at the cell bodies of the upper motor neurons -they go down to the region called the brain stem -at the modulla oblongata -a point where the brain stem joins the spinal cord -if you follow it down you will take a turn and cross over the midline called the decussation of the pyramids -decussation means cross over -these processes continue into the spinal cord -remember if this is the spinal cord there are 31 pairs of spinal cords -the white matter is heavily myelinated -these upper motor neurons are clustered at a region in the white matter called the lateral cortico spinal tract-if we were to follow the upper motor neuron then it will get off the tract and find its way into the ventral horn -all the motor neurons of the hand are all located in the ventral horn of the cervical spinal cord -the lower motor neuron then sends a process out into the ventral root and the neuron then joins the spinal nerve (bundle of conductile processessensory afferent and motor efferent) -the nerve will then find its way to synapse onto a muscleHow lower motor neuron innervates muscle -the motor unit: the lower motor neuron and group/squad of muscle fibers or cells that that it innervates -when we are talking about muscle we are talking about skeletal voluntary muscle -each lower motor neuron forms synapses on many muscle fibers but each muscle fiber only receives input from one motor neuron -each muscle contains several thousand of these muscle fibers -the muscle fibers are all skeletal/voluntary muscle -each one of these individual muscle fibers receives input from only lower motor neuron-the functional implication is when the upper motor neuron comes over and innervates the different lower motor neurons the action potential goes along the membrane and innervates different fibers -when one fires an action potential only the muscles it innervates respond -you will still have a reflex without these neurons going with the lower motor neurons Muscle Cell-extremely elongated -large diameter -3-5cm in length -.1mm diameter-one place on the muscle fiber where we form neuronmuscular synapse -synaptic clef-output region that is characterized by the synaptic vesicles -V-gated calcium channels -there are ligand gated ionotropic channels that contain nicotic acetycholine
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