Exam 8 (CH. 13) Flashcards
What is a motor unit? What is a motor pool?
- one alpha motor neuron and all the skeletal muscle fibers it innervates
- all the alpha motor neurons innervating the fibers of a single skeletal muscle
What are lower motor neurons? What are alpha motor neurons? What are gamma motor neurons? Where are all these located? What is their function? Where are the cell bodies?
- is the somatic motor neuron in the ventral horn of the spinal cord. Directly commands muscle contraction
- are lower motor neurons that directly trigger the generation of force by muscles (spinal cord; anterior grey column of the spinal cord)
- are lower motor neurons that that innervates intrafusal fibers (spinal cord; anterior grey column of the spinal cord)
What are some of the spinal reflexes we have talked about? What do they provide?
- myotatic (stretch) reflex: leads to muscle contraction in response to muscle stretch, mediated by the monosynaptic connection between group Ia axons from a muscle spindle and an alpha motor neuron innervating the same muscle.
- flexor reflex: (excitatory interneuron) used to withdraw a limb from a aversive stimulus (withdrawal of your foot from a thumbtack)
- crossed extensor reflex: used to compensate for the extra load imposed by limb withdrawal on the antigravity extensor muscles of the opposite leg.
Within the muscle fiber, what structures are present, and what is their function? Think about this from a few levels-what structures are present, and what happens to generate muscle contractions? Consider the cellular structure – what what organelles, what proteins?
sarcoplasmic reticulum has a bag of Ca2+ and when an action potential from that motor neuron hits that muscle, it’s going to generate a lot of Ca2+ running out of SR. The Ca2+ then binds to the troponin and that the myosin heads will stick and flex to the actin. The release is driven by ATP. It shortens the fiber
With regard to proprioception, be able to describe the muscle spindles and golgi tendon organs in detail. What is the function of each?
- muscle spindles (Ia)
- stretch gauge (muscle length)
- basis for myotatic reflex
- in parallel with muscle - GTO (Ib)
- tension gauge (muscle tension)
- in series with muscle
- helps with fine grip
both influence one’s movement
We described some elaborate spinal circuitry for locomotion (remember the “French horn” cells?). What does that provide from a functional standpoint?
When your biceps contracts, the triceps typically relax. Why?
- because they are an antagonistic pair.
How are muscles controlled, in terms of amount of force? Is it easier to move lighter objects with more precision than heavier ones? Why or why not?
- small and large motor units
- Yes smaller motor units are recruited first and then larger. so you’re recruiting additional large motor units that are exerting a lot more force at a time when picking up something heavy. Takes away the fine motor ability
- smaller motor units = finer control by CNS
Where do motor neurons get their inputs?
- input from upper motor neuron (plan)
- input from spinal interneurons (red alert/inhibitory)
- sensory input from muscle spindles (letting muscle know it’s going to get moved).
What is an upper motor neuron vs lower motor neuron deficit?
- upper motor neuron deficit: damage to descending pathways (go tense) (ex. cerebral palsy)
- lower motor neuron deficit: damage direct to motor neurons (go limp) (ex. polio)
Know some muscle types, and terms for which body parts they might move (axial, distal, etc).
- axial muscles are responsible for movement of the trunk
- proximal (girdle): move the shoulder, elbow, pelvis, and knee
- distal: move the hands, feet, and digits (fingers and toes)
Is the spinal cord the same diameter throughout? Why or why not?
No because of the cervical enlargement and the lumbar enlargement. more cells are packed in each because of the muscles of the arms and legs.
