Control Of Movement

Control Of Movement

1. ANATOMY

   • Skeletal Muscle (Monosynaptic)
     • Flexion
       • Muscle contracts
       • Bending the arm
     • Extrafusal Muscle Fiber
       • Force Exertion
       • Alpha Motor Neuron
         • Action Potential = Contraction (Force)
         • Paralysis if destroyed
         • Motor Unit (+ associated E muscle fibers)
     • Intrafusal Muscle Fiber
       • Stretch Receptor
         • Increased firing rate = Increased stretching
           • Patella Reflex (knee jerk)
             • 1. Muscle stretch > Increased afferent signals to SC
               • 2. SC Increased efferent output through alpha motor neurons
                 • 3. Muscle Contracts, Firing rate of afferent sensory neuron decreases
       • Gamma Motor Neuron
         • Contractions = no force
         • Firing rate ^ = Spindle Shortens
     • Extension
       • Straightening the arm
       • Muscle Relaxes
     • Maintains posture
   • Myofibril
     • made up of Sarcomere
       • Actin
         • thin
         • Troponin & Tropomyosin
       • Myosin
         • thick
         • Cross bridges interact w actin to pull towards M-line
           • Shortens sarcomere = contraction
   • Golgi Tendon Organ (GTO)
     • Stretch receptor organ @ junction of tendon & muscle
       • Slightly slower than muscle spindles
         • 1. Tension activated sensory neurons
           • 2. Sensory neurons stimulates interneuron
             • 3. Interneuron inhibits alpha motor neuron
               • 4. Inhibition of alpha = muscle relax.

2. NEUROMUSCULAR JUNCTION

   • 1. Release of ACh & NA comes in, causes depolarization, resulting in action potential
     • 2. Calcium causes muscles to fuse (contraction)
       • 3. Contraction ceases when ACh is gone (by AChE)
         • Inhibition of AChE extends contraction time & unable to breathe = death (poison)
   • Motor Endplate
     • Postsynaptic membrane
   • Endplate potential
     • Postsynaptic potential in response to release of ACh (depolarization)
       • Nicotinic ACh receptors usually therapeutic targets

3. PHYSIOLOGY OF CONTRACTION

   • Sarcolemma generates AP
     • T Tubules goes down to muscle fiber, carrying AP
   • Calcium is stored in Sarcoplasmic Reticulum
     • releases calcium
       • Calcium binds to troponin = moves tropomyosin
         • Myosin binding sites exposed
           • Pulls actin filaments towards M-line
             • Sarcomere shortens
             • Cycle continues till calcium goes away

4. REFLEXES

   • Monosynaptic Reflex Arc
     • 1. Muscle spindles innervated by sensory neurons (cell body in dorsal root ganglion)
       • 2. Muscle spindles stretch, excitatory signals stimulate neurons = AP
         • 3. Excitatory neurotransmitters activated @ terminal, exciting alpha, contracting muscle
   • Polysynaptic Inhibitory Reflex
     • 1. When GTO stretches, excitatory neurotransmitter is released onto inhibitory interneuron
       • 2. The more excitation, the more inhibition @ alpha
         • 3. No action potentials, no contraction

5. MOTOR CORTEX

   • Somatotopic
     • Certain parts have a higher concentration of nerves
     • Stimulate primary MC to initiate movement
       • Diff pathways to SC
   • 1. Association cortex sends signals to prefrontal (plans movements)
     • 2. Prefrontal > Pre-supplementary & premotor
       • 3. Premotor & pre-supplementary > primary motor
     • Assc = memories, learning, reasoning
   • Supplementary Motor Area
     • Important for behavior sequences
   • Premotor Cortex
     • executes complex movements guided by sensory info
   • Basal Ganglia
     • Globus Pallidus
       • Facilitates desired & suppresses undesired movements
     • Subthalamic Nucleus
   • Striatum
     • Caudate & Putamen
     • Nigrostriatal Dopamine (DA) System
       • Parkinson's, Addictions, etc
       • Getting rid of dopamine will affect indirect & direct pathways
         • Parkinson's, Huntington's
   • Thalamus
     • Consciousness, sleep, etc

6. PATHWAYS

   • Direct
     • 1. PMC > Caudate & Putamen
       • 2. Excitation of inhibition
         • 3. GABA Neuron excitated = release of GABA
           • 4. Inhibits Globus Pallidus, less GABA released (disinhibition)
             • 5. Thalamus excited, ^ movement
               • 6. Exciting inhibition of inhibition = excitation
     • INCREASED MOVEMENT
   • Indirect
     • 1. Excitation of inhibition, ^ GABA released in GP
       • 2. Inhibits neurons = v GABA @ Subthalamus nucleus
         • 3. ^ GABA @ Globus pallidus Internal, exciting it
           • 4. v Activity @ thalamus, v movement
     • DECREASED MOVEMENTS

7. MIRROR NEURONS

   • Posterior & Anterior sends info back & forth
     • STS sends input > posterior > anterior
       • F5 - Grasping
         • F4 - Head & Neck
           • Anterior (motor)