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• Pre-command level


  - highest level

  - cerebellum & basal nuclei

  - regulate motor activity

  - cerebral cortex outputs

  -ex. start/stop movements
• Projection level


  - middle level

  - motor cortex (pyramidal pathway) & brain stem nuclei (vestibular, etc.)

  - convey info to SC motor neurons & send copy to higher levels
• Segmental level


  - lowest level

  - SC, central pattern generator (CPGs)

  - reflexes

  -CPGs: patterned motor production (walking, swimming)
• Upper motor neurons


  cell body in primary motor cortex/, run through projection tracts & synapse on lower
• Lower motor neurons


  cell body in brain stem nucleus/ventral horn & innervate SKM
• Direct (pyramidal) motor pathway


  Lateral (limbs) and anterior (trunk) corticospinal

  - Fast and fine (skilled) movements (voluntary)

  - Upper (by midbrain?) and lower (ventral root) motor neurons

  - Originate in; primary motor cortex

  - Decussate in; medulla (lateral) or SC (anterior)
• Indirect pathway


  - Regulate balance & posture

  - Originate in brain stem

  - modify & control segmental level -SC

  - Ex. Spinal tracts?
• Anterior corticospinal


  DIRECT

  funiculus= anterior

  decussation= SC

  function=fine control of limbs
• Lateral corticospinal


  DIRECT

  funiculus= lateral

  decussation= medulla

  function= fine control of limbs
• tectospinal


  INDIRECT

  funiculus= anterior

  decussation= midbrain

  function=head turn as response to visual and auditory stimuli
• Lateral reticulospinal


  INDIRECT

  funiculus= lateral

  decussation=none

  function=balance and posture
• Medial reticulospinal


  INDIRECT

  funiculus= anterior

  decussation= none

  function= balance and posture
• Lateral vestibulospinal


  INDIRECT

  funiculus= anterior

  decussation= none

  function= balance and posture
• Medial vestibulospinal


  INDIRECT

  funiculus= anterior

  decussation= none

  function= control of head position
• Effectors of somatic motor NS


  Motor endings of somatic lower motor neurons activate effectors on skeletal muscles for in/vol movement
• How is somatic motor NS involved in somatic reflexes

  Somatic reflexes controlled @ spinal cord
• Flaccid paralysis


  (lower MNs); SC or ventral roots damaged, nerve impulses cant reach muscles (atrophy)

  - disruption between muscles and SC
• Spastic paralysis


  (upper MNs); only upper MNs damaged, no voluntary movement, reflex activity continue to stimulate muscle

  - disruption between SC and brain
• Paraplegia


  loss of movement & sensation in lower half of body (T1-L1)
• Quadriplegia


  loss of movement & sensation in all 4 limbs (cervical)
• ALS


  "no muscle nourishment"

  - destroy upper & lower MNs

  - neurodegenerative

  - usually ~5 years left
• Reflex arc

  Receptor -> Sensory neuron -> integration center -> motor neuron -> effector

  - brain is not involved, automatic

  
• Afferent neurons


  relay message from sense organs TO brain
• Efferent neurons


  motor neruons send signal from brain to gland & muscle
• Interneurons


  carry impulses between neurons in body
• Acquired reflex


  learned (driving, riding bike)
• Innate reflex


  inborn, modified w learning/effort (moro reflex)
• Somatic reflex


  activate SKM
• Autonomic reflex


  smooth/cardiac muscle, glands
• Muscle spindle


  length of muscle

  
• Intrafusal vs. extrafusal muscle fibers

  Extrafusal muscle fibers comprise the bulk of muscle and form the major force-generating structure. Intrafusal muscle fibers are buried in the muscle, and they contain afferent receptors for stretch, but they also contain contractile elements.
• Alpha-gamma coactivation


  In voluntary muscle contraction, both alpha & gamma fibers are activated together

  - Prevent muscle spindle from being useless as a receptor

  - Ensures they can detect length changes
• Stretch reflex


  - Myotatic reflex/patellar

  o Stretch activate muscle spindles, sensory neurons -> SC, synapse w/ motor neurons, excite extrafusal fibers, efferent impulses of a-motor neurons cause muscle contraction

  o Antagonist muscle- sensory fibers synapse w/ interneurons that inhibit motor neurons, efferent impulses reduced in antag muscle

  o Monosynaptic, maintain posture

  
• Flexor reflex


  - Withdrawal reflex

  o Ipsilateral

  o Reduce thinking time to prevent/limit tissue damage

  o Stepping on glass, pull leg up

  - Crossed extensor reflex

  o Accompany flexor reflex

  o Maintain balance

  o Divergent interneurons send info to brain so person feel pain

  o Contralateral

  
• Superficial Reflex


  - Plantar reflex

  o Stimulation on skin/bottom of foot, flex toes down

  
• Tendon reflex


  -receptor responds to tendon

  -tension too great = reflex inhibit motor fibers attached to muscle, prevent development of too much tension

  - function = equalize force among muscle fibers
• How are cranial and spinal nerves organized

  12 pairs of cranial nerves - head & neck/31 pairs of spinal nerves - rest of body

  - Connected via dorsal (sensory) and ventral(motor) roots

  - RAMI = MIXED

  o Dorsal ramus - supplies posterior body trunk

  o Ventral ramus - supplies rest of trunk & limbs

  + Branch & join in interlacing nerve plexuses; become redistributed
• Dermatome


  Area of skin supplied by a single spinal nerve
• dermatome and anesthesia importance

  need to know what levels for pain relief
• Autonomic vs somatic NS

  ANS - involuntarily controls smooth & cardiac muscle & glands to maintain HOMEOSTASIS

  - Stimulate effectors to adjust homeostatic variables

  - 2 divisions; sympathetic (fight/flight), parasympathetic (rest & digest)

  Somatic - voluntary, skeletal muscles, conduct impulses from CNS to SKM