Lower MN Flashcards
Describe the 4 subsections of neuronal centers for movement
Lower motor neurons (final common path) + internuerons receiving sensory and descending inputs
Upper motor nuerons (in brainstem and cerebral cortex)
Cerebellum
Basal ganglia
What two structures only modulate upper MN?
Cerebellum and basal ganglia
What are lower MN?
Directly contact the effectors (skeletal muscles)
What are upper MN?
Originate in cerebral cortex and brainstem that carry motor information down to the lower motor neurons
What is the final common path for movement?
Integrate information form different sources and carry them to the effectors
Describe number of nerves to muscles
Single motor neuron to single muscle
All neurons innervating the same muscle are clustered together in the spinal cord
Somatotrophic organization of muscle nerve in spinal cord?
Rostral muscles in rostral segments
Caudal muscles in caudal segments
Neurons innervating axial muscles are where? Control what?
Medially
Control of balance and posture
Lateral lower MN to axial motor neuron pools do what?
Innervate muscles progressively more laterally
Control of skilled behaviors
Descending inputs that run through the spinal lateral to the white matter
Local circuits of spinal cord grey matter?
Medial - high intersegmental connections and bilateral connections - controls posture
Lateral - restricted connectivity, no more than 5 segments, remain on single spinal cord side - individualized motions
Describe the stretch reflex
Local circuitry referred to as stretch, deep tendon, or myotactic reflex.
Negative feedback loop used to maintain muscle length at desired value
What is muscle tone?
Resiting level of tension in muscle allowing it to respond optimally to voluntary or reflexive commansd
Tone depends on?
Level of discharge of alpha motor neurons modulated in part by the stretch reflex
Describe flexion reflex?
Reflex modulating withdrawal of a limb from painful stimulus leads to motor regulation in both lower limbs
Flexion of stimulated limb and opposite reaction in the contralateral limb (contralateral extensor muscles while excited flexor muscles are inhibited).
Crossed extension reflex is for postural support
Damage to the lower motor neurons of the brainstem and spinal cord is referred to as?
Lower motor neuron syndrome
What are central pattern generators?
Located in the spinal cord and brain stem and control the timing and coordination of complex patterns of movement and adjusting them
Phases of locomotion?
Stance phase - limb is extended and placed in contact with the ground to propel forward
Swing phase - limb is flexed to leave the ground and brought forward to begin the next stance phase
Increase in speed shortens what for locomotion?
Duration of stance phases
Central pattern generators and locomotion?
Each limb has its own CPG coupled with other local circuits to achieve the coordinated movements that occur during different speeds
What is unsteady gait?
Abnormal function of almost any part of the NS as well as orthopedic conditions. Not enough information for localization
Lower MN of the visceral motor system?
Located outside the CNS in autonomic ganglia close to the spinal cord (symp) or close to target organ (para)
Principal action of somatic motor system controlled by? Visceral?
Somatic - motor cortical areas
Visceral - distributed set of cortical and subcortical structures comprising a central autonomic network
Visceral motor terminal NT?
Symp - NE
Parasym - Ach
Also peptides
Number or autonomics vs somatics?
For a given organ, effectors for ANS is greater than somatic in number
