Spinal Motor Circuits Flashcards
What are the 4 main neural circuits controlling vertebrate movement?
Higher control circuits
Brainstem-spinal cord circuits
Spinal cord circuits
Spino-muscular circuits
What is the role of higher control circuits and where do they receive inputs from?
Intention and movement selection
Visual inputs
What is the role of brainstem-spinal cord circuits and where do they receive inputs from?
Integrate inputs - generate command
Auditory, limb sensory afferent inputs
What is the role of spinal cord circuits and where do they receive inputs from?
Organise commands
Limb sensory afferent inputs
What is the role of spino-muscular circuits and where do they receive inputs from?
Effectors
Limb sensory afferent inputs - affect this input
Where is there a large proportion of white matter in the spinal cord?
Upper cervical region
Where is there a small proportion of white matter in the spinal cord?
Sacral region
What was Sherrington’s theory of locomotion?
Locomotion controlled by sequence of reflexes
What was Brown’s theory of locomotion?
Locomotion controlled by CPGs in spinal cord - not reflexes
What is the current view of locomotion?
Sherrington reflex control vs Brown central control is false dichotomy
Spinal cord can produce rhythm and pattern of locomotion
But sensory inputs required for normal locomotion
Define a motor unit
Motor neuron and muscle fibres it innervates
What are the 3 muscle fibre types?
Slow twitch
Intermediate
Fast twitch
What are the characteristics of slow twitch muscle fibres?
Many mitochondria
Weak, slow, sustained contraction
Slow MN
What are the characteristics of intermediate muscle fibres?
Fast-resistant MN
Intermediate properties
What are the characteristics of fast twitch muscle fibres?
Few mitochondria
Powerful, fast, brief contraction
Fast-fatiguable MN
What do muscle spindles detect?
Stretch
What type of MNs innervate muscle spindles and what is their role?
Gamma MNs
Control spindle contraction - controls length - controls sensitivity
What do the 2 types of sensory fibres in a muscle spindle detect?
Muscle length
Contraction speed
What is state dependence?
Neuronal networks respond differently to inputs depending on their state
What are the 4 fundamental classes of ventral horn interneurons?
V0, V1, V2, V3
What are the roles of V0 interneurons in locomotion?
Commissural inhibitory
Left-right alternation
What are the roles of V1 interneurons in locomotion?
Ipsilateral inhibitory
Speed, flexor-extensor driven movements
What are the roles of V2 interneurons in locomotion?
Some excitatory - left-right alternation
Some inhibitory - flexor-extensor driven movements
What are the roles of V3 interneurons in locomotion?
Mainly commissural excitatory - some ipsilateral
Locomotion robustness
Where do d13 interneurons receive inputs from?
Peripheral excitatory inputs from muscle and non-muscle afferents
What is the role of d13 interneurons?
Mediate disynaptic excitatory cutaneous reflexes - e.g. grasp reflex
Are d13 interneurons excitatory/inhibitory?
Excitatory
What is the role of comparator neurons? Give an example of an comparator neruon type
Integrate predicted and actual sensory activity - enable adaptation of motor behaviour
e.g. d13 interneurons
What is needed for short-term motor behaviour adaptation/longer-term motor plasticity?
Sensory feedback
Feedforward motor efference copy
