Chapter 13: Spinal Control of Movement Flashcards
Muscles and neurons that control muscles
motor system
role of motor system:
generation of coordinated movements
Parts of motor control (2 types of motor programs)
- spinal cord - control of coordinated muscle contraction
- brain - modulates control of motor programs in spinal cord
types of muscle
smooth, striated
Each muscle has hundreds of (), the fused skeletal muscle cells (multiple nuclei). And each fiber is innervated by a single axon branch from the CNS
muscle fibers
Inner movement of arms: (1) -> Promoted by (2) muscles
- flexion
- flexor
outward movement of arms: (1) -> Promoted by (2) muscles
- extension
- extensor
Groups of Somatic Musculature and Distribution of Lower Motor Neurons
Axial muscles: trunk movement/ maintaining posture
Proximal muscles: shoulder, elbow, pelvis, knee movement/locomotion
Distal muscles: hands, feet, digits (fingers and toes) movement/manipulation of objects
(): neurons in the brain that supply input to the spinal cord;
Upper motor neurons
Somatic muscles are majorly innervated by (1), whose somas are found in (2)
- lower motor neurons
- ventral horn of spinal cord
Motor neurons innervating proximal and distal muscles are found mainly in the (1) segments of the spinal cord, whereas those innervating axial muscles are found (2).
- cervical and lumbar-sacral
- at all levels
Motor neurons controlling flexors lie (dorsal/ventral) to extensors.
dorsal
Motor neurons controlling axial muscles lie (lateral/medial) to those controlling distal muscles.
medial
() motor neurons directly trigger the generation of force by muscle
Alpha
(): motor neuron and all the muscle fibers it innervates
Motor unit
(): all the alpha motor neurons that innervate a single muscle
Motor neuron pool
The () is one important way the CNS grades muscle contraction
rate of firing of the motor unit
Recruiting additional synergistic motor units -> muscles with a large number of small motor units can be ().
more finely controlled by the CNS
Inputs to Alpha Motor Neurons (3)
- sensory input from muscle spindles
- upper motor neurons in brain
- spinal interneurons
Sensory input from muscle spindles: via (1); provide feedback about (2)
- stretch receptors
- muscle length
Upper motor neurons in the brain: ()
initiation and control of voluntary movement and will
Spinal interneurons can be ()
excitatory or inhibitory
types of motor units
fast and slow motor units
types of fast motor units (fibers)
fatigue-resistant (FR)
fatigable (FF)
(): large number of mitochondria and enzymes for oxidative energy metabolism, slow to contract, can sustain contraction
Red muscle fibers (slow motor unit)
(): fewer mitochondria, anaerobic metabolism (no need for O2), contract and fatigue rapidly-escape reflex
Fast motor units (White muscle fibers)
(): white fibers with moderate strength and fast contractions
Fatigue-resistant (FR) fast fibers
(): fastest, strongest white fibers, but rapidly fatiguing
Fast fatigable (FF) fibers
rank strength of contraction of types of motor units
FF > FFR > S
() are important for transporting AP towards SR to induce significant Ca2+ release
T-tubules
(): division of myofibril into segments (sarcomeres) by disks
Z lines
(): two Z lines and myofibril; basic unit of muscle fiber
Sarcomere
(): series of bristles anchored to Z lines
Thin filaments
(): between and among thin filaments
Thick filaments
Muscle contraction occurs when the thin filaments slide along the thick filaments, bringing adjacent Z lines toward one another.
Sliding-Filament Model of Muscle Contraction
() allows myosin heads (thick filaments) to bind to actin (thin filament)—myosin heads then pivot, causing filaments to slide.
Ca+ binding to troponin
Sensory feedback from muscle spindles—()
stretch receptor (proprioceptors)
stretch receptors are specialized for body sense () : how our body is positioned and moving in the space
proprioception
() axons -> thickest myelinated axons in the boy -> conduct AP very rapidly
Group I
Stretch reflex: muscle pulled results in () as a result
strong and rapid tendency to pull back
feedback loop involved in stretch reflex:
Bet. G IA axons and alpha motor neurons
Discharge rate of sensory axons of Group 1a: related to ()
muscle length
Innervate intrafusal fibers inside muscle spindle (both ends) -> Like a “sensory organ” of muscle
Gamma Motor Neurons
Keeps spindle “on air” – sensitive, able to activate Ia axons; Changes set point of the stretch feedback loop
Gamma loop
() activation -> decrease Ia activity
Alpha
() activation -> increase Ia activity
Gamma
Alpha motor neurons can inhibit (1) and stimulate (2) based on sensory input from muscle spindle
- further muscle stretching
- contraction
During (), muscle spindle is short and “loosened” -> Ia sensory axons cannot be activated -> no AP transmitted
off-air
- Gamma motor neurons work on ends of muscle spindle to keep it ()
long and “tight”
Additional proprioceptive input—acts like strain gauge— monitors muscle tension.
Golgi Tendon Organs
Golgi Tendon Organs exist inside (1), among (2)
- tendons
- collagen fibers
Golgi Tendon Organs are innervated by () -> deliver signals spinal cord if tendons are stretched
Ib axons
Tendons are stretched when muscles are ()
contracted
2 types of sensing in the muscle
Spindles in parallel with fibers— sense muscle length
Golgi tendon organs in series with fibers – sense muscle tension
function of golgi tendon organs is to: regulate () -> Important for the proper execution of fine motor acts
muscle tension within optimal range
Golgi tendon organs sense tension in muscle -> fire AP via Ib axons -> stimulate () -> inhibits alpha motor neurons to suppress muscle contraction
inhibitory interneurons
Most input to alpha motor neurons mediated by ()
spinal interneurons
Variety of synaptic inputs to spinal interneurons; modulate overall activity of motor neurons
Primary sensory axons (e.g. muscle spindles, Golgi tendon organs, etc)
Descending axons from brain
Collaterals of lower motor neuron axons
Other interneurons
(): contraction of one muscle set accompanied by relaxation of antagonist muscle
Reciprocal inhibition
