chapter 3 rosenbaum

muscle spindle

proprioceptive receptor inside the muscle that detects length and rate of stretch

golgi tendon organ (GTO)

proprioceptive receptor in the muscle-tendon junction that detects force/tension

joint receptors

receptors in joint capsules that respond to extreme joint positions

cutaneous receptors

skin-based receptors that detect pressure, touch, and vibration important for grip control

proprioception

sense of body position and movement from muscles, joints, and skin

kinesthesia

sense of movement (subset of proprioception)

motor unit

one motor neuron and all the muscle fibers it activates

motor unit recruitment

increasing the number and size of motor units to increase force output

length–tension relationship

muscles generate the most force at intermediate length due to optimal filament overlap

henneman’s size principle

small motor units are recruited first, then larger ones as force increases

α-motor neuron

activates extrafusal (force-generating) muscle fibers

γ-motor neuron

activates intrafusal muscle fibers in spindles to maintain spindle sensitivity

α–γ coactivation

simultaneous activation of alpha and gamma motor neurons to preserve spindle function during movement

stretch reflex

spinal reflex that contracts a muscle in response to stretch (via muscle spindle)

reciprocal inhibition

when a muscle contracts, its antagonist is inhibited via spinal interneurons

recurrent inhibition

self-inhibition of a motor neuron via Renshaw cells to limit overactivation

servo theory

model of reflex control as an adjustable feedback loop, maintaining movement accuracy

central pattern generator (CPG)

neural network in spinal cord that generates rhythmic movement without sensory input (e.g., walking)

smart spinal cord

the spinal cord integrates, modulates, and adapts reflexes based on context

long-loop reflex

reflex that involves the cortex, slower but more flexible than spinal reflexes

primary motor cortex (M1)

cortical region responsible for executing voluntary movement

population coding

movement direction is determined by the combined activity of many neurons

force coding in M1

firing rate of M1 neurons increases with the force required for movement

premotor cortex

involved in planning externally driven movements using visual cues

supplementary motor area (SMA)

plans internally generated movement sequences and bilateral coordination

cerebellum

brain region that fine-tunes movement, maintains timing, balance, and motor learning

cerebellar damage

causes ataxia, dysmetria, intention tremor, and hypotonia

dysmetria

inability to judge distance, leading to overshooting/undershooting movements

dysdiadochokinesia

difficulty with rapid alternating movements

hypotonia

reduced muscle tone, often seen in cerebellar disorders

motor learning (cerebellar)

cerebellum adjusts future movement by comparing intended vs actual outcome (error correction)

climbing fibers

input to cerebellum that signals movement errors for motor learning

basal ganglia

subcortical nuclei that initiate and inhibit movements, and support motor learning

direct pathway

facilitates movement by reducing inhibition on the motor cortex

indirect pathway

suppresses movement by increasing inhibition on the motor cortex

dopamine

neurotransmitter that excites direct pathway (via D1) and inhibits indirect pathway (via D2)

parkinson’s disease

dopamine loss → reduced movement, bradykinesia, resting tremor, rigidity

huntington’s disease

striatal degeneration → excessive movement (chorea), especially from indirect pathway loss

action selection theory (basal ganglia)

basal ganglia filter and select desired actions, suppress competing ones

reinforcement learning theory (basal ganglia)

dopamine encodes reward prediction error to strengthen successful actions

mirror neurons

neurons that fire when performing or observing an action; involved in imitation and learning

motor plasticity

the motor system can reorganize and adapt with experience, practice, or injury

tool use adaptation

motor system incorporates tools into body schema, extending perceived limb capabilities