Motor Systems

Muscle spindles

Belly of the muscle; detects stretch in the skeletal muscles; response is muscle contraction

Golgi tendon organs

Tendon; detects tension in the tendon; response is muscle relaxation

Reflexes

Automatic response to a stimulus, body movement without conscious thought

Reflex arc

Neural pathway that controls a reflex

Monosynaptic reflex

Sensory neuron synapses directly with motor neuron, with no interneuron

Polysynaptic reflex

Multiple synapses with interneurons between sensory and motor neurons

Muscle stretch reflex

Sudden stretch of a muscle results in muscle spindles detecting stretch, sensory neurons conducting action potentials to the spinal cord, and alpha motor neurons causing the muscle to contract and resist being stretched

Golgi tendon reflex

Protects the muscles and tendons from damage caused by excessive tension

Flexor withdrawal reflex

Removes a limb or another body part from a painful stimulus

Pontine reticular nuclei

Excites antigravity muscles

Medullary reticular nuclei

Inhibits antigravity muscles

Upper motor neurons

Connect the cerebral cortex to lower motor neurons directly or through interneurons

Lower motor neurons

Connect upper motor neurons to skeletal muscles

Primary motor area

BA4; carries out the individual movements of different parts of the body and serves as the final station for conversion of the design into execution of the movement

Premotor area

BA6; stores programs of motor activity assembled as a result of past experience and acts as a staging area where motor functions are organized before they are initiated in the primary motor cortex

Mirror neurons

Mirrors the behavior of another person as though the observer was performing the specific motor task and transforms sensory representations of acts that are heard or seen into motor representations

Supplementary motor area

BA6; responsible for bilateral movements and provides background for the finer motor control of the arms and hands

Prefrontal cortex

BA 9 10 11 12; concerned with the makeup of the individual personality, acts as a regulator of the person depth of feeling, and controls the motivation and foresight to plan and initiate movements

Direct pathways

Pyramidal; maintain muscle tone and control speed and precision of skilled movements

Indirect pathways

Extrapyramidal; less precise control of motor functions, overall body coordination, posture, and fine control of direct pathway

Corticospinal tract

Pyramidal upper motor neuron pathway with decussation in the medulla, terminating in interneurons and alpha motor neurons to control precise movements of the distal muscles of the limbs

Rubrospinal tract

Indirect pathway located in the tegmentum of the midbrain that facilitates activity of flexor muscles

Pontine reticulospinal tract

Excitatory reticulospinal tract originating from the reticular formation

Medullary reticulospinal tract

Inhibitory reticulospinal tract originating from the reticular formation

Vestibulospinal tract

Facilitates activity of extensor muscles, inhibits flexor muscles, and controls balance

Tectospinal tract

Located in the superior colliculus of the midbrain, functioning in reflex postural movement in response to visual stimuli

Basal ganglia

Plays a role in the preparation and initiation of movement, facilitates selected movement, inhibits unwanted movements, and handles timing, scaling, and complex skilled movement

Vestibulocerebellum

Flocculonodular lobe of the cerebellum involved in balance and eye movements

Crossed extensor reflex

Reflex where pain sensory neurons stimulate flexor muscles on one side and cross the spinal cord to stimulate extensor muscles in the opposite limb to support body weight

Reciprocal innervation

Process where collateral branches of sensory neurons synapse with inhibitory interneurons supplying antagonist muscles causing them to relax and avoid opposing contracting muscles

Spinocerebellum

Region of the cerebellum involved in motor execution and control of medial and lateral descending systems

Cerebrocerebellum

Region of the cerebellum involved in motor planning and communication with motor and premotor cortices

Parkinson disease

Clinical condition characterized by akinesia bradykinesia dyskinesia rigidity tremor masklike face and a stooped posture resulting from basal ganglia dysfunction