NSB 502 Control of Movement

Exam 2

extrafusal muscle fibers

served by axons of alpha motor neurons

intrafusal muscle fibers (aka muscle spindles)

served by 2 axons: 1 sensory and 1 motor. contain sensory endings that respond to strech

a motor unit

alpha motor neuron, its axon and associated extrafusal muscle fibers

afferent fibers

towards the brain, sensory nerve cell

efferent fibers

away from the brain, alpha motor, gamma motor

myofibrils

made of overlapping strands of actin and myosin

myosin cross bridges

spikes on myosin filament, where they interact with actin filaments to produce muscle contractions

striated muscles

where they overlap forms dark stripes or striations

neuromuscular junction

the synapse between the terminal button of an efferent neuron and the membrane of a muscle fiber

efferent neuron action potential

Ach is released and the postsynaptic membrane depolarizes which is called an endplate potential

strength of contraction determined by

the average rate of firing

Golgi tendon organ

a proprioceptive sensory receptor organ that senses changes in muscle tension. stretch receptors located within the tendon

slow, passive extension of the arm

the rate of firing of the muscle spindle afferent neuron MS1 changes its firing rate, but the Golgie tendon organ (GTO) doesn’t change

rapid extension of the arm

the rate of firing of the muscle spindle afferent neuron MS2 changes its firing but GTO doesn’t change

addition of weight to the hand

• MS1 and MS2 fire because a brief drop then bring the hand back

• GTO detects strength of the contraction

• fires in proportion to the stress

• increases its rate as soon as the weight is added

monosynaptic stretch reflex

a stimulus applied to the patellar tendon (just below the kneecap), which briefly stretches the muscle

more sensitive afferent axons from GTO

tell the brain how hard the muscle is pulling

less sensitive afferent axons from GTO

synapse on spinal cord interneurons. these synapse onto alpha motor neurons serving the same muscle

primary motor cortex

lies on the precentral gyrus rostral to central sulcus. contains somotopic organization

lateral group of descending motor tracts

independent limb movements (as opposed to coordinated like walking)

lateral corticospinal tract

• fingers, hands and arms

• grasping and manipulating objects

pyramidal tracts (lateral)

at the caudal medulla the fibers cross to the contralateral side, which then forms at the lateral coritcospinal tract. remaining fibers descend the ipsilateral side forming the ventral coricospinal tract

corticobulbar tract (lateral)

• face and tongue

• face and tongue movements

rubrospinal tract (lateral)

• hands (not fingers), lower arms, feet and lower legs

• movement of forearms and hands independent from that of the trunk

ventromedial group of descending motor tracts

originates in the brain stem, more automatic movements, coordinated movements involved in posture and locomotion

vestibulospinal tract (ventromedial)

• trunk and legs

• posture

tectospinal tract (ventromedial)

• neck and trunk

• coordination of eye movements with those of trunk and head

lateral reticulospinal tract (ventromedial)

• flexor muscles of legs

• walking

medial reticulospinal tract (ventromedial)

• extensor muscles of legs

• walking

ventral corticospinal tract (ventromedial)

• control upper leg/trunk

• locomotion and posture

motor association cortex

includes supplementary motor area and premotor cortex

• involved in planning movements

• imitating movements

• receives visual information from parietal and temporal cortex

supplementary motor area (SMA)

learning and performing sequences of movements

premotor cortex

learning and executing responses that are signaled by the presence of arbitrary stimuli

reticular formation

• regulates muscle tone

• control of posture

• different nuclei control automatic and semiautomatic responses (breathing, sneezing, coughing)

fluculonodular lobe

caudal portion

• input from vestibular system - projects to vestibular nucleus

• postural reflexes

vermis

located on the midline

• receives auditory and visual information from tectum

• receives cutaneous and kinesthetic information from spinal cord

fastigial nucleus

deep in cerebellum

• send neurons to vestibular nucleus and motor nuclei in reticular formation

pontine tegmental reticular nucleus

input from primary motor and association cortexi

interposed nuclei

receives projections from intermediate zone of cerebellum

lateral zone of the cerebellar cortex

• receives info about impending movements from frontal lobes

• helps smooth and integrate movements

• connects to primary motor cortex through the dentate nucleus and ventral thalamus

lateral zone

control of independent limb movements

• rapid, skilled movements

• controls circuitry needed to calculate complex, closely timed sequences

pontine nucleus

receives info from association and motor cortex about intended movements, also receives sensorimotor info

dentate nucleus

receives info to plan movements

• passes info to ventrolateral thalamus

• then projects to primary motor cortex

• predicts next movements in a sequence

lesion to flocculonodular lobe

disturbance in posture/balance

lesion to vermis

disturbance in posture/balance

lesion to intermediate zone

deficits in movements controlled by rubrospinal system (principle symptom = limb rigidity)

lesion to lateral zone

weakness, decomposition of movement (no smooth movement)

direct pathway (basal ganglia circuitry)

• globus pallidus sends inhibitory neurons to ventral anterior and ventrolateral thalamus

  • which send excitatory inputs to motor cortex

• a disinhibitory pathway

  • caudate and putamen inhibit neurons in the globus pallidus which usually inhibit other neurons

  • therefore other neurons in the VA/VL become excited

indirect pathway (basal ganglia circuitry)

• globus pallidus neurons end inhibitory input to subthalamic nucleus

  • subthalamic nucleus then excites globus pallidus

  • ultimate effect on the thalamus and frontal cortex is inhibitory

  • inhibits motor cortex

hyperdirect pathway (bypasses caudate and putamen)

• Pre-SMA sends excitatory input to subthalamic nucleus

• sends excitatory input to globus pallidus, which inhibits motor cortex

• hyperdirect therefore inhibits movements

Parkinson’s

• impaired initiation of movements, especially automatic movements

• degeneration of dopamine cells in substantia nigra

Huntington’s

• uncontrollable movements, impaired ability to stop movements

• degeneration of GABA and Ach neurons in the caudate and putamen

• loss of inhibition which leads to increased globus pallidus activity which inhibits subthalamic nucleus

  • results are excessive movements

parietal reach region

• active when pointing or reaching (reaching is controlled by vision)

• parietal cortex determines location

  • sends that info to frontal cortex

POS

parieto-occipital sulcus

anterior intrapartietal sulcus (AIS)

grasping, controlling hand and finger movements

• receives info from dorsal stream of visual system

• also involved in visually recognizing grasping behavior

constructional apraxia

• caused by lesions of the parietal right hemisphere

• can use objects properly, pretend, or imitate

  • can’t draw or assemble objects correctly

  • can’t perceive and imagine geometrical relations