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Page 1: Motor Systems. Motor Unit Motoneuron + muscle fibers it innervates Range in size from a few muscle fibers (e.g. extraocular muscles) To hundreds of

Motor Systems

Page 2: Motor Systems. Motor Unit Motoneuron + muscle fibers it innervates Range in size from a few muscle fibers (e.g. extraocular muscles) To hundreds of
Page 3: Motor Systems. Motor Unit Motoneuron + muscle fibers it innervates Range in size from a few muscle fibers (e.g. extraocular muscles) To hundreds of

Motor UnitMotoneuron + muscle fibers it innervates

Range in size from a few muscle fibers(e.g. extraocular muscles)

To hundreds of fibers(e.g. digits)

To thousands of fibers(e.g. trunk and major limb segments)

Smaller motor units yield more refined controla motor “fovea”

Page 4: Motor Systems. Motor Unit Motoneuron + muscle fibers it innervates Range in size from a few muscle fibers (e.g. extraocular muscles) To hundreds of
Page 5: Motor Systems. Motor Unit Motoneuron + muscle fibers it innervates Range in size from a few muscle fibers (e.g. extraocular muscles) To hundreds of

sarcomere

Page 6: Motor Systems. Motor Unit Motoneuron + muscle fibers it innervates Range in size from a few muscle fibers (e.g. extraocular muscles) To hundreds of
Page 7: Motor Systems. Motor Unit Motoneuron + muscle fibers it innervates Range in size from a few muscle fibers (e.g. extraocular muscles) To hundreds of

Excitation of a Muscle Fiber•An action potential in an alpha motoneuron axon.

•ACh is released by the axon terminal at the neuromuscular junction (synapse between motoneuron and muscle.

•Nicotinic receptor channels open, Na+ enters and the membrane depolarizes (EPSP).

•Voltage-gated Na+ channels open and an action potential is propagated down the muscle fiber.

•Depolarization produces Ca2+ release from intracellular stores.

Page 8: Motor Systems. Motor Unit Motoneuron + muscle fibers it innervates Range in size from a few muscle fibers (e.g. extraocular muscles) To hundreds of

Contraction of a Muscle Fiber•Ca2+ binds to tropinin.

•Myosin binding sites are exposed.

•Myosin heads bind actin.

•Myosin cross-bridges pivot.

•Myosin heads disengage at the expense (ATP-dependent).

•Recycle as long as Ca2+ and ATP are present.

Page 9: Motor Systems. Motor Unit Motoneuron + muscle fibers it innervates Range in size from a few muscle fibers (e.g. extraocular muscles) To hundreds of

Relaxation of a Muscle Fiber•As EPSPs end, membrane returns to resting potential.

•Free Ca2+ is sequestered by metabolically driven pump.

•Myosin binding sites covered.

Page 10: Motor Systems. Motor Unit Motoneuron + muscle fibers it innervates Range in size from a few muscle fibers (e.g. extraocular muscles) To hundreds of
Page 11: Motor Systems. Motor Unit Motoneuron + muscle fibers it innervates Range in size from a few muscle fibers (e.g. extraocular muscles) To hundreds of
Page 12: Motor Systems. Motor Unit Motoneuron + muscle fibers it innervates Range in size from a few muscle fibers (e.g. extraocular muscles) To hundreds of
Page 13: Motor Systems. Motor Unit Motoneuron + muscle fibers it innervates Range in size from a few muscle fibers (e.g. extraocular muscles) To hundreds of
Page 14: Motor Systems. Motor Unit Motoneuron + muscle fibers it innervates Range in size from a few muscle fibers (e.g. extraocular muscles) To hundreds of

Co-activation of α-motoneuronsand γ-motoneurons

at restα-motoneuron activation

α-, γ-motoneuron co-activation

Page 15: Motor Systems. Motor Unit Motoneuron + muscle fibers it innervates Range in size from a few muscle fibers (e.g. extraocular muscles) To hundreds of
Page 16: Motor Systems. Motor Unit Motoneuron + muscle fibers it innervates Range in size from a few muscle fibers (e.g. extraocular muscles) To hundreds of

Meissner’s Merkel’s

Pacinian Ruffini’s Free nerve ending

Page 17: Motor Systems. Motor Unit Motoneuron + muscle fibers it innervates Range in size from a few muscle fibers (e.g. extraocular muscles) To hundreds of

Monosynaptic stretch reflex

Golgi tendon organ reflex

Page 18: Motor Systems. Motor Unit Motoneuron + muscle fibers it innervates Range in size from a few muscle fibers (e.g. extraocular muscles) To hundreds of

somatosensoryafferents

motor afferents

Page 19: Motor Systems. Motor Unit Motoneuron + muscle fibers it innervates Range in size from a few muscle fibers (e.g. extraocular muscles) To hundreds of

(Aδ)

(C)

Page 20: Motor Systems. Motor Unit Motoneuron + muscle fibers it innervates Range in size from a few muscle fibers (e.g. extraocular muscles) To hundreds of

Muscle Spindles (intrafusal fibers)

Golgi Tendon Organs

respond to muscle length, or stretch

insensitive to tension

1a afferents for dynamic spindles

Group II afferents for postural spindles

monosynatic stretch reflex (excitatory)

respond to muscle tension

insensitive to muscle length, or stretch

1b afferents

disynaptic reflex (inhibitory)

Page 21: Motor Systems. Motor Unit Motoneuron + muscle fibers it innervates Range in size from a few muscle fibers (e.g. extraocular muscles) To hundreds of

Problem of LocomotionDegrees of freedom problem (Bernstein)

Dozens of joints controlled by hundredsof muscles

Muscles can contract in any combination,in any order, for any duration, and withany force.

Possibilities are virtually limitless, makingcontrol of complex movementsat the level of individual musclesimpossible

Page 22: Motor Systems. Motor Unit Motoneuron + muscle fibers it innervates Range in size from a few muscle fibers (e.g. extraocular muscles) To hundreds of

Reciprocal inhibition between motorunits of antagonistic muscles

Page 23: Motor Systems. Motor Unit Motoneuron + muscle fibers it innervates Range in size from a few muscle fibers (e.g. extraocular muscles) To hundreds of

Crossed extensor reflex

Page 24: Motor Systems. Motor Unit Motoneuron + muscle fibers it innervates Range in size from a few muscle fibers (e.g. extraocular muscles) To hundreds of

oscillators = “legos” of movementCPGs = what you can build with legos

Page 25: Motor Systems. Motor Unit Motoneuron + muscle fibers it innervates Range in size from a few muscle fibers (e.g. extraocular muscles) To hundreds of
Page 26: Motor Systems. Motor Unit Motoneuron + muscle fibers it innervates Range in size from a few muscle fibers (e.g. extraocular muscles) To hundreds of

Central Pattern Generators vs. Reflexes

Central Pattern GeneratorsFast

Act as “clocks”Flexible--<100 oscillators necessary

ReflexesRefine timing

Respond to the unexpectedAcquisition of new skills

Page 27: Motor Systems. Motor Unit Motoneuron + muscle fibers it innervates Range in size from a few muscle fibers (e.g. extraocular muscles) To hundreds of

Descending motor pathwaysLateral and ventromedial pathways

Pyramidal and extra-pyramidal systems

Page 28: Motor Systems. Motor Unit Motoneuron + muscle fibers it innervates Range in size from a few muscle fibers (e.g. extraocular muscles) To hundreds of
Page 29: Motor Systems. Motor Unit Motoneuron + muscle fibers it innervates Range in size from a few muscle fibers (e.g. extraocular muscles) To hundreds of
Page 30: Motor Systems. Motor Unit Motoneuron + muscle fibers it innervates Range in size from a few muscle fibers (e.g. extraocular muscles) To hundreds of
Page 31: Motor Systems. Motor Unit Motoneuron + muscle fibers it innervates Range in size from a few muscle fibers (e.g. extraocular muscles) To hundreds of
Page 32: Motor Systems. Motor Unit Motoneuron + muscle fibers it innervates Range in size from a few muscle fibers (e.g. extraocular muscles) To hundreds of
Page 33: Motor Systems. Motor Unit Motoneuron + muscle fibers it innervates Range in size from a few muscle fibers (e.g. extraocular muscles) To hundreds of
Page 34: Motor Systems. Motor Unit Motoneuron + muscle fibers it innervates Range in size from a few muscle fibers (e.g. extraocular muscles) To hundreds of

Supplementary Motor Area (SMA)important for instituting motor programsactivated prior to voluntary movementactivated during mental rehearsal

Premotor cortexsensory guided movementcooperatively with basal gangliamirror neurons

Pre-frontal cortexdecisions for actionslong-term planning

Page 35: Motor Systems. Motor Unit Motoneuron + muscle fibers it innervates Range in size from a few muscle fibers (e.g. extraocular muscles) To hundreds of
Page 36: Motor Systems. Motor Unit Motoneuron + muscle fibers it innervates Range in size from a few muscle fibers (e.g. extraocular muscles) To hundreds of
Page 37: Motor Systems. Motor Unit Motoneuron + muscle fibers it innervates Range in size from a few muscle fibers (e.g. extraocular muscles) To hundreds of
Page 38: Motor Systems. Motor Unit Motoneuron + muscle fibers it innervates Range in size from a few muscle fibers (e.g. extraocular muscles) To hundreds of
Page 39: Motor Systems. Motor Unit Motoneuron + muscle fibers it innervates Range in size from a few muscle fibers (e.g. extraocular muscles) To hundreds of
Page 40: Motor Systems. Motor Unit Motoneuron + muscle fibers it innervates Range in size from a few muscle fibers (e.g. extraocular muscles) To hundreds of

Cortex

Cerebellum

Substantia

Nigra

Caudate-

putamen

(stria

tum)

GlobusPallidus

Thalamusand STN

RedNucleus(nucleu

sruber)

Reticulospinal tract

Rubrospinal tract

Page 41: Motor Systems. Motor Unit Motoneuron + muscle fibers it innervates Range in size from a few muscle fibers (e.g. extraocular muscles) To hundreds of

Cortex

Cerebellum

Substantia

Nigra

Caudate-

putamen

(stria

tum)

GlobusPallidus

Thalamusand STN

RedNucleus(nucleu

sruber)

Reticulospinal tract

Rubrospinal tract

cortex

pontine nuclei

cerebellum thalamus

Page 42: Motor Systems. Motor Unit Motoneuron + muscle fibers it innervates Range in size from a few muscle fibers (e.g. extraocular muscles) To hundreds of

Cortex

Cerebellum

Substantia

Nigra

Caudate-

putamen

(stria

tum)

GlobusPallidus

Thalamusand STN

RedNucleus(nucleu

sruber)

Reticulospinal tract

Rubrospinal tract

cortex

striatum

globuspallidus thalamus

Page 43: Motor Systems. Motor Unit Motoneuron + muscle fibers it innervates Range in size from a few muscle fibers (e.g. extraocular muscles) To hundreds of

Cortex

Cerebellum

Substantia

Nigra

Caudate-

putamen

(stria

tum)

GlobusPallidus

Thalamusand STN

RedNucleus(nucleu

sruber)

Reticulospinal tract

Rubrospinal tract

cortex

striatum

substantianigra thalamus

Page 44: Motor Systems. Motor Unit Motoneuron + muscle fibers it innervates Range in size from a few muscle fibers (e.g. extraocular muscles) To hundreds of

Cortex

Cerebellum

Substantia

Nigra

Caudate-

putamenGlobu

sPallidus

Thalamusand STN

RedNucleus(nucleu

sruber)

Reticulospinal tract

Rubrospinal tract

degenerate in Huntington’s disease

Page 45: Motor Systems. Motor Unit Motoneuron + muscle fibers it innervates Range in size from a few muscle fibers (e.g. extraocular muscles) To hundreds of
Page 46: Motor Systems. Motor Unit Motoneuron + muscle fibers it innervates Range in size from a few muscle fibers (e.g. extraocular muscles) To hundreds of

Cortex

Cerebellum

Substantia

Nigra

Caudate-

putamenGlobu

sPallidus

Thalamusand STN

RedNucleus(nucleu

sruber)

Reticulospinal tract

Rubrospinal tract

degenerates in Parkinson’s disease

Treatments:

1. l-DOPA to compensate for lost DA projections

2. Deep brain stimulation

of striato-pallidal projections

3. Surgical destruction of

cells in medial pallidum

Page 47: Motor Systems. Motor Unit Motoneuron + muscle fibers it innervates Range in size from a few muscle fibers (e.g. extraocular muscles) To hundreds of

Subthalamus pedunculopontine nucleus (PPN)reticulospinal tractspinal CPGs

Page 48: Motor Systems. Motor Unit Motoneuron + muscle fibers it innervates Range in size from a few muscle fibers (e.g. extraocular muscles) To hundreds of

ALS: Upper motoneuron diseasePolio: Spinal motoneuron diseaseApraxias: Frontal cortical damage


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