Motor System Flashcards
Pyramidal motor system
Motor function traveling through the
“pyramids” of the medulla
Newer
* Origin in cerebral cortex
* Voluntary
* Skilled movements
The pyramidal motor system controls the
contralateral side of the body
Extrapyramidal motor system
- Refers to non-pyramidal motor systems
(e.g. motor systems NOT traveling through
pyramids of the medulla) - Classically, used to describe aspects of
basal ganglia motor function - But, also applies to cerebellar motor
function– And a few other minorish motor systems - Older
- Origin in basal ganglia,
cerebellum, red nucleus - Axial and postural control,
coordination, balance
The cerebellar motor system controls the ipsilateral side of
the body (double-crosses)]
- involuntary (non-conscious)
- modulate a-motor neuron function but do
not directly synapse on them - Reticulospinal
- Vestibulospinal
- Rubrospinal
- Tectospinal
- Cerebellum
– ipsilateral control - Basal ganglia
– contralateral control - Their pathways are distinct from pyramidal motor
systems
Upper Motor Neuron (Motor Cortex)
precentral gyrus
Betz cells: giant pyramidal cells
– send long axons that synapse onto alpha-motor
neurons in the spinal cord
– largest neurons of the CNS, cell bodies are in
layer V
– long axons
- Other cortical areas
involved in motor control:
– Posterior parietal cortex (PPC) - production of planned movements
– Supplementary motor area (SMA) - projects directly to spinal cord
- can control both sides of body; many muscle groups; sequences of movements
frontal eye fields
* in prefrontal cortex
initiation of eye movements by
stimulating saccadic eye movements
* have a topographic representation of
space in retinotopic coordinates
Broca’s area
- speech production
Corticospinal tract
Originates in multiple
cortical areas
– Primary motor cortex
– Pre-motor cortex
* Route via:
– Internal capsule
* Between Thalamus &
Basal Ganglia
– Cerebral peduncles
* Contralateral crossing at
the pyramids (medulla)
internal capsule (coronal view)
internal capsule (horizontal view)
Where do pyramidal motor tracts travel?
Pyramidal motor tracts travel in
ventral brain stem/ pons
pyramidal dessucation
Pyramidal
decussation
– Near complete
crossing of the
pyramidal tracts
* 90% contralateral
* 10% ipsilateral
– Ipsilateral tract
thought to be partially
responsible for
recovery after
unilateral motor
cortex damage
Corticobulbar tract
- motor cortex to cranial nerve
nuclei in the brainstem - muscles of face, head, and
neck - usually innervate bilaterally
- travel in the genu of the
internal capsule - do NOT have major crossing
in the pyramids
Reticulospinal tract
- extrapyramidal
- arises from the
reticular formation - primary roles are for
postural control and
locomotion
– particularly proximal
and axial muscle
groups
Vestibulospinal Tract
- extrapyramidal
- relays information from
the vestibular nuclei
(VIIIth-
vestibulocochlear nerve) - support posture and
balance, control head
movements
Rubrospinal
tract
- extrapyramidal
- originates in red nucleus
– in midbrain, neighboring
substantia nigra - axon fibers cross/decussate
in midbrain - function
– cerebellar inputs: carry out planned
movements
– alternative to the corticospinal system
Tectospinal tract
- extrapyramidal
- originates in midbrain tectum,
terminates in spinal cord - mediates reflex postural
movements of the head, based
on visual input arriving at the
superior colliculus
Spinal Cord Motor Organization
- Gray Matter
– Dorsal/Posterior Horn
– Ventral/Anterior Horn - Where the a-motor neurons live
- White Matter
– Posterior Funiculus
– Lateral Funiculus - Carries the descending corticospinal
tract (from the opposite side)
– Anterior Funiculus - Dorsal Root Ganglion
– Sensory Input - Ventral Root (aka
Anterior root)
– Where the motor output heads out to
the muscles
a-motor neuron
the “lower motor neuron”
* cell body is in the spinal cord, but axon extends
into the PNS
* axon can be up to 3-4 feet long
* innervates extrafusal (skeletal) motor fibers
* motor unit: a-motor neuron + its muscle fibers
* the number of a-motor neurons is proportional to
the degree of control
* #finger a-motor neurons»_space; #quadriceps a-motor neurons
- cell bodies sit in the ventral cord
– aka ventral horn
– aka anterior horn
Neuromuscular
Junction
- synaptic connection from the
nervous system to the muscle - Action potential triggers calcium
release - Docking and then release of vesicles
containing ACh
The Motor Unit
*a-Motor neuron and
the extrafusal muscle
fibers it innervate
* The building block
of movement
- Extrafusal (skeletal) muscle
– innervated by a-motor neurons
– generate tension by contracting
- Intrafusal muscle
– innervated by g-motor neurons or sensory
neurons
– comprise the muscle spindle
– proprioceptor reporter of muscle contraction
Golgi Tendon Organ
- Forcereceptor in tendon of muscles
- a proprioceptive sensory receptor organ
– tree-like sensory ending enclosed in a spindle-like connective tissue capsule, that
lies near the junction of a tendon with a muscle - Sensory input
reporting on muscle
contraction - Strongly activated
by muscle contraction
– Less activated by
passive muscle
stretch
Muscle Spindles
- sensory receptor in
extrafusal muscles
– senses changes in
length of muscle - Innervated by g-motor
neurons
– to contract sensory
fibers
– Keeps gamma
fiber/sensor at same
proportional length as
the rest of the muscle
Step reflex
- Present at birth
- When sole of foot touches a flat surface,
infant will “walk” by placing one foot in
front of another - Reflex suppressed ~ 6 weeks of age
- alternating contractions of flexor and
extensor muscles
does not require
cortical input
Walking is controlled by which muscle tracks?
extrapyramidal. use gait analysis to test this
- CPG: central pattern generator
– located in ventral spinal cord
– functions independently:
“a neural network that produces rhythmic
patterned output without motor or sensory input”
– exist for locomotion, swallowing, respiration…
Locomotor CPG
- vertebrate locomotor CPG comprises a distributed
network of interneurons and motor neurons - generates an organized motor rhythm
- Descending inputs from the brainstem, basal ganglia and
cortex control the selection and shaping of outputs from
the locomotor CPG
– basal ganglia
– corticospinal
– rubrospinal
– reticulospinal - additional modulation coming from sensory and vestibular
pathways that converge on CPG neurons
– tectospinal
– vestibulospinal
CPG Organization
in Mammals
- CPGs at different levels in the spinal cord
have different functions
CPG interneurons have unique properties
and have distinct developmental profiles
