Motor Pathways Flashcards
walking, chewing, and other pre-programmed movements may be initiated independent of higher brain input. This is mainly an interaction between local circuit neurons and motor neurons
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Motor cortex mostly responsible for what?
planning, initiating, and directing voluntary movements
Brainstem centers responsible for?
regulating tone, and orienting posture with respect to sensory info
Cerebellum does what?
acts as a servomechanism, detects the difference between an intended movement and the movement actually performed
The cerebellum uses this movement to mediate both real-time and long-term adjustments
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Basal ganglia does what?
Suppresses unwanted movements an dprepares upper motor neuron circuits for the initiation of movements
What the hell is an upper motor neuron
One contained entirely within the central nervous system. No part of this neuron leaves
What is a lower motor neuron?
A neuron that has a cell body in the CNS but is projecting its axon into the peripheral nervous system to innervate something anc cause an action
What layers of Rexed’s laminae are the local circuit, autonomic, and commisural neurons found in?
layers 7 and 8
Lower motor neurons are located in what level?
layer 9
Lateral corticospinal tract serves what?
Anterior corticospinal tract serves what
ipsilateral motor neurons serving the distal extremities
Anterior corticospinal tract serves axial musculature
What corticospinal tract serves axial muscles?
Ventral
Does one motor neuron innervate several muscle fibers?
Yes…the larger the cell body of a motor neuron, the greater th enumber of fibers it synapses with
Know that fine motor control is achieved by having only a single motor neuron innervate only a few muscle fibers, thus achieving precise control
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Three general muscle fiber types are
1) Slow Fatigue Resistant
2) Fast Fatigue Resistant
3) Fast Fatiguable
The motor neurons of slow resistant fibers tend to be small in size, thus the ratio of muscle fibers per neuron are also small. They also tend to be rich in mitochondria, myoglobin, and capillary beds
ok….dark meat, because of their myoglobin content
SLow fatigue resistant muscles function mostly via which type of metabolism
aerobic
Fast fatiguable muscle is inervated by much larger motor neurons and thus the muscle fiber to neuron ratio is very high
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What is a motor unit
a group of muscles innervated by a single lower motor neuron
What is the name of neurons that innervate skeletal muscle fibers to form motor units?
alpha motor neurons
Alpha motor neurons can receive feedback from sensory organs within the bed of the muscle (spindle organs). The afferent neurons from these sensory organs have cell bodies in the DRG.
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What is a common excitatory neurotransmitter for alpha motor neurons
acidic amino acids
Common inhibitory neurotransmitters
GABA and Glycine
muscle spindles give rise to what tpes of afferent nerves
Types Ia and type II
What are the two types of sensory organs within the muscle bed
Spindle organs and Golgi Tendon organs
Golgi Tendon organs give rise to what type of afferent nerves
Type Ib
What does a gamma motor neuron do?
fires in concert with alpha motor neurons to insure that the intrafusal muscle fibers don’t become relaxed and non-responsive.
Type II afferent nerves from muscle spindles…encodes muscle length information in the frequency of action potentials. Greater length = increased frequency of action potential, decreased lenght means decreased frquency
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What does type Ia afferent encode
length and velocity of muscle change….quick change in muscle length generates a drastic increase in frquency
Know golgi tendon organ stuff
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Atrophy, decreased reflexes, decreased muscle tone, and fasiculations are all features of what kind of nerve lesion
lower motor neuron.
Origins of upper motor neuron cell body located in the motor cortex which is located where?
precentral gyrus
What are large motor neurons called?
Betz cells
Precentral gyrus also called what?
Brodmann area
Premotor area associated with which Brodmann area?
Brodmann area 6
Primary somatosensory cortex associated with which Brodmann area
3,1,2
Parietal asssociation cortex associated with which Brodmann area?
5,7
Corticolubular tract is responsible for what?
fibers from the motor cortex to the cranial nerve motor nuclei
Vestibulospinal tract does what
Fibers originate from vestibular nuclei, terminate at the cervical and thoracic spinal cord levles to innervate neck and trunk muscles
Reticulospinal tract does what?
Fibers originate from neurons in the reticular system located diffusely in the brainstem. This tract along with the vestibulospinal tract terminates largely at the cervical and thoracic spinal cord level to innervate neck and trunk muscles
Rubrospinal tract
fibers originate in the red nucleus. Travels closely with the lateral corticospinal tract and participates in control of arm muscles.
Colliculospinal / tecto-spinal tract
Fibers originate from the superior colliculous. Terminates largely at the cervical spine to to innervate neck muscles. Coordinates head movements with eye movements
Normal plantar response to stroking the lateral side of the foot with a blunt object=
flexion of the big toe and sometimes other toes
Abnormal response to stroking the lateral side of the foot with a blunt object
Babinski sign…extension of the big toe and fanning of the other toes. means you have an upper motor neuron lesion, dawg
Lower motor neurons serving the extremities are located where in the ventral horn?
Laterally
Lower motor neurons serving the axial musculature located where
medial
motor unit=
a group of muscle fibers inervated by a single lower motor neuron (or alpha neuron). Motor units vary in size and their size is determined by the number of fibers that are innervated which is in direct correlation with size of the motor neuron.
When excitatory connections are made to motor neurons from afferents projecting above or below the spinal cord segment in which the motor neuron resides, the connection is through….
an excitatory interneuron!!!
Corticobulbar pathway
fibers from the motor cortex to the cranial nerve motor nuclei
