Motor Systems: Spinal Cord and the Motor Unit Flashcards
Types of motor organs
Cilia
Glands
Muscles
Types of glands
endocrine
exocrine
Types of exocrine glands
internal
external
Types of muscles
smooth
striated
Types of smooth muscles
visceral
peripheral
Types of striated muscles
cardiac
skeletal
Motor Pools
Clusters of motor neurons in the spinal cord
Lower motor neurons reside in the _____ horn of the spinal cord.
ventral
Neurons that control the proximal muscles are located in the _____.
medial ventral horn
Neurons that control the distal muscles are located in the _____.
lateral ventral horn
Pathways in the medial part of the spinal cord control _____.
posture
Pathways in the lateral spinal cord control _____.
fine movements in extremities
Flexor and extensor muscles work together through _____.
complementary excitation and inhibition
Length change in _____ create the reflex negative feedback control mechanism.
muscle fibers
_____ innervate the extrafusal, force-producing fibers which control posture and movement.
alpha motor neurons
_____ innervate intrafusal muscle fibers (_____) to control tension on the receptors.
gamma motor neurons
muscle spindles
a single _____ innervates many muscle fibers.
alpha motor neurons
_____ spread force evenly across a muscle.
alpha motor neurons
Types of alpha motor neurons
fast fatigable
fast fatigue-resistant
slow
Fast fatigable alpha motor neurons are _____ and have a _____ threshold.
large
high
Fast fatigue-resistant alpha motor neurons are _____ and have a _____ threshold.
medium size
medium
Slow alpha motor neurons are _____ and have a _____ threshold.
small
low
Slow alpha motor neurons are mainly used for _____.
posture
Fast fatigable alpha motor neurons are used for _____.
generating a lot of force
ex: running
At higher frequencies, muscle fiber twitches _____.
summate
Higher force requirements recruit more and more _____.
neurons
Group Ia afferents - known as _____ - respond phasically to _____.
nuclear bag fibers
small stretches
Group II afferents fire tonically to signal _____.
degrees of sustained stretch
_____ help maintain posture and balance, allowing one to walk without consciously thinking about each step.
Monosynaptic stretch reflexes
Feed-forward inhibition enhances the effect of the _____ by suppressing the _____.
active pathway
opposing pathway
Activation of the _____ ensure that only the appropriate muscle gets activated.
inhibitory interneurons
Feed-back inhibition serves as a _____ to prevent _____.
self-regulating mechanism
over-excitation
_____ regulate excitability of muscle spindles.
gamma motor neurons
Mechanoreceptors in golgi tendon organs predominantly signal changes in _____.
muscle tension
Golgi tendon organs provide _____ via inhibitory interneurons in the spinal cord.
negative feedback
Painful esnsory stimulation leads to _____.
flexion reflex
Flexion reflex inhibits the _____ and activates the _____.
extensor
flexor
The flexion reflex is accompanied by the _____.
crossed extension reflex
The crossed extension reflex serves to _____ by activating the _____.
maintain posture/balance
opposite side
_____ are excited by collaterals from motor neurons and inhibit those same motor neurons.
Renshaw cells
Local circuit neurons in the intermediate zone of the spinal cord are _____.
topographically arranged
Upper motor neurons in the cortex reside in layer __ of the _____.
5
primary motor cortex
Betz-cells are _____ than pyramidal cells.
larger
Betz-cells are specific to _____.
layer 5 of the primary motor cortex
Layer 5 neurons from the primary motor cortex and premotor cortex form the _____.
pyramidal tract
The corticospinal and corticobulbar tracts intersect at the _____.
internal capsule (forebrain)
The pyramidal tract consists of the _____ and _____ tracts.
corticospinal
corticobulbar
The pyramidal tract first enters the midbrain through the _____.
cerebral peduncle
The pyramidal tracts projections through the _____ give its name.
meduallary pyramids
Corticobulbar projections of the pyramidal tract terminate only in the _____.
brainstem
The corticospinal projection innervates the _____.
spinal cord
__% of fibers in the cortical spinal tract form the lateral tract.
90
__% of fibers in the cortical spinal tract form the ventral tract.
10
_____ is the reason why a side of the brain controls the contralateral side of the body.
decussation
The corticobulbar tract terminates on motor neurons within the _____.
brainstem motor nuclei
The corticospinal tract controls _____.
spinal motor neurons
Pyramidal tract neurons innvervate multiple motor neurons that control _____.
multiple/different muscles
maps of movement/coordination
__% of axons in the corticospinal tract arise directly from the premotor cortex.
30
Activity of the _____ is related to motor planning, preparatory activity, and selection of a movement.
premotor cortex
_____ in the prefrontal cortex are responsible for understanding movements of others.
mirror neurons
Mirror neurons do not fire when an experimenter _____.
uses a tool
Mirror neurons encode _____.
intentions of self and others
Extrapyramidal tracts are responsible for _____.
involuntary reflexes, movement and it’s modulation
Motor control of the brainstem controls _____, _____ and _____.
balance
posture
gaze
Feedforward mechanisms act through the _____ to predict resulting disturbances in stability and generate stabilizing responses.
reticulospinal pathway
Extrapyramidal tract projections terminate in the _____.
reticular formation
The reticulospinal pathway projects to motorneurons in the spinal cord that control _____ to stabilize posture.
axial and proximal muscles
The tectospinal pathway targets the _____.
tectum
superior/inferior colliculus
The reticulospinal pathway targets the _____.
pontine and medullary reticular formation
The vestibulospinal pathway targets the _____.
lateral and medial vestibular nuclei
The colliculospinal pathway from the superior colliculus controls _____ to orient _____.
neck muscles
head and eye movements
The reticulospinal pathway controls temporal and spatial coordination of _____.
limb and trunk movements
The vestibulospinal pathway controls _____.
reflex control of neck muscles (medial)
The vestibular nuclei receive inputs from cranial nerve __.
VIII
inputs from semicircular canal and otolith organ
The reticulospinal pathway integrates information from the motor systems to coordinate _____.
automatic movements of locomotion and posture
The reticulospinal pathway facilitates and inhibits _____ and influences _____.
voluntary movement
muscle tone