Upper Motor Neurons Flashcards
- lowest, and perhaps most simple, level of organization is present within the
- provides the mechanisms for reflex motor functions
spinal cord
final common path for neurons that innervate skeletal muscle, which constitute the___ for motor responses.
lower motor neurons
- lower motor neurons for both the body and head region are controlled by
- innervate lower motor neurons of the spinal cord and brainstem, either directly or through an interneuron
- arise from the brainstem or cerebral cortex
upper motor neurons
pathways of importance
- vestibulospinal tract
- reticulospinal tract
- rubrospinal tract
- tectospinal tract
most significant of all the upper motor neurons are those that arise from the
cerebral cortex
upper motor neurons that project to the spinal cord are called the
corticospinal tract
- project to lower motor neurons of the brainstem are called the ___
- provide the anatomical substrates for voluntary control of movement.
corticobulbar tracts
- participate in the control of movement by receiving significant inputs from the cerebral cortex and feeding back signals to different regions of the frontal cortex involved in the initiation of movement
- serve to modulate the activity of neurons of the motor regions of the cortex
basal ganglia
receives inputs from most parts of the CNS that contribute to motor functions
cerebellum
corticospinal (or pyramidal) tract arises from three different regions of the cortex
- precentral gyrus
- postcentral gyrus
- supplemental motor area (SMA) & premotor cortex (PMC)
- Approximately 30% of the fibers arise from the
- referred to as the primary motor cortex called βMIβ
precentral gyrus
- Forty percent of the fibers arise from the
- primary somatosensory cortex [S-1] and includes areas 3, 1, and 2
postcentral gyrus
- 30% of the fibers originate from the region immediately rostral to the precentral gyrus (area 6)
supplemental motor area [SMA] and the premotor cortex [PMC]
Electrical stimulation of the dorsal and medial aspect of the precentral gyrus in humans produces movements associated with the
lower limb
stimulation of more lateral aspects of the motor cortex produces movements of the
upper limb
stimulation of the far lateral aspect of the precentral gyrus produces movements of the
face and tongue
functional representation of the precentral gyrus is referred to as a
motor homunculus
- two layers (external & internal)
- receive information mainly from the thalamus and other regions of the cortex
granule cells
- two layers (external & internal)
- serve as the origins of the efferent pathways of the cortex
pyramidal cells
arise from the internal pyramidal cell layer situated mainly in layer V
corticospinal tracts
located within the region of the genu
corticobulbar fibers
Fibers associated with the ___ are located in a more lateral position than those associated with the arm
leg region
fibers associated with the ___ (i.e., corti- cobulbar fibers) are located medial to the corticospinal fibers
head region
At that level, 90% of the fibers cross over to the opposite side in the pyramidal decussation and descend through the lateral funiculus of the contralateral spinal cord, largely as the
lateral corticospinal tract
remaining 10% of the fibers, which remain uncrossed, descend into the
spinal cord
8% as the
anterior corticospinal tract,
2%
crossed lateral corticospinal tract.
cross over to the contralateral side
anterior corticospinal tract
% of the corticospinal tract fibers project to the contralateral spinal cord
98%
% of the lateral corticospinal tract remains ipsilateral over its entire course
2%
Fibers contained within the corticospinal tract are distributed throughout the entire ___ extent of the spinal cord
rostrocaudal
neurons located medially innervate the ___musculature
axial
neurons located more laterally innervate the ___ musculature
distal
innervate the cervical and lumbar cord serve to control fine movements of the extremities
lateral corticospinal fibers
innervate the medial aspect of the ventral horn serve to regulate postural mechanisms
anterior corticospinal tract
innervate the dorsal horn serve to modulate primary sensory afferent information to the cerebral cortex rather than to produce movement
corticospinal neurons
- receives indirect inputs from several important regions that are known to regulate motor activity
- cerebellum and globus pallidus
primary motor cortex
conscious proprioception, position sense, pain, and tactile information
primary somatosensory cortex
sequences of movements require the transmission of βpositiveβ sensory feedback to the regions of motor cortex associated with those movements
descending fibers
regulation of sensory transmission through the nuclei of the dorsal columns and may respond to one or more of the following aspects of movement
(1) alteration of the position of the limb,
(2) rate of change of the position of the limb,
(3) magnitude of the muscular contraction in relation to the force exerted upon an object, and
(4) a combination of force as well as rate of change
contributes 30% of the fibers to the corticospinal tract, consists of two secondary motor regions: the SMA and the PMC
area 6
- provides integrated somatosensory and visual information to area 6
- necessary for the programming of motor sequences
posterior parietal cortex (PPC)
- coordinating voluntary movements
- governs postural adjustments
- affect both the axial and the distal musculature
SMA
Patients who have lesions of the SMA display
apraxia
inability to initiate specific, purposeful movements, even though the sensory and motor pathways for the execution of the movement remain intact.
apraxia
ability to execute a movement upon request. An example is the failure of a patient to be able to brush his or her hair or tie his or her shoelaces
ideomotor apraxia
- inability to conceptualize the movements, and the patient is unable to identify the sequences of movements that are necessary for carrying out the response in question
- apraxia becomes evident when the patient is asked to perform, simultaneously, different movements of both arms
ideational apraxia
- the patient is unable to coordinate the movement of both arms at the same time.
- loss of strength in the proximal muscles of the contralateral arm or leg and have difficulty in raising or abducting that limb
lesions of the PMC
Somatosensory inputs from the postcentral gyrus as well as vestibular inputs are directed to
area 5
- concerned with visual signals
- receives inputs from area 5
area 7
- patient denies the disease condition or is unaware of it
- patient with a right hemispheric lesion may deny or ignore the fact that he or she cannot move his or her left leg
- patient is asked to draw the numbers on a clock, he or she will draw them all on the right-hand side of the clock, while ignoring the left-hand side
sensory neglect (or anosognosia)
responsible for voluntary control over precise movements that affect primarily (but not exclusively) the distal musculature
primary motor cortex (area 4)
- project to the dorsal column nuclei and dorsal horn of the spinal cord
- serve as a sensory filtering mechanism
- allows specific sensory signals, such as the position of a limb or digit of the hand and the force of contraction of a muscle or group of muscles, to reach the relevant regions of the primary motor cortex while preventing sensory signals irrelevant to the movement in question from reaching the cortical neurons critical for that response sequence
primary somasensory cortex (areas 3,1, and 2)
- supplementary and premotor cortices
- serve to provide the programming mechanism for the sequencing of response patterns that are essential for producing movements, such as lacing up oneβs shoes and walking
- project directly to the spinal cord and send signals to the primary motor cortex
area 6
actions of area 6 neurons can only occur if they receive integrated somatosensory and visual signals from the ___
PPC (areas 5 and 7)
arise from the lateral aspect of the primary motor cortex
corticobulbar tracts