CH 8: Motor Pathways Flashcards
Brodmann areas:
based on differences in cytoarchitecture in the cerebral cortex
52 anatomic areas
what area is the primary motor area?
Brodmann’s area 4
lies in the precentreal gyrus and paracentral lobule of the frontal lob
the left motor strip of the primary motor area controls the ..?
right side of the body
the right motor strip of the primary motor area controls the …?
left side of the body
neurons in the lowest lateral part of the primary motor area influence the:
followed in:
larynx and tongue
followed in upward sequence by neurons affecting the face, thumb, hand, forearm, upper arm, thorax, abdomen, thight, leg, foot and perineal muscles
the neurons controlling the leg, foot and perineal muscles are in the :
paracentral lobula
areas for the hand, tongue and larynx are :
disproportionally large and conform to the development of elaborate motor control of these muscle groups
what is a homunculus?
the functional map of the motor cortex
resembles a distorted image of the body turned upside down and reversed left for right
immediately rostral to the primary motor area lies the:
premotor cortex (Brodmann’s area 6) on the lateral surface of the hemispheres
contains a homunculus similar to the one in area 4
what is the supplementary motor area?
the most medial aspect of area 6 can be observed on a midsagittal section of the brain just rostral to the paracentral lobule
also contains a functional map of body movements
what are additional regions of cerebral cortex that can influence movement?
Brodmann’s areas 3,1,2 on the postcentral gyrus
and the secondary motor area
where is the secondary motor area?
where the pre and post central gyri are continuous at the base of the central sulcus
overlaps the secondary somatosensory cortex
what is brodmann’s area 8 called?
frontal eye fields
contains neurons that specifically influence eye movements
the brainstem and the SC contain pattern generators for:
complex movements such as locomotion and other rhythmic activities
the descending pathways of the NS have the important task of:
interacting with and controlling lower-level neuronal patterns of discharge in a hierachical manner
at the level of the cerebral cortex, individual neurons can:
control the contractions of individual muscles and can determine the force of these contractions
populations of motor cortical neurons act together to:
specify the direction of movements and the force of movements
these functions pertain not only to neurons in the primary motor cortex but also to those in the premotor, supplementary, and postcentral regions
the premotor and supplementary motor areas are important in:
planning movements
the supplementary motor area appears to have a special role in:
integrating movements performed simultaneously on both sides of the body
skeletal muscle activity results from the:
net influence of higher nervous system structures on motoneurons of the SC and cranial nerve nuclei
what are lower motor neurons?
collectively SC and brain stem neurons provide the final direct link with muscles through neuromuscular junctions (motor end plates)
their cell bodies reside within the CNS and their axons make synaptic contact with extrafusal and intrafusal muscle fibers of somatic and branchiomeric origin
somatic muscle fibers derive from the:
myotomes of true somites in the developing embryo
branchiomeric muscles develop from:
the branchial arches of the embryo
are not true somites but muscles develop from them
like somatic muscle they are striated and under voluntary control
includes muscles of mastication and facial expression, and muscles of the pharynx and larynx
what are upper motoneurons?
regulate lower motoneuron activity
the cerebral cortex, cerebellum and basal ganglia control these descending pathways either directly or indirectly
synapse directly or through interneurons on alpha, beta and gamma motoneurons in the SC and cranial nerve nuclei
contained completely within the CNS
refers to the corticospinal tract and the corticobulbar tract
the corticospinal tract is also know as:
the pyramidal tract
what does the corticospinal tract control?
primarilly skilled movements of the distal muscles of the limbs and facilitates the alpha, beta, and gamma motoneurons that innervate distal flexor musculature
where do the axons in the corticospinal tract originate?
1/3 originate in primary motor cortex (area 4)
1/3 arise in the premotor and supplementary motor regions in area 6
1/3 originate in the parietal lobe (areas 3,1,2)
together, the areas of cortex that contribute to the corticospinal and corticobulbar pathways are called the :
sensorimotor cortex
the corticospinal tract passes through the ____ and then ____
posterior limb of the internal capsule and the middle of the cerebral peduncle
it then breaks up into bundles in the basilar portion of the pons and finally collects into a discrete bundle to form the pyramid of the medulla
the corticospinal tract bears the name the pyramidal tract because of :
its passage through the medullary pyramid
in the lower level of the medulla, most of the corticospinal tact:
crosses (decussates) to the opposite side
termed the level of the motor or pyramidal tract decussation
about 90% of the corticospinal tract fibers cross at the level of the pyramidal tract decussation and descend through the SC as the :
lateral corticospinal tract
which passes to all SC levels in the lateral funiculus and synapses in the lateral aspects of the laminae IV-VIII
the remaining 10% of corticospinal tract fibers that don’t decussate in the medulla descend:
in the anterior funiculus of the cervical and upper thoracic cord levels as the Ventral corticospinal tract
doesn’t not extend below the upper thoracic SC
at their individual levels of termination, most fibers in this pathway descussate through the ventral white commissure before they synapse on interneurons and motoneurons of the contralateral side
the corticospinal tract fibers that synapse on interneurons in the base of the dorsal horn (IV, V and VI) can influence:
local reflex arcs and cells of origin of ascending sensory pathways
through this system, the cerebral cortex can control reflex motor output and can also modify sensory input reaching the brain
the cortical neurons that give rise to the corticospinal tracts use:
glutamate as a neurotransmitter and excite the neurons on which they synapse
the corticospinal tract can exert either __ or ___ effects on motoneurons
excitatory
inhibitory
excitatory effects result from:
direct (monosynaptic) connections with motorneurons
inhibitory effects occur through:
synaptic connections on inhibitory interneurons
many of the interneuons mediating inhibitory effects use glycine as a neurotransmitter
fibers of the coricobulbar tract arise from:
neurons in the ventral part of the sensorimotor cortex on the lateral surface of the hemisphere from brodman’s area 8
the cranial nerve motor nuclei receive innervation from:
both cerebral hemispheres, and in most cases, the muscles they control cannot be contracted voluntarily on one side only
a lesion of one cerebral hemisphere results in:
weakness primarily on the contralateral side
like the corticospinal tract, the corticobulbar tract contains fibers that terminate on:
sensory “relay” neurons
what is the corticotectal tract?
pathway that arises from the cerebral cortical areas in the occipital and inferior parietal lobes and projects to the upper parts of the brain stem to influence extraocular muscle activity
many of these fibers synapse in the superior colliculus, the interstitial nucleus of Cajal, or the nucleus of Darkschewitsch. these nuclei project to the pontine reticular formation and from there through the medial longitudinal fasciculus (MLF) to synapse on the oculomotor, trochlear and abducens nuclei
corticotectal fibers make connections in the:
deep layers of the superior colliculus with neurons that give rise to the tectospinal tract
axons of these cells cross the midline in the dorsal tegmental decussation and descend through the brain stem ventral to the MLF
in the SC, the tectospinal tract becomes incorporated into the:
MLF, with which it travels through the ventral funiculus.
the tectospinal fibers extend only through the :
cervical segments of the SC, where they influence neurons innervating muscles of the neck, including the neurons of the spinal accessory nucleus (CN XI)
the corticotectal-tectospinal projections are concerned with:
turning movements of the head and eyes, possibly combined with reaching movements of the arm
corticotectal fibers have a greater influence on reflexive than on voluntary eye movments
the corticorubral and rubrospinal tracts represent:
an indirect route from the cerebral cortext to the SC
fibers originating from the same cortical areas that give rise to the corticalspinal tract also form the :
corticorubral tract
the corticorubral tract projects to the :
ipsilateral red nucleus in the tegmentum of the midbrain
neurons of the red nucleus give rise to the:
rubrospinal tract
which crosses the midline in the central tegmental decussation and descends through the lateral tegmentum of the pons, midbrain and medulla
the rubrospinal tract is functionally similar to the:
corticospinal tract in that it generally facilitates flexor and inhibits extensor alpha, beta and gamma motoneurons, particularly those innervating the distal parts of the arms
the reticular formation consists of :
a matrix of nuclei in the core of the brain stem that receives sensory info from numerous systems and interconnects heavily with the cerebellum and the limbic system
the reticular formation receives a large input from :
corticoreticular fibers which accompany the corticospinal and corticalbulbar fibers
corticoreticular fibers from each hemisphere terminate bilaterally in the brain stem
the corticoreticular system arises from cells outside and within the sensorimotor cortex
what are the 2 areas of the reticular formation that send major projections into the SC?
1- pontine (medial) reticulospinal tract
2- medullary (lateral) reticulospinal tract
the pontine reticular formation gives rise to the:
uncrossed pontine (medial) reticulospinal tract
in the medulla and the cervical segments of the SC this pathway travels within the MLF
in the thoracic SC, where the MLF ends, the medial reticulospinal tract continues through the ventral funiculus to all cord levels. its fibers synapse in laminae VII and VIII
the pontine tract is mainly excitatory for:
extensor alpha motoneurons, particularly those innervating the midline musculature of the body and the proximal parts of the extremities.
it also provides an important input to gamma motoneurons.
through these connections the pontine reticulospinal tract influences posture and locomotion
the medullary reticular formation gives rise to the:
medullary (lateral) reticulospinal tract
primarily uncrossed but has a small crossed component.
this tract passes to all spinal cord levels in the lateral funiculus immediately anterior to the rubrospinal tract
it synapses in laminae VII and IX
the medullary reticulospinal tract conveys:
autonomic information from higher levels to the preganglionic sympathetic and parasympathetic neurons to influence respiration, circulation, sweating, shivering and dilation of the pupils as well as the function of the sphincteric muscles of the GI and urinary tracts
raphe nuclei
constitute a special subgroup of the larger group of nuclei that make up the reticular formation
fibers arising from neurons within the caudal raphe nuclei project to the SC where they influence transmission of incoming sensory signals and motor responsiveness. these fibers pass down the entire length of the SC near the surface of the lateral funiculus and terminate with laminae I, II V and VII
doesn’t evoke movement but depending on the inputs it receives, can produce either general excitatory or general inhibitory effects that greatly influence motoneurons responsiveness to reflex or corticospinal inputs.
thus they function as a gain setting system that determines overall motoneuron responsiveness.
particularly important in modulating the responsiveness of the motor system in different phases of sleep-waking cycles and with changes in emotional state
vestibulospinal tracts arise from:
neurons in the vestibular nuclei of the medulla
what are the 2 vestibulospinal tracts?
lateral : extends the entire length of the cord
medial: becomes incorporated into the MLF and ends with the MLF in upper thoracic levels
both vestibularspinal tracts pass:
into the anterior funiculus and synapse on cells in laminae VII and VIII
the lateral vestibulospinal tract evokes:
excitatory postsynaptic potentials in extensor motoneurons innervating the neck, back, forelimb and hindlimb muscles
these excitatory postsynaptic potentials are monosynaptic for neck motoneurons and some back and leg motoneurons
stimulation also evokes reciprocal inhibition in flexor motoneurons through disynaptic or polysynaptic connections
stimulation of the medial vestibulospinal tract evokes:
monosynaptic inhibition and excitation in neck and back motoneurons but does not influence limb motoneurons
the vestibulospinal pathways affect:
postural adjustments of the body accompanying head movements and the maintenance of postural tone
the MLF consists of:
a bundle of several tracts in the midline of the brain stem and the ventral funiculus of the SC
the descending portion of the MLF in the SC contains:
the pontine (medial reticulospinal tract)
the medial vestibulospinal tract
the interstitiospinal tract
the tectospinal tract
the MLF modulates :
reflex movements of the head and neck in response to visual and vestibular stimuli
lateral and ventral corticospinal tracts provide:
the capacity for control of finely fractionated movements- independent movements of the fings
aside from the lateral and ventral corticospinal tracts the remaining pathways descending from the brain that regulate movement cab be described as 2 general projection systems from the brain stem:
lateral and ventromedial sytems
the lateral brain stem system consists of:
fibers arising in the contralateral magnocellular red nucleus that project to the SC through the rubrospinal tract and ibers from the ventrolateral portion of the contralateral pontine and medullary tegmentum that project through the lateal column of the SC
this pathway terminates in the lateral aspect of the dorsal and ventral horns of the SC
like the corticospinal tracts, the lateral brain stem system participates in:
the control of fine manipulative, independent movements of the limbs, particularly of the hands and feet and with discrete motor patterns
these pathways generally facilitates the activity of motoneurons projecting to flexor muscles and inhibits the activity of motoneurons projecting to extensors
the ventromedial brain stem system terminates in the:
ventral and medial aspects of the anterior horn of the SC
the ventromedial pathways participate in:
maintenance of the erect posture, integrated movements of the body and limbs and progression movements of the limbs
these pathways generally facilitate the activity of motoneurons projecting to extensor muscles and inhibit the activity of motoneurons projecting to flexors.
the lateral (medullary) reticulospinal system participates in the:
regulation of autonomic motoneurons
propriospinal pathways play an essential role in”
spinal cord function
