UMN and LMN Flashcards
UMN division: Cortical = Pyramidal motor system
- regulates LMN activity that results in highly skilled motor activity
- includes discretely organized, interconnected white matter structures formed by axons that pass through the pyramids
UMN system division: non-cortical = extrapyramidal motor system
- regulates LMN activity responsible for muscle tone, posture, and stereotyped/coarse movement (lower level movement)
- includes motor centers scattered in each division of the brain with axons that are not associated with the pyramids
Anatomy of pyramidal system: Motor cortex
- Cell bodies located in the pre- and post- cruciate gyri depending on species
- descending axons from the cell bodies contribute to the formation of discretely organized and identifiable bundles of white matter
White matter structures of the pyramidal motor system
- corona radiata: fan-shaped
- internal capsule: coarse of white matter axons
- Crus cerebri: at midbrain
- Longitudinal fibers of the pons: at level of metencephalon
- pyramids: at the level of myelencephalon
- axons continue to form corticospinal tract (lateral and ventral divisions)
Tracts of the pyramidal system: Corticonuclear system
(named based on destination)
-from the pyramidal motor cortex to LMN nuclei in the brainstem of cranial nerves III-VII and IX-XII
Tracts of the pyramidal system: Corticospinal system
- From the pyramidal motor cortex to LMN in the spinal cord
- > lateral corticospinal tract: 75% of pyramidal fibers cross pyramidal decussation, descend into the spinal cord to regulate appropriate contralateral LMN in ventral gray column
- > ventral corticospinal fibers: 25% of pyramidal fibers do not cross in the pyramid but descend ipsilaterally through rest of the brainstem and then in the ventral gray column
Cord location for corticospinal fibers
within lateral funiculus and ventral funiculus
Anatomy of the extrapyramidal motor system
extrapyramidal centers are found in all five divisions of the brain with some nuclei more important than others in animals
telencephalic centers
- cerebral cortex - neurons scattered on the surface
- subcortical nuclei called basal ganglia forming an area known as the corpus striatum
Corpus Striatum
- area of telencephalon under surface of the cortex formed by alternating bundles of white matter and extrapyramidal nuclei
a) external capsule (white matter)
b) lentiform nucleus - facilitates appropriate movement and inhibits inappropriate movement- putamen: receives information (afferent)
- pallidum (globus pallidus): Sends information out of corpus striatum to other extrapramidal areas (efferent)
c) internal capsule (white matter fibers)
d) Caudate nucleus - receives information (afferent)
Cerebral input: Pyramidal system
- Corticopontine fibers = Corticopontocerebellar tract
- from the pyramidal motor cortex to pontine nucleus for synapse
- fibers cross to form cortralateral middle cerebellar peduncle that enters cerebellum (pontocerebellar fibers)
Cerebral input: Extrapyramidal system
- Olivocerebellar tract
- olive nucleus: receives info from extrapyramidal structures and sends to the cerebellum as olivocerebellar fibers
Clinical signs of UMN disease
Due to loss of regulatory inhibition of the LMN; disturbance of mechanism for regulation of voluntary motor function and maintenance of muscle tone
1) hyperreflexia
2) hypertonus
3) spastic paralysis
4) slow muscular atrophy over time
anatomy of extrapyramidal motor system: Diencephalon
- zona incerta
- endopeduncular nucleus
- subthalamic nucleus
anatomy of extrapyramidal motor system: Mesencephalon
- substantia nigra (affected in parkinson’s dz)
- tegmental nucleus
- *RED NUCLEUS = most important extrapyramidal center in animals
Red Nucleus
- afferent information: into the nucleus - info from motor cortex, other extrapyramidal nuclei, cerebellum
- efferent information: out to the spinal cord for LMN regulation - rubrospinal tract in lateral funiculus
anatomy of extrapyramidal motor system: metencephalon
-pontine reticular formation and nucleus (excitatory)
-axons cross to form the pontine reticulospinal tract
(also called the ventral reticulospinal tract)
anatomy of extrapyramidal motor system: Myelencephalon
-Medullary reticular formation and nucleus (inhibitory)
-axons cross to form the medullary reticulospinal tract
(also called the lateral reticulospinal tract)
extrapyramidal output to spinal cord: main paths
-rubrospinal, pontine reticulospinal, medullary reticulospinal represent summated output of extrapyramidal system to the spinal cord LMN
Summary of Pyramidal tract
- corticonuclear tract to LMN nuclei in the brainstem to face (and head)
- Corticospinal tracts to LMN in ventral gray horn of spinal cord limbs (and trunk)
Summary of extrapyramidal system
rubrospinal, pontine reticulospinal, and medullary reticulospinal tracts = output
vestibulospinal = important for regulation, posture, and m. tone
Upper Motor Neurons
- neurons contained within CNS that regulate LMN in the brainstem and spinal cord
- Function to initiate voluntary movement, maintain m. tone and posture, and regulate viscera
Final common pathway
- innervation to the largest target structure
- convergence: number of fibers converging on a cell
- summation: adds up all fibers coming down (excitatory and inhibitory fibers = inhibitory influence)
component of the LMN system: spinal neurons
- one functional group based on target structure but to cell sizes
- ventral horn: neuron cell bodies classified by size and what they innervate
- GSE neurons to extrafusal fiber: regular skeletal m. fibers (alpha motor neurons - large)
- GSE neurons to intrafusal fiber: modified skeletal m. fiber - specialized m. spindle (gamma motor neurons - small)
component of the LMN system: Cranial neurons
- GSE (general somatic efferent) = voluntary skeletal m. located in head and face
- SVE (special visceral efferent) = skeletal m. of branchial arch origin aka pharyngeal arch origin
- GVE (general visceral efferent) = cardiac and smooth m., glands
reflex arc
receptor -> interneuron (usually) -> efferent fiber -> effector/target
monosynaptic arc
myotatic reflex (Ex. knee jerk)
polysynaptic arc
more common, interneurons present
Ex. fibers traveling up and down forming fasiculus proprious
lesion sites
- Neuromuscular junctions: toxins block transmission
- peripheral nerve: inflammation or trauma (ex. cut nerve)
- spinal nerve proper: trauma, fracture, neoplasia (short segment where 2 branches have fusion at level of intervertebral foramen)
- ventral root: trauma, fracture, neoplasia (initial part of nerve fiber coming from spinal cord)
- cell body: pressure, ischemia (produce signs of LMN dz)
LMN signs
- hyporeflexia
- hypotonia
- flaccid paralysis
- atrophy of muscle in relatively short time
What produces cranial nerve nuclei (2)
Neurobiotaxis - cell body wants to be close to its target
columnar fragmentation - movement causes column to become fragmented
Nucleus location for oculomotor nerve/CN III
Rostral colliculus
Nucleus location for trochlear nerve/CN IV
Caudal colliculus
Nucleus location for abducens nerve/CN VI
Caudal cerebellar peduncle
Nucleus location for hypoglossal nerve/CN XII
Obex
If CN III/IV/VI are affected, what general GSE signs will you see
Strabismus (extraocular mm.)
If CN XII is affected, what general GSE signs will you see
Atrophy, usually on the side of the lesion
GSE innervation and location
Innervation of extraocular and tongue mm., located at midline
SVE innervation and location
Innervation of skeletal m. of branchial arch origin, most lateral
GVE innervation and location
Visceral motor system and autonomic motor innervation, located between GSE and SVE
SVE nuclei and nn.
CN 5, 7, 9, 10, 11
Trigeminal n. origin
Motor nucleus of the trigeminal nerve, in metencephalon at level of the rostral cerebellar peduncle
Trigeminal n. innervation
mm. of mastication - 3 mm. act to close, 1 to open (also innervated by facial n. so can still open)
Trigeminal n. signs
Inability to close jaw (“dropped”)
Facial n. origin
Motor nucleus of the facial nerve, in myelencephalon halfway b/w trapezoid body and olive, forms genu that goes around root for CN VI - can also be affected
Facial n. Innervation
mm. of facial expression
Facial n. signs
Facial paralysis
CN IX-XII origin
Nucleus ambiguus
CN IX and X innervation
Palate, pharynx, larynx, esophagus
CN IX-XI signs
Difficulty swallowing = dysphagia, squeaky bark (voice box mm.)
CN XI innervation (internal and external roots)
- internal root - to larynx and esophagus with CN X
- external root - to cervical m.
CN XI signs
Muscle atrophy (external root); internal root can’t be distinguished bc mixed with CN X
2 neuron model for autonomic (symp and parasymp) innervation
Synapse in ganglion prior to teaching target of innervation; synapse in cranial part of system is a “named” or “terminal” ganglion
Origin (preganglionic cell body) and synapse (postganglionic cell body) for parasymp nucleus CN III
Origin - Edinger Westphal
Synapse - ciliary ganglion
Origin (preganglionic cell body) and synapse (postganglionic cell body) for parasymp nucleus CN VII
Origin - rostral salivatory, lacrimal
Synapse - mandibular and pterygopalatine ganglia
Origin (preganglionic cell body) and synapse (postganglionic cell body) for parasymp nucleus CN IX
Origin - caudal salivatory
Synapse - otic ganglion
Origin (preganglionic cell body) and synapse (postganglionic cell body) for parasymp nucleus CN X **synapse in a terminal ganglion (vs. named - all others)
Origin - dorsal vagal nucleus
Synapse - terminal ganglia in organ walls
Functional LMN components in CN III
GSE - extraocular mm.
GVE - intraocular mm.
Functional LMN components in CN IV
GSE - extraocular
Functional LMN components in CN V
SVE - mastication
Functional LMN components in CN VI
GSE - extraocular
Functional LMN components in CN VII
SVE - facial expression
GVE - lacrimal and salivary gl.
Functional LMN components in CN IX
SVE - pharyngeal mm., palate
GVE - salivary gl.
Functional LMN components in CN X
SVE - pharynx, larynx
GVE - body organs, cardiac and smooth m.
Functional LMN components in CN XI
SVE (external root) - cervical mm. (Disregard internal root - functionally part of CN X)
Functional LMN components in CN XII
GSE - lingual mm.
