Neuro 6 Corticospinal Tract And Other Motor Pathways

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brodmann's area for primary motor cortex

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four

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brodmann's areas for primary somatosensory cortex

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3, 1, and 2

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arms and legs generalization in somatotopic representations

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arms are medial to legs with 2 exceptions: primary sensorimotor cortices and posterior columns

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what is in the ventral (anterior) horn of the spinal cord

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motor neurons

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what is in the intermediate zone of the spinal cord

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interneurons and certain specialized nuclei

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columns of white matter in spinal cord

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dorsal (posterior), lateral, and ventral (anterior) columns

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where is white matter the thickest in the spinal cord

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cervical levels where most ascending fibers have entered and more descending fibers have not terminated

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where is there more gray matter in the spinal cord

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cerival and lumbosacral due to nerve plexuses for arms and legs

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where is the intermediolateral cell column

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lateral horn in thoracic cord

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where does the artery suppling the spinal cord from the vertebral arteries run

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anterior spinal artery runs along ventral surface; two posterior spinal arteries on doral surface (may also come from posterior inferior cerebellar arteries)

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radicular arteries

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segmental arterial branches that reach the spinal cord (about 6-10)

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where are common prominent radicular arteries found

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L side btwn T5 and L3 (usually btwn T9 and T12) = great radicular artery of Adamkiewicz

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importance of great radicular artery of Adamkiewicz

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major blood supply to lumbar and sacral cord

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vulnerable zone of spinal cord to infarction

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T4 to T8

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why is T4 to T8 vulnerable to infarction

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btwn main blood supplies

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veins in spinal cord

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plexus of veins initially draining into epidural space before reaching circulation

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Batson's plexus

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epidural veins; do not contain valves

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importance of no valves in Batson's plexus

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metastatic cells or pelvic infections can travel into epidural space with elevated intra-abdominal P

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two lateral motor systems in spinal cord

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lateral corticospinal tract and rubrospinal tract

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origin of lateral corticospinal tract

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primary motor cortex, other frontal/parietal areas

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four medial motor systems in spinal cord

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anterior corticospinal tract, vestibulospinal tracts, reticulspinal tracts, and tectospinal tract

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why don't unilateral lesion of medial motor systems produce no obvious effects

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terminate on interneurons that project to both sides of the spinal cord-control movements that involve multiple bilateral spinal segments

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what pathway controls movement of the extremities

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lateral coricospinal tract

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lateral corticospinal tract fiber origination

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over half fibers originate in primary motor cortex (5), the rest from premotor and supplementary motor areas (6) or from parietal lobe (3, 1, 2, 5, 7)

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Where do lateral corticospinal neurons synapse

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Layer 5 pyramidal cell projections synapse directly onto motor neurons in the ventral horn and spinal interneurons

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Betz cells

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giant pyrimidal cells; 3% of corticospinal neurons

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Where do axons from cerebral cortex of lateral corticospinal tract go

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upper portion of cerebral white matter (corona radiata), descend toward internal capsule

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What does cerebral white matter convey

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bidirection info btwn different cortical areas, btwn cortex and deep structures (like basal ganglia, thalamus, and brainstem)

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location of internal capsule

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thalmus and caudate nucleus are always medial to and globus pallidus and putamen are always lateral to

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three parts of internal capsule

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anterior limb, posterior limb, genu

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anterior limb location

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separates head of caudate from the globus pallidus and putamen

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posterior limb location

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separates thalamus from globus pallidus and putamen

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genu location

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transition from anterior and posterior limbs at the level of the foramen of Monro

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where is the corticospinal tract in the internal capsule

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posterior limb

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corticobulbar fibers

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project from cortex to brainstem (bulb)

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orientation of somatotopic map in corticospinal tract

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anterior to posterior and medial to lateral: face, arm, trunk, leg

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what does the internal capsule continue into

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midbrain cerebral peduncles

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basis pedunculi

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ventral portion of the cerebral peduncles containing white matter

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what does the middle 1/3 of the basis pedunculi contain

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corticobulbar and corticospinal fibers with face, arm, and leg axons arraged medial to lateral

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what do other portions of the basis pedunculi contain

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primarily corticopontine fibers

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where do corticospinal fibers travel after basis pedunculi

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descend through ventral pons forming scattered fascicles

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where do the scattered fascicles collect

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ventral surface of medulla to form medullary pyramids

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transition from medulla to spinal cord

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cervicomedullary jxn; at level of foramen magnum

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What occurs to corticospinal tract at cervicomedullary jxn

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85% pyramidal tract fibers cross over in pyramidal decussation to enter lateral white matter columns

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What occurs to remaining 15% of corticospinal fibers

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continue ipsilaterally without crossing and enter anterior white matter columns

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where are preganglionic neurons of the sympathetic division located

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intermediolateral cell column in lamina VII or spinal cord levels T1 to L2-3

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two sets of sympathetic ganglia

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paravertebral sympathetic trunk ganglia and paired prevertebral ganglia

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examples of prevertebral ganglia

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celiac around aorta, superior mesenteric, inferior mesenteric

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where do parasympathetic preganglionic fibers arise from

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cranial nerve parasympathetic nuclei and sacral parasympathetic nuclei in lateral gray matter of S2-4

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what receptors do parasympathetic postganglionic neurons activate

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muscarinic cholinergic receptors

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what receptors do preganglionic neurons activate

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nicotinic receptors (acetylcholine)

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what are sympathetic and parasympathetic outflow controlled by

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directly and indirectly by higher centers like hypothalamus, brainstem nuclei (nucleus soltaris), amygdala, several regions of limbic cortex

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what else can autonomic responses be regulated by

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afferent sensory info (chemoreceptors, osmoreceptors, thermoreceptors, baroreceptors)

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signs of LMN lesions

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muscle weakness, atrophy, fasiculations, hyporeflexia

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signs of UMN lesions

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muscle weakness, combination of increased tone and hyperreflexia (spasticity); Babinski's sign, Hoffmann's sign, posturing, etc also seen

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acute UMN lesion

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initially flaccid paralysis with decreased tone and reflexes, which gradually change over hours/months into spastic paresis

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Why is it suspected that damage to inhibitory pathways that travel closely with the corticospinal tract must be injured in order to produce spasticity

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corticospinal lesions alone did not produce symptoms in experimental animals

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what does loss of descending inhibitory influences cause

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increased excitability of alpha motor neurons in anterior horn resulting in brisk reflexes and increased tone; not definitely proven

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unilateral face, arm, and leg weakness or paralysis - Pure motor hemiparesis potential lesion locations

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coticospinal and cortibulbar tract fibers below cortex and above medulla (posterior limb internal capsule, basis pontis, or midle third of cerebral peduncle)

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unilateral face, arm, and leg weakness or paralysis - Pure motor hemiparesis lesion causes

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lacunar infarct of internal capsule or pons, infarct of cerebral peduncle-less common

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unilateral face, arm, and leg weakness or paralysis - Pure motor hemiparesis lesion associated features

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UMN signs present; Dysarthria common; ataxia of affected side occasionally due to involement of cerebellar pathways

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unilateral face, arm, and leg weakness or paralysis - with associated somatosensory, oculomotor, viual, or higher cortical deficits: potential lesion locations

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entire primary motor cortex; corticospinal and corticobulbar tract fibers above medulla

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unilateral face, arm, and leg weakness or paralysis - with associated somatosensory, oculomotor, viual, or higher cortical deficits: associated features

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aphasia or neglect; dysarthria or ataxia; UMN signs

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unilateral face, arm, and leg weakness or paralysis - with associated somatosensory, oculomotor, viual, or higher cortical deficits: causes

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numerous: infarct, hemorrhage, tumor, trauma, herniation, post-ictal state, etc

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unilateral arm and leg weakness or paralysis alternative names

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hemiplegia/hemiparesis sparing the face; brachiocrural plegia or paresis

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unilateral arm and leg weakness or paralysis - lesion locations

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arm and leg area of motor cortex; corticospinal tract from lower medulla to C5

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unilateral arm and leg weakness or paralysis - associated features

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UMN signs; often in watershed distribution - proximal affect more than distal; aphasia or hemineglect if cortical; medial medulla-loss of vibration and joint position sense ilsilateral and tongue weakness contralateral; spinal cord-Brown-Sequard syndrome; high cervical-spinal trigeminal nucleus and tract-decreased facial sensation

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unilateral arm and leg weakness or paralysis - causes

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watershed infarct; medial or combined medial and lateral medullary infarcts; multiple sclerosis; lateral trauma; compression of c-spine

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unilateral face and arm weakness or paralysis - alternative names

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faciobrachial paresis or plegia

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unilateral face and arm weakness or paralysis - lesion locations

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face and arm areas of cerebral cortex; over lateral frontal convexity

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unilateral face and arm weakness or paralysis - associated features

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UMN signs and dysarthria; Broca's aphasia in dominant hemisphere lesions; hemineglect occasionally; sensory loss if extends into parietal lobe

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unilateral face and arm weakness or paralysis - causes

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middle cerebral artery superior division infarct is classic cause; tumor, abcess, or other lesion

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unilateral arm weakness or paralysis - alternative names

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brachial monoparesis or monoplegia

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unilateral arm weakness or paralysis - lesion locations

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arm area of primary motor cortex; peripheral nerves supplying arm

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unilateral arm weakness or paralysis - associated features in motor cortex

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UMN signs, cortical sensory loss, aphasia, subtle involvement of face or leg; pattern of weakness/paralysis

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unilateral arm weakness or paralysis - associated features in peripheral nerve

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LMN signs; pattern of weakness/paralysis

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unilateral arm weakness or paralysis - causes in motor cortex

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infarct of small cortical branch of middle cerebral artery, small tumor, abscess, etc

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unilateral arm weakness or paralysis - causes in peripheral nerve

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compression injury, diabetic neuropathy, etc

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unilateral leg weakness or paralysis - alternative names

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crural monoparesis or monoplegia

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unilateral leg weakness or paralysis - lesion locations

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leg are of primary motor cortex; lateral corticospinal tract below T1 in spinal cord or peripheral nerves of leg

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unilateral leg weakness or paralysis - associated features in motor cortex lesions

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UMN signs, cortical sensory loss, frontal lobe signs (grasp reflex), subtle involvement of arm or face; look at pattern of weakness

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unilateral leg weakness or paralysis - associated features in spinal cord lesions

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UMN signs; Brown-Sequard syndrome, sensory level, or some subtle spasticity of contralateral leg; sphincter fxn; look at pattern

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unilateral leg weakness or paralysis - associated features in peripheral nerve lesions

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LMN signs; pattern of weakness/paralysis

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unilateral leg weakness or paralysis - causes in motor cortex lesions

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infarct in anterior cerebral artery tertiary, mall tumor, abscess, etc

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unilateral leg weakness or paralysis - causes in spinal cord lesions

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unilateral cord trauma, compression by tumor, multiple sclerosis

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unilateral leg weakness or paralysis - causes in peripheral nerve lesions

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compression injury, diabetic neuropathy, etc

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unilateral facial weakness or paralysis - alternative names

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Bell's palsy (peripheral nerve); isolated facial weakness

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unilateral facial weakness or paralysis - lesion locations

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peripheral CN VII; lesions in face area or primary motor cortex or genu of internal capsule; facial nucleus and exiting nerve fascicles in pons or rostral lateral medulla

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unilateral facial weakness or paralysis - associated features in facial nerve or nucleus lesions

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LMN signs; forehead and orbicularis oculi not spared; nerve-hyperacusis, decreased taste, pain behind ear on affected side

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unilateral facial weakness or paralysis - associated features in motor cortex/genu

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forehead relatively spared; dysarthria and unilateral tongue weakness common; subtle arm involvement

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unilateral facial weakness or paralysis - causes in facial nerve

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Bell's palsy; trauma, surgery

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unilateral facial weakness or paralysis - causes in motor cortex, capsular genu, pons, or medulla

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infarct

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bilateral arm weakness or paralysis - lesion locations

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medial fibers of both lateral corticospinal tracts; bilateral c-sine ventral horn cells; peripheral nerve or muscle disorders affecting both arms

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bilateral arm weakness or paralysis - associated features

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central cord syndrome or anterior cord syndrome may be present

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bilateral arm weakness or paralysis - causes for central cord syndrome

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central cord syndrome: syringomyelia, intrinsic spinal cord tumor, myelitis

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bilateral arm weakness or paralysis - causes for anterior cord syndrome

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anterior cord syndrome: anterior spinal artery infarct, trauma, myelitis

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bilateral arm weakness or paralysis - causes for peripheral nerve

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peripheral nerve: bilateral carpal tunnel syndrome or disc herniations

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bilateral leg weakness or paralysis - lesion locations

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primary motor cortex-medial surface; lateral corticospinal tracts below T1; cauda equina syndrome or other peripheral nerve/muscle disorders

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bilateral leg weakness or paralysis - associated feature of bilateral medial frontal lesions

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UMN signs; frontal lobe dysfunction including confussion, apathy, grasp reflexes, and incontinence

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bilateral leg weakness or paralysis - associated features of spinal cord lesions

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UMN signs; sphincter dysfunction, autonomic dysfunction may be present; sensory level may help determine segment of lesion

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bilateral leg weakness or paralysis - associated features of bilateral peripheral nerve/muscle disorders

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cauda equina syndrome-sphincter and erectile dysfunction, sensory loss in lumbar, LMN signs; symmetrical polyneuopathies-distal muscles; neuromuscular-proximal more than distal

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bilateral leg weakness or paralysis - causes of bilateral medial frontal lesions

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parasagittal meningioma, bilateral anterior cerebral artery infarct, cerebral palsy

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bilateral leg weakness or paralysis - causes of spinal cord lesions

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numerous: tumor, trauma, myelitis

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bilateral leg weakness or paralysis - causes of bilateral peripheral nerve/muscle disorders

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cauda equina: tumor, trauma, disc herniation; Guillain-Barre syndrome, Lambert-Eaton syndrome, numerous muscle disorders, etc

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bilateral arm and leg weakness or paralysis - lesion locations

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bilateral arm and leg areas in motor cortex; bilateral lesions of corticospinal tracts from lower medulla to C5; peripheral nerve motor neuron/muscle disorder

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bilateral arm and leg weakness or paralysis - lower medullary lesions

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UMN signs; occipital headache, tongue weakness; sensory loss, hiccups, respiraory weakness, autnomic dysfunction, sphincter dysfunction, abnormal eye movements

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generalized weakness or paralysis - lesion locations

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bilateral lesions of entire motor cortex; bilateral lesions of corticospinal and corticobulbar tracts anywhere from corona radiata to pons; diffuse disorders of LMNs, peripheral axons, neuromuscular jxns, muscles

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generalized weakness or paralysis - common causes

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global cerebral anoxia, pontine infarct or hemorrhage, advanced amyotrophic lateral sclerosis, Guillain-Barre, myathenia, botulism, etc

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pronator drift test

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patient holds arms extended, palms up, and eyes closed; slight inward drifting or slight curling of fingertips is abnormal

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classic clinical definition of multiple sclerosis

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2 or deficits separated in neuroanatomical space and time; MRI white matter lesions, oligoclonal bands in CSF

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examples of motor neuron diseases

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amyotrophic lateral sclerosis (ALS or Lou Gehrig's disease)

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ALS characterisitcs

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progressive degeneration of both UMN and LMN leading to respiratory failure and death