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Neuroanatomy > Motor Control Systems > Flashcards

Motor Control Systems Flashcards

1
Q

What are the 2 major systems of motor control?

A

Somatic and Visceral

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2
Q

Somatic motor system

A

-Controls skeletal muscle
-Voluntary

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3
Q

Visceral motor system

A

-Aka autonomic nervous system
-Controls smooth & cardiac muscle and glands
-Mostly involuntary

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4
Q

Upper motor neurons

A

From control regions rostral to ventral horn of spinal cord
➢ basically, everything other than the lower motor neurons

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5
Q

Primary motor area

A

All three motor cortical areas contribute to the corticospinal tract (CST)
▪ CST fibers decussate at pyramidal decussation
▪ influence lower motor neurons

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6
Q

Extrapyramidal systems

A

Forebrain & brainstem areas that are not part of the CST
➢ vestibulospinal
➢ reticulospinal
➢ tectospinal
➢ rubrospinal

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7
Q

Lower motor neurons

A

Both α- and γ- motor neurons
▪ in ventral horn of the spinal cord
➢ note differences in UMN & LMN lesion symptoms

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8
Q

Upper motor neuron modulators

A

Regions that have few, if any, direct inputs on lower motor neurons, but have a significant influence on motor activity
-Basal ganglia
-Cerebellum
-Association cortex
-Thalamus

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9
Q

Corticospinal tract (CST)

A

Premotor/supplementary/primary motor areas–>from cortex via post. limb of internal capsule–>decussate (pyramidal) at caudal medulla –>SC descend in the lateral funiculus =LCST

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10
Q

Lateral CST

A

Decussate in pyramids (~85%)
Descend in CL spinal cord in lateral funiculus
Act on more lateral lower motor neurons in ventral horn of spinal cord
Influence peripheral/limb muscles

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11
Q

Medial (anterior) CST

A

Fibers stay ipsilateral at caudal medulla (~15%)
Travel in ventral funiculus of ipsilateral spinal cord
Decussate low in spinal cord
Influence more medial ventral horn neurons; axial/trunk muscles

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12
Q

Both CST pathways

A

Project to both α- and γ- motor neurons
➢ alpha = extrafusal; gamma = intrafusal (muscle spindles)
▪ alpha/gamma coactivation
Project directly and indirectly (by way of interneurons)

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13
Q

Premotor cortex and supplementary motor cortex

A

➢ premotor area is just rostral to primary motor cortex in frontal lobe
➢ supplementary is similar, but on medial surface of hemisphere
▪ both regions are involved with the initiation of voluntary movement
➢ neural activity seen before movement
▪ activity even if movement is just imagined or contemplated
▪ both regions receive inputs from prefrontal cortex (decision making) and somatosensory association areas (spatial/kinesthetic information about body and objects)

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14
Q

Primary motor area

A

Precentral gyrus of frontal lobe
▪ ‘final output’ from cerebral cortex
Somatotopic: motor homunculus

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15
Q

Ventral horn

A

α-motor neurons in ventral horn of spinal cord
▪ innervate skeletal muscle (extrafusal fibers)
➢ at least three types of muscle fibers based on metabolic pathways and physiological properties

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16
Q

Organization of ventral horn

A

▪ medial = axial (proximal) muscles; lateral = peripheral (distal) muscles (limbs)
▪ dorsal = flexors; ventral = extensors

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17
Q

Motor Unit

A

➢ one α-motor neuron and all the muscle fibers it innervates
▪ function of muscle helps determine the size of the motor unit
Each neuron innervates a single type of muscle (I, IIa, IIb)

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18
Q

Small motor units

A

▪ relatively few muscle fibers innervated
* as low as 1:3 (!)
▪ allows very small, precise contractions
* e.g., ocular muscles

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19
Q

Large motor units

A

▪ many muscle fibers innervated by a single neuron
* 1:1,000+
▪ allows larger, stronger (although less precise) contractions
* e.g., gastrocnemius

20
Q

Basics of Spinal reflexes

A

➢ simplest demonstration of interplay between PNS & CNS
▪ sensation→integration→response

21
Q

Stretch reflexes

A

▪ e.g., Q.f. extension after hitting the patellar ligament with a hammer
➢ sensor = muscle spindles
➢ Info ascends via spinocerebellar tract
➢ collaterals of neurons signaling the stretch sensation reach LMN in the ventral horn
▪ reciprocal innervation
 common feature of almost every somatic reflex
* one muscle (or group of muscles) is activated while the antagonist muscle(s) are inhibited
* allows limb movement

22
Q

Flexor (withdrawal) reflexes

A

➢ sensor = nociceptors
➢ Info ascends via spinothalamic tract
➢ some collaterals ascend to innervate ventral horn at appropriate level (via interneurons)
▪ but respond to (potentially) damaging stimuli

23
Q

Crossed extensor reflexes & Central pattern generators

A

➢ more obvious in lower limbs
➢ as one limb is flexed, other limb is extended
▪ signals must decussate to other side of cord (thus the name)
➢ this basic circuitry of alternating flexion and extension of limbs forms the basis of locomotion
▪ movement pattern is generated in the central nervous system
▪ may allow decreased specificity from the upper motor neurons
* i.e., may decrease computational demands on the motor cortex

24
Q

Vestibulospinal tract
(extrapyramidal pathway)

A

From vestibular system in inner ear
Two pathways; lateral and medial

25
Q

Lateral vestibulospinal tract

A

Helps control anti-gravity muscles in whole body
Compensation for tilt and movement of body (head movement)
▪ sensors also responsible for feelings of dizziness

26
Q

Medial vestibulospinal tract

A

Bilateral projection to cervical spinal cord
Coordinates head and eye movements
▪ e.g., stabilizes head & eyes while moving/walking

27
Q

Reticulospinal tract
(extrapyramidal pathway)

A

Major alternative to pyramidal pathway
from reticular formation
postural control & postural controls during locomotion
Medullary (lateral) reticulospinal tract
inhibits trunk extensors
Pontine (medial) reticulospinal tract
activates trunk extensors (anti-gravity)

28
Q

Tectospinal tract
(extrapyramidal pathway)

A

From superior and inferior colliculus
Mediate muscles controlling reflexive head turning to ocular and auditory stimuli, respectively

29
Q

Rubrospinal tract
(extrapyramidal pathway)

A

From red nucleus
Minor in humans (major in lower mammals)
- is primary in babies’ crawling (before myelination of CST)
▪ note that the red nucleus is critical in human cerebellar→cerebral motor pathways

30
Q

Corticobulbar Pathway

A

Upper motor neurons for Cranial nerves V, VII, & XII (trigeminal, facial & hypoglossal)
▪ controls most facial muscles
▪ facial expression & mastication
-usually bilateral in upper face and to muscles of mastication
-usually unilateral to lower face

31
Q

Corticobulbar Pathway

A

1st Order: pre- supple-, and primary motor areas travels with CST fibers decussate at appropriate brainstem level depending on what they are controlling
2nd Order: Trigeminal (V), Facial (VII), Nucleus ambiguus (X), Spinal accessory nucleus (XI), and hypoglossal nucleus (XII)

32
Q

Damage to UMN

A

weakness, spasticity, increased tendon reflexes, increased Babinski sign, little atrophy, and tend to have greater influence on:
▪ affect extensors & ABductors of arm
▪ flexors of leg

33
Q

Examples of Lesion to the UMN

A

Cerebral cortex (stroke)
▪ focal motor deficit to contralateral face, hand, limb, etc
Internal capsule (lacunar stroke)
▪ contralateral hemiparesis
▪ often widespread
➢ fig 13-8 of Greenberg
Lesion rostral to red nucleus
▪ contribute to decorticate rigidity
➢ flexion of elbows, wrists & fingers
➢ extension & internal rotation of legs
Lesion caudal to red nucleus
▪ contribute to decerebrate rigidity
➢ extension of arms & legs (esp. elbow)
➢ internal rotation of both arms & legs
Brainstem
▪ often bilateral
▪ often associated sensory and cranial nerve disturbances
Spinal cord (white matter tract)
▪ increases tone (spasticity)
▪ often sensory deficits
➢ includes other pathways

34
Q

Damage to LMN

A

weakness, flaccid paralysis (hypotonia), atrophy (ipsilateral, along myotome), usually involves adjacent white matter
▪ so upper motor neuron damage symptoms seen below level of injury

35
Q

Visceral Motor (Autonomic) nervous system (ANS)

A

▪ motor control of smooth muscle, cardiac muscle, & glands
▪ homeostatic control

36
Q

3 systems of the visceral motor [ANS]

A

1 Sympathetic division
2 Parasympathetic division
3 Enteric nervous system

37
Q

Enteric NS

A

Neurons and plexuses that control the gastrointestinal tract
▪ e.g., myenteric & submucosal plexus
Influenced by sympathetic & parasympathetic divisions
▪ but separate & independent
➢ helps explain GI tract function even in patients with high spinal cord injuries
Large, but not well understood
▪ as many or more neurons than the spinal cord!

38
Q

Similarities between sympathetic & parasympathetic divisions

A

Both influence internal organs
usually dual opposing innervation
▪ at each tissue, one system inhibits and the other activates
➢ depends on tissue
▪ there are several major exceptions (only symp, only parasym, cooperative)

39
Q

Both PNS and SNS have two neuron chains that synapse in a PNS ganglia

A

Preganglionic neurons
▪ originate in CNS
▪ myelinated
▪ cholinergic

Postganglionic neurons
▪ originate in autonomic ganglia
▪ unmyelinated
▪ have nicotinic receptors on soma & dendrites
▪ act on target tissues

40
Q

Sympathetic nervous system

A

▪ ‘fight or flight’
▪ energy expenditure

41
Q

SNS Preganglionic neurons

A

originate from lateral horn [intermediolateral nucleus (IML)]
▪ only from T2-L1
➢ “thoracolumbar system”
➢ control of head must re-ascend outside of spinal cord
▪ have shorter distance to travel to synapse in ganglia

42
Q

SNS Ganglia

A

Sympathetic chain ganglia
▪ majority of synapses
▪ close to spinal cord on either side
Prevertebral ganglia
➢ celiac, inferior & superior mesenteric ganglia
▪ site of synapses other than chain ganglia
▪ preganglionic axon travelling to these prevertebral ganglia = splanchnic nerves
Postganglionic neurons: longer distance to terminal tissue

43
Q

SNS Adrenergic

A

▪ use norepinephrine (NE) and/or epinephrine (Epi) as neurotransmitter
➢ released onto target tissues
➢ tissues respond due to adrenergic receptors
▪ α- & β- receptors
* many subtypes, various sensitivity and response to NE/Epi

44
Q

Parasympathetic nervous system

A

▪ ‘rest and relax’/ ‘rest and digest’
▪ energy conservation

45
Q

PNS Preganglionic neurons

A

Originate from brainstem and sacral spinal cord
➢ ‘craniosacral’
▪ CN III (oculomotor)
➢ iris
▪ CN VII (facial)
➢ lacrimal & submandibular salivary glands
▪ CN IX (glossopharyngeal)
➢ parotid salivary gland
▪ CN X (vagus); 90%+ of all parasympathetic axons
➢ innervates most thoracic and abdominal organs
▪Sacral: lateral horn of T12-L1

46
Q

PNS Ganglia

A

▪ terminal ganglia
➢ located next to within target tissues

47
Q

PNS Postganglion neurons

A

➢ shorter
▪ cholinergic
➢ release Ach onto target tissues
▪ tissues respond due to muscarinic receptors

Neuroanatomy (18 decks)

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