09 05 2014 Upper Motor Neurons

Question 1

Where are ideas about movement formed?

Answer 1

Frontal lobe

Question 2

where does planning (organization of movement) occur

Answer 2

Pre motor cortical areas: -premotor cortex (lateral) -supplementary motor area (medial and going over longitudinal fissure) Areas are active prior to movement.

Question 3

Parietal association cortex

Answer 3

Area behind the central gyrus (areas 5 and 7 -brodman) -integrated picture of where your body is lined up (proprioception) + visual input. -Lets ou know where you are in relation to the environment. -invovled with planning areas of brain = coordinate movement. Signals to pre central cortex which sends signals down the spinal cord.

Question 4

apraxia

Answer 4

lesions in motor planning areas (premotor cortical areas or the posterior parietal cortex) -diffuclty using body part to perform complex voluntary actions. -contralateral - no obvious muscle weakness, no paralysis, no alteration in tone. no decreased reflexes. -They just can’t organize movement ex. pour water into a cup. -they can’t plan a movement

Question 5

Who is in charge of the “execute” part of motor movement?

Answer 5

primary motor cortex (precentral gyrus) -origin of corticospinal tract

Question 6

Large Betz cells

Answer 6

Lamina layer 5 in primary motor cortex -project directly to motor neurons (no interneurons)

Question 7

What type of connection do Corticospinal tract neurons have with motor neurons ?

Answer 7

Direct connection to motor neurons - -enable fine movements – finger muscles.

Question 8

What is the somatotopical organization of the pre central gyrus?

Answer 8

-Lower extremity are most medial. -Trunk -upper extremity is most lateral

Question 9

Where is the corticobulbar tract in relation to the pre central gyrus?

Answer 9

superior to the sylvan fissure and in the pre central gyrus. (Broadmann area 4)

Question 10

Does the motor cortex “code” for specific muscles?

Answer 10

no. it codes for purposeful movements. (slide 8 – experiments with monkeys) 1. stimulation to one site elicits completely different sets of muscle patterns depending on start position 2. motor cortex codes for endpoints (goals) of movements.

Question 11

Corticospinal tract (overall tract)

Answer 11

(Aka Pyramidal track) -Starts in precentral gyrus and traces down brainstem (ventral surface of brain). -decussates at bottom of medulla (pyramidal decussation) -travesl down spinal cord and innervates motor neurons directly or indirectly

Question 12

Where does the corticospinal tract originate?

Answer 12

Area 4 of Bodmann but there are also inputs from area 6 (rostral), 3,1,2 (all are caudal).

Question 13

What path does the corticospinal tract take (in cortex) to start heading down to brainstem?

Answer 13

Posterior limb of the internal capsule

Question 14

Does the corticospinal tract decussate?

Answer 14

yes. pyramidal decussation. -caudal medulla. =lateral corticospinal tract

Question 15

Does all the corticospinal tract decussate?

Answer 15

no. 10% of tract does not decussate. -forms the anterior corticospinal tract

Question 16

Arrangement of motor neurons going to thumb as it goes from pre central gyrus –> thumb

Answer 16

-thumb is most lateral in precentral gyrus. - It is most anterior and medial structure when it hits the caudal medulla. -after it hits the caudal medulla it continues as the most medial structure in both the lateral and anterior corticospinal tracts.

Question 17

Based on the location of the lateral corticospinal tract… what (general) types of muscles will it innervate

Answer 17

since it is lateral to the ventral horn: -distal muscles

Question 18

Based on the location of the anterior corticospinal tract… what (general) types of muscles will it innervate

Answer 18

since it is ventral to the ventral horn: -promixal muscles

Question 19

What happens if there is stroke in the middle cerebral artery?

Answer 19

• can affect the posterior internal capusl. -Everything would be affected. So if right middle arterial artery was blocked –> affect corticospinal tract for left side of the body –> contralateral hemiparesis.

Question 20

Typical features of stroke of middle meningeal artery?

Answer 20

-head tilted -Paresis of lower facial muscles -upper limb is flexed -lower lim is extended -foot is inverted

Question 21

Lateral corticospinal tract projects into what?

Answer 21

Projects directly or indirectly to motor neurons and motor interneurons in the lateral vernal horn to distal muscles

Question 22

Anterior corticospinal tract projects into what?

Answer 22

Remains ipsilateral in ventral column Projects bilaterally to motor neurons and interneurons in medial ventral horn (to proximal and trunk muscles)

Question 23

Where are deficits of corticospinal tract if lesion happens above the caudal medulla?

Answer 23

Affects contralateral side of body

Question 24

Lesions in the spinal cord will affect who?

Answer 24

symptoms on the same side of the lesion below the level of the lesion.

Question 25

What are some deficits associated with lesion of Corticospinal tract

Answer 25

-loss of skilled movement -Babinski sign -Upper motor neuron syndrom

Question 26

reticulospinal tracts

Answer 26

projects ipsilaterally (some bilaterally) to medial alpha-motor neurons throughout length of spinal cord. They contribute to posture and gait-related movements (proximal muscles) -activated by premotor cortex (planning) Also control autonomic centers and receives output from cerebellum

Question 27

What is function of mesencephalic and rostral pontine reticular formation

Answer 27

modulates forebrain activity

Question 28

Caudal pontine and medullary reticular formation

Answer 28

premotor coordination of lower somatic and visceral motor neuronal pools. (pons–> down) -goes all the way down spinal cord to control proximal and trunk muscles

Question 29

Pontine retriculospinal tract

Answer 29

Mainly ipsilateral —facilitates extensors: soleus, back muscles

Question 30

Medullary reticulospinal tract

Answer 30

Mainly ipsilateral –some bilateral -inhibits extensors

Question 31

Vestibuar system

Answer 31

Elaborate sensory system that helps monitor head position, movement, and acceleration -helps keep balance -medial and lateral vestibular system

Question 32

Medial vestibular system -originates?

Answer 32

Arises from CN #8 : arises in rostral medulla–medial vestibular nucleus -goes only to cervical layer –> head and neck -projects bilaterally to control head position in response to acceleration -also controls eyes

Question 33

Lateral vestibular system -originates? -travels where?

Answer 33

Arises from CN #8 : lateral ponto-medullary junction – lateral vestibular nucleus -ipsilateral and travels all the way down the body -synapses with medial LMNS – proximal muscles (facilitate extensors)

Question 34

Tectospinal -originates

Answer 34

arises in superior collicus (midbrain) and projects contra laterally in the medialwhite matter to the medial ventral horn of CERVICAL SPINAL CORD (only goes to this level). Orientates head movement in response to visual or auditory stimuli. -helps coordinate eyes in addition to head

Question 35

Rubrospinal tract

Answer 35

originates in red nucleus of midbrain. -gets input from cerebellum too. Travels with the LCST to control hand movements (in lateral feniculus) -flexor muscles! Only projects in cervical cord.

Question 36

what are the lateral pathways talked about in this lecture?

Answer 36

Lateral corticospinal tract Rubrospinal tract

Question 37

What are the medial pathways talked about in this lecture

Answer 37

2 reticulospinal tracts (contralateral) 2 Vestibulospinal tracts (contralateral) tectospinal tract (contralateral) Anterior corticospinal tract (ipsilateral/bilateral)

Question 38

upper motor neuron syndrome effects

Answer 38

lesion can produce an initial “spinal shock” – complete shut down of spinal circuits that can last some days. Then this is followed by UMN syndrome - weakness -no atrophy or mild atrophy -no fasciculations -increased reflexes -increased tone (looks tight/ spastic)

Question 39

who do upper motor neurons project to? What do they control?

Answer 39

control alpha-motor neurons directly or indirectly. -control the excitability of spinal reflexes

Question 40

hypertonia

Answer 40

UMN disorder that causes an increase in muscle tone – increased resistance to passive movement (move hand/wrist) -more resistance in beginning of movement vs. end. -velocity dependent – if go fast = more resistance. - loss of descending inputs = increased firing rate of alpha or gamma motor neurons.

Question 41

hyperreflexia

Answer 41

ex. 4+ or 5+ on tendon (patellar/ achillies) or any tendon

Question 42

Clonus

Answer 42

reflex so strong that muscle contracts a number of times in a 5-7 hz oscillation

Question 43

Hoffman’s sign

Answer 43

Flick fingernail downward. Causes rebound extension of finger and flexion + adduction of thumb.

Question 44

extent of hyprtonia depends on area of brain damage 1. lesion above midbrain 2. lesion below midbrain

Answer 44

1. Decorticate lesions: Upper extremeties flex, LE extended -rubrospinal tract still helping out 2. Decerebrate lesions: all limbs extended -hit rubrospinal tract (facilitates flexion)

Question 45

What are the CN that have lower motor neuron components?

Answer 45

CN#3,4,5 (jaw dropping),6,7,9,10, 11

Question 46

CN #7 is tested in two parts

Answer 46

1. Upper neuron: close eye, raise eyebrows 2. retract mouth * in brainstem there is an upper part of the nucleus that goes to the upper part of the face and a lower part of nucleus that goes to a lower part of face.

Question 47

Corticobulbar tract -originates? -path? - important thing to know about CNs. -Lesions causes what?

Answer 47

originates in precentral gyrus -travels down next to corticospinal tract -goes through genu of internal capsule and is more medial in cerebral peduncle. -ends in brainstem (bulb). Originates CN bilaterally except for CN 7. -upper portion is bilateral -lower portion is contralateral only! CN 12 is also mostly contralateral Lesions to one corticobulbular tract = paralysis to contralateral lower face.

Question 48

Causes of upper motor neuron syndrome

Answer 48

-trauma -stroke -Multiple Sclerosis -Amyotrophic Lateral Sclerosis (ALS) -Cerebral palsy

Question 49

What motor deficit would you expect if someone had stroke to lateral cortex (arms and face)

Answer 49

contralateral lower-face and arms.

Question 50

motor effects when there is a Lesion in internal capsule

Answer 50

• affects lower contralateral face as well as entire body.
• pure motor hemiparesis

common with lacunar strokes

*recall that all motor pathways pass through internal capsule!

Question 51

Effect of a Stroke in area of lower limb placement (cortex)

Answer 51

loss of motor/sensory in lower contralateral limb – leg.

Question 52

Effect (motor) of lesion in spinal cord

Answer 52

Ipsolateral deficit (because pathway has already crossed and is goin gdown to innervate motor neurons on the same side.