NS 4: Motor system

Question 1

2 types of lower motor neurones?

Answer 1

alpha and gamma

Question 2

define a lower motor neurone

Answer 2

cells of ventral horn of SC or cranial nerve motor nuclei that give rise to axons that supply skeletal muscles

Question 3

define an upper motor neurone

Answer 3

neurones of cerebral motor cortex and brainstem nuclei that in turn connect with lower motor neurones

Question 4

upper motor neurone lesion signs?

Answer 4

hypereflexia
spastic paralysis (increased muscle tone)
minimal/no atrophy
no fasciculations

Question 5

lower motor neurone lesion signs?

Answer 5

flaccid paralysis (atonia)
atrophy
fasciculations
hyporeflexia/areflexia

Question 6

what is the pyramidal system of upper motor neurones?

Answer 6

those with direct (monosynaptic) contact with lower motorneurones supplying distal muscles of extremities.

Question 7

3 tracts of pyramidal motor pathways?

Answer 7

lateral corticospinal
anterior/ventral corticospinal
corticoblubar

Question 8

function of pyramidal motor pathways?

Answer 8

voluntary movement

Question 9

origin of pyramidal motor pathways?

Answer 9

motor and premotor cortex and precentral gyrus

Question 10

site of decussation of lateral corticospinal tract?

Answer 10

medulla (pyramidal decussation)

Question 11

site of decussation of ventral corticospinal tract?

Answer 11

SC

Question 12

site of decussation of corticobulbar tract?

Answer 12

brainstem

Question 13

termination of corticospinal tracts?

Answer 13

contralateral SC

Question 14

termination of corticobulbar tract?

Answer 14

contralateral motor cranial nerve nuclei

Question 15

extrapyramidal motor pathways?

Answer 15

tectospinal
rubrospinal
reticulospinal
vestibulospinal

Question 16

function of tectospinal tract and its origin?

Answer 16

turns head toward sights or sounds

origin= tectum(colliculi) of brain

Question 17

decussation site of tectospinal and rubrospinal tracts?

Answer 17

brainstem

Question 18

termination site of tectospinal and rubrospinal tracts?

Answer 18

neck and upper thoracic SC

Question 19

where is the cell body of upper motor neurones located?

Answer 19

cerebral cortex or brain stem

neurones remain in CNS

Question 20

where is cell body of lower motor neurones located?

Answer 20

ventral horn of SC or cranial nerve motor nuclei

Question 21

function of rubrospinal tract?

Answer 21

flexor muscle tone

Question 22

function of reticulospinal tract?

Answer 22

automatic movement (locomotion)

Question 23

function of vestibulospinal tract?

Answer 23

balance and posture

Question 24

origin of reticulospinal tract?

Answer 24

reticular formation in medulla and pons

Question 25

origin of vestibulospinal tract?

Answer 25

vestibular nucleus (nuclei located in pons and medulla)

Question 26

origin of rubrospinal tract?

Answer 26

red nucleus in midbrain

Question 27

termination of reticulospinal and vestobulospinal tracts?

Answer 27

SC

Question 28

decussation of reticulospinal and vestibulospinal tracts?

Answer 28

``` reticulospinal= partially in brainstem vestibulospinal= none! ```

Question 29

define spasticity

Answer 29

increase in resistance to velocity-dependent passive stretch in absence of voluntary movement, so more rapid stretch= greater resistance. Spastic paralysis characterises UMN lesions, as does the clasp-knife reflex in anti-gravity muscles (flexor muscles of arm and fingers, extensors of leg): resistance increases with movement, but then suddenly disappears (like when removing a pen knife), and resistance more with faster movements. suggested that abnormal stretch reflexes are underlying basis for hypertonicity.

Question 30

describe and explain the presentation of capsular stroke

Answer 30

vascular accident in internal capsule interrupts corticospinal and corticobulbar tracts - paralysis of contralateral (as tracts decussate in medulla, SC and bstem) upper and lower limbs - paralysis of contralateral lower facial muscles (as decussation of corticobulbar in b.stem, and frontal sparing seen as frontalis receives bilateral innervation from facial nerve) - may be transient weakness on CL side of tongue and soft palate due to corticobulbar tract damage.

Question 31

characteristics on inspection of a patient who has suffered a left capsular stroke

Answer 31

``` right spastic hemiplegia (paralysis): head tilted to right paralysis of lower facial muscles- facial drooping elbow flexed forearm pronated fingers flexed hip circumducted knee extended foot plantar flexed ```

Question 32

gait of an individual having suffered a left capsular stroke?

Answer 32

patient will swing their right leg outwards when trrying to walking as right knee extended and right floot plantar flexed with right spastic hemiplegia.

Question 33

where does 30% of corticospinal tract originate from?

Answer 33

pre-central gyrus/M1/area 4

Question 34

which part of the brain is very prone to haemorrhagic strokes and why?

Answer 34

internal capsule: circle of Willis surrounds this area, and this arterial collateral circulation is prone to aneurysms capsule separates caudate nucleus and thalamus from lentiform nucleus (globus pallidus and putamen)

Question 35

outputs of motor cortex (M1) ?

Answer 35

pyramidal tracts: corticospinal and corticobulbar

Question 36

inputs to motor cortex (M1) ?

Answer 36

PMA (premotor area) SMA (supplementary motor area) S1 (somatosensory cortex)

Question 37

areas of cerebral cortex involved in planning movements?

Answer 37

premotor area | And subcortical areas

Question 38

outputs of M2 (pre-motor cortex)

Answer 38

pyramidal tracts, espec. ventral corticospinal tract also extrapyramidal tracts, M1, SMA (supplementary motor area) and cerebrocerebellum- key to motor planning. codes motor plan, epec. visually guided movements, and body set - regulates core musculature when making a prime movement, (regulates other movements of body.)

Question 39

outputs and functions of supplementary motor area (SMA)?

Answer 39

outputs: M1 and PMA functions: codes motor plan, espec. complex bilateral movements.

Question 40

what are +ve and -ve signs in terms of neurological lesions?

Answer 40

``` +ve= emergence of a feature -ve= loss of function or capacity ```

Question 41

signs and causes of LMN lesions?

Answer 41

``` distribution= peripheral nerves flaccid paralysis- hypotonia/atonia hypo/areflexia fasciculations- spontaneous contractions and relaxtions initially atrophy- as no innervation ``` causes: traumatic injury, peripheral neuropathy- diabetes mellitus or MND

Question 42

signs and causes of UMN lesions?

Answer 42

mono/hemiparesis (weakness) spastic paralysis: hypertonia- may swing out affected lower limb hyperreflexia no atrophy initially as still innervation, but later= disuse atrophy no fasciculations clasp-knife reflex +ve Babinski sign causes: stroke, SC injury

Question 43

define a reflex

Answer 43

an involuntary, unlearned, repeatable, automatic reaction to a particular stimulus, which doesn't require an intact brain

Question 44

what is a reflex movement?

Answer 44

an unlearned and automatic displacement of a limb in response to a particular stimulus being applied to some part of the body

Question 45

why might a patient be unable to perform voluntary movements but is capable of displaying reflex movements?

Answer 45

voluntary movements require brain to be intact, so this patient may be braindead but if their SC is intact and perfused normally with blood, reflexes can still be displayed as these require a functioning SC but not an intact brain.

Question 46

sub-types of stretch reflexes under the umbrella term- muscle stretch reflex?

Answer 46

monosynaptic disynaptic oligosynaptic/multisynaptic

Question 47

why is a monosynaptic stretch reflex most commonly elicited in healthy individuals when testing tendon reflexes?

Answer 47

monsynpatic= excitation pathway recruits only a subset of muscle spindles afferents. The spindle afferents of the other pathways won't have been recruited whilst at the same time the SC motor nucleus is under descending inhibition- this is more pronounced in the other pathways as they are doubly or multiply inhibited, with many synapses that can be acted upon.

Question 48

define motorneurone

Answer 48

a somatic efferent that supplies skeletal muscles to bring about displacement of limbs and to set muscle tone

Question 49

where is the spinal motor nucleus located?

Answer 49

lamina IX of grey matter of SC

Question 50

define a motor unit

Answer 50

an alpha-motorneurone and all the muscle fibres it supplies- will be all type F, FR or S, but never a mixture. unit= minimal functional unit of NS smaller motor units= smaller number of muscle fibres supplied= finer control? e.g. extraocular muscles- only 10 fibres

Question 51

5 components to a reflex arc?

Answer 51

``` receptor e.g. muscle spindle afferent neurone integration centre e.g. synapse efferent neurone effector e.g. skeletal muscle ```

Question 52

importance of muscle stretch reflex?

Answer 52

is the template neural circuit from which all motor circuits of the body are built from • It is the minimal neural circuit that underlies all movements of muscles of the body • It is the neural circuit that sets all motor tone of the body

Question 53

in which muscles is motor tone still present in REM sleep?

Answer 53

muscles of breathing extra-ocular muscles anal sphincter urinary sphincter

Question 54

why does clonus occur with UMNLs?

Answer 54

loss of inhibition to various interneurones so not only monosynaptic pathway fires, but disynaptic and oligosynpatic pathways also fire, which result in many APs being transmitted along efferent fibre, and resultant muscle contractions at different times **