NS 4: Motor system Flashcards
2 types of lower motor neurones?
alpha and gamma
define a lower motor neurone
cells of ventral horn of SC or cranial nerve motor nuclei that give rise to axons that supply skeletal muscles
define an upper motor neurone
neurones of cerebral motor cortex and brainstem nuclei that in turn connect with lower motor neurones
upper motor neurone lesion signs?
hypereflexia
spastic paralysis (increased muscle tone)
minimal/no atrophy
no fasciculations
lower motor neurone lesion signs?
flaccid paralysis (atonia)
atrophy
fasciculations
hyporeflexia/areflexia
what is the pyramidal system of upper motor neurones?
those with direct (monosynaptic) contact with lower motorneurones supplying distal muscles of extremities.
3 tracts of pyramidal motor pathways?
lateral corticospinal
anterior/ventral corticospinal
corticoblubar
function of pyramidal motor pathways?
voluntary movement
origin of pyramidal motor pathways?
motor and premotor cortex and precentral gyrus
site of decussation of lateral corticospinal tract?
medulla (pyramidal decussation)
site of decussation of ventral corticospinal tract?
SC
site of decussation of corticobulbar tract?
brainstem
termination of corticospinal tracts?
contralateral SC
termination of corticobulbar tract?
contralateral motor cranial nerve nuclei
extrapyramidal motor pathways?
tectospinal
rubrospinal
reticulospinal
vestibulospinal
function of tectospinal tract and its origin?
turns head toward sights or sounds
origin= tectum(colliculi) of brain
decussation site of tectospinal and rubrospinal tracts?
brainstem
termination site of tectospinal and rubrospinal tracts?
neck and upper thoracic SC
where is the cell body of upper motor neurones located?
cerebral cortex or brain stem
neurones remain in CNS
where is cell body of lower motor neurones located?
ventral horn of SC or cranial nerve motor nuclei
function of rubrospinal tract?
flexor muscle tone
function of reticulospinal tract?
automatic movement (locomotion)
function of vestibulospinal tract?
balance and posture
origin of reticulospinal tract?
reticular formation in medulla and pons
origin of vestibulospinal tract?
vestibular nucleus (nuclei located in pons and medulla)
origin of rubrospinal tract?
red nucleus in midbrain
termination of reticulospinal and vestobulospinal tracts?
SC
decussation of reticulospinal and vestibulospinal tracts?
reticulospinal= partially in brainstem vestibulospinal= none!
define spasticity
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.
describe and explain the presentation of capsular stroke
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.
characteristics on inspection of a patient who has suffered a left capsular stroke
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
gait of an individual having suffered a left capsular stroke?
patient will swing their right leg outwards when trrying to walking as right knee extended and right floot plantar flexed with right spastic hemiplegia.
where does 30% of corticospinal tract originate from?
pre-central gyrus/M1/area 4
which part of the brain is very prone to haemorrhagic strokes and why?
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)
outputs of motor cortex (M1) ?
pyramidal tracts: corticospinal and corticobulbar
inputs to motor cortex (M1) ?
PMA (premotor area)
SMA (supplementary motor area)
S1 (somatosensory cortex)
areas of cerebral cortex involved in planning movements?
premotor area
And subcortical areas
outputs of M2 (pre-motor cortex)
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.)
outputs and functions of supplementary motor area (SMA)?
outputs: M1 and PMA
functions: codes motor plan, espec. complex bilateral movements.
what are +ve and -ve signs in terms of neurological lesions?
\+ve= emergence of a feature -ve= loss of function or capacity
signs and causes of LMN lesions?
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
signs and causes of UMN lesions?
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
define a reflex
an involuntary, unlearned, repeatable, automatic reaction to a particular stimulus, which doesn’t require an intact brain
what is a reflex movement?
an unlearned and automatic displacement of a limb in response to a particular stimulus being applied to some part of the body
why might a patient be unable to perform voluntary movements but is capable of displaying reflex movements?
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.
sub-types of stretch reflexes under the umbrella term- muscle stretch reflex?
monosynaptic
disynaptic
oligosynaptic/multisynaptic
why is a monosynaptic stretch reflex most commonly elicited in healthy individuals when testing tendon reflexes?
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.
define motorneurone
a somatic efferent that supplies skeletal muscles to bring about displacement of limbs and to set muscle tone
where is the spinal motor nucleus located?
lamina IX of grey matter of SC
define a motor unit
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
5 components to a reflex arc?
receptor e.g. muscle spindle afferent neurone integration centre e.g. synapse efferent neurone effector e.g. skeletal muscle
importance of muscle stretch reflex?
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
in which muscles is motor tone still present in REM sleep?
muscles of breathing
extra-ocular muscles
anal sphincter
urinary sphincter
why does clonus occur with UMNLs?
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 **
