Movement pathways and centre Flashcards
What are lower motor neurons (LMNs) ?
neurons that originate from the brain stem and spinal cord
What are the components to the lower motor neuron (LMN)?
- spinal nerve
- ventral root
- dorsal root ganglion
- dorsal root
- dorsal grey horn
- ventral grey horn
What are lower motor neuron lesions due to?
- peripheral nerve injury - crush or poliomyelitis
2. poliomyelitis
What do lower motor neuron lesions lead to?
- muscle wasting
- muscle weakness/ reduced power
- hypotonia
- absent tendon reflexes
- fasciculations/ fibrillation
What are fasiculations?
small uncontrollable localised contractions
What is an example of a descending mortor pathway?
upper motor neurons (UMNs)
What 2 types of descending motor pathways are there?
- corticospinal - cortex to spine - spinal nerves
2. corticobulbar - cortex to brainstem - cranial nerves
What does the descending motor pathways/ upper motor neurons do?
- influence LMN activity
- modify local reflex activity
- superimpose more complex patterns of movement
How many important descending pathways are there and what are they named after?
4
named after origin
What is the typical route for descending patwhays/ upper motor neurons?
- cerebral cortex
- precentral gyrus
- internal capsule
- brainstem/spinal cord
Do all descending pathways work separately or together?
together
What are the descending pathways often referred to as?
pyramidal system
What happens initially if there is damage to the corticospinal tract only?
- flaccid paralysis of opposite limbs
2. loss of tendon reflexes
What happens after several days to a week if there is damage in the corticospinal tract only?
- motor function recovers
2. but there is hypertonia
What happens in the long term if there is damage to the corticospinal tract?
- spasticity
- hyperreflexia - increased reflexes
- left with pernamanet inability to carry out fine movements of hands and feet
What do other pathways seem to do if there is damage to the corticospinal tract only?
appear to take over most corticospinal functions
What type of homunculus do you have?
- somatosensory
2. motor homunculus
Where is the somatosensory homunculus?
in the post-central gyrus
Where is the motor homunculus?
in the pre-central gyrus
What is the order of the motor homunculus in the pre-cnetral gyrus medial to lateral?
- knee
- hip
- trunk
- shoulder
- arm
- elbow
- wrist
- hand
- fingers
- thumb
- neck
- brow
- eye
- face
- jaw
- tongue
- pharynx
- larynx
What is the order of the somatosensory homunculus in the post-central gyrus medial to lateral?
- leg
- hip
- trunk
- arm
- elbow
- forearm
- hand
- fingers
- thumb
- eye
- nose
- face
- lips
- teeth
- gums
- jaw
- tongue
- pharynx
- abdomen
Where does the descending pathway (descending corticospinal/bulbar fibres) or upper motor neuron travel?
- from pre central gyrus to internal capsule
What is the internal capsule?
deep bundle of white matter between the deep nuclei
What is the structure of the internal capsule?
- anterior limb of internal capsule
- lower limb of internal capsule
- genu
Where do descending fibres for the body go?
posterior limb of the internal capsule
Where do descending fibres fro the face and muscles of the head go?
genu
What is the structure of the brainstem?
- cerebral peduncle
- basal pons
- pyramids
- olives
midbrain
pons
medulla
How does the descending pathway travel from internal capsule to spinal cord?
in the brainstem from cerebral peducnle to basal pons to pyramids and to contralateral spinal cord
How does the corticospinal pathway travel from cortex to spinal cord?
- pre-central gyrus in cortex
- inetrnal capsule
- basis peduncles
- pyramid
- pyramidal decusstaion
- lateral corticospinal tract
In terms of the decussation of pyramids what percentage of fibres cross and enter the lateral corticospinal tract?
85% fibres cross
In terms of the corticospinal tract what percentage of UMNs descend the cord contra laterally?
85%
In terms of the corticospinal tract what percentage of UMNs descend the cord ipsilaterally?
15% remain ipsilateral in anterior/ventral CST
then cross at appropriate spinal cord level
Where do the UMNs contact cell bodies of LMNs?
in contralateral ventral grey horn
What do second order neurons of LMNs do in the corticospinal tract?
leave spinal cord as ventral rootlets to form spinal nerve
What is retained throughout the cord?
somatotopic representation
Where does the corticospinal tract leave and descend to?
leave pre-central gyrus
descend - posterior limb of internal capsule
then goes to cerebral peduncle of midbrain, ventral ons and pyramids of the medulla
How does the corticospinal tract extend to skeletal/straiated muscle?
via segemental spinal nerve
Where does the corticobulbar pathway influence the LMNs?
in cranial nerve motor nuclei
Where do the fibres of the corticobulbar pathway originate from?
laterally within the pre-central gyrus
Is the innervation of LMNs bilateral or unilateral?
bilateral - corticospinal tract on left supplies muscles on the left and right and vice versa
Where does the facial nerve nuclei receive UMNs from?
from a specific motor area of the pre-central gyrus
Wheer does the LMNs leave and pass through and exit?
leave from the facial nerve nuclei
pas through substance of the pons
exit brainstem at the cerebellopontine angle
Where does the facial nucleus originate from?
floor of the 4th ventricle
What are the 5 divisions of the facial nerve?
To Zanzibar By Motor Car
NOTE
LEARN THE CORTICOBULBAR INPUT TO CRANILA NERVE MOTOR NUCLEI
NOTE
LEARN TEH CORTICOBULBAR INPUT TO FACIAL MOTOR NUCELI
If there is right corticobulbar damage what is affected?
upper motor neuron type facial weakness
left facial weakness from below the eye to the chin
If there is left facial nerve damage what is affected?
lower motor neuron type facial weakness
whole left side of the face
What is another word fro unilateral damage to corticobulbar fibres?
supranuclear lesion
What happens in unilateral damage to corticobulbar fibres/ supra nuclear lesion?
it deprives the lower half of the opposite facla motor nucleus of corticobulbar input
results in paralysis of the whole half of the face on the opposite side to the lesion
What does paralysis of the whole of one side of the face indicate?
damage to the facial nerve itself
How do you differentiate between a supra nuclear and facial nerve lesion?
look up
What are features of upper motor nerve lesions?
contralateral lower quadrant weakness
angle of mouth
opposite side
What are features of the lower motor nerve lesion?
ipsilateral orbicularis oculi muscles and facila muscles involved
half of face - unable to close eyes
weakness of angle of the mouth
cannot elevate eyebrows
same side
