MOTOR SYSTEMS Flashcards
Where is the 4th ventricle in the brain?
between the cerebellum and the brain stem
describe the anatomical features of the midbrain in ventral view?
there are 2 cerebral peduncles which are like stalks that attach the cerebrum to the brain stem.
In between we have the interpeduncular fossa.
at the top we have the mammillary bodies
describe the anatomical features of the medulla in ventral view?
down the middle is an anterior median fissure which is continuous with the spinal cord, either side we have the pyramids and lateral to these we have the olives.
describe the anatomical features of the midbrain in dorsal view?
we have 2 superior and 2 inferior colliculi
describe the anatomical features of the pons in dorsal view?
a pair of superior, a pair of inferior and a pair of lateral cerebellar peduncles.
describe the anatomical features of the medulla in dorsal view?
the cuneate fascicule and gracile fascicule (more medial) are visible
what is the function of the 4th ventricle in the brain?
To protect the human brain from trauma (via a cushioning effect) and to help form the central canal, which runs the length of the spinal cord.
why is the brain stem so important?
it houses cranial nerves 3-12.
3 and 4 airse from the midbrain
5,6,7 and 8 arise from the pons
9,10,11,12 arise from the medulla
what are the functions of the brain stem?
Controls the flow of messages between the brain and the rest of the body
Controls basic body functions such as breathing, swallowing, heart rate, blood pressure, consciousness, and wakefulness
what is brain stem death?
Patient unconscious (related to reticular system in the pons which controls wakefulness) Patient cannot breathe or cough (CNX) Patient cannot swallow (CNV, VII) No pupillary reflex (CNII & III) No gag reflex (CNIX)
how are motor pathways different to sensory pathways?
motor information is passed along a 2 neuron pathway rather than 3. an upper motor neurone and a lower motor neurone
what are the key features of upper motor neurones?
they’re entirely within the CNS, their origin is either cerebral cortex, cerebellum or brainstem, they form descending tracts
where and what do upper motor neurones synapse with?
lower motor neurones in brainstem or spinal cord
what are lower motor neurones?
cranial or spinal nerves that project to muscles and produce a response
what are the 2 broad groups of descending tracts?
dorsolateral and ventromedial
what is the function of dorsolateral descending tracts?
to supply distal muscles and control fine movement
what is the function of the ventromedial descending tracts?
to supply proximal limbs and trunk muscles as well as control posture and movement correction
what are the 2 dorsolateral descending tracts called?
lateral corticospinal and rubrospinal
what are the 4 ventromedial descending tracts called?
anterior corticospinal, reticulospinal, tectospinal and vestibulospinal
describe the reticulospinal tract?
1st order neurones arise from the pons and the medullary reticular formation, it remains ipsilateral and runs the entire length of the spinal cord. it then synapses with a lower motor neurone in the medial aspect of the ventral horn. the lower motor neurone supplies the trunk and the proximal upper/lower limbs
what is the function of the reticulospinal tract?
posture, gait related movements
has a role in modulating sensation
what is sensory modulation?
The ability to respond appropriately to sensory information and remain at an appropriate level of alertness
describe the tectospinal tract?
1st order neurone arise from the superior colliculi.
it decussates in the midbrain and receives input from the peripheral retina. it then synapses with a lower motor neurone in the cervical spinal cord and this lower motor neurone innervates the shoulder girdle and neck.
what are the functions of the tectospinal tract?
to turn the head in response to visual stimuli and to coordinate head and eye movement
Describe the vestibulospinal tract?
1st order neurones arise from the vestibular nuclei. it remains ipsilateral. it synapses with a lower motor neurone in the medial aspect of the ventral horn. the lower motor neurone innervates the shoulder girdle and neck.
what is the difference between medial and lateral vestibulospinal tracts?
medial stops in the cervical region whilst lateral travels down through all the spinal segments
what are the functions of the vestibulospinal tracts?
to position the head an neck
balance and controlling movements in response to sudden postural changes
what does polysegmental mean?
that nerves come out at every spinal level
describe what it means to say the ventromedial tracts provide bilateral innervation?
why is this important?
the unilateral axon (one side) innervates both sides of the body
this is important as we need to have control over both sides of out body simultaneously
what would happen if we had a unilateral lesion on a ventromedial tract?
what about a bilateral lesion?
unilateral- no obvious defects
bilateral- loss of posture correction reactions, loss of navigational control, loss of trunk mobility and loss of ability to reach out. however you would still be able to flex the elbow and use the digits
describe the rubrospinal tract?
1st order neurone originates in the red nucleus of the midbrain and decussates in the midbrain.
what is the function of the rubrospinal tract?
to control muscle tone in upper limbs and to coordinate movement
what would happen if there was an isolated lesion in the rubrospinal tract?
you would get impaired distal arm and hand movement and intention tremors
describe the corticospinal tract pathway?
1st order neurones arise from the primary and motor cotexes and the sensory cortex. they pass through the internal capsule and then through the cerebral peduncles in the midbrain. 85% of fibres decussate below the pyramids in the medulla (lateral corticospinal tract= in dorsolateral region) but 15% remain ipsilateral (anterior corticospinal tract-in ventromedial region).this neurone then synapses with a lower motor neurone in the ventral horn at all spinal segments
what are the functions of the corticospinal tract?
voluntary motor control of skeletal muscles, fine movement and sensory modulation
which skeletal muscles do a)the lateral corticospinal tract and b)the anterior conticospinal tract supply?
lateral= limbs anterior= trunk
when does the corticospinal tract become fully myelinated?
at 2 years of age
what is the Babinski test?
what is a positive sign? what is a negative sign?
running a sharp object up the lateral aspect of the sole of the foot
posititive= toes extend (something wrong)
negative= toes flex
what happens if you get a lesion above decussation in the corticospinal tract?
Contralateral spastic paresis (very high muscle tone and severe weakness) & +ve Babinski’s (upgoing toe)
what happens if you get a lesion below decussation in the cotricospinal tract?
Ipsilateral spastic paresis & +ve Babinski’s
what are the symptoms of lesions in the corticospinal tract?
loss of independent finger flexion. loss of speed and agility. clumsiness. weakness
what are the effects of lesions in the dorsolateral pathways?
normal walk and posture correction but arms hang imply and to reach the patient would use shoulder circumduction and fingers would flex together
