corticospinal tract and other motor pathways

Question 0

what are the arteries that perfuse the spinal cord

Answer 0

two posterior arteries, from vertebral artery and PICA

one anterior artery from the vertebral arteries

connected circumferentially by a spinal arterial plexus

Question 1

what are the three main tracts of the nervous system

Answer 1

corticospinal tract - motor
spinothalamic/anterolateral - sensory (pain and temperature)
posterior column, medial lemniscus - sensory (vibration, proprioception, fine touch)

Question 2

what is the name of the anatomical structure which returns blood from the spinal cord

Answer 2

batsons plexus, which is valveless and moves with increased intraabdominal pressure. it is also been implicated in prostatic cancer metastasis.

Question 3

the descending motor tracts have two main pathways

Answer 3

lateral motor system
(includes the lateral corticospinal tract and the rubrospinal tract)
and directs movement of contralateral limbs

and

medial motor systems
anterior corticospinal tract, vestibulospinal tract, reticulospinal tracts, tectospinal tracts (involved in axial and girdle muscles, posture, head and neck position and balance)

Question 4

the lateral corticospinal tract

Answer 4

begins at the primary motor cortex (precentral gyrus) and decussate and the medullary pyramids and travel down the length of the spinal cord to direct messages to lower motor neurons which direct muscle movement

Question 5

the internal capsule

Answer 5

are white matter tracts, containing motor information from the primary motor cortex, and enter from the corona radiata to create the internal capsule

is best visualised in horizontal brain sections

the thalamus and caudate are always medial, where the putamen and the globus pallidus are always lateral

contains three parts, anterior limb, genu, and posterior limb

Question 6

the lateral corticospinal tracts are located in which portion of the internal capsule

Answer 6

the posterior limb - face is most anterior, and the arm, trunk and leg are more posterior

Question 7

the internal capsule enters the midbrain and forms what structure, is the somatotropy the same?

Answer 7

cerebral peduncles - basis pedunculi

face, arm, trunk, leg (medial to lateral)

Question 8

upper motor neurons

Answer 8

motor cortex to anterior horn cell of the spinal cord

Question 9

lower motor neurons

Answer 9

anterior horn cell to skeletal muscle

Question 10

hyperreflexia, 
hypertonia, 
clonus, 
weakness of upper limb flexors and lower limb extensors
and an upgoing babinski (extensor)

are signs of what

Answer 10

an upper motor neuron lesion

Question 11

hyporeflexia, muscle atrophy, widespread muscular weakness, fasiculation, hyotonia, absent clonus

Answer 11

are indicative of a lower motor neuron lesion

Question 12

downgoing or flexor Babinski response

Answer 12

a lower motor neuron lesion

Question 13

describe multiple sclerosis

Answer 13

it is an autoimmune inflammatory disorder which attacks the oligodendroglial myelin and leads to demyelinating plaques

sclerotic glial scars appear throughout the CNS over time

it is twice as common in females and peak of onset is 20-40 years

classic definition is two or more deficits seperated in neuroanatomical space and time

typical clinical features: white matter lesions (periventricular lesions on T2 MRI - creating Dawsons fingers), slowed conduction velocities, presense of oligoclonal bands in CSF

50% will have had an episode of optic neuritis or transverse myelitis

the onset produces a relapsing remitting stage, but progresses to a refractory chronic progressive phase

acute treatment involves steriods, first line agents include beta-interferon, second line is monoclonal antibodies with cyclophosphamide and mitoxantrone

in addition to upper motor neuron symptoms, there is sensory loss, pain, cerebellar disturbances, cranial nerve problems, bowel/bladder dysfunction, and psychiatric symptoms

Question 14

describe motor neuron disease

Answer 14

this is known as amyotrophic lateral sclerosis or Lou Gehrigs

it is accompanied by umn signs such as brisk reflexes and hypertonia, with lmn signs (fasiculations and atrophy) and there is no sensory loss

there is bulbar (medulla- mouth, pharynx and larynx) effects which spare the extraocular muscles and this includes dysarthria and dysphagia with uncontrollable bouts of laughter and crying

patients die from respiratory failure, and no cure available

Question 15

what are the two main types of reflexes?

Answer 15

1. stretch of myotactic reflex:
   e. g. when lifting a mug of beer, the weight of the mug causes the biceps muscle spindle fibres to stretch, this activates the Ia and II fibres, which activates the alpha motor neurons and and causes contraction of the biceps, bringing the beer closer to the mouth, additional, the Ia fibres activate interneurons to inhibit the alpha motor neurons of the antagonist triceps muscle, preventing extension
2. the withdrawal reflex
   when you step on a noxious object with your foot, the alpha motor neurons are activated and cause the elevation of the foot away from the noxious stimulus by knee flexion, but coversely, the other leg is promoted in extension to keep the balance of the body, so you do not fall down and create more damage

Question 16

lower motor neurons are known as

Answer 16

alpha motor neurons and activate muscle fibres, these extend from the anterior horn cells of the spinal cord

Question 17

a motor unit

Answer 17

is a term used to descibe all motor fibres that are innervated by a single alpha motor neuron

Question 18

describe the differences between the primary motor cortex, the premotor and supplementary motor cortex

Answer 18

the motor cortex does simple movements such as finger flexion and has the final say in motor execution following motor planning (supplementary motor areas) and refinement of the motor plan (by the basal ganglia and cerebellum)

the premotor cortex creates a motor response in response to an external stimulus e.g. seeing a red light on a traffic light, and pressing on the brake

the supplementary motor cortex works bilaterally and allows for an internally generated sequence of movements such as learning to play the piano