2.2The Brain: Motor (descending) Pathways Flashcards
Somatic Motor systems functions:
- Anti-gravity
- Stable posture
- Stop, start & control voluntary movement
what are the main neurons used in motor pathways & what are their characteristics:
Neurons of the ventral horn and spinal cors: myelinated, either:
- γ- neuron (fusimotor): thin axon, slow conducting
- α-neuron (skeletomotor): thick axon, fast conducting
pyramidal:
- voluntary movement, detailed muscle movement, basis of “skilled activity”
- Important in man
- Present in mammals only, but less importance in domestic species
Extrapyramidal:
- automatic muscular activity
-posture, rhythmical activity - or, semi-automatic, “deep-rooted” somatic activity - locomotion, feeding, defense
- dominant system in domestic animals
Where does the Pyramidal/Corticospinal (CST) System originate, where does it travel through, and where does it end up?
1) originates in the primary motor cortex in the cerebral cortex where axons traveling within CST as part of large fiber bundles known as Cerebral peduncles
2) descend through the brain stem
3) Fibers reach medullary pyramids within the medulla the pyramidal decussation in the base to decussate/ crossover
For the Pyramidal system: the left side of the brain orders which side of the body?
the right side of the body
What lobe is the motor cortex located in?
Frontal Lobe
What is between the midbrain and medulla oblongata?
Pyramidal system
What do the Upper motor neurones in the pyramidal system do?
modulate how powerful those lower motor neurons react
pyramidal system: Could a lesion in the UMN potentially affect the LMN
yes
What could happen if there is a bleed in the internal capsule of the brain?
vulnerable damage for strokes
Wha kind of relay does the pyramidal system represent?
Controlateral relay - left brain controls right side of body
What kind of relay does the pyramidal system represent?
Controlateral relay - left brain controls right side of body
How many neurones doe the pyramidal system have
3 ( 2 main & 1 interneuron)
neuron 1 = UMN,
- cell body in PMC of the cerebrum
- longest axon
- travels via internal capsule to pyramid in the brainstem
- crosses over at pyramid
- confined to CNS
Neuron 2 = Interneuron
Neuron 3 = LMN,
- cell body = ventral horn
- terminating on the effector’s muscles
- skeletomotor alpha neurons
pyramidal system: Would the muscle be able to contract if there was a lesion on the LMN area?
No
pyramidal system: Would the muscle be able to contract if there was a lesion on the UMN area?
The muscle will still contract, but the amplitude at which its contracts at the force and range of motion will be effected
Feedback pathways on the pyramidal system:
- same in humans & domestic species
- projections from higher motor centers –> cerebellum
- informs cerebellum of intended action / keep motor activity in check
- Cerebellum regulates actions via return pathways to the cortex
- fibers crossover from the left cortex to the right cerebellum
The cerebellums INDIRECT control of muscle activity is?
ipsilateral (same side)!
UMN disease:
LMN still working, not paralyzed
- lack of control from higher centers
ex: reflexes present but abnormal in magnitude
LMN disease:
Parslysis of muscles (complete lose of motor activity in muscles)
- muscles atrophy
Extrapyramidal system:
Command system involved in automatic muscular activity
- posture, rhythmical activity
- semi-automatic, “deep-rooted” somatic activity, locomotion, feeding, defense
-phylogenetically primitive
- either inhibitory (-) or facilitatory (+)
List the extra pyramidal relay tracts
1) Rubrospinal tract (RuST)
2) Recticulospinal tract (RetST)
3) Vestibulospinal tract (VestST)
4) Tectospinal tract (TectoST)
Rubriospinal tract:
red semi-skilled nuclei of the midbrain
- Facilitatory
- conscious
Recticulospinal tract:
mid to hindbrain region
- pontine and medullary
- facilitatory and inhibitory
- arousal –> extensors
Vestibulospinal tract:
sits closely to the vestibular nuclei of CN VIII
- balance and posture –> extensors
- Facilitatory
Tectospinal tract:
nuclei operate in the mid to hindbrain region and send projections to muscles of the neck
- Reflex control of head and neck in response to sight / sound stimuli
How many total motor pathways are there? How many are major?
Total: 9
Major: 4
How many (main) neurones from command center?
2
Are the majority of UMN Facilatory or Inhibitory?
Inhibitory
What is the final common pathway?
LMN/ alpha neuron
Where does the reticular tract crossover?
hind brain
where does the rubrospinal tract crossover?
midbrain
where doe the tecospinal tract crossover?
midbrain
Known as executive management?
cerebral cortex
spokesperson for other nuclei?
globus pallidus
does the vestibular nuclei crossover?
no, its ipsilateral
In the extrapyramidal system: the left side of the brain governs?
the left side LMN on left side of body
Which 2 serve as felexors/ inhibitory
Cerebral spinal tact and rubriospinal tract
Which 2 serve as extensors / facilitary
vestibular spinal tract and reticular spinal tract
Archi: Flocculus /nodules =
- balance / posture
- brainstem inputs = vestib, visual
neo: caudal hemispheres =
voluntary motor -cortical inputs
Paleo: vermis / rostral =
- tone / posture
- spinal cord inputs (spindles / golgi’s)
Take home message: Cerebellum
- concerned with posture
- does NOT initiate contraction
Take home message: Cerebellum
- concerned with posture
- does NOT initiate contraction
What initiates contraction?
pyramidal and extrapyramidal system
Which does Cerebellar disease involve? incoordination or paralysis?
incoordination
Above decussation - deficits
opposite side
Below deccussation - deficits
same side
sensory decussation location if touch & conscious proprioception was affected
Medulla site of decussation via the dorsal columns
sensory decussation location for effective unconscious proprioception
No site of decussation:
sensory decussation location for pain
Bilateral site of decussation
Motor decussation locations:
nearly all pons/medulla
symptoms of lesion localization: motor deficits
· Functional
UMN Vs. LMN symptoms
symptoms of lesion localization: sensory deficits
· Ataxia
· Loss of touch/pain sensation
