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
