Cortical Control of Motor Activity – The Corticospinal Tract Flashcards
1
Q
Cortical structures:
A
- primary motor cortex
- prefrontal cortex
- somatosensory and parietal association cortex
2
Q
Subcortical structures:
A
- basal ganglia
- cerebellum
- thalamus
3
Q
Types of Movement:
A
-
Reflexes
- Stereotyped responses to stimuli
-
Voluntary
- Goal-directed
- Internally generated
- Improve with practice
- Automatic Postural Adjustments
4
Q
Motor Pathways: Two Main Systems
A
- Lateral:
- Lateral Corticospinal Tract
- Rubrospinal Tract
- Medial:
- Anterior Corticospinal Tract
- Lateral Vestibulospinal Tract
- Medial Vestibulospinal Tract
- Corticotectal and Tectospinal Tract
- Reticulospinal Tract
5
Q
What is the most important system for voluntary movement?
A
Coritcospinal tract
6
Q
Coritcospinal Tract:
A
-
One neuron
- Upper Motor Neuron
-
Projects to:
- Lower motor neurons (LMN) in ventral horn of ALL levels of spinal cord
-
Function
- Voluntary movement of distal extremities
- Skilled movements
- Excites flexor m.’s, inhibits extensor m.’s
7
Q
Corticospinal Tract:
Route
A
- CST axons arise from:
- Primary motor cortex (area 4) (33% of fibers)
- Betz cells (large pyramidal neurons in lamina V of the precentral gyrus) (3% of fibers).
- Premotor cortex (area 6) and Supplementary motor area (area 6) (33% of fibers)
- Parietal lobe (areas 3, 1 and 2) (33% of fibers)
- CST axons pass through:
- corona radiata
- posterior limb of internal capsule
- the middle of the cerebral peduncle (crus cerebri)
- medullary pyramids
8
Q
Upper Motor Neuron (UMN) Route:
A
- Cerebral cortex
- Corona radiata
- Internal capsule
- Posterior limb
- Crus cerebri
- Ventral pons
- Medullary pyramid
- Pyramidal decussation
- Lateral funiculus
9
Q
Primary Motor Cortex (M-I):
A
- Somatotopically Organized
-
Tasks that require great precision:
- Structures have disproportionately larger representations
- motor homunculus
- Motor map exhibits overlap & plasticity
- can change with increased use or disuse
10
Q
Lateral Corticospinal Tract:
A
- 90% of fibers decussate in pyramidal decussation
- descend in lateral funiculus to all sp cd levels
11
Q
Anterior / Ventral corticospinal tract:
A
- 10% of fibers do NOT decussate in pyramids
- descend in the anterior funiculus
- decussate in ventral white commissure to thoracic sp cd.
12
Q
- Lesions ABOVE the pyramidal decussation result in _____________ weakness
- Lesions BELOW the pyramidal decussation result in ___________ weakness
A
- Above ⇒ contralateral
- **Below ⇒ **ipislateral
13
Q
What signs would you expect to find with an UMN lesion?
A
- Paresis (weakness) or paralysis
- Spasticity
- Hyperreflexia
- Loss of abdominal reflexes
-
Babinski sign:
- stroking the plantar surface of the foot along the lateral border ⇒ dorsiflexion of the great toe (normal response is plantar flexion)
14
Q
What signs would you expect to find with an LMN lesion?
A
- Muscle atrophy
- Fasciculations
- Hypotonia
- Hyporeflexia
15
Q
Lesion in the Cortex:
A
Contralateral paresis of a particular body part corresponding to area of cortical damage.