Lecture 13 - Descending Tracts Flashcards
Name the 4 descending pathways
- Corticospinal (Pyramidal) tract
- Corticoreticulospinal tract
- Corticorubrospinal tract
- Vestibulospinal tract
Function of corticospinal tract
Skilled movement of limbs
3 functions of corticoreticulospinal tract
- Posture
- Locomotion
- Autonomic functions (respiration, shivering, sweating, circulation, etc)
Function of the corticorubrospinal tract
Similar to corticospinal so skilled movements of limbs
2 functions of vestibulospinal tract
1.Postural reactions
2. Standing balance
[blank] and [blank] feed input to the brain to regulate descending systems
Basal ganglia and cerebellum
What 4 areas of the brain are important for planning movements and what area are they found in?
They are found in area 4 (primary motor cortex):
1. Somatosensory Cortex
2. Prefrontal cortex
3. Premotor cortex
4. Supplementary motor cortex
Where is area 4/primary motor cortex of the brain located
Precentral gyrus and paracentral lobule of frontal lobe
What is another name for area 4
Primary motor cortex
T or F: The left strip of the primary motor cortex controls the left side, and the right controls the right side
F, left controls right and right controls left
What 2 somatosensory tracts feed into the primary motor cortex/area 4?
- Spinothalamic tract
- Dorsal-column medial lemniscus
What is area 6 also called
Motor Associations Area
What 2 areas comprise the motor associations area/area 6?
- Premotor Area
- Supplementary Area
Function of the premotor area
Input is primarily visual and neuronal activity is triggered by external events
Is the premotor area lateral or medial
Lateral
Function of the supplementary motor area
Input is primarily somatosensory and its neuronal activity is triggered by internal representations
What does internal representations of the supplementary motor area mean
It is memorized sequences or manual tasks/procedures that we do often
What two methods were used to discover somatotopic organization and explain how
- Electrical stimulation
- Transcranial Magnetic Stimulation
How: Stimulate certain areas of brain to see what body part reacted
Which parts of the body are represented more medial in the motor cortex
lower extremities
Which parts of the body are represented more lateral in the motor cortex
Face
Somatotopy
How the brain is organized (Where each body part is found in the brain)
Describe what is meant by movement vectors of neurons
Neurons are specialized to move in a particular direction (ex. movement in flexion or extension)
Homunculus
How much of the brain is dedicated to each body part
Explain what is meant by larger areas of a homonculus
These areas are larger because they are dedicated to fine motor control
What two neurons make up descending pathways
- Upper motor neuron
- Lower motor neuron
T or F: The upper motor neuron regulates the lower motor neuron
T
What would happen if there was a lesion to the upper motor neuron
The lower motor neuron would be unregulated resulting in spasticity or paralysis
Where are cell bodies of lower motor neurons found
Ventral horn of spinal cord
Where do lower motor neurons innervate
Muscle fibers
Dorsal and ventral roots fuse to form a
spinal nerve
Why do we have cervical and lumbar enlargements
Where innervation of nerves from upper and lower extremities is found
Axial muscles are closer or farther from spine
closer
Flexor muscles are closer or farther form spine
farther
The origin of the corticospinal tract is
The sensorimotor cortex
What 3 areas of the brain make up the sensorimotor cortex
- Primary motor cortex
- Supplementary Motor Area
- Parietal Lobe
Describe the path of the corticospinal tract
1.Passes through the corono radiata/internal capsule
2. Through the base of the cerebral peduncle in midbrain
3. Enters basilar portion of pons
4. Forms a medullar pyramid as it enters the medulla
5. Decussation of pyramids occurs at the caudal medulla
6. 90% form lateral corticospinal tract while the rest remains uncrossed and is called the ventral corticospinal tract
Does the lateral or ventral corticospinal tract stay ipsilateral
ventral
Another name for the lateral corticospinal tract
Lateral funiculus
The lateral corticospinal tract synapse on
Lower motor neurons and motor neurons that innervate distal extremities (hands, feet)
Where does the lateral corticospinal tract terminate and why
Ventral, intermediate, and dorsal horn
Why: To modulate multiple things like reflexes and responses, allowing movement to occur
What do corticospinal tracts that synapse on interneurons in the dorsal horn influence
Local reflex arcs
What happens if the corticospinal tract was damaged in terms of reflexes
Spasticity and increased muscle tone
What would happen if the corticospinal tract was damaged in terms of skilled, voluntary movements
- Cant use tools
- Play competitive sports
- Loss of hand and finger movements
- Reaching
- Loss of regulation of reflex
Why does some of the corticospinal tract not decussate
Redundancy to ensure movement occurs still if there is damage
Pathway of the corticorubrospinal tract
- Same cortical areas as cortico spinal but also the cerebellum (corona radiata)
- Projects to ipsilateral red nucleus of midbrain
- Decussates in pons
- Projects to ventral horns
Does the corticospinal or corticorubrospinal tract decussate higher up
corticorubrospinal tract
What does the corticorubrospinal tract control
- Extrinsic muscles of hand, wrist, elbow and shoulder
- Muscles at multiple joints
What is the role of corticorubrospinal tract
Reaching and coordinated action of hand/arm positioning during task
Pathway of the corticoreticulospinal tract
- Starts at reticular formation which receives sensory info and links cerebellum and limbic system
- Corticoreticular fibers terminate bilaterally in the brain stem and form the pontine(medial) reticulospinal tract and the medullary (lateral) reticulospinal tract
Function of the pontine (medial) reticulospinal tract (4)
- Influences posture
- Locomotion
- Gross limb movements
- rapid postural reactions
Does the pontine (medial) reticulospinal tract have larger or smaller axons than medullary (lateral) spinal tract
larger axons
Function of the medullary (lateral) reticulospinal tract (2)
- Autonomic functions
- Involved in spinal central pattern generator for locomotion
Does the reticulospinal tract display redundancy?
Yes
Pathway of vestibulospinal tract
- Originates in vestibular nuclei of medulla
- Projects down spinal cord to neck and lumbar levels by forming the medial and lateral vestibulospinal tracts
Function of the medial vestibulospinal tract
Head movements
Function of the lateral vestibulospinal tract
Postural reactions
Refresher card to go over spinal cord schematic pathways
Name 3 ways a lesion could occur to the corticospinal tract
- Vascular damage
- Trauma
- Demyelinating diseases
What happens if a lesion occurs above decussation
Symptoms detected of opposite side of lesion
What happens if lesion is below decussation
Symptoms detected on same side of lesion
What are 3 characteristic signs of upper motor neuron lesions (corticospinal tract)
- Spastic paralysis: No input to reflex arc
- Clonus: Beat movement that is repeated (uncontrolled reflex)
- Babinski sign: Toes fan or flare (flare = positive result, curl = negative result)
What happens if there is a lesion to the corticospinal tract in the left capsular region?
There will be a right side spastic hemiplegia (paralysis on one side) and hypertonia because lesion is above decussation
