descending tracts Flashcards
- What are lower motor neurons, and where are they located?
Motor neurons in the anterior gray columns of the spinal cord that send axons through the anterior roots to innervate skeletal muscles.
- What are upper motor neurons?
Neurons that originate in the brain (cerebral cortex, brainstem) and influence lower motor neurons via descending tracts.
- What are the three types of neurons involved in motor control?
First-order (cerebral cortex), second-order (internuncial neuron in spinal cord), third-order (lower motor neuron to muscle).
- What is the function of the corticospinal tract?
Controls voluntary, skilled movements, especially in distal limbs.
- What is the function of the reticulospinal tracts?
Influence voluntary movement and reflex activity by facilitating or inhibiting motor neurons.
- What is the function of the tectospinal tract?
Controls reflex postural movements in response to visual stimuli.
- What is the function of the rubrospinal tract?
Facilitates flexor muscles while inhibiting extensor muscles.
- What is the function of the vestibulospinal tract?
Facilitates extensor muscles and inhibits flexor muscles to maintain balance.
- What is the function of the olivospinal tract?
Its role is uncertain, but it may be involved in muscular activity.
- What is the function of descending autonomic fibers?
Regulate visceral activity through connections with autonomic motor neurons.
- Where do corticospinal tract fibers originate?
Primary motor cortex (area 4), secondary motor cortex (area 6), and parietal lobe (areas 3, 1, 2).
- What structure organizes the body’s motor control in the cortex?
The motor homunculus.
- Describe the pathway of corticospinal fibers.
Corona radiata → internal capsule → basis pedunculi → pons → medullary pyramids → spinal cord.
- Where do most corticospinal fibers decussate?
In the pyramids of the medulla oblongata.
- What are the two corticospinal tracts, and how do they differ?
Lateral corticospinal tract (crossed, controls limb muscles) and anterior corticospinal tract (uncrossed, controls axial muscles).
- Where do corticospinal fibers terminate?
In the anterior gray column, mostly on internuncial neurons.
- Where do reticulospinal tracts originate?
Scattered neurons in the reticular formation of the brainstem.
- What are the two divisions of the reticulospinal tract?
Pontine reticulospinal (uncrossed, anterior white column) and medullary reticulospinal (crossed and uncrossed, lateral white column).
- What is the function of the reticulospinal tracts?
Modulate voluntary movement, reflexes, and autonomic functions.
- Where does the tectospinal tract originate?
Superior colliculus of the midbrain.
- Where does the tectospinal tract terminate?
In the anterior gray column of the cervical spinal cord.
- What is the function of the tectospinal tract?
Controls reflex postural movements of the head and neck in response to visual stimuli.
- Where does the rubrospinal tract originate?
Red nucleus of the midbrain.
- What is the function of the rubrospinal tract?
Facilitates flexor muscles and inhibits extensor muscles.
- Where does the vestibulospinal tract originate?
Vestibular nuclei in the pons and medulla.
- What sensory input influences the vestibulospinal tract?
Input from the inner ear (vestibular nerve) and cerebellum.
- What is the function of the vestibulospinal tract?
Facilitates extensor muscles and inhibits flexor muscles to maintain balance and posture.
- Where does the olivospinal tract originate?
Possibly from the inferior olivary nucleus of the medulla.
- Why is the olivospinal tract debated?
Its existence and function remain uncertain.
- Where do descending autonomic fibers originate?
Higher autonomic centers (cerebral cortex, hypothalamus, amygdala, reticular formation).
- How do descending autonomic fibers influence visceral activity?
By synapsing with autonomic motor neurons in the lateral gray column.
