Chapter 13: Spinal Cord Flashcards
Three types of muscles referring to locations
Axial muscles: trunk movement, maintains posture (most medial)
Proximal muscles: shoulder, elbow, pelvis, knee movement, important for locomotion
Distal muscles: hands, feet, digits (fingers and toes) movement (most lateral)
What are the three main roles of the spinal cord?
1) Carrie’s motor information from the brain to the periphery
2) Carries sensory input from periphery to the brain
3) mediates reflexes for nody
What is the anatomy of the spinal cord?
- dorsal root-sensory (afferents)
- dorsal root ganglion- contains somas of sensory afferents entering the cord
- ventral root - motor (efférents)
- spinal nerves - mixed sensory and motor roots
What’s e the three divisions of the gray matter?
Dorsal horn
Intermediate gray
Ventral horn
What’s are the types of neurons you can find in gray matter?
Ventral horn: mainly motor neurons whose axons exit the spinal cord
Dorsal horn: mainly neurons responding to sensory inputs
Intermediate gray: sensory neurons, motor neurons and interneurons
Define a motor unit
One alpha motor neuron and all the muscle fibers it innervates
What is a motor neuron pool?
The collection of alpha motor neurons that innervates a single muscle
What are the two types of lower motor neurons in the spinal cord? What do they innervate and trigger?
1) alpha motor neurons: - innervate extrafusal muscle
- trigger the generation of force in the muscle
2) gamma motor neurons: - innervate intrafusal muscle fibers of the muscle spindles
LMN vs UMN
- lower motor neuron (LMN) - provide direct input into muscle contraction, split into Alpha and Gamma motor neurons, cell body in ventral horn, death leads to ALS (paralysis)
- upper motor neuron (UMN) - provide input into LMN, cell body in cortex, death leads to spasticity
What does the descending spinal pathway command?
Modulates spinal reflexes or directly drive motor output
What can you say about the lateral pathways?
- voluntary movement of distal musculature
- under direct cortical control
- innervate distal musculature
What are the lateral pathways?
Corticospinal tract
Rubrospinal tract
What can you say about ventromedial pathways?
- control of posture, locomotion, orienting and balance
- under brainstem control
- innervate axial and proximal musculature
Why are the ventromedial pathways?
- tectospinal tract
- vestibulospinal tract
- pontine reticulospinal tract
- medullary reticulospinal tract
What’s the the two mechanisms for the force of muscle contraction by lower motor neurons? Explain each one
- By varying firing rate of motor units
——-> 1 AP in the alpha motor neuron causes an end plate potential (epp) strong enough to generate one postsynaptic AP in the muscle. 1 AP in the muscle causes a twitch. Increasing the AP frequency causes twitch summation and eventually sustained contraction - Recruitment of synergistic motor units: large motor units (fast twitch) generate more force but tire easily
Small motor units(slow twitch) generate less force for endurance