Spinal Movement Flashcards
How are motor systems organized?
Hierarchically
What are coordinated movements produced by?
Spatial and temporal patterns on muscle contractions ordered by the brain and spine
What are the two parts of motor control?
1) Spinal cord -> contains motor programs
2) Brain -> controls spinal motor programs
What are spinal nerves?
Mix of sensory and motor
What are the two types of muscles?
Smooth (inner gated by ANS fibers) and Striated
Do muscles pull or push on a joint?
Pull
What direction to flexors and extensors pull on a joint?
Opposite directions in order to antagonize each other
What are the 3 groups of muscles that act on joints?
Axial, proximal, distal
What do axial muscles control?
Trunk movement, posture
What do proximal muscles control?
Shoulder, elbow, pelvis, knee
What do distal muscles control?
Hands, feet, and digit movements
What are somatic muscles innervated by?
Somatic motor neurons (pretty tricky huh?)
Where are somatic motor neurons found?
Ventral horn of the spinal cord (lower motor neurons)
What do lower motor neurons do?
Directly command muscle contraction
Where are somas of upper motor neurons?
The brain
What do upper motor neurons provide?
Input to lower motor neurons
What does damage to UMNs cause?
Spasticity/Hypertonia
What does damage to LMNs cause?
Paralysis
What is meant by “limb enlargements”?
The spinal cord sections of muscles in the ventral horn are not even and are bigger the more skeletal muscle there is somewhere (ex. Lumbar section of spine has much larger ventral horns for the legs)
Where do motor neurons controlling flexors lie relative to extensors?
Dorsal
Where do motor neurons that control axial muscles lie relative to distal muscles?
Medial
What are two categories of LMNs?
Alpha and gamma
What do alpha neurons innervate?
Extrafusal muscle fibers
What do gamma LMNs innervate?
Intramural muscle fibers
What do alpha motor neurons do?
- branch and innervate many fibers over a wide area
- triggering generation of force by muscles
What is a motor unit?
An alpha neuron and all the muscles fibers it innervates
What is a motor neuron pool?
All alpha motor neurons that innervate a single muscle
What are the 2 types of muscle fibers?
Red and white
What are red muscle fibers?
Slow twitch, fatigue resistant, shit ton of mitochondria, myoglobin, and capillaries
What are white muscle fibers?
Sparse in mitochondria, anaerobic metabolism, contrast and fatigue fast, FAST TWITCH
What are the 3 types of motor units?
Slow, fast fatigue resistant, fast fatigable
What are slow motor units?
Small, innervated by small alpha motor neurons, resistant to fatigue, red muscle, important for sustained muscle contraction
What are fast fatigue resistant motor unites?
Intermediate size, innervated by intermediate sized alpha neurons, generate TWICE the force of slow motor units
What are fast fatiguable motor units?
Large motor units, innervated by LARGE alpha motor neurons, pale muscles, brief bursts
What are the two ways to control force of muscle contraction in a fine way?
Varying firing rate of AMNs and the size principle
How does varying the firing rates of AMNs work?
- a single AMN AP causes a muscle twitch
- sustained contraction requires CONTINUED stimulation
- # of and freq of APs increases
How does increasing the # of active MUs change the force produced by a muscle?
INCREASES it
What happens when you switch the alpha motor neuron controlling a muscle?
The muscle changes phenotype (ex. Making a fast motor neuron a slow one will make the muscle it innervates slow)
What are the 3 major sources of input of AMNs?
DRG neurons (innervate muscle spindle), upper motor neurons (in brain stem and motor cortex), and interneurons (Biggest input, can excite or inhibit)
What are muscle spindles?
8-10 intrafusal fibers arranged parallel to extrafusal fibers inside belly of muscle
What type of sensory axons wrap around the muscle fibers?
1a
What are muscle spindles specialized in?
Detecting changes in muscle length
What do muscle spindles contain that make them sensitive to stretch?
Mechanosensitive ion channels
What is the stretch reflex used to test?
If nerves and muscles are in tact
Describe the stretch reflex dumb
In dumb terms:
- ur holding a cup thats getting heavier from pouring
- your muscles send info from the spindle to the spine which it then messages back saying to inhibit your tricep (your extensor) and excite your bicep (your flexor)
Describe the stretch reflex smart
- monosynaptic reflex arc
- stretching a muscle spindle increases 1a activity
- the 1a detects a stretch and sends info to alpha motor neuron to contract that muscle
What are gamma motor neurons?
LMNs that innervate INSIDE muscle spindles
What are intrafusal fibers?
Skeletal muscle within the fibrous capsule (the purple thing of the muscle spindle)
What is the gamma motor neurons main job?
Keep the muscle spindle taut (not loose)
What is a gamma motor neuron activated?
When the spindle is limp after the muscle contracts
What are golgi tendon organs?
Strain gauges meant to protect muscles from overload and help fine motor acts
Where are golgi tendon organs found?
Between muscles and the tendon
What innervates golgi tendon organs?
1b sensory axons
How are 1b sensory axons activated in golgi tendon organs?
Inside the golgi tendon organs are collagen fibrils which get more tense with muscle contraction, these fibrils squeeze 1b sensory axons and cause their mechanosensitive channels to open
What is a golgi tendon organs NORMAL function?
Regulate muscle tension within an optimal range to not overload a muscle
What do the 1b sensory axons branch to into the spine?
Inhibitory interneurons in the ventral horn which inhibit the muscle the 1b sensory axons were tensed by
What are the main differences between muscle spindles and golgi tendon organs?
Muscle spindles
- parallel to muscle fibers
- 1a axons
- detect muscle LENGTH
Golgi
- in series of muscle fibers
- 1b axons
- detect muscle TENSION
During passive stretch (think cup) which one is more important?
Spindles
During active contraction, which one is more important?
Golgi
What basic reflexes do inhibitory interneurons do?
Contracting one muscle group and relaxing another
What do excitatory interneurons mediate?
The flexor withdrawal reflex
What is the flexor withdrawal reflex?
Withdraws a limb, slower than stretch, Adelta nociceptive axons enter spinal chord and active interneuron which excited AMNs to withdraw the limb
Where is the program for walking located?
Spine
