Two types, Striated and smooth

Straited

• Cardiac in heart
• Skeletal, bones, eyes, lungs

Smooth

Reproductive, arterries, digestive

Muscle Fibers

Bundles
long, thin cells, running length of each muscle

• Muscle fibers are made of sarcomeres laid end to end
• contain actin and myosin proteins, z lines seperate
• m lines found in middle
  • anchoring point for myosin filaments
• form fast and efficient synapses at neuro muscular junction, released acetylecoline here

Muscle Contraction

occurs when actin and myosin slide by eachother

• relaxed muscle, tropomyosin prevents this,
• in put, releasing acytlecoline, produce action ppotential in fibers
• action potential produces a twin, realizing calcium from internal organelles, binding with tropomnin, displacing tropomyosin, allowing actin and myosin to interact
• Myosin binds to actin, myosin filaments rotate and move relative to action, shortening sarcomere
• when done, reuptake occurs

Types of Myosin Filiments

3 types

• slow twitch, typoe win
• fast twithc, type 2 (a and B)
• contain all three in diff proporitons
• muslces, back and legs have slow
• muscles n shoulders have fast
• slow require o2, fast dont
• Endurance rely on slow, appear red, due to high levels of myoglobin, storing o2
• most have equal in quads
• elite altheles have different amounts
• spinal injury have huge loss of slow twitch, high fast twitch
• neural requried to maintain slow, but not high
• astronauts experience loss of 20% of muscle mass, with 2 weeks, bc of less work done by posteal muscles

Aging

Muscle mass decrease by as early as 25, by 50, lose 10%, by 80, 50%
aging changes quant, shape, distro of muscle fibers
motor neurons have lower rate of firing in older adults
offset changes by remaining active

Distribution of Spinal Motor Neurons

Larger ventral horn serve harms and legs
Volumes are not equal
Gamma fibers provide motor input to intrafusal fibers.

Neuromuscluar junction

Single aciton potential can muscle twitch
one neuron can activate many muscles
motor unit, 1 type of fiber, fine movement have less fibers
variation in force and duration, managed in two ways, alpha fibers rate of fire varies, fast firing has sustantied contraction
recruitment occurs when more and more neurons go to help with neural low
ensures dont use more force than needed

Feedback

• alpha motar neurons dont movement on own
• guided by muscle spindles, golgi tendons, spjnal interneurons, higher levles of motor neural systems in brain
• Spjndles embeded in muscle provide info about muscle stretch
• recieve input matching length of outside spjndle fibers
• wrapped around centers are AA sensory fibers, bigger and faster than fibers serveing mechanoreceptors
• fires everytime stretch
• compensatory myotatic reflex
• bending one sde stretches muscles, intehguhj[gfdf

Myotatic Reflexes

compensatory contraction when muscle is stretch
patellar or knee-jerk reflex checked by docker, tapping below knee stretches quadreceps muscle at the top of thigh, produciing compensatory contraction, leg kicks out

• not fast enough to inhibit since spine does it before brain processes it happened