Somatic Motor System Flashcards
Muscle Spindle Components
-on skeletal muscles to sense stretch
Intrafusal Muscle in non-contractile regions
-Dynamic nuclear bag (1a, dynamic y)
-Static Nuclear Bag (1a, II, static y)
-Nuclear Chain (1a, II, static y)
Large Diameter myelinated sensory receptors
-central regions of fibers
Small Diameter myelinated motor endings
-innervate polar contractile regions
Extrafusal Muscle Fibers
Outer skeletal muscle that generate movement by attaching to tendon
-innervated by alpha motor neuron
Intrafusal Muscle Fibers
Inner skeletal muscles that form spindle
-non-contractile
-proprioceptors (length and velocity)
Nuclear Bag Fibers
Type of Intrafusal Fibers
-centrally located, only 1
-large
-innervated by Group 1a fibers: detect change in length
-innervated by gamma motor at ends
Static
Dynamic
Nuclear Chain Fibers
Type of intrafusal fiber
-smaller, more abundant
-length dependent
-innervated by Group 1a fibers: detect change in length
-innervated by Group 2 fibers: at ends, detect length
-innervated by gamma motor at ends
-activate alpha motor neurons
Ia Fibers
-primary sensory on muscle spindle
-phasic and tonic discharges
-changes to length
IIa
-secondary sensory endings
-tonic discharges
-responds to steady state length at ends of muscles
- in nuclear chain only
Gamma Motor Neuron
-keeps muscle spindle fibers sensitive at different lengths by contracting intrafusal fibers sto avoid going limp
-innervate polar regions and stretch
-motor supply to intrafusal fibers
Dynamic: innervate dynamic NB, increase sensitivity of Ia
Static: innervate NB and NC, increase tonic activity both, decrease dynamic sensitivity Ia
Alpha-Gamma Co-activation
Gamma: innervate polar regions and initiate stretch causing; mechanical gated channels to depolarize on intrafusal fibers
Alpha: …. contract the muscle to maintain length-tension relationship
Stretch sensed by 1a fibers < travels to SC < gamma neurons contract intrafusal to maintain sensitivity to muscle spundle < alpha motor neuron contracts muscle
Reciprocal Inhibition
-1 muscle contracts and opposing muscle is inhibited
- Intrafusal fiber senses stretch
- Info travels to dorsal horn
- Interneuron
4.Travels to ventral horn - Opposite muscle contracts
Golgi Tendon Organ
-proprioceptive structures at junction between muscle fibers and tendon
-sensitive to stretch in tendon/contraction of muscle
-tension in tendon < innervated by Ib fibers that send AP to SC < inhibits muscle
Motor Neuron Pools
-clusters MNs in SC
-innervate a single muscle
Medal MN: innervate axial and proximal limb muscles, laterally, distal
Ventrally MN: innervate extensors and dorsal flexors
Small MNs
-innervate slow twitch fibers
-less force
-long periods of time
Large MNs
-fast twitch fibers
-large forces
-fatigue quickly
Rate Coding
-MN signals amount of force exerted by muscle
-increased rate increases force (force summation)
Size Principle of MNs
-smaller MNs are recruited and fire before larger
Ohm’s Law: V=IR (voltage= current x resistance)
- smaller motor units have larger excitatory potential, small current can cause an action potential faster (but the conduction is slower and smaller motor units)
Transverse Tube
(T-tube)
-surrounds sarcoplasmic reticulum and propagates AP
Sarcoplasmic Reticulum
-released acetylcholine
-stores Ca+
Z Line
-fibrous disc at end of each sarcomere
M line
-holds together fibers at sarcomere center
Titin
-maintains actin/myosin positions to prevent them from being pulled apart
Troponin
-calcium binding causes tropomyosin to move and uncover sites on actin
Muscle Tone
Resistance to stretch of a muscle
Muscles immobilized in shortened position
-lose sarcomeres
Muscles immobilized in lengthened position
Gain sarcomeres
Phasic Stretch Reflex
-DTR
-muscle contraction in response to quick stretch
-monosynaptic
Cutaneous Withdrawl Reflex
-monosynaptic
-response to pain, withdrawal/flexion before consciously aware of pain
Muscle Cramps
-painful contractions due to overstimulation of nerve tracts
Fasciculations
-fast twitches of all motor fibers in a MU
-eyelash twitching
Myoclonus
-brief contractions of a group of muscles
Tremors
-involuntary rhythmic movements
-with movement or at rest
Polio and post-polio syndrome (types)
- normal MNs
- death of selected MNs
- Neuroplasticity cause giant motor units
- Muscle fatigue and pain
