The Motor System Flashcards
Flex
- Decrease Joint angle, flexor contracts and shortens
- Extensor is stretched and lenghtens
Extend
- Increase joint angle, Extensor contracts and shortens,
- Flexor is stretched and lengthens
Antigravity Muscles
Extensors
Postural fixation
Elimination of unwanted movement at a joint (necessary for useful movement)
Parameters of muscle action
- Force
- Speed of contraction
- Resistance to fatigue
- Fineness of control
(1,2,3 result from the structure of muscle )
(4 from the structure and pattern of innervation of muscle)
Fast Twitch (white muscle)
FF fibers- fast and fatigable
FR- Fast and Resistant to fatigue
Slow twitch (Red Muscle)
S fibers- least force slowest contraction time BUT MORE RESISTANT to FATIUGUE
ALS
absence of trophic factors for muscle; spinal cord and cortex.
Poliomyelitis
Viral infection, Motor neurons die; muscles atrophy (paralysis)
Motor Unit:
Single motorneuron and all muscle fibers it innervates.
- All muscle fibers in a motor unit are of the same type.
Large motor units
FF fibers
Small motor units
S fibers
Small motor unit size (Muscle Properties)
Fine Control
Large motor unit size (Muscle properties)
Force, Speed
Motor units are recruited in order of increasing size :
Smallest First, Largest Last, and drop out in reverse order.
Feedback information
Muscle Length :
Receptor is the muscle spindle
Feedback information
Muscle Force :
Receptor is the Golgi Tendon Organ (GTO)
Structure of Muscle Spindle
- intrafusal fibers
(Ordinary muscle fibers are extrafusal fibers) - attached in parallel with extrafusal fibers
Have both sensory and motor innervation
Intrafusal Fibers
- Contractile poles (Motor innervation)
- Noncontractile centers (Sensory innervation)
2 Types : - Nuclear Bag Fibers (dynamic)
- Nuclear Chain Fibers (Static)
2 Types of Sensory Fibers
Group IA 12-20 μm diameter, CV = 70 -120 m/sec.(bigger and faster)
Group II 5-12 μm diameter, CV = 30 - 70 m/sec.
(Smaller and slower)
- CV’s change in Diabetic Neuropathy
Group IA Fibers
- innervate every intrafusal fiber
- Form primary or annulospiral endings
- convey both dynamic and static information
Group II Fibers
- innervate only Nuclear chain fibers, secondary or flower spray endings.
-Code static information - When muscle stretched, endings are depolarized(stretch sensitive channels, action potentials generated with enough stretch.
Motor innervation of the spindle : the gamma motoneuron
Motor innervation of contractile poles of intrafusal fibers, adjust the length of spindle in parallel with length of extrafusal fibers.
- somata in the ventral horn
GTO and Muscle Force
- Attached in series with muscle at the junction of the muscle and tendon.
