lect 22 - motor system l

what is the efferent activity

motor system control's skeletal muscle activity , behavior & vegetative functions

somatic motor system controls what

skeletal muscle

autonomic NS controls what

smooth & cardiac muscles

3 classes of movements in somatic motor system (generate behavior )

1. simple reflex movements

2. coordinated, more complex reflex movements (walking,etc)

3. voluntary, skilled movements ( writing, speech)

anatomy of skeletal muscle

- striated muscle (very highly organized)

- enclosed by connective tissue & adheres to bone via a tendon

- each muscle bundle made up numerous muscle fibers (cells)

- each muscle fiber is innervated by motor neuron fibers at neuromuscular junction

innervation ratio

# of muscle fibers in a single motor unit

- small motor units are used to make fine movements

- larger units provide more force during contraction

small motor units includes

fingers & eyes (3 muscles/ motor neuron)

large motor units include

antigravity muscles of leg to hold you up ( 1000:1)

spatial distribution is found where

lower motor neurons in spinal cord

lower motor neurons that innervate AXIAL muscles are found where

ALL levels of spinal cord in ventral horn

lower motor neurons that innervate DISTAL & PROXIMAL muscles are found where

CERVICAL & LUMBOSACRAL enlargements

- C3-T1

- L1 - S3

medial-lateral rule

cell bodies in ventral horn that innervate axial muscle

axial - medial

distal - lateral

dorsal - ventral rule

flexors - dorsal

extensors - ventral

excitation of muscle requires what

requires synaptic transmission at motor end-plate (neuromuscular junction )

- requires AP in motor neuron to excite muscle fiber

ACh is released by

motor neuron onto nicotinic ACh receptors (nAChR) at motor end plate which then causes a deplo

safety factor

motor neuron a.p ALWAYS leads to a muscle a.p & muscle contraction bc of sufficient ACh

- lots of vesicles of ACh

activation of nACh Rs generates

an end plate potential (EPP) sufficiently large to produce a muscle AP (passes threshold)

in crossbridge formation what happens at rest

low Ca2+ prevents myosin from binding to actin

tetanus

largest force produced when freq of successive twitches is rapid & sum together, appearing smooth & continuous

- max sum of all twitches = largest force

twitch

spread out over time

- unitary contraction ; smallest unit of force

what can be a treatment for myasthenia gravis & what happens

patient makes antibodies against nACh Rs & treatment is called plasmapheresis ( dialyze blood & pass it through machine & remove certain antibodies & has to be repeated over &over) or acetylcholinesterase inhibitors (prevent breakdown of ACh & alleviate some muscle fatigue)

muscle fatigue

weakness indicates muscle failure to respond due to fewer nACh Rs

dystrophin

rod shaped cytoplasmic protein

- component of protein complex that connects cytoskeleton of muscle fiber to surrounding extracellular matrix through cell memb

mutations in dystrophin gene can lead to

lead to production of partially functional (beckers) or non functional (duchenne's ) dystrophin protein

* carried on X chromosome so boys are more susceptible