Is it possible to consciously control a part of the body that is normally under autonomic control?

Somatic nervous system Signals from CNS are sent to skeletal muscles. Final result is a muscle contraction. Motor neuron starts in CNS and its axon ends at a muscle cell. Alpha motor neuron

Alpha motor neurons branch into several terminals (can be over 1000), each contacting a separate muscle cell.

Nerve meets muscle Acetycholinesterase Motor end plate Axon of motor neuron Action potential of motor neuron Terminal button Voltage-gated calcium channels Action potential propagation in muscle fiber Voltage-gated Na+ channel acetylcholine Acetycholinesterase Motor end plate

Organization of cells

Sarcomere Myofibril Muscle cell

Sarcomere – the unit of contraction, made of thin (actin) and thick (myosin) filaments Myofibril sarcomere sarcomere Z band Z band Z band A band

Contraction of filaments Before Contraction After Contraction Z Z Z Z Length of sarcomere shortens with contraction but filament length is unchanged Myosin Actin

Myosin

Actin

Tropomyosin normally covers the myosin binding site on actin When calcium binds with troponin, it pulls tropomyosin away from the binding sites troponin tropomyosin myosin actin myosin binding site blocked Calcium myosin actin cross-sectional view

Figure 8.2 (3) Page 259 Sarcomere Myosin Actin Actin Myosin

Muscle Contraction Signal from motor neuron causes action potential in muscle cell Calcium ions released (from sarcoplasmic reticulum) Actin and myosin filaments slide relative to each other

bridge bends, pulling thin filament. BINDING Myosin cross bridge binds to actin Myosin cross bridge POWER STROKE Cross bridge bends, pulling thin filament. DETACHMENT Cross bridge detaches and returns to original shape- *ATP required* BINDING to next actin molecule; repeat

Bending (power stroke) Figure 8.13 Page 267 Myosin needs ATP to change shape Energized Resting Detachment Binding Bending (power stroke) Myosin has a binding site for ATPase Rigor complex

Signal coming to muscle Sarcoplasmic reticulum (Ca+2 storage) motor neuron T tubule

From action potential to contraction Calcium is the link Acetylcholine released at the neuromuscular junction - action potential on muscle fiber Action potential down “T tubule” to sarcoplasmic reticulum at muscle fibers Calcium released from the SR to muscle fibers

Pathway review Terminal button Action potential A calcium pump T tubule Action potential Acetylcholine- gated cation channel (Na+ moves in) Acetylcholine A calcium pump in SR allows muscle to relax Troponin Tropomyosin Actin Cross-bridge binding Myosin cross bridge

How does polio virus cause paralysis? How do botox injections decrease wrinkles? How is chronic nerve pain or pain from spinal injuries treated?

Muscles contain groups of motor units Units are recruited during motor activity Muscle force depends on # muscle fibers contracting Motor unit = motor neuron + muscle fibers it innervates

The number of muscle fibers varies among different motor units. muscles can have many small units or a few large units Asynchronous recruitment of motor units delays or prevents muscle fatigue.

Tension and frequency of stimulation twitch - brief contraction resulting from 1 action pot’l tetanus - twitch summation from sustained Ca+2

Muscle length and force

Fast and slow twitch muscle cells Differences in time when maximum tension is reached Type IIb Type IIa Type I Slow twitch (Type I) - have myoglobin, many mitochondria, oxidative Fast twitch (Type IIa) - myoglobin, mitochondria, oxidative & glycol. “Very” Fast twitch (Type IIb) - use glycolysis, split ATP quickly

Fast and slow twitch muscle cells Oxidative - resistant to fatigue, high rate of O2 transfer from blood, recruited 1st Glycolytic - more prone to fatigue b/c less ATP produced, harder to recruit Endurance vs. Bursts of power

People are born with certain ratio of slow vs. fast twitch fibers usually an even mix in most skeletal muscles

Contracting and elastic parts of a muscle Contractile section Contractile section Series-elastic section Series-elastic section Load Load

Sensation at muscle Spindle muscle fibers (deep within muscle) and Golgi tendon organs (in tendons) sense stretch and tension. Intrafusal (spindle) muscle fibers

Knee reflex Muscle spindle Extensor muscle motor neuron Patellar tendon

What happens when we stretch? How does it help muscles, exercise? Muscles don’t actually become longer, but you can train your NS to tolerate lengthening When golgi tendons activate, they cause a reflexive inhibition (relaxation) of muscle Activate golgi t. with a pattern of isometric contraction/relaxation of lengthened muscle Leg gets lifted, relax, press against hand, relax w/more range

Primary types of contraction Isometric contraction - muscle tension is not enough to move load. Muscle doesn’t shorten. Isotonic contraction Concentric – muscle shortens to lift a load. Eccentric - shortened muscle has controlled lengthening. slowly lowering the weight

Exercising your muscles Endurance training type IIb type IIa more mitochondria, glycogen, vascularization

Exercising your muscles Strength training hypertrophy of type II fibers

Hypertrophy: how muscles get bigger Muscle cells have satellite cells nearby that respond to muscle injury and wear Why are muscles sore after lifting?

Hypertrophy: how muscles get bigger Satellite cells: activated at microtears add nucleus to muscle cell more myofibrils made cell wider

Muscle hypertrophy vs. hyperplasia

Functional vs non-functional hypertrophy (strength vs. size) Some hypertrophy can be due to growth of sarcoplasmic reticulum, increased glycogen (attracts water), but this is small You cannot ‘train for’ sarcoplasmic hypertrophy

But can you gain force without hypertrophy? The CNS can become trained to provide more force (apparent in early training) Better inhibition of antagonistic muscles Improved recruitment of different muscles over a movement to gain power

ATP sources at muscles 2 3a 1 3b

What does creatine do?

What are muscle cramps..can I eat a banana to avoid them? When muscle fibers contract without our control it is a muscle spasm or cramp Due to motor neurons being hyperexcited, often b/c of a shift in body fluids or ion levels (dehydration, low Ca, Mg, K) or vigorous activity

Smooth muscle Smooth muscle cells are small and unstriated No sarcomeres Smooth muscle cells contract when Ca+2 enters Myosin cross bridges are phosphorylated and bind to actin

What is the cause of a ‘pulled’ muscle? How can muscle hypertrophy help failing joints, ligaments? Muscles lifting with and w/out adrenaline Physiology bw bulky muscles and lean muscle growth Why is a day off good when working muscles?

Smooth muscle Multiunit - similar to skeletal motor units Single unit - gap jxns b/w muscle cells. Many cells contract as a unit. (uterus, intestine, bladder) Smooth muscle Striated muscle

Cardiac muscle Pacemaker muscle cells - action potential gradually depolarizes, then repolarizes Contraction spreads from pacemaker through gap jxns Spontaneous action potential Pacemaker cell Action potential spread to other cells Gap junctions