Physio Lecture 1

• Visceral smooth muscles
• Gap junctions between each individual smooth muscle cells

Functional synctytium

Multi-unit smooth muscles

Multi-unit

• Skeletal muscle. with these characteristics:
• Nuclei located right under the sarcolemma of the cell,
• on the outside around the myofiber

• myofiber
• IMPORTANT: If you're talking about the even small component, it's fibrils

• 1. Tendon
• 2. Ligament

• Superficial fascia (1st layer of connective tissue)
• ---->A second layer of connective tissue: epimycium
• ---->Perimycium, another connective tissue surrounding bundles called fascicles
• ---->Inside each fascicles: individual myofibers
• ----->3rd layer of connective tissue: endomycium: surroudning each myofiber
• --->ind. myofilaments inside the myofiber

• plasmalemma
• plotoplasm

Below the surface of the sarcolemma, outside or eccentrically placed in the myofiber, long cylindrical fibers

• 1. One branch of an alpha motor neuron.
• 2. Neuromuscular junction
• 3. In the belly or center region of the muscle

Individual myofilament proteins-thin and thick filaments

• 1. One layer runs right below the surface of the sarcolemma
• The primary purpose is to maintain Na+/K+ active transport pump and concentration gradiens, which require energy (the same gradient we saw in the nerve)
• 2. The other layer is spread throughout/in between all of the myofibrils-
• The purpose of these mitochondria is to produce ATP to provide energy necessary for the sliding of the filaments that actin over the thick myosin filament

A muscle cell contracts a large number of times, it isn’t changing the concentration gradient of extracellular fluid to a large extent,but in the t-tubule, with Na+/K+ pumps active and concentration gradients are changing in that small volume within the t-tubule

So if K+ is leaving the sarcoplasm and entering the t-tubule all of a sudden the K+ concentration of the extracellular fluid is elevated inside the t-tubule. The action potential is going to spread across the surface, but it also spreads across the t-tubule membrane with equal speed to get inside the cell to induce the contraction mechanisms for all of the myofibrils as near simultaneously as possible.

No, they are near simultaneous as possible- can't have them go out of sync

• 1. myosin
• 2. Actin

• Z-disk to the next z disc
• 1. I band/ A band
• 2. H band
• 3. I band (light area)---A band the really dark area(includes H band in the middle, including the M line)----I band
• *Also, realize that in 3 dimentions, the z line is actually a disk

• Alpha actinin, and to serve as anchor to the action filament'
• Sarcomere

• i. Add sarcomeres
• ii. add more thin and thick myofilament proteins

• 1. Elastic coil of muscles to help them return to their resting length during muscle relaxation
• 2. Aid in centering thick filamnent equidisitant between actin thin filaments

Obscurin

Nebulin

Dystrophin (right underneath the sarcolemma)

• -Many forms of muscle dystrophy
• -Make sarcolemma more easily damaged
• -Leads to necrosis of the cell

Repair of damaged myofibers (but may not recover from muscular dystrophy)

• 1. No more Ach being released and stimulating the cholinergic receptors at the site
• The membrane starts to flatten out and Ach receptors start to drift out along the sarcolemma asway from the damaged region
• 2. Disuse Atrophy- this is experienced also by astronauts in outerspace with little gravity

• 1. Action potential travels down sarcolemma into the t-tubules down into the cell where it results in the release of Ca2+ that will initiate the contraction. Ventralhorn gives rise to large alpha motor neurons and branches.
• 2. Ach receptors on the motor end-plate and Ach in
• synaptic vesicles. When an action
• potential comes down, Ca2+ permeability changes, Ca2+ comes into the cell
• results in tubular formation that results in migration of neurotransmitter
• vesicles to pre-synaptic membrane where they are exocytosed, Ach drifts across
• neuromuscular synaptic cleft and binds to receptors.

• One somatic motor neuron and all of the myofibers
• it innervates is referred to as a motor unit
• Motor end-plate is only the specialized,
• post-synaptic region of the sarcolemma that is part of the neuromuscular
• junctions and does not include the terminal button of the axon

• Adding more motor units to contraction. This is depended on the RECRUITMENT by the CNS to decide how many myofibers to recruit
• -Another way is to send action potentials more rapidly to give a summation effect

• A band
• I band
• The I band dissapears because the myosin thick filament was pulling the actin over it, leading to the shortening of each myofibril within each myofiber