smooth muscle excitation and contraction (midterm 1) Flashcards
what is the difference between smooth and skeletal muscle (control-wise)
smooth is involuntarily controlled (i.e. intestines) and skeletal is voluntarily controlled (i.e. bicep)
what are smooth muscles composed of
small fibers (1-5 um in diameter and 20-500 um in length)
how much bigger are skeletal muscle fibers then smooth muscle fibers
30x greater in diameter and several 100x as longer
what causes contraction in both smooth and skeletal muscle
the same attractive forces between myosin and actin filaments
what are the outer surfaces of multi-unit smooth muscle covered by
thin layer of collagen and glycoprotein to help insulate separate fibers from one another
what are the types of smooth muscle
multi-unit smooth muscle and unitary smooth muscle
what is the main difference between unitary and multi-unit smooth muscles
multi-unit contract independently and unitary contract together as a single unit
what’s an example of multi-unit smooth muscle
iris muscle of the eye
what’s an example of unitary smooth muscle
uterus and blood vessels
how are smooth and skeletal muscles similar
- contains both actin and myosin filaments that bind to create force
- contraction process is activated by Ca++
- ATP provides the energy for contraction
what are the major differences between smooth and skeletal muscle (mechanisms)
- smooth muscle doesn’t contain the normal troponin complex found in skeletal muscle contraction
- smooth muscle is irregular compared to skeletal
what does polar myosin filaments (such as in cross-bridges) allow for
contraction in opposite direction
what are dense bodies
attached to cell membrane (particularly actin) and dispersed inside the cell - they serve the same role as Z discs in skeletal muscle
what does binding dense bodies of adjacent cells together by intercellular protein bridges cause
transmit force from cell to cell
how much myosin is interspersed among actin
15x less myosin than actin
what do cross-bridges allow myosin to do
pull an actin filament in one direction while pulling another actin in the opposite direction on the other side, leading to smooth muscle cells contraction 80% their length (<30 % for skeletal)
how long does smooth muscle contraction last for
hour or days maintaining force
what is the latch mechanism
actin-myosin binding cycle is slow (1/10-1/300 as skeletal energy consumption), so the actin-myosin binding time is long
how does maintaining force of smooth muscle occur
initially, A-M binding frequency increases => force
then decreases and time increases
why is the max force of contraction of smooth muscle greater than skeletal
due to the prolonged period of attachment of myosin cross-bridges to actin filaments
what is stress-relaxation
the original force of contraction may be returned within seconds after it has been elongated or shortened
what is an example of stress-relaxation
bladder
bladder volume increases, tension increases
bladder stretch increases, decreased A-M overlap and tension
- can increase bladder volume with no change in tension
what is calmodulin
initiates contraction by activating myosin cross-bridges
what is skeletal muscle activated by
nervous system
what is smooth muscle activated by
nervous system, hormones, mechanical stimulation
what do autonomic nerve fibers do
contract smooth muscles independently and branch diffusely on top of a sheet of muscle fibers
what do vesicles of the autonomic nerve fiber endings contain
acetylcholine in some fibers, norepinephrine in others
what determines if a smooth muscle is inhibited or excited
the type of receptor or circulating hormones - if acetylcholine is excitatory norepinephine is inhibitory and vice versa
what is the resting membrane potential of smooth muscles
~ - 60 mV (~ 0 with action potential)
what has the same action potential as skeletal muscle and what is it
unitary smooth muscle
- spike AP = typical
- slow wave potentials = self-excitatory
- plateauAP = prolonged contraction
how many voltage-gated Na+ channels does smooth muscle have
fewer than skeletal, but more v-gated Ca+ channels (open slow and remain open longer)
when does relaxation occur for smooth muscles
with low O2, high CO2, high H+, which can cause AP
