Muscles 9 Flashcards
Smooth muscle must operate
Over a range of lengths
Smooth muscle layers run
In many directions
Smooth muscles contract and relax
slowly compared to skeletal muscle
Smooth muscle use less energy than skeletal to:
Generate and maintain force
Smooth muscle can sustain
Contraction without fatigue
Smooth muscle contraction is initiated
Electrically or chemically
Smooth muscle is controlled by
The autonomic nervous system
Smooth muscle gets Ca2+ from
The extracellular space and/ or the SR
Smooth muscle Ca2+ initiates cascade which
Which turns on myosin ATPase
Smooth muscle characteristics
Spindle shaped
Uninucleated
Troponin and t-tubules absent
Non contractile filaments
Dense bodies (similar to z-lines of skeletal)
Thin filaments anchored to cell membrane or dense bodies
6 locations of Smooth Muscle in humans
- vascular -blood vessel walls
- Gastrointestinal -walls of digestive tract and associated organs (gallbladder)
- Urinary -wall of bladder and ureters
- respiratory -airway passages
- Reproductive -uterus (female) and more
- Ocular -iris and ciliary body
Smooth muscle 4 contraction patterns:
- Physic smooth muscle is relaxed -esophagus
- Physic smooth muscle cycles between contraction and relaxation -intestine
- Tonic smooth muscle usually contracted -sphincter that relaxes to allow passage
- Tonic smooth muscle whose contraction varies -vascular smooth muscle
Smooth muscle Communication with Neighbouring cells: 2 parts
Unitary (single unit) smooth muscle
Multi unit smooth muscle
Unitary (single unit) smooth muscle:
Contains gap junctions similar to cardiac muscle cell
-allows coordinated contraction of many cels causing muscle to contract as a single unit
-makes up walls of most visceral organs
AKA Visceral Smooth Muscle
Multi unit Smooth Muscle
Not electrically coupled
-iris and cilliary body of eye
-in male reproductive tract and uterus except just prior to delivery
Smooth muscle may contract in response to
Synaptic transmission or electrical coupling
Smooth muscle is usually innervated by
The autonomic nervous system
-sympathetic and parasympathetic
-by multiple neurons capable of releasing different neurotransmitters
Alpha adrenergic vs Beta adrenergic in smooth muscle
Alpha: Gi vessel constriction
Beta: airway dilation
Other factors that can alter smooth muscle tension: (5)
Circulating hormones
Stretch and local factors (including paracrine signals)
Acidity
O2 and CO2 concentration
Osmolarity
Action potentials of smooth muscle can be initiated by what stimulations? (3)
Neural, hormonal, or mechanical stimulation
Smooth muscle APs are similar to
Skeletal in the way the upstroke is slower because Ca2+ channels propagate the AP instead of Na+
-repolarizatio also slower because Ca2+ channels inactive slowly -delayed activation of voltage gated K+ and some Ca2+ activated K+ channels
As in smooth muscle usually don’t happen in which unit:
Multi unit smooth muscle
Smooth muscle cells produce a wide range of
Membrane potentials
-some oscillations can lead to tonic contractions in absence of AP
Single Unit smooth muscle APs:
Autonomic AP initiation: spikes or plateaus
Spontaneous AP: slow wave, pacemaker
Multi unit smooth muscle APs:
Graded potentials
=contraction due t electrical signaling
Electromechanical Coupling
Extracellular entry and Intracellular release of Ca2+ activate contraction and cytosolic is increased by three different mechanisms:
- Ca2+ entry through voltage gated or ligand gated ion channels
- Ca2+ release from SR
=Ca2+ induced release from ryanodine receptor
-IP3 CA2+ release from IP3R - Ca2+ entry through voltage independent channels -store Ca2+ and stretch activated channels
