Neuro physiology week 4 smooth muscle

types of smooth muscle

single unit and multi unit

size of smooth muscle

Much smaller than skeletal and cardiac muscle

Smooth muscle is organized into _____ or ____

Bundles or sheets

Smooth muscle responds to different types of stimuli such as

Nerves, hormones, mechanical and endothelial mediators

Smooth muscle is innervated by ____

autonomic nervous system

Smooth muscle function is

Controls size of organs, release of substances and control the rate of flow

Single unit smooth muscle

Large aggregates of smooth muscle cells which act as a single unit

multi-unit smooth muscle

Single smooth muscle cells usually with a single nerve connection

Examples of multi-unit smooth muscles

Arrector pili muscles, Vas deferens and iris of the eye

Smooth muscle is found in

•walls of large arteries

•airway of lungs

•arrector pili muscles attached to the hair

•radial and circular muscles of the iris

Single unit smooth muscle usually line the ____ _____ such as blood vessels or the GI tract

Hollow organs

Smooth muscles that are seldom exhibit ______ ____

Spontaneous contraction

Single unit smooth muscle AKAs

Unitary smooth muscle

Syncytial smooth muscle

Visceral smooth muscle

Smooth muscles form large networks and an ____ _____ causes contraction of the entire organ

Action potential

Where are the neurotransmitters in smooth muscles released

The varicosities

Smooth muscles are stimulated by

nervous system, hormones, mechanical manipulation, self stimulation

_____ and _____ are never secreted by the same nerve fiber

Acetylcholine and norepinephrine

Acetylcholine can be _____ or _____ which is determined by the type of receptor expressed by target cell

Excitatory;inhibitory

Acetylcholine and norepinephrine usually cause the _____ reaction at a target cell

Opposite

Have little to no nerve supply

Arterioles, met arterioles and precapillary sphincters

postganglionic sympathetic neurons secrete

norepinephrine

postganglionic parasympathetic neurons secrete

acetylcholine

preganglionic neuron secretes

Acetylcholine

What causes vasodilation?

•Lack or decrease in O2 levels

•Increase in CO2

•Increase in hydrogen ions

•Decrease in ECF Ca++

•Adenosine or increased lactic acid

Most hormones affect smooth muscle through ____ messengers

Second

Important hormones

Norepinephrine, epinephrine, acetylcholine, angiotensin 2, oxytocin, vasopressin, serotonin and histamine

Action of hormones is controlled by the type of receptors expressed by the target cell

Hormone gated excitatory and inhibitory receptors

Smooth muscles contain ____ and ____ filaments

Actin;myosin

Smooth muscle does not have a troponin complex but has a

Calmodulin complex

Major differences between smooth and skeletal muscle

•physical organization

•excitation contraction coupling

•control of the contraction process by calcium

•duration of contraction (smooth muscle longer)

•energy is less in smooth muscle

dense bodies in smooth muscle

Attachment points for contractile proteins, replace sarcomere (like the Z disc for skeletal muscle)

____ ratio of actin to myosin in smooth muscle

15:1

Smooth muscle contraction starts ____ but lasts ____

Slower;longer

Smooth muscle has _____ contraction-up to hours to days

Prolonged

Smooth muscle can ____ or ____ to a greater extent

Shorten; stretch

contraction of smooth muscle is initiated by calcium indulgence in the _____

Sarcoplasm (outside the cell)

Sarcoplasmic reticulum in smooth muscle is ____

Sparse

Smooth muscles have no _____

T tubules

Smooth muscle has less _____ activity which causes less degradation of ATP

ATPase

Smooth muscle only needs ____ to _____ of the energy that skeletal muscle requires

1/10;1/300

Only ____ ATP is required per smooth muscle contraction

1

Smooth muscle reaches full contraction about ____ second after stimulation

1/2

Contractile force reaches maximum within smooth muscle within ____ seconds after stimulation

1-2

Smooth muscle rate of contraction is ___ times slower than skeletal muscle

30

Contractions of smooth muscle can last from ___ to ____ seconds

0.2-30

Smooth muscle force of contraction can be approximately __ that of skeletal muscle

2x

Smooth muscle can shorten to a greater degree than ____ muscle

Skeletal

Latch Mechanism in Smooth Muscle

Prolonged holding in smooth muscle

After smooth muscle contraction is initiated, less stimulus and energy are needed to maintain the _____

Contraction

Smooth muscle contractile mechanism

Lower activation of enzymes, myosin head remains attached to actin for long periods of time but large numbers are attached and the force is great

Stress

Relaxation of smooth muscle

Smooth muscle can undergo great changes in length and still retain the ability to ____ ____

Contract effectively

Smooth muscle down regulation of contraction done by

Calcium ions

____ ____ is the initiating event for smooth muscle contraction

ICF calcium

An increase in calcium influx can be caused by

Nerve stimulation

Hormones

Chemical changes in environment (ligands)

Mechanical stretch of fiber

____ combines with 4 calcium ions causing activation

Calmodulin

activated calmodulin activates

myosin light chain kinase

The activated myosin light chain kinase phosphorylates the myosin light chains by using ___

ATP

As calcium drops below a critical level

Myosin phosphatase removes the phosphate from the myosin light chains and concentrations stops

Regulation of the myosin light chain and smooth muscle contraction

While the MLCK adds a P group to the MLC dependent on myosin light chain phosphatase removes it deactivating the myosin head

Smooth muscle cross sectional area is as ____ as skeletal muscle

Strong

Smooth muscle fibers are thickest in the ____ with tapered ends

Middle

Smooth muscle has a centrally located ____ ____ ____

Single oval nucleus

Smooth muscle has 10-20 times more ____ filaments than thick filaments

Thin

Smooth muscle contraction

•sliding filament mechanism involving thick and thin filaments generates tension that is transmitted to the thin filaments

•does not contain troponin complex

•actin and myosin pull on dense bodies attached to the sarcolemma

•shortening of the smooth muscle fiber is lengthwise, the middle of the fiber thickens

Shortening of the smooth muscle causes bubble like expansion of the ____

Sarcolemma