Single-unit
Encyclopedia
Single-unit smooth muscle, or visceral smooth muscle is a type of smooth muscle
found in the uterus
, gastro-instestinal tract, and the bladder
. In SUVSM, a single smooth muscle cell in a bundle is innervated by an autonomic nerve fibre
. An action potential
can be propagated through neighbouring muscle cells due to the presence of many gap junctions between the cells. Due to this property, SUVSM bundles form a syncytium that contracts in a coordinated fashion (such as uterine muscles do during childbirth.)
Single-unit visceral smooth muscle is myogenic
; it can contract regularly without input from a motor neuron (as opposed to multiunit smooth muscle, which is neurogenic - that is, its contraction must be initiated by a motor neuron.) A few of the cells in a given SUVSM unit may behave as pacemaker cells, generating rhythmic action potentials due to their intrinsic electrical activity. Because of its myogenic nature, single-unit smooth muscle is usually active, even when it's not receiving any neural stimulation.
Smooth muscle
Smooth muscle is an involuntary non-striated muscle. It is divided into two sub-groups; the single-unit and multiunit smooth muscle. Within single-unit smooth muscle tissues, the autonomic nervous system innervates a single cell within a sheet or bundle and the action potential is propagated by...
found in the uterus
Uterus
The uterus or womb is a major female hormone-responsive reproductive sex organ of most mammals including humans. One end, the cervix, opens into the vagina, while the other is connected to one or both fallopian tubes, depending on the species...
, gastro-instestinal tract, and the bladder
Bladder
Bladder usually refers to an anatomical hollow organBladder may also refer to:-Biology:* Urinary bladder in humans** Urinary bladder ** Bladder control; see Urinary incontinence** Artificial urinary bladder, in humans...
. In SUVSM, a single smooth muscle cell in a bundle is innervated by an autonomic nerve fibre
Autonomic nervous system
The autonomic nervous system is the part of the peripheral nervous system that acts as a control system functioning largely below the level of consciousness, and controls visceral functions. The ANS affects heart rate, digestion, respiration rate, salivation, perspiration, diameter of the pupils,...
. An action potential
Action potential
In physiology, an action potential is a short-lasting event in which the electrical membrane potential of a cell rapidly rises and falls, following a consistent trajectory. Action potentials occur in several types of animal cells, called excitable cells, which include neurons, muscle cells, and...
can be propagated through neighbouring muscle cells due to the presence of many gap junctions between the cells. Due to this property, SUVSM bundles form a syncytium that contracts in a coordinated fashion (such as uterine muscles do during childbirth.)
Single-unit visceral smooth muscle is myogenic
Myogenic
Myogenic contraction refers to a contraction initiated by the myocyte cell itself instead of an outside occurrence or stimulus such as nerve innervation.- Unstable Membrane Potentials :...
; it can contract regularly without input from a motor neuron (as opposed to multiunit smooth muscle, which is neurogenic - that is, its contraction must be initiated by a motor neuron.) A few of the cells in a given SUVSM unit may behave as pacemaker cells, generating rhythmic action potentials due to their intrinsic electrical activity. Because of its myogenic nature, single-unit smooth muscle is usually active, even when it's not receiving any neural stimulation.