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A muscle spindle, with γ motor and Ia sensory fibers. A type Ia sensory fiber, or a primary afferent fiber, is a type of afferent nerve fiber. [1] It is the sensory fiber of a stretch receptor called the muscle spindle found in muscles, which constantly monitors the rate at which a muscle stretch changes.
The Purkinje fibers are further specialized to rapidly conduct impulses (having numerous fast voltage-gated sodium channels and mitochondria, and fewer myofibrils, than the surrounding muscle tissue). Purkinje fibers take up stain differently from the surrounding muscle cells because of having relatively fewer myofibrils than other cardiac cells.
As the left posterior fascicle is shorter and broader than the right, impulses reach the papillary muscles just prior to depolarization, and therefore contraction, of the left ventricle myocardium. This allows pre-tensioning of the chordae tendinae, increasing the resistance to flow through the mitral valve during left ventricular contraction. [5]
There are two branches of the bundle of His: the left bundle branch and the right bundle branch, both of which are located along the interventricular septum. The left bundle branch further divides into the left anterior fascicle and the left posterior fascicle. These structures lead to a network of thin filaments known as Purkinje fibers.
When a muscle is stretched, primary type Ia sensory fibers of the muscle spindle respond to both changes in muscle length and velocity and transmit this activity to the spinal cord in the form of changes in the rate of action potentials. Likewise, secondary type II sensory fibers respond to muscle length changes (but with a smaller velocity ...
When left bundle-branch block (LBBB) is accompanied by right axis deviation (RAD), the rare combination is considered to be highly suggestive of dilated or congestive cardiomyopathy. [29] [30] Echocardiogram shows left ventricular dilatation with normal or thinned walls and reduced ejection fraction.
Sensory fiber types Type Erlanger-Gasser Classification Diameter Myelin Conduction velocity Associated sensory receptors; Ia: Aα: 13–20 μm: Yes: 80–120 m/s [5] Muscle spindle fibres Ib Aα: 13–20 μm: Yes: 80–120 m/s: Golgi tendon organ: II: Aβ: 6–12 μm: Yes: 33–75 m/s: All cutaneous mechanoreceptors including pacinian ...
The papillary muscles of both the right and left ventricles begin to contract shortly before ventricular systole and maintain tension throughout. [1] This prevents regurgitation—backward flow of ventricular blood into the atrial cavities—by bracing the atrioventricular valves against prolapse—being forced back into the atria by the high ...