Muscle Spindles

Muscle Spindles

Muscle spindles are sensory specialization of the muscular tissue. A number of small specialised intrafusal muscle fibres (nuclear bag fibres and nuclear chain fibres) are surrounded by a capsule of connective tissue. The intrafusal fibres are innervated by efferent motor nerve fibres. Afferent sensory nerve fibres surround the intrafusal muscle fibres.
If the muscle is stretched, the muscle fibres in the muscle spindle are stretched, sensory nerves are stimulated, and a change in contraction of the muscle is perceived. Different types of intrafusal fibres and nerve endings allow the perception of position, velocity and acceleration of the contraction of the muscle.
The contraction of the intrafusal fibres, after stimulation by the efferent nerve fibres, may counteract or magnify the changes imposed on the muscle spindle by the surrounding muscle. The intrafusal fibres and the efferent nerves can in this way set the sensitivity for the sensory nerve ending in the muscle spindle.

Cardiac Muscle

• Cardiac muscle, the myocardium, consists of muscle cells, cardiomyocytes, with one centrally placed nucleus.
  Nuclei are oval, rather pale and located centrally in the muscle cell which is 10 - 15 µm wide.
• Cardiac muscle cells exhibit cross-striations.
• Cardiac muscle cells excitation is mediated by rythmically active modified cardiac muscle cells.
• Cardiac muscle is innervated by the autonomic nervous system, which adjusts the force generated by the muscle cells and the frequency of the heart beat.
• Cardiac muscle is for these reasons also called involuntary striated muscle. 

Title: Muscle Spindles
by:om at 2013-02-15T03:11:00+07:00
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Muscle Spindles