Muscle tone and Physiology of muscle tone | muscle tone definition,effect and physiology

Muscle tone & Physiology of muscle tone | muscle tone examination

Muscle tone is defined as an increase in the resistance of a muscle tone during passive range of motion.

                                               

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Muscle resistance to passive stretch during resting state.       

Physiology of muscle tone

physiology of muscle tone

- Tone is responsible to maintain the posture

- Muscle consist of muscle spindle and each spindle contain specialized muscle fibers they are 

intrafusal fibers and extrafusal fibers

The intrafusal fibers are (a) Nuclear bag fibers

                                       (b) Nuclear chain fibers

 In nuclear bag fibres their nuclei are clustered together in a bag like enlargement near the center of the fibres.

- In nuclear chain they donot have any enlargement and their nuclear chain has been arranged in chain fashion

- Thus both nuclear fibers have the contracting ability

- And the nuclear bag have greater diameter than the nuclear chain. So a typical muscle spindle might have 8 nuclear chain and 2 bags

- In this nuclear chain is attached to the nuclear bags, which in turns attached to the endomysium of the extafusal muscle which is the large contractile fibers.

- Thus intrafusal muscle consist two types of fibers which has both motor and sensory innervations and one or two gamma motor neuron

- So firing of gamma motor neuron will stimulate the intrafusal muscle fibers to contract

- Which activate the reflex action

- And an impulse from intrafusal muscle fibers passes through afferent fibers (1^o sensory nerve fibers) and reaches the anterior gray horn of spinal cord

- Which stimulate alpha motor neuron

- Sending impulse to extrafusal fibers through efferent fibers and this will result in the contraction of muscle fibers

Effect:

Due to lesion in the UMN & LMN cause abnormal muscle tone:

(a) Hypertonia : Increase in the muscle tone on passive movement.eg: spasticity , rigidity (lead pipe and cog wheel)

(b)Hypotonia : Decrease in the muscle tone on passive movement. eg: flaccidity, floppy

(c) Myotonia : It is a congenital disease characterized by continuous contraction of muscle and slow relaxation even after the cessation of the voluntary action