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Questions and Answers
What type of nerve fibers are the afferent nerves arising from the spindles?
What type of nerve fibers are the afferent nerves arising from the spindles?
What is the function of the gamma-d (dynamic) fibers?
What is the function of the gamma-d (dynamic) fibers?
What type of nerve fibers are the efferent nerves arising from the spindles?
What type of nerve fibers are the efferent nerves arising from the spindles?
Which type of intrafusal muscle fibers are supplied by the gamma-s (static) fibers?
Which type of intrafusal muscle fibers are supplied by the gamma-s (static) fibers?
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What is the function of the type II nerve fibers?
What is the function of the type II nerve fibers?
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What is the main difference between the gamma-d (dynamic) and gamma-s (static) fibers?
What is the main difference between the gamma-d (dynamic) and gamma-s (static) fibers?
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What is the main function of the nuclear chain fibers in the muscle spindle?
What is the main function of the nuclear chain fibers in the muscle spindle?
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What is the main purpose of the muscle spindle?
What is the main purpose of the muscle spindle?
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What is the primary function of the afferent nerves arising from the muscle spindle?
What is the primary function of the afferent nerves arising from the muscle spindle?
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Which type of intrafusal muscle fibers are supplied by the gamma motor neurons?
Which type of intrafusal muscle fibers are supplied by the gamma motor neurons?
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Study Notes
Stretch Reflex
- The stretch reflex is a -ve feedback reflex that returns the muscle to its normal length when stretched
- It has four components: receptor, afferent, center, and efferent
Components of Stretch Reflex
- Receptor: Muscle spindle (central portion)
- Afferents: Thick myelinated fibers (primary Ia & secondary II)
- Center: Alpha motor neuron in spinal cord (AHCs)
- Efferent: Thick myelinated A α fibers
- Response: Muscle contraction
Muscle Spindles
- They are encapsulated mechanoreceptors
- They monitor muscle length or rate of change of muscle length
- They are spindle shaped and encapsulated
- Each muscle contains many spindles, distributed throughout the belly of the muscle
Structure of Muscle Spindles
- Each muscle spindle contains 2-10 intrafusal muscle fibers
- There are two types of intrafusal fibers: nuclear bag (1-3) and nuclear chain (3-9)
- The central part of the intrafusal fibers is the receptor area, which detects stretch of the muscle
- The peripheral part of the intrafusal fibers is contractile and receives output from γ fibers from the spinal cord
Types of Muscle Spindles
- Nuclear bag fibers: have a dilated central area filled with nuclei
- Nuclear chain fibers: have multiple nuclei arranged as a chain in the receptor area
Innervation of Muscle Spindle
- Type Ia nerve fibers: arise from the receptor areas of both nuclear bag and chain muscle fibers
- Type II nerve fibers: arise from the sides of the primary endings in the nuclear chain fibers
- Gamma efferent nerves: supply the peripheral (contractile) parts of the intra-fusal fibers
Alpha Gamma Linkage
- Alpha motor neurons are activated simultaneously with gamma motor neurons
- The role of gamma efferent co-activation is to prevent relaxation of muscle spindles during muscle contraction
- It increases sensitivity to the stretch reflex
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Description
Test your knowledge on the components of the stretch reflex, including the pathway, receptors, afferents, center, efferent fibers, and response. Understand the role of muscle spindles, alpha motor neurons, and muscle contraction in this negative feedback reflex.
