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All reflex arcs are classified as either somatic or autonomic.
True
The stretch reflex is an example of a polysynaptic reflex.
False
The muscle spindle is primarily innervated by alpha motor neurons.
False
An effector in a reflex arc is always a muscle or gland.
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A reflex response can be voluntary and requires cognitive processing.
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The knee jerk reflex is a prime example of a stretch reflex.
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The afferent nerve in a reflex arc carries signals away from the central nervous system.
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Reflex arcs can only involve one synapse.
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In the reflex arc, the receptor is responsible for detecting the stimulus.
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The GTO reflex is primarily located at the junction between tendon and muscle.
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Gamma motor neurons are not involved in the function of muscle spindles.
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Muscle spindles are primarily responsible for detecting muscle tension.
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The flexor withdrawal reflex is the weakest reflex in the human body.
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Gamma motor neurons are involved in unloading the muscle spindle during contraction.
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The reflex relaxation caused by the GTO occurs only during passive muscle stretching.
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GTO reflexes are considered monosynaptic reflexes.
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Stretch reflexes are crucial in maintaining normal posture and balance.
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Tension information from muscle contractions is carried by Ib afferents.
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The crossed-extensor reflex is unrelated to the flexor withdrawal reflex.
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Reflex contraction initiated by muscle spindles helps prevent overstretching of a muscle.
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Intrafusal fibers are responsible for detecting muscle tension in the Golgi tendon organ.
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Type 1a afferents are characterized as slower conducting neurons compared to Type II afferents.
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The reflex involving muscle spindles is an example of positive feedback.
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Gamma (γ) motor neurons innervate extrafusal fibers within the muscle spindle.
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The muscle spindle responds only to dynamic changes in muscle length.
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Nuclear bag fibers and nuclear chain fibers are two types of extrafusal fibers found in muscle spindles.
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Co-activation involves simultaneous stimulation of alpha and beta motor neurons.
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The spindle becomes slack when a muscle is undergoing reflex contraction.
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Sensory nerve endings in muscle spindles primarily innervate nuclear bag fibers.
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Spindle sensory neurons increase their firing rate when a muscle is stretched.
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Study Notes
Introduction to Physiology of Reflexes
- Reflexes are involuntary, stereotyped, but coordinated responses to a stimulus.
- Reflexes may be somatic or autonomic.
- A reflex arc involves a sequence of events: receptor, afferent nerve, center, efferent nerve, effector.
Components of Reflex Arc
- A reflex arc is an orderly sequence of events.
- Reflex arcs can be monosynaptic or polysynaptic.
The Stretch Reflex
- Muscle "fights back" when stretched.
- The sensory receptor is the muscle spindle.
- The afferent nerve fiber is the IA afferent.
- The reflex is an example of negative feedback.
Muscle Spindle - Structure
- Muscle spindles are mechanoreceptors that respond to stretch and therefore detect length changes in the muscle.
- Muscle spindles consist of intrafusal muscle fibers that lie parallel to extrafusal fibers.
- Intrafusal fibers have non-contractile centers and contractile tissue at the poles.
Spindle Structure Continued
- There are two types of intrafusal fibers: nuclear bag and nuclear chain.
- Primary (annulospiral) nerve endings innervate both nuclear bag and chain fibers.
- Secondary (flower spray) nerve endings innervate primarily the nuclear chain fibers.
Importance of Gamma Motor Neurones for Muscle Spindle Function
- Gamma motor neurons innervate the intrafusal fibers of the muscle spindle.
- Gamma motor neurons cause contraction of spindle fibers, which takes the slack out of the spindle, even while the muscle is contracting.
- Co-activation occurs when alpha and gamma motor neurons are simultaneously stimulated.
GTO Reflex Arc
- The Golgi tendon organ (GTO) is located at the junction between the tendon and muscle.
- The GTO is sensitive to muscle tension and functions in series with the muscle.
- Nerve terminals innervate collagen of the tendon.
- Sensory information is carried to the spinal cord via Ib afferents.
How Does The GTO Reflex Work?
- The GTO detects tension in a contracting muscle.
- Sensory information from the GTO synapses in the spinal cord with an interneuron.
- If tension becomes excessive, this inhibits contraction of the muscle, leading to reflex relaxation.
Summary Points on Muscle Spindles and Golgi Tendon Organs
- Muscle spindles and GTOs provide continuous feedback about the state of contracting muscle to the brain.
- Muscle spindles, particularly in anti-gravity muscles, neck muscles, and muscles requiring fine control, help prevent overstretching.
- GTO reflexes prevent excessive force generation.
Flexion (Withdrawal) Reflex
- The flexion reflex is the most powerful flexion reflex and takes precedence over all others.
- The flexion reflex is also called a crossed-extensor reflex.
- The pathway for the flexion reflex shows considerable divergence of one afferent nerve.
Flaccid Paralysis
- Flaccid paralysis is a condition where muscle tone is lost.
- Occurs due to damage to the alpha motor neurons.
- Characterized by limpness and weakness.
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Description
This quiz explores the physiology of reflexes, detailing the components of reflex arcs, including the stretch reflex and muscle spindles. It covers the involuntary nature of reflexes and their classifications into somatic and autonomic types.
