Reflexes and Muscle Spindles

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Questions and Answers

What type of nerve fibers are responsible for the dynamic response in muscle spindles?

Gamma motor neurons

Type 1a afferents (correct)

Type II afferents

Type 1b afferents

Which component of the muscle spindle responds to stretch?

Extrafusal fibers

Alpha motor neurons

Nuclear bag fibers (correct)

Gamma motor neurons

What is the role of gamma motor neurons in muscle spindle function?

They detect static muscle stretch

They transmit pain signals from muscle

They innervate extrafusal fibers

They stimulate the contraction of intrafusal fibers (correct)

What does the Golgi tendon organ primarily detect?

Muscle contraction force Signup and view all the answers

How are the intrafusal fibers arranged in relation to extrafusal fibers in the muscle spindle?

Intrafusal fibers lie parallel to extrafusal fibers Signup and view all the answers

Which type of sensory innervation primarily detects the static response of stretch?

Type II afferents Signup and view all the answers

What phenomenon occurs during the co-activation of alpha and gamma motor neurons?

Maintenance of muscle spindle sensitivity Signup and view all the answers

Which type of intrafusal fiber is mainly associated with type II sensory endings?

Nuclear chain fibers Signup and view all the answers

What is the primary feedback mechanism of the muscle spindle reflex?

Negative feedback Signup and view all the answers

What happens to the muscle spindle at point 'B' during a reflex contraction?

It becomes slack Signup and view all the answers

Which of the following accurately describes a component of a reflex arc?

Sequential process involving sensory and motor nerves Signup and view all the answers

Which of the following correctly outlines the structure of a muscle spindle?

A sensory organ encapsulated within muscle fibers Signup and view all the answers

How are the gamma motor neurones primarily involved in muscle spindle function?

They regulate the sensitivity of the muscle spindle Signup and view all the answers

Which type of reflex is exemplified by the knee jerk response?

Monosynaptic reflex with one synapse Signup and view all the answers

Which of the following statements about autonomic reflexes is correct?

They regulate involuntary bodily functions Signup and view all the answers

What role does the afferent nerve play in the reflex arc?

Conveys sensory information to the central nervous system Signup and view all the answers

What is the primary response initiated by the stretch reflex?

Reflex contraction of the muscle being stretched Signup and view all the answers

In a reflex arc, what is the function of the effector?

To execute the responsive action Signup and view all the answers

Which of the following best distinguishes monosynaptic reflexes from polysynaptic reflexes?

Monosynaptic involves fewer components than polysynaptic Signup and view all the answers

What role do gamma motor neurons play in the function of muscle spindles?

They tighten intrafusal fibers to maintain spindle responsiveness. Signup and view all the answers

What is a primary feature of the Golgi tendon organ (GTO) reflex?

It prevents excessive tension in a muscle by inducing relaxation. Signup and view all the answers

What effectively happens during the flexor (withdrawal) reflex?

It involves multiple synapses and provides a strong withdrawal response. Signup and view all the answers

How do muscle spindles contribute to motor control?

By providing continuous feedback on muscle length during contraction. Signup and view all the answers

What do Golgi tendon organs primarily respond to?

Tension generated in the muscle during contraction. Signup and view all the answers

What is the primary purpose of stretch reflexes?

To maintain posture and balance through automatic adjustments. Signup and view all the answers

What distinguishes the GTO reflex from the stretch reflex?

GTO reflexes inhibit muscle contraction while stretch reflexes promote it. Signup and view all the answers

What does flaccid paralysis refer to?

Complete loss of muscle tone and reflexes. Signup and view all the answers

What is a key characteristic of polysynaptic reflexes?

They are slower than monosynaptic reflexes. Signup and view all the answers

Which muscle groups are most affected by muscle spindles and stretch reflexes?

Postural and fine motor control muscles. Signup and view all the answers

Study Notes

Reflexes

Reflexes are involuntary, stereotyped, and coordinated responses to stimuli, involving an orderly sequence of events called a reflex arc.
Reflexes can be classified as somatic or autonomic.
Reflex arcs involve the following components:
- Receptor
- Afferent Nerve (sensory)
- Centre (CNS or Spinal Cord)
- Efferent Nerve (motor)
- Effector
- Response
Reflexes can be:
- Monosynaptic (e.g., stretch reflex)
- Polysynaptic (e.g., withdrawal reflex)

The Stretch Reflex

The stretch reflex is a simple reflex, exemplified by the knee jerk reflex.
When a muscle is stretched, it contracts reflexively.
This reflex uses negative feedback to maintain muscle length.

The Muscle Spindle

The muscle spindle is a mechanoreceptor that responds to stretch and length changes in the muscle.
It consists of intrafusal muscle fibers that lie parallel to extrafusal fibers.
Intrafusal fibers have both contractile (poles) and non-contractile (centre) regions.
There are two types of intrafusal fibers: nuclear bag and nuclear chain fibers.

Muscle Spindle Innervation

Motor innervation: Gamma (γ) motor neurons innervate intrafusal fibers, controlling their contraction.
Sensory innervation:
- Primary (annulospiral) nerve endings: Type 1a afferents, detect both the amount of muscle stretch (static response) and the rate of stretching (dynamic response). They are rapidly conducting myelinated neurons.
- Secondary (flower spray) endings: Type II afferents, detect only static response. They are slower conducting myelinated neurons.

Importance of Gamma (γ) Motor Neurons

Gamma motor neurons are crucial for maintaining spindle sensitivity during muscle contraction.
When a muscle contracts, the spindle goes slack, reducing its ability to detect length changes.
Gamma motor neurons co-activate with alpha motor neurons, contracting intrafusal fibers to keep the spindle "loaded" despite muscle contraction, ensuring ongoing length feedback.

Golgi Tendon Organ (GTO) Reflex

Location: At the junction of the tendon and muscle.
Function: Detects muscle tension.
Structure: Nerve terminals innervate collagen fibers in the tendon.
Sensory information: Transmitted via Ib afferents (large diameter, rapidly conducting fibers).
Action: When tension becomes excessive, GTO triggers inhibition of the contracting muscle via an interneuron, leading to reflex relaxation.
Role: Protects against excessive force in the muscle.

Summary of Muscle Spindle and GTO

Both provide continuous feedback to the brain about muscle status during contraction.
Muscle Spindle: Important for maintaining posture, balance, and rapid automatic adjustments in muscle length.
GTO: Prevents excessive force generation in muscles, contributing to smooth movements.

Flexion (Withdrawal) Reflex

A protective reflex triggered by painful stimuli, causing rapid withdrawal of a limb.
Involves divergence of sensory information from the afferent neuron.
Can also be called the crossed-extensor reflex.

Flaccid Paralysis

A state of complete muscle relaxation caused by damage to the spinal cord or motor neurons, disrupting the reflex pathways.

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Description

This quiz covers the concepts of reflexes, including their classifications, components of the reflex arc, and specifics about the stretch reflex and muscle spindles. Test your understanding of somatic and autonomic reflexes, along with their mechanisms in maintaining muscle function.