Reflexes and Reflex Arcs

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Questions and Answers

What are the primary components of a reflex arc?

The primary components are the receptor, afferent nerve (sensory), central nervous system (CNS or spinal cord), efferent nerve (motor), and effector.

Describe the stretch reflex arc using an example.

The stretch reflex arc happens when a muscle is stretched, leading to a reflex contraction, such as in the knee-jerk reflex.

Outline the structure of a muscle spindle.

A muscle spindle consists of specialized muscle fibers called intrafusal fibers, a capsule, and sensory endings.

How is the muscle spindle innervated?

Muscle spindles are innervated by gamma motor neurons and sensory afferent neurons. Signup and view all the answers

What is the function of gamma motor neurons in relation to muscle spindles?

Gamma motor neurons adjust the sensitivity of the muscle spindle by activating intrafusal fibers. Signup and view all the answers

Differentiate between somatic and autonomic reflexes.

Somatic reflexes involve skeletal muscles while autonomic reflexes regulate internal organs. Signup and view all the answers

What roles do afferent and efferent nerves play in the reflex arc?

Afferent nerves transmit sensory information to the CNS, while efferent nerves carry motor commands from the CNS to the effector. Signup and view all the answers

Explain the concept of a monosynaptic reflex.

A monosynaptic reflex involves only one synapse between a sensory neuron and a motor neuron. Signup and view all the answers

What is the response generated by a stretch reflex?

The response generated is a reflex contraction of the muscle that was stretched. Signup and view all the answers

Identify the sequence of events in a reflex arc from stimulus to response.

The sequence includes stimulus reception, activation of afferent nerve, processing in the CNS, activation of efferent nerve, and response by the effector. Signup and view all the answers

What type of nerve fibers are involved in the sensory innervation of muscle spindles?

Type IA afferents and Type II afferents. Signup and view all the answers

How do gamma (γ) motor neurons contribute to muscle spindle function during contraction?

They contract intrafusal fibers, removing slack from the spindle and ensuring sensitivity during muscle contraction. Signup and view all the answers

What role do intrafusal fibers play within the muscle spindle?

Intrafusal fibers detect changes in muscle length and respond to stretch. Signup and view all the answers

Identify the two types of intrafusal fibers found in muscle spindles.

Nuclear bag fibers and nuclear chain fibers. Signup and view all the answers

What constitutes a reflex arc involving muscle spindles?

A sensory receptor, afferent nerve fibers, synapse in the spinal cord, and alpha motor neurons leading to muscle contraction. Signup and view all the answers

Explain the function of Golgi tendon organs (GTO).

GTOs sense tension in the muscle and help prevent excessive force, promoting safety during muscle contraction. Signup and view all the answers

What type of sensory response does the primary (annulospiral) nerve endings provide?

They provide both static and dynamic responses to muscle stretch. Signup and view all the answers

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

The spindle becomes slack, which can decrease its sensory input. Signup and view all the answers

Which components are responsible for the co-activation of muscle spindles?

Alpha and gamma motor neurons are stimulated simultaneously. Signup and view all the answers

Describe the role of mechanoreceptors in muscle spindles.

Mechanoreceptors in muscle spindles respond to stretch and changes in muscle length. Signup and view all the answers

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

The GTO reflex inhibits muscle contraction to prevent excessive tension. Signup and view all the answers

Describe how muscle spindles contribute to the stretch reflex.

Muscle spindles detect changes in muscle length and initiate reflex contractions. Signup and view all the answers

Outline the pathway of the flexor (withdrawal) reflex.

The pathway involves afferent neurons synapsing with interneurons in the spinal cord. Signup and view all the answers

What characterizes flaccid paralysis?

Flaccid paralysis is characterized by a complete loss of muscle tone and reflexes. Signup and view all the answers

What occurs to the muscle spindle during muscle contraction?

During contraction, the muscle spindle becomes slack and is unable to detect changes in length. Signup and view all the answers

How do Ib afferents contribute to the GTO reflex?

Ib afferents transmit sensory information about muscle tension to the spinal cord. Signup and view all the answers

What protective role do GTOs serve during muscle contractions?

GTOs help prevent excessive force generation in muscles during contractions. Signup and view all the answers

Explain the significance of feedback from muscle spindles and GTOs.

They provide continuous information about muscle status, aiding in movement control. Signup and view all the answers

What is the role of interneurons in the flexor reflex pathway?

Interneurons facilitate communication between afferent sensory neurons and motor neurons. Signup and view all the answers

How do muscle spindles assist with fine motor control?

Muscle spindles detect minute changes in muscle length, aiding precise movement adjustments. Signup and view all the answers

Study Notes

Reflexes

Reflexes are involuntary, stereotyped, coordinated responses to a stimulus.
Reflexes can be somatic or autonomic.
Reflexes involve an orderly sequence of events called a reflex arc.
Reflex arcs can be monosynaptic or polysynaptic.

Components of a Reflex Arc

A reflex arc involves a receptor, sensory neuron, integration center (CNS or spinal cord), motor neuron, and effector.

The Stretch Reflex

The stretch reflex is a simple reflex that involves the contraction of a muscle in response to stretch.
The stretch reflex is an example of negative feedback.
The sensory receptor for the stretch reflex is the muscle spindle.
Muscle spindles are mechanoreceptors that respond to muscle stretch.
The muscle spindle contains intrafusal muscle fibers which lie parallel to extrafusal fibers.

Muscle Spindle Structure

Intrafusal muscle fibers have non-contractile centers and contractile ends.
There are two types of intrafusal fibers: nuclear bag and nuclear chain.
Muscle spindles are innervated by gamma motor neurons and sensory neurons: Type Ia (primary) and Type II (secondary).

Muscle Spindle Innervation

Type Ia afferents innervate both nuclear bag and chain fibers and detect static and dynamic stretch.
Type II afferents primarily innervate nuclear chain fibers and detect static stretch.

The Role of Gamma Motor Neurons

Gamma motor neurons innervate intrafusal fibers, allowing for the maintenance of spindle sensitivity during muscle contraction.
Co-activation of alpha and gamma motor neurons ensures that the spindle remains taut during muscle contraction.

The Golgi Tendon Organ (GTO) Reflex

The GTO is located at the junction between muscle and tendon and detects muscle tension.
The GTO is innervated by Ib afferent fibers.
The GTO reflex is polysynaptic and serves as a protective mechanism to prevent excessive force generation.

Features of Muscle Spindle and GTO Reflexes

Stretch reflexes are prominent in anti-gravity muscles, neck muscles, and muscles requiring fine control.
Stretch reflexes help prevent muscle overstretching by initiating reflex contraction.
GTO reflexes help prevent excessive force generation in a muscle.
Both muscle spindle and GTO reflexes play important roles in feedback control of muscle length and movement.

The Flexor/Withdrawal Reflex

The flexor reflex is a protective reflex that causes withdrawal of a limb from a painful stimulus.
The flexor reflex often involves the crossed-extensor reflex, which causes extension of the opposite limb to maintain balance.

Flaccid Paralysis

Flaccid paralysis is a condition characterized by loss of muscle tone and reflex activity, often due to damage to motor neurons.

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Description

Explore the mechanisms of reflexes, including the components of reflex arcs and the specific function of the stretch reflex. Understand how muscle spindles contribute to these involuntary responses. Test your knowledge on somatic and autonomic reflexes as well.