Flexor Reflex Mechanism and Structure

Questions and Answers

What is the function of the flexor reflex?

In both UE and LE, it causes movement of the flexor muscles to move a limb away from a harmful stimulus. In the LEs, it is also used for locomotion.

The flexor reflex is initiated by which type of receptors?

Cutaneous

Where are cutaneous receptors located?

In the skin; they respond to touch, pressure, pain, and temperature.

The flexor reflex arc is:

Multi-synaptic Signup and view all the answers

What is the flexor reflex receptor organ?

The cutaneous receptors Signup and view all the answers

The afferent neuron of the flexor reflex arc is in what group?

Either group II or group III. Signup and view all the answers

In the flexor reflex arc, the interneuron is:

Excitatory Signup and view all the answers

What type of neuron is the effector (efferent) neuron in the flexor reflex arc?

An alpha motor neuron that synapses on a flexor muscle. Signup and view all the answers

List the five components of the flexor reflex arc.

<ol> <li>A receptor organ: cutaneous receptors, 2. An afferent neuron: group II or III, 3. An excitatory interneuron, 4. An effector (efferent) neuron: alpha motor neurons, 5. An effector organ: flexor muscle.</li> </ol> Signup and view all the answers

Describe the mechanism of the Flexor Reflex Afferents (FRA).

<ol> <li>FRAs are fibers from cutaneous sensory receptors. 2. The receptors are stimulated by sensations. 3. The action potential travels to the SC, synapses on an excitatory interneuron, which then synapses on an alpha motor neuron. 4. Axon collaterals go to higher centers for additional movements.</li> </ol> Signup and view all the answers

Interneurons are also known as what?

Internuncials Signup and view all the answers

What is the purpose of FRA collaterals that synapse on various interneurons in the spinal cord?

Allow for reciprocal innervations and additional movements. Signup and view all the answers

Describe the purpose of various interneurons for reciprocal innervation in the flexor reflex.

Excitatory interneurons facilitate motor neurons to flexor muscles; inhibitory interneurons inhibit motor neurons to extensor muscles. Signup and view all the answers

Interneurons for the reflex arc and reciprocal innervation synapse with cell bodies of motor neurons in which part of the spinal cord?

Ventral horn. Signup and view all the answers

What is the function of alpha motor neurons?

They synapse with skeletal muscle fibers to produce a motor response (movement). Signup and view all the answers

What motor response do alpha motor neurons cause in the flexor reflex?

Flexor withdrawal of the body part (UE or LE) away from stimulus. Signup and view all the answers

When does flexor withdrawal in the LE occur?

When you step on a sharp object, withdrawing the leg/foot. Signup and view all the answers

Describe reciprocal innervation in the flexor withdrawal of the LE.

Knee flexors (hamstrings) are facilitated and knee extensors (quadriceps) are inhibited. Signup and view all the answers

Every movement has reciprocal innervation.

True Signup and view all the answers

What is the crossed extension (extensor) reflex in the LE?

During the flexor reflex of the LE, one leg is withdrawn, and to prevent falling, the contralateral leg extends. Signup and view all the answers

Describe reciprocal innervation in the crossed extension reflex of the LE.

Flexor reflexers activated by pain or touch on the ipsilateral leg lead to flexors being facilitated and extensors inhibited. In the contralateral leg, extensors are facilitated and flexors inhibited. Signup and view all the answers

What type of interneuron is required for the movement of the contralateral leg in the crossed extension reflex?

Commissural interneurons. Signup and view all the answers

What is locomotion?

Movement or the ability to move from one place to another (walking, running, gait, etc). Signup and view all the answers

How does locomotion relate to the flexor reflex?

In the LE, flexor withdrawal and crossed extension reflexes are involved in locomotion. Signup and view all the answers

What two principles are involved with locomotion (and flexor reflex)?

<ol> <li>Reciprocal innervation, 2. Intersegmental interneurons.</li> </ol> Signup and view all the answers

How are intersegmental interneurons involved with locomotion?

They allow interaction with the spinal segments that control the UE, ensuring smooth and coordinated movement. Signup and view all the answers

How does the cerebrum influence spinal reflexes during locomotion?

Via descending tracts, the cerebrum changes gait patterns in different terrains. Signup and view all the answers

Role of reciprocal innervation for locomotion?

It allows for smooth and coordinated movement during activities such as running. Signup and view all the answers

Flexor withdrawal in UE - typical chain of neural events?

Someone hits finger with a hammer or touches a hot stove, causing withdrawal of the hurt finger or hand. Signup and view all the answers

Reciprocal innervation of UE in flexor reflex?

Excitatory interneurons excite flexors (brachialis, biceps) and inhibitory interneurons inhibit extensors (triceps). Signup and view all the answers

What happens during flexor reflex in the UE when there is a stronger stimulus?

The FRAs excite additional interneurons, causing more than just the hurt hand to move. Signup and view all the answers

Describe associated reaction (UE).

Additional movement of the contralateral limb in the UE. Signup and view all the answers

Describe crossed extension (UE).

Additional movement of the lower extremities (LE). Signup and view all the answers

Describe the effects of the associated reaction and crossed extension during flexor withdrawal of the UE.

The strength of the stimulus causes withdrawal of the affected finger and additional reactions in the contralateral hand and the opposite leg. Signup and view all the answers

Describe the mechanisms of Associated Reactions.

Involves withdrawing the contralateral hand/limb due to commissural interneurons. Signup and view all the answers

Describe the mechanisms of Crossed Extension during flexor reflex of UE.

Involves shifting the body weight to the contralateral leg to activate cross-extension reflex. Signup and view all the answers

Describe how the ipsilateral leg is flexed via reciprocal innervation.

Excitatory interneurons synapse with and excite alpha motor neurons innervating flexor muscles of the ipsilateral leg. Signup and view all the answers

Describe how the contralateral leg is flexed via reciprocal innervation.

Excitatory commissural interneurons synapse and excite extensor muscles in the contralateral leg while inhibiting flexors. Signup and view all the answers

Which of the following are proprioceptive reflexes? (Select all that apply): a) Flexor reflex, b) Stretch reflex, c) GTO reflex.

b) Stretch reflex and c) GTO reflex. Signup and view all the answers

What are the structures responsible for initiating the stretch reflex and the GTO reflex?

Stretch reflex = Muscle Spindle; GTO reflex = Golgi tendon organ (GTO). Signup and view all the answers

Study Notes

Function of the Flexor Reflex

Facilitates movement of flexor muscles to withdraw a limb from harmful stimuli.
In lower extremities (LE), assists in locomotion.

Receptor Types

Initiated by cutaneous receptors found in the skin.
Respond to touch, pressure, pain, and temperature.

Structure of the Reflex Arc

Flexor reflex arc is multi-synaptic.
Includes cutaneous receptors as the receptor organ.
Afferent neurons classified as Group II (touch, pressure) or Group III (pain, temperature).
Interneurons are excitatory, while afferent fibers synapse on them.

Neuron Types

Alpha motor neurons act as effector (efferent) neurons, synapsing on flexor muscles to generate movement.
The flexor reflex arc consists of three neurons: afferents, interneurons, and motor neurons.

Mechanism of Flexor Reflex Afferents (FRA)

FRA fibers are stimulated by cutaneous sensations.
Action potentials travel to the spinal cord, synapsing on excitatory interneurons, which in turn synapse on alpha motor neurons.
Axon collaterals extend to higher centers and additional interneurons for reflexive movement coordination.

Function of Interneurons

Interneurons facilitate reciprocal innervation during the reflex: excitatory for flexors and inhibitory for extensors.
Located in the ventral horn of the spinal cord for motor neuron synapses.

Response Types

Alpha motor neurons produce flexor withdrawal (movement away from stimuli) in both upper extremities (UE) and lower extremities.
In the LE, this is notably activated when stepping on sharp objects.

Crossed Extension Reflex

Occurs in the contralateral leg during LE flexor withdrawal to maintain balance by extending the opposite limb.
Involves reciprocal innervation: ipsilateral leg flexors activated while extensors inhibited; contralateral leg extensors activated while flexors inhibited.

Locomotion and Reflex Coordination

Involves flexor withdrawal and crossed extension reflexes for coordinated movement during walking or running.
Intersegmental interneurons ensure smooth coordination between upper and lower body movements.

Cerebrum's Influence on Reflexes

Changes gait patterns based on terrain through descending tracts affecting spinal reflex responses.

Reciprocal Innervation Role

Ensures efficient and coordinated movement patterns during activities like running, facilitating flexor activation and extensor inhibition.

Specifics of Upper Extremity Flexor Reflex

Strong stimuli can lead to associated reactions affecting the contralateral limb and crossed extension affecting the lower limbs.
Flexor muscles (e.g., brachialis and biceps) are excited, while extensor muscles (e.g., triceps) are inhibited during reflex actions.

Mechanisms of Associated Reactions and Crossed Extension

Associated reactions involve bilateral flexor withdrawal due to excitatory and inhibitory commissural interneurons.
Crossed extension involves shifting weight and activating or inhibiting motor neurons in an intersegmentally coordinated manner across the body.

Proprioceptive Reflexes

Stretch reflex and Golgi tendon organ (GTO) reflex are considered proprioceptive reflexes, while the flexor reflex is classified as a cutaneous reflex.

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Description

Explore the function and structure of the flexor reflex in this quiz. Learn about the role of cutaneous receptors, neuron types, and the multi-synaptic nature of the reflex arc. Test your knowledge of how flexor muscles respond to harmful stimuli and assist in locomotion.