Aula: Neurofisiologia - Reflexos Medulares e Tônus Esquelético | Neurofisiologia Humana

Summary

This video explores key reflexes in the nervous system, explaining their roles in protecting the body from injury. It covers the stretch reflex, which triggers muscle contraction in response to stretching; the Golgi tendon reflex, which prevents muscle damage by detecting excessive tension; and the withdrawal reflex, which causes the body to pull away from painful stimuli. The video also delves into the neural circuits involved in these reflexes, highlighting their protective functions and their regulation by higher brain centers. These reflexes are crucial for maintaining muscle function and preventing injury.

Takeaways

• 😀 The stretch reflex is a monosynaptic reflex that helps maintain muscle tone by responding to changes in muscle length.
• 😀 The Golgi tendon reflex (or inverse stretch reflex) prevents muscle damage by responding to excessive tension in the muscle or tendon.
• 😀 The Golgi tendon reflex involves the Golgi tendon organ, which detects muscle tension and triggers an inhibitory response to prevent over-contraction.
• 😀 The muscle spindle (responsible for the stretch reflex) detects changes in muscle length, while the Golgi tendon organ detects muscle tension.
• 😀 The stretch reflex operates quickly and autonomously, helping muscles react to sudden length changes and maintain stability.
• 😀 The inverse stretch reflex (Golgi tendon reflex) prevents muscle damage by inhibiting contraction when excessive tension is detected.
• 😀 The withdrawal reflex (flexor reflex) is triggered by painful stimuli, causing the body to pull away from potential harm.
• 😀 The withdrawal reflex involves both excitatory and inhibitory interneurons to coordinate muscle contraction and relaxation.
• 😀 In intense withdrawal reflex responses, the crossed extensor reflex is activated to maintain balance by engaging the opposite side of the body.
• 😀 Reflexes play an important role in protecting the body from injury, and their function can be modulated by higher neural centers.
• 😀 The withdrawal reflex can vary in intensity depending on the severity of the stimulus, with more severe stimuli leading to stronger reflexive movements.

Q & A

What is the primary function of the muscle spindle (fuso neuromuscular)?

The muscle spindle primarily detects the length of the muscle and the rate at which it is stretched. This information helps in coordinating muscle contractions during movements.

How does the Golgi tendon organ (fuso neurotendíneo) differ from the muscle spindle in terms of sensitivity?

While the muscle spindle is sensitive to the length of the muscle, the Golgi tendon organ is sensitive to the tension or force exerted by the muscle on the tendon. It plays a protective role by preventing excessive tension that could damage the muscle or tendon.

What is the role of the reflex of Golgi tendon (reflexo de Golgi)?

The reflex of Golgi tendon helps protect muscles from excessive tension by inhibiting muscle contraction once the tension exceeds a certain threshold. This prevents injury due to overstretching or force.

What type of circuit is involved in the reflex of Golgi tendon?

The reflex of Golgi tendon involves a **dissynaptic circuit**, which includes two synapses: one between the sensory neuron and an inhibitory interneuron, and another between the interneuron and the motor neuron.

How does the reflex of Golgi tendon help in the scenario of trying to lift an extremely heavy object?

When a person attempts to lift an extremely heavy object, the muscle contracts with high tension. The Golgi tendon organ detects this tension, and if it becomes too high, it activates a reflex to inhibit further muscle contraction, protecting the muscle from injury.

What is the difference between a monosynaptic and a disynaptic reflex?

A **monosynaptic reflex** involves a single synapse between the sensory and motor neurons (e.g., the stretch reflex), whereas a **disynaptic reflex** involves two synapses: one between the sensory neuron and an interneuron, and another between the interneuron and the motor neuron (e.g., the Golgi tendon reflex).

What is the role of reciprocal inhibition in reflexes?

Reciprocal inhibition ensures that when one set of muscles contracts, the opposing muscles are inhibited. This mechanism is crucial for efficient movement, as seen in the reflexes that involve muscle contraction and relaxation (e.g., in the Golgi tendon reflex and flexor withdrawal reflex).

How does the flexor withdrawal reflex (reflexo de retirada) work in response to a painful stimulus?

When a painful stimulus, like stepping on a nail, activates pain receptors in the skin, the impulse is sent to the spinal cord. The spinal cord then activates flexor muscles to withdraw the body part and inhibits the antagonist muscles through reciprocal inhibition, providing a rapid protective response.

Why is the flexor withdrawal reflex sometimes accompanied by a crossed extensor reflex?

The crossed extensor reflex helps maintain balance when a person withdraws a body part in response to pain. It activates the extensor muscles on the opposite side of the body to stabilize the person and prevent a fall, while inhibiting the flexors on the opposite side.

What is the difference between the reflex of Golgi tendon and the muscle spindle reflex in terms of their protective functions?

The muscle spindle reflex protects muscles by regulating the muscle's length and contraction speed to avoid overstretching, while the Golgi tendon reflex protects by controlling the force exerted by the muscle, preventing damage due to excessive tension.