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Muscle Spindles and Reflex Actions

Muscle Spindles

  • Muscle spindles are specialized sensory receptors located within the belly of muscles.

  • Function as stretch receptors and play a crucial role in proprioception (the sense of body position).

Proprioception

  • Definition: The body's ability to perceive its own position in space and movement.

Tendon Reflex

  • Tendon Reflex: A reflex that helps regulate muscle tension.

  • Drawing: Should include:

    • Muscle and tendon involvement.

    • Sensory neuron (input) pathway to the spinal cord.

    • Motor neuron (output) pathway back to the muscle.

  • Example: The knee-jerk reflex when the patellar tendon is tapped.

Reciprocal Inhibition

  • Definition: A neurophysiological process where the excitation of one muscle leads to the inhibition of its antagonist muscle.

  • Inclusion in drawing: Show how sensory input leads to inhibition of antagonist muscle during a tendon reflex.

Flexor (Withdrawal) Reflex

  • Definition: A protective reflex that causes limb withdrawal from harmful stimuli.

  • Polysynaptic Reflex Arc: Involves multiple synapses (more than one) and is typically slower because it integrates signals from both sensory and interneurons. The withdrawal reflex uses this arc to coordinate complex responses.

  • Drawing Components:

    • Multiple sensory neurons, interneurons, and motor neurons.

Crossed Extension Reflex

  • Definition: A reflex that helps maintain balance by extending the opposite limb when one limb withdraws.

  • Function: Activated when standing and not when lying down; this helps to stabilize the body during withdrawal from a painful stimulus.

Golgi Tendon Organs

  • Definition: Proprioceptors located in tendons near their junction with muscles.

  • Function: Monitor tension (force) in the muscle and help prevent excessive force generation, thereby maintaining muscle safety.

Spinal Cord Trauma Insights (Referencing Insight 13.5)

  • Flaccid Paralysis: Loss of muscle tone and reflexes; muscle becomes limp due to lower motor neuron damage.

  • Spastic Paralysis: Increased muscle tone and exaggerated reflexes; results from upper motor neuron damage.

  • Stages of Spinal Cord Trauma:

    1. Initial injury phase, where cellular damage occurs.

    2. Secondary injury phase, which may involve inflammatory responses and cell apoptosis leading to further damage.

Paralysis Types

  • Quadriplegia: Paralysis of all four limbs due to damage in the cervical region.

  • Paraplegia: Paralysis of the lower limbs, usually due to damage in the thoracic or lumbar regions.

  • Hemiplegia: Paralysis affecting one side of the body, often due to a stroke.

  • Paresis: Partial paralysis or weakness of muscle function.

Key Terms Review

  • Ischemia: Reduction in blood supply to tissues, causing oxygen deprivation.

  • Apoptosis: Programmed cell death that may occur in damaged cells.