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.