Search for:. Components of a Reflex Arc A reflex arc defines the pathway by which a reflex travels—from the stimulus to sensory neuron to motor neuron to reflex muscle movement. Learning Objectives Describe the components of a reflex arc. Key Takeaways Key Points Reflexes, or reflex actions, are involuntary, almost instantaneous movements in response to a specific stimulus. Reflex arcs that contain only two neurons, a sensory and a motor neuron, are considered monosynaptic.
Examples of monosynaptic reflex arcs in humans include the patellar reflex and the Achilles reflex. Most reflex arcs are polysynaptic, meaning multiple interneurons also called relay neurons interface between the sensory and motor neurons in the reflex pathway. Key Terms motor neuron : A neuron located in the central nervous system that projects its axon outside the CNS and directly or indirectly control muscles. There are two types of reflex arcs: autonomic reflex arc affecting inner organs and somatic reflex arc affecting muscles.
Spinal Reflexes Spinal reflexes include the stretch reflex, the Golgi tendon reflex, the crossed extensor reflex, and the withdrawal reflex. Learning Objectives Distinguish between the types of spinal reflexes. Key Takeaways Key Points The stretch reflex is a monosynaptic reflex that regulates muscle length through neuronal stimulation at the muscle spindle. The alpha motor neurons resist stretching by causing contraction, and the gamma motor neurons control the sensitivity of the reflex. The stretch and Golgi tendon reflexes work in tandem to control muscle length and tension.
Both are examples of ipsilateral reflexes, meaning the reflex occurs on the same side of the body as the stimulus. The crossed extensor reflex is a contralateral reflex that allows the body to compensate on one side for a stimulus on the other. The withdrawal reflex and the more-specific pain withdrawal reflex involve withdrawal in response to a stimulus or pain. When pain receptors, called nociceptors, are stimulated, reciprocal innervations stimulate the flexors to withdraw and inhibit the extensors to ensure they are unable to prevent flexion and withdrawal.
Key Terms golgi tendon reflex : A normal component of the reflex arc of the peripheral nervous system. In this reflex, a skeletal muscle contraction causes the agonist muscle to simultaneously lengthen and relax. This reflex is also called the inverse myotatic reflex because it is the inverse of the stretch reflex.
Although muscle tension is increasing during the contraction, the alpha motor neurons in the spinal cord that supply the muscle are inhibited. However, antagonistic muscles are activated. They innervate the extrafusal muscle fibers of skeletal muscle and are directly responsible for initiating their contraction.
Alpha motor neurons are distinct from gamma motor neurons that innervate the intrafusal muscle fibers of muscle spindles. Licenses and Attributions. CC licensed content, Shared previously. Reflexes protect your body from things that can harm it. For example, if you put your hand on a hot stove, a reflex causes you to immediately remove your hand before a "Hey, this is hot! Other protective reflexes are blinking when something flies toward your eyes or raising your arm if a ball is thrown your way.
Even coughing and sneezing are reflexes. They clear the airways of irritating things. The reflex that the doctor checks by tapping your knee is called the patellar, or knee-jerk, reflex. It is also known as a deep tendon reflex DTR because the doctor is actually tapping on a tendon called the patellar say: puh-TEL-ur tendon. This tap stretches the tendon and the muscle in the thigh that connects to it. A message then gets sent to the spinal cord that the muscle has been stretched. A reflex arc starts off with receptors being excited.
They then send signals along a sensory neuron to your spinal cord, where the signals are passed on to a motor neuron. As a result, one of your muscles or glands is stimulated. The knee-jerk reflex involves a sudden kicking movement of your lower leg after the tendon just below your kneecap has been tapped. Doctors often trigger this reflex to test the function of your nervous system. If the reaction is exaggerated or absent, it may indicate a damage to the central nervous system.
Most reflexes go completely unnoticed because they don't involve a visible and sudden movement. Body functions such as digestion or blood pressure, for example, are all regulated by reflexes. These reflexes are known as autonomic reflexes.
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