Reflexes and the Nervous System

Reflexes

• A reflex is a response to a stimulus that doesn't require the involvement of consciousness.
• All reflexes have two parts: the afferent part and the efferent part.

Afferent Part

• The afferent part involves bringing information about a stimulus into the central nervous system.
• It includes receptors that detect the stimulus and neurons that carry the information to the central nervous system.

Efferent Part

• The efferent part carries information away from the central nervous system to cause a response in the periphery.
• It includes neurons that carry the response information to the peripheral nervous system.

Muscle Stretch Reflex

• The muscle stretch reflex is a simple reflex that occurs when a skeletal muscle is rapidly stretched.
• It causes the muscle to contract quickly as a protective response to prevent injury.
• The reflex occurs on the same side of the body, with the afferent part bringing information in from one side and the efferent part causing a response on the same side.

Knee-Jerk Reflex

• The knee-jerk reflex is a type of muscle stretch reflex that occurs when the tendon below the kneecap is stretched.
• It causes the leg to kick out without conscious control.
• The reflex is triggered by the stretching of the tendon, which pulls on the muscle and activates the muscle spindles.

Muscle Spindles

• Muscle spindles are specialized receptors in skeletal muscles that detect muscle stretch.
• They are made up of specialized fibers and neuron axons that wrap around them.
• The axons carry information about the muscle stretch back to the central nervous system.

Afferent Neurons

• Afferent neurons are somatosensory neurons that carry information about the stimulus into the central nervous system.
• They form an excitatory synapse with another neuron in the central nervous system.

Efferent Neurons

• Efferent neurons are lower motor neurons that carry response information from the central nervous system to the peripheral nervous system.
• They synapse on and control skeletal muscle cells, causing them to contract.

Diminished Reflexes

• Diminished reflexes can occur if there is a problem with either the afferent or efferent part of the reflex.
• Problems with the lower motor neurons or somatosensory neurons can cause a diminished muscle stretch reflex.

Characteristics of Reflexes

• Reflexes do not require the involvement of consciousness.
• They occur at the lower levels of the nervous system, such as the spinal cord or brain stem.
• Reflexes can be affected by problems with either the afferent or efferent part of the reflex.

Additional Mechanism

• In some reflexes, an additional mechanism involves the relaxation of the opposing muscle to increase the response.
• This is achieved through inhibitory neurons that inhibit the lower motor neurons to the opposing muscle.

Reflexes

• A reflex is a response to a stimulus that doesn't require conscious involvement.
• Reflexes have two parts: afferent and efferent.

Afferent Part

• Involves bringing information about a stimulus into the central nervous system.
• Includes receptors that detect the stimulus and neurons that carry information to the CNS.

Efferent Part

• Carries information away from the CNS to cause a response in the periphery.
• Includes neurons that carry response information to the peripheral nervous system.

Muscle Stretch Reflex

• Occurs when a skeletal muscle is rapidly stretched.
• Causes the muscle to contract quickly to prevent injury.
• Occurs on the same side of the body.

Knee-Jerk Reflex

• A type of muscle stretch reflex that occurs when the tendon below the kneecap is stretched.
• Causes the leg to kick out without conscious control.
• Triggered by tendon stretching, which activates muscle spindles.

Muscle Spindles

• Specialized receptors in skeletal muscles that detect muscle stretch.
• Composed of specialized fibers and neuron axons.

Afferent Neurons

• Somatosensory neurons that carry information about the stimulus into the CNS.
• Form an excitatory synapse with another neuron in the CNS.

Efferent Neurons

• Lower motor neurons that carry response information from the CNS to the peripheral nervous system.
• Synapse on and control skeletal muscle cells, causing them to contract.

Diminished Reflexes

• Can occur if there is a problem with either the afferent or efferent part of the reflex.
• Problems with lower motor neurons or somatosensory neurons can cause a diminished muscle stretch reflex.

Characteristics of Reflexes

• Do not require conscious involvement.
• Occur at lower levels of the nervous system (spinal cord or brain stem).
• Can be affected by problems with either the afferent or efferent part.

Additional Mechanism

• Involves relaxation of the opposing muscle to increase the response.
• Achieved through inhibitory neurons that inhibit lower motor neurons to the opposing muscle.

Reflexes

• A reflex is a response to a stimulus that doesn't require conscious involvement.
• Reflexes have two parts: afferent and efferent.

Afferent Part

• Involves bringing information about a stimulus into the central nervous system.
• Includes receptors that detect the stimulus and neurons that carry information to the CNS.

Efferent Part

• Carries information away from the CNS to cause a response in the periphery.
• Includes neurons that carry response information to the peripheral nervous system.

Muscle Stretch Reflex

• Occurs when a skeletal muscle is rapidly stretched.
• Causes the muscle to contract quickly to prevent injury.
• Occurs on the same side of the body.

Knee-Jerk Reflex

• A type of muscle stretch reflex that occurs when the tendon below the kneecap is stretched.
• Causes the leg to kick out without conscious control.
• Triggered by tendon stretching, which activates muscle spindles.

Muscle Spindles

• Specialized receptors in skeletal muscles that detect muscle stretch.
• Composed of specialized fibers and neuron axons.

Afferent Neurons

• Somatosensory neurons that carry information about the stimulus into the CNS.
• Form an excitatory synapse with another neuron in the CNS.

Efferent Neurons

• Lower motor neurons that carry response information from the CNS to the peripheral nervous system.
• Synapse on and control skeletal muscle cells, causing them to contract.

Diminished Reflexes

• Can occur if there is a problem with either the afferent or efferent part of the reflex.
• Problems with lower motor neurons or somatosensory neurons can cause a diminished muscle stretch reflex.

Characteristics of Reflexes

• Do not require conscious involvement.
• Occur at lower levels of the nervous system (spinal cord or brain stem).
• Can be affected by problems with either the afferent or efferent part.

Additional Mechanism

• Involves relaxation of the opposing muscle to increase the response.
• Achieved through inhibitory neurons that inhibit lower motor neurons to the opposing muscle.

Reflexes

• A reflex is a response to a stimulus that doesn't require conscious involvement.
• Reflexes have two parts: afferent and efferent.

Afferent Part

• Involves bringing information about a stimulus into the central nervous system.
• Includes receptors that detect the stimulus and neurons that carry information to the CNS.

Efferent Part

• Carries information away from the CNS to cause a response in the periphery.
• Includes neurons that carry response information to the peripheral nervous system.

Muscle Stretch Reflex

• Occurs when a skeletal muscle is rapidly stretched.
• Causes the muscle to contract quickly to prevent injury.
• Occurs on the same side of the body.

Knee-Jerk Reflex

• A type of muscle stretch reflex that occurs when the tendon below the kneecap is stretched.
• Causes the leg to kick out without conscious control.
• Triggered by tendon stretching, which activates muscle spindles.

Muscle Spindles

• Specialized receptors in skeletal muscles that detect muscle stretch.
• Composed of specialized fibers and neuron axons.

Afferent Neurons

• Somatosensory neurons that carry information about the stimulus into the CNS.
• Form an excitatory synapse with another neuron in the CNS.

Efferent Neurons

• Lower motor neurons that carry response information from the CNS to the peripheral nervous system.
• Synapse on and control skeletal muscle cells, causing them to contract.

Diminished Reflexes

• Can occur if there is a problem with either the afferent or efferent part of the reflex.
• Problems with lower motor neurons or somatosensory neurons can cause a diminished muscle stretch reflex.

Characteristics of Reflexes

• Do not require conscious involvement.
• Occur at lower levels of the nervous system (spinal cord or brain stem).
• Can be affected by problems with either the afferent or efferent part.

Additional Mechanism

• Involves relaxation of the opposing muscle to increase the response.
• Achieved through inhibitory neurons that inhibit lower motor neurons to the opposing muscle.

Learn about reflexes, their components, and how they work in the nervous system. Understand the afferent and efferent parts of a reflex and their roles in responding to stimuli.