Reflexes

• A reflex is a stereotypic (the response to stimulus is always more or less the same) , involuntary and unconscious response to a stimulus.
• Reflexes maintain homeostasis

1. Somatic reflexes : through the somatic motor nervous system and include responses that remove the body from painful stimuli that would cause tissue damage or keep our body from suddenly falling or moving because of external forces.
2. Autonomic reflexes : through the autonomic nervous system (ANS) and responsible for maintaining variables within their normal ranges.

• Reflexes are produced by reflex arcs. A reflex arc is the functional unit of nervous system. It has five basic components :

• Convergent and divergent pathways interact with reflexes.
• Reflexes are integrated within the brain and spinal cord. Higher brain centers can suppress or exaggerate reflexes.
• Reflexes occur unconsciously because reflex arcs are not part of the brain where consciousness occurs.

Reflex Arc

1. A sensory receptor detects a stimulus.
2. A sensory neuron conducts action potentials through the spinal nerve and dorsal root to spinal cord.
3. in the spinal cord,the sensory neuron synapses with an interneuron
4. The interneuron synapses with motor neuron.
5. A motor neuron axon conducts action potentials through the ventral root and spinal nerve to an effector organ.

Stretch Reflex

• Muscle spindles detect the stretch of skeletal muscles and cause the muscle to shorten reflexively.
• Sudden stretch of a muscle results in :

1. Muscle spindles detect stretch of the muscle.
2. sensory neurons conduct action potential to the spinal cord.
3. Sensory neurons synapse directly with motor neurons.
4. Motor neurons conduct action potentials to the muscle,causing it to contract and resist being stretched. (muscle contract=muscle is stretched)

Golgi Tendon Reflex

• Respond to increased tension within tendons and caused skeletal muscles to relax.
• Intense stretch of a skeletal muscle results in :

1. Golgi tendon organs detect tension applied to tendon.
2. Sensory neurons conduct action potentials to the spinal cord.
3. Sensory neurons synapse with inhibitory interneurons that synapse with motor neurons.
4. Inhibition of the motor neurons causes muscle relaxation, relieving the tension applied to tendon. (muscle relax is attached to the tendon to which tension is applied)

Withdrawal Reflex

• Activation of pain receptors cause contraction of muscles and the removal of some part of the body from a painful stimulus.
• Stimulation of pain receptors result in :

1. Pain receptors detect a painful stimulus
2. Sensory neurons conduct action potentials to the spinal cord.
3. Sensory neurons synapse with excitatory interneurons that synapse with motor neurons.
4. Excitation of the motor neurons results in contraction of the flexor muscles and withdrawal of the limb from the painful stimulus.