Reflex Arc

The Reflex Arc Includes Receptor Sensory Neuron Motor Neuron Effectors Involved in a particular reflex interneurons may or may not be present The arc makes a REFLEX possible- or “rapid automatic responese to stimuli” Reflexes make RAPID ADJUSTMENTS in the functions of organs or organ systems

Kinds of Reflexes Reflexes are categorized in several ways: 1) on the basis of DEVELOPMENT a) INNATE REFLEXES- result from the connection of neurons that form during normal development Are genetically determined Include: withdrawal from pain, blinking and sucking

b) ACQUIRED REFLEXES are still rapid, and automatic but are LEARNED responses 2) - by MOTOR RESPONSES- a) SOMATIC REFLEXES control activities of the muscular system b) VISERAL REFLEXES or autonomic involuntary reflexes- control the actions of smooth and cardiac muscles and glands

3) - by PROCESSING SITE- a) SPINAL REFLEXES - control the activities of the muscular system b) CRANIAL REFLEXES - are reflexes processed in the brain

4) – by the COMPLEXITY OF THE CIRCUIT- a) Monosynaptic Reflexes - in which the sensory neuron synapses DIRECTLY with the motor neuron - there is little delay between sensory input and motor output - control the most RAPID reflexes

b) Polysynaptic Reflexes - involves a sensory neuron an interneuron and… a motor neuron - the involvement of interneuron's allows for the motor control of several different muscle groups - polysynaptic reflexes allow for more complicated responses

Classification of Reflexes can be Combined Examples: A. Monosynaptic (complexity of circuit) spinal (processing site) reflex - The stretch reflex -provides automatic regulation of skeletal muscle length - is responsible for muscle tone - the STIMULUS is the stretching of the muscle - the RECEPTORS are in the muscle cells - the SENSORY NEURON synapses directly with - the MOTOR NEURON which triggers and immediate response in the -EFFECTOR = the muscle

The Knee Jerk or PATELLAR REFLEX is an example of a MONOSYNAPTIC REFLEX by passive (relaxed) muscles

Postsynaptic Reflexes - Can be one of two types: IPSILATERAL- the sensory stimulus and motor response are on the same side of the body ……or….. CONTRALATERAL- the motor response is required on the opposite side of the body

Five Basic Characteristics of Postsynaptic Reflexes 1. They involve “pools” of neurons 2. They are “intersegmental” involve more than one pair of spinal nerves 3. They involve reciprocal innervations e.g. the contraction of one group of muscles is opposed by the inhibition of another group of opposing muscles - The contraction of a flexing muscle may trigger the STRETCH REFLEX of another muscle 4. They have reverberating circuits that PROLONG the reflex motor response even after the initial stimulus has failed 5. Several reflexes may cooperate to produce a coordinated controlled response Example: Stepping on a Tack with your bare foot