Reflex• Reflex is the mechanism by which sensory impulse is automatically converted into a motor effect thru the involvement of CNS.
Reflex arc• Pathway for any reflex action is known as reflex arc. it consists of:• Afferent limb: receptor and afferent nerve.• Efferent limb: efferent nerve and effector organ.• Centre: part of CNS where afferent limb ends and either synapses directly with efferent motor neuron or establish connection with efferent neuron thru intercalated neurons.
Classification of Reflexes• Clinical• Anatomical• Physiological• Depending upon inborn or acquired reflexes
Clinical classification• Superficial: initiated by stimulating appropriate receptors of skin or mucous membrane.• Are usually multisynaptic .• Are usually involving moving away from stimulus• E.g. plantar response, corneal and conjunctival reflexes.
Deep reflexes• Are elicited on stroking the tendon.• Are basically stretch reflexes• Are also called tendon reflexes• E.g. knee jerk, ankle jerk etc.
Visceral reflexes• Are the reflexes where at least one part of the reflex arc is autonomic nerve• E.g, pupillary reflex, carotid sinus reflex.
Pathological reflexes• Are not found normally• Presence indicates pathological condition within the body• E.g, Babiniski’s sign.
Anatomical classification of reflexes• Segmental reflexes: in these end of afferent neuron and beginning of efferent neuron are in the same segment of spinal cord.• Intersegmental reflexes: end of afferent neuron and beginning of efferent neuron are in the spinal cord but in different segments.• Suprasegmental: centre for such reflex lies above the spinal cord.
Physiological classification• Flexor reflexes: are produced when nociceptive stimulus is applied.• Stimulus causes flexion of joint.• E.g thorn prick to a sole causes flexion of knee, hip joints.• Extensor reflexes: stretch reflexes are extensor reflexes which are the basis of tone and posture.
Depending upon inborn or acquired reflexes• Unconditioned reflexes: are inborn reflexes.• E.g pulling the hand away from a burning hot object.• Conditioned reflexes: are reflexes that develop after birth, are result of practice and learning.
Spinal cord integrates many basic reflexes• Serve as a link for transmission of information b/w the brain and the remainder of body.• Integrate reflex activity b/w afferent input and efferent output without involving the brain. This type of reflex activity is called a spinal reflex.
Stretch reflex• Is simplest reflex.• Is monosynaptic.• In which an afferent neuron originating at a stretch detecting receptor in a skeletal muscle terminates directly on the efferent neuron supplying the same skeletal muscle to cause it to contract and counteract the stretch.
Withdrawal reflex• When a person receives any painful stimulus, a withdrawal reflex is initiated to withdraw from painful stimulus.• Afferent neuron stimulates excitatory interneurons that stimulate the efferent motor neurons supplying the muscle, that flexes and pulls away from painful stimulus.• The afferent neuron also stimulates inhibitory interneurons that inhibit the efferent neurons supplying the antagonistic muscle to prevent it from contracting.
Reciprocal inhibition• The type of connection involving stimulation of nerve supply to one muscle and simultaneous inhibition of the nerves to its antagonistic muscle is known as reciprocal innervation.
Withdrawal reflex• Afferent neuron also stimulates interneurons that carry signal up the spinal cord to brain via an ascending pathway.• When impulse reaches sensory area of cortex person becomes aware of pain, its location and type of stimulus.• The activity at the conscious level is above and beyond the basic reflex.
Crossed extensor reflex• Reflex arc initiate to withdraw injured limb from painful stimulus, while opposite limb prepares to suddenly bear all the weight so that the person does not lose balance or fall.• Bending of injured extremity’s knee is accomplished by concurrent reflex stimulation of muscles that flex the knee and inhibition of muscles that extend the knee.• Extension of opposite limb’s knee is accomplished by activation of pathways that cross over to the opposite side of the spinal cord to reflexly stimulate extensors and inhibit flexors.
Spinal reflexes• All spinal reflexes can be voluntarily overridden at least by higher brain centers.