,an intercalated neuron, wilh Ihe efferent motoneuron The receptor (present in the skin) 'catches'the stimulus, then transmits the impulse to the cent

commands came for Ihe constraction of those muscler, of the limb which would cause its Fig I0 4. 1 Reflex arc contraction of Ihe muscles Therefore, if now the spinal cord is destroyed, this reflex will disappear and in actual practice, this happens This experiment is rather dramatic, but all reflexes have these two basic characteristics, viz . (i) sensory to motor conversion is through CNS participation, (ii) non participation of volition Numerous such examples may be given Thus while walking bare footed, a person Treads over a thorn -> he withdraws his affected limb while extends his other limb (to support ihe body weight),the whole action is reflex and does not require the presence of will (That the person becomes aware of the pain due to the thorn prick is merely an accompanying phenomenon, not necessary for the reflex actron) THE REFLEX ARC To slart with, reflex arc of a spinal reflex may be considered A painful stimulus is applied to The limb -> flexor muscles of the limb contract withdrawal (flexion) of The limb The reflex arc consists of: (A) the afferent limb, consisting of, (i) receptor, and (n) Ihe afferent (sensory) nerve (B) Ihe efferent limb. consisting of. (i) Ihe moloneuf on and (it) Ihe effector organ. (C) the center This is The part ol Ihe CNS, where Ihe allerenl limb ends and either synapse’ directly with the efferent motaneuron or establishes its connection via an intercalated neuron, wilh Ihe efferent motoneuron The receptor (present in the skin) 'catches'the stimulus, then transmits the impulse to the center via the afferent limb. the center integrates the afferent stimulus and the efferent response The efferent nerve transmits the command (the signal) of the cenler and the effector organ contracts (or secretes) The fig 10A 4,1 is a highly schematic diagram but highlights the essential components of a reflex arc In fig 10 A4.1 the integration between the afferent and efferent limb occurs at a segment of spinal cord, hence it is called a 'spinal reflex' The integration may occur, instead, at somewhere in Ihe brain stem (brain stem reflexes, e g some reflexes concerned! with posture and equilibrium, control of blood pressure etc ) or in the cerebral cortex [cortical reflex) and so on CLASSIFICATION OF REFLEX Reflexes have been classified in various ways. Some common classifications are given in Table 1DA.4.1 Table IDA4 1. Classification of reflexes A. Clinical B Anatomical C. Physiological D. Inborn or acquired I. Superficial 1 Segmenlal 1. Flexor 1. Conditioned 2 Deep 2 Inter segmenlal (withdrawal) 2 Unconditioned 3 Visceral 3 Suprasegrnental 2. Exlensur 4 Pathological Clinical classification of relieves (table 10A.42) This classification is the most popular and practical one for the practising clinicians. V Superficial refleies These are elicited by stimulating the appropriate receptors of skin or mucous membrane Example, (i) plantar response (li) abdominal (in) cremastenc (iv) cornea! (v) conjunctiva! (vi) sucking. reflexes. 2. Deep reflexes These are basically stretch reflexes and are elicited by stroking the appropriate lendon or by other related methods, which results in sharp passive stretching of the muscle, resulting m muscular contraction The/ are also called tendon jerks. Examples knee jerk, biceps jerk, ankle jerk, jaw jerk and so on 3 Visceral reflexes These are reflexes where al least a part of the reflex arc is formed by autortomit nerve Examples Pupillary reflex, barorecepfor reflex, gastric reflexes and so on 4 Pathological reflexes These are reflexes which are not found m normal persons, their presence indicates some pathological condition within Ihe body That is, they are found only in pathological states Example. Babinski's sign Anatomical Classification A segmenlal reflex is one where ihe end of the afferent neuron and the beginning of the efferent neuron are in the same segment. In intersegmental mental reflex, end of the afferent neuron and The beginning of efferent neuron are in the spinal cord but in different segments. In suprasegmental reflexes the integrating part of Ihe CNS (center) extends from the spinal cord to the brain. Physiological Classification (i) Flenor (or flexion) reflexes are produced, when nocicepine (injurious) stimuli are applied, such stimuli cause flexion of ihe joint (s), thai is, withdrawal from the source of injury. Thus, a thorn prick in the sole of foot causes flexion of The knee and hip joints These reflexes are therefore protective in nature (n) Stretch reflenes are extensor reflexes When the muscle is stretched, it responds by contraction, stretch reflei forms the basis of muscle Lone and posture of Ihe body Reflexes can also be classified whether they are (i) conditioned or (ii) unconditioned Unconditioned reflexes are all inborn (present since birth) and do not de -) end upon previous experience On Ihe other hand, conditioned reflexes develop after birth and their appearance depends upon previous experience It is believed that many of our social habits owe Their ongm to the conditioned reflflxes This means, our faiths (base d on religion/social customs).thinking processes, many of our do's and don'ts of life are due to conditioned reflexes. [Viewed in this way, conditioned reflexes may form the basis of "brainwashing] for' further details see chap 6 sec XD PROPERTIES OF REFLEXES [particularly demon reflex) Introduction Experimental studies on ihe properties of ihe reflexes were made in the animals )n most cases, a 'spinal preparation' was made, thai is. spinal cord was transected al cervical region and respiration maintained by respiratory pump In such a 'spinal animal' Ihe influences of Ihe brain on Ihe spinal cord are lost and properties of spinal reflexes (uninfluenced by the brain) can be studied The properties described below are largely the properties of such spinal