2.Reflex Activity.ppt
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This document discusses reflex activity, defined as unconscious responses to peripheral nervous stimulation that serve as protective mechanisms for the body. It details the structure of the reflex arc, the classification of reflexes based on various criteria (such as physiological purpose and anatomical location), and includes examples of reflex actions along with their physiological properties. Additionally, it covers the effects of upper and lower motor neuron lesions on reflex activity.
2.Reflex Activity.ppt
- 1. REFLEX ACTIVITY By Dr.M.Selvin Innocent Dhas,MD(s) Maria Siddha Medical College
- 2. DEFINITION AND SIGNIFICANCE OF REFLEXES Reflex activity is the response to a peripheral nervous stimulation that occurs without our consciousness. It is a type of protective mechanism and it protects the body from irreparable damages. Example: when hand is placed on a hot object, it is withdrawn immediately. When a bright light is thrown into the eyes, eyelids are closed and pupil is constricted to prevent the damage of retina by entrance of excessive light into the eyes.
- 3. Reflex arc is the anatomical nervous pathway for a reflex action. A simple reflex arc includes five components 1. Receptor Receptor is the end organ, which receives the stimulus. When receptor is stimulated, impulses are generated in afferent nerve. 2. Afferent Nerve Afferent or sensory nerve transmits sensory impulses from the receptor to center. 3. Center Center receives the sensory impulses via afferent nerve fibers and in turn, it generates appropriate motor impulses. Center is located in the brain or spinal cord. 4. Efferent Nerve Efferent or motor nerve transmits motor impulses from the center to the effector organ. 5. Effector Organ Effector organ is the structure such as muscle or gland where the activity occurs in response to stimulus.
- 5. In some places, one or moreneurons are interposed between these nerve fibers and the center. Such neurons are called connector neurons or internuncial neurons or interneurons.
- 6. CLASSIFICATION OF REFLEXES Reflexes are classified by six different methods depending upon various factors. 1. Depending upon whether inborn or acquired 2. Depending upon situation – anatomical classification 3. Depending upon purpose – physiological classification 4. Depending upon number of synapse 5. Depending upon whether visceral or somatic 6. Depending upon clinical basis – Superficial ,Deep tendon
- 7. 1. INBORN OR ACQUIRED REFLEXES i. Inborn Reflexes or Unconditioned Reflexes Natural reflexes, which are present since the time of birth, hence the name inborn reflexes. Such reflexes do not require previous learning, training or conditioning. Best example is the secretion of saliva when a drop of honey is kept in the mouth of a newborn baby for the first time. The baby does not know the taste of honey, but still saliva is secreted. ii. Acquired Reflexes or Conditioned Reflexes These reflexes are not inborn but, acquired after birth (after conditioning or training). Example is the secretion of saliva by sight, smell, thought or hearing of a known edible substance.
- 8. 2. ANATOMICAL CLASSIFICATION In this method, reflexes are classified depending upon the situation of the center. i. Cerebellar Reflexes Cerebellar reflexes are the reflexes which have their center in cerebellum. ii. Cortical Reflexes Cortical reflexes are the reflexes that have their center in cerebral cortex. iii. Midbrain Reflexes Midbrain reflexes are the reflexes which have their center in midbrain. iv. Bulbar or Medullary Reflexes Bulbar or medullary reflexes are the reflexes which have their center in medulla oblongata. v. Spinal Reflexes Reflexes having their center in the spinal cord are called spinal reflexes. Depending upon the segments involved, spinal reflexes are divided into three groups: a. Segmental spinal reflexes b. Intrasegmental spinal reflexes c. Suprasegmental spinal reflexes.
- 9. 3. PHYSIOLOGICAL CLASSIFICATION In this method, reflexes are classified depending upon the purpose (functional significance). i. Protective Reflexes or Flexor Reflexes Protective reflexes are the reflexes which protect the body from nociceptic (harmful) stimuli. These reflexes are also called withdrawal reflexes or flexor reflexes. Protective reflexes involve flexion at different joints hence the name flexor reflexes. ii. Antigravity Reflexes or Extensor Reflexes Antigravity reflexes are the reflexes that protect the body against gravitational force. These reflexes are also called the extensor reflexes because, the extensor muscles contract during these reflexes resulting in extension at joints.
- 10. 4. DEPENDING UPON THE NUMBER OF SYNAPSE Depending upon the number of synapse in reflex arc, reflexes are classified into two types: i. Monosynaptic Reflexes Reflexes having only one synapse in the reflex arc are called monosynaptic reflexes. Stretch reflex is the best example for monosynaptic reflex and it is elicited due to the stimulation of muscle spindle. ii. Polysynaptic Reflexes Reflexes having more than one synapse in the reflex arc are called polysynaptic reflexes. Flexor reflexes (withdrawal reflexes) are the polysynaptic reflexes.
- 11. 5. SOMATIC OR VISCERAL REFLEXES i. Somatic Reflexes Somatic reflexes are the reflexes, for which the reflex arc is formed by somatic nerve fibers. These reflexes involve the participation of skeletal muscles. And there may be flexion or extension at different joints during these reflexes. ii. Visceral or Autonomic Reflexes Visceral or autonomic reflexes are the reflexes, for which at least a part of reflex arc is formed by autonomic nerve fibers. These reflexes involve participation of smooth muscle or cardiac muscle. Visceral reflexes include •pupillary reflexes, •gastrointestinal reflexes, •cardiovascular reflexes, •respiratory reflexes, etc.
- 12. 6. DEPENDING UPON CLINICAL BASIS Depending upon the clinical basis, reflexes are classified into four types: i. Superficial reflexes ii. Deep reflexes iii. Visceral reflexes iv. Pathological reflexes.
- 13. Reflex Stimulus Response Afferent Nerve Center Efferent Nerve 1. Corneal reflex Irritation of cornea Blinking of eye (closure of eyelids) V cranial nerve Pons VII cranial nerve 2. Conjunctival reflex Irritation of conjunctiva Blinking of eye V cranial nerve Pons VII cranial nerve 3. Nasal reflex (sneezing reflex) Irritation of nasal mucus membrane Sneezing V cranial nerve Motor nucleus of V cranial nerve X cranial nerve and upper cervical nerves 4. Pharyngeal reflex Irritation of pharyngeal mucus membrane Retching or gagging (opening of mouth) IX cranial nerve Nuclei of X cranial nerve X cranial nerve 5. Uvular reflex Irritation of uvula Raising of uvula IX cranial nerve Nuclei of X cranial nerve X cranial nerve Superficial mucous membrane reflexes
- 15. SUPERFICIAL CUTANEOUS REFLEXES Reflex Stimulus Response Center – spinal segments involved 1. Scapular reflex Irritation of skin at the interscapular space Contraction of scapular muscles and drawing in of scapula C5 to T1 2. Upper abdominal reflex Stroking the abdominal wall below the costal margin Ipsilateral contraction of abdominal muscle and movement of umbilicus towards the site of stroke T6 to T9 3. Lower abdominal reflex Stroking the abdominal wall at umbilical and iliac level Ipsilateral contraction of abdominal muscle and movement of umbilicus towards the site of stroke T10 to T12 4. Cremasteric reflex Stroking the skin at upper and inner aspect of thigh Elevation of testicles L1, L2 5. Gluteal reflex Stroking the skin over glutei Contraction of glutei L4 to S1,2 6. Plantar reflex Stroking the sole Plantar flexion and adduction of toes L5 to S2 7. Bulbocavernous reflex Stroking the dorsum of glans penis Contraction of bulbocavernosus S3, S4 8. Anal reflex Stroking the perianal region Contraction of anal sphincter S4, S5
- 16. DEEP REFLEXES Reflex Stimulus Response Center – spinal segments involved 1. Jaw jerk Tapping middle of the chin with slightly opened mouth Closure of mouth Pons – V cranial nerve 2. Biceps jerk Percussion of biceps tendon Flexion of forearm C5, C6 3. Triceps jerk Percussion of triceps tendon Extension of forearm C6 to C8 4. Supinator jerk or radial periosteal reflex Percussion of tendon over distal end (styloid process) of radius Supination and flexion of forearm C7, C8 5. Wrist tendon or finger flexion reflex Percussion of wrist tendons Flexion of corresponding finger C8, T1 6. Knee jerk or patellar tendon reflex Percussion of patellar ligament Extension of leg L2 to L4 7. Ankle jerk or Achilles tendon reflex Percussion of Achilles tendon Plantar flexion of foot L5 to S2
- 17. SUPERFICIAL REFLEXES Superficial reflexes are the reflexes, which are elicitedfrom the surface of the body. Superficial reflexes are of two types: 1. mucus membrane reflexes 2. skin reflexes. DEEP REFLEXES Deep reflexes are elicited from deeper structures beneath the skin like tendon. These reflexes are otherwise known as tendon reflexes. VISCERAL REFLEXES Visceral reflexes are the reflexes arising from pupil and visceral organs. Following are the visceral reflexes: 1. Pupillary reflexes 2. Oculocardiac reflex 3. Carotid sinus reflex.
- 18. PUPILLARY REFLEXES Pupillary reflexes are the reflexes in which, the size of pupil is altered. Pupillary reflexes are: i. Light reflex ii. Accommodation reflex iii. Ciliospinal reflex. i. Light Reflex When retina of the eye is stimulated by a sudden flash oflight, constriction of pupil occurs. It is called light reflex. Light reflex of two types: a. Direct light reflex, in which stimulation of retina in one eye by flash of light causes constriction of pupil in the same eye b. Indirect or consensual light reflex, in which stimu lation of retina in one eye by flash of light causes simultaneous constriction of pupil inthe other eye also.
- 19. ii. Accommodation Reflex While eyes are fixed on a distant object and if another object is brought in front of the eye (near the eye) the vision shifts form far object to near object. During that time some changes occur in the eyes. Changes during accommodation reflex are: a. Constriction of pupil b. Convergence of eyeball c. Increase in anterior curvature of lens. iii. Ciliospinal Reflex Ciliospinal reflex is the dilatation of pupil due to stimulation of skin over the neck.More details of pupillary reflexes
- 20. „ OCULOCARDIAC REFLEX Oculocardiac reflex is the reflex, in which heart rate decreases due to the pressure applied over eyeball. „ CAROTID SINUS REFLEX Carotid sinus reflex is the decrease in heart rate and blood pressure caused by pressure over carotid sinus in neck due to tight collar.
- 21. PATHOLOGICAL REFLEXES Pathological reflexes are the reflexes that are elicited only in pathological conditions. Well-known pathological reflexes are: 1. Babinski sign 2. Clonus 3. Pendular movements.
- 22. BABINSKI SIGN Abnormal plantar reflex is called Babinski sign. It is also called Babinski reflex or phenomenon. It is named after the discoverer Joseph Babinski. In normal plantar reflex, a gentle scratch over the outer edge of the sole of foot causes plantar flexion and adduction of all toes. But in Babinski sign, there is dorsiflexion of great toe and fanning of other toes. When Babinski reflex is present, the condition is commonly called Babinski positive sign and when it is negative, the condition is called Babinski negative sign. Babinski sign is present in upper motor neuron lesion. Physiological conditions when Babinski sign is present are infancy and deep sleep. It is present in infants because of non-myelination of pyramidal tracts.
- 24. „ CLONUS Clonus is a series of rapid and repeated involuntary jerky movements, which occur while eliciting a deep reflex. clonus occurs when the deep reflexes are exaggerated due to hypertonicity of muscles in pyramidal tract lesion. Clonus is well seen in calf muscles producing ankle clonus and quadriceps producing patella clonus. Ankle Clonus Ankle clonus is the repeated rhythmical contractions of calf muscles caused by sudden dorsiflexion of foot. Repeated rhythmical contractions of calf muscles lead to a series of rhythmic plantar flexion at ankle joint. Sudden dorsiflexion of foot is done by supporting patient’s knee in a slightly flexed position. Patellar Clonus Patellar clonus is the rhythmic jerky movements of patella produced by grasping it between thumb and index finger of the examiner and pushing it down forcibly towards the foot. It is caused by clonic contractions of quadriceps muscle.
- 26. PENDULAR MOVEMENTS Pendular movements are the slow oscillatory movements (instead of brisk movements) that are developed while eliciting a tendon jerk. Unlike clonus, pendular move ments occur because of hypotonicity of muscles. Pendular movements are very common while eliciting the knee jerk or patellar tendon reflex in the patients affected by cerebellar lesion. In cerebellar lesion,the leg swings forwards and backwards several times before coming to rest.
- 27. PROPERTIES OF REFLEXES 1. ONE WAY CONDUCTION 2. REACTION TIME 3. SUMMATION 4. OCCLUSION 5. SUBLIMINAL FRINGE 6. RECRUITMENT 7. AFTER DISCHARGE 8. REBOUND PHENOMENON 9. FATIGUE
- 28. PROPERTIES OF REFLEXES (Refer Synapse Slide 35) „1. ONE WAY CONDUCTION (BELL-MAGENDIE LAW) During any reflex activity, impulses are transmitted in only one direction through the reflex arc as per Bell- Magendie law. The impulses pass from receptors to center and then from center to effector organ. „2. REACTION TIME Reaction time is the time interval between application of stimulus and the onset of reflex. It depends upon the length of afferent and efferent nerve fibers, velocity of impulse through these fibers and central delay. Central delay is the delay at the synapse. It is also called synaptic delay. „3. SUMMATION Refer Chapter 140 for details of summation. Summation in reflex action is of two types: I. Spatial Summation When two afferent nerve fibers supplying a muscle are stimulated separately with subliminal stimulus, there is no response. But the muscle contracts when both the nerve fibers are stimulated together with same strength of stimulus. It is called spatial summation. ii. Temporal Summation When one nerve fiber is stimulated repeatedly with subliminal stimuli, these stimuli are summed up to give response in the muscle. It is called temporal summation.
- 29. 4. OCCLUSION Occlusion is demonstrated in a flexor reflex involving a muscle, which is innervated by two motor nerves. These nerves can be called A and B. When both the nerves, A and B, are stimulated simultaneously, the tension developed by the muscle is less than the sum of the tension developed when each nerve is stimulated separately. Occlusion is due to the overlapping of the nerve fibers during the distribution. OCCLUSION
- 30. 5. SUBLIMINAL FRINGE In some reflexes involving the muscle with two nerve fibers, the tension developed by simultaneous stimulation of two nerves is greater than the sum of tension produced by the stimulation of these nerves separately. Thus, the tension here is greater than the sum of tension produced, if A and B are separately stimulated.This phenomenon is called subliminal fringe. . SUBLIMINAL FRINGE
- 31. 6. RECRUITMENT Recruitment is defined as the successive activation of additional motor units with progressive increase in force of muscular contraction. increase in force Recruitment is similar to the effect of temporal summation. When an excitatory nerve is stimulated for a long time, there is a gradual increase in the response of reflex activities.
- 32. 7. AFTER DISCHARGE After discharge is the persistence or continuation of response for some time even after cessation of stimulus. When a reflex action is elicited continuously for sometime and then the stimulation is stopped, the reflex activity (contraction) will be continued for sometime even after the stoppage of the stimulus. Echo Effect like
- 33. 8. REBOUND PHENOMENON Reflex activities can be forcefully inhibited for some time. But, when the inhibition is suddenly removed, the reflex activity becomes more forceful than before inhibition. It is called rebound phenomenon. Reason for this state of over excitation is not known. 9. FATIGUE When a reflex activity is continuously elicited for a long time, the response is reduced slowly and at one stage, the response does not occur. This type of failure to give response to the stimulus is called fatigue.
- 34. RECIPROCAL INHIBITION AND RECIPROCAL INNERVATION RECIPROCAL INHIBITION Reciprocal inhibition is one of the important features of both flexor and extensor reflexes. Usually, excitation of one group of muscles is associated with inhibition of another, i.e. antagonistic group of muscles on the same side. For example, when a flexor reflex is elicited, the flexor muscles are excited (contracted) and the extensor muscles are inhibited (relaxed) in that side. This phenomenon is called the reciprocal inhibition.
- 35. „SIGNIFICANCE OF RECIPROCAL INHIBITION Reciprocal inhibition and reciprocal innervation are very important in spinal reflexes, which are involved in locomotion. It helps in the forward movement of one limb while causing the backward movement of the opposite limb.
- 36. „REFLEXES IN MOTOR NEURON LESION „UPPER MOTOR NEURON LESION During upper motor neuron lesion, all the superficial reflexes are lost. Deep reflexes are exaggerated and the Babinski sign is positive. „LOWER MOTOR NEURON LESION During lower motor lesion, all the superficial and deep reflexes are lost.
- 37. RECIPROCAL INNERVATION SHERRINGTON LAW Neural mechanism involved in reciprocal inhibition was postulated by Sherrington. Hence, it is called Sherrington law of reciprocal innervation. According to this law, the reciprocal inhibition is due to segmental arrangement of afferent and efferent connections in the spinal cord. Afferent nerve fibers, which evoke flexor reflex in a limb, have connections with motor neurons supplying flexors and the motor neurons supplying the extensors of same side. Afferent nerve excites the motor neurons, which supply the flexors.
- 38. CROSSED EXTENSOR REFLEX Crossed extensor reflex is the withdrawal reflex in which the flexors of the withdrawing limb are excited (contracting) and extensors are inhibited (relaxed), while the opposite occurs in the other limb. For example, while eliciting a flexor reflex activity in a limb, that limb is flexed. Simultaneously the opposite limb is extended. This type of crossed extensor reflex is because of reciprocal inhibition. It occurs in upper motor neuron lesion.