Reflex activity, Reflex arc, Classification of reflexes

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In this blog, we will learn about reflex activity, reflex arc, and classification of reflexes.

This is very important and interesting topic. This is gift of God to us. Have you ever thought that why you pull your hand when unknowingly touches to hot water? why your eyes becomes closed when suddenly bright light comes to your eyes? why you close your eyes when insect comes nearer to your eyes? This is reflex activity, that you do without your consciousness. You not need any efforts or analysis to do so.

DEFINITION OF REFLEXES

Reflex activity is the response to a peripheral nervous stimulation that occurs without our consciousness. It is type of protective mechanism and it protects our body from irreparable damages.

This simply means that it is one kind of response to stimuli that occurs on their owns. We not need to analysis and not need to give commands for that. When we touches hot water unknowingly, we withdraw hand within millisecond due to this god gifted reflex activity. Particular pathway needed for this reflex activity, it is called reflex arc.

REFLEX ARC

nervous system reflex
diagram of reflex arc

Reflex arc is the anatomical nervous pathway for a reflex action. A simple reflex arc includes five components.

Receptor

Receptor is the end organ, which recieved the stimulation. When receptor is stimulated, impulses are generated in sensory nerve as shown in image. For example, your fingers are receptor when it touches to hot water.

Sensory nerve

Sensory nerve transmits impulse from the receptor to centre.

Centre

Centre means brain or spinal cord. When message reaches to centre. It return the message through motor nerve. 

Motor nerve

Motor nerve transmits the impulse from centre to effector organ. 

Effector organ

Effector organ is the structure such as muscle or gland where the activity occurs in response to stimuli. Eg. When your finger touches to hot water, it sends message to centre. Centre returns the message of withdrawal to that muscle.
This way reflex activity works & protects our body from harmful stimuli.

CLASSIFICATION OF REFLEXES

Reflexes are classified by six different methods depending upon various factors. 

  1. Inborn or aquired
  2. Anatomical classification
  3. Physiological classification (purpose)
  4. As per number of synapse
  5. Somatic or autonomic
  6. Clinical basis

1. INBORN OR AQUIRED REFLEXES

  1. Unconditional or inborn reflexes

    Inborn reflexes means these reflexes are present since the time of birth.
    These reflexes not required previous learning, training or conditioning.
    Eg. When we put drop of honey for first time in new born baby, child secrete the saliva. The baby does not know the taste of honey, but still saliva secreted.

  2. Conditioned reflexes

    Aquired reflexes are the reflexes that are developed after conditioning or training. These reflexes are not inborn but, aquired after birth. Such reflexes need previous training, learning or conditioning.
    Eg. Secretion of saliva by sight, smell, thought or even hearing of a known edible substance.

2. ANATOMICAL CLASSIFICATION

anatomical classification diagram

Reflexes are classified according to their situation of the centre.
Cerebellar reflex – centre in cerebellum
Cortical reflex – centre in cerebral cortex
Midbrain reflex – if centre in mid brain
Medullary reflex – if centre in medulla oblongata
Spinal reflex – centre in spinal cord

3. DEPENDING UPON PURPOSE
FLEXOR OR EXTENSOR REFLEX 

  1. Flexor reflexes
    Flexion means decreasing the joint angle. In this reflex, there at flexion at different joint so called flexor reflex. It is protective reflex which protect from harmful stimuli.Eg. When we unknowingly touch the hot water, we withdraw our hand immediately. At that time our joint angle decreases. So, its called flexor or withdrawal reflex.
  1. Extensor reflex
    Extension means increasing joint angle. In this reflex, there is extension at different joint so called extensor reflex. It is also called anti-gravity reflex because it protects body against gravitational force.

4. DEPENDING UPON THE NUMBER OF SYNAPSE

  1. Monosynaptic reflexes

    Monosynaptic reflexes means in reflex arc there is only one synapse. Stretch reflex is the best example of this reflex.

  2. Polysynaptic reflex

    Reflexes having more than one synapse in the reflex arc are called polysynaptic reflexes. Flexor or withdrawal reflex is best example of this reflex.

5. DEPENDING UPON WHETHER SOMATIC OR AUTONOMIC      REFLEXES

  1. Somatic reflexes

    Somatic reflexes are the reflexes, in which the reflex arc is formed by somatic nerve fibers. It involve the participation of skeletal muscles. There is flexion or extension at different joints during these reflexes.

  2. Autonomic reflexes

    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. It involves body organ, so also called visceral reflexes.

    Autonomic or visceral reflexes include papillary reflexes, gastrointestinal reflexes, cardiovascular reflexes, respiratory reflexes, etc. Some reflexes like swallowing, coughing or vomiting are considered as visceral reflexes.

6. DEPENDING UPON CLINICAL BASIS

According to this, it divide into four types:

  1. Superficial reflexes
  2. Deep reflexes
  3. Visceral reflexes
  4. Pathological reflexes

A. SUPERFICIAL REFLEXES

It is called superficial because reflex is elicited from the surface of the body. There are two types : mucous membrane reflexes and skin reflexes.

  1. Mucous membrane reflexes
    We mostly feel at some point of life. If irritation occurs to nose by dust or else, sneezing starts. It is one kind of mucous membrane reflex. Detail is mention in below chart.
  2. Skin reflexes
    Skin or cutaneous reflexes are elicited from skin by the stimulation of cutaneous receptors. Detail of these reflexes mention in below chart.

B. DEEP REFLEXES

Deep reflexes are elicited from deeper structure under the skin eg. like tendon. Neurophysician or genral practitioner do some test to find out what problem patient may have. Eg. If patient if suffering from cervical pain than bicep or tricep jerk is helpful to find out any abnormality in cervical region. 

Detail of deep reflexes mention in below chart.

C. VISCERAL REFLEXES

Following are the visceral reflexes

  1. Pupillary reflexes
  2. Oculocardiac reflex
  3. Carotid sinus reflex
i. PUPILLARY REFLEX
Light reflex

When ratina of the eye is stimulated by sudden flash of light, constriction of pupil occurs. It is called light reflex.

Accomodation reflex

Accomodation reflex means when eyes are fix on a distant object and if another object we bring nearer in front of the eye, than vision shifts from far object to near object. During that time there is constriction of pupil occur. So, we can see clearly the nearer object.

ii. OCULOCARDIAC REFLEX
Oculocardiac reflex is the reflex, in which heart rate decreases due to the pressure applied over eyeball.
iii. CAROTID SINUS REFLEX
carotid sinus reglex means when we give pressure around neck eg. tight collar, it decreases heart rate and blood pressure. 

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