HumanreflexesHumanreflexes By: Dr. Khaled Ibrahim Lecturer of Physiology Mansoura Faculty of Medicine By: Dr. Khaled Ibrahim Lecturer of Physiology Mansoura.

Humanreflexes

By: Dr. Khaled IbrahimLecturer of Physiology

Mansoura Faculty of Medicine

HUMAN REFLEXES

Definition: It is involuntary response of an organ to a stimulus. It is the functional unit of the nervous system. The Spinal Reflex Pathway : = The Reflex Arc- It is the arrangement of neurons through which the reflex is

carried out.

- It is usually formed of:

1) Afferent (sensory) neuron.

2) An interneuron (may be absent).

3) nerve center (cell body of the efferent neuron).

4) Efferent (motor) neuron.N.B.: Synapses are present < > different neurons in the reflex arc. All human reflexes are polysynaptic except the stretch reflex which is monosynaptic as it contains no interneurons.

Classification of Human Reflexes

Human Reflexes

Conditioned reflexes- Acquired reflexes.

-seeing, smelling, hearing or even thinking of the stimulus in its

absence causes the response.

-requires intact cortex & previous

training.

Unconditioned reflexes

Spinal (see

later)

Medullary-

Cardiovascular reflexes: HR & ABP.

- Respiratory functions: Herring-

Bruer reflex.- Digestive functions: Swallowing & vomiting.

Midbrain- Visual

reflexes as pupillary

light reflex.- Postural reflexes: righting

reactions.

Hypothalamic

- Hunger.- thirst.

- Regulation of body

temperature.

Pupillary Light Reflex

Baroreceptor Reflex

Spinal Reflexes- Their center is present in the

spinal ventral horn.

- Classified according to the site of receptor into:

1) Superficial:

- Their receptor are present on the body surface (skin, cornea, conjunctiva,….).

- Example:

Planter reflex.

Flexion withdrawal reflex.

Crossed extensor reflex.

Abdominal reflex.

2) Deep:

- Their receptor are present in deep structures (skeletal

muscle, tendons, ……).

- Examples:

Stretch reflex.

3) Visceral:

- Their receptor are present in the viscera.

- Examples:

Micturition reflex.

Defecation reflex.

Erection reflex.

1) In normal subjects , the response consists of plantar flexion of all the toes .

Planter Reflex- Scratch of the sole of the foot along its lateral margin, from the heal toward the toes will result in:

2) Babinski sign is an abnormal response of the plantar reflex, named after the Polish physician. It consists of dorsiflexion of the big toe and separation (or fanning out) of the other four toes

2- Pathological causes: Upper Motor Neuron Lesion (UMNL) which is lesion in higher motor areas or descending motor tracts.

Babinski sign may be due to:

1- Physiological causes: Newly born infants during the first few months of their life, because during this period the corticospinal tract fibers are not yet completely myelinated or functioning. Normal adults under conditions in which the cerebral cortical function is considerably depressed, such as during general anesthesia, coma, or even deep sleep.

N.B.: Center of planter reflex is present in spinal ventral horn of 1st sacral spinal segment (S1)

Flexion Withdrawal Reflex Crossed Extensor Reflex

- They are reflexes that move the affected portions of the body away from a source of painful stimulation. - When a strong painful stimulus applied to one lower limb, flexion of one limb is accompanied with extension of the contralateral one. Mechanism & pathway: see illustration

Importance

1) Withdrawal reflexes are of survival value because they help to immediately remove the stimulated part of the body away from sources of painful stimuli that could be harmful to the individual. Thus, it is prepotent.

2) Crossed extensor are of postural value as it supports the body weight which is shifted to the other limb. Otherwise, the subject may lose the equilibrium & fall to the ground.

Micturition Reflex

- Distention of urinary bladder with urine will result in reflex evacuation of the bladder (Micturition).

Mechanism & pathway:

Receptors: stretch (receptor) in the wall of bladder. Center: sacral segments 2, 3 & 4. Afferent & efferent: pelvic nerve. Response:

Contraction of detrusor muscle (body). Relaxation of internal sphincter of urethra.Relaxation of external urethral sphincter via the pudendal nerve

which is somatic nerve originating from AHC of sacral segment 2, 3, & 4.

N.B.: This reflex is automatic in infants below 2 years BUT in adults it is under voluntary control.

Infants Adults

Definition:

Tapping of the tendon of a skeletal muscle (using a medical hammer) results in brief contraction followed by rapid relaxation.

Mechanism:

Tendon Jerk

Receptor: Nuclear bag.

Afferent: 1ry endings.

Center: α-MNs of the stretched skeletal muscle

Efferent: Thick myelinated type Aα nerve fiber

Response: brief contraction followed by rapid relaxation.

Efferent (Motor) Innervation:

- Supplies the peripheral contractile parts on the intrafusal muscle fibers.

- Their cell bodies are located in gamma motor neurons (-MNs) which are

the small AHCs (30% of AHCs).

- Stimulation of -MNs -----> afferent impulses along -afferent fibers -----

> contraction of the peripheral contractile parts of the intrafusal muscle

fibers stretch of the central (receptor) part ------> depolarization of the

central part -----> action potential & impulse discharge along 1ry & 2ry

endings ----> stimulation of α-MNs innervating the stretched muscle -----

> muscle contraction (stretch reflex).

Examples of Tendon Jerks:

Tapping of Contraction of Movement Center

The Knee Jerk

The Ankle Jerk

The Biceps Jerk

The Triceps Jerk

patellar tendon

tendo-achilles

biceps tendon

triceps tendon

quadriceps femoris

gastrocnemius & soleus

biceps muscle

triceps muscle

Extension of the knee

plantar flexion of the foot flexion of the arm at the elbow jointextension of the arm at the elbow joint

L 2,3,4

S 1,2

C 5,6

C 6,7

Clinical Significance of the Tendon Jerks:

a) Assess the Integrity of Reflex Pathways of the Tendon Jerks:

Absent tendon jerk indicates damage of any part of the reflex pathway which may be:

- Lesion of the afferent as in Tabes dorsalis.- Lesion in the nerve center as in poliomyelitis.- Lesion in the efferent as in trauma.

b) Localize the level of the lesion in the nervous system.

c) Examine the State of the Supraspinal Centers:

- Exaggerated tendon jerks indicate damage of Supraspinal inhibitory centers.- Inhibited tendon jerks indicate damage of Supraspinal facilitatory centers.

Hyperactive Tendon Jerks(Exaggerated)

Hypoactive Tendon Jerks(Inhibited)

i.e., TJ becomes faster and stronger than normal. It is due to ↑supraspinal facilitation of -

MNs, ----> ↑sensitivity of muscle spindles to the stretch.

May be: a) physiological: anxiety & nerotic persons.b) Pathological: tetany, lesions in any of the

supraspinal inhibitory centers.

i.e., TJ becomes delayed and weaker than normal. It is due to ↓ supraspinal facilitation of -MNs, ----> ↓ sensitivity of muscle spindles to the stretch May be: a) physiological: sleep, anaethesiab) Pathological: coma, lesions in any of the

supraspinal facilitatory centers.

Clonus- It is regular rhythmic contractions of a muscle.- It is a sign of increased supraspinal facilitation.- It is produced by applying a sudden maintained stretch on the tendon of a muscle -----> regular rhythmic contractions that continue as long as the stretch is applied. - Clinically, clonus has 2 types:a) Patellar Clonus:- initiated by grasping the patella inbetween the examiner’s fingers, then applying a sudden maintained downward pull. - This causes clonic contractions of the quadriceps muscle, producing rhythmic oscillation of the patella.

- initiated by applying a sudden maintained dorsi-flexion of the foot. - This causes clonic contractions of the calf muscles causing regular rhythmic plantar flexions of the foot.

b) Ankle Clonus:

The Reflex Hammer

You will need to use a reflex hammer when performing this aspect of the exam. A number of the most commonly used models are pictured below. Regardless of the hammer type, proper technique is critical. The larger hammers have weighted heads, such that if you raise them approximately 10 cm from the target and then release, they will swing into the tendon with adequate force. The smaller hammers should be swung loosely between thumb and forefinger.

Medical

Hammer

The muscle group to be tested must be in a neutral position (i.e. neither stretched nor contracted) (= semiflexed & in dependent position).

The muscle group to be tested must be exposed.

The tendon attached to the muscle(s) which is/are to be tested must be clearly identified. If you are having trouble locating the tendon, ask the patient to contract the muscle to which it is attached. When the muscle shortens, you should be able to both see and feel the cord like tendon, confirming its precise location.

Technique

Strike the tendon with a single, brisk, stroke. While this is done firmly, it should not elicit pain. Occasionally, due to other medical problems (e.g. severe arthritis), you will not be able to position the patient's arm in such a way that you are able to strike the tendon. If this occurs, do not cause the patient discomfort. Simply move on to another aspect of the exam.

The vigor of contraction is graded on the following scale:0 No evidence of contraction.1+ Decreased, but still present (hypo-reflexic)2+ Normal3+ Super-normal (hyper-reflexic)4+ Clonus: Repetitive shortening of the muscle after a single stimulation

If you are unable to elicit a reflex, stop and consider the following:1) Are you striking in the correct place? Confirm the location of the tendon by observing and palpating the appropriate region while asking the patient to perform an activity that causes the muscle to shorten, making the attached tendon more apparent.

2) Make sure that your hammer strike is falling directly on the appropriate tendon. If there is a lot of surrounding soft tissue that could dampen the force of the strike, place a finger firmly on the correct tendon and use that as your target.

3) Make sure that the muscle is uncovered so that you can see any contraction (occasionally the force of the reflex will not be sufficient to cause the limb to move).

4) Reinforcement is accomplished by asking the patient to clench their teeth, or if testing lower extremity reflexes, have the patient hook together their flexed fingers and pull apart. This is known as the Jendrassik maneuver.

Sometimes the patient is unable to relax, which can inhibit the reflex even when all is neurologically intact. If this occurs during your assessment of lower extremity reflexes, ask the patient to interlock their hands and direct them to pull, while you simultaneously strike the tendon. This sometimes provides enough distraction so that the reflex arc is no longer inhibited.

Occasionally, it will not be possible to elicit reflexes, even when no neurological disease exists. This is most commonly due to a patient's inability to relax. In these settings, the absence of reflexes are of no clinical consequence. This assumes that you were thorough in your history taking, used appropriate examination techniques.

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