Neurophysiology Reflexes Department of Physiology

NEUROPHYSIOLOGY REFLEXES DEPARTMENT OF PHYSIOLOGY

DR. K. MEDAGODA REFLEX

• A RAPID AUTOMATIC RESPONSE TO A STIMULUS. • CARRIED OUT BY A RELATIVELY SIMPLE NEURAL CIRCUIT. • KNOWN AS - REFLEX ARC • CONSIDERED AS THE BASIC UNIT OF NEURAL ACTIVITY. • REFLEX ARC CONSISTS OF • A SENSE ORGAN • AFFERENT NEURON • ONE OR MORE CENTRAL SYNAPSES • AN EFFERENT NEURON • AN EFFECTOR ( MUSCLE,GLAND)

Dr Kushan Medagoda – Neurophysiology Reflexes REFLEX ARC

• AFFERENT FIBERS • TRAVEL ALONG THE DORSAL ROOTS OR CRANIAL NERVES . • CELL BODIES LIE IN THE DORSAL ROOT GANGLIA OR CRANIAL NERVE GANGLIA. • EFFERENT FIBERS • LEAVE VIA THE VENTRAL ROOTS OR CORRESPONDING MOTOR CRANIAL NERVES.

Dr Kushan Medagoda – Neurophysiology Reflexes THE REFLEX ARC

Dr Kushan Medagoda – Neurophysiology Reflexes TYPES OF REFLEXES

• MONOSYNAPTIC REFLEXES • DISYNAPTIC REFLEXES • POLYSYNAPTIC REFLEXES • MONOSYNAPTIC REFLEXES • HAS ONLY ONE SYNAPSE BETWEEN THE AFFERENT AND EFFERENT NEURONS E.G. STRETCH REFLEX • POLYSYNAPTIC REFLEXES • HAS ONE OR MORE INTERNEURONS BETWEEN AFFERENT AND EFFERENT NEURON. • HAS TWO OR MORE SYNAPSES IN THE ARC. • E.G. WITHDRAWAL REFLEX

Dr Kushan Medagoda – Neurophysiology Reflexes MONOSYNAPTIC REFLEXES THE STRETCH REFLEX

• WHEN A SKELETAL MUSCLE WITH AN INTACT NERVE SUPPLY IS STRETCHED, IT CONTRACTS. • STIMULUS -STRETCH OF THE MUSCLE • SENSE ORGAN -MUSCLE SPINDLE • AFFERENT -FAST SENSORY FIBERS • EFFERENT - MOTOR NEURONS • EFFECTOR- MUSCLE • EFFECT- CONTRACTION OF THE MUSCLE • IMPORTANT TO MAINTAIN THE MUSCLE TONE.

Dr Kushan Medagoda – Neurophysiology Reflexes MUSCLE SPINDLE- STRUCTURE

• CONSISTS OF ABOUT 10 MUSCLE FIBERS ENCLOSED IN A CONNECTIVE TISSUE CAPSULE. • HAS LESS DISTINCT STRIATIONS THAN THE REST OF THE MUSCLE FIBERS – NOT VERY CONTRACTILE • ARE CALLED INTRAFUSAL FIBERS

• REST OF THE MUSCLE FIBERS - EXTRAFUSAL FIBERS • EXTRAFUSAL FIBERS- REGULAR CONTRACTING FIBERS • SPINDLE IS ATTACHED PARALLEL TO THE EXTRAFUSAL FIBERS

Dr Kushan Medagoda – Neurophysiology Reflexes MUSCLE SPINDLE – STRUCTURE

• CONTAINS TWO TYPES OF FIBERS • * NUCLEAR BAG FIBERS - 2 FIBERS PER SPINDLE • HAS DILATED CENTRAL AREA • * NUCLEAR CHAIN FIBERS - 4 FIBERS PER SPINDLE • THINNER AND SHORTER • ENDS CONNECTED TO THE SIDES OF THE BAG FIBERS • ENDS OF THE INTRAFUSAL FIBERS ARE CONTRACTILE BUT PROBABLY NOT THE CENTRAL PORTION

Dr Kushan Medagoda – Neurophysiology Reflexes MUSCLE SPINDLE- AFERENTS

• SENSORY ENDINGS - AFFERENT FIBERS • TWO KINDS OF AFFERENTS • 1. IA PRIMARY AFFERENTS (ANNULOSPIRAL ENDINGS) • ONE BRANCH INNERVATES NUCLEAR BAG FIBER 1 • ONE BRANCH INNERVATES NUCLEAR BAG FIBER 2 AND NUCLEAR CHAIN FIBERS • THESE SENSORY FIBERS WRAP AROUND THE CENTER OF THE BAG AND CHAIN FIBERS • 2. SECONDARY AFFERENTS (FLOWER SPRAY ENDINGS) • GROUP II SENSORY FIBERS • LOCATED NEAR THE ENDS OF THE NUCLEAR CHAIN FIBERS ONLY

Dr Kushan Medagoda – Neurophysiology Reflexes MUSCLE SPINDLE- EFFERENTS

• MOTOR NERVE SUPPLY TO THE SPINDLE- EFFERENT FIBERS • HAVE THEIR OWN SUPPLY •  EFFERENT FIBERS • BELONGS TO A GROUP • CONSTITUTE 30% OF THE FIBERS IN THE VENTRAL ROOT • 3-6 M IN DIAMETER • SUPPLY EXCLUSIVELY NUCLEAR CHAIN AND BAG FIBERS • MOTOR NEURONS • INNERVATE BOTH INTRA AND EXTRAFUSAL FIBERS

Dr Kushan Medagoda – Neurophysiology Reflexes MUSCLE SPINDLE- STRUCTURE

Dr Kushan Medagoda – Neurophysiology Reflexes FUNCTION OF THE MUSCLE SPINDLE

• OPERATES TO MAINTAIN MUSCLE LENGTH • SENDS INFORMATION TO THE CNS ABOUT • I) MUSCLE LENGTH • II) RATE OF CHANGE IN MUSCLE LENGTH • WHEN A MUSCLE IS PASSIVELY STRETCHED IT INITIATES A REFLEX CONTRACTION OF THE EXTRAFUSAL FIBERS AND SHORTENING OF MUSCLE.

Dr Kushan Medagoda – Neurophysiology Reflexes FUNCTION OF THE MUSCLE SPINDLE

*** WHEN A MUSCLE IS PASSIVELY STRETCHED • SPINDLE GET STRETCHED • SENSORY ENDINGS (AFFERENTS) ARE DISTORTED • RECEPTOR POTENTIALS ARE GENERATED • SET UP ACTION POTENTIALS IN THE SENSORY FIBERS • STIMULATES MOTOR NEURONS TO THE EXTRAFUSAL FIBERS • CONTRACTION OF EXTRAFUSAL FIBERS • SHORTENING OF THE MUSCLE AND THE SPINDLE • MUSCLE LENGTH IS MAINTAINED

Dr Kushan Medagoda – Neurophysiology Reflexes FUNCTION OF THE MUSCLE SPINDLE

• THE RESPONSE PATTERN OF THE PRIMARY IA AFFERENT ENDINGS ON THE NUCLEAR BAG AND CHAIN FIBERS DIFFERS • DYNAMIC RESPONSE IN NUCLEAR BAG FIBERS • NERVE ENDINGS ON THE NUCLEAR BAG FIBERS DISCHARGE MOST RAPIDLY WHILE THE MUSCLE IS BEING STRETCHED • LESS RAPIDLY DURING SUSTAINED STRETCH • STATIC RESPONSE IN NUCLEAR CHAIN FIBERS • NERVE ENDINGS ON NUCLEAR CHAIN FIBERS DISCHARGE RAPIDLY THROUGH OUT THE PERIOD OF THE STRETCH • ** PRIMARY ENDINGS RESPONDS TO BOTH CHANGES IN THE LENGTH AND THE CHANGES IN THE RATE OF STRETCH

Dr Kushan Medagoda – Neurophysiology Reflexes EFFECTS OF GAMMA EFFERENT

• STIMULATION OF THE GAMMA EFFERENT • CONTRACTS THE CONTRACTILE ENDS OF THE INTRAFUSAL FIBERS • SHORTEN THE SPINDLE • STRETCHES THE NUCLEAR BAG PORTION • INITIATES IMPULSES IN THE IA AFFERENTS • REFLEX CONTRACTION OF THE EXTRAFUSAL FIBERS OCCURS • MUSCLE CAN BE CONTRACTED • VIA MOTOR NEURON STIMULATION • VIA GAMMA EFFERENT

Dr Kushan Medagoda – Neurophysiology Reflexes EFFECTS OF GAMMA EFFERENT

•  EFFERENT INCREASES MUSCLE SPINDLE SENSITIVITY TO STRETCH • WHEN RATE OF  EFFERENT DISCHARGE INCREASES • INTRAFUSAL FIBERS BECOME SHORTER • WITH STRETCHING OF THE MIDDLE PORTION OF THE BAG FIBER • PASSIVE STRETCHING OF THE MUSCLE • ADDITIONAL STRETCHING OF THE NUCLEAR BAG PORTION • INCREASED DISCHARGE IN THE IA FIBERS

Dr Kushan Medagoda – Neurophysiology Reflexes FUNCTION OF THE MUSCLE SPINDLE

Dr Kushan Medagoda – Neurophysiology Reflexes CONTROL OF GAMMA EFFERENT DISCHARGE

• INFLUENCED BY • 1. DESCENDING TRACTS FROM THE BRAIN • 2. ANXIETY • 3. SKIN STIMULATION IN GUARDING REFLEX

• ALPHA – GAMMA LINKAGE • INCREASED  DISCHARGE WITH ALPHA MOTOR NEURON DISCHARGE • SPINDLE DISCHARGE CONTINUE THROUGHOUT THE CONTRACTION

Dr Kushan Medagoda – Neurophysiology Reflexes RECIPROCAL INNERVATION

• WHEN A STRETCH REFLEX OCCURS • THE MUSCLE CONTRACTS • AGONISTS ARE STIMULATED • AND THE MUSCLES THAT ANTAGONIZES THE ACTION HAS TO BE RELAXED • IMPULSES IN THE IA FIBERS VIA A COLLATERAL BRANCH CAUSES POSTSYNAPTIC INHIBITION OF THE ANTAGONIZING MOTOR NEURONS

Dr Kushan Medagoda – Neurophysiology Reflexes RECIPROCAL INNERVATION

Dr Kushan Medagoda – Neurophysiology Reflexes INVERSE STRETCH REFLEX (DISYNAPTIC REFLEX)

• RELAXATION OF THE MUSCLE IN RESPONSE TO EXCESSIVE STRETCHING • UP TO A POINT GREATER THE STRETCHING HARDER THE CONTRACTION • BUT WHEN EXCESSIVE STRETCHING OCCURS MUSCLE RELAXATION OCCURS • RECEPTOR- GOLGI TENDON ORGAN • AFFERENT - IB FIBERS • STIMULATION BY PASSIVE STRETCH OR ACTIVE CONTRACTION • RESULTS INHIBITION OF ALPHA MOTOR NEURONS • VIA A INHIBITORY INTERNEURONE • ALSO STIMULATES NEURONS OF ANTAGONIZING MUSCLE

Dr Kushan Medagoda – Neurophysiology Reflexes INVERSE STRETCH REFLEX

Dr Kushan Medagoda – Neurophysiology Reflexes • REACTION TIME (HUMAN 19-24MS) • TIME BETWEEN APPLICATION OF THE STIMULUS AND THE RESPONSE • CENTRAL DELAY • TIME TAKEN FOR THE REFLEX ACTIVITY TO TRAVERSE THE SPINAL CORD • MUSCLE TONE • RESISTANCE OF A MUSCLE TO STRETCH • DECREASED RESISTANCE- FLACCID- HYPOTONIC • INCREASED RESISTANCE - SPASTIC- HYPERTONIC

Dr Kushan Medagoda – Neurophysiology Reflexes • LENGTHENING REACTION • IN HYPERTONIC MUSCLES • MODERATE STRETCH - MUSCLE CONTRACTION • EXCESSIVE STRETCH - MUSCLE RELAXATION • USUALLY ELICITED BY PASSIVE FLEXION OF ELBOW • INITIALLY RESISTANCE COMES AND WITH FURTHER STRETCHING RESISTANCE SUDDENLY COLLAPSES • KNOWN AS CLASP KNIFE EFFECT • CLONUS • REGULAR SUSTAINED RHYTHMIC CONTRACTION OF A MUSCLE SUBJECTED TO SUDDEN STRETCH • DUE TO INCREASE GAMMA EFFERENT DISCHARGE

Dr Kushan Medagoda – Neurophysiology Reflexes STRETCH REFLEX

• HAS RAPIDLY CONDUCTING AFFERENT AND EFFERENT FIBERS • MONOSYNAPTIC • HAS A SHORT LATENCY • E.G. TENDON REFLEXES

Dr Kushan Medagoda – Neurophysiology Reflexes POLYSYNAPTIC REFLEXES

• COMPLEX • INVOLVING NUMBER OF SYNAPSES • PROLONGED RESPONSES ARE SEEN WITH A SINGLE STIMULUS • E.G. WITHDRAWAL REFLEX