Reflexes, Reflex Arc, Reflex Time, Classification Spinal Reflexes Reflexes, Reflex Arc, Reflex Time, Classification Spinal Reflexes April 4, 2019

Spinal Reflexes Nervous activity consists of passage of nerve impulses from one nerve cells to another Simplest reaction of nervous system is that in which External stimulus is immediately followed by a response of the organism Spinal Reflexes April 4, 2019

Spinal Reflexes For this to occur there must be A receptor An integrating center An effecter organ A conducting pathway to carry the impulses from one to the other Spinal Reflexes April 4, 2019

Reflex Action An involuntary stereotyped coordinated response to a specific form of a sensory stimulus Stimulus produces a response without Any conscious or voluntary effort Examples Corneal reflex, cough reflex, withdrawal reflex, swallowing reflex, knee jerk reflex Spinal Reflexes April 4, 2019

Reflex Arc Series of neuronal network required for the elicitation of the reflex action For spinal reflexes you have the following essential elements Sensory limb Motor limb Most spinal reflexes also have one or more interneurons Spinal Reflexes April 4, 2019

Reflex Arc Afferent pathway (sensory) Stimulus Receptor Integrating centre Efferent pathway (motor) Effector organ Spinal Reflexes April 4, 2019

Reflex Arc The sensory limb include It extends Dorsal root Receptor Afferent (sensory neuron) It extends From the skin (or other receptor location) To gray matter of spinal cord Synapses with another neuron Dorsal root Interneuron Anterior Horn Cell Ventral root Effector Spinal Reflexes Receptor April 4, 2019

Reflex Arc Motor limb includes Motor (efferent) neuron Effector organ Skeletal muscle Smooth muscle Heart Gland Dorsal root Interneuron Anterior Horn Cell Ventral root Effector Spinal Reflexes Receptor April 4, 2019

Reflex Arc Motor limb extends From ventral horn of gray matter By way of ventral root To the location of effector Dorsal root Interneuron Anterior Horn Cell Ventral root Effector Spinal Reflexes Receptor April 4, 2019

Reflex Arc Time between Depends on onset of stimulus & Action of effector Depends on Speed of conduction of sensory and motor nerves Dorsal root Interneuron Anterior Horn Cell Ventral root Effector Spinal Reflexes Receptor April 4, 2019

Reflex Arc Also depends on Central delay Synaptic conduction time Number of synapses Dorsal root Interneuron Anterior Horn Cell Ventral root Effector Spinal Reflexes Receptor April 4, 2019

Stretch Reflex Control mechanism for the regulation of muscle length All skeletal muscle exhibit stretch reflex of some degree Stimulus Stretch, vibration Receptor Stretch receptors (muscle spindles) Spinal Reflexes April 4, 2019

Stretch Reflex Response: Contraction of the stretched muscle Inhibition of the antagonist muscle Spinal Reflexes April 4, 2019

Stretch Reflex Reflex Spinal phenomenon Very brief latency No after discharge Spinal phenomenon Best developed in extensors Antigravity muscles Spinal Reflexes April 4, 2019

Sequence of Events Stretch of the muscle Stretches receptor’s (muscle spindle’s) central portion Stimulating group Ia sensory fibers Spinal Reflexes April 4, 2019

Sequence of Events Impulses originating from the muscle spindle Conducted to CNS by fast sensory fibers (Ia) Pass directly to AHC making a monosynaptic contact Excite the AHC (alpha motor neuron) Spinal Reflexes April 4, 2019

Sequence of Events Leading to contraction of stretched muscle Shortening the stretched muscle Reflex maintenance of muscle length Important for reflex maintenance of posture Spinal Reflexes April 4, 2019

Sequence of Events Impulses from muscle spindles are also Conducted to the antagonist muscle Causing inhibition Feed forward inhibition Spinal Reflexes April 4, 2019

Knee Jerk Reflex Group Ia sensory fibres Stretch receptors -Motor neuron Extensors Flexors Patella Spinal Reflexes April 4, 2019

Receptors Stretch receptors (muscle spindles) Spindle shaped Found in skeletal muscles Attached to skeletal muscle fibers Spinal Reflexes April 4, 2019

Muscle Spindle Skeletal muscle fibers (extrafusal fibers) Muscle spindles with spindle shaped capsule Inside the capsule are small muscle fibers (intrafusal fibers) Spinal Reflexes April 4, 2019

Muscle Spindles The number of spindles/gm of muscle Varies widely according to function Eye muscle 130 spindle/gm Small digital muscles 119 spindles/gm Large muscles (gastrocnemius) 5 spindles/gm Spinal Reflexes April 4, 2019

Muscle Spindles Each spindle is enclosed in a connective tissue sheath (capsule) Inside the capsule are 2 to 12 small muscle fibers (intrafusal fibers) Nuclear chain Nuclear bag Spinal Reflexes April 4, 2019

Muscle Spindles There are two types of intrafusal fibres Nuclear bag Nuclear chain Nuclear chain Nuclear bag Spinal Reflexes April 4, 2019

Muscle Spindles Nuclear bag fibres Nuclear chain fibres All nuclei are collected at a central bag Nuclear chain fibres Nuclei are spread throughout the muscle fibre Nuclear bag Spinal Reflexes April 4, 2019

Muscle Spindles Motor innervation Gamma motor neuron Gamma fibres Gp Ia sensory fibre Nuclear chain Motor innervation Gamma motor neuron Small fibres 3 to 8µm in diameter End on muscle spindles Gamma static Gamma dynamic Gp II sensory fibres Nuclear bag Spinal Reflexes April 4, 2019

Muscle Spindles Gamma static Influence chiefly nuclear chain Gamma fibres Gp Ia sensory fibre Nuclear chain Gamma static Influence chiefly nuclear chain To increase response of sensory receptor Respond to certain muscle Length or Degree of stretch Gp II sensory fibres Nuclear bag Spinal Reflexes April 4, 2019

Muscle Spindles Gamma dynamic Gamma fibres Gp Ia sensory fibre Nuclear chain Gamma dynamic Selectively connect to nuclear bag fibers Increase response to primary spindle ending Respond to the velocity of lengthening Gp II sensory fibres Nuclear bag Spinal Reflexes April 4, 2019

Muscle Spindles Sensory innervations Primary sensory fibers (gp Ia) Gamma fibres Gp Ia sensory fibre Nuclear chain Sensory innervations Primary sensory fibers (gp Ia) Large fibers 12 - 20µm in diameter Secondary sensory fibers (gp II) Diameter 6 – 12 µm Gp II sensory fibres Nuclear bag Spinal Reflexes April 4, 2019

Spindle Activity Stretch of the extrafusal fiber Ia fibres Stretch of the extrafusal fiber Stretches the muscle spindle Stimulates the receptors Impulses relayed to spinal cord via group Ia afferents γ MN α MN α MN to antagonist Extrafusal fibre Spinal Reflexes April 4, 2019

Spindle Activity Makes monosynaptic connection Ia fibres Makes monosynaptic connection To α MN innervating the stretched muscle Causing it to contract γ MN α MN α MN to antagonist Extrafusal fibre Spinal Reflexes April 4, 2019

Spindle Activity It also makes connection to an inter neuron which Ia fibres It also makes connection to an inter neuron which inhibit α MN of antagonist muscle Causing the relaxation of antagonist muscle γ MN α MN α MN to antagonist Extrafusal fibre Spinal Reflexes April 4, 2019

α MN and γ MN activation  MN and γ MN receive supra spinal impulses Ia fibres  MN and γ MN receive supra spinal impulses Corticospinal tract Rubrospinal tract Reticulospinal tract Vestibulospinal tract γ MN α MN α MN to antagonist Extrafusal fibre Spinal Reflexes April 4, 2019

MN and γ MN activation Muscle contraction can occur as a result of Ia fibres Muscle contraction can occur as a result of Activation of α MN from supra spinal sources Activation of γ MN from supra spinal sources γ MN α MN α MN to antagonist Extrafusal fibre Spinal Reflexes April 4, 2019

α MN and γ MN activation Activation of γ MN lead to Ia fibres Activation of γ MN lead to Contraction of two ends of the intrafusal fibres This stretches the central portion Causes activation of receptor γ MN α MN α MN to antagonist Extrafusal fibre Spinal Reflexes April 4, 2019

α MN and γ MN activation Sensory impulses conducted to Ia fibres Sensory impulses conducted to Spinal cord to the α MN innervating the extrafusal muscle fiber Causing it to contract γ MN α MN α MN to antagonist Extrafusal fibre Spinal Reflexes April 4, 2019

Golgi Tendon Organ Excessive contraction of muscle Golgi organ Excessive contraction of muscle Develops high tension in the tendons Potentially dangerous Golgi tendon organs stimulated Ib fibres γ MN α MN α MN to antagonist Extrafusal fibre Spinal Reflexes April 4, 2019

Golgi Tendon Organ Golgi organ Sensory impulses relayed to spinal cord via Ib causing Inhibition of α MN innervating the contracting muscle Causing it to relax Ib fibres γ MN α MN α MN to antagonist Extrafusal fibre Spinal Reflexes April 4, 2019

Golgi Tendon Organ Golgi organ Stimulation of α MN innervating the antagonist muscles Causing contraction Ib fibres γ MN α MN α MN to antagonist Extrafusal fibre Spinal Reflexes April 4, 2019

The Flexor Reflex Application of noxious stimulus Reflex pattern Induces flexion upwards and away from the stimulus Reflex pattern Facilitation of flexor muscles Inhibition of extensor muscles of the stimulated limb Spinal Reflexes April 4, 2019

Flexor Reflex If the stimulus intensity increases Flexion response becomes more marked (ankle, knee, hip) Irradiation of reflex More synergist MN pool are excited More antagonist MN pools are inhibited Spinal Reflexes April 4, 2019

Flexor Reflex When the stimulus is interrupted Leg does not return abruptly to its original position It extends gradually Certain amount of after discharge Spinal Reflexes April 4, 2019

Flexion Reflex Response Withdrawal of stimulated limb Extension of contra -lateral limb Crossed extensor reflex Spinal Reflexes April 4, 2019

Withdrawal reflex Extensors inhibited Crossed extensor reflex Flexors stimulated Extensors stimulated Noxious stimulus Flexors inhibited Spinal Reflexes April 4, 2019

Flexion reflex (withdrawal reflex) Ventral horn Dorsal horn Withdrawal from noxious stimulus Nociceptors Spinal Reflexes April 4, 2019