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Reflexes, Reflex Arc, Reflex Time, Classification
Spinal Reflexes Reflexes, Reflex Arc, Reflex Time, Classification Spinal Reflexes April 4, 2019
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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
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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
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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
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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
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Reflex Arc Afferent pathway (sensory) Stimulus Receptor
Integrating centre Efferent pathway (motor) Effector organ Spinal Reflexes April 4, 2019
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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
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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
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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
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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
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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
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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
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Stretch Reflex Response: Contraction of the stretched muscle
Inhibition of the antagonist muscle Spinal Reflexes April 4, 2019
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Stretch Reflex Reflex Spinal phenomenon Very brief latency
No after discharge Spinal phenomenon Best developed in extensors Antigravity muscles Spinal Reflexes April 4, 2019
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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
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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
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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
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Sequence of Events Impulses from muscle spindles are also
Conducted to the antagonist muscle Causing inhibition Feed forward inhibition Spinal Reflexes April 4, 2019
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Knee Jerk Reflex Group Ia sensory fibres Stretch receptors
-Motor neuron Extensors Flexors Patella Spinal Reflexes April 4, 2019
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Receptors Stretch receptors (muscle spindles) Spindle shaped
Found in skeletal muscles Attached to skeletal muscle fibers Spinal Reflexes April 4, 2019
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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
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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
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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
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Muscle Spindles There are two types of intrafusal fibres Nuclear bag
Nuclear chain Nuclear chain Nuclear bag Spinal Reflexes April 4, 2019
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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
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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
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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
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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
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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 µm in diameter Secondary sensory fibers (gp II) Diameter 6 – 12 µm Gp II sensory fibres Nuclear bag Spinal Reflexes April 4, 2019
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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Flexion Reflex Response Withdrawal of stimulated limb
Extension of contra -lateral limb Crossed extensor reflex Spinal Reflexes April 4, 2019
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Withdrawal reflex Extensors inhibited Crossed extensor reflex
Flexors stimulated Extensors stimulated Noxious stimulus Flexors inhibited Spinal Reflexes April 4, 2019
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Flexion reflex (withdrawal reflex)
Ventral horn Dorsal horn Withdrawal from noxious stimulus Nociceptors Spinal Reflexes April 4, 2019
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