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84 Cards in this Set
- Front
- Back
Peripheral Nervous System (PNS) includes what?
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all neural structures outside the brain and spinal cord
Includes sensory receptors, peripheral nerves, associated ganglia, and motor endings Provides links to and from the external environment |
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Sensory Receptors
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Structures specialized to respond to stimuli
The realization of these stimuli, sensation and perception, occur in the brain |
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The activation of sensory receptors results in:
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depolarizations that trigger impulses to the CNS
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Receptor Classification by Stimulus TYPE
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Mechanoreceptors
Thermoreceptors Photoreceptors Chemoreceptors Nociceptors |
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Mechanoreceptors
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respond to touch, pressure, vibration, stretch, and itch
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Thermoreceptors
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sensitive to changes in temperature
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Photoreceptors
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respond to light energy (e.g., retina)
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Chemoreceptors
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respond to chemicals (e.g., smell, taste, changes in blood chemistry)
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Nociceptors
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sensitive to pain-causing stimuli
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Receptor Class by Location: Exteroceptors
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-Respond to stimuli arising outside the body
-Found near the body surface -Sensitive to touch, pressure, pain, and temperature -Include the special sense organs |
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Receptor Class by Location: Interoceptors
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Respond to stimuli arising within the body
Found in internal viscera and blood vessels Sensitive to chemical changes, stretch, and temperature changes |
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Receptor Class by Location: Proprioceptors
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Respond to degree of stretch of the organs they occupy
Found in skeletal muscles, tendons, joints, ligaments, and connective tissue coverings of bones and muscles Constantly “advise” the brain of one’s movements |
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Receptor Classification by Structural Complexity
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Receptors are structurally classified as either simple or complex
Most receptors are simple and include encapsulated and unencapsulated varieties Complex receptors are special sense organs |
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Free dendritic nerve endings
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Simple Receptors: Unencapsulated
Respond chiefly to temperature and pain |
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Merkel (tactile) discs
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Simple Receptors: Unencapsulated
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Hair follicle receptors
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Simple Receptors: Unencapsulated
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Meissner’s corpuscles (tactile corpuscles)
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Simple Receptors: Encapsulated
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Pacinian corpuscles (lamellated corpuscles)
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Simple Receptors: Encapsulated
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Ruffini’s corpuscles
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Simple Receptors: Encapsulated
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Sensation & Perception
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Survival depends on both
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Sensation is:
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the awareness of changes in the internal and external environment
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Perception is:
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the conscious interpretation of those stimuli
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Organization of the Somatosensory System
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Input comes from exteroceptors, proprioceptors, and interoceptors
outside, inside or where your body is in space |
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The three main levels of neural integration in the somatosensory system are:
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Receptor level – the sensory receptors
Circuit level – ascending pathways Perceptual level – neuronal circuits in the cerebral cortex |
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Processing at the Receptor Lever
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The receptor must have specificity for the stimulus energy
The receptor’s receptive field must be stimulated Stimulus energy must be converted into a graded potential A generator potential in the associated sensory neuron must reach threshold |
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Adaptation of Sensory Receptors
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Adaptation occurs when sensory receptors are subjected to an unchanging stimulus-
*Receptor membranes become less responsive *Receptor potentials decline in frequency or stop |
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Adaptation of Sensory Receptors
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Receptors responding to pressure, touch, and smell adapt quickly
Receptors responding slowly include Merkel’s discs, Ruffini’s corpuscles, and interoceptors that respond to chemical levels in the blood Pain receptors and proprioceptors do not exhibit adaptation |
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Processing at the Circuit Level
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Chains of three neurons conduct sensory impulses upward to the brain
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First-order neurons
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conduct impulses from the skin to the spinal cord or brain stem
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Second-order neurons
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transmit impulses to the thalamus or cerebellum
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Third-order neurons
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conduct impulses to the somatosensory cortex of the cerebrum
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Main Aspects of Sensory Perception:
Perceptual detection |
detecting that a stimulus has occurred from several receptors
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Main Aspects of Sensory Perception:
Magnitude estimation |
how intense the stimulus is
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Main Aspects of Sensory Perception:
Spatial discrimination |
identifying the site or pattern of the stimulus (two point discrimination)
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Main Aspects of Sensory Perception:
Feature abstraction |
used to identify a substance that has specific texture or shape
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Main Aspects of Sensory Perception:
Quality discrimination |
the ability to identify submodalities of a sensation (e.g., sweet or sour tastes)
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Main Aspects of Sensory Perception:
Pattern recognition |
ability to recognize patterns in stimuli (e.g., melody, familiar face)
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Classification of Nerves
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Sensory and motor divisions
Sensory (afferent) – carry impulse to the CNS Motor (efferent) – carry impulses from CNS Mixed – sensory and motor fibers carry impulses to and from CNS; most common type of nerve |
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Number of Cranial Nerves?
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12 pairs arise from the brain
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Characteristics of cranial nerves:
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They have sensory, motor, or both sensory and motor functions
Each nerve is identified by a number (I through XII) and a name Four cranial nerves carry parasympathetic fibers that serve muscles and glands |
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Cranial Nerve I
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Olfactory- SMELL
carrying afferent impulses for the sense of smell |
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Cranial Nerve II
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Optic- VISION
carrying afferent impulses for vision Arises from the retina of the eye |
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Cranial Nerve III
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Oculomotor
Functions in raising the eyelid, directing the eyeball, constricting the iris, and controlling lens shape Fibers supply the extrinsic eye muscles |
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Cranial Nerve IV
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Trochlear
Fibers innervate the superior oblique muscle Primarily a motor nerve that directs the eyeball |
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Cranial Nerve V
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Trigeminal
Conveys sensory impulses from various areas of the face (V1) and (V2), and supplies motor fibers (V3) for mastication |
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3 divisions of Cranial Nerve V: Trigeminal
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ophthalmic (V1),
maxillary (V2), mandibular (V3) |
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Cranial Nerve VI
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Abducuens- ABducts the eye
Primarily a motor nerve innervating the lateral rectus muscle (abducts the eye) |
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Cranial Nerve VII
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Facial
Mixed nerve with five major branches Motor functions include facial expression, and the transmittal of autonomic impulses to lacrimal and salivary glands Sensory function is taste from the anterior two-thirds of the tongue |
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Cranial Nerve VIII
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Vestibulocochlear
*Functions are solely sensory – equilibrium and hearing Fibers arise from the hearing and equilibrium apparatus of the inner ear Two divisions – cochlear (hearing) and vestibular (balance) |
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Cranial Nerve IX
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Glossopharyngeal
Fibers run to the throat Nerve IX is a mixed nerve with motor and sensory functions |
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Motor function of Cranial Nerve IX
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innervates part of the tongue and pharynx, and provides motor fibers to the parotid salivary gland
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Sensory function of Cranial Nerve IX
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fibers conduct taste and general sensory impulses from the tongue and pharynx
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Cranial Nerve X
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Vagus
The only cranial nerve that extends beyond the head and neck The vagus is a mixed nerve |
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Motor function of Cranial Nerve X
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Most motor fibers are parasympathetic fibers to the heart, lungs, and visceral organs
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Sensory function of Cranial Nerve X
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Its sensory function is in taste
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Cranial Nerve XI
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Accessory
Primarily a motor nerve -Supplies fibers to the larynx, pharynx, and soft palate -Innervates the trapezius and sternocleidomastoid, which move the head and neck |
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Cranial Nerve XII
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Hypoglossal
Innervates both extrinsic and intrinsic muscles of the tongue, which contribute to swallowing and speech |
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Spinal Nerves
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Thirty-one pairs of mixed nerves arise from the spinal cord and supply all parts of the body except the head
They are named according to their point of issue |
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Cervical Spinal Nerves
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8 cervical (C1-C8)
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Thoracic Spinal Nerves
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12 thoracic (T1-T12)
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Lumbar Spinal Nerves
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5 Lumbar (L1-L5)
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Sacral Spinal Nerves
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5 Sacral (S1-S5)
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Coccygeal Spinal Nerves
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1 Coccygeal (C0)
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Spinal Nerves: Roots
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Each spinal nerve connects to the spinal cord via two medial roots
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Ventral roots contain:
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motor (efferent) fibers
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Dorsal roots contain:
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sensory (afferent) fibers
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Dermatomes
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A dermatome is the area of skin innervated by the cutaneous branches of a single spinal nerve
All spinal nerves except C1 participate in dermatomes |
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Reflexes
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A reflex is a rapid, predictable motor response to a stimulus
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Reflexes may:
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Be inborn (intrinsic) or learned (acquired)
Involve only peripheral nerves and the spinal cord Involve higher brain centers as well |
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Reflex Arc
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There are five components of a reflex arc:
-Receptor -Sensory neuron -Integration center -Motor neuron -Effector |
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Reflex Arc:
Receptor |
site of stimulus
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Reflex Arc:
Sensory neuron |
transmits the afferent impulse to the CNS
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Reflex Arc:
Integration center |
either monosynaptic or polysynaptic region within the CNS
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Reflex Arc:
Motor neuron |
conducts efferent impulses from the integration center to an effector
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Reflex Arc:
Effector |
muscle fiber or gland that responds to the efferent impulse
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For skeletal muscles to perform normally:
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The Golgi tendon organs (proprioceptors) must constantly inform the brain as to the state of the muscle
Stretch reflexes initiated by muscle spindles must maintain healthy muscle tone |
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Muscle Spindles are wrapped with 2 types of Afferent endings:
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primary sensory endings of type Ia fibers and secondary sensory endings of type II fibers
These regions are innervated by gamma (γ) efferent fibers |
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Stretching the muscles activates the muscle spindle
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There is an INCREASED rate of action potential in Ia fibers
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Contracting the muscle reduces tension on the muscle spindle
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There is a DECREASED rate of action potential on Ia fibers
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Excited γ motor neurons of the spindle cause the stretched muscle to ____
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contract
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Afferent impulses from the spindle result in
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inhibition of the antagonist
(ex: tapping patellar tendon) |
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What is the Golgi Tendon Reflex?
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The opposite of the stretch reflex
Contracting the muscle activates the Golgi tendon organs Afferent Golgi tendon neurons are stimulated, neurons inhibit the contracting muscle, and the antagonistic muscle is activated As a result, the contracting muscle relaxes and the antagonist contracts |
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The flexor reflex is:
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initiated by a painful stimulus (actual or perceived) that causes automatic withdrawal of the threatened body part
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The crossed extensor reflex has two parts
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The stimulated side is withdrawn
The contralateral side is extended |