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Learning Targets Reflex Arc Lab 1-Diagram and label the path of each nerve impulse in the reflex arc tested from sensation to response ( pupil, deep tendon, gag, eye blink, accommodation, and plantar reflexes) 2-Reason and record (then research) the purpose for each reflex- why does this particular reflex happen? 3-Observe, record and compare typical human reaction times. 1 Reflex Arcs • Reflexes are automatic, subconscious responses to stimuli within or outside the body • Simple reflex arc (sensory – motor) • Most common reflex arc (sensory – association – motor) 2-neuron vs. 3-neuron reflex arc Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sensory or afferent neuron Receptor Central Nervous System Motor or efferent neuron Effector (muscle or gland) 12 2 (a) Reflex Arcs 3 General Components of a Spinal Reflex Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Spinal cord Interneuron Dorsal 1 Receptor 3 2 Sensory neuron Cell body of sensory neuron White matter Gray matter 4 Ventral Motor neuron Central canal 5 Effector (muscle or gland) (b) 4 Patellar Reflex • Example is the knee-jerk reflex • Simple monosynaptic reflex • Helps maintain an upright posture & prevents overstretching Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Axon of sensory neuron Cell body of sensory neuron Spinal cord Cell body of motor neuron Axon of motor neuron Direction of impulse Effector (quadriceps femoris muscle group) Receptor associated with dendrites of sensory neuron Patella Patellar ligament 5 Withdrawal Reflex • Prevents or limits tissue damage Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cell body of sensory neuron Axon of sensory neuron Direction of impulse Dendrite of sensory neuron Pain receptor in skin Tack Effector (flexor muscle contracts and withdraws part being stimulated) Interneuron Axon of motor neuron Spinal cord Cell body of motor neuron 6 Crossed Extensor Reflex •Contralateral reflex •Maintain balance Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Interneuron + = Stimulation – = Inhibition – + – Sensory neuron Extensor relaxes + Extensor contracts Flexor relaxes Motor neurons Motor neurons Flexor contracts 17 7 Some Additional Human Reflexes acoustic reflex In response to high sound intensities, contraction of the stapedius and tensor tympani muscles in the middle ear. blushing A reddening of the face caused by embarrassment, shame or modesty. corneal reflex Blinking of both eyes when the cornea of either eye is touched. rooting reflex Turning of an infant's head toward anything that strokes the cheek or mouth. shivering Shaking of the body in response to early hypothermia in warm-blooded animals. vestibulo-ocular reflex Movement of the eyes to the right when the head is rotated to the left, and vice versa. 8 Nervous Impulse Pathway in a Reflex Arc Nervous Impulse Pathway in a Reflex Arc Interneuron/Association Neurons These neurons are the vital part of the reflex arc They connect the Sensory neuron to the Motor/Effector neuron They can be found in the grey matter of the spinal cord and in the midbrain Advantage of Reflexes The reflex arc allows a much quicker response to stimuli This is especially important where the stimuli is a source of potential damage e.g. a hot object, a sharp pin Inhibition of the Reflex Response The reflex response is considerably inhibited in several situations: Exposure to Noradrenalin (Parasympathetic nervous system) Tiredness High Blood Alcohol Effect from Sedative Drugs (e.g. Cannabis) Stimulation of the Reflex Response The speed of the reflex response can be increase by several factors: Exposure to adrenaline (Sympathetic Nervous System) Exposure to stimulant drugs (Caffeine, Beta Amphetamines/Speed) The Pupil Reflex Response The pupil response allows the iris to contract and dilate This changes the size of the pupil In the eye the pupil acts like an aperture It controls the amount of light which enters the eye.. … and protect the retina from “overexposure” Bright Light, Bright Light When light levels are high Circular muscles in the iris contract This causes the pupil to become smaller This is controlled by the parasympathetic nervous system In the Dark… When light levels are low Radial muscles contract This causes the pupil to increase in size This is caused by the sympathetic nervous system Diagram of Pupil Response Control of the Pupil Reflex: In Detail When high levels of light strike photoreceptors in the retina they cause nervous impulses to be sent along the Sensory neuron (Optic Nerve) These impulses are co-ordinated by relay neurons in the Midbrain Signals are then sent along the parasympathetic nervous system Diagram of the Pupil Reflex Arc Atropine Atropine is a sedative drug made from the deadly nightshade plant (Atropa belladonna) It was apparently used in the middles ages by women to dilate there pupils This is the source of the word belladonna in Latin and Belle in French What are all the components that make a reflex happen? stimulus sensor touch coordinator effector response pain receptor nervous system muscle movement Looking at this sequence of steps, this is what happens when something sharp touches you on your hand: The stimulus is touch, your pain receptor is the sensor that senses it and relays it to the nervous system (spinal cord and brain) which is the coordinator. The coordinator makes the decision of how to react, and then commands the hand muscles (effector) to move the hand away (response). Thus, we go from stimulus (touch) to response (hand movement). Assignment during lab: Sketch out how the stimulus to response sequence for each of the reflexes tested. Identify all the components as in the example above. 22 Reaction Times & Response Times The time taken to respond to stimulus is the response time. Response time = reaction time + movement time Reaction time depends on the stimulus type: * auditory ~ 150 ms * visual ~ 200 ms * touch ~ 700 ms Movement time varies considerably, and is dependent on age, fitness etc. Given these variables, the time to respond (aka the response time) to a stimulus varies among people. 23 24 CN I Olfactory CN II CN III Optic Occulomotor Olfactory epithelium Retina Midbrain CN IV Trochlear Midbrain CN V Trigeminal Pons CN VI Abducens Pons CN VII Facial Pons CN VIII CN IX Vestibulocochlear Glossopharyngeal Pons Medulla CN X Vagus Medulla CN XI Accessory Medulla CN XII Hypoglossal Medulla Smell Vision Eye movement; accommodation Eye movement (superior oblique) Sensation to face; chewing Eye movement ( lateral rectus) Facial expression; taste to anterior 2/3 of tongue Hearing & balance Salivation; swallowing; taste to posterior 1/3 of tongue Digestion; taste to pharynx Movement of trapezius & SCM Movement of tongue 26