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Preparation
Reflexes are predictable, automatic responses to specific stimuli. The nerve impulses for reflexes travel over pathways called reflex arcs. The arcs are composed of a receptor, an afferent neuron, an efferent neuron, and an effector. Afferent and efferent neurons synapse within the CNS.
Reflexes are commonly used to evaluate the functional status of neural pathways – locally or systemically. For example, in surgical operations, an anesthesiologist may try to initiate a reflex response on a patient who is being anesthetized in order to determine how the anesthetic drug is affecting nerve functions. In the case of an injury to a specific area of the nervous system, various types of reflexes may be tested to pinpoint the location and the extent of the damage.
Reflexes may be classified into somatic and visceral (autonomic) based on motor response. Somatic reflexes involve the contraction of voluntary (skeletal) muscles whereas visceral reflexes involve the secretion of glands or the contraction of smooth muscles. In this lab, we will explore both somatic and visceral reflexes.
Activity 1: Patellar reflex
Background
The patellar reflex is an example of a somatic reflex. It is also called a deep reflex because it involves the stimulation of receptors (muscle spindles) located deep within the quadriceps femoris. Deep reflexes tend to be hypo-reactive or absent when there is peripheral nerve (lower motor neuron) damage or ventral horn disease, and hyper-reactive in corticospinal tract (upper motor neuron) lesions. Nerve impulses for the patellar reflex travel along the L2, L3, and L4 spinal nerves. The patellar reflex involves extension of the leg after tapping of the patellar ligament.
The purpose of this experiment is to learn how to perform a spinal reflex, to see the normal responses of spinal reflexes, and to emphasize the clinical importance of this type of reflex. Watch this video TWICE before you begin:
Patellar Reflex Links to an external site.
Materials needed
willing subject ruler notebook
pencil Procedure
Place all materials to be used in this experiment on a table and take a picture.
The subject must be seated on a table with legs hanging free from the edge, or with knees crossed. The subject should be relaxed.
Locate the patellar ligament located just below the knee cap with your finger. This is where you will test the reflex.
Tap sharply with the flat edge of the ruler on the patellar ligament. The subject should respond with an extension of the leg. NOTE: The subject should not be wearing long pants. Clothing material may act as a cushion and interfere with the response; that is, the leg may not extend.
Record your findings as specifically as you can.
Give the subject a notepad with a column of three digit numbers. Ask the subject to add them and not to be concerned about the tapping on the patellar tendon.
Record your results.
Activity 2: Pupillary Light Reflex
Background
The pupillary light reflex is an autonomic reflex. It is mediated through two cranial nerves (optic and oculomotor). The optic nerve conveys sensory impulses from the retina (ganglion cells functions receptors) to the thalamus; the oculomotor nerve conveys motor impulses from the midbrain to the circular smooth muscles (sphincter pupillae) of the iris. Some of the sensory impulses bypass the thalamus and terminate in the midbrain (pretectal nucleus). From here internuncial fibers relay information to parasympathetic nuclei (Edinger-Westphal) located on both sides (right and left) of the midbrain. Notice that fibers that crossover to the contralateral (opposite) side are responsible for causing responses on the opposite side (non-stimulated side). Concerning the pupillary light reflex, if we stimulated the right eye with a beam of light, we would see a pupillary constriction (response) in the right eye. In addition, there is papillary constriction in the left eye. The response you see on the left eye is called a consensual response. Consensual responses are characteristic of autonomic reflexes and are absent in somatic reflexes. A consensual response, therefore, is defined as a response observed on the non-stimulated side of the body.
In the midbrain, the parasympathetic fibers join somatic motor fibers from the oculomotor nuclei, and both emerge (from the brainstem) as components of each oculomotor nerve. The parasympathetic fibers of the oculomotor nerve then innervate the sphincter pupillae while the somatic motor fibers innervate the extrinsic muscles that move the eyeball.
The pupils of a dying person often dilate markedly and do not contract to bright light. In persons who have taken narcotics (such as heroin or morphine) the pupils constrict greatly (called “pinpoint pupils”) and do not dilate. This fact is often used to determine if a person is intoxicated with narcotics. The pupillary reflexes are also important indicators in general anesthesia; the anesthetist checks the degree of dilation or constriction of the eyes (as well as other signs) to determine the depth of unconsciousness.
The purpose of this experiment is to learn how to perform an autonomic reflex, to see the normal responses of autonomic reflexes, and to emphasize the clinical importance of this type of reflex. This activity also gives the student an opportunity to see the similarities and differences (anatomically and physiologically) of reflexes.
The purpose of this experiment is to learn how to perform a spinal reflex, to see the normal responses of spinal reflexes, and to emphasize the clinical importance of this type of reflex. Watch this video TWICE before you begin:
BBC – Eye Pupil Reflex Links to an external site.
Materials needed
willing subject with light colored pupils
keylight or penlight
3″ x 5″ index card
metric ruler
Procedure
Draw five half-circles of different diameters (2mm, 3mm, 4mm, 5mm, and 6mm) at 1mm intervals at the edge of the index card. The half-circles will be used to measure the diameter of the subject’s pupils.
Measure the diameters of the subject’s pupils in a dimly lit room. Record the results.
Ask the subject to place his or her hand (vertically) between the eyes, in front of the nose. Direct a beam of light to the subject’s left eye for a few seconds. NOTE: the hand between the eyes should prevent stimulation to the right eye. Now, observe what happens to both pupils as you stimulate the left eye. Repeat two or three times.
Stimulate the left eye again and measure the diameters of the constricted pupils (right and left eyes). Record them.
Results: Complete the activities for each section as indicated. This will comprise the data in the data / analysis section of your word document
Submission: Create your document using word-processing software, such as Microsoft Word and save it to your computer as a .doc, .docx, or .rtf file. To submit the report, choose the link titled, Lab 11: Reflexes, above. Use the “Browse My Computer” button in the Attach File area to attach your document. Be sure to complete your submission by choosing the “Submit” button at the bottom of the screen.
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