MLS 111L AnaPhy Laboratory (The Nervous System -Cranial Nerves and Reflexes) (3) PDF

 Reflex is an action that occurs automatically and predictably in response to a particular stimulus, independent of the will of the individual It includes inborn (intrinsic) reflex and learned (acquired) reflex A. Intrinsic reflex is a rapid, predictable motor response to a stimulus...

 Reflex is an action that occurs automatically and predictably in response to a particular stimulus, independent of the will of the individual It includes inborn (intrinsic) reflex and learned (acquired) reflex A. Intrinsic reflex is a rapid, predictable motor response to a stimulus that is unlearned, unpremeditated, and involuntary reflex built into the neural anatomy B. Learned (acquired) reflex results from practice or repetition  Reflexes are specific and predictable and are usually purposeful and adaptive. They depend on an intact neural pathway between the stimulation point and a responding organ known as the REFLEX ARC. Reflexes are classified functionally: I. SOMATIC REFLEXES if they activate skeletal muscle II. AUTONOMIC REFLEXES (VISCERAL) if they activate visceral effectors (smooth or cardiac muscle or glands)  COMPONENTS OF REFLEX ARC: 1. RECEPTOR: Site of the stimulus action 2. SENSORY NEURON: Transmits afferent impulses to the CNS 3. INTEGRATION CENTER Monosynaptic reflex: In simple reflex arcs, the integration center may be a single synapse between a sensory neuron and a motor neuron Polysynaptic reflex: More complex reflex arcs involve multiple synapses with chains of interneurons  COMPONENTS OF REFLEX ARC: 4. MOTOR NEURON: Conducts efferent impulses from the integration center to an effector organ 5. EFFECTOR: Muscle fiber or gland cell that responds to the efferent impulses  DERMATOMES An area of skin innervated by the cutaneous branches of a single spinal nerve I. PUPILLARY LIGHT REFLEX 1. Light shined in one eye stimulates retinal photoreceptors, and subsequently retinal ganglion cells, whose axons travel through the optic nerve, chiasm, and tract to terminate in the pretectum (pretectal nucleus). 2. The pretectal neurons project to a portion of the nucleus of Edinger-Westphal on both sides. This preganglionic parasympathetic nucleus projects to ciliary ganglion neurons, which in turn send postganglionic axons to innervate the pupillary constrictor muscle. I. PUPILLARY LIGHT REFLEX 3. Thus, light shined in one eye normally results in the constriction of both pupils a. Ipsilateral pupillary constriction: direct response b. Contralateral pupillary constriction: consensual response I. PUPILLARY LIGHT REFLEX CLINICAL SIGNIFICANCE A. Afferent Pupillary Defect Lesions of CN II produce an unresponsive pupillary light reflex on both sides (from light shined in the eye on the side of the CN II lesion). With light shined in the unaffected eye, both pupils constrict B. Efferent Pupillary Defect Lesions of CN III result in unresponsive ipsilateral pupillary constriction on the affected side (the pupil is “fixed and dilated”) when light is shined in either eye I. PUPILLARY LIGHT REFLEX CLINICAL SIGNIFICANCE C. Optic Neuritis Swelling of the eye’s optic nerve. The optic nerve carries light signals from the back of your eye to your brain so you can see. If the optic nerve is swollen, damaged or infected, you cannot see clearly. II. ACCOMMODATION REFLEX The accommodation reflex is an adjustment of the eye for near vision. Three phenomena are involved: 1. INCREASED CONVEXITY OF THE LENS The suspensory ligament of the lens inserts peripherally into it. At rest, the ligament maintains tension on the periphery of the lens, such that it remains flat. During the process of accommodation, the parasympathetic neurons of the Edinger– Westphal nucleus govern the contraction of the ciliary muscle which relaxes some of the tension on the ligament, modifying the shape of the lens. II. ACCOMMODATION REFLEX 2. PUPILLARY CONSTRICTION Parasympathetic fibers convey the impulse for the contraction of the sphincter pupillae. The pupil constricts and thereby increases the depth of focus 3. CONVERGENCE OF THE EYES The oculomotor nuclei send the impulses for contraction of both medial rectus muscles, causing the eyes to converge. II. ACCOMMODATION REFLEX CLINICAL SIGNIFICANCE A. MYOPIA (near-sighted or short-sighted) Progressive visual disorder that results in poor distance vision If the myopia is severe, it will impair near vision as well. In addition to weakening vision, it also changes the physical structure of the eye It can steepen the front surface of the eye (cornea) and/or stretch the retina (axial elongation) II. ACCOMMODATION REFLEX CLINICAL SIGNIFICANCE B. FARSIGHTEDNESS / HYPEROPIA A vision condition in which distant objects can be seen clearly, but close ones do not come into proper focus Farsightedness occurs if your eyeball is too short or the cornea has too little curvature III. CILIOSPINAL REFLEX (PUPILLARY-SKIN REFLEX) It consists of dilation of the ipsilateral pupil in response to pain applied to the neck, face, and upper trunk If the right side of the neck is subjected to a painful stimulus, the right pupil dilates (increases in size 1-2mm from baseline) III. CILIOSPINAL REFLEX(PUPILLARY- SKIN REFLEX) CLINICAL SIGNIFICANCE HORNER SYNDROME (OCULOSYMPATHETIC PARESIS) Results from an interruption of the sympathetic nerve supply to the eye and is characterized by the classic triad of miosis (constricted pupil), partial ptosis (upper eyelid droops), and loss of hemifacial sweating (anhidrosis)  Tension / Myotactic / Stretch reflex are muscle reflexes that help determine how responsive the spinal cord is It may become so sensitive that just tapping the tendon of the knee with the tip of your finger can cause the leg to jump a considerable distance If, however, the cord is overwhelmed by other impulses from the brain, it may be impossible to cause the muscles or tendons to respond I. KNEE JERK/ PATELLAR REFLEX The tapping of the tendon applies a stretch to quadriceps tendon and muscle spindles Sudden stretch of the patellar tendon stimulates the muscle spindle and increases their charge to the spinal cord Some of these messages continue up to higher centers in the brain and some to the motor neuron of the muscle which cause muscle to contract (extension) I. KNEE JERK/ PATELLAR REFLEX CLINICAL SIGNIFICANCE A. LOWER MOTOR NEURON LESION Affects nerve fibers traveling from the ventral horn or anterior grey column of the spinal cord to the relevant muscle(s) – the lower motor neuron One major characteristic used to identify a lower motor neuron lesion is flaccid paralysis – paralysis accompanied by loss of muscle tone This is in contrast to an upper motor neuron lesion, which often presents with spastic paralysis – paralysis accompanied by severe hypertonia (excess muscle tone) I. KNEE JERK/ PATELLAR REFLEX CLINICAL SIGNIFICANCE B. MYASTHENIA GRAVIS A chronic autoimmune neuromuscular disease that causes weakness in the skeletal muscles, which are responsible for breathing and moving parts of the body including the arms and legs The name myasthenia gravis, which is Latin and Greek in origin, means "grave, or serious, muscle weakness” Hallmark is muscle weakness that worsens after periods of activity and improves after periods of rest I. KNEE JERK/ PATELLAR REFLEX CLINICAL SIGNIFICANCE C. AMYOTROPHIC LATERAL SCLEROSIS (ALS) Lou Gehrig’s disease A rapidly progressive, invariably fatal neurological disease that attacks the nerve cells (neurons) responsible for controlling voluntary muscles (muscle action we are able to control, such as those in the arms, legs, and face) II. ACHILLES TENDON REFLEX (ANKLE REFLEX TEST) It is a deep tendon reflex that can be elicited easily with the use of a standard reflex/neurological hammer which takes part in a simple and effective part of a complete lower extremity examination. It is also part of the nervous system portion of a complete history and physical examination. Tendon can be palpated easily on most patients and is easy to find just superior to the posterior aspect of the calcaneus Primarily assess the S1 nerve root which innervates the area Feet jerks downward (plantar flexion) II. ACHILLES TENDON REFLEX (ANKLE REFLEX TEST) CLINICAL SIGNIFICANCE A. LUMBAR RADICULOPATHY (SCIATICA) Refers to disease involving the lumbar spinal nerve root which can manifest as pain, numbness, or weakness of the buttock and leg Typically caused by a compression of the spinal nerve root which causes pain in the leg rather than in the lumbar spine which is called "referred pain" II. ACHILLES TENDON REFLEX (ANKLE REFLEX TEST) CLINICAL SIGNIFICANCE B. CHARCOT–MARIE–TOOTH DISEASE (CMT) One of the hereditary motor and sensory neuropathies, a group of varied inherited disorders of the peripheral nervous system characterized by progressive loss of muscle tissue and touch sensation across various parts of the body Currently incurable, this disease is the most commonly inherited neurological disorder and affects about one in 2,500 people Previously classified as a subtype of muscular dystrophy. III. BICEPS REFLEX A reflex test that examines the function of the C5 reflex arc and the C6 reflex arc Performed by using a tendon hammer to quickly depress the biceps brachii tendon as it passes through the cubital fossa Activates the stretch receptors inside the biceps brachii muscle which communicates mainly with the C5 spinal nerve and partially with the C6 spinal nerve to induce a contraction (flexion) of the biceps muscle and jerk of the forearm III. BICEPS REFLEX A strong contraction indicates a “brisk” reflex and a weak or absent reflex is known as “diminished” Brisk or absent reflexes are used as clues to the location of neurological disease Typically, brisk reflexes are found in lesions of upper motor neurons and absent or reduced reflexes are found in lower motor neuron lesions III. BICEPS REFLEX CLINICAL SIGNIFICANCE A. DEGENERATIVE DISC DISEASE If the disc between the C5 and C6 vertebrae loses hydration and degenerates, either through the normal aging process or accelerated by an injury, then the disc itself can become painful, the nearby C6 nerve can become irritated, and/or muscle spasms may develop in response to spinal instability III. BICEPS REFLEX CLINICAL SIGNIFICANCE B. C5-C6 DISC HERNIATION A herniated disc occurs if the jelly-like inner portion of the disc leaks out—or herniates— through a tear in its protective outer layer (the annulus) Cause pain and may possibly cause neurological symptoms in the adjacent C6 nerve root III. BICEPS REFLEX CLINICAL SIGNIFICANCE B. C5-C6 DISC HERNIATION If the nerve root becomes pressed or irritated, then cervical radiculopathy can result with pain, tingling, numbness, or weakness radiating down the shoulder and arm, usually along the side of the forearm and into the thumb and index finger. Pain may be worsened by certain positions of the head and neck. III. BICEPS REFLEX CLINICAL SIGNIFICANCE C. C5-C6 OSTEOARTHRITIS If one or both of the facet joints that connect the C5 and C6 vertebrae lose enough protective cartilage and become arthritic, then pain can result from bone-on-bone grinding movements, inflammation, or bone spurs that grow big enough to impinge a nearby nerve. III. BICEPS REFLEX CLINICAL SIGNIFICANCE D. C5-C6 SPINAL STENOSIS WITH MYELOPATHY If the C5-C6 spinal segment degenerates enough, arthritic changes in the facet joints and along the back portion of the disc space could lead to a narrowing of the spinal canal, potentially putting the spinal cord at risk. IV. TRICEPS REFLEX The triceps reflex is used to examine the integrity of the C7 reflex arc supplied via the radial nerve A reduced or absent triceps reflex may be indicative of a lower motor neuron lesion affecting the C7 nerve root Contraction of the triceps brachii (extension) IV. TRICEPS REFLEX CLINICAL SIGNIFICANCE Nerves control elbow extension and some finger extension Most can straighten their arm and have normal movement of their shoulders Can do most activities of daily living by themselves but may need assistance with more difficult tasks May also be able to drive an adapted vehicle Little or no voluntary control of bowel or bladder but may be able to manage on their own with special equipment IV. TRICEPS REFLEX C7 SPINAL CORD INJURY Threshold for retention of functional independence Px with this injury will have full use of the head and neck muscles Good movement of the shoulders and retains control of elbow flexion, however manual dexterity will be degraded Breathing will be somewhat problematical but he will be able to breathe on his own using his diaphragm The severity of the injury will determine the nature of his disability and his hope of recovering function in the future IV. TRICEPS REFLEX C7 SPINAL CORD INJURY The speed, force, and amplitude of the reflex response must be observed and graded using a scale Always compare the response of one side with the other Reflexes are usually graded on a 0 to 4 scale.  AKA as Cutaneous Reflexes is a group of polysynaptic reflexes which are evoked by cutaneous stimulation I. CORNEAL REFLEX (BLINK REFLEX) An involuntary blinking of the eyelids elicited by stimulation of the cornea (such as by touching or by a foreign body), though it could result from any peripheral stimulus Stimulation should elicit both a direct and consensual response Reflex occurs at a rapid rate of 0.1 seconds Purpose of this reflex is to protect the eyes from foreign bodies and bright lights (the latter known as the optical reflex) I. CORNEAL REFLEX Also occurs when sounds greater than 40–60 dB is made Blink reflex studies are useful for assessing the pathway from the trigeminal nerve through the brainstem to the facial muscles In this technique, the CN V is stimulated at the supraorbital notch and both ipsilateral and contralateral responses are recorded from the CN VII A comparison of the ipsilateral and contralateral latency periods can be used to infer disease localized to the trigeminal nerve, pons, medulla, or facial nerve I. CORNEAL REFLEX Before the development of brain magnetic resonance imaging, blink reflex results were often used to localize disorders of the posterior fossa, medulla, and central demyelinating conditions Blink reflex testing can be used to evaluate patients with facial pain Blink reflex results can be abnormal in many peripheral demyelinating conditions, such as Guillain-Barré syndrome, diabetic neuropathy, chronic renal failure, and Charcot-Marie- II. PHARYNGEAL REFLEX (GAG REFLEX) The gag reflex is centered in the medulla and consists of the reflexive motor response of pharyngeal elevation and constriction with tongue retraction in response to sensory stimulation of the pharyngeal wall, posterior tongue, tonsils, or faucial pillars This reflex is examined by touching the posterior pharynx with the soft tip of a cotton applicator and visually inspecting for elevation of the pharynx II. PHARYNGEAL REFLEX (GAG REFLEX) Both sides of the pharynx should be examined for both the afferent and the efferent limbs of the reflex by touching one side first and then the other while watching for symmetry of pharyngeal movement The normal reflex response varies, and it may be reduced in the elderly or in smokers Asymmetry of the reflex is the feature most indicative of pathology II. PHARYNGEAL REFLEX (GAG REFLEX) CLINICAL SIGNIFICANCE Palatal elevation and the gag reflex are controlled by cranial nerves IX and X Botulinum toxin can impair gag The “spatula test” showing hyperactive gag can be useful in clinically confirming tetanus CN X and its nucleus are important mediators of nausea and emesis in response to toxic substances in the gut III. SUPERFICIAL ABDOMINAL REFLEX T7-T12 segments are involved which can be helpful in determining the level of CNS lesion It is a superficial neurological reflex stimulated by stroking of the abdomen around the umbilicus Being a superficial reflex, it is polysynaptic III. SUPERFICIAL ABDOMINAL REFLEX Abdominal reflex is noted as either present or absent An absent response can be physiological --> due to obesity, tolerance, children, and multiparous lax abdominal wall Pathological absence can be due to: a. Multiple sclerosis b. Motor neuron disease (late) c. Neurogenic bladder d. Brown-Séquard syndrome e. Chiari malformations IV. PLANTAR REFLEX It is a reflex elicited when the sole of the foot is stimulated with a blunt instrument The reflex can take one of two forms: 1. In normal adults, the plantar reflex causes a downward response of the hallux (flexion) 2. An upward response (extension) of the hallux is known as the Babinski response or Babinski sign (neurologist Joseph Babinski) The presence of the Babinski sign can identify disease of the spinal cord and brain in adults and also exists as a primitive reflex in infants IV. PLANTAR REFLEX CLINICAL SIGNIFICANCE UPPER MOTOR NEURON LESION (Pyramidal Insufficiency) Occurs in the neural pathway above the anterior horn cell of the spinal cord or motor nuclei of the cranial nerves Conversely, a lower motor neuron lesion affects nerve fibers traveling from the anterior horn of the spinal cord or the cranial motor nuclei to the relevant muscle(s) An abnormal reflex seen in stroke, cerebral palsy, multiple sclerosis  A state of alertness in which a person is fully aware of his or her thoughts, surroundings, and intentions It involves arousal accompanied by awareness of one’s environment In practice, consciousness is said to be present when a person is awake, alert, and oriented to his or her surroundings  Encompasses perception of sensations, voluntary initiation and control of movement, and capabilities associated with higher mental processing (memory, logic, judgment, etc.) Consciousness is defined on a continuum that grades behavior in response to stimuli as: 1. Alertness 2. Drowsiness or Lethargy (which proceeds to sleep) 3. Stupor (lack of critical consciousness) 4. Coma (unresponsiveness) I. ALERT WAKEFULNESS The patient perceives the environment clearly and responds quickly and appropriately to visual, auditory, and other sensory stimuli. II. CONFUSION An acute or chronic disorganized mental state in which the abilities to remember, think clearly, and reason are impaired. II. CONFUSION (2 TYPES) A. ACUTE CONFUSION Can arise as a symptom of delirium, in which brain activity is affected by fever, drugs, poisons, or injury People with acute confusion may also have hallucinations and behave violently II. CONFUSION (2 TYPES) B. CHRONIC CONFUSION Associated with alcohol dependence, long-term use of antianxiety drugs, and certain physically based mental disorders Many of the conditions that cause chronic confusion (for example dementia) are progressive Features include absentmindedness, poor short-term memory, and a tendency to be repetitive. If the underlying cause of confusion can be treated, there may be marked improvement. IV. DROWSINESS The patient does not perceive the environment fully and responds to stimuli appropriately but slowly or with delay He or she may be aroused by verbal stimuli but may ignore some of them Patient is capable of verbal response unless aphasia, aphonia, or anarthria is present Lethargy and obtundation also V. STUPOR Patient is aroused by intense stimuli only Loud noise may elicit a nonspecific reaction Motor response and reflex reactions are usually preserved unless the patient is paralyzed V. COMA Patient does not perceive the environment and intense stimuli produce a rudimentary response, if any A significant unresponsiveness to sensory stimuli for an extended period In coma patients, oxygen use is always below normal resting levels  A brief loss of consciousness Most often, syncope indicates inadequate cerebral blood flow due to low blood pressure, as might follow hemorrhage or sudden emotional stress