Lab #10 Nervous System I

Transcription

1 Page1 Nervous System I: Histology, Brain, & Reflexes Lab #10 Nervous System I Histology, Brain, & Reflexes Objectives: View slides of nervous tissue Observe the external and internal anatomy of the brain Dissect a sheep brain and identify major structures Observe and identify the ventricles of the brain on a model Demonstrate common reflexes and understand reflex arcs Become acquainted with cranial nerves and their functions Equipment: Bring gloves, goggles, dissecting kit, photographic atlas, and proper shoes. I. The Nervous System A. Introduction The nervous system can be divided into two major components: the central nervous system (CNS) composed of the brain and spinal cord and the peripheral nervous system (PNS) composed of the cranial and spinal nerves. The cells that make up the nervous system are either nerve cells (neurons) or supporting cells (neuroglia). Neurons carry electrical impulses to other neurons or effector cells such as muscle or gland cells. B. Nervous tissue slides View the following nervous tissue slides using your microscope. Refer to the atlas and identify the listed structures. Draw and label a crosssection of the spinal cord in the lab report. Neuroglia and neuron neuron, neuroglia Motor neuron cell body Spinal cord white matter, gray matter, neuron cell body, central canal Nerve epineurium, perineurium, endoneurium, fascicle Figure 1. Human nervous system Last Modified 08/05/14

2 Page2 Nervous System I: Histology, Brain, & Reflexes II. The Brain A. Introduction Within the skull, the brain is enclosed by three protective layers called the meninges. The outermost meningeal layer, the dura mater, is a tough connective tissue sheath. The innermost layer, the pia mater, is a thin, transparent layer directly adhered to the surface of the brain. The middle layer is a fragile, spiderweb-like tissue, the arachnoid mater, which spans the space between the other two meningeal layers. Superficially the brain can be divided into three regions: the cerebrum, the cerebellum, and the Figure 2. Sagittal section of human brain brainstem. The cerebrum is the largest part of the brain and it surrounds most of the other structures including a fourth internal region, the diencephalon. The cerebrum controls all voluntary actions of the body. The cerebellum (little brain) coordinates the brain s communication. The brainstem connects the spinal cord to the brain and coordinates basic functions such as heart rate and breathing. The surface of the cerebrum is folded into ridges called gyri (gyrus sing.). The depressions between the gyri are called sulci (sulcus sing.) if shallow, and fissures if deep. The deepest of the fissures, the longitudinal fissure, superficially divides the cerebrum into left and right hemispheres. Each hemisphere contains four lobes named for the skull bones that cover them. These are the frontal, parietal, temporal, and occipital lobes. Each lobe has a role in a different set of brain functions. Internally, the right and left cerebral hemispheres are connected by the corpus callosum, a wide band of neural fibers. Cerebrospinal fluid (CSF) bathes and cushions the brain and spinal cord. Within the brain, CSF flows through a series of cavities called ventricles. The center of each cerebral hemisphere contains a large, U-shaped lateral ventricle. CSF moves in one direction from the lateral ventricles through the interventricular foramina to the third ventricle located midline within the diencephalon. CSF flows from the third ventricle through the cerebral aqueduct to the fourth ventricle which is anterior to the cerebellum. The fourth ventricle empties into the central canal of the spinal cord. B. Observation and dissection of sheep brain 1. Preparation a. Wear goggles, gloves, and an apron for the entire time that you are working with preserved specimens. b. Obtain a dissecting tray and a sheep brain. Last Modified 08/05/14

3 Page3 Nervous System I: Histology, Brain, & Reflexes 2. Exterior Observations The sheep brain is similar to the human brain with two exceptions. In sheep, the cerebrum is smaller in proportion to the entire brain and the orientation is anterior to posterior rather than superior to inferior as in humans. First use your photoatlas to help you locate the pituitary gland, optic chiasma and olfactory bulbs on the inferior surface of the brain. These may be damaged when you remove the dura mater, so it is best to see them first. Once you have seen these structures, then you can carefully remove the dura mater. Find an area where the dura is loose and snip an opening with scissors. Continue to remove the dura by snipping slowly around the attachment points. Once you have successfully removed the dura mater, no further dissection is needed to see structures listed below in the superior, inferior, and posterior views. a. Superior View dura mater (observe demo brain if not present) cerebrum hemisphere gyrus sulcus longitudinal fissure central sulcus cerebellum spinal cord b. Inferior View olfactory bulbs optic chiasma optic nerve pituitary gland pons medulla spinal cord c. Posterior View To better observe the structures found in the posterior cerebrum, gently bend the cerebellum and cerebrum away from each other. Refer to the atlas to identify the structures listed below. corpora quadrigemina superior colliculi inferior colliculi pineal body d. Sagittal View To observe the structures listed below, use a scalpel to slice the brain in half. The longitudinal fissure is a convenient guide for the mid-sagittal cut. cerebrum corpus callosum cerebellum arbor vitae pons medulla spinal cord thalamus ventricles lateral third fourth 3. Clean Up Dispose of dissected brains and brain parts in the red biohazard containers. Wash out your dissecting pan with soap and water. Gloves go in the regular trash. Last Modified 08/05/14

4 Page4 Nervous System I C. Observation of Brain Ventricle Model View the model of brain ventricles on display. Locate the paired lateral ventricles, the third ventricle and the fourth ventricle. Also identify the channels that connect them, the interventricular foramina and the cerebral aqueduct. Label these structures in your lab report. III. The Cranial Nerves There are twelve pairs of cranial nerves that emerge directly from the brain. In addition to being named, each cranial nerve pair is sequentially numbered with Roman numerals I-XII, beginning with the most anterior pair of cranial nerves. The first and second cranial nerve pairs arise from the cerebrum, and the remaining ten pairs arise from the brainstem. Use the information in Table 1 to complete the matching exercise in the lab report. Figure 3. Cranial nerves Table 1. List of Cranial Nerves and Major Functions # Nerve Name Major Functions I Olfactory Smell II Optic Vision III Oculomotor Eye movement, pupillary constriction, lens accommodation, sense body position IV Trochlear Eye movement, sense body position V Trigeminal Chewing, tenses tympanic membrane and soft palate, general sensation in scalp, face, tongue, and teeth VI Abducens Lateral eye movement, sense body position VII Facial Facial expression, hearing, lacrimation, mucous secretion, salivation, taste, general sensation in inner ear VIII Vestibulocochlear Hearing, equilibrium IX Glossopharyngeal Swallowing, salivation, taste, general sensation in tongue, palate, upper pharynx, and inner ear X Vagus Gland secretion, peristalsis, speech, taste, general sensation in outer ear, thoracic and abdominal sensation, slows heart rate XI Accessory Speech, head and shoulder movement XII Hypoglossal Tongue movement

5 Page5 Nervous System I IV. The Reflexes A. Introduction A reflex is a quick and involuntary response to a stimulus. There are five parts to a reflex arc: 1. a receptor detects the stimulus, 2. a sensory neuron carries the signal from the periphery to the CNS, 3. an interneuron relays the signal within the CNS, 4. a motor neuron carries a signal from the CNS, 5. an effector responds to the motor neuron signal. Failure of a reflex response may indicate damage along the neural pathway, typically in the tracts of the spinal cord or in the peripheral nerves. For this reason, checking reflex responses is a useful tool for clinical evaluation of nerve function. Reflexes can be classified as either somatic or autonomic. In somatic reflex pathways, skeletal muscles produce the response; therefore an individual is typically aware or conscious that the reflex action is occurring. The knee jerk reflex is an example of a somatic reflex. In autonomic reflex pathways, responses are produced by cardiac muscle, smooth muscles, or glands, and the subject is generally not consciously aware of the reflex action occurring. Examples of autonomic reflexes include digestion, sweating, hormone release, and dilation and contraction of blood vessels. B. Testing reflexes Work in pairs to perform the reflex tests as described. For each exercise, position the body part being tested so that the muscle(s) involved can be completely relaxed. Conduct the tests on both the right and left sides five times each for a total of ten trials. Observe the responses carefully as reflex reactions are subtle. Record the number of normal responses in Table 3. Materials: percussion hammer, mat, pen light 1. Patellar Reflex (Knee Jerk Reflex) The patellar reflex is used to evaluate the function of the L2, L3, and L4 levels of the spinal cord. Normal response = extension of the leg at the knee, often called the knee jerk Place the subject in a seated position with legs relaxed and hanging freely over the edge of the chair or table, not touching the floor. Use a rubber percussion hammer to strike the patellar ligament just below the patella and observe the response. 2. Achilles Reflex (Ankle Jerk Reflex) The ankle jerk reflex is used to evaluate the function of the S1 and S2 levels of the spinal cord. Normal response = plantar flexion of the foot Place the subject in an upright position next to a chair or lab stool with one flexed knee resting on the stool, as if kneeling. The foot should hang free over the edge in a relaxed, slightly dorsiflexed position. Use the rubber percussion hammer to gently strike the Achilles tendon just above its insertion on the calcaneus (heel) bone and observe the response.

6 Page6 Nervous System I 3. Biceps Jerk Reflex The biceps jerk reflex is used to evaluate the function of level C5 and C6 spinal nerves. Normal response = slight twitch of the biceps brachii or flexion of the forearm at the elbow Position the subject with one bare arm resting flat on the lab bench with palm up and arm flexed at slightly less than a 90 angle. Grip the upper arm near the bent elbow with the thumb pressed firmly over the large tendon that attaches the biceps brachii muscle to the radius. Strike the thumb with the pointed end of the rubber percussion hammer and observe the response. 4. Plantar Reflex The plantar reflex evaluates the function of the S1 and S2 levels of the spinal cord. Normal response = curling of the toes and plantar flexion of the foot (known as a negative Babinski reflex) or no reaction Abnormal response = toes spread apart and dorsiflexion of the great toe (known as a positive Babinski reflex). This is a normal response for infants until the axons of the neurons have become completely myelinated. Position the subject on a mat on the floor, lying flat on his/her back with Figure 4. Abnormal shoes and socks removed and the lateral surface of the foot resting on the mat. plantar reflex response. Using firm pressure, run the handle of the rubber percussion hammer along the lateral edge of the bottom of the foot in this motion--begin at the heel, move up toward the small toe, then curve across the ball of the foot toward the great toe. Observe the response. 5. Pupillary Light Reflex The pupillary reflex evaluates the function of cranial nerves II and III. a. Direct pupillary light reflex: Normal response = decrease in diameter of pupil currently directly exposed to bright light Abnormal response = no change in pupil size in various light environments b. Consensual pupillary light reflex: Figure 5. Pupillary light response A. dilated pupil Normal response = decrease in diameter of pupil NOT currently B. constricted pupil. exposed to bright light Abnormal response = no change in pupil size when opposite eye is exposed to light Place the subject in a seated position, facing forward with head level. Have the subject focus on a point over the right shoulder of the evaluator. To test direct reflex: Use a pen light to shine a beam of light directly into one eye. Observe the response of the pupil currently exposed to light. Repeat procedure on opposite eye. Alternate the trials from eye to eye. To test consensual reflex: Use the same procedure as for the direct reflex but observe the eye NOT being exposed to light. Alternate the trials from eye to eye. C. Pupillary Light Reflex Arc Fill in the components of this reflex arc in your lab report.

7 Page7 Nervous System I Lab Report # 10 Nervous System I I. B. The Nervous System A. Spinal Cord Draw a cross-section as observed using the 4x objective. Label these structures white matter, gray matter, neuron cell body, central canal Name Spinal Cord II. B. The Brain For each label on the sheep brain figure, list the name of the structure below. C D B E A F H G A. B. C. D. E. F. G. H.

8 Page8 Bio 150 II. C. Brain Ventricle Model Label the ventricles and connecting channels. Draw arrows on the diagram to show the direction of CSF flow III. The Cranial Nerves Using the numbers (I-XII), match the cranial nerves (CN) with the symptoms listed in Table 2. I Olfactory nerve VII Facial nerve IX Glossopharyngeal nerve II Optic nerve VIII Vestibulocochlear nerve X Vagus nerve III Oculomotor nerve V Trigeminal nerve XI Accessory nerve IV Trochlear nerve VI Abducens nerve XII Hypoglossal nerve Table 2. Impaired Cranial Nerve Function CN # 1. The heart rate drops when this nerve is stimulated in the neck region. 2. The patient has a decreased sense of taste (3 nerves). 3. The patient is deaf. 4. One shoulder droops. 5. The patient has lost some sense of smell after a hard blow to the face. 6. What nerve would be affected if a diabetic has reduced blood flow to the retina? 7. After surgery the patient the patient lost sensation on one side of the face and difficulty chewing. 8. The patient has Bell s Palsy (drooping of one side of the face). 9. The patient cannot abduct (laterally move) the eye due to damage to this nerve. 10. The pupil of one eye is dilated due to reduced function of muscle in the iris. Modified and adapted with permission from Theresa S. Biddle. HAPS-Educator Summer 2008, pg 15.

9 Page9 Bio 150 IV. B. The Reflexes Record data from the reflex tests in the table. Also state the region evaluated by each test and state whether the reflex is somatic or autonomic. Reflex Tested Patellar Reflex Ankle Jerk Reflex Plantar Reflex Biceps Jerk Reflex Direct Pupillary Reflex Consensual Pupillary Reflex Table 3. Summary of Human Reflex Evaluations Number of Normal Response (X of 10) Region of the CNS Evaluated Somatic or Autonomic Reflex? IV. B. The Reflexes On the diagram below, label the level of the spinal cord associated with each of the somatic reflex tests performed in Table 3. IV. C. Pupillary Light Reflex Arc List the specific components of this reflex arc below. You may need to use other sources such as your text or the internet. 1. Receptor (name the structure) 2. Sensory neuron (name the nerve) 3. Interneuron (name the organ) 4. Motor neuron (name the nerve) 5. Effector (name the structure) On the back of this page, draw a simple diagram to show how the components of this reflex arc are organized together. Clearly label each component. Use arrows to show the direction impulses will travel.