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Home , Pseudounipolar neuron

Medical Academy named after S.I. Georgievsky of Vernadsky CFU

Department of Neurology and Neurosurgery

Class 1. Anatomy and Physiology of Sensation.

Elements of the . Anatomy, physiology, morphology of the Nervous System. . Pathways. Aids to the examination of the Somatosensory System. Somatosensory Deficits due to Lesions at Specific Sites along the Somatosensory Pathways.

Key poin ts: 1. Elements o f the Nervous System. 2. Peripheral Components of the Somatosensory System 3. Posterior Columns. 4. Spinothalamic Tracts. 5. Central Components o f the Somatosensory System 7. Testing for somatosensory deficits. 8. Somatosensory Deficits due to Lesions at Specific Sites along the Somatosensory Pathways

Questions for students:

Define the following terms: , Nissl substance, axonal transport, Wallerian degeneration, chromatolysis, regeneration of nerve cells, glial cells, pigments and inclusions, nerve fibers, receptor, peripheral nerve, nerve plexus, posterior root, dorsal root , superficial sensation, deep sensation, posterior columns, spinothalamic pathway, dermatome, conscious proprioception, stereognosis, graphesthesia, 2-point discrimination, anesthesia, hypoesthesia, hyperpathia, allodynia, hyperesthesia, dysesthesia, paresthesia.

1. What are the steps involved in the sensory exam? 2. How is it possible to lose some types of sensations and not others? 3. What sensations are conveyed by the small-diameter fibers in a peripheral nerve? 4. What sensations are conveyed by large-diameter sensory nerve fibers in a peripheral nerve? 5. What sensations are conveyed by the dorsal columns? 6. What sensations are conveyed by the ? 7. What is tested by double simultaneous stimulation? 8. Where would the lesion be if the patient was able to detect all modalities of sensation but could not recognize an object placed in the right hand? 9. What is the common sensory loss from damage to the spinothalamic tract? 10. What is the common sensory loss from damage to the posterior columns? 11. What is the characteristic of sensory loss due to damage of dorsal roots? 12. What is the characteristic of sensory loss due to damage of peripheral nerves in a limb? Elements of the Nervous System. are classified by the number of processes (Figure 1-1). A. PSEUDOUNIPOLAR NEURONS are located in the spinal (dorsal root) ganglia and sensory ganglia of (CN) V, VII, IX, and X. B. BIPOLAR NEURONS are found in the cochlear and vestibular ganglia of CN VIII, in the olfactory nerve (CN I), and in the retina. C. MULTIPOLAR NEURONS are the largest population of nerve cells in the nervous system. This group includes motor neurons, neurons of the autonomic nervous system, , pyramidal cells of the cerebral cortex, and Purkinje cells of the cerebellar cortex. D. There are approximately 1011 neurons in the brain and approximately 1010 neurons in the neocortex.

NISSL SUBSTANCE is characteristic of neurons. It consists of rosettes of polysomes and rough endoplasmic reticulum; therefore, it has a role in protein synthesis. Nissl substance is found in the nerve cell body (perikaryon) and , not in the hillock or axon.

AXONAL TRANSPORT mediates the intracellular distribution of secretory proteins, organelles, and cytoskeletal elements. It is inhibited by colchicine, which depolymerizes microtubules.

Sensory (receptor) neurons

Synaptic endings (boutons terminaux) Nerve endings in muscle (myoneural junction) • Figure 1-1 Types of nerve cells. Olfactory neurons are bipolar and unmyelinated. Auditory neurons are bipolar and myelinated. Spinal (dorsal root) ganglion cells (cutaneous) are pseudounipolar and myelinated. Motor neurons are mul­ tipolar and myelinated. Arrows indicate input through the of other neurons. Nerve cells are characterized by the presence of Nissl substance and rough endoplasmic reticulum. A. FAST ANTEROGRADE AXONAL TRANSPORT is responsible for transporting all newly synthesized membranous organelles (vesicles) and precursors of neurotransmitters. This process occurs at the rate of 200 to 400 mm/day. It is mediated by neurotubules and kinesin. (Fast transport is neurotubule- dependent.) B. SLOW ANTEROGRADE TRANSPORT is responsible for transporting fibrillar cytoskeletal and protoplasmic elements. This process occurs at the rate of 1 to 5 mm/day. C. FAST RETROGRADE TRANSPORT returns used materials from the to the cell body for degradation and recycling at a rate of 100 to 200 mm/day. It transports nerve growth factor, neurotropic viruses, and toxins, such as herpes simplex, rabies, poliovirus, and tetanus toxin. It is mediated by neurotubules and dynein.

WALLERIAN DEGENERATION is anterograde degeneration characterized by the disappearance of axons and sheaths and the secondary proliferation of Schwann cells. It occurs in the (CNS) and the peripheral nervous system (PNS).

CHROMATOLYSIS is the result of retrograde degeneration in the neurons of the CNS and PNS. There is a loss of Nissl substance after axotomy.

REGENERATION OF NERVE CELLS A. CNS. Effective regeneration does not occur in the CNS. For example, there is no regeneration of the optic nerve, which is a tract of the diencephalon. There are no basement membranes or endoneural investments surrounding the axons of the CNS. B. PNS. Regeneration does occur in the PNS. The proximal tip of a severed axon grows into the endoneural tube, which consists of basement membrane and . The axon sprout grows at the rate of 3 mm/day (Figure 1 -2).

GLIAL CELLS are the nonneural cells of the nervous system. A. MACROGLIA consist of and . 1. Astrocytes perform the following functions: a. They project foot processes that envelop the basement membrane of capillaries, neurons, and . b. They form the external and internal glial-limiting membranes of the CNS. c. They play a role in the metabolism of certain neurotransmitters (e.g., r-aminobutyric acid (GABA), serotonin, glutamate). d. They buffer the potassium concentration of the extracellular space. e. They form glial scars in damaged areas of the brain (i.e., astrogliosis). f. They contain glial fibrillary acidic protein (GFAP), which is a marker for astrocytes. g. They contain glutamine synthetase, another biochemical marker for astrocytes. h. They may be identified with monoclonal antibodies (e.g., A 2B 5). 2. Oligodendrocytes are the myelin-forming cells of the CNS. One can myelinate as many as 30 axons. B. arise from monocytes and function as the scavenger cells (phagocytes) of the CNS. C. EPENDYM AL CELLS are ciliated cells that line the central canal and ventricles of the brain. They also line the luminal surface of the choroid plexus. These cells produce cerebrospinal fluid (CSF). D. are modified ependymal cells that contact capillaries and neurons. They mediate cellular transport between the ventricles and the . They project to hypothalamic nuclei that regulate the release of gonadotropic hormone from the adenohypophysis. E. SCHWANN CELLS are derived from the neural crest. They are the myelin-forming cells of the PNS. One Schwann cell can myelinate only one internode. Schwann cells invest all myelinated and unmyelinated axons of the PNS and are separated from each other by the nodes of Ranvier.

THE BLOOD - BRAIN BARRIER consists of the tight junctions of nonfenestrated endothelial cells; some authorities include the astrocytic foot processes. Infarction of brain tissue destroys the tight junctions of endothelial cells and results in vasogenic edema, which is an infiltrate of plasma into the extracellular space.

THE BLOOD - CSF BARRIER consists of the tight junctions between the cuboidal epithelial cells of the choroid plexus. The barrier is permeable to some circulating peptides (e.g., insulin) and plasma proteins (e.g., prealbumin).

PIGMENTS AND INCLUSIONS A. LIPOFUSCIN GRANULES are pigmented cytoplasmic inclusions that commonly accumulate with aging. They are considered residual bodies that are derived from lysosomes. B. MELANIN (NEUROMELANIN) is blackish intracytoplasmic pigment found in the substantia nigra and locus coeruleus. It disappears from nigral neurons in patients who have Parkinson’s disease. C. LEW Y BODIES are neuronal inclusions that are characteristic of Parkinson’s disease. D. NEGRI BODIES are intracytoplasmic inclusions that are pathognomonic of rabies. They are found in the pyramidal cells of the hippocampus and the Purkinje cells of the cerebellum. E. HIRANO BODIES are intraneuronal, eosinophilic, rodlike inclusions that are found in the hippocampus of patients with Alzheimer’s disease. F. NEUROFIBRILLARY TANGLES consist of intracytoplasmic degenerated . They are seen in patients with Alzheimer's disease. G. COW DRY TYPE A INCLUSION BODIES are intranuclear inclusions that are found in neurons and in herpes simplex encephalitis.

THE CLASSIFICATION OF NERVE FIBERS is shown in Table 1-1 TABLE 1-1 CLASSIFICATION OF NERVE FIBERS

Conduction Velocity Fiber Diameter (jim)* (m/sec)______Function

Sensory axons la (A-a) 12-20 70-120 Proprioception, muscle spindles lb (A-a) 12-20 70-120 Proprioception, Golgi tendon, organs II (A-|i) 5-12 30-70 Touch, pressure, and vibration III (A-5) 2-5 12-30 Touch, pressure, fast pain, and temperature IV (C) 0.5-1 0.5-2 Slow pain and temperature, unmyelinated fibers Motor axons Alpha (A-a) 12-20 15-120 Alpha motor neurons of ventral horn (innervate extrafusal muscle fibers) Gamma (A-y) 2-10 10-45 Gamma motor neurons of ventral horn (innervate intrafusal muscle fibers) Preganglionic <3 3-15 Myelinated preganglionic autonomic autonomic fibers (B) fibers Postganglionic 1 2 Unmyelinated postganglionic autonomic fibers (C) autonomic fibers ‘ Myelin sheath included if present.

Somatosensory System

RECEPTORS are specialized sensory organs that register physical and chemical changes in the external and internal environment of the organism and convert (transduce) them into the electrical impulses that are processed by the nervous system. Receptors are found at the peripheral end of afferent nerve fibers. Some receptors inform the body about changes in the nearby external environment (exteroceptors) or in the distant external environment (teleceptors, such as the eye and ear). Proprioceptors, such as the labyrinth of the inner ear, convey information about the position and movement of the head in space, tension in muscles and tendons, the position of the joints, the force needed to carry out a particular movement, and so on. Processes within the body are reported on by enteroceptors, also called visceroceptors (including osmoceptors, chemoceptors, and baroceptors, among others). Each type of receptor responds to a stimulus of the appropriate, specific kind, provided that the intensity of the stimulus is above threshold. Most receptors in the skin are exteroceptors.

CUTANEOUS RECEPTORS (Figure 1-5) are divided into two large groups: free nerve endings and encapsulated endings.

A. Free nerve endings are (pain) and thermoreceptors (cold and heat). B. Encapsulated endings are touch receptors (Meissner’s corpuscles) and pressure and vibration receptors (Pacinian corpuscles). C. Merkel disks are unencapsulated light touch receptors.

Figure 1-5 Three important cutaneous receptors. Free nerve endings mediate pain and temperature sensation. Meiss- ner corpuscles of the dermal papillae mediate tactile two-point discrimination. Pacinian corpuscles of the dermis medi­ ate touch, pressure, and vibration sensation. Merkel disks mediate light touch. The further “way stations” through which an afferent impulse must travel as it makes its way to the CNS are the peripheral nerve, the , and the posterior nerve root, through which it enters the .

PERIPHERAL NERVE. Action potentials arising in a receptor organ of one of the types described above are conducted centrally along an afferent fiber, which is the peripheral process of the first somatosensory neuron, whose cell body is located in a dorsal root ganglion.

NERVE PLEXUS AND POSTERIOR ROOT. Once the peripheral nerve enters the spinal canal through the intervertebral foramen, the afferent and efferent fibers go their separate ways: the peripheral nerve divides into its two “sources,” the anterior and posterior spinal roots.

The anterior root contains the efferent nerve fibers exiting the spinal cord, while the posterior root contains the afferent fibers entering it. In total, there are 31 pairs of spinal nerves; each spinal nerve is formed by the junction of an anterior and a posterior nerve root within the spinal canal. There are just as many pairs of nerves in each of these regions as there are vertebrae (12 thoracic, 5 lumbar, and 5 sacral). Lastly, there is a single pair of coccygeal nerves (or, occasionally, more than one pair).

DORSAL ROOT GANGLION. The dorsal root ganglion is macroscopically visible as a swelling of the dorsal root, immediately proximal to its junction with the ventral root (Fig. 2.4). The neurons of the dorsal root ganglion arepseudounipolar, i.e., they possess a single process that divides into two processes a short distance from the cell, in a T-shaped configuration. There are no synapses within the dorsal root ganglion itself.

The fibers of individual nerve roots are redistributed into multiple peripheral nerves by way of the plexuses, and each nerve contains fibers from multiple adjacent radicular segments. The fibers of each radicular segment regroup in the periphery, however (Fig. 2.6), to innervate a particular segmental area of the skin (DERMATOME). Each dermatome corresponds to a single radicular segment, which, in turn, corresponds to a single “spinal cord segment.’ Fig. 2.6 Segmental innervation of the skin (after Hansen-5 eh Hack), a Anterior view, b Posterior view. When a peripheral nerve is injured, the fibers within it, derived from multiple nerve roots, can no longer rejoin in the periphery with fibers derived from the same nerve roots but belonging to other peripheral nerves— in other words, the fibers in the injured nerve can no longer reach their assigned dermatomes. The sensory deficit thus has a different distribution from that of the dermatomal deficit seen after a radicular injury (Fig. 2.8). POSTERIOR (DORSAL) COLUMN-MEDIAL PATHWAY (Figures 2.15, 2.16, 2.17)

A. FUNCTION. The posterior (dorsal) column—medial lemniscus pathway mediates tactile discrimination, vibration sensation, form recognition, and joint and muscle sensation (conscious proprioception). B. RECEPTORS include Pacinian and Meissner’s tactile corpuscles, joint receptors, muscle spindles, and Golgi tendon organs. C. FIRST-ORDER NEURONS are located in the spinal (dorsal root) ganglia at all levels. They project axons to the spinal cord through the medial root entry zone. First-order neurons give rise to 1. The gracile fasciculus (Goll) from the lower extremity. 2. The cuneate fasciculus (Burdach) from the upper extremity. 3. The collaterals for spinal reflexes (e.g., myotatic reflex). 4. The axons that ascend in the dorsal columns and terminate in the gracile and cuneate nuclei of the caudal medulla. D. SECOND-ORDER NEURONS are located in the gracile and cuneate nuclei of the caudal medulla. They give rise to axons and internal arcuate fibers that decussate and form a compact fiber bundle (i.e., medial lemniscus). The medial lemniscus ascends through the contralateral brain stem and terminates in the ventral posterolateral (VPL) nucleus of the thalamus. E. THIRD-ORDER NEURONS are located in the VPL nucleus of the thalamus. They project through the posterior limb o f the internal capsule to the postcentral gyrus, which is the primary somatosensory cortex (Brodmann’s areas 3, 1, and 2). The somatotopic projection on the postcentral gyrus resembles a person standing on his head— an inverted “homunculus” (Fig. 9.19). F. TRANSECTION OF THE POSTERIOR (DORSAL) COLUMN-MEDIAL LEMNISCUS TRACT 1. Above the sensory decussation, transection results in contralateral loss of the posterior (dorsal) column modalities. 2. In the spinal cord, transection results in ipsilateral loss of the posterior (dorsal) column modalities.

LATERAL SPINOTHALAMIC TRACT (Figures 2.15, 2.16, 2.17)

A. FUNCTION. The lateral spinothalamic tract mediates pain and temperature sensation. B. RECEPTORS are free nerve endings. The lateral spinothalamic tract receives input from fast- and slow-conducting pain fibers (i.e., A-8 and C, respectively). C. FIRST-ORDER NEURONS are found in the spinal (dorsal root) ganglia at all levels. They project axons to the spinal cord through the dorsolateral tract of Lissauer (lateral root entry zone) to second-order neurons. D. SECOND-ORDER NEURONS are found in the dorsal horn. They give rise to axons that decussate in the ventral white commissure and ascend in the contralateral lateral . Their axons terminate in the VPL nucleus o f the thalamus. E. THIRD-ORDER NEURONS are found in the VPL nucleus of the thalamus. They project through the posterior limb of the internal capsule to the primary somatosensory cortex (Brodmann’s areas 3, 1, and 2). F. TRANSECTION OF THE LATERAL SPINOTHALAMIC TRACT results in contralateral loss o f pain and temperature below the lesion. j £ и го — 3 k/l3 сл "га 4—1О о о .О v і—QJ с и V"i о с ГО c ■О 4-і о o с ~Q ГО ■_l QJ tc fO 3 ■1—■ га -О с з ■о > С E Е с го C3 с в— W о QJ "oj о v > " О с 4—1 CL C l "С ф lc QJ Ф и "C l QJ и ф С а— о QJ О 3 і__ QJ * с un CL Сі C l un |Л -1—I ф О !_О 1— £ ■4— о _ E 1 а_

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ілC l О 'к_ QJ in in the spinal cord Fig. 2.15 Fig. 2.15 Position of fibers of different somatosensory modalities in the posterior root and root entry zone, and their further course

Paleo- cerebellum

Posteriorspino- 1 9 cenebellartiact f E Alter і or spino- h C l с cenebellar tract 2 і Cl

Do rsa I externa I a reuate fibers Nucleus gracilis a nd nucleus cuneatus — Accessory cuneate nucleus

Posterio rspino- Proprioception cerebellar (muscle spindles, tract Golgi organs, joint bodies, etc,)

Anterior Position sense, spin o- vibration, pressure, cerebellar discrimination, tract touch (cutaneous leceptors, Anterior muscle and tendon splno- ’ lecepto rs, Vater- Pacini thalamic oorpusdes) ■ - IPressuie, toutb (peritrichial nerve endings andvarious cutaneous receptors)

Pain, tempiratum (free nerve endings, Krause and Ruffin і oorpusdes?)

Fig. 2.17 Spinal cord with major ascending pathways and their further course to target struc tures in the cerebrum and cerebellum (schematic drawing) Like the posterior columns, the lateral spinothalamic tract is somatotopically organized; here, however, the fibers from the lower limb lie laterally, while those from the trunk and upper limb lie more medially (Fig. 2.20). Anterior Spinothalamic Tract. The impulses arise in cutaneous receptors (peritrichial nerve endings, tactile corpuscles) and are conducted along a moderately thickly myelinated peripheral fiber to the pseudounipolar dorsal root ganglion cells, and thence by way of the posterior root into the spinal cord. Inside the cord, the central processes of the dorsal root ganglion cells travel in the posterior columns some segments upward, while collaterals travel 1 or 2 segments downward, making synaptic contact onto cells at various segmental levels in the gray matter of the posterior horn (Fig. 2.16c). These cells (the second neurons) then give rise to the anterior spinothalamic tract, whose fibers cross in the anterior spinal commissure, ascend in the contralateral anterolateral funiculus, and terminate in the ventral posterolateral nucleus o f the thalamus, together with the fibers of the lateral spinothalamic tract and the medial lemniscus (Fig. 2.17). The third neurons in this thalamic nucleus then project their axons to the postcentral gyrus in the thalamocortical tract. b v > Fig. 9.19 Relative sizes of the cortical representations of different parts of the body in the human primary somatosensory (a) and motor (b) cortical fields.

TESTING FOR SOMATOSENSORY DEFICITS Testing for pain The best screening test for sensory loss uses a safety pin to lightly prick the face, torso, and 4 limbs; the patient is asked whether the pinprick feels the same on both sides and whether the sensation is dull or sharp. The pin is discarded after use to avoid potential transmission of bloodborne disorders (e.g., HIV infection, hepatitis). Testing for light touch A cotton wisp can be used to test light touch.

Testing for temperature sense Temperature sense can be tested with a cold tuning fork that has one prong rubbed warm by the examiner's palm or with test tubes containing warm and cold water.

Testing for proprioception Joint position sense is tested by moving the terminal phalanges of the patient's fingers, then the toes, up or down a few degrees. If the patient cannot identify these tiny movements with eyes closed, larger up-and- down movements are tried before testing the next most proximal joints (e.g., testing the ankles if toe movement is not perceived). Romberg test Inability to stand with feet together and eyes closed (Romberg test) indicates impaired position sense in the lower extremities. When cerebellar disease is present, the patient stands with the feet apart but as close together as possible without falling and only then closes the eyes.

Testing for vibration sense To test vibration sense, the examiner places a finger under the patient's distal interphalangeal joint and presses a lightly tapped 128-cycle tuning fork on top of the joint. The patient should note the end of vibration about the same time as the examiner, who feels it through the patient's joint.

Testing for stereognosis, graphesthesia and 2-point discrimination Cortical sensory function is evaluated by asking the patient to identify a familiar object (e.g., coin, key) placed in the palm o f the hand (stereognosis) and numbers written on the palm (graphesthesia) and to distinguish between 1 and 2 simultaneous, closely placed pinpricks on the fingertips (2-point discrimination).

LESIONS AFFECTING THE ASCENDING AND DESCENDING TRACTS

Posterior column lesions. The posterior columns mainly transmit impulses arising in the proprioceptors and cutaneous receptors. If they are dysfunctional, the individual can no longer feel the position of his or her limbs; nor can he or she recognize an object laid in the hand by the sense of touch alone or identify a number or letter drawn by the examiner’s finger in the palm of the hand. Spatial discrimination between two stimuli delivered simultaneously at different sites on the body is no longer possible. As the sense of pressure is also disturbed, the floor is no longer securely felt under the feet; as a result, both stance and gait are impaired (gait ataxia), particularly in the dark or with the eyes closed. These signs o f posterior column disease are most pronounced when the posterior columns themselves are affected, but they can also be seen in lesions of the posterior column nuclei, the medial lemniscus, the thalamus, and the postcentral gyrus. The clinical signs of a posterior column lesion are, therefore, the following: - Loss of the sense of position and movement (kinesthetic sense): the patient cannot state the position of his or her limbs without looking.

- Astereognosis: the patient cannot recognize and name objects by their shape and weight using the sense of touch alone.

- Agraphesthesia: the patient cannot recognize by touch a number or letter drawn in the palm of the hand by the examiner’s finger.

- Loss of two-point discrimination: the patient cannot distinguish between 1 and 2 simultaneous, closely placed pinpricks on the fingertips.

- Loss of vibration sense: the patient cannot perceive the vibration of a tuning fork placed on a bone.

- Positive Romberg sign: The patient cannot stand for any length of time with feet together and eyes closed without wobbling and perhaps falling over. The loss of proprioceptive sense can be compensated for, to a considerable extent, by opening the eyes (which is not the case, for example, in a patient with a cerebellar lesion).

Lesions of the lateral spinothalamic tract. The lateral spinothalamic tract is the main pathway for pain and temperature sensation. If the lateral spinothalamic tract is transected in the ventral portion o f the spinal cord, pain and temperature sensation are deficient on the opposite side one or two segments below the level of the lesion, while the sense o f touch is preserved (dissociated sensory deficit).

A unilateral lesion o f the somatosensory cortex produces a subtotal impairment o f the perception o f noxious, thermal, and tactile stimuli on the opposite side of the body; contralateral discrimination and position sense, however, are totally lost, as they depend on an intact cortex. SOMATOSENSORY DEFICITS DUE TO LESIONS AT SPECIFIC SITES ALONG THE SOMATOSENSORY PATHWAYS

Figure 2.21 shows some typical sites of lesions along the somatosensory pathways; the corresponding sensory deficits are discussed below. - A cortical or subcortical lesion in the sensorimotor area corresponding to the arm or leg (a and b, respectively, in Fig. 2.21) causes paresthesia (tingling, etc.) and numbness in the contralateral limb, which are more pronounced distally than proximally. An irritative lesion at this site can produce a sensory focal seizure; because the motor cortex lies directly adjacent, there are often motor discharges as well (Jacksonian seizure). - A lesion of all sensory pathways below the thalamus (c) eliminates all qualities of sensation on the opposite side of the body. - If all somatosensory pathways are affected except the pathway for pain and temperature (d), there is hypesthesia on the opposite side of the body and face, but pain and temperature sensation are unimpaired. - Conversely, a lesion of the trigeminal lemniscus and of the lateral spinothalamic tract (e) in the impairs pain and temperature sensation on the opposite side of the body and face, but does not impair other somatosensory modalities. - If the medial lemniscus and anterior spinothalamic tract (f) are affected, all somatosensory modalities of the contralateral half of the body are impaired, except pain and temperature. - Lesions of the spinal nucleus and tract of the trigeminal nerve and of the lateral spinothalamic tract (g) impair pain and temperature sensation on the ipsilateral half of the face and the contralateral half of the body. - Posterior column lesions (h) cause loss of position and vibration sense, discrimination, etc., combined with ipsilateral ataxia. - If the posterior horn of the spinal cord is affected by a lesion (i), ipsilateral pain and temperature sensation are lost, but other modalities remain intact (dissociated sensory deficit). - A lesion affecting multiple adjacent posterior roots (j) causes radicular pain and paresthesiae, as well as impairment or loss of all sensory modalities in the affected area of the body, in addition to hypotonia or atonia, areflexia, and ataxia if the roots supply the upper or lower limb.

QUESTIONS FOR SELF-EDUCATION

1. Which of the following symptoms is true about NEURONS (choose applicable): 1. Neurons are basic cells of the nervous system 2. Neurons receive information, integrate it, and pass it along 3. Neurons can be located in the skin, muscles or 4. Neurons consist of several parts 5. Neurons can be different (by types of processes) 6. Neurons mostly have only one process - axon 7. Neurons can make several types of synaptic contacts 8. Neurons can have different function 9. Neurons use neurotransmitters to transmit signals across a 10. Signals between neurons occur via synapses

2. Name the entire structure. 1. Cell body 2. Myelin sheath 3. Dendrites 4. 5. Axon 6. Schwann cell 7. Node o f Ranvier 8. 9. 10. Axon terminals 11. Oligodendrocyte 12. 13. Microglia 3. Name the structure under the red arrow. 1. Cell body 2. Myelin sheath 3. Dendrites 4. Soma 5. Axon 6. Schwann cell 7. 8. Astrocyte 9. Axon hillock 10. Axon terminals 11. Oligodendrocyte 12. Neurilemma 13. Microglia

4. Name the structure under the red arrows. 1. Cell body 2. Myelin sheath 3. Dendrites 4. Soma 5. Axon 6. Schwann cell 7. Node of Ranvier 8. Astrocyte 9. Axon hillock 10. Axon terminals 11. Oligodendrocyte 12. Neurilemma 13. Microglia

5. Name the structure under the red arrows. 1. Cell body 2. Myelin sheath 3. Dendrites 4. Soma 5. Axon 6. Schwann cell 7. Node of Ranvier 8. Astrocyte 9. Axon hillock 10. Axon terminals 11. Oligodendrocyte 12. Neurilemma 13. Microglia 6. Name the structure under the red arrow. 1. Cell body 2. Myelin sheath 3. Dendrites 4. Soma 5. Axon 6. Schwann cell 7. Node o f Ranvier 8. Astrocyte 9. Axon hillock 10. Axon terminals 11. Oligodendrocyte 12. Neurilemma 13. Microglia

7. Name the entire structure. 1. Myelin sheath 2. Soma 3. Axon 4. Schwann cell 5. Node of Ranvier 6. Axon hillock 7. Axon terminals 8. Neurilemma 8. Name the structure between red arrows. 1. Myelin sheath 2. Soma 3. Axon 4. Schwann cell 5. Node of Ranvier 6. Axon hillock 7. Axon terminals 8. Neurilemma 9. Name the layers. 1. Myelin sheath 2. Soma 3. Axon 4. Schwann cell 5. Node of Ranvier 6. Axon hillock 7. Axon terminals 8. Neurilemma 10. Name the outer membrane. 1. Myelin sheath 2. Soma 3. Axon 4. Schwann cell 5. Node of Ranvier 6. Axon hillock 7. Axon terminals 8. Neurilemma 11. Name the gap. 1. Myelin sheath 2. Soma 3. Axon 4. Schwann cell 5. Node of Ranvier 6. Axon hillock 7. Axon terminals 8. Neurilemma 12. Name the area. 1. Myelin sheath 2. Soma 3. Axon 4. Schwann cell 5. Node of Ranvier 6. Axon hillock 7. Axon terminals 8. Neurilemma

13. MYELIN SHEATH is (choose applicable): 1. Layers of electrically insulating material (dielectric) around the axon of a neuron 2. It is essential for the proper functioning of the nervous system 3. It is an outgrowth of a type of glial cell 4. Its main purpose is to increase the speed at which impulses propagate along the myelinated fiber 5. It helps preventing the electrical current from leaving the axon 6. It has gaps, more commonly known as nodes of Ranvier 7. Schwann cells supply the myelin for peripheral neurons 8. Oligodendrocytes myelinate the axons of the central nervous system

14. Define components of a NEURON (choose applicable): 1. Soma 2. Axon 3. Myofibrils 4. 5. Receptors 6. Axon terminal 7. Axon hillock 8. Synapses 9. Organelles 16. Using the figure on the left indicate : a) 1 b) 2 c) 3 d) 4

17. Using the figure on the left indicate : is a) 1 b) 2 c) 3 d) 4

SS 18. Using the figure on the left indicate Pseudounipolar Neuron: a) 1 b) 2 c) 3 ss d) 4 19. Which of the following symptoms is true about NISSL SUBSTANCE (choose applicable): 1. This is a large granular body found in neurons 2. Its function is synthesis and release of proteins 3. Nissl substance can be found in different types of cells in the human body 4. In pathological conditions they may dissolve and disappear 5. Nissl substance are responsible for synthesis of proteins for intercellular use 6. It consists of granules of rough endoplasmic reticulum with rosettes of free ribosomes

20. Which of the following symptoms is true about WALLERIAN DEGENERATION (choose applicable): 1. It begins only after a nerve fiber has been cut or crushed 2. It can occur even without preceding axonal injury 3. Part of the axon separated from the soma degenerates distal to the injury 4. It is also known as anterograde or orthograde degeneration 5. It can occur after axonal injury only in the peripheral nervous system 6. It can occur after axonal injury only in the central nervous system 7. It occurs in the axon stump distal to a site of injury 8. It usually begins within 24-36 hours of a lesion 9. It occurs after axonal injury in both the peripheral nervous system and central nervous system 10. It usually begins within 84-108 hours of a lesion 11. The nerve fiber's neurolemma does not degenerate and remains as a hollow tube

21. From different cells below choose GLIAL CELLS: 1. Bipolar neurons 2. Macroglia 3. Microglia 4. Miniglia 5. Ependymal cells 6. Pseudounipolar neurons 7. Tanycytes 8. Astrocytes 9. Schwann cells 10. Oligodendrocytes

22. Which of the following symptoms is true about a RECEPTOR (choose applicable): 1. It is a small neuron 2. Receptor is the first component in a sensory system 3. It is found at the peripheral end of afferent nerve fibers 4. It is specialized sensory organ 5. It is a part of motor system 6. It registers physical and chemical changes in the external and internal environment of the organism and convert them into the electrical impulses that are processed by the nervous system 7. There are different types of receptors in the human body 8. There is only one type of receptors in the skin 9. Each type of receptor responds to a stimulus of the appropriate, specific kind, provided that the intensity of the stimulus is above threshold 10. Most receptors in the skin are exteroceptors 11. There are 4 groups of receptors in the skin 12. Receptors function by depolarizing neurons and producing action potentials

23. Which of the following symptoms is true about DORSAL ROOT GANGLION (choose applicable): 1. It is macroscopically visible as a swelling of the dorsal root 2. It can be found in different visceral organs 3. It contains the cell bodies of autonomic nerves 4. It contains pseudounipolar neurons 5. It is specialized sensory organ 6. There are many synapses within the dorsal root ganglion itself 7. It contains the 2nd order sensory neurons 8. It contains the 1st order sensory neurons 9. Lesions of dorsal root ganglia can produce intensive pain and rash

24. Which of the following symptoms is true about DERMATOME (choose applicable): 1. It is an area of skin supplied by sensory neurons that arise from a spinal nerve ganglion 2. There are 7 cervical dermatomes 3. There are 8 cervical dermatomes 4. There are 12 thoracic dermatomes 5. There are 5 lumbar dermatomes 6. There are 3-4 sacral dermatomes 7. There are 5 sacral dermatomes 8. Each dermatome corresponds to a single radicular segment, which, in turn,corresponds to a single “spinal cord segment” 9. The sensory deficit seen after a radicular injury has the same distribution as if the a peripheral nerve is injured 25. Which of the following symptoms indicates impairment of the DORSAL ROOTS C5-D1 on the right side: 1. Loss of all types of sensation below the lesion 2. Loss of proprioception alone in the right arm 3. Loss of deep and superficial sensory types in the right arm 4. Loss of superficial sensation alone in the right arm 5. Loss of all types of sensation in the left arm 6. Positive Romberg test 7. Loss of vibration sense in the right arm 8. Loss of vibration sense in the left arm 9. Loss of pain and temperature sensation in the right arm 10. Loss of pain and temperature sensation below the lesion 11. Intensive spontaneous pain in the right arm 12. Intensive spontaneous pain on the right side below the lesion 13. Absence of spontaneous pain 14. Weakness in the right arm 15. Astereognosis in the right arm

26. Which of the following symptoms indicates impairment of the DORSAL HORNS C5-D1 on the right side: 1. Loss of all types of sensation below the lesion 2. Loss of proprioception alone in the right arm 3. Loss of deep and superficial sensory types in the right arm 4. Loss of superficial sensation alone in the right arm 5. Loss of all types of sensation in the left arm 6. Positive Romberg test 7. Loss of vibration sense in the right arm 8. Loss of vibration sense in the left arm 9. Loss of pain and temperature sensation in the right arm 10. Loss of pain and temperature sensation below the lesion 11. Intensive spontaneous pain in the right arm 12. Intensive spontaneous pain in on the right side below the lesion 13. Absence of spontaneous pain 14. Weakness in the right arm 15. Astereognosis in the right arm

27. Which of the following symptoms is true about POSTERIOR COLUMN of the spinal cord (choose applicable): 1. It is an area of in the dorsomedial side of the spinal cord 2. It is an area of gray matter in the central part of the spinal cord 3. It contains sensory neurons of different modalities 4. It contains highly-myelinated fibers - axons of the 1st order neurons located in the dorsal root ganglia 5. It contains axons of the 2nd order neurons located in the medulla 6. It is also known as funiculus cuneatus Burdach 7. It is also known as funiculus gracilis Goll 8. Fasciculus gracilis conducts sensory impulse from lower part of the body 9. Fasciculus cuneatus conducts sensory impulse from upper part of the body 10. Fasciculus gracilis reaches the nucleus gracilis in the medulla 11. Fasciculus cuneatus reaches the nucleus cuneatus in the pons 12. Lesions of posterior columns produce ataxia 13. Lesions of posterior columns produce anesthesia of pain and temperature below the lesion 14. Positive Romberg test indicates impairment of posterior columns 15. Lesions of posterior columns can diminish or completely abolish tactile sensations and movement or position sense below the lesion. 28. Which of the following symptoms is true about LATERAL SPINOTHALAMIC PATHWAY (choose applicable): 1. It is a part of the anterolateral system 2. It is a bundle of axons of 1st order sensory neurons located in the dorsal ganglia 3. It is a bundle of axons of 2nd order sensory neurons located in the dorsal horns of the spinal cord 4. It contains highly-myelinated fibers 5. It is a bundle of sensory axons carrying sensory information from the brain to the skin 6. It includes fibers (axons) and sensory neurons 7. It carries pain and temperature sensory information to the thalamus of the brain 8. It decussates in the anterior white commissure 9. It makes synaptic connections with neurons in the nuclei gracilis and cuneatus in the medulla 10. It ascends through the medulla, pons and midbrain until synapsing in the Ventral Postero-Lateral nucleus of the thalamus 11. AS fibers conduct immediate, sharp pain and also temperature 12. C fibers conduct dull, burning pain and also temperature 13. Lesions of lateral spinothalamic tract produce ataxia 14. Lesions of lateral spinothalamic tract produce anesthesia of pain and temperature 15. Positive Romberg test indicates impairment of lateral spinothalamic tract

29. Indicate SENSORY DISTURBANCES (choose applicable): 1. Hyperpathia 2. Paresthesia 3. Hypoesthesia 4. Allodynia 5. Hyperesthesia 6. Paralysis 7. Pain 8. Dysesthesia 9. Graphesthesia

30. Indicate symptoms of unilateral partial damage of the PRECENTRAL GYRUS (choose applicable): 1. Ipsilateral monoanesthesia of all sensory types 2. Paresthesiae in lower limbs 3. Contralateral monoanesthesia of deep sensation alone 4. Hyperesthesia in upper limbs 5. Contralateral hemianesthesia of all sensory types 6. Spontaneous pain 7. Contralateral monoanesthesia of all sensory types 8. Ipsilateral hemianesthesia of all sensory types 9. Contralateral monoanesthesia of superficial sensation alone