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147 Cards in this Set

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What vessels comprise the anterior circulation?
Internal carotid artery, middle cerebral artery, anterior cerebral artery
What vessels comprise the posterior circulation?
vertebral artery, basilar artery, posterior cerebral artery
What two arteries connect anterior circulation to the posterior circulation of the brain?
Posterior communicating artery, anterior communicating artery
What foramen connect the lateral ventricle's to the third ventricle?
Foramen of Monro
What connects the third ventricle of the fourth ventricle?
Cerebral aqueduct
What three foramen allow for CSF to exit the fourth ventricle?
Foramen of Magendie (midline), two Foramen of Luschka (laterally)
Where is CSF formed?
Choroid plexus
What structure allows CSF to return to circulation?
Arachnoid villi
What are the three meninges?
dura mater, arachnoid, pia
What problem occurs with impaired draining of the CSF fluid?
What is the blood brain barrier?
impermeability of central nervous system blood vessels to most substances in serum
What substances can cross the blood brain barrier?
Lipid soluble substances or those that have specific endothelial transporters
Where is the cervical and enlargement of the spinal cord?
C5 -- T1
Where is the lumbar enlargement of the spinal cord?
L1 -- S2-3
What is the vertebral extent to the spinal cord in neonates versus adults?
Neo-Nate -- L3, adult -- L1-2
What is the lumbar cistern?
Subarachnoid space caudal to the conus medullaris (L1-2 to S2-3)
What three structures make up a somite?
dermatome, myotome, scleratome
What distinguishes a dermatomal from a peripheral nerve cell sensory loss?
The dermatomal: will follow a cutaneous area innervated by a single dorsal nerve root.
Peripheral nerve: includes portions of several dermatomes
What are denticulate ligaments?
To flattened bands of pial tissue that attach to the spinal dura with about 21 teeth
What is the filum terminale?
A pial filament extending from the conus medullaris to the end of the dural sac
What are general somatic afferent (GSA) fibers?
Convey sensory input from skin, muscle, bone, and joints to the central nervous system
What are general visceral, afferent (GVA) fibers?
Conveys sensory input from visceral organs to the central nervous system
What are General somatic efferent (GSE) fibers?
convery motor output from ventral horn motor neurons to skeletal muscle
What are general visceral efferent (GVE) fibers?
convey motor output from intermediolateral cell column neurons via paravertebral or prevertebral ganglia to glands, smooth muscle, and visceral organs
What type of neurons reside in the DRG?
pseudounipolar neurons
What are the five main surface structures and sulci of the spinal cord?
ventral median fissure, venetral lateral sulcus, dorsal lateral sulcus, dorsal intermediate sulcus, dorsal median sulcus
What is the ventral median sulcus?
a deep ventral midline groove underlying the ventral spinal artery
What is the ventral lateral sulcus?
a shallow groove from which the ventral rootlets emerge
What is the dorsl lateral sulcus?
a shallow groove from which the dorsal rootlets emerge
What is the dorsal intermediate sulcus?
a shallow groove found between the dorsal lateral and dorsal median sulci rostral to T6, it separates fasciculus gracilis from fasciculus cuneatus
What is the dorsal median sulcus?
a shallow dorsal midline groove that is continuous with the dorsal median septum
What four nuclei lie within the dorsal horn?
dorsomarginal nucleus (rexed I); substantia gelatinosa (rexed II), nucleus proprius (rexed III & IV), nucleus dorsalis of Clarke (rexed VII)
What is the Dorsal Marginal nucleus?
dorsal horn nucleus; Rexed lamina I; found at all cord levels, is associated with light touch, pain, and temperature sensation, one site of orgin of the ventral and lateral spinothalamic tract
What is the Substantia gelatinosa?
dorsal horn nucleus, Rexed lamina II; found at all cord levels, is associated with light touch, pain, and temperature sensation; homologous to the spinal trigeminal nucleus; integrates input for the ventral and lateral spinothalamic tracts
What is Nucleus proprius?
dorsal horn nucleus, Rexed lamina III and IV; found at all cord levels, associated with light touch, pain, and temperature sensation, gives rise to the ventral and lateral spinothalamic tracts
What is the Nucleus dorsalis of Clarke?
dorsal horn nucleus, Rexed lamina VII; extends from C8 to L3, homologous to the accessory cuneate nucleus of the medulla, origin of the dorsal spinocerebellar tract, subserves unconscious proprioception from muscle spindles and golgi tendon organs
What is the Lateral Horn or intermediolateral nucleus?
Rexed lamina VII; extends between T1 to L3, contains the visceromotor nucleus with preganglionic sympathetic neurons (GVE)
What five nuclei are located in the ventral horn of the spinal cord?
Spinal border cells, sacral parasympathetic nucleus (Rexed VII), Somatic motor nuclei (Rexed IX), spinal accessory nucleus (Rexed IX), Phrenic nucleus (Rexed IX)
What are spinal border cells (Cooper-Sherrington)?
extend from L2 to S3; provide unconscious proprioception from GTOs and muscle spindles, are the orgin of the ventral spinocerebellar tract
What is the sacral parasympathetic nucleus?
Anterior horn nucleus, rexed lamina VII; extends from S2 to S4, gives rise to preganglionic parasympathetic fibers that innervate the pelvic viscera via the pelvic nerve
What is the somatic motor nuclei?
anterior horn nucleus, rexed lamina IX, found at all cord levels, subdivided into medial and lateral groups that innervate axial and appendicular muscles respectively
What is the Spinal accessory nucleus?
anterior horn nucleus, rexed lamina IX, extends from C1 to C6, gives rise to the spinal root of the spinal accessory nerve, innervates sternocleidomastoid and trapezius.
What is the Phrenic nucleus?
anterior horn nucleus, rexed lamina IX, extends from C3 to C6, innervates the diaphragm
What are the four tracts of the White matter of the spinal cord?
Dorsal funiculus, Lateral funiculus, Ventral funiculus, Dorsolateral fasciulus
What makes up the dorsal funiculus?
located btw the dorsal median sulcus and dorsal lateral sulcus; fasciculus gracilis is found at all cord levels and is located btw the dorsal median sulcus and dorsal intermediate sulcus; fasciculus cuneatus is found only btw C1 and T6 btw the intermediate sulcus and dorsal lateral sulcus.
What is the ventral white commissure?
A region of the ventral funiculus btw the central canal and the ventral medial fissure which contains decussating spinothalamic tracts
What is the intermediomedial nucleus?
anterior horn nucleus, Rexed lamina VII, found at all cord levels, receives visceral afferents, projects to the intermediolateral nucleus which has the sympathetic efferents
Rexed Lamina I
Posteromarginal Nucleus
Rexed Lamina II
Substantia Gelatinosa
Rexed Lamina III and IV
Nucleus Proprius
Rexed Lamina V and VI
Rexed Lamina VII
IML, IMM, Clarke's Nucleus, Sacral autonomic nucleus (S2-S4)
Rexed Lamina VIII
Coordinates intersegmental reflexes, receives input from major descending tracts from the visual, auditory, and reticular systems, projects bilaterally to laminae VII and IX
Rexed Lamina IX
alpha motor neurons, gamma motor neurons that innervate muscle spindle fibers, phrenic nucleus, spinal accessory nucleus, orgin of lower motor neurons
Rexed Lamina X
central canal region
What is Special Visceral Afferent (SVA)?
taste, olfaction
What is Special somatic Afferent (SSA)?
teloception (vision, audition, balance)
Free Nerve Endings
Nonencapsulated, slow adapting, function with pain/temperature sensation, distributed in deep skin and viscera
Merkel's Disk
Nonencapsulated, slow adapting, function with touch, distributed in feet, hands, genitalia, and lips
Hair Follicle
Nonencapsulated, fast adapting, function with touch, distributed anywhere with hair
Meissner's Corpuscle
Encapsulated, fast adapting, function with 2 point discrimination, found in hairless skin, fingertips, joints and ligaments
Pacinian Corpuscles
encapsulated, fast adapting, function with vibration, found on fingers toes, palms, mesenteries, and peritonium
Ruffini Endings
encapsulated, slow adapting, function with stretch and pressure, found in dermis
Joint Receptor
encapsulated, slow adapting, function with joint position, found in joint capsules and ligaments
Neuromuscular Spindle
encapsulated, slow adapting, function with limb muscle stretch/length, found within muscles
Golgi Tendon Organs
encapsulated, slow adapting, function with muscle tension, found within muscle tendon junction
What three receptor types are nonencapsulated?
free nerve endings, merkel's disk, hair follicles
What six receptor types are encapsulated?
meissner's corpuscles, pacinian corpuscles, ruffini endings, joint receptors, neuromuscular spindles, golgi tendon organ
What is receptor adaptation and the difference between slow and fast adapting?
receptor adaptation: a decrease in receptor sensitivity during a maintained stimulus such that fast adapting receptors become desensitized and stop reacting to the stimulus quickly which slow adapting receptors do not.
What are the characteristics of the lateral division of the dorsal root afferents?
Thin, lightly myelinated fibers; pain and temp, light touch, visceral afferents
What are the characteristics of the medial division of the dorsal root afferents?
Thick, heavily myelinated fibers; 2-point touch, limb position, muscle stretch, sends collaterals to medulla
What kind of information is sent in the dorsal column pathways?
2 point discrimination; vibration sense; proprioception; GSA
Where do the neurons of the dorsal column pathway decussate?
Cross in Caudal Medulla as the Interal arcuate fibers which form the medial lemniscus
Where do the internal arcuate fibers of the dorsal column pathway synapse?
Ventral posterolateral (VPL) nucleus of the thalamus
What is exteroception?
The sensation of contact on the external body surface. Ie. fine touch, light touch, temperature, pain, vibration
What is proprioception?
The perception of limb position and movement
What are the characteristics of slow adapting receptors?
respond best to unchanging stimuli
What are the characteristics of fast adapting receptors?
respond best to changing stimuli, such as touch
What is Romberg sign?
unsteadiness with eyes closed, used to distinguish dorsal column ataxia from cerebellar ataxia
What kind of information is sent in the spinothalamic pathway?
pain, temperature, and itch; visceral pain; light or crude touch
Where is the origin of the spinothalamic tract?
Dorsal horn, nucleus proprius
Where is the primary somatosensory cortex region?
Area 312 of the postcentral gyrus
Where do the neurons of the spinothalamic tract decussate?
At the spinal cord level of entry within the ventral white commissure
What is the effect of a lesion within the spinothalamic tract?
contralateral loss of pain and temperature sensation below the level of lesion
Where do the 2 order neurons of the spinothalamic tract synapse?
Vental posterolateral (VPL) nucleus of the thalamus
What is the topographical localization of different regions of the body within the spinothalamic tract?
Cervical neurons are most medial and sacral neurons are most lateral within the tract
What is a syringomyelia?
A spinal cord lesion which results in the formation of a tube forming from the central canal. This leads to sacral sparing and a vest like loss of sensation because the cervical neurons within the spinothalamic and dorsal column tracts are most medial
What is the spinoreticular tract?
represents most of the neurons within the spinothalamic tract, conveys crude touch, pain, and temperature information
What kind of information is sent in the dorsal spinocerebellar tract?
relays muscle tension, stretch from muscle spindles and golgi tendon organs
What is the origin and course of the dorsal spinocerebellar tract?
Arises from the dorsal nucleus of Clarke, afferents below L3 ascend in fasciculus gracilis to reach Clarke's nucleus or afferents above C8 travel in fasciculus cuneatus (cuneocerebellar tract) and ascends ipsilaterally and enters the inferior cerebellar peduncle
What is the origin and course of the ventral spinocerebellar tract?
Arises from the dorsal horn and intermediate gray (Laminae V-VII); ascends contralaterally and enters superior cerebellar peduncle and recrosses to make its final destination ipsilateral
What kind of information is sent in the ventral spinocerebellar tract?
Information from spinal motor interneurons especially in the lower extremities
What is a motor unit?
a single alpha motor neuron with all the skeletal muscle fibers it innervates
What do small versus large motor units control?
Small- precise movements of finger and eye muscles
Large - axial and some limb movements
What are Ia afferent neurons?
sensory neurons which synapse with alpha, gamma, and inhibitory interneurons
What are Gamma motor neurons?
neurons which innervate intrafusal fibers to control the sensitivity of muscle spindles when a muscle changes length
What is the origin of the corticospinal tract?
the motor and somatosensory cortexes (area 4), with major fibers from giant Betz cells in the primary motor cortex
Where does the corticospinal tract decussate?
In the pyramids of the medulla and descends in the lateral funiculus to all spinal cord levels.
Where are the three spinal terminations of the corticospinal tract and what are their functions?
Dorsal horn- modulates sensory afferents
Lateral horn - controls gross limb movements and rapid movements
Ventral horn - controls indepented digital movements and precise movements, esp. flexor muscle groups
What is the function of the rubrospinal tract?
controls limb movements, coordinating pathway for cerebral and cerebellar influences
Where is the origin of the rubrospinal tract?
red nucleus, which receives inputs from cerebral motor cortex and cerebellar nuclei
What is the function of the tectospinal tract?
reflex movements of the head and forelimb to visual, auditory, and somatosensory stimuli
What is the function of the vestibulospinal tracts?
reflex pathways to vestibular stimuli
Which two tracts are part of the lateral motor system?
lateral corticospinal tract; rubrospinal tract
Which four tracts are part of the medial motor system?
anterior corticospinal tract; vestibulospinal tract; tectospinal tract; reticulospinal tract
What are type I muscle fibers?
Slow twitch; red muscle; fatigue resistant; oxidative; moderate speed of contraction; mainly found in posture muscles which tetanize at low frequencies; tonic
What are type IIa muscle fibers?
fast twitch; red in color; found in pale muscle; rapid contraction; oxidative; moderate fatigue resistance; phasic
What are type IIb muscle fibers?
fast twitch; white in color; found in pale muscle; rapid contraction; glycolytic (anaerobic), fatigable; phasic
What is a motor pool?
the number of motor units that innervate a single muscle
What is Henneman's size principle?
the motor unit size is proportional to the neuron's diameter and body size, such that small, slow units are more excitable and recruited first to perform smooth control while large, fast units are active only during high force contractions with poor control
What is muscle compensation?
The increase in discharge frequency of remaining neurons if part of a motor pathway is damaged. The neuronal loss may not be noticed until >50% is lost.
What happens to the histochemical muscle fiber type after denervation?
The normal checkerboard pattern is lost as the active motor units compensate and hypertrophy forming larger clusters of single fiber types.
What are the types of muscle receptors?
Muscle spindle organs, golgi tendon organ, paciniform corpuscles and free nerve endings
What is the function of muscle spindle organs?
senses change in muscle length, intrafusal fiber
What is a reflex?
a neural-mediated involuntary change in the response of an effector organ induced by an applied stimulus
What are the five elements of a reflex?
Receptor; afferent nerve fiber; interneurons; efferent nerve fiber; effector organ
What is a polysynaptic reflex vs. a monosynaptic reflex?
Polysynaptic involves one or more interneurons while monosynaptic lacks any interneurons
What are the two types of fibers within the muscle spindle organ?
Nuclear bag: responds to rapid length change
Nuclear chain: responds to slow length change
What is the function of Golgi Tendon Organs?
senses muscle contraction and tension
What is the function of gamma motor neurons?
provide a mechanism to adjust the sensitivity of the muscle spindle and thus the contractile state of the muscle
What is a homonymous muscle?
the muscle where the afferent fibers sensing the stimulus to a reflex arise
What is reciprocal innervation?
activation of the motor neuron to a homonymous muscle with concomitant inhibition of the antagonist muscle
What is recurrent inhibition?
inhibition of alpha motor neurons by glycinergic activity of Renshaw cells (RC) which adjust the sensitivity of alpha motor neurons
What is the stretch reflex?
The stretching of the muscle sensed by muscle spindle organ via afferent Ia fibers leading to the stimulation of the alpha MN and contraction of the homonymous muscle.
What is the Golgi Tendon Organ Reflex?
The increase tension of a muscle is sensed by the GTO and signaled via afferent Ib fibers leading to inhibition of contraction of the homonymous muscle and contraction of the antagonist to reduce tension.
What is the withdrawl reflex?
withdrawl from a source of afferent stimulus mediated by flexor relex afferent fibers and nociceptors leading to exitation of alpha MN to flexor muscles
What is the crossed extensor reflex?
contralateral antagonistic MN activation or inhibition, muscle groups excited on one side are inhibited on the opposite, allowing for weight to be supported during a contralateral withdrawl reflex
What are multisegmental reflexes?
relexes involving several segments and help coordinate muscle groups at different spinal levels, mediated by interneurons, ie. Moro reflex and Tonic neck reflex
What is the Moro reflex?
infantile reflex stimulated by sudden movement of the head backwards leading to abduction of the arms and rapid intake of breath followed by flexion of the legs
What is the Tonic neck reflex?
infantile reflex stimulated by rotation of the head to one side leading to extension of the ipsilateral arm and flexion of the contralateral arm
What is hyperreflexia and two examples of it?
increased myotatic reflex excitability due to loss of inhibitory or gain of excitatory receptors, commonly a sign of upper motor neuron lesions; ie. clonus and clasp knife reflexes
What is spasticity?
increased reflex tone indicated by abnormally strong muscle stretch reflexes
What is Clasp-Knife reflex?
abnormal reflex with strong reflex muscle contraction to gradual stretch followed by a sudden inhibition of the myotatic reflex and loss of muscle tone observed in patients with lesion of descending motor pathway
What is Clonus reflex?
abnormal reflex associated with lesion of descending motor pathways characterized by repetitive rhythmical refex contraction and relaxation of a muscle when stretching an abnormally hyperreflexic tendon
What is hyporeflexia?
abnormal decrease in myotatic reflexes, often reflecting a lesion of sensory inputs from muscle spindles, a motor nerve lesion, or a lesion of the spinal cord anterior horn
What are the steps of normal neuromuscular transmission?
Action potential depolarizes neuron terminal; calcium influx; release of ACh vesicles; ACh bind to AChR on muscle; end-plate depolarization and electrical propagation; muscle contracts; AChE limits the action of Ach
What is the pathophysiology of Myasthenia gravis (MG)?
antibodies to AChR block receptor sites at neuromuscular junctions
What are the symptoms of MG?
initially ptosis and diplopia with subsequent muscle weakness and fatigue in other regions
What is the difference between ocular and generalized MG?
Ocular: muscle weakness is confined to the eyes
Generalized: eventually leads to slurred speech, difficulty swallowing, weakness in face, jaw, limbs, and respiratory muscles
How is MG diagnosed?
Clinical features; positive tensilon test (AChE inhibitor); EMG; elevated serum Ab titer to AChR
How is MG treated?
Anticholinesterase drugs inhibit AChE, Thymectomy, immunosuppresants (corticosteroids); Plasmapheresis; intravenous gamma globulin infusions
What is the pathophysiology of Lambert-Eaton myasthenic syndrome (LEMS)?
immunologic attack on presynaptic calcium channels impairing the release of Ach; often related to an underlying cancer (small cell lung carcinoma)
What are the symptoms of Lambert-Eaton myasthenic syndrome (LEMS)?
fatigable weakness of proximal limbs and trunk, short improvement with exercise; dry mouth; impotence
How is Lambert-Eaton myasthenic syndrome (LEMS) diagnosed?
EMG; nerve stimulation tests; presynaptic calcium channel Ig
What is the role of the thymus in MG?
Thymus abnormalities often occur and if AChR-like material is present here then the harmful Igs can be formed
How is Lambert-Eaton myasthenic syndrome (LEMS) treated?
Treat the underlying cancer; drug enhancement of ACh release; immunosuppresants; plasmapheresis
What is the difference between general somatic efferent (GSE) and special visceral efferent (SVE) fibers?
GSE innervate muscle derived from myotomes (nuclei of III, IV, VI, XII); SVE innervate muslce derived from branchial arches (nuclei ambiguus, inferior and superior salivary, Edinger-Westphal)