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196 Cards in this Set

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How does a reflex (such as the knee-jerk reflex) work?
A tap on the tendon stretches the muscle. Muscle spindles containing sensory fibers synapse in the spinal cord on a motor neuron.
What is divergence?
One sensory neuron can influence a number of motor neurons.
What is convergence?
One motor neuron receives contacts from a number of sensory inputs.
What is the resting membrane potential of a neuron?
-70 mV
How long does an action potential usually last?
1 millisecond
What is the typical amplitude of an action potential?
1/10 of a volt
How is intensity encoded in action potentials?
Frequency of firings and number of neurons sending the action potential.
What is depolarization?
The potential of the cell gradually becomes less negative.
What does the speed of transmission of an action potential depend on?
Diameter and conductance velocity.
How can an EPSP lead to an action potential?
Temporal or spatial summation.
What is the basis of the membrane potential?
Concentration gradients, equilibrium potentials of ions, and selective permeabilities of ions.
What is the net driving force?
The force that moves an ion through a cell membrane. Vdf = Vm - Eion
How many Na+ are moved for each K+?
3 Na+ out for each 2 K+ in
What does ouabain do?
Inhibitor of Na-K ATPase enzyme that blocks active movement of Na/K but does not effect passive movement.
What is the effect of low temperature on active and passive movement?
Reduces both, but active transport more strongly.
What will happen if you remove external K+ or internal Na+ from the cell?
It will inhibit the activity of the Na-K pump
What is the nerve cell membrane potential due primarily to?
Passive movement of K+ out of the cell.
What vertebral level does the spinal cord extend to?
L1-L2
What portion of the spinal cord does the anterior spinal artery supply?
Anterior 2/3
What area of the spinal cord do the two posterior spinal arteries supply?
Posterior 1/3
What attaches the dura mater to the end of the vertebral canal?
Coccygeal ligament
What are extensions of the pia mater that help anchor the spinal cord to the dural sheath?
Denticulate ligament
What is an extension of the pia mater that anchors it to the end of the vertebral canal?
Filum terminale
What is the name for the caudal end of the spinal cord?
Conus medullaris
What are the cervical and lumbar enlargements located?
C3-T2 and L1-S3
Which lamina are located in the dorsal horn?
Nucleus posteromarginalis
Substantia gelatinosa
Nucleus Proprius
Clarke's nucleus/Nucleus dorsalis
Which lamina are located in the lateral horn?
Intermediolateral cell column
Sacral autonomic nuclei
What is located in the ventral horn?
Alpha motor neurons
Interneurons

Medial nuclear group-innervation of neck and trunk, axial
Lateral nuclear group- limbs; lateral = distal, ventral = extensors, dorsal = flexors
What happens during an action potential?
There is an influx of Na+ through voltage-dependent channels, then an outflux of K+ through voltage-dependent channels, finally followed by inactivation of Na+ channels
What is the function of the dorsal column system?
Conveys pressure, vibration, movement, position and discriminative touch
What are the receptors of the dorsal column system?
Meissner's and Pacinian corpuscles, highly specialized mechanoreceptors.
Where does the dorsal column system decussate?
In the medial leminiscus
What is the ultimate destination of the dorsal columns?
The somatosensory cortex in the postcentral gyrus of the parietal lobe.
Describe the path of the dorsal column system.
Fasciculus gracilis and cuneatus from DRG -->
Nucleus gracilis and cuneatus -->
Internal arcuate fibers -->
Medial leminiscus -->
VPL nucleus in thalamus -->
Somatosensory cortex
What tracts make up the anterolateral system?
Neospinothalamic, paleospinothalamic, spinomesencephalic, spinoreticular and anterior spinothalamic tracts.
What is the function of the neospinothalamic tract?
Conveys pain and thermal sense.
Describe the path of the neospinothalamic tract.
Free nerve endings -->
Lissauer's tract -->
Lamina I and V -->
Bifurcate in spinal cord -->
VPL -->
Somatosensory cortez
What is the function of the paleospinothalamic tract?
Sensation of dull, poorly localized pain.
Describe the path of the paleospinothalamic tract.
Unmyelinated C fibers -->
Interneurons in substantia gelatinosa -->
Decussate at each level -->
lamina VI-VII -->
Intralaminar nucleus -->
Cingulate cortex
What is the function of the spinomesencephalic tract?
Control of pain sensation
Describe the path of the spinomesencephalic tract.
Decussate in spinal cord -->
Lamina I and V -->
Terminates in mesencephalic reticular formation and raphe nuclei in ponto-mesencephalic region
What is the function of the spinoreticular tract?
Sensation of poorly localized pain.
Describe the path of the spinoreticular tract.
Decussates at each level -->
Lamina VI-VIII -->
Reticular formation -->
Thalamus
What is the function of the anterior spinothalamic tract?
Carries crude touch and pressure information
Describe the path of the spinothalamic tract.
Myelinated Ab fibers -->
Ascend bilaterally -->
VPL nucleus
What is the function of the dorsal (posterior) spinocerebellar tract?
Muscle sense information from lower limbs and distal muscles in upper limbs.
Describe the path of the dorsal spinocerebellar tract and cuneocerebellar tract.
Muscle spindles and golgi tendon organs -->
Clarke's column/External cuneate nucleus -->
Inferior cerebellar peduncle -->
Vermis of cerebellum
What is the function of the cuneocerebellar tract?
Muscle sense information for upper limbs.
What is the function of the ventral/rostral spinocerebellar tract?
Integration of muscle activity
Ventral = lower limbs
Rostral = upper limbs
Describe the path of the spinocerebellar tracts.
Golgi tendon organs -->
Spinal border cells -->
Ventral bifurcates twice, rostral none -->
Superior cerebellar peduncle -->
Cerebellum
What is the function of the corticospinal tract?
Execution and control of voluntary movements, especially finger movements
Describe the path of the corticospinal tract.
Motor and premotor cortex in precentral gyrus -->
Descends through internal capsule -->
Through cerebral peduncle -->
Through pyramids -->
Lateral path decussates, anterior does not -->
Lamina VII-VIII -->
interneurons
What is the function of the rubrospinal tract and raphespinal tract?
Regulation of muscle tone, modulation of motor activity, reflexes, postural maintenance.

Rubrospinal = distal flexors
Raphespinal = pain sensation in spinal cord
Describe the path of the rubrospinal tract.
Red nucleus -->
Ventral tegmental decussation -->
Interneurons in lamina V-VIII in cervical and lumbar enlargements
Describe the path of the raphespinal tract.
Raphespinal nucleus -->
Decussate locally -->
Lamina I, II, and V
What is the function of the tectospinal tract?
Mediates postural and head motor reflex responses to moving visual stimuli.
Describe the path of the tectospinal tract.
Superior colliculus in tectum -->
Dorsal tegmental decussation -->
Project bilaterally to interneurons/motor neurons at upper cervical levels
What is the funtion of the reticulospinal tract?
Alternate pathway to control spinal motor neurons to reulate muscle tone of axial muscles and to adjust posture.
Describe the path of the reticulospinal tract.
Pontine/medullary reticular formation -->
Mostly do not decussate
What is the function of the lateral vestibulospinal tract?
Trigger responses to adjust posture and keep body balance.
Describe the path of the lateral vestibulospinal tract.
Lateral vestibular nucleus -->
Do not decussate -->
Interneurons
What is the function of the medial vestibulospinal tract?
Exerts a facilitatory effect on flexor motor neurons in response to bestibular sensory information--> controls head position
Describe the path of the medial vestibulospinal tract.
Medial vestibulospinal nucleus w/ info from MLF -->
Do not decussate -->
Cervical spinal levels
What do Nissl stains stain?
Neuronal cell bodies
What do silver stains stain?
Fibrillar components
What do golgi stains stain?
Some neurons in entirety
What is the only technique that shows the entire nuclear morphology of a neuron?
Intracellular filling with substances such as horseradish peroxidase or lucifer yellow
What are the characteristics of excitatory synapses?
WEAR = Wide synaptic cleft, excitatory, asymmetric densities, round
What are the characteristics of inhibitory synapses?
PINS = Pleomorphic, inhibitory, narrow synaptic cleft, symmetric densities
What cranial nerves are involved with taste and in what area?
VII--Anterior 2/3 of tongue
IX--Posterior 1/3 of tongue
X--pharynx
What cranial nerves contribute to the tractus solitarius?
VII, IX, X
Where do taste fibers ultimately project to?
VPM in thalamus --> insula, also hypothalamus and amygdala
Do taste fibers decussate?
No
Where do auditory fibers decussate? Why is this important?
They decussate at the trapezoid body, allowing one to localize where a sound is coming from.
Describe the path of auditory signals.
Spiral ganglion in cochlea -->
Decussate at trapezoid body -->
Superior olivary nucleus -->
Lateral leminiscus -->
Inferior colliculus -->
Brachium of inferior colliculus -->
Primary auditory cortex
What are the major differences between the somatic and autonomic NS?
Somatic is a single neuron between CNS and skeletal muscle and leads only to muscle contraction; Autonomic is a two neuron system that innervates smooth and cadiac muscle and glands and can be either excitatory or inhibitory.
What are the two areas of the CNS that control the ANS?
Hypothalamus and limbic system
What are the pre and postsynaptic neurotransmitters in the sympathetic/parasympathetic ANS?
Sympathetic = ACh, NE
Parasympathetic = ACh, ACh
What organs DO NOT receive innervation from both ANS systems?
Sweat glands, adrenal medulla, and peripheral blood vessels (sympathetic only)
Which branch of the ANS has more divergence?
Sympathetic
What are the two types of ACh receptors and where are they located?
Nicotinic on skeletal muscle and ANS gangla; Muscarinic on smooth and cardiac muscle and glands
What is the function of curare?
Blocks nicotinic receptors at skeletal muscle (N1)
What is the function of hexamethonium?
Blocks nicotinic receptors in the ANS (N2)
What are the 4 NE receptors and what are their functions?
A1 = blood vessel constriction
A2 = inhibits NE release
B1 = increases HR and force of contraction
B2 = relaxes GI and dilates vessels
What factors affect the release of NE from varicosities?
Frequency of action potentials, synthesis/breakdown/reuptake rates, receptors at varicosities, concentration of NE in synaptic cleft
How can NE action be terminated?
Reuptake for reuse or degradation or diffusion
Is the ANS usually initiatory or modulatory?
Modulatory
What happens to a lower motor neuron when its upper motor neuron is damaged?
It fires constantly due to loss of inhibition
What are the symptoms of upper motor neuron damage?
Increased muscle tone
Brisk reflexes
Weakness in upper body extensors and lower body flexors
What are the symptoms of lower motor neuron damage?
Decreased muscle tone
Muscle atrophy
Fasciculations
Absent reflexes
Pain in root distribution
What is a motor unit?
A motor neuron, its axon, and the muscle it innervates
What are the symptoms of Brown-Sequard syndrome?
Loss of pain sensation on contralateral side, loss of sensation/movement on ipsilateral side
Describe the actions of G-protein Gs.
Activates adenylyl cyclase -->
Produces cAMP from ATP -->
Activates protein kinase
Describe the actions of G-protein Gc.
Activates guanylate cyclase -->
Produces cAMP from ATP -->
Activates protein kinase
Describe the actions of G-protein Gi.
Inhibits adenylyl cyclase -->
Decreases cAMP production by Gs
Describe the actions of G-protein Gq.
Activates PLC -->
Produces IP3 and DAG

IP3 causes Ca2+ release from ER; DAG activates protein kinase C
What are the three second messengers in the Gq second messenger system?
IP3, DAG, Ca2+
Describe the actions of G-protein Golf.
Activated by odorants -->
Increase in cAMP -->
Increases permeability to Na+/Ca2+ in olfactory neurons
Describe the actions of G-protein Gt.
Activated by light in retina -->
Activates PDE -->
Hydrolyzes cGMP -->
Hyperpolarizes photoreceptors
What symptoms will decreased NE or serotonin cause?
Depression
What illness is marked by a decreased level of dopamine? An increased level (and more receptors)?
Decreased = Parkinson's disease
Increased = Schizophrenia
What action do amphetamines and cocaine have on dopamine?
Inhibits reuptake, prolonging its action.
What is the only serotonin receptor that is not a G-protein coupled receptor?
5-HT
What effect does ecstasy (MDMA) have on serotonin?
Release and depletion of 5-HT, leading to euphoria followed by depression
What is the main excitatory NT in the brain?
Glutamate
What is the main inhibitory NT in the brain?
GABA
What effect do barbituates/benzos have on GABA?
Enhances its inhibitory action
What is the function of strychnine?
Blocks glycine receptors, leading to convulsions and hyperactivity
What is responsible for Familial Startle Disease?
Mutation of glycine receptors
What is responsible for the stimulatory effects of caffeine?
Inhibition of the action of adenosine (which is inhibitory)
What is the adequate stimulus?
The type of energy that a receptor is specific for
What does the Doctrine of Specific Nerve Energies state?
That the sensation evoked by activity in a given receptor is that of the adequate stimulus for that receptor, regardless of the type of stimulus used to excite the receptor.
What is adaptation?
When a receptor slowly becomes less sensitive to a stimulus, such as the pressure of ones shirt on ones body
Describe each of the following in terms of their field and adaptation speed: Meissner's corpuscle, Merkel's disk, Ruffini's capsule, Pacinian corpuscle.
Meissners = small field, rapidly adapting
Merkels = small field, slowly adapting
Ruffinis = wide fields, slowly adapting
Pacinian = vibration, rapidly adapting
What is lateral inhibition?
It serves to limit the increase in receptive field size of a given cell due to convergence and the spatial spread of excitation due to divergence.
What is the best stain for viewing neuroglial cells?
Nissl stain
What is the intermediate filament that makes up the cytoskeleton of astrocytes?
GFAP-Glial fibrillary acidic protein
What are the two typs of astrocytes and where are they found?
Protoplamsmic--grey matter
Fibrous--white matter
What are the functions of astrocytes?
-structural support for neurons
-form "glial limitans"
-may act as electrical insulators
-act as phagocytes and form glial scars
-contributes to blood brain barrier
What is the function of oligodendrocytes?
-supply myelin sheaths to axons in the CNS for saltatory conduction
-wrap around multiple axons
What is the function of a microglial cell?
-immunological sentry for monitoring the brain
-phagocytes/inflammation mediators
What is the function of ependymal cells?
-ciliated movements contribute to flow of CSF
-NOT a diffusion barrier!
What cell secretes CSF?
Choroid cells
How many layers of dura are present in the brain and spinal cord?
One in the skull, two in the spinal column
Describe the path of CSF.
Lateral/3rd ventricles -->
Cerebral aqueduct -->
4th ventricle -->
Foramena of Luschka and Magendie -->
Subarachnoid space
What are the three layers of the neural tube, from inside out? What takes place in each layer?
Ependymal layer--cell division
Mantle layer--newborn neurons live here
Marginal layer--axons of new neurons projecting through here
What does the sulcus limitans divide the mantle layer into?
Alar plates (dorsally)
Basal plates (ventrally)
What structure of the spinal cord is the mantle layer analogous to? The marginal layer?
Gray matter
White matter
Why does the brainstem appear different than the spinal cord?
Flexures, necessity for special nuclei, no regular spinal nerves, cephalization
Describe the structure of the three-vesicle stage.
Prosencephalon (tel/diencephalon)
Mesencephalon
Rhombencephalon (Met/Myel)
What is included within the diencephalon?
Thalamus
Hypothalamus
Surrounds 3rd ventricle
What is included within the mesencephalon?
Tectum
Tegmentum
Surrounds aqueduct of Sylvius
What is included within the metencephalon?
Pons
Cerebellum
Surrounds 4th ventricle
What is included within the myencephalon?
Medulla
Surrounds 4th ventricle
What are the three flexures that develop in the brain?
Ventral = Cervical flexure, Mesencephalic flexure
orsal = pontine flexure
What is the only flexure that remains in the adult brain?
Mesencephalic flexure
What does the cerebellum develop from?
Thickenings of the alar plates of the metencephalon (pons/cerebellum)
What are the four evaginations of the prosencephalon that occur during development?
Optic vesicles
Posterior pituitary
Pineal gland
Cerebral hemispheres
What is the hypothalamic sulcus?
A sulcus that divides the thalamus and hypothalamus in the diencephalon
What does the telencephalon develop from?
The alar plate
Which part of the brain develops through inside-out laminar development?
Cerebral cortex
Which is the only area of the brain that has special sense nuclei?
Metencephalon (containing cochlear and vestibular nuclei)
Where does CNI develop from?
Telencephalon
Where does CNII develop from?
Diencephalon
Is Ca2+ necessary for the generation of an action potential? For the synaptic transmission?
No
Yes
What are SNARE proteins?
Proteins that are implicated in the control of exocytosis
What afferents come into the reticular formation?
Somatic/Visceral from Spinal Cord
Cerebellar
Vestibular
Corticospinal/bulbar
Sup/Inf Colliculus
Hypothalamus
What area gives rise to dopamine projections?
Substantia nigra and ventral tegmental area
What area gives rise to serotonin projections?
Raphe nuclei
What area gives rise to norepinephrine projections?
Locus coeruleus
Which branch of the corticospinal tract projects to axial musculature? To distal musculature?
Axial = anterior
Distal = lateral
What is analogous to dorsal horn gray matter in the trigeminal system?
Spinal trigeminal nucleus
What is analogous to Lissauer's tract in the trigeminal system?
Spinal tract of trigeminal
What is analogous to the VPL in the trigeminal system?
VPM
What are the three classes of nociceptors?
Mechanical, Thermal, Polymodal
What are some examples of pain modulator molecules? What are their specific functions?
Substance P-released from nociceptor, acts on self to make it more sensitive
Bradykinin-dilates vessels, converts arachidonic acid to prostaglandin
Prostaglandins-sensitize nociceptors
What are the two fibers that generally transmit pain?
A-delta and C
What type of pain do A-delta fibers transmit? What spinal tract are they associated with?
Fast, stinging pain
Neospinothalamic
What type of pain do C fibers transmit? What spinal tract are they associated with?
Slow, burning pain
Paleospinothalamic
What tract projects to periaqueductal gray?
Spinomesencephalic tract
What is the system most thought to be involved in pain suppression? How does it work?
Periaqueductal gray-nucleus raphe magnus system. PAG releases enkephalin, which inhibits other PAG neurons that project to serotonergic neurons in raphe nucleus. This excites enkephalinergic interneurons in spinal cord, releasing enkephalin into spinal cord. This reduces pain sensation.
Why do some NSAIDs cause upset stomachs?
Because COX-1 is an enzyme that protects the stomach, and some NSAIDS are COX-1/2 inhibitors
What is the function of COX?
It is involved in the conversion of arachidonic acid to prostaglandin at the site of injury
How many decibels would a sound wave with a pressure 10 times greater than a reference level be?
20 dB (Sounds pressure level = 20 log10 (ratio)
How does the ear compensate for impedence mismatch?
-eardrum is 20 times larger than stapes
-lever movement gives mechanical advantage of 1.5
What are of stereocilia of hair cells is connected?
Distal tip by a "tip link"
What causes depolarization of hair cells?
Influx of K+
What encodes for pitch? Loudness?
Pitch = which fibers are activated
Loudness = how many/frequency of firing
Describe the path of central auditory processing fibers.
Cochlear nucleus -->
Bilaterally to superior olive -->
Nucleus of the lateral leminiscus -->
Inferior colliculus -->
Medial geniculate body -->
Cerebral cortex-Brodman's
How is sound localized in the central nervous system?
Medial superior olive - processes interaural time difference
Lateral superior olive - processes interaural level difference (works indirectly wih medial nucleus of trapezoid body)
Explain the tonotopic organization of the cochlear nucleus.
Dorsal = higher frequency
Ventral = lower frequency
Describe the tonotopic organization of afferent projections from the cochlear nucleus to the inferior olive.
Dorsal = low frequencies
Ventral = high frequencies
Describe the tonotopic organization of the auditory cortex,
Rostral = low frequencies
Caudal = high frequencies
What happens in summation columns?
Neurons are excited by a sound reaching either ear.
What happens in suppression columns?
Neurons are excited by a sound reaching the ipsilateral ear but inhibited by a sound reaching the contralateral ear.
How does Wernicke's area connect to Broca's area?
Projects via arcuate fasciculus and uncinate fasciculus
What is the typical lifespan of a taste bud?
10 days
Which type of taste bud is the actual sensory receptor?
Type 3 (types 1 and 2 are just supporting cells, type 4 is a basal cell)
What branch of what nerve caries taset from the anterior part of the tongue?
Chorda tympani of VII
How do we taste salt?
Passive influx of Na+ causes depolarization
What chemical blocks the taste of salt or possibly sour foods?
Amiloride--blocks passive Na+ channels, which also transmit protons
How do we taste sour food?
Proton influx through passive Na+ channels or K+ influx through K+ channels
How do we taste bitter foods?
K+ influx through passive channels or G-protein coupled receptor with Gastducin-->PLC-->IP3
How do we taste sweet foods?
Gastducin-->PLC-->IP3-->increased CA2+

Gastducin-->AC-->cAMP-->PKA-->phosphorylates K+ channels
What is the lifespan of olfactory receptors?
60 days
How is olfaction transduced?
-olfactory molecule stimulates receptors
-AC-->cAMP
-opens CNG channels
-influx of Na+/K+
-depolarization
How do olfactory neurons become deactivated?
Ca-CAM complex desensitizes channels, even if cAMP is still present
What area does the anterior cerebral artery supply?
Primary somatosensory area
What area does the middle cerebral artery supply?
Primary auditory area
What area does the posterior cerebral artery supply?
Amygdala
What are the two factors that control the rate of ion movement through the membrane?
Conductance
Driving force
What are the three major factors that affect conduction velocity?
Size (diameter)
Myelination
Temperature
What ion is responsible for neurotransmitter release?
Inward current of Ca2+
What is the most important benefit of using a second messenger system for post-synaptic transmission?
The possibility of amplification
How is Dopa converted to NE?
By DbetaH, which is released along with NE into the synaptic cleft
What do fasciculations indicate?
Sick lower motor neurons