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210 Cards in this Set
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What is athetosis?
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slow, writhing, continual movements of limbs; usually occurs distally in limbs and coexists with chorea
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What is chorea?
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purposeless, random, nonstereotyped movements of the limbs, face, and trunk; may be due to lesion of the caudate nucleus or dopaminergic medications
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What is hemiballismus?
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rapid, violent flinging movements of proximal limbs; due to lesion of contralateral subthalamic nucleus
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What is Tourette's syndrome?
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an autosomal dominant inherited disorder with variable penetrance that involves motor and visual tics and is accompanied by attention deficit and behavioral disorders
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What is the pharmacotherapy for Parkinsonian resting tremor?
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anticholinergics, L-dopa, dopamine agonists
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What is the pharmacotherapy for essential tremor?
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β-adrenergic blockers or barbituates
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What is the pharmacotherapy for choreoathetosis, ballismus, and tics?
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dopamine antagonists
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What is the pharmacotherapy for dystonia?
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anticholinergics, benzodiazepines, botulinum toxin injections
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What structures make up the basal ganglia?
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striatum (caudate and putamen); globus pallidus, substantia nigra, and subthalamic nucleus
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What are symptoms of basal ganglia dysfunction?
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hypokinesia or akinesia (few spontaneous movements like in parkinsons); hyperkinesia (excessive spontaneous movements ie choreoathetosis or hemiballismus)
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What is the pathophysiology within the basal ganglia which leads to a bradykinetic syndrome?
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increased inhibitory output of the medial globus pallidus to the VL which impairs its stimulation of the motor cortex; in parkinson's ↓dopaminergic neurons→↓direct pathway (inhibition) and ↑indirect pathway (stimulation) of GPm→↑inhibition of VL
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What is the pathophysiology within the basal ganglia which leads to a hyperkinetic syndrome?
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↓ inhibitory output of the GPm to the VL which excessively stimulates the motor cortex; in Hemiballismus (no STN→↓stimulation of GPm→↓inhibition of VL); in huntington's (↓indirect pathway→↓GPm inhibition of VL)
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What is the etiology of basal ganglia disorders?
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1. ischemic infarct, hemorrhage, or tumor in striatum or STN; 2. degenerative disorders (parkinson's/huntington's); 3. medication side effects (dopamine agonists/antagonists)
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What can be a side effect of dopamine agonist drugs?
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hyperkinesia (chorea, dystonia) which requires lower the dose of the drug
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What can be a side effect of dopamine antagonist drugs?
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hypokinesia (parkinsonism), which requires lowering the dose of the drug
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What are movement disorders which are not caused by basal ganglia disfunction?
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essential tremor; myoclonus and asterixis (metabolic disturbance/structural lesions); dystonia and tic
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What are the four primary clinical signs of parkinsonism?
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resting (pill-rolling) tremor; rigidity; bradykinesia (slow turning, no arm swing); loss of postural reflexes (risk of falling)
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What are the secondary clinical signs of parkinsonism?
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masked facies (expressionless); hypophonic speech (soft/hoarse); stooped posture with shuffling and propulsive gait; micrographia (smaller handwriting); autonomic dysfunction (constipation, urinary problems, orthostatic hypotension)
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What are the causes of clinical parkinsonism?
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Parkinson's disease (most common); neurodegenerative disorders (progressive supranuclear palsy, striatonigral degeneration, Shy-Drager syndrome); dopamine antagonist medications (halperidol); manganese or CO poisoning
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When do the symptoms of Parkinson's disease usually begin?
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btw 40 and 70 years of age; 100-150/100,000 prevalence
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What is the pathology of Parkinson's disease?
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pallor of the substantia nigra and locus ceruleus from loss of pigmented cells; Lewy bodies (eosinophilic, intraneuronal cytoplasmic inclusions); loss of striatal dopamine
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What are Lewy bodies?
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microscopic, eosinophilic, intraneuronal cytoplasmic inclusions that are indicative of Parkinson's disease
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What are the drug therapies for Parkinson's disease?
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anticholinergic drugs (limited effect); amantadine (↑dopamine release, limited effect); Levodopa or L-dopa (dopamine precursor, greatest symptomatic benefit, given with carbidopa to prevent catabolism); dopamine agonists; monoamine oxidase type B inhibitor (↓catabolism of dopamine); COMT inhibitor (↓catabolism of L-dopa prior to entry into brain)
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What are surgical therapies for Parkinson's disease?
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Pallidotomy (surgical lesion in GPm); *subthalamic nucleus stimulator (inhibits STN via electrical stimulation to prevent inhibition of VL)
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What are the symptoms of Huntington's disease?
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choreoathetosis, behavioral changes, dementia
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What is the epidemiology of Huntington's disease?
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familial autosomal dominant; 5-10/100,000; symptoms begin btw 35 and 40 years of age
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How is Huntington's disease diagnosed?
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genetic blood testing: multiple trinucleotide repeats in the huntingtin gene coded on chromosome 4
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What is the pathology of Huntington's disease?
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atrophy of the caudate nuclei more so than the cerebral cortex, loss of GABA-ergic neurons
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How is Huntington's disease treated?
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no curative: dopamine antagonists (haloperidol) to lessen choreoathetosis (block D2 receptors and indirect pathway) and control behavioral changes
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What are the functions of the limbic system?
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neuroendocrine and autonomic regulation; olfactory sensory processing; emotion, motivation and memory
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What are the nine principal components of the limbic system?
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olfactory bulb, hypothalamus, amygdala, septal nuclei, anterior nucleus of thalamus, piriform olfactory cortex, hippocampal formation, limbic ring of neocortex, ventral striatum (nucleus accumbens)
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What makes up the limbic ring of neocortex?
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insular cortex, orbitofrontal cortex, subcallosal cortex, anterior and posterior cingulate cortex, parahippocampal-entorhinal cortex
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What percentage of the human genome makes up the olfactory receptor gene family?
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1%
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What are characteristics of olfactory receptors?
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undergo continuous turnover ever 30-60 days, each receptor cell respond to odor molecules of only one type bc it only expresses one of the 100s of receptor molecules; send their axons through the cribriform plate of ethmoid bone into the olfactory bulb
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What is a glomerulus of the olfactory bulb?
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specialized region of synaptic contacts between olfactory receptor axon terminals and mitral cells of the olfactory bulb where the axons from cells expressing the same olfactory receptor converge
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What are the origin and terminations of the olfactory tract?
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origin: mitral cell of the olfactory bulb; terminations: olfactory tubercle (in anterior perforated substance of ventral striatum), piriform olfactory cortex (rostral uncus), medial amygdala, entorhinal cortex
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What structures in the diencephalon and telencephalon are involved with olfaction?
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mediodorsal nucleus of thalamus (input from ventral pallidum from olfactory tubercle; input from piriform cortex; output to orbitofrontal cortex); ventromedial nucleus of the hypothalamus (input from medial amygdala via stria terminalis)
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What is the location of the amygdala?
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nuclear group rostral to medial portion of the temporal lobe beneath the uncus
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What are the two subgroups of the amygdala?
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basolateral subgroup (larger and has cortical interconnections), corticomedial subgroup (related to olfaction)
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What are the afferents to the amygdala?
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olfactory tract; solitary nucleus and parabrachial nucleus (taste, visceral afferents); limbic neocortex
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Where do the the efferents from the amygdala go?
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via stria terminalis and ventral amygdalofugal pathways to ventromedial nucleus of hypothalamus, limbic neocortex, autonomic centers (PAG, parabrachial nuclei, solitary nucleus, parasympathetic dorsal motor nucleus of vagus, symp. Preganglionic neurons of IML)
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What is the function of the amygdala?
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relates environmental stimuli to coordinated behavioral, autonomic, and endocrine responses: feeding and drinking, agnositc (fighting) behavior, mating, maternal care, responses to physical and emotional stress
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What symptoms result from a lesion of the amygdala?
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reduced endocrine, autonomic,and behavioral responses during emotional stress; bilateral lesion impairs ability to recognize facial expression of fear
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Where are the septal nuclei located?
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btw the frontal horns or the lateral ventricles, ventral to hypothalamus and dorsal to the anterior commissure
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What are the afferents to the septal nuclei?
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hippocampal formation (CA1 and subiculum); amygdala; preoptic area of hypothalamus
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What are the efferents from the septal nuclei?
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hippocampal formation (cholinergic); amygdala; preoptic area of the hypothalamus, mammillary body, median eminence
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What are the functions of the septal nuclei?
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regulation of gonadal hormone release and reproductive behaviors via GnRH projections, facilitates memory formation via cholinergic projection to hippocampus
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What are the components of the hippocampus?
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subiculum (next to entorhinal cortex); cornu ammonis: CA1-CA4 pyramidal cell regions; dentate gyrus (with granule cells)
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What are the afferents to the hippocampus?
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septum (cholinergic); entorhinal cortex (receives projections from neocortex, olfactory from piriform cortex)
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What is the trisynaptic pathway of the hippocampus?
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neuronal pathway through hippocampus from entorhinal cortex to fornix involved in making memories; first neuron from entorhinal cortex synapses in dentate gyrus on granule cell which synapses on a schaffer collateral of CA3 which synapses on a CA1 cell which exits the hippocampus via the fornix
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What are the efferents from the hippocampus?
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Fornix (from CA1 and subiculum and go to mammillary bodies, anterior nucleus of the thalamus, and subcallosal cortex); reciprocal back to entorhinal cortex
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What are the three main functions of the hippocampus?
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glucocorticoid hormone (cortisol) neuroendocrine control; "mapping" of the environment; declarative memory (forming new memories)
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How does the hippocampus regulate corticosteroids?
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has a high concentration of glucocorticoid receptors and inhibits plamsa corticosteroid levels, receptors diminished with age so elderly cannot terminate stress related corticosteroid secretion quickly
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What can result from a bilateral hippocampal lesion?
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permanent anterograde amnesia, intact procedural memory
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What is long term potentiation (LTP) in the hippocampus?
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a proposed mechanism for memories, where a high frequency, repetitive excitatory synaptic input to a cell causes long-term enhancement of the effects of a single activation, involves NMDA glutamate receptors activating intracellular pathways that ↑ number of AMPA glutamate receptors and ↑EPSP response to glutamate
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What are the cause and symptoms of Kluver-Bucy Syndrome?
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bilateral lesion of the temporal lobe (neocortex, olfactory cortex, amygdala, and hippocampus); visual agnosia (psychic blindness), oral tendencies (put everything in mouth); loss of fear and anger emotions; hypersexuality
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What is Papez Circuit?
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theoretical emotional circuitry of CNS; hippocampus via fornix to mammillary bodies via mammillothalamic tract to anterior nucleus of thalamus to cingulate cortex back to hippocampus; now appears to be related to coding head direction
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What general classification of activities does the limbic system control?
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self and species preservation activities
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What cell type of the hippocampus is very vulnerable to ischemia?
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CA1
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What is hippocampal sclerosis?
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degeneration of neurons in the CA1 and subiculum of hippocampus which results in dementia similar to Alzheimer's dz
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Where are long term memories stored?
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in the neocortex, not in the hippocampus or medial temporal lobe
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What is Wernicke's encephalopathy?
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degenerative brain disorder caused by the lack of thiamine (vitamine B1) due to alcoholism, dietary deficiency, vomiting, chemotherapy causes confusion, vision impairment, stupor, coma, hypothermia, hypotension, and ataxia; is the acute phase of Wernicke-Korsakoff syndrome
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What is Korsakoff's syndrome?
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an amnesic disorder due to the lack of thiamine (vitamin B1); due to alcoholism, causes amnesia, confabulation, attention deficit, disorientation, and vision impairment; is the chronic phase of Wernicke-Korsakoff syndrome
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What kind of seizures often arise in the subiculum of the hippocampus?
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complex partial seizures
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What are olfactory ensheathing cells (OECs)?
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specialized type of glial cell that guides olfactory receptor axons to their targets in the olfactory bulb, may be used to guide to growth of other neurons elsewhere in the body
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Which limbic structures directly affect autonomic outflow?
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hypothalamus, amygdala, and limbic cortex
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What are the two primary phases of sleep?
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Non-rapid eye movement (NREM)/slow wave sleep, and rapid eye movement (REM)
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How are the stages of sleep measured?
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EEG (electroencephalogram); EMG (electromyogram); EOG (electrooculogram)
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What are characteristics of REM sleep?
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paradoxical/desynchronized sleep (cortex is very active), deep sleep, easy to wake from internal stimuli not external, recallable dreams, reinforcing memory traces, reoccurs ~every 90 mins and duration increases, ↓ muscle tone (except resp, oculomotor m., ear ossicle m., pupillary constrictors); ↓ body temp control, ↑ sympathetic activity (↑HR, resps), awake-like EEG with pontogeniculooccipital (PGO) waves
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What are the 5 stages of NREM sleep?
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O: awake; 1: drowsy; 2: asleep but easily aroused; 3: transition to deep sleep; 4: deep sleep, difficult to arouse (stages 3 and 4 are slow wave sleep (SWS) )
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What is slow wave sleep (SWS)?
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stages 3 and 4 (deepest stages) of NREM sleep, slow frequency delta and theta waves of EEG, dreaming is reiteration of daily scenarios; involved with restoration, growth and immunity (↑blood to m.; ↓body temp; ↓metabolic activity for repair; ↑growth hormone secretion; ↑immune regulators)
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How do the stages of sleep cycle throughout the night?
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cycles are about 90 min. in duration as the night progresses the amount of time spent in SWS shortens and the time spent in REM lengthens
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What does deprivation of suppresion of REM sleep cause?
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anxiety, hostility, hallucinations, and amnesia
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What are the possible reasons for REM?
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consolidation of memories, rehersal of behaviors
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What are the differences between NREM and REM?
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NREM: iterates information; dull sensation/perception; logical thought; episodic movement; REM: integration of information; vivid internally generated sensation, illogical, commanded but inhibited movement
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How do sleep patterns change with age?
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total amount is reduced from 15h as newborn to 6h in elderly; %REM decreases from 50% as newborn to 20% in elderly; %SWS decreases while stages 1 and 2 increase with age
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What is the ascending arousal system?
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responsible for awake state and participates in REM, originates in rostral pons-caudal midbrain, posterior hypothalamus, and basal forebrain nuclei, uses Ach, NE, serotonin, and histamine to activate the cerebral cortex directly or via the thalamus, suppresses the ventral lateral preoptic area of hypothalamus
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What hypothalamic nuclei control the origin and expression of circadian rhythms?
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suprachiasmatic nucleus, and dorsomedial nucleus
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What nuclei in the diencephalon control the onset of sleep?
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ventrolateral preoptic nucleus, lateral nucleus (arousal), and tuberomammillary nucleus (responds to histamine to keep you awake) of hypothalamus; and Basal forebrain (nucleus basalis promotes arousal from sleep)
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What pontine nuclei control the REM-NREM cycle of sleep?
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(ascending reticular formation) mesopontine nuclei (laterodorsal tegmental, pedunculopontine, dorsal raphe, locus cereleus)
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What makes up the ascending arousal system?
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locus cereleus, dorsal raphe, tuberomammillary nucleus, lateral dorsal tegmental nucleus, peduculopontine nucleus
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How does the ventrolateral preoptic area interact with the ascending arousal system?
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inhibits it via GABA-ergic connections
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How does the lateral hypothalamus interact with the ascending arousal system?
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activates it via orexin-ergic connections
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What peptide accumulates during the day and decreases the cholinergic arousal networks of the basal forebrain and brainstem and activates sleepiness?
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adenosine - Caffiene used to block adenosine's receptor and maintain arousal
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What is the pontine REM center?
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located in dorsolateral pons, coordinates REM sleep, causes eye movements in REM by activating gaze centers, activates reticulospinal paths to ↓muscle tone and ↑autonomic activity
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What is insomnia?
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an inadequate quantity and quality of sleep to maintain normal daytime behavior, contributing factors include jet lag, constant light, excess sleep, low SWS, organic dz or pain, alcohol and drug addiction
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What is somnambulism?
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sleepwalking, usually occurs in stage 4 of NREM, usually decrease with age
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What are night terrors?
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associated with stage 4 of NREM
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What is sleep apnea?
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cessation of breathing during sleep, symptoms include daytime sleepiness, restless sleep, unrefreshing naps; can lead to fatal pulmonary HTN or cardiac arrhythmias due to chronic noctural hypoxemia
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What are two types of sleep apnea?
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obstructive (upper airway obstruction, usually in obese and people with short neck, treat with weight reduction, surgery, +pressure air mask); central (treat with medication (progesterone) and ventilation)
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What is narcolepsy?
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several syndromes: narcoleptic attacks (inappropriate, abrupt sleep attacks); cataplexy (episodic loss of muscle tone, prompted by emotional stimuli); sleep paralysis (transient feeling of paralysis on waking); hypnagogic hallucinations (vivid dreams with onset of sleep) ultimately REM sleep occuring at inappropriate times
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None
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What is chronic insomnia?
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3 nights/week for several weeks, usually in conjunction with other health problems
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What is acute insomnia?
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1 night/week for <3wks, emotion or physical discomfort, stress, acute illness, environmental disturbances, perturbations in circadian rhythms
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What is restless leg syndrome?
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irresistable urge to move limbs, causes daytime sleepiness, negative mood, impaired performance
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What is within the external histological layer of the eye?
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sclera and cornea, continuous with the coverings of the optic nerve and dura
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What does the eye (retina and optic nerve) develop from?
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the lateral walls of the diencephalon evaginate as the optic vesicle at 22 days and invaginates to form a 2 layered optic cup
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What does the inner layer of the developing optic cup develop into? Outer layer?
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inner layer: retinal pigment epithelium; outer layer: sensory portion of retina
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What do the iris and ciliary body differentiate from during development?
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the outer rim of the optic cup
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How is the cornea formed?
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from the lens vesicle which is formed from the surface ectoderm (lens placode) overlying the optic vesicle; also has an inner layer derived from neural crest cells
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What is the sclera?
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tough, white protective covering of eye, continous with dura around the optic nerve, in external histological layer
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What is the cornea?
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external transparent layer on the anterior part of the eye also known as conjunctiva, is avascular, with lots of sensory fibers from V1, in external histological layer
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What is the origin of the retina, lens, iris, and epithelial layer of the cornea?
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ectodermal
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What is within the middle histological layer of the eye?
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choroid, ciliary body, iris; sometimes this layer is called the uvea and is continuous with the pia mater of the brain
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What is the choroid of the eye?
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contains choroidal blood vessels supplying outer portion of the retina (photoreceptors), also contains melanin black pigment to reduce light scattering, part of middle histological layer
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What is the ciliary body?
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has ciliary muscles to control the shape of the lens (optical power), and ciliary processes which form the aqueous humor, part of middle histological layer
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What is the iris?
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has sphincter-like smooth m. cells innervated by parasymp. From ciliary ganglion to constrict pupil; has radial smooth m. innervated by symp. from superior cervical ganglion to dilate pupil, part of middle histological layer
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What is within the inner histological layer of the eye?
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neural retina and retinal pigment epithelium, layer is continuous with the CNS via the optic nerve and tract
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What are the three fluid chambers of the eye?
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anterior chamber (btw cornea and iris, contains aqueous humor); posterior chamber (btw iris and lens, contains aqueous humor); vitreous body (btw lens and retina, contains vitreous humor)
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How is the aqueous humor reabsorbed?
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leaves via the trabecular meshwork (btw iris and corneal margin) to the canal of schlemm and anterior ciliary vein
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What results from an inbalance in aqueous humor clearance?
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glaucoma (intraocular pressure >25mmHg), either due to obstruction (closed angle) or flow impairment (open angle), can lead to vision loss
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What is the vascular supply of the eye?
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arteries from the opthalmic artery off the internal carotid: central retinal branch to supply inner retina, ciliary a. branch to choroidal capillaries to supply outer retina via diffusion; central retinal vein returns blood to cavernous sinus
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What two structures focus images on the retina?
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cornea (~3/5 of optical power due to large change in the index of refraction at the air-eye interface and its curvature); lens
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What is optical power?
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the ability to bend light, measured in diopters
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What is the role of the lens
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sharply focuses images on the retina, varies its optical power (accommodates) by changing its curvature
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What determines the optical power of the lens?
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the equilibrium btw elasticity of the lens which pull inward and the suspensory ligaments and lens capsule which pull outward
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What changes occur in/around the lens to allow for focusing on near objects (<6m)?
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ciliary m. of the ciliary body contract and take tension off the suspensory ligaments of the lens and allow the elastic forces of the lens to pull inward and increase its curvature and optical power
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What changes occur in/around the lens to allow for focusing on distant objects (>6m)?
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absence of ciliary m. contraction allows for the suspensory ligaments to pull on the lens capsule and oppose the lens elasticity and reduce the curvature and optical power
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What are the three components of the near reflex?
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accommodation of the lens to increase its optical power; pupillary constriction to increase depth of focus; convergence of the eyes to place the visual axis on the retina
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What is myopia?
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nearsightedness; optical power is too strong, far objects are focused in front of the retina, near objects can be focused; requires negative diopter (concave) lens
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What is hyperopia?
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farsightedness; optical power is too weak, near objects are focused behind the retina, distant objects can be focused, corrected with positive diopter (convex) lens
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What is astigmatism?
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blurred vision because different planes of light are focused differently so some are in front and others are behind the retina, corrected with cylindrical lenses with varying optical powers
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What is presbyopia?
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weakening of the optical power of the eye due to loss of elasticity of the lens with age (after 40), accommodation is insufficient and near images are focused behind the retina, corrected with positive diopter (convex) lens; or in pt that has myopia as well with bifocals
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What is amblyopia?
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visual defect of one eye with no gross pathology, weakened visual pathway that is not correctable with glasses, result of disuse
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How do the cornea and lens remain transparent?
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dehydration which results in phase cancellation and allows the photon to pass through unchanged, requires energy to remove water via Na/K ATPase pump (aerobic in cornea, anaerobic in lens) glucose energy source from aqueous humor
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What are cataracts?
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opacity of the lens due to hydration of the lens, aging, exposure to UV light, free radicals, and diabetes
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What is aqueous humor?
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fluid formed by ciliary processes on the ciliary body with a composition similar to CSF and occupies the anterior and posterior chambers of the eye
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What is vitreous humor?
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gelatinous material of the vitreous chamber of the eye, is formed from retinal secretions, contains macrophages to remove debris and prevent obscured vision
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What is within the outer layer of the retina?
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contains retinal pigmented epithelium
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What is within the inner layer of the retina?
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neural elements of the retina, low columnar epithelium on back of iris, ciliary body
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What is a scotoma?
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blind spot, region of visual field without vision, usually ignore and not noticed to be missing; due to detached retina, vascular insufficiency, or nerve damage among other causes
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What causes the physiological scotoma?
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optic disc or optic papilla, entry of the optic nerve and opthalmic artery and vein into the eye
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What is the macula lutea?
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lateral to the optic disc has high visual acuity, contains few blood vessels
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What is the fovea?
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region at the center of the macula lutea which is the region of highest visual acuity (contains elongated cones), almost all cellular elements of the retina except for the photoreceptors are pushed aside here, the center is in line with the visual axis
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What are the 10 histological layers of the retina?
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retinal pigment epithelium; photoreceptors (rods/cones); outer limiting membrane; outer nuclear layer; outer plexiform layer; inner nuclear layer; inner plexiform layer; ganglion cell layer; nerve fiber layer; inner limiting membrane
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What are the five major cell types of the retina?
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photoreceptors (rods/cones); bipolar cells; horizontal cells; ganglion cells; amacrine cells
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What are general characteristics of photoreceptors?
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transduce light and send info to horizontal and bipolar cells via synaptic transmission, have photosensitive lamellae in outer segment which are sloughed off, respond to light in a graded fashion, do not use APs
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What are characteristics of Rods?
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contain the photopigment rhodopsin, most useful in low-light conditions, highly sensitive to light, located outside the macula, high convergence on bipolar cells (decreases visual acuity of these receptors)
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What is visual acuity?
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ability to distinguish two different points in space
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What are characteristics of Cones?
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three types (red, green, blue) each with different photopigment, smaller outer segment, less sensitive to light, color sensitive, located in macula esp. fovea, low convergence on bipolar cells leads to high visual acuity
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What are characteristics of Horizontal cells?
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receive synaptic input from photoreceptors; send inhibitory GABA feedback in graded manner to neighboring photoreceptors to alter NT release, also inhibit bipolar cells, establish the concentric receptive field responsiveness
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What are characteristics of Bipolar cells?
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receive input from photoreceptors and horizontal cells and synaptically excited amacrine and ganglion cells, don't have Aps just graded, passive depolarization when excited, have concentric "on-center" and "off-center" fields
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What are characteristics of Amacrine cells?
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extensive processes, receive activity from bipolar cells, contribute to receptive field properties of ganglion cells, have APs, synapse on ganglion cells and neighboring bipolar cells
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What are characteristics of Ganglion cells?
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receive input from bipolar cells and amacrine cells, send APs along their axon through the optic nerve, are two main types with a less common third (large, small, W)
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What is the function of retinal pigment epithelium?
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separates the neural retina from the fenestrated choroid capillaries, metabolically supports photoreceptors, forms the outer blood-retinal barrier
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What are large (magnocellular, class Y) ganglion cells?
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have large receptive fields, little color discrimination, responsive to onset and movement of light; project to magnocellular (layers 1 and 2) of LGN
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What are small (parvocellular, class X) ganglion cells?
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have small receptive fields (fovea), responsive to cones and project to the parvocellular (layers 3-6) of LGN
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What are Mueller cells?
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glial cells of the eye similar to astrocytes that extend across the thickness of the retina and regulate the ionic and NT environment of the retina
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How does phototransduction occur?
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a photosensitive pigment with two components (opsin and retinal) is struck by photon → Δretinal from cis to trans form→activates transducin G protein→activates cGMP phosphodiesterase→hydrolyzes cGMP to GMP→cGMP dissociates from Na/Ca channels, closes them, and hyperpolarizes cell, ↓glutamate release
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What are the characteristics of On-center (depolarizing) bipolar cells?
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glutamate is inhibitory to these cells, light causes hyperpolarization of photoreceptor and ↓glutamate release→depolarization of the BP cell at center of field, hyperpolarize in response to light in the surround
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What are the characteristics of Off-center (hyperpolarizing) bipolar cells?
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glutamate is excitatory, light in the center of the field causes the cells to hyperpolarize, light in their surround causes depolarization
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How do horizontal cells mediate the effects of the retinal receptive fields?
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horizontal cells are excited by glutamate so when a photoreceptor is hyperpolarized by light, less glutamate is released and the horizontal cells are also hyperpolarized, thus disinhibiting neighboring PR and BPs, causing more glutamate to be released by those PRs, this mediates the formation of a contrast of light reception
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What is the purpose of concentric receptive fields?
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central excitatory portion surrounded by an inhibitory region enhances the contrast of visual images, making the borders stand out
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Where does the left side of the visual field project?
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right side of the retina of both eyes, right lateral geniculate nucleus, right optic radiations, right striate cortex
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What are the characteristics of the optic nerve?
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extends from the eye to the optic chiasm, carries info from the ipsilateral retina, axons are myelinated by oligodendrocytes and maintain retinotopic tomography, surrouded by pia, arachnoid, and dura mater
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What are the characteristics of the optic chiasm?
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midline structure btw optic nerves and tracts, nerve fibers from nasal retinal decussate to contralateral optic tract, while temporal retinal fibers remain uncrossed, some fibers project to the suprachiasmatic nucelus of the hypothalamus
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What is the cause of bitemporal heteronymous heminopsia?
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pituitary enlargement and compression of the middle, decussating fibers of the optic chiasm from the nasal retina bilaterally
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What are the characteristics of the optic tract?
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conduct retinal ganglion axons from optic chiasm to LGN where 90% terminate, the other 10% project to the pretectal region and superior colliculus (are motion sensitive and light intensity sensitive)
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Which laminae of the LGN receive ipsilateral eye input?
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2, 3, 5
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Which laminae of the LGN receive contralateral eye input?
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1, 4, 6
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Which laminae of the LGN receive parvocellular (X), small ganglion cells?
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3-6 (the outer 4 layers), involved in color vision and high acuity
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Which laminae of the LGN receive magnocellular (Y), large ganglion cells?
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1 and 2, involved in perception of movement, depth, and contrast
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Where is the macula projected in the striate cortex?
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the posterior portion of the cortex, with the inferior macular visual field fibers projecting above the calcarine sulcus
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What are the characteristics of the geniculocalcarine tract, or optic radiations?
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project from LGN to striate cortex; projections maintain retinotopic tomography (L visual field on R visual cortex), peripheral visual field is anterior, while macula is posterior
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What is Meyer's loop?
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pathway of projections from the LGN corresponding to the upper visual field which course around the inferior horn of the lateral ventricle to terminate on the striate cortex
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What is the cause of left superior homonymous quadrantanopsia?
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right temporal lobe compression of Meyer's loop which courses around the inferior horn of the lateral ventricles
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What is the cause of left homonymous hemianopsia with macular sparing?
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Right occipital lobe lesion (posterior cerebral a. occulusion)
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What kind of serial processing of information occurs in the LGN?
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concentric receptive fields process the component's basic shape and orientation and converge onto simple cells within the striate cortex
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What kind of parallel processing of information occurs in the LGN?
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when magnocellular and parvocellular regions of the LGN representing the same image are each processed separately to relay color, location, motion, depth, etc
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What visual elements are processed by the extrastriate cortical area of the posterior parietal lobe?
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non-color info on where the object is in the visual field
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What visual elements are processed by the extrastriate cortical area of the inferior temporal cortex?
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non-color info on the form and shape of the object (what it is - lesion here can cause visual agnosia); color info of the object
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What visual elements are processed by the extrastriate cortical area of the medial superior temporal gyrus?
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non-color info on motion and depth perception
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What makes up the outer ear?
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pinna, external auditory meatus, tympanic membrane
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What makes up the middle ear?
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eustachian tube, ossicles
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What makes up the inner ear?
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cochlea, perilymph and endolymph
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What are the two routes of sound conduction to the inner ear?
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bone conduction (via bones of the skull causing fluid in the inner ear to oscillate); ossicular route (air conduction from tympanic membrane through middle ear ossicles to oval window, most important physiologically)
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What are the three ossicles of the middle ear?
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malleus (attached to tympanic membrane), incus, and stapes (attaches to the oval window to transmit vibrations), function to amplify the pressure oscillations transmitted from air to the liquid of the inner ear
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What is the tensor tympani muscle?
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fast striated m. which attaches to the wall of the middle ear and to the malleus, is innervated by the trigeminal nerve, function to decrease the amplification of sound oscillations, esp low frequencies because there is poor impedance matching
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What is the stapedius muscle?
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fast striated m. which attaches to the wall of the middle ear and to the stapedius, is innervated by the facial nerve, function to decrease the amplification of sound oscillations, esp low frequencies
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What is the acoustic stapedius reflex?
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loud sound stimulates cochlear nerve fibers →ventral cochlear nucleus→superior olivary nucleus→facial motor neurons→stapedius muscle contraction; this rxn is too slow for explosive sounds, is most effective in response to low frequencies
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What is the modiolus?
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bone surrounding the snail-shaped cavern in the petrous part of the temporal bone which houses the inner ear
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What is the Helicotrema?
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the apex of the cochlea
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What are the two canals and one duct which makes up the choclea?
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scala tympani, scala vestibuli, scala meda (cochlear duct)
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What is the spiral lamina?
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a bony shelflike projection which separates the scala vestibuli from the scala tympani
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What fluid lies within the scala vestibuli and scala tympani?
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perilymph
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What is the course of the scala tympani?
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from the helicotrema to the round window separating it from the middle ear
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What is the course of the scala vestibuli?
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from the oval window to the helicotrema, is also continuous with the bony labyrinth of the vestibular apparatus
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What makes up the bony labyrinth of the inner ear?
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scala tympani, scala vestibuli, modiolus
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What makes up the membranous labyrinth of the inner ear?
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cochlear duct (scala media) which contains the organ of Corti
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What is the ductus reuniens?
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the connection btw the membranous labyrinth of the vestibular apparatus to that of the cochlea/inner ear
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What is the vestibular (Reissner's) membrane?
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separates the scala vestibuli from the cochlear duct
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What is the Basilar membrane?
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separates the scala tympani from the cochlear duct, extends from the spiral lamina to the outer wall of the cochlea
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What makes up the outer wall of the cochlear duct?
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is formed by the spiral ligament, has the stria vascularis which secretes the endolymph into the cochlear duct
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What are the characteristics of the perilymph of the inner ear?
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secreted by the periosteal lining of the scalae tympani and vestibuli, similar to interstitial fluid, flows from the scala tympani to the scala vestibuli to the vestibular apparatus and into the subarachnoid space via the perilymphatic duct
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What are the characteristics of the endolymph of the inner ear?
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actively secreted by stria vascularis, has low protein and Na and very high K (+80mV) so low viscosity, flows into the membranous labyrinth of the vestibular apparatus and into the subdural endolymphatic sac via the endolymphatic duct and absorbed into the blood
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What are the characteristics of the organ of corti of the inner ear?
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located on top of the basilar membrane, contains 3 outer rows (insert into tectorial membrane) and 1 inner row of hair cells, each hair cell has stereocilia tethered in a V-shape pointed toward the spiral ligament, supporting cells surround the hair cells
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How is sound transduced within the cochlea?
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the oscillations of the oval window due to the ossicles changes the pressure of the scala vestibuli which are transmitted through the vestibular membrane to the cochlear duct and then to the scala tympani via to the basilar membrane
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What is the tonotopic distribution of hair cells in the cochlea?
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high frequency are sensed low in the cochlea while low frequency are sensed near the apex, helicotrema; this is due to the distensibility of the basilar membane which becomes wider and more distensible toward the helicotrema, also longer stereocilia are near the helicotrema and move better to lower frequencies
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What is the primary purpose of the inner hair cells vs. outer hair cells?
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inner: most of the sensory transduction of sound bc of lots of afferent innervation; outer: amplify the movements of the inner hair cells
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How is the movement of the stereocilia of the hair cells result in a change in membrane potential?
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when stereocilia move toward the spiral ligament the K permeability of the cell increases and the cell depolarizes (enhanced by the large 150mV gradient across the membrane), this causes Ca channels to open and NT (glutamate) vesicles to be released on cochlear nerve fibers
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How does the olivocochlear efferent system affect frequency discrimination in the cochlea?
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attenuates responses of certain hair cells/auditory frequencies; inhibits inner row hair cells and inhibits outer row to control their amplifying effects
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What factors affect frequency discrimination in the cochlea?
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tonotopic distribution of hair cells, olivocochlear efferent system, variations in ciliary length (longer near helicotrema); inherent tendency
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What makes up the peripheral auditory pathway?
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spiral ganglion cells within the bony modiolus send branches to innervate cochlear nerve cells and centrally to the cochlear nerve fibers
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What is the central auditory pathway?
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cochlear nerve fibers enter brainstem and go to dorsal and ventral cochlear nuclei some fiber os these project to ipsi and contralateral superior olivary nuclei (cross in trapezoid body) others travel as lateral lemniscus to inferior colliculus to medial geniculate to transverse temporal gyri
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What is Rinne's test?
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put vibrating tuning fork on mastoid process and when it is no longer heard should still be heard via ossicular route, if it cannot this suggests that there is conduction deafness on that side
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What is Weber's test?
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put vibrating tuning fork on midline skull and sound should be heard equally in both ears, however if there is conduction loss, or impairment of ossicular route, then there is no cancellation of the sound waves btw the ossicular and bone routes and sounds louder on the affected side
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What is conduction deafness?
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impaired transmission of vibrations to the basilar membrane, normal bone conduction; due to foreign object, middle ear infection, ear wax, overgrowth of the temporal bone around the oval window (otosclerosis); treat with antibx, surgery, or hearing aids
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What is sensorineural deafness?
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loss of both air and bone conduction, affects higher frequencies, associated with hair cell damage; due to chronic exposure to loud noise, aminoglycoside antibiotics, in utero virus, quinine, aspirin, rubella infections, old age (presbyacusis); not corrected by hearing aids
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What is neural deafness?
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unilateral hearing loss, due to lesion of auditory nerve (acoustic neuroma is most common), sometimes surgically corrected
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What is central deafness?
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CNS lesion, unilateral loss is rare since there are multiple crossings, auditory space or locating sound source becomes difficult
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If a person has unilatearl hearing loss, what are the possible sites of a lesion?
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both dorsal and ventral cochlear nuclei, the auditory nerve, or peripheral receptor
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