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84 Cards in this Set
- Front
- Back
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What are the two questions that the vestibular system is designed to answer?
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Where way is up?
Where am I going? |
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What type of acceleration is detected by the utricle and the saccule?
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linear
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What type of acceleration is detected by the semicircular canals?
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angular
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Where is endolymph and perilymph found?
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The endolymph is found in the membranous labyrinth. The membranous labyrinth is surrounded by the perilymph. The perilymph is surrounded by the bony labyrinth.
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Compare the ionic composition of endolymph and perilymph.
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The endolymph is rich in K+, but poor in Na+ and Ca2+.
The perilymph is rich in Na+. |
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Compare the responses of hair cells in the vestibular labyrinth to bending of the hair bundle in the cochlea.
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It is the same:
Bending toward the tallest stereocilium causes depolarization and increased transmitter release Bending away from the tallest stereocilium causes hyperpolarization and decreased transmitter release |
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What type of potential changes are produced in the hair cells of the vestibular apparatus?
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Graded membrane potentials
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Describe the activity of a sensory afferent that contacts a hair cell in the vestibular labyrinth where there is no acceleration and when there is acceleration.
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At rest, the afferent fiber fires at a tonic rate, which increases when acceleration deflects the hair cell toward the kinocilium and decreases when acceleration deflects the hair cell away from the kinocilium.
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What kind of information do slowly and rapidly adapting sensory afferents in the vestibular apparatus convey?
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Slowly adapting afferents provide information about sustained stimulation (like acceleration due to gravity) while rapidly adapting sensory afferents provide information about abrupt changes in body position.
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Why are the utricle and saccule called the "otolithic organs"?
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A prominent featurs is the presence of millions of otoconia (dense calcium carbonate particles).
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What is the orientation of the macula in the utricle?
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horizontal
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What type of linear acceleration does the utricle detect?
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acceleration in the horizontal plane
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What is the orientation of the macula in the saccule?
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vertical in the parasagittal plane
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What type of linear accerlation does the saccule detect?
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vertical acceleration, including gravity;
certain saccular hair cells can also respond to accelerations in the anterior-posterior horizontal direction |
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Describe the arrangement of the cupula and the hair cells of the ampullary cristae in the semicircular canal.
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The cupula forms a gelatinous blockade at the ampulla of each semicircular canal. The cupula extends from the crista to the roof of the ampulla. The hair cells that lie in the thickened epithelium of the ampullary crista extend into the cupula.
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What are the symptoms of Meniere's disease?
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Intermittent, relapsing vertigo (mild to debilitating)
Tinnitus and distorted hearing Attacks usually afflict middle-aged individuals for minutes to hours and can be precipitated by high salt intake and anxiety |
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How is Meniere's disease treated?
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There is no consistently effective therapy, but diuretics, sedatives, or steroids may give some relief. In extreme cases, it is necessary to surgically remove the labyrinth or destroy the vestibular hair cells with streptomycin.
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What is known about the cause of Meniere's disease?
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The cause is unknown, but edema of endolymphatic spaces and subsequent damage to epithelial cells is indicated. Poor drainage of the endolymph is thought to cause attacks.
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What is the function of the vestibulo-ocular reflex?
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It keeps the eyes still when the head moves.
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What is the function of the vestibulospinal reflex?
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It enables the skeletomotor system to compensate for head movement.
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What are the proper terms to designate molecular signals that excite the specialized receptor cells of the taste and olfactory pathways?
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odorants and tastants
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What are the maximum number of odorants and tastants that human beings can distinguish?
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5000 odorants
100 tastants |
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Describe the olfactory sensory neuron.
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It is a bipolar nerve cell. A dendrite extends from the apical pole to the surface of the nasal epithelium where it terminates in a large knob. 5-20 thin cilia protrude from the knob into the layer of mucus that coats the epithelium. One axon projects from the basal pole, through the cribiform plate to the olfactory bulb, where it forms synapses with olfactory bulb neurons that relay signals to the olfactory cortex.
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What distinguishes olfactory neurons from other neuronal types?
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They are short-lived with an average turn-over rate of 30-60 days.
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What is the hypothetical function of the odorant binding proteins that are found in the mucus of the olfactory mucosa?
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They are thought to contribute to odorant concentration or removal.
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What type of membrane potential change is produced in stimulated olfactory sensory neurons?
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action potential
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How can olfactory sensory neurons detect such wide range and large number of odorant molecules?
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The family of odorant receptors includes an extremely diverse membership of as many as 1000 types.
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Describe the cAMP-dependent second messenger cascade that is the transduction mechanism in many olfactory sensory neurons.
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1) The odorant binds to the ligand binding site of the odorant receptor.
2) Odorant binding activates the GTP-bound G protein and frees it to interact with adenylyl cyclase III 3) Activation of adenylyl cylcase III by the G protein allows production of the second messenger cAMP 4) Increased cAMP opens gated ion channels, depolarizing the membrane and initiating an action potential. |
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What sensory modalities have receptors that utilize a transduction mechanism?
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Vision (phototransduction)
Olfaction |
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What 4 second messengers play a role in signal transduction in the olfactory system?
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cAMP, IP3, CO, cGMP
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Describe the two mechanisms by which olfactory receptors adapt to odorants after a prolonged exposure.
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1) They can inactivate an odorant receptor through phosphorylation (desensitization)
2) They can adjust the sensitivity of the cyclic nucleotide-gated channel in a method analogous to light sensitization. |
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What is the function of olfactory information transmitted to the neocortex (orbitofrontal lobe) by way of the thalamus?
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Perception and discrimination of odors
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What is the function of olfactory information transmitted to the amygdala and hypothalamus?
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Emotional and motivational aspects of smell, and the behavioral and physiological effects of odors.
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What are pheromones?
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Chemical substances released by the surroundings by an individual to influence the behavior or physiology of other members of the same species.
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What are the sources of pheromones?
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Urine and glandular secretions
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What functions are affected by pheromones?
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1) estrus cycles
2) age of onset of puberty 3) prevention of embryo implantation 4) signal receptivity of females for mating |
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What two olfactory systems are used by animals for sensing pheromones?
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Main olfactory system
Accessory olfactory system (vomeronasal system) |
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Do humans have an accessory olfactory system?
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No
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What is specific anosmia?
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Lowered sensitivity to a specific odorant with normal sensitivity to other; relatively common
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What is general anosmia?
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Complete lack of olfactory sensation; may be caused by damage to olfactory epithelium by infection, damage to olfactory nerves in the cribiform plat by head trauma, or Parkinson's disease
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What is hyposmia?
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diminished sense of smell; causes are the same as general anosmia
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What is cacosmia?
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hallucination of repugnant smells; may be caused by epileptic seizures
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Describe the structure of a taste bud.
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Each is bulb-shaped and has basal cells, dark cells, light cells, and intermediate cells. Basal cells are located deep in the taste bud and appear to be stem cells from which the other three taste cells are derived. The other three types, about 100 in number, are elongated and have microvilli projecting into the taste pore at the epithelial surface. Taste cells are innervated by sensory afferents at their basal ends.
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What is the difference between turnover in taste receptor cells and turnover in taste neurons?
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Taste cells are continuously regenerated, while neurons are not.
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What kind of membrane potential changes occur in stimulated taste cells?
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action potential
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What are the 5 tastes?
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Bitter, salty, sweet, sour, umami (monosodium glutamate)
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How is the sweet taste signaled to the taste cell?
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1) Tastants bind to receptors at the apical membrane. The receptor activates a G protein which activate adenylyl cyclase to produce cAMP which activates cAMP-dependent kinase to phosphorylate K+ channels and close them.
2) Tastants bind to receptors which activate G protein. G protein activates enzyme to produce IP3 which cuases release of Ca2+ from intracellular stores. 3) Tastants bind to receptors which activates gustducin which breaks down cAMP and close gated channels. |
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How is the bitter taste signaled to the taste cell?
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Different mechanisms: some toxic compounds induce G-protein pathways including phosphodiesterase activation (which breaks down cAMP and cGMP), PLC-IP3, and gustducin; other membrane-permeable bitter tastants may be sensed by mechanisms that do not involve G-proteins.
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How is the salty taste signaled to the taste cell?
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Diffision of Na+ down an electrochemical gradient through amiloride-sensitive Na+ channels
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How is the sour taste signaled to the taste cell?
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1) Passage of H+ through amiloride-sensitive Na+ channels
2) The blockade of K+ channels by H+ |
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What are the 3 categories of movement?
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Reflexive
Rhythmic Voluntary |
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What is feedback control?
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It monitors sensory signals and uses this information to act directly on the limb itself.
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What is feedforward control?
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It uses multiple senses to detect imminent perturbations and acts proactively based on this experience.
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What is the receptor in muscle that triggers a feedback control mechanism?
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Muscle spindle
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What is an example of feedforward/anticipatory control?
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When lifting the arm, leg muscles will contract in advance to counteract the anticipated change in center-of-mass.
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What is a motor program?
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The planning of a movement before it actually occurs. It specifies the spatial features of the movement, the angles through which the joints will move, and the forces required to rotate the joints to produce the desired movement.
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What is a positive sign?
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It is the same thing as a release phenomenon: abnormal and stereotyped response that is explained by the withdrawal of tonic inhibition from neuronal circuits mediating behavior.
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What is a negative sign?
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The loss of a particular capacity that is controlled by the damaged system (like loss of strength).
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What are the two organizational features of motor systems that allow them to perform so many different motor tasks with speed and accuracy?
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1) The processing of sensory inputs and commands to motor neurons is distributed in hierarchically interconnected areas of the CNS and each level has circuits that can organize or regulate complex motor responses.
2) Sensory information relating to movement is processed in different systems that operate in parallel. |
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What are the three levels of the motor control hierarchy?
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Spinal cord
Brainstem Cortex/forebrain |
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What aspects of motor function are influenced by the spinal cord?
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It mediates a variety of reflexes and rhythmic automatisms like locomotion and scratching. Descending axons modify the reflex responses through interneurons.
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What aspects of motor function are influenced by the brainstem?
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It mediates reflex movements in the face and mouth. Medial descending systems contribute to posture by integrating visual, vestibular, and somatosensory information. Lateral descending systems control more distal limb muscles and mediate goal-directed movements. Other systems move the eyes and the head/face. The brainstem receives input from the cerebral cortex and subcortical nuclei, and it projects to the spinal cord.
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What aspects of motor function are influenced by the cortex/forebrain?
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It projects to the spinal cord through the corticospinal tract, and to the brainstem through other tracts. The premotor areas are important for planning and coordinating complex sequences of movement. They receive information from the posterior parietal and prefrontal association cortices. This is the highest level of motor control.
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Describe the stepping behavior of a cat with a cervical spinal cord transection.
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The cat with a transected spinal cord will exhibit normal stepping behavior (controlled by spinal circuits) if its body is supported. The cat can move its paw around objects in its path only after its paw hits the object - it cannot anticipate.
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What does the behavior of a cat with a cervical spinal cord transection illustrate?
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Feedforward/anticipatory control requires intervention of spinal circuit rhythmic movements by the motor cortex.
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What are the functions of the basal ganglia and cerebellum?
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Both provide feedback circuits that regulate cortical and brainstem motor areas. They are also necessary for smooth movement and posture.
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What is the result of damage to the basal ganglia?
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involuntary movements
abnormalities in posture impairments in cognitive processing |
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What is the result of damage to the cerebellum?
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Loss of coordination and accuracy of limb movement
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What is the contribution of the medial descending pathways to movement?
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They control posture by integrating visual, vestibular, and somatosensory information.
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What is the contribution of the lateral descending pathways to movement?
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They control distal limb muscles and are important for goal-directed movements, especially in the arm and hand.
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What are the 3 major descending medial tracts?
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Vestibulospinal
Reticulospinal Tectospinal |
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What is the major lateral descending tract in anthropoid apes and humans?
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Corticospinal
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What is the major lateral descending tract in non-human primates and other mammals?
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Rubrospinal
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What cortical pathway controls voluntary movements of the muscles of the head and neck?
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Corticobulbar fibers
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What cortical pathway controls voluntary movements of the trunk and limbs?
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Corticospinal fibers
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What are the 3 types of muscles and their functions?
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Skeletal muscle is used to move bones.
Smooth muscle is used for internal actions like peristalsis and control of blood flow. Cardiac muscle is specially formed to pump blood exclusively. |
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Describe the innervation of a typical skeletal muscle.
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A typical muscle is controlled by about 100 large motor neurons.
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How many muscle fibers are innervated by a single motor neuron?
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100-1000 muscle fibers.
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How many motor neurons innervate a single skeletal muscle fiber?
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1 motor neuron
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What is a motor nucleus?
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a cluster of cell bodies located in the spinal cord that all innervate the same muscle
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What is a muscle unit?
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the ensemble of muscle fibers innervated by a single motor neuron
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What is a motor unit?
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A muscle unit along with its motor neuron
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What are antagonist muscles?
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muscles that have contradictory actions at the same joint.
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What does an electromyogram (EMG) measure?
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It measures the electrical signal generated by the action potentials that fire in muscle fibers when a muscle contract. EMG measure the aggregate activity of motor neurons that innervate each muscle. This is important for studying motor systems and for diagnosing pathology in the motor systems and in the muscles themselves.
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