Chapter 14 Sensory Processes and nervous system

Chemoreception

A sensory response to a chemical stimulus. Chemoreception includes taste (also termed the gustatory sense) and olfaction (the sense of smell), as well as other chemical sensitivities.

Outer hair cells

In the organ of Corti of the cochlea, the three rows of hair cells that amplify the sound-produced local movements that stimulate the inner hair cells to activate cochlear sensory neurons.

Straight-through pathways

In the retina, neural pathways that extend through the retina from external photoreceptors to internal ganglion cells. Contrast with lateral pathways.

Cortex

The outer layer of something (such as the cerebrum or the adrenal gland), as opposed to the medulla, or inner portion.

Cerebellar cortex

The outer layer of the cerebellum of the vertebrate hindbrain; involved in motor coordination and learning.

The ANS regulates circulation and the activity of internal organs. The sympathetic division: Sympathetic nerves mediate the "fight or flight" response.

The parasympathetic division: Parasympathetic mediate "rest and digest" functions.

Outer segment

The part of a retinal rod or cone that contains stacked membranes of photopigment and transduces light into an electrical signal.

PNS

The peripheral nervous system, including the neurons, nerves, glia, and synapses located anywhere else. PNS includes peripheral ganglia, which are associated with peripheral nerves.

Sensory system

The sense organs (or other sensory receptors) for a particular sensory modality and all of the central processing areas and pathways associated with those organs (or other receptors).

Sweet is also sensed by metabotropic GPCRs, i.e. sweet sensing is transduced through secondary messengers.

Umami is also sensed by metabotropic GPCRs, i.e. umami sensing is transduced through secondary messengers.

If K+ leak channels are blocked, what should be the effect on the cell?

Depolarization

Rhodopsin activation hyperpolarizes the membrane

Light changes the confirmation of the rhodopsin receptor, located on intracellular disk membranes, activating its G protein. cGMP, the secondary messenger, is then degraded, deactivating plasma membrane Na+ channels, hyperpolarizing the rod cell.

Taste is chemoreception from direct contact. Classical four tastes: Salty, Sour, Bitter, Sweet

"New" tastes: Umami (e.g. MSG), fat? other amino acids? Each taste bud is made up of several chemoreceptive cells, but each cell can taste only one flavor.

Stimulus

(1) At a cellular level, a form of energy (sometimes called stimulus energy) that excites sensory receptor cells; the form of energy is specific for each type of receptor cell. (2) At a whole-animal level, a change in the external environment or in internal conditions that an animal can detect and respond to. (2) A change in the external environment or in internal conditions that can be detected by an animal.

There are two main types of Ach receptors:

(1) Muscarinic receptors: Gprotein mediated metabotropic receptors that activate secondary messenger systems. These receptors inhibitory and are located only at post-ganglionic synapses of parasympathetic division

There are two main types of Ach receptors:

(1) Nerve-specific nicotinic receptors: ionotropic receptors, permeable to Na+ ,K+ , Ca2+, that are functionally similar in action to the muscle nicotinic receptors at the NMJ. These receptors are excitatory.

You walking leisurely to Einstein's (or maybe Chick-fil-A) on a Tuesday at 9:38 am, when you check your find out that it is actually Wednesday - and there is an exam today. What is LEAST likely to happen to your body at this point?

. Increase in gut motility

Idiosyncrasies:

1. Photoreceptors are depolarized in dark and hyperpolarized when stimulated by light. 2. Olfactory chemosensors (~1000) far outnumber taste (~5-10), photo (~4), and mechanoreceptors (~4).

Exocrine gland

A gland with ducts in which secretions exit the gland by way of the ducts, rather than being secreted into the blood. Examples include salivary glands and sweat glands. Contrast with endocrine gland.

Gray matter

A histological region of a vertebrate central nervous system that contains neuronal cell bodies, dendrites, and synapses as well as axons. See also white matter.

Transient receptor potential (TRP) channel

A kind of ion channel found in membranes of many sensory cells; it opens in response to stimuli and produces a receptor potential.

Ionotropic transduction (in sensory function)

A kind of sensory transduction in which a sensory receptor molecule is itself an ion channel, changing ion flow into the cell in direct response to a sensory stimulus. It is analogous to ionotropic synaptic action, and stands in contrast to metabotropic (sensory) transduction. See also metabotropic transduction.

If the smell of bananas is comprised of 20 different odorant molecules, what is the minimum number of types of olfactory receptor cells that must be present to smell bananas?

20

How many different types of receptor cells exist in the vertebrate retina?

4

Transducin

A G protein that is activated by rhodopsin in photoreceptors, leading to a receptor potential.

Interval timer

A biological clock that times an interval shorter than a day but appears to be noncyclic, having to be restarted each time it operates, like a kitchen timer or an hourglass. Also called an "hourglass" timer.

Commissure

A bundle of axons that connects the two sides of a bilaterally symmetrical central ganglion or bilateral regions of a central nervous system.

Connective

A bundle of neuronal axons in the central nervous system that connects central ganglia; found in the ganglionic nervous systems of arthropods, annelids, and molluscs.

Fovea

A central region in a vertebrate retina specialized for high-resolution processing of visual information.

Photochemical reaction

A chemical reaction triggered by light absorption.

Biological Clocks

A circadian rhythm has a period of about a day. It is an example of an endogenous rhythm, one that does not require sensory information for timing. A circadian rhythm of an animal will drift, or free-run, in constant light or darkness, when there are no sensory timing cues. A light-dark cycle entrains the circadian rhythm to exactly 24 h. A biological clock is the physiological basis of an animal's ability to time an endogenous rhythm. Biological clocks exert rhythmically changing control, modulating the outputs of the nervous and endocrine systems to prepare an animal for daily changes and seasonal changes. In mammals, the suprachiasmatic nucleus (SCN) of the brain is the principal biological clock for circadian rhythms. Animals may possess other timing mechanisms for shorter rhythmic periods (such as circatidal rhythms) or longer periods (such as circannual rhythms) than those of circadian rhythms

Nerve

A collection of axons running together in the peripheral nervous system.

Taste bud

A collection of epithelial taste receptor cells and support cells on the tongue or, in fish, on the skin surface.

Autonomic ganglia

A collection of peripheral (postganglionic) neurons in the autonomic nervous system; preganglionic neurons synapse onto these postganglionic neurons, which control autonomic effectors.

Sense organ

A complex multicellular structure specialized to detect a particular type of sensory stimulus.

Semicircular canal

A component of the vestibular organ of the vertebrate inner ear containing receptors that respond to head rotation.

Ganglion (plural ganglia

A discrete collection of neuronal cell bodies. In arthropod nervous systems, most ganglia are segmental components of the central nervous system; in vertebrates, ganglia are components of the peripheral nervous system.

Disc

A flat structure. Retinal rods have membrane-bound discs that are the site of phototransduction of rhodopsin.

Most sensory receptors are what kind of molecule?

A membrane bound protein

Channel

A membrane protein that aids the passive transport of a solute across a membrane without undergoing any sort of chemical binding with that solute. Channels participate particularly in passive transport of inorganic ions across membranes.

Basilar membrane

A membranous tissue within the cochlea of the vertebrate ear that contains the auditory sensory hair cells and is vibrated by sound waves

Sensory receptor molecule

A molecule in a sensory receptor cell that is particularly sensitive to a kind of sensory stimulus, and that participates in transducing a stimulus into a cellular response.

Compound eye

A multifaceted eye characteristic of arthropods, composed of many individual optical units called ommatidia.

Tract:

A nerve within the CNS

Simple cell

A neuron found in the mammalian primary visual cortex that has an elongated orientation-selective receptive field, so that it responds most to a bar or edge at a particular angle of orientation. The receptive fields of simple cells have distinct excitatory and inhibitory subregions.

Complex cell

A neuron found in the mammalian primary visual cortex that has an orientation-selective receptive field but lacks distinct subparts excited or inhibited by reception of light. A complex cell responds to a bar or edge of a certain size and orientation, anywhere in the cell's receptive field.

On-center cell

A neuron in the retina that is depolarized in response to light in the center of its receptive field. Contrast with off-center cell.

Off-center cell

A neuron in the retina that is hyperpolarized in response to light in the center of its receptive field. Contrast with on-center cell.

Horizontal cell

A neuron in the vertebrate retina that is part of the lateral pathway, mediating center-surround antagonistic effects in retinal neuron receptive fields

Motor neuron

A neuron that conveys motor signals from the central nervous system to the periphery to control an effector such as skeletal muscle.

Interneuron

A neuron that is confined to the central nervous system and is therefore neither a sensory neuron nor a motor neuron.

Cholinergic neuron

A neuron that synthesizes and releases acetylcholine as a neurotransmitter.

Adrenergic neuron

A neuron that synthesizes and releases norepinenphrine (noradrenaline) or epinephrine (adrenaline) as a neurotransmitter.

Papilla

A nipple-shaped structure. Mammalian taste buds are collected in lingual papillae on the tongue surface

Cochlea

A part of the inner ear of many vertebrates, coiled in mammals, that contains the auditory sensory hair cells.

Ciliary photoreceptor

A photoreceptor cell in which the light-sensitive part is a modified cilium; characteristic of vertebrates. Contrast with rhabdomeric photoreceptor.

Rhabdomeric photoreceptor

A photoreceptor cell in which the photopigment rhodopsin is collected in microvillar membranes. Contrast with ciliary photoreceptor.

Biological clock

A physiological mechanism that gives an organism an endogenous capability to keep track of the passage of time.

Organ of Corti

A region of the cochlea in the vertebrate ear containing the inner and outer hair cells that transduce sound vibrations into electrical signals.

Lateral geniculate nucleus (LGN)

A region of the thalamus in the diencephalon of the vertebrate brain that receives axons of retinal ganglion cells and relays visual information to the primary visual cortex.

Amacrine cell

A retinal neuron that mediates lateral antagonistic effects and is sensitive to visual movements

Endogenous rhythm

A rhythmic pattern of physiological or behavioral activity, the rhythmicity of which arises as an intrinsic property of an animal's cells (e.g., in the nervous system) without need of external timing information

Statocyst

A sense organ that can detect acceleration and the direction of gravitational force.

Sensory receptor cell

A sensory cell that is specialized to respond to a particular kind of environmental stimulus.

Hair cell

A sensory epithelial cell in a vertebrate acoustico-lateralis system that transduces displacement of its apical stereocilia into an electrical signal

Sensillum

A sensory hair of arthropods; not related to vertebrate hair, but rather a hollow chitinous projection of the exoskeleton that is associated with sensory receptor neurons.

Mechanoreceptor

A sensory receptor cell specialized to respond to mechanical stimulation.

Rapidly adapting receptor

A sensory receptor cell that exhibits a rapidly decreasing response to a maintained stimulus. Also called a phasic receptor.

Exteroceptor

A sensory receptor cell that is activated by stimuli from outside the body.

Interoceptor

A sensory receptor cell that is activated by stimuli within the body and thus monitors some aspect of the internal state.

Slowly adapting receptor

A sensory receptor cell that responds to a maintained stimulus in a way that decreases slowly and incompletely. Also called a tonic receptor.

Proprioceptor

A sensory receptor that provides an animal with information about the relative position or movement of parts of its body.

A scientist studying sensory systems delivers a small electrical current to the axon of an olfactory sensory neuron capable of initiating an AP. What is the subject likely to feel?

A smell

Muscle spindle

A stretch receptor that is arranged in parallel with the tension-producing fibers of a muscle and sends action potentials to the central nervous system when the muscle is stretched.

Effector

A tissue, organ, or cell that carries out functions under the direction of the nervous system or another physiological control system (e.g., the endocrine system).

Bipolar cell

A type of neuron in the vertebrate retina that mediates the direct (straight-through) pathway connecting rods and cones to ganglion cells.

Dorsal root ganglion

A type of peripheral ganglion found at the dorsal root of a spinal nerve, containing cell bodies of the sensory neurons in that nerve.

Cone

A type of photoreceptor in the vertebrate retina. Cones are smaller and less light sensitive than rods and are used for diurnal vision and color vision

Rod

A type of photoreceptor in the vertebrate retina. Rods are larger than cones, respond at lower light levels, and are used for nocturnal vision.

Vestibular organ

A vertebrate sense organ consisting of statocysts (maculae) and semicircular canals, which together detect gravity and acceleration.

Dark Current leads to a graded response. Under light conditions: cGMP is enzymatically degraded by cGMP phophodiesterase, closing cGMP-gated Na+ channels. This minimizes the dark current and leads to hyperpolarization, graded by the intensity of the light stimulus.

Absorption of single light photon can will cause a detectable change in dark current.

Photoreception is widespread in animals and the anatomy of photoreception morphology is diverse, from light / dark sensing eye spots to the complex vertebrate eye.

All photoreceptors work fundamentally the same way, using a light-absorbing pigment. Eyes can sense light in most wavelengths, but most single eyes can only see a limited range of light, e.g. the visible spectrum for humans is ~380 - 750 nm

Vomeronasal organ

An accessory olfactory organ of vertebrates that mediates many (but not all) sensory responses to pheromones.

Cochlear amplifier

An active physiological process that amplifies the movement of the basilar membrane in the cochlea in response to sound.

Melatonin

An amine hormone derived from the amino acid tryptophan; synthesized in and secreted from the pineal gland; influences circadian and seasonal rhythms; promotes sleep.

Autonomic effector

An effector other than skeletal muscle; includes smooth and cardiac muscles and tissues of the viscera and exocrine glands

Free-running rhythm

An endogenous rhythm that is not entrained by an environmental rhythm

Circatidal rhythm

An endogenous rhythm with a period approximating a tidal cycle (ca. 12.4 hours).

Circannual rhythm

An endogenous rhythm with a period of about a year.

cGMP phosphodiesterase (PDE)

An enzyme that hydrolizes cyclic GMP to 5′-GMP.

Camera eye

An eye that optically resembles a camera, with a lens that focuses an image on a retina of light-sensitive cells.

Cyclic guanosine monophosphate (cyclic GMP, cGMP)

An intracellular messenger in rod and cone photoreceptors and a second messenger in some neurotransmitter actions.

Tympanal organ

An organ of hearing in which sound vibrates a tympanal membrane ("eardrum") to activate auditory receptor cells. The term is usually used for insect hearing organs, although the vertebrate ear is also a tympanal organ.

Nervous system

An organized constellation of neurons and glial cells specialized for repeated conduction of electrical signals (action potentials) within and between cells. These signals pass from sensory receptors and neurons to other neurons and effectors. Nervous systems integrate the signals of convergent neurons, generate new signals, and modify the properties of neurons based on their interactions.

Otolith organs

An otolith is a hard structure in the ear of a vertebrate (oto = ear, lith = stone) that stimulates hair cells to produce the sense of gravity and linear acceleration. The saccule and utricule of the inner ear are the otolith organs that mediate these senses.

Ganglion cell

An output cell of the vertebrate retina, with an axon extending in the optic nerve to visual processing areas of the brain.

Photopigment

An unstable pigment molecule that undergoes a chemical change when it absorbs light, e.g., rhodopsin.

The Organization and Evolution of Nervous Systems

Animals have evolved nervous systems with varying degrees of centralization and complexity. There are homologies between the nervous systems of different animal groups. Most phyla of animals have bilateral symmetry and have evolved central nervous systems (CNSs) that centralize control functions. Sensory neurons convey information into the CNS, and motor neurons convey outward commands to effectors. CNSs usually have some degree of cephalization (concentration of neural structures into a clear anterior brain). Arthropods have a ganglionic nervous system, one major form of nervous system organization. The arthropod CNS is a ventral ladderlike chain of segmental paired ganglia joined by connectives. A vertebrate CNS, in contrast, is a continuous column of cells and axons.

Some animals can perceive radiation outside of the human visual spectrum

Bees

CNS:

Brain, spinal cord and all the neurons, glia, synapses, and tracts within

Of chemical and electrical synapses, which statement is best?

Chemical synapses influence learning

Taste

Chemoreception of stimuli that are dissolved or suspended in liquids, typically requiring higher stimulus concentrations than olfaction. Taste chemoreceptors are often, but not always, localized around the mouth.

Rhabdomere

Collection of microvilli from the retinular cells of an ommatidium of a compound eye

Rods n' Cones The vertebrate photoreceptors: Rods are more sensitive and used for vision in dim light

Cones are used in bright light to produce color vision

Olfactory receptor cells have short very thing unmyelinated axons that extend into the olfactory bulb in the brain. Olfactory receptor proteins are GPCRs

Each olfactory receptor cell expresses only one type of odorant receptor.

Internal effectors

Effectors other than skeletal muscle, such as glands, cardiac muscle, and smooth muscle, which are controlled by the autonomic nervous system

Nerves:

Enclosed cable-like bundles of peripheral axons. These include cranial and spinal nerves depending on the location of connection.

For the majority of sensory receptors, how do they deliver information about the intensity of a stimulus?

Frequency of sensory action potentials varies

Metabotropic synapses involve __________ receptors while ionotropic synapses involve __________ receptors.

G-protein coupled...ligand-gated

Phototransduction

Generation of an electrical response in a photoreceptor cell in response to a light stimulus.

Efferent

Going away. Thus, for example, an efferent blood vessel carries blood away from an organ of interest. Contrast with afferent.

Afferent

Going toward. Thus, for example, an afferent blood vessel carries blood toward an organ of interest. Contrast with efferent.

Vestibular Organs and Hearing

Hair cells are sensitive and versatile vertebrate mechanoreceptors that transduce displacement of stereocilia into a receptor potential. They are the major receptors of vertebrate hearing and equilibrium sense. The structure of the vertebrate ear effectively conveys sound-pressure waves into the inner ear. Sounds of different frequencies stimulate hair cells at different locations along the length of the basilar membrane of the cochlea. Central auditory pathways of vertebrates sort coded information about sounds in order to discriminate and map different sound frequencies and locations. The auditory systems of insects, although less complex, can nonetheless provide them with behaviorally important information.

Inner hair cells

In the organ of Corti of the cochlea, a single row of hair cells that transduce sound vibrations into voltage changes that excite auditory sensory neurons.

A single EPSP from a sensory neuron is not sufficient to bring about an action potential in the postsynaptic cell. In addition, a nearby synapse causes an IPSP of relatively equivalent in strength to the EPSP. Which would most increase the odds of reaching an action potential?

If we trigger another EPSP quickly after the first

Inner ear

In a vertebrate, the cochlea and the semicircular canals of the vestibular organ.

Time difference

In sensory physiology, a time difference between responses of different receptors can localize a stimulus; for example, sound that reaches the left ear first comes from the left.

Intensity difference

In sensory processes, intensity refers to the amount of a stimulus, as opposed to the kind of a stimulus (modality or quality).

Receptive field

In sensory systems, the region of a sensory surface within which stimulation changes the activity of a particular neuron.

Macula

In the vertebrate ear, a sensory area in the vestibular organs containing hair cells that monitor tilt and acceleration of the head.

Dark adaptation

Increase in light sensitivity of a photoreceptor or visual system after a period in the dark.

Rods and cones have two main segments: Outer segment (which contains the photosensitive membranes)

Inner segment (which contains the rest of the cell, e.g. nucleus, mitochondria, etc). The membrane folds in the outer segments contain the vertebrate photoreceptive pigment, rhodopsin.

Mechanoreception and Touch

Insect bristle sensilla exemplify mechanoreceptor responses Touch receptors in the skin of mammals have specialized endings Proprioceptors monitor internal mechanical stimuli

Chemoreception and Taste

Insect taste is localized at chemoreceptive sensilla Taste in mammals is mediated by receptor cells in taste buds BOX 14.2 Genomics and sweet taste in hummingbirds

Vestibular Organs and Hearing

Insects hear with tympanal organs BOX 14.1 Echolocation Vertebrate hair cells are used in hearing and vestibular sense Vertebrate vestibular organs sense acceleration and gravity Sound stimuli create movements in the vertebrate cochlea that excite auditory hair cells The localization of sound is determined by analysis of auditory signals in the CNS

Mechanoreception and Touch

Mechanoreceptors have many sensory functions. In addition to surface mechanoreceptors that convey information about environmental touch and pressure, mechanoreceptors can serve as proprioceptors that monitor body and limb position and muscle length and force. (They can also serve as equilibrium and auditory receptors, as we will see in the next section.) Mechanoreceptors have stretch-activated ion channels that mediate ionotropic transduction. Many sensory receptors produce a response that diminishes over time and are said to adapt to sustained stimulation. Tonic (slowly adapting) receptors signal the intensity and duration of a stimulus, whereas phasic (rapidly adapting) receptors signal changes in stimulus intensity.

Stretch-gated channels respond to touch

Mechanoreceptors: Mechanical pressure leads to opening of stretch-activated ion channels, due to cytoskeletal tension.

Midbrain

Middle region of the vertebrate brain, between the forebrain and the hindbrain

As you move your finger to touch your nose, specialized neurons called Purkinje cells in the cerebellum are receiving weak motor function signals from hundreds of thousands of other neurons. What aspect of Purkinje cells would you expect to be more extensively developed than other neurons?

More dendrites

Combinations:

Most mammals can distinguish ~10,000 odors, but have "only" ~1,000 receptor genes (which accounts for 3% of the genome).

Chemoreception and Taste

Most animals possess two types of chemoreceptors for external stimuli: contact or taste chemoreceptors that respond to near-field chemicals at relatively high concentrations, and distance or olfactory chemoreceptors that respond to low concentrations of chemicals from sources over a larger area. This generalization is useful but oversimplifies a greater diversity of external chemical senses, as well as internal chemoreceptors involved in homeostatic regulation. Taste chemoreceptors of mammals monitor five taste qualities: sweet, sour, salty, bitter, and umami. Insects have taste sensilla that provide at least analogous information. Transduction mechanisms of chemoreceptors are diverse, both within an animal and across animal phyla. Taste sensory transduction in mammals may involve ionotropic activation of ion channels (salty, sour) or G protein-coupled receptors (sweet, bitter, umami).

1. Photoreceptors are depolarized in dark and hyperpolarized when stimulated by light. 2. Olfactory chemosensors (~1000) far outnumber taste (~5-10), photo (~4), and mechanoreceptors (~4).

Nerve nets, peripheral, and central nervous systems

The Organization and Evolution of Nervous Systems

Nervous systems consist of neurons organized into functional circuits Many types of animals have evolved complex nervous systems BOX 15.1 Genomics and the Evolution of Nervous Systems

Reflex arcs:

Nervous systems evolved through elaboration of reflex arcs

The Vertebrate Nervous System: A Guide to the General Organizational Features of Nervous Systems

Nervous systems have central and peripheral divisions The central nervous system controls physiology and behavior Five principles of functional organization apply to all mammalian and most vertebrate brains BOX 15.2 Functional Magnetic Resonance Imaging, Scott A. Huettel The peripheral nervous system has somatic and autonomic divisions that control different parts of the body The autonomic nervous system has three divisions

Neurons:

Nervous systems of all animals are based on neurons

Visual Sensory Processing

Neural circuits of the vertebrate retina integrate the responses of retinal photoreceptors to excite and inhibit retinal ganglion cells. Ganglion cell receptive fields may be excited or inhibited by light at the center of the field, whereas light in the surround antagonizes the effect of light in the center. Straight-through pathways (photoreceptor → bipolar cell → ganglion cell) produce the center (on- or off-center) of a ganglion cell's receptive field. Lateral pathways through horizontal cells and amacrine cells produce the antagonistic surround. Axons of ganglion cells make up the optic nerve, relaying visual information to several brain areas. The geniculostriate pathway projects to the lateral geniculate nucleus (LGN) and from there to the primary visual cortex. Simple and complex cells in the primary visual cortex respond to light or dark bars or edges oriented at particular angles. Parallel pathways in the visual cortex convey information about different aspects of a visual stimulus, such as details of visual form, movement, color, and binocular determination of object distance. Color vision depends on the ratio of activation of three classes of cone photoreceptors sensitive to different wavelengths of light. Retinal circuitry integrates color contrasts based on red-green and blue-yellow opponencies.

Centralization:

Neurons tend to be gathered into a central nervous system

The resting membrane potential of a cell is -65 mV. The voltage threshold of the cell is -40 mV. The cell is electrically stimulated to reach -39 mV. What should happen?

No action potential

The adrenal medulla is under sympathetic control, and when activated, releases norepinephrine into the blood.

Norepinephrine mobilizes energy stores, promotes uptake of glucose into skeletal muscle, stimulates glycolytic enzymes, and stimulates release of glucocortocoids to replenish energy stores.

In phase

Occurring at approximately the same phase of a cycle as something else. Two events that occur at approximately the same phase of a cycle are said to be in phase

Olfactory receptors are very similar to taste receptors.

Olfaction normally senses airborne chemicals, sometimes at a very low concentration, i.e. some sharks can detect blood in 1 / 1,000,000 concentration. Olfaction is important for detection of food, but also to detect predators, competitors, and potential mates.

Signal transduction

Olfactory GPCRs depolarize the membrane through activation of Ca2+ dependent Cl- channe

Olfaction

Olfactory chemoreceptors of the main olfactory epithelium of vertebrates are neuronal receptor cells with cilia that contain intramembrane receptor proteins. Each receptor cell expresses the gene for one of these membrane receptor proteins, and all the receptor neurons that express that same protein synapse in the same glomerulus of the olfactory bulb. Insect olfactory neurons have broadly similar connection patterns but unrelated receptor proteins. Vertebrate olfactory receptor proteins are G protein-coupled receptors, which stimulate production of a second messenger, cAMP. The vomeronasal organ of vertebrates is an accessory olfactory organ that senses pheromonal and other stimuli. Vomeronasal sensory cells are microvillar rather than ciliary, and express GPCR proteins that stimulate production of IP3 and DAG.

Enteric division

One of three divisions of the autonomic nervous system; exerts largely autonomous control over the gut.

The simplest animal eyes sense

Only light and dark.

Biological Clocks

Organisms have endogenous rhythms BOX 15.3 Sleep, David S. Garbe Biological clocks generate endogenous rhythms Control by biological clocks has adaptive advantages Endogenous clocks correlate with natural history and compensate for temperature Clock mechanisms are based on rhythms of gene expression The loci of biological clock functions vary among animals Circannual and circatidal clocks: Some endogenous clocks time annual or tidal rhythms Interval, or "hourglass," timers can time shorter intervals

Utriculus

Otolithic organ in the vertebrate inner ear containing hair cells that are stimulated by horizontal movements and accelerations.

Sacculus

Otolithic organ in the vertebrate inner ear containing hair cells that are stimulated by vertical movements and forces (including gravity).

Centralization

Over the course of evolution, the tendency of animal groups to concentrate integrative neural functions into a central nervous system.

In a life or death situation, which of the following is not taking place

Parasympathetic control of the heart rate

Diencephalon

Part of the vertebrate forebrain that contains the thalamus and hypothalamus.

Color vision is a product of having three different cone pigments

Perception of color is dependant upon the ratio of activation of these three pigments, blue, green, and red cones.

Cranial nerves

Peripheral nerves that connect to the brain.

Retinular cell

Photoreceptor cell in the ommatidium of a compound eye

Photoreception

Photoreceptor cells and eyes of different groups have evolved similarities and differences Rhodopsin consists of retinal conjugated to opsin, a G protein-coupled receptor Phototransduction in Drosophila leads to a depolarizing receptor potential The vertebrate eye focuses light onto retinal rods and cones Rods and cones of the retina transduce light into a hyperpolarizing receptor potential Enzymatic regeneration of rhodopsin is slow

Myelencephalon

Posterior part of the vertebrate hindbrain.

Hindbrain

Posterior portion of a vertebrate brain, consisting of the cerebellum, pons, and medulla.

Primary visual cortex

Posterior region of the mammalian cerebral cortex that receives input from the lateral geniculate nucleus; serves as the first stage of visual information processing in the cerebral cortex.

Receptor cells are specialized cells which are excited by certain stimuli and transmit graded response to an afferent neuron

Receptor potential amplitude varies with stimulus strength. AP frequency varies with potential amplitude.

Chemo, Photo, and Mechanoreception Common themes:

Receptors are membrane bound proteins, which are either ionotropic or metabotropic. 2. Sensory stimulation is usually graded, not all-or-none. 3. Sensory cells can habituate to stimuli 4. Sensory cells can transduce only one message

Mechanoreception is often mediated by

Receptors that respond to stretch.

Photoreception

Response of a sensory cell to light stimulation. Photoreceptor cells contain a photopigment that absorbs light and triggers a response.

Visual Sensory Processing

Retinal neurons respond to contrast The vertebrate brain integrates visual information through parallel pathways BOX 14.3 What roles do individual neurons play in higher visual integration? Color vision is accomplished by populations of photoreceptors that contain different photopigments

Tasting salty

Salty: Probably the most simplistic of the senses, sensing "salt" is simply allowing salt to flow into taste cells. Na+ diffuses into the cytoplasm

Labeled lines

Sensory signals are distinguished by which axons carry the signal, but the signal is the same: APs

Organization of Sensory Systems

Sensory receptor cells can be classified in four different ways Sensory receptor cells transduce and encode sensory information

Organization of Sensory Systems

Sensory receptor cells respond to stimulation by a form of energy. Most sensory cells are specialized to respond to one form of stimulus energy. Sense organs contain clusters of similar receptor cells as well as nonneural cells. Receptor cells transduce stimulus energy into an electrical response, usually a depolarizing receptor potential. The transduction depends on specific receptor molecules and can be ionotropic (directly opening ion channels) or metabotropic (triggering a metabolic cascade via a G protein-coupled receptor, or GPCR). The receptor potential in a sensory neuron can trigger action potentials that propagate to the CNS. Sensory receptor cells often have cilia or microvilli that increase the area of the membrane surface

Specificity

Sensory specificity is the ability to distinguish among different stimulus types (modalities or qualities).

Metabotropic transduction (in sensory function)

Sensory transduction by means of a signal transduction cascade, rather than by direct ionotropic action. The sensory receptor molecule is a G protein that activates a second messenger, ultimately producing a receptor potential. See also ionotropic transduction.

The Vertebrate Nervous System: A Guide to the General Organizational Features of Nervous Systems

The CNS of vertebrates consists of the brain and spinal cord. Cranial and spinal nerves emanate from the CNS to form the PNS. The brain is divided into a forebrain, midbrain, and hindbrain; the forebrain is enlarged in birds and especially in mammals. Vertebrate brain functions are somewhat localized. However, brain functions are also somewhat distributed, involving circuits rather than centers. Many vertebrate brain regions preserve the orderly spatial arrangements of the corresponding external world, for example, as somatotopic maps of body sensory input and motor output. Brains change with development, experience, and learning and memory. Understanding the structural and synaptic bases of these changes is a major challenge to investigators. The PNS of vertebrates has a somatic division that controls skeletal muscle and an autonomic division that controls effectors associated with internal organs. The autonomic nervous system is divided into sympathetic and parasympathetic divisions, which usually have opposite physiological effects, and the enteric division, which controls gut contraction and other aspects of digestive tract physiology.

Sensitivity

The ability of a sensory cell to distinguish stimuli of different intensity. Receptor sensitivity may also refer to the adequate stimulus, the kind of stimulus to which the receptor is responsive

Metencephalon

The anterior part of the vertebrate hindbrain, containing the cerebellum and pons.

Forebrain

The anterior portion of the brain, consisting in vertebrates of the telencephalon and diencephalon.

Circadian oscillator

The biological clock that times a circadian rhythm.

If humans only have ~1,000 odorant receptors, how can they distinguish over 10,000 different scents?

The brain integrates the combination of many different simultaneous odorant signals.

Which of the following situations would interfere with the ability to discriminate whether a stimulus was light or touch?

The central nervous system can't tell which axon generated an action potential

Sensory modality

The class of stimulus that evokes a sensory response. The classical sensory modalities are vision (light is the stimulus that evokes a response), hearing (sound), touch, smell, and taste.

Cephalization

The concentration of structures of the nervous system toward the anterior end of an animal, a trend underlying the evolution of anterior brains in many animal groups

Central nervous system (CNS)

The consolidated integrative part of an animal's nervous system; in vertebrates, consists of the brain and spinal cord.

Autonomic nervous system (ANS)

The division of the nervous system that innervates and controls autonomic effectors and conveys sensory information from internal organs

Bilateral species have bilateral nervous systems

The evolution of bilaterally symmetrical body plans coincided with the evolution of cephalization and central nervous systems (CNS), where neurons are clustered into a central processing structure.

Receptor potential

The graded change in membrane potential that occurs in a sensory receptor cell when it is stimulated.

Dark current

The ionic current, carried mainly by Na+ ions, that flows into the outer segments of vertebrate photoreceptors in the dark. Light absorption leads to closing of the Na+ channels, turning off the dark current and hyperpolarizing the photoreceptor.

Retina

The layer of photoreceptor cells and other neurons that line the inside of a vertebrate eye.

Rhodopsin

The light-absorbing pigment of photoreceptors that initiates the visual response to light; composed of retinal and the protein opsin.

Olfaction

The mammalian olfactory epithelium contains odor-generalist receptor cells The vomeronasal organ of mammals detects pheromones

Imagine a cell that has a high number of both Na+ and K+ leak channels. What effect should this have on the membrane?

The membrane should be continually hyperpolarizing

Mesencephalon

The midbrain region of the vertebrate brain.

Peripheral nervous system (PNS)

The portion of a nervous system outside of the central nervous system, consisting of afferent and efferent nerves that connect the central nervous system to various parts of the body.

Inner segment

The portion of a retinal rod or cone that does not contain specialized light-sensitive membranes.

External ear

The portion of the ear external to the eardrum or tympanic membrane

Middle ear

The portion of the vertebrate ear between the tympanic membrane and the cochlea.

How is it possible that acetylcholine acts as both an excitatory and inhibitory neurotransmitter in the parasympathetic pathway?

The postganglionic neuron expresses different acetycholine receptors than the effector tissue (e.g. heart).

Labeled lines

The principle that sensory neurons encode the modality or quality of a sensory stimulus by having different sensory receptor cells respond to different kinds of stimuli, so that the CNS can decode the stimulus by monitoring which axons ("lines") deliver action potentials.

Sensory transduction

The process by which the energy of a physical stimulus is converted into an electrical signal in a sensory receptor cell.

Entrainment

The process of synchronizing an endogenous rhythm to an environmental rhythm.

Olfaction

The sense of smell; chemoreception of molecules released at a distance away from the animal. Among chemoreceptors, olfactory receptors are typically more sensitive than taste receptors and respond to distant or dilute chemical stimuli (odorants) that are usually airborne in terrestrial animals.

Coordinating the stress response

The sympathetic nervous system works in concert with the endocrine system to mediate an acute stress response to quickly enable shortterm burst capabilities.

What is the difference between the sympathetic and parasympathetic nervous systems?

The sympathetic nervous system mediates the stress response, while the parasympathetic nervous system controls tissues during non-stressful conditions.

Hair bundle

The tuft of microvilli (stereocilia) at the apical end of a hair cell. It responds to mechanical stimulation.

Basic structure of the vertebrate brain All vertebrate brains share a common structure, displaying three major regions.

The two major outgrowths which become more pronounced in higher vertebrates are the cerebrum (forebrain) and the cerebellum (hindbrain).

Vertebrate CNS

The vertebrate CNS is structured into a brain and spinal cord. Both are packed with neurons and are the sites of central processing and control. The vertebrate spinal cord is a continuous column of cells

Photoreception

The vertebrate eye is a camera eye that focuses light onto retinal rod and cone photoreceptors. Rods and cones are unusual in that light produces a hyperpolarizing receptor potential. The photopigment rhodopsin is a GPCR molecule conjugated to retinal. It is contained in membranes of outer segments of vertebrate rods and cones. When rhodopsin absorbs light, it acts via a G protein to decrease the concentration of cGMP in the cytoplasm, leading to closing of cGMP-gated Na+ channels that keep the photoreceptor depolarized in the dark. Light-induced closure of these channels hyperpolarizes the photoreceptors. In arthropods such as Drosophila the photopigment rhodopsin is similar to that of vertebrates and activates a similar G protein, but it is linked to a different intracellular effector and leads to the production of DAG and IP3, opening ion channels and producing a depolarizing receptor potential. Rhodopsin is deactivated and ultimately regenerated to 11-cis rhodopsin after activation. In vertebrates, most regeneration is a slow enzymatic process, part of which occurs outside the photoreceptors in the adjacent pigment epithelium.

That's great for light and dark, but how are images formed in the vertebrate retina?

The vertebrate retina has many different cells

Histologically, the nervous tissue of vertebrates can be categorized into types: The gray matter consists of cell bodies, synapses, and unmyelinated neural processes

The white matter consists of tracts (CNS bundles) of myelinated axons.

Bitter is sensed by metabotropic GPCRs, i.e. bitter sensing is transduced through secondary messengers

There are a wide variety of bitter compounds and consequently there are a wide variety of bitter receptors.

Segmentation: Many local responses are contained completely within repeated segments.

These segments are often associated with small peripheral neural hubs, called ganglia. Arthropods have a ventral ladder of connected CNS ganglia.

Multiple cell reflex arcs are more complex

They begin with the sensory neuron, transmits through 2 or more interneurons, then affects a muscle.

Hypothesis: Sour taste is likely mediated by H+ ion deactivation of ionotropic K+ leak channels.

With K+ trapped in the cell, Na+ becomes more permeable than K+ and begins to dominate the resting membrane potential. This results in depolarization. Probably not true,

If action potentials are all-or-none, can the intensity of a stimulus be transmitted via sensory neurons?

Yes, by the sensory neuron producing multiple action potentials

A neuron receives signals from five other neurons, A-E. Assuming local signal strength is equal, poisoning which synapse would result in the largest decrease of the neuron's likelihood of reaching threshold potential?

a

Vestibular organs

are used for reception of equilibrium. The most simple is the statocyst, common to many animals.

A presynaptic nerve terminal releases a neurotransmitter that activates K+ conductance in the postsynaptic membrane. If the postsynaptic cell body had an initial voltage of -65 mV and ENa = +70 mV, ECl = -70 mV and EK = -90 mV, the new postsynaptic voltage will be:

between -70 mV and -90 mV

A hollow ball of mechanosensory cells within an animal's brain contains a calcareous sphere, which moves freely with gravity. The animal turns upside down. Which cells should be excited?

c

Under dark conditions:

cGMP-gated Na+ channels are always open. Thus, the permeability of Na+ in dark rods is very high and the cell is in a constant state of depolarization (~ -30 mVs). This Na+ leak, called dark current, is also costly, as Na+ /K+ pumps need to maintain a constant potential.

Unlike other stimulus receptors, those in the eye which have rhodopsin _____________.

cause hyperpolarization

Which area of the human brain is proportionally much larger than a fish or amphibian?

cerebrum

Some receptor types:

chemoreceptors, electroreceptors, mechanoreceptors, photoreceptors, osmoreceptors and thermoreceptors.

Airborne chemicals

dissolve in the mucous layer of the olfactory epithelium.

Neural control is __________ than endocrine control, and ____________.

faster, shorter-lasting

Complex animals

have more complex nervous systems

Lateral pathways

in the retina, neural pathways that extend parallel to the retinal surface, rather than from the external to the internal side. Contrast with straight-through pathways

Chemoreception

is among the simplest of receptors. Bacteria display chemoreception.

smell

is chemoreception at a distance

Taste

is chemoreception from direct contact.

A snail initially only tucks into its shell when dropped. Physiologists repeatedly applied the dropping sensation neurotransmitter simultaneous with an unrelated neurotransmitter that normally is present during high temperature. Now the snail tucks in whenever its too warm even if it's not dropping. What happened?

long term potentiation

Single cell reflexes

may have been the earliest of neural systems

Relative size

of each brain region is related to the relative importance of that region's sensory input or motor output

Receptor molecules

on the sensory cilia sense the dissolved chemicals, which can cause transduction

Sensory organs

provide the only channels of communication from the external (and internal) world into the nervous system

You taste a fruit that tastes very sweet. Which of the following is most likely involved in this reception of flavor?

secondary messengers

Which of the following would contain mechanoreceptors?

semi-circular canals

The simple circuit diagram above shows three sensory nerves A, B and C forming synapses on the dendrites of motor nerve D. Sensory nerves B and C are inhibitory, and sensory nerve A is excitatory. Assuming local synapse strength is equivalent, which of the following would be most likely to generate action potentials in motor nerve D?

simultaneous action potentials in nerves A and B

Sour

taste is likely not mediated by H+ ion diffusion into the cell. Instead, H+ ion likely changes the conductance of other ion(s).

Which of the following does not involve metabotropic transduction?

tasting salt

Ex 1 and Ex 2 are EPSPs located at different locations on an axon, and In1 is an IPSP. In the above diagram, ____ would represent ____________.

temporal summation

Receptor cells

transduce a stimulus into electrochemical nerve impulses (i.e., APs)

If Na+ channels are open, what would be the effect of increasing extracellular Na+ concentration on the membrane potential?

when it comes to taste depolarization

The simplest form of a nervous system is a nerve net,

which contains no central organizing neural structure.