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What are the purpose of sensory systems?
Sensory systems provide animals with essentially all of the information they have about their external environment.
Sensory systems of all kinds depend on specialized sensory receptor cells that respond to stimuli, either environmental stimuli or stimuli arising inside the body.
Different sensory cells respond to different stimuli, and they vary greatly in sensitivity and specificity.
What does sensitivity mean?
The ability to distinguish among stimuli of different intensity
What does specificity?
The ability to distinguish among stimuli of different types
What is a sensory receptor cell?
A sensory receptor cell is a cell that is specialized to transform the energy of a stimulus into an electrical signal. The kind of stimulus that excites different receptor cells may be chemical, mechanical, or electromagnetic.
What is sense organs?
Sensory receptor cells are commonly clustered together in sense organs, anatomical structures that are specialized for the reception of specific kinds of stimuli.
What is a sensory system?
Sense organs and all of their associated CNS processing areas.
What is sensory transduction?
The basic function of a sensory receptor cell is to convert stimulus energy into an electrical signal, a process known as sensory transduction.
Sensory transduction requires specialized molecules called sensory receptor molecules
What are sensory receptor molecules and their function?
Specialized molecules which are particularly sensitive to a sensory stimulus.
Sensory receptor molecules initiate the transduction of the stimulus to produce an electrical response called a receptor potential.
What is receptor potential?
An electrical response.
The receptor potential may lead to action potentials carried to the CNS, where sensory information is processed.
How can sensory receptor cells be classified?
In 4 different ways
Sensory modality,
Form of stimulus energy,
Mechanism of transduction
Location of the source of the stimulus
What is sensory modality?
The subjective nature of the sensory stimulus.
Oldest way of classifying sensory receptor cells is by sensory modality
Which types of transduction are there?
Ionotropic transduction
The sensory stimulus is received and then transduced into an electrical signal.
Metabotropic transduction
Meaning the sensory receptor molecule acts like a neurotransmitter- or hormone-activated GPCR in activating a metabotropic cascade.
Vision, vertebrate olfaction, and some forms of taste reception
Both ionotropic and metabotropic sensory receptor molecules are membrane proteins.
What are exteroreceprors?
Sensory cells that respond to stimuli outside the body, such as light or sound.
What are interceptors?
Sensory cells that respond to internal stimuli, such as the pH or osmotic concentration of the blood.
What are the functional role of sensory receptor cells?
A sensory receptor cell transduces some form of stimulus energy converting it to an electrical signal termed a receptor potential.
A sensory receptor cell encodes information about a stimulus; this information is carried via trains of action potentials that are transmitted to the CNS.
What is the principle of labeled lines?
A concept that suggests sensory information from different modalities (such as taste, smell, and touch) is transmitted to the brain through separate dedicated pathways or "labeled lines."
What is and what does dorsal root ganglia (DRG) cells do?
A type of peripheral ganglion found at the dorsal root of a spinal nerve, containing cell bodies of the sensory neurons in that nerve
Send their distal processes into the skin and their central axons into the dorsal or sensory part of the spinal cord.
The distal processes of the DRG cells form four kinds of specialized endings with epithelial cells.
Merkel discs and Meissner corpuscles are superficial, just beneath the epidermis.
Pacinian corpuscles and Ruffini endings are larger and more deeply located.
What is adaptation?
The decrease in respons caused continuous and constant stimulation by frequency of action potentials
What is tonic and phasic responses?
Two basic types of responses
Tonic (slowly adapting)
Tonic receptor cells have a slow and incomplete decrease in impulse frequency
Phasic (rapidly adapting).
Phasic receptor cells have a rapid, complete decrease in impulse frequency and thus convey information about change in stimulus intensity.
What is a hair cell?
A sensory epithelial cell in a vertebrate acoustico-lateralis system that transduces displacement of its apical stereocilia into an electrical signal. Hair cells do not possess axons and do not generate action potentials. Instead, they release neurotransmitter onto afferent neurons that conduct action potentials into the CNS.
What is a hair bundle?
The tuft of microvilli (stereocilia) at the apical end of a hair cell. It responds to mechanical stimulation.
What is stereocilia?
The microvilli on the apical surface of hair cells, arranged in a bundle. Despite their name, they are not true cilia but actin-rich microvilli that help convert mechanical movements into electrical changes in the hair cell.
What are tip links?
Filamentous structures connecting adjacent stereocilia, responsible for opening ion channels when the stereocilia move. These tip links are sensitive to calcium concentrations, and their stretching or relaxing opens or closes ion channels in response to mechanical movement.
What are ion channels?
Tiny, non-selective cation channels found at the ends of the stereocilia, responsible for allowing ion flow and generating the electrical response in hair cells. They open and close based on the tension in the tip links.
What is the external ear?
The portion of the ear external to the eardrum or tympanic membrane.
What is the middle ear?
The portion of the vertebrate ear between the tympanic membrane and the cochlea.
What is the inner ear?
In a vertebrate, the cochlea and the semicircular canals of the vestibular organ.
What is the cochlea?
A part of the inner ear of many vertebrates, coiled in mammals, that contains the auditory sensory hair cells.
What is the vestibular organs?
A vertebrate sense organ consisting of statocysts (maculae) and semicircular canals, which together detect gravity and acceleration.
What is 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.
What is the 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.
What is 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.
What is 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.
What is the cochlear amplifier?
An active physiological process that amplifies the movement of the basilar membrane in the cochlea in response to sound.
What is prestin?
A motor protein in the outer hair cells that enables them to shorten and lengthen in response to changes in membrane potential, crucial for cochlear amplification and hearing sensitivity.
What is spatial coding?
The organization of the basilar membrane so that different regions respond to specific sound frequencies, creating a spatial map of sound, which is maintained throughout the auditory pathways to the brain.
What is Von Békésy’s traveling wave?
The discovery that sound frequencies cause a traveling wave along the basilar membrane, with each frequency having a specific point of maximum vibration.
What is auditory localization?
The process by which animals determine the location of a sound source. This is primarily done by comparing sound input between two ears.
What does time difference mean?
The difference in the arrival time of sound at each ear. This helps detect the horizontal (left-right) position of the sound source.
What does intensity difference mean?
The difference in sound loudness between the two ears, caused by sound shadowing (blocking by the head). This is especially useful for high-frequency sounds and aids in both horizontal and vertical localization.
What is sound shadowing?
The phenomenon where the head blocks sound waves, creating a "shadow" that affects sound intensity at the farther ear. This is more prominent for high-frequency sounds.
What is vestibular organs?
Structures in the inner ear responsible for detecting balance, acceleration, and spatial orientation. They include the semicircular canals and otolith organs (sacculus and utriculus).
What are the semicircular canals?
A component of the vestibular organ of the vertebrate inner ear containing receptors that respond to head rotation
What is the 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
What is sacculus and utriculus?
The two otolith organs that detect linear acceleration. The sacculus senses vertical motion, while the utriculus senses horizontal motion. Both structures have hair cells located in the macula.
Sacculus: Otolithic organ in the vertebrate inner ear containing hair cells that are stimulated by vertical movements and forces (including gravity).
Utriculus: Otolithic organ in the vertebrate inner ear containing hair cells that are stimulated by horizontal movements and accelerations.
What is macula?
In the vertebrate ear, a sensory area in the vestibular organs containing hair cells that monitor tilt and acceleration of the head.
What is chemoreception?
Sensory response to chemical stimuli.
Olfaction stimuli is airborne but must dissolve in mucus before binding to receptor.
What is papillae?
Tastebuds in mammals
Three types
Fungal papillae
Foliate papillae
Circumvallate papillae.
Taste buds have similar structures
Type 1, 2 and 3 mediate different taste qualities.
Receptors live for 5-10 days before being replaced
How is salt and sour transduced?
Salt
Ionotropic, channels permeable to Na+. Increase of Na+ in mouth depolarizes membrane potential in receptor cells -> synapse to cranial sensory neurons -> information to the brain.
Sour
Ionotropic. Channel formed from related proteins (PKD2L1). H+ too low in concentration to depolarize receptor cells, instead H+ modulate permeability channels to numerous ions.
How is sweet, bitter and umami transduced?
Metabotropic, mediated by GPCRs
The transduction for sweet, bitter and umami is very similar to one another.
Sweet and umami even share one of their two types of receptor proteins meaning that T1R3 can receive information from both sweet and umami molecules.
The receptor family responsible for bitter taste, T2R receptors, are much more diverse than those for sweet and umami. This could be because of the variety in the structures of the chemical compounds of bitter taste.
The signal transduction of these three tastes all uses similar G proteins that activate a phospholipase C. This does in turn produce second messengers, like IP3, which releases intracellular Ca^2+ that end the transduction by opening another TRP channel, called TRPM5
What is the olfactory epithelium?
All vertebrates have a main olfactory system located in the nasal cavity, consisting of the olfactory epithelium, which varies significantly in size among species (e.g., 2-4 cm2 in humans vs. 18 cm2 in dogs). Humans have around 10 million olfactory receptor neurons, while dogs can have up to 4 billion
What is the structure of the olfactory receptors?
Each olfactory receptor cell is a bipolar neuron with a dendrite that extends to the mucus-covered surface. The cilia on these dendrites are where olfactory transduction occurs. Odorant molecules dissolve in the mucus and bind to odorant-binding proteins before interacting with the receptors
Which transduction mechanism does olfactory use?
When an odorant binds to an olfactory receptor (OR), it activates a G protein (Golf), leading to the production of cAMP, which opens cyclic nucleotide-gated channels. This allows Na+ and Ca2+ to flow into the cell, causing depolarization
What is olfactory receptor cell dynamics?
Olfactory receptor cells continuously regenerate throughout adult life, differentiating from basal cells in the epithelium. They typically have a life span of about 60 days
What is olfactory receptor gene families?
The olfactory receptor proteins are a large family of GPCRs, with nearly 1 000 identified in mice. These receptors have variable regions that bind diverse odorants, allowing for a wide range of detection
What is combinatorial coding?
Each olfactory receptor cell expresses a single type of receptor, but many odors can activate different receptor cells, creating a combinatorial code that enhances the detection of a wide array of scents
What is the olfactory bulb and how is information processed?
Axons from olfactory receptor cells project to the olfactory bulb, where they synapse in the glomeruli. Different receptor types are segregated, but signals from these glomeruli converge in the olfactory cortex for processing.
What is the vomeronasal organ?
Many mammals also have a vomeronasal organ that detects pheromones. This organ is structurally similar to the main olfactory epithelium but uses different receptor types (V1R and V2R) that respond to pheromones, playing crucial roles in various behaviors such as mating and aggression
How does the vomeronasal organ perform pheromone detection?
The vomeronasal organ specializes in detecting pheromones with high sensitivity. Although traditionally associated with pheromone detection, recent studies suggest that the main olfactory epithelium also plays a role in pheromonal communication
What are photoreceptors?
Sensory receptor cells that are sensitive to light—are easier to identify, isolate, grind up, clone, and study with physiological techniques than other receptor cells.
Photoreceptor cells are subdivided into ciliary and rhabdomeric:
In ciliary photoreceptor cells, modified cilia contain the rhodopsin molecules.
Rhabdomeric photoreceptor cells, in contrast, have collections of microvilli that increase the membrane surface area.
What is photopigment?
Pigment that absorbs the light
A photopigment consists of a protein and a nonpeptide organic molecule called a chromophore, which means "color bearing."
What happen when a chromophore absorbs light?
When a chromophore absorbs light, it triggers a chemical reaction and initiates a transduction cascade. In animal photoreceptors, the chromophore is retinal, which is bound to the protein opsin to form the light-sensitive pigment rhodopsin. Retinal is an aldehyde of vitamin A and is crucial for vision in most animals, including mammals.
How is the vertebrate eye structured?
The vertebrate eye is a camera-like structure that focuses light onto retinal rods and cones, creating an inverted image. Refraction mainly occurs at the cornea, with the lens adjusting focus by changing shape. In aquatic vertebrates, the cornea's role is reduced.
The retina, a brain outgrowth, contains photoreceptors and neurons that process visual information. Its inverted structure places photoreceptors away from incoming light, but it remains mostly transparent, minimizing image distortion. The fovea is a high-acuity region filled with cones and lacks rods.
Retinal ganglion cell axons form the optic nerve, creating a blind spot at the optic disc. Humans typically don't notice this blind spot due to binocular vision and quick eye movements that compensate for visual gaps.
What is rods and cones?
Rods and cones are the two types of photoreceptors in the retina, responsible for converting light into a hyperpolarizing receptor potential:
Rods are highly sensitive and function in dim light, while cones are used for bright light, color vision, and high-acuity vision, particularly in areas like the fovea. Nocturnal animals(nattdjur) typically have retinas dominated by rods, whereas diurnal animals have more cones.
How is rods and cones structured?
Both rods and cones contain an outer segment with photosensitive membranes and an inner segment housing the nucleus and organelles. The outer segments of rods consist of stacked, internalized discs, while cones have lamellae that remain connected to the outer membrane. Light activates rhodopsin in these membranes, triggering a cascade that lowers cyclic GMP (cGMP) levels, causing cation channels to close. This reduces sodium influx, leading to hyperpolarization of the photoreceptor.
This phototransduction mechanism allows rods and cones to detect even single photons, making them highly sensitive to light. The response to light results in a graded change in membrane potential, correlating with light intensity.
What is 11-cis retinal?
A crucial molecule in the visual process. It is a derivative of vitamin A and serves as the chromophore in rhodopsin, the light-sensitive pigment found in the photoreceptor cells of the retina.
Rhodopsin regeneration in rods is a slow process, especially after exposure to bright light, which converts 11-cis retinal to all-trans retinal, a phenomenon known as bleaching. This causes a prolonged recovery period called dark adaptation.
In vertebrate rods, most regeneration occurs enzymatically. After bleaching, all-trans retinal detaches from opsin and is converted to all-trans retinol by the enzyme retinol dehydrogenase. The retinol is then transported to the pigment epithelium by interphotoreceptor retinoid binding protein (IRBP), where it is re-isomerized back to 11-cis retinal. This retinal is returned to the photoreceptors and recombines with opsin to restore visual pigment. Although the process is slow and complex, it ensures that visual sensitivity fully recovers only after all pigment is restored.
How does visual sensory processing happen?
The vertebrate visual system responds to pattern: contrasts, or changes in light level over space and time. The conversion from photoreceptors and vertebrate visual system occurs partly in the retina and partly in higher visual-processing areas of the brain.
For example, a small dark area (spatial pattern) for a frog has great behavioral importance (a fly for lunch)- particularly if it moves (poral pattern) relative to the rest of the visual field.
What are the five types of cells in the layers of the retina?
In the first synaptic layer, called the outer plexiform layer, rods and cones provide synaptic inputs to bipolar and horizontal cells.
In the inner plexiform layer, bipolar cells synapse onto amacrine and retinal ganglion cells.
The retinal ganglion cells are the output from retina; their axon from the optic nerve extends to the brain.
The ganglion cell generates action potentials when they depolarize.
How can the receptive field of rods and cones be influenced?
For a rod or cone the receptive field (visual field) within which the electrical activity of a neuron can be influenced by light corresponds for most part to the retinal area occupied by the receptor itself, and the response to light is always a hyperpolarizing receptor potential. For retinal ganglion cells, in contrast, the receptive field is typically much larger, embracing many photoreceptors, and can also include different regions giving responses of different polarity.
How is the receptive field divided?
The cells have receptive fields divided into two areas: a center and a surround. The first cell, termed an on-center cell (center), increases its firing rate (maximally stimulated) when the center of its receptive field is illuminated by a spot of light, but none of the surround. The off-center cell also has a concentric antagonistic center and surround. The off-center cell is inhibited by light in its center and excited by light in its surround. Most retinas consist of equal numbers of on- and off-center cells.
What happens when photoreceptors are stimulated?
Photoreceptors release glutamate to act on two types of bipolar cells. It hyperpolarizes on-center bipolar cells, which express inhibitory metabotropic glutamate receptors. In contrast, glutamate depolarizes off-center bipolar cells, which express excitatory ionotropic glutamate receptors. With light stimulation, photoreceptors hyperpolarize, decreasing the amount of glutamate released, which in turn depolarizes on-center bipolar cells. Bipolar cells communicate with ganglion cells through the release of glutamate. On- and off-center bipolar cells send their axons to distinct regions of the inner plexiform layer, where they synapse onto on- and off-center ganglion cells, calling a straight-through pathway. The antagonistic property of surround arises from lateral pathways which extend along the retinal sheet via horizontal cells and amacrine cells. Horizontal cells make inhibitory (sign-reversing) synapses onto photoreceptor terminals. This light-induced output inhibits neighboring cells in an array, termed lateral inhibition.
In most vertebrates there is ganglion cells that respond to movement and even to the direction of the movement, firing rapidly when a stimulus moves in one direction but not at all for motion in opposite direction, amacrine cells plays a significant role by producing these fields. Which explains the frog mentioned in the beginning. This could also be the ganglion cells to help us get moving objects to the center of gaze.
What happens with visual information in the brain?
The responsiveness to stimuli pattern or contrast is continued in CSN visual projections of the brain. A general principle is that visual information is transmitted over several different CNS pathways in the vertebrate brain, the different pathways conveying information about different aspects of a complex visual stimulus, such as color, fine details of form and stimulus movements.
In fish and amphibians, the major visual projection of the optic nerve is to the optic tectum of the midbrain. The optic nerves cross the brain midline at the optic chiasm and connect to neurons in the opposite tectum. In mammals the region homologous to the optic tectum is the superior colliculus. Visual projection is important in many aspects of visual behavior including the control of eye movements.
A special type of light-sensitive ganglion cell, with their own photopigment is sensitive to absolute levels of illumination and plays a significant role in regulating circadian rhythms.
What is lateral geniculate nucleus (LGN)?
The pathway for the axons of the optic nerve in a region of the thalamus is termed lateral geniculate nucleus (LGN) and these neurons project to the primary visual cortex (V1).
The mixing of input from two eyes allows mammals with forward-facing eyes to merge binocular input for depth perception at the visual cortex. The receptive fields of neurons in the visual cortex are quite different from those in retina and LNG. There are simple cells and complex cells. Both are binoculars and they can respond to visual stimuli presented in either eye, although one eye may have ocular dominance.
What does simple cell and complex cell respond to?
A simple cell responds best to a bar of light in a particular orientation, some respond to dark bars or edges.
Among the simple cells in cortex are complex cells, that have the same features as simple cells but is also insensitive to the position of a stimulatory bar or edge within the receptive field.
The best edge or bar stimulus in the visual field is the one with the same angle for both cells.
How is color vision accomplished?
The ability to distinguish color depends on the differential sensitivities of photopigments to different wavelengths of light.
Although many animals are colorblind, many other animals with well-developed visual systems have evolved color vision, for example: frogs, turtles, birds and primates.
Humans and primates have three populations of cone photoreceptors. Two kins of color-opponent processes are present in the mammalian retina: red-green opponency and blue-yellow opponency. This explains why we can see colors as bluish green or reddish yellow but not reddish green or bluish yellow.
Frogs have two or more rod photopigments; their color vision involves input from both rods and cones. Birds, mice and some other vertebrates have UV visual sensitivity.
What is a nervous system?
An organized constellation neurons and glial cells that are specialized for the conduction of electrical and chemical signals within and between cells. Nervous systems receive and integrate sensory information and generate commands for coordinated control of effector cells
Nearly all nervous animals have nervous systems, but they vary in the complexity of their organization and behavioural output
The nervous system consists of two major divisions: the central nervous system (CNS) and the peripheral nervous system (PNS).
What is the central nervous system?
The consolidated integrative part of an animal’s nervous system; in vertebrates, consists of the brain and spinal cord
The CNS has a large number of both neurons and support cells that interact to achieve integrative functions
What is interneurons?
A neuron that is confined to the central nervous system and is therefore neither a sensory neuron nor a motor neuron
What is sensory neurons?
A sensory receptor that is a neuron, or a peripheral neuron that is excited by a non-neuronal sensory receptor cell. Convey information to the CNS
What is motor neurons?
A neuron that conveys motor signals from the central nervous system to the periphery to control an effector such as skeletal muscle.
What is an 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)
What is the peripheral nervous system?
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
The PNS serves as an intermediary between the CNS and the rest of the body. The PNS provides information from both external and internal sources to the CNS and transports the response (or signals originating from the CNS) via the motor neurons
There are two primary divisions of the PNS: the somatic and the autonomic nervous system (ANS). It is the somatic nervous system that controls skeletal muscles, and these muscles are therefore referred to as somatic effectors. In the same way the PNS controls autonomic effectors (or internal effectors). The autonomic effectors include all neuron-controlled effectors other than skeletal muscles (e.g. cardiac muscles, smoot (nonstriated) muscles and glands
What is a nerve?
A collection of axons running together in the peripheral nervous system
The structures that in the PNS are called nerves (the axons of multiple neurons bundled together) are in the CNS called tracts, commissures or connectives
What is centralization?
Over the course of evolution, the tendency of animal groups to concentrate integrative neural functions into a central nervous system
Centralization of nervous systems refers to a structural organization in which integrating neurons are collected into central integrating areas rather than being randomly dispersed
What is 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
What is integrative functions?
The functions that are not directly involved in the processing of sensory inputs or in the activity of the motor and Autonomic centers. E.g. motivation, language and consciousness
What is connectives?
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
What is 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
What are cranial nerves?
Peripheral nerves that connect directly to the brain
What are spinal nerves?
In a vertebrate, segmental nerves of the peripheral nervous system that attach to the spinal cord
What does afferent mean?
Going toward. Thus, for example, an afferent blood vessel carries blood toward an organ of interest
What does efferent mean?
Going away. Thus, for example, an efferent blood vessel carries blood away from an organ of interest
What is peripheral ganglia?
A collection of neuronal cell bodies outside the CNS
What is the somatic nervous system?
The part of the vertebrate peripheral nervous system that controls skeletal muscles and provides afferent information from sensory receptors not associated with internal organs
The somatic nervous system controls most observable behaviour
Somatic motor and sensory neurons exit and enter the CNS in the spinal and cranial nerves. The spinal nerves serve areas of the body below the neck, and are arranged segmentally with one pair of spinal nerves per vertebra along the spinal column
The axons of sensory neurons enter the spinal cord in the dorsal roots of the spinal nerves. The cell bodies of these neurons are located in dorsal root ganglia (enlargements of the dorsal roots outside the spinal cord).
The ventral roots of the spinal nerves contain the axons of somatic motor neurons that innervate skeletal muscles . They also contain autonomic neurons that innervate autonomic ganglia.
In the periphery, the dorsal and ventral roots are fused together such that sensory and motor components course together in nerves that innervate somatic tissues
Mammals have 12 pairs of cranial nerves that provide both/either sensory inputs and/or motor outputs between the brain and areas of the head and neck. Some of them are associated with the major sense organs of the head.
Somatic motor neurons synapse directly in muscle fibers, without synapsing on other neurons after leaving the CNS
What is somatic effectors?
Skeletal (striated) muscle, as opposed to internal effectors
What is the autonomic nervous system?
The division of the nervous system that innervates and controls autonomic effectors and conveys sensory information from internal organs (to the CNS)
The ANS includes both autonomic effectors and sensory neurons that convey afferent signals from internal organs to the CNS
Some examples of autonomic effectors that are, at least partly, controlled by the vertebrate ANS are:
Smooth muscles
Exocrine glands
A few endocrine glands
Acid secreting cells
The pacemaker region of the heart
The brown adipose tissue of mammals
The swim bladders and integumentary chromatophores (colour-changing cells) of fish
The vertebrate ANS consists of three divisions: sympathetic, parasympathetic and enteric. The application of these divisions is debatable for other animal groups
The sympathetic and parasympathetic divisions have opposing effects on the autonomic effectors (fight-or-flight/rest-and-digest)
The enteric (gut) division is largely contained in the walls of the gut, although it has some connection with the CNS
What is autonomic effectors (internal effectors?
An effector other than skeletal muscle; includes smooth and cardiac muscles and tissues of the viscera and exocrine glands
What is exocrine glands?
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
What is the parasympathetic division?
A division of the vertebrate autonomic nervous system that is connected to the CNS via cranial and sacral nerves; the parasympathetic and sympathetic divisions tend to exert opposing controls on autonomic effectors
What is the enteric division?
One of three divisions of the autonomic nervous system; exerts largely autonomous control over the gut
The enteric division consists of relatively diffusely structured neuron-networks, contained entirely within the walls of the gut. It controls e.g. patterns of contraction of the gut wall and regulates gut absorption and secretion
The enteric nervous system can function autonomously by responding to stimuli applied to the gut, but is normally under the control of the CNS
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