Channels of Communication

Sensory Modalities

Behavior requires that an animal obtains information about its environment. Thus, to understand behavior we need to understand how organisms perceive their environment (i.e., sensory systems biology, sensory biology). Jelly Bean Example. Hawaiian punch and Cherry have the same color. Visual information about jelly beans is incomplete. By blocking your nose while eating a jelly bean, you prevent smell from providing information. Taste does not allow you to determine which bean is punch and which is cherry. With olfactory information, this decision is easy. Finally, the cinnamon bean activates your trigeminal system. This provides critical information independent of taste and smell. By understanding how your senses gather information, we gain a better and more thorough understanding of our behavior. Common research questions in sensory biology focus on:

• What is the stimulus (modality of information)? Is it mechanical, chemical, etc.
• How does the sensory system encode the stimulus? Sensory filtering, transformation, transduction, amplification
• Where is this information processed? Neural anatomy, network connections, etc.

Interior of a statocyst gravity receptor, a common equilibrium organ of invertebrates. A fluid-filled vesicle lined with mechanoreceptors (hair cells) encloses one of more dense objects (eg. sandy or stone-like elements) - the statoliths. As gravity pulls these objects down, activity of sensory cells below them increases when their cilia are sheared. From this, the central nervous system can extract information about the direction of gravitational pull. When the animal molts it loses the lining of the statocyst and with it the sand grains. After molting the animal rebuilds the otoliths with surrounding materials. © 2000 lobsterman

• Reception: the ability of a cell to respond when matter or a specific form of energy acts upon a <Sensory Receptor>: A cell endowed with the ability to absorb a specific kind of stimulus energy. Stimulus filtering (also stimulus tuning): A receptors responds only to a narrow cocktail of (physical) characteristics.
• <Sensory Transduction>: chain of physiological reactions which convert sensory input into electrical impulses. This process translates the amount of stimulus energy into changes in membrane permeability (e.g., opening sodium channels towards the production of an action potential). Initial receptor responses are often graded and proportional to the strength of the input signal (e.g. membrane permeability of stretch receptors to ions is proportional to the force applied to the receptor).
• Amplification: weak sensory inputs are intensified
• Transmission: input signals are conveyed to the nervous system. The intensity of the graded response determines the frequency of generated action potentials. The rapid depolarisation and hyper-polarisation of an all-or-nothing action potential spike is fairly uniform in amplitude and duration (< 2 msec). <Frequency code>: Information transfer based on the rate of action potentials of up to 500AP/s for intense stimuli. Sensory receptors may be neurons who themselves project axons to the CNS or non-neuronal receptors which activate neurons via synaptic (i.e., neurotransmitter) signals
• Integration: Processing of information begins as soon as stimuli are received (e.g. Sensory adaptation). Summation of multiple graded responses influences frequency of action potentials.

Peripheral processing, Central processing. <Perception> interpretation of sensory signals within the CN where it produces an internal representation of electrical activity from sensory organs. Specificity of sensory impulses derives from transmission via labelled lines as it is largely dependent on which part of the brain receives the signals.

Stimulus Energy: There are three main forms of energies that can alter cellular processes and thereby activate sensory systems:

• Mechanical - (particle movement - near field, pressure waves - far field, compressional vs. transverse waves): Hearing, Vestibular, Touch (via hair cells in cochlea, statocyst, or semicircular canals) via hair cells in acoustic, equilibrium and lateral-line systems are responsible for the transduction process from cilia that respond to shearing forces and end with processes that depolarize the cell membrane of afferent neurons. Stimulus specificity is provided through Accessory Structures (e.g. tectal mebrane, statolith, and cupula)
• Electromagnetic - (waves): Light, Heat, Electrical, Magnetic (e.g., Phototransduction, heat sensors)
• Chemical - (particle movement): Olfaction/Pheromones/Taste (via chemical receptors trigeminal, taste, smell
• Signals can be binary or graded
• Signal to noise ratio
• physical and neural filtering.

Blind cave crickets of Mammoth Caves, KY, featuring long, tactile antennae © 2000 lobsterman

• Odor: chemoreception, pheromones species-specific odor cues (priming, releasing), Example: silk moths
• Sound and Vibration: mechanoreception, proprioreceptors, sound window, transmission in water vs. air, boundaries (surface waves), complex content (frequency modulation, amplitude modulation), Example: bird and whale songs, human speech, echolocation in bats and whales, long-distance communication in elephants and whales
• Movement of particles: Example: spiders
• Touch: routing response in babies, lordosis, grooming
• Radiant Heat: thermoreception, Example: Detection of prey in rattlesnakes
• Electric Fields: electroreception, Examples: Detection of prey in sharks, communication in electric fish
• Light: perception of absolute light levels, color balance, polarization, Examples: fireflies

Sensory Receptors

• Mechanoreceptors:
  • Hair Cells:
  • Stretch receptors (MRO): The muscle receptor organ spans the joint between two adjacent abdominal segments in crayfish. These are sensory organs that provide information about posture and movement of the individual. Each MRO has a thin muscle fibre that runs in parallel to a muscle bundle used by the animal to maintain the position of its abdomen. When the muscles contract or are stretched they cause the MRO to change its firing pattern, providing information to the nervous system regarding the relative position of the abdominal segments. There are two kinds of MROs. Tonic MROs respond to chronic stretch with continuous firing and habituate slowly. Phasic MROs respond to rapid changes in posture, but habituate quickly when the posture is maintained for more than a few moments.
• Electro-Magnetic Receptors:
  • Light-sensitive Pigment: retina
  • Electroreceptors: Electric fish, Sharks, Platypus: Some animal possess specialised sensory cells that enable them to detect changes in the electromagnetic field around them. These organs can be used by predators to locate prey by the electrical activity of their nervous systems and muscles, or in some cases as a means of communication (when coupled with the ability to produce pulses of electricity as seen in some electric fish).
  • Thermoreceptors: Snakes: Some snakes hunt their prey using body heat. Heat travels through the the atmosphere as infra-red (long wavelength) electromagnetic radiation, and is detected by cells sensitive to changes in temperature.
• Chemical Receptors:

Species Specific Differences in Sensory Reception

Human perception utilizes 5 sensory modalities: sight, hearing, touch, taste, and smell. Receptors are classified based on the source of the stimulus. Interoreceptors convey information from within the organism; Proprioreceptors report on the spatial position of body parts relative to one another; Exteroreceptors obtain information about the outside. Subcategories of the latter include Somatoreceptors that capture events on the body's surface and Teloreceptors which monitor stimuli at a distance fro the body. Sensory selectivity: refers to the subset of stimuli, which an animal detects and responds to; the <Umwelt>: Sensory World. Subjective set of stimuli to which an animal is responsive in a given motivational state. Each species has evolved responses only to those stimuli that prove relevant. It is this simpler world that actually falls within the animal's perception at any particular moment. (Jakob von Uexküll). <Psychophysics>: uses behavioral assays to establish sensory abilities of organisms.

Handout:

• Sensory Modalities

Reading Assignment

• Chapter 12: Communication

Food for Thought

• "The Department of Biological Sciences at BGSU has just received major funding to acquire the most powerful light microsope ever built (Zeiss Ultrascan 9000 Pro). Specifications promise the acquisition of high resolution images down to <10 Angstrom thus providing images of intact molecules and allowing a study of their folding patterns" -- This announcement may have just appeared as a press release on the BGSU media access website. Is there anything fishy about this release?

Links of Interest

• Acoustic communication in bladder grasshoppers