Animal Physiology Lecture 9 Exam 3

Senses

what animals use to interact with and respond appropriately to the world around them

To maintain homeostasis

animals must be able to detect changes in external and internal environments to maintain homeostasis

Five basic senses

olfaction(smell), gustation(taste), audition(hearing), somatic sensation(touch), and vision(sight)

Lesser known sensory stimuli

temperature, pressure, inertia, gravity, electric fields, magnetic fields

Mechanoreception

detection of mechanical stimuli such as pressure, distortion, tension, or displacement;

Senses associated with mechanoreception

consists of touch hearing proprioception, nociception, and inertia

Proprioception

sense of knowing where your body parts are located in space and in relation to each other

Nociception

detection of pain

Inertia

acceleration and deceleration

Chemoreception

detection of chemical stimuli

Senses associated with chemoreception

taste, smell, nociception, pruritoception

Pruritoception

the sensation of itching

Photoreception

light detection

Thermoreception

temperature detection

Magnetoreception

detection of magnetic fields

Functions of all sensory systems

filtering, transduction, and encoding

Filtering

the process of detecting relevant stimuli only; specialized based on different receptors for each sense

Transduction

way of transferring what is sensed into information the CNS can interpret; involves a change in current flow and amplification

Encoding

when the message is sent to CNS for interpretation; involves action potentials that change in frequency and pattern

Filtering steps

stimulus reaches receptor cells, receptor protein is activated

Amplification steps

first stage of transduction where cascade of protein interactions modifies intracellular second messengers and ion channels open/close

Graded potential steps

second stage of transduction where a change in conductance produces a receptor current that changes membrane potential that could either change transmitter concentration released from receptor cells or spread to the spike initiating zone (axon hillock)/presynaptic terminus

Spread of graded potentials to spike initiating zone

alters how much neurotransmitter is released from the sensory cells

Encoding step

when the numbers and or frequency of action potentials conducted along the axon or the axon of an afferent neuron changes resulting in an all or none response

How does the brain interpret sensory stimuli?

interpreted based on the type, location, and number of activated receptors as well as their pathway to the brain and the frequency, duration, and patterns of action potentials that initiate them

Perception

interpretation of the external world as created by the brain from action potential delivered by sensory receptive cells

Senses more important to animal’s survival

have more afferent neurons than efferent neurons with areas that interpret this being larger

Bony fish and birds

have relatively large optic tectum meaning they rely heavily on vision

Mammals, shark, and lamprey have large olfactory bulbs suggesting smell is of vital importance for these organisms

Filtering using receptory specialization

first step in perception where receptive cells are tuned to particular stimuli and will send signals to specific parts of the brain pertaining to the sense

Transduction (sensory receptive cells)

produces an excitatory postsynaptic potential is created in sensory receptive cells ionotropically or metabotropically

Ionotropic transduction

when a stimulus triggers channels to poem by direct action such as binding to the channel

Metabotropic transduction

when a stimulus triggers channels to open indirectly via a second messenger

Encoding: location (sensory receptive cells)

only sights stimulated enough to fire action potentials send messages to the brain, telling the brain the exact location of the stimulus; can be enhanced by lateral inhibition

Mechanosensory hairs of flies

mechanically gated channels in the cell membrane of a sensory neuron are displaced when this is lost resulting in the triggering of APs and sending a message to the brain via a specific pathway that indicates the location

Intensity/strength of stimulus

encoded by number of receptive cells stimulated and number of action potentials fired

The more displacement of the fly hair

the more action potentials were fired and the stronger the stimulus would be considered

What info does the brain use to interpret the world?

type and location of sensory cell sending signals and strength and pattern of the action potentials

Pattern of action potentials generated

can provide more nuanced information for the brain to interpret such as whether or not an odor is pleasant or nasty, and deciphering different flavors

Mechanically gated channels (stretch gated)

type of channels used by all mechanoreceptive senses and are usually sodium channels; integral proteins located on the dendrite cell bodies or cilia of mechanoreceptive cells

Trimers/PIEZO channels

complex mechanically gated channels that consist of three arms that create a small EPSP when one pore is opened and a large one when all of the pores are open

Components of touch receptor cells

meissner corpuscle, merkel disc, free nerve endings, ruffini ending, pacinian corpuscle, and hair follicle plexus

Hair follicle plexus

sensory nerves associated with hair follicles

Somatosensory receptors

may be rapidly or slowly adapting (tonic and phasic receptors)

Tonic receptors

slowly adapting sensory receptors that fire several action potentials initially when stimulus is added then become less frequent, but still present

Merkel discs and ruffini corpusles

slowly adapting sensory receptors

Phasic receptors

rapidly adapting sensory receptors that fire action potentials when a stimulus is applied, then stop firing despite presence of the stimulus

Off response

cellular response where a few action potentials are fired when a stimulus is removed

Off response and tonic receptors

let the brain know the duration of the stimulus

What is the difference between the somatosensory receptors and the olfactory and thermoreceptors?

olfactory and thermo receptors lack the off response in their rapidly adapting sensors, having adaptive receptors instead i.e getting used to a smell

Touch free nerve endings

c fibre LTM and mechanonociceptor polymodal nociceptor

Hair follicles, meissner corpuscle, and pacinian corpuscle

touch receptors with a low threshold and rapid adapting receptor responses

Merkel cell/neurite complex, ruffini corpuscle, and C fibre LTM

touch receptors and a free nerve ending that have a slow adapting receptor responses and a low threshold

Mechanonociceptor polymodal nociceptor

free nerve ending that has a slow adapting receptor response; only touch receptor with a high threshold for painful stimuli and slowest adapting receptor

Hair follicles function

detect skin movement

Meissner corpuscle function

detects skin motion such as slipping objects

Pacinian corpuscle function

detects vibratory cues transmitted by body contact when grasping an object

Merkel cell/neurite complex function

fine tactile discriminations such as form and texture perception like braille

Ruffini corpuscle function

skin stretch; direction of object motion, hand shape, and finger position

C fibre LTM function

pleasant contact; social interaction

Mechanoniciceptor polymodal nociceptor function

skin injury; pain

Receptive field of a neuron

region of space in which the presence of a stimulus will alter the firing of that neuron; smaller these are, the more accurate of a representation the stimulus signaled to the brain is

How are touch receptors distributed?

they are distributed to areas with more receptors

Somatosensory cortex

area of the brain where tactile sensations are interpreted for perception; mostly dedicated to areas of the body with more sensory cells

Two point discrimination test

test where the subject is blinded and poked with one or two stimuli and asked to differentiate between 1 poke or two pokes

Lateral inhibition

process that improves the acuity (sharpness) of touch using neurons to inhibit signals from nearby neurons via an intermediate neurons in the central nervous system,

Effect of lateral inhibition

enhances the differences between strong signals the point of stimulus and weaker signals generated near the stimulus so the body can identify exactly where stimulus is from

First order sensory neurons

first neurons to be stimulated by activation of sensory receptors; strongest one stimulate interneurons to release neurotransmitters

Are neurotransmitters always released in touch sensory neurons?

yes, as touch receptors have a baseline of activity consisting of action potentials with a slow receptor to constantly release

Antifacilitating interneurons

types of neurons that cause lateral inhibition in the CNS and connect the first order sensory neurons; release neurotransmitters that cause an IPSP in the axon terminus of neighboring sensory neurons

Effect of antifacilitating interneurons

stops neurotransmitters from being released in neighboring neurons, decreasing the baseline state of those neurons to indicate the main point of stimulation

Second order sensory neurons

neurons that relay the signal from the first order sensory neurons along the neural pathway to the somatosensory cortex

Pitch (tone)

depends on the frequency of sound waves where low notes=wide wavelengths and high notes=skinny wavelengths and

Intensity (loudness)

depends on the amplitude of the wave and has the same note but can be soft (short waves) or loud (tall waves)

Timbre (quality)

depends on overtones

Overtone

frequency that has a higher tone than the base note and is overlaid on the base tone

Hearing in terrestrial vertebrate

occurs in three stages: eardrum (tympanic membrane) collecting sound, impedance conversion by ossicles, and frequencies detected by the cochlea

Impedance convergence

the conversion of sound in air to sound traveling in a fluid so that energy is not lost; performed by bones in the middle ear

Outer ear

collects and sends sound waves to the eardrum; includes the pinna and the ear canal

Pinna

first part of the ear to encounter sound waves and has distinct structure for collecting sound

Middle ear

where impedance conversion occurs as the tympanic membrane vibrates when sound hits it and that energy is transferred through the three bones of the ear

Eustachian tube

connects the middle ear to the upper throat and can open to let small amounts of air through to equalize the pressure between the atmosphere and the middle ear

Oval window

first part of the cochlea to encounter sound waves

Cochlea

bony structure with three chambers: the scala tympani, scala media, and scala vestibuli which are each filled with fluid

Scala tympani and scala vestibuli

portions of the cochlea filled with perilymph

Scala media

portion of the cochlea filled with endolymph

Organ of Corti

located at the base of the scala media

Vibration of the oval window

causes movement of the perilymph in the scala vestibuli, that continue around the helicotrema (tip of the cochlea), through the perilymph of scala tympani to the round window, with the perilymph causing the organ of corti to move

Hair cells

modified epithelial cells with stereocilia on their apical surfaces and release neurotransmitter from their basal surfaces in rows; can be inner or outer with the outer version detecting sound; form synapses with afferent sensory neurons

Stereocilia

microvilli with a more rigid structure than cilia, bathed in endolymph which has high levels of extracellular potassium

Outer hair cells

type of hair cells only found in mammals that are thought to help amplify sounds; connected to efferent neurons and deiters’ cells; depolarized by movement of stereocilia causing them to change length causing displacement of basilar membrane, amplifying sound detection of the inner hair cells

Change in length of outer hair proteins

accomplished by motor proteins, specifically Prestin

Prestin

motor protein embedded in the hair cell membrane responsible for the change in length of outer hair cells as its proteins move towards each other shortening the cell

Endolymph of scala media

has a high potassium concentration

Basal portion of hair cells

bathed in perilymph which has normal low extracellular potassium

Depolarization due to potassium influx into hair cells

opens voltage gated calcium channels which allow vesicles to fuse with hair cell membrane, allowing the hair cells to release neurotransmitters, also allowing potassium to repolarize the hair cell

Basilar membrane

allows animals to detect particular tones; moves in response to sound waves moving through the perilymph; particular sections of this move based on particular sound frequencies

Width of the basilar membrane

determines what tones an ear can detect; is narrow at the base and wide at the tip

High frequency tones

detected by hair cells at the base of the cochlea closest to the oval window where the basilar membrane is narrow

Low frequency tones

detected by hair cells at the tip near the helichotrema of the cochlea where the basilar membrane is wide