Sensory System Flashcards
The sensory System - what it does
-General principles
-Detects changes in the external and internal environment
General Principles:
-Specialised receptor cell converts physical or chemical signal into electrical signal
-Electrical signal travels via PNS to CNS
-signals processed by CNS
-Efferent signals from CNS elicit appropriate response
Mechanoreceptors - how they work (generally)
-e.g.
-stretching of cell membrane causes opening of ion channels
e. g. Pressure and vibration
- Osmoreceptors
- balance (equilibrium)
- Sound
- muscle length and tension
- joint position and movement
Chemoreceptors
- How they work (general)
- e.g.
- Chemicals bind to specific receptors on cell membrane
- Open channels via secondary messengers
e. g. CO2, pH, various organic and inorganic molecules
*thermoreceptors operate in similar way, but they respond to temperature
Photoreceptors
- How they work
- Default position
- Respond to light
- When stimulated, initiate chain in chemical reactions terminating in breakdown of secondary messenger molecules and closure of ion channels
- Dark is default position
- Go out in sunlight = ion channels close
Sensory Neuron axon features
-Have a peripheral axon (where signal comes in) and a central axon (where signal goes out)
Sensory Transduction
-how works if sensory receptor is specialised nerve ending
- Stimulus opens ion channels, depolarising membrane and producing receptor (generator) potential)
- Receptor (generator) potentials are graded potentials - if afferent nerve sufficiently depolarised, APs generated, propagating to CNS.
Sensory transduction
-How works if receptor cell is separate from afferent nerve
- Stimulus changes membrane potential of receptor, opening or closing Calcium channels, increasing or decreasing calcium conc in cell
- Triggers or inhibits release of chemical transmitter
- signals receptor on afferent neuron
- excitory or inhibitory potentials generated in afferent neurons
- if sufficiently depolarised, APs generated, travelling to CNS
Sensory Systems in Vertebrates (3 broad types)
- Somatosensory system (senses external enviro)
- e.g. mechanoreceptors in skin detect touch, stretch and vibration, muscles, tendons, joints
- thermoreceptors
- nociceptors in skin detect tissue-damaging mechanical, thermal or chemical stimuli
- e.g. mechanoreceptors in skin detect touch, stretch and vibration, muscles, tendons, joints
- Visceral sensory system (sense internal environment)
- e.g. mecahnoreceptors for blood pressure; chemoreceptors and nociceptors
- Special sensory systems (sense external environment)
- involved in structures
- photoreception, mehcanoreception and chemoreception
- involved in structures
CNS processing of sensory information
- Conscious and unconscious signal perception
- Where processed in brain
- Some are perceived at lvl of conscious awareness(goes to cortex);
- some somatic senses (touch, temp, conscious proprioception and noxious stimuli)
- Special senses (taste, smell, vision, hearing) - Others processed at subconscious level (goes to cerebellum);
- Some propioceptive signals (eg. muscle length and tension)
- Signals from visceral sensory system (blood, pressure, body temp)
Sensory Coding
-4 things nervous system is able to identify
- When a stimulus sensory receptor, nervous system able to identify:
- Modality (Receptor type and signal pathway)
- Location (Receptive fields)
- Intensity
- Duration of stimulus (receptor adaptation)
Modality Receptor Type
-how it works
- Each type of sensory receptor responds only to specific form of energy (or modality)
- i.e. eye has photoreceptors
- modality to which receptor responds best is called adequate stimulus
- modalities other than the right stimulus may activate receptor, but only at high energy levels (e.g. getting hit hard in eye)
Modality: Labelled lines
-what it is
- each form of sensory stimulus follows fixed specific neural p/way to CNS
- same pathway activated every time
- p/way for each modality terminates in specific area of brain (if occurs in cerebral cortex, modality perceived)
Stimulus Location: Receptive fields
-2 ways stimulus localisation is enhanced
- In skin, stimulus localisation enhanced by;
- Smaller receptive fields
- Greater overlap of receptive fields of different afferent nerves
- lips more sensitive than back in humans
- difference in acuity differs over body surface and between sides
How is the intensity of a stimulus worked out?
- Action potential Rate and Burst duration
- Also, recruitment of additional neurons - stimuli of increasing intensity activates greater number of receptors
- may be within a single sensory unit of by stimulation of additional units
Stimulus duration: Tonic receptors
- what they are
- what suited for
- e.g.
- Most receptors adapt to stimulus
- w/ constant stimulus intensity, there is a decrease in magnitude of receptor potential and AP rate in afferent neuron
- tonic receptors adapt slowly -> are suited to signaling prolonged stimuli
e.g. tension receptors in tendons and stretch receptors in skin
Stimulus Duration: Phasic Receptors
- What they do
- what suited for
- e.g.
- Phasic receptors adapt rapidly
- Suited to detecting dynamic qualities of mechanical stimuli
- examples are Pacinian corpuscls in skin (detect high-frequency vibrations)
Sensor Receptors on Body surface
- Mechanoreceptors: detect various forms of mechanical energy, including pressure, vibration, touch and stretch
- Thermoreceptors: detect temperature
- Nociceptors: detect tissue-damaging (noxious) mechanical, therma and chemical stimuli.
Temperature Receptors
- how they work
- temperatures detected
- Free nerve endings (mainly in skin, lining or oral cavity and on surface of tongue)
- activation of receptor opens ion channels in cell membrane -> allows ions to enter cell, eliciting generator potential
- are separate receptors for cold, cool, warm and hot
In humans: perceived as thermal gadations from cold to hot (43 are tissue damaging)
- distribution of receptors not uniform
- cold receptors more superficial and in greater numbers
Thermo transient receptor protein
- what it is
- what else they can detect
Thermoreception in snakes
-what’s special about it?
- Series of 6 temp.-activated ion channels called transient receptor potential (TRP)
- some also respond to chemicals
- TRPA1, TRPV1 and TRPV2 are nociceptive
In snakes;
- some snakes have highly sensitive thermoreceptors -> enables them to locate prey in darkness
- are in small pits in skin on eiyher side of head (in pit organs)
Nociceptors on Body surfaces
-what they are perceived as
- Free nerve ending receptors that respond to tissue-damaging stimuli
- in brain, signals perceived as pain - activated by high intensity mechanical and thermal stimuli - most also w/ chemical
Proprioceptors in Muscles, tendons and Joints
- Where occurs
- where signal travels to (3)
- Mechanoreceptors in S.M., tendons and joints
- Detect changes in muscle length, changes in muscle tension and position of joints
- Signals go to cerebral cortex (conscious perception), spinal cord (generation of spinal reflexes) and unconscious area of brain (cerebellum)
Spinal Reflex
- info from somatosensory receptors travels to spinal cord (which acts as integrating centre)
- initiate reflex response w/out input from brain
- but also travel to brain where conscious perception occurs
- initiate reflex response w/out input from brain
Spinal reflexes: Knee jerk reflex
- Hammer tap stretches tendon, which, in turn, stretches sensory receptors in leg extensor muscle
- sensory neuron synapses w/ and excites motor neuron in spinal cord
- sensory neuron also excites spinal interneuron
- interneuron synapse inhibits motor neuron to flexor muscles
- Motor neuron conducts AP to synapses, causing contraction
- Flexor muscle relaxes b.c. activity of its motor neurons has been inhibited
- leg extends
Somatosensory Cortex
-how organised
- Sensory area of brain in which somatic sensations perceived
- info arising from adjacent areas of body register in adjacent areas of cortex
- size of specific area relates to sensitivity of body region
- areas close together on skin are close together in brain
- called somatrophic organisation
Chemoreceptors; Taste
- where found
- how organised
- Each taste bud contains 50-150 taste receptor cells (TRCs)
- found on dorsal surface of human tongue has ~5000 taste buds contained in 3 types of papillae
- taste buds on places other than tongue
Basic Tastes in Humans
- How we taste
- Flavours and places they are recognised
- Chemicals in food dissolve in saliva (how we taste)
- Probable that each TRC detects only 1 chemical
- signal TRC via specific receptor or ion channel
- Can taste all flavours everywhere, but some places are more sensitive
3 types of receptor cells in taste buds
-which one connects to afferent nerves
- Type 1: (support or glial cell) - cells probably detect Na+ ions via ion channel
- Type 2: (receptor) cells detect either sweet, umami or bitter tastes
- Type 3: (Presynaptic) cells detect sour taste
- only cells to synapse w/ afferent nerves, signalling via serotonin
Neural coding for Taste (Humans)
- Where on tongue tastes most sensitive
- Relation to brain
- All regions of tongue respond to 5 basic tastes (sweet, sour, bitter, umami
- Some regions more sensitive to certain tastes
- Tip of tongue most sensitive to salty, sweet and umami
- salty also on side of tongue
- bitter at back of tongue
- sour on sides
- Specific regions of cerebral cortex respond to specific tastes
Chemoreception: Smell (olfaction)
- How it works
- State of chemicals
- where travel
- What they are
- How they occur
- Chemoreceptor response depends on mechanisms similar to those involved in tastes
- chemicals must dissolve in mucus in nasal passage -> bind to specific chemoreceptors on afferent neurons
- signals travel to olfactory cortex where registered as various odours
- Olfactory receptor cells are neurons
- Receptor neuron cilia extend into layer of mucus lining nasal cavity
- Receptor neurons travel to olfactory bulb through series of small holes in holes in skull to synapses in olfactory bulb
Olfactory Neural Pathways
-Where signal goes
- From nose, signals travel to olfactory cortex where recognition of odour occurs
- olfactory signals also travel to parts of brain that register whether odour is pleasant or unpleasant
- also travel to parts of brain involved w/ emotion, memory and sex drive
- olfactory signals also travel to parts of brain that register whether odour is pleasant or unpleasant
- Establishes links between smell, memory, emotion and sexual behaviour
Species differences in olfactory Ability
- what greater smell in reflected by
- Vomeronasal Organ, what it is
- Domestic animals have much better olfactory ability than humans
- greater surface area of nasal cavity lining and in size of olfactory region of brain
Vomeronasal Organ: Accessory olfactory organ; detection of pheromones
Photoreception; Different types for different animals
- Single cell animals: retinal plate
- Flatworms: eyecup
- Higher vertebrates: camera eye (us included)
- Arthropods: Compound eye
Outermost layer of eye (2 parts)
- Sclera: Tough CT coat over majority of outside of eye (makes up “white”)
- Cornea: Transparent structure in front of eye -> allows light to enter
Middle layer of eye (4 parts)
- Choroid: Vascular, pigmented layer under sclera
- provides blood to retina and stops reflection of light that reaches back of eye
- Lens: focuses light on the retina
- Ciliary Body: Contains ciliary muscles, which attach to lens by zonular fibres
- change shape of lens to focus light - Iris: Located in front of lens; regulates amount of light entering eye by adjusting diameter of pupil
Inner Layer of eye (Retina)
- Fovea and Optic Disk
- 2 types of photoreceptors
- Fovea: Where light from centre of visual field strikes retina; area of greatest visual acuity
- Optic Disk (papilla): Where optic nerve and blood vessels supplying eye pass through retina
- No photoreceptor cells
- also called “blind spot”
-2 types of photoreceptors: rods and cones
Inner layer of eye in Animals
- what animals (but pig have)
- what it is and what it does
- All but pig have dorsal reflective tapetum lucidum
- avascular layer that lacks pigment - cells contain crystalline rods
- is a nocturnal adaptation
- avascular layer that lacks pigment - cells contain crystalline rods
- Reflects light, increasing stimulation of overlying retinal cells
Internal Chambers of eye (2)
-what they’re called and their major purpose
- lens and ciliary body separate eye into 2 chambers
- Anterior (front) chamber: contains clear, watery fluid (aqueous humour)
- supplies nutrients to cornea and lens
- Posterior (rear) chamber: contains firm, jelly-like materia (vitreous humour)
- maintains spherical structure of eye
- Anterior (front) chamber: contains clear, watery fluid (aqueous humour)
Refraction of Light waves by eye
- How Retina changes to look close and further away
- Control of what system
- Convex lens causes light waves entering eye to converge onto retina
- given point in visual field comes to focus on single point on retina - For near vision (accomodation): Ciliary muscles contract, causing ciliary fibres to relax and lens to round up
- occurs under parasympathetic control - For distant vision: Ciliary muscles relax and suspensory ligaments pull lens to a flatter shape
- occurs in absence of parasympathetic control
Structure of Photoreceptors
- what they do
- Outer and inner segment
- Change light signal to electrical signal
- Phototransduction carried out by rods and cones
- have same basic structural components - Outer segment has disks that contain photopigment
- Inner segment contains nucleus
- Synaptic terminal contains stores for the neurotransmitter used for communicating with nerves
Characteristics of Rods and Cones
- Type of vision
- Sensitivity to light
- Abundance
- Visual acuity
Rods: Ability to see black and white in low light; high sensitivity; 100 million per retina; low visual acuity
Cones: Provides ability to see colour in bright light; low sensitivity; 3 million per retina; High visual acuity
Phototransduction
- How light affects light-sensitive pigment (rhodopsin)
- need to also explain what it is bound to
-Dark and light
- Light sensitive pigment (rhodopsin) located in disks in outer segment
- rhodopsin comprises protein called opsin - is bound to vitamin A derivative called retinal
- On exposure to light, retinal dissociates from opsin, initiating sequence of reactions that decrease lvls of cBMP inside cells
*signalling increases in dark (become more depolarised); in light channels begin to close (become hyperpolarized)
Neural pathways for vision
- pathway
- decussate -> what it is and what it means
- From ganglion cells, signals travel in optic nerve
- optic nrve exit eye at optic disc
- 2 optic nerves combine at optic chiasm - variable proportion of nerve fibres cross over (decussate) to enter opp side of brain
- amount related to position of eyes in head (more if eyes more on side) - Info from right and left sides of visual field processed in left and right sides, respectively
Regulation of Light entering eye
- pupillary constriction and dilation
- how it occurs and why
-when else pupils also dilate
- Contraction or relaxation of inner circular muscle of iris smooth muscle regulates how much light enters eye
- in bright light, parasympathetic stimulation causes pupillary constriction (decreasing light entering)
- in low light, lack of parasympathetic stimulation allows inner circular muscle to relax (pupillary dilation)
- Pupils also dilate in fight or flight (response to fear/excitement)
- this is mediated by sympathetic nervous system
Pupillary Light Reflex (PLR)
- what is it
- direct and indirect reflex
-Relationship to decussation
- Light shone in one eye cases pupillary constriction in both eyes
- Direct reflex in stimulated eye and indirect (CONSENSUAL) reflex in unstimulated eye
*Strength of consensual reflex decreases as percent of decussation increases
Mechanoreception: Detection of sound
- Sound transmission through ear
- all structures it hits
- when and where AP initiated
- Sound waves strike tympanic membrane -> vibrates
- Vibrations transferred through malleus, incus and stapes - which amplifies signal
- Vibrations transferred from stapes to oval window -> setting up fluid waves within cochlea
- these waves push on flexible membranes of chochlea duct, bending haris cells in organ of Corti
- Neurotransmitter released from receptor cells creates APs in axons of cochlear division of vestibulocochlear nerve -> travels to CNS
- Energy in fluid waves transferred to tympanic duct; is dissipated back into the middle ear by flexible round window
Anatomy of Cochlea
- What the sensory organ for sound is
- what 3 parts it has - more detail on hair cells
- Sensory organ for sound = organ of Corti
- is on basilar membrane - contains hair cells, supporting cells and overlying tectorial membrane
- Hair cells: are the receptor cells; have hair-like projections called sterocilia w/ tips embedded in tectorial membrane
Sound Transduction by hair cells
- stereocilia
- how they are involve in sound transduction and generation of APs
- Oscillations of cochlear membranes cause hair cell sterocilia to bend
- Sterociliar are different lengths
- either bend towards or away from tallest sterocilium
- if towards longest - K+ comes in (usu. is lower conc outside) - causes depolarisation, opens voltage-gated Ca channels - increases neurotransmitter release, depolarising and generating APs
- if away from longest = become hyperpolarised and little action potentials (opposite to above)
- if towards longest - K+ comes in (usu. is lower conc outside) - causes depolarisation, opens voltage-gated Ca channels - increases neurotransmitter release, depolarising and generating APs
- signals from hair cells transmitted to brain via cochlear nerve
How Amplitude and Frequency are determined
-What regions are tuned for high/low frequencies?
- Sounds that vary in amplitude cause stereocilia to bend further in either direction (increasing or decreasing no. of AP generated)
- Cochlea “tuned” to frequency
- Different frequencies cause different regions of basilar membrane to deflect
- cochlear base (close to oval and round windows) “tuned” to high frequencies
- Cochlear apex “tuned” for low frequencies
Neural Pathways for sound
-what part in brain it goes to
- Afferent signals from hair cells travel in vestibulocochlea nerve -> terminate in cochlear nuclei
- from cochlear nuclei, nerves carry signals to thalamus, where more nerves transmit signals to auditory cortex in brain
- in auditory cortex, organisation is tonotopic (frequency “map”)
Sound Localisation
-2 things used
- Brain uses subtle differences in timing and level of sound (amplitude)
- the head also deflects sound, leading to lower amplitude at ear facing away from source
Mechanoreception: Detection of Motion and Body position
- In invertebrates (lobsters)
- Statocyst
- Statocyst: simple form of gravity receptor
- in lobsters, is a chamber lined w/ hairs at base of 2 antennae
- each statocyst contains statolith (comprise of grains of sand held together by mucus
- in lobsters, is a chamber lined w/ hairs at base of 2 antennae
- Gravity moves statoliths w/in statocyst - gives animal info about orientation
Lateral Line Neuromasts in Aquatic animals
- what they are and what they do
- How they work -> cupula
- Aquatic animals have lateral line that runs just below level of skin on either side of body
- contains mechanoreceptors called “neuromasts”
- detect motion in water
- contains mechanoreceptors called “neuromasts”
- similar concept to hearing (as fish moves, fluid pusses moves in lateral line and pushes against cupula; cupula contains hair cells whose stereocilia are embedded in gelatinous materia -> sterociliar on hair cells in cupula bend that creates signal)
Motion and position detectors in vertebrates: Vestibular System
- Vestibular labyrinth
- What output from brain affects
*is the only structure to detect motion
-Mechanoreceptors in a set of interconnected chambers of ear (vestibular labyrinth)
-info from vestibular receptors travels to brain
Output of brain plays major role in:
-control of posture and movement
-orientation of head
-Stabilisation of gaze
-Maintaining sense of spatial orientation of body
Mammalian vestibular apparatus
- parts (3 different)
- features
- Comprised of; 3 semicircular canals (fluid-filled at right angles to each other), 1 utricle, 1 saccule
- canals contain endolymph
- at base of each = ampulla (jug)
- canals contain endolymph
- W/in each ampulla is cupula (cap)
Structure of Ampullae
- crista
- cupula
-how info is transmitted to brain
- Each has ridge that extends into lumen of ampulla
- mechanoreceptor hair cells extend out of crista into gelatinous cupula
- cupula bridges width of ampulla - forms bridges width of ampulla & mobile barrier through which endolymph can’t circulate
-hair cells transmit info to vestibulocochlear nerve
Semicircular canals
- what they enable
- Function of cupula in head rotation
- Semicircular canals: enables detection of rotational movements of head in 3 planes
- when head is rotated in plane of canal, inertia of endolymph creates force that displaces cupula, causing bending of hair cells (stereocilia)
Transduction by rotation
-what occurs within semiciruclar canal and w/in ampulla
- Movement of stereocilia towards or away from kinocilium causes K channels to open or close (to = open)
- causes depolarisation or hyperpolarisation of hair cells - causing changes in calcium concentration
*what happens on one side will be different to what happens on the other (brain can decipher)
Utricle and Saccle
- what they do
- macula and where orientated in each
- Detect displacements and linear accelerations of head (e.g. tilting)
- Both contain macula (has sterocilia and associated structures)
- Utricles has them horizontally; saccular has them vertically
Structure of utricles and saccule
- how the structures contribute to movement
- Vertigo
- otoliths sit on top of gelatinous layer
- stereocilia on top of hair cells (under gelatinous layer)
-otoliths pulls gel, which moves hair
Vertigo: otoliths break off and block channel
Transduction of Linear acceleration (utricle and saccule)
-part of brain involved
- Utricle: detects backward and forward accelaration (also in detecting position of head relative to gravity
- Saccule: Detects up and down linear acceleration (e.g. riding in elevator)
*cerebellum is involved in balance and equilibrium
Electroreception in aquatic animals
- Ampullae of lorenzini
- structure and what they do
- skin has electroreceptors that aids in navigation and locating prey
- modified neuromasts called ampullae of Lorenzini
- contain salty gel-like material that detects small electrical currents in enviro
- modified neuromasts called ampullae of Lorenzini
- may also be sensitive to salinity and temperature
- In sharks, electroreceptors clustered around head
Active Electroreception -> in fish (freshwater)
-what they can do and how it works
- Some freshwater fish are able to receive feedback from electrical signals produced by fish itself
- fish produces weak electrical field from organ in tail and receives signals from ampullae along its body
- Important for navigation and prey location
