Sensory Systems Flashcards
(18 cards)
Differences between Phasic and Tonic
Phasic - rapidly adapting receptors signal the onset and offset of a stimulus (adoptive ability is a property of a sensory receptor)
Tonic - slowly adapting receptors continuously signal the intensity and the duration of the stimulus
Explain Skin receptors - Pascinian Corpuscles
Large mechanorecptors, Compresseion of intricate sheath of concentric connective tissue lamellae triggers single nerve ending in the clear central space of receptor organ.
Large myleinated axons allows for fast propagation of action potentials to the dorsal horn of spinal cord. Phasic
Other mechanoreceptors
Meissner’s corpuscles- phasic
Merke cell - tonic
Ruffini’s corpuscles - tonic
Cutaneus Mechanoreceptors
Those with small receptive fields are involved in spatial discrimination, unlike receptors with larger receptive fields are less spatial precise.
Overlap of receptive fields allows lateral inhibition to occur in the ascending pathways and increases sensory acuity
Thermoreceptors
Free nerve endingd found in epidermis, Spot-like receptive fields - each responds to specific temperature.
Cold receptors are mylinated and increase there tonic firing rate as temperature decreases within their range of sensitivity.
Warm receptors fire continuously, but increase their firing rates as temperature increases
Explain pain receptors - Nocieptors
Small receptive field, free nerve endings, c-terminals. Mechanorecptors stimulated by firm pressure or sharp penetrating objects. Myleinated or unmyleinated, thermal or mechanothermal receptors, excited by high temperatures, inflammation chemicals
Explain Proprioceptors
Sensory receptors in muscles or joints, nerve teminal branch extensively within the tendon, Fast-prpagating fibres conducts information on muscle and tendons, Golgi tendon organ occupy tendon at junction with muscle - responsible for stretch reflex.
Explain Hearing
Sound waves conducted down the ear vibrate against thin tympanic membrane (ear drum), causing it to vibrate, causing the vibration of the ossicles
The stapes vibrates against a small thin membrane at the oval window, which transmits the vibrations to the fluid of the cochlea. Vibration of a membrane at the round window serves to cushion and dampen fluid movement within the cochlea
3 Main structures of the ear
3 separate main canals: tympanic canal, the vestibular canal and the middle
Structure of the ear
Sound vibrates in cochlear fluid, transmitted to long thin membrane that separates the tympanic and vestibular canals, the basilar membrane. Broadens as it runs the length of the coild cochlea.
High pitch sounds maximally vibrate the thin basal (proximal) end.
Low pitch sounds maximally vibrate the broader apical (distal) end.
movement of the basilar membrane causes displacement of organ of corti.
Cilia of the thin hair cells are in contact with the overlaying tectcrial membrane.
Each hair cell has 3 rows of cilia progressing in length.
Movement of the hair cells due to vibration of he basiler membrane cause the hair cell cilia to move relative to the tecterial membrane.
Dispplacement of the hair cell leads to an increase/decrease in firing of the auditory nerve depending on the direction of cilia movement.
Taste (Gustation) central pathway
Pathways go directly through the thalamus before they project to their relevant cortical area, taste afferent from the midbrain are involved in visceral reflexes
Different type of taste receptors
- T1R- large extracellualr domain for ligand-binding - sweet stimuli
- T2R - sense bitter stimuli
- t-mGluR4 is the candidate umami receptor, detects glutamate (Activate on intracellular side through GPCR)
- MDEG/ENaC - receptors belong to a superfamily of ion channels implicated in sodium salt and acid sensation
Explain taste transduction
Bitter and sweet ligands use GCPR.
Bitter ligand, transduction, release Ca from intracellular stores.
Sweet lignad, gusducin, activates cAMP 2nd messenger which closes K channels ans depolarises cell.
Ionic ligand for sour and salt alter ion channels and depolarise cell, triggering extracellualr Ca entry.
In all case increased intracellular Ca triggers neurotransmitter release
Explain Small (olfaction) structure
Cilia on olfactory receptive neurons bind with adorants and the transduction process involves a G-protein 2nd messenger.
The bipolar olfactory cells are link to the olfactory bulb via short axons.
Explain odorant signalling (transduction)
Chemical bonding to odorant receptors leads to cAMP production. cAMP activates Ca channels leading to Ca and Na infulx and depolarisation. Depolarisation is potentiated by Ca, this activates Cl channels. Cl leaves cell. Feedback occurs, re-establishes membrane potential. Ca binds to calmodulin which reduces affinity of cyclic nucleotide - gated Ca channel for cAMP -> activates CaM Kinase which Phosphoralites adenylate cyclase and reduces cAMP production. Na/Ca exchanger removes C from cell
How is topography achieved?
Within a target region, gradients of inhibitory axon guidance ligands are established. Extend when incoming axons invade target, depends on sensitivity of axon to inhibitory ligand. Achieved by differential expression on axons of the receptor for the ligand, or of active form of the receptor. Axon expressing less receptor progress further then those expressing more receptor. If a complementary gradient of active receptor is expressed on neighbouring projecting neurons, topography is achieved by axons originating from the same areas managing to project to complementary positions in the target
Explain Vision
Lens is held in place by suspensory ligaments and can change by contraction and relaxation of ciliary muscle.
Light is focused by refractory through the lens onto the sensory area. Point of greatest acuity is the fovea. where the greatest concentration of photoreceptor cell are found.
Near vision - ciliary muscle contracts to round lens up, thus increasing the diffraction of light in order to focus retina
Distant vision - less diffraction is required, and ciliary muscles relax to elongate lens.
Light transmitted to brain via optic nerve.
Explain Light
Light detected by rods and cones - lined by pigmented epithelium (absorbs excess light). Activation of photoreceptors leads to the release of pigment and depolarisation of bipolar cells. This activates retinal ganglion cells (RGC) -> there axon converge on optic nerve and exit eye into optic nerve. The fovea is the most sensitive spot on retina - contains no rods but contains cones. Optic nerve head (ONH/optic disc) is where the RGC fibres leave the eye, hence no photoreceptors and hence blind spot.
Pigment activates elects a cAMP-mediated change in release of neurotransmitter and postsynaptic of bipolar cells.
Convergence of the signal occurs due to many receptors synapcing onto bipolar cells, and lateral inhibition mediated by horizontal cells.
