Senses and Reflexes

taste, smell - chemoreceptors temperature change - thermoreceptors threat detection - nociceptors what are the different type of sensory inputs and receptors touch (proprioception), hearing mechanoreceptors vision- electromagnetic receptors What is proprioception? sense of body position and movement - sense that lets you known where your body parts are and how they move without looking at them mechanoreceptors - Touch - Proprioception - sense that lets you known where your body parts are and how they move without looking at them - Hearing 1. Pacinian corpuscle 2. ruffini's endings 3. golgi tendon apparatus Different types of sensory fibres what is a sensory fibre? Carry impulse towards the central nervous system 1 / 21 - Can be either myelinated or unmyelinated General properties of tactile receptors - Tactile receptors are end organs that respond to light touch. - Send impulse to the cerebral cortex As the strength of the stimulus increases, the amplitude of the observed receptor potential also increases When the membrane potential increases stimulus effect on AP from receptors: in- and reaches the threshold level, there tensity , amplitude & frequency are more frequent action potentials per millisecond 1. rapid adapting (change receptors) what are the 2 types of adaptation of receptors? 2. slow adapting (tonic) • Rapid-adapting (change receptors) à Rate receptors, movement receptors, phasic receptors - Adapt rapidly to stimulus - Respond maximally but briefly to stimuli explain these receptor adaptations: 1. rapid adapting (change receptors) 2. slow adapting (tonic) • Slow-adapting (tonic)à receptors of the macula in the vestibule, nociceptors, baroreceptors, chemoreceptors of the aorta and carotid bodies - Tonic receptors are slow adapting receptors that respond to stimulus as long as it persists, and produce a continuous frequency of action potentials. 2 / 21 1. Temporal 2. Spatial 2 types of summation Spatial summation: - When multiple presynaptic neurones signal neurotransmitter towards one post synaptic neurone to generate a strong action potential what is spatital and temporal summation Temporal summation: - When one presynaptic neurone accumulates sufficient neurotransmitter until the threshold potential is reached, and then the action potential is fired to one post-synaptic neurone The ascending tract are sensory pathways that carry information from the spinal cord up to the brain The spinal cord Descending tract of the spinal cord are pathways by which motor signals are sent from the brain to the spinal cord Grey matter - composed of neuronal cell bodies, responsible for processing information White matter - composed of myelinated 3 / 21 The brain : grey matter white matter axons, responsible for transmitting signals between different areas of the brain - Somatosensory cortex is the most front portion of the parietal lobe - Receives information from touch receptors on the skin The Brain: the somatosensory cortex - Areas with more touch receptors apwhere is it found? pear larger in the somatosensory cortex what information does it process? - Interprets tactile stimuli e.g., touch, where is this information received from? pain, proprioception and temperature examples of tactile receptors · Merkel cells, which sense light touch and softness in the epidermis · Meissner corpuscles, which sense light touch and vibrations in the upper dermis · Ruffini endings, which sense stretch and pressure in the dermis • Aalpha, ABeta fibres • One central nerve ending surrounded by a layered capsule -tissue lamellae which can vibrate • Viscous fluid between capsule layers • Rapid tissue deformation - When sufficient pressure is used as stimuli, this causes the voltage gated sodium ion channels to open as the 4 / 21 how do tactile receptors work? what is the structure? threshold potential has been reached. Sodium ions move in, depolarise the membrane of the nerve and an action potential is sent through the axon • Very rapid adaptation - Only receptors present on the cornea A´Fibers (Sigma Fibers): - Primary afferent nerve fibres - Lightly myelinated - Respond to mechanical and thermal stimuli - Transmit rapid, shar pain signals - Role in reflex response to acute pain - Quick messengers of pain signals C fibres: - Smallest type of primary afferent fibres - Unmyelinated - Slowest conduction - Polymodal: respond to various stimuli: chemicals, mechanical, thermal - Activation of C fibres leads to a slow burning pain sensation, so have a big role in chronic pain and contribute to the emotional experience of pain what is an afferent fibre? carry sensory impulse from receptor to CNS 5 / 21 Structure: - Enlarged nerve terminal - Single afferent nerve fibre - Myelinated - Expanded tip tactile receptors - Abeta fibres ending à type 2 afferent fibres from stretch receptors - Merkel's cells is a type of mechanoreceptor -> Merkel cells is a mechanoreceptor found in hairy skin containing a cluster of Merkel cells with a single A-beta merkel disc structure, location and signal slowly adapting type 1 low threshold mechanoreceptor Found in: - Hairy areas and fingertips Signal: - Strong and adapting signal, followed by weaker and slow-adapting - Continuous touch High tactile acuity for objects' features, like texture, shape and edges - Are Merkel's discs grouped together in a receptor organ. - Located on the underside of the epithelium of the skin - Sensitive to touch What is the Iggo Dome Receptor 6 / 21 - Senses length and change of length from intrafusal muscle fibres Different from extrafusal muscle fibres - Responses to changes in muscle length - Ia fibers - Support from secondary II fibre receptors - Important for inhibitory reflex Tactile receptors in proprioception: mus- Most important contribution to propriocle spindle ception is made by muscle spindles. - Muscle spindles are stretch-sensitive mechanoreceptors found in all skeletal muscles - muscle spindle detect changes of length of muscle fibres • Detect muscle tension • 10-15 muscle fibers for each Golgi tendon organ • Important for inhibitory reflex • Equalises the tension among muscle fibers GTO is a proprioceptor- a type of sensoTactile receptors in proprioception: golgi ry receptor that senses changes in muscle tension. It lies at the interfacebetween tendon apparatus a muscleand its tendon (musculotendinous junction) summary of tactile receptor: on skin 7 / 21 summary of tactile receptors: muscle and joints signal to brain via tactile receptors including structure found in the brain This term refers to a sensory receptor located in the muscle that senses how much the muscle is stretched. What is muscle spindle muscle reflexes è Muscle spindle is a sensory receptor located within the middle of a muscle è It detects changes in muscle length and conveys this information to the CNS è For the response of proprioception 0 the sense of the relative position of one's own body parts -simplest form of sensory-motor integration -integration at spinal cord level -no conscious sense of plan - signal not transmitted to brain, only to spinal cord - quick response to prevent danger 8 / 21 patellar tendon muscle reflex Patellar tendon: - Patellar tendon below the kneecap is knocked and quadricep muscle in the thigh is stretched - The muscle spindle detects this stretchsignally the sensory neurone, and singles the spinal cord NOT BRAIN AS THIS IS A REFLEX and then the motor neurone - Motor neurone conducts impulse to quadricep, for a leg kick - Spinal reflex, does not require any activation of the brain - Stimulates the withdrawal of the arm - Protects against tissue damage from contact with noxious (stimuli that threaten or cause tissue damage) stimuli Flexor reflex: Sensory receptors: hearing Mechano-receptors: hearing Tympanic membrane - Tympanic membrane is the ear drum thin tissue which separates the outer ear from the middle Ossicles - three of the smallest bones. Play a role in hearing by transmitting sound waves 9 / 21 from the air to the fluid filled cochlea in the inner ear • Malleus - attached to the eardrum. When the ear drum vibrates due to sound waves, it moves the malleus. function of 3 ossicles • Incus - connected to both the other ossicles. Acts as an intermediary, transmitting vibrates from the malleus to the third ossicles. • Stapes - communicated with the incus and is the central part of the inner ear. Medical to the eardrum and behind the cochlea. cochlea - Cochlea (inner ear) - inner part of the ear and is responsible for our sense of hearing • Oval window - sound waves enter the cochlea through the oval window • Membranous labyrinth - system of fluid-filled tubes and has roles in hearing and balance Sound vibrates the eardrum, causing the tiny bones in the middle of the ear to vibrate transferring the vibrations to the inner ear fluids. The vibration propagates Sound propagation along the cochlea from the base of the cochlea to its apex along the cochlear partition. 10 / 21 Interior of cochlea has 3 fluids: - scala tympani contain the fluid perilymph - scala media and scala vestibuli both contain the fluid endolymph When the oval window is depressed by the ossicles, it creates waves that travel through the fluid of the cochlea. This causes the basilar membrane to move. Function: Structure in the inner ear needed to hear Location: The organ of Corti (aka spiral organ) is the receptor organ for hearing and is located in the mammalian cochlea Hearing: the organ of Corti Specially, it sits on top of the basilar membrane, extending along the entire length of the cochlear spiral from the base at the oval window to the apex. Structure: There are 2 types of hair cells - Inner hair cells: arranged in a single row -Outer hair cells: arranged in three rows 11 / 21 - Reside within the spiral organ of the corti, in the cochlea of the inner ear - 2 types of hair cells in cochlear: outer hair cells and inner hair cells Outer hair cells: amplify low-level sound Hearing: the hair cells difference between outer and inner hair Inner hair cells: transform sound vibrations in the cochlear fluids into electrical signals which are relayed to the auditory nerve to allow ions to enter cell and generate action potential - The auditory nerve carries this electrical signal from the hair cells to the brain. - In the brain, specialized areas receive these signals and translate them into recognizable sounds. Hearing: signal to the brain - We perceive these sounds as loud or which nerve carries electrical signal from quiet, speech, music, or other auditory hair cell to the brain? experiences. 12 / 21 Light passes through the cornea and the pupil before it reaches the lens, by which it is focused onto the retina. Vision: The retina Structure and function: - Retina processes visual information and sends it to the brain for interpretation - Captures light and converts it into neural signals Sensory receptors: vision Components of retina: Rods: black and white vision, working in dim light Cones: colour perception Ganglion cells: needed for reflex response and sleep Vision: rods and cones - Is a G-protein-couples receptor with a crucial role in visual phototransduction Vision: rhodopsin Location and Function: - Found in rod cells of the retina - Crucial role in phototransduction - When light strikes rhodopsin, it triggers a cascade of events leading to the generation of electrical signals 13 / 21 Vision: activation of photoreceptors Phototransduction process: Phototransduction process: - Light hits a photoreceptor (cone or rod) - Light causes a shape change in the retinal molecule - from cis bent to trans linear isomer - Shape change activates rhodopsin - Cascade reaction of other biochemical reaction within the photoreceptor cell - This leads to an action potential - Neurotransmitter is released to the optic nerve (the brain) for interpretation The retina, located at the back of the eye, contains specialized sensory cells called photoreceptors. These photoreceptors come in two main types: - Rods: Highly sensitive to light and function primarily in night vision. Vision: colour photoreceptors - Cones: Responsible for colour vision - wavelength specifity applies to rods or and operate best in bright light cones? - what are the different types of cones? Wavelength Sensitivity: Different types of cone cells respond to specific ranges of light wavelengths. Three Types of Cones: Humans have three types of cones, each sensitive to different parts of the spectrum: - S-cones (Short): Sensitive to short wavelengths (blue light). 14 / 21 - M-cones (Medium): Sensitive to medium wavelengths (green light). - L-cones (Long): Sensitive to long wavelengths (red light). Vision: colour blindness - Inherited and is present from birth - It results from variations in the functionality of the three classes of cone cells in the retina - Genes responsible for these cones are on the X chromosome but males have only 1 X, therefore colour blindness is more prevalent in males Red-green color blindness Protanope à Red blindness Deuteranope à Green blindness Vision: signal processing in the retina lateral inhibition - 100 million rods/ 3 million cones - 1.6 ganglion cells à 60 rods and 2 cones for each ganglion cell - Lateral inhibition in the retina = process where excited neurones inhibit their neighbouring neurones in the lateral direction in the retina o Horizontal cells and amacrine cells = inhibitory interneurons 15 / 21 Retinal Processing: - The retina, located at the back of the eye, captures visual input. - Photoreceptor cells (rods and cones) convert light into electrical signals. -These signals are then transmitted to bipolar cells and amacrine cells within the retina. Optic Nerve: - The optic nerve carries these electrical signals from the retina to the brain. - It exits the eye at the optic disc (also known as the blind spot). Visual information to the brain Lateral Geniculate Nucleus (LGN): - The optic nerve fibers reach the lateral geniculate nucleus (LGN) in the thalamus. - The LGN acts as a relay station, sorting and distributing visual information. Visual Cortex: - From the LGN, visual signals travel to the visual cortex located at the rear of the brain. - The visual cortex is one of the most studied parts of the brain. - Here, elementary features like contrast, color, and motion are combined to create our rich visual perception. 16 / 21 Pupillary reflex Response that occurs in response to changes in light intensity - Adjusts the size of the pupil - When exposed to bright light, the sphincter pupillae muscle contracts (located in the irus), causing the pupil to constrict and become smaller. Reducing amount of light entering the eye - In dim light, the dilator pupillae muscle relaxes allowing pupil to dilate (widen) and allow more light to enter Chemoreceptors respond to chemicals : taste Chemoreceptor: smell Clusters of taste receptor cells? gustatory cells taste receptor location Taste receptors are located around tiny structures cells papillae, found on the upper surface of the tongue what are the 4 types of papillae? 1. Filiform - These cover the tough surface of the tongue but do not contain taste buds. 2. Fungiform - Located near the front of the tongue. 3. Circumvallate - Found near the back of the tongue. 4. Foliate - Situated on the sides of the tongue 17 / 21 - Type I cells - 50% Serve as support cells within taste buds 1. Glia-like functions - elimination of neurotransmitters and spatial buffering of K+ explain type 1,2,3 taste bud cells - Type II Cells - 30% (sweet/bitter/umami) Chemosensory receptors for taste: bitter, sweet etc 1. mostly organic chemicals (sugars, glycols, alcohols, aldehydes, ketones, etc) 2. mostly organic chemicals (long-chain organic substances and alkaloids) 3. L-glutamate - Type III cells - 2-10% 1. Sour taste and salty 1. Type II and type III cells - ATP, serotonine and GABA 2. Type III to nerve fibres via serotonine and glutamate Type 2 cells express taste G protein cou- Intercellular communication taste cell ples receptors, and their downstream effectors, allowing them to detect flavour, communication taste receptors • Type I receptors (T1R) - GPCRs • Venus flytrap module (VFM) • T1R2/ T1R3 heterodimers recognize sweet taste • T1R1/ T1R3 heterodimers recognize umami taste • Type II receptors (T2R) - GPCRs • Function as monomers • 20 or more genes encoding for T2Rs • GLUT and SGLT1 - transporters 18 / 21 • Alternative sensing of glucose • SGLT1 à Na+/Glucose transporter possible explanation for salt enhancing sweet taste! At the apical tips of taste bud cells, molecular recognition occurs. Taste bud cells communicate with each other through various pathways. ATP (adenosine triphosphate) acts as an afferent taste transmitter taste signal processing Other signaling molecules like serotonin and GABA also mediate cell-cell interactions within taste buds, shaping transmission to sensory afferent fibers. Taste signals travel from taste buds to the brain via nerve fibers. These fibers carry the signal to the brainstem, where central taste processing begins. - Early release of insulin, triggered by sensory stimuli related to food - It occurs before actual food consumption - when we smell food Functional roles: 19 / 21 Glucose homeostasis- CPIR prepares the body for incoming nutrients. Early Reflexes - Cephalic phase of insulin re- insulin release ensures efficient glucose lease uptake what is this? functional role of this cephalic phase Chemoreceptors- Smell Olfactory receptors: location structure function The olfactory bulb: Location and function: Chemoreceptors- Smell Olfactory receptors: - Olfactory epithelium is located at the back of the nose - Tissue contains millions of sensory neurones with specialised proteins called olfactory receptors - Receptor binds to odour molecules, initiating the process of smell perception - Processes information about odours sent by cells in the nasal cavity - Once sensory input has been received, nasal cavity transfers it to several brain regions: 1. Amygdala 2. Orbitofrontal cortex 3. Hippocampus 20 / 21 Transduction and Neural Signals: Odorant binding activates G-protein coupled receptors (GPCRs) on OSNs. This leads to the opening of ion channels, allowing calcium ions to flow into the cell. Calcium influx initiates an action potential, creating an electrical signal Olfactory signal processing: Olfactory Bulb Processing: The olfactory nerve enters the olfactory bulb in the brain. Here, glomeruli receive input from specific types of OSNs. Glomeruli sort and relay signals to higher brain regions Pattern Recognition and Perception: Each odor activates a unique pattern of glomeruli. The brain deciphers these patterns, allowing us to recognize specific smells. 21 / 21