Handout 1.1 Biological Bases of Perception and Motricity PDF

10/2/25 UNIT 1 BIOLOGICAL MECHANISMS OF PERCEPTION AND MOVEMENT WARM-UP QUESTIONS: 1.What is the difference between sensation and perception? 2. How many senses do we have? 3. What are the stimulus for each sense? 4. How is the information perceived? 5. How are sensory ev...

10/2/25 UNIT 1 BIOLOGICAL MECHANISMS OF PERCEPTION AND MOVEMENT WARM-UP QUESTIONS: 1.What is the difference between sensation and perception? 2. How many senses do we have? 3. What are the stimulus for each sense? 4. How is the information perceived? 5. How are sensory events transformed into changes in cells’ membrane potential? 1  10/2/25 1. What is the difference between sensation and perception? Sensation is the activation of sensory receptor cells at the level of the stimulus. Perception is the central processing of sensory stimuli into a meaningful pattern. Sight: Vision Hearing: Audition 2. How many senses do we Balance: Vestibular system have? Smell: chemosenses Taste: chemosenses Touch: Somatosenses 2  10/2/25 3. What are the stimuli for each sense? Light (Short-wave length is perceived as blue) Sound Chemical properties (sugar on the tongue is perceived as sweet) Physical properties How is the information sensed? Sensory receptors: Specialized cells that convert physical energy in the environment or the body to electrical energy that can be transmitted as nerve impulses to the brain. 3  10/2/25 How do we receive information? How do we dectect changes in the environment? Sensory Receptors Specialized cells (neurons) that detect a variety of physical events. Sensory transduction The process by which sensory stimuli are transduced into changes in the cells’ membrane potential Receptor potentials: electrical change induced in the receptors as a response to stimulation. Affect the release of neurotransmitters and modify the pattern of firing in neurons that synapses 4  10/2/25 VISION AND AUDITION (short) Cerebral pathways 5  10/2/25 Three Different Classes of Visual Cortex Primary visual Secondary visual Visual association cortex cortex cortex Located in occipital lobe Located in the prestriate Located in cortex Inferotemporal cortex Receives most inputs from visual relay nuclei of Receives input from Posterior parietal cortex thalamus primary visual cortex Receives input from secondary visual cortex Visual Areas of Cortex The visual areas of the human cerebral cortex. 6  10/2/25 Damage to primary visual cortex results in Damage to scotomas Primary Visual Areas of blindness in corresponding areas of visual field Scotomas are plotted by perimetry tests Cortex: Scotomas Completion and Completion Blindsight These phenomena support parallel models rather than serial Perimetric Maps The perimetric maps of a man with a bullet wound in his left primary visual cortex. The scotomas (areas of blindness) are indicated in gray. (Based on Teuber, Battersby, & Bender, 1960.) 7  10/2/25 Scotoma and Completion The completion of a migraine-induced scotoma, as described by Karl Lashley (1941). Portions of secondary and association cortex Functional Areas of Areas specialized for particular type of visual analysis Secondary and Association PET, fMRI, and evoked potentials have helped with identification Visual Cortex Mimic what has previously been found in macaque monkeys 8  10/2/25 Visual Areas of the Brain Some of the visual areas that have been identified in the human brain. Two anatomically and functionally distinct pathways Dorsal stream Ventral stream Information flows from primary visual cortex Information flows from primary visual cortex Travels through the ventral prestriate Travels through dorsal prestriate secondary secondary visual cortex visual cortex Ends in inferotemporal cortex Ends in association cortex of posterior parietal Originally proposed to be “what” pathway region More recently proposed to be conscious perception pathway Originally proposed to be “where” pathway More recently proposed to be behavioral control path 9  10/2/25 Dorsal and Ventral Streams Information about particular aspects of a visual display flows out of the primary visual cortex over many pathways. They can be grouped into two general streams: dorsal and ventral. Two Theories of Dorsal and Ventral Stream The “where” versus “what” and the “control of behavior” versus “conscious perception” theories make different predictions. 10  10/2/25 Prosopagnosia (face blindness) Agnosia=inability to recognize or identify objects Causes of prosopagnosia Damage to the fusiform Conditions such as face area (FFA) in the strokes, traumatic brain Developmental causes linked to genetic factors brain, which is injuries, encephalitis, specialized for facial Alzheimer's disease, or or neurodevelopmental conditions like autism recognition. brain tumors. 11  10/2/25 ü Difficulty recognizing familiar faces in person or in photographs. ü Inability to distinguish between different faces or describe facial features. Symptoms ü Reliance on non-facial cues like voice, hairstyle, clothing, or accessories to identify people. ü Challenges recognizing emotions, age, or gender from facial expressions. ü Problems following plotlines in movies or TV shows with multiple characters May be difficult distinguishing between visually similar members of stimuli groups May not be Confirmed prosopagnosia specific to sufferers could recognize faces faces unconsciously Prosopagnosia may not be a unitary disorder 12  10/2/25 Deficiency in the ability to see smooth movement Can be triggered by high doses of antidepressants Patients tend to have unilateral or bilateral damage to MT Damage to medial temporal Akinetopsia area (MT) Activity in the MT increases when humans view movement Four lines of research support MT as area affected Blocking activity of the MT with TMS produces motion blindness Electrical stimulation of the MT induces visual perception of motion Prosopagnosia vs. Akinetopsia (motion blindness) The location of the fusiform face area (FFA), the occipital face area (OFA), and area MT. Damage to the FFA or OFA is associated with prosopagnosia. Damage to area MT is associated with akinetopsia. The FFA and OFA are not visible in this figure; they lie on the ventral surface of the temporal lobe and occipital lobe, respectively. 13  10/2/25 Audition Two Models of Sensory System Organization Two models of sensory system organization: The former model was hierarchical, functionally homogeneous, and serial; the current model, which is more consistent with the evidence, is hierarchical, functionally segregated, and parallel. Not shown in the current model are the many descending pathways that are the means by which higher levels of sensory systems can influence sensory input. 14  10/2/25 Physical and Perceptual Dimensions of Sound The relation between the physical and perception dimensions of sound. Anatomy of the Ear 15  10/2/25 From the Ear to the Primary Auditory Cortex Pathway (from inner ear to brain) Hair cells synapse on neurons Axons enter metencephalon Synapse in ipsilateral cochlear nucleus Travel to superior olives Travel to the inferior colliculus via the lateral lemniscus Fibers ascend to the medial geniculate nucleus of the thalamus Fibers ascend to the primary auditory cortex in the lateral fissure Projections from each ear are bilateral Pathway from Ear to Primary Auditory Cortex Some of the pathways of the auditory system that lead from one ear to the cortex. 16  10/2/25 Auditory Cortex -1 Auditory cortex Receives input from Medial geniculate nucleus Organization of primate auditory cortex Core region Belt Tonotopically organized Parabelt areas Contains functional column Secondary cortex responds best to complex tones Poorly understood compared to vision Natural sounds optimal for studying auditory cortex Integrates information Two streams of auditory cortex Auditory Anterior auditory pathway: identifies sound Posterior auditory pathway: identifies where sound is Cortex-2 Auditory-visual interactions Occurs early in pathway Integral part of sensory processing Pitch perception Anterior to primary auditory cortex 17  10/2/25 Auditory Cortex Anterior and Posterior Auditory Pathways 18  10/2/25 Auditory cortex damage Bilateral lesions do not cause deafness Effects of Creates difficulty in localization Creates difficulty in recognizing rapid complex Damage to sequences of sound Deafness the Total deafness is rare Two types Auditory Conductive (damage to ossicles) Nerve (damage to cochlea or nerve) System Age-related hearing loss (high frequencies helped by hearing aids or cochlear implant) Tinnitus (ringing) UNIT 1 THE VESTIBULAR SYSTEM: 19  10/2/25 VESTIBULAR SYSTEM The functions of the vestibular system: Balance Maintenance of the head in an upright position Adjustment of eye movement to compensate for head movements We are not directly aware of the information received from these organs. Vestibular stimulation does not produce any sensation. Alteration of the system induces nausea, dizziness and rhythmic eye movements (nystagmus) 2-Minute Neuroscience: Vestibular System: https://youtu.be/P3aYqxGesqs VESTIBULAR SYSTEM ANATOMY Two components: vestibular sacs and semicircular canals. They represent the 2nd and 3rd components of the Labyrinths of the inner ear: Cochlea (Audition) 20  10/2/25 VESTIBULAR SYSTEM ANATOMY Semicircular canals (sagittal, transverse, and horizontal): respond to angular acceleration (changes in the rotation of the head) but not to steady rotation. They also respond (but rather weakly) to changes in position or to linear acceleration. Vestibular sacs: respond to the force of gravity and inform the brain about the head’s orientation, changes in the tilt. SEMICIRCULAR CANALS The semicircular canals approximate the three major planes of the head: sagittal, transverse, and horizontal. Sagittal, transverse or horitzontal Receptors in each canal respond maximally to angular acceleration in one plane 21  10/2/25 Semicircular canals are filled with endolymph Membranous canal floating within a bony one in a fluid called endolymph. An enlargement called ampulla contains the sensory receptors. Hair cells are embedded in the cupula An enlargement called ampulla contains the sensory receptors. Sensory receptors: hair cells similar to those in the cochlea. Cilia embedded in a gelatinous mass called the cupula. 22  10/2/25 SEMICIRCULAR CANALS The semicircular canal approximate the three major planes of the head: sagittal, transverse, and horizontal. Receptors in each canal respond maximally to angular acceleration in one plane. Endolymph Motion Demonstration https://www.youtube.com/watch?v=d SHnGO9qGsE 23  10/2/25 The effects of angular acceleration on the semicircular canals Experiment: If we place a glass of water on the exact center of a turntable and then start the turntable spinning, the water in the glass will, at first, remain stationary (the glass will move with respect to the water it contains). Eventually, however, the water will begin rotating with the container. If we then stop the turntable, the water will continue spinning for a while because of its inertia. The semicircular canals operate on the same principle. The endolymph within these canals, like the water in the glass, resists movement when the head begins to rotate. If you spin around and then stop, the liquid inside your semicircular canals moves awhile longer and the hairs continue to send the message that you are spinning even though you're not. That's why you feel dizzy after amusement park rides. SEMICIRCULAR CANALS RESPOND TO ANGULAR ACCELERATION The inertial resistance pushes the endolymph against the cupula, causing it to bend, until the fluid begins to move at the same speed as the head. If the head rotation is then stopped, the endolymph, still circulating through the canal, pushes the cupula the other way. Angular acceleration is translated into bending of the cupula, which exerts a shearing force on the cilia of the hair cells 24  10/2/25 VESTIBULAR SACS: UTRICLE AND SACCULE The vestibular sacs contain a patch of receptive tissue (macula) Receptive tissue is located on the “floor” of the utricle and on the “wall” of the saccule. UTRICLE: Horizontal SACCULE: Vertical https://www.youtube.com/watch?v=h3AsFe1QgfM Cilia from hair cells are embedded in a gelatinous mass The cilia of these hair cells https://www.youtube.com/watch?v=h3AsFe1QgfM are embedded in an overlying gelatinous mass, which contains “otoconia”, small crystals of calcium carbonate. The weight of the crystals causes the gelatinous mass to shift in position as the orientation of the head changes. Thus, movement produces a shearing force on the cilia of hair cells. 25  10/2/25 Transduction Hair cells of the semicircular canals and vestibular sacs resemble the auditory hair cells found in the cochlea, and their transduction mechanism is also similar. Transduction https://www.youtube.com/watch?v=P3aYqxGesqs A shearing force of the cilia opens ion channels: entry of potassium ions depolarizes the ciliary membrane. 26  10/2/25 The Vestibular Pathway Vestibular + cochlear nerves are the 2 branches of the VIII cranial nerve (auditory nerve) àcerebellum àmedulla à vestibular nuclei in the medulla àspinal cord axons of the vestibular nerve synapse within àpons àtemporal cortex àdirectly to the cerebellum https://www.youtube.com/watch?v=phpe_RVGqcA Vestibulo-ocular reflex As we walk or (especially) run, the head is jarred quite a bit. The vestibular system exerts direct control on eye movement to compensate for the sudden head movements. This process, called the vestibulo-ocular reflex, maintains a fairly steady retinal image. When we make a head movement, our eye muscles are triggered instantly to create an eye movement opposite to that of our head movement at the exact same speed to readjust the visual world, which, in turn, stabilizes our retinal image by keeping the eye still in space and focused on an object, despite the head motion. 27  10/2/25 Dizziness and vertigo are symptoms of a vestibular balance disorder. Investigators believe that the cortical projections are responsible for feelings of dizziness; the activity of projections to the lower brain stem can produce the nausea and vomiting that accompany motion sickness. Vestibulo-ocular reflex 2-min video (from 01:15) https://youtu.be/OZvIk76cSAI?si=cGD7pySlqF_TRGjC As we walk or (especially) run, the head is jarred quite a bit. The vestibular system exerts direct control on eye movement to compensate for the sudden head movements. This process, called the vestibulo-ocular reflex, maintains a fairly steady retinal image. https://youtu.be/_1kVVn2pcHA?si=RQL5TEoOq-tB14o- Nystagmus. You do that because it helps you focus when you can't hold your gaze steady. 28  10/2/25 UNIT 1:BIOLOGICAL MECHANISMS OF PERCEPTION AND ATTENTION: CHEMICAL SENSES The nature of the stimulus: CHEMICALS IN THE EXTERNAL WORLD The stimuli that we have encountered so far produce receptor potentials by imparting physical energy: photic (involving light), mechanical (involving changes in air pressure)… The stimuli received by gustation and olfaction—interact with their receptors chemically. 29  10/2/25 UNIT 1: OLFACTION Availability of foods Important social function in some species track prey or detect predators and to identify friends, foes, and receptive mates. THE NATURE OF THE STIMULUS Although many other mammals, such as dogs, have more sensitive olfactory systems than humans do, we should not underrate our own Perfumers can distinguish 5000 types of odorants 30  10/2/25 THE NATURE OF THE STIMULUS The stimulus for odor (known formally as odorants) consists of volatile substances having a molecular weight in the range of approximately 15–300. à The olfactory system is second only to the visual system in the number of sensory receptor cells, with an estimated 10 million cells. à We can smell some substances at lower concentrations than the most sensitive laboratory instruments can detect. OLFACTORY CELLS ARE ON THE OLFACTORY EPITHELIUM Olfactory receptor cells are bipolar neurons whose cell bodies lie within the olfactory epithelium. 5cm2 Short-lived: There is a constant production of new olfactory receptor cells (30-60 days) 31  10/2/25 OLFACTORY CELLS ARE ON THE OLFACTORY EPITHELIUM Olfactory receptor extends a dendrite toward the surface of the mucosa, which divides into 10-20 cilia that penetrate the layer of mucus. Odorous molecules must dissolve in the mucus and stimulate receptor on the olfactory cilia. bundles of axons, ensheathed by glial cells, enter the skull through small holes in the cribriform plate. The olfactory bulbs lie at the base of the brain. TRANSDUCTION G-protein-coupled receptors: Golf https://www.youtube.com/watch?v=0xcLbPkzN9w Olfactory cilia contain odorant receptors linked to G-protein-coupled receptors. Molecules of odorant bind with olfactory receptors, and the G proteins coupled to these receptors open sodium channels and produce depolarizing receptor potentials. 32  10/2/25 6 milion olfactory cells 350 receptors Mice: 1000 1. Each olfactory receptor cell sends a single axon to the olfactory bulb, where it forms synapses with mitral cell dendrites and tuft cells. 2. These synapses occur in the axonal complex and in dendritic arborizations called olfactory glomeruli. 3. The axon of the mitral cells travel to the rest of the brain through the olfactory pathways 4. Some of these axons end in other regions of the ipsilateral forebrain; others pass through the brain and end up in the contralateral olfactory bulb SENSORY INPUTS IN THE OLFACTORY BULB ARE ARRANGED BY RECEPTOR TYPE Each glomeruli receive information from particular olfactory receptors Neurons with the same receptor are randomly scattered within the zone so that neurons with different receptors are interspersed. Although one zone may have more receptors for a particular odorant compared to other zones, all zones contain a variety of receptors, so that a specic odorant may be recognized by receptors in several different zones. 33  10/2/25 350 different olfactory receptors for 10,000 different odorants How is a large array of different odorant receptors organized to generate diverse odor perceptions? How are different odorant receptors organized to generate diverse odor perceptions? Each olfactory cell contain only one type of receptor and each receptor recognizes multiple odorants Recognizing a particular odor is recognizing a particular pattern of activity Different odorant molecules attach to different combinations of receptor molecules. Unique patterns of activation represent particular odorants. 34  10/2/25 DIFFERENT COMBINATIONS OF RECEPTORS ENCODE DIFFERENT ODORANTS Each odorant is detected by a unique constellation of receptors and thus causes a distinctive pattern of signals to be transmitted to the brain. The combinatorial coding of odorants greatly expands the discriminatory power of the olfactory system. https://www.nobelprize.org/prizes/medicine/2004/summary/ 35  10/2/25 Olfactory system pathway Olfaction has direct access to the brain (no thalamic relay) The axons of the olfactory bulb project directly into the amygdala and into two regions of the limbic cortex: amygdala à hypothalamus Olfactory bulb the piriform cortexà dorsomedial nucleus of the thalamus, hypothalamus and orbitofrontal cortex entorhinal cortex à hippocampus Olfactory cortex: Olfactory system pathway 1. Anterior olfactory nucleus 2. Olfactory tubercle 3. Piriform cortex: the major olfactory cortex 4. Amygdala 5. Entorhinal cortex 4 5 3 1 2 36  10/2/25 UNIT 1: TASTE TASTE ≠ FLAVOUR Perception of flavour is a composite of gustatory, olfactory and somatosensory inputs. Sensations of flavor also frequently have a somatosensory component that includes the texture as well as sensations evoked by spicy and minty food and by carbonation. Anosmic people (who lack the sense of smell) or people whose nostrils are stopped up have difficulty distinguishing between different foods by taste alone. Retronasal olfaction “mouth-smelling” 37  10/2/25 THE NATURE OF THE STIMULUS The primary function of the gustatory system is nutritional Evolutionary significance? 5 qualities of taste: bitterness, sourness, sweetness, saltiness, umami. 1. Sweet—sugars 2. Sour—hydrogen ions in solution 3. Salty—NaCl+ 4. Bitter—alkaloids such as quinine and nicotine; caffeine 5. Umami—amino acids glutamate, proteins TASTE BUDS ARE LOCATED IN THE PAPILLAE Primarily tongue but also on the palate, pharynx, epiglottis and esophagus. Fungiform papillae Foliate papillae Circumvallate papillae 38  10/2/25 Taste Receptors, Taste Buds, and Papillae Taste receptors, taste buds, and papillae on the surface of the tongue, and a cross- section of a papilla that shows a taste bud and its taste receptors. Two sizes of papillae are visible in the photograph; only the larger papillae contain taste buds and receptors. TASTE BUDS ARE LOCATED IN THE PAPILLAE Primarily on the tongue but also on the palate, pharynx, epiglottis and esophagus. Fungiform papillae Foliate papillae Circumvallate papillae 39  10/2/25 TASTE BUDS ARE LOCATED IN THE PAPILLAE Fungiform papillae, are on the anterior two-thirds of the tongue (1-8 taste buds) along with receptors for pressure, touch, and temperature. TASTE BUDS ARE LOCATED IN THE PAPILLAE Fungiform papillae, are on the anterior two-thirds of the tongue (1-8 taste buds) along with receptors for pressure, touch, and temperature. Foliate papillae are along each edge of the back of the tongue (1300 taste buds are located in these folds). 40  10/2/25 TASTE BUDS ARE LOCATED IN THE PAPILLAE Fungiform papillae, are on the anterior two-thirds of the tongue (1-8 taste buds) along with receptors for pressure, touch, and temperature. Foliate papillae are along each edge of the back of the tongue (1300 taste buds are located in these folds). Circumvallate papillae, arranged in an inverted V on the posterior third of the tongue (250 taste buds). TASTE RECEPTOR CELLS OCCUR IN TASTE BUDS Tastants are detected by taste receptor cells that are clustered in taste buds. 41  10/2/25 TASTE RECEPTOR CELLS OCCUR IN TASTE BUDS Cilia are located at the end of each cell and project through the opening of the taste bud (taste pore) TASTE RECEPTOR CELLS OCCUR IN TASTE BUDS Short-lived: continually replaced by 10 days Exposed to hostile environment 42  10/2/25 Similar to the chemical transmission at synapses: TRANSDUCTION The taste molecule binds with the receptor and produces changes in membrane permeability that cause receptor potentials. h ng d wit oduci in pr n ces b ptors, ta e t subs of rec ions. n s t ere ype nsa Diff rent t ste se e a diff rent t fe dif h ng Types of taste wit oduci c in d es b ptors, pr receptors ta n e t subs of rec ions. n s t ere ype nsa Diff rent t ste se e a diff rent t Sweet (2), bitter (25) and umami (1): fe dif metabotropic receptors Sour (3) i salty (2): ionotropic receptors 43  10/2/25 EACH TASTE IS DETECTED BY TWO DIFFERENT SENSORY TRANDUCTION MECHANISM G-protein-coupled receptors Bitter, sweet and umami Ion channels Salt and sour EACH TASTE IS DETECTED BY TWO DIFFERENT SENSORY TRANDUCTION MECHANISMS Sweet: T1R2 + T1R3 Umami: T1R1 + T1R3 Bitter T2Rs Salty: Na+ Sour: H+ 44  10/2/25 SWEET Sugars, carbohydrates T1R2, T1R3 receptors SALTINESS Saltiness receptors detect the presence of sodium ions (abundant in sodium chloride) Injuries that cause bleeding deplete an organism of its supply of sodium rapidly, so the ability to find it quickly can be critical. Essencial for electrolyte balance 45  10/2/25 UMAMI § Existence of a fifth taste quality: umami (Japanese= good taste) § It refers to the taste of monosodium glutamate (MSG), a substance that is often used as a flavor enhancer in Asian cuisine § The umami receptor detects the presence of glutamate, an amino acid found in proteins, provides the ability to detect them Most species of animals are attracted to foods that are rich in amino acids, which explains the use of MSG as a flavor enhancer. Tend to avoid sour and bitter BITTER Many plants produce poisonous alkaloids, which protect them from being eaten by animals. Alkaloids taste bitter; thus, the bitterness receptor undoubtedly serves to warn animals away from these chemicals. Bitterness is almost universally avoided and cannot easily be improved by adding some sweetness. 46  10/2/25 SOUR § Because of bacterial activity, many foods become acidic when they spoil. § Also, most unripe fruits are acidic. § Acidity tastes sour and causes an avoidance reaction. (AND ALSO FAT) Researchers have known that many species of animals (including our own) show a distinct preference for high- fat foods We detected fat by its odor and texture (“mouth feel”) Rats whose olfactory sense was destroyed continued to show a preference for a liquid diet containing a long-chain fatty acid, one of the breakdown products of fat When fats reach the tongue, some of these molecules are broken down into fatty acids by an enzyme called lingual lipase, which is found in the vicinity of taste buds. The activity of lingual lipase ensures that fatty acid detection 47  10/2/25 The Human Gustatory System Gustatory system pathway o Gustatory information is transmitted through cranial nerves VII, IX, and X. o Information from the anterior part of the tongue travels through the chorda tympani, a branch of the seventh cranial nerve (facial nerve) o Taste receptors in the posterior part of the tongue send information through the lingual branch of the IX cranial nerve (glossopharyngeal nerve) o The X cranial nerve (vagus nerve) carries information from receptors of the palate and epiglottis in the pharynx 48  10/2/25 Gustatory system pathway o The first relay station for taste is the nucleus of the solitary tract, located in the medulla. o The information travels to the thalamus (ventroposterior medial nucleus) and from there, axons project to the primary gustatory cortex, located in the base of the frontal cortex and in the insular cortex. o Also to the hypothalamus o Unlike most other sense modalities, taste is ipsilaterally represented in the brain; that is, the right side of the tongue projects to the right side of the brain, and the left side projects to the left. 49  10/2/25 Neural representation of tastes is idiosyncratic but stable o Schoenfeld et al. (2004) had people sip water that was flavored with sweet, sour, bitter, and umami tastes. o They found that tasting each flavor activated different regions in the primary gustatory area of the insular cortex. o Although the locations of the taste- responsive regions differed from subject to subject, the same pattern was seen when a given subject was tested on different occasions Functional MRI images of the brains of six subjects revealed that the responsive regions varied between subjects but were stable for each subject. UNIT 1:BIOLOGICAL MECHANISMS OF PERCEPTION AND ATTENTION: SOMATOSENSES 50  10/2/25 Somatosenses: information about what is happening on The nature of the surface of our body and within it. the stimulus (Greek soma, the body) The nature of the stimulus Somatosenses: information about what is happening on the surface of our body and within it. Cutaneous (exteroceptive) sense: sensitivity to stimuli that involve the skin (touch, temperature, pain) Proprioception and kinesthesia: perception of the body’s position, posture and movement Organic senses (interoception): receptors located within the inner organs of the body (respiratory, digestive) 51  10/2/25 The nature of the stimulus Cutaneous sense: sensitivity to stimuli that involve the skin (exteroceptive) Pressure and vibration: mechanical deformation of the skin TOUCH Changes in temperature: heating, cooling TEMPERATURE Events that cause tissue damage: PAIN The nature of the stimulus Proprioception and kinesthesia: perception of the body’s position, posture and movement. Receptors that responds to changes in stretching of the skin during movements of the joints or muscles Stretch receptors in skeletal muscles, joint capsules and skins reports changes in muscle length 52  10/2/25 The nature of the stimulus Organic senses: receptors located within the inner organs of the body (interoceptive) Provide unpleasant and pleasant sensations Chemoreceptors: indicators of blood gases and pH Nausea, thirst, breathing hunger, sexual arousal 53  10/2/25 The nature of the stimulus Somatosenses: information about what is happening on the surface of our body and within it. Cutaneous sense: sensitivity to stimuli that involve the skin (exteroceptive) Proprioception and kinesthesia: perception of the body’s position, posture and movement Organic senses: receptors located within the inner organs of the body (interoceptive) 3 most important qualities of cutaneous stimulation are touch, temperature, and pain February 10th Start here 54  10/2/25 Sensory organ: skin Epidermis The outermost layer of skin acts as a mechanical and antimicrobial barrier. The top part, prevents water from leaving the body and toxic substances from entering. Dermis Nerve endings in skin’s middle layer help people to feel sensations such as itching, pain, pleasure and heat. The dermis produces sweat and oils, and contains hair follicles. It also hosts a variety of immune cells. Subcutaneous fat Skin’s deepest layer is sandwiched between the dermis and skeletal muscles. Its roles include fat storage, connecting the dermis to muscle and bone, and controlling body temperature. Sensory organ: skin The skin is a complex and vital organ of the body— one that we tend to take for granted. Our cells, which must be bathed by a warm fluid, are protected from the hostile environment by the skin’s outer layers. Mucous, hairy, hairless or glabrous skin. 55  10/2/25 Sensory organ: skin Most of the body is covered in hairy skin but the palms of the hands and the soles of the feet are covered in glabrous skin. The fingerprints are formed by a regular array of parallel ridges in the epidermis, the papillary ridges. Each ridge is bordered by epidermal folds—the limiting ridges—that are visible as thin lines on the fingers and palm border. ANATOMY OF THE SKIN AND ITS SENSORY RECEPTORS The skin contains several scattered receptors along these layers. The hairless skin contains a dense and complex mixture of receptors, which reflect the fact that we use the palms of the hands and the inner surfaces of the fingers to actively explore the environment: we use the hands and fingers to hold and touch objects. 56  10/2/25 TOUCH: MECHANORECEPTORS Touch is mediated by four types of mechanoreceptors in the human hand. The receptors differ in morphology, innervation patterns, location in the skin, receptive !eld size, and physiological responses to touch. Encapsulated receptors Hairy skin Ruffini corpuscle detects stretching or static force against the skin Pacinian corpuscle: detects vibration from an object being held. (Hair Follicles) Merkel’s disk: touch-sensitive cutaneous receptor, compression Glabrous skin Merkel’s disk, Ruffini and Pacinian corpuscles Meissner’s corpuscle: detects edge contours (Braille-like) especially by fingertips. 57  10/2/25 Receptive fields define the zone of tactile sensitivity Deep receptors: large receptive fields Big patches of skin: low spatial resolution. Pacinian corpuscles, Ruffini corpuscles Superficial receptors: small receptive fields Small patches of skin: high spatial resolution. Meissner’s corpuscles, Merkel’s disk The fields are small because of the high density of receptors in the fingertips. Receptive fields become progressively larger consistent with the lower density of mechanoreceptors in these regions. Receptive fields define the zone of tactile sensitivity The ability of humans to resolve spatial details of textured surfaces depends on which part of the body is contacted. Tactile acuity is highest on the fingertips and the lips, where receptive fields are smallest. 58  10/2/25 Receptive fields define the zone of tactile sensitivity The two-point threshold measures the minimum distance at which two stimuli are resolved as distinct. This distance varies for different body regions; it is approximately 2 mm on the fingers, but as much as 40 mm on the back TRANSDUCTION Mechanoreceptors sense physical deformation of the tissue in which they reside. Mechanical distension such as pressure on the skin is transduced into electrical energy by the physical action of the stimulus on ion channels Mechanical stimulation deforms the receptor protein, thus opening stretch-sensitive ion channels and increasing Na+ and CA2+ conductances that depolarize the receptor neuron 59  10/2/25 Receptive fields in the somatosensory cortex comprise a somatotopic map of the body: the homunculus It has a large representation of the face and hands compared with the torso, arms and legs. The brain maps each sensory receptor onto the cortex. The more receptors there are in a given area of skin, the larger that area’s map will be represented on the surface of the cortex. As a result, the size of each body region in the homunculus is related to the density of sensory receptors. TOUCH: primary somatosensory cortex 60  10/2/25 TEMPERATURE Feelings of warmth and coolness are relative Neutral point is not a absolute value: prior experience There are two categories of thermal receptors: Cold sensors beneath the epidermis: TEMPERATURE: myelinated A-delta fibers Thermoreceptors Warmth sensors more deeply in the skin: unmyelinated C fibers. 8ºC – 52ºC noxious https://www.youtube.com/watch?v=Ux-t1VWNlsA 61  10/2/25 TEMPERATURE: Thermoreceptors Six mammalian thermoreceptors: TRP family Transient receptor potential channel https://www.youtube.com/watch?v=Ux-t1VWNlsA TEMPERATURE: Thermoreceptors Six mammalian thermoreceptors: TRP family Transient receptor potential channel Some thermal receptors also responds to chemicals The neutral point is not an absolute value. https://www.youtube.com/watch?v=a5b9-_UQEzI 62  10/2/25 TEMPERATURE: Some thermal receptors also responds to chemicals Thermoreceptors Perception of Pain When experienced as part of a ritual, normally excruciating conditions (e.g., walking on hot coals) often produce little pain. 63  10/2/25 PAIN Unpleasant sensory and emotional experiences associated with actual or potential tissue damage. Prime motivator of survival The perception of pain is subjective and is influenced by many factors. An identical sensory stimulus can elicit quite distinct responses in the same individual under different conditions. PAIN Cox et al (2006): The case of the Pakistani family Mutations of the gene for this protein produce total insensitivity to pain. Autosomal recessive allele allocated in chromosome 2 A particular voltage-dependent sodium channel, Nax1.7, plays an essential role in pain sensation Unnoticed injuries: lips, tongue, bone fractures 64  10/2/25 PAIN: Nociceptors Free nerve endings: nociceptors (nocere= to injure) 3 categories: High-threshold mechanoreceptors: free nerve endings that respond to intense pressure (hit, stretch, pinch) Extreme heat, acids and capsaicin (chili peppers), TRPV1 receptor TRPA1 receptors sensitive to pungent irritants found in mustard, horseradish, garlic... (presence of chemicals that produce inflammation) Pain: lack of clear cortical representation Painful stimuli actívate many areas (Thalamus, SI, SII, Insula, ACC… None necessary for pain parpection ACC = most linked área & expectation of pain Emotional reaction Adaptive responses 65  10/2/25 Descending Analgesia Circuit Basbaum and Field’s (1978) model of the descending analgesia circuit. PAIN: The case of ITCH More formal: pruritus “unpleasant sensation that elicits the desire or reflex to scratch” Two types of unknown receptors Pain and itch are mutually inhibitory. Scratching reduces itching because pain suppresses itching Presumably, the scratch response to stimuli that produce itching helps rid skin of irritating debris or parasites. 66  10/2/25 Somatosensory information enters the central nervous system through cranial and spinal nerves 31 spinal nerves: enter through openings between vertebrae of the spine The somatosensory pathway Somatosensory axons from the skin, muscles, or internal organs enter the central nervous system via spinal nerves. Those located in the face and head primarily enter through the trigeminal nerve. 67  10/2/25 Skin innervated by the afferent fibres of a spinal nerve constitute a DERMATOME The somatosensory pathway Cell bodies of the unipolar neurons located in the dorsal root ganglia and cranial nerve ganglia. Axons that convey precisely localized information, such as fine touch, ascend through the dorsal columns in the white matter of the spinal cord to nuclei in the lower medulla. From there, axons cross the brain and ascend through the medial lemniscus to the ventral posterior nuclei of the thalamus, the relay nuclei for somatosensation Axons from the thalamus project to the primary somatosensory cortex. 68  10/2/25 The somatosensory pathway The cell bodies of the unipolar neurons are located in the dorsal root ganglia and cranial nerve ganglia. In contrast, axons that convey poorly localized information, such as pain or temperature, form synapses with other neurons as soon as they enter the spinal cord. The axons of these neurons cross to the other side of the spinal cord and ascend through the spinothalamic tract to the ventral posterior nuclei of the thalamus Receptive fields in the somatosensory cortex comprise a somatotopic map of the body The somatosensory cortex has a columnar arrangement, within a column, neurons respond to a particular type of stimulus (e.g., temperature or pressure) applied to a particular part of the body. 69  10/2/25 Axons from the thalamus project to the primary The somatosensory cortex. The primary somatosensory cortex (S-I) forms the anterior somatosensory part of the parietal lobe The secondary somatosensory cortex (S-II) is located on the pathway upper bank of the lateral sulcus (Sylvian fissure) and on the parietal operculum Damage to the somatosensory association cortex can cause tactile agnosia, inability to recognize common objects by means of touch. Patients with lesions of the parietal cortex: may have preserved ability to feel pinprick, temperature, vibration, and proprioception, fail to identify objects palpated by the contralateral hand. Can readily identify the object by sound or sight èfulfilling the criteria for associative tactile agnosia. 70  10/2/25 Attention Selective attention test https://youtu.be/vJG698U2Mvo?si=rVL6VK81rqm63R3x 71  10/2/25 May be top-down or bottom-up May be focused on internal cognitive processes Characteristics Endogenous attention of Selective Believed to be top-down Attention May be focused on external events Exogenous attention Believed to be bottom-up Cocktail-party phenomenon Classic example of selective attention Demonstrated by showing people two Change Blindness photographs identical in every aspect but one If allowed a brief delay, people have difficulty seeing change 2-min video https://youtu.be/bh_9XFzbWV8 1-min video https://www.youtube.com/watch?v=EARtANyz98Q 72  10/2/25 Change Blindness The change blindness phenomenon. These two illustrations were continually alternated, with a brief (less than 0.1 second) interval between each presentation, and the subjects were asked to report any changes they noticed. Amazingly, it took most of them many seconds to notice the disappearing and reappearing picture in the center of the wall. Neural locations Faces activate ventral visual pathway Position of the face activates dorsal Neural pathway Top-down processing originates in Mechanisms prefrontal lobe and posterior parietal cortex of Attention Selective attention strengthens representation of attended-to stimuli Selective attention weakens representation of external stimuli Spatial attention can induce plastic changes in visual fields 73  10/2/25 Visual simultanagnosia Difficulty attending to more than one object at a Simultanagnosia time Occurs due to damage to the posterior parietal cortex Your turn, questions and comments. 74  10/2/25 Exam-like questions Areas of neocortex that receive most of their input from the thalamic relay nuclei of one sensory system are classified as a. association cortex. b. tertiary cortex. c. motor cortex. er: E d. secondary sensory cortex. nsw e. primary sensory cortex. A 75  10/2/25 Modern neuroscientific theory considers sensory systems to be a. analog, parallel, and general. b. functionally segregated, serial, and parallel. wer: C c. hierarchical, functionally segregated, and parallel. Ans d. functionally segregated, serial, and sequential. e. sequential and general. Which structure contains the receptors of the vestibular system? a. basilar membrane er: B b. semicircular canals sw An c. ossicles d. vestibular nucleus e. cochlea 76