520 likes | 1.18k Views
Mechanisms of Perception: Hearing, Touch, Smell, Taste & Attention. 5 exteroceptive sensory systems Visual Auditory (hearing) Somatosensory (touch) Olfactory (smell) Gustatory (taste). Somatosensory System. Somatosensations : sensations from your body
E N D
Mechanisms of Perception: Hearing, Touch, Smell, Taste & Attention
5 exteroceptive sensory systems • Visual • Auditory(hearing) • Somatosensory (touch) • Olfactory (smell) • Gustatory (taste)
Somatosensations: sensations from your body • 3 separate but interacting systems • Exteroceptive system • Senses external stimuli interacting with the skin • Proprioceptive system • Monitors body position • Receptors in the muscles, joints & organs of balance • Interoceptive system • General info on the internal body conditions • Ex: temp, BP
Exteroceptive System • 3 distinct divisions for perceiving different types of stimuli • Mechanical (touch) • Thermal (temperature) • Nociceptive (pain)
Cutaneous Receptors • Receptors in the skin; many types • Free nerve endings • Simplest; neuron endings with no specialized structures • Sensitive to temperature change & pain • Pacinian corpuscles • Largest & deepest • Adapt rapidly • Respond to sudden displacements of skin, not constant pressure • Merkel’s disks • Adapt slowly • Respond to gradual skin indentation • Ruffiniendings • Adapt slowly • Respond to gradual skin stretch
Cutaneous Receptors • When constant pressure is applied to the skin, there is a burst of firing in all of the receptors, corresponding to the sensation of touch. • But after a bit, only the slowly adapting receptors stay active & the sensation changes (often becoming unnoticeable) • So to maintain constant input, you move & manipulate objects in your hands • Stereognosis: identification of objects by touch
Cutaneous receptors • Each type has its own unique structure, but they all basically work the same way • Stimuli to the skin changes the chemistry of the receptor, which changes the permeability of the receptor cell membrane to ions, which sends a neural signal
Dermatomes • Nerve fibers from cutaneous receptors come together and enter the spinal cord at the doral root • The area of the body innervated by the left & right dorsal root at a given spinal segment is a dermatome
2 major somatosensory pathways • Dorsal-column medial-lemniscus system • Info about touch & proprioception • Anterolateral system • Info about pain & temperature • However, there is overlap in the type of info each pathway carries
Dorsal-column medial-lemniscus system • Ipsilateral, decussates at the dorsal column nuclei, contralateral • Neurons of this path that start in the toes are the longest neurons in the human body! • Anterolateralsystem • Spinothalamic tract • Neurons decussate immediately upon entering the spinal cord & travel up contralaterally • If both paths are cut by a spinal cord injury, there will be no sensation from below that point.
Cortical Areas of Somatosensation • The primary somatosensory cortex is located on the postcentralgyrus • Most input is contralateral • It is organized somatotopically; according to a map of the body surface • Referred to as the homunculus (“little man”) *my fave!*
Cortical Areas of Somatosensation • Secondary somatosensory cortex is just ventral to the primary • Association cortex is in the posterior parietal lobe
SomatosensoryAgnosias • Astereognosia • Inability to recognize objects by touch • Rare • Asomatognosia • Inability to recognize parts of your own body • Usually only affects the left side of the body after damage to the right posterior parietal lobe
Perception of Pain • Pain is the response to any kind of harmful stimulation • Serves as a warning system • There is no clear cortical area involved in pain • Although the anterior cingulate cortex is activated during the emotional reaction to physical pain • Amazingly, we can exhibit a lot of control over our perception of pain • Gate-control theory: descending cognitive signals from the brain can activate neural gate circuits in the spinal cord to block incoming pain signals
Descending Pain-Control Circuit • Activity in the periaqueductal gray has analgesic (pain blocking) effects • Also has specialized receptors for opioids, including endorphins • Potentially involves stimulation of serotonergic neurons
Neuropathic Pain • Severe chronic pain in the absence of a recognizable pain stimulus • Often after an injury has healed & there should be no more reason for pain
These senses respond to chemicals in our environment • Smell for airborne chemicals • Taste for those that dissolve in our oral cavity • Smell & taste are highly integrated • Together they produce what we know as flavor • We use these senses primarily to recognize flavor, but many other species use it for communication, via pheromones
Olfactory System: Smell • Receptor cells are in the upper part of your nose, within the olfactory mucosa • The axons of these neurons actually project through the cribriform plate in your skull & enter the olfactory bulbs, which go via the olfactory tracts to the brain • Your olfactory receptor neurons can be regenerated throughout your life • Primary olfactory cortex: piriform cortex • Medial temporal cortex next to the amygdala • Only sensory system that does not first go through the thalamus!!
Gustatory System: Taste • Taste receptors are on the tongue & elsewhere in the oral cavity • Occur in clusters of 50 called taste buds • So each taste bud sends out many axons and many individual neural signals • The 5 traditional tastes • Sweet • Salty • Sour • Bitter • Umami • But not every taste we experience can be made from any combo of those 5…
Gustatory Pathway • Afferent neurons leave the mouth as the facial, glossopharyngeal & vagus cranial nerves; which terminate in the solitary nucleus of the medulla, to the ventral posterior nucleus of the thalamus, to the primary gustatory cortex • Primary cortex: near the face area of the somatosensory homunculus
Damage to the Chemical Senses • Anosmia: inability to smell • Caused by blows to the head that rip the olfactory nerves as they pass through the cribriform plate • Symptom along with several other neurological disorders • Ageusia: inability to taste • Rare
Selective Attention • At any instance, we are receiving a LOT more sensory input than we consciously perceive • Selective attention is the process by which we are able to “ignore” the rest • Works to essentially enhance the signals that we are focusing on & get rid of interference caused by the signals we’re ignoring • Cocktail-party phenomenon • Change blindness