med phys e3 Flashcards
somesthetic receptor
- aka somatosensory
- a sensory end organ concerned with reception of stimuli producing one of the generalized sensations such as temp, pressure, position or movement
sensation
- signals transmitted by receptors to brain in form of light, sound, tactile, thermal, pain, etc
- receptors respond specifically to one form of energy more than any other but may respond to other forms (photoreceptors may respond to pressure; we might see “stars”
- unconscious processing/at subcortical level
- ex. nociception is sensation; pain is perception
perception
- refers to how sensory information is organized, interpreted and consciously experienced
- conscious processing/at cortical level
- ex. nociception is sensation; pain is perception
Meissner’s corpuscles
- mechanoreceptors present in highly sensitive areas like fingertips, palms, soles, tongue, lips & genital skin
- have small receptive fields to allow two-point discrimination
- respond to low frequency stimuli (flutter)
Pacinian corpuscles
rapidly adapting mechanoreceptors for pressure and vibration
Merkel’s disks
slow adapting mechanoreceptor that respond to pressure and touch
hair follicle receptors
rapidly adapting mechanoreceptors that respond to movement across surface of skin
Ruffini’s corpuscles
slow adapting mechanoreceptors that respond to stretch found in dermis & joints
thermal receptors
- free nerve endings that respond to temp changes
- divided in cold and warm slow adapting receptors
nociceptors
- free nerve endings found in skin, muscle, joints, periosteum and visceral organs capsules
- respond to noxious (harmful/unpleasant) chemicals, mechanical stimuli (stretch) and temp
muscle spindles (in muscles) and golgi tendon (in tendons)
- important in proprioception & coordination of motor activity
sensory receptive fields
- region of skin that elicits a response in somatic sensory neuron (2 pt discrimination)
- vary in diameter (1-2 mm on fingertips [high precision]; 5-10 mm on palms; larger in abd & back [lower precision]) and may overlap
ascending (afferent) tracts - anterior column
ventral spinothalamic tract (pressure and crude touch - can’t localize)
ascending (afferent) tracts - lateral column
lateral spinothalamic tract (pain and temperature); ventral & dorsal spinocerebellar tracts
ascending (afferent) tracts - posterior column
fasciculus cuneatus & gracilis (vibration, proprioception, fine touch - can localize)
descending (efferent) tracts - anterior column
ventral corticospinal/pyramidal tract (voluntary mvoements, reflexes)
descending (efferent) tracts - lateral column
lateral corticospinal/pyramidal tract (voluntary movements, reflexes)
thalamus
- awareness of nociceptive stimuli (non-discriminative form)
- subjective response to sensation
- activation and arousal with reticular formation
- modification of affective component of behavior with limbic system
reticular formation
- network of neurons located throughout brainstem
- reticular activating system (RAS)
- conscious awareness and behavioral responses to stimuli
- maintain wakefulness
- muscle tone & posture
- respiratory centers (rhythm, depth, pattern)
- BP, CO & blood distribution to organs
limbic system
- hippocampus, amygdala, anterior thalamic nuclei, limbic cortex
- emotion, behavior and long term memory
wernicke’s area
comprehension of written and spoken language
broca’s area
production of language
somatosensory cortex
part of brain in parietal lobe that processes sensation
- somatic sensory cortex (sensory homunculus, skin sensation, proprioception, stereognosis, integrates info w/ visual & auditory signals)
- sensory association area (complex sensory information processing, spatial relationships, two-point discrimination, graphesthesia)
stereognosis
mental perception of depth or 3D by senses, usually in reference to ability to perceive form of solid objects by touch
graphesthesia/graphagnosia
ability to recognize symbols when they’re traced on skin
pain
free nerve endings detect damage to tissues
- group A fibers (bigger) = sharp, shooting, intense pain
- group C fibers (smaller) = steady, slow, constant pain
- visceral pain = produced by distension, spasm, contraction, torsion, ischemia, chemical irritation or inflammation of viscera
ascending pain pathways
- spino-thalamic-somatosensory cortex = sensation of pain
- spino-thalamic-frontal cortex/anterior cingulate gyrus = subjective psychological and physiological effects of pain
descending pain pathways
- inhibitory fibers modulate pain sensation (gate control)
- modulation by fibers from periaqueductal grey matter, nucleus raphe & RF to dorsal horn
- neurotransmitters - Serotonin, Adrenaline, GABA, Endorphins (opioids)
gate control theory of pain
- explains how non-painful sensation can override & reduce painful sensations
- substantia gelatinosa at tip of dorsal horn - gate controlling
- painful, nociceptive sitmulus stimulates primary afferent fibers → to brain via transmission cells → increased perceived pain
therapeutic use of gate control theory
- pain is lessened when area is rubbed because activation of non-nociceptive fibers inhibits firing of nociceptive one
- transcutaneous nerve stimulation (TENS): use of electrodes to selectively stimulate non-nociceptive fibers to lessen pain
- stimulation of central areas (periaqueductal grey matter) produces analgesia (not total numbness) by activating descending pathways (opioid neurons in spinal cord)
referred pain
- brain is unable to distinguish visceral signals from more common signals that arise from somatic receptors
- theories
- — nociceptive sensory fibers from different viscera (pericardium) can use same set of 2nd order neurons (neck, arm, jaw muscles)
- — visceral nociceptors may activate somatic nociceptive 2nd order neurons
hyperalgesia
- enhanced sensitivity and responsivity to stimulation of area around damaged tissue that may be caused by sensitization of nociceptors (lower threshold to respond)
- sensitization to local signals (prostaglandins, leukotrienes from damaged cells, substance P from afferent nerve fibers, etc)
taste
- mediated by taste receptor cells (rapidly adapting) which are bundled in clusters called taste buds within tongue papillae
- food MUST BE DISSOLVED IN SALIVA to reach receptors
- taste sensation can change according to body’s specific nutritional needs
taste modalities and how taste gets in
- taste ligands (molecules) dissolve in saliva → reach taste pores (surrounded by taste hairs) → bind to chemoreceptors on taste buds → receptor-ligand interaction increases intracellular calcium → release of NT → graded potentials → AP in sensory neurons
- sweet = sugars; G protein, coupled
- bitter = alkaloids; G protein, coupled
- sour = H+; ion channel
- salty = Na+; ion channel
- umami = glutamate; both
anterior 2/3rd of tongue nerve innervation
- trigeminal nerve (CN V) = somatosensation (touch, pain, pressure)
- facial nerve (CN VII) = taste sensation
posterior 1/3rd of tongue nerve innervation
- glossopharyngeal nerve (CN IX) = taste and somatosensation
root of tongue nerve innervation
- vagus nerve (CN X)
how smell gets in
- odorant molecules bind to G protein coupled receptors on cilia of olfactory neurons → activation triggers graded potential → AP → signal to olfactory cortex
- molecules MUST BE DISSOLVED IN MUCUS to activate receptors
- – proteins in mucus help keep it dissolved & transport odorants to olfactory dendrites
- axons from olfactory bulb project to limbic cortex, amygdala, hippocampus (temporal lobe - long term memory formation)
- NO THALAMUS - intimate connection w/ brain cortex & reticular formation
- smell neurons replaced every 60 days
structures involved in olfaction
- olfactory bulb contains mitral cells that receive info from olfactory cells
- olfactory cells found within nasal epithelium & pass their info thru cribriform plate of ethmoid bone
how light gets in
- light detected by retina receptors (cones and rods) → retina changes shape → activating photopigment, rhodopsin → if light, present → rods & and cones hyperpolarize → activate neurons → stimulate ganglion cells which sent APs via optic nerve to lateral geniculate nucleus (thalamus) → visual cortex in occipital lobe
- if light is not present, neurons are inhibited by rods and cones
- horizontal cells can create lateral inhibition, which enhances light & dark contrast in images
- tonic activity - when photoreceptors become slightly active even when not stimulated by light
- rhodopsin - a light-sensitive pigment in rod cells of retina; consists of opsin protein bound to carotenoid retinal
visual system
- higher cortical areas process & integrate visual inputs, supporting coherent visual perception what & where (retinal sensation/image converted to our personal view/percept of outside world)
- optic nerve can be considered part of CNS (axons have oligodendrocytes & surrounded by meninges)
- macula - part of retina where we process a high-definition visual information (shapes, colors)
anatomical structures involved in visual system
- cornea & lens - bend to focus image on retina
- iris & pupil - regulate amount of light entering eye
- aqueous humor - maintains convex shape of cornea
- vitreous humor - supports lens & maintains shape of entire eye
- presbyopia occurs because image focuses behind retina
- – hyperopia (farsightedness) = eyeball that is too short
- – myopia (nearsightedness) = eyeball is elongated
- rods - rod-shaped cell located in outer retina of eye that is sensitive to light; used for peripheral and nighttime vision
- retina - thin layer of cells at back of eyeball where light is converted into neural signals sent to brain
- cone - cell located near center of retina that is weakly photosensitive & is responsible for color vision in relatively bright light; used for daytime and color vision
- fovea - acute vision because it has high density of cones
retinal receptors
Rods: high sensitivity to light, and scattered light, specialized in night vision, more sensitivity to movement, low resolution, monochromatic
Cones: low sensitivity to light, more sensitive to direct light rays, high acuity, concentrated in fovea, polychromatic (3 types of cones)
types of cones
- trichromatic system
- color is a result of ratio of activity of three types of cones
- S cones = respond to short waves
- M cones = respond to medium waves
- L cones = respond to light to long waves
fovea
- special area where cells are displaced to allow light to be directly absorbed
- focal point of image & region where most cone cells are concentrated
- constantly move our eyes to view the foveal image
- at optic dis, fibers leave the eye - no photoreceptors here (blind spot)
