Sensory (1) Flashcards
What is the basic organization of the sensory system?
stimulus->filter->modified stimulus-> transducer-> receptor potential-> encoder -> AP-> to CNS-> sensory systems-> association systems-> effector systems (motor)-> to periphery effectors-> response
What is the filter?
first functional element of sensory receptor, usually non-neuronal, only a portion conveyed to transducer, conditions the stimulus making receptor function with relative specificity of modality; limits access and changes stimulus parameters
What is the transducer?
converts stimulus energy to change in the voltage across the membrane of sensory receptor with minimal loss of information; creates the receptor potential(generator or local potential); doesn’t respond to electrical stimulus
How is the receptor potential generated?
simultaneous change in membrane permeability of Na and K ions; it is a graded potential (increases in magnitude as stimulus gets stronger); travels short distance doesn’t propagate
What is the encoder?
converts the magnitude of a receptor potential into a frequency code that is carried by AP along an axon (aka trigger zone)
What is the filter, transducer and encoder for a pacinian corpuscle?
F: CT, T: unmyelinated free nerve ending, produces receptor potential when deformed, E: trigger zone, first node of Ranvier
What are the different types of sensory receptors? examples.
mechanical- touch, proprioception, joint position, hearing and balance; chemical- pain, itch, taste, smell, pH and osmolarity; thermal- body temperature, temperature of ambient air and objects we touch; electromagnetic- vision; and poly-modal- nociceptors respond to 2 or more stimuli (mechanical or thermal)
What is a sensory unit?
connected to sensory receptors of all the same kind
What is a receptive field?
fraction of the total energy of a particular modality that initiates a response in a sensory receptor or sensory unit; sensory unit with the most sensory receptors has the largest receptive field
What are the four basic attributes of a stimulus?
modality, location, intensity, and timing
What does the modality tell the body?
along with submodality is codes for what is present
What are examples of submodalities and their corresponding modalities?
vision- color, shape movement; hearing- pitch; taste- sweet, sour, salty; smell- pungent, musk, floral, putrid; somesthesis- temperature, texture and rigidity
What is the place theory?
modality coding in labeled lines- an anatomical grouping of receptors of pathways devoted to the particular modality
How are sub-modalities coded?
by pattern coding; pattern activity within the system of labeled lines
How is location coded?
anatomical sorting or organization of pathways and their central projections; i.e. homunculus
How is intensity coded?
by total number of impulses per second coming from receptor population; rate, recruitment, adaptation, threshold and saturation
What is recruitment? How does it code for intensity?
number of units that get activated by stimulus increase with stimulus intensity; higher frequency is found in unit closest to the stimuli
What is adaptation and how does it code for intensity?
measure of how well a sensory receptor maintains its response to a constant stimulus; slowly adapting receptors keep producing membrane potentials as long as stimulus is applied; rapid adapting sensory receptors stop even with stimulus still present
What is saturation and how is it used to code for intensity?
as intensity increases eventually nerve fiber reaches upper limit for carrying impulses; further increases in stimulus do not produce a corresponding increase in response
What types of stimuli is the somatosensory system sensitive to?
pressure, joint position, muscle position, temperature of limbs and pain
how is the somatosensory system different than other systems?
receptors spread throughout rather than concentrated at small specialized locations; it is a group of at least 4 senses rather than just one- touch temperature, body position, pain and various subdivisions
What are the different sub modalities of touch?
itch/tickle- indiscriminate; discriminate touch- touch, pressure, flutter, and vibration
What are the sub-modalities of pain?
sharp cutting pain, dull burning pain, and deep aching pain
What are the sub modalities of proprioception?
position (static forces)- muscle length and tension; movement (dynamic)- muscle length and tension, joint position, pressure and angle
Primary afferent axons come in different sizes, order them from big to small. What sense do they correspond with?
Aalpha- proprioceptors of muscles, Abeta- mechanoreceptors of skin, Asigma- pain and temperature, and C- temperature, pain
What are the parallel pathways of somatic sensation? Fibers in them and sensation associated with it?
Dorsal column-medial lemniscal pathway; A alpha beta and sigma; touch, vibration, two point discrimination and proprioception; or spinothalamic- A sigma and C; pain, temperature, some touch
What are the different types of mechanoreceptors? what do they sense?
Hair, Pacinian corpuscle, Ruffini ending, Meissner’s corpuscle and Merkel disk receptor
What are the relative sizes of mechanoreceptor receptive fields?
Meissner’s very small- pen, Pacinian very large, Merkel’s small and Ruffini’s large
Which mechanoreceptors are fast or slow adapting?
fast- Meissner’s, Pacinian, hair folicle; slow- Merkles and Ruffini’s
How does the Pacinian corpuscle work?
capsule with fluid between the layers and free nerve ending in the center; layers are distended in and put pressure initially on the nerve then fluid spreads around so nerve isn’t pinched; esp sensitive to vibrating and high frequency stimuli
Characterize the Meissner corpuscle by type and sensation.
encapsulated and layered; touch; flutter movement
Characterize the Ruffini corpuscle by type and sensation.
encapsulated collagen, touch: stretch of skin
Characterize the hair follicle by type and sensation.
unencapsulated; touch and movement; rapid
Characterize the Merkel complex by type and sensation.
specialized epithelial cell; touch, pressure, form
Characterize the free nerve ending by type and sensation.
unencapsulated; pain, touch or temperature; adaptation depends
Over what range to warm receptors sense?
30-45 degrees celsius
Over what range to cold receptors sense?
30 down to -10 degrees Celsius
What effects the rate of firing in thermoreceptors?
cold fires faster during decreases in temperature and warm faster during increases
What are the four categories of nociceptors and their stimuli?
mechanoreceptor- intense mechanical (pinching, sutting and stretching), Thermal- burning heat or extreme cold (>45 tissue damage), Chemically sensitive (mechanically insensitive)- variety of agents, K, pH, histamine, bradykinin, and polymodal- high intensity combo of mechanical, thermal and chemical
What are the characteristics of slow pain? examples
burning or soreness, transmitted by thin fibers, poorly localized, all internal organs except brain, body wants to be immobile so see guarding, rigidity and spasm, diffuse slower onset,; labor pain, chemical burn, pain after fast pain in response to injury
What are the characteristics of fast pain? examples
prickling, faster conducting because fibers are thicker, A-delta fibers, well localized, mainly skin, mouth and anus, immediate withdrawl on stimulation to avoid damage, pain does not radiate, short duration; surgical incision
What is phantom pain?
pain of missing limb
What are the causes of intracranial headache?
alcohol- toxicity irritates meninges and constipation- from absorbed toxic products or changes in circulatory system resulting from loss of fluid in the gut
What are the causes of external headache?
muscle spasm- emotion/tension causes muscles of head to become spastic, pain referred to head; sinus- pain from mucus membranes, referred to behind the eyes or forehead or face; eye disorders- difficulty focusing stresses cilliary muscles and can cause spasms in facial and extra ocular muscles, excessive irradiation by light esp. UV causes irritation of the membranes around the eyes
What substances activate nociceptors?
globulin and protein kinases, arachidonic acid, histamine, nerve growth factor, substance P and calcitonin gene related peptide, K, serotonin, ACh, low pH, ATP, muscle spasm, and lactic acid
What is the gate theory of pain?
pain can be modified by nonpainful sensory input and neural activity from various nuclei within the brain (simultaneous activation of low threshold mechanoreceptors A-alpha and beta fibers- excites inhibitory interneuron in spinal cord lessoning signal sent to the brain)
