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52 terms

sensory physi

Sensory Function
specialized cells that monitor internal and external conditions
Two types of senses
receptors are distributed throughout the body
1. Afferent impulses are sent to the somatosensory cortex
receptors are concentrated in sense organs
1. Afferent impulses are sent to special sense cortexes
Afferent (sensory) division
carries sensory info from receptors to the CNS
i. Somatic afferent fibers
carries impulses from skin, skeletal
muscles and joints
ii. Visceral afferent fibers
carries impulses from organs within
ventral body cavities
iii. Special sense afferent fibers
eyes, ears, taste, smell
Pseudounipolar neuron(sensory neuron) except special sensory
1. Cell body lies in the dorsal root ganglia
2. Action potential is initiated at the peripheral end of the
Sensory Receptors
-found on the peripheral end of sensory neurons.
-Act as transducers to change an incoming stimulus of one type into an electrical impulse
Adequate stimulus
receptors are specific for the type of stimulus it is
sensitive to an can transducer, ie cants shine light in ear and hear something.
Receptors can respond to other types of stimuli if strong enough. ie press on eye (mechainal stress) you will see flashes of light.
"Law of Specific Nerve Energies
regardless of the type of stimulus the sensation is perceived as what the receptor is specific for
Sensory Transduction
i. A stimulus alters the membrane permeability of the receptor. This leads to the production of a graded receptor potential
Sensory Transduction
ii. Receptors that are modified endings of the afferent neuron produce generator potentials
Sensory Transduction
iii. Receptors that are separate cells from the afferent neuron produce receptor potentials
Sensory Transduction
iv. Release chemicals that open ligand gated channels on the afferent neuron
i. Free nerve endings
1. Nociceptors
2. Themoreceptors
1. Nociceptors
activation causes the sensation of pain
a. Free nerve endings found in the skin, joints, bones,
and blood vessels
b. Sensitive to chemicals, tissue damage, and extreme
2. Themoreceptors
react to changes in temperature
a. Free nerve endings in the dermis,
hypothalamus, and liver
b. You have 3X more cold receptors than
warm receptors, cold vs colder= more action potiental high fequency, 10 degree or less you feel pain /45 then pain
stimulated by physical change such as pressure or movement
Merkel cells
cells in the stratum basale associated with
free nerve endings, detect fine touch
Hair root plexus
free nerve endings associated with hair follicles, detect movement of hair
Meissner's corpuscles
-detect touch, found in dermal papillae
Ruffini corpuscles
sensitive to stretch and distortion, found in the dermis
Pacinian corpuscles
deep pressure receptors found in the dermis
sensitive to internal pressures. Monitors
blood pressure in vessels (carotid sinus and aorta), lungs,
bladder, intestines
monitors position and stretch of muscles, tendons, ligaments, and joint capsules. Helps maintain posture and sense of body position
detect chemicals dissolved in solution. Olfactory, taste, osmolarity, pH, CO2, O2 alot of special senses
Ascending tracts
a bundle of axons transmitting impulses towards the
brain. Usually involves three successive neurons (three levels of processing) tend to be on dorsal and lateral sides of your spinal cord
i. Receptor level
Primary neuron running from the receptor to the
posterior horn of the spinal cord or medullary nuclei
ii. Circuit level
Secondary neuron synapses with the first and transmit impulses to the thalamus (all sensors go to thalamus but olfactory)
iii. Perception level
Tertiary neuron running from the thalamus to
the primary somatosensory cortex or a special senses cortex. The
cerebral cortex is responsible for
cerebral cortex is responsible for
1. Sensation - the awareness of the stimuli
2. Perception - the interpretation of the stimuli
Each sensory fiber is a "labeled line
the type, location, strength, and the intensity of the stimuli is encoded in the area of the cortex it travels to and the frequency of the impulse
Determining type of stimulus or receptor activated
1. Depends on the pathway it takes and the area of the
cerebral cortex it travels to
Determining type of stimulus or receptor activated
2. The area of the cortex devoted to each region is related to the regions sensitivity (# of receptors
Referred pain
many primary neruons sinape with the same secondary neruon, usually defalt to the most frequently stimulated ie skin not heart
Phantom pain
remodeling of the cortex, or a secondary neuron is irritated
Localization of the stimulus
Accuracy of localization depends on the size of the
receptor field. The smaller the receptor field the more
Localization of the stimulus
Accuracy also depends on lateral inhibition. Only the
most intensely stimulated pathway is excited. Less excited
pathways surrounding the stimulated area are inhibited
Number of receptors stimulated - stronger stimuli
usually affect larger areas
Number of receptors stimulated - stronger stimuli
usually affect larger areas
usually affect larger areas
Frequency of action potentials - stronger stimuli generate
larger receptor potential, therefore a greater frequency of
action potentials
Duration of the stimulus
Adaptation - receptors change their sensitivity in the
presence of constant stimulus ie a watch on your wrist
Phasic receptors
fast adapting
i. Report changes in the environment
ii. Burst of firing at the beginning and end of stimulus
iii. Examples: temperature, smell, touch
Tonic receptors
slow adapting or not at all
i. Constant firing rate
ii. For situations were continuous information about a stimulus is valuable
iii. Examples: proprioceptors pain, muscle stretch
is subjective , influenced by past adn present experiences, and is coupled with emotional responses
fast pain pathways
sharp pain, easy to localize, myleineated
slow pain pahtways
unmyleined, dull aching pain, persists long and hard to locialize
what stimulates the pain pathway
nociceptors are sensite to chemcials released by damaged tissues.
prostaglandins, bradykinins, histamine, capsaicin
pain pathway
nocicieptors stimulated and primary neurion relases suspstance P- secondary neuron then thalamus and to the reticular formation(brain stem- level of alertness) and hypothamlus( emotinal response)
analgesic pathway
endorphins bind to opiate recepotros on the axon termainal and block the release of susbstance P(example of presnapic inhibition)