"Exam 4" Flashcards
Conscious Processing
Special Senses (vision, hearing, taste, smell, equilibrium)
Somatic senses (touch, temperature, pain, itch, proprioception)
Proprioception
3D awareness, sense of body in space around us
Subconscious processing
Somatic stimuli (muscle length, tension, proprioception)
Visceral stimuli (BP, GI stretch, blood glucose, core body temp, osmolarity, pH)
Common elements of sensory pathways
Stimulus in the form of physical energy (heat, chemical conc., light, sound)
Sensory receptor- converts stimulus to electrical signal (sub-threshold or threshold)
Simple receptors
Have free nerve endings (diagram on slide 369)
Complex Receptors
Have endings enclosed in connective tissue (diagram on slide 369)
Special Senses Receptor
Release NT onto neurons (diagram on slide 369)
4 types of sensory receptors
Chemoreceptors, mechanoreceptors, photoreceptors, thermoreceptros
Chemoreceptors
Oxygen, pH, various organic molecules like glucose
Mechanoreceptors
Pressure, cell stretch, vibration, acceleration, sound
Photoreceptors
Photons of light
Thermoreceptors
Varying degrees of heat
Transduction
Sensory neurons converting physical stimuli to electrical signal
Physical/chemical signal usually opens ion channels and change membrane potential –> lead to graded potential
Convergent Receptive fields
Large. Receptive fields of multiple primary sensory neurons overlap to form one large secondary receptive field.
Sum of primary neuron stimuli on secondary neuron to reach threshold and send AP
Found in legs, trunk, arms…
Small recepetive fields
Fewer neurons converge, secondary receptive fields are much smaller. One or 2 primary neurons per each secondary neuron.
Found in skin, nose, hands, mouth, spinal cord…
Simple Receptive field
One primary sensory neuron synapses onto one secondary neuron
Smaller but more sensitive
Complex Receptive fields
Convergent, multiple presynaptic neurons provide input to smaller number of postsynaptic neurons
Larger but less sensitive
Where do spinal cord afferents go
Thalamus and then sensory cortex (Diagram slide 405)
Where do special senses go
Directed to sensory area like vision cortex (Diagram slide 405)
Perceptual threshold
The stimulus intensity necessary for you to be consciously aware of it
Habituation
When your brain decreases perception of the stimulus, tune out
Why do we have habituation
Efficiency, we have so much to take in we have to pick our battles.
What sense is the only one that does not go through the thalamus
Olfactory (Nose)
4 properties of a stimulus for CNS to distinguish
Modality, Location, Intensity, Duration
Modality
the TYPE of stimulus
touch vs. pain vs. temperature
Labeled-line coding
Labeled-line coding
A cold receptor always perceives cold, pain receptor doesn’t send temperature info
Location
Where the stimulus originated, depends on receptive field that is activated
Receptors project to specific area of sensory cortex
Lateral inhibition
Lateral Inhibition
Isolates the stimulus and increase the sensitivity (contrast) of the signal (diagram slide 407)
Occurs at secondary level
“Noise cancelling headphones”
Intensity
Population coding- # of receptors activated
Frequency coding- frequency of action potentials being sent
Duration
Duration of AP. Too much info can be disruptive so receptors adapt and dismiss some senses/info
Tonic and Phasic receptors
Tonic receptors
Slowly adapting receptors
Fire rapidly at first and then slow down but maintain firing of AP; never turn off
Used for things that constantly need monitoring
Ex: BP, breathing
Phasic Receptors
Rapidly adapting receptors
Fire rapidly but cease firing if strength remains constant
Ignore info once it is perceived; turn off
Ex: pain
Sensory receptor overview
- each receptor is sensitive to particular type of stimulus
- A stimulus above threshold indicates AP in a sensory neuron that projects to the CNS
- Stimulus intensity and duration are coded in the pattern of APs reaching CNS
- Stim location and modality are coded according to which receptors are activated by the timing of activation
- Each sensory pathway projects to a specific region of the cerebral cortex dedicated to its particular receptive field.
Four somatic senses
Touch, temperature, Nociception (pain), Proprioception (spacial awareness)
where are receptors for somatic sensation found
Skin and viscera
Secondary neurons cross the midline in SC or brain stem
Somatosensory cortex
Thalamus relays secondary neurons here, recognizes stimulus origin, can be reorganized after loss of digit/limb
The amount of space in the somatosensory cortex devoted to each part of the body is proportional to the sensitivity of that part
The types of physical contact touch receptors respond to and touch receptors structure
Stretch, steady pressure, fluttering, vibration, texture
Receptors Structure: Free nerve endings or encapsulated in connective tissue
Skin, hair, under skin
Temperature receptors
Free nerve endings embedded in skin
Cold: temps below 37C
Warm: Temps between 37-45C
above 45C activates pain receptors
Nociceptors
Free nerve endings that respond to harmful/noxious stimuli (chemical, mechanical, thermal)
Found in Skin, joints, muscles, bones, and some internal organs but not in CNS
Afferent signals carried to CNS by A-delta or C-fibers
A-delta nociceptor
faster, myelinated fibers
more intense pain
C-fibers nociceptor
slower, unmyelinated
Dull pain