Lec 13 Flashcards by Mahan Tavakolian

Stimulus detected by

Receptor
Sensory cells
Neurons or anything

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Signal is sent via ——— to cns

Neurons
Having Action Potential

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How many neurons between receptor to cerebral cortex

3 neurons typically

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If signal reaches cerebral cortex

Stimulus enters our consciousness

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If signal does not reach cerebral cortex

Response is elicited without our conscious

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Special senses

Special regions in brain

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Somatic senses

Touch
Temperature
Pain
Itch
Proprioception

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Somatic senses

Incoming/afferent

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Somatic senses region in brain

Primary sensory cortex

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Proprioception

Awareness of body movements and position in space

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Subconscious processing example

Blood pressure
GI tract
Internal Temperature/PH/Osmolarity

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Sensory receptors are

Transducer

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Sensory cell specifically

Convert stimulus into an intracellular response
May or may not be neurons

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4 main types of sensory neurons

Chemoreceptor
Mechanoreceptors
Thermoreceptors
Photoreceptors

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Chemoreceptor example

PH, Na, Oxygen, Glucose

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Mechanireceptor

Pressure, vibration, acceleration

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Thermoreceptor example

Hot
Cold

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Photoreceptor example

Light

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Adequate stimulus

Form of energy to which sensory neuron is most responsive
-receptor may respond less strongly to other forms of stimulus

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Stimulus

Change in membrane potential of receptor cell

*RECEPTOR POTENTIAL
(Graded potential in sensory cell)

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Receptor potential can be

Depolarization (skin is touch)
Or
Hyperpolarization (light on retina)

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Threshold stimulus

Minimum stimulus needed to generate enough receptor potential to produce intracellular response

Intracellular response can be

AP firing (if receptor is neuron)
Or neurotransmitter release (if non-neuron) often release neurotransmitters for partner neuron, then neuron fire AP

Sensory cells kind

1- neurons — sensory neurons
2- non-neurons — specialized sensory cell

Transduction means

Extracellular to intracellular

Primary sensory nerve endings

- free nerve endings **pain and temperature receptor** Unmyelinated axon Slower rate -enclosed nerve endings **pressure** Layers of connective tissue Myelinated axon Faster rate

Primary sensory Synapse in ———

Spinal cord Grey matter Dorsal region

Sensory receptors that are not neurons

Hair cell in inner ear Machanoreceptor which has synapse with neuron

Most special senses receptors are cells that ———

Release neurotransmitters onto sensory neurons EXCEPT SMELL/olfactory

Stimulus properties

Modality—what kinds Location—where Intensity—how strong(population and frequency) Duration—how long

Modality determined by

-sensory receptor that is activated -area of the brain which sensory signal is sent

Labeled Line Coding

Brain associate signal from particular receptors with specific modality *photoreceptors are perceived as light even if activated by mechanical stress

All sensory stimulus move through ——— instead ———

Thalamus Olfactory

Sensory neurons receptive field

Convergence—large receptive field Small receptive field

Convergence receptive field

Primary sensory neurons overlap to form one large secondary receptive field Convergence primary fields allows simultaneous sub threshold stimuli to sum at secondary sensory neuron Two stimuli within same secondary receptive field are perceived as one single point *NO TWO POINT DISCRIMINATION

Small receptive field

Fewer neuron convergence, smaller secondary receptive fields Two stimuli active separately, point perceived as distinct stimuli *TWO-POINT DISCRIMINATION

Perception thresholds

Minimum stimulus intensity for activation higher neurons in sensory pathway

Somatosensory cortex is proportional to

Sensitivity of that part

More sensitive has higher chance of

Two point discrimination

Lateral inhibition

Enhance contrast between activated receptive field and inactive neighbor Makes stimulus easier to perceive

Stimulus intensity

Proportional to number of receptors activated Frequency of AP

Duration

Coded by duration of AP Some receptors can adapt

Receptors adaptation

Tonic receptors: —adapt slowly - fire for long duration Phasic receptors: —adapt rapidly - fore when stimulus changes

Phasic receptors example

Olfactory neuron

Somatic senses

Cutaneous: (free endings) 1-touch—mechanoreceptor 2-pain/itch—nociceptor 3-temperature—thermoreceptor Proprioceptive: Where you are and organs position

Sense and respond rate is proportional to

Size and myelination

Fiber types from fastest to slowest

I>II>III>IV

Fiber type I example

Muscle/Proprioception

Fiber type II example

Mechanical stimuli

Fiber type III example

Cold, fast pain

Fiver type IV example

Heat, slow pain

Cutaneous sensory receptor types

Free nerve endings Meissner corpuscle Pacinian corpuscles Ruffini corpuscles Merkel corpuscles

Free nerve endings Stimulus/location/structure/adaptation

Stimulus: temperature/noxious/hair movement Location: around hair roots and under surface of skin Structure: unmyelinated Adaptation: variable

Pacinian corpuscles

Stimulus: vibration Location: deep layers of skin Structure: encapsulated in connective tissue Adaptation: rapid