I. Sensation A. Coding of signals into action potentials 1. receptor cells.

I. SensationA. Coding of signals into action potentials

1. receptor cells

1. receptor cells2. afferent neurons

1. receptor cells2. afferent neurons3. sensory cortex

I. SensationB. Modalities (types of input)

1. touch: mechanoreceptors2. hearing: mechanoreceptors3. vision: photoreceptors4. taste: chemoreceptors

I. SensationB. Modalities (types of input)

5. smell: chemoreceptors6. unconscious

- interoceptors (include proprioceptors)7. thermoreceptors

I. SensationC. Perception (awareness) of stimulus

1. transduction - conversion of one form of energy to another2. action potentials reach brain from sensors

- sensory (afferent) pathways3. interpretation (meaning)

I. SensationD. Specificity

1. most neurons will produce only one type of stimulus2. response specific no matter what the stimulus

I. SensationE. Mechanisms

- promote conformational change (of protein)- activate second messenger cascade- open an ion channel

1. detectiona. via receptorsb. commonality of receptor structural motifs

- vision, smell, sweet/bitter taste- similarity to muscarinic

2. amplificationa. single photon activates transducin (G protein)b. leads to activation of multiple cGMPsc. each cGMP modifies an ion channel

3. encodinga. due to a change in gm (conductance through ion channels)b. depolarization action potential?c. can impart information about intensity of stimulus

4. adaptation - allows detection of new stimulus in the presence of ongoing inputa. tonic (continuous action potentials)

- provide input about duration of stimulus

4. adaptation b. phasic (rapidly adapting)

- action potentials at onset of stimulus- amplitude may eventually drop below threshold- not much info about duration

II. Receptor Potentials and Impulse Propagationgenerator potentials generated on neurons having the sensory

receptorsA. Generator potentials analogous to EPSPs (pictured in (a) below)1. can vary in amplitude (graded)

- receptor current2. generate action potentials at threshold

3. stimulus of sensor generator potential current AP?

II. Receptor Potentials and Impulse PropagationB. Intensity of stimulus determines:

1. amplitude of generator potentials2. frequency of action potentials3. brain receives action potentials

- only variation is frequency- an AP is an AP

II. Receptor Potentials and Impulse PropagationC. Initial stimulus can be on sensory epithelial cells (as in (b) below)

- does not generate an action potential- graded receptor potentials- graded release of neurotransmitter onto primary sensory neuron

II. Receptor Potentials and Impulse PropagationD. Primary (first-order) sensory neuron

1. may also be the receptor2. axon may travel to CNS as a sensory (afferent) fiber3. will synapse with second-order (2˚) neuron

II. Receptor Potentials and Impulse PropagationE. Adaptation

sometimes sensation is just a matter of perceptionis the intensity less, or is our brain just adapting?

II. Receptor Potentials and Impulse PropagationE. Adaptation (several mechanisms)

1. transducer molecules can be “used-up”2. sustained stimulation may cause electrical changes

Ca++ in cell3. enzyme cascade inhibited by accumulation

4. sensory adaptation at higher levels

II. Receptor Potentials and Impulse PropagationF. Sensitivity

1. many receptors always on (just modify up or down)- greater sensitivity

2. or in frequency can imply direction of stimulus (hair cells)

II. Receptor Potentials and Impulse PropagationG. Sensitivity

3. lateral inhibitiona. interneurons inhibit neurons receiving less stimulusb. sharpens cutaneous sensation

II. Receptor Potentials and Impulse PropagationG. Sensitivity

4. feature detectiona. selective detection of given features of a sensory stimulusb. examples: shape, angle, or movement by the visual cortex

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Cerebral CortexMap of cerebral hemispheres

Cerebral CortexMap of cerebral hemispheres (functional organization)

Cerebral CortexMap of cerebral hemispheres (Brodmann’s cytoarchitectural map)

Cerebral CortexLaminar organization

Cerebral CortexColumnar hypothesis: views the cortex as being organized vertically

Cerebral CortexCortex that is predominantly sensory has a prominent layer IV

Motor areas have a prominent layer V

Cerebral CortexAfferent impulses will project project first to lamina IV.They will then project vertically to layers II, III, and V.These will then project to other cortical and subcortical regions

Cerebral CortexCerebral cortex forms in a vertical fashion from cells arising from the areas immediately surrounding the ventricles (neural tube)

Ideas on Perception“Grandmother cells”

The cell at the top of the column does the “perceiving”

Ideas on PerceptionParallel pathways

Each pathway analyzes one specific aspect of the stimulus

Ideas on PerceptionDistributed system theory

one single column may be a member of a number of different pathways

Ideas on PerceptionBoth ideas are basically correct

vertical hierarchy used in the different cortical regions used to perceive sensory input

I. Sensation A. Coding of signals into action potentials 1. receptor cells.

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