Sensation and Perception

What is sensory processing

How the brain knows about the world around it

Sensory processing is essentially:

• Converts WHAT into WHAT

• Dedicated and specific WHAT

Sensory processing is essentially:

• Converts ENERGY into NEURAL CODE

• Dedicated and specific WHAT

Every species has a distinct window on the world:

• WHAT to different stimuli 

• Unique WHAT to interpret these stimuli 

Every species has a distinct window on the world:

• SENSITIVE to different stimuli 

• Unique CNS to interpret these stimuli 

For every sense there is a WHAT:

• Filter WHAT stimuli

• detects and responds to some events not others 

• Transduce physical signals into WHAT 

For every sense there is a SENSORY RECEPTOR ORGAN:

• Filter ENVIRONMENTAL stimuli

• detects and responds to some events not others 

• Transduce physical signals into NEURAL CODE  

Sensory modality:

• Each type of sensory neuron can respond to one type of WHAT

Sensory modality:

• Each type of sensory neuron can respond to one type of SENSATION (hearing, taste, touch, vision, pain) 

Modalities can be grouped into 2 classes

1. General senses 

2. Special senses

General senses

Receptors throughout the body

Somatic, tactile, thermal, pain, proprioreceptive

Special senses

Receptors located in snese organs (eye, ear, nose) 

Smell, hearing, balance, vision, taste 

Special adaptation other than vision:

• Sharks have WHAT detectors (detect changes in ion flow) 

• Detect the itty-bitty WHAT a fish makes when it flexes its muscles 

• WHAT can also do this 

Special adaptation other than vision:

• Sharks have ELECTRICAL FIELDS detectors (detect changes in ion flow) 

- Ampullae of Lorenzini

• Detect the itty-bitty ELECTRICAL CHARGES a fish makes when it flexes its muscles 

• PLATYPUS can also do this 

Some species sense WHAT

Some species sense MAGNETIC FIELDS

• The earths magnetic fields provide WHAT

• Fish, birds, butterflies and bats orient and WHAT 

• All contain WHAT in their brains (mineral sensitive to magnetic fields) 

• The earths magnetic fields provide ORIENTATION CUES

• Fish, birds, butterflies and bats orient and MIGRATE  

• All contain MAGNETITE in their brains (mineral sensitive to magnetic fields) 

How many types of signals can a neuron send 

One, an action potential 

How does the brain know what type of sensory stimuli it has received

called WHAT hypotheses 

Each sense has a single pathway to the brain (not completely true)

called LABELLED LINES hypotheses 

Ranges of detection is limited

• For each sense there is a limited range of WHAT to which we are sensitive to 

• Differs between species 

• WHAT range 

• WHAT range 

Ranges of detection is limited

• For each sense there is a limited range of INTENSITIES to which we are sensitive to 

• Differs between species 

• HEARING range 

• VISUAL range 

Sensory receptors are not evenly WHAT across the body or its organs 

Sensory receptors are not evenly DISTRIBUTED across the body or its organs 

Density is important for determining the WHAT of a sensory (more tactile receptors on the fingers than on the arm) 

Density is important for determining the SENSITIVITY of a sensory (more tactile receptors on the fingers than on the arm) 

Differences in receptor density determine the WHAT of many animals (olfactory ability of dogs)

Differences in receptor density determine the SPECIAL ABILITY of many animals (olfactory ability of dogs)

Sensory processing starts at the WHAT

Sensory processing starts at the RECEPTOR

Transduction

Changing a physical stimulus (analog signal - continuous) into a neural (digital) signal

Initial stage:

• Change in WHAT of the receptor cells 

• Creates a WHAT 

Initial stage:

• Change in ELECTRICAL POTENTIAL of the receptor cells 

• Creates a GENERATOR POTENTIAL 

Generator potential

A graded response to a stimulus, or a grade depolarization induced in the terminal of a sensory receptor, which after achieving a threshold level is capable of producing an action potential in the afferent (toward body) axon in the nearby sensory neuron (think graded potentials or EPSP)

Touch:

Vibration detector in the skin

Pacinian Corpuscule - free nerve ending surrounded by an onion like structure 

Touch:

Stretching the membrane opens WHAT 

Stretch-activated ion channels 

Touch:

Vibrations produce WHAT

• Proportional to WHAT of stimulus 

• Intense enough will produce WHAT 

Touch:

Vibrations produce GRADED POTENTIALS 

• Proportional to INTENSITY of stimulus 

• Intense enough will produce ACTION POTENTIALS  

There are some general features of sensation that apply to most of our senses:

1. WHAT 

2. WHAT 

3. WHAT 

4. WHAT 

5. WHAT 

6. WHAT 

There are some general features of sensation that apply to most of our senses:

1. Coding  

2. Adaptation 

3. Pathways 

4. Surpression 

5. Receptive fields  

6. Attention

1. Sensory coding

• Sensory information is encoded by WHAT

• WHAT vs WHAT 

1. Sensory coding

• Sensory information is encoded by ACTION POTENTIALS 

• Sensitive range vs discrination threshold 

Coding intensity:

• In general sensitive range is WHAT than the response repertoire of a single cell 

Solution:

• Multiple parallel neurons with different HWAT

• Higher intensity = WHAT

Coding intensity:

• In general sensitive range is WIDER than the response repertoire of a single cell 

Solution:

• Multiple parallel neurons with different THRESHOLDS

• Higher intensity = More cells recruited (RANGE FRACTIONATION)

2. Sensory adaptation 

Detects change, ignore unchanging events, simplifies sensory flow (Notice your clothes when you put them on then become unaware of them quickly) 

2. Sensory adaptation

• Response can WHAT (reduce) despite constant stimulation

• Response can be WHAT - change in WHAT with constant stimulus

• Response can be WHAT - maintain response rate 

2. Sensory adaptation

• Response can CHANGE (reduce) despite constant stimulation

• Response can be PHASIC - change in FREQUENCY with constant stimulus

• Response can be TONIC - maintain response rate 

3. Sensory pathways - Neural relays

• Each sense has a specific WHAT

• Pathway made up of WHAT or regions

• Each level serves a WHAT

• WHAT gets the most sensory input

3. Sensory pathways - Neural relays

• Each sense has a specific HIERARCHY

• Pathway made up of DISTINCT NON-OVERLAPPING NUCLEI or regions

• Each level serves a SPECIFIC FUNCTION 

• THALAMUS gets the most sensory input

Thalamus:

• sends information to WHAT

• Specific WHAT regions for each sense (senses have specific pathways that stay specialized until the brain)

Talamus:

• sends information to CORTEX

• Specific CORTICAL regions for each sense (senses have specific pathways that stay specialized until the brain)

4. Sensory receptive fields

• Many WHAT areas respond to a given sense

• Cells arranged in an WHAT (maps)

• WHAT

• WHAT

4. Sensory receptive fields

• Many CORTICAL areas respond to a given sense

• Cells arranged in an ORDERLY FASHION (maps)

• PRIMARY CORTEX

• SECONDARY CORTEX

Primary cortex:

• Most WHAT goes here

• This are WHAT to others

Primary cortex:

• Most INPUT goes here

• This are PROJECTS to others

Secondary cortex:

• Gets input from WHAT 

• Processes specific aspects of WHAT 

Secondary cortex:

• Gets input from PRIMARY 

• Processes specific aspects of STIMULUS  

Receptive field

The region of the sensory organ to which a particular neuron will respond

Sensory receptive fields:

• Usually exhibit a WHAT arrangement 

• Neurons at each level of the hierarchy have WHAt - progressively more complex 

Sensory receptive fields:

• Usually exhibit a CENTRE-SURROUNDED arrangement 

• Neurons at each level of the hierarchy have RECEPTIVE FIELDS - progressively more complex 

5. Sensory suppression

Two forms of suppression sensory input:

1. Use of an WHAT to decrease input (closing eyes)

2. WHAT pathways (neural inhibition of the receptors activity)

5. Sensory suppression

Two forms of suppression sensory input:

1. Use of an ACCESSORY SYSTEM to decrease input (closing eyes)

2. DESCENDING pathways (neural inhibition of the receptors activity)

6. Sensory attention 

• Alterness 

• Attuned to WHAT 

• Focus on WHAT 

• WHAT cortex is involved in this focusing

• WHAT cortex  

6. Sensory attention 

• Alterness 

• Attuned to INPUTS 

• Focus on STIMULUS  

• CINGULATE cortex is involved in this focusing

• POSTERIOR PARIETAL (association) cortex  

Posterior parietal cortex:

• WHAT cells 

• Damage = WHAT 

• Neglect affects usually one side of the body = WHAT 

Posterior parietal cortex:

• POLY MODAL cells 

• Damage = NEGLECT 

• Neglect affects usually one side of the body = CONTRALATERAL  NEGLECT (left site of brain affect → affects right side of body)

The sense of smell = WHAT

The sense of smell = OLFACTION

Olfaction:

• Wide WHAT between people (some specific anosmias = smell blindness) 

• WHO have better sense of smell than WHO 

• Sensitivity WHAT with age 

• Environment can affect WHAT (smokers usually have poor olfactory abilities) 

Olfaction:

• Wide VARIABILITY between people (some specific anosmias = smell blindness) 

• FEMALES have better sense of smell than MALES 

• Sensitivity DECREASES with age 

• Environment can affect SENSITIVITY (smokers usually have poor olfactory abilities) 

Receptor organ in the nose

• WHAT (how many receptors) 

Receptor organ in the nose

• Olfactory Epithelium (6 million receptors) 

Each receptor of the nose has:

• Long WHAT extend to WHAT layer 

• Many fine WHAT along epithelial surface 

• Fine WHAT axons

- Projects from WHAT plate

- Synapse in WHAT

• Constantly replaced throughout life

Each receptor of the nose has:

• Long DENDRITE extend to EPITHELIAL layer 

• Many fine CILIA along epithelial surface 

• Fine UNMYELINATED axons

- Projects from CRIBRIFORM plate

- Synapse in OLFACTORY BULB

• Constantly replaced throughout life

Olfactory receptors innervate WHAT cells in particular WHAT located in the olfactory bulb

Olfactory receptors innervate MITRAL cells in particular GLOMERULI located in the olfactory bulb

Only one type of olfactory receptor neuron inputs to the WHAT

Only one type of olfactory receptor neuron inputs to the GLOMERULUS

• Humans have about HOW MANY different olfactory receptors (only HOW MANY are functional)

• All the olfactory receptors are WHAT 

• Humans have about 1000 different olfactory receptors (only 350-400 are functional)

• All the olfactory receptors are G-protein couples receptors  

• How many different odors can we smell

• How can we do this 

• How many different odors can we smell - 5000

• How can we do this PATTERN CODING - each particular odorant activates an array of receptors 

Olfaction is the only sense that does not need to go through the WHAT to get to the cortex

Olfaction is the only sense that does not need to go through the THALAMUS to get to the cortex

Central projections of olfaction directly innervates areas in the brain involved in WHAT - WHAT 

Central projections of olfaction directly innervates areas in the brain involved in EMOTION - AMYGDALA 

Central projections of olfaction - Prepyriform cortex 

Part of the PRIMARY olfactory cortex = the cortical brain regions that receives the MITRAL cell axon projections 

Projections in the nose are WHAT

Projections in the nose are TOPOGRAPHICAL

• Olfactory receptors are arranged in an orderly fashion in the WHAT

• Ordered arrangement preserved throughout the WHAT 

• Olfactory receptors are arranged in an orderly fashion in the EPITHELIUM

• Ordered arrangement preserved throughout the CNS 

COVID-19 Anosmia

• Olfactory receptors cells do not have the WHAT receptor (binding site of SARS-CoV-2 virus) 

• But critical support cells (WHAT cells) have a lot of WHAT receptors

• COVID-19 damages the olfactory WHAT, major loss of WHAT 

COVID-19 Anosmia

• Olfactory receptors cells do not have the ACE2 receptor (binding site of SARS-CoV-2 virus) 

• But critical support cells (SUSTENTACULAR cells) have a lot of ACE2 receptors

• COVID-19 damages the olfactory EPITHELIUM, major loss of CILIA 

Taste

The perception of the sensory cells in your taste buds

Taste does not equal WHAT - flavour involves the sense of WHAT 

Taste does not equal FLAVOUR - flavour involves the sense of SMELL 

Taste is not WHAT dependent 

Taste is not EXPERIENCE dependent 

Taste receptors are found: In special cells also called WHAT cells

Taste receptors are found: In special cells also called TASTE cells

Many taste cells group together to form an WHAT structure also known as WHAT 

Many taste cells group together to form an ONON-LIKE structure also known as TASTE BUD 

Thousands of taste buds are found in WHAT like structures called WHAT at the upper surface of the WHAT 

Thousands of taste buds are found in NIPPLE like structures called PAPILLAE at the upper surface of the TONGUE 

There are also taste receptors in your WHAT and WHAT 

There are also taste receptors in your THROAT and GUT 

There are 5 different taste receptor types:

• WHAT 

• WHAT 

• WHAT 

• WHAT 

• WHAT 

There are 5 different taste receptor types:

• Sweet 

• Salty 

• Sour 

• Bitter 

• Umami 

Each of the five taste receptor types responds to a different WHAT of food

Each of the five taste receptor types responds to a different CHEMICAL COMPONENT of food

Taste transduction is preformed by WHAT receptors 

Taste transduction is preformed by TASTE receptors 

Taste receptors are found on WHAT

Taste receptors are found on PAPPILLAE

• Each papillae has 1 or more WHAT 

• Each taste bud has HOW MANY cells and several receptor types - arranged with a WHAT at the end 

• Recycled every HOW MANY days 

• Each papillae has 1 or more TASTE BUD 

• Each taste bud has 50-150 cells and several receptor types - arranged with a PORE at the end 

• Recycled every 10-14 days 

Besides taste receptors, also WHAT (pain receptors) at the surface of the tongue

Besides taste receptors, also NOCICEPTORS (pain receptors) at the surface of the tongue

3 different papillae:

1. WHAT 

2. WHAT 

3. WHAT 

Each participate in transduction of WHAT 

3 different papillae:

1. Fungiform (most numerous - one bud/papillae) 

2. Foliate 

3. Circumvallate 

Each participate in transduction of ALL TASTE 

Taste transduction for SALTY foods:

• WHAT ion channels  

• Salt = WHAT 

• WHAT from salt enters the cell and causes it to WHAT

Taste transduction for SALTY foods:

• Na+ ion channels  

• Salt = NaCl 

• Na+ from salt enters the cell and causes it to DEPOLARIZE

Taste transduction for SOUR foods:

• WHAT ions

• Block WHAT leak channel, WHAT cannot leave the cell causing it to WHAT 

Taste transduction for SOUR foods:

• H+ ions

• Block K+ leak channel, K+ cannot leave the cell causing it to DEPOLARIZE 

Taste transduction for SWEET foods:

• SpecialWHAT

• ClosureWHATchannels;depolarization

Taste transduction for SWEET foods:

• SpecialG-protein couples receptors 

• ClosureK+channels;depolarization

Taste transduction for BITTER foods:

• SpecialWHAT

• HOW MANYdifferentreceptorsubtypes

• Somepeoplecan’ttastesometypesofbitter

Taste transduction for BITTER foods:

• SpecialG-proteincoupledreceptors

• 30differentreceptorsubtypes

• Somepeoplecan’ttastesometypesofbitter

Taste transduction for UMAMI foods:

• TypeofWHATreceptor(G- proteincoupledreceptor)

• RespondstocertainWHAT

• MSG(=monosodiumglutamate);a flavourenhancer,addedincertainfood butalsofoundnaturallyinsomefoodsincludingtomatoesandcheese)

Taste transduction for UMAMI foods:

• TypeofGLUTAMATEreceptor(G- proteincoupledreceptor)

• RespondstocertainAMINOACIDS

• MSG(=monosodiumglutamate);a flavourenhancer,addedincertainfood butalsofoundnaturallyinsomefoodsincludingtomatoesandcheese)

Central pathways fro taste: 3 different cranial nerves:

• WHAT 

• WHAT 

• WHAT 

Central pathways fro taste: 3 different cranial nerves:

• VII = Facial nerve 

• IX = Glossopharyngeal nerve 

• X = Vagus nerve  

Central pathway for taste:

WHAT → WHAT → WHAT

Central pathway for taste:

BRAINSTEM → THALAMUS → CORTEX

Central pathway for taste are not as simple as labelled lines:

• WHAT coding 

• WHAT of different incoming signals 

Central pathway for taste are not as simple as labelled lines:

• PATTERN coding 

• RELATIVE ACTIVITY of different incoming signals