Sensation And Perception

Front 1

Bottom-up Processing

Back 1

1) Processing based on incoming stimuli from the environment
2) Also called data-based processing

Front 2

Top-down Processing

Back 2

1) Processing based on the perceiver’s previous knowledge (cognitive factors)
2) Also called knowledge-based processing

Front 3

Psychophysical approach (PP)

Back 3

The stimulus-perception relationship

Front 4

Physiological approach (PH1)

Back 4

The stimulus-physiology relationship

Front 5

Physiological approach (PH2)

Back 5

The physiology and perception relationship

Front 6

Dorsal

Back 6

Toward the back, away from the ventral (stomach) side. The top of the brain is considered dorsal because it has that position in four-legged animals.

Front 7

Ventral

Back 7

Toward the stomach, away from the dorsal (back) side.

Front 8

Anterior

Back 8

Toward the front end.

Front 9

Posterior

Back 9

Toward the back end.

Front 10

Superior

Back 10

Above another part.

Front 11

Inferior

Back 11

Below another part.

Front 12

Lateral

Back 12

Toward the side, away from the midline.

Front 13

Medial

Back 13

Toward the midline, away from the side.

Front 14

Proximal

Back 14

Located close (approximate) to the point of origin or attachment.

Front 15

Distal

Back 15

Located more distant from the point of origin or attachment.

Front 16

Ipsilateral

Back 16

On the same side of the body. (e.g. left side of brain, left side of body)

Front 17

Contralateral

Back 17

On the opposite side of the body. (e.g. left side of the brain, right side of the body)

Front 18

Coronal Plane

Back 18

A plane that shows brain structures as seen from the front (or frontal plane).

Front 19

Sagittal Plane

Back 19

A plane that shows brain structures as seen from the side.

Front 20

Horizontal Plane

Back 20

A plane that shows brain structures as seen from above (or transverse plane).

Front 21

Vision

Back 21

Stimulus - Electromagnetic energy

Receptor - Photoreceptor

Sensory structure - Eye

Cortex - Primary visual cortex

Front 22

Hearing

Back 22

Stimulus - Airpressure waves

Receptor - Mechanoreceptors

Sensory structure - Ear

Cortex - Auditory cortex

Front 23

Touch

Back 23

Stimulus - Tissue distortion

Receptor - Mechanoreceptors, Thermoreceptors

Sensory structure - Skin, muscle, etc.

Cortex - Somatosensory cortex

Front 24

Balance

Back 24

Stimulus - Gravity, Acceleration

Receptor - Mechanoreceptors

Sensory structure - Vestibular organs

Cortex - Temporal cortex

Front 25

Taste/Smell

Back 25

Stimulus - Chemical composition

Receptor - Chemoreceptors

Sensory structure - Nose, Mouth

Cortex - Primary taste cortex, Olfactory cortex

Front 26

Transduction

Back 26

The process by which individual sense organs convert energy from environmental events into neural activity.

Front 27

The Perceptual Process (Loop)

Back 27

1) Environmental stimuli

2) Attended stimulus

3) Stimulus on the receptors

4) Transduction

5) Processing (involves prior knowledge)

6) Perception

7) Recognition

8) Action

Front 28

Three stages of Perception

Back 28

1) Stimulus

2) Electricity

3) Experience and Action

Front 29

Stage 1 of Perception - Stimulus

Back 29

o All objects in the environment are available to the observer.
o Observer selectively attends to objects.
o Stimulus impinges on receptors resulting in internal representation.

Front 30

Stage 2 of Perception - Electricity

Back 30

o Transduction occurs which changes environmental energy to nerve impulses
o Transmission occurs when signals from the receptors travel to the brain.
o Processing occurs during interactions among neurones in the brain.

Front 31

Stage 3 of Perception - Experience and Action

Back 31

o Perception occurs as a conscious experience.
o Recognition occurs when an object is placed in a category giving it meaning.
o Action occurs when the perceiver initiates motor activity in response to recognition.

Front 32

Neuroanatomy

Back 32

The anatomy of the nervous system.

Also refers to the study of the various parts of the nervous system and their respective function(s).

Front 33

The Nervous System

Back 33

1) Central Nervous System (CNS)
2) Peripheral Nervous System (PNS)

Front 34

Central Nervous System (CNS)

Back 34

1) Brain

2) Spinal Cord

Front 35

Peripheral Nervous System (PNS)

Back 35

1) Somatic - Controls voluntary muscles and conveys sensory information to the central nervous system.

2) Autonomic - Controls involuntary muscles.

Front 36

The Autonomic Nervous System

Back 36

1) This system sends and receives messages to regulate the automatic behaviours of the body (heart rate, blood pressure, respiration, digestion, etc).

2) Divided into two systems:
- Sympathetic (expends energy)

- Parasympathetic (conserves energy)

Front 37

Sections of the Brain

Back 37

1) Forebrain

2) Midbrain

3) Hindbrain

Front 38

The Forebrain

Back 38

1) Thalamus

2) Hypothalamus

3) Cerebral Cortex

4) Limbic System

5) Corpus Callosum

Front 39

The Hindbrain

Back 39

1) Cerebellum

2) Pons

3) Medulla

Front 40

The Medulla

Back 40

1. This regulates our cardiovascular and respiratory systems (heartbeat, blood circulation and breathing rate).
2. Responsible for reflexes (such as swallowing,
coughing & sneezing, vomiting).
3. Maintaining body balance by controlling head
and limbs position with respect to gravity.

Front 41

The Pons

Back 41

1. This integrates information from movements of and sensations from facial muscles, tongue,
eye and ear.
2. Involved in regulating brain attentiveness
levels and in initiating sleep and dreaming.

Front 42

The Cerebellum

Back 42

This imposes fine control and coordination of balance and movements using the information from muscles, joints and tendons. (It’s a big job,
hence its size; it contains over 30 billion neurones!)

Front 43

The Cerebral Cortex

Back 43

1) This contains up to six distinct laminae (layers)
that are parallel to the surface of the cortex.
2) Cells of the cortex are also divided into
columns that lie perpendicular to the laminae.
3) Divided into four lobes: occipital, parietal,
temporal, and frontal.

Front 44

The Four Lobes of the Cerebral Cortex

Back 44

1) Frontal lobe

2) Parietal lobe

3) Temporal lobe

4) Occipital lobe

Front 45

Frontal Lobe

Back 45

This lobe is concerned with the planning of movements, recent memory, and some aspects of emotion.

Front 46

Parietal Lobe

Back 46

This lobe is concerned with bodily sensations.

Front 47

Temporal Lobe

Back 47

This lobe is concerned with hearing and advanced visual processing.

Front 48

Occipital Lobe

Back 48

This lobe is concerned with vision.

Front 49

The Thalamus

Back 49

This contains a large number of relay centres conveying nearly all the sensory information to the cortex (e.g. from the eyes - LGN).

Front 50

The Hypothalamus

Back 50

1) This controls the autonomic nervous system and the endocrine system.
2) Organises the basic behaviour for survival:
fighting, feeding, fleeing and mating.

Front 51

The Limbic System

Back 51

1) This is an important set of interconnecting structures, surrounding the thalamus and lying just under the cortex.
2) It includes structures such as the amygdala and the hippocampus and has neural links to the hypothalamus and the cortex.
3) It is involved in emotional and motivational activities as well as in some aspects of learning and memory.

Front 52

The Primary Sensory Projection Areas

Back 52

These serve as the receiving stations for information arriving from the eyes, ears etc.

Front 53

The Primary Motor Projection Area

Back 53

This is the departure point for signals to the muscles.

Front 54

Key Components of Neurones

Back 54

1) Cell body

2) Dendrites

3) Axon or nerve fibre

Front 55

Receptors

Back 55

These are specialised neurones that respond to specific kinds of energy.

Front 56

Soma

Back 56

The cell body of a neurone, which contains the nucleus.

Front 57

Dendrite

Back 57

A branched treelike structure attached to the soma of a neurone; receives information from the terminal button of other neurones.

Front 58

Axon

Back 58

The long thin cylindrical structure that conveys information from the soma of a neurone to its terminal button.

Front 59

Synapse

Back 59

A junction between the terminal button of an axon and the membrane of another neurone.

Front 60

Terminal Button

Back 60

The bud at the end of a branch of an axon; forms synapses with another neurone; sends information to that neurone.

Front 61

Neurotransmitter

Back 61

A chemical that is released by a terminal button;
has an excitatory or inhibitory effect on another
neuron.

Front 62

Glial Cells

Back 62

A type of cell in the central and peripheral nervous system that forms myelin sheaths.

Front 63

Myelin Sheath

Back 63

A sheath that surrounds axons and insulates them, preventing messages from spreading between adjacent axons.

Front 64

Node of Ranvier

Back 64

A naked portion of a myelinated axon, between
adjacent glial cells.

Front 65

White Matter

Back 65

The axons, covered with myelin are White.

Front 66

Grey Matter

Back 66

Cell bodies, dendrites, and un-myelinated axons are Grey.

Front 67

Ions

Back 67

• Neurones are surrounded by a solution containing ions.
– Ions carry an electrical charge.
– Sodium ions (Na+) - positive charge
– Chlorine ions (Cl-) - negative charge
– Potassium ions (K+) - positive charge
– Electrical signals are generated when such ions cross the membranes of neurones.

Front 68

Action Potential Occurrence

Back 68

1) Electrical signals or action potentials occur when:
– Permeability of the membrane changes
– Na+ flows into the fibre making the neurone more positive
– K+ flows out of the fibre making the neurone more negative
2) This process travels down the axon in a
propagated response.

Front 69

Properties of Action Potentials

Back 69

1) Show propagated response.
2) Remain the same size regardless of stimulus intensity.
3) Increase in rate to increase in stimulus intensity.
4) Have a refractory period of 1 ms.
5) Show spontaneous activity that occurs without stimulation.

Front 70

Synaptic Transmission of Neural Impulses

Back 70

Neurotransmitters are:
1) Released by the presynaptic neurone from
vesicles.
2) Received by the postsynaptic neurone on
receptor sites.
3) Matched like a key to a lock into specific
receptor sites.
4) Used as triggers for voltage change in the
postsynaptic neurone.

Front 71

Excitatory Neurotransmitters

Back 71

These cause depolarisation.
– Neurone becomes more positive (less negative inside)
– Increases the likelihood of an action potential

Front 72

Inhibitory Neurotransmitters

Back 72

These cause hyperpolarisation.
– Neurone becomes more negative
– Decreases the likelihood of an action potential

Front 73

Excitatory postsynaptic potential (EPSP)

Back 73

This is an excitatory depolarisation of the postsynaptic membrane of a synapse caused by the release of a neurotransmitter by the
terminal button.

Front 74

Inhibitory postsynaptic potential (IPSP)

Back 74

This is an inhibitory hyperpolarisation of the postsynaptic membrane of a synapse caused by the release of a neurotransmitter by the terminal button.

Front 75

Synaptic Reuptake

Back 75

The reentry of a neurotransmitter just released by a terminal button back through its membrane, thus terminating the postsynaptic potential.

Front 76

Synaptic Enzymatic Deactivation

Back 76

The destruction of a neurotransmitter by an enzyme after its release.

For example, the destruction of acetylcholine
by acetylcholinesterase.

Front 77

Visible Light

Back 77

This is a specific band of energy within the
electromagnetic spectrum.

Front 78

Cornea

Back 78

1) The transparent tissue at the very front of the eye.

2) It is fixed, and accounts for about 80% of
focusing.

Front 79

The Lens

Back 79

1) This acts like an aperture that prevents
(or restricts) the mapping of “many points
to one” between an object and its image.

2) It adjusts shape for object distance,
and accounts for 20% of focusing.

Front 80

Sclera

Back 80

Tough white tissue that coats the rest of the eye.

Front 81

Iris

Back 81

Muscle tissue that controls the size of the pupil.

Front 82

Pupil

Back 82

This controls the amount of light that enters the eye.

Front 83

Rods

Back 83

Cylinder-shaped receptors in the retina that are responsible for vision at low levels of illumination.

Front 84

Cones

Back 84

Cone-shaped receptors in the retina that are primarily responsible for vision in high levels of illumination and for colour vision and detail vision.

Front 85

Colour perceived by short wavelengths:

Back 85

Blue

Front 86

Colour perceived by medium wavelengths:

Back 86

Green

Front 87

Colour perceived by long wavelengths:

Back 87

Red

Front 88

Colour perceived by long and medium wavelengths:

Back 88

Yellow

Front 89

Colour perceived by long, medium and short wavelengths:

Back 89

White

Front 90

Principle of Univariance

Back 90

• Individual cones are “colour blind”: the
absorption of light by the photopigment in the
photoreceptor always causes the same effect (i.e. isomerisation) no matter what the wavelength is.
• Thus, for any of our 3 cone types, light intensity (or brightness) and wavelength are completely interchangeable.

Front 91

Trichromatic Theory

Back 91

Theory that different amounts of red, green and blue combine to make up all the colours that we perceive.

Front 92

Opponent-Process Theory of Colour Vision

Back 92

– Three mechanisms - red/green,
blue/yellow, and white/black.
– The pairs respond in an opposing fashion,
such as positively to red and negatively to
green.
– These responses were believed to be the
result of chemical reactions in the retina.

Front 93

Additive Colour Mixing

Back 93

– Mixing lights of different wavelengths
– All wavelengths are available for the observer to see
– Superimposing blue and yellow lights leads to
white

Front 94

Subtractive Colour Mixing

Back 94

– Mixing paints with different pigments
– Additional pigments reflect fewer wavelengths
– Mixing blue and yellow leads to green

Front 95

What is Colour?

Back 95

- Colour is a percept. There are NO physical colours in the outside world, only different spectral distributions of lights that are reflected from different objects.
- We can perceive colour because we have 3 types of cone, whose spectral sensitivities occupy different parts of the visible spectrum.

Front 96

Cue Approach to Depth Perception

Back 96

- Focuses on information in the retinal image that is correlated with depth in the scene.

- We learn the connection between cue and depth, and this association becomes automatic through repeat exposure.

Front 97

Cues for Depth Perception

Back 97

1) Oculomotor cues

2) Binocular cues

3) Monocular cues

Front 98

Oculomotor Cues

Back 98

- Involves two sets of muscles.

1) Convergence - the inward movement of our eyes as we look at nearby objects.

2) Accommodation - the changes in shape of our lens as we focus on nearby objects.

Front 99

Binocular Depth Cues

Back 99

- Depend on information received from both eyes.

- Convergence can be labelled as a binocular depth cue as well.

- Main binocular depth cue is disparity.

Front 100

Binocular Disparity

Back 100

- The difference in the position of the images in our two eyes.

Front 101

Stereopsis

Back 101

- The perception of depth as a result of retinal disparity.

Front 102

Corresponding Retinal Points

Back 102

- These are the places on each retina that connect to the same places in the visual cortex.

- The two foveas are an example of two such corresponding retinal points.

Front 103

Horopter

Back 103

- An imaginary sphere that passes through the point of focus.

- Objects on the horopter fall on corresponding points on the two retinas.

Front 104

Non-corresponding Points

Back 104

- These are objects that do not fall on the horopter.

- These points make disparate images.

- The angle between these points is the absolute disparity.

- The amount of disparity indicates how far an object is from the horopter.

Front 105

Relative Disparity

Back 105

- The difference between the absolute disparity of two objects.

Front 106

Depth perception in other species

Back 106

- Animals use same range of cues as humans.

- Frontal eyes are necessary for binocular disparity.

- Lateral eyes provide a wider view, which allows them to watch for predators.

Front 107

Monocular Depth Cues

Back 107

- Cues provided from only one eye.

1) Pictorial cues

2) Movement base cues

Front 108

Motion Parallax

Back 108

- The difference in the perceived speed of movement for near and far objects.

- Nearby objects appear to glide rapidly past us, whereas more distant objects appear to move more slowly.

Front 109

Eye movement

Back 109

This allows us to:
1) Place the image of things that interest us on the fovea; the high resolution portion of the fovea.

2) Keep images of moving objects stationary on the retina.

3) Compensate for our head movements.

Front 110

Main Types of Eye Movements

Back 110

1) Vergence (or Conjugate) movements

2) Saccadic movements

3) Pursuit movements

4) VOR - Vestibular Ocular Reflex

Front 111

Vergence/Conjugate Movements

Back 111

- Vergence points both fovea at a near or a far target.

- Vergence prevents double vision

- During vergence, the eyes rotate in opposite directions (left eye moves right, right eye moves left)

Front 112

Saccadic Movements

Back 112

- Saccades move the fovea to an object of interest.

- They are very fast and accurate.

- No voluntary control over their speed

- Effectively blind during every saccade.

- Both eyes move together

Front 113

Pursuit Movements

Back 113

- Their purpose is to keep the fovea pointing at a moving target.

- Pursuit is involuntary; you cannot initiate a pursuit in absence of a moving target.

Front 114

VOR (Vestibular Ocular Reflex) Movements

Back 114

- These keep the image of the world stationary on the retina when we move our head.

Front 115

What happens when images don't move on retina?

Back 115

- Appear normal at first

- Then they begin to fade

- After a short while, they cannot be seen at all

Front 116

How come the world doesn't fade when we fixate?

Back 116

- Eyes are never perfectly still.

- Always a bit of a tremor in the 3 pairs of extraocular antagonist muscles even when we think we are holding a steady fixation.

Front 117

Neural Circuits

Back 117

- Groups of neurons connected by excitatory and inhibitory synapses.

- A simple circuit has no convergence and only excitatory impulses.

- Each circuit can only indicate single spot of stimulation.

Front 118

Convergent Circuit with only Excitatory Connections

Back 118

- Input from each receptor summates into
the next neuron in the circuit.
– Output from convergent system varies
based on input.
– Output of circuit can indicate single input
and increases output as length (or area) of
stimulus increases.

Front 119

Convergent Circuit with Excitatory and
Inhibitory Connections

Back 119

– Inputs from receptors summate to
determine output of circuit.
– Summation of inputs result in:
• weak response for single inputs and
long stimuli.
• maximum firing rate for medium length
stimulus.

Front 120

Center-Surround Receptive Fields

Back 120

- Excitatory and inhibitory effects are found in
receptive fields.
- Center and surround areas of receptive fields
result in:
• Excitatory-center-inhibitory surround
• Inhibitory-center-excitatory surround

Front 121

Center-Surround Antagonism

Back 121

- Output of center-surround receptive fields
changes depending on area stimulated:
– Highest response when only the excitatory
area is stimulated
– Lowest response when only the inhibitory
area is stimulated
– Intermediate responses when both areas
are stimulated

Front 122

The receptive field of a neuron

Back 122

- The Receptive Field of a visual neuron is the
small area on the retina which, when
stimulated, influence the firing rate of this
visual neuron

Front 123

Why are the receptive fields of retinal ganglion
cells so important ?

Back 123

• All the visual information that the eye sends to the brain is (must be) encoded in the responses (i.e. trains of action potentials or spikes) of these retinal ganglion cells.
• Their RFs capture and enhance certain properties in the retinal image.
- The RFs of retinal ganglion cells are fundamental for understanding our perception of colour, luminance, contrast & edges and lightness & darkness.

Front 124

Pathway from Retina to Cortex

Back 124

Signals from the retina travel through the
optic nerve to the:
1) Lateral geniculate nucleus (LGN)
2) Primary visual receiving area in the
occipital lobe (the striate cortex)
3) And then through two pathways to the
temporal lobe and the parietal lobe
4) Finally arriving at the frontal lobe

Front 125

Other neurons in the visual cortex

Back 125

Complex cells
– Like simple cells
• Respond to bars of light of a particular
orientation
– Unlike simple cells
• Respond to movement of bars of light in
specific direction

Front 126

Neurons in Striate Cortex

Back 126

End-stopped cells
– Respond to:
• Moving lines of specific length
• Moving corners or angles
– No response to:
• Stimuli that are too long

Front 127

Feature Detectors

Back 127

• Neurons that fire to specific features of a
stimulus
• Pathway away from retina shows neurons
that fire to more complex stimuli
• Cells that are feature detectors:
– Simple cortical cell
– Complex cortical cell
– End-stopped cortical cell

Front 128

Optical Nerve Fibre (Ganglion Cell)

Back 128

- Center-surround receptive field.

- Responds best to small spots, but will also respond to other stimuli.

Front 129

Simple Cortical Cell

Back 129

- Excitatory and inhibitory areas arranged side by side.

- Responds best to bars of a particular orientation.

Front 130

Complex Cortical Cell

Back 130

- Responds best to movement of a correctly oriented bar across the receptive field.

- Many cells respond best to a particular direction of movement.

Front 131

End-Stopped Cortical Cell

Back 131

- Responds to corners, angles or bars of a particular length moving in a particular direction.

Front 132

What makes a sound ?

Back 132

Two definitions of “sound”
– Physical definition - sound is pressure changes in
the air or other medium.
– Perceptual definition - sound is the experience
we have when we hear.

Front 133

The two components of a pure sound wave

Back 133

1. Amplitude – the difference between the baseline pressure and the peak or the trough in air pressure.
2. Wavelength – the time difference between two adjacent peaks.

Front 134

Amplitude

Back 134

• The amplitude determines the loudness of a tone.
• Amplitude is the difference between the high and the low pressure regions in a sound wave.

Front 135

Frequency

Back 135

• Frequency = 1/Wavelength.
It determines the perceived pitch.
• Two different pure tones will have two different
frequencies.

• A tone’s frequency is measured in units called
Hertz (Hz) where 1 Hz = 1 cycle per second.

Front 136

Timbre & Overtones

Back 136

• We can tell a guitar from a piano or a clarinet
by the combination of their overtones:- the
unique components of their complex sound
waves whose frequencies are multiples of the
fundamental frequency of each tone.

Front 137

The Outer ear

Back 137

– Pinna helps with sound location (more
later).
– Auditory canal - tube-like 3 cm long
structure
• It protects the tympanic membrane at
the end of the canal.

Front 138

The Middle Ear

Back 138

• Two cubic centimeter cavity separating inner from outer ear
• It contains the three ossicles:
– Malleus (Hammer) - moves due to the vibration of the tympanic membrane
– Incus (Anvil) - transmits vibrations of malleus
– Stapes (Stirrup) - transmit vibrations of incus to the inner ear via the oval window of the cochlea.

Front 139

Function of Ossicles

Back 139

• Outer and inner ear are filled with air.
• Inner ear is filled with fluid that is much
denser than air.
• Pressure changes in air transmit poorly into
the denser medium.
• Ossicles act to amplify the vibration for better
transmission to the fluid.

Front 140

Transduction by the Hair Cells

Back 140

• Movement of a bundle of cilia in different directions changes the firing rate of an auditory neuron.
• Movement of the bundle towards the tallest one causes an increase in the firing rate of an auditory neuron.
• Movement in the other direction causes a decreases in the firing rate of the neuron.

Front 141

Place Coding (High to Middle Frequencies)

Back 141

• High and middle frequency are represented at
different locations (places) on the basilar
membrane
• Their loudness is represented by the
amplitude of the vibrations.

Front 142

Coding of low frequencies

Back 142

• In this case, the basilar membrane actually follows the vibrations and the rate of firing of auditory neurons changes with the frequency of vibration.
• i.e. Not “Place coding” but Temporal- (or Rate-)
coding.
• Loudness of low frequency sounds is represented by “how many” auditory hair cells are active.

Front 143

Summary of Auditory Transduction

Back 143

• Vibrations of the oval window by the 3 ossicles cause movement of the fluid in the cochlea and of the basilar membrane.
• The basilar membrane moves relative to the tectorial membrane and the “bending” of the cilia of hair cells depolarises (excites) them.
• The hair cells cause neurons in the auditory nerve to fire and they are connect to the brain (Auditory Cortex).
• Low (less than 200Hz) are coded differently to medium and high- frequencies (Anatomical vs Temporal codes).

Front 144

Locating the source of a sound

Back 144

• Left vs. Right (azimuth):
1. Intensity Differences
2. Time of Onset Differences
3. Phase Differences
• Front vs. back: Timbre Differences

Front 145

The three main somatosenses

Back 145

1) Cutaneous sense
• Sensitivity to stimuli that involve the skin.
• e.g. pressure, vibration, heating/cooling, and
events that cause tissue damage (i.e. pain).
2) Organic (internal) sense
• A sense modality that arises from receptors
located within the inner organs of the body.
• Proprioception - ability to sense position of the
body and limbs
3) Vestibular
• Perception of the body’s balance.

Front 146

Types of Cutaneous receptors

Back 146

Free nerve endings:
• Found in both hairy and non-hairy skin (e.g. on the palms and soles of feet).
• In hairy skin, they surround the hair follicles.
Other specialised receptors:
• Detection of touch, stretch, warmth or coolness.

Front 147

Cutaneous System

Back 147

• Skin - heaviest organ in the body:
– Protects the organism by keeping damaging
agents from penetrating the body.
– Epidermis is the outer layer of the skin, which
is made up of dead skin cells.
– Dermis is below the epidermis and contains
mechanoreceptors that respond to stimuli
such as pressure, stretching, and vibration.

Front 148

Mechanoreceptors (Close to surface of skin)

Back 148

– Merkel receptor fires continuously while
stimulus is present.
• Responsible for sensing fine details
– Meissner corpuscle fires only when a
stimulus is first applied and when it is
removed.
• Responsible for controlling hand-grip

Front 149

Mechanoreceptors (Deeper in skin)

Back 149

– Ruffini cylinder fires continuously to
stimulation
• Associated with perceiving stretching of the
skin
– Pacinian corpuscle fires only when a stimulus is first applied and when it is removed.
• Associated with sensing rapid vibrations and
fine texture

Front 150

Somatosenses (Internal Senses)

Back 150

• Sensory endings located in our internal organs,
bones and joints. e.g. receptors in the muscles &
tendons protect against possible damage from
strain.
• Specialised receptors include, muscle spindles
that detects changes in muscle length and
mechanoreceptors that respond to the movement and the angles of our joints.
• Those sensations are called Proprioception: our
sense of body position and movement

Front 151

Anatomy of the vestibular apparatus

Back 151

Vestibular sac
- One of a set of two receptor-organs in each inner ear that detects changes in the tilt of the head.
Semicircular canal
- One of the three ring-like structures of the vestibular apparatus that detect changes in head rotation in any direction.

Front 152

The Chemosenses

Back 152

1. Gustation = Taste
2. Olfaction = Smell

Front 153

The Taste System

Back 153

• Sweetness is usually associated with
substances that have nutritive value.
• Bitter is usually associated with substances that
are potentially harmful.
• Salty taste indicates the presence of sodium.
• However, there is not always a perfect
connection between tastes and function of
substances.

Front 154

Five basic taste qualities

Back 154

– Salty
– Sour
– Sweet
– Bitter
– Umami - described as meaty, brothy or
savory and associated with MSG

Front 155

Structure of the Taste System

Back 155

• Tongue contains different papillae:
• Filiform - shaped like cones and located
over entire surface – no taste buds.
• Fungiform - shaped like mushrooms and
found on sides and tip
• Foliate - series of folds on back and sides
• Circumvilliate - shaped like flat mounds in
a trench located at back

Front 156

Taste Buds

Back 156

• Taste buds are located in papillae except for
filiform.
• The entire tongue contains approximately
10,000 taste buds.
• Each taste bud has 50-100 taste cells with
tips that extend into the taste pore.
• Transduction occurs when chemicals
contact the receptor sites on the tips.

Front 157

Tongue

Back 157

- The receptor sheet for taste. Contains papillae, taste buds, taste cells, and receptor sites.

Front 158

Taste Cells

Back 158

- Cells that make up a taste bud. There are a number of cells for each bud, and the tip of each one sticks out into a taste pore. One or more nerve fibres are associated with each cell.

Front 159

Tongue Receptor Sites

Back 159

Sites located on the tips of the taste cells. There are different types of sites for different chemicals. Chemicals contacting the sites cause transduction by affecting ion flow across the membrane of the taste cell.

Front 160

The neural pathway from tongue to brain

Back 160

Receptor cells send information
through 3 different nerves:
1) The Facial nerve
2) The Glossopharyngeal
3) The Vagus

• All three converge on the Solitary Nucleus in the
Medulla, and then project to the Ventral posterior nucleus in the Thalamus (ref relay).
• From the Thalamus, neurons project to the Primary- and Secondary Gastatory cortex.

Front 161

The olfactory apparatus

Back 161

Olfactory mucosa
• The mucus membrane that contains the cilia of
the olfactory receptors. The membrane is located at the roof of the nasal sinus, just under the base of the brain.
Olfactory bulbs
• The structures at the base of the brain, containing the neural circuits that process olfactory information. These neurons receive information directly from the axons of the olfactory receptors.

Front 162

Functions of Olfaction

Back 162

• Many animals are macrosmatic - having a
keen sense of smell that is necessary for
survival
• Humans are microsmatic - a less keen sense
of smell that is not crucial to survival

Front 163

Detecting Odors – Sensitivity

Back 163

• Rats are 8 to 50 times more sensitive to
odors than humans.
• Dogs are 300 to 10,000 times more sensitive.
• However, individual receptors for all of these
animals are equally sensitive.
• The difference lies in the number of receptors
they each have.
– Humans have ten million and dogs have
one billion olfactory receptors.

Front 164

Identifying Odors - Recognition

Back 164

• Recognition threshold - concentration needed
to determine quality of an odorant
• Humans can discriminate among 100,000
odors, but they cannot label them accurately.
• This appears to be caused by an inability to
retrieve the name from memory, not from a
lack of sensitivity.

Front 165

The Perception of Flavor

Back 165

• Combination of smell, taste, and other
sensations (such as burning of hot peppers
with ref to the body senses)
• Odor stimuli from food in the mouth reaches
the olfactory mucosa through the retronasal
route.
• The taste of most compounds is influenced by
olfaction, but a few, such as MSG are not.

Front 166

Orbital Frontal Cortex (OFC)

Back 166

• Responses from taste and smell are first
combined in the orbital frontal cortex (OFC).
• OFC also receives input from the primary
somatosensory cortex and the inferotemporal
cortex in the visual “what” pathway.
– Bimodal neurons in this area respond to
taste and smell, as well as taste and vision.
– Firing of these neurons is also affected by
the level of hunger of the animal for a
specific food.