6 - 1 © 2000 Pearson Education Canada Inc.,Toronto, Ontario Sensation Lectures # 6 & 7 Biology of Behaviour Sensory I

Sensation 6 - 1 © 2000 Pearson Education Canada Inc.,Toronto, Ontario

Lectures # 6 & 7Biology of Behaviour Sensory I


Control of Internal Functions and Automatic

Behaviour

The Brain Stem: controls automatic behaviours (breathing, blood pressure etc)

The Cerebellum: coordinates and learns movement

Structures within the Cerebral Hemispheres: involved in cognition, sensations and reactions to them


The Brain Stem and Cerebellum

F 4.30


Glandular Structures involved in behaviour

F 4.31


Sensation

1. Vision2. Audition3. Gustation4. Oflaction5. The Somatosenses


Basic Principles of Sensory information Processing•A signal (light, odour, movement etc) from the environment is transformed by a sensory organ into action potential.

•Usually a graded stimulus is encoded by the brain…. varying the number and frequency of action potentials (APs).

•The APs travel in anatomically distinct nerve pathways that define the nature of the sensation

Most sensory information (APs) is relayed through a large brain area called the thalamus which is then passed on to the appropriate area in the cerebral cortex


Principles of sensory information: Basics of signal transduction spinal

cordF 4.13

Sensory information relayed by the spinal cord travels discreet anatomically defined nerve tracks (columns) that are specific the type of information (pain, touch position sense) The APs traverse the spinal cord and travel in the opposite side from which the information was received

Once in the brain the signals arrive in anatomically discreet regions of the thalamus

The thalamus then relays the information to anatomically discreet regions of the cortex


Organization of the Cerebral CortexF 4.24


Structures within the HemispheresF 4.33


Sensory Processing

Transduction

Psychophysics


TransductionLocation of Sense Organ

Environmental Stimuli

Energy Transduced

Eye Light Radiant Energy

Ear Sound Mechanical Energy

Vestibular System Tilt and Rotation Mechanical Energy

Tongue Taste Recognition of Molecular Shape

Nose Odour Recognition of Molecular Shape

Skin, Internal Organs

Touch Mechanical Energy

Temperature Thermal Energy

Vibration Mechanical Energy

Pain Chemical Reaction

Stretch Mechanical Energy

T 6.1


Vision

Light The Eye and Its Functions Transduction of Light Eye Movements Colour Vision


Basic Wave Physics (What is light?) F 6.6

Waves come in many sizes and frequencies but all are rhythmic fluctuations electromagnetism

They travel at the speed of “light” which is 298,000 km/sec

This is constant so if the frequency is 88.5 MHz (Mega = 1,000,000)

Then the wavelength is: 298,000,000(metres/sec)

88,500,000 (cycles /sec)

= 3.38 metres/cycle

These are radio waves what happens as the wavelength shortens?


Light

F 6.7

1 nanometre = 1 billionth a metre (10-9metres)

So visible light has a wavelength of about 400 nm (violet) to 750 nm (red)

So how do our eyes work to see this electromagnetic radiation?


The Eye and Its FunctionsF 6.8cornea: transparent

tissue that covers the front of the eye

iris: a formation of muscle that forms a circle with a hole in middle ; it controls the amount of light that enters the lens

lens: is transparent flexible tissue that focussed the light entering the on retina

retina: layer of tissue at the back of the eyeball that contains specialized cells that can sense the light


The Eye and Its Functions

F 6.12

Organisation of the retina

There are many different types of cells (all basically neurones) that make up the retina

Photoreceptors: convert light into chemical energy that releases neurotransmitter onto bipolar cell.

Bipolar cell fire action potentials to release neurotransmitter that excite ganglion cell.

Ganglion cells axons make-up the optic tract that then make synapsesin the thalamus.


Basic Light Sensory Physiology

Light is transformed into chemical energy by receptors (analogous to neurotransmitter receptors) on two types of cells either a cone (colour vision) or a rod (high sensitivity but colour blind)

The bipolar cells are excited by the reduction in inhibitory neurotransmitter than is constantly being released.

The bipolar cells then release excitatory neurotransmitter and the ganglion cell is excited


Transduction of Light by Photoreceptors

F 6.13


Colour Vision

F 6.16

White light is can be divided into a full spectrum of colour

Our eyes detect different wavelengths and then combine this colour in our brains in order to complete our perception our surroundings

There are three different kinds of cones: red green and yellow

This means that each cone is maximally stumulated when light of certain wavelength strikes it.


Colour Vision

F 6.17

But colour vision is not like mixing paint Mixing red, green and yellow light makes a perception of white

While mixing the same colours of paint results in a dull grey or black pigment


Colour VisionF 6.18

Three kinds of responses

Two kinds of wiring

Cells that are excited by red light but inhibited by green light (and vice versa)

Cells that are excited by yellowlight but inhibited by blue light

pure red wave length pure green wavelength

Yellow stimulates both red and green cones


Colour Vision

F 6.15

Rods

become

more

important

Cones become more important


Audition

Sound

The Ear and its Functions

Detection and Localizing Sounds


Sound

F 6.21

Sounds waves are not electromagnetic phenomena but are alterations in air pressure

Nevertheless these alterations in air pressure deform the ear drum so as to mechanically stimulate actions potentials in the auditory system


Sound

F 6.22


The Ear and Its Functions

F 6.23


The Ear and Its FunctionsF 6.24


The Ear and Its Functions

F 6.25


Detecting and Localizing Sounds

F 6.27

Sound is less loud because air pressure changes have been blunted by head therefore we learn that direction of sound is on the same side of head where it is louder


Detecting and Localizing Sounds

F 6.28

Sound in front synaptic delay equals zero

Synaptic activation has delay that is equal to the time that it takes for sound to travel from one side of head to other this is relatively short about about 1 ms or 2 ms


Gustation

Receptors and the Sensory Pathway

The Four Qualities of Taste


The Four Qualities of TasteF 6.30


Receptors and the Sensory Pathway

F 6.29


Olfaction

Anatomy of the Olfactory System


Anatomy of the Olfactory System

F 6.31


Combining gustation and olfaction gives us our sense of “taste”

Odours or flavour results from combining the activation of hundred of receptors in the olfactory tract but….

Sour sweet, bitter and salty comes from just four different receptors on the tounge


The Somatosenses

The Skin Senses


Compartmentalisation of Function

F 4.28


The Skin Senses

F 6.32


The Skin Senses

F 6.33


Representation of the sensations in the cortex are not anatomically proportional

Our faces and hand make by far the most connection to the cortex while other larger areas (trunk) have only a relatively small representation


PsychophysicsF 6.2

Documents

6 - 1 © 2000 Pearson Education Canada Inc.,Toronto, Ontario Sensation Lectures # 6 & 7 Biology of Behaviour Sensory I