Sensory receptors

• What are the general functions of receptors?

• Reception

• Transduction

• Amplification

• Transmission

• Integration

Types of Receptors

• Mechanorecpetors – stimulated by mechanical energy

• Chemoreceptors – detect solute concentration differences

• Electromagnetic receptors – detect forms of electromagnetic energy

• Thermoreceptors – respond to hot or cold

• Pain receptors – naked dendrites in dpidermis of skin

Touch

• Sensory receptors in the skin receive the touch stimulus

• Mechanoreceptors in human skin are in the form of naked dendrites

• Prostaglandins intensify the pain by sensitizing the receptors

Taste and Smell• Chemoreceptors sense chemicals in the

environment

• Olfactory receptors line nasal cavity

• Taste receptors respond to specific stimuli (sugar/ salt)

• Taste and smell are functionally similar:– Molecule dissolves in liquid to reach

receptor– Head cold interferes with taste perception

Vision

• Eye cup in planaria

• Compound eye in insects

• Vertebrate eye

• Vertebrate eye and focusing mechanisms

Photoreceptors• Cones – color vision, used in daytime,

found at center (fovea) – Photopsins as visual pigment– Known as red, blue and green cones

• Rods – more sensitive to light, don’t distinguish color– Visual pigment rhodopsin– Rods absorb light shape change causes

signal transduction pathway that leads to receptor potential in rod cell membrane

What sort of neuro-transmitters must be released from the rod cell to neurons in the dark?

Why are you temporarily blinded when you enter a dark movie theatre on a sunny day?

• Visual integration:

• Receptive fields feed information to one ganglion cell

• Larger receptive fields result in a less sharp image

• Ganglion cells of fovea have small receptive fields

• Left side of brain receives information from right visual field

• Right side of brain receives information from left visual field

• Feeds information to lateral geniculate nucleus

• These nuclei relay information to visual cortex (in cerebrum)

• Where do you actually see?

                                                             

The Human Ear

Where are sound waves

collected?

What is the role of the eustachian

tube?

How are the sound waves conducted to the

inner ear?

This cross section of the cochlea shows 3 canals

Transduction of the impulse occurs in cochlea as wave vibrations are converted to membrane potential

Explain how the action potential is generated

Organ of Corti and Tectorial Membrane

Describe how the cochlea distinguishes pitch.

Where is pitch perceived?

How do the structures of the inner ear help to distinguish body movements?

Why do you struggle with balance after spinning around for a few minutes?

Movement

• Different amounts of energy are expended on different means of transport

• Skeletons:• Hydrostatic skeleton allows for

peristaltic movement• Exoskeleton seen in arthropods• Endoskeleton seen in chordates…

Muscles and Skeletons

• What are ligaments?

• Join bone to bone

• What are tendons?

• Join muscle to bone

• How do muscles cooperate in movement if they can only contract?

Skeletal muscles

Sliding filament theory

As the muscle contracts which

muscle bands stay the same and which

get smaller?

Control of Muscle

Contraction

Why isn't the muscle always

contracting?

T Tubule Contraction

What neuro-transmitter initiates the muscle contraction?

Graded Contraction• Contractions of muscle fibers are all or

none• How does the nervous system produce

graded muscle contractions?– Vary the frequency of action potentials– Rate of stimulation that is very fast results

in tetanus

• Motor units = single motor neuron and all of the muscle fibers it controls

• The neuron can cause many muscle fibers to contract at the same time

Other Vertebrate Muscles

• Smooth muscle :– Lacks striations– Has less myosin than skeletal muscle– Found in walls of hollow organs (e.g. digestive

tract organs)

• Cardiac Muscle:– Structurally similar to skeletal muscle– Differs in action potential generation:

• Action potentials spread throughout the heart through direct contact between cells