Lecture 21Major Senses

Sensory Perception

The sensory nervous system tells the central nervous system what’s happenin’!

Sensory receptors Specialized sensory cells

that detect changes inside and outside the body

Sensory organs Complex sensory

receptors

Eyes, ears, taste buds

The path of sensory information

1. Stimulation Physical stimulus activates a sensory receptor

2. Transduction Converting the stimulus into an action potential

Stimulus-gated ion channels in sensory neuron are opened or closed

An action potential is generated

3. Transmission Nerve impulse is conducted to the CNS

Two main types of sensory receptors Extroreceptors sense stimuli in external environment Introreceptors sense stimuli in internal environment

Vertebrates use many different sensory receptors to respond to changes in internal environment

Temperature Change Two nerve endings in the skin

One stimulated by cold, the other by warmth

Blood chemistry Receptors in arteries sense blood CO2 levels

Pain Special nerve endings within tissues near the surface

Sensing the Internal Environment

Sensing Pressure & Strectch

Muscle contraction Sensory receptors called

proprioceptors embedded within muscle & tendons sense stretch of muscle

Touch Pressure receptors

buried below skin

Blood pressure Neurons called

baroreceptors in major arteries

Sensing Chemicals: Taste

Taste

Taste buds are located in raised areas called papillae

Food chemicals dissolve in saliva and contact the taste cells

Sensing Chemicals: Smell

SmellOlfactory receptor cells are embedded in the epithelium of the nasal passage

These are far more sensitive in dogs than in humans

Lateral Line and the fish’s sense of hearing

Fish are able to sense objects that reflect pressure waves and low-frequency vibrations

The system consists of canals running the length of the fish’s body under the skin

Canals have sensory structures containing hair cells projecting into a gelatinous cupula

Vibrations produce movements of the cupula

Hair cells bend and depolarize associated sensory neurons

Evolution of Balance & Hearing

Human Sensation of Gravity and Motion

Receptors in the ear inform the brain where the body is in three dimensions

Motion Motion is detected by the deflection of hair cells by fluid in a

direction opposite to that of motion These hair cells are found in the cupula, tent-like assemblies in

the three semicircular canals

Balance Gravity is detected by shifting of

otolith sensory receptors These are located in a

gelatin-like matrix in the utricle and saccule chambers of the inner ear

Properties of Sound

Amplitude – intensity of a sound measured in decibels (dB) Loudness – subjective interpretation of sound intensity

Sound is: A pressure disturbance (alternating areas of high and low pressure)

originating from a vibrating object Composed of areas of rarefaction and compression Represented by a sine wave in wavelength, frequency, and amplitude

Frequency – the number of waves that pass a given point in a given time Pitch – perception of different frequencies (we hear from 20–20,000 Hz)

Sensing Sounds: Hearing

When a sound is heard, air vibration is detected

Eardrum membrane is pushed in and out by waves of air pressure

Three small bones (ossicles) located on other side of eardrum increase the vibration force

Amplified vibration is transferred to fluid within the inner ear

Inner ear chamber is shaped like a tightly coiled snail shell and is called cochlea

Sensing Sounds: Hearing

Cochlea are hair cells that rest on a membrane running up and down the chamber They are covered by another

membrane

Sound waves entering the cochlea cause this membrane “sandwich” to vibrate Bent hair cells send nerve

impulses to brain

Pitch is determined by different frequencies causing different parts of the membrane to vibrate Different sensory neurons are

fired

Sound intensity is determined by how often the neurons fire

PLAY Transduction of Sound Waves

The Evolution of Vision

Vision begins with the capture of light energy by photoreceptors

Many invertebrates have simple visual systems Photoreceptors are clustered in an

eyespot Perceive light direction but not a

visual image

Members of four phyla have evolved well-developed, image-forming eyes Annelids Mollusks Arthropods Vertebrates

The eyes are strikingly similar in structure but are believed to have evolved independently

Eyes in Three Phyla of Animals

The vertebrate eye works like a lens-focused camera

Structure of the Vertebrate Eye

Cornea – Transparent covering that focuses light

Lens – Completes the focusing

Ciliary muscles – Change the shape of the lens

Iris – Shutter that controls amount of light

Pupil – Transparent zone

Retina – The back surface of the eye Contains two types of

photoreceptors: rods and cones Fovea – Center of retina

Produces the sharpest image

Rods are extremely sensitive to dim light Cannot distinguish colors Do not detect edges Produce poorly defined

images

Cones can detect color Detect edges well Produce sharp images

How Rods and Cones Work

How Light is Converted to a Nerve Impulse

Pigment in rods and cones are made from carotenoids

cis-retinal is attached to a protein called opsin This light-gathering complex is called rhodopsin

When light is absorbed by cis-retinal, it changes shape to trans-retinal

This induces a change in the shape of the opsin protein

A signal-transduction pathway is initiated leading to generation of a nerve impulse

Three kinds of cone cells exist, each with its own opsin type

Differences in opsin shape, affect the flexibility of the attached cis-retinal

Color Vision

420 nm – Blue530 nm – Green560 nm – Red

This shifts the wavelength at which it absorbs light

Colorblindness is a condition in which a person cannot see all three colors

Colorblindness

Caused by a lack of one or more types of cones

It is inherited as a sex-linked trait and is more likely to affect males

Rods and cones are at the rear of the retina, not front! Light passes through

four types of cells before it reaches them

Photoreceptor activation stimulates bipolar cells, and then ganglion cells

Nerve impulse travels through the optic nerve to the cerebral cortex

Conveying the Light Information to the Brain

Focusing the Eye

Focusing for Distant Vision: Light from a distance needs little

adjustment for proper focusing Far point of vision – the distance

beyond which the lens does not need to change shape to focus (20 ft.)

Focusing for Close Vision: Accommodation – changing the

lens shape by ciliary muscles to increase refractory power

Constriction – the pupillary reflex constricts the pupils to prevent divergent light rays from entering the eye

Convergence – medial rotation of the eyeballs toward the object being viewed

Problems of Refraction

Normal eye (Emmetropic) – with light focused properly Nearsighted (Myopic) – the focal point is in front of the retina

Corrected with a concave lens Farsighted (Hyperopic) – the focal point is behind the retina

Corrected with a convex lens

Muscles That Move the Eye

Six strap-like extrinsic eye muscles Enable the eye to follow moving objects Maintain the shape of the eyeball

Four rectus muscles originate from the annular ring Two oblique muscles move the eye in the vertical plane

Primates and most predators have eyes on front of the head

The two fields of vision overlap allowing the perception of 3-D images and depth

Prey animals generally have eyes located on sides of the head

This prevents binocular vision but enlarges the perceptive field

Binocular Vision

Lacrimal Apparatus

Consists of the lacrimal gland and associated ducts

Lacrimal glands secrete tears

Tears Contain mucus, antibodies,

and lysozyme Enter the eye via lacrimal

excretory ducts Exit the eye medially via the

lacrimal punctum & lacrimal canal

Drain into the nasolacrimal duct

Other Types of Sensory Reception

Heat

Pit vipers can locate warm prey, using infrared radiation

Heat-detecting pit organs

Electricity

Used by aquatic vertebrates to locate prey and mates

Magnetism

Eels, sharks and many birds orient themselves in relation to the Earth’s magnetic field