Sensory Receptors

Receptors

• There are millions of receptors all over the body. Receptors may be simple naked nerve endings, encapsulated nerve endings or complex structures.

• Receptors detect stimuli (internal or external) & convert them to nerve impulses

The sensory receptors

Each sensory system has three component parts:

1)Sensory receptors which are the branched endings of sensory neurons or specialized cells adjacent to them that detect specific stimuli.

2)Nerve pathways lead to the brain.

3)Brain regions process the information into a sensation; later, perhaps, a perception (understanding) of the sensation will be made.

How does a sensory receptor work?

• Some sensory receptors are activated when they are bent, squished, or disturbed in some way.

• Others are activated by chemicals. • Others by temperature. • And others by light. • Whatever the outside world influence is, we

can call it a stimulus for the receptor

• Whatever the appropriate stimulus is, that will cause a depolarization to occur in the sensory receptor cell

• The depolarization within the sensory dendrite itself (due to the stimulus) is called a receptor potential

• When the dendrite is deformed, its membrane stretches, and ions can flow through the stretch-gated channels. If this occurs enough, there will be enough of a receptor potential to trigger an action potential.

In summary

Sense of touch• Touch may be considered one of

five human senses; however, when a person touches something or somebody this gives rise to various feelings: the perception of pressure (hence shape, softness, texture, vibration, etc.), relative temperature and sometimes pain.

• The term "touch" is usually replaced with somatic senses, to better reflect the variety of mechanisms involved

• Free nerve endings are simply branched endings of sensory neurons in the skin that function as mechanoreceptors, thermoreceptors, and pain receptors.

• Meissner corpuscles adapt slowly to vibrations of low frequencies.

• The bulb of Krause is a thermoreceptor that is sensitive to temperatures below 20 degrees C.

• Ruffini endings are sensitive to steady touching and pressure, and to temperatures above 45 degrees C.

• Pacinian corpuscles are located both in the dermis and near joints; they are able to detect rapid pressure changes associated with touch and vibrations.

Sense of vision• Vision requires a complex

system of photoreceptors and neural program in the brain that can interpret the patterns of action potentials

• All photoreceptors incorporate pigment molecules that can absorb photon energy, which can be converted into excitation energy in sensory neurons.

• The photoreceptors are located in the retina

Results

1.Normal Color Vision: A: 29, B: 45, C: --, D: 26

2. Red-Green Color-Blind: A: 70, B: --, C: 5, D: --

3.Red Color-blind: A: 70, B: --, C: 5, D: 6

4.Green Color-Blind: A: 70, B: --, C: 5, D: 2

Sense of hearing• Hearing is the perception of sounds, which

are traveling vibrations of mechanical energy

Hearing test

• Normal human hearing ranges from 20 Hz to 20 kHz

• A gradual decline with age is considered normal

The middle ear contains small bones with amplify the soundsbefore transmittal to the inner ear.

The external ear in mammals has a pinna for collecting the sounds.

In the cochlea of the inner ear, acoustical receptors in theform of hair cells respond to pressure waves transmitted through the surrounding fluid.

• Impulses are sent along the auditory nerve to the brain for interpretation.

• The hair cells of the human ear can be permanently damaged by prolonged exposure to intense sounds

Sense of smell• Olfactory receptors are

responsible for our sense of smell.

• They respond to a variety of odour molecules

• Humans have about 5 million olfactory receptor neurons

• Olfactory receptor neurons reside on the olfactory epithelium in the nasal cavity

Sense of taste• Taste receptors enable

animals to distinguish nutritious from noxious substances.

Receptors of some animals are located on antennae, legs, tentacles, or fins.

In humans, taste receptors are often components of taste buds distributed mostly on the tongue.

Questions

• What are receptors?• What are the three components of the sensory

system?• How many sense do we humans have? Five or more?

Name them• How does a sensory receptor work? (Brief description)• What is the name of the receptor involved in your

sense of smell?• Where are the sense of taste receptors located in the

human body?