Sensation Chapter 46

Natasha McDougal and Kaleb Hood

Background and Purpose

Nerve impulses occur because of a change in action

potential

Graded potentials in the dendrites and cell body can

have either temporal or spatial summation

The purpose of this chapter is to discuss how sensory

receptors change sensory stimuli into nerve signals that

are conveyed to the nervous system and work through

the functions listed above

Types of Receptors

Mechanoreceptors

Detects mechanical compression or stretching of the receptor or

of tissues adjacent to the receptor

Thermoreceptors

Detect changes in temperature with some receptors detecting

cold and others warmth

Nociceptors (pain receptors)

Detect damage occurring in the tissues, either physical or

chemical

Types of Receptors

Electromagnetic Receptors

Detect light on the retina of the eye

Chemoreceptors

Detect taste in the mouth, smell in the nose, oxygen level in the

arterial blood, osmolality of the body fluids, carbon dioxide

concentration, and other chemical factors of the body

Classes of Receptors (Table 46-1)

Mechanoreceptors

Skin Tactile Sensibilities

Free Nerve Endings

Expanded Tip Endings

Merkel’s discs

Several other variants

Spray Endings

Ruffini’s Endings

Encapsulated Endings

Meissner’s corpuscles

Krause’s corpuscles

Hair End-organs

Deep Tissue Sensibilities

Free Nerve Endings

Expanded Tip Endings

Classes Of Receptors

Equilibrium

Vestibular Receptors

Arterial Pressure

Baroreceptors of carotid

sinuses and aorta

Thermoreceptors

Cold

Cold Receptors

Warmth

Warm Receptors

Deep Tissue Sensibilities (cont’)

Ruffini’s Endings

Encapsulated Endings

Pacinian corpuscles

Plus a few other variants

Muscle endings

Muscle Spindles

Golgi tendon receptors

Hearing

Sounds Receptors of Cochlea

Classes Of Receptors

Nociceptors

Pain

Free Nerve Endings

Electromagnetic Receptors

Vision

Rods

Cones

Chemoreceptors

Taste

Receptors of Taste Buds

Smell

Receptors of olfactory epithelium

Arterial Oxygen

Receptors of Olfactory Epithelium

Osmolality

Neurons in or near supraoptic

nuclei

Blood CO2

Receptors in or on surface of

medulla and in aortic and carotid

bodies

Blood Glucose, amino acids, fatty

acids

Receptors in hypothalamus

Specialization of Sensory Receptors

Differential Sensitivities

Each receptor is sensitive to one type of stimulus and

nonresponsive to other types

Labeled Line Principle

Each nerve fiber transmits only one modality of sensation

Receptor components of sensory receptors are dendrites

Receptor Potential

Regardless of the type of stimulus receptor potentials all

have the immediate effect of changing the membrane

electrical potential of the receptor.

Ways to cause receptor potentials:

1. Mechanical deformation of the receptor

Stretches the membrane and opens ion channels

2. Application of a chemical to the membrane

Opens ion channels

Receptor Potential

3. Change of the temperature of the membrane

Alters membrane permeability

4. Electromagnetic Radiation

Directly or indirectly changes the receptor membrane characteristics and

allows ions to flow through membrane channels

All result in changes to the transmembrane potential by changes in

membrane permeability

Receptor action potentials are graded

Allows sensitivity to weak signals

Receptors do not reach a maximum firing rate until signals are very intense

Receptor Potential and Action Potentials

When receptor potential

rises above threshold it

elicits an action potential

in the nerve fiber

The more that the

receptor potential rises

above threshold level the

greater the action

potential frequency

Figure 46-2

Clicker Question

Receptor potentials are caused by:

A.Mechanical Deformations

B.Chemical Application

C.Temperature Change

D.Electromagnetic Radiation

E. All of the Above

Signal Transduction in Nerves

Spatial Summation

Signal strength is increased by

stimulation of more fibers

Each individual nerve is a free nerve ending

Together, these create a receptor

field

Signals are stronger at the center

of the field

Strong signals will spread to more

fibers

Temporal Summation

Frequency of stimulation affects

the strength of the stimulus

Signal Transduction in Nerves

Figure 46-7

Signal Transduction in Nerves

Figure 46-8

Clicker Question

True or False:

In spatial summation signal strength is

decreased by the stimulation of more fibers

Receptor Adaptation

Sensory receptors will adapt partially or completely to a

constant stimulus

Various receptors adapt at different rates, some very

quickly and some barely at all

Some sensory receptors are “nonadapting” receptors

Adaptation of receptors is an individual quality

Receptor Adaptation

In mechanoreceptors adaptation occurs two ways:

1. Physical changes reducing stimulation

2. Accommodation

Changes to nerve fibril that inactivate sodium channels

Tonic receptors detect continuous stimulus strength

Phasic receptors detect changes as they are actually

taking place

Receptor Adaptation

Figure 46-5:

Adaption of different types of

receptors, showing rapid

adaption of some receptors and

slow adaption of others.

Pacinian Corpuscle An example of a sensory receptor

• Capsule layers can be

compressed or altered in many

ways

• Once compressed, ion channels

are opened to sodium

• This creates a local circuit

• This leads to the standard action

potential signals to the central

nervous system

• The corpuscle is not myelinated,

but soon after the central nerve

leaves it becomes that way

Clicker Question

True of False:

Sensory receptors are not myelinated.

Figure 46-3

Figure 46-4