Transcript Sensory Receptors

LAB EXERCISE 18
GENERAL SENSES
Sensory Information

Afferent Division of the Nervous
System
– Receptors
– Sensory neurons
– Sensory pathways


Spinal cord to brain
Deliver somatic and visceral
sensory information to their final
Sensory
processing
centers in
brain
Sensory
pathways
destinations inside the CNS using:
– Nerves
– Nuclei
– Sensory tracts
General
sensory
receptors
Conscious and
subconscious
motor centers
in brain
Higher-Order Functions
Memory, learning, and
intelligence may
influence interpretation
of sensory information
and nature of motor
activities
Sensory Information

Somatic Motor Portion of the Efferent
Division
– Controls peripheral effectors


Skeletal muscle
Somatic Motor Commands
– Travel from motor centers in the
brain along somatic motor
pathways of:

Motor nuclei

Tracts

Nerves
Motor
pathways
Somatic
Nervous
System (SNS)
Skeletal
muscles
Sensory Receptors

General Senses
– Describe our sensitivity to:

Temperature

Pain

Touch

Pressure

Vibration

Proprioception
Sensory Receptors

Special Senses

The Special Senses
– Are provided by special sensory receptors
– Olfaction (smell)
– Vision (sight)
– Gustation (taste)
– Equilibrium (balance)
– Hearing
SENSATION VS PERCEPTION

Sensation
– Occurs when nerve impulses arrive at
the cerebral cortex
 From sensory neurons created by an
action potential.
–Chemoreceptors
–Thermoreceptors
–Nociceptors
–Baroreceptors
– What we are not aware of
SESNSATION VS PERCEPTION
 Perception
–Perception is the conscious
awareness & interpretation of a
sensation
–Occurs when the cerebral cortex
interprets the meaning of
sensations.
We have no perception of some information
because it never reaches the cortex.
Blood pressure is received in the medulla
Sensory Integration


Input comes from
–
Exteroceptors
–
Interoceptors
–
Proprioceptors
Input is relayed toward the
head, and is processed along
the way
Sensory Receptors
1.
Exteroceptors
–
Respond to stimuli arising
outside the body
–
Receptors in the skin

Touch

Pressure

Pain

Temperature
–
Most special sense organs

Vision

Hearing

Equilibrium

Taste

Smell
Sensory Receptors
2.
Interoceptors
**Visceroceptors
– Respond to stimuli
arising in internal
viscera and blood
vessels
– Sensitive to







Chemical changes
Tissue stretch
Temperature changes
Pain
Discomfort
Hunger
Thirst
Sensory Receptors
3.
Proprioceptors
–
Provide a purely somatic sensation
–
Respond to stretch in

Skeletal muscles

Tendons

Joints

Ligaments

Connective tissue coverings of bones
and muscles
– Inform the brain of one’s body movements
– No proprioceptors in the visceral organs of
the thoracic and abdominopelvic cavities

You cannot tell where your spleen,
appendix, or pancreas is at the moment
Processing at the Circuit Level

This level consists of
pathways of three
neurons conduct sensory
impulses upward to the
appropriate brain regions
– First order neurons
– Second order neurons
– Third order neurons
Processing at the Circuit Level

First order
neurons
– Conduct
impulses from
the receptor
level to the
second-order
neurons in the
brain stem or
spinal cord
Processing at the Circuit Level

Second-order neurons
– Transmit impulses to the
 Thalamus
–Tracts cross over
Processing at the Circuit Level

Third-order neurons
– Conduct impulses
from
 The thalamus to
 The
somatosensory
cortex
–Perceptual
level
Processing at the Perceptual Level

The axons of the third order
continue to ascend without
crossing over to the
somatosensory area.
– As a result
Left cerebral hemispheres
receive info from the right
side
 Right cerebral
hemispheres receive info
from the left side

Sensory Receptors
 Learning
Outcomes
15-3 Identify the receptors for the
general senses, and describe
how they function.
Sensory Receptors

General Sensory Receptors
–
Are divided into four types by the nature of the stimulus that
excites them
1. Chemoreceptors
**Chemical concentration
2. Nociceptors
**Pain
3. Thermoreceptors
**Temperature
4. Mechanoreceptors
**Physical distortion
Classifying Sensory Receptors

Nociceptors (Pain Receptors)
– Most concentrated in the superficial portions of the skin
– In joint capsules
– Within the periostea of bones
– Around the walls of blood vessels
Classifying Sensory Receptors

Nociceptors
– Are free nerve endings with large receptive fields
– May be sensitive to:
1.
Temperature extremes
2.
Mechanical damage
3.
Dissolved chemicals, such as chemicals
released by injured cells
*Associated with tissue damage
Type A or Type C
Classifying Sensory Receptors
– Myelinated Type A Nociceptor fibers

Carry sensations of fast pain, or prickling pain,
such as that caused by an injection or a deep cut

Sensations reach the CNS quickly and often
trigger somatic reflexes

Relayed to the primary sensory cortex and receive
conscious attention
Classifying Sensory Receptors
– Type C Nociceptor fibers

Carry sensations of slow pain, or burning and
aching pain

Cause a generalized activation of the reticular
formation and thalamus

You become aware of the pain but only have a
general idea of the area affected
Classifying Sensory Receptors
-Referred pain
“Incorrect" source perceived
*Pain in the forehead when eating ice cream too quick
*Heartburn
*Dentistry
*Angina
–Pain in the arm when the heart does not receive enough oxygen
Classifying Sensory Receptors

Thermoreceptors
– Also called temperature receptors
– Are free nerve endings located in:

The dermis

Skeletal muscles

The liver

The hypothalamus
Classifying Sensory Receptors

Mechanoreceptors
– Sensitive to stimuli that distort their plasma
membranes
– Contain mechanically gated ion channels
whose gates open or close in response to:

Stretching

Compression

Twisting

Other distortions of the membrane
Classifying Sensory Receptors

Three Classes of Mechanoreceptors
1. Tactile receptors

Provide the sensations of
– Touch
» Shape & texture
– Pressure
» Degree of distortion
– Vibration
» Pulsing or oscillating pressure
Classifying Sensory Receptors

Three Classes of Mechanoreceptors
2. Baroreceptors

Detect pressure changes in
– Walls of blood vessels
– Portions of the digestive
– Portions of the reproductive
– Portions of the urinary tracts
Classifying Sensory Receptors

Three Classes of Mechanoreceptors
3. Proprioceptors

Monitor the positions of joints and muscles

The most structurally and functionally complex of
general sensory receptors
Classifying Sensory Receptors

Tactile Receptors
– Fine touch and pressure receptors

Are extremely sensitive

Have a relatively narrow receptive field

Provide detailed information about a source of
stimulation
– Including its exact location, shape, size, texture,
movement
Classifying Sensory Receptors

Tactile Receptors
– Fine touch and pressure receptors

Are extremely sensitive

Have a relatively narrow receptive field

Provide detailed information about a source of
stimulation
– Including its exact location, shape, size, texture,
movement
Classifying Sensory Receptors

Tactile Receptors
– Crude touch and pressure receptors

Have relatively large receptive fields

Provide poor localization

Give little information about the stimulus
Classifying Sensory Receptors

Six Types of Tactile Receptors in the Skin
1. Free Nerve Endings

Sensitive to touch and pressure

Situated between epidermal cells

Free nerve endings providing touch sensations are tonic
receptors with small receptive fields
Classifying Sensory Receptors

Six Types of Tactile Receptors in the Skin
2. Root hair plexus nerve endings

Monitor distortions and movements across the body surface
wherever hairs are located

Adapt rapidly, so are best at detecting initial contact and
subsequent movements
Classifying Sensory Receptors

Six Types of Tactile Receptors in the Skin
3. Tactile discs

Also called Merkel discs

Fine touch and pressure receptors

Extremely sensitive to tonic receptors

Have very small receptive fields
Classifying Sensory Receptors

Six Types of Tactile Receptors in the Skin
4. Tactile corpuscles

Also called Meissner’s corpuscles

Perceive sensations of fine touch, pressure, and lowfrequency vibration

Adapt to stimulation within 1 second after contact

Fairly large structures

Most abundant in the eyelids, lips, fingertips, nipples,
and external genitalia
Classifying Sensory Receptors

Six Types of Tactile Receptors in the Skin
5. Lamellated corpuscles

Also called Pacinian corpuscles

Sensitive to deep pressure

Fast-adapting receptors

Most sensitive to pulsing or high-frequency vibrating stimuli
Meissner’s vs Pacinian

If you close your eyes and have a friend place an object in the open
palm of your hand, chances are good you will be able to detect the
object but you will not be able to identify it.

By moving the object to your finger tips where Meissner's corpuscles are
abundant, you gather information about its shape, texture, and density,
information your brain uses to identify the object.

– The Pacinian corpuscles enable you to detect the object due to its
weight.
– Meisner’s enable you to define it by fine touch
Classifying Sensory Receptors

Six Types of Tactile Receptors in the Skin
6. Ruffini corpuscles

Also sensitive to pressure and distortion of the skin

Located in the reticular (deep) dermis

Tonic receptors that show little if any adaptation
Classifying Sensory Receptors

Baroreceptors
– Monitor change in pressure
– Consist of free nerve endings that branch
within elastic tissues

In wall of distensible organ (such as a blood
vessel)
– Respond immediately to a change in
pressure, but adapt rapidly
Classifying Sensory Receptors

Proprioceptors
– Monitor:

Position of joints

Tension in tendons and ligaments

State of muscular contraction
Classifying Sensory Receptors

Three Major Groups of Proprioceptors
1. Muscle spindles
2. Golgi tendon organs
3. Receptors in joint capsules
Classifying Sensory Receptors

Muscle Spindles
– Monitor skeletal
muscle length
– Trigger stretch
reflexes
Classifying Sensory Receptors

Golgi Tendon Organs
– Located at the junction between skeletal muscle and its tendon
– Stimulated by tension in tendon
– Monitor external tension developed during muscle contraction
Classifying Sensory Receptors

Receptors in Joint Capsules
– Free nerve endings detect pressure, tension,
movement at the joint
Chemoreceptors
Respond to small
concentration changes of
specific molecules
(chemicals)
Internal chemoreceptors
monitor blood composition
(e.g. Na+, pH, pCO2 )
Found within aortic and carotid
bodies
Very important for homeostasis
Chemoreceptors
Respond to small
concentration changes of
specific molecules
(chemicals)
Internal chemoreceptors
monitor blood composition
(e.g. Na+, pH, pCO2 )
Found within aortic and carotid
bodies
Very important for homeostasis
IN REVIEW
IN REVIEW