Lecture 12
Introduction of the senses
Senses are derived from sensory receptors that detect changes in the environment and
stimulate neurons to send nerve impulses to the CNS for processing
General senses
- Widely distributed and structurally simple
- Example: touch, pressure, temperature, pain
Special senses
- Have complex specialized sensory organs in the head
- Vision, hearing, smell, taste and balance
Receptors, Sensations and perception
- Chemoreceptors – receptors sensitive to changes in chemical concentration
- Pain receptors – detect tissue damage
- Thermoreceptors – respond to temperature differences
- Mechanoreceptors – respond to changes in pressure or movement
- Photoreceptors – respond to light; found in the eye
Sensation and Perception
- Sensation occurs when receptors are stimulated and send impulses to the
brain
- A perception is conscious awareness of stimuli
- The brain uses projection to send the sensation back to its point of origin so
the person can pinpoint the area of stimulation
Sensory adaption
- brain must prioritize all incoming sensory impulses to prevent overwhelmed
- The brain can become less responsive to a maintained stimulus
- Sensory adaption – ability of nervous system to become less responsive to a
maintained stimulus
General senses
- Receptors for touch pressure sense deformation or
displacement of tissues
o Free nerve ending - sensory nerve fibers in
the epithelial tissues are associated with
itching and other sensations
o Tactile corpuscles – flattened connective
tissue sheaths surrounding two or more
nerve fibers
, o Lamellated corpuscles – large structures of connective tissues fibers
and cells; function to detect deep pressure
Temperature senses
- Warm receptor
o Respond to temp. between 25 and 45 degree
o Above this range pain receptors are stimulated
- Cold receptor
o Respond to temp. between 10 and 20 degree
o Below this range pain receptor ae stimulated
**Both receptors adapt quickly; upon continuous stimulation for 1 minute,
sensations start to fade**
Proprioception
- Sense of body position, location in space
- Associated with skeletal muscle, prevent possible injury to muscles and
tendons
o Muscle spindles – Bundles of special skeletal muscle fibers within
skeletal muscle
Monitor state of muscle
contraction
o Golgi tendon organs (GTO) – cause
muscle to shut down; detect force
stretches during muscle contraction
Example: if they detect possible damage in muscle, they fire,
muscle shut down
Sense of pain
Pain receptors (nociceptors)
- Some consist of free nerve endings that are stimulated when tissues are damaged
- Overstimulation of other types of receptors
- Substance P and Glutamate -> neurotransmitter involved to transmit pain to brain
- Tissue damage causes prostaglandin release, increasing nociceptor sensitivity and pain
intensity
o Morphine, heroin and natural painkiller (endorphins and
enkephalins) -> inhibit release of Substance P
Visceral pain
- Visceral pain receptor is the only receptor in the viscera that
produce sensations
- respond differently than those of surface tissues
Introduction of the senses
Senses are derived from sensory receptors that detect changes in the environment and
stimulate neurons to send nerve impulses to the CNS for processing
General senses
- Widely distributed and structurally simple
- Example: touch, pressure, temperature, pain
Special senses
- Have complex specialized sensory organs in the head
- Vision, hearing, smell, taste and balance
Receptors, Sensations and perception
- Chemoreceptors – receptors sensitive to changes in chemical concentration
- Pain receptors – detect tissue damage
- Thermoreceptors – respond to temperature differences
- Mechanoreceptors – respond to changes in pressure or movement
- Photoreceptors – respond to light; found in the eye
Sensation and Perception
- Sensation occurs when receptors are stimulated and send impulses to the
brain
- A perception is conscious awareness of stimuli
- The brain uses projection to send the sensation back to its point of origin so
the person can pinpoint the area of stimulation
Sensory adaption
- brain must prioritize all incoming sensory impulses to prevent overwhelmed
- The brain can become less responsive to a maintained stimulus
- Sensory adaption – ability of nervous system to become less responsive to a
maintained stimulus
General senses
- Receptors for touch pressure sense deformation or
displacement of tissues
o Free nerve ending - sensory nerve fibers in
the epithelial tissues are associated with
itching and other sensations
o Tactile corpuscles – flattened connective
tissue sheaths surrounding two or more
nerve fibers
, o Lamellated corpuscles – large structures of connective tissues fibers
and cells; function to detect deep pressure
Temperature senses
- Warm receptor
o Respond to temp. between 25 and 45 degree
o Above this range pain receptors are stimulated
- Cold receptor
o Respond to temp. between 10 and 20 degree
o Below this range pain receptor ae stimulated
**Both receptors adapt quickly; upon continuous stimulation for 1 minute,
sensations start to fade**
Proprioception
- Sense of body position, location in space
- Associated with skeletal muscle, prevent possible injury to muscles and
tendons
o Muscle spindles – Bundles of special skeletal muscle fibers within
skeletal muscle
Monitor state of muscle
contraction
o Golgi tendon organs (GTO) – cause
muscle to shut down; detect force
stretches during muscle contraction
Example: if they detect possible damage in muscle, they fire,
muscle shut down
Sense of pain
Pain receptors (nociceptors)
- Some consist of free nerve endings that are stimulated when tissues are damaged
- Overstimulation of other types of receptors
- Substance P and Glutamate -> neurotransmitter involved to transmit pain to brain
- Tissue damage causes prostaglandin release, increasing nociceptor sensitivity and pain
intensity
o Morphine, heroin and natural painkiller (endorphins and
enkephalins) -> inhibit release of Substance P
Visceral pain
- Visceral pain receptor is the only receptor in the viscera that
produce sensations
- respond differently than those of surface tissues
