Lecture 5: Special and general senses Flashcards
Where are general senses found
- all over the body
- pain, touch, temp
Where are specialized senses found
- in specific areas
- they have specialized and complex receptors
- smell, taste, vision, hearing, and balance
What is sensation
- the activation of specialized cells/ receptors which send impulses to the CNS
- there is no “experience” of the sensation
What is perception
- the integration of sensory info at the level of the brain (thalamus)
- allows for the “experience” of the sensation
When do you get the experience of sensation
only when the activation of sensory receptors are integrated by the brain
What is the all or nothing principle
- neurons (& receptors) will either fire or not
- no “half potential)
What is adaptation
- decreased response from a receptor over time
- speed depends on receptor (ex. touch= fast, proprioception= slow)
What is graded response
- arises from critical threshold
- receptor will only respond to stimulus greater than threshold
- these thresholds can be altered
What are somatic senses
-senses that present throughout the body
= the genral senses
-distribution is not uniform
-two-point discrimination
Name some examples of the general senses / somatic senses
skin, mucosa, muscles, tendons, joints, viscera, etc..
What senses are specific to one area of the body
special senses
ex. photoreceptors (retina)
What are the 3 different ways to classify receptors
- location
- stimulus
- structure
What are the 3 different kinds of receptors classified by location
- Exterocaptors
- Visceroceptors
- Proprioceptors
What are Exteroceptors
- on or near surface of body
- respond to external stimuli
- includes special sense organs
- pain, touch, temp
what are Visceroceptors
- located internally, within viscera
- typically stimulated by pressure, stretching, chem changes
- mediate hunger and thirst
what are proprioceptors
- special type of visceroceptor
- limited to skeletal muscle, tendons, joints
- info bat movement, orientation
- tonic vs phasic
What are the 6 different kinds of receptors classified by stimulus
- Mechanoreceptors
- Chemoreceptors
- Thermoceptors
- Nociceptors
- Photoreceptors
- Osmoreceptors
What stimulates mechanoreceptors
mechanical stimulus changes shape or position of receptor
What stimulates chemoreceptors
- respond to chemical compounds
- either total amount or change in concentration
what stimulates thermoreceptors
changes in temp
what stimulates nociceptors
- respond to tissue damage which is perceived as pain
- toxins, light, sound, pressure, heat
what stimulates photoreceptors
respond to light
what stimulates osmoreceptors
- respond to osmotic pressure
- large concentration in hypothalamus
What are the 2 kinds of receptors classified by structure
- Free nerve endings
- Encapsulated nerve endings
(somatic receptors only )
What are the free nerve endings
- simplest, most common, widely distributed
- located on surface and internally
- fibres terminate in enlarged dendritic knobs
What are encapsulated nerve endings
- have some type of CT that surrounds dendrites
- most are primary mechanoreceptors
- vary in size and distribution
What are tactile (Meissner) corpuscles
- encapsulated nerve ending / exteroceptor
- activation stimulus: mechanical, light pressure
- function: touch and low frequency vibration
What are Bulboid (krause) corpuscle
- encapsulated nerve ending / exteroceptor
- activation stimulus: mechanical
- function: touch, texture and low frequency vibration
What are Bulbous (ruffini) corpuscle
- encapsulated nerve ending / exteroceptor
- activation stimulus: mechanical
- function: crude and persistent touch
What are Lamellar (pacinian) corpuscle
- encapsulated nerve ending / exteroceptor
- activation stimulus: mechanical, deep pressure
- function: deep pressure, high frequency vibration, stretch
What are muscle spindles
- encapsulated nerve ending / visceroceptors
- activation stimulus: mechanical, stretch
- function: sense of muscle length
What are the Golgi tendon receptors
- encapsulated nerve ending / visceroceptors
- activation stimulus: mechanical, tendon stretch, contraction strength
- function: sense of muscle tension
What detects pain
Nociceptors
What are the 2 types of nociceptor fibres
acute and chronic
What type of fibre carries somatic pain and from where
- acute fibres, fast
- concentration in skin, mucosa, superficial areas
What type of fibre carries visceral pain and from where
- chronic fibres, slow
- originates in visceral structures
where are there no nociceptors
brain tissue
what is typically the first indication of injury of disease
the nociceptors detection of pain
what is referred pain
- misinterpretation of nerve signals
- pain perceived at a location other than the site of the painful stimulus/ origin
Characteristics of thermoreceptors (5)
- free nerve endings
- receptive fields ~1mm
- detects hot or cold but not both
- not uniformly distributed
- rapid adaptation
when do thermoreceptors start firing and increase to in heat stimulus
around 25° C, increase in rate until 45 ° C
when does heat temp in thermoreceptors start causing pain
Temperatures above 48° C start to cause pain
When are thermoreceptors most active to cold
Most active between 10° C and 40° C
when do thermoreceptors start lacking ability to fire in cold
Lack of firing below 10° C
what mediates light touch
-tactile disks (merkel disks)
what are the 2 components of merkel disks
- tactile epithelial cell
- tactile disk
what are 4 characteristics of light touch
- subtle detection in exact areas of skin
- epithelial cell is stiff and easily deformed
- slow adaptation
- can also detect contours and surfaces
What is characteristics of Bulbous corpuscles
- flat shaped, located deep in dermis
- slow adapting
- crude, persistent touch
- deep touch
what are characteristics of Lamellar corpuscles
- thick laminated C.T.
- found in deep dermis
- abundant in hands and feet, joint capsules
- fast adapting
- high freq. vibration and stretch
- deep touch
what are 3 additional touch sensations
- skin movement
- itch
- tickle
Describe skin movement
- slight movement on or in skin
- movement of hair causes sensation
- mediated by root hair plexuses
describe itch sensation
- caused by chem irritation of free nerve endings
- histamine, bradykinin
- can also be induced by suggestion
describe the tickle sensation
- tactile stimulation by someone else
- mediated by free nerve endings
- interaction of neural circuits in thalamus, cerebellum, and cortex
what is proprioception
location of body parts w/o visual info
what informs proprioception
- muscle spindles
- golgi tendon receptors
what are intrafusal fibres that compose muscle spindles
- striated ends that contract
- central portion contains nucleus and sensory fibres
- found btw and parallel to extrafusal fibres
what is structure and function of muscle spindles
- composed of 5-10 intrafusal fibres
- 2 sensory nerve fibres
- monitor changes in muscle length
- special gamma motor neurons can cause contractions (stimulated to maintain posture - stretch reflex)
What are the 2 sensory nerve fibres
- wrapped perpendicular to intrafusal fibres
- type I (rapid) & type II (slow)
- encircle central are of each spindle
Where are golgi tendon organs located
at junction btw muscle and tendon
what 2 things does golgi tendon organ consist of
-dendrites (golgi tendon receptors)
-sensory fibres (type
I b)
structure and function of golgi tendon organ
Surrounded by connective tissue capsule
Stimulated by excessive stretch in tendon
Antagonistic to muscle spindles
Causes skeletal muscle to relax – Golgi tendon reflex
Prevent muscle tearing
What are the 4 special senses
- taste
- smell
- vision
- hearing / balance
What 2 senses are intimately linked
taste and smell
- breathing collects chemicals to specialized sense organs for taste
- chemoreceptors are activated to give info about toxic & chem properties
What % of sense of taste comes from the sense of smell?
80%
-thus nasal congestion reduces ability to taste