Special sense-1 Flashcards
Perception
is the conscious interpretation of the external world created by patterns of activity in the brain
Perception is Limited by
- Our receptor types
example: humans do not sense magnetic fields or UV light - Our level of sensitivity
example: we only hear certain frequencies of sound - Central processing and filtering
example: what grabs your attention in a crowded room is based on your sensitivity, past experience, etc
What is responsible for perception and sensation
The outer region of the brain, the cerebral cortex
the awareness of the stimuli
Sensation
the interpretation of the stimuli
Perception
Sensory Receptor Action
Sensory Receptors convert (transduce) information from the environment into electrical signals.
Stimulus:
change detectable by the body
Receptor:
structure within an afferent neuron that responds to stimuli by producing depolarizing graded potentials (receptor potentials)
Sensory Transduction:
conversion of stimulus energy (ex: light, heat, sound) into electrical energy
The _______ consists of nerve fibers that carry information between the CNS and other parts of the body.
peripheral nervous system
The _________ of the PNS sends information about the external and the internal environment to the CNS.
afferent division
Stimuli exist in various energy forms, or modalities, such as
heat, light, sound, pressure, and chemical changes.
Afferent neurons have sensory receptors at their _________ that respond to stimuli in both the external world and the internal environment.
peripheral endings
Receptors must convert these other forms of energy into
electrical signals
Stimuli bring about graded potentials known as _______ in the receptor.
receptor potentials
sensory transduction.
The conversion of stimulus energy into a receptor potential
Receptor potentials in turn trigger ________ in the afferent fibres
action potentials
Sensory Receptors are activated by a specific stimulus with different sensitivities, this is called the
adequate stimulus
Some receptors can respond weakly to stimuli other than their adequate stimulus, but even when activated by a different stimulus, a receptor still gives rise to the sensation usually detected by that receptor type
True or false?
True
Photoreceptors
responsive to visible light
Mechanoreceptors
sensitive to mechanical energy
Thermoreceptors
sensitive to heat and cold.
Osmoreceptors
detect changes in the concentration of solutes in the extracellular fluid (ECF) and the resultant changes in osmotic activity
Chemoreceptors
sensitive to specific chemicals
Nociceptors, or pain receptors
sensitive to tissue damage
What causes changes in electrical activity in a sensory neuron
An adequate stimulus at a receptor
Some receptors can respond weakly to other stimuli in addition to their adequate stimulus.
Give an example
photoreceptors respond to light, but also weakly to mechanical touch, a mechanical compression of the eye will result in “perception” of light.
What increases stimulus intensity
Number of receptors stimulated
– stronger stimuli usually affect larger areas
Frequency of action potentials
– stronger stimuli generate a larger receptor
potential, therefore a greater frequency of
action potentials
T/F
The body is able to adjust to stimulus as more information is brought in.
True
Response to a stimulus can be altered in 3 ways
Receptor Adaptation
Neuron Habituation
Neuron Sensitivity
Sensory Receptor Adaptation
Receptors can “adapt” to stimuli by decreasing the extent of depolarization to sustained or repeated stimuli.
If a stimulus is repeated enough times, then the frequency of action potentials generated to the SAME stimulus will decrease, and the receptor no longer responds to the same degree as it did before
Tonic Receptors:
[do not adapt, or adapt very slowly]
- Constant firing rate
- For situations where continuous information
about a stimulus is valuable
Examples: proprioceptors pain, muscle stretch
continue to generate action potentials, even with multiple repeated stimuli used for maintenance functions,
example balance and posture information always relayed to CNS via stretch receptors
Phasic Receptors:
[rapidly adapting] - Report changes in the environment - Burst of firing at the beginning and end of stimulus Examples: temperature, smell, touch
stop responding quickly when stimulus is repeated
used for signalling stimulus changes and intensity,
example touch receptors on skin adapt to items frequently worn such as a ring or a watch.
Habituation:
Neurons will reduce their response to repeated stimuli by depressing synaptic activity
Neuron Habituation example mechansim
repeated stimulus reduces activity through changes in the voltage-gated Ca2+ channels in the presynaptic terminal
Sensitization:
Neurons will increase their responsiveness to stimuli following strong or noxious stimulus
Neuron Sensitization example mechanism
painful or strong stimulus leads to serotonin release, acting via a 2nd messenger cAMP cascade, which blocks K+ channels, prolonging action potentials in the pre-synaptic neuron
receptive fields
Sensory neurons respond to stimulus information within small regions of input
The sensitivity of an area is determined by
the amount of receptors per area, where the most receptors in a small space leads to the highest sensitivity.
fingertip touch receptors
Small, dense receptive fields correspond to the most sensitive areas
lower leg touch receptors
Large, diffuse receptive fields correspond to the least sensitive areas
Lateral Inhibition
> helps to increase sensory discrimination
and localization when receptive fields are
very dense
The receptive field closest to the stimulus
will be most active, and the receptive fields
nearby will be only weakly activated
This occurs at the level of the receptors
and the CNS via inhibitory neuron
activation and increases the contrast of
stimuli perception
Major Sensory Pathways
Somatic Sensation Pain Sensation Special Senses - Vision - Hearing - Equilibrium - Taste Visceral Sensation (unconscious)
Somatic Sensation
the sensation of body surfaces, including skin, muscle and joint sensation.
Somatic Sensation
the sensation of body surfaces, including skin, muscle and joint sensation.
Somatic Sensory Receptors
Skin Sensation
Muscle Sensation
Joint Sensation
Somatic Sensory Processing:
Spinal cord and Brain
Somatic Sensory Receptors:
Tactile (touch) receptors
hair receptors: hair movement, rapidly adapting
Merkel’s disc; soft touch, slowly adapting
Pacinian corpuscle; vibration and deep pressure, rapidly adapting
Ruffini endings; deep pressure, slowly adapting
Meissner’s corpuscles; soft touch, tickle, rapidly adapting
more than a direct response to a stimulus.
Pain
The sensation of pain is accompanied by
motivated behavioral responses and emotional reactions.
The subjective perception of pain can be influenced by
other past or present experiences.
Categories of Pain Receptors
- Mechanical nociceptors
- Thermal nociceptors
- Polymodal nociceptors
Mechanical nociceptors
respond to mechanical damage such as cutting, crushing, or pinching
Thermal nociceptors
respond to temperature extremes, especially heat
Polymodal nociceptors
respond equally to all kinds of damaging stimuli, including irritating chemicals released from injured tissues.
