Module 3 Flashcards
What are afferent neurons?
carry nerve impulses to CNS from peripheral receptors and special sense organs
- small, round cell body found in clusters (ganglia) right outside of spine
- single, long dendrite that extends to periphery and acts as an axon, so once appropriate stimulus is received, it conducts action potentials toward cell body
- short axon that extends to the dorsal horn of the spinal cord
what does transduction mean?
conversion of environmental signal to electrical signal
what are the four properties afferent neurons use to allow the CNS to accurately differentiate incoming PNS signals?
modality, intensity, location, duration
define modality and the four types of receptors.
each type of receptor is specialized to respond to a different energy/stimulus type
- photoreceptors: responsive to visible wavelengths of light
- mechanoreceptors: responsive to mechanical energy, vibration and acceleration
- thermoreceptors: sensitive to heat
- chemoreceptors: sensitive to specific chemicals
define intensity.
strength of signal as determined by frequency of action potentials
define location and terms related to it.
site of sensory stimulation, can be found by brain using location of activated afferent fibres
- receptive field: each neuron’s region of the environment to which it is sensitive, meaningif stimulus appears here, neuron will fire and location is communicated to the brain
- multiple sensors: brain can compare inputs from more than one sensor
- gradients: with smell, we can determine location based on this, since smell get stronger as we move towards the source
explain the concept of duration in terms of how the CNS differentiates between input.
how long a stimulus is present, which afferent neurons can encode and communicate to brain
– some cells fire entire time stimulus is present
– others fire when stimulus goes on, then stop, then fire briefly when it turns off
define receptor potential and compare it to generator potential.
receptor potential: change in potential due to incoming signal in specialized receptor cells
generator potential: change in potential due to incoming signal in the ending of an afferent neuron
- both are graded potentials, meaning the duration and amplitude can vary depending on strength and duration of stimulus
- if they are strong enough they will initiate action potential in the afferent neurons, by acting as either excitatory postsynaptic potentials or inhibitory postsynaptic potentials
identify the difference between the mechanisms of creating graded potentials based on receptor type.
specialized afferent ending: receptor potential itself can cause afferent nerve fibre to reach threshold, triggering action potential
separate receptor cell: when receptor potential is strong enough it will release a chemical messenger, which diffuses to afferent neuron and opens chemically gated sodium channels
– if threshold achieved, afferent nerves fibre will initiate and propagate an action potential
how are afferent neurons able to encode the intensity of a signal to transmit this information to the CNS?
larger intensity stimulus can increase the size of receptor/generator potential which cannot bring about a larger action potential due to the all or none law, but it can induce rapid firing of action potentials in the afferent neurons
– stronger stimuli can also affect many neighbouring receptors, which further communicates to the CNS the intensity of the stimulus
define receptor adaptation.
ability of receptors to regulate their responses
– results in stimulus of same intensity not always causing same magnitude of receptor potential
– in some situations, receptors adapt to signal by enhancing or lessening their response
what are two different types of receptors that vary in speed of adaptation?
tonic receptors: slow or no adaptation, important for situations where near constant signals from stimulus is necessary
phasic receptors: rapidly adapting
– upon initiation of stimulus, action potentials are generated, but then stop generating action potentials rapidly even in continued presence of stimulus
– once stimulus is removed, action potentials are again generated, as phasic receptors respond with depolarization called an “off“ response
– important for monitoring changes in stimulus intensity
define nociception. why is it important to the body’s defence system?
pain, unpleasant sensation
– critical to body’s defence system as it alerts CNS to immediate physical harm
– external and internal events are included
– can also include perceived events
how is nociception/pain different from other somatosensory modalities?
can be accompanied by behavioural or emotional responses
– examples include withdrawal reflex or crying
what are nociceptors?
specialized nerve endings of afferent nerve fibres (which are specifically known as pain fibres)
what are the two broad categories of pain fibres and what is their categorization based on?
fast pain fibres and slow pain fibres
conduction speed
what are fast pain fibres or A–delta fibres?
myelinated, have larger diameter than slow pain fibres
– respond to temperature, chemical, and mechanical stimuli
– acute, sharp, or stabbing pain upon activation of these fibres
describe slow pain fibres or C–fibres.
unnmyelinated
– respond to thermal, chemical, and mechanical stimuli (like fast pain receptors fibres)
– throbbing, chronic pain
what are polymodal receptors?
can be activated by slow pain fibers, can respond to more than stimuli
– perceived associated sensations include burning, aching, throbbing
why is bradykinin commonly associated with the slow pain fibres pathway?
bradykinin is a chemical activated by enzymes that are released from damaged cells
– can directly stimulate nociceptors once it’s activated
(since no adaptation to stimulus in nociceptors; they are stimulated until bradykinin is removed, which might explain long lasting, persistent pain)
describe the three types of nociceptors based on modality.
mechanical nociceptors: respond to physical damage
– like cutting or crushing
thermal nociceptors: respond to temperature
– especially heat
chemical nociceptors: respond to noxious chemicals
– both internal or external to body
why do pain receptors not adapt?
due to important role in survival that sensing pain has
describe how the brain processes pain and which areas of the brain are involved.
when the action potential reaches end of afferent pain fibre axon, it triggers release of neurotransmitters
– in particular substance P and glutamate as these are most well studied
reticular formation increases level of alertness and awareness of painful stimulus
thalamus processes info, allowing for perception of pain
hypothalamus and limbic system receive input from thalamus and reticular formation
– subsequently allow for behavioural and emotional responses to pain stimuli
cortical somatosensory processing localizes pain to discrete body region
