KIN 103 (Chp: 10 - Neurons) Flashcards
What are the three types of neurons? (Simple neuron)
- may or may not have myelinated axons
- free nerve endings
What are the three types of neurons? (Complex neuron)
- enclosed nerve endings
- connective layers of tissue around them (Pacinian corpuscle)
- myelinated axons
- usually for sensing touch
What are the three types of neurons? (Special neurons)
- Specialized receptor hair end
- Synaptic vessicles
- synapses
- myelinated axons
- usually for the senses of the body
Adequate stimulus:
Adequate stimulus: each type of receptor responds preferentially to a particular type of stimulus or form of energy.
Chemoreceptors
stimulated by: oxygen, pH, organic molecules
Mechanoreceptors
Stimulated by: pressure, cell stretch, vibrations
Photoreceptors
Stimulated by: Photons of light
Thermoreceptors
Stimulated by: Varying degrees of heat
Transduction
Transduction: stimulus energy converted into information processed by CNS, ion channels or second messengers initiate membrane potential change in sensory receptor (graded potentials)
Receptor potential:
Receptor potential: change in membrane potential of sensory receptor (graded potential), can initiate action potentials or release neurotransmitter
Threshold
Threshold: minimum stimulus required to generate large enough receptor potential to initiate action potentials (or release neurotransmitter)
Receptive field
Receptive field: neurons are activated when stimuli fall within a specific physical area (i.e. region on the skin or on the retina)
Primary and secondary sensory neurons (which have larger sensory fields?)
Primary and secondary sensory neurons have primary (smaller) and secondary (larger) receptive fields, respectively.
Do secondary receptive fields overlap?
Yes they do, in fact secondary receptive fields are a combination of primary receptive fields in a said area
Two point discrimination
Essentially the principle that when we touch two places on someone’s skin it may trigger a feeling of only one place since the neurons go through convergence
Modalities (what are they?)
Different types of information (modalities) are processed in different regions of the brain
Does all sensory information reach the brain?
Some information does not reach the brain, eg: Visceral reflexes are integrated in brain stem or spinal cord and usually do not reach conscious perception (eg. control of blood pressure)
What type of pathways does sensory information travel through?
Most sensory information travels from the body to the brain along ascending pathways in the spinal cord or from the head to the brain via cranial nerves
Four properties of all stimuli: (What are they?)
Modality, location, intensity, duration
Modality (Definition)
Modality: What kind of stimulus is it (touch, sound, light)?
- indicated by which sensory neurons are activated and where those neurons terminate in brain
- specific to receptor type (adequate stimulus)
labeled line coding (what is it?)
labeled line coding
- 1:1 association of receptor with sensation
- Each type of receptor projects to a specific part of the brain.
Lateral inhibition (what is it?)
Lateral inhibition: increases contrast between active receptive fields and inactive neighbors (slide 13)
Population coding (what is it?)
Population coding: the CNS evaluates input from multiple receptors to obtain more information than can be provided by a single receptor (slides 7, 12, 13)
Intensity
Intensity = frequency of APs (frequency coding) and number of receptors activated (population coding)
Duration
Duration = duration of AP discharge “train” and resulting neurotransmitter release.
Tonic receptors
Tonic receptors: are slowly adapting receptors that responds for the duration of the receptor
- Provides continuous feedback as long as the stimulus is applied
(eg. Baroreceptors, proprioceptors)
Phasic receptors
Phasic receptors: rapidly adapt to a constant stimulus and turn off, they fire once more when stimulus turns off
- Signals and on and an off
- “event detectors”
Modality (its 4 types)
- Touch
- Proprioception
- Temperature
- Nociception
- Pain
- Itch
Where do fine touch and proprioception synapse in the CNS?
- They synapse in the medulla
- once more in the thalamus
Where do nociceptors and course touch senses synapse in the CNS?
- They synapse in the dorsal root of the spinal cord
- once more in the thalamus
What is important to note about sensory pathways?
- they all enter from one side (either left or right) and contact the opposite side of the brain
Tertiary sensory neurons (where do they terminate?)
- They terminate in the somatosensory cortex
Somatosensory cortex
- Within it the body is mapped
- The maps created are “plastic” and can change over time and with use
- The amount of space each part has in the somatosensory cortex is proportional to the sensitivity of the part
The axons of Somatosensory neurons differ for each their purposes (what are these differences? - A(beta)
A(beta)
- Large, myelinated
- Fast conduction
- Mechanical stimuli
The axons of Somatosensory neurons differ for each their purposes (what are these differences? - A(delta)
A(delta)
- Small, myelinated
- Medium speed
- Cold, fast pain, mechanical stimuli
The axons of Somatosensory neurons differ for each their purposes (what are these differences? - C)
C
- Small, unmyelinated
- Slow speed
- Slow pain, heat, cold, mechanical stimuli
Merkel receptors (What are they?)
Merkel receptors: sense steady pressure and texture
Meissner’s corpuscle
Meissner’s corpuscle: responds to flutter and stroking movements
Pacinian corpuscle
Pacinian corpuscle: sense vibration
Ruffini corpuscle
Ruffini corpuscle: responds to skin stretch
Temperature Receptors
- Located throughout the body
- Play a role in homeostasis
- In the skin they are free nerve endings
located in subcutaneous layers - Cold receptors
- Activated at temperatures below body
temperature - Warm receptors
- Activated above body temperature to
about 45°C
- Pain receptors activated above 45°C
Nociceptors (Definition)
Nociceptors are free nerve endings that respond to strong chemical, mechanical, thermal stimuli that may damage tissue (Fig 10.10)
Pain (Definition)
Pain is our subjective perception of the activation of nociceptors.
- Fast pain, sharp and localized (Adelta fibers)
- Slow pain, more diffuse (C fibers) (see Table 10.3)
Itch (Definition)
Itch is our subjective perception of the activation of nociceptors in the skin
How can Nociceptor discharge be altered?
- Nociceptor discharge can be altered by local chemicals
○ Chemicals that mediate inflammatory response (histamine, serotonin) increase nociceptor discharge by activating the receptor or decreasing their threshold
○ Leads to inflammatory pain, increases sensitivity to pain at inflammation site
Nociceptor pathways (Reflex pathway)
Reflex pathways through the spinal cord produce an integrated “withdrawal” response…
Nociceptor pathways (Ascending pathway)
Ascending pathways to the brain (Fig. 10.8) mediate conscious sensation (pain or itch) and can initiate autonomic responses (nausea, sweating).
Referred pain (What is it?)
Referred pain: pain from a heart attack is often felt in the neck, shoulder and left arm
- Because they share a common secondary field receptor
- (THIS HAS A LOT TO DO WITH THE TWO POINT DISCRIMINATION)
Pain control (gate modulation theory)
Essentially the theory that there are C neurons connected to an inhibitory gate that opens when a signal is fired but close when there is no signal firing
(NEURONS CAN TURN ON AND OFF INHIBITORY NEURONS)
