Ch 3 - Neurophysiology Flashcards
Decussations
They are crossing fibers We have: -Anterior white commissure -Internal arcuate fibers -Corpus Callosum (connects L&R side of the brain) -Anterior & Posterior Commisure
The greater the degree of myelination ->
Means increased diameter which means increased conduction
Typical Sensory pathways
Sensory receptors; 1st order neurons -> 2nd order neurons -> 3rd order neurons -> 4th order neurons -> cortex
Sensory Transduction
Environmental stimulus (e.g., pressure, light, chemicals) activating a receptor, altering the membrane potential (receptor potential) via opening/closing of ion channels, and increasing the chances of an AP which is then conducted as an impulse/signal
Opening of channels & current flow
Receptor potential or generator potential
Inward flow
Depolarization. Membrane potential moves toward threshold and increases the likelihood of an AP
Outward flow
Hyperpolarization. Membrane potential moves away from threshold, decreasing the likelihood of an AP
Definition of Receptive Fields
Area of the body that when stimulated results in a change in firing rate of a sensory neuron
Types of Receptive Fields
Excitatory: increases in the firing rate of a sensory neuron
Inhibitory: decreases in the firing rate of a sensory neuron
The smaller the receptive field…
The more precise
Lateral Inhibition
Is a protective mechanism which increases precision of sensory localization by defining its boundaries & providing a contrasting border
Stimulus Modality
Pathways are specific to sensory type
Ex: your eyes are not hearing or your nose is not seeing
Stimulus Location
Encoded by the receptive field
Enhanced by lateral inhibition
Threshold
Minimum stimulus that can be detected by receptive field to produce an AP
Stimulus Intensity is encoded by these 3 methods
- Based on # of receptors activated
- Based on firing rates of neurons
- Based on type of receptor activated; ex: light touch; mechanoreceptor & intense dragging stimulus; nocioceptors
Adaptation of Sensory Receptors
Being desensitized by long exposure to stimulus
Phasic Receptors
Pacinian corpuscle; light touch & vibration; rapidly adapting
Tonic Receptors
Muscle spindle, merkel’s receptors; steady pressure or slow pain; slowly adapting
Thermoreceptors
Slowly adapting receptors
Detect skin temperature
Warm vs Cold Thermoreceptors
Warm: Optimal @ approximately 42-43 C; Quiescent @ 45 C
Cold: Optimal @ approximately 30 C; Quiescent @ below 25 C
Both function @ approximately 36 C
Nociceptors
- Respond to noxious stimuli that can produce tissue damage
Types of Nociceptors
Mechanical: Respond to mechanical stimuli such as sharp, pricking pain. Supplied by finely myelinated A-delta fibers which allow for medium conduction
Polymodal: Respond to high-intensity mechanical or chemical stimuli and hot and cold stimuli. Supplied by unmyelinated C fibers which allow for slow conduction
Fast pain
- Carried by group II and group III fibers
- Rapid onset & offset
- Precise localization
- Ex: pin prick
Slow pain
- Carried by C fibers
- Characterized as aching, burning, or throbbing pain
- Poorly localized
- Ex: burn
Referred pain
- Of visceral origin
- Pain is “referred” according to the dermatomal rule, which states that sites on the skin are innervated by nerves arising from the same spinal cord segments as those innervating the visceral organs
- Ex: Ischemic heart pain is referred to the chest & shoulder
Examples of Phasic Receptors
Pacinian Corpuscles; light touch & vibration
Examples of Tonic Receptors
Muscle spindles, merkel’s receptors; steady pressure or slow pain
Mechanical Nociceptors respond to
Respond to mechanical stimuli such as sharp, pricking pain
Polymodal Nociceptors respond to
Respond to high-intensity mechanical or chemical stimuli and hot and cold stimuli
Fast pain are carried by which fibers?
Group II & III fibers
Slow pain is carried by which fibers?
Group C fibers
Are thermoreceptors fast or slow adapting?
Slow
