Nerve Conduction and excit Flashcards
describe the five factors in nervous communication
Sensor (Receptor/transducer for a specific stimulus); Stimulus (exceeds minimum threshold/energy); Conduction (Fast transmission of electrically isolated signal); Processing (interneurons enhance modify and relate signals); Contextual perception (signal reaches consciousness is moderated by context)
what are the function units of communication in the nervous system?
Neurones
Neurons at rest:
Have negative resting membrane potential; receive inputs which summate to change membrane potential transiently
Neurons in action:
Have sufficient summated input to change membrane potential to more positive threshold levels; this triggers OUTPUT (the action potential)
how to ions move across neuron membranes? Is it Active or passive?
Specific Transporter proteins (both active and passive; move ions Against their gradients); Ion channel proteins (always passive; allow ions to move with gradients
Resting membrane potential is due to what enzyme? It is largely determined by what ion?
Na+-K+ ATPase pump; K+
inputs to the neurons summate making it?
Inputs to neurons summate; making it MORE or LESS likely to produce an ACTION POTENTIAL
Excitatory synaptic potentials ________ the resting membrane potential pushing the neuron ________ to the threshold
Excitatory synaptic potentials depolarize the resting membrane potential pushing the neuron closer to the threshold
Inhibitory synaptic potentials ________ the resting membrane potential pushing the neuron ________ to the threshold
Inhibitory synaptic potentials hyperpolarize the resting membrane potential pushing the neuron away from the threshold
Depolarizing the resting membrane potential occurs by?
Opening ion channels permeable to ions with Nernst potential +ve to Em
Hyperpolarizing the resting membrane potential occurs by?
Opening ion channels permeable to ions with Nernst potential ?ve to Em
ion channels can be opened by?
Membrane potential or direct electrical stimulation; Neurotransmitters; Mechanical/chemical forces
What is the order of channels that open in an action positional?
once the threshold has been reached; voltage-sensitive Na+ ion channels rapidly open this leads to a strongly depolarizing the resting membrane positional; This channels automatically close; then the voltage-sensitive K+ channels slowly open strongly Hyperpolarizing the resting membrane positional
describe the flow of an action potential
AP normally travel from soma to synaptic terminals at the end of the axon; this triggers the synaptic release of neurotransmitters which generate PSPs in target neurons or tissues
what does the conduction velocity of an AP depend on?
Dependent on axon diameter and degree of myelination
regular breaks in myelin allow what kind of conduction? What are these breaks called?
Saltatory Conduction of nerve impulse from node to node; Node of Ranvier
myelin insulation allows?
Rapid passive spread of current within axon cytoplasm rather than leaking across axon membrane
describe what happens to an AP as it spreads from a Node of Ranvier
Ap depolarization generated at single node spreads passively to adjacent membrane and decreases with distance from node
Rate of spread depends on?
Rate of spread depends on axon diameter
Voltage gated Na+ channels are concentrated where?
At the Axon Hillock
how does the international association for the study of pain define pain?
an unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage
how did Margo (No Suggestions) describe pain?
Pain is whatever the experiencing person says it is existing whenever s/he says it does
Describe Acute Pain
useful protective warning of external/internal environmental change which can harm body leading to adaptive avoidance behaviour
Describe Chronic Pain
Maladaptive signal which can lead to long-term withdrawal and environmental indifference
what are the four steps in sensing pain
Transduction (painful tissue stimuli transduced into electrical neural activity by peripheral nociceptors); Transmission (nociceptor afferents transmit pain signals to spinal cord and brain); Perception (pain perception involves central processing of nociceptor signals in spinal cord/brainstem/thalamus and cortex); Modulation (descending inhibitory and facilitator input from higher brain centres influences nociceptive transmission in spinal cord)
what do Nociceptors respond to?
Nociceptors response to stimuli which damage tissue or could potentially damage tissue; this may be due to a direct response from a stimuli or factors released by the stimuli
Where do nociceptors synapses? Where is the cell body
Axon synapses in the dorsal horn of the spinal cord or brainstem sensory nuclei; Cell body is in the Dorsal root or cranial nerve ganglia
what are the four types of nociceptors? What do they respond to?
Noxious Mechanoreceptors: Respond only with strong mechanical stimulation and most effectively with sharp objects; Heat Nociceptors: Respond only when temp > 45 deg C; Polymodal nociceptors: respond equally to all mechanical temperature and chemical noxious stimuli; “Sleeping” nociceptors: Normally unresponsive unless tissue is inflamed or injured then show Polymodal responses
Activation of nociceptive transducer receptor/ion channel complexes causes?
Generator potential: graded membrane depolarization with increasing intensity of noxious stimuli
Nociceptor afferent firing rate is lower or higher than non-nociceptor sensory afferent firing rate?
Lower
Many nociceptors show what kind of firing rate with prolonged noxious stimulus? This is know as?
Many nociceptors show slowing firing rate with prolonged noxious stimulus; know as adaptation
Aps are due what ion channel in Nociceptors?
NA+
spinal cord and cranial sensory nuclei exhibit layering these are know as what?
Laminae in the gray mater
how do Nociceptors and somatosensory project into the grey matter?
Nociceptors and somatosensory receptors project into different Laminae
where do fast pain nociceptors project to? What neurotransmitter do they use? What type of fibres are these?
Project into the Laminae I and they release Glutamate; these fibres are Alpha-alpha or type III fibres
where do slow pain nociceptors project to? What neurotransmitter do they use? What type of fibres are these?
Project into the Laminae II and III and they release Glutamate and Substance p; these fibres are C fibres or type IV
where do somatosensory receptors project to?
Project into the Laminae III and IV
Describe the general flow of information once a painful stimulus is presented
Nociceptors in the affected area triggers the spinothalamic tract ->brainstem->midbrain-> Thalamus -> Limbic system and Cingulate cortex and Somatosensory cortex
The descending pathways from the periaqueductal gray can?
Descending pathways from the periaqueductal gray and brainstem can inhibit spinal projection neurons receiving pain signals (Modulating the pain)
what neurotransmitter do the descending pain pathways utilise to modulate pain? What type neuron is used? What other substance utilises this system?
Interneurons release enkephalin which reduces or blocks synaptic neurotransmitter release evoked by pain; Exogenous opiates
Rank the nerve fibres in terms of Conduction velocity and Axon Diameter: are they the same and why?
Alpha-alpha > Alpha-Beta > Alpha-Gamma > Alpha-Delta > Beta > C; same with axon diameter because speed is directly related to diameter
