Unit 1 Flashcards
what are the 2 aspects of pain
- pain perception
2. pain reaction
what is pain perception
- physical process by which pain is received from stimuli and transmitted by the nervous system (CNS and PNS)
what is pain reaction
- a person’s expression of or reaction to the perceived pain
- varies from person to person
what does a high pain threshold lead to vs a low pain threshold in reference to pain reaction
- high pain threshold: low pain reaction
- low pain threshold: high pain reaction
what 3 factors can a person’s reaction to pain
- cognitive factors
- emotional factors
- symbolic factors
what are cognitive factors for pain
- factors that influence how a person thinks about pain
- what you say affects how patients thinks/reacts to pain
- always inform patient of what is happening
- important to make the patient feel like they are in control
what are emotional factors for pain
- emotional factors, such as anxiety, influences patient’s tolerance to pain
- increased anxiety decreases pain tolerance
what are symbolic factors for pain
- unique to each person. pain may symbolize an attack, damage or threat
what are some other factors that may affect pain reactions
- male: higher pain threshold
- tired: low pain threshold
- Latin American, European: low pain threshold
what do neurons do in the physiological generation of pain
- nerve cell which conducts impulses from the skin, mucous membranes and other sense organs to the brain and spinal cord
what are the 2 types of nerves
- afferent nerves
- efferent nerves
what are afferent nerves
- sensory
- conduct signals from the sensory neurons to the spinal cord or brain (ie receiving a burn)
what are efferent nerves
- motor
- conduct signals away from the brain or spinal cord (ie moving hand away from the object causing the burn)
what are the functional regions of a sensory neuron
- dendrites (input)
- cell body
- axon
what 2 things does a sensory neutron need to be able to do to get a message to the CNS
- sense a message
- move the message
what is excitability
- sensing the message
- nervous tissue has property of excitability
- responds to a change in the environment or stimuli (injury, chemical, electrical or temperature)
what is conductivity
- moving the message
- when stimulated, nerve tissue has the property of conductivity, which is the ability to transmit nerve impulses to the CNS
- messages from the brain are then conveyed back to the various effectors to make adjustments
what is the mechanism of the nerve impulse
- a stimulus excites the nerve, leading to the following sequence of events
1. polarization/resting potential
2. depolarization and firing potential
3. repolarization
4. return to resting state
what is polarization
- means that the electrical charge on the outside of the membrane is positive, while the electrical charge on the inside of the membrane is negative
- nerve membrane is polarized and negatively charged at -70mV
how is the charge maintained
- gates of Na+ ion channels are closed, keeping the Na+ outside the cell
- gates of K+ ion channels are open, but K+ remains mostly inside the cell due to the negative charge
- Na+ ion channels are kept closed by Ca+ ions bonded onto receptor sits on the cell membrane
- Na+ ions are in complexes that are too large to fit through K+ channels
- remember, there are many different electrolytes (ions) in both the cell and extracellular environment
what is depolarization
- outer surface of the membrane becomes electronegative
- inner surface becomes electropositive
- occurs when stimuli temporarily alter the permeability of the membrane, opening the Na+ channel gates
- calcium gates move to allow movement of ions
- sodium ions rush inside the axon
- potassium ions leave the cell
what happens when a stimulus challenges the resting potential
- depolarization is slow at first until it goes from -70mV to -55 mV, but then it picks up to rapid depolarization
what is another name for rapid depolarization
- threshold potential or firing potential
what will be the electrical charge when the neuron is at threshold potential
- +40mV inside
what happens with neuron firing when using local anesthetic
- firing threshold is raised, requiring more current to pass through the membrane to decrease the negativity to the point where depolarization occurs
what is repolarization
- occurs once the peak of the firing potential is reached and the membrane potential begins to move back toward the resting potential
- normal membrane potential is restored to -70mV, and the membrane again becomes impermeable to sodium ions
after depolarization occurs, what happens to remaining sodium in the cell
- some can travel out along the concentration gradient
- sodium pump will help transfer additional sodium which would require lots of energy to go against the concentration gradient
- potassium is also actively transported back into the cell
in summary, what are the events in a successful nerve impulse
- resting state (polarization)
- depolarization (slow, then rapid)
- repolarization (return to resting state)
what is the absolute refractory period
- immediately after a stimulus has initiated an impulse, the nerve is unable to respond to another stimulus, for a time, regardless of its strength
what is the relative refractory period
- this follows the absolute refractory period. a new impulse can be initiated but only by a stronger than normal stimulus
why are sodium ions bigger than potassium ions
- because water is attached to sodium ions. this makes them too big to pass through the potassium channels
what is action potential
- the rapid sequence of changes in the cell membrane (- to + and + back to -) is termed action potential
how is an impulse conducted in an unmyelinated axon
- nerve impulses travel along the fiber
- impulses move continuously as waves
- impulses move at a much slower rate compared to myelinated
how is an impulse conducted in a myelinated axon
- nerves that are protected against stimulated by a myelin sheath (a lipid covered)
- impulse jumps from nodes of ranvier
what are nodes of ranvier
- weak susceptible area along the myelinated nerve, where there is little or no myelin and the membrane is 500 times more permeable than some non-myelinated nerves
what is saltatory conduction
- hop or leap
- conduction of a nerve impulse via the nodes of ranvier
- impulse travels down the nerve fibre by jumping from one node to the next, sometimes skipping a node
for anesthetic to be effective, how much of the nerve must be covered
- about 8-10 mm or at least 2-3 nodes of ranvier
- this stops saltatory conduction as the message cannot jump that far to be transmitted
what are 2 advantages of saltatory conduction
- increased speed of impulse travel
2. conservation of energy since only nodes depolarize thus causing only minimal work for the sodium and potassium pumps
if a nerve fibre is larger, what does this mean for local anesthetic
- the larger the nerve fibre, the thicker the myelin sheath, the more rapid the impulse transmission
- the larger the diameter of the nerve fibre, the greater the amount of local anesthetic needed (IA and PSA blocks require more anesthetic than infiltration)
what is the all or nothing principle
- stimuli must be of a certain magnitude (minimal threshold level) to cause a nerve impulse
- if a neutron responds at all, it must respond completely = ALL
- if the stimulus is of insufficient magnitude, nothing happens = NOTHING
how does local anesthetic work
- mainly inhibit sodium influx through sodium ion channels in the neutron cell membrane
- LA agents work by displacing the calcium ions that block sodium ion channels
- LA agents bond more tightly to the receptors than the calcium, which means that the sodium ion channels will remain closed
- LA agents decrease the rate of depolarization
in NB, what is necessary for a hygienist to deliver anesthetic
- a specific written order, signed by a licensed dentist or a physician
- changes to HH require a new signature
