Exam Study Notes

Neuron Firing and Neurotransmitters

• Excitatory messages: Increase the likelihood of a neuron firing.
• Local depolarization: Makes a neuron more likely to fire.
  • Involves neurotransmitters.
• Neurotransmitters: Assist in the local potential phase, promoting neuron firing.
• Potential: The most potential for change exists at a negative value.
• Hyperpolarization: Shifts to a negative value, creating the greatest membrane potential.
  • Greatest membrane potential occurs at negative 70.

Excitatory vs. Inhibitory

• Excitatory: Increases the likelihood of neuron firing.
• Inhibitory: Decreases the likelihood of neuron firing.
• Repolarization: Returns the neuron to its resting negative 70 potential.

Electrolyte Balance

• Electrolytes: Crucial for electrical charges.
  • Sodium influx, potassium efflux.
• Hyponatremia: Electrolyte dilution due to excessive water intake.
  • Can impair muscular contraction and brain function.
• Electrolyte replenishment: Necessary during fluid replacement (e.g., with IVs containing sodium and potassium).
• Proper Function: Signals from the nervous and muscular systems require electrolytes.

Action Potential Generation

• Action potential: Not created in the soma (cell body).
• Trigger zone: Located near the brainstem-axon junction.
  • The site of action potential generation.
  • Action potential then travels down the nerve.
• Plasma membrane: Regulates charge with gated channels.
  • Fluctuations occur until gates open for electrolyte influx.

Threshold and Action Potential

• Local action potential: Increases until the threshold is met.
• Threshold: Required for an electrical message to be sent.
  • All-or-nothing principle.
• Resting membrane potential: Negative 70.
• Threshold number: Required for action to take place.
• Sodium ions: Facilitate depolarization.
• Positive feedback: Occurs during spike at number three in the diagram.

Depolarization and Repolarization

• Depolarization: Leads to action.
• Cycle: Resting potential → action → return to baseline.
• Threshold: The body allows more potassium exchange to generate charge.
• Positive 35: The point where repolarization back to resting state is needed.

Refractory Period

• Refractory period: A recovery phase where the neuron cannot immediately refire.
• Absolute refractory: Nothing will cause it to refire.
• Recovery: Recovery is needed before the neuron can fire again.

Myelin and Signal Transmission

• Myelin: Insulating layer that allows signals to skip along the axon.

Synaptic Transmission

• Synapse: Electrical activity in the postsynaptic area.
• Neurotransmitters: Cross over to cause muscle contraction.
• Dendrites: Receive information and connect to the soma, leading to the trigger zone.
• Electrical conversion: Electrical signals convert to chemical signals for communication with other cells.
• Reservoir: Maintain a rotating reserve to ensure continuous messaging.
• Pre-synaptic neuron: Where neurotransmitters are produced.
  • Stimulation caused by their production.
  • Must bind to specific receptors.

Reflexes: Predictable Responses

• True reflex: Predictable motion response.
  • Caused by pain or deformation (e.g., patellar tendon).
• Reflex Components: Need a signal to occur.
  • Quick, automatic motion.
  • Stereotyped and predictable.

Reflex Pathways

• Signals: Arise from skin, muscles, or tendons.
• Somatic receptors: Detect pain.
• Afferent fibers: Communicate with the dorsal horn of the brain stem or spinal cord.
• Muscle spindles: Important for reflexes.
• Muscle compensation to avoid pressure on pain points.
• Compensations can cause improper motion, different injury.
• Relearning takes more time than learning.

Efferent Signals and Muscle Spindles

• Efferent: Away from the nervous system.
• Muscle spindle engagement: Due to stretch receptors.
• Proprioceptors: Maintain balance, monitoring the situation and providing feedback.
• Equilibrium: Stabilizing that joint.

Patellar Tendon Reflex

• Location: Two finger widths below the patella.
• Process: Quick reflex loop; monosynaptic.
• Troubleshooting: If the reflex is difficult to elicit, create tension elsewhere (e.g., pull against fingers).
• Withdrawal reaction