Nervous System Anatomy and Physiology Quiz

Nervous System Anatomy and Physiology

• Course: PHR2001
• Date: 27/09/2024
• Time: 10:00am - 1:00pm
• Lecturer: Dr. Richard Ngomba
• Course Code: NDH1010 & MB0312
• Location: University of Lincoln, School of Pharmacy

Workshop Material (Week 4 - Neurophysiology)

• This section details the content for the workshop covering neurophysiology.

Ohm's Law

• Voltage (V) = Current (I) x Resistance (R)
• Voltage forces current around a circuit (-70mV).
• Current is the flow of ions (K+).
• Resistance depends on:
  • Number of ion channels present
  • Number of open ion channels
• Capacitance is the ability of the cell membrane to store charge.

Measuring Membrane Potential

• Microelectrode probes the inside of a cell.
• Reference electrode provides a stable 0mV baseline.
• Amplifier measures the difference and resting membrane potential
• Resting potential is -80mV

Intracellular Glass Microelectrodes

• Cells are very small; hence access to the inside is challenging.
• Ling and Gerard (1949) developed the first glass microelectrodes.

The Resting Membrane Potential

• Requires:
  • Intact cell (semi-permeable membrane)
  • Ionic concentration gradients, particularly for K+ ions.
  • Metabolic processes (long-term).
• Julius Bernstein (1880s) proposed the ionic theory, the Nernst equation (calculates membrane potential), and the semi-permeable membrane.

Ionic Concentration Gradients

• Intracellular:
  • 12 mM Na+
  • 125 mM K+
  • 5 mM Cl-
  • 108 mM anions1.2-
• Extracellular:
  • 120 mM Na+
  • 5 mM K+
  • 125 mM Cl-
• Ideal plasma membranes are impermeable to Na+

Equilibrium and Resting Potential

• At equilibrium, there's a balance between K+ ions moving into and out of the cell.
• This occurs at the resting potential (-80 mV).
• Concentration gradient (125 mM K+ inside) opposes electrical gradient (ions moving to balance inside and outside charge).

Simple Models: Ion Concentrations

• Equal concentrations: No voltage difference is measured due to no net movement of ions.
• Unequal concentrations: A voltage difference arises due to unequal ion movement. This leads to different charges on either side of a selective membrane.

The Balance Point (Nernst Equation)

• Nernst equation calculates the equilibrium potential for a single ion: Ek = RT/ZF × log10([K+]out/[K+]in)
• RT/ZF is approximately 58 mV at room temperature for monovalent ions.
• The membrane potential is -58 mV when the extracellular K+ concentration is 10 times lower than the intracellular concentration.

Membrane Potential Changes with [K+]

• As extracellular K+ concentration increases, the membrane potential less negative.

Other Ion Contributions to Membrane Potential

• Membrane permeability to Na+ has minimal effect on resting membrane potential (Em) because the membrane isn't permeable to Na+ ions.

ATP-Dependent Ion Pumps

• ATP-dependent ion pumps (e.g., Na+/K+ ATPase) maintain ionic gradients.
• These pumps actively transport ions against their concentration gradient, requiring energy from ATP.

Quiz - Question 4

• Mitochondria generate ATP for the cell.

Transport Across Cell Membranes

• Diffusion, Facilitated diffusion (ligand gated, mechanically gated, voltage gated), Active transport

Membrane-bound Proteins (Table)

• Membrane-bound Protein | Example | Where
• Na+/K+ ATPase | Na+, K+ |
• Voltage-gated | Na+, K+ | Hillock and un-myelinated axon
• Mechanically/stretch-gated | Ca2+, Na+ |
• Ligand-gated (ACh, GABA, cAMP, cGMP, ATP) | Cl-, Ca2+, K+, Na+ | Dendrite and cell body
• Leaky channels | K+ |

Na+/K+ ATPase Diagram (Page 19)

• Detailed diagram showing the mechanism of the Na+/K+pump described and located.

Potential change

• Action potentials: long-distance neural communication.
• Graded potentials: short-distance neural communication.
  • Postsynaptic
  • End plate potentials
  • Receptor potentials

The Action Potential

• Major mechanism of neural communication.
• Travels down axon to terminals.
• Does not decrement.
• Triggers transmitter release.
• Phases: depolarization, repolarization, undershoot (afterhyperpolarization), resting state.

Rising Phase Action Potential

• Rising phase caused by Na+ influx (positive ions moving into the neuron).

Na+ Channels and Depolarization

• Voltage-gated Na+ channels open in response to depolarization.
• This allows Na+ influx, further depolarizing the membrane.
• During repolarization, voltage-gated Na+ channels inactivate, slowing down further depolarization.

Na+ Movement (Page 25)

• Concentration gradient: Na+ moves from outside to inside the neuron (high to low concentration).
• Electrical gradient: Na+ moves to inside the neuron (positively charged ion attracted to negative membrane inside the neuron).

Channels Opening and Neuronal Depolarization

• Various factors can induce depolarization, which opens voltage-gated channels.

Na+ channel opening (regenerative)

• Depolarization causes Na+ channels to open leading to Na+ influx into the neuron.

Action Potentials and Threshold

• Action potentials have a threshold.
• Subthreshold stimuli do not generate an action potential.
• Threshold triggers a rapid and all-or-none response.

How to Repolarize (Page 29)

Depolarization (initial phase) of an action potential is followed by repolarization, and both phases are related to the movement of Na+ and K+ ions across the neuronal membrane, respectively.

Ion Flow and Action Potential

• Graphs show Na+ and K+ conductance during stages of action potential.
• Sodium conductance is higher than potassium conductance immediately after stimulus but is eventually lower than potassium conductance during the later stages.

Quiz- Question 30

• Action potentials are first generated at the axon hillock due to the presence of voltage-gated Na+ (sodium) channels.

Signal Transmission

• Neuron depolarization at the stimulation site moves the signal down the neuron..

Quiz- Question 31

• Absolute refractory period is the time period following an action potential where no additional action potentials can be formed.

Refractory Period

• Absolute refractory period: Neuron cannot be re-stimulated; Na+ channels are inactivated.
• Relative refractory period: Greater stimulation is necessary to trigger action potentials, K+ channels are still activated.

Myelin Sheath and Conduction

• Myelin sheath surrounds axons of some neurons, increasing the speed of signal transmission (saltatory conduction).
• Nodes of Ranvier are gaps in the myelin sheath where ion channels are concentrated, allowing rapid signal propagation.

Synapse Structure and Function

• Synapse is the junction between two neurons.
• The presynaptic neuron releases neurotransmitters into the synaptic cleft.
• Neurotransmitters bind to receptors on the postsynaptic neuron.
• Drugs can affect how neurotransmitters work in synapses.

Synaptic Transmission

• Nerve impulse triggers calcium influx.
• Calcium causes vesicles to release neurotransmitters into the synaptic cleft.
• Neurotransmitter binds to receptors on the postsynaptic neuron, triggering a response.

Reflex Arc

• Rapid, involuntary response to stimuli.
• Involves sensory receptors, sensory neurons, an integration center (spinal cord), motor neurons, and effectors (e.g., muscles).

Demyelination Causes

• Autoimmune disease
• Bacterial infection
• Meningitis
• Drug abuse

This quiz assesses your understanding of the neurophysiology concepts outlined in the PHR2001 course. Focus on critical topics such as Ohm's Law, measuring membrane potential, and the importance of ion channels in the nervous system. Test your knowledge to prepare for the upcoming workshop.