Nervous System Anatomy & Physiology

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Questions and Answers

What causes the regenerative opening of Na+ channels during synaptic transmission?

Closure of K+ channels

Increased K+ conductance

Inactivation of Na+ channels

Na+ influx into the neuron (correct)

Where are action potentials first generated in a neuron?

Axon hillock (correct)

Synaptic cleft

Myelin sheath

Dendrites

What is the nature of the absolute refractory period?

Neurons can be stimulated as Na+ channels are inactivated

Neurons require greater stimulation to trigger an action potential

Neurons can be re-stimulated with normal stimuli

Neurons cannot be re-stimulated due to activated Na+ channels (correct)

What happens during the relative refractory period?

Greater stimulation is needed to trigger an action potential Signup and view all the answers

Demyelination is most likely to occur in which of the following conditions?

Auto-immune disease Signup and view all the answers

What maintains the ionic gradients across the cell membrane?

ATP-dependent ion pumps Signup and view all the answers

Which type of ion channel is activated by changes in voltage?

Voltage-gated channels Signup and view all the answers

What is the primary result of the influx of Na+ ions during an action potential?

Depolarization of the membrane Signup and view all the answers

What is the approximate resting membrane potential of a neuron?

-70 mV Signup and view all the answers

During the action potential, what happens at the peak known as the overshoot?

Potassium efflux begins Signup and view all the answers

What is an example of passive transport across cell membranes?

Facilitated diffusion Signup and view all the answers

What is the driving force for Na+ ions to move into the neuron?

Concentration and electrical gradients Signup and view all the answers

Which of the following ions has a higher concentration outside the neuron at rest?

Na+ Signup and view all the answers

What do graded potentials primarily affect?

Short-distance neural communication Signup and view all the answers

What mechanism triggers the release of neurotransmitters at axon terminals?

Propagation of action potentials Signup and view all the answers

What equation represents the relationship between voltage, current, and resistance?

V = I x R Signup and view all the answers

Which condition is NOT required for the maintenance of resting membrane potential?

Presence of Na+ ions Signup and view all the answers

What is the resting membrane potential in millivolts (mV) mentioned in the content?

-80 mV Signup and view all the answers

What does capacitance refer to in the context of cell membranes?

The ability to store a charge Signup and view all the answers

Which of the following ionic gradients is crucial for establishing resting membrane potential?

[K+] concentration outside is higher than inside Signup and view all the answers

Who proposed the ionic theory that contributes to the understanding of resting potential?

Julius Bernstein Signup and view all the answers

Which configuration would NOT lead to a net movement of K+ ions?

Equal concentrations of K+ on both sides Signup and view all the answers

Which of the following components contributes least to the change in membrane potential if the cell is only permeable to K+ ions?

Intracellular Na+ concentration Signup and view all the answers

In terms of membrane potential, what would be the result of decreasing the concentration of K+ outside the cell?

Increase in the resting potential Signup and view all the answers

What is represented by the Nernst equation?

Equilibrium potential for a specific ion Signup and view all the answers

What primarily establishes the resting potential of a neuron?

K+ ionic permeability Signup and view all the answers

What does a glass microelectrode allow researchers to measure?

Resting membrane potential Signup and view all the answers

What happens at equilibrium concerning K+ ions in a cell?

K+ ions move in and out at the same rate Signup and view all the answers

What is the typical concentration of extracellular Na+ ions?

120 mM Signup and view all the answers

Study Notes

Nervous System Anatomy and Physiology

Course: PHR2001
Date: 27/09/2024
Time: 10:00 AM – 1:00 PM
Instructor: Dr. Richard Ngomba
Course Code: NDH1010 & MB0312
Location: University of Lincoln, School of Pharmacy

Workshop Material (Week 4 - Neurophysiology)

The workshop materials cover neurophysiology.

Ohm's Law

Voltage (V) = Current (I) × Resistance (R)
Voltage: forces current around the circuit (-70mV)
Current: flow of ions (K⁺)
Resistance: governed by the number of ion channels present and how many are open

Capacitance

The ability of the cell membrane to store charge.

Measuring Membrane Potential

A microelectrode and a reference electrode are used to measure the resting potential
The resting potential is -80 mV.

Intracellular Glass Microelectrodes

Cells are small making it difficult to get access inside
The first glass microelectrodes were developed by Ling and Gerard in 1949.

The Resting Membrane Potential

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

Ionic Concentration Gradients

Intracellular: 12 mM Na⁺, 125 mM K⁺, 5 mM Cl⁻, 108 mM anions
Extracellular: 120 mM Na⁺, 5 mM K⁺, 125 mM Cl⁻
Plasma membrane is impermeable to Na⁺

Equilibrium and Resting Potential

At equilibrium, there's balance between K⁺ ions moving in and out.
This happens at the resting potential, -80mV.
The concentration gradient opposes the electrical gradient for K⁺.

Simple Models of Ion Flow

Equal concentrations: No voltage difference, no net movement
Unequal concentrations: Voltage difference (positive/negative) between compartments, net ion movement
Selective membrane (e.g., permeable to K+ but not Cl-) establishes a voltage difference.

Nernst Equation

Used to calculate the equilibrium potential (E_k) for an ion.
𝔼_k = RT/ZF log10 ([K⁺]_out / [K⁺]_in)
RT/ZF ≈ 58mV at room temperature for monovalent ions
A 10-fold difference in K+ concentration inside versus outside corresponds to a -58mV membrane potential

How Membrane Potential Changes with K⁺

Reducing the K⁺ concentration gradient leads to a decrease in the membrane potential towards resting potential.

Other Ion Contributions to E_m

The membrane is ideally impermeable to Na⁺ ions. Changes in Na⁺ concentration do not affect resting potential.

ATP-Dependent Ion Pumps

Maintain ionic gradients (e.g., Na⁺/K⁺ pump)
The Na+/K+ pump uses ATP to move 3 Na+ ions out and 2 K+ ions in creating an electrochemical gradient.

Quizzes (Examples)

Mitochondria: Mitochondria produce ATP for cellular energy, not cytoplasm or glucose
Action Potential Location: Voltage-gated Na⁺ channels are primarily located at the axon hillock.

Transport Across Cell Membranes

Diffusion (passive)
Facilitated diffusion (passive, uses carrier proteins)
Active transport (requires ATP)

Types of Channels

Voltage-gated: Activated by changes in membrane potential
Mechanically-gated: Activated by mechanical forces
Ligand-gated: Activated by binding of a specific molecule (ligand)
Leak channels: Always open allowing ions to flow passively.

Membrane Bound Proteins & Location of Channels

Na⁺/K⁺ ATPase (membrane bound protein)
Voltage-gated Na⁺ channels: axon hillock & unmyelinated axons
Mechanically/stretch-gated Ca²⁺, Na⁺ channels: Cell body and dendrites
Ligand-gated channels (e.g., ACh, GABA etc.): dendrites & cell body
Leaky channels: in most cell membranes

Action Potential Changes

Action potential includes depolarization, repolarization, and afterpotential phases.

Sodium Influx during Action Potential

The rapid influx of Na⁺ ions initiates and maintains depolarisation during the action potential
The membrane is permeable to Na⁺ ions for a brief moment
Na+ concentration gradient is the main driving force, also the electrical gradient

What Initially Depolarizes Neurons to Open Voltage-Gated Na⁺ Channels

Synaptic transmission (EPSPs)
Generator (receptor) potentials (sensory neurons)

Na⁺ Channel Opening: Regenerative

Depolarization opens Na⁺ channels allowing Na⁺ influx
This positive feedback loop makes the action potential self-regenerating

Action Potentials and Thresholds

Action potentials need to reach a threshold voltage before they can begin

Repolarization

The returning phases of the action potential (from the peak to its resting state)
Repolarisation is due to voltage-gated K+ channels opening slowly after Na+ channels open and inactivate. Then the K+ ions flow out

Ion Flow During Action Potential

Shows how Na+ and K+ conductances change over time, causing the membrane potential to fluctuate.

Signal Transmission (along axon)

Neuron depolarizes at stimulus site
Depolarization moves signal down the axon.

Refractory Period

Absolute refractory period: Neuron cannot be re-stimulated; Na+ channels are inactivated.
Relative refractory period: Needs greater stimulation to initiate an action potential, K⁺ channels are still active.

Saltatory Conduction and Myelin Sheath

Saltatory conduction involves action potentials jumping between nodes of Ranvier in myelinated neurons.
Myelin sheath speeds up action potential propagation

Synapse

Junction between nerve cells.
First (presynaptic) cell release chemical neurotransmitter to trigger second (postsynaptic) cell.
Drugs often affect nerve cell communication at the synapse

Reflex Arc

Simplest nerve circuit, doesn't require higher-level processing
Five parts: receptor, sensory neuron, integration center (spinal cord), motor neuron, effector.

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Description

This quiz focuses on the anatomy and physiology of the nervous system, particularly covering neurophysiology topics outlined in the PHR2001 course. Key concepts such as Ohm's Law, capacitance, measuring membrane potential, and the use of intracellular glass microelectrodes will be explored. Prepare to test your understanding of these critical topics!

Nervous System Anatomy & Physiology - PHR2001

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