BMS Quiz 6

Chapter 12: 12.6, 12.7, 12.8, 12.9, and 12.10 Chapter 14: 14.1, 14.2, 14.3, and 14.5 (only the first bullet point plus it's 2 sub-bullets)

Distinguish between a pump and a channel

• Channels:

  • Allow substances to move down their concentration gradient

  • Do not require cellular energy

• Pumps:

  • Maintain concentration gradients by moving substances against their gradient

  • Require cellular energy

Leak channels

• Always open

• Allow for continuous diffusion of one type of ion

• Ex: K+ leak channel

Chemically-gated channels

• Ligand-gated channels

• Closed at rest

• Open briefly in response to Neurotransmitter binding

• Allow for diffusion of one type of ion

• Ex: Chemically-gated cation channel

Voltage-gated channels

• Closed at rest

• Open briefly in response to changes in electrical charge across the membrane

• Allow diffusion of one type of ion

• Ex: Voltage-gated Na+ channel

Sodium/potassium pumps

• Maintain the resting membrane potential

• Account for 2/3 of neurons energy expenditure

• Move 3 Na+ to ECF and 2 K+ to ICF

Calcium pumps

• Establish a concentration gradient for Ca2+ in the axon terminal

  • important for synaptic transmission

• Moves Ca2+ to the ECF

• Can be used for later work

List the four functional neuron segements

• Receptor segment

• Initial segment

• Conductive segment

• Transmissive segment

What is in the Receptive segment and the 3 channels

• Dendrites

• Soma

• Receives signals

• Chemically gated cation channel​

• Chemically gated K+ channels​

• Chemically gated Cl- channels

What is in the Initial segment and the 2 channels

• Axon hillock

• Generates initial action potentials

• Voltage-gated Na+ channels

• Voltage-gated K+ channels

What is in the conductive segment and the 2 channels

• Axon

• Propagates action potentials

• Voltage-gated Na+ channels

• Voltage-gated K+ channels

What is in the transmissive segment?

• Axon terminals

• Releases neurotransmitters

• Voltage-gated Ca2+ channels

• Ca2+ pumps

Define the terms: electrical gradient, electrical potential, voltage, membrane potential

• Electrical gradient: There is an unequal distribution of Ions across the plasma membrane

• Electrical potential: An electrical gradient represents potential energy of electrical potential (think of a dam with a hole)

• Membrane potential and voltage: Membrane potential refers to the difference in electric charge inside and outside of a cell, which can change in response to ion movement. Voltage is the measure of that electric potential difference.

A cell is polarized due to

The unequal distribution of ions across its membrane results in a difference in electrical charge inside and outside the cell. Like the North and South polls.

Resting Membrane Potential (RMP)

• The potential difference across a cell’s plasma membrane when it is not being stimulated (at rest)

• -70 mV

Explain how the RMP is established and maintained in neurons

​

• Diffusion of K+ through K+ leak channels (primary)

  • down the electrochemical gradient​

• Diffusion of Na+ through Na+ leak channels​

• Na+/K+ pumps (always)​

  • to maintain RMP

Describe the distribution of substances between the inside and the outside of a neuron

• The outside of the cell (ICF):

  • More Na+ (sodium), Cl- (chloride), Ca2+ (calcium)

• The inside of the cell (Cytosol):

  • More K+ (potassium)

Explain the roles of K+, Na+, and Na+/ K+ pumps in establishing and maintaining the RMP

• K+ diffuses out of the cell through leak channels, making the inside negative.

• Na+ diffuses in but less so due to fewer channels.

• The Na+/K+ pump actively transports 3 Na+ out and 2 K+ in, maintaining the RMP at approximately -70 mV.

Depolarization

• Gain of positive charge makes the cytosol less negative

• Ex: Influx of Na+

What are the 2 definitions for Hyperpolarization

• Loss of positive charge makes the cytosol more negative

  • Ex: Efflux of K+

• Gain of negative charge makes the cytosol more negative

  • Ex: Influx of Cl-

Repolarization

• The Na+/K+ pump returns the membrane potential to RMP/polarized state

Define a graded (postsynaptic) potential

• A.K.A. Postsynaptic Potentials, Local Potentials​

• Occur along the RECEPTIVE SEGMENT​

• Result from the opening of chemically-gated channels​

• May cause depolarization or hyperpolarization​

• Size of the change in membrane potential varies ​

• Travels only a short distance​

Describe the events of a graded (postsynaptic) potential

• Graded (postsynaptic) potentials are changes in membrane potential that occur in response to synaptic transmission. They result from neurotransmitter binding to receptors, leading to the opening of ion channels, which can cause local depolarization or hyperpolarization.

Chemically-gated cation channel graded potential

• Neurotransmitter binds receptor/opens the channel

• Na+ diffuses into the cell (influx)

• Depolarization (less negative)

• Excitatory Postsynaptic Potential (EPSP)

Chemically-gated K+ channel graded potential

• Neurotransmitter binds receptor/opens channel

• K+ diffuses out of the cell (Efflux)

• Hyperpolarization (More negative)

• Inhibitory Postsynaptic Potential (IPSP)

Chemically-gated Cl- channel graded potential

• Neurotransmitter binds receptor/opens channel

• Cl- diffuses into the cell (Influx)

• Hyperpolarization (more negative)

• IPSP

Excitatory

• Increase the likelihood the axon will fire an axon potential

Inhibitory

• Decrease the likelihood the axon will fire an axon potential

Define summation

• The changes in membrane potential generated by all the graded potentials (EPSP + IPSP) are:

  • Added together at the initial segment

Explain how summation relates to threshold potential

• An action potential will be generated of graded potentials arriving at the axon hillock move them membrane potential to:

  • Threshold potential → -55mV

What happens when threshold is reached?

• Voltage-gated channels at the axon hillock open, initiating an ACTION POTENTIAL

Describe an action potential

• Begins in the INITIAL SEGMENT​

• Occurs along the CONDUCTIVE SEGMENT​

• Results from the sequential opening and closing of voltage-gated channels​

• Causes a large, stereotypical change in the membrane potential​

• “All or none”​

Describe what causes depolarization, repolarization, and hyperpolarization in an action potential

1. ​Depolarization

• Na+ influx causes “rising phase”​

2. ​Repolarization

• K+ efflux causes “falling phase”​

3. ​Hyperpolarization

• Excess K+ efflux causes “refractory period”​

4. ​Return to resting membrane potential

Depolarization phase

• Mediates by voltage-gated Na+ channels

• A. Na+ enters from adjacent areas, and membrane potential changes: -70mV to -55mV​

• Reaching threshold, VGNCs open & membrane potential depolarizes: -55mV to +30mV​

• VGNCs close​

Repolarization, hyperpolarization, and return to RMP

• Mediated by voltage-gated K+ channels

• D. VGKCs open slowly, to coincide with peak depolarization, and K+ exits the cell & the membrane repolarizes: +30mV to -70mV​

• VGKCs remain open for longer time than needed, & the membrane hyperpolarizes: -70 mV to -80mV​

• VGKCs close and RMP is reestablished by Na+/K+ pumps (-70mV)​

Refactory period

• Brief time period after an action potential (AP) when it is impossible or difficult to fire another AP​, during which a neuron cannot fire another action potential due to inactivated sodium channels and increased potassium permeability.

Continuous conduction

• Unmyelinated axons

• Sequential opening of VGNCs along the entire length of the axon

• A method of action potential propagation in which action potentials are generated at each segment of the axon, allowing impulses to travel continuously down the membrane.

Saltatory conduction

• Myelinated axons

• Action potentials jump between nodes of Ranvier

• A method of action potential propagation that increases the speed and efficiency of impulse transmission.

• Requires less energy

Action potential: Velocity

• The velocity of an AP is influenced by

  • Myelination axons = faster velocity

  • Axon diameter = Bigger = Faster velocity

Synaptic transmission

• Occurs in the TRANSMISSIVE SEGMENT​

• Initiated by the arrival of an action potential at theaxon terminal​

• Causes release of neurotransmitter from thesynaptic knob​

• Depends on a concentration gradient for Ca2+

What are the steps os synaptic transmissions?

1. Arrival of an action potential in the synaptic knob opens voltage-gated Ca2+ channels (VGCCs)​

2. Ca2+ enter the synaptic knob & binds synaptic vesicles ​

3. Synaptic vesicles fuse with the plasma membrane &neurotransmitter is released by vesicular exocytosis​

4. Neurotransmitter diffuses across the synaptic cleft and binds receptors on the plasma membrane of the postsynaptic neuron​

Action potential: Frequency

• Amplitude of an AP: is always the same

• Frequency of an AP: depends on stimulus strength

  • Stronger stimulus = more frequent action potentials

Identify the four classes of neurotransmitters based on structure

Structural classification = chemical structure​

1. Acetylcholine (Ach)

• Significantly different from the others​

2. ​Biogenic amines (monoamines)

• Modified amino acid​

• Melatonin

3. ​Amino acids

4. ​Neuropeptides

• Chains of amino acids​

• opioids

Describe how neurotransmitters are classified based on function

Functional classification = effect on membrane potential

1. Excitatory: ​induce an EPSP

• E.g. Glutamate​

2. Inhibitory: ​Induce an IPSP

• E.g. GABA (gamma-Aminobutyric acid)​

What are the 5 subdivisions of the spinal cord and their nerves

• Cervical

  • (C1-C8)

• Thoracic

  • (T1-T12)

• Lumbar

  • (L1-L5)

• Sacral

  • (S1-S5)

• Coccygeal

  • (Co1)

Describe the locations and function of the spinal cord meninges.

• The meninges are three protective membranes surrounding the spinal cord that provide structural support, contain cerebrospinal fluid, and cushion the spinal cord.

  • Deepest = Pia Mater

  • Middle = Arachiod Mater

  • Superficial = Dura Mater

Distinguish the anatomical locations of gray and white matter in the spinal cord

• Grey matter

  • Deep/middle and forms a butterfly

  • cell bodies, dendrites, unmyelinated axons

• White matter

  • Outer part of the spinal cord

  • myelinated axons

Name each sub-region of gray and white matter

• White matter:

  • Dorsal/Posterior funiculus

  • Lateral Funiculus

  • Ventral/Anterior funiculus

• Grey matter:

  • Posterior horn

  • Lateral horn

  • Anterior horn

Differentiate the four functional groups (nuclei) found within each gray matter region

• Sensory nuclei: receive stimuli

  • Somatic and visceral

  • In the posterior horn

• Motor Nuclei: Send out signals to muscles and glands

  • Somatic and autonomic

  • In the lateral and anterior horns

Describe the components (roots) of a typical spinal nerve.

• Formed by:​

• ​Posterior (Dorsal) root: Contains sensory axons

  • Cell bodies in the posterior root ganglion​

• ​Anterior (ventral) root: contains motor axons

  • Cell bodies in anterior & lateral horns of spinal cord​

Classify spinal nerves based on function (sensory, motor, or mixed)

• A spinal nerve is always a mixed nerve