AP 151 LEC EXAM 2: Nervous System

AP 151 LEC EXAM 2

What are the different divisions of the Nervous System?

Central Nervous System (CNS) and Peripheral Nervous System (PNS)

Which Pathways are Afferent and Efferent?

Afferent: Sensory

Efferent: Motor

What is the Somatic Nervous System?

Voluntary skeletal muscle control

What is the Autonomic Nervous System?

Involuntary control of smooth muscle, cardiac muscle, and glands.

What is the Sympathetic Division?

Fight or flight

What is the Parasympathetic Division?

Rest and digest

What are the parts of the Neuron?

Cell body (Soma), Dendrites, Axon, Axon terminals, Myelin, Nodes of Ranvier.

What is the function of the Cell Body (Soma)?

The control center of the neuron

What is the function of Dendrites?

Receive incoming information from neighboring cells and transfer it to the integrating region in the CNS

Send signals back and forth

Make proteins (Polyribosomes)

What is the function of the Axon?

Transmit outgoing electrical signals from the integrating center to the end of the axon

What is the function of Axon Terminals?

Secrete neurotransmitters, neuromodulators, or neurohormones to transmit the neuron’s signal to other cells

What is the function of Myelin?

Provides support for neurons

Acts as insulation around axons

Speeds up signal transmission of the axons

What is the function of the Nodes of Ranvier?

Tiny gaps between myelin-insulated areas that allow electrical signals to propagate rapidly along the axon

What is the function of Glial Cells?

Provide physical support for neurons

Communicate with and provide biochemical support to neurons

What type of cells are Astrocytes?

Glial cells in the CNS

What are the functions of Astrocytes? (Six Answers)

• Take up and release chemicals at synapses

• Provide neurons with substrate for ATP production

• Maintain homeostasis of the CNS ECF (taking up K+ and H2O)

• Form a blood-brain barrier that regulates the movement of materials between the blood and the ECF

• Secrete glial-derived growth and trophic factors that maintain and guide neurons during repair and development

• Source of neural stem cells

What type of cells are Oligodendrocytes?

Glial cells in the CNS

What is the function of Oligodendrocytes?

Insulate and support axons by forming myelin; one oligodendrocyte can wrap around several axons

What type of cells are Schwann Cells?

Glial cells in the PNS

What is the function of Schwann Cells?

Insulate and support axons by forming myelin; one Schwann cell wraps around a single axon

What is the structure of the Blood-Brain Barrier?

• Tight junctions between endothelial cells

• Stimulated and regulated by astrocyte signaling

• Communication between endothelial cells and astrocytes maintains the barrier

What is the purpose of the Blood-Brain Barrier?

Regulates what enters the brain by forcing substances to pass through the endothelial cells

Protects the brain from harmful substances while allowing necessary nutrients to pass

What are the two forces that determine the movement of ions into or out of a cell?

Chemical gradient and Electrical gradient

What is meant by the Electrochemical Equilibrium potential of an ion?

The membrane potential at which the chemical and electrical forces on an ion are balanced, so there is no net movement of that ion

What does a calculation by the Nernst Equation tell you?

Tells me the predicted equilibrium potential for a single ion and the membrane voltage at which that ion would be at electrochemical equilibrium

What are the different types of Gated Ion Channels?

Voltage-gated channels, Ligand-gated (chemically-gated) channels, Mechanically-gated channels

What triggers Voltage-Gated Channels?

Responding to changes in the cell’s membrane potential

What triggers Ligand-Gated (Chemically-Gated) Channels?

Responding to ligands

What triggers Mechanically-Gated Channels?

Open in response to physical forces (pressure or stretch); found in sensory neurons

Where would Graded Potentials occur?

When Chemically and Mechanically Gated Channels open, and An open channel closes

How does a Graded Potential differ from an Action Potential?

• Graded potentials are variable-strength signals that travel only short distances and lose strength as they spread.

• Action potentials are large, brief depolarizations that travel long distances through a neuron without losing strength

What would an Excitatory Graded Potential do to the membrane potential?

Makes the inside of the cell less negative (Depolarization), bringing it closer to the threshold for firing an action potential

What would an Inhibitory Graded Potential do to the membrane potential?

Makes the inside of the cell more negative (Hyperpolarization), moving it further from the threshold and reducing the chance of an action potential

Where is the Trigger Zone in Efferent Neurons and Interneurons?

At the axon hillock and initial segment.

Where is the Trigger Zone in Sensory Neurons?

Immediately adjacent to the receptor, where dendrites join the axon.

What is the Purpose of the Trigger Zone?

Act as the integrating center of the neuron and Determines whether a graded potential is strong enough to initiate an action potential

What would you find in High Concentration at the Trigger Zone Membrane?

Voltage-gated Na⁺ channels.

What is the Absolute Refractory Period?

No action potential can be triggered, no matter how strong the stimulus.

What causes the Absolute Refractory Period?

Na⁺ channels are inactivated after the first action potential.

Can an Action Potential occur during the Absolute Refractory Period?

NO

What is the Relative Refractory Period?

A second action potential can be triggered, but requires a stronger-than-normal stimulus

What causes the Relative Refractory Period?

Some Na⁺ channels are still inactivated, and K⁺ channels are open, hyperpolarizing the membrane.

Can an Action Potential occur during the Relative Refractory Period?

Yes, if the stimulus is strong enough.

How does Axon Diameter affect the rate of conduction of an action potential, and why?

A larger diameter lowers internal resistance, so the AP travels faster.

How does Membrane Resistance (Leakiness) affect the rate of conduction of an action potential, and why?

Higher resistance reduces ion leakage, speeding conduction.

How does Myelination Affect the rate of conduction of an action potential, and why?

Myelin insulates the axon, and the action potential jumps between Nodes of Ranvier, increasing speed.

How does Temperature affect the rate of conduction of an action potential, and why?

Higher temperatures speed up ion channel kinetics, increasing the conduction rate

What affects the Rate of Conduction of an Action Potential?

Axon diameter, membrane resistance, myelination, temperature, and AP properties

How does Myelin Affect Conduction?

By insulating the axon, preventing current leakage and allowing action potentials to travel faster

What is the term for conduction along a myelinated axon?

Saltatory Conduction

How does a demyelinating disease affect conduction, and what are examples?

Loss of myelin slows or blocks action potential conduction. Examples include multiple sclerosis (fatigue, muscle weakness, difficulty walking, vision loss) and Guillain-Barré syndrome.

What is the definition of Monoamine Neurotransmitters?

Neurotransmitters derived from a single amino acid

What are the Monoamine Neurotransmitters and their Precursors?

Catecholamines – Derived from Tyrosine;

Serotonin – Derived from L-Tryptophan;

Histamine – Derived from Histidine

How does a Monoamine Signal at the Postsynaptic Neuron? (Five Answers)

• Monoamines bind to G-protein-coupled receptors (GPCRs) on the postsynaptic neuron

• Activate second messenger pathways

• Adenylate cyclase is activated and produces cAMP

• cAMP activates protein kinases

• Protein kinases can open ion channels and phosphorylate other proteins to change postsynaptic activity

What is the function of Serotonin?

• Regulation of mood

• Regulation of appetite

• Regulation of cerebral circulation

What are the two major pathways for Dopamine Transmission?

Nigrostriatal and Mesolimbic

What behavior is the Nigrostriatal Pathway involved in?

Movement

What behavior is the Mesolimbic Pathway involved in?

Reward

What is the Major Excitatory Neurotransmitter of the CNS?

Glutamate

What is the Major Inhibitory Neurotransmitter of the CNS?

GABA (Gamma-aminobutyric acid)

What is Spatial Summation?

Summation of several subthreshold EPSPs adds together to create a suprathreshold potential at the trigger zone

What is Temporal Summation?

Two subthreshold graded potentials from the same presynaptic neuron, arriving at the trigger zone close enough together in time

How do Spatial and Temporal Summation relate to Action Potential Activation?

Both determine if the graded potentials can combine to reach the threshold and activate an action potential

What creates the Resting Membrane Potential?

K⁺ gradients, Selective membrane permeability, and the Na⁺/K⁺ pump.

What does it mean by All-or-None regarding an action potential?

A action potential that either happens fully if the stimulus reaches threshold, or doesn’t happen if it’s below threshold. The size of the action potential doesn’t change with stronger stimuli. The action potential at the end of the axon is the same as the one that started at the trigger zone. This ensures signals are reliably sent over long distances

Since APs are all the same amplitude, how does the strength of the stimulus get coded?

By the frequency of action potentials. Stronger stimuli make the neuron fire more often, while weaker stimuli make it fire less often. This method of coding is called frequency coding

What are the differences between Chemical and Gap Junctions?

• Chemical Junctions: Use neurotransmitters, Slower, Flexible, Found at axon terminals and dendrites

• Gap Junctions: Use direct ion flow, Faster, Less flexible, Found in CNS neurons, glia, heart, and smooth muscle

What are the effects of Neurotransmitters on the Postsynaptic Membrane?

They bind to receptors, open ion channels or activate second messengers, change the membrane potential, and may trigger an action potential

How does GABA signal?

By binding to its receptor, it opens chloride channels. Chloride enters the cell, causing hyperpolarization

How might you Increase the actions of Monoamines at the Synaptic Cleft?

• Blocking reuptake transporters so neurotransmitters stay in the cleft longer

• Inhibiting enzymes that break down monoamines

• Increasing neurotransmitter release from the presynaptic neuron

How might you Decrease the actions of Monoamines at the Synaptic Cleft?

• Blocking receptors on the postsynaptic neuron

• Enhancing reuptake or breakdown of the neurotransmitter

• Reducing neurotransmitter release from the presynaptic neuron