BIOL 220: CH. 13 - SPINAL CORD & REFLEXES

What is membrane potential associated with?

Membrane potential is associated with changes that serve as signals.

What is a graded potential?

A graded potential, also known as a local potential, is a temporary change in membrane potential that is short-range.

How strong is a graded potential?

It has variable strength, meaning its magnitude can change.

Where does a graded potential occur?

It occurs in a small region of the membrane.

What is an action potential?

An action potential is a type of membrane potential that allows for long-distance signaling.

How strong is an action potential?

An action potential has a constant strength, maintaining its magnitude over distance.

What are graded potentials?

Graded potentials are changes in membrane potential that vary in magnitude based on the strength of the stimulus.

How does the current of graded potentials behave over distance?

The current from graded potentials decreases as it moves further from the point of origin.

Can graded potentials be excitatory or inhibitory?

Yes, graded potentials can be either excitatory, leading to depolarization, or inhibitory, leading to hyperpolarization.

What type of channels does a stimulus open to generate graded potentials?

A stimulus opens ligand-gated channels to generate graded potentials.

Where do graded potentials originate from?

Graded potentials can originate from a sensory receptor or from a neuron.

What role do graded potentials play in action potentials?

Graded potentials can initiate action potentials if they reach the threshold at the axon hillock.

What is summation in the context of graded potentials?

Summation refers to the process by which multiple graded potentials combine, either through temporal summation (over time) or spatial summation (from different locations), to influence the overall membrane potential.

What triggers an action potential in a neuron?

An action potential is triggered when a graded potential towards the axon is strong enough to reach the threshold.

What occurs during an action potential?

There is a rapid change in membrane potential due to the opening of voltage-gated ion channels.

Where are voltage-gated ion channels highly concentrated?

They are concentrated in areas of the axon where the density of these channels is high enough.

Which ions play a key role in action potentials?

Sodium (Na⁺) and potassium (K⁺) ions are crucial in generating an action potential.

How does the membrane potential change during an action potential?

The membrane potential shifts from a negative value to a positive one inside the axon.

Does an action potential weaken as it travels along the axon?

No, an action potential does not weaken with distance; it remains consistent throughout its propagation.

What is meant by the "all or nothing" nature of action potentials?

It means that an action potential either fully occurs or does not occur at all; there is no partial action potential.

What is a synapse?

A synapse is the junction between two neurons or between a neuron and another type of cell, where the transmission of signals occurs.

What are synaptic vesicles?

Synaptic vesicles are small sacs located in the axon terminals of neurons, containing neurotransmitters that are released into the synaptic cleft during neurotransmission.

Why can't action potentials pass directly from a neuron to another cell?

Action potentials cannot pass directly from a neuron to another cell because the electrical signal needs to be converted into a chemical signal using neurotransmitters to cross the synaptic gap.

What is the resting state in an action potential?

The resting state is when the neuron is at a stable membrane potential, typically around -70 mV, with more sodium ions outside the cell and more potassium ions inside.

What occurs during depolarization in an action potential?

During depolarization, local currents cause a small area of the membrane to become less negative, moving toward the threshold.

What happens when the membrane potential reaches the threshold during depolarization?

When the membrane potential reaches the threshold, it triggers the opening of voltage-gated sodium (Na⁺) channels, leading to a rapid influx of sodium ions.

How does self-depolarization contribute to the process?

Self-depolarization causes an increasing influx of sodium ions, which opens more voltage-gated sodium channels, creating a positive feedback loop.

What is the peak potential reached during depolarization, and what is its significance?

The membrane potential reaches about +30 mV, which marks the peak of the depolarization phase, causing the inside of the cell to become positively charged compared to the outside.

What happens during repolarization in an action potential?

During repolarization, voltage-gated sodium (VG Na⁺) channels become inactivated, and voltage-gated potassium (VG K⁺) channels open.

• This allows potassium (K⁺) to flow out of the axon, helping to return the membrane potential to a more negative value.

What occurs during hyperpolarization?

During hyperpolarization, the potassium channels remain open longer than necessary, causing the membrane potential to become more negative than the resting potential.

• The sodium-potassium (Na⁺ K⁺) pumps then help restore the membrane to its resting state.

What happens to the stability of the inactivated state compared to the open conformation in a depolarized membrane?

In a depolarized membrane, the inactivated state is more stable than the open conformation.

Why is the inactivated state more prevalent in a depolarized membrane?

The inactivated state is more stable than the open conformation when the membrane is depolarized.

What is necessary for action potential propagation?

For an action potential (AP) to travel along a neuron, the signal must be propagated.

What is saltatory conduction?

Saltatory conduction is a process by which nerve impulses travel along myelinated fibers, allowing for faster signal transmission.

How do myelinated fibers contribute to saltatory conduction?

Myelinated fibers insulate the nerve axon, allowing the action potential to travel more efficiently by jumping between nodes.

How does saltatory conduction prevent Na⁺ leaking?

The myelin sheath helps to prevent the leakage of sodium ions, ensuring that the action potential maintains its strength as it travels along the axon.

What role does ionic separation play in saltatory conduction?

In saltatory conduction, the myelin sheath separates ionic attraction across the membrane, which reduces the need for continuous ion exchange along the axon.

Why is saltatory conduction often described as "leaping" or "jumping"?

Saltatory conduction is described as "leaping" or "jumping" because the nerve impulses jump from one Node of Ranvier to the next, bypassing the myelinated sections of the axon.

How are action potentials (APs) related to stimulus strength?

All action potentials are identical in form regardless of the stimulus strength.

Does the strength of a stimulus affect the form of an action potential?

No, action potentials are independent of stimulus strength; they do not change in size or shape.

How is the strength of a stimulus coded in the nervous system if all action potentials are the same?

The strength of a stimulus is coded by the frequency of action potentials.

• A stronger stimulus results in a higher frequency of action potentials.

How does the response of a sensory receptor vary?

The response of a sensory receptor varies with the intensity of the stimuli.

How is the strength of a stimulus indicated in sensory receptors?

The strength of the stimulus is indicated by the frequency of action potentials generated.

What happens when a stimulus is strong?

A strong stimulus generates many action potentials in a short period of time.

How does a neuron receive signals?

A neuron receives signals from thousands of other neurons.

What types of signals can a neuron receive?

A neuron can receive excitatory and inhibitory signals.

What happens to all the signals received by a neuron?

All signals are added up in a process similar to a "majority vote" to determine the response.

How can a neuron reach a signaling threshold?

A neuron can reach a signaling threshold through temporal summation or spatial summation.

What is temporal summation?

Temporal summation occurs when multiple signals are received in quick succession over time, allowing them to build up.

What is spatial summation?

Spatial summation happens when signals from different neurons are received simultaneously, contributing to the overall signal strength.

An endurance runner is likely to have __________ muscle fibers.

___________ undergo summation to stimulate APs.

During repolarization, ________ channels open, resulting in voltage changing in the negative direction.

________ transports ions back to their resting state after hyperpolarization.

What is the absolute refractory period?

The absolute refractory period is a phase during which no new action potential (AP) can be generated while an AP is ongoing.

Why can't separate action potentials occur during the absolute refractory period?

Separate action potentials are unavailable during this time because Na⁺ channels are either already open or inactivated.

What is the relative refractory period?

The relative refractory period occurs during repolarization when sodium (Na⁺) channels are closed, but potassium (K⁺) channels remain open.

Why is a stronger stimulus needed during the relative refractory period?

During hyperpolarization, a stronger stimulus than usual is required to reach the threshold for triggering an action potential.

What factors affect conduction velocity in neurons?

Conduction velocity is influenced by axon diameter and axon myelination.

How does axon diameter affect conduction velocity?

Larger axon diameters result in faster conduction velocities due to lower resistance to the flow of ions along the axon.

How does axon myelination influence conduction velocity?

Myelination increases conduction velocity by insulating the axon and allowing electrical impulses to jump between nodes of Ranvier through saltatory conduction.

What are the characteristics of Group A fibers?

Group A fibers are thick and heavily myelinated, making them the fastest in terms of conduction.

• They are involved in transmitting somatic sensory and motor signals.

What distinguishes Group B fibers?

Group B fibers have an intermediate thickness and are less myelinated compared to Group A fibers.

• They primarily carry visceral sensory information.

What are the features of Group C fibers?

Group C fibers are thin and non-myelinated, resulting in slower conduction speeds.

• They are typically associated with autonomic functions and have a conduction velocity of about 2 mph.

What is the conduction velocity of small, unmyelinated fibers?

The conduction velocity of small, unmyelinated fibers is about 0.5 to 2.0 m/s.

What is the conduction velocity of small, lightly myelinated fibers?

The conduction velocity of small, lightly myelinated fibers is between 3 to 15.0 m/s.

What is the conduction velocity of large, myelinated fibers?

The conduction velocity of large, myelinated fibers can reach up to 120 m/s.

What is a synapse?

A synapse is the point where an axon terminal meets another cell, such as another neuron, a gland cell, or a muscle cell.

What is an electrical synapse?

An electrical synapse is a type of synapse where cell-to-cell communication occurs through gap junctions.

How do electrical synapses differ from chemical synapses in speed?

Electrical synapses are very fast, enabling rapid communication between cells.

What is an example of synchronization provided by electrical synapses?

Electrical synapses are involved in synchronizing activities, such as coordinating the movement of neurons responsible for eye movement.

What is a drawback of electrical synapses compared to chemical synapses?

Electrical synapses are much faster but less modifiable than chemical synapses.

What components make up a chemical synapse?

A chemical synapse consists of an axon terminal and a receptor region separated by a synaptic cleft.

How do chemical synapses transmit signals?

In chemical synapses, voltage-gated calcium channels open, leading to a Ca²⁺ influx.

• This triggers vesicle fusion, releasing neurotransmitters that bind to postsynaptic receptors.

What is the complexity of synaptic signaling in motor neurons?

The complexity of synaptic signaling is evident as thousands of synapses form on the cell body and dendrites of a motor neuron in the spinal cord.

What is Acetylcholine (ACh)?

Acetylcholine is a neurotransmitter involved in transmitting signals across neuromuscular junctions, playing a key role in muscle contraction.

Where are neuromuscular junctions found?

Neuromuscular junctions are found between nerve cells and muscle fibers, where they facilitate the transmission of nerve impulses that lead to muscle movement.

What are biogenic amines?

Biogenic amines are a class of neurotransmitters derived from amino acids, including examples like epinephrine, dopamine, and serotonin.

What are amino acids without a carboxyl group (-COOH)?

These are amino acids that lack the carboxyl group, which can affect their function as neurotransmitters or other biological roles.

How is emotional behavior linked to neurotransmitters?

Certain neurotransmitters, such as dopamine and serotonin, are closely associated with the regulation of emotional behavior.

Which neurotransmitters are associated with mental illness?

Neurotransmitters like dopamine and serotonin are often linked to mental illnesses, such as depression and schizophrenia.

How do some drugs interact with neurotransmitter receptors?

Certain drugs can bind to neurotransmitter receptors, either mimicking or blocking the effects of natural neurotransmitters. For example, LSD interacts with serotonin receptors.

What is an example of a drug that binds to neurotransmitter receptors?

LSD is an example of a drug that binds to serotonin receptors, altering perception and mood.

What are examples of biogenic amines?

Epinephrine, dopamine, and serotonin are examples of biogenic amines that play roles in mood regulation and the body's response to stress.

What are amino acid neurotransmitters?

Amino acid neurotransmitters include substances like GABA, which is inhibitory, and glutamate, which is excitatory.

What role does GABA play in the brain?

GABA (gamma-aminobutyric acid) functions as an inhibitory neurotransmitter, reducing neuronal activity in the brain.

What role does glutamate play in the brain?

Glutamate acts as an excitatory neurotransmitter, increasing the likelihood that neurons will fire.

What are peptides in the context of neurotransmitters?

Peptides are short chains of amino acids (2-40 AAs) that function as neurotransmitters or neuromodulators in the brain.

How are peptides associated with pain pathways?

Certain peptides, such as endorphins, are involved in pain regulation, reducing pain signals in the nervous system.

What are endorphins, and how do they function?

Endorphins are neurotransmitters that help to reduce pain and create feelings of well-being, such as during childbirth or a "runner’s high."

What is an example of a situation where endorphins are released?

Endorphins are released during intense physical activity, such as during a runner’s high or childbirth, helping to reduce pain.

What are purines in the context of neurotransmission?

Purines like ATP and adenosine can act as neurotransmitters, with adenosine serving as an inhibitory neurotransmitter in the brain.

What is ATP's role as a neurotransmitter?

ATP can function as a neurotransmitter, participating in cell signaling in the nervous system.

What role does adenosine play in the brain?

Adenosine acts as an inhibitory neurotransmitter in the brain, promoting relaxation and sleep.

How does caffeine affect adenosine in the brain?

Caffeine blocks adenosine receptors, reducing the inhibitory effects of adenosine and leading to increased alertness.

After depolarization, the ___________ closes and prevents Na⁺ from entering the cell. (be specific)

The relative refractory period begins around the time ________ closes in the VG Na⁺ channels.

The signal your neurons send to activate your quadriceps when running include ______ type fibers.

___________ is one of the most common inhibitory NTs.

What are spinal reflexes?

Spinal reflexes are rapid responses that involve minimal processing within the spinal cord.