Biology Nerve Impulse Transmission LESSONS 15.6 TO 15.8

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

Which of the following factors directly influences the speed at which an action potential travels down an axon?

The presence of a myelin sheath

The diameter of the axon

The temperature of the environment

All of the above (correct)

How does the myelin sheath contribute to the speed of nerve impulse transmission?

It reduces the amount of energy required to maintain the resting potential.

It increases the resistance of the axon membrane to ion flow.

It increases the permeability of the axon membrane to sodium ions.

It allows action potentials to jump between nodes of Ranvier, called saltatory conduction. (correct)

What is the relationship between the diameter of an axon and the speed of nerve impulse transmission?

Larger diameter axons transmit impulses slower due to increased resistance.

There is no relationship between axon diameter and transmission speed.

Smaller diameter axons transmit impulses faster due to increased ion concentration.

Larger diameter axons transmit impulses faster due to reduced ion leakage and increased current flow. (correct)

What is the refractory period in the context of nerve impulse transmission?

The time period during which a new action potential cannot be generated in a section of the axon. (B) Signup and view all the answers

Why is the speed of nerve impulse transmission important?

It determines the speed of response to stimuli. (B) Signup and view all the answers

How does temperature affect the speed of nerve impulse transmission?

Higher temperatures speed up transmission due to increased ion diffusion. (B) Signup and view all the answers

Which of the following is NOT a factor affecting the speed of nerve impulse transmission?

The frequency of the signal being transmitted (A) Signup and view all the answers

What structure is crucial for the release of neurotransmitters at a cholinergic synapse?

Synaptic knob (A) Signup and view all the answers

What type of synapse is most common in transmitting impulses between neurones?

Chemical synapse (B) Signup and view all the answers

Which statement accurately describes the function of synapses in the nervous system?

They can only transmit impulses in one direction. (C) Signup and view all the answers

What role do calcium ions play in synaptic function?

They trigger the release of neurotransmitters from vesicles. (D) Signup and view all the answers

What is the width of the synaptic cleft in a chemical synapse?

20-30 nm (C) Signup and view all the answers

Which of the following describes the process of divergence at a synapse?

One impulse generating multiple outputs. (C) Signup and view all the answers

Which component of the synapse contains receptor molecules for neurotransmitters?

Dendrite of the postsynaptic neurone (C) Signup and view all the answers

How many synapses are estimated to be present in the human brain?

100 trillion (C) Signup and view all the answers

What is the main consequence of a synapse only passing impulses in one direction?

Limits the complexity of neural circuits. (D) Signup and view all the answers

What is the maximum duration of the refractory period?

6ms (A) Signup and view all the answers

During the absolute refractory period, what is the neurone excitability?

Zero (D) Signup and view all the answers

In the relative refractory period, what condition is required for a new impulse to be generated?

Stimulus above the normal threshold value (B) Signup and view all the answers

Which of the following is NOT a purpose of the refractory period?

Increasing the speed of action potential transmission (A) Signup and view all the answers

What is the term used to describe the phenomenon where the size of a stimulus is indicated by the number of impulses passing in a given time?

Frequency coding (A) Signup and view all the answers

What is a key characteristic of the 'all or nothing' principle of nerve impulses?

The action potential is generated only if the stimulus exceeds the threshold value (C) Signup and view all the answers

Which of the following statements BEST describes how the brain determines the size of a stimulus?

By interpreting the frequency and type of neurones firing (C) Signup and view all the answers

What is the role of different neurones having different threshold values in determining the size of a stimulus?

They allow for the brain to interpret the size of a stimulus based on the number and type of neurones firing (A) Signup and view all the answers

Which of the following statements accurately describes the relationship between the refractory period and action potential propagation?

The refractory period prevents the backward propagation of action potentials (C) Signup and view all the answers

Study Notes

Speed of Nerve Impulse Transmission

Nerve impulses travel at varying speeds, from 0.5 m/s to 100m/s.
Factors influencing speed include axon diameter and myelin sheath presence.
Myelin sheath: acts as an insulator, allowing faster conduction via saltatory conduction (jumping between nodes of Ranvier) from 0.5ms⁻¹ to 100 ms⁻¹.
Axon diameter: Larger diameter axons conduct impulses faster due to less ion leakage and higher current flow.
Temperature: Higher temperatures increase ion diffusion rates, leading to faster nerve impulse conduction. However, beyond a certain temperature, membrane proteins denature, ceasing impulse conduction.
Refractory period: A period following an action potential where no new impulse can be generated. Comprised of two parts:
- Absolute refractory period: lasts ~1ms, no new impulses can be generated, regardless of stimulus strength.
- Relative refractory period: lasts ~5ms, new impulse can be generated, but requires stronger stimulus than normal based on the increase in stimulus needed from normal resting excitability.

All or Nothing Response

Nerve impulses are "all or nothing."
A stimulus reaching a threshold value triggers an impulse, with impulse size remaining constant regardless of stimulus intensity exceeding the threshold,
Impulse frequency and different neurone threshold values are how the organism determines stimulus size.
Frequency coding measures the number of impulses per unit time, larger stimuli result in higher impulse frequencies.

Multiple Sclerosis

Multiple sclerosis (MS) is an autoimmune disorder affecting the myelin sheath.
Gradual breakdown of the myelin sheath (plaques) form and leave axons demyelinated.
Myelin breakdown results in impaired impulse conduction.
Characterized by symptoms affecting young adults, including limb weakness, sensory disturbances, and blurred vision.

Synapses

Synapses are the connections between neurons.
Can be electrical or chemical, but chemical synapses are more common.
Presynaptic neuron releases neurotransmitters into the synaptic cleft (the gap between neurons).
Postsynaptic neuron's receptors bind to the neurotransmitters triggering a response.
Synapses are unidirectional enabling impulses to only flow one way.

Synaptic Transmission Summary

Action potential arrives at the presynaptic terminal, causing voltage-gated calcium channels to open and allowing calcium ions (Ca²⁺) to enter.
Influx of calcium triggers synaptic vesicles to fuse with the presynaptic membrane, releasing neurotransmitters into the synaptic cleft via exocytosis.
Neurotransmitters bind to receptors on the postsynaptic membrane, opening sodium ion channels.
Sodium ions (Na⁺) diffuse in causing a temporary depolarisation called EPSP (excitory postsynaptic potential).
Acetylcholinesterase enzyme breaks down released neurotransmitter into smaller components (choline and acetate) for reabsorption into the presynaptic neuron.
This process recycles the neurotransmitters.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

This quiz covers the speed of nerve impulse transmission, including factors that influence it such as axon diameter and the presence of myelin sheath. You'll explore concepts like saltatory conduction and the effects of temperature and refractory periods on nerve impulses.