Nervous system part 2

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Questions and Answers

What term describes a nerve impulse running towards the brain and CNS?

Motor

Afferent (correct)

Sensory

Efferent

Which type of nerve fibers conduct impulses more quickly?

Unmyelinated fibers

Sensory fibers

Myelinated fibers (correct)

Afferent fibers

What is the primary mechanism for the generation of an action potential?

Movement of ions across the nerve cell membrane (correct)

Myelination of axons

Cellular metabolism increase

Stimulated sensory organ activation

What is the resting membrane potential primarily due to?

Ion differences across the plasma membrane Signup and view all the answers

How do nerve impulses travel within an axon?

In one direction from cell body to dendrite Signup and view all the answers

What is the primary role of the Nodes of Ranvier in nerve conduction?

To facilitate saltatory conduction Signup and view all the answers

Which of the following statements about nerve impulses is correct?

The frequency of impulses may vary with the situation. Signup and view all the answers

What initiates a nerve impulse?

Stimulation of sensory nerve endings or another nerve impulse Signup and view all the answers

Which of the following correctly describes the nature of action potentials?

They have a consistent speed once initiated. Signup and view all the answers

What best describes the significance of myelination in nerve conduction?

It increases the overall speed of impulse conduction. Signup and view all the answers

What is the main function of the sodium/potassium pump during neuronal activity?

To restore the original ion distribution at resting levels. Signup and view all the answers

What triggers the opening of voltage-gated sodium channels in a neurone?

An adequate external stimulus causing depolarization. Signup and view all the answers

During the repolarization phase of the action potential, which ion channels are primarily responsible for returning the membrane potential to a negative value?

Voltage-gated potassium channels. Signup and view all the answers

What occurs at the synapse during synaptic transmission?

Neurotransmitters are released and diffuse across the synaptic cleft. Signup and view all the answers

Which statement about the action potential is true?

It travels in a wave of depolarization along the axon. Signup and view all the answers

What characterizes the period during which the neurone cannot be re-stimulated?

The neurone is undergoing repolarization. Signup and view all the answers

What is exocytosis in the context of synaptic transmission?

The release of neurotransmitters from synaptic vesicles. Signup and view all the answers

What happens when the membrane potential becomes more positive during an action potential?

More sodium ions enter the neurone. Signup and view all the answers

Which ions are primarily involved in establishing the resting membrane potential of a neurone?

Sodium and potassium. Signup and view all the answers

What process describes the release of neurotransmitters from the synaptic vesicles?

Exocytosis Signup and view all the answers

Which neurotransmitter is NOT mentioned as being present in the brain and spinal cord?

GABA Signup and view all the answers

What effect do local anaesthetics have on sodium channels in nerve cells?

They block the action of sodium channels. Signup and view all the answers

What is one of the effects of increased membrane threshold for excitation caused by anaesthetics?

Decreased synaptic transmission Signup and view all the answers

Which condition is a result of excessive nerve impulses?

Trigeminal neuralgia Signup and view all the answers

How do neurotransmitters achieve their action on post-synaptic membranes?

By diffusion across the synaptic cleft Signup and view all the answers

What modifies neuronal excitability according to the content?

Changes in pH. Signup and view all the answers

What happens to neurotransmitter action after it has occurred?

It is quickly inactivated by enzymes. Signup and view all the answers

What occurs during the transport of neurotransmitters along axons?

Active transport Signup and view all the answers

Which of the following statements about the journey of a neurotransmitter is true?

It is synthesized by nerve cell bodies. Signup and view all the answers

Study Notes

Neurotransmission

Nerve impulses are initiated by sensory nerve endings or by the passage of an impulse from another nerve.
An impulse to the brain is known as Afferent (sensory).
An impulse from the brain is known as Efferent (motor).
Nerve impulses (action potential):
- Travel in one direction.
- Can only send one message at a time but the frequency can vary depending on the situation.
Nerve impulses travel in one direction - from the cell body down the axon to the dendrite.
Some axons transmit action potential faster:
- Myelinated fibres conduct much more quickly.
- Action potential jumps along gaps between cells, called NODES OF RANVIER.
The transmission of action potential is carried out by the movement of ions across the nerve cell membrane.
Resting/unstimulated state:
- The nerve cell membrane is polarized from ion differences across the plasma membrane.
- Different electrical charge on either side of the membrane - resting membrane potential.
- At rest, the outside is positive (+) and the inside is negative (-).
- Main ions: sodium and potassium.
- Ion channels in the axon are voltage gated.
- If the stimulus is strong enough, the voltage-gated sodium channels open.
- The membrane depolarizes, and the membrane potential becomes more positive.
- Depolarization at one segment triggers the opening of other ion channels in the next segment.
- The action potential spreads along the axon in a wave of depolarization.
- After depolarization, the segment repolarizes as the slower voltage-gated potassium channels open.
- Potassium ions flow out, making the membrane less positive and more negative.
- Returning to the resting state.
- Cannot be re-stimulated while repolarizing, the closed potassium channels will not respond.
Sodium-potassium pump:
- Actively transports sodium ions back out and potassium ions back in.
- Restores the original ion distribution.
- Restores the electrolyte chemical gradient at the resting level.
- The gated channels open and close to allow the movement of ions and transmission of impulses.

Synaptic Transmission

Nerves are not joined together or connected.
Most information is passed chemically.
The point at which a nerve impulse jumps from one nerve to another is known as a synapse.
There are approximately 1,000 trillion synapses in the brain.
When the action potential reaches the presynaptic nerve terminal, neurotransmitters are released from synaptic vesicles in the synaptic knob of the axon.
They diffuse into the synaptic cleft and attach to neuro-receptors on the synaptic knob of the dendrite of another nerve.
Synaptic knobs contain spherical, membrane-bound synaptic vesicles that store neurotransmitters.
Neurotransmitters are chemicals released into the synaptic cleft.
Exocytosis moves materials from the interior of the cell to the exterior.
It requires energy and is a form of active transport.
The journey of a neurotransmitter:
- Synthesized by nerve cell bodies.
- Actively transported along the axons.
- Stored in the synaptic vesicles.
- Released by exocytosis in response to the action potential.
- Diffuse across the synaptic cleft.
- Act on specific receptor sites on the postsynaptic membrane.
- Action is short lived.
- After action, inactivated by enzymes or taken back into the synaptic knob.
There are over 50 known transmitters in the brain and spinal cord:
- Noradrenaline.
- Adrenaline.
- Dopamine.
- Histamine.
- Serotonin.
- Acetylcholine.
Neurotransmitter function is modified by extrinsic and intrinsic factors:
- Changes in pH can alter neuronal excitability.
They are dependent on an adequate oxygen supply.
Many drugs increase neuronal excitability or inhibit the action of neurotransmitters.
Anaesthetics increase the membrane threshold for excitation and decrease synaptic transmission at many points in the nervous system.
Local anaesthetics block the nerve transmission to pain centres in the central nervous system.
Local anaesthetics block the movement of nerve impulses near the site of injection by binding to and inhibiting the function of ion channels (sodium channels) in the nerve cell membrane.
Excessive nerve impulses can result in neuralgia:
- Most commonly, trigeminal neuralgia.

Teeth and Nerve Impulses

Teeth are highly innervated by myelinated and non-myelinated fibres.
Teeth are highly susceptible to tactile, thermal, or painful stimuli.
Local anaesthetics cause a reversible block in nerve transmission to pain centres in the central nervous system.
Local anaesthetics block sodium channels which prevents action potentials.

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Description

This quiz covers the basics of neurotransmission, including the processes behind nerve impulses, the roles of afferent and efferent signals, and the significance of myelinated fibers. Learn about how action potentials travel and the importance of ion movement across nerve cell membranes.