chapter 7

What are the two main divisions of the peripheral nervous system?

Somatic nervous system and autonomic nervous system.

What does the somatic nervous system control?

Skeletal muscle.

What does the autonomic nervous system control?

Internal organs.

How many neurons are typically involved in the autonomic nervous system pathway?

Two neurons: preganglionic and postganglionic.

What neurotransmitter is released at skeletal muscle by the somatic nervous system?

Acetylcholine (ACh).

What neurotransmitters can the autonomic nervous system release?

Acetylcholine (ACh) or norepinephrine (NE).

What is the general function of the sympathetic nervous system?

Fight or flight response.

What is the general function of the parasympathetic nervous system?

Rest and digest functions.

Where do sympathetic preganglionic neurons originate?

Thoracolumbar region of the spinal cord.

Where do parasympathetic preganglionic neurons originate?

Brain stem and sacral spinal cord.

What is a common effect of sympathetic activation?

Increased heart rate.

What is a common effect of parasympathetic activation?

Decreased heart rate.

What type of receptor is a nicotinic receptor?

Ligand-gated ion channel.

What type of receptor is a muscarinic receptor?

G-protein-coupled receptor.

What happens when acetylcholine binds to nicotinic receptors?

It typically causes depolarization.

What is the effect of norepinephrine on α₁ adrenergic receptors?

Excitation.

What is the effect of norepinephrine on α₂ adrenergic receptors?

Inhibition.

What is the effect of norepinephrine on β₁ adrenergic receptors?

Excitation.

What is the effect of norepinephrine on β₂ adrenergic receptors?

Inhibition.

What is the mechanism of action for muscarinic receptor activation?

ACh binds to the receptor, activating a G protein and altering intracellular signaling.

What is the major neurotransmitter difference between sympathetic and parasympathetic postganglionic neurons?

Sympathetic usually releases norepinephrine, while parasympathetic releases acetylcholine.

What is the role of the postganglionic neuron in the autonomic nervous system?

Carries action potentials toward the target organ.

What is a memory trick to differentiate between nicotinic and muscarinic receptors?

Nicotinic = direct ion channel; Muscarinic = G protein.

What is the function of the autonomic ganglion?

Contains the cell body of the postganglionic neuron.

What is the result of ACh binding to nicotinic receptors?

Inward positive charge leading to depolarization.

What neurotransmitter is released by sympathetic postganglionic neurons?

Norepinephrine (NE)

What is the role of adrenergic receptors in target cells?

They bind norepinephrine and can produce different responses based on the receptor subtype.

What effect does β₁ receptor activation have on the heart?

It contributes to increased heart rate.

What is the mechanism of sympathetic activation?

Sympathetic preganglionic neuron fires AP → ACh released → Nicotinic receptor activation → Postganglionic neuron fires AP → NE released → Adrenergic receptor activation → Target organ activity changes.

What neurotransmitter is released by parasympathetic postganglionic neurons?

Acetylcholine (ACh)

What is the role of muscarinic receptors in target organs?

They bind acetylcholine and mediate parasympathetic effects.

What is the mechanism of parasympathetic activation?

Parasympathetic preganglionic neuron fires AP → ACh released → Nicotinic receptor activation → Postganglionic neuron fires AP → ACh released → Muscarinic receptor activation → Target organ activity changes.

What is the neuromuscular junction (NMJ)?

It is the site where a somatic motor neuron communicates with a skeletal muscle fiber.

What is the function of acetylcholinesterase at the NMJ?

It breaks down acetylcholine in the synaptic cleft to limit its action.

What is an end plate potential (EPP)?

It is the graded depolarization produced by ACh at the NMJ, leading to muscle action potential.

What distinguishes EPP from EPSP?

EPP occurs at the NMJ and is normally sufficient to trigger a muscle action potential, while EPSP occurs in postsynaptic neurons and may need summation.

What constitutes a motor unit?

A motor unit consists of one motor neuron and all the skeletal muscle fibers it innervates.

What happens if Ca²⁺ entry is blocked at the motor neuron terminal?

There is reduced or absent ACh release.

What is the effect of blocking nicotinic receptors at the NMJ?

ACh cannot normally depolarize the motor end plate.

What is the role of a preganglionic neuron?

It is the first neuron in a typical autonomic pathway.

What is the role of a postganglionic neuron?

It is the second neuron in a typical autonomic pathway.

What is the function of cholinergic neurons?

They use acetylcholine as their neurotransmitter.

What is the function of adrenergic neurons?

They use norepinephrine or epinephrine as their signaling molecules.

What are nicotinic receptors?

Ligand-gated ACh receptors found at the NMJ and autonomic ganglia.

What are muscarinic receptors?

G-protein-coupled ACh receptors found in various target organs.

What is the significance of a motor neuron firing?

When a motor neuron fires, all muscle fibers in its motor unit are activated.

What happens if ACh release is blocked?

There will be no normal end plate potential (EPP).

What is the expected result of inhibiting acetylcholinesterase?

Acetylcholine remains active longer, prolonging its effects.

What is the typical pathway for sympathetic activation?

ACh → Nicotinic receptor → NE → Adrenergic receptor.

What is the typical pathway for parasympathetic activation?

ACh → Nicotinic receptor → ACh → Muscarinic receptor.