Neural Physiology

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Anatomy › Neural Physiology

Questions 1 - 10
1

Which of the following is NOT a property of neurons?

Undergo reactive gliosis in response to injury

Permanent cells

Cells do not divide during adulthood

Compose the nervous system

Explanation

Neurons are the cells that make up the nervous system. Neurons are large, permanent cells that do not divide during adulthood and spend most of their lives in the G0 phase of the cell cycle. If part of a neuron is damaged, it undergoes Wallerian degeneration, meaning that the neuron degenerates distal to the injury, and does not undergo reactive gliosis in response to injury. Astrocytes, a type of glial cell, do this.

2

What are the two gates of the voltage-gated channels along the axonal plasma membrane?

Activation and inactivation

Activation and reactivation

and

Positive and negative

Explanation

The voltage-gated channels along the axonal plasma membrane open and close in response to changes in voltage, and may exist in three distinct states: deactivated, activated, and inactivated. While the axon is at rest, these channels are said to be deactivated; they are impermeable to sodium ions since their activation gates are closed. Once the neuron gets depolarized to the threshold of the voltage-gated sodium channels, the activation gates open, allowing the influx of sodium down its concentration gradient into the cell. During this time the channels are in their activated state. At the peak of the action potential the activation gates are still open, but the inactivation gates close, stopping the flow of sodium through the channels. The channels are in the inactivated state due to the cell becoming depolarized. Once the membrane potential drops back down towards resting, the inactivation gates open, and the activation gates close, thereby deactivating the channels again, until another action potential depolarizes the membrane.

3

What are the two gates of the voltage-gated channels along the axonal plasma membrane?

Activation and inactivation

Activation and reactivation

and

Positive and negative

Explanation

The voltage-gated channels along the axonal plasma membrane open and close in response to changes in voltage, and may exist in three distinct states: deactivated, activated, and inactivated. While the axon is at rest, these channels are said to be deactivated; they are impermeable to sodium ions since their activation gates are closed. Once the neuron gets depolarized to the threshold of the voltage-gated sodium channels, the activation gates open, allowing the influx of sodium down its concentration gradient into the cell. During this time the channels are in their activated state. At the peak of the action potential the activation gates are still open, but the inactivation gates close, stopping the flow of sodium through the channels. The channels are in the inactivated state due to the cell becoming depolarized. Once the membrane potential drops back down towards resting, the inactivation gates open, and the activation gates close, thereby deactivating the channels again, until another action potential depolarizes the membrane.

4

The putamen, caudate nucleus, and globus pallidus are part of the __________.

basal ganglia

diencephalon

cerebellum

corpus callosum

None of these

Explanation

The basal ganglia is a structure of the cerebrum that contains grey matter called the putamen, caudate nucleus, and globus pallidus. There are also two midbrain structures called the subthalamic nucleus and substantia nigra.

5

Which of the following is a feature of the sympathetic nervous system?

Some sympathetic fibers pass through the paravertebral ganglia of the sympathetic trunk; other sympathetic fibers synapse there

Some sympathetic fibers leave the central nervous system (CNS) by specific cranial nerves

Sympathetic fibers exit the spinal cord by dorsal roots of spinal nerves

Sympathetic stimulation causes dilation of blood vessels in the skin of the back and limbs

Explanation

The sympathetic nervous system is one of two divisions of the autonomic nervous system; it is responsible for the "fight or flight" response and is involved in homeostasis. Some sympathetic fibers pass through the paravertebral ganglia of the sympathetic trunk, while other sympathetic fibers synapse there.

Parasympathetic nerves are associated with cranial nerves, and the dilation of blood vessels in skin of the back and limbs (the sympathetic system constricts these vessels). Preganglionic neurons originate in the thoracolumbar region of the spinal cord (T2 to L1) then travel to a paravertebral ganglion or prevertebral ganglion, where they synapse with a postganglionic neruon. The paravertebral ganglion are found throughout the length of the spinal cord, including the cervical, thoracic, lumbar, and sacral areas.

6

The autonomic nervous system consists of three divisions.

Which of the following is not a division of the autonomic system?

Somatic

Sympathetic

Parasympathetic

Enteric

Explanation

The autonomic nervous system (ANS) consists of a set of pathways to and from the central nervous system (CNS) that innervate and regulate smooth muscle, cardiac muscle, and glands. The ANS is distinct from the somatic nervous system, which innervates skeletal muscle. The ANS has three divisions the sympathetic, parasympathetic, and enteric nervous systems.

7

The electrical impulse that a neuron conveys to other neurons begins at the cone-shaped __________ and travels at high speed along the axon toward the __________.

axon hillock . . . axon terminal

dendrite . . . axon

dendrite . . . cell body

axon . . . dendrite

axon . . . terminal

Explanation

The axon hillock is the last place where membrane potentials are summated before the generation of an action potential. The newly-created action potential travels down the axon to the axon terminal.

8

Atropine is a molecule that is an antagonist to muscarinic cholinergic receptors. Based on your knowledge of autonomic nervous system physiology, how would you expect the pupils to respond to topical administration of atropine?

You will observe mydriasis (pupil dilation)

You will observe miosis (pupil constriction)

There will be no change in pupil size because the pupils do not have muscarinic receptors

The iris sphincter muscles would experience a relaxed paralysis

The iris sphincter muscles would experience a contracted paralysis

Explanation

The pupillary sphincter muscles contain muscarinic cholinergic receptors that help the eyes to respond to parasympathetic tone. When this parasympathetic signal is blocked (antagonized) via atropine, you will observe a "sympathetic response" at the level of the pupil. In this scenario, you would observe the sympathetic response of pupil dilation. Hint: "aTROP'ine" and "seeing a TROPical setting" both cause your pupils to dilate nice and wide!

9

How is the parasympathetic branch of the autonomic nervous system organized?

Long preganglionic fiber, short postganglionic fiber

Short preganglionic fiber, long postganglionic fiber

Short preganglionic fiber, short postganglionic fiber

Long preganglionic fiber, long postganglionic fiber

Explanation

Cell bodies of preganglionic neurons are located in the central nervous system (CNS); they synapse onto autonomic ganglia. Parasympathetic ganglia are located in or near the effector organs giving them long preganglionic fibers and short postganglionic fiber. Sympathetic ganglia are located in the paravertebral chain, thus they have short preganglionic fibers and long postganglionic fibers.

10

Which of the following is a feature of the sympathetic nervous system?

Some sympathetic fibers pass through the paravertebral ganglia of the sympathetic trunk; other sympathetic fibers synapse there

Some sympathetic fibers leave the central nervous system (CNS) by specific cranial nerves

Sympathetic fibers exit the spinal cord by dorsal roots of spinal nerves

Sympathetic stimulation causes dilation of blood vessels in the skin of the back and limbs

Explanation

The sympathetic nervous system is one of two divisions of the autonomic nervous system; it is responsible for the "fight or flight" response and is involved in homeostasis. Some sympathetic fibers pass through the paravertebral ganglia of the sympathetic trunk, while other sympathetic fibers synapse there.

Parasympathetic nerves are associated with cranial nerves, and the dilation of blood vessels in skin of the back and limbs (the sympathetic system constricts these vessels). Preganglionic neurons originate in the thoracolumbar region of the spinal cord (T2 to L1) then travel to a paravertebral ganglion or prevertebral ganglion, where they synapse with a postganglionic neruon. The paravertebral ganglion are found throughout the length of the spinal cord, including the cervical, thoracic, lumbar, and sacral areas.

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