Neuroscience Chapter: Ion Channels and Spinal Cord

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Questions and Answers

What triggers the opening of voltage-gated ion channels in the axon?

An increase in potassium ion concentration

A sustained resting potential

A decrease in voltage potential

A local reversal of the membrane potential (correct)

What happens during the refractory period of an ion channel?

The channel is unable to open for a short duration (correct)

The channel closes permanently after one action potential

The channel remains open to maintain action potential

The channel can open immediately after closing

What is the significance of the all-or-nothing principle of action potentials?

Action potentials can vary in intensity depending on the strength of the stimulus

Once the threshold is reached, the action potential will always reach +40mV (correct)

Action potentials can be partially completed if the threshold is not fully reached

All ion channels must open simultaneously for an action potential to occur

How does the action potential travel along the axon?

Only downstream ion channels open due to the refractory period Signup and view all the answers

What prevents the summation of action potentials in the axon?

The presence of a refractory period Signup and view all the answers

What structure carries sensory information into the spinal canal?

Dorsal nerve root Signup and view all the answers

Which part of the spinal cord contains the cell bodies of motor neurons?

Gray matter Signup and view all the answers

What is the purpose of interneurons in the spinal cord?

To connect sensory and motor pathways Signup and view all the answers

What anatomical feature of the spinal cord is considered to be deeper and wider?

Anterior median fissure Signup and view all the answers

What is the cauda equina?

A collection of spinal nerves descending from the conus medullaris Signup and view all the answers

How many pairs of spinal nerves are attached to the spinal cord?

31 pairs Signup and view all the answers

What defines the structure of the spinal cord?

An oval-shaped cylinder with deep grooves Signup and view all the answers

Which type of neuron makes up the dorsal root ganglion?

Unipolar neurons Signup and view all the answers

How many pairs of cervical spinal nerves are there?

8 pairs Signup and view all the answers

What are dermatomes specifically associated with?

Sensory input from skin Signup and view all the answers

What distinguishes cranial nerves from spinal nerves?

Cranial nerves connect directly to the brain Signup and view all the answers

Which of the following cranial nerves is responsible for the sense of smell?

Olfactory nerve (I) Signup and view all the answers

What component of the nervous system primarily regulates involuntary functions?

Autonomic nervous system Signup and view all the answers

Which nervous system is divided into sympathetic and parasympathetic divisions?

Autonomic nervous system Signup and view all the answers

What is the primary function of myotomes?

To supply muscle with motor fibers Signup and view all the answers

Which cranial nerve is responsible for controlling the heart rate and digestive tract?

Vagus nerve (X) Signup and view all the answers

Which system is dominant during danger and stressful activities?

Sympathetic nervous system Signup and view all the answers

What neurotransmitter is released by the postganglionic fibers of the sympathetic nervous system?

Norepinephrine Signup and view all the answers

What type of receptors are found in the postganglionic fibers of the parasympathetic nervous system?

Muscarinic receptors Signup and view all the answers

What is the primary change occurring during depolarisation?

A change from negative to positive potential Signup and view all the answers

What happens to the electrical potential during re-polarisation?

It changes back to the negative resting potential Signup and view all the answers

Which statement correctly describes the length of autonomic fibers in the sympathetic nervous system?

Preganglionic fibers are short, and postganglionic fibers are long. Signup and view all the answers

The action potential moves along the axon in which manner?

Automatically in one direction Signup and view all the answers

What is the primary function of the parasympathetic nervous system?

Controlling routine body activities and relaxation Signup and view all the answers

What triggers the opening of sodium channels during depolarisation?

The reaching of a threshold voltage Signup and view all the answers

Where do preganglionic fibers of the sympathetic nervous system originate?

Thoracic and lumbar regions of the spinal cord Signup and view all the answers

What is the resting potential of a neuron?

Negative charge registered when the neuron is at rest Signup and view all the answers

What occurs immediately after the action potential is initiated?

A refractory potential is triggered Signup and view all the answers

Which type of neurotransmitter is primarily released at the effector in the parasympathetic nervous system?

Acetylcholine Signup and view all the answers

Why is it important for the action potential to propagate in one direction along the axon?

To ensure that adjacent channels open sequentially Signup and view all the answers

What role does sodium ions ($Na^+$) play during the action potential?

They diffuse into the axon, causing depolarisation Signup and view all the answers

What is the result of the voltage-gated sodium channels opening?

Influx of sodium ions leading to depolarisation Signup and view all the answers

What primarily gives gray matter its pinkish-gray color?

A rich network of blood vessels Signup and view all the answers

Which structures are primarily involved in afferent input in the gray matter?

Posterior horns Signup and view all the answers

What type of nerve fibers are predominantly found in the white matter?

Myelinated fibers Signup and view all the answers

What are the bundles of fibers within each funiculus of the white matter called?

Tracts Signup and view all the answers

Which type of tract carries impulses from the brain down the spinal cord?

Descending tracts Signup and view all the answers

What is the function of lateral horns in the gray matter?

Filter information to higher centers Signup and view all the answers

What term describes the mixed spinal nerve that carries various signals between the spinal cord and the body?

Mixed spinal nerve Signup and view all the answers

In the gray matter, which of the following structures functions in cross reflexes?

Gray commissure Signup and view all the answers

Study Notes

Organization of the Nervous System (Function) - Part 3

The nervous system is organized into a structural classification of neurons and neuroglia.
Neuroglia: Includes astrocytes, ependymal cells, microglial cells, oligodendrocytes, and Schwann cells.
The brain: Has protective coverings including the cerebrum, cerebellum, brainstem, and diencephalon.

Spinal Cord

An elongated cylinder, extending from the brainstem through the foramen magnum of the skull.
Interior gray matter surrounded by white matter.
Contains 31 pairs of spinal nerves attached by dorsal and ventral nerve roots.
Lies within the spinal cavity, extending from the foramen magnum to the first lumbar vertebra.
Oval-shaped, tapering slightly from the top (cervical region) to the bottom (lumbar region).
Two bulges, one in the cervical region and one in the lumbar region.
Anterior median fissure and posterior median sulcus, two deep grooves, the anterior fissure is deeper and wider.

Spinal Cord - Nerve Roots

Fibers of dorsal nerve root carry sensory information into the spinal canal.
Dorsal root ganglion contains cell bodies of unipolar sensory neurons.
Fibers of ventral nerve root carry motor information out of the spinal cord.
Cell bodies of multipolar motor neurons are located in the gray matter of the spinal cord.

Spinal Cord - Cauda Equina

A collection of spinal nerves extending from the conus medullaris (in the inferior end of the spinal cord).
Resembling a horse's tail, hence the name.
Descends through the lower third of the spinal canal.

Gray Matter

Consists of nerve cell bodies, dendrites, axon terminals (unmyelinated), and neuroglia.
Pinkish-gray, due to a rich network of blood vessels.
Forms an "H" shape, composed of three columns of neurons: posterior, anterior, and lateral horns.
Projections of gray matter towards the outer surface are called horns.

Gray Matter (Function)

Two dorsal horns function in afferent (sensory) input.
Two ventral horns function in efferent (motor) somatic output.
Two lateral horns function in both somatic and autonomic output.
Gray commissure connects the two halves of the gray matter, associated with cross reflexes.
Filters information and integrates spinal reflexes.

White Matter

Composed mostly of myelinated nerve fibers, giving it a whitish color.
Divided into three pairs of columns (funiculi), anterior, posterior, and lateral, and a commissure area.
Bundles of fibers within funiculi called fasciculi.
Ascending tracts carry sensory impulses up the spinal cord to the brain.
Descending tracts carry motor impulses from the brain down the spinal cord.

Learning Outcome 4

Defines spinal nerve, dermatome, and myotome.
Compares somatic motor and autonomic function.
Compares sympathetic and parasympathetic function.
Compares the difference in the effects of the autonomic nervous system.
Describes membrane potentials and impulse transmission.

Cranial Nerves

12 pairs of nerves connected to the brain.
Carry sensory and motor signals.
Identified by Roman numerals (I-XII).
Originate and terminate within the brainstem (cranial nerve nuclei).

Somatic vs. Autonomic Nervous Systems

Somatic: Controls voluntary muscle functions, with one neuron (motor neuron) between CNS and the skeletal muscle. Receives input from sense organs, output to skeletal muscles (muscle contractions). Uses only acetylcholine as neurotransmitter.
Autonomic: Controls involuntary functions. Two-neuron chain (preganglionic and postganglionic) between CNS and target organ, innervates cardiac, smooth muscle, exocrine, and endocrine glands. Uses acetylcholine or norepinephrine as neurotransmitters.

Sympathetic vs. Parasympathetic Nervous Systems

SNS (Sympathetic): Active in times of stress, danger, or exertion. Increases blood pressure, heart rate.
PSNS (Parasympathetic): Active during rest or relaxation. Decreases heart rate, stimulates digestion.

Membrane Potentials

Resting potential: The negative charge inside the nerve cell when not conducting an impulse.
Depolarization: Change from negative to positive potential as action potential. Positive ions (sodium) flow in, changing the electrical charge to positive.
Repolarization: The change back to negative potential as positive sodium ions flow out.
Threshold: Trigger for the start of an action potential. The stimulus must exceed to trigger an action potential.
Explains the formation of resting and action potentials.
Describes mechanisms of impulse transmission and spreading along the axon.

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Description

This quiz explores essential concepts in neuroscience, focusing on ion channels and the anatomy of the spinal cord. It covers topics like action potentials, the refractory period, sensory information pathways, and neuron types. Test your knowledge on the critical structures and functions of the nervous system.