Neuroscience Chapter 5 Quiz

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Questions and Answers

What is the primary event that causes depolarization during an action potential?

K+ efflux from the neuron

Na+ influx into the neuron (correct)

Ca2+ efflux from the neuron

Cl- influx into the neuron

What occurs during the relative refractory period of a neuron?

The neuron can respond to any stimulus regardless of strength.

Threshold for action potential generation is elevated. (correct)

The neuron generates action potentials continuously.

The neuron is at resting membrane potential.

In the context of action potentials, what is meant by the term 'all-or-none phenomenon'?

A stimulus must be strong enough to cause depolarization.

Neurons can fire multiple action potentials at varying amplitudes.

Once the threshold is reached, the action potential is generated fully or not at all. (correct)

Action potentials vary in size based on the strength of the stimulus.

What primarily dictates the direction of nerve impulse propagation along an axon?

The refractory period of the previous segment Signup and view all the answers

What characterizes graded potentials compared to action potentials?

Graded potentials are localized and brief changes in membrane potential. Signup and view all the answers

Which statement accurately describes the role of neuroglia in the nervous system?

Neuroglia segregate, insulate neurons, and assist them in various functions. Signup and view all the answers

What distinguishes the somatic system from the autonomic system within the efferent division?

The somatic system innervates skeletal muscle while the autonomic system innervates smooth and cardiac muscle. Signup and view all the answers

In the context of the nervous system, a 'tract' refers to which of the following?

A bundle of nerve fibers in the central nervous system. Signup and view all the answers

Which type of neuroglia is responsible for providing myelin in the peripheral nervous system?

Schwann cells Signup and view all the answers

What is the primary function of dendrites in neurons?

To receive signals from other neurons. Signup and view all the answers

What is the primary function of the sodium-potassium pump in a resting neuron?

To maintain the resting membrane potential by exchanging sodium and potassium ions Signup and view all the answers

Which type of neuron primarily carries impulses toward the central nervous system?

Sensory neurons Signup and view all the answers

What is the role of nodes of Ranvier in myelinated axons?

To increase the speed of transmission of impulses Signup and view all the answers

What characterizes the resting membrane potential of a neuron?

It is caused by permeability differences of the membrane to sodium and potassium ions Signup and view all the answers

Which statement correctly describes a feature of myelinated and nonmyelinated fibers?

Nonmyelinated fibers are surrounded by supporting cells but lack myelin sheath Signup and view all the answers

Study Notes

Nervous System Overview

The nervous system is anatomically divided into the central nervous system (CNS) and the peripheral nervous system (PNS).
The CNS includes the brain and spinal cord.
The PNS includes mainly cranial and spinal nerves.
Major functional divisions of the PNS include the sensory (afferent) division and the motor (efferent) division.
The sensory division carries impulses to the CNS.
The motor division carries impulses from the CNS.
The motor division is further divided into somatic (voluntary) and autonomic (involuntary) systems.
The somatic system serves skeletal muscles.
The autonomic system innervates smooth and cardiac muscle, and glands.

Nervous System Cells

The nervous system consists of two types of cells: neuroglia and neurons.
Neuroglia (supporting cells) support and insulate neurons.
CNS neuroglia include astrocytes, microglial cells, ependymal cells, and oligodendrocytes.
Astrocytes are the most abundant CNS neuroglia.
Microglial cells act as defensive cells in the CNS.
Ependymal cells line cerebrospinal fluid-filled cavities.
Oligodendrocytes form myelin sheaths around CNS nerve fibers.
PNS neuroglia include Schwann cells and satellite cells.
Schwann cells (which form myelin) surround neurons in the PNS.
Satellite cells surround neurons in the PNS.

Neurons

Neurons have a cell body and cytoplasmic processes called axons and dendrites.
A bundle of nerve fibers is called a tract in the CNS and a nerve in the PNS.
A collection of cell bodies is called a nucleus in the CNS and a ganglion in the PNS.
The cell body is the biosynthetic center (and receptive center) of the neuron.
Most neurons have many dendrites, which are receptive processes that conduct signals toward the nerve cell body.
All neurons have one axon, which generates and conducts nerve impulses away from the nerve cell body.
Axon terminals release neurotransmitters.
Bidirectional transport along axons uses ATP-dependent motor proteins that "walk" along microtubule tracks.
This transport moves substances to and from the axon terminals and the cell body.
Large nerve fibers (axons) are myelinated.
Myelin sheaths are formed by Schwann cells in the PNS and oligodendrocytes in the CNS.
Myelin sheath gaps are called nodes of Ranvier.
Anatomically, neurons are classified as multipolar, bipolar, or unipolar.

Classification of Neurons

Functionally, neurons are classified as sensory, motor, or interneurons.
Sensory neurons conduct impulses toward the CNS.
Motor neurons conduct impulses away from the CNS.
Interneurons (association neurons) lie between sensory and motor neurons in neural pathways.

Basic Principles of Electricity

Voltage (V) measures the potential energy of separated electrical charges.
Current (I) is the flow of electrical charge.
Resistance (R) hinders current flow.
Ohm's law states: I = V/R.
In the body, ions provide the electrical charges.
Cellular plasma membranes provide resistance to ion flow.
Membranes contain leakage channels (non-gated, always open) and gated channels.

The Resting Membrane Potential

A resting neuron exhibits a resting membrane potential of -70 mV (inside negative).
This potential is due to differences in sodium (Na+) and potassium (K+) ion concentrations and membrane permeability to these ions.
The sodium-potassium pump ejects 3 Na+ from the cell for each 2 K+ transported in.

Membrane Potentials That Act as Signals

Depolarization reduces membrane potential (inside becomes less negative).
Hyperpolarization increases membrane potential (inside becomes more negative).
Graded potentials are small, brief, local changes in membrane potential that act as short-distance signals.
Action potentials (APs) are large, brief depolarization signals, and are important for long-distance neural communication.
APs are an all-or-none phenomenon.
During an AP, the membrane potential rapidly rises and falls.
Repolarization and hyperpolarization are caused by K+ efflux.
The current produced by APs dissipates with distance.
In nonmyelinated fibers, APs are produced in a wave along the axon by continuous conduction.
In myelinated fibers, APs are generated only at myelin sheath gaps, and are propagated more rapidly by saltatory conduction. During the absolute refractory period, a neuron cannot respond to another stimulus.
During the relative refractory period, the neuron's threshold is elevated because repolarization is ongoing.

The Synapse

A synapse is a functional junction between neurons.
The presynaptic neuron transmits information.
The postsynaptic neuron receives information.
Electrical synapses allow ions to flow directly from one neuron to another.
Chemical synapses involve neurotransmitter release and binding.
When an impulse reaches the presynaptic axon terminals, voltage-gated Ca2+ channels open, and Ca2+ enters the cell, mediating neurotransmitter release.
Neurotransmitters diffuse across the cleft and bind to postsynaptic membrane receptors.
Neurotransmitter effects are terminated by diffusion, enzymatic breakdown, or reuptake.

Postsynaptic Potentials and Synaptic Integration

Binding of neurotransmitter at excitatory synapses results in local graded potentials called excitatory postsynaptic potentials (EPSPs).
Neurotransmitter binding at inhibitory synapses results in hyperpolarizations called inhibitory postsynaptic potentials (IPSPs).
IPSPs move the membrane potential farther from threshold.
The axon hillock acts as a neuronal integrator.
Presynaptic inhibition is mediated by axoaxonal synapses that reduce neurotransmitter release.

Classification of Neurotransmitters

Neurotransmitters are classified by function (inhibitory or excitatory) and by chemical structure (e.g., acetylcholine, biogenic amines, amino acids, peptides, purines, dissolved gases, and lipids).

Neurotransmitter Receptors

Neurotransmitter receptors are either channel-linked receptors (leading to fast changes in membrane potential) or G protein-coupled receptors (leading to slow synaptic responses).

Cerebral Hemispheres

The two cerebral hemispheres exhibit gyri, sulci, and fissures.
The longitudinal fissure partially separates the hemispheres.
Other fissures subdivide each hemisphere into lobes.
Each hemisphere consists of the cerebral cortex, white matter, and basal nuclei.

Brain Regions and Organization

The adult brain is divided into the cerebral hemispheres, diencephalon (thalamus, hypothalamus, pituitary gland), brain stem (midbrain, pons, medulla oblongata), and cerebellum.
The cerebral hemispheres and cerebellum have gray matter nuclei surrounded by white matter and an outer cortex of gray matter.
The diencephalon and brain stem lack a cortex.
The brain contains four ventricles filled with cerebrospinal fluid (CSF).
Two lateral ventricles are located in the cerebral hemispheres.
The third ventricle is in the diencephalon. The fourth ventricle is between the brain stem and the cerebellum.

Blood Brain Barrier

The blood-brain barrier includes the least permeable capillaries of the body.
This barrier excludes many potentially harmful substances by limiting their transport.
It's not completely impermeable to all substances though (e.g., fats, respiratory gases, alcohol, nicotine, and anesthesia).

Spinal Cord

The spinal cord extends from the medulla oblongata to the region of T12.
Below T12 is the cauda equina (a collection of spinal nerves).

Peripheral Nervous System

The peripheral nervous system has an afferent and efferent system
Structure of a nerve includes the endoneurium, perineurium, and epineurium, surrounding individual fibers, fascicles, and the whole nerve respectively.
Branches of the peripheral nervous system include the somatic motor system, the autonomic system, and its sympathetic and parasympathetic divisions.

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Description

Test your knowledge on key concepts in neuroscience, including action potentials, graded potentials, and the roles of various types of neurons and neuroglia. This quiz covers essential topics such as the all-or-none phenomenon and nerve impulse propagation. Challenge yourself with these thought-provoking questions!