Chapter 12- Nervous Tissue

What are some of the functions of the CNS?

The CNS processes many different kinds of sensory information; is the source of thoughts, emotions, and memories; and gives rise to signals that stimulate muscles to contract and glands to secrete.

What roles do the dendrites, cell body, and axon play in communication of signals?

Dendrites and the cell body receive input; the axon conducts nerve impulses (action potentials) and transmits the message to another neuron or effector cell by releasing a neurotransmitter at its synaptic end bulbs.

Which type of neuron is the most abundant type of neuron in the CNS?

Most neurons in the CNS are multipolar neurons.

Where are most unipolar neurons located in the body?

Most unipolar neurons are located in the PNS; the cell bodies of these neurons are mainly in the ganglia of cranial and spinal nerves.

How did pyramidal cells get their name?

The cell body of a pyramidal cell is shaped like a pyramid.

Which CNS neuroglia function as phagocytes?

Microglia function as phagocytes in the central nervous system.

How do Schwann cells and oligodendrocytes differ with respect to the number of axons they myelinate?

One Schwann cell myelinates a single axon; one oligodendrocyte myelinates several axons.

What is the functional advantage of myelination?

Myelination increases the speed of nerve impulse conduction.

What is responsible for the white appearance of white matter?

Myelin makes white matter look shiny and white.

In which region of the brain does perception primarily occur?

Perception primarily occurs in the cerebral cortex.

What type of gated channel is activated by a touch on the arm?

A touch on the arm activates mechanically gated channels.

The resting membrane potential of a neuron typically is -70mV. What does this mean?

The -70mV resting membrane potential of a neuron means that the inside of the neuron is 70mV more negative than the outside when the neuron is at rest (not excited by a stimulus).

Suppose that the plasma membrane of a neuron has more sodium ion leak channels than potassium ion leak channels. What effect would this have on the resting membrane potential?

More sodium ions would leak into the cell and fewer potassium ions would leak out of the cell, which would make the resting membrane potential more inside-positive.

What kind of graded potential describes a change in membrane potential from -70 to -60 mV?

A change in membrane potential from -70 to -60 mV is a depolarizing graded potential since the membrane potential is inside less negative than at rest.

What kind of graded potential describes a change in membrane potential from -70 to -80 mV?

A change in membrane potential from -70 to -80 mV is a hyperpolarizing graded potential since the membrane potential is inside more negative than at rest.

Which parts of a neuron contain mechanically gated channels? Ligand-gated channels?

Ligand-gated channels and mechanically gated channels can be present in the dendrites of sensory neurons, and ligand-gated channels are numerous in the dendrites and cell bodies of interneurons and motor neurons.

Why does a stronger stimulus cause a larger graded potential than a weaker stimulus?

A stronger stimulus opens more mechanically gated channels or ligand-gated channels than a weaker stimulus.

What would happen if summation of graded potentials in a neuron did not occur?

Since individual graded potentials undergo decremental conduction, they would die out as they spread through the dendrites and cell body if summation did not occur and an action potential would not be generated at the trigger zone of the axon.

Which channels are open during the depolarizing phase? During the repolarizing phase?

Voltage-gated sodium ion channels are open during the depolarizing phase, and voltage-gated potassium ion channels are open during the repolarizing phase.

Will an action potential occur in response to a hyperpolarizing graded potential that spreads from the dendrites or cell body to the trigger zone of the axon of a neuron? Why or why not?

An action potential will not occur in response to a hyperpolarizing graded potential because a hyperpolarizing graded potential causes the membrane potential to become inside more negative and, therefore, farther away from the threshold (-55 mV).

Given the existence of leak channels for both potassium ions and sodium ions, could the membrane repolarize if the voltage-gated potassium ion channels did not exist?

Yes, because the leak channels would still allow potassium ions to exit more rapidly than sodium ions could enter the axon. Some mammalian myelinated axons have only a few voltage-gated potassium ion channels.

What factors determine the speed of propagation of an action potential?

The diameter of an axon, presence or absence of a myelin sheath, and temperature determine the speed of propagation of an action potential.

Why may electrical synapses work in two directions, but chemical synapses can transmit a signal in only one direction?

In some electrical synapses (gap junctions), ions may flow equally well in either direction, so either neuron may be the presynaptic one. At a chemical synapse, one neuron releases neurotransmitter and the other neuron has receptors that bind this chemical. Thus, the signal can proceed in only one direction.

The neurotransmitter acetylcholine (ACh) is excitatory at some synapses and inhibitory at other synapses. How is this possible?

At some excitatory synapses, ACh binds to ionotropic receptors with cation channels that open and subsequently generate EPSPs (excitatory postsynaptic potentials) in the postsynaptic cell. At some inhibitory synapses, ACh binds to metabotropic receptors coupled to G proteins that open potassium ion channels, resulting in the formation of IPSPs (inhibitory postsynaptic potentials) in the postsynaptic cell.

Suppose that EPSPs summate in a postsynaptic neuron in response to simultaneous stimulation by the neruotransmitters glutamate, serotonin, and acetylcholine released by three separate presynaptic neurons. Is this an example of spatial or temporal summation?

This is an example of spatial summation since the summation results from the buildup of neurotransmitter released simultaneously by several presynaptic end bulbs.

Suppose that the net summation of EPSPs and IPSPs is a depolarization that brings the membrane potential of the trigger zone of the postsynaptic neuron to -60 mV. Will an action potential occur in the postsynaptic neuron?

Since -60 mV is below threshold, an action potential will not occur in the postsynaptic neuron.

Why are norepinephrine, epinephrine, dopamine, and serotonin classified as biogenic amines?

Norepinephrine, epinephrine, dopamine, and serotonin are classified as biogenic amines because they are derived from amino acids that have been chemically modified.

A motor neuron in the spinal cord typically receives input from neurons that originate in several different regions of the brain. Is this an example of convergence or divergence?

A motor neuron receiving input from several other neurons is an example of convergence.

What is the role of the neurolemma in regeneration?

The neurolemma provides a regeneration tube that guides regrowth of a severed axon.

Schwann’s cells begin to form myelin sheaths around axons in the peripheral nervous system

During Fetal Development

Which ion channel opens in response to a change in membrane potential and participates in the generation and conduction of action potentials?

Voltage-Gated Channel

What are the divisions of the peripheral nervous system?

Somatic nervous system, autonomic nervous system, and enteric nervous system.

The resting membrane potential in neurons ranges from:

-40mV to -90mV

Which types of channels are used in production of electrical signals in neurons?

Leak channel, ligand-gated channel, mechanically gated channel, and voltage-gated channel.

Name the type of membrane channel that randomly opens and closes and is found in dendrites, cell bodies and axons of all types of neurons.

Leak channel

Schwann cells are functionally similar to ________.

Oligodendrocytes

What are ciliated CNS neuroglia that play an active role in moving the cerebrospinal fluid called?

Ependymal Cells

Plasticity means

Ability to change based on experience.

Immediately after an action potential has peaked, which cellular gates open?

Potassium

Describe graded potentials.

They are short-lived, can be called postsynaptic potentials, and can form on receptor endings.

Collections of nerve cell bodies outside the central nervous system are called ________.

Ganglia

An inhibitory postsynaptic potential (IPSP) is associated with ________.

Hyperpolarization

True or False: A stimulus traveling toward a synapse appears to open calcium ion channels at the presynaptic end, which in turn promotes fusion of synaptic vesicles to the axonal membrane.

True

WIth respect to neurons, the term, "nerve fiber" refers to

Both Axons and Dendrites

What is the role of acetylcholinesterase?

Destroy ACh a brief period after its release by the axon endings.

True or False: Cell bodies of sensory neurons may be located in ganglia lying outside the central nervous system.

True

The sheath of Schwann is also called the ________.

Neurilemma

Which organelle is a common site of protein synthesis in neurons?

Nissl Body

Which types of cells display the property of electrical excitability?

Skeletal muscle cells, neurons, and cardiac muscle cells.

What are the functions of the nervous system?

Sensory function, integrative function, and motor function.

What are the divisions of the peripheral nervous system?

Somatic nervous system, autonomic nervous system, and enteric nervous system.

The motor portion of the autonomic nervous system can be divided into

Sympathetic and Parasympathetic Divisions

Which types of cells display the property of electrical excitability?

Muscle Cells and Neurons

Which organelle is a common site of protein synthesis in neurons?

Nissl Body

With respect to neurons, the term "nerve fiber" refers to

Both Axons and Dendrites

This type of neuron has one dendrite and one axon emerging from the cell body.

Bipolar Neuron

Schwann’s cells begin to form myelin sheaths around axons in the peripheral nervous system

During Fetal Development

This type of nervous tissue contains neuronal cell bodies, dendrites, unmyelinated axons, axon terminals, and neuroglial cells.

Gray Matter

Which types of channels are used in production of electrical signals in neurons?

Leak channel, ligand-gated channel, mechanically gated channel, voltage-gated channel.

The resting membrane potential in neurons ranges from:

-40 to -90 mV

A polarized cell

Has a charge imbalance across its membrane, includes most cells of the body, and exhibits a membrane potential.

Na+/K+-ATPase is considered to be an electrogenic pump because

It contributes to the negativity of the resting membrane potential.

A depolarizing graded potential

Makes the membrane less polarized.

When a depolarizing graded potential makes the axon membrane depolarize to threshold,

Voltage-gated Na+ channels open rapidly.

During this period, a second action potential can only be initiated by a larger than normal stimulus

Relative Refractory Period

Saltatory conduction

Occurs only in myelinated axons.

Which type of axons has the largest diameter?

A Fibers

The nervous system can distinguish between a light touch and a heavier touch by

Changing the frequency of impulses sent to sensory centers.

Which terms are used to describe a type of synapse?

Axodendritic, Axosomatic, and Axoaxonic.

Faster communication and synchronization are two advantages of

Electrical Synapses

An excitatory neurotransmitter _________ the postsynaptic membrane.

Depolarizes

IPSP stands for

Inhibitory Postsynaptic Potential

Diffusion, enzymatic degradation, and uptake by cells are all ways to

Remove a Neurotransmitter

When the summed total of postsynaptic potentials rises above threshold, creation of action potentials occurs

At the Trigger Zone

A postsynaptic neuron responds to neurotransmitters released by a presynaptic neuron by creating

Either EPSPs or IPSPs

Name the small-molecule neurotransmitters.

Acetylcholine, glutamate, aspartate, gamma aminobutyric acid (GABA), glycine, norepinephrine, epinephrine, dopamine, serotonin, ATP, nitric oxide, and carbon monoxide.

This type of neural circuit consists of a single presynaptic neuron synapsing with several postsynaptic neurons.

Diverging Circuit

Plasticity means

Ability to change based on experience

Which type of neuron is the most common type of neuron found in the brain and spinal cord?

Multipolar Neuron

Which type of neurons have one axon and one dendrite emerging from the cell body and are found in the retina of the eye, inner ear, and olfactory region of the brain?

Bipolar Neuron

Name the type of membrane channel that randomly opens and closes and is found in dendrites, cell bodies, and axons of all types of neurons.

Leak Channel

Name the type of membrane channel that opens in response to chemical binding and is found in dendrites of some sensory receptors like pain receptors, and in the dendrites and cell bodies of interneurons and motor neurons.

Ligand-Gated Channels

Name the type of membrane channel that opens in response to touch, pressure, vibration, or tissue stretching and is found in the auditory receptors of the ear, and in touch and pressure receptors in the skin.

Mechanically Gated Channels

Name the type of membrane channel that opens in response to changes in membrane potential and is located in axons of all types of neurons.

Voltage-Gated Channels

Chromatolysis refers to

Break up of Nissl bodies after neural injury.

Wallerian degeneration refers to

Degeneration of the distal end of axon and myelin sheath after neural injury.

Hearing your cell phone ring in an otherwise quiet lecture hall is an example of which type of nervous system functions?

Sensory Function

Which type of electrical signals allow rapid long-distance communication within the nervous system?

Nerve Action Potential

In an action potential, the current that flows down the axon of a neuron is generated by the movement of ______ across the membrane.

Ions

In the process of spatial summation, ______ are added together and _____ are subtracted from that total to determine whether _____ will be created at the trigger zone of the postsynaptic neuron.

EPSPs; IPSPs; action potentials

In temporal summation, a single presynaptic neuron stimulates the creation of action potentials in a postsynaptic neuron when it

Fires at a fast enough rate that the sum of EPSPs in the postsynaptic neuron moves above threshold.

Which neurotransmitters are used in virtually all of the inhibitory synapses found in the spinal cord?

Gama aminobutyric acid (GABA) and glycine.

A neurotransmitter that binds to an ionotropic receptor that contains a chloride channel would be classified as an

Inhibitory neurotransmitter and would produce an IPSP in the postsynaptic neuron.