A&P Lecture 15

What does the abbreviation CNS stand for, and what structures constitute it?

Central Nervous System; Brain and Spinal Cord

What does PNS stand for and which two structures comprise it?

Peripheral Nervous System; Nerves and Ganglia

What are nerves? Is a nerve fiber the same as an axon

Cordlike structures that conduct information; Yes, they are the same

What are ganglia? And ganglion?

Knotlike swelling in a nerve where the cell bodies of neurons are concentrated; Ganglion in singular term, referring to only one structure

What does afferent mean? And efferent?

Afferent means “toward” and efferent means “away” in reference to CNS

Sensory information is transmitted from sensory receptors found in organs to the CNS by afferent or efferent nerve fibers?

Afferent fibers

What do efferent nerve fibers transmit, sensory or motor information?

Motor information

What is a mixed nerve?

Those nerves that contain motor and sensory fibers

Which subdivisions of the PNS (sensory/motor, somatic/visceral) are involved in transmitting sensory information, such as a painful stimulus from the skin to the CNS?

Sensory somatic

Which subdivisions of the PNS are involved in transmitting sensory information, such as a painful stimulus, from organs in the thoracic and abdominal cavities (e.g. heartburn) to the CNS for processing?

Sensory visceral-recall the concept of viscera

Which divisions of the PNS (sensory/motor, somatic/visceral) are involved in relaying information from the CNS to the skeletal muscle for contracting?

Motor somatic

Which subdivisions of the PNS (sensory/motor, somatic/visceral) are involved in relaying information from the CNS to the cardiac or smooth muscle for contracting/relaxing?

Visceral motor = Autonomic nervous system

Which subdivisions of the PNS (sensory/motor, somatic/visceral) are involved in relaying information from the CNS glands to release their contents (such as enzymes, saliva, pancreatic juice, etc.)?

Motor visceral = Autonomic nervous system

Which subdivisions of the PNS (sensory/motor, somatic/visceral) correspond to the autonomic NS?

Motor visceral

Which PNS subdivisions (sensory/motor, somatic/visceral) are responsible for involuntary somatic reflexes involving skeletal muscle contraction?

Motor somatic

Which PNS subdivision handles (a) sensing a “satisfied stomach” after a meal, (b) starting leg muscle contractions for kicking a ball, ( c) increasing heart rate, and (d) controlling bowel movements?

(a) visceral sensory, (b) somatic motor, (c, d) visceral motor (ANS)

Is it possible to locate nuclei within the PNS? (Note: this term should not be confused with the cell nucleus.)

Nuclei structures are confined to the CNS

Which term represents the equivalent of ganglia in the CNS?

Nuclei

What is a tract? What is the primary differentiating factor between nerves, and tracts, particularly in terms of their locations?

Bundles of axons in the CNS; The term “nerves” refers to the same concept but in the PNS

What are the three types of neurons, considering their role (function)?

Sensory (afferent) neurons, interneurons, motor (efferent) neurons

What are effectors?

Those organs or body structures that carry out the motor action (typically muscles and glands)

What is the meaning of the prefix “inter-” in the term interneurons?

Between (refers to the fact that they are between the sensory and motor neurons)

What does “integration” mean? What type of neurons carry out the integrative function and where are they?

The processing, storing, retrieving of information, making decisions that determine how the body responds to the stimuli-interneurons located in the CNS

Where are the cell bodies of sensory and motor neurons located? (consider whether they are found in the PNS or CNS and whether they are associated with receptors or effector organs)

Sensory neurons: cell bodies in ganglia (PNS), associated with receptor organs; Motor neurons: cell bodies in CNS, associated with effectors

Are sensory neurons the same as efferent neurons?

No, they are different neurons

What are the three primary components of a neuron, and which two of these constitute neuron processes?

Neuron processes: dendrites and axon; the other component is the cell body

Which neuron part receives and conveys incoming messages toward the cell body?

Dendrites

Which part of a neuron is the control center? What are the other four names for this part of the cell?

Cell body= soma = neurosoma = perikaryon

Which part of the neuron generates and conducts nerve impulses away from the nerve cell to the terminal arborization?

Axon

Where does synthesis of chemicals, such as neurotransmitters, occur in the neuron?

Cell body

Why is it essential to increase the surface of the dendrites and which structures facilitate this? Can dendrites receive information for more than one neuron at the same time?

To integrate multiple input (information) from different neurons- dendritic spines

What do Nts stand for? Where are they stored within a neuron?

Neurotransmitters; In synaptic vesicles at the terminal buttons

What channels can you find in dendrites: chemically regulated or voltage-regulated ion gates? Specifically, for which ion?

Chemically regulated; For sodium (Na+)

What does “chemically regulated” mean when referring to ion channels?

To open the channel, they need a chemical (NT) to bind to a receptor

What two parts of a neuron form the trigger zone? Why is called a “trigger zone?” (tip: what does trigger mean?)

Trigger zone: axon hillock + initial segment; it will “trigger” (initiate) the action potential (nerve signal)

(a) Where is the axon hillock, in the soma or in the axon? (b) What is the first part of the axon called?

(a) Soma; (b) Initial segment

What types of gates/channels have the axon: chemically-regulated or voltage-regulated? What does voltage regulation mean when referring to channels?

Voltage-regulated; These channels open/close with changes in the voltage potential of the membrane

Why is the axon called the “conducting region?”

Only the axon has voltage-regulated ion gates able to produce action potentials (nerve signals)

Where are the terminal arborization and terminal buttons in a neuron? Why is the terminal arborization known as the secretory region of the neuron?

Terminal arborization refers to the branching network at the end of an axon, where synaptic buttons or end bulbs contain vesicles with neurotransmitters

What are the three main types of neurons according to the number of processes extending from the soma? What are the most abundant type of neurons in the CNS?

Multipolar (most neurons), bipolar, and unipolar

How many dendrites and axons do a multipolar neuron have? And a bipolar neuron? Unipolar?

Multipolar: multiple dendrites + 1 axon

Bipolar: 1 dendrite + 1 axon

Unipolar: only 1 process (axon) divided into two segments: peripheral and central (processes)

Do unipolar neurons have dendrites? What name do dendrites receive in this type of neuron? Are they at the end of the peripheral axon or the central axon part?

They have receptive endings at the peripheral process that function as dendrites

Dorsal root ganglion cell is a type of unipolar neuron that carry sensory signals from receptor organs to the spinal cord (CNS). Which part of the axon (peripheral or central) is closest to the CNS (spinal cord)? Does it make sense to call it “central?”

The central process

Classify the following types of neurons as multipolar, bipolar, and unipolar, and indicate their locations (a) retinal cell, (b) pyramidal cell, ( c) olfactory cell, and (d) purkinje cell

(a) bipolar; eye

(b) multipolar; cerebral cortex

(c ) bipolar; around nose

(d) multipolar; cerebellum

(a) what are glial cells? (b) are they neurons? (c ) are neuroglia and glial cells the same?

(a) glial cells are supportive and protective cells in the nervous system that assist neurons and help maintain the overall health of the nervous tissue

(b) No

(c ) Yes

(a) what are the four types of glial cells present in the CNS? (b) what are the two types of glial cells present in the PNS?

(a) oligodendrocytes, ependymal cells, astrocytes, microglial cells

(b) Schwann cells and satellite cells

Which two types of neuroglia create insulating coverings known as the myelin sheaths?

Oligodendrocytes in the CNS and Schwann cells in the PNS

(a) Which glial cells are responsible for the production of CSF? (b) Which glial cells acts as phagocytes in the CNS? (c ) Which type of neuroglia contributes to forming the blood-brain barrier?

(a) ependymal cells

(b) microglial cells

(c ) astrocytes

Which glial cells manage the ESF environment surround neuronal cell bodies in the CNS? How about the PNS?

Astrocytes in the CNS, Satellite cells in the PNS

What is insulation? What provides insulation for the axon (similar to the plastic covering that surrounds the wires of an electrical cord?)

Insulation refers to the process of restricting or impeding the flow of ions along the axon’s membrane, typically achieved through the presence of a myelin sheath, which enhances the efficiency of electrical signal propagation

(a) What is the main component of myelin? (proteins, lipids, or carbs?) (tip: think of which component allows for better insulation for example in cold environments)

Lipids

Does myelin speed up or decrease the electrical signal (current) conduction (i.e., the flow of ions from one point to another?)

Speed up

How is a myelin sheath formed in the CNS? (Tip: Which cells? Are these whole cells wrapping around the axons or just their processes?) Does an oligodendrocyte myelinate only one axon or multiple axons?

Each oligodendrocyte extends its processes to provide myelination for multiple nerve fibers

(a) What is the name of the small gap or space in the myelin sheath that surrounds an axon? (b) What is the term for the myelinated axon segment between two adjacent nodes of Ranvier?

(a) Node of Ranvier

(b) internode

How is a myelin sheath formed in the PNS? (tip: which cells? Are these whole cells wrapping around the axons or just their processes?) In the PNS, each myelinated internode is formed by one or more Schwann cells?

Schwann cell spirals repeatedly around a single nerve fiber; Each myelinated segment (internode) of axon is wrapped by a different Schwann cell

What are neurilemma and axolemma? Which of this is needed for axon regeneration in the PNS?

The neurilemma is the outermost membrane of Schwann cells, which surrounds and insulates axons. The axolemma is the cell membrane that surrounds the axon. To regenerate: Soma intact + at least some neurilemma remains

(a) What is local potential, and which part(s) of the neuron can be created? (b) Is a local potential the same as a graded potential? (c ) What does it mean by “graded” potential?

(a) temporary change in the electrical voltage or mb potential that occurs in response to the activation of NT receptors on the dendritic membrane of a neuron

(b) Yes

(c ) they vary in magnitude depending on stimulus strength

(a) Which type of stimulus initiates a local potential?

(b) Through which type of channel?

(c ) chemical/ligand or voltage-gated channels

(a) chemical (neurotransmitter) or sensory stimulus (e.g., light, pressure, temperature)

(b) ligand-gated Na+ channels

(a) What is the typical path of a local potential from origin to destination in a neuron?

(b) Is the electrical signal in a local potential the same strength at the beginning compared to the end (i.e. close to the axon)

(a) typically from dendrites to soma and axon hillock

(b) signals decay with distance

Is a decrease in resting mb potential (e.g., from -70 mV to -90 mV) caused by a local potential excitatory or inhibitory, and does it make triggering an AP easier or harder; is this phenomenon called depolarization or hyperpolarization?

Inhibitory local potential; more difficult to generate an AP; hyperpolarization

Which travels further, a graded potential or an action potential (AP)? Which initiates the other?

An AP; for an AP to occur, first a local potential must be created (to depolarize the mb to the threshold value)

What is the difference between temporal summation and spatial summation?

Temporal: increase in frequency of the stimulus

Spatial: stimuli being received from multiple neurons at the same time

Does the local potential stop generating if you remove a neurotransmitter from its receptor at the dendrites?

Yes

(a) What is an action potential (AP), and where does it occur?

(b) What is the typical path of an AP from origin to destination in a neuron?

(a) a brief, rapid, and reversible change in the electrical voltage or mb potential that allows for transmission of electrical signals in neurons

(b) it starts in trigger zone and go down the axon towards the terminal arborization

Is the electrical in an action potential the same strength at the beginning compared to the end (i.e., close to the terminal arborization)?

Yes (opposite to local potential)

Which type of stimulus initiates an action potential? Through which type of channel? (chemical/ligand or voltage-gated channels?)

Voltage (depolarization, triggered by local potential reaching threshold). Voltage-gated channels

What is the all-or-none law considering an action potential?

It states that once a stimulus reaches the threshold potential, the neuron will fire an AP of a consistent magnitude and duration, regardless of the stimulus’s strength/intensity; if threshold is not reached, no AP will occur

How is the nerve signal conducted in a neuron from the dendrite to the end of an axon? What type of potentials, local, or action potentials, are generated along this path?

First, LP in dendrites- arrives at axon hillock, if threshold is reached, first AP is generated (then though axon). At terminal buttons, NTs are released and bind to receptors in other neuron producing local (postsynaptic) potentials

Where does continuous conduction occur in nonmyelinated or in myelinated axons? Why is it called continuous?

In nonmyelinated “continuous” because the AP spreads continuously along the entire length of the mb without interruption; this is because every part of the axon mb is capable of generating AP

What is a nerve signal (also known as nerve impulse)?

It is a traveling wave of membrane excitation produced by an action potential, involving the flux of ions in the axon, that carries information within the nervous system

(a) Where are the voltage-gated channels in nonmyelinated axons? Are they at specific regions or along the entire axon length?

(b) Where can you find higher concentrations of these channels in myelinated axons, at the nodes or internodes?

(a) Through all the membrane of axon

(b) At the nodes

In which type of axons does saltatory conduction occur: nonmyelinated or myelinated axons? Why?

In myelinated axons because voltage-gated channels needed to create APs are only at specific places (nodes)

Are voltage-gated ions required to initiate an action potential?

Yes, that is why AP are not generated in dendrites (they have chemically-gated channels instead)

Which ions travel along the node (inside the nerve fiber) and initiate depolarization of the membrane at the next node?

Sodium ions

What characteristic of the internodes increases the flow of sodium ions (current=electrical signal) at that place?

The presence of myelin sheath. In the internodal segments the conduction is very fast, it only requires movement of sodium ions and not opening of channels that might require more time

Can AP be generated at the internodes? Why (not)?

No; there is not voltage-gated channels there and are covered by myelin which provides insulation

What is the reason behind the faster conduction of action potentials in a myelinated axon compared to a non-myelinated axon?

The continuous opening of voltage-gated channels in nonmyelinated axons requires more time compared with the flow of Na+ in the internodes