ch 12 nervous system

What two organ systems are dedicated to maintaining internal coordination?

endocrine; nervous

The nervous system carries out its coordinating task in three basic steps. 1. receives info, transmits messages to _____ 2. CNS processes and determines response 3. CNS gives ______

CNS; commands

The nervous system has two major anatomical subdivisions: the ______ nervous system and _________ nervous system; the latter has additional subdivisions.

central; peripheral

What does the central nervous system (CNS) consist of? ________ and _____ _____

brain; spinal cord

What does the peripheral nervous system (PNS) consist of? What is it composed of?

the rest; nerves and ganglia

What is a nerve?

bundle of nerve fibers wrapped in fibrous connective tissue

What is a ganglion?

knotlike swelling in a nerve where the cell bodies of peripheral neurons are concentrated

What two divisions is the PNS divided into?

sensory and motor

What division carries sensory signals from receptors to the CNS; this pathway informs the CNS of stimuli?

sensory; stimuli from within and around the body

The somatic sensory division carries signals from where?

receptors in the skin, muscles, bones, and joints

The visceral sensory division carries signals from where?

viscera of thoracic and abdominal cavities (heart, lungs, stomach, urinary bladder)

What division carries signals from the CNS to gland and muscle cells that carry out the body's responses? What are the cells and organs that respond called?

motor division; effectors

The somatic motor division carries signals where? What are somatic reflexes?

to skeletal muscles; unconcious skeletal muscle motor responses

The visceral motor division carries signals where? What are visceral reflexes?

to glands, cardiac muscle, and smooth muscle; non skeletal muscle response carried out internal organs

The autonomic nervous system has two further divisions.

sympathetic and parasympathetic

The sympathetic division tends to arouse the body for action. What are some examples of this?

by accelerating the heartbeat, increase respiratory flow

The parasympathetic division tends to have a calming effect. What is an example of this?

slowing down the heartbeat

Nerve cells, or neurons, have three fundamental physiological properties that enable them to communicate with other cells. What are these three properties?

excitability, conductivity, secretion

Neurons fall into three functional classes based on the three major aspects of nervous system function. What are these three classes and what are they doing?

sensory/afferent - toward CNS; interneuron - integrate; motor/efferent - away from CNS

A _______ neuron of the spinal cord illustrates the general structure of a neuron.

motor

What is the control center known as?

neurosoma/soma/cell body

What does the soma contain?

nucleus and nucleolus

What does the cytoplasm contain?

mitochondria, lysosomes, Golgi complex, inclusions, rough endoplasmic reticulum, and cytoskeleton

What does the cytoskeleton consist of? What are Nissl bodies?

microtubules and neurofibrils; rough ER, rosettes of free ribosomes, site of protein synthesis

Do mature neurons divide?

no

What are dendrites and what function do they serve?

branched processes from a neuron; primary site for recieving signals from other neurons

The axon (nerve fiber) originates on a mound on the soma called the axon __________.

hillock

The axon is cylindrical and relatively unbranched for most of its length, although it may give rise to axon ___________ along the way.

collaterals

An axon is specialized for what?

rapid conduction of nerve signals to remote points from soma

What is the axoplasm and axolemma?

cytoplasm of axon; axon membrane

At the distal end, an axon usually has a terminal arborization (an extensive complex of fine branches). Each branch ends in a synaptic _______ (terminal button) that forms a _________ (synapse) with the next cell.

axon terminal; junction

The synapse contains synaptic vesicles full of what?

neurotransmitters

Neurons vary in structure, and they are classified according to the number of _________ extending from the soma.

processes

What are multipolar neurons?

neurons with one axon and multiple dendrites; most neurons of brain and spinal cord

What are bipolar neurons? Can you give some examples?

neuron with one axon and one dendrite; olfactory cells of nose, sensory neurons of the ear

What are unipolar neurons? Where are these found?

neuron w one single process from soma

Anaxonic neurons have multiple dendrites but no axon. They communicate through their dendrites and do not produce action potentials; Where are these found?

brain, retina, adrenal medulla

_________ transport refers to the passage of proteins, organelles, and other materials along an axon, to and from the cell soma.

Axonal

What is anterograde transport? What is retrograde transport?

movement away from the soma down the axon; movement up the axon toward the soma

Materials travel along microtubules of the _____________.

axon

Neurons are outnumbered by as much as 10 to 1 by cells called _______, or glial cells. What is one of the main roles of these cells in regards to neurons?

neuroglia; protect neurons and help them function

There are six types of neuroglia, each of which has a unique function; four types occur only in the ______.

CNS

What do Oligodendrocytes resemble? What is myelin sheath and what does it do?

an octopus; insulates the nerve fiber, speeds up signal conduction in the nerve fiber

What do Ependymal cells resemble? What do they produce?

cuboidal epithelium; cerebral spinal fluid

What are Microglia, and what do they do? Where would they become concentrated in?

small macrophagesthat develop from white blood cells called monocytes; sites of brain injury

What do Astrocytes look like? What are some of their functions?

starlike shape; supportive framework, monitor neuron activity, convert blood glucose to lactate

Where are Schwann cells found (which division of the nervous system) and what do they do?

PNS; produce myelin sheath, assist in regeneration of damaged fibers

Where are Satellite cells found and what do they do?

PNS; provide insulation around soma and regulate chemical environment of neurons

The ________ ________ is a spiral layer of insulation around a nerve fiber.

myelin sheath

What is the composition of myelin?

20% protein, 80% lipids

Production of the myelin sheath is called what? When does it begin and when is it complete?

myelination; begins in 14th week of fetal develop, completed in late adolescence

In the PNS, a Schwann cell spirals repeatedly around a single nerve fiber, laying down up to 100 compact layers of its own membrane with almost no _________.

cytoplasm

What is the neurilemma, and what does it contain?

thick, outermost layer of myelin sheath

What are nodes of Ranvier?

gaps between segments of myelin sheath

What are internodes?

myelin-covered segments from each node to the next

Many nerve fibers in the CNS and PNS are unmyelinated, but in the PNS, even unmyelinated fibers are enveloped in ________ cells.

Schwann

The speed at which nerve signals are conducted along a nerve fiber depends on the _________ of the fiber and the presence or absence of myelin.

diameter

Signal conduction occurs where?

along the surface of a fiber

Large fibers have more surface area and conduct more _________ than small fibers.

rapidly

Slow unmyelinated fibers are sufficient for many processes. Fast myelinated fibers occur where speed is vital, such as in motor commands to ________ _________.

skeletal muscles

Nerve fibers of the PNS are vulnerable to trauma, but may regenerate if its ______ is intact and at least some neurilemma remains. Can you briefly describe this process?

soma; The fiber distal to the injury degenerates. Axon stump sprouts multiple growth processes. Schwann cells, basal lamina, and neurilemma form a regeneration tube.

Two key issues in neurophysiology are:

how does a neuron generate an electrical signal; how does it transmit a meaningful message to the next cell

How does a neuron generate an electrical signal?

How does it transmit a meaningful message to the next cell?

What is an electrical potential? What is an electrical current?

a difference in the concentration of harged particles btw one point and another; flow of charged particles from one point ot another

As long as a battery has an electrical potential, it is ________.

polarized

Living cells are polarized because a ________ difference, the resting membrane potential (RMP), exists across the plasma membrane.

charge

The membrane potential is -______ mV in a "resting" neuron. The negative value means more negative charges are on the inside of the membrane than on the outside.

70

Electrical currents in the body are created by the flow of ions such as ___+ and ___+ through gated channels.

Na, K

The resting membrane potential exists because __________ are unequally distributed between the extracellular fluid (ECF) and the intracellular fluid (ICF).

electrolytes

Three factors collectively determine the RMP. What are these three factors?

diffusion of ions down their concentraiton gradients through the membrane; selective permeability of the membrane, allowing some ions to pass more easily than others; the electrical attraction of cations and anions to each other

What ions have the greatest influence on RMP and why?

potassium ions, the plasma membrane is more permeable to K+ than to any other ion

Many cytoplasmic anions cannot escape from the cell because of their size or charge, so that diffusion of K+ out of the cell down its concentration gradient leaves the ICF with a net _________ charge.

negative

The negative ICF attracts K+ back into the cell and eventually _________ is reached between concentration-driven diffusion and electrical attraction, resulting in no further net diffusion of K+.

equilibrium

At equilibrium, K+ is ____ times as concentrated in the ICF as in the ECF.

40

______ ions (Na+) also influence the RMP.

sodium

Na+ is 12 times more concentrated in the _____ than in the _____.

ECF; ICF

Although the resting membrane is less permeable to _____, it does diffuse down its concentration gradient into the cell and is attracted by the anions of the ICF.

Na+

The ________ pump continually compensates for the leakage of Na+ and K+ into and out of the cell.

Na+-K+

For every 1 ATP consumed by the Na+-K+ pump, ___ Na+ are pumped out of the cell and ___ K+ are brought in.

3; 2

The Na+-K+ pump accounts for about ____% of the ATP requirement of the nervous system and it works continually, which is why the nervous system consumes so much glucose and oxygen.

70%

The net effect of K+ diffusion outward, Na+ diffusion inward, and the action of the Na+-K+ pump is the RMP of -____ mV.

70

Local changes in membrane potential occur when a ______ is stimulated.

neuron

Typically, a neuron's response begins at the _______, spreads through the soma, travels down the _____, and ends at the synaptic knobs.

dendrite; axon

A stimulus at the dendrite binds to receptors that open _____ gates in the membrane so that Na+ flows into the cell, neutralizing some of the negative charge.

Na+

What is meant by depolarization?

voltage shifts to a less negative value

Incoming Na+ ions diffuse for a short distance and produce a _______ (local potential) that travels from the stimulus point toward the cell's ______ zone.

short-range change in voltage; trigger

Four characteristics distinguish local potentials from action potentials. What are these four and what do they mean?

graded - vary in magnitude according to strength of stimulus; decrememntal - get weaker as they spread; reversible - if stim ceses, cell returns to resting potential; excitatory or inhibitory - can make cell more positive or negative

An action potential is a rapid up-and-down shift in membrane ________ produced by voltage-gated ion channels in the plasma membrane.

voltage

When do action potentials occur?

if an excitatory local potential spreads all the way to the trigger zone and is still strong enough when it arrives, can open channels and generate action potential

If a local potential spreads all the way to the trigger zone and is still strong enough, what can happen?

generate action potential

The sequence of events in an ________ potential is as follows.

action

The current arrives at the axon hillock and ____________ the membrane as a local potential.

depolarizes

The local potential must rise to the _________ (about -55 mV) to open the voltage-gated channels.

critical voltage/threshold

The neuron produces an ______ _________. The voltage-gated Na+ do what? What are K+ gates doing at this time? What happens to the membrane?

action potential; open quickly; open more slowly; depolarization

As the rising membrane potential passes 0 mV, Na+ channels are ____________ and begin closing. By the time they all close, the voltage peaks at about +35 mV.

inactivated

By the time the voltage peaks, the slow K+ gates are fully ______, and K+ now ______ the cell, which acts to __________ the membrane.

open; exits; repolarizes

What is hyperpolarization (or afterpotential)? What is happening here to create this?

when voltage drops more negative than RMP; More K+ leaves than Na+ that enters, making it more negative

During hyperpolarization, Na+ diffusion into the cell and (in the CNS) the removal of extracellular K+ by ___________ gradually restore the RMP.

astrocytes

Only about one ion in a million crosses the membrane to produce an _______ potential, and an action potential affects distribution only in a thin layer near the membrane.

action