(N)Chapter 8 Cells of the Nervous System単語カード | Quizlet

Brain and spinal cord

function: integration, processing, sending info out

CNS components and function

Nerves

sensory component: afferent (sends info towards CNS)

motor component: effect (info is sent away from CNS)

PNS components and function

PNS

breaks down to

A. Sensory or B. Motor

1. Somatic motor division (volun.)

2. Autosomatic motor division (invol.)

a. parasympathetic

b. sympathetic

What is the break down of the PNS?

somatic motor division

Division of PNS

Carries signals to skeletal muscles, voluntary control

autonomic motor division

Division of the PNS that regulates involuntary responses such as heart rate

1. parasympathetic

2. sympathetic

What are two branches of the autonomic motor division?

parasympathetic nervous system

the division of the autonomic nervous system that calms the body, conserving its energy

rest and digest

sympathetic nervous system

the division of the autonomic nervous system that arouses the body, mobilizing its energy in stressful situations

fight or flight

enteric nervous system

autonomous control and autonomic division control

under the influence of autonomic but can also control itself

ex: GI tract

neurons & glial cells

The nervous system is composed primarily of two cells; what are they?

neurons

basic signaling units of nervous systems

dendrites

receive incoming signals

increases surface area of a neuron, allowing it to communicate with multiple other neurons

some nerve cells can have 1 or more of these

receive incoming info and transfer it to an integrating region within the neuron

What is the function of dendrites in the PNS?

sends signals back and forth w/ other neurons in the brain

What is the function of dendrites in the CNS?

axons

sends/carry outgoing information

can be myelinated or unmyelinated

have collaterals (branching)

axon terminals: where you synaspe

somatic motor division

can have varicosities (pooling/swelling along the neuron where the NT is released)

- transmit outgoing electrical signals from soma (integration center) of neuron to the target cells at the end of the axon

- @ distal end of axon, the electrical signal usually causes a secretion of a NT (passing through gap functions in some CNS neurons)

What is the primary function of an axon?

presynaptic neuron

synaptic cleft

postsynaptic neuron

What makes up a synapse?

Axodendritic

Axoaxonic

Axosomatic

dendodendritic

neuroeffector junction

What are some of the variations of synaspes?

cell body/soma

contains the nucleus and axon hillock

axon hillock

The conical region of a neuron's axon where it joins the cell body; typically the region where nerve signals is generated.

1. pseudounipolar (most common)

2. bipolar (in the eye and nasal)

What are two types of sensory (afferent) neurons?

interneurons

Central nervous system neurons that internally communicate and intervene between the sensory inputs and motor outputs

anaxonic - no apparent axon

multipolar - highly branched but lack long extensions

multipolar

What are mostly motor (efferent) neurons?

efferent neurons

Multipolar: PNS

has 5-7 dendrites, each branching 4-6 times.

a single long axon may branch several times and

the region where an axon terminal meets it's target cell

What is a synapse?

presynaptic cell

the neuron that delivers a signal to the synapse

postsynaptic cell

neuron that receives the signal

synpatic cleft

a narrow space between two cells where information is transfered

chemical

The vast majority of synapses in the body are what kind of synapse?

chemical synapses

a presynaptic cell releasing a chemical signal that diffuses across a synaptic cleft and binds to a membrane receptor on the postsynaptic cell

one direction

what kind of synapse is this?

electrical synapses

a presynaptic and postsynaptic cell are connected by gap junctions channels

the channels allow electrical current to flow directly from cell to cell

communication is bidirectional and faster than chemical

direct transfer of ATP

what kind of synapse is this?

ribosomes and ER

The axon cytoplasm is filled with many types of fibers and filaments, but what does it lack?

nucleus, ER and packaged by Golgi

Where are the proteins that are made for the axon and axon terminal synthesized?

slow axonal transport

materials are moved by cytoplasmic streaming in the axon from soma to axon terminal

used for components like: structural proteins, enzymes, cytoskeleton proteins

fast axonal transport

walks vesicles and mitrochondria down along with microtubules network (cytoskeleton)

used for transport of NT and vesicles

can go in two directions:

anterograde - vesicles move down axon

retrograde - empty vesicles move back up axon (recycling)

cell body

nucleus, ER, golgi: protein synthesis

Where are NT produced, transported, stored?

communicate with neurons and provide important biochemical support

basically assists the neurons

function of glial cells?

Schwann cells

Satellite cells

What are two types of glial cells in the PNS?

schwann cells

support and insulate axons by forming myelin

found in PNS

1 neuron axon associates w/ many schwann cells

1 schwann cell associates with 1 neuron axon

myelin sheath

A layer of fatty tissue segmentally encasing the fibers of many neurons;

enables vastly greater transmission speed of neural impulses

nodes of ranvier

gaps between schwann cells/neurofibril nodes

segments of myelin sheath

allow for saltatory conduction

saltatory conduction

Rapid transmission of a nerve impulse along an axon, resulting from the action potential "hopping" from one node of Ranvier to another

satellite cells

non-myelinating cells in the PNS

multiple cells surround cell bodies in PNS ganglia

support PNS cell bodies by providing nutrients, clean stuff up

Oligodendrocytes

astrocytes

microglia

ependymal cells

What are the glial cells in the CNS?

Guillain-Barre syndrome

inflammatory response leading to loss of PNS myelin

- demyelination

can cause paralysis and loss of sensations

recoverable for most, given time

astrocytes

communication network via gap junctions

blood-brain barrier

support neurons by providing nutrients

regulate ions in ISF

uptake and release of chemicals at synapses

microglia

immune cells - phagocytosis

release reactive oxygen species (ROS) - form free radicals

ependymal cells

neural stem cells: differentiate into neurons and glial cells

line ventricles & central canal

- with capillaries form choroid plexus

PRODUCES CSF

selectively permeable endothelial layer

Yes

If the cell body dies, does the entire neuron die?

the neuron survives

the damaged part of the axon will degrade

But the Schwann cells may form a scaffolding for re-growth of the axon in the PNS

If the cell body survives, but the axon is damaged, what happens?

rarely

still experimental

In the CNS, can undifferentiated ependymal cells be stimulated to help damaged/dying neurons?

1. the uneven distribution of ions across the cell membrane. Normally, Na, Cl, and Ca are more concentrated in the ECF than in the cytosol. K is more concentrated in the cytosol than the ECF.

2. Differing membrane permeability to those ions. The resting cell membrane is much more permeable to K than to Na or Ca. This makes K the major ion contributing to the resting membrane potential

What two factors influence the membrane potential?

-90 mV

What is the equilibrium potential (Eion) for K?

-70 mV

What is the resting membrane potential for neurons?

by adding the Ek + Ena + Ecl + E ca together inside the cell

How is -70 mV the resting membrane potential?

1. K+ conc. gradient

2. cell's resting permeability to K, Na, Cl.

*** a change in either the K conc. gradient or ion permeabilities changes the membrane potential.

What are key factors that determine resting membrane potential?

electrochemical gradient and ion channels

ions movement is based on what?

Correct - if the membrane suddenly increases its Na permeability, Na enters the cell, moving down its electrochemical gradient

At rest, the cell membrane of a neuron is only slightly permeable to Na.

depolarizes the cell membrane (less negative)

creating an electrical signal

The addition of positive Na ions entering the cell's ICF does what to the cell's membrane and creates what?

membrane potential graph

If the cell membrane suddenly becomes more permeable to K, positive charge is lost from inside the cell and the cell becomes more negative (hyperpolarize)

K+ channels open

a cell may also hyperpolarize if negatively charged ions, such as Cl, enter the cell from the ECF.

How does a cell membrane become hyperpolarized?

very FEW

the ICF and ECF concentrations of ions remain essentially unchanged even when the membrane potential changes a lot.

A significant change in membrane potential occurs with the movement of ______ ____ ions

1. Na channels

2. K channels

3. Ca channels

4. Cl channels

What are the four major types of selective ion channels in the neuron?

leak channels

spend most of their time in the open state

- the K leak channels are the major determinant of the resting membrane potential

1. mechanically gated ion channels

2. chemically gated ion channels

3. voltage gated ion channels

What are the 3 types of gated channels?

mechanically gated ion channels

found in sensory neurons and open in response to physical forces like pressure or stretch

chemically gated ion channels

in most neurons, they respond to a variety of ligands, such as extracellular NT and neuromodulators or intracellular signal molecules

voltage-gated ion channels

opens and closes in response to changes in the cell's membrane potential.

Voltage-gated Na and K channels play an important role in the initiation and conduction of electrical signals along the axon.

some "leak" channels may actually be voltage gated channels that remain open in the voltage range of the resting membrane potential

Different voltage gated channels open at different voltages.

Give an example about leak* channels.

Na and K channels of axons are both activated by cell depolarization

Na channels open rapidly, K channels are slower to open.

The result is an initial flow of Na across the membrane, followed later by K flow.

Different channels open at different speeds, give an example

many channels that open in response to depolarization only close when the cell repolarizes.

the gating portion of the channel protein has an electrical charge that moves the gate between open and closed positions as the membrane potential changes.

open or closed positions: K

open, inactivated, closed positions: Na

**they must go through these cycles before they can open again

Different channels behave differently during repolarization. Examples?'

(different conformations)

out of

K+ flows ______ the cell.

into

Na, Cl, Ca flow ______ the cell.

- tend to occur in dendrites and cell body

- can depolarize or hyperpolarize

- vary in strength (strong/weak)

- spreads towards trigger zone but is not propagated or conducted

- decremental (becomes weaker as it travels throughout cell)

Characteristics of graded potentials

chemically (ligand) gated channels

mechanically gated channels

occasional voltage gated

What channels can initiate a graded potential?

graded potential

variable strength signals that travel over short distances and lose strength as they travel through the cell.

Used for short distance communication

IF a depolarizing graded potential is strong enough when it reaches an integrating region within a neuron, the graded potential initiates action potential.

action potentials

very brief, large depolarizations that travel for long distances through a neuron without losing strength. Their function is rapid signaling over long distances, like from toe to brain.

input

What type of signal is a graded potential?

entry of ions through gated channels

What can initiate a graded potential signal?

no

Is there a minimum level required to initiate a graded potential?

If a graded potential is strong enough, it will reach the trigger zone.

- located at the axon hillock or initial segment

What is the trigger zone? (graded potential)

subthreshold graded potential

a graded potential that is below threshold by the time it reaches the trigger zone

suprathreshold graded potential

a graded potential that is strong enough to cause an action potential when it reach the trigger zone ( -55 mV)

-55 mV

What is threshold that must be reached to initiate an action potential?

- occurs at the trigger zone (axon hillock or initial segment)

- ONLY depolarizing

- uses voltage gated ion channels

- strength: ALL or none; cannot be summed

- propagated current flow (new action potential is initiated in each segment of axon)

- non-decremental

Characteristics of Action Potential

suprathreshold graded potential at the trigger zone opens ion channels

What initiates an action potential signal?

because of the refractory period.

Absolute refractory period - cannot initiate another action potential. What is there must be all or none

Why can't two signals coming close together in time cannot sum during an action potential?

conduction of action potential

spreads towards axon terminal

new action potential initiated at each segment of axon

propagated in one direction

non decremental

What is propagated current flow - action potential?

- limits the # of action potentials

- one way propagation

What does a refractory period do?

1. resting membrane potential (-70 mV)

2. depolarizing stimulus

3. membrane depolarizes to threshold. (-55mV) Voltage-gated Na and K channels begin to open.

4. rapid Na entry depolarizes cell (flows into the cell down its conc. gradient)

(overshoot: reach ENa, Na channels inactivate and K open)

5. Na channels close and slower K channels open

6. K moves from cell to extracellular fluid

7. K channels remain open and additional K leaves cell, hyperpolarizing it. (after hyperpolarization - undershoot)

8. Voltage gated K channels close, less K leaks out of the cell.

9. cell returns to resting ion permeability and resting membrane potential

Explain the steps in an action potential.

refractory period

once an action potential has begun, a second action potential cannot be triggered for about 1-2 msec, no matter how large the stimulus.

The delay is called the absolute refractory period:

the time required for the Na channel gates to reset to their resting positions.

absolute refractory period

time during which another action potential is impossible; limits maximal firing rate

Na channel gates must reset to their resting positions

relative refractory period

follows the absolute refractory period.

some but not all Na channel gates have rest to their original positions, in addition K channels are still open

*** it is possible to initiate another action potential but it all depends on:

1. how many channels close

2. how strong the stimulus is

Action potential propagation

trigger zone/initial segment

- suprathreshold graded potential

- voltage gated Na channels open

- stimulation of adjacent area

Adjacent area:

- voltage gated Na channels

- depolarization

- nondecremental

- stimulation of adjacent area

Previous area:

- absolute refractory period

- one directional flow

larger axons, less resistance, faster conduction

Rates of conduction: diameter

unmyelinated and small: slower conduction

- 0.5-2 m/s

myelinated: faster conduction

120 m/s, large and myelinated

Rates of conduction: myelination

salatory

myelinated axons have what type of conduction?

continuous

unmyelinated axons have what type of conduction?

concentration of voltage gated Na channels

saltatory conduction

efficiency: saves time and space

metabolically efficient

-fewer ions to move back

What type of conduction do Nodes of Ranvier have?

K balance is important - key ion in determining resting membrane potential

hyperkalemia

hypokalemia

What is the importance of ECF ion concentrations?