Bio 225 - Exam 2 - Neuroanatomy

Neurons are the ________ ____ of the nervous system

fundamental unit

Label

1) signal reception 2) signal integration 3) signal conduction 4) signal transmission 5) soma (soma) 6) dendrites 7) nucleus 7.5) incoming signal 8) Endoplasmic reticulum 9) mitochondrion 10) axon hillock 11) axon 12) Schwann cells of the myelin sheath 13) direction of signal 14)axon terminal 15) muscle cell 16) axon terminal 17) synapse (neuromuscular junction) 18) neurotransmitter release

neurons are specialized to use _____ in membrane potential to________ _______ across ____ distances

changes; communicate signals; long

What kind of transport helps to develop a typical neurons membrane potential

primary active transport - Na+/K+ ATPase/Pump

electrical potential is

separated (opposite) charges have potential energy

Voltage difference across cell is defined as

charge difference from inside to outside of cell — inside cell is neg. compared to outside of cell beign pos.

Concentration of ions in cytoplasm v. extracellular and equilibrium potential

K+: high inside 400 mM and low outside 20 mM; -75 mV

Na+: low inside 50 mM and high outside 440 mM; +55 mV

Cl-: low inside 51 mM and high outside 560 mM: -60 mV

Organic Anions (A-): high inside 385 mM and none outside 0 mM

Ca2+: very low inside and low outside 1 mM: +130 mV

Membrane potential changes with ________ ______ of ____

selective movements; ions

Equilibrium potential (Eion) is

aka:

The membrane potential at which the net flow of an ion is zero

aka reversal potential of an ion

Equilibrium potential (E ion) can be
calculated using

Nernst Equation

Equilibrium potentials can be used to

predict ion movements

Membrane potential is calculated using the

Goldman Equation - describes how membrane potential is determined by ionic concentration gradients and permeabilities

resting potential value for neurons

-70 mV

What factors establish/contribute to the resting membrane potential

ions: more (+) outside, more (-) inside

Na+/K+ Pump

Leaky channels: Na+ Channels and K+ channels

Equilibrium potential of main ions

K+: -75 mV

Na+: +55 mV

Cl-: -60 mV

How do neurons maintain concentraiton gradients

(active) transport

The resting membrane potential approaches (but does not reach)

Ek+

Rapid changes in membrane potential occur by

opening and closing ion channels

What governs ion flow

driving force

Driving force is

the difference b/w the membrane potential and the ion equilibrium potential

larger the difference, the stronger the driving force

Changes in potential are described relative to

the resting membrane potential: depolarization, repolarization, hyperpolarization

Local potential changes occur as

ions flow through the membrane

Depolarization

membrane potential becomes less negative

+ ions enter or - ions exit

Hyperpolarization

membrane potential becomes more negative

+ ions exit and - ions enter

net difference in electrical charge occurs at _______ surfaces of the ______

the inside and outside; membrane

large potential changes caused by…

minuscule ionic concentrations changes

rate of ion movement is proportional to

the difference b/w the membrane potential and the equilibrium potential (driving force)

What is the driving force

the net electrical force acting on an ion to move across a neuronal cell membrane

the difference between the actual membrane potential and an ion's equilibrium potential

integration area of neuron

axon hillock

where the decision is made

reception area of neuron

dendrites and soma

where messages are received (soma can receive messages)

conduction area of neuron

axon

conducts action potential

transmission area of neuron

axon terminal

electrical (ion transfer) or chemical synapse (releases neurotransmitters)

Resting membrane potential

at rest / -70 mV

created by Na+/K+ pump

maintained by (persists due) to leaky channels

Graded potentials

transient changes that occur locally

short distance signals - decay over short distances

vary in magnitude (proportional to the strength of the stimuli - not all or nothing) and duration

Action potentials

all-or-none

long distance signals (maintain amplitude)

same magnitude and duration for a given cell

occur in axons

caused by opening and closing of valtage-gated channels

electrotonic spread

the spread of electrical activity through cells or living tissue - graded potentials spread in all directions

Graded potential mechanism

neurotransmitter binds to a ligand-gated Na+ channel > Na+ entes cell thru the open channel > current spreads through the cell > strength of signal decreases with distance

Length constant

the distance that electrotonic current can spread along the membrane

distance to dec. to 37% of the original value

graded potetial signal strength depends on / is proportional to

ligand concentration: more ligands —> more ion channels open —> more/higher change in membrane potential

AND

Distance

Threshold potential

membrane potential required to initiate an action potential

around -55 mV

What is the final trigger for action potential

at axon hillock, stimulus must surpass threshold for AC

Integration of graded potentials occurs in

space in time

temporal summation and spatial summation

Graded potentials can cause _____ or _____ through what potential types

depolarization (excitatory post-synaptic potential)

hyperpolarization (inhibitory post-synaptic potential)

Components of Voltage-gated Na+ channels

activation gate and inactivation gate

activation gate

voltage sensor and opens at threshold

inactivation gate

closes from cytoplasmic side

Voltage-gated Na+ channels display

intrinsic inactivation

intrinsic inactivation

a property of certain ion channels that closes the conduction pathway when the membrane depolarizes

Depolarization of the membrane causes

intrinsic inactivation - inactivation gate closes in voltage-gated Na+ channel

AND
activates voltage-gated K+ channels

The differing _____ of the voltage gated Na+ and K+ channels account for the ____ of the action potential

kinetics; shape

Parts of action potential

resting membrane potential (produced by Na+/K+ pumps and maintained by leaky channels) —> summation (either spatial or temporal) - graded potentials due to some stimuli (neurotransmitter) —> threshold reached (voltage-gated Na+ channels open both inactivation and activation gates open) —> depolarization —> before top voltage reached, K+ channels opens then Na+ channels close (inactivation gate) (both are open at same time for a short period) —> top voltage reached —> repolarization (inactivation gate is closed of Na+ voltage gated channel and K+ voltage-gated channel is open)—> inactivation gate opens after absolute refractory period and K+ still open (relative refractory period) —> afterhyperpolarization (return to resting membrane potential due to Na+/K+ pumps and Na+ and K+ leaky channels)

summation

the process by which multiple electrical impulses at the synapse and axon hillock are added together to determine whether an action potential is generated

either spatial or temporal

caused by graded potentials due to some stimuli

voltage gated K+ channels (how they work)

when membrane potential (inside/cytosol) becomes more pos. —> repels pos. charges in the K+ protein channel —> opens channel up b/c pos. charges move and the protein channel changes conformation

Action potential refractory periods

absolute refractory period and relative refractory period

Absolute refractory period

Starts at the initiation of AP until the end of the Na+ channel inactivation - the time during which another AP cannot be triggered

inactivation gate closes before the top voltage

relative refractory period

Start of afterhyperpolarization to restored resting membrane potential - time during which a much stronger stimulus is required to trigger an AP

due to hyperpolarization, a large current is required to reach threshold

Na+ channels are ready to depolarize but K+ are still open

APs move down the ____ ____ _____ over a long distance

axon rapidly over

When _____ flows into the neuron, it flows ______ in both ______

current; passively; direction

When _____ ___ flow into the neuron, ____ ____ flows passively in both ______ (bidirectional flow)

Na+ ions; positive current; directions

______ ___ of voltage-gated ___ channels ensures unidirectional APs

Inactivation gate; Na+

Action potentials display typical ____ and ____

durations; amplitudes

Stimulus strength is encoded by

AP frequency

What is necessary for high frequency APs

strong, sustained depolarization

Different types of stimulus (in regards to AP frequency)

subthreshold stimulus; brief threshold stimulus; sustained threshold stimulus; sustained suprathreshold stimulus

APs spread from the

axon hillock to the axon terminal

How do neurons transmit their signals to other cells

electrical synapses or chemical synapses

chemical synapse (basic)

synaptic vesicles release neurotransmitter by exocytosis

Chemical Synapse mechanism

Voltage-gated Ca2+ channels open in response to AP induced depolarization —> increased intracellular Ca2+ facilitates neurotransmitter release (snare protein aka docking protein moves vesicles w/ neurotransmitters to synaptic side of neuron and vesicles fuses w/ membrane to release neurotransmitter via exocytosis)

Neurotransmitter

synthesized in neuron

released at presynapse following depolarization

bind and cause effect at post-synapse

There is a great diversity of ______ and _____

neurotransmitters; receptors

neurotransmitters

Amines:

• acetylcholine

• amino acids: glycine, asparate, glutamate

• biogenic amines: dopamine, norepinephrine, epinephrine

Peptides

• endorphins

• neuropeptide Y

Other

• Gas: nitric oxide

• Nucleic acid: adenosine

A ____ ____ can have very different effects on _____ target cells

single neurotransmitter; different

Different ______ to the same transmitter can have ______ ____ on _____ neurons

receptors; opposite effects; target

Classification of receptors

ionotropic or metabotropic

Ionotropic receptor pathway

Metabotropic receptor pathway

Graded potentials are faster or slower than APs

faster

Synthesis of Acetylcholine as a neurotransmitter

Acetylcholine (Cholingeric) receptor subtypes

Norepinephrine differing responses due to

Binds to several diff. receptor types

• alpha-1 adrenergic receptor

• alpha-2 adrenergic receptor

• beta-1 adrenergic receptor

• beta-2 adrenergic receptor

Alpha-1 adrenergic receptor

excitation - cause vasoconstriction in smooth muscles of blood vessels

location: skin, GI system, kidney (renal artery), salivary glands, NOT bronchioles

GPCR > PLC > PKC > calcium channels

NE > E

Alpha-2 adrenergic receptor

Inhibitation - inactivates calcium channels and reduce release of NE

location: presynaptic nerve terminals, platelets, and fat cells

dec.s neurotransmitters and insulin and inc.s glucagon

NE = E

Beta-1 adrengeric receptor

Excitation - activate calcium channels and increase muscle contraction

location: cardiac muscle

inc.s contraction and HR and renin

GPCR > AC > PKA > activates Ca2+ channels

(NE = E) > alpha

Beta-2 adrengeric receptor

Relaxation reduces muscle contraction and casues vasodilation

Location: vascular smooth muscle, bronchioles, and GI

(E>>NE) > alpha

alpha-1 adrenergic receptor mechanism

alpha-2 adrenergic receptor mechanism

AC: adenylate cyclase

PKA: protein kinase A

Beta-1 adrenergic receptor mechanism

Beta-2 adrenergic receptor mechanism

Differing effect of NE

1. Cause pupil dilaiton

2. Cause stronger heart contraction

3. Inc. none-shivering thermogenesis in brown adipose tissue

4. constrict arteries - inc.d BP

5. Cause release of renin and Na+ in kidneys

6. Inc. glycogenolysis (inc. BGL)

7. Inc. release of glucagon (inc. BGL)

8. Inc. glucose uptake in skeletal muscles

9. Inc. lipolysis

10. Reduce digestive activity in digestive system

Structural diversity of neurons occurs ____ and ___ ____

within; across species

structural classes of neurons

multipolar neuron; bipolar neuron; and unipolar neuron

Funcional classes of neurons

sensory (afferent) neurons; interneurons; and motor (efferent) neurons

Afferent neurons

considered unipolar neurons

trigger zone is at the interface b/w the dendrites and the axon

carry impulses from the periphery to CNS

Interneuron

connect one neuron to another

typically multipolar and may have multiple axon terminals

varying functional class

many dendrites

Efferent neuron

carry signal from CNS to some external target organ (muscle, glands, and other tissues) which are stimulated

generally multipolar

elicits a response in the effector organ

______ increases the speed of AP ______ down the _____

myelination; conduction; axon

AP generation is slower than _______ _____

electrotonic spread

electrotonic current ______ with distance, while APs maintain _____

decreases; amplitude

Myelin sheath

insulates regions of the axon

restricts APs to nodes of Ranvier

Forces electrotonic spread through internodes

Best compromise b/w APs and electronic spread [uses both graded (speed it up) and action potentials (reestablish high amplitude)]