BIO 3200 Chapter 8 Review

what are neurotransmitters secreted from? for what purpose?

neurons with processes; communication

what is another word for “emergent properties”?

consciousness

what does the central nervous system (CNS) consist of?

brain and spinal cord

What does the peripheral nervous system consist of?

* sensory (afferent) neurons
* efferent neurons

What are the two divisions of efferent neurons?

somatic and autonomic

What branches make up the autonomous nervous system?

sympathetic (fight-or-flight) and parasympathetic (rest-and-digest)

what is the function unit of the nervous system? What do they carry?

neurons; they carry electrical signals

What is the definition of neuron structure? What are the possible structures of neurons?

Structure = number of processes: multipolar, pseudounipolar, bipolar, anaxonic

What are the three different functions of neurons?

sensory (afferent), efferent, and interneurons

What does the general structure of a neuron consist of?

• the cell body is the control center

• dendrites receive incoming signals

  • dendritic spines

  • collaterals, axon terminals vs. varicosities

• axons carry outgoing signals

  • axon hillock

How is axonal transport classified and what are the two types?

classified by the speed at which the material moves; fast axonal transport and slow axonal transport

What happens during fast axonal transport?

• moves organelles at rates of up to 400 mm/day

• anterograde transport

• retrograde transport

anterograde transport definition

from cell body to axon terminal; form of fast axonal transport

retrograde transport definition

from axon terminal to cell body; form of fast axonal transport

How does slow axonal transport work?

moves material by axoplasmic (cytoplasmic) flow at 0.2-2.5 mm/day

what does establishing synapses depend on?

chemical signals

synapse definition

the region where axonal terminal meets its target cell

What does a synapse consist of?

• presynaptic cell vs. postsynaptic cell

• synaptic cleft

what are examples of chemical synapses and signals vs electrical synapses?

chemical - neurotransmitters; electrical - gap junctions

What do growth cones and neurotrophic factors do?

allow developing neurons to find (sniff out) their targets

Why is neuroplasticity possible?

Synapses are not fixed for life and can be rearranged

what are the types of glial cells? Where are they located in the nervous system?

• schwann cells (PNS)

  • satellite cells (PNS) - nonmyelinating Schwann cell

• oligodendrocytes (CNS)

• astrocytes (CNS)

• microglia (CNS)

• ependymal cells

what do Schwann cells and oligodendrocytes do?

wrap around axon and form insulating myelin sheaths

nodes of Ranvier definition

gaps in insulation from Schwann cells and oligodendrocytes

what do satellite cells do?

around cell bodies in both the CNS (nucleus) and PNS (ganglion)

What do astrocytes do?

(CNS) several subtypes, multiple roles, half of all cells in the brain

what do microglia do?

(CNS) specialized immune cells, act as microphages for the brain

what are ependymal cells?

one source of neural stem cells

what happens when the cell body dies?

the neuron dies

how can stem cells repair damaged neurons?

* if axon is severed, then cell body and attached segment survives; severed portion degenerates

what happens when a motor neuron is damaged?

target muscle results in permanent paralysis

what happens when a sensory neuron is damaged?

experience loss of sensation from innervated area

what are the steps of neuron regeneration?

1. axoplasm leaks out and seals the damaged end and attached segment of axon swells

2. Schwann cells (PNS) release chemical signals altering of tissue damage

   1. degeneration of the distal axon segment

   2. myelin sheath unravel

   3. cellular debris removed

3. Schwann cells secrete neurotropic factors to keep cell body alive and encourage axon regeneration

   1. axon behaves like a growth cone

what is membrane potential influenced by?

• concentration gradient of ions (Nernst equation and the GHK)

• membrane permeability to those ions (only GKH)

equilibrium potential definition

the membrane potential at which the electrical and chemical forces acting on the ion are equal and opposite

resting membrane potential difference (membrane potential) definition

• resting is the steady state

• potential energy stored in the electrochemical gradient

• difference in electric charges inside and outside of the cell (between ECF and ICF)

  • mostly due to potassium

what is the resting membrane potential determined primarily by?

• K+ concentration gradient

• cell’s resting permeability to K+, Na+, and Cl-

changes in a membrane’s permeability result in what?

• movement creates an electrical signal

• very few ions move to create large changes in membrane potentials

what are gated channels?

ion channels that control the ion permeability of the neuron

what are the 3 types of gated channels?

• mechanically gated

• chemically gated

• voltage-gated

how do mechanically gated channels work?

open in response to physical forces such as pressure or stretch

how do chemically-gated channels work?

respond to a variety of ligands, such as extracellular neurotransmitters

how do voltage-gated channels work?

respond to changes in the cell’s membrane potential

conductance definition

the ease with which ions flow through a channel

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

NA+, K+, Ca2+, Cl-

graded potentials definition

• variable strength

• used for short distance communication

action potentials definition

• very brief, large depolarizations

• rapid signaling over long distances

compare graded and action potentials: type of signal

input signal vs regenerating conduction signal

compare graded and action potentials: occurs where?

usually dendrites and cell body vs trigger zone through axon

compare graded and action potentials: types of gated ion channels involved

mechanical, chemical, or voltage vs. voltage only

compare graded and action potentials: ions involved

usually Na+, K+, Ca2+ vs. Na+ and K+

compare graded and action potentials: type of signal

depolarizing and hyperpolarizing vs depolarizing

compare graded and action potentials: strength of signal

depends on initial stimulus and can be summed vs all-or-nothing and cannot be summed

compare graded and action potentials: what initiates the signal?

entry of ions through gated channels vs above-threshold graded potential at the trigger zone opens ion channels

graded potentials unique characteristics

• no minimum level required to initiate

• two signals coming close together in time will sum

• initial stimulus strength is indicated by frequency of a series of action potentials

action potentials unique characteristics

refractory period: two signals too close together in time cannot sum

strength of graded potentials

• graded potentials lose strength as they move through the cell due to current leak or cytoplasmic resistance

• if strong enough, summation of graded potentials reaches the trigger zone in the axon hillock and initial segment

are graded potentials excitatory or inhibitory?

can be either excitatory or inhibitory

how does an action potential begin?

when graded potential reached trigger zone which depolarizes to threshold

what happens during the rising phase of the action potential?

voltage-gated Na+ channels open and Na+ entry depolarizes cell

what happens during the falling phase of the action potential?

• at peak, Na+ channels close, slower voltage-gated K+ channels open

• K+ exit repolarizes then hyperpolarizes cell

• voltage-gated K+ channels close, less K+ leaks out of the cell

• cell returns to resting membrane potential of -70 mV

what causes absolute refractory period?

separate activation gates and inactivation gates

will action potentials fire during the absolute refractory period?

no

what happens before an absolute refractory period?

voltage-gated Na+ channels resetting

what happens after an absolute refractory period?

a relative refractory period follows

What is the purpose of relative refractory period? How long is the delay?

prevents backward conduction (wrong-way axon conduction); 1-2 milliseconds

what happens during depolarization? what does it depend on?

• positive charge spreads along adjacent sections of axon by local current flow

• dependent on voltage-gated Na+ channels

local current flow definition

wave of depolarization that moves through the cell

how are action potentials conducted?

1. depolarization

2. local current flow causes new section of the membrane to depolarize

how does the size of the neuron affect the speed at which action potentials are conducted? How does myelin affect speed?

• larger neurons conduct action potentials faster

• conduction is faster in myelinated ions

how do chemicals alter the conduction of action potentials?

chemicals bind to the channel

how do alterations in ECF concentration affect electrical activity?

hyperkalemia & hypokalemia

what does hyperkalemia do?

brings neurons closer to threshold

what does hypokalemia do?

moves neurons farther from threshold

what are the two types of synapses neurons communicate at?

electrical and chemical

properties of electrical synapses

• pass electrical signals through gap junctions

• signal can be bi-directional

• synchronizes the activity of a network of cells

what is the main property of chemical synapses?

they use neurotransmitters that cross synaptic clefts

what are the three classes of neurocrines?

neurotransmitters, neurohormones, and neuromodulators

What do neurotransmitters and neuromodulators have in common?

paracrine signals (target cells located close to the neuron that secrete them)

properties of neurohormones

secreted into blood and distributed throughout the body

what is another name for ionotropic receptors and what do they do?

• aka receptor-channels

• alter ion flow across the membrane (can be single ion or multiple ions)

what are metabotropic receptors? Why is their response slower than ionotropic receptors?

G protein-coupled receptors for neuromodulators; slower response because they involve second messengers

T/F: Neurotransmitters, such as NO, bind to specific receptors.

False: NO is the exception but generally neurotransmitters do bind to specific receptors

agonist molecules definition

substances that bind to synaptic receptors and increase the effect of the neurotransmitter

antagonist definition

substances that bind to synaptic receptors and decrease the effect of the neurotransmitter

how is acetylcholine synthesized?

• from choline (in membrane phospholipids) and acetyl CoA (in citric acid cycle)

• in axon terminals

what does acetylcholine do? name two examples

binds cholinergic receptors → nicotinic receptors and muscarinic receptors

where are nicotinic receptors and what type of cation channels do they use?

• on skeletal muscles and in autonomic division of PNS and CNS

• monovalent cation channels: Na+ and K+

where are muscarinic receptors and what are they derived from?

• in CNS and on target cells for autonomic parasympathetic division of PNS

• G protein-coupled receptors

What are the three classes of neurotransmitters we have to know?

• acetylcholine

• amines

• amino acids

where are amines active and what are they derived from?

• active in the CNS

• derived from single amino acid

  • serotonin from tryptophan

  • histamine from histidine

  • dopamine, norepinephrine & epinephrine from tyrosine

Where is norepinephrine secreted from? ?

adrenergic/noradrenergic neurons

Which type of receptors bind norepinephrine and epinephrine

adrenergic receptors

What are the amino acids that function as neurotransmitters?

• glutamate

• aspartate

• gamma - aminobutyric acid (GABA)

  • Glycine and D-serine

what is the function of glutamate as a neurotransmitter?

• excitatory in the CNS

• AMPA receptor

• NMDA receptor

what is the function of aspartate as a neurotransmitter?

• excitatory in the brain

• hyperpolarizes target cells by opening Cl- gates

what is the function of GABA as a neurotransmitter?

• inhibitory in the brain

• hyperpolarizes target cells by opening Cl- gates

what is the function of glycine and D-serine as neurotransmitters?

enhance the excitatory effect of glutamate

what can also function as neurotransmitters?

• peptides

• purines

• gases that diffuse in the cells

• lipids

How do peptides function as neurotransmitters?

• substance P and opioid peptides (enkephalins and endorphins)

  • function as neurotransmitters, neuromodulators, and neurohormones

• cholystokinin, vasopressin, atrial natriuretic peptide

  • function as neurotransmitters and neurohormones