Ch 22: Signal Transcription

Animals have nervous systems that:

1) collect,

2) process and 

3) elicit responses to biological information.

central nervous system: CNS

brain and spinal cord with both sensory and motor cells

peripheral nervous system: PNS

somatic nervous system [voluntary skeletal muscle movements] and 
autonomic nervous system [involuntary movements of heart, GI, blood vessels and some glands]

___ neurons act to detect stimuli (photoreceptors, olfactory, touch) 
___ neurons transmit signals from CNS to muscles (and glands) 
___ process signals from other neurons.

Sensory

Motor

Interneurons

____ are phagocytes that fight infection.

Microgllia

___ and ___ form the insulating myelin sheath around the neurons

Oligodendrites

Schwann cells

____ form blood-brain barrier.

Astrocytes

Neurons have various shapes:

    a) pyramidal (cerebral cortex), 
    b) short-axon cells (also cerebral cortex), 
    c) Purkinje cell (cerebellum), 
    d) axonless horizontal cell (retina:eye)

An axon ends with _______ that transmit the signal through a specialized junction: _____.

terminal bulbs or synaptic knobs

the synapse

______ is a property of all cells & reflects a difference in charge on either side of the cell membrane

Membrane potential

Normally, cells are net ____ inside the cell

negative

In neurons, the action potential moves _ the axon as a nerve impulse

The ____ is high in potassium due to the sodium-potassium pump

cytosol

The flow of oppositely charged ions towards each other is ____

the potential or voltage

the sodium/potassium pump transport sodium back out and potassium back into the cell through ____

ATP hydrolysis

Depolarization (or a lowering of the membrane potential) results from flow of _____ into the cell. 

positive sodium ions

_________ allow the activity of single ion channels to be monitored.

Patch clamping (single-channel recording)

___________ act as voltage sensor. 

A specific transmembrane stretch of amino acids

Based upon the conformation of the voltage-gated channel, the channel can be ___ but sensitive to a ____ or _____ to the signal (channel inactivation) by the _______, a stopper-like part of the channel protein itself

closed

depolarizing signal (channel gating)

completely desensitized

inactivating particle

A small amount of depolarization (___) will normally result in recovery without effect

<+20 mV

A brief stimulation by a pulse of ______ will surpass the threshold potential and trigger an action potential. 

20 mV (~-60 mV to ~-40 mV)

Then hyperpolarization occurs and the membrane potential drops to ___ before restabilizing at ___

-60 mV

-75 mV

The action potential results from the rapid movement of ions through axonal membrane channels and the increased sodium current results in a ___ feedback loop known as _____

positive

the Hodgkin cycle

Once the membrane potential peaks, the ____ phase begins with the inactivation of the ____ (blocking the ____) and the opening of the voltage-gated potassium channels. 

repolarizing

sodium channels

Hodgkin cycle

The membrane potential returns to resting sate with the ________

closing of the voltage-gated potassium channels.

the absolute refractory period (~few milliseconds), sodium channels ___ be opened by depolarization and no action potential ___ be generated. 

cannot

can

At the _____, a great influx of sodium ions can occur which specify that action potentials initiated here are propagated down the axon

axon hillock

Action potentials jump node to node (_____) which is very rapid when compared to propagation in neurons that have the myelin removed

saltatory propagation

Neurotransmitter molecules that are kept in the terminal bulbs or synaptic knobs are secreted into the synaptic cleft and then bind to receptors on the postsynaptic neuron. This generates _________________.

a signal to stimulate or inhibit a new action potential

A ______ is a small molecule that, through the interaction with a specific receptor (a key and lock mechanism), relays a signal across nerve synapses

neurotransmitter

An ____ neurotransmitter causes depolarization and an ____ neurotransmitter causes hyperpolarization in the postsynaptic neuron

excitatory

inhibitory

A neurotransmitter must do 3 things:

1) cause a response when  injected into the synaptic cleft, 
2) occurs naturally in the presynaptic neurons and 
3) be released when the presynaptic neurons are stimulated.

the most common neurotransmitter in vertebrates outside of the CNS

Acetylcholine

Acetylcholine forms:

cholinergic synapses 1) between PNS neurons and 2) at neuromuscular junctions. 

_____________ are found in adrenergic synapses at junctions between nerves and smooth muscles and nerve-nerve junctions in the brain. 

Catecholamines

Examples of Catecholamines are:

dopamine, norepinephrine, epinephrine: all tyrosine derivatives

Other neurotransmitters are _____ (histamine, serotonin, gamma-aminobutyric acid [GABA], glycine, glutamate). 

amino acids and derivatives

____ functions as an excitatory neurotransmitter in the CNS by indirectly closing the potassium channels.

Serotonin

____ are short chains of amino acids formed by cleavage of precursor proteins and stored in secretory vesicles. 

Neuropeptides

_____ are neuropeptides that are produced in the brain to inhibit pain reception

Enkephalins

Neuropeptide endocrine hormones (prolactin, growth hormones and leutinizing hormone) act on _______

tissues other than the brain.

synaptotagamin, synaptobrevin, & syntaxin are all _____

docking proteins

The ______ is a ligand-gated sodium channel that binds __ molecules of acetylcholine to open

acetylcholine receptor

two

The acetylcholine receptor is specifically bound by ______ 

snake venon components (alpha-bungarotoxin and cobratoxin).

The GABA (gamma-aminobutyric acid) receptor is a ligand-gated chloride channel which produces an influx of chloride ions in the postsynaptic neuron. 

_______ enhance the effects of GABA on the receptor to produce a tranquilizing effect.

Benzodiazeprine drugs (Valium and Librium)

Some neurotransmitters are returned to the ________ by specific transporter proteins (_______).

presynaptic axon terminal bulbs

endocytosis

Nerve signals are integrated by accounting of small changes in membrane potential caused by _________

binding of neurotransmitters to receptors. 

_______ must build up in the postsynaptic neuron to the threshold level to allow the formation of an action potential. 

excitatory Postsynaptic potentials (EPSP)

Methods for Postsynaptic excitatory potentials to build an action potential

1) through temporal summation (where a number of EPSPs occur quickly without enough recovery time between the EPSPs to cause a depolarization event) or 
2) through spatial summation (a number synaptic inputs combine to cause a depolarization event). 

Thus the summation of synaptic inputs leads to whether or not an action potential is formed in the _____

postsynaptic neuron.