Chapter 12

Dopamine

biogenic amines, are active during emotional responses, addictive behaviors, and pleasurable experiences. Regulate skeleta muscle tone and some aspects of movement due to contraction of skeletal muscles.

Nitric oxide synthase (NOS)

catalyzes formation of NO from the amino acid arginine. More than 2% of neurons,

Diverging circuit*

the nerve impulse from a single presynaptic neuron causes the stimulation of increasing numbers of cells along the circuit. One action potential can cover a great area

Converging circuit

the postsynaptic neuron receives nerve impulses from several different sources. For ex: a single motor neuron that synapses with skeletal muscle fibers at neuromuscular junctions receives input from several pathways that originate in different brain regions.

How many types of neurons do we have structurally?

three. (Unipolar, multipolar & bipolar)

Effect on the postsynaptic neuron which may respond in the follownig ways:

1) EPSP: if the total excitatory effects are greater than the total inhibitory effects but less than threshold level of stimulation, the result is an EPSP that does not reach threshold. Following an EPSP, subsequent stimuli can more easily generate a nerve impulse through summation b/c the neuron is partially depolarized. 2) Nerve impulse(s): if the total excitatory effects are greater than the total inhibitory effects and threshold is reached, one or more nerve impulses (action potentials) will be triggered. Impulses continue to be generated as long as the EPSP is at or above the threshold level. 3) IPSP: if the total inhibitory effects are greater than the excitatory effects, the membrane hyperpolarizes (IPSP). The result is inhibition of the postsynaptic neuron and an inability to generate a nerve impulse.

Neuropeptides (largest neurotransmitter)

3 to 40 amino acids link by peptide bonds are numerous and widespread in both CNS and PNS. Bind to metabotropic receptors and have excitatory or inhibitory actions depending on the type of metabotropic receptor at the synapse. Neuropeptides are formed in the neuron of the cell body, packed into vesicles and transported to axon terminals. Serve also as hormones that regulate physiological responses elsewhere in the body.

Inhibitory

A neurotransmitter that causes hyperpolarization of the post-synaptic membrane is inhibitory. During hyperpolarization generation of an action potential is more difficult than usual b/c the membrane potential becomes inside more negative and thus even farther from threshold than in its resting state. Release glycino because replacing negative ions into the cell

ATP and other Purines

Adenosine itself, as well as its triphosphate, dipohsphate and monophosphate derivatives (ATP, ADP, AMP) is an excitatory neurotransmitter in both CNS & PNS

Voltage gates open during action potentials

During action potential two types of voltage-gated channels open and then close during an action potential. These channels are present mainly in the axon plasma membrane & axon terminals. The first channels that open the voltage-gated Na+ channels, allow Na+ to rush into the cell, which causes the depolarizing phase (-55mV to +30 mV), an AP is generated. Then voltage gated K+ channels open, allowing K+ to flow out, which produces the repolarzing phase(goes from +30 mV to -70mV). The after-hyperpolarizing phase occurs when the voltage-gated K+ channels remain open after the repolarzing phase ends.

When you push down very hard?

Firing more action potentials in short amount of time increasing frequency.

Catecholamines

Norepinephine, epinephrine and dopamine are classified chemically as catecholamines. They all include an amino group, and a catechol ring composed of 6 carbons and 2 adjacent hydroxyl (-OH) groups. Catecholamines are synthesized from the amino acid tyrosine. They are either recycled back into synaptic vesicles or destroyed by enzymes.Two enzymes that break down are Catechol-o-methyltranserase or COMT and monoamine oxidase or MAO.

Summation of postsynaptic potentials at the trigger zone of a postsynaptic neuron

Postsynaptic neurons 1,3,5 release excitatory neurotransmitters (red dots) that generate excitatory presynaptic potentials (EPSPs) (red arrows) in the membrane of a postsynaptic neuron. Presynaptic neurons 2 & 4 release inhibitory neurotransmitters (purple dots) that generate inhibitory postsynaptic potentials (IPSPs) (purple arrows) in the membrane of the postsynaptic neuron. The net summation of these EPSPs and IPSPs determines whether an action potential will be generated @ the trigger zone of the postsynaptic neuron.

reverberating circuit*

The incoming impluse simulates the first neuron, which stimulates the second, which sitmualtes the third and so on. Branches from later neurons synapse with earlier ones. Among the body responses though to be the result of output signals from reverberating circuits are breathing, coordinated muscular activities, waking up and short-term memory.

Excitatory postsynpatic potential (EPSP)

a neurotransmitter that causes depolarization of postsynaptic membrane is excitatory because it brings the membrane closer to threshold. Releases ACh

Parallel after-discharge circuit

a single presynaptic cell stimulates a group of neurons, each of which synapses with a common postsynaptic cell. A differing number of synapses between the first and last neurons imposes varying synaptic delays, so that hte last neuron exhibits multiple EPSPs and IPSPs. May be involved in precise activities such as math calculations.

Suprathreshold Stimulus

a stimulus that is strong enough to depolarize the membrane ABOVE threshold. Same amplitude (size) as a threshold stimulus.

Serotonin

also known as 5-ydroxytriptamine (5-HT), is concentrated in the neurons in a part of the brain called the raphe nucleus. Involved in sensory perception, temperature regulation, control of mood, appetite, and the induction of sleep

threshold stimulus

an action potential will occur in response to a threshold stimulus, a stimulus that is just strong enough to depolarize the membrane to threshold.

Nitric Oxide (NO)

is an important exciatotry nerurotransmitter secreted in the brain, spinal cord,adrenal glands, and nerves to the penis and has widespread effects throughout the body. NO is a highly reactive free radical, it exists for less than 10 seconds before combining with oxygen and water to form inactive nitrates. Endothelial cell sin blood vessel walls release NO, which diffuses into neighboring smooth muscle cells and causes relaxation.

Carbon Monoxide

isn't produced in advance and packed into synaptic vesicles. It is formed as needed and diffuses out of cells that produce it into adjacent cells. Excitatory neurotransmitter produced in the brain and in response to some neuromuscular and neuroglandualr functions.

Norepinephrine (NE)

it is a biogenic amines. Plays roles in arousal (awakening from deep sleep), dreaming and regulating mood. A smaller number of neurons in the brain use epinephrine as a neurotransmitter, both serve as hormones. Cells of the adrenal medulla inner portion of the adrenal gland release them into the blood

All-or-none principle

once started it does not stop

Ligand-gated channels

opens and closes in response to the binding of a ligand (chemical) stimulus. A wide variety of chemical ligands-including neurotransmitters, hormones, and particular ions- can open or close ligand-gated channels. The neurotransmitter Acetylcholine (ACh) for example, opens cation channels that allow Na+ and Ca2+ to diffuse inward and K+ to diffuse outward. Ligand gated channels are located in the dendrites of some sensory neurons, such as pain receptors, and in dendrites and cell bodies of interneurons and motor neurons.

Voltage-gated channels

opens in response to a change in membrane potential (voltage). Voltage-gated channels participate in the generation and conduction of action potentials in axons of all types of neurons.

Mechanically gated channels

opens or closes in responses to mechanical stimulation in the form of vibrations (such as sound waves), touch, pressure, or tissue stretching. The force distorts the channel from its resting position, opening the gate. Examples of mechanically gated channels are those found in auditory receptors in the ears, in receptors that monitor strecthing of internal organs, and in touch receptors and pressure receptors in the skin.

Leak channel

randomly alternate between open & closed positions. Typically plasma membranes have many potassium ion (K+) leak channels than sodium ion (Na+) leaks channels, and the potassium ion leak channels leakier than sodium ion leak channels. The membranes permeability to K+, is much higher than its permeability to Na+. Leak channels are found in nearly all cells, including dendrites, cell bodies and axons of all types of neurons

Acetycholine (ACh)

released by many PNS neurons and by some CNS neurons. Is an excitatory neurotransmitter at some synapses, such as the neuromuscular junction, which the binding of ACh to ionotropic receptors opens cation channels. It is also an inhibitory neurotransmitter at other synapses, where it binds to metabotropic receptors coupled to G proteins that open K+ channels. EX: released during muscle contraction

Amino Acids (GABA)

several amino acids are neurotransmitters in the CNS (ONLY FOUND IN CNS). Glutamate and aspartate have powerful excitatory effects. Most excitatory neurons in the CNS and perhaps half of the synapses in the brain communicate via glutamate. Gamma aminobutyric acid (GABA) and glycine (spinal cord) are important inhibitory neurotransmitters. The binding of GABA to ionotropic recpetors opens Cl- channels. GABA is only found in the CNS, where it is the most most common inhibitory neurotransmitter.

Spatial summation

summation of post-synaptic potentials in response to stimuli that occur at different locations in the membrane of a postsynaptic cell at the same time. Results from the build up of neurotransmitters releases simultaneously by several presynaptic end bulbs. Sequence by which they fire all together. (all @ once)

Temporal summation

summation of postsynaptic potentials in response to stimuli that occur at the same location in the membrane of the postsynaptic cell but at different times. Fired by a SINGLE presynaptic end bulb two or more times in rapid succession. Blowing the balloon in lecture it will eventually pop but will take multiple breaths.