Bio 201 Nervous System Flashcards

Excitability (irritability)–ability to respond to changes in the body and external environment called stimuli

Conductivity–produce traveling electrical signals

Secretion–when electrical signal reaches end of nerve fiber, a chemical neurotransmitter is secreted

Neurons - The basic functional units of the nervous system – the communicators!

Supporting cells

1.) CNS (central nervous system) - neuroglia (glial cells)

Astrocytes, microglia, ependymal cells, oligodendrocytes

2.) PNS (peripheral nervous system)– satellite cells, Schwann cells

Structural and functional center of the entire nervous system.

Consists the brain and spinal cord

Integrates(combines) incoming pieces to sensory information, evaluates the information, and initiates an response.

Consists of the nerve tissues that lie in the periphery or "outer regions" of the nervous system. Fibers extending away from the CNS.

Neurons and Neuroglia

1. Astrocytes
2. Oligodendrocytes
3. Microglia
4. Ependymal

1. Satellite Cells

2. Schwann Cells

RECIEVE

Highly branched SEND electrical signal toward the cell body

Dendritic spines:

–many fine processes

–receive information from other neurons

–80–90% of neuron surface area

AWAY

Conduct electrical impulses away from the cell body

Only one per neuron

Carries electrical signal (action potential) to target

Axon structure is critical to function

Cytoplasm of axon

Contains neurotubules, neurofibrils, enzymes, organelles

Perikaryon

–specialized cell membrane

–covers the axoplasm

branches of a single axon

fine extensions of distal axon

tips of axon

Primary function-Increases the speed of transmission of nerve impulses (up to 150 times faster)

Serves to protect and electrically insulate axon

Whitish, fatty protein layer (20% protein and 80 % lipid)

Only associated with axons, not dendrites

All myelination completed by late adolescence

Nodes of Ranvier

Endoneurium surrounds each fiber

Groups of fibers are bound into fascicles by perineurium

Fascicles are bound together by epineurium

It is characterized by myelin loss and destruction accompanied by varying degrees of oligodendrocytes injury and death. As the myelin surrounding nerve fibers is lost, nerve conductions is impaired and weakness, loss of coordination, visual impairment, and speech disturbances.

• Autoimmune
• Oligodendrocytes and myelin sheaths of CNS degenerate
• Replaced by hardened scar tissue
• Between 20-40 yrs
• Double vision, blindness, speech defects, neurosis, tremors, numbness
• Variable cycles until bedridden
• No Cure

Astrocytes

Protect neuron cell bodies

Ependymal cells

Dispose of debris in areas of infection, trauma or stroke

Ependymal cells

In the PNS, the Schwann cells form myelin.
In the CNS, the Oligodendrocytes form myelin

Na+ concentrated outside of cell (Extracellular Fluid)
K+ concentrated inside cell (Intracellular Fluid)

***If threshold potential (-55mV) is reached voltage-gated Na+ channels open (Na+ enters causing depolarization)

The action potential is an explosion of electrical activity that is created by a depolarizing current. This means that some event (a stimulus) causes the resting potential to move toward 0 mV. When the depolarization reaches about -55 mV a neuron will fire an action potential. This is the threshold.

(Na+ enters causing depolarization)

K+

Slow K+ gates fully open

K+ exits repolarizing the cell

Negative overshoot produces
hyperpolarization

–excessive exiting of K+

Sodium potassium pump is a mechanism in the plasma membrane actively pumps sodium ions (Na+) out of the neuron and potassium ions (K+) into the neuron. This occurs at an unequal rate. 3 sodium ions out and 2 potassium ions in. Because very little sodium reenters the cell via diffusion, this maintains an imbalance in the distribution of ions and thus maintains the resting potential.

3 Na+ out

2 K+ in

nondecremental (do not get weaker with distance)

–irreversible (once started goes to completion and can not be stopped)

Absolute refractory period

–as long as Na+ gates are open

–NO stimulus will trigger AP

Relative refractory period

–as long as K+ gates are open

–***only especially strong
stimulus will trigger new AP

Diameter of fiber presence of myelin

large fibers have more surface area for signals

think of a larger diameter pipe having less resistance than a smaller pipe

Myelinated faster than unmyelinated

Transmission is faster in myelinated axon. The myelinated axon is considered the Salutatory conduction. Fast signals supply skeletal muscles and transport sensory signals for vision and balance.

Transmission is slower in the unmyelinated axon. Slow signals supply the stomach and dilate the pupil.

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-70 mV

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Also called a ligand – gated receptor

No second messenger is involved

Think ion = direct effect on channel

?????

Inotropic sensory receptors- Mechonoreceptor, Thermoreceptor, Electroreceptor

Metabotropic- Chemoreceptor, Photoreceptor

Acetylcholine - formed from acetic acid and choline

Amino acid neurotransmitters

Monoamines

Neuropeptides

1.Excitatory neurotransmitters:

–cause depolarization of postsynaptic membranes

–promote action potentials

2.Inhibitory neurotransmitters:

–cause hyperpolarization (goes in opposite direction of depolarization) of postsynaptic membranes

–suppress action potentials

IPSP = inhibitory postsynatic potential

–NT causes postsynaptic membrane to become more permeable to Potassium (moves out) OR Chloride (moves in)

EPSP = excitatory postsynaptic potential

–NT causes opening of more ligand gated Sodium channels on postsynaptic membrane

When several knobs are activated simultaneously, neurotransmitters stimulate different locations on the postsynaptic membrane. these local potentials may spread far enough to reach the axon hillock, where they add together, or summate. If the sum of the local potentials reach the threshold potential, voltage gated channels in the membrane open, causing an action potential.

When synaptic knobs stimulate a postsynaptic neuron in rapid succession, their effects can add up over a brief period of time to produce an action potential.

*A synaptic delay of 0.2–0.5 milliseconds occurs between:

–arrival of action potential at synaptic knob

–and effect on postsynaptic membrane

*Rate limiting factor in transmission of a nerve impulse

*Not as much of a factor in an electrical synapse

–Allow ions to pass between cells

–Produce continuous local current and action potential propagation

–Are found in areas of brain, eye, ciliary ganglia

• Nerve signal opens voltage-
  gated calcium channels
  in synaptic knob
• Triggers release of ACh which
  crosses synapse
• ACh receptors trigger opening
  of Na+ channels producing
  local potential (postsynaptic
  potential)
• When membrane reaches threshold, triggers AP
  in postsynaptic neuron

If acetylcholinesterase activity is inhibited, the synaptic concentration of acetylcholine will remain higher than normal. If this inhibition is irreversible, as in the case of exposure to many nerve gases and some pesticides, sweating, bronchial constriction, convulsions, paralysis, and possibly death can occur. Although irreversible inhibition is dangerous, beneficial effects may be derived from transient (reversible) inhibition. Drugs that inhibit acetylcholinesterase in a reversible manner have been shown to improve memory in some people with Alzheimer's disease.

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Alcohol is one of the depressant drugs in widest use, and is believed to cause its effects by interacting with the GABA receptor. Initially anxiety is controlled, but greater amounts reduce muscle control and delay reaction time due to impaired thinking.

Neurotransmitter is recycled back into presynaptic neuron
Synapse more active when 5-HT (Serotonin) reuptake is blocked by an SSRI (Serotonin Specific Reuptake Inhibitor)

Neurotransmitter is sometimes broken down into smaller pieces once it is taken back into the presynaptic neuron
An enzyme, monoamine oxidase breaks down many types of NT's
Some old antidepressant drugs (called MOAI's) inhibit this enzyme increasing availability of some NT's involved with depression