Nervous System

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Nervous system

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Controls rapid activity like muscle movement with both electrical and chemical stimulation. Typically adjusts for short-term changes

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Neurons

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Functional cells of nervous system. Relay messages to and from central nervous system

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Glial cells

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Non-condensing cells that protect and support neurons. Binds nervous tissue to other structures, helps repair cells and protects nervous tissue

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Dendrites

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Neuron fibers. Receive info from sensory receptors and other neurons. Conduct impulses toward the cell body of neuron.

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Cell body of neuron

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Part of neuron with the nucleus and most of the cell's organelle

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Axons

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Neurons fibers that conduct impulses away from the cell body of the neuron. Relay neural impulses to other neurons, muscles or glands. May be covered with myelin sheath

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Myelin sheath

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Neuron insulation made of Schwann cells (glial cells) that wrap around the axon. Increases the rate of neural transmission

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Nodes of Ranvier

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Small spaces between sections of myelin sheath that are important in speeding up the conduction of nerve impulses.

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Neurilemma

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Thin coating formed by outermost layer of Schwann cells in peripheral nervous system. Plays a role in repair of damaged myelinated neurons

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White matter

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Neurons in brain/spinal cord with myelinated sheaths

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Grey matter

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Neurons in brain/spinal cord without myelinated sheaths. Not regenerated- damage is permanent

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Multiple sclerosis

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Autoimmune disease where immune system attacks myelin sheath. Causes loss of muscle control and brain function. No cure, but can be treated with immunosuppressive drugs

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Nerve

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Banded bundle of neurons with myelinated axon fibers

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Sensory neuron

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Afferent neuron. In peripheral nervous system only. Relays info about environment, from sensory receptors to central nervous system for processing. Cell body in center of neuron

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Interneuron

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Link between sensory and motor neurons. Only in central nervous system

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Motor neuron

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Efferent neurons. Relays info from central nervous system to effectors

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Effectors

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Any tissue or organ that carries out a command from the nervous system. Muscle or gland

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Reflex arc

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Receptor to sensory neuron to interneuron (spinal cord) to effector. Simplest nerve pathway. Same stimulus leads to the same response

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Electrical potential

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Force that causes charged particles to move- measured in volts. Occurs when charge on either side of a membrane varies

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Sodium-potassium pump

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Specialized pump in the cell membranes. Moves potassium into cytoplasm while removing sodium from the cytoplasm. Requires ATP as it moves ions against the concentration gradient (low to high conc)

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Number of Na+ and K+ moved in pump

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3 Na+ pumped outside the cell for every 2 K+ pumped into the cell

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Diffusion channels

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Don't require ATP, as Na and K move with the concentration gradient. Na+ in and K+ out

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Resting membrane potential

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-70 mV. Voltage difference across cell membrane when it is not transmitting nerve impulse. Membrane is polarized. Sodium diffusion channels are closed, some potassium are open. Net result: much greater negative charge inside the cell membrane

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Action potential

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Viltage difference across a membrane when it is stimulated. Sodium diffusion channels open and potassium channels close. Positive charge inside the cell, negative outside- membrane depolarized.

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Repolarization

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Original polarity of nerve cell membrane is restored. K+ channels open, Na+ close. Returns to resting potential

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Refractory period

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Recovery time required for a nerve cell to become repolarized or to produce another action potential

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Threshold level

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Minimum level of stimulus required to produce a response. Action potential won't occur unless polarity changes enough- different for every neuron

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Neural transmission

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All or nothing response. Only one nerve impulse that doesn't increase or decrease in magnitude

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Intensity of stimulus

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Indicated to brain by variations in frequency and number of impulses

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Synapse

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Occurs when action potential is converted to chemical message and transmitted to another cell

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Presynaptic neuron

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Neuron carrying the impulse to synapse

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Postsynaptic neuron

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Neuron that carries impulses away from synapse

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Stimulatory neurotransmittors

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Causes Na+ channels to open- depolarization

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Inhibitory neurotransmitters

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Causes K+ channels to open- hyperpolarization occurs. Inhibits action potential

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Summation

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Effect produced by accumulation of neurotransmitters from 2 or more neurons. Increased muscle contraction

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Acetylcholine

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Neurotransmitter commonly found in brain and neuromuscular junctions. Stimulatory. Causes Na channels to open in postsynaptic neuron- depolarization

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(Acetyl)cholinesterase

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Neurotransmitter/enzyme that is released following acetylcholine and destroys it. Long-term exposure leads to respiratory arrest

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Norepinephrine (noradrenalin)

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Neurotransmitter that plays a role in the sympathetic nervous system to help induce the fight or flight response.

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GABA

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Inhibitory neurotransmitter. Too little causes anxiety disorders

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Glutamate

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Stimulatory neurotransmitter. Too much will kill neurons- Lou Gehrig's disease

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Serotonin

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Neurotransmitter involved in emotion and mood. Too little causes depression

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Dopamine

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Inhibitory neurotransmitter associated with feelings of pleasure. Excessive amounts associated with schizophrenia. Parkinson's disease with too little