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MCAT Bio Ch. 4

Neurons Highly specialized cells responsible for the conduction of impulses
Electrical Communication Of Neurons Occurs Via: Ion exchange and the generation of membrane potentials down the length of the axon
Chemical Communication Of Neurons Occurs Via: Neurotransmitter release from the presynaptic cell and the binding of those neurotransmitters to the postsynaptic cell
Dendrites Appendages that receive signals from other cells
Soma Location of the nucleus as well as organelles such as the endoplasmic reticulum and ribosomes
Axon Hillock Where the cell body transitions to the axon and where action potentials are initiated
Axon Long appendage down which an action potential travels
Nerve Terminal / Synaptic Bouton End of the axon from which neurotransmitters are released
Nodes Of Ranvier Exposed areas of myelinated axons that permit saltatory conduction
Synapse Consists of the nerve terminal of the presynaptic neuron, the membrane of the postsynaptic cell, and the space between the two called the synaptic cleft
Myelin Insulating substance that prevents signal loss
Myelin Is Created By: Oligodendrocytes in the central nervous system and Schwann cells in the peripheral nervous system
Myelin Prevents: Dissipation of the neural impulse and crossing of neural impulses from adjacent neurons
Nerves / Tracts Are: Bundles of individual axons
A Single Nerve May Carry: Multiple types of info., including sensory, motor, or both.
Tracts Only Carry: One type of information.
Cell Bodies Of Neurons Of The Same Type Within A Nerve Cluster In: Ganglia in the Peripheral Nervous System (PNS)
Cell Bodies Of The Individual Neurons With A Tract Cluster In: Nuclei in the central nervous system.
Neuroglia / Glial Cells Cells within the nervous system in addition to neurons
Astrocytes Nourish neurons and form the blood-brain barrier, which controls the transmission of solutes from the bloodstream into nervous tissue
Ependymal Cells Line the ventricles of the brain and produce cerebrospinal fluid which physically supports the brain and serves as a shock absorber
Microglia Phagocytic cells that ingest and break down waste products and pathogens in the central nervous system
Oligodendrocytes (CNS) and Schwann Cells (PNS) Produce: Myelin around axons
Resting Membrane Potential Of All Neurons -70 mV. This is maintained by using selective permeability of ions as well as the Na+/K+ ATPase
Na+/K+ ATPase Pumps: Three sodium ions out of the cell for every 2 potassium ions pumped in
Excitatory Signals Cause: Depolarization of the neuron
Inhibitory Signals Cause: Hyperpolarization of the neuron
Temporal Summation Addition of multiple signals near each other in time.
Spatial Summation Addition of multiple signals near each other in space.
Action Potential Used to propagate signals down the axon
Mech. of Action Potential (Step 1) Excitatory stimulation --> cell depolarizes to thresh. volt. --> volt-gated sodium channels open
Mech. of Action Potential (Step 2) Sodium flows into the neuron due to its strong electrochemical gradient. This continues to depolarize the neuron.
Mech. of Action Potential (Step 3) At the peak of the action potential (approx. +35 mV), sodium channels are inactivated and potassium channels open
Mech. of Action Potential (Step 4) Potassium flows out of the neuron due to its strong electrochemical gradient, repolarizing the cell. Potassium channels stay open long enough to overshoot the action potential, resulting in a hyperpolarized neuron. Then, the potassium channels close.
Mech. of Action Potential (Step 5) The Na+/K+ ATPase brings the neuron back to the resting potential and restores the sodium and potassium gradients.
Mech. of Action Potential (Step 6) While the axon is hyperpolarized, it's in its refractory period. During the abs.refractory period, cell is unable to fire another AP. During the relative refractory period, the cell requires a larger than normal stimulus to fire an action potential.
Mech. of Action Potential (Step 7) The impulse propagates down the length of axon because influx of Na+ in one seg. of axon brings subsequent segment of the axon to threshold. The preceding segment of the axon is in its refractory period means that the AP can travel in only one direction.
Steps Of AP At Nerve Terminal (NT Are Released Into Synapse) Volt-gated Ca+2 channels open. Influx of Ca+2 causes fusion of vesicles filled with NT with the presynaptic membrane --> exocytosis of NT into the synaptic cleft. NT bind to receptors (ligand-gated ion channels or G protein-coupled) on postsynaptic cell
Steps Of NT Cleared From Postsynaptic Receptors To Stop Propagation Of The Signal NT can be enzymatically broken down. NT can be absorbed back into the presynaptic cell by reuptake channels. NT can diffuse out of the synaptic cleft.
Three Types Of Neurons In The Nervous System Include: Motor (efferent) neurons, interneurons, and sensory (afferent) neurons
Nervous System Is Made Up Of: The central nervous system (CNS, which includes the brain and spinal cord), and the peripheral nervous system (PNS, cranial and spinal nerves)
White Matter Consists Of: Myelinated axons.
Grey Matter Consists Of: Unmyelinated cell bodies and dendrites
In The Brain, White Matter Is: Deeper than grey matter.
In The Spinal Cord, Grey Matter Is: Deeper than white matter
PNS Is Divided Into The: Somatic (voluntary) and autonomic (automatic) nervous systems.
Branches Of The Autonomic Nervous System Include: Parasympathetic (rest and digest) and sympathetic (fight or flight) branches
Reflex Arcs Use The Ability Of Interneurons In The Spinal Cord To: Relay information to the source of the stimuli while simultaneously routing it to the brain
In A Monosynaptic Reflex Arc, The Sensory (Afferent, Presynaptic) Neuron Fires Directly: Onto the motor (efferent, postsynaptic) neuron
In A Polysynaptic Reflex Arc, The Sensory Neuron May Fire: Onto a motor neuron as well as interneurons that fire onto other motor neurons.
Created by: SamB91