click below
click below
Normal Size Small Size show me how
MCAT Bio Ch. 4
Term | Definition |
---|---|
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. |