Neurophysiology Part 1 Flashcards
Neural Communication
We master our environment using highly developed senses (vision, audition etc) that provide comprehensive information to a flexible decision-making device: the brain
The brain analyses sensory information (sensations), endows them with meaning (perceptions), and stores salient information for future reference (memory)
Microglial
Neural phagocytes produced by macro-phages and activated after injury, infection or disease.
Macroglial
Oligodendrocytes (CNS) and Schwann (PNS) cells insulate axons, forming a myelin sheath by winding their membrane around the axon in a spiral. The more numerous astrocyte cells help maintain dynamic equilibrium and also act as reuptake vehicles.
Neuron Feature = Soma
The metabolic center, includes the nucleus and the endoplasmic reticulum.
Neuron Feature = Dendrites
(receivers), apical vs. basal
Neuron Feature = Axon
Conveys electrical signals known as action potentials (1 ms electrical impulses traveling at 1 – 100 m / second)
Neuron Feature = Presynaptic terminals
The branches of the axon, may connect with 1000 or more other neurons
Neurons
> . However, for a long time it was still thought that the brain was a continuous, web-like, recticulum
. Neurons (i.e., soma) mostly aggregate in Gray Matter.
. Nervous impressions are received, stored, and transformed into efferent impulses
. Mylinated axons can clump together in nerve tracts to form White Matter, conducting neural information across long distances.
. Each neuron is a discrete cell clearly segregated from other neurons
Types of Neurons = Unipolar
Found in the spine, single process (or branch). Relays touch information, and controls organs and glands. They are found in the ANS
Types of Neurons = Bipolar
Sensory Neurons (all modalities except touch) with two distinct processes
Types of Neurons = Multipolar
An axon with many dendrites. Varying greatly in shape, they include Interneurons (bridging motor and sensory neurons) and Motor Neurons, and are the most common neurons in the CNS
Functional Neuron = Sensory
Carry information from periphery into the CNS for the purposes of both perception and motor coordination. Sometimes called afferent neurons
Functional Neuron = Motor
Carry instructions from the CNS or the spinal cord to muscles, glands, and organs. Sometimes called efferent neurons
Functional Neuron = Interneurons
a) Relay or projection interneurons, long axons carrying information between brain regions
b) Local interneurons, short axons in local circuits
•Begins with the stimulation of a neuron.
The action potential (electrical)
The action potential is an electrical current that flows from the axon hillock and terminates at the terminal buttons
Synaptic transmission (chemical & electrical)
Synaptic transmission involves molecules, known as neurotransmitters, crossing the synaptic cleft from the terminal buttons to a receptor resident in the membrane of the receiving neuron.
Action Potential: Part 1
The action potential underlies all information transfer in the brain, and as an event considered homogenous
Thus, the information is determined by the pathway the signal is traveling, with the brain analysing patterns of incoming signals
At its terminus, the axon divides into fine branches that connect to other neurons. When two neurons connect we say we have a synapse
The principle of dynamic polarisation: electrical signals within a nerve flow in a single direction only
Action Potential: Part 2
> . The electrical charge inside of an axon relative to the outside charge is the membrane potential
. The resting potential is -70mV (re: the outside)
. The resting potential is maintained by a concentration gradient (diffusion) and the electrical force
. Voltage-dependent ion channels control the entry of Na+ and K+ into the cell
. The Na+/K+ pump controls their exit from the cell
Action Potential: Part 3
> . The action potential begins when voltage dependent ion channels open and allow Na+ to flow into the cell
. A narrow region of the axon membrane then depolarizes (becomes + with respect to the outside)
. At 1-ms it begins to repolarize (return to the resting potential)
. The next narrow region of the axon then depolarizes
And so on, like a Mexican wave along the axon’s length
Action Potential: Part 4
- If an Action potential is generated at the axon hillock, it will travel all the way down to the synaptic button
- The manner in which it travels depends on whether the neuron is myelinated or unmyelinated
- Unmyelinated neurons undergo the continuous conduction of an AP whereas myelinated neurons undergo saltatory conduction of an AP.
Action Potential: Part 5
Continuous conduction occurs in unmyelinated axons
In this situation, the wave of de- and repolarization simply travels from one patch of membrane to the next adjacent patch
•Saltatory conduction occurs in myelinated axons.
•Saltare is a Latin word meaning “to leap”
•Recall that the myelin sheath is not completed. There are myelin free regions along the axon, the nodes of Ranvier
Temporal summation
–The same presynaptic neuron stimulates the postsynaptic
neuron multiple times in a brief period. The depolarization resulting from the combination of all the EPSPs may be able to cause an AP
Spatial summation
•Multiple neurons all stimulate a postsynaptic neuron resulting in a combination of EPSPs which may yield an AP
Refractory Periods
- Absolute – impossible to initiate another action potential
- Relative – harder to initiate another action potential
- Prevent the backwards movement of APs and limit the rate of firing
