Princeton Psych Ch 3 - Biological Functions of Behavior Flashcards
Describe the structure of a neuron and its function.
Nuerons process and transmit action potentials. Neurons have a central cell body, the nucleus containing soma where most of the biosynthetic activity takes place; axons and dendrites extend from the cell body. Neurons with one dendrite are termed bipolar.
Two primary membrane proteins establish the resting membrane potential of -70mV. What are they?
The Na+/K+ ATPase and the potassium leak channels. The are very few Na+ leak channels relative to K+. Hence the leaving K+ makes the MB potential more negative.
How many sodium and potassium ions does the Na+/K+ pump?
The Na+/K+ pumps three sodium ions out of the cell and two potassium ions into the cell with the hydrolysis of one ATP molecule. Example of primary active transport.
What is depolarization? Repolarization?
Depolarization is the change in the MB potential from the resting of -70mV to a less negative or positive potential. After depolarization, repolarization returns the MB potential to normal.
The first step of an AP is a change in MBΨ caused by the movement of ions into and out of the neuron through ion channels. What happens next? Hint: this step is called depolarization.
Voltage-gated Na channels are opened by the depolarization of the membrane from the resting potential of -70mV to a threshold potential of approximately -50mV. Once this threshold is reached, the VOLTAGE gated Na channels are opened fully. Before, they are closed shut.
How does an AP propagate down a neuron?
Some of the Na ions flow down the axon interior, depolarizing the neighboring section of the MB. When the next section of the MB reaches a threshold, those voltage-gated Na sodium channels open as well. AP go to COMPLETION.
Describe the first two steps of repolarization.
1) Voltage-gated Na channels inactivate quickly after they open. 2) Voltage-gated K+ channels open slower than voltage Na, but they stay open longer. As K+ leaves the cell, the MBΨ returns to neg values, overshooting to -90mV. At this point voltage K+ channels close.
Describe what happens after voltage-gated K+ channels close after repolarization.
3) K+ leak channels and the Na/K ATPase continue to function (as they always do) to bring the MBΨ back to resting.
Saltatory Conduction. Axons of neurons are wrapped in insulating sheath called ___. The sheath is created by glial cells called _____.
Myelin, Schwann Cells. There is no MB depolarization and no voltage-gated Na channels in regions of MB wrapped in myelin. Rather than impeding AP, the MS dramatically speeds up the movement of AP by forcing the AP to jump from node to node. The jumping is called saltatory conduction.
There are periodic gaps, called ______.
Nodes of Ranvier. Na gated and K+ channels are concentrated in these gaps.
What are glial cells?
Specialized non-neuronal cells that typically provide structure and metabolic supports to neurons. Examples include Schwann (PNS) and Oligodendrocytes (CNS), which form myelin for increased AP speed conduction.
Describe what equilibrium potential is.
The EQΨ is the MBΨ in which there is no net movement of ions across the MB. The EQΨ is specific for a particular ion. For Na + it’s +50mV and for K+ it’s -90mV. It is the balance of electrical and chemical gradients. Chemical would drive Na in but being too positive in the cell would drive it out.
Explain the refractory period when it comes to action potentials.
The passage of 1 AP makes the neuron nonresponsive to MB depolarization and unable to transmit another AP for a short period of time.
What is the difference between absolute and relative refractory period.
Absolute - a neuron will not fire another AP no matter how strong a MB depolarization is induced. During this time, VG Na channels have been inactivated (not same as closed) after depolarization. During the RR period, a neuron can be induced to transmit an AP, but the depolarization required is > normal bc the MB is hyperpolarized.
What is a synapse?
A junction between the axon terminus of a neuron and the dendrites, soma, or axon of a second neuron.
What is the difference between electrical and chemical synapses?
E synapses occur when the cytoplasms of two cells are joined by gap junctions. C synapses are more common and are found at the ends of axons where they meet their target cell; here, the AP is converted to a chemical signal.
Describe the steps in the transmission of a signal across a chemical synapse.
1) an AP reaches the end of an axon. 2) depolarization of presynaptic MB opens VG Ca channels. 3) Ca influx into the pre-syn cell causes exocytosis of NT stored in secretory vesicles. 4) NT diffuse across cleft. 5) NT binds to receptor proteins in the post syn MB. These receptors are ligand-gated ion channels. 6) opening of ion channels alters the MB polarization 7) If the MB depolarization of the post syn cell reaches the threshold of VG Na channels (-50mV), an AP is initiated. 8) NT is the cleft is degraded an/or removed to terminate signal.
Role of Acetylcholine?
Acetylcholine is commonly used in neuromuscular junctions. It stimulates muscle contractions. It is excitatory.
Neurotransmitters than induce hyperpolarization of the postsynaptic MB are termed ____.
Inhibitory.
Describe the all or nothing concept when it comes to AP.
Once an AP is initiated in a neuron, it will propagate to the end of the axon at a speed and magnitude of depolarization that do not vary from one AP to another. This is an all or nothing event. An AP is initiated when a threshold of -50mV is reached
Excitatory NTs can postsynaptic depolarization or _____. Inhibitory NTs cause _______.
Excitatory postsynaptic potentials (EPSPs); the other is inhibitory postsynaptic potentials (IPSPs)
Explain the difference between temporal and spatial summation.
Temporal summation: presynaptic neuron fires AP so rapidly that the EPSPs or IPSPs pile on top top of each other. Spatial summation: EPSPs and IPSPs from all of the synapses on the postsynaptic membrane are summed at a given moment in time.
What is the function of the PNS and CNS?
PNS - receiving information is the sensory function of the NS; acting on integrative function is the motor functino of the NS; CNS - processing information is the integrative function of the NS.
Describe the function of motor neurons.
Motor neurons carry info from the NS toward organs which can act upon that info, called effectors (muscles and glands). Since motor neurons carry info away from the CNS and innervate effectors, they are called efferent neurons.
Describe the function of sensory neurons.
Sensory neurons carry info toward the CNS; these are afferent neurons.
Describe what a reflex is.
A direct motor response to sensory input which occurs without conscious thought. Simplest reflex can occur without brain involvement. Ex. muscle stretch reflex, which is a simple, monosynaptic reflex arc.
When the muscle stretch reflex with the patellar tendon, the quadriceps contract, but the hamstrings also relaxes. Explain the neuron responsible for relaxing.
The sensory neuron that detects stretch synapses with not only a motor neuron for the quads, but also with an inhibitory interneuron. This short neuron forms an inhibitory synapse with a motor neuron innervating the hamstring.
What is the PNS and its subdivisions.
The PNS: all nerves and sensory structures outside of the brain and spinal cord; somatic: voluntary control of muscle; autonomic: involuntary control of glands and smooth muscle
Subgroups Autonomic: 1) sympathetic: fight or flight; 2) parasympathetic
What is the PNS’s autonomic division responsible for?
The autonomic division is responsible for digestion, circulation, perspiration, and other involuntary processes. It has afferent and efferent functions.
With the parasympathetic NS, what happens with the digestive, urinary, bronchial smooth muscle, CV, eyes, and genitals.
DG: glands - stim, motility - stim digestion, sphincter - relax; Urinary: bladder - contract, urethral spincter - relax; bronchials: constrict (close airways); CV - HR and contractility decreases; pupils constrict + near vision; genitals: erect/lubrication.
With the sympathetic NS, what happens with the digestive, urinary, bronchial smooth muscle, CV, eyes, and genitals.
DG: glands - inhibit, motility - inhibit digestion, sphincter - contract; Urinary: bladder - relax, urethral spincter - contract; bronchials: relax (open airways); CV - HR and contractility increases; pupils dilate + far vision; genitals: ejaculate, orgasm.
