Central Nervous System
Brain and spinal cord
Peripheral Nervous System
Consist of the nerves that connect the brain
Cell Body (Soma)
Contains nucleus and ribosomes
Dendrites
Receive inputs from other neurons
Axon
Carries output to target cells
Axon Terminals
Responsible for releasing neurotransmitters from axon; diffuse across an extracellular gap, called a synapse
Glial Cells
Surround soma, axon, and dendrites of neurons and provide them with physical and metabolic support
Obligodendrocytes
Produce myelin sheath in CNS
Schwann Cells
Form myelin sheaths around the larger nerve fibers in PNS
Nodes of Ranvier
Spaces between adjacent sections of myelin where the axon's plasma membrane is exposed to extracellular fluid
Astrocytes
Support cells, control extracellular environment of neurons
Ependymal Cells
Ciliated, production and movement of Cerebrospinal fluid
Microglia
Immune system of CNS
Afferent Neurons
Convey information from the tissues and organs of the body towards the CNS; contain sensory receptors; propagate electrical signals from their receptors into brain and spinal cord; usually only contain an axon
Efferent Neurons
Convey information away from the CNS to effector cells like muscle, gland, or other nerve cells; their cell bodies and dendrites are within CNS, and axons are in periphery
Interneurons
Connect neurons within the CNS (majority of neurons); entirely in CNS; function as integrators and signal changers; integrate gouts of afferent and efferent neurons into reflex circuits; 99% of all neurons
Sensory Receptors
Respond to various physical or chemical changes in their environment by generating electrical signals in the neuron
Nerves
Groups of afferent and efferent neurons, together with connective tissue and blood vessels
Synapse
Anatomically specialized junction between two neurons where one neuron alters the electrical and chemical activity of another
Presynaptic Neuron
Neuron that conducts a signal toward the synapse
Postsynaptic Neuron
Neuron conducting signals away from synapse
Electric Potential
Potential energy associated with attractive charges of opposite sign
Potential Difference
Difference in the amount of charge between two points
Current
Movement of electrical charge
Resistance
Hinderance to current
Resting Membrane Potential
All cells, at resting conditions, have a potential difference across the plasma membranes, with the inside of the cell negatively charged with respect to the outside
Depolarized
When potential becomes less negative (closer to 0)
Repolarized
When membrane potential that has been depolarized returns toward resting value (-70)
Hyperpolarized
Potential is more negative than resting (-70)
Threshold Stimuli
Stimuli that is just strong enough to depolarize the membrane enough to cause the positive feedback of Na (usually 15mV lower than rest, -55mV)
Absolute Refractory Period
During depolarization, section cannot be stimulated, cannot trigger another AP, when Na+ gates open
Relative Refractory Period
During depolarization, membrane can be stimulated by a STRONG stimulus, AP won't be as strong
Electrical Synapse
Pre- and post-synaptic cells are connected by gap junctions; allow the local currents resulting from arriving action potentials to flow DIRECTLY across the junction through the connecting channels
Chemical Synapse
Pre-synaptic neurons release neurotransmitter from their axon terminals, neurotransmitter binds to receptors on post-synaptic neurons; contain synaptic cleft that prevents direct propagation of current
Axon Transport
1. It refers to the passage of materials from the cell body of neuron to the axon terminals
2. It refers to the passage of materials from axon terminals to the cell body of a neuron
3. It is especially important for maintaing the integrity of neurons with
Glial Cells
1. They form myelin
2. They deliver fuel molecules to neurons and remove the waste products of metabolism
3. They are important for the growth and development of the nervous system
4. They regulate the composition of the extracellular fluid in the CNS
Membrane Potential
Requires very few ions to be distributed unevenly
Which is true about typical, resting neurons?
The permeability of the plasma membrane to potassium ions is much greater than sodium ions
The membrane potential of most neurons at rest is
More positive than the equilibrium potential for potassium
The diffusion potential due to the concentration gradient for Na+ across a nerve cell membrane
Favors its movement into the cell at the resting membrane potential
Which would result from an increase in the extracellular concentration of K+ above normal
Depolarization of resting nerve cells
Which is true about the Na+, K+, ATPase pump in neurons?
It generates a small electrical potential such that the inside is made negative with respect to the inside
Which of these would occur if the concentration of ATP were depleted in a typical nerve cell
Resting membrane potential would become less negative
Equilibrium Potential
1. A function of the concentration of that ion on both sides of the membrane
2. It's the potential at which there is no net movement of that ion across the membrane
3. A permeable ion will move in the direction that will tend to bring the membrane potenti
Which of the following statements concerning the permeability of a typical neuron membrane at rest is true
Most of the voltage-gated Na+ channels are in the closed state
A threshold stimulus applied to an excitable membrane is one that is just sufficient to
Trigger an action potential
What must happen in order for an action potential to begin?
Na+ influx must exceed K+ efflux
Which describes the response of the voltage-gated channels when axon is stimulated to threshold?
Na+ channels are activated and then inactivated
During the rising (depolarizing) phase of a neuronal action potential
Pna+ becomes much greater than Pk+
Why are action potentials sometimes described as being "all-or-none" in character?
An action potential occurs whenever a supra threshold stimulus occurs, and its amplitude does not very with the size of a stimulus
Neuronal action potential
During the after-hyperpolarization phase, the permeability of the membrane to potassium ions is greater than its permeability at rest
The relative refractory period of an axon coincides with the period of
Increased K+ permeability of the cell
How is strength of a stimulus encoded by neurons?
By the frequency of action potentials
Interneurons
1. They receive synaptic input from other neurons in the CNS
2. They sum excitatory and inhibitory synaptic inputs
3. They deliver synaptic input on other neurons
4. They can transmit information between afferent neurons and efferent neurons
Exocytosis of neurotransmitter into the synaptic cleft is triggered by an influx of ____ in response to the arrival of an action potential in the axon terminal
Ca2+
The main role of calcium ions at chemical synapses is to
Cause fusion of synaptic vesicles with the plasma membrane of the axon terminal
At an excitatory chemical synapse between two neurons
There is increased permeability of the post-synaptic cell to both Na+ and K+
An inhibitory postsynaptic potential
Occurs when a ligand-gated ion channel increases its permeability to K+
EPSP's
1. They are produced by the opening of chemically-gated sodium channels
2. They transmit signals over relatively short distances
3. They depolarize postsynaptic cell membranes
4. They are able to summate
Temporal Summation
A synapse is stimulated a second time before the effect of a first stimulus at the synapse has terminated
Presynaptic Synapse
A synapse between an axon terminal and another axon's terminal that can be either excitatory or inhibitory
Acetylcholine is the main neurotransmitter released by
Pre-ganglionic sympathetic neurons and motor neurons
Serotonine
Acts as a neuromodulator
Alzheimer's disease is thought to involve primarily
Loss of cholinergic neurons
The portion of the peripheral nervous system that is composed of nerve fibers that innervate skeletal muscle is called the
Somatic motor nervous system
The region of the brain that is the most important control area for homeostatic regulation of the internal environment
Hypothalamus
Which best describes the reticular formation of the brain
It integrates information from all regions of the CNS, and incorporates the mechanisms that regulate sleep and wakefulness
Limbic System
An interconnected group of brain structures including parts of the frontal lobe-cortex, temporal lobe, thalamus, and hypothalamus, that is associated with learning, emotional experience, and behavior
Post-ganglionic neuron cell bodies of the autonomic nervous system have which category of neurotransmitter receptor
Nicotinic acetylcholine receptors