Neurons
Sensory Neuron
A neuron that is directly affected by changes in the environment (light, odor, touch); take information from the periphery and bring it back to the spine and brain; afferent to the CNS (dorsal)
Interneuron
A neuron that is neither a sensory neuron nor a motor neuron; it receives input from and sends output to other neurons; short axons
Receptor
A protein that binds and reacts to molecules of a neurotransmitter or hormone
What are autoreceptors?
A receptor that is located in the presynaptic membrane, telling the axon how much NT has been released
Axon
A single extension from the nerve cell that carries nerve impulses from the cell body to other neurons
Schwann Cell
A type of glial cell that forms myelin in the PNS (rest of the body)
Oligodendrocyte
A type of glial cell that makes myelin in the CNS (brain, spinal chord)
Axo-Axonic
Axon to axon
Where do sensory neurons enter the spinal cord?
The dorsal side
Axon Terminal
The end of an axon, which forms a synapse on a neuron
What determines what action the NT has on the post-synaptic neuron?
Whether or not the receptor is inotropic (direct) or metabotropic (indirect)
What are neurotransmitters?
Chemicals that allow communication between neurons
What ion movement would hyperpolarize a membrane?
Cl
Microglial Cells
Clean up crew; small glial cells that remove cellular debris from injured or dead cells; make a sphere of containment around a neural injury; important for the maintenance of synapses; involved in neural pain systems; interference with their function can lead to Alzheimer's and other dementias
What are the functions of astrocytes?
Contribute to information processing: synchronize activity of neurons; control about of blood flow to brain areas, release chemicals that modify neighboring neurons
What events take place during the action potential and what are the specific effects on the membrane potential?
Depolarization occurs and decreases the membrane potential. Then, after the action potential, the cell briefly hyperpolarizes and increases the membrane potential
What ion movement might result in an EPSP? What ion movement might result in an IPSP?
EPSP: Na or K in ISPS: Cl in or K out
Are motoneurons afferent/efferent? Why?
Efferent because they travel away from the CNS
What causes the fusion of synaptic vesicles with the presynaptic terminal membrane?
Electrical activity in the membrane; the more APs the more vesicles fuse, the more NTs diffuse across the membrane
From what do sensory neurons receive signals?
From receptors in sensory structures (eyes, ears, tongue, nose, skin) and in skeletal muscles and joints
From what do interneurons receive input?
From sensory neurons or interneurons
In what direction(s) does the depolarization spread on an axon?
From the cell body to the presynaptic terminal
What is the primary difference between neurons and glial cells?
Glial cells don't transmit information
What is the difference between graded potentials and action potentials?
Graded potentials did not reach threshold and action potentials did; graded potentials die out but actions potentials don't
What is the function of radial glia?
Guide migration of neurons and growth of axons during embryonic development
What is a metabotropic effect? Why is it important?
Indirectly affecting the receptor via G proteins; it keeps the ion channels open for longer
What is an IPSP?
Inhibitory postsynaptic potential; increase electric potential; hyperpolarize
What do sensory neurons synapse onto?
Interneurons
What do we mean when we say that a neuron is "at rest"?
It is not currently generating an action potential
What is the distribution of Na+ and K+ ions in a neuron at rest?
Na: more concentrated on the outside of the cell K: more concentrated on the inside of the cell
Do all NTs fit into any receptor?
No, because it has to fit like a lock and key
Does the AP grow weaker as it travels down the axon? Why or why not?
No, because it is regenerated at the nodes of ranvier
Does each NT only have one type of receptor?
No, because they have different receptor subtypes --> could be inhibitory in one and excitatory in another
Glial Cells
Non neuronal brain cells that provide structural, nutritional, and other types of support to the brain
Dendrites
One of the extensions of the cell body that are the receptive surfaces of the neuron
What do interneurons synapse onto?
Other interneurons or motoneurons
Dendritic Spines
Outgrowths from the dendrites that increase surface area and allow for extra synaptic contacts; the number and structure of them can change quickly due to training or sensory stimuli
What is the electrical gradient/electrostatic pressure?
Potential homogenizing force (opposites attract)
What is the function of microglia?
Remove waste, viruses, fungi, and other microorganisms from the brain
What prevents the NT from just floating away in the extracellular fluid in the synaptic cleft?
Scaffolding proteins help guide them to the receptors
What are the four zones of the neuron?
The input zone, the integration zone, the conduction zone, and the output zone
How does myelin and axon diameter affect the velocity of the AP?
The larger and fatter the axon is is, the faster the velocity will be. This is because the axon does not need to regenerate the AP as much
What do we mean when we say the membrane is selectively permeable?
The membrane allows some things to pass freely, some can't get in at all, some can pass through protein channels
Presynaptic Membrane
The membrane of the axon terminal that transmits information by releasing neurotransmitter
Postsynaptic Membrane
The membrane on the surface of the cell that receives information by responding to neurotransmitter
Conduction Zone
The part of the neuron over which the nerve's electrical signal may be actively propagated; usually refers to the axon
Integration Zone
The part of the neuron that initiates nerve electrical activity; can also be the cell body but is usually the axon hillock
Input Zone
The part of the neuron that receives information (from other neurons or specialized sensory structures)
Output Zone
The part of the neuron, usually corresponding to the axon terminal, at which the cell sends information to another cell
What is the threshold?
The point at which an action potential is reached; -55mV
Myelination
The process of myelin formation
During what period is it harder to stimulate another AP on a given segment of the axon?
The relative refractory period
Identify the structures and functions of different parts of the neuron.
The soma, the axon hillock, the axon, nodes of ranvier, myelin sheathes, presynaptic terminal, postsynaptic terminal (dendrite of the receiving axon)
Synaptic Cleft
The space between the presynaptic and postsynaptic elements
Axonal Transport
The transportation of materials to and from the neuronal cell body to distant regions in the dendrites and axons; electrical signals go along the outside of the axon and substances travel through the inside of the axon
What if a current is applied and the threshold is reached?
The voltage activated Na channels open and then close due to the equilibrium potential; the K channels open to push them out and then they close again once the EG is - again --> causes the cell to hyperpolarize temporarily
What do we mean when we say that sensory neurons have selectivity of response?
They only respond to certain kinds of stimuli (e.g. light, odor, touch)
What effect do larger depolarizations have the on the AP?
They will cause an action potential but the size of the action potential will not change
What if a current is applied and the threshold is not reached?
This is a graded potential, and the current will diffuse across space and time
Why are reuptake and enzymatic breakdown important?
To conserve resources and also to make sure that the NTs don't interfere with other neurons that don't need them
Innervate
To provide neural input
What is the function of a neuron?
To receive, conduct, and transmit information in the form of an electrochemical sequence
Axon Collateral
A branch of an axon from a single neuron
What is the direction of the electrostatic pressure for Na+ and K+ in a neuron at rest?
Both are pressured to go inside the cell (bc opposites attract)
What are the concentration gradient and diffusive force?
CG: unequal distribution of ions DF: the tendency to move down the concentration gradient from a high concentration to a lower one
Define depolarize/hyperpolarize?
D: making the inside more + relative to the outside; decreasing the membrane potential; closer to 0; can lead to an action potential H: making the inside more - relative to the outside; increased the membrane potential; further away from 0; will not lead to an action potential
Dendro-Dendritic
Dendrite to Dendrite
What is an ionotropic effect?
Directly affecting the receptor
What is enzymatic breakdown?
Enzymes come in and break down NT into unusable chemicals so they can't continue to fire and effect the postsynaptic neuron
What is an EPSP?
Excitatory postsynaptic potential; decrease electric potential; depolarize
In a neuron at rest, do Na+ and K+ ions passively flow across the membrane? If so, in what direction and why?
K ions flow passively through the membrane to the outside of the cell through slightly open channels because of their concentration gradient, but the membrane resists passive flow of Na.
What is the difference between multipolar, bipolar, and unipolar neurons?
Multipolar neurons have one axon and many dendrites. A bipolar neuron has one dendrite and one axon. A unipolar neuron has a cell body that extends in a branch that becomes axons going in two different directions. It has dendritic branches on one end and the axon terminal at the other end.
What do motoneurons synapse onto?
Muscles, organs, and glands
What ion movement would depolarize a membrane?
Na
What is the direction of the diffusive force for Na+ and K+ in a neuron at rest?
Na: inside the cell K: outside the cell
What is the sodium-potassium pump and what does it do?
Pumps out 3 Na and pumps in 2 K; requires energy; a protein machine that pumps in K and pumps out Na
From what do motoneurons receive input?
Receives excitation from other neurons
Postsynaptic
Referring to the region of a synapse that receives and responds to a neurotransmitter
Presynaptic
Referring to the region of a synapse that releases neurotransmitter
Astrocytes
Star shaped glial cells with numerous processes that run in all directions; connect to blood vessels to regulate blood flow, monitor the activity of local neurons, communicate with other glial cells
What is the sequence of events that take place when the AP reaches the presynaptic terminal?
Synaptic vesicles fuse with the cell membrane, neurotransmitters release into synapse, NTs diffuse across the synapse, NTs attach to receptors on postsynaptic neuron
What is the neuron doctrine?
That the brain is made up of separate cells that are distinct structurally, metabolically, and functionally
Edema
The swelling of tissue, especially in the brain, in response to injury
What is the equilibrium potential?**
The voltage that is required to prevent an ion from from moving down its concentration gradient
Synapse
The gap between neurons where information is passed from one to there other
Define the resting membrane potential.
A difference in electrical potential across the membrane of a nerve cell during an inactive period (negative)
Multiple Sclerosis
A disorder characterized by widespread degeneration of myelin; "many scars"
How long are axons?
A few micrometers long, usually
Node of Ranvier
A gap between successive segments of the myelin sheath where the axon membrane is exposed
What is spatial summation?
A lot of APs coming in at the same place; additive
What is temporal summation?
A lot of APs coming in at the same time; additive
What is an action potential?
A massive, momentary reversal of the membrane potential from a resting state (-70mV) to up to +40mV
Motor Neuron
A nerve cell that transmits motor messages, stimulating a muscle or a gland or an organ; have long axons (ventral)
Unipolar Neuron
A neuron that has a cell body that branches into two axons that go in two different directions with dendritic spines on one end and axon terminals on the other end. (only touch information from body to the spinal chord)
Multipolar Neuron
A neuron that has many dendrites and one axon (most common neuron)
Bipolar Neuron
A neuron that has one dendrite and one axon (most common in sensory systems like sight)
What are receptors?
A protein that receives NTs; the NTs have to fit like a key into a lock
Synaptic Vesicle
A small bubble in the axon terminal that contains molecules of neurotransmitter (30-140nm)
Are sensory neurons afferent/efferent? Why?
Afferent because they approach the CNS (go into the spinal chord)
Axo-Somatic
Axon to cell body
Axo-Dendritic
Axon to dendrite
Why does the AP travel in one direction?
Because the channels behind it close.
Why isn't the membrane electrically neutral at rest?
Because there are big, negatively charged proteins inside the cell and there is a net loss of positive charge with the pump; and K can leak out
Why do temporal and spatial summation exist?
Because they both increase the likelihood that the voltage change will be enough to reach threshold
What types of glial cells build the myelin sheath in the CNS? What about the PNS?
CNS: Oligodendrocyte PNS: Schwann Cells
What is a neuron?
Cells that are the basic signaling unit of the brain; made up of dendrites and axons
Neural Plasticity
The ability of the nervous system to change in response to experience or the environment
During what period it is impossible to stimulate another AP on a given segment of the axon?
The absolute refractory period
Axon Hillock
The area where the axon originates from the cell body; the integration zone of the neuron
Arborization
The branching of dendrites
Neurotransmitter
The chemical released from the presynaptic axon terminal that serves as the basis of communication between neurons
How is the AP propagated down the axon?
The depolarization spreads to each node of ranvier to regenerate the action potential
Myelin
The fatty insulation around an axon, formed by glial cells, that improves the speed of conduction of nerve impulses
Why are AP's all-or-none?
Unless the threshold is reached, it won't trigger; if you stimulated it more, it won't change the size of the action potential
How many NT's do neurons release into the synapse?
Usually a combination of 2 or 3
Are vertebrate or invertebrate axons covered in myelin?
Vertebrate axons
What is reuptake?
When the NTs remain whole and stable and are channeled back into the presynaptic neuron to be recycled