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