UNC PSYC 220 - Exam 1 (Dankert)

Dendrites

Branching fibers from a neuron that receive information from other neurons

Synaptic receptors

Line the surface of the dendrites and receive information from other neurons

Dendritic Spines

short outgrowths that increase the surface area available for synapses

Cell Body or "Soma"

structure containing the nucleus, ribosomes, and mitochondria; in many neurons, covered in synapses

Axons

Thin fiber of constant diameter; the neuron's information sender; has branches near its end

Myelin Sheath

insulating material that covers vertebrate axon

Nodes of Ranvier

interruptions in the myelin sheath of vertebrate axons

Presynaptic Terminal

(end bulb or bouton) point where an axon releases chemicals

Afferent Axon

axon that brings information into a structure

efferent Axon

neuron that carries information away from a structure

Intrinsic Neuron (interneuron)

neuron whose axons and dendrites are all confined within a given structure

Glial Cells vs Neurons

Glial Cells - function mainly to modulate neuron function and signaling

Neurons - generate and propagate electrical and chemical signals (slightly outnumber glia)

Astrocytes

star-shaped glia that synchronize the activity of the axons; A single astrocyte might surround the tips of a few hundred dendrites; important for generating rhythms, such as your rhythm of breathing; also dilate the blood vessels to bring more nutrients into the most active brain areas

microglia

cells that remove waste material and other microorganisms from the nervous system; proliferate after brain damage, removing dead or damaged neurons; provide negative feedback to put the brakes on neuronal activity; A loss of microglia leads to seizures

Oligodendrocytes

glia cells that build myelin sheaths; in the brain and spinal cord; respond to neural activity by altering the myelin sheaths, thereby altering the timing of axons' responses

Schwann Cells

glia cells that build myelin sheaths; in the periphery of the body

Radial Glia

cells that guide the migration of neurons and the growth of axons and dendrites during embryological development

importance of blood brain barrier

This allows essential nutrients and oxygen to pass through but will keep harmful chemicals from other parts of the body out; when immune system finds a cell infected with a virus, they kill both virus and the cell - vertebrate brain cannot replace damaged neurons like the skin and blood can, can't afford to lose neurons, viruses must be kept out entirely.

How does the blood brain barrier prevent the entry of certain chemicals?

- body lines the brain's blood vessels with tightly packed cells that keep out most viruses and bacteria (endothelial cells that form the walls of the capillaries)

- the membrane is made of fats --> chemicals that dissolve in fats cross freely through the cell wall (oxygen, carbon dioxide, vitamins A and D, and all the drugs that affect the brain)

- The brain uses active transport, a protein-mediated process that expends energy, to pump glucose (the brain's main fuel), amino acids (the building blocks of proteins), omega-3 fatty acids, and several vitamins from the blood into the brain

Chemicals that pass through brain blood barrier

- oxygen, carbon dioxide, vitamins A and D, and all the drugs that affect the brain (fat-soluble chemicals)

- Water (through special protein channels)

- Sodium, potassium, and chloride ions (through specific channels)

- glucose, amino acids, omega-3 fatty acids, and several vitamins from the blood (via active transport)

non-gated channels

known as leakage or passive channels, have no gating mechanism --> means no trigger is required for their opening and closing, hence the reference to leaking

gated channels

A protein channel in a cell membrane that opens or closes in response to a particular stimulus; gated channel proteins usually stay closed until they receive a specific electrical or external chemical stimulus

Voltage-gated channels

membrane channel whose permeability to sodium (or some other ion) depends on the volt difference across the membrane

protein pumps

energy from ATP is used to pump small molecules and ions across the cell membrane; Its main function is to transport sodium ions out of the cell and potassium ions into the cell

ligand-gated channels

open in the presence of a specific binding substance, usually a hormone or neurotransmitter; proteins in the membrane of neurons that are activated by chemical signals, or ligands

mechanically gated channels

open and close in response to physical deformation of receptors

Neuronal Cell Membrane at Rest

the membrane maintains an electrical gradient, also known as polarization—a difference in electrical charge between the inside and outside of the cell; resting potential is typically -70 mV (slightly more negative inside the cell)

Ion Concentration in Cell Membrane at Rest

membrane is at rest, the sodium and potassium channels are closed, permitting almost no flow of sodium and only a small flow of potassium

- Sodium ions are more concentrated outside the cell, and potassium is more concentrated inside

Electrical gradient causes flow of ions

Sodium is positively charged, and the inside of the cell is negatively charged, mainly because of negatively charged proteins. Opposite electrical charges attract, so the electrical gradient attracts sodium into the cell.

concentration gradient causes flow of ions

at rest - the difference in distribution of ions across the membrane. Sodium is more concentrated outside than inside, so just by the laws of probability, it is more likely to enter the cell than to leave.

Action Potential - Step 1

- Neuron at rest (-70mV)

- Sodium (Na+): more concentrated outside

- Potassium (K+): more concentrated inside

- Na+ channels are closed, K+ channels are partially closed

- Na+/K+ pump maintains the resting membrane potential

Action Potential - Step 2

- Stimulation at the axon hillock

- Stimulation at the axon hillock causes some Na+ channels open

- Na+ starts to enter the cell --> Causes slight depolarization of the membrane

Action Potential - Step 3

- Threshold of excitation is met

- Many voltage-gated Na+ channels open

- Na+ floods into the cell due to the concentration and electrical gradient

Action Potential - Step 4

- Depolarization causes voltage-gated K+ Channels open

- K+ begins to leave the cell due to due to the concentration and electrical gradient

- Even with K+ leaving, there is so much Na+ still entering the cell that the membrane potential becomes positive

Action Potential - Step 5

- Action potential reaches its peak

- Inside of the cell is now more positive than the outside•

- Na+ channels REFRACT and become INACTIVE

- Not the same as being closed

- K+ channels remain open

Action Potential - Step 6

- Repolarization

- K+ continues to leave due to the concentration and electrical gradient

- Brings the membrane potential back below zero

- K+ channels slowly close

Action Potential - Step 7

- Neuron is temporarily hyperpolarization

- Due to accumulation of K+ ions right around the membrane

- Na+ channels move from refracted to closed

- K+ channels are closed

- Distribution of ions is off (more K+ outside the cell and more Na+ inside the cell)

Action Potential - Step 8/1

- Neuron returns to resting state

- Membrane returns to resting potential as K+ions diffuse away from the membrane

- Eventually, the Na+/K+ pump restores the concentration gradient

- Pump 3 Na+ out and 2 K+ in

- Takes time

All-or-none Law

the amplitude and velocity of an action potential are independent of the intensity of the stimulus that initiated it, provided that the stimulus reaches the threshold

absolute refractory period

not possible for another action potential to occur

- Due to Na+ channels being refracted

- Can not go from refracted to open- need to close first

relative refractory period

neuron can fire an action potential, but a stronger stimulus is required

- Due to hyperpolarization

Chemical Events at a Synapse - 1

The neuron synthesizes chemicals that serve as neurotransmitters, either in the cell body or at the end of the axon

Chemical Events at a Synapse - 2

Action potentials travel down the axon. At the presynaptic terminal, the depolarization enables calcium to enter the cell. Calcium releases neurotransmitters from the terminals and into the synaptic cleft, the space between the presynaptic and postsynaptic neurons

Chemical Events at a Synapse - 3

The released molecules diffuse across the narrow cleft, attach to receptors, and alter the activity of the postsynaptic neuron in any of several ways

Chemical Events at a Synapse - 4

The neurotransmitter molecules separate from their receptors

Chemical Events at a Synapse - 5

The neurotransmitter molecules may be taken back into the presynaptic neuron for recycling, or they may diffuse away

Chemical Events at a Synapse - 6

Some postsynaptic cells send reverse messages to control the further release of neurotransmitter by presynaptic cells

How does the action potential cause the release of neurotransmitters?

The arrival of an action potential (a nerve impulse characterized by a rapid change in voltage across a membrane) at the presynaptic terminal causes synaptic vesicles to move toward the presynaptic membrane, where the vesicles then fuse with the membrane and release neurotransmitters.

How does synaptic transmission end?

1. Neurotransmitters separate from receptors

2. Removed from the synaptic cleft via:

- Re uptake- taken back into the presynaptic neuron via transporters

- Enzymatic degradation- broken down in the synapse

- Diffusion- diffuse away from the synapse

3. Postsynaptic cell releases retrograde neurotransmitters

4. Negative feedback at the presynaptic neuron inhibits further neurotransmitter release

Receptors for retrograde neurotransmitter

Autoreceptors

Ionotropic Receptors

- Ligand-gated ion channel

- Neurotransmitter binding required to open the channel

- Ions flow through the channel and cause changes in membrane potential

- Quick, short-lasting effects

- Glutamate (excitatory) -->Non-selective cation channel (Na+:depolarization

- GABA (inhibitory) --> Cl- channel: hyperpolarization

Metabotropic Receptors

- Linked to G-protein (Gq/Gs, Gi/Go)

- Coupled with associated ion channels by second messenger

- G-protein subunit activates an enzyme, producing a second messenger -->Messenger has a variety of effects, including opening ion channels

- Slower, long-lasting effects

- Many neurotransmitters: dopamine, norepinephrine, serotonin

Autoreceptors

- Metabotropic

- Sensitive to the neurotransmitter they released

- Negative feedback

Synthesis and Release - Neurotransmitters

- Generally smaller

- Synthesized in cytoplasm/vesicles of axon terminal

- Vesicles come from soma or terminal buttons

- Stored (not all) in clusters near the release zone

- One action potential leads to release

Synthesis and Release - Neuropeptides

- Generally larger

- Synthesized in soma

- Vesicles from soma

- Stored further from release zone and in other areas of the neuron

- Released from all over the cell

- Requires repeated stimulation for release

Effects - Neurotransmitters

- Quick effect

- Rapid termination

- Short distance

Effects - Neuropeptides

- Delayed effect

- Longer effect

- Dispersed effects

Hormones

- Chemicals secreted by cells in one-part of the body that travel via the bloodstream to influence other cells

- Non-specific targets (unlike neurotransmitters)

- Activity similar to metabotropic receptors

- Attach to membrane receptors, activate second messenger in cell

Glutamate

The most common neurotransmitter in the brain. Excitatory; opens sodium gates

GABA

a major inhibitory neurotransmitter; opens chloride channels

Acetylcholine

A neurotransmitter that enables learning and memory and also triggers muscle contraction

Dopamine

excitatory & inhibitory, movement, reinforcements

Norepinephrine

increases vigilance (ready for action)

Serotonin

decreases impulsivity, mood, eating, hallucinogenic

EPSP & IPSP

excitatory postsynaptic potential: sodium flows into the cell

inhibitory postsynaptic potential: potassium leaves and chloride enters

temporal summation and spatial summation

- a cumulative effect of repeated stimuli within a brief time

- combination of effects of activity from two or more synapses onto a single neuron

Full Agonist

A full agonist binds to a receptor and produces the maximum response possible

Partial Agonist

A partial agonist binds to a receptor but only partially activates it, producing a submaximal response

Antagonist

blocks or inhibits the effect of agonists at a receptor

Inverse Agonist

decreases the activity of a receptor

Allosteric Modulator

changes the receptors response to a stimulus

Affinity

degree to which a drug binds to a receptor

Efficacy

degree to which a drug produces and effect at a receptor

Amphetamine

Blocks reuptake of dopamine and several other transmitters

Cocaine

Blocks reuptake of dopamine and several other transmitters

Methylphenidate (Ritalin)

Blocks reuptake of dopamine and others, but gradually

MDMA ("Ecstasy")

Releases dopamine, serotonin, and norepinephrine

Nicotine

Stimulates nicotinic-type acetylcholine receptor, which increases dopamine release

Opiates (e.g., heroin, morphine)

Stimulates endorphin receptors

Cannabinoids (marijuana)

Excites negative-feedback receptors on presynaptic cells

Hallucinogens (e.g., LSD)

Stimulates serotonin type 2A receptors

dorsal

located toward the back

ventral

toward the stomach

Anterior

Toward the front end

Posterior

Toward the rear end

Superior

Above another part

Inferior

Below another part

Lateral

Toward the side, away from the midline

Medial

Toward the midline, away from the side

Proximal

Located close (approximate) to the point of origin or attachment

Distal

Located more distant from the point of origin or attachment

Ipsilateral

On the same side of the body (e.g., two parts on the left or two on the right)

Contralateral

On the opposite side of the body (one on the left and one on the right)

Coronal Plane (or Frontal Plane)

A plane that shows brain structures as seen from the front

Sagittal Plane

A plane that shows brain structures as seen from the side

Horizontal Plane (or transverse plane)

A plane that shows brain structures as seen from above

Nervous System

brain, spinal cord, nerves; CNS, PNS

Central Nervous System (CNS)

Sensory activities, memory, emotion; Brain, Spinal Cord

Peripheral Nervous System (PNS)

Connects CNS with the rest of the body; Autonomic Nervous System, Somatic Nervous System

Autonomic Nervous System (ANS)

Involuntary movements; Receives information from and sends commands to the organs, Regulates functions like heart rate, digestion, blood pressure, respiration

Spinal Cord

- Communicates with all the sense organs and muscles except those in the head

- Composed of white and grey matter

- Grey: cell bodies and dendrites

- White matter: myelinated axons, carries information away from the grey matter