biol 216 exam 2

Interneurons

Only in the CNS; Integrate information and formulate a response

Afferent neurons

Are sensory neurons, pick up stimulus via sensory receptors, transmit information to interneurons

Efferent neurons

Carry response signal to muscles and glands so that a response can be carried out

Motor Neuron

type of efferent neuron that carries signals to skeletal muscles

White matter

has myelinated axons and glial cells

Grey matter

contains neuronal cell bodies

Glial cells

non neuronal cells that provide nutrition and support to neurons

ependymal cells

produce CSF

Microglia

phagocytic cells of the CNS

Astrocytes

cover surfaces for structural support, help maintain ion concentration in nervous system, exist in the CNS

Satellite cells

similar function to astrocytes, exist in the PNS

Schwann cells

Form myelin sheath in the PNS

Oligodendrocytes

form myelin sheath in the CNS

Electrical Synapses

Gap junctions that allow a current to flow between cells. Found in cardiac muscle and many types of smooth muscle. The action potential of one cell causes an action potential in the next cell.

Connexons

protein tubes in the cell membrane

Chemical Synapse

Electrical impulse arrives at axon terminal and neurotransmitter is released. It diffuses across synaptic cleft and binds to receptor on postsynaptic cell, generating a new electrical impulse.

Electrical vs. Chemical synapse

electrical is faster because current flow across gap junction is instantaneous and without delay, and enables synchronized electrical activity among populations of neurons. Chemical neurons can be better modulated however

What is the distribution of charged particles of a membrane at rest?

Higher sodium concentration outside with higher potassium concentration inside. Sodium-potassium pump pumps 3 sodium out and 2 potassium in

Selective permeability

Membrane allows some ions to move in or out of cell. In neuron, more K+ leaves than Na+ enters, creating a positive charge outside of the cell.

Potassium leak channels

allow K+ to move in and out of cell freely. they are drawn to the inside of the cell by negatively charged organic molecules, which balances tendency of potassium to want to leave the cell.

What role does potassium play in the membrane potential?

[K+] is high inside the cell, and it wants to leave due to concentration gradient. But as it leaves, there becomes an unbalanced negative charge inside cell, which stops the further outflow of potassium

Resting potential

Equilibrium condition, no net flow of ions across the plasma membrane

Equilibrium potential

membrane potential at which voltage gradient of ion balances the concentration gradient of the ion, still no net flow of ion through ion channels

Electrochemical gradient

Drives the flow of any ion through membrane channel protein. Consists of voltage gradient and concentration gradient of an ion across membrane.

Nernst equation

Can predict equilibrium potential across membrane of cell for single positive ion, for potassium it is -90mV

Membrane at resting potential

-70mV. Few sodium channels are open, some ions get in which makes the resting potential less negative because E for sodium is +60mV

Goldman equation

allows prediction of membrane potential when membrane is permeable to more than one ion

Leak channels

are ungated; many more potassium leak channels open than sodium in membrane at rest

Voltage gated ion channel

Integral membrane proteins that are controlled by the membrane potential. For potassium, some inactivate fast while others inactivate slowly, which guarantees that there will always be an available source for repolarization.

Steps of action potential

1. Stimulus causes sodium ions to flow into neuron

2. Membrane potential becomes less negative

3. Initial depolarization is slow until threshold potential is reached

4. Rapid increase in membrane potential due to the sodium gated channels opening and sodium flowing in faster now

5. Potential hits peak, then falls again when potassium ions begin to leave the cell causing re-polarization

6. Membrane potential returns to resting potential

Absolute refractory period

Time when excitable membrane cannot generate another action potential. Occurs when voltage gated sodium channels are already open or inactive, and the inactivation gate must be removed by repolarizing the membrane.

Relative refractory period

Time when membrane will produce action potential but only if the stimulus is greater than the previous one. Most of the voltage gated sodium channels are in resting state, while some of the potassium channels are still open. A new stimulus can depolarize the membrane but it has to be large and outlast the relative refractory period.

Frequency of action potentials

The intensity of a stimulus is indicated by frequency of action potentials. The larger the stimulus, the more frequent the action potentials.

A-alpha nerve fibers

Largest nerve fibers. Carry information related to proprioception

A-beta nerve fibers

carry information related to touch

A-delta nerve fibers

carry information related to pain and temperature

C-nerve fibers

Smallest nerve fiber. carry information related to pain, temperature, and itch

How does the diameter of axon affect the action potential?

The larger the diameter, the greater the conduction velocity of the action potential. There is lower internal resistance which leads to faster conduction.

Cable theory

uses math to calculate flow of current along axons using capacitances and resistance

Capacitance and resistance

Capacitance of neuronal fiber is due to electrostatic forces that act through the phospholipid bilayer. The resistance is due to the cytosol's resistance to movement of electrical charge

Lambda length constant

Characteristic lengths on which voltage across a membrane decays. At distance lambda, the size of the applied voltage will decline to 37% of original size. It measures how far voltage can travel down an axon before it decays. The larger the constant the greater the conduction velocity.

Conduction velocity

It is the speed that the voltage travels down an axon. With a larger constant it can reach threshold further down the axon and AP doesn't have to be regenerated as many times.

Relationship of resistance and velocity

When resistance is increased, lambda length constant is increased, which increases conduction velocity, due to more current remaining inside the cytosol.

Myelin

Fatty layer around axons that increase conduction of APs. APs are only regenerated at the nodes of ranvier

Longitudinal resistance

The higher the longitudinal resistance, the smaller the lambda, which makes it harder for current to travel through cytosol, so the current won't be able to travel as far.

Neurotransmitters

Mode of communication in chemical synapses. They are small signal molecules that are secreted by the presynaptic cell to relay the signal to the postsynaptic cell.

Direct neurotransmission

Neurotransmitters bind directly to ligand gated ion channel, which opens/closes and affects the flow of ions into the postsynaptic cell. Very quick. Ionotropic receptors form the ion channel pore.

Indirect neurotransmission

Neurotransmitter first binds to GPCR on postsynaptic membrane, and the 2nd messenger pathway is activated. Ion channels are then opened/closed and the signal is propagated. A slower process, and the effects can last minutes or hours. Metabotropic receptors are indirectly linked with the ion channels on the plasma membrane.

Acetylcholine

Between nerves and muscle, found in the brain for memory, attention, and learning. Also found in the heart for parasympathetic. Alzheimer's is the degeneration of acetylcholine releasers.

GABA

An inhibitor of neurotransmission. It opens and closes chloride channels on the post synaptic membrane

Glycine

an inhibitor of neurotransmission

Glutamate

involved with learning and memory, generally is excitatory

Nor/epinephrine

also called adrenaline. Act as both hormones and neurotransmitters. Involved in attention and mental focus, can be excitatory or inhibitory. Plays a role in pleasure and reward pathway, memory, and motor control.

Dopamine

Neurotransmitter and neurohormone. Controls behavior, cognition, voluntary movements, reward, prolactin production, sleep, mood, learning, etc. Parkinson's is the degeneration of dopamine releasing neurons in substantia nigra.

Serotonin

Derived from tryptophan. It regulates intestinal movements, mood, appetite, and sleep.

Neuropeptides

Are indirect neurotransmitters

Endorphins

are released during pleasurable experiences. Reduces perception of pain, work on the PNS

Enkephalins

subset of endorphins, work in the CNS and modulate pain response

Substance P

Released by the spinal cord and increases perception of pain

Dissolved Carbon monoxide

regulates the release of hormones from the hypothalamus

Dissolved Nitric Oxide

involved in learning and muscle movement. Relaxes the smooth muscle in the walls of blood vessels and causes dilation.

Synaptic vesicles

Store neurotransmitters in the cytoplasm of the axon terminal

What happens when an action potential arrives at the axon terminal?

The voltage gated calcium channels open, which allows calcium to flow into axon terminal. Synaptic vesicles fuse with membrane and release neurotransmitters into the synaptic cleft. When the stimulus stops, voltage gated calcium channels close and calcium is pumped out, and vesicles no longer fuse with the membrane and any remaining neurotransmitters go away.

What happens in the postsynaptic cell?

Ligand gated ion channels open when neurotransmitter binds to them, and the flow of ions can stimulate or inhibit the generation of an action potential in the post synaptic cell. Sodium channels open and sodium flows in, depolarizing the cell membrane and creating an AP.

Excitatory post synaptic potential

A change in the membrane potential that moves the neuron closer to threshold potential. They are precursors to action potentials.

Inhibition

The potassium channels open and potassium exits the cell, and the membrane becomes hyperpolarized.

Inhibitory post synaptic potential

A change in the membrane potential that pushes the membrane further from the threshold

Graded potentials

Increase or decrease in membrane potential that is below threshold so it does not trigger an action potential. EPSPs and IPSPs. Do not have refractory periods.

When can graded potentials occur?

They can occur in a sensory cell when excited by a stimulus or in a postsynaptic cell when a neurotransmitter binds to it. It results in ions entering or exiting the cell creating a change in membrane potential.

Temporal summation

Summation of more than one EPSP produced by successive firing of a single presynaptic neuron over a short period of time

Spatial summation

Summation of EPSPs produced by firing of different presynaptic neurons

Nerve nets

loose mesh of neurons found in radially symmetrical animals

Nerve cord

bundle of nerves which extend from central ganglia to the rest of the body

Ganglia

functional clusters of neurons

Bilateral symmetry

Body parts are mirror images on either side of the midline. Organization of nervous system so that paired nerves that allow for sophisticated sensory processing

Blood-bran barrier

Separation of circulating blood and the CSF, occurs along all capillaries and consists of tight junctions around capillaries that do not normally exist in circulation. Cells in the barrier actively transport metabolic products like glucose.

Roll of endothelial cells in BBB

They restrict diffusion of microscopic objects and large hydrophilic molecules into the CSF. Only small hydrophobic molecules can get in.

Meninges

Layers of connective tissue covering the brain and spinal cord. 3 layers, the pia, arachnoid, and the dura mater. They provide structural support for blood vessels.

CSF

Produced in the choroid plexus, found in the CNS. It circulates nutrients and chemicals filtered from the blood. It protects the brain from striking the skull and provides buoyancy and support against gravity.

Ventricles

Cavities in the brain filled with CSF, 4 total.

Forebrain

Forms the cerebrum with the two hemispheres.

How do the cerebral hemispheres work?

Left responds to sensory signals from the right side of the body and controls the right side of the body and vice versa. The hemispheres are connected by the corpus callosum.

Left hemisphere

Focus on details, spoken and written language, reasoning, math

Right Hemisphere

broad background, intuitive thinking, conceptualization, music, art.

Cerebral cortex

outermost, thin layer of grey matter covering core white matter. Regulates cognitive functions

Primary somatosensory area

Located in the parietal lobes. Receives and integrates sensory information such as temp, touch, pain. If stimulated in brain, it causes tingling on other side of body.

Primary motor area

Located anterior to primary somatosensory area. Involved in planning, control, and execution of voluntary movements

Association areas

Integrate sensory information, formulate responses, relay responses to the motor area

Frontal lobe

controls executive function such as thinking, organizing, planning, problem solving, memory

Parietal lobe

Sits behind the frontal lobe. Deals in perception and integration of stimuli from the senses

Occipital lobe

Sits at the back of the brain. Deals in vision

Temporal lobe

runs along the side of the brain. Deals in the senses of smell, sound, and formation and storage of memories

Cerebellum

Coordinates and refines body movements. Receives sensory input from receptors in muscles and joints and from balance receptors in inner ear. It yields info about body position and direction of movement from limbs.

Brain stem

Made up of the medulla, pons, and midbrain. It connects the forebrain with the spinal cord. Controls vital functions such as heart and respiration rate, vasodilation, blood pressure, and digestive reflexes.

Midbrain

Smallest region of the brain and it acts as a relay station for auditory and visual info. Controls eye movement