HN220 Midterm 1

What does the central nervous system consist of

brain and spinal cord

What does the CNS do

receives and processes information from sensory organs and the viscera and determines the state of the external environment and internal environment integrating the information and sending instructions to organs to complete tasks

What does the peripheral nervous system consist of

neurons that provide communication between the central nervous system and organs throughout the body

What do afferent neurons do

transmit sensory and visceral information from the organs to the CNS including somatic senses, special senses and visceral information pertaining to the internal environment

What do efferent neurons do

transmit information from the CNS to organs in the periphery; usually muscles and glands that perform functions in respose to commands from neurons

What does the somatic nervous system consist of

the motor neurons which regulate skeletal muscle contractions

What does the autonomic nervous system consist of

neurons that regulate the function of internal organs and other structures that are not under voluntary control

What branches is the autonomic nervous system divided into

parasympathetic and sympathetic

What is a neuron

the functional unit in the nervous system, excitable cells that communicate by transmitting electrical impulses

What are excitable cells

cells capable of producing large, rapid electrical signals called action potentials

What do glial cells do

provide various types of support to the neurons including structural and metabolic support

What are the three main components of a neuron

cell body, dendrites, axon

Can neurons undergo cell division

no

neurogenesis

the production of new neurons in the central nervous system

what does the neuron cell body contain

nucleus, endoplasmic reticulum, Golgi, most of the free ribosomes, mitochondria

What does the neuron cell body do

carries out most of the functions that other cells perform such as protein synthesis and cellular metabolism

Where do dendrites branch from

the cell body

dendrites contain specialized junctions called ________ where they receive signals from other neurons

synapses

Stellate cells

star shaped neurons with multiple branching dendrites

purkinje cells

highly branched neurons

What does the axon do

functions in the rapid transmission of information over relatively long distances in the form of electrical signals

Collaterals

branches of an axon

What is an action potential

a brief large change in membrane potential during which the inside of the cell becomes positively charged relative to the outside

Axon hillock

end of the axon, the site where the axon originates from the cell body, specialized in the initiation of action potentials

Axon terminal

end of an axon, specialized to release neurotransmitters on arrival of an action potential

Presynaptic cell

the neuron sending the signal

postsynaptic cell

the neuron receiving the signal

What does the axon terminal need to carry out its function

enzymes to synthesize neurotransmitters, transporter molecules to move neurotransmitters or their substrates across membranes, vesicles to store neurotransmitters before release

Anterograde transport

moves materials from the cell body to the axon terminal

Retrograde transport

moves materials from the axon terminal to the cell body

characteristics of slow axonal transport

0.5-40mm/day, moves small soluble molecules in the cytosol, used for slow moving materials that don’t need rapid delivery

characteristics of fast axonal transport

100-400mm/day, moves vesicles, uses microtubules as tracks for motor molecules, needs ATP to function

Leak channels

found in the plasma membrane throughout a neuron, always open, responsible for the resting membrane potential

Ligand gated channels

mostly in the dendrites and cell body, open/close in response to the binding of a chemical to a specific receptor in the plasma membrane

voltage gated sodium and potassium channels

found throughout the neuron, open/close in response to changes in membrane potential, necessary for the initiation and propagation of action potential

How do voltage gated sodium and potassium channels work

Na+ channel opens —> Na+ enters —→ depolarization —> K+ channels open —> K+ exits —> repolarization

Voltage gated calcium channels

found in axon terminals, open when an action potential reaches the axon terminal allowing Ca2+ to enter the cytosol of the axon terminals and triggers the release of a neurotransmitter

Bipolar neurons

generally sensory neurons, two projections from cell body (one axon, one dendrite), functions in the senses of olfaction and vision

Pseudo-unipolar neurons

one projection that splits into two. dendrite process—> peripheral axon (acts like a dendrite but functions as an axon), axon process—> central axon

Multipolar neurons

most common, multiple projections, one axon multiple dendrites

Characteristics of interneurons

99% of all neurons, located entirely in the CNS, perform all functions of the CNS

Oligodendrocytes location

CNS

oligodendrocytes how it works

one oligodendrocyte can wrap around many axons

Schwann cells location

PNS

schwann cells how it works

one schwann cell wraps around only one axon

primary function of oligodendrocytes and Schwann cells

form an insulating layer of myelin around the axons of neurons

Myelin

made of multiple layers of plasma membrane, helps nerve impulses travel faster

Nodes of Ranvier

small gaps between myelin, contain voltage gated sodium and potassium channels

Voltage key notes

electrical potential, opposite charges attract, like charges repel, separating charges stores energy in the form of voltage, the greater the charge separation the higher the voltage

Current key notes

expressed by I, movement of electrical charges, typically expressed in microamps

Resistance key notes

expressed by R, how hard it is for ions to move throughout something, neuron membrane has high reisstance but fluids inside and outside the cell have low resistance

Conductance key notes

g, the opposite of resistance- how easily ions can move, neurons adjust their conductance to send electrical signals efficiently

Ohm’s law

I= E/R

Potential difference definition

E, difference in voltage between two points

Membrane potential definition

Vm, difference in voltage across the plasma membrane, given in terms of voltage inside of the cell relative to voltage outside

Resting membrane potential definition

difference in voltage across the plasma membran when a cell is at rest

Graded potential definition

a relatively small change in the membrane potential produced by some type of stimulus that triggers the opening or closing of ion channels, the strength of the graded potential is given relative to the strength of the stimulus

Synpatic potential definition

graded potentials produced in the post-synaptic cell in response to neurotransmitters binding to receptors

Receptor potential definition

graded potentials produced in response to a stimulus acting on a sensory receptor

Action potential definition

a large, rapid change in the membrane potential produced by depolarization of an excitable cell’s plasma membrane to threshold

Equilibrium potential definition

the membrane potential that counters the chemical forces acting to move an ion across the membrane, putting the ion at equilibrium

What establishes the resting membrane potential for potassium and sodium ions

the chemical forces for moving sodium and potassium ions across the plasma membrane, the differences in the permeability of the plasma membrane to these two ions

How would a membrane potential of a cell permeable only to potassium work

1: sodium high outside the cell, potassium high inside the cell, membrane potential at 0

2: membrane only allows K+ to move, it moves outside the cell following its concentration gradient, negative membrane potential develops

3: K+ is pulled back in because the inside of the cell becomes more negative

4: no net movement occurs because K+ is at equlibrium with a membrane potential of -94 mV

How would a membrane potential of a cell permeable only to sodium work

1: sodium is more concentrated outside the cell and then moves into cell following its concentration gradient, making the inside more positive than outside

2: Na+ keeps moving into the cell until the electrical force is strong enough to stop further movement, this is typically when the inside of the cell is 60mV more positive than the outside

How is the resting membrane potential of -70mV formed?

1: K+ moves out of cell and Na+ moves into cell, the membrane is more permeable to K+ creating a net loss of positive charge and the inside of the cell becomes negative

2: as the inside gets more negative, it starts to pull K+ in and push Na+ out (electrical force) until the movement balances out

Why is the final resting potential closer to K+’s equilibrium potential

the membrane is much more permeable to K+ but since Na+ is still leaking in the final potential won’t be as negative as -94mV

What would happen if Na+ and K+ permeability were equal

the resting potential would be less negative than -7-mV, closer to 0mV because more Na+ would enter the cell

How far away is sodium from the equilibrium

130 mV

How far away is potassium from equilibrium

24 mV

Sodium current formula

Ina = gna(Vm-Ena)

Mechanically gated cannels

open/close in response to mechanical forces on a membrane, associated with sensory of visceral receptors located at the end of afferent neurons

Tetrodotoxin key notes

blocks voltage gated sodium channels preventing action potentials, stops nerve signals, extremely potent, found in pufferfish

Saxitoxin key notes

blocks voltage gated sodium channels, spreads through contaminated shellfish

What causes graded potentials

chemical stimuli and sensory stimuli

What does it mean for a graded potential to be decremental

the change in membrane potential decreases in size as it moves along the membrane away from the site of stimulation

Why are graded potentials decremental

some of the electrical ion current leaks out of the membrane

How graded potentials spread in neurons (step by step)

1: a stimulus changes the membrane potential in one area of the neuron creating a difference in charge inside and outside of the cell

2: separation of charge generates currents in intra and extracellular fluids

3: the currents travel to adjacent areas of the cell membrane causing voltage changes in those areas

4: as the graded potential spreads fro the site of the stimulation, the current is spread over a larger area and some current leaks across the plasma membrane

Excitatory graded potentials

depolarization, increase the likelihood of an action potential, bring the membrane closer to threshold

neurotransmitter binding to its receptors causes Na+ channels to open making inside more positive

Inhibitory graded potentials

hyperpolarization, decrease the likelihood of an action potential, moves the membrane further away from the treshhold

neurotransmitter binding to its receptors causes K+ channels to open making inside more negative

Temporal summation

a stimulus is applied repeatedly in rapid succession such that the graded potential from the first application does not dissipate before the net graded potential occurs, effects of the potentials sum, the greater the overlap in time the greater the summation

Spatial summation

the effects of stimili from different sources occuring close together in time sum

multiple stimuli happen at the same time but at different places on the neuron, they sum if they are the same time (excitatory/inhibitory) and cancel each other out if opposite

Graded potential location

dendrites, cell body, sensory receptors

Action potential location

axon

graded potential strength

relatively weak, proportional to the strength of the stimulus, dissipates with distance from the stimulus

action potential strength

100 mV, all or none

Graded potential direction of change in membrane potential

can be depolarizing or hyperpolarizing depending on stimulus

Action potential direction of change in membrane potential

depolarizing

Graded potential summation

spatial and temporal

action potential summation

none

graded potential refractory periods

none

action potential refractory periods

absolute and relative

graded potential channel types involved in producing change in potential

ligand gated, mechanically gated

action potential channel types involved in producing change in potential

voltage gated

graded potential ions involved

Na+, Cl-, K+

Action potential ions involved

Na+ and K+

graded potential duration

few ms to seconds

action potential duration

1-2 msec

Step 1 of action potential

rapid depolarization

the neuron quickly becomes more positive inside (-70mV → +30mV in 1 ms) because sodium rushes into cell through open channels

Step 2 of action potential

repolarization

the neuron returns to normal because sodium sotps entering and potassium exits the cell

Step 3 of action potential

after-hyperpolarization

the neuron briefly becomes more negative than usual because potassium keeps leaving for a short time before stabilizing`