IB 202 exam 3

The Real One

Neurons

the cells responsible for the working of the brain and the rest of the nervous system

Neurons conduct informationin the form of

electrical signals from point to point

Interneurons (CNS)

integrates sensory information and sends signals to effector cells

How Does Information Flow in a Neuron?

dendrites to cell body to axons to terminals

dendrites

convert chemical signals to electrical signals

cell body

integrates incoming electrical signals

axon

conducts electrical signals

Membrane potential

The voltage across a cell's plasma membrane. Separation of charge immediately adjacent o the plasma membrane

Resting potential

The difference in charge across membrane when neuron is not communicating with other cells. Typically, -65 mv

Equilibrium potential

the membrane potential at which chemical and electrical forces are balanced for a single ion

action potential

a neural impulse; a brief electrical charge that travels down an axon

Graded potential

a membrane potential that varies in magnitude in proportion to the intensity of the stimulus

Passive transport

Diffusion

electrochemical gradient

Ions move through channels in response to concentration gradients as well as charge gradients

Equilibrium potential: Equilibrium between:

Concentration gradient that favors movement of K+ out and Electrical gradient that favors movement of K+ in

During resting potential

Interior side of membrane: Has low concentrations of Na + and Cl− , High concentrations of K + and organic anions (-), amino acids, and other organic molecules

How Is the Resting Potential Maintained through active transport?

Na + /K + -ATPase pump actively pumps 3 Na + out of cell and 2 K + into cell. Outcome: Concentration of K + is higher on inside of plasma membrane while concentration of Na + is lower on the inside. Inside becomes more negatively charged relative to the outside. Creates a concentration gradient that has potential energy

How Is the Resting Potential Maintained through passive transport?

Na+/K+ pump increases concentration of K+ inside of the cells. Neurons have a relatively high number K + leak channels (non-gated channels, always open). K+ leaks in due to electrical gradient. K+ leaks out due to concentration gradient. Equilibrium potential. With the combined ion pumping and leakage of ions, the cell can maintain a stable resting membrane potential. Na+ channels have small effect on resting potential

What processes maintain the resting potential of a neuron? How?

Na+/K+ pump actively transports 3 Na⁺ out and 2 K⁺ in

K⁺ leak channels allow K⁺ to leave

These maintain a negative inside and positive outside.

Sodium starts outside the cell, in high concentration.

When sodium channels open

it rushes in, making the inside rapidly more positive.

Potassium starts inside the cell in high concentration. When potassium channels open

it flows out, which makes the inside more negative

The membrane is more "excited" by

Na⁺ than K⁺ during the action potential

Sodium (Na+)

the main ion that causes the spike in voltage during a signal.

The sodium-potassium pump pumps

3 Na⁺ for every 2 K⁺ it brings in, which makes the inside more negative overall, and Na⁺ rushing in later has a big effect

Na⁺ rushing in

makes the inside of the neuron more positive (depolarization).

K⁺ going out

brings the positivity back down (repolarization).

What are the basic types of nervous systems observed in animals?

nerve net (e.g., in cnidarians) and the centralized nervous system (CNS), which includes a brain and spinal cord (e.g., in vertebrates).

sensory neurons

detect stimuli

interneurons

process information

motor neurons

control muscle for movement

Reflexes

bypass the brain and involve a direct sensory-interneuron-motor neuron circuit

axon terminals

release neurotransmitters

Myelin sheath

speeds up signal transmission

difference between neurons and nerves

Neurons are individual nerve cells.

Nerves are bundles of axons from multiple neurons in the PNS.

How are neurons similar to other cells?

Have a nucleus, cytoplasm, organelles.

How are neurons different from other cells?

Excitable, transmit electrical signals, have axons and dendrites.

Pumps

use energy (ATP)/ATPase to move Na+ ions against gradients

Leak channels

allow passive ion flow along gradients, especially for K⁺.

K+ leak channel changes in membrane potential?

Makes inside more negative because more Na+ is being pumped out than K+ being pumped in

Chemical Gradient

difference in ion concentration across a membrane.

Electrical gradient

difference in charge across a membrane

Action potential

rapid, temporary change in a membrane potential; has three phases: depolarization, repolarization, hyperpolarization

depolarization

Voltage-gated Na⁺ channels open, allowing Na⁺ to rush in. Increasing membrane potential

repolarization

Na⁺ channels close, and voltage-gated K⁺ channels open, letting K⁺ exit the cell. Decreasing membrane potential

hyperpolarization

The movement of the membrane potential of a cell away from rest potential in a more negative direction until it reaches threshold.

How do voltage-gated ion channels work?

they open or close in response to changes in membrane potential, allowing specific ions (e.g., Na⁺ or K⁺) to flow in or out of the neuron.

How are action potentials propagate?

The depolarization of one segment of the axon causes the next segment to reach threshold, opening its Na⁺ channels and continuing the signal down the axon, like a domino effect.

threshold potential

The minimum membrane potential that must be reached in order for an action potential to be generated.

How does the shape of voltage-gated channels influence the action potential?

at resting potential, voltage-gated Na+ channels are closed. when depolarized, a shape change opens the channels

propagate

spread, increase

refractory period

Just after opening, those same Na⁺ channels become inactivated and cannot reopen immediately. Preventing backwards movement

1st step of action potential

Na+ channels open, Na+ begins to enter cell. Attracting - charges and repelling + charges

2nd step of action potential

charge spreads. membrane downstream depolarizes

3rd step of action potential

Voltage-gated ion of membrane downstream opens, resulting in a new action potential

What causes depolarization?

a stimulus causes the neuron's membrane potential to reach threshold. high concentration of Na⁺ outside the cell (chemical gradient). inside of the cell is negatively charged (electrical gradient)

myelin sheath

covers the axon of some neurons and helps speed neural impulses.

node of Ranvier

gap in myelin sheath. dense concentration of voltage-gated Na + and K + channels, so new action potentials can be generated. action potentials jump from one to the next-->faster

saltatory conduction

Rapid transmission of a nerve impulse along an axon, resulting from the action potential jumping from one node of Ranvier to another, skipping the myelin-sheathed regions of membrane.

continuous conduction

the step-by-step depolarization and repolarization of each adjacent segment of the plasma membrane in unmyelinated axons

What does it mean that the action potential is an all-or-none signal?

If the membrane potential reaches threshold (usually about -55 mV), an action potential will occur fully.

If it does not reach threshold, no action potential happens at all.

No partial firing

synapse structure

pre-synaptic cell, axon terminals, synaptic cleft, post-synaptic membrane

pre-synaptic cell

The cell SENDING information (from axon)

synaptic cleft

gap between adjacent neurons

post-synaptic membrane

on a dendrite of receiving neuron

action potential triggers the release of…

neurotransmitters

1st step of synapsis

action potential reaches axon terminal and depolarizes membrane

2nd step of synapsis

voltage-gated Ca2+ channel is open and Ca2+ flows in

3rd step of synapsis

Ca2+ influx triggers synaptic vesicles to release neurotransmitter

4th step of synapsis

Neurotransmitter binds to receptors on target cell (in this case causing positive ions to flow in)--> depolarization-more likely to fire action potential

types of neurotransmitter receptors

ligand-gated channels and non-ion receptors

ligand-gated channels

channel that opens when a neurotransmitter attaches-->depolarization

non-ion receptors

second messenger system

Neurons integrate information from

many synapses

most neurons receive information from

many other neurons

EPSP (excitatory post-synaptic potential on post-synaptic neurons)

make postsynaptic action potentials more likely (depolarization)

IPSPs (inhibitory post-synaptic potential on post-synaptic neurons)

make postsynaptic action potentials less likely (Hyperpolarization)

simultaneous EPSPs and IPSPs

may cancel each other out

Summation of EPSPs and IPSPs

determines whether an action potential begins in the postsynaptic cell

Inhibitory synapses tend to form

closer to the neuron's cell body (soma) or on the axon hillock

axon hillock

Cone shaped region of an axon where it joins the cell body.

axons of pre-synaptic neurons attach to

dendrites of post-synaptic neurons, potentially promoting action potential

How do learning and memory work at the synaptic level?

involve synaptic plasticity

synaptic plasticity

the ability of synapses to strengthen or weaken over time

long-term potentiation (LTP)

an increase in a synapse's firing potential after brief, rapid stimulation. Believed to be a neural basis for learning and memory.

The Vertebrate Nervous System Has Several Functional Divisions

afferent division, central nervous system (CNS), efferent division

afferent division

carries sensory information from PNS sensory receptors (skin/other organs) to CNS

Peripheral nervous system (PNS)

the sensory and motor neurons that connect the central nervous system (CNS) to the rest of the body. Made up of neurons outside the CNS

efferent division

carries signals that allow the body to respond to the changed conditions in an appropriate way (involuntary or voluntary)

what are the CNS

brain and spinal cord (interneurons)

what are the PNS

cranial nerves, spinal nerves, peripheral nerves (sensory neurons and motor neurons)

components of the Efferent Division

autonomic nervous system and somatic nervous system

autonomic nervous system

carries out involuntary responses, which are not under conscious control: Smooth muscle, cardiac muscle, and several glands serve as the effectors

somatic nervous system

carries out voluntary responses, which are under conscious control: Skeletal muscles serve as the effectors

components of the Autonomic Nervous System

sympathetic and parasympathetic

parasympathetic nervous system

promotes "rest and digest" functions that conserve or restore energy. Example: Cooking dinner

sympathetic nervous system

prepares organs for stressful situations—"fight or flight". Example: exercise

Most sympathetic nerves originate in the

spinal cord (spinal nerves)

Parasympathetic nerves originate at the

base of the brain (cranial) and sacrum

Most sensory and motorneurons project to or from the

spinal cord

Other than reflexes, all the information that travels to or from the spinal cord is sent to the

brain for processing