Lessons 50 - 57 (temp, 57 isn't here yet)

Order of events after sensory input

sensory input, then integration in the central nervous system, then motor output from peripheral nervous system, goes to effector

Neurons

specialized cells that transmit electrical impulses within the nervous system

Three types of neurons

sensory, relay, motor

Three components of neurons

dendrites, axon, soma

What are dendrites

branched fibers that convert chemical information into electrical signals

Axon

elongated fiber that transmits electrical signals to terminal regions for communication with other neurons or effectors

Soma

a cell body containing the nucleus and organelles

Myelin sheath

insulating layer that improves the conduction speed of electrical impulses along the axon

Disadvantage of myelin sheath

needs more space and energy

How do neurons generate electrical signals?

pumping positively charged ions across their membrane

What is the charge difference from unequal distribution of ions called?

a membrane potential

What is a resting potential?

the difference in charge across the membrane when the neuron is not firing

What is the comparative voltage of inside and outside of the neuron?

inside is more negative than the outside approximately -70 mV

What proteins create the resting potential?

sodium potassium pumps

Is the maintenance of resting potential an active process?

yes, through hydrolysis of ATP

What do sodium potassium pumps transfer, in what amounts, and where?

sodium and potassium ions. Three sodium ions out for every two potassium ions moved in. This makes inside more negative than outside.

What is the movement of the sodium and potassium ions in the sodium potassium pump called?

antiport

What are autotransporters in antiport transport?

they move two molecules in opposite directions across the membrane

Outline the events that occur to establish resting potential using sodium potassium pump just the sodium part

three sodium ions bind to intracellular sites of the pump. A phosphate group is transferred to the pump via the hydrolysis of ATP. Pump goes through conformational change. Sodium moves across.

Outline the events that occur to establish resting potential using sodium potassium pump just the potassium part

The change exposes potassium binding sites. Phosphate is released, which causes the pump to return to original conformation and translocate potassium across the membrane.

What is an action potential?

rapid changes in charge across the membrane that occur when a neuron is firing

What is the charge inside the neuron during an action potential?

temporarily more positive approximately +30 mV

Stages of action potential

depolarization and repolarization

Why does the membrane potential change in action potentials?

sodium AND potassium CHANNELS along the axon open. Positive ions move along the concentration gradient established by the resting potential.

What happens in depolarization?

sodium ions move into the neuron to create a positive membrane potential

What happens in repolarization?

potassium ions flow out to re-establish a negative membrane potential

Ion channels in the axon are ____ - ____

voltage gated

What does voltage gated mean in axon ion channels?

a change in voltage at one point of an axon will trigger the opening of ion channels in the next segment of the axon

Why are voltage gated ion channels useful for the action potential?

the action potential can be propagated along the length of the axon in a unidirectional wave

What happens after the action potential?

the resting potential must be restored by sodium potassium pumps before the next action potential

What is the period between nerve impulses called?

the refractory period

When do nerve impulses occur?

when the membrane potential is changed from the resting potential to an action potential

When do action potentials occur?

the external stimulus triggers a sufficient change in membrane polarity

What is the threshold potential for an action potential?

-55 mV

What is used to measure the membrane potential across a neuronal membrane?

oscilloscope

What does the oscilloscope graph look like?

time on the x axis and membrane potential on the Y axis

Stages of an action potential

resting potential, depolarization, repolarization, refractory period

Describe the oscilloscope graph

resting potential as a flat line at -70. A rising spike for depolarization up to +30 mV. A falling spike that corresponds to repolarization, which undershoots to around -80 mV. In the refractory period, the oscilloscope trace returns to the resting potential level.

Why are nerve impulses unidirectional?

because a resting potential has to be established before another action potential can occur

What is the direction of nerve impulses?

dendrites to axon terminals

How is the speed of nerve impulses in larger organisms, and why?

slower, because they have more complex neural pathways and more synaptic gaps, creating a delay in transmission

Factors that affect speed of nerve impulse propagation

axons with wider diameters have faster conduction speeds. Axons that are insulated with a myelin sheath increase flow of current.

Why do wider axon diameters speed up impulse?

less longitudinal resistance

Why does myelination speed up impulse?

reduces generation of action potentials to fewer points along the axon, increasing flow of current

Disadvantage of myelination

requires space and energy

What are the axons of giant squids like?

large axon diameters

How does giant squid nerve impulse speed compare to myelinated fibers?

slower

What is myelin made of?

protein and phospholipids

What produces myelin?

glial cells

What is the process by which myelin speeds up electrical transmission called?

saltatory conduction

How is the myelin sheath structured?

segments, with ion channels in the gaps between segments

What are the gaps between myelin sheath segments called?

nodes of Ranvier

Why are action potentials faster with the segmented myelin sheath?

the action potentials hop between nodes of Ranvier, increasing transmission speeds

Types of receptors through which stimulus for a nerve impulse can come from

mechanoreceptors, thermoreceptors, baroreceptors, chemoreceptors

What receptors get the input for pain?

nociceptors

Where are nociceptors located?

free nerve endings in the sensory neurons in the skin

How do nociceptors work?

they have channels that open to allow input of positively charged ions in the dendrite, which can cause depolarization and lead to an action potential if the threshold potential is reached.

Sequence of locations of nerve impulse from nociceptor

nociceptor, sensory neuron, interneuron in spinal cord, cerebral cortex

Can neurons function without semi-permeable membranes?

no

What are synapses?

physical gaps that separate neurons from other cells

How do neurons transmit information across synapses?

converting electrical signals into a chemical signal called a neurotransmitter

Steps to neurotransmitter release from a pre-synaptic neuron

action potential reaches the axon terminal, voltage gated calcium channels open, calcium ions diffuse into cells and promote fusion of vesicles with neurotransmitters with cell membrane, neurotransmitters released by exocytosis into synaptic cleft

Steps to neurotransmitter acceptance to a post-synaptic neuron

neurotransmitters bind to specific receptors on the post-synaptic membrane and open ligand-gated ion channels. This generates an electrical impulse in the post-synaptic neuron, propagating the pre-synaptic signal.

What happens to neurotransmitters after binding to post-synaptic membrane?

released into the synapse and recycled or degraded

What neurotransmitter used for muscle contractions?

acetylcholine

What is acetylcholine used for 2 things?

voluntary muscle contractions and parasympathetic responses

How is acetylcholine created in the axon terminal?

combining choline with an acetyl group

What happens to acetylcholine after it stimulates post-synaptic membrane and why?

continually removed, as overstimulation can cause fatal convulsions and paralysis

How is acetylcholine removed?

broken into its two component parts using the synaptic enzyme acetylcholinesterase

What happens to the liberated choline from acetylcholine breakdown?

returned to the presynaptic neuron where it is coupled with another acetate to reform acetylcholine

What are exogenous chemicals?

substances that enter an organism from an external source and interfere with the way neurons process signals from neurotransmitters

Two examples of exogenous chemicals

neonicotinoids and cocaine

What are neonicotinoids

pesticides that are structurally similar to acetylcholine

Why are neonicotinoids dangerous?

bind irreversibly to cholinergic receptors. Cannot be broken down by acetylcholinesterase, so continually depolarize post-synaptic neurons, causing fatal convulsions and paralysis.

Why are neonicotinoids used as pesticides?

insects have more cholinergic receptors than mammals

How does cocaine cause euphoria?

blocks dopamine reuptake pumps on the pre-synaptic neurons in the dopamine reward pathway. This causes dopamine accumulation, stimulating the mesolimbic system.

What are the small changes in membrane potential caused by neurotransmitters called?

graded potentials

When is action potential reached?

when threshold potential is reached

Two types of neurotransmitters

excitatory and inhibitory neurotransmitters

What do excitatory neurotransmitters do?

depolarization by opening ligand gated sodium or calcium channels

What do inhibitory neurotransmitters do?

hyperpolarization by opening ligand gated potassium or chlorine channels

How is it determined whether the threshold potential is reached?

the combined action of all neurotransmitters acting on a target neuron. If more depolarization than hyperpolarization and a threshold potential is reached, the neuron fires. If vice versa, then it won’t fire.

What are the potentials from excitatory and inhibitory neurotransmitters called, respectively?

excitatory post-synaptic potentials and inhibitory post-synaptic potentials

What is the combination of graded potentials in the post-synaptic neuron called?

summation

What is cancellation?

when excitatory and inhibitory graded potentials cancel each other out

What is spatial summation?

when excitatory post-synaptic potentials are generated from multiple presynaptic neurons simultaneously to reach threshold

What is temporal summation?

when multiple excitatory post-synaptic potentials are generated from a single presynaptic neuron in quick succession

What are emergent properties?

functions that emerge when individual components interact to create a novel outcome

Example of emergent property from neurons

interaction of neurons within the brain gives rise to consciousness

What is consciousness?

the state of being awake and aware

Example of neurotransmitter gated ion channel

nicotinic acetylcholine receptors

Example of voltage gated ion channel

sodium and potassium channels

What is important for multicellular organisms to perform the functions of life?

coordination of the different organ systems

Emergent properties hierarchy

cells, tissues, organs, systems, organisms

Two communication systems that allow for coordination between body organs

nervous system and endocrine system

What does the nervous system consist of?

network of neurons that transmit electrochemical impulses

Two parts of the nervous system network

central nervous system and peripheral nervous system

What does the endocrine system consist of?

endocrine glands that release hormones into the bloodstream

What part of the brain links the nervous and endocrine systems?

hypothalamus

Two parts of the brain

cerebrum and cerebellum