Biology Chapter 48 - Neurons, Synapses, and Signaling

3 stages of information

Sensory input → Integration → Motor output

Sensory neurons

Afferent

Transmit information from sensors that detect external/internal stimuli

Interneurons

Neurons that receive, analyze, & interpret sensory input

Motor Neurons

Efferent

Communicates with effector cells to produce motor response

Reaction

A voluntary, conscious response that involves the brain processing the stimulus and making a decision

Reflex

An involuntary, automatic, and rapid response to a stimulus, bypassing the brain

Actions your body performs without you consciously thinking about them

Dendrites

Highly-branched extensions that receive signals from other neurons

Axon

Much longer extension that transmits signals to other neurons at synapses

Axon hillock

Where axon joins cell body

Myelin Sheath

Fatty sheath enclosing axons

Synaptic terminal

End of axon

Synapses

Site of communication between neurons

Junction between 2 neurons

Presynaptic Cell

Transmitting neuron

Postsynaptic Cell

Receiving cell

Neurotransmitters

Chemical messengers transmitted between neurons

Electrical Potential

Voltage difference across a cell membrane Aka membrane potential

Membrane potential of cell

Inside of a neuron is negative relative to the outside

-60 and -80 m

Na/K pump

Transports 3 Na⁺ out of cell and 2 K⁺ in cell

Resting potential

Membrane is polarized – inside more negative than outside

-70mV charge

At rest, sodium and potassium channels are closed

Na/K pump maintains negative charge

Depolarization

Stimulus causes membrane to change polarity

Na gates open allowing Na ions to diffuse inside cell making inside more positive, outside becomes more negative

-65mV to 35mV

Threshhold

Once a -55-65 mV (more positive) charge reached, action potential is triggered

-55 to -65mV

All-or-None Response

Impulse is either sent along axis or not at all

Action Potential

Nerve impulse caused by reversed membrane polarity → gets propagated along length of axon membrane

Repolarization

Na gates close but K gates open

K ions diffuse out and negative polarity is restored

+35mV to -90mV

Hyper polarization

As more K+ leaves cell, inside becomes even more negative than at rest

Neuron cannot fire an action potential

Nodes of Ranvier

Gaps within myelinated axons with lots of Na+ and K+ channels

Saltatory Conduction

Action Potential jumps from node to node increasing speed of transmission

Schwannn Cell

Produces lipid myelin

Electrical Synapse

Ion current flows between cells at gap junctions

Chemical Synapse

Neurotransmitters that are stored in synaptic vesicles are released by the presynaptic neuron → interact with postsynaptic neuron

Action potential causes Ca⁺² gates to open → Ca⁺² ions enter and cause vesicle fuse to membrane → neurotransmitters are released into cleft

What happens to action potential at axon terminal

Excitatory Postsynaptic Potentials

Depolarizes membrane towards threshold

Inhibitory Postsynaptic Potentials

Hyper polarizes membrane away from threshold

Acetylcholine

Most common; inhibitory or excitatory

Important in muscle contraction

Nicotine binds to same receptors

Epinephrine/Norepinephrine

Also function as hormones

Excitatory

Dopamine/Serotonin

Related to sleep, mood, attention & learning

Parkinson’s Disease

Lack of dopamine in brain

LSD/MESC

Bind to same receptors is dopamine & serotonin

Prozac

Enhances effect of serotonin

Depression often treated with drugs that increase amine

Amino Acids

GABA

Glycine

Glutamate/Aspartate: excitatory

GABA

Inhibitory

Sleeping neurotransmitter

Glycine

Inhibitory amino acid neurotransmitter

Glutamate/Aspartate

Excitatory Amino Acid neurotransmitter

Neuropeptides

Short chains of aa’s

Substance P

Endorphins

Opiates

Substance P

Excitatory, mediates perception of pain

Endorphins

Natural analgesics, decreases pain perception

Opiates

Bind to same receptors → mimic endorphins, produce euphoria