IB Biology: Neurons and Synapses

peripheral nervous system

sensory receptors are responsive to external and internal stimuli; such input is conveyed to integration centers, which is interpreted and associated with a response.

motor output

the conduction of signals from integration centers to effector cells

effector cells

carry out the body’s response to a stimulus (ex: muscles, glands)

central nervous system

responsible for integration; message conveyed through relay neurons to interneurons

nerves

signals of the nervous system are conducted by…

neuron

structural and functional unit of the nervous system; where nerve impulses are conducted

myelin sheath

axon coated with myelin and composed of many layers of phospholipid bilayer, which increases transmission

schwann cells deposit the myelin by growing around the nerve fiber, depositing a double layer of phospholipid bilayer

cell body

where most of a neuron’s organelles are located

dendrite

highly-branched extension that receives signals from other neurons

axon

a much longer extension than the dendrite that transmits signals to other cells at synapses

axon hillock

cone-shaped base of an axon

synaptic terminal

another name for axon endings; contain neurotransmitters which conduct a signal across a synapse

synapse

junction between a presynaptic and a postsynaptic cell, or a neuron and some other cell

presynaptic cell

cell that SENDS signals

postsynaptic cell

cell that RECEIVES signals

membrane potential

all living cells possess some sort of electrical charge difference, with one side being more negatively charged than the other. this difference is known as…

-70 mV

membrane potential of a neuron in its resting state (resting potential)

difference in ion concentation

why potential exists; difference between cytoplasm and extracellular fluid

Na+

sodium; naturally wants to follow concentration gradient and flow into the cell

K+

potassium; naturally wants to diffuse out of the cell

sodium-potassium pump

helps maintain concentration differences; uses active transport to pump 3 Na+ out and 2 K+ in; represents chemical potential energy

gated ion channels

make changes possible in membrane potential by opening and closing in response to stimuli; excitable, show specificity

voltage-gated ion channels

respond to external stimuli, such as a specific voltage, and respond to changes in potential difference.

threshold potential

depolarization is graded with stimulus intensity only up to a particular voltage

action potential

only triggered once the threshold is reached, can only be generated in the axon of a neuron; triggered by graded (specific) depolarization that originates in a dendrite, or in a cell body and spreads to the axon

nerve impulse

action potential of an axon; non-graded (all-or-nothing propagation) event! reaching the threshold initiates it

factors of impulse speed

axon diameter, myelinated neurons insulated with schwann cells; voltage gates concentrate in nodes of ranvier

schwann cell

any of the cells in the peripheral nervous system that produce the myelin sheath around neuronal axons

nodes of ranvier

gaps in-between schwann cells; extracellular fluid is only in contact with the neuron at these points, so the flow of ions may only take place here

saltatory conduction

action potential travels from node to node

electrical synapse

allows action potential to travel cell to cell through gap junctions

chemical synapse

has neurotransmitters that are released into the synaptic cleft

excitatory synapse

opens ion gates that allow Na+ to enter and K+ to leave

inhibitory synapse

opens Na+ and/or K+, causing hyperpolarization

Ach

aka acetylcholine; one of the most common transmitters, degraded by acetylcholinesterase; both inhibitory and excitatory, depending on the type of receptor

neonicotinoids

synthetic compound similar to nicotine, which binds to the Ach receptor in cholingeric (uses choline) synapses in the CNS of insects; acetylcholinesterase doesn’t break it down, so binding is irreversible and nerve transmission is prevented (but also the insect is paralyzed and dies rather than just being poisoned)