Animal Nervous Systems (SI 2025)

Central Nervous System (CNS)

brain and nerve cord (spinal cord in vertebrates)

Peripheral Nervous System (PNS)

all neurons and their projections that are outside of the CNS

Dendrites

convert chemical signals to electrical signals

Cell body

integrates incoming electrical signals and generates outgoing electrical signal to axon

Axon

conducts electrical signals; passes chemical signals to dendrites of another cell or to an effector cell

Glial cells

support cells found in the nervous system that perform various functions (may function as stem cells)

astrocytes

metabolic support

microglia

remove cellular debris

sensory neurons

detect information from the outside world or internal body conditions and transmit to CNS

motor neurons

send signals away from CNS to elicit a response

resting potential

membrane potential of a neuron at rest (not sending signals)

Sodium Potassium Pump

exports 3 NA+ ions out and imports 2 K+ ions in

Ion leak channels

allows ions to cross plasma membrane down their electrochemical gradient

depolarization

cell membrane becomes less polarized (less negative)

hyperpolarization

cell becomes more polarized (more negative)

Action potenial

a rapid temporary change in membrane potential

repolarization

changes the membrane back to a negative charge

graded potential

depolarized membrane to threshold potential

refractory period

membrane cannot mount an action potential (Na+ channels inactivated, K+ channels open)

Schwann cells

wrap around axons and act as electrical insulation (myelin sheath) preventing ions leaking out (PNS)

Oligodendrocytes

wrap around axons and act as electrical insulation (myelin sheath) preventing ions leaking out (CNS)