nerves and synapses

central nervous system

composed of the brain and spinal cord

peripheral nervous system

consisting of nerves that connect CNS to peripheral structures

neuron

functional unit of nervous system that generates electrical signals (action potentials)

glial cells

non neuronal cells that support neurons but do not generate action nerve impulses/action potential

afferent neurons

sends the signal to the CNS (body → brain)

efferent neurons

sends signal out of CNS (brain → body)

astrocytes

brings nutrients from the blood to the neuron and maintains blood-brain barrier and sustains neurons metabolically

oligodendrocytes

myelinates neurons in the CNS

microglia

immune cells in the CNA

ependymal cells

produces and circulates CSF and separates CSF from neural tissue

Schwann cells

myelinates neurons in the PNS

pumps

active transport - requires energy (ATP)

ion channels

passive - goes down the concentration gradient

leak (passive) channels

always mostly open

gated channels

opens only in response to a stimulus

ligand-gated and voltage-gated

pumps and channels that set membrane potential

Na+/K+ ATPase

Na leak channels

K leak channels (most important)

Na+/K+ ATPase

spends ATP to push 3 Na+ out for every 2 K+ in (losing 1+ on the inside)

creates high K+ concentration inside the cell and high Na+ concentration outside the cell

net loss of 1+ form the cell each cycle - makes the inside a lil more negative than the outside

potassium leak channels

chemical force pushes outwards (more K+ in but wants to push out)

electrical force pushes inwards (more negative inside so it wants to push K+ in)

-90mV

sodium leak channels

the chemical force pushes inwards (more Na outside wants to move from high to low concentration)

the electrical force pushes inwards (inside is negative wants to move in)

+60mV

equilibrium potential

the membrane potential at which the electrical and chemical forces acting on a specific ion are equal and opposite, resulting in no net movement of that ion across the membrane

permeant ion rule

the more permeant the ion is the greater its ability to force Em towards its own equilibrium potential → more open doors means more permeability

during rest potassium is more permeable than Na because it has more leak channels

increased extracellular K+

depolarization (less negative/more positive membrane potential)

increased extracellular Na+

slight depolarization (because Na+ permeability is low at rest)

increased K+ permeability

resting membrane potential becomes more negative

increased Na+ permeability

resting membrane potential becomes more positive

resting membrane potential

a steady state membrane potential determined by membranes permeability to Na+ and K+

voltage gated ion channels

gate opens with voltage change

ligand gated ion channel

gate opens when ligand attaches

action potenial

rapid change in a membranes potential due to opening of voltage gated Na+ and K+ channels causing ion flow across the membrane (and then back to resting)

iniating stimulus (starts depolarization)

ligand-gated or mechanically gated

all-or-none law

neuron fires completely or not at all (the amplitude is always fixed → but a stronger stimuli increases the # of frequencies of an action potential)

G