Neurons

central nervous system

brain + spinal cord

peripheral nervous system

neural tissue outside CNS

• nerves

axon hillock

junction |b| soma + axon

soma

cell body of neuron

axon

• takes signal to destination

• can connect to multiple cells

dendrite

receive electrochemical signals from other cells + send them to soma

synaptic terminal

transmits electrical/chemical signal to target cell

what are the structural classifications of neurons?

• anaxonic

• bipolar

• unipolar

• multipolar

anaxonic neuron

axons can’t be distinguished from dendrites

bipolar neuron

2 processes separated by soma

unipolar neuron

have single process w/soma off to side

multipolar neuron

single axon w/multiple dendrites

afferent neurons

carry info toward CNS

(a for arrive, arrive @CNS)

efferent neurons

carry info away from the CNS

(e for Exit, exit CNS)

somatic motor neuron

innervate skeletal muscles

somatic sensory neurons

info from external world + body position

visceral sensory neurons

info about internal systems

visceral motor neurons

innervate smooth + cardiac muscle, glands

interneurons

communicate |b| neurons

neuroglia

• supporting cells

• ½ of all neural tissue

ependymal cells

• generate CSF

• CNS

astrocytes

• maintain BBB (blood brain barrier)

• regulate nutrients

• structural support

• CNS

oligodendrocytes

• myelination

• structural support

• hold onto axons

• ONLY IN CNS

microglia

• phagocytes

• remove waste/dead cells

satellite cells

• regulate nutrients

• PNS

schwann cells

• myelination

• repair

• PNS

• hold onto axon

Cerobrospinal fluid (CSF)

• clear fluid found in CNS

• protection/support

• circulation of nutrients

• remove waste

• immune prot

blood brain barrier (BBB)

• highly selective permeable membrane

• specialized neuroglia + capillaries regulate what moves into CSF from plasma

myelin

• membranes that surround some axons

• outgrowth of specialized neuralgia

• increase speed of action potential moving down axon

white matter

axons surrounded by myelin

grey matter

unmyelinated axons, cell bodies, dendrites

myelinated axon (PNS)

• schwann cells fully wrap around axon

• multiple layers of myelin

• prevents exchange

unmyelinated axon (PNS)

• schwann cells not wrapping fully around axon (like hotdog)

• exposed, exchange possible

what is the big picture of neural physiology?

resting potential —> graded potential —> action potential —> synaptic activity —> info processing

resting membrane potential (RMP)

• electrical potential difference across cell membrane during resting conditions

• -70 mV

what are the contributing factors to rmp?

• passive chemical gradient

• passive electrical gradient

• active transport

what is the permeability of K+ to Na+?

k+ is more permeable (will leave cell)

na+ wants to go into cell

What is the equilibrium potential of freely permeable K+/Na+?

K+: -90 mV

Na+: 66 mV

tell me about RMP and leak channels

more k+ leak channels than na+ leak channels

what is the goal of the na+/K+ pump in rmp

• remove the na+ that leaks in a recapture the k+ that leaks out

• helps maintain and establish concentration differences of K+ and Na+ at RMP

what causes change in rmp?

• activation of chemically gated channels

• activation of voltage gated channels

polarized

inside cell neg. relative to outside

depolarization

process of making inside of cell less negative (towards 0)

repolarization

process of returning membrane potential back to RMP

hyperpolarization

process of making inside cell MORE negative than RMP

graded potential

change in membrane potential in dendrites + soma

Excitatory post-synaptic potentials (EPSPs)

• stimulus opens na+ channels

• depolarization

• increases likelihood of action potential

inhibitory post-sypnaptic potentials (IPSP)

• stimulus opens gated K+ channels

• hyperpolarization

• decreases likelihood of action potential

action potential

propagated change in membrane potential down the axon

describe how action potential happens

• signals from dendrites + soma = graded potential

• localized ions currents travel to axon hillock

• axon hillock summates electrical msg

• if reaches threshold, action potential triggered down axon

what propagates the action potential down an axon

voltage gated na+ and K+ channels

Steps of action potential:

1. threshold

2. depolarization

3. repolarization

4. hyperpolarization

Threshold (in action potential)

• -60 to -55 mV

• all or nothing —> once achieved action potential starts

depolarization (in action potential)

• voltage gated Na channels open

• Na+ enters cell

• rapid depolarization of membrane

repolarization (in action potential)

• voltage na+ channels close

• voltage K+ channels OPEN —> k+ leaves cell

• potential decreases to RMP

hyperpolarization

• k+ movement out of cell cont.

• potential drops below RMP

• Voltage K+ channels close —> return to RMP

Rest Voltage gated ion channels

• na+: activation=closed, inactivation=open

• K+: closed

threshold Voltage gated ion channels

• na+: activation=opens, inactivation=open

• k+: closed

depolarization Voltage gated ion channels

• na+: both open

• k+: closed

repolarization Voltage gated ion channels

• na+: activation=open, inactivation=closed

• k+ open (begin to close at ~ -70 mV)

hyperpolarization Voltage gated ion channels

• na+: activation=closed, inactivation=open

• k+ channel: open/closing (fully closed ~ -90 mV)

Absolute Refractory Period (ARP)

• cell can’t be stimulated to fire another action potential

what is the mechanism behind ARP

• Volt. gated Na+ channels are open (depolarization)

• The inactivation gates of the volt. gated Na+ channels are closed (repolarization)

Relative Refractory Period

cell can only be stim to fire another action potential if depolarization event is greater than usual

mechanism behind relative refractory period

• cell is hyperpolarized (further away from threshold)

Continuous Propagation (what is it, and describe it)

• unmyelinated axons

• step by step movement of action potential down the length of axon

• depolarization of membrane in one region

• passive Na+ travels locally and increases next region’s potential to threshold —> volt. gated chanels open —> action pot. propagated

unidirectional propagation of action potential

regions behind action potential are in refractory period, can’t be reactivated

saltatory propagation

• MYELINATED axons

• passive na+ current travels along until reaches Node of ranvier —> action potential stim

• ions can’t flow thru the membrane at myelinated regions

• action potential jumps from node to node

• FASTER

nodes of ranvier

• gaps in |b| the myelin sheath along axons

• high density of volt. gated channels

synapse

site of neural communication

A synapse contains:

• presynaptic cell

• postsynaptic cell

• synaptic cleft

describe what happens at the synapse

• action potential reaches synaptic terminal

• vesicles attach to presynaptic membrane —> release neurotransmitter (nt) into the cleft

• nt binds to receptors on postsynaptic membrane (excite or inhibit)

• synaptic terminal can reabsorb + reuse nt from cleft

cholinergic synapse (what is it, the steps?)

acetylcholine (Ach) is active neurotransmitter

• AP causes volt. gated Ca channels —> causes vesicles to release Ach —> released into cleft

• Ach binds to receptors —> opens na channel —> depolarizes, triggers AP

• acetylcholinesterase breaks down Ach

glutamate

• excitatory NT

• depolarization in synaptic cell

GABA

• inhibitory NT

• hyperpolarization in post-synaptic cell

norepinephrine

• excitatory NT

dopamine

• excitatory/inhibitory NT (depends where)

serotonin

• primarily excitatory NT

• heavily involved in attention + emotion

nitric oxide

• innervate smooth muscle associated w/BV

• causes vasodilation