306 part 2

what is the cell body called

the soma

what do dendrites do

recieve input

what do astrocytes do

maintain brain homeostasis by regulating synaptic activity, supporting neuronal metabolism, forming the blood-brain barrier, and modulating neuroinflammation.

what do microglia do

CNS immune cells

what do ependymal cells do

line the brains ventricles, secrete CFS

what do oligodendria do

produce and maintain myelin sheath 

what do schwann cells do

structural support and insulate axons ( form myelin sheath) 

how do neuroglia differ from neurons

they dont form synapese

have only one type of projection 

able to divide

less electrically excitable 

what do afferent pathways do

deliver sensory input from the PNS to the CNS

what do somatic efferent pathways control

voluntary/ skeletal muscle

what do autonomic efferents control

smooth and cardiac muscle

what does the PNS include

all peripheral nerves exiting the spinal cord

sensory receptors ( muscle, skin, special senses)

where does the PNS interface with the cns

in the dorsal and ventral horns of the spinal cord 

what does the ascending dorsal column medial lemniscus do 

carry sensory input on fine touch, vibration, and proprioception to the brain

what does the ascending spinothalamic pathway do 

carry sensory input on temperature, crude touch and pain to the brain 

what do corticospinal tracts

carry motor signals from the brain to skeletal muscles to control movement

functions of the cns

gather, integrate, process, percieve infromation from the PNS

organize reflex and autonomic responses 

planning and executing voluntary movements 

higher functions like cognition, learning, and memory

what are the major regions of the brain

cerebrum, cerebellum, pons, medulla, brain stem

what properties can pass through the biomembrane

small, lipophillic, uncharged

what is used to regulated channels

intracellular proteins, second messengers, ions

structure of CaV and NaV channels

pores formed by monomers with four repeating 6TM-spanning regions

structure of ion channels

transmembrane channels with a centeral pore

some are multimers of homoeric or heteromeric subunits (KV, HCN)

some are monomers with repeating transmembrane units

what are the states of gated channels

closed(resting)

open(active)

inactive (until channel has been reset)

can have sub states 

changes in gate status involve protein conformational changes 

gating of the NaV channel

depolar opens the activiation gates

inactivation gate then closes halting ion flow 

inactivation gate cannot be removed until the membrane repolarizes

what is the RMP

-70mV

what are the values for K in and outside the cell

120-150

3.5-5.0

what are the values for Na in and outside the cell

10-15

135-147

what are the values for CI in and outside the cell

20-30

95-105

what are the values for HCO3 in and outside the cell

12-16

22-28

what determines the direction the ion channels will move 

chemical and electrical gradients 

what does the opening and closing of ion channels do 

changes the cell permeability 

what is the driving force for ion movement 

the difference between the membrane charge and the equilibrium potential

whst happens when Vm (membrane charge) - Eion (eq potential) is greater than 0

ion flow outward

what happens when Vm (membrane charge) - Eion (eq potential) is less than 0

ions flow inward

whst happens when Vm (membrane charge) - Eion (eq potential) is equal to  0

no net ion flow 

what is Eion influenced by

concentration gradient and membrane permeability

the nernst equation

61/z log [ion]out/[ion]in

what does the nernst equation predict

the equilibrium potential for a single ion

what does the goldman-hodgkin-katz equation do

predicts membrane potential using multiple ions

goldman-hodgkin-katz equation

what is the ohms law equation

I = gV

g is open probability 

v is membrane potential 

what does a stimulus cause

a stimulus is a change in current which will change membrane potential 

how can a stimulus occur

from input of another neuron

spontanteous ( pacemaker cell)

introduced into the system using electrophysiological techniques 

what is cable theory

a mathematical model that describes the passive propagation of electrical signals in neurons and other cells with cable-like structures, such as dendrites and axons

what happens as the passive potential moves away from the stimulus site

the ions diffuse away causing decay because they are not being replenished / regenerated

what are the 3 passive properties

membrane capacitance, resistance

geometeric factors like length and diameter 

what do capaciters do

separate charge

what do the passive properties determine

how far a passive potential generated in the dendrite will tavel, and whether a AP is generated

what does high resistance cause 

little leak of ions so passive AP are going to hold onto the ions over a longer distance so there is slower decay 

what does Rm and Cm determine 

the shape and magnitude of the voltage response

what else does Rm determine

how likely a small applied current is to generate an appreciable voltage response

AP only occur when the threshold is reached for opening of 

Na V channels 

outward current is positive charge 

efflux

inward current is positive charge

influx

where does synaptic integration occur 

at the axon hillock because it have the highest density of Nav channels, meaning the threshold for spike initiation is lowest 

what is spatial summation

the AP are more spread out when they sum

what is temporal summation

the AP are close when they sum

what is the shunting effect

a form of neural inhibition that occurs when excitatory and inhibitory signals are active simultaneously near each other on a neuron's membrane.

It works by creating a "leak" in the membrane, which causes the neuron to lose the positive charge from the excitatory input, reducing the depolarization needed to trigger an action potential

what is a EPSP

a excitatory postsynaptic potential 

transient depolar of postsynaptic neuron due to increased conductance of membrane in response to neurotransmitter binding 

what happens to membrane in EPSP

driving force of na to enter cell is greater than for k to leave causing depolar 

what is a IPSP

inhibitory postsynaptic potential

transient hyperpolar of postsynaptic due to increased CI conductance of membrane in repsonse to neurotransmmitter binding 

what happens to membrane in IPSP

CI enters the cell at rmp causing hyperpolar 

what is saltatory conduction

when a AP jumps from node to node

when is conductance fastest

in large, myelinated axons

where exactly are Nav channels most densely populated 

in the nodes of ranvier 

what is the conductance velocity of Ia and b fibre types (Aalpha)

80-120 m/sec

what is the conductance velocity of II fibre types (Abeta)

35-75 m/sec

property of a hyperpolarizing stimulus

the electronic potential decays as a distance from the stimulus increases 

properties of a depolar stimulus

remains constant in shape and magnitude

delay between stimulus and repsonse increases with distance 

where are AP regenerated

nodes of ranvier

why are AP regenerated at the node of ranvier

membrane conductance is high

membrane resistance is low 

Nav and Kn density is high 

why do passive potentials propagate rapidly between nodes

membrane resistance is high

membrane capacitance is low 

ways to improve conduction (3)

increase axon diameter ( decrease axial resistance)

myelinate axon ( increase membrane resistance)

as axon diameter increases, conductance velocity will increase as internal resistance decreases 

why is myelin important 

Myelin's insulating effect (high resistance) prevents electrical current from leaking out of the axon, while its structure (low capacitance) reduces the amount of charge needed to change the membrane potential.

what makes myelin in the CNS

oligodendrocytes

what makes myelin in the PNS

schwann cells

what happens when myelin is removed

transmittion slows down or isnt received

how does synaptic transmission work

1. input received on dendrite is passively propagated to the hillock 

2. summation occurs at the hillock (inhibt or excite)

3. if suprathreshold -ap will propagate down the axon 

if subthreshold - no AP

4. At the synapse, electrical singals are converted to chemical signals and then back to electrical signals 

what is the presynaptic terminal in axons

the axon terminus

what is the postsynaptic terminal in axons

the dendrite or cell body of a neighbouring neuron

types of neurotransmitters

small - glutamate, GABA, acytelcholine

gas - NO

Amines - dopamine, serotonin, norepinephrine

how do gases work in synaptic transmission

they diffuse out of the cell of origin and directly into other cells 

they can act inside cell of origin or in cells distant from point of release 

how do peptides work in synaptic transmission

they get excocytosed from the presynaptic terminal and then diffuse in extracellular space and bind to synaptic and extrasynaptic G protei - complex receptors 

what are the excitatory NTs 

glutamate - primary excitatory in brain 

acetylcholine - in pns at NMJ and autonomic ganglia, also CNS in basal ganglia and spinal cord

what are the two types of aceytlcholine receptors

nicotinic - neuromuscular junction 

muscarinic - autonomic ganglia 

what are the inhibitory NT

gamma-aminobutyric acid (GABA) - inhibitory in brain

glycine - inhibitory in spinal cord

what are the ligand gated ion channels called

ionotropic (NT receptor)

what are the g protein coupled receptors called

metabotropic

how do g-protein coupled recpetors work

1. NT binds

2. g-protein is activated 

3. g protein subunits or intracellular messengers modulate ion channels 

4. ion channels opens

5. ion flow across membrane

what are ligand gated ion channels called in cns, NMJ

cns: ionotropic glutamate receptors, GABA(A),GABA(C)

what are g protein - coupled receptors called in cns, pns

both : metabotropic glutamate receptors

PNS : muscarinic ach receptors

CNS : GABA (B)

idk

what are two mechanisms important for AP being unidirectional 

1. Nav inactivation

2. increased Pk

what is EPSC

excitatory post synaptic currents

active ionotropic channels ( open then close)

faster then epsp

how are extracellular signals converted into intracellular events

through signal transduction

what is the structure of ligand gated ion channels 

heteromeric, vary in subunit composition

generally 5 subunits with 4 TM spanning helices

what is direct gating ion channels

NT binds to its receptor

ex. Ach binding to nicotinic receptor

what is indirect gating ion channels

ion channels are down stream of NT binding to its receptor 

ex. muscarinic Ach receptors 

How fast are ionotropic and metabotropic channels

fast

slow 

can NT have both ionotropic and metabotropic channels 

yes, virtually all classical NT have both receptors