Bio 232: Exam 4

the synapse

neuron - neuron communication

Multiple bits of information to a

single neuron

spinal motor neuron

Soma

Presynaptic Neuron

“sending” impulse towards synapse

postsynaptic neuron

“receiving” impulse away from synapse

chemical synapses:

step 1: presynaptic cell

electrical signal at axon terminal

depolarization

Open VG Na+ & Ca2+ channels

chemical synapses:

step 2: NT released by exocytosis

synaptic vesicles fuse w/ membrane

release NT to synaptic cleft

NT released by

exocytosis

chemical synapses:

step 3: postsynaptic cell

NT binds to NT receptor

chemical synapses:

step 4: NT/NT receptor channels open

conformational change - opens

ions flow changes membrane potential (graded)

excitation or inhibition

signal size

higher frequency at the presynaptic neuron

higher frequency at the presynaptic neuron =

more NT released

Bigger electrical signal at

postsynaptic membrane

chemical synapses - review

step 1

electrical signal - presynaptic

VG Na+ and Ca2+ increases in Ca2+

chemical synapses - review

step 2

NT released by exocytosis - presynaptic

synaptic vesicles fuse with membrane

chemical synapses - review

step 3

post synaptic cell - NT binds to NT receptor

chemical synapses - review

step 4

post synaptic cell - receptor channel opens

changing MP of postsynaptic neuro

gap junction =

electrical junction

drugs (toxins) block release of

NT - presynaptic cell

drugs block release of the

vesicle containing the NT

example of blocking NT at neuromuscular junction

Neurons controlling muscles “motoneurons”

NT and ACh

neuron releases ACh to muscle

termination of NT response is a __________ response

transient (temporary)

If the process f termination was not transient

paralysis

termination:

enzyme degrades

at synaptic cleft or postsynaptic neuron

termination:

“reuptake”

of NT by presynaptic neuron

Termination:

diffusion of NT

out of synaptic cleft

dilution of the NT

Excitatory Post Synaptic Potential

depolarization

small stimulus - EPSP

small depolarization in PSC

no AP as K+ flows out (LEAK CHANNELS) prevents excessive '“+” charge in cell

small or below threshold

no AP

large stimulus

EPSPs move down dendritic process/cell body to axon hillock - graded potential

generate an AP on the axon (LARGER POSITIVE CHARGE)

at or above threshold

AP

inhibitory postsynaptic potentials (IPSPs)

cause hyperpolarization - reduces MP

will not cause an AP at axon

bigger depolarization needed to fire an AP

EPSPs can

summate

add together

Multiple excitatory presynaptic neurons induce EPSPs on

a single postsynaptic neuron

EPSPs are more likely to reach

threshold - induce AP

Axon hillock “integrates” all

EPSPs and IPSPs

Axon hillock “integrates” all EPSPs and IPSPs determines

response

threshold or sub-threshold

example of integration

graded potential

criteria 1 for a NT

NT present presynaptic terminal and released w/stim

criteria 2 for a NT

NT applied to postsynaptic neuron produces response (EPSP or IPSP)

criteria 3 for a NT

natural mechanism exist to terminate response

if all 3 are met,

substance is a NT

new messenger

nitric oxide (NO)

diffuses across membranes

new messengers (NTs) ________ neuron to _________ neuron

postsynaptic neuron to presynaptic neuron

new messengers:

retrograde signal

helps us understand learning/memory in “long term potentiation”

NO is released and goes to

PSN

NT ACh

Causes muscles to contract



If stim, ACL will release into the synaptic cell



Transient

glutamate

depolarization (excitatory)

GABA

hyperpolarization (inhibitory)

ACh

binds to 4 different Ach receptors

ACh neuromuscular junctions

excitatory

ACh cardiac muscle

inhibitory

channel-linked receptors

ionotropic or metabotropic

ionotropic

G Protein-linked NT receptors

ionotropic or metabotropic

metabotropic

channel-linked receptors

direct or indirect

direct

G Protein-linked NT receptors

direct or indirect

indirect

Channel-linked receptors - direct action

open an ion channel

allows ion to cross membrane

channel-lined receptors

rapid or slow

rapid response localized, brief

G Protein-linked NT receptors - indirect action

via second messenger

G Protein-linked NT receptors

rapid or slow

slow response, prolonged, complex

facilitated zone

subthreshold stim

stim from other sources can induce AP

discharge zone

closely lined to presynaptic input

likely to reach threshold

circuits

pattern of connections of neuronal pools

divergence

amplification

single sensory receptor

divergence - single sensory receptor

up signal cord and multiple brain regions at once

convergence - multiple presynaptic inputs

concentrated effect

convergence increases

response

convergence results

multiple stimuli causes same response

Example of convergence with a new mother

loving feeling

sound, seeing, and hearing her baby

what circuit is this

reverberating or parallel

what circuit is this

reverberating or parallel

serial processing

predictable all-or-none manner

neural processing pieces

receptor

sensory neuron

CNS integration

Motor neuron

Effector (muscle)

parallel processing

inputs into many different pathways (processed simultaneously)

One stimulus travels through multiple pathways can provide

multiple - unique responses

parallel processing is important in

higher mental function

examples of parallel processing in higher mental function

problem solving or connecting parts to a whole

function of PNS

information conveyed to and from the CNS

PNS includes all

neuronal tissue outside the brain and spinal cord

Everything outside of

CNS is PNS

components of the PNS

1. sensory receptors
2. peripheral nerves (and ganglia)


1. efferent motor ending (from the CNS)

mechanoreceptors

skin (afferent) tip of finger to CNS

mechanical pressures - nerve impulse

thermoreceptors

temperature

chemoreceptors

chemicals in solution

nociceptors

pain damaging stimuli

tissues

nerve structure is like

a fiberoptic cable

outer coating of nerve

epineurium has blood vessels and fascicles

outer layer of bundle/fascicle

perineurium

each tube inside fascicle iis wrapped in

endoneurium

after endoneurium

myelinated axon

ganglia

neuron cell bodies and supporting cells

Dorsal Root Ganglia

ganglia with afferent nerve fibers - outside back to CNS

touch or pain receptor

Dorsal Root Ganglia cell bodies from

sensory neurons

reflex arcs

reflexes occur over specific neuronal pathways

reflex arcs steps:

step 1:

receptor

reflex arcs steps:

step 2:

sensory neuron

reflex arcs steps:

step 3:

CNS integration center

reflex arcs steps:

step 4:

motor neuron

reflex arcs steps:

step 5:

effector

receptor

site of stimulation