topic 5 biol 216: the neuron

flashcards for exam 2, spr 2025

afferent neuron

transmits signals to CNS (away from stimulus)

efferent neuron

sends signals to muscles/glands; allows for response to be carried out

interneurons

integrate information

motor neuron

type of efferent neuron that is specific to skeletal muscle

Gross steps of information processing

1. sense

2. integrate

3. act

More specific steps of information processing

1. external (light, movement) or internal (BP, internal body temp) stimuli affect the body

2. sensory receptors of afferent neurons detect stimulus

3. message travels from afferent to interneurons

4. neural messages are sorted and interpreted

5. the message travels to efferent neurons

6. messages on efferent neurons are transmitted to effectors

7. action occurs

dendrites

pick up signals from other neurons

cell body

contains nucleus of neuron

axon

conducts electrical impulses along neuron cell

myelin sheath

insulates axon to protect and speed up transmission

axon terminal

transmits electrical and chemical signals to postsynaptic cells

is morphology for every neuron the same?

NO! depends on neuron function

afferent neuron location on spinal cord

dorsal root

efferent neuron location on spinal cord

ventral root

afferent neuron anatomy

dendrites are not located on soma

double branched axon

central branch of afferent neuron

cell body to spinal cord

peripheral branch of afferent neuron

cell body to periphery (skin, joint, muscle, etc)

do all sensory receptors look the same?

NO! dependent on function (can be encapsulated or free)

nerve

bundle of axons located in PNS

white matter

myelinated axons and glial cells

gray matter

neuronal cell bodies

glial cells

non-neuronal cells that provide nutrition/support to neurons

ependymal cells

produce cerebrospinal fluid

microglia

phagocytic cell; ingest/break down pathogens and waste (CNS)

astrocytes

cover surfaces of blood vessels, structural support, maintain ion conc in interstitial fluid around BVs (CNS)

satellite cells

cover surfaces of blood vessels, structural support, maintain ion conc in interstitial fluid around BVs (PNS)

schwann cells

form myelin sheath in PNS

oligodendocytes

form myelin sheath in CNS

presynaptic neuron

transmitting

postsynaptic neuron

receiving

node of ranvier

expose axon membrane to extracellular fluid (propagate action potentials)

axon hillock

initiation zone for action potentials

synapse

junction between axon terminals and postsynaptic cell

axosomatic synapse

presynaptic terminal and soma

axoaxonic synapse

presynaptic axon and post synaptic axon

axodendritic synapse

axon to dendrite

electrical synapse

uniform, contractile activity; acts as one cell

steps of electrical synapse transmission

1. connect contractile cells (i.e. cardiac muscle cells)

2. connexons connect membranes of two cells

3. AP generates local currents that go through gap junction

4. local current stimulates production of AP, causing propagation along plasma membrane

5. local current flows through gap junction, stimulates AP in adjacent cell

chemical synapse

release neurotransmitter after impulse reaches terminals, causing an influx of ions

which type of synapse is faster?

electricalw

which type of synapse is more controlled?

chemical

electrochemical gradient

concentration gradient and an electrical gradient

influences of ion movement/membrane potential

diffusion and electric fields

concentration of important ions

HIGH conc Na outside, HIGH conc K inside

why is there more K on the inside?

K leak channels allow for more freedom of K movement

4 ion channels

voltage gated, ligand gated, mechanically gated, ungated

voltage gated

open and close according to goldman equation

goldman equation

Vm= (concentration out/concentration in) * 62 log10

key regions of Na voltage gated channels

voltage sensing, pore inactivation

how does voltage change affect Na channels?

conformational change in polypep chain of AA

why are there so many types of voltage K channels

speeds up ability to create another AP

types of voltage gated K channels

fast-inactivate (A-type current), slow-inactivate, no inactivate

mechanically gated channel

channels open/close based on physical changes

example of mechanically gated channel

hair cell in ear

ligand gated channel

opens in response to chemical (often neurotransmitter)

nicotinic acetylcholine receptor mechanism of action (nAChR)

1. channel opens when acetylcholine (ligand) binds

2. ions flow through cell membrane (Na and Ca)

3. response triggered in muscle cell

AP process

1. stimulus causes positive ions to flow into the neuron

2. membrane potential becomes depolarized

3. depolarization occurs slowly until threshold is met

4. sudden increase in membrane potential

5. membrane potential falls (usually hyperpolarizes)

6. membrane potential returns to resting potential

action potential

abrupt/transient change in membrane potential that occurs when electrically excitable cells conduct an electrical impulse (ew)

AP breakdown (specific)

1. VG channels open (Na)

2. Threshold is met, more Na channels open (depolarization)

3. Na channels start to become blocked/inactivated, K channels open (repolarization)

4. Na channels are completely blocked/inactivated, K channels remain open (repolar to hyperpolarization)

5. Na channels close, K channels close (except for leaky) (end hyper, back to resting)

propagation of an AP

ions flow from firing node and adjacent unfired node, causing the next section to fire

what prevents AP from happening in reverse?

sodium channels are occluded

refractory period

sensitivity to stimulation decreases for a set amount of time

absolute refractory

complete insensitivity to another stimulus (depolar/repolar)

relative refractory

a stronger-than-threshold stimulus can initiate another AP (hyperpolar)

why do we have relative refractory periods?

Na channels are no longer inactivated, and instead are only closed and are once again sensitive to stimuli

what causes all action potential peaks to be the same height?

number of channels on the membrane

intensity of stimulus is indicated by…

frequency of APs

a-alpha nerve

muscle sense (largest)

a-beta nerve

touch

a-delta nerve

pain/temperature

c-nerve

pain, temperature, and itch

length constant is dependent on…

resistance of membrane (rm) and resistance of axoplasm (rl)

lambda formula

sqrt(rm/rl)

myelin sheath prevents….

action potentials from occurring in myelinated segments

neurotransmitter

signal molecules secreted by presynaptic neuron to postsynaptic neuron

types of chemical synapses

direct or indirect

direct neurotransmission

neurotransmitter binds to ligand gated channel, channel opens/closes depending on neurotransmitter (quick!)

indirect neurotransmission

neurotransmitter binds to g-protein coupled receptors, messenger pathway is activated, channels open/close dep on neurotransmitter, signal is propagated (slow 😢, but lasts)

acetylcholine

nerves to muscle, present in heart, responsible for memory, attention and learning

degeneration of acetylcholine causes…

alzheimers disease

GABA

inhibitor; opens Cl- channels of post-synaptic membrane

glycine

inhibitor of neurotransmission (inc Cl- influx)

glutamate

excitatory; learning and memory

norepinephrine/epinephrine

excitatory or inhibitory; work as hormones and neurotransmitters, involved in attention and mental focus, memory, pleasure/reward pathway, motor control

dopamine

behavior/cognition, voluntary movement, motivation/reward, inhibition of prolactin (lactation), sleep, mood, attention, and learning

degeneration of dopamine leads to…

parkinson’s disease

tyrosine derivatives

norepinephrine, epinephrine, dopamine

serotonin

intestinal movements, mood, appetite, sleep (tryptophan derivative)

neuropeptides are…

indirect neurotransmitters

types of neuropeptides

endorphins, enkephalins, substance P

endorphines

pleasurable experiences, reduce pain, work on PNS

enkephalins

subset of endorphins, work in CNS, modulate pain response

substance P

released by spinal cord, increase pain perception

carbon monoxide

release of hormones to hypothalamus

nitric oxide

learning, muscle movement, relaxation of smooth muscle in BVs

chemical synapse summary

1. ap arrives at axon terminal, opens Ca channels

2. vesicle fuses with membrane and releases neurotransmitters (exocytosis)

3. Ca channels close when stimulus subsides (no APs)

4. Ca is pumped outside of the axon terminal, vesicles stop closing

5. neurotransmitters are either diffused away from cleft, broken down, or reuptake into the presynaptic terminal

acetylcholine reuptake steps

1. acetylcholine binds to receptor

2. acetylcholine unbinds from receptor

3. acetylcholinesterase splits acetylcholine into choline and acetic acid, preventing acetylcholine from rebinding to receptors

4. choline is used to make new acetylcholine that is repackaged for later use

norepinephrine reuptake steps

1. norepinephrine binds to receptor

2. norepinephrine unbinds to receptor

3. norepinephrine is taken back up by presynaptic terminal, preventing it from re-binding to receptor

4. norepinephrine is repackaged by synaptic vesicles or broken down by MAO (monoamine oxidase)

EPSP

excitatory post synaptic potential; moves neuron closer to threshold

IPSP

inhibitory post synaptic potential; pushes membrane away from threshold