A&P unit 3 - neurons and neurotransmitters

components of CNS vs PNS

CNS = brain, spinal cord

PNS = nerves, ganglia (bundles of nerves)

Afferent nervous system

sensory neurons, go TO CNS

(afferent = arrive)

-somatic and visceral

somatic sensory system

-afferent

-detect stimuli we consciously perceive

→ 5 senses, propioreceptors

visceral sensory system

-afferent

-detect unconscious stimuli

→ signals from internal organs

Efferent nervous system

initiate motor output FROM CNS

(efferent = effect)

→ somatic and autonomic motor systems

→ sympathetic and parasympathetic

somatic motor system

-efferent

-send voluntary signal to skeletal muscles

autonomic/visceral motor system

-efferent

-send involuntary signal to cardiac and smooth muscle

-includes sympathetic and parasympathetic

sympathetic vs parasympathetic

sympathetic = fight or flight

parasympathetic = rest and digest

afferent, efferent motor system diagram (photo)

nerve diagram

need to know

-epineurium

-perineurium

-endoneurium

-fasicle

neuron diagram

dendrites = receive input

-cell body/soma = integrate incoming signals

-axon hillock = trigger zone for new signal

-pre-synaptic terminals/axon terminals = send output to other cells

What are the 5 characteristics of neurons?

1) excitability - respond to a stimulus

2) conduct signal across axon

3) secrete neurotransmitter

4) longevity - lasts across your lifetime

5) amototic - can’t do mitosis

anterograde transport

move FROM cell body

-move newly synthesized material toward synaptic knob

retrograde transport

move TO cell body

-moves used materials from axon for breakdown/recycling

Fast axonal transport (image)

Kinesin = anterograde

Dynein = retrograde

*both require ATP

-move 400mm per day

slow axonal transport

-move 0.1-3mm per day

-flow of axoplasm (axon cytoplasm)

-only in anterograde direction (from body)

-moves enzymes, cytoskeletal components, new axoplasm

multipolar neuron

-many dendrites

-1 axon

→ all motor neurons

bipolar neuron

-1 dendrite

-1 axon

-soma in middle

→ sensory neurons of 5 senses

unipolar neuron

-single short process from cell body → 1 axon

-one side of axon in peripheral direction (to PNS), one side in central direction (to CNS)

→ sensory neurons

anaxonic neuron

-no axons

-dendrites come directly off cell body

→ interneurons

neuron input, output diagram

sensory neurons

-afferent (conduct input to CNS)

-unipolar and bipolar

motor neurons

-efferent (conduct input from CNS to effectors)

-multipolar

interneurons

-in between afferent and efferent neurons

-receive and process info from other neurons

-multipolar or anaxonic

-make up 99% of neurons

components of glial cells

-non-excitable

-capable of mitosis

-protect & nourish neurons

-physical scaffold for neurons

-90% of cells in CNS

what kind of cells do brain tumors form from?

glial cells → they are capable of mitosis and neurons are not

Astrocytes

-most common glial cell

-form blood brain barrier

-structural support

-assist neuronal development

-occupy space of dying neurons

-regulate tissue fluid composition (ex. can regulate [K+])

Ependymal cells

-glial cell

-line cavities in brain and spinal cord

-cushion neurons and provide nutrients

-produce CSF of CNS

Microglia

-smallest glial cells

-phagocytic, immune system

-wander CNS and replicate during infection

-also remove debris

Oligodendrocyte

-very large glial cells

-form myelin sheath of CNS

Neurolemmocytes

-glial cells

-Schwann cells

-form myelin sheath of PNS

synaptic plasticity / plasticity

neuron signal pathway can be strengthened or weakened over time depending on how much we use it → how learning happens

post synaptic facilitation/inhibition vs

presynaptic facilitation/inhibition

post = EPSP/IPSP thru synapse

→it is axosomic = axon to soma of next cell, 2 cell action

pre = axoaxonal - axon release directly onto axon, 3 cell action

postsynaptic facilitation/inhibition image

how does presynaptic inhibition work?

cell B release NT → opens chem gated Cl- channel on Cell A

Cell A gets more negative → prevent Ca VGC opening → no new NT release onto cell C

result = AP is not transferred

NT chemical structure category

1) Acetylcholine (ACH)

-needed for skeletal muscle contraction

-different structure than amino acid based categories

NT chemical structure category

2) biogenic amines

-modified Amino acid

-decarboxylase takes carboxyl off an AA

-includes catecholamine and indolamine

catecholamines

-subclass of biogenic amine

-has single ring catechol + R group

epinephrine

norepinephrine

dopamine

indolamines

-subclass of biogenic amine

-has double ring indole + R group

histamine

serotonin

NT chemical structure category

3) Amino acids

-unchanged form of AA acting as a NT

GABA - EPSP

glutamate - IPSP

glycine - IPSP

NT chemical structure category

4) neuropeptides

-long chains of AAs

endorphins

NT chemical structure image/graph

NT function category

effects

divided into excitatory (EPSP) or inhibitory (IPSP)

NT function category

actions - Ionotropic

-NT directly opens ion channels by binding to receptor

-immediate postsynaptic effect

NT function category

actions - Metabotropic

-NT indirectly causes response by binding to GPCR

-slower, but more diverse effects

NT function image/graph

Acetylcholine synthesis

A) synthesis = acetate + choline, then gets stored in vesicles. released when AP signal

-more signal → more ACH release

Acetylcholine removal

B) removal from cleft = acetylcholinesterase breaks ACH into acetate and choline. binds to muscarinic receptors

-type of muscarinic determines if it’s EPSP or IPSP

how do MAOI’s work?

“monoamine oxidase inhibitors”

monoamine oxidase = enzyme that breaks down NT

→ MAOI inhibits this enzyme so NT doesn’t get broken down

→ more NT available = more released = more binding to post-synaptic cell

How do tricyclics and SSRI’s work?

both block reuptake so NT stays in synapse longer = greater chance NT will bind to post-synaptic cell

→ tricyclics = serotonin & norepinephrine

→ SSRIs = serotonin ONLY