physiology exam 1: neuronal excitability + CNS

three layers of spinal meninges

dura mater (tough/rigid), arachnoid mater, and pia mater (innermost)

spinal nerves

31 pairs extend from the spinal cord: responsible for bringing sensory into from receptors to CNS and bringing motor info from CNS to effectors

subarachnoid space

CSF flows through here to spinal cord; can be draws from this region between L4 and L5

dorsal root

afferent division bundle of axons that carry sensory input to CNS

ventral root

efferent division bundle of axons that carry motor output from CNS to effectors

gray matter

processes sensory input and motor output; made of soma and nuclei (unmyelinated regions of neural cells)

white matter

contain ascending (input) and descending (output) tracts; lateral and central columns initiate action; dorsal delivers input

dorsal columns feel:

touch, pressure, vibration, and proprioception

ventral spinocerebellar tract feels:

movement

spinothalamic tract feels:

skin (pain, temp, itch, tickle)

vestibulospinal tract

motor tract that controls balance via ears (cochlear)

motor tracts that allow for precise controlled limb movements

ventral and lateral corticospinal tracts

spinothalamic tract feels:

pain, cold, and heat

reflex arc components

receptor to sensory neuron to integration center (cns) to motor neuron to effector

brain protection layers

cranium, meninges, blood brain barrier, cerebrospinal fluid

dura mater details

two layers plus sinus vein that supplies blood to bbb

where the brain can get a feel for the chemical environment in the cranium

in the diencephalon where circumventral organs line the third ventricle: includes hypothalamus, pineal gland, and thalamus

cerebrospinal fluid

produced by choroid plexus by ependymal cells that line the 3rd and 4th ventricles; serves as shock absorber and protects from chemical injury; circulates throughout cns and subarachnoid space; approx 15ml per day is produced

olfactory nerve

I; sensory; smell input from nose

optic nerve

II; sensory; visual input from eyes

oculomotor nerve

III; motor; eye motion, pupil changes, lens adjustment

trochlear nerve

IV; motor; eye movement

trigeminal nerve

V; both; facial nerves (three)

abducens nerve

VI; motor; eye movements

facial nerve

VII; both ; tongue movement, facial expression, saliva, tears

vestibulocochlear nerve

VIII; sensory; hearing and balance equilibrium

glossopharyngeal nerve

IX; both; taste and pharynx

vagus nerve

X; both; digestion, glands, heart

accessory nerve

XI; motor; muscle control of head and neck

hypoglossal nerve

XII; motor; tongue movements

brainstem components

the midbrain contains the four colliculi and substantia nigra and red nuclei; other regions are pons, and medulla oblongata

functions of colliculi

vision tracking (superior) and auditory startle reflexes (inferior)

substantia nigra and red nuclei function

control body movements and dopamine production; no dopamine = parkinson’s disease

pons function

pontine respiratory control center

medulla oblongata function

lower portion of brain stem control cardiovascular functions and works with the pontine respiration center

cerebellum

regulates posture, balance, and the quality of motor movements

thalamus structure and function

masses of gray matter in the upper diencephalon that relay almost all sensory input to the cerebral cortex and contributes to motor control

efferent division

PNS carries out effects (responses to input): somatic controls skeletal, while autonomic controls automatic functions like gastric digestion (enteric) and smooth muscle contractions and gland excretions (parasympathetic and sympathetic)

axon

extension of neural cell into the cytoplasm

microglia cells

remove pathogens and debris (quality control)

oligodendrocytes and schwann cells

produce myelin sheaths in cns and pns respectively

astrocytes

form tight junctions for synapses, the blood brain barrier, and neural development

ependymal cells

line the ventricles of the brain and produce csf as part of the choroid plexus

neural plasticity

ability to change throughout life or reroute synaptic contacts

neural repair

limited to pns and occurs if the cell soma and schwann cells are still healthy; does not occur in cns due to scar tissue formation from astrocyte growth and lack of growth hormones

ligand gated channels

open or close in response to a chemical stimulus; found in dendrites of sensory neurons

mechanically gated channels

open or close in response to physical stimulation; found in dendrites of touch, pressure, and pain receptors

voltage gated channels

open in response to a change in membrane potential; found in axons of neurons

ohms law

I = V/R: current of charged particles is determined by voltage over resistance. membranes and myelin sheaths are high resistance materials, which allows them to create resting potential energy via the difference in charges inside and outside the cell

sodium potassium pump

3 na+ are pumped out and 2 k+ are pumped in; restores the resting membrane charge by counteracting the leak of these ions against their concentration gradients thru leak channels; results in net positive outside and net negative inside the cell

graded potentials

small deviations in membrane potential that can depolarize or hyperpolarize the cell to prompt or inhibit a potential AP occurrence; the larger the stimulus, the greater the response

action potential

a stimulus depolarizes the cell membrane to threshold and an action follows; all or nothing series of events

depolarization phase

na+ channels are open after a stimulus causes depolarization

recovery phase

voltage k+ channels open and na+ channels close

ultra recovery phase

mini hyper polarization after recovery to compensate before equilibrium at -70 mV; voltage k+ gates are still open and na+ channels are closed

synapse

the point at which one neuron communicates with another neuron or target tissue to relay a signal

how to block conduction of action potentials

inhibit (bind to) sodium channels

isps vs esps

isps inhibits a neuron by causing hyperpolarization of the membrane whereas esps excites a neuron by causing depolarization; the sum of isps and esps that a neuron receives determines if the membrane potential reaches the threshold requires for an AP

ionotropic receptors

ligand gated channels that are opened by nicotinic ach trigger esps

metabotropic receptors

g protein receptors that are bound by muscarinic ach and cause isps

termination of signal

enzymatic degradation, reuptake, or release

spatial vs temporal summation

multiple neurons hit a specific communal ps receptor with NTs; temporal summation is when neuron bombards one target with NTs to stimulate an AP

diverging and converging neural circuits

one presynaptic neuron synapses with multiple post synaptic neurons (cascade style, like optic input to multiple brain regions); multiple presynaptic neurons converge at a single post synaptic neuron (like parts of the eye to optic nerve)

reverberating and parallel circuits

action potentials get sent through the loop constantly because later neurons synapse with earlier ones (e.g. breathing muscles); action potential stimulates different groups of neurons which synapse at a common neuron at different times, causing a recurrence (e.g. seeing circles after staring at the sun)

gap junctions

connexins for tunnels called connexons that allow for rapid diffusion and communication of ions and small molecules

hormones vs local mediators

hormones travel through the bloodstream to distant target cells whereas local mediators travel through interstitial fluid to nearby cells

types of local mediators

cytokines for cell growth, nitric oxide for blood vessel relaxation, growth factors, and eicosanoids for pain signal delivery

leukotrienes

bring leukocytes and inflammation; produced by lipoxygenase pathway; not blocked by aspirin

prostaglandins

cause inflammation, fever, and pain intensification through changes in smooth muscle contraction and signal transmission; come from cyclooxygenase pathway; inhibited by aspirin and glucocorticoids

thromboxanes

contract blood vessels and cause platelet gatherings; produced from cyclooxygenase pathway; inhibited by aspirin and glucocorticoids

eicosanoids derivative

membrane phospholipid —> phospholipase A2 —> arachidonic acid —> cyclooxygenase or lipoxygenase pathway

extracellular messenger classifications

water soluble to go membrane receptors and travel freely through the bloodstream while lipid soluble ones enter the cell to go to a receptor in the nucleus and might have to travel via transport protein in the bloodstream due to their nonpolar/hydrophobic structure of carbon chains and hydrocarbon rings

receptor properties

specificity (does it fit), affinity (is it the target cell’s favorite ligand), saturation, and competition (which ligand wins and causes an actions or lack thereof)

affinity of adrenergic receptors

alpha has no E and neither does B3 (norepinephrine > epinephrine); B1 favors no one

signal transduction of water soluble messengers

bind to receptor, second messenger is sent, relay protein or kinase is activated, effector protein in activated and cellular response is carried out

signal transduction of lipid soluble messengers

enter the cell via bypassing the membrane, bind to intracellular receptors (dimerization!), the complex binds to a dna region and alters transcription of a gene that carries out a specific function coded for by the original messenger

nitric oxide signal transduction

NO binds to guanylyl cyclades, which turns gtp into cgmp as a second messenger, which activates kinase g, which inactivates mlck thus causing the relaxation of the muscle cell

receptor tyrosine kinase

ligand lands, tyrosine kinases dimerize and cross phosphorylate each other, a relay protein docks and gets a phosphate thus activating the rest of the intracellular pathway

guanylyl cyclase receptor

kinase g phosphorylates serine or threonine in an effector protein after receptors dimerize and convert gtp into cgmp, which activates kinase g

enzyme coupled receptor: janus kinase

ligand binds, causing dimerization of receptors and phosphorylation of both receptors and attached janus kinases (4 P total); a stat protein docks and becomes active after gaining a phosphate and then enters the nucleus to stimulate/increase the transcription of the gene for an effector protein, which then carries out the cellular response

g protein coupled receptors

a messenger binds to a gpcr, the g protein alpha subunit separates and triggers a change in a target protein (ex: adenylyl cyclase) which then activates the next step in the pathway via a second messenger or phosphorylation of a trigger kinase

gpcr ip3 example

Gq protein activates phospholipase c, which pulls pip2 from the plasma membrane and turns it into ip3 and dag, which activate ca2+ channels in the endoplasmic reticulum and kinase c respectively, which then phosphorylates an effector protein and triggers a cellular response

cholera toxin

leads to Gs continues activation and unlimited levels of camp, which triggers the secretion of lots of salts and water into the large intestine and causes life threatening diarrhea

pertussis toxin

permanently inactivates Gi; adenylyl cyclase is unable to be inhibited, causing whooping cough