Week 6 Physiology Knowt

electrogenic/electrogenerative/electroreceptive

electrogenic: generating electricity

• electric eel

• electric ray

electrogenerative: generate their own electricity

• elephant nose fish

• knifefish

electroreceptive: receive electricity

• platypus

• sharks

electricity

separation or manipulation of electric charge

bioelectricity

electrical phenomena generated by living organisms

every living cell has

transmembrane electrical potentials

voltage across the plasma membrane

communication inside

charge carriers

mostly electrolytes (Na+, K+, Cl+, Ca²+)

not electrons (e-)

voltage (electrical potential)

across every living cell in the body

• separation of charge

difference expressed in volts (stored potential energy)

opposite charges attracts & like charges repel

cathode attracts cations

anode attracts anions

electrical activation of switches

open channel

allow through transmembrane proteins triggered/turned on

higher concentration of K+ in cell

wants to move out of cell via facilitated diffusion

• positive charge leaves the cell

• inside becomes more negative

• outside becomes relatively more positive

the more K+ that leaves, the more negative the inside becomes

eventually the negative charge inside starts pulling K+ back into cell

concentration vs. electrical force for K+

concentration force: wants K+ to leave

electrical force: wants K+ to come back in

electrochemical equilibrium

where the concentration force and electrical force balance

• use nernst equation to find

equilibrium potential

the membrane voltage where an ion has no net movement because the electrical and concentration forces balance

• use nernst equation to find

K+ and Na+ values inside & outside of cell

K+

inside: 140 mM

outside: 5 mM

• K+ leaves inside of the cell until inside becomes more negative

Na+

inside: 10 mM

outside: 140 mM

• Na+ wants to enter the cell, inside becomes more positive

membrane potential depends on which ion has more influence

K+ and Na+ channels

more K+ channels open:

• K+ has more influence

• membrane becomes more negative

more Na+ channels open:

• Na+ has more influence

• membrane becomes more positive

Goldman-Hodkin-Katz (Goldman Equation) used here

Depolarization

membrane potential becomes more positive

Ex.: Na+ enters, Ca²+ enters

• makes cells more activa/excited

Hyperpolarization

membrane potential becomes more negative

Ex.: K+ leaving cell, Cl- entering

• makes cells less active

similar gradients

Na+ & Ca²+

• both higher outside & lower inside

• membrane potential as they move in…becomes more positive

K+

• higher inside & lower outside

• membrane potential becomes more negative as K+ enters

Cl-

• higher outside & lower inside

• membrane potential becomes more negative as Cl- enters

Na+/Ca²+ enter cell: depolarization…active cells

K+/Cl- enter cell: negative membrane potential…inactive cells

electrical triggering by depolarization

neurotransmitter release

hormone release

muscle contraction (skeletal, cardiac, smooth)

• Ca²+ enters

• plasma membrane depolarization (more positive)

electrical signals are important for:

• neurons

• endocrine cells

• muscle cells

opening/closing channels

open Na+/Ca²+ channels: depolarization

close K+ channels: depolarization

channels allow ions through at a rate of 10,000 times faster than a pump

resting membrane potential

voltage difference between inside & outside of plasma membrane in resting neuron

• cell at rest has negative membrane potential

• usually closer to K+ equilibrium potential than the Na+ potential

• normally more pathways for K+ than Na+ at rest

Resting Membrane Potential (Equilibrium Potential for Na+/K+)

• inside of cell compared with outside of cell

ion permeability

K+ is more permeable in resting cells

when K+ channels open…this keeps membrane potential negative

fat is NOT a conductor (hydrocarbon tails are insulated)

Na+/Ca²+ opened in excited cells, closed in resting cells

sodium potassium pump

pump 3 Na+ out, 2 K+ in

loss of +1 charge from inside of cell

• makes the inside of the cell more negative

properties of all cells

• negative resting membrane potential

• some use electrical signals more extensively

  • neurons

  • muscle cells

  • endocrine cells

  • this leads to long-distance signaling

long-distance signaling

Endocrine & Nervous system

• make use of extracellular chemical messages

• have receptors on target cells (cells that receive message)

Nervous System

• uses electrical signals along neurons

• releases neurotransmitters

• fast

• usually brief

• voluntary (skeletal muscle) & involuntary control (ANS…cells are close)

neuron connects close to its target & chemical messenger travels tiny distance across synapse

Endocrine System

• releases hormones in the blood

• slower

• hormones travel long distance

• long-lasting

• involuntary (growth hormone…cells are far apart)

hormone released to blood & travels through body

neurotransmitters

chemical messengers released by neurons

• hydrophilic

• packaged in vesicles

• released by exocytosis

• receptors are generally on the surface of the target cell

can be:

• Excitatory

  • depolarize cell…more positive

• Inhibitory

  • hyperpolarize cell…more negative

same neurotransmitters can be excitatory in 1 tissue & inhibitory in another

• depends on receptor & target

cell to cell chemical signaling

chemical messengers often are transmembrane proteins

1) chemical signal is released outside of cell

2) receptor for signal is:

• on plasma membrane (extracellular)

• in cytoplasm (intracellular)

cell to cell chemical signaling: Autocrine

chemicals that exert effects on the same cells that secrete them

• “self signaling”

• cell releases chemical messenger…same cell has receptors for it

Ex.: Waking yourself up when falling asleep driving

Ex.: Skin cells are damaged…ATP releases…tells itself its damaged

cell to cell chemical signaling: Paracrine

chemicals released by cells that effect other nearby cells

Ex.: Yelling hey to wake up the driver that’s falling asleep

Ex.: Damaged cells release ATP…nearby cells detect it & get to work

cell to cell chemical signaling: Endocrine

secretion into the blood for signaling with cells far away

• “long distance”

• chemical messenger travels through the blood to reach distant target cells

Ex.: In back of bus full of people, only one to realize driver is falling asleep

Ex.: Hormones

cell to cell chemical signaling: Exocrine

secretion into the external environment through duct, usually in an epithelium

• releasing substances through ducts or onto surfaces

  • saliva

  • digestive secretions

  • sweat

Exocrine vs. Endocrine

Endocrine: hormones/signaling

Exocrine: secretion of substances

Nervous System Organization

1) Sensory input: sensory receptors detect changes inside & outside of body

• CNS makes decisions & sends motor output

2) Integration: processing & interpretation of sensory input via CNS

3) Motor output: response caused by activation of effector organs (muscles & glands)

• signal goes to a target

affterent vs efferent

afferent: arriving

• info traveling toward CNS

• usually sensory

efferent: exiting

• info traveling away from CNS

• usually motor

CNS vs. PNS

CNS: brain + spinal cord

• integration/command center

PNS: everything else

• sensory/motor input

Neuronal signaling

sensory cells (have sensory receptors)

sensory neuron (PNS)

CNS

motor neuron (PNS)

muscle or gland

*neurotransmitter between every step

neurotransmitters for nervous system

• acetylcholine*

• ATP

• epinephrine/norepinephrine*

• glutamate (commonly inhibitory)

• GABA

• serotonin

endocrine system is much more complicated…many more

Peripheral Nervous System Organization

sensory (input, afferent)

motor (output, efferent)

• somatic (we can control, voluntary, Ex. skeletal m.)

• autonomic (we can’t control, involuntary, autonomic, Ex. cardiac/smooth m./glands

  • parasympathetic (rest/digest, feed/breed)

  • sympathetic (fight/flight)

*acetylcholine used in somatic & parasympathetic

• all skeletal muscles have receptors for acetylcholine

parasympathetic: slows down heart, increases digestion (ACH)

sympathetic: speeds up heart, decreases digestion (norepinephrine/epinephrine)

acetylcholine vs. norepinephrine/epinephrine

acetylcholine

• skeletal muscle…excitatory

• parasympathetic heart…slows heart rate

• digestive system…increased activity

• can be excitatory/inhibitory for parasympathetic

norepinephrine/epinephrine

• increased heart rate

• prepare body for fight or flight

• can be excitatory/inhibitory for sympathetic

*these two work against each other

sensory input

sensory cells communicate to sensory neurons

• sensory cells pick up stimulus via sensory receptors:

  • protein-based

  • many are transmembrane proteins

  • either ion channels or G-protein coupled receptors

Ion channels: movement changes membrane potentials

G-protein coupled receptors: have 7 transmembrane domains, detect a stimulus, activate proteins in cell

produce cellular response

chemoreceptors

bind to chemical message, activate another protein in cell

photoreceptors

take photon of light via vitamin A molecule, get activated, G1 protein coupled receptor

mechanoreceptors

detect mechanical force

Ex.: touch, pressure, stretch, hearing, body position

can also open ion channels

• ions move

• membrane depolarizes

• signal is sent to nervous system

includes proprioceptors: detect where body parts are position

• Ex.: know where body is without looking

nociceptors

detect potentially damaging stimuli (pain occurs when sensory receptors are overstimulated)

TRP channels (transient receptor potential) channels

sensory ion channels

different TRP channels respond to different stimuli

• TRPA1: chemicals like mustard/wasabi & irritants

• TRPM8: associated with menthol/cooling sensation

• TRPV1: detects heat/capsaicin from hot peppers

  • senses temp/chemicals…depolarizes plasma membrane

capsaicin: activates TRPV1 (produces sensation of heat/burning

Inputs & sensory damage

physical: mechanical, electromagnetic (light)

inputs: chemical or physical

sensory damaged…can’t feel pain (due to a mutation on Na+ channel)

• leprosy interferes with ability to sense pain…leads to damage