1 - CELL AND MUSCLE PHYSIOLOGY

Greater

Permeability of the cell membrane to K+ is ________ than its permeability to Na+

Proteins (55%)

Integral and peripheral proteins make up majority of the cell membrane

Macromolecule comprising majority of the cell membrane

Phospholipids (25%)

Most abundant lipid component of the cell membrane

Cholesterol

Cell membrane component that confers membrane fluidity and determines permeability of water-soluble substances

Glycolipids

Cell membrane component that confers antigenicity

Glycocalyx

Loose carbohydrate coat of the cell surface

Tight; Hydrophobic

Integral proteins have _______ attachment using ____________ interactions

Loose; Electrostatic

Peripheral proteins have ______ attachment using ______ interactions

Osmosis (using Aquaporins)

Water moves through cell membranes by means of

Simple diffusion

Lipid-soluble substances (non-polar, hydrophobic) move through cell membranes by means of

Carrier-mediated transport

Water-soluble substances (polar, hydrophilic) move through cell membranes by means of

Zonula occludens (tight junctions)

Intercellular structures that divide the cell into apical and basolateral side

Gap junctions

Made up of functional units called connexons, which in turn, are composed of connexins

Intercellular structures that allow rapid intercellular communication by acting as bridges for sharing of small molecules

Claudins

Integral proteins found in tight junctions

Permeability, area, concentration gradient

J = PA x (C1 - C2)

Factors that affect simple diffusion of a substance across a membrane

Stereospecificity, saturation, competition

Three important characteristics of carrier-mediated transport

GLUT2

GLUT transporter found in liver, pancreatic beta cells, basement membrane of small intestine, kidney

GLUT4

Insulin-dependent glucose transporter found in muscle and adipose

Transports 3 Na+ out, 2 K+ in

Source of energy: ATP hydrolysis (primary active transport)

Activity of the Na+-K+ ATPase

Na+ gradient (created by the Na+-K+ ATPase)

Source of energy in secondary active transport

From hypotonic solution to hypertonic solution

Direction of water movement in osmosis

Reflection coefficient (between 0 and 1)

RC 1: no solute penetration; effective osmole

RC 0: complete solute penetration; ineffective osmole

Effective osmotic pressure is calculated by multiplying osmotic pressure with the ________________

Equilibrium potential (Nernst potential)

The greater the concentration gradient, the greater the size of the diffusion potential

Diffusion potential that exactly balances (opposes) the tendency for diffusion caused by a concentration gradient

Nernst potential for Na+ and K+, K+ leak channels, Na+-K+ ATPase

The resting membrane potential is established by

Stereotypical size and shape, Propagation, All or none response

Characteristics of an action potential

Absolute refractory period

Basis: closed Na+inactivation gates

Occurs during an AP when no new AP can be elicited no matter how large the stimulus

Relative refractory period

Basis: prolonged opening of K+channels

Occurs during an AP when a new AP can be elicited but requires greater than usual Na+ inward current

Larger nerve fiber size, Myelination

Factors that increase conduction velocity

Astrocytes

Glial cell that helps form the blood-brain barrier, maintain appropriate ion concentrations, and helps in the reuptake of neurotransmitters

Nodes of Ranvier

Allow saltatory conduction

Unmyelinated portions of the axon

Voltage-gated calcium channels (VGCC)

These channels are targeted by autoantibodies in patients with Lambert-Eaton Myasthenic Syndrome

Channels in the terminal boutons of the axon that trigger release of neurotransmitter into the synapse

Opening of Cl- channels (Cl- influx), opening of K+ channels (K+ efflux), closure of Na+ or Ca2+ channels

Ionic currents that generate fast inhibitory postsynaptic potentials (IPSP)

Na+ influx,  Ca2+ influx

Ionic currents that generate fast excitatory postsynaptic potentials (EPSP)

Acetylcholine (ACh)

Levels are decreased in Huntington and Alzheimer dementia

Neurotransmitter that opens Na-K channel that depolarizes the muscle endplate

Dopamine

Also known as prolactin-inhibiting factor or PIF

Neurotransmitter secreted by the hypothalamus to inhibit prolactin

Nitric oxide (NO)

Inhibitory non-adrenergic, non-cholinergic neurotransmitter that is a permeant gas and most importantly, a vasodilator

Glycine

Increased Cl- influx

Main inhibitory neuro-transmitter in the spinal cord

GABA

Increases Cl- influx (GABAA) or K+ efflux (GABAB)

Main inhibitory neuro-transmitter in the brain

Glutamate

Main excitatory neurotransmitter in the brain

Glutamate

Neurotransmitter for fast pain

Substance P

Neurotransmitter for slow pain

Intrafusal fibers

Innervation: gamma motor neurons

Skeletal muscle fibers that detect changes in muscle length

Extrafusal fibers

Innervation: alpha motor neurons

Skeletal muscle fibers for voluntary muscle contraction

Slow, red fibers that use oxidative phosphorylation to allow sustained contraction in endurance training

1 slow, red ox with a perfect posture

Characteristics of type 1 skeletal muscle fibers

Fast, white, anaerobic glycolysis, for weight/resistance training, sprinting

2 fast white sprinting antelopes

Characteristics of type 2 muscle fibers

Unitary smooth muscle

(+) gap junctions, (+) syncytium

Smooth muscle type responsible for GROSS motor movements

Multi-unit smooth muscle

(-) gap junctions

Smooth muscle type responsible for FINE motor movements

Troponin T

T for tropomyosin

Troponin subunit that attaches the troponin complex to tropomyosin

Troponin I

I for inhibition

Troponin subunit that inhibits actin-myosin binding

Troponin C

C for calcium

Troponin subunit that serves as a calcium binding protein

A band

Part of the sarcomere that remains constant in length when the muscle contracts

H band, I band, the entire sarcomere

Mnemonic: H-I-S

Parts of the sarcomere that shorten during contraction

Transverse tubules or T-tubules

Contain dihydropyridine receptors (DHPR)

Invaginations of the sarcolemma; spreads the action potential to all parts of the muscles

Dihydropyridine receptors (DHPR)

Voltage-sensitive channels in the T-tubules that activate ryanodine receptors

Sarcoplasmic reticulum

Stores and releases Ca2+ needed for muscle contraction

Ryanodine receptor

Ca2+ release channel in the sarcoplasmic reticulum activated by DHPR

Sarcoendoplasmic reticulum Calcium ATPase (SERCA)

Pumps Ca2+ from ICF back to the SR

Botulinum toxin

Blocks release of ACh from presynaptic terminals

Curare

Competes with ACh for receptors on motor end plate

Neostigmine

Inhibits acetylcholinesterase

Hemicholinium

Blocks reuptake of choline into presynaptic terminal

Isometric

No muscle shortening or lengthening

Type of muscle contraction where length is held constant while muscle contracts

Isotonic

Type of muscle contraction where load is held constant while muscle contracts

Rigor mortis

Usually occurs 3-6 hours after death due to lack of ATP

Ca2+ influx (Phase 2)

Ionic event responsible for the plateau of the cardiac action potential

Phase 4 (unstable RMP), Phase 0 (depolarization), and Phase 3 (repolarization)

No phase 1 and phase 2

Phases seen in pacemaker action potentials

Myosin light chain kinase (MLCK)

MLCK is activated by calcium-calmodulin complex

Phosphorylates and activates myosin heads

Myosin light chain phosphatase (MLCP)

Dephosphorylates and inactivates myosin heads

Calmodulin

Smooth muscle protein that binds calcium (analogous to troponin C)

Caldesmon, calponin

Smooth muscle proteins that inhibit contraction (analogous to troponin I)

Latch mechanism

Allows smooth muscle to maintain sustained contraction with minimal energy usage

Na+ influx

Ionic event responsible for P0 (upstroke) of the AP in skeletal muscle

Ca2+ influx

Ionic event responsible for P0 of the AP in the SA node

Na+ influx

Ionic event responsible for P0 of the AP in the atria, ventricles, Purkinje fibers

Cardiac muscle, Smooth Muscles

Ca2+-induced Ca2+ release is seen in

Cardiac muscle, unitary smooth muscle

Muscle types with gap junctions

Smooth muscle

Skeletal and cardiac muscle have actin-based regulation (thin filament-regulated)

Only muscle type with myosin-based regulation (thick filament-regulated)