Endocrine System
Difference between alpha and beta cells
Alpha (α) cells - Constitute about 17% of pancreatic islet cells
Secrete glucagon
Beta (β) cells - Constitute about 70% of pancreatic islet cells
Secrete insulin
Afferent - electrical away from the Muscle
Efferent - signals FROM the CNS to SKM
What is typical resting membrane potential? How do we overcome this ?
-55 mV
through a graded potential past the threshold from neurotransmitters or sensory neurons; considered passive since it comes from the neuron’s membrane
During muscle contraction, what protein does calcium bind to?
Troponin C of Actin protein
What is it called when there are elevated levels of glucose in the blood? What cells does this stimulate?
Purpose of insulin?
Hyperglycemia
Beta cells - secretes insulin
uptake glucose into the cell
Discuss the differences between PNS AND ANS
PNS-nervous tissue outside the Central Nervous System (CNS) and is divided into afferent and efferent divisions
ANS - conveys output from the CNS to smooth muscle, cardiac muscle, and glands, and is considered involuntary
Functions of Nervous Sytem (3)
Sensory : Sensory receptors detect external or internal stimuli, and relay sensory information to the brain and spinal cord for integration.
Integration : CNS analyzes sensory information, and makes decisions for appropriate responses.
Motor: Motor information is conveyed from the CNS through cranial and spinal nerves of the PNS to appropriate effectors (muscles and glands).
Discuss the properties of myosin AND actin
2 globular heads
Myosin heavy chain (MHC) is the motor protein of muscle thick filament
2 chains per myosin head
contains an ATP binding site and actin binding site
ACTIN:
Thin, Double stranded binding site for myosin
Individual actin molecule: G actin
G actin links together: F actin
Low levels of blood glucose is called?
What does this stimulate?
Hypoglycemia
alpha cells - glucagon - break down glucose (glycogenolysis)
What is the membrane potential based on?
*hint, how does it operate?
Voltage: electrical potential difference between opposite charges
Voltage that exists across the plasma membrane
Accumulation of positive and negative charges right along the membrane
Resistance: hindrance of flow of charges
Difference between graded potential and action potential?
Graded - occurs along dendrtites, mechanical or chemical- come from neurotransmitters or sensory neurons; considered passive since it comes from the neuron’s membrane
Action potential - occur due to the active membrane depolarization reaching a threshold to fire, caused by a shift of ions; occur along axons, voltage gated
Discuss regulatory and structural proteins
What protein is responsbile to stabilize the sarcomere during eccentric contractions?
TITIN
Tropomyosin
Covers the active sites on actin, preventing myosin from binding to actin when fiber is at rest
Troponin
Binds with Ca+2, changes shape, causes tropomyosin to move off active site, allowing myosin to bind to actin
Titin, Alpha-actinin, Myomesin, Nebulin, Dystrophin
Elastic proteins
Contribute to the alignment, stability, extensibility, and elasticity of sarcomere
Difference between water soluble and lipid soluble hormones
Lipid soluble: Carried in blood via transport proteins
Lipid soluble hormones such as steroids and thyroid hormones can easily pass through the lipid rich plasma membrane.
Steroid hormones; Thyroid hormones
Water soluble: Circulate alone/free in blood; Lipid insoluble hormones such as peptide hormones cannot pass through the plasma membrane and enter the target cell.
Can only interact with the surface of the target cell
These hormones binds to membrane receptors on the outer surface of the target cell's plasma membrane.
Amine hormones; Peptide/protein based hormones
Discuss depolarizing, repolarizing, and after-hyper polarizing phase
Depolarizing -
Negative membrane potential becomes less negative, reaches zero, then becomes positive
The rising of phase of the action potential. Occurs until the membrane potential goes up to +30mV
Na+ channel activation gates open
Repolarizing-
The falling of phase of the action potential. This occurs until the membrane potential gets back to rest –70mV; Na+ channel gates close and K+ open
Hyperpolarizing -
After resting membrane potential is re-established, the membrane potential becomes even more negative; Typically goes down to –90mV; K+ continues outflow, building up more negative charge
Discuss different types of channels
Ligand - Participate in the generation of graded potentials
Leak channels - establishes resting membrane potential
Mechanically gated - Involved in the formation of graded potentials (touch, pressure, tissue, stretching)
Voltage - Responsible for the generation and conduction of action potentials
Discuss the structure/ components of the Skeletal muscle fiber
& organization
Sarcolemma: plasma membrane of muscle fiber
Surrounds muscle fiber and regulates entry and exit of materials
Sarcoplasm: cytoplasm of muscle fiber - Site of metabolic processes for normal muscle fiber activities
Sarcoplasmic reticulum: smooth endoplasmic reticulum in muscle fiber - Stores Ca+2 needed for muscle contraction
Terminal cisternae: expanded ends of the sarcoplasmic reticulum that are in contact with the transverse tubules (2 + T-tubule = triad)- Site of Ca+2 release
Transverse tubule (T-tubule): extension of the sarcolemma into the sarcoplasm, wrapped around myofibrils - Quickly transport a muscle impulse from the sarcolemma throughout the entire muscle fiber
Muscle - Covered by Epimysium - Bundle of fascicles
Fascicles- Covered by Perimysium - Bundle of Muscle Fibers
Muscle Fibers (muscle cell)*- Covered by Endomysium - Contains myofibrils
Myofibrils - Contractile element - Composed of myofilaments
Myofilaments* Contractile proteins
Thick- myosin & Thin- actin, tropomyosin, and troponin
Discuss insulin-function uptake of glucose
1.Insulin binds to an insulin receptor in the plasma membrane of its target cell
2.Activates tyrosine kinase, causing them to phosphorylate each other at tyrosine amino acids
3.Sites serve as docking sites where insulin-receptor substrates (IRSs)can bind
4.Once phosphorylated, IRS are activated and trigger intracellular pathways
5.Causes insertion of glucose transporters (GLUTs); the isoform that is insulin-dependent is GLUT4
6.GLUT4 molecules enhances diffusion of glucose into the cell
List all the components of the Neuron and functions
Cell Body - Contains organelles; control center for neuron; Cluster of cell bodies in the PNS is called ganglion; cluster in CNS is called nucleus
Dendrite - receives signals from other neurons
Tips of axon terminals swell into Synaptic end bulbs
axon - Functions as the output portion of the neuron by generating action potentials and then propagating them toward another neuron, muscle fiber, or gland cell
Within synaptic end bulbs are synaptic vesicle - stores NTs
Myelin Sheath - increases speed of conductin of APs
Discuss signal transmission at a chemical synapse
1.An action potential arrives at a synaptic end bulb of a presynaptic axon
2.The membrane of the synaptic end bulb contains voltage-gated Ca+2channels in addition to the Na+ and K+ channels
depolarization phase of AP opens not only Na+ but Ca+2 as well
3.An increase in Ca+2 triggers exocytosis of the synaptic vesicles
This results in fusion of the synaptic vesicle with the presynaptic membrane, releasing neurotransmitter molecules into the synaptic cleft
Example: acetylcholine
4.Neurotransmitter molecules diffuse across the synaptic cleft and bind to neurotransmitter receptors on ligand-gated channels
5.This binding opens the channels and allow ions to flow across the membrane
6.As ions flow, voltage changes (postsynaptic potential)
may be depolarization or hyperpolarization based on which ion channels open
7.When a depolarizing postsynaptic potential reaches threshold, it triggers an action potential in the axon
Discuss Excitation contraction coupling
1.A nerve AP in a somatic motor neuron travels to the NMJ and triggers the release of ACh
2.ACh binds to receptors in the motor end plate potential causing depolarization of the sarcolemma (EPP) by opening ion channels and allowing Na+ in and K+out of the muscle cell
Acetylcholinesterase destroys ACh so another AP does not arise unless more ACh is released
3.Depolarization creates a wave of AP across the sarcolemma and down the T-tubule
4.This triggers dihydropyridine receptors (DHP) to open Ca+2 release channels (ryanodine receptors)
5.Ca+2 is released from the terminal cisternae of the sarcoplasmic reticulum (SR) into the sarcoplasm
6.Ca+2 binds with troponin, which removes the blocking action of Tropomyosin from the actin binding sites
7.ATP binds to myosin, and is hydrolyzed, giving myosin energy
8.Myosin attaches to actin and forms a cross bridge
9.Myosin cross bridge pivots, pulling the thin filament past the thick filament toward center of sarcomere
10.ATP attaches to myosin, detaching from actin; contraction continues until AP stops and Ca+2 is returned (sequestered) to the SR