Answers Objectives-2, BIO 3360
- Neurons are the cells that receive, process and transmit information and make up about 1/2 of the nervous system. Neuroglia are the supportive cells such as astrocytes. Polarized means that there is a charge difference inside vs. outside of the cell; depolarized it becomes less negative or more positive in cell and hyperpolarized it becomes more negative inside cell. Repolarized is when a cell returns from a changed state back to its resting membrane potential. Local potential describes the permeability change and RMP change occurs locally and graded is the magnitude of the change. It is called local, because it is a localized change in membrane potential due to a change in permeability to sodium and it is graded in response to stimulus, it may be hyperpolarization or depolarization. An action potential is defined as depolarization to threshold. The steps include that the membrane becomes more permeable to sodium and sodium enters (depolarization) until a threshold is reached at which point it becomes a positive feedback process. The sodium gates rapidly close and then the potassium gates open resulting in repolarization. It overshoots a bit and then hits the RMP. An action potential is an all or none phenomenon. This means you either have enough depolarization for it to become a run away process or not which means you either reach threshold or not. Once you reach threshold all AP’s are identical. Threshold is the amount of depolarization it takes to make the voltage sensitive gates open and the process of depolarization become a run away cycle. Saltatory conduction is the jumping of nerve impulse conduction from one node of Ranvier to next. Absolute refractory period means a rest period following an AP that will not result in another AP no matter how strong the stimulus is; a relative refractory period is following an AP, when a stimulus can cause another AP if it is a strong stimulus.
- Dendrite is receptive portion, cell body integrates, axon conducts, terminal transmits impulse to next cell.
- Schwann cells form a regeneration scaffolding allowing regrowth of axons and they are only in the PNS.
- Schwann cells form a regeneration scaffolding allowing regrowth of axons and they are only in the PNS.
- -70 mV is an average RMP, with potassium diffusing out but being attracted to the fixed anions inside the cell and able to do so, the sodium wants to diffuse in and is attracted by electrical charge but the resting membrane is not permeable to sodium and the sodium/potassium pump is shipping three positive sodium out but only bringing in 2 potassium.
- White is myelinated vs. gray is non-myelinated.
- A neurotransmitter is a chemical released at synapse and e.g. are acetylcholine, norepinephrine, dopamine, serotonin…A synapse is a junction between neurons or neuromuscular junction. Reciprocal and rectifying synapses are electrical synapses and in reciprocal, the electrical current can flow equally in both directions but in rectifying the current flow can only pass in one direction. A presynaptic neuron is coming into the synapse and postsynaptic is the neuron leaving the synapse. The space between the neurons is the synaptic cleft; the vesicle is containing neurotransmitter in the presynaptic neuron. The end plate potential is depolarization in the sarcolemma of neuromuscular junction and it is a graded potential. Depolarization in the postsynaptic neuron is EPSP (excitatory postsynaptic potential). Hyperpolarization in the postsynaptic neuron is IPSP (inhibitory postsynaptic potential), and both are graded. Presynaptic inhibition is where the amount of NT released by the excitatory neuron is reduced and facilitation is where the amount of NT is increased.
- When an AP in the presynaptic neuron reaches the axon terminal voltage-gated Ca channels open. • Ca ++flows into the knob and triggers the release of the neurotransmitter • Neurotransmitter results in IPSP or EPSP in postsynaptic neuron. Neurotransmitter is removed from cleft. • Ion channels return to initial condition.
- The ACH opens the Na-K channels and you can get depolarization due to Na influx.
- ACH is broken down by ACHesterase & diffuses away. Calcium is pumped out of synaptic knob.
- Spatial summation is as in convergence in which several presynpatic neurons all release enough NT together to reach threshold in postsynaptic neuron; temporal summation is in time where rapid release of neurotransmitter results in enough to reach threshold in postsynaptic neuron.
- Any part of these five steps may be affected by a poison or medication. 1. When an AP in the presynaptic neuron reaches the axon terminal voltage-gated Ca channels open. 2. Ca ++flows into the knob and triggers the release of the neurotransmitter 3. Neurotransmitter results in IPSP or EPSP in postsynaptic neuron. 4. Neurotransmitter is removed from cleft. 5. Ion channels return to initial condition. Additionally, poisons and medications can act as neuromodulators, which influence the neurotransmitters by potentiating their effects, blocking them (for example endorphins block the pain neurotransmitters).
FUNCTIONAL ORGANIZATION of NERVOUS SYSTEM
- CNS is brain and spinal cord. PNS is everything else including afferent – bringing sensory info towards CNS, and may originate externally (somatic) or internally (visceral). Efferent is the motor portion taking info away from CNS and either goes to skeletal muscle (somatic) or to smooth muscle, cardiac muscle & glands (visceral = ANS). ANS is in turn divided into parasympathetic and sympathetic. Parasympathetic is for rest and digest; sympathetic is for fight or flight. Centralization is a centralized integration region which tends to be in the head region. Cephalization has that centralized area located in the head. Cholinergic neurons release ACH as neurotransmitter and are found as the preganglionic neurons in both divisions and the postganglionics in PNS; adrenergic releases norepinephrine as neurotransmitter and is found as the postganglionic neuron in SNS only.
- Nuclei are groups of neuron cell bodies in the CNS and ganglia are the same in the PNS.
- White is myelinated axons and gray is unmyelinated axons or nerve cell bodies/dendrites.
- Somatic efferent uses one motor neuron that travels to skeletal muscles whereas in Autonomic Nervous System,2 neurons (preganglionic and postganglionic) travel to smooth muscle, cardiac muscle, and glands.
- ACH receptor is nicotinic on postganglionic neurons in both divisions; ACH receptor is muscarinic in effector in PNS; NE/E receptor is alpha or beta on effector in SNS.
- Atropine is anti-muscarinic so blocks PNS.
- PNS causes decreased heart and respiratory rates, small airways, increased digestion, constriction of pupils, and contracts bladder wall while relaxing its sphincter. SNS does the opposite but is the only division swerving sweat glands (causes sweating) and blood vessels. Cutaneous and abdominal blood vessels constrict in SNS but those going to skeletal muscles dilate.
MUSCLE – PART ONE
- Tendon is connective tissue connecting muscle to bone; myofiber is a muscle cell, myofibrils are cylinders that are striated within cell; a sarcomere is the functional unit of contraction containing actin and myosin between 2 Z lines; a sarcoplasmic reticulum is the muscle cell’s ER filled with calcium; a sarcolemma is the cell membrane of muscle cell; a T tubule is the extension of cell membrane to SR; myofilaments are the muscle proteins including actin and myosin. Cross bridge is between the actin and myosin heads. The power stroke is the swiveling of the myosin heads towards the center of the sarcomere pulling the actin with it.
- Skeletal and cardiac muscles are striated and smooth muscle is not.
- Muscle allows movement, guards exits & entrances, posture, support and heat production.
- A bands are dark region containing myosin and overlapping actin; I bands are light region containing actin only; H zone is within A band and contains myosin only; Z line anchors actin and is end of sarcomere. Myosin is a thick myofilament which looks like 2 golf clubs wound together with the heads having a binding site for actin and ATP; actin is a thin myofilament that looks like two strands of beads wound together with binding site for myosin. Tropomyosin is another thin myofilament that looks like a ribbon wrapping around actin and blocking the active sites and is held together with spots of “glue” called troponin which holds tropomyosin onto actin and has a binding site for calcium. Troponin is a thin myofilament that binds tropomyosin to actin.
- Filaments in each sarcomere move past each other propelled by movement of cross bridges. • Heads of myosin bind to the actin (cross bridge). • The heads move producing tension that moves the thin filament. • The bond between the head and the actin is broken. • Another cycle starts. Excitation contraction coupling is • Sequence of events by which an AP on the sarcolemma leads to cross-bridge activation. • AP does not act directly on the filaments but induces an increase in [Ca ++].
- ATP is needed to energize the myosin head for the power stroke and is needed for actin & myosin to let go of each other for relaxation.
- Calcium is like the “on-off” switch for muscle contraction. It will determine whether or not muscle can contract. Calcium binds troponin which moves the tropomyosin out of the away allowing for cross bridges to form.
- Lack of ATP results in muscle fatigue. After exercise, the oxygen debt is through breathing to replenish ATP and glycogen debt, through eating, is to replenish glucose.
- Slow twitch (type I) are slow but fatigue resistant and geared towards aerobic metabolism with lots of blood supply, mitochondria and myoglobin; fast twitch glycolytic (IIb) are fast and fatiguable geared towards anaerobic metabolism with few myoglobins, little blood supply; Fast twitch oxidative are the IIb but with exercise they can do a bit more aerobic metabolism (type IIa).
MUSCLE – PART TWO
- Isometric contraction develops tension but muscle length does not change; isotonic involves shortening. The mechanical response to a single AP is a muscle twitch. Motor neuron plus how ever many muscle cells it innervates is the definition of a motor unit. • Tension: Force exerted by a contracting muscle on an object. • Load: Force exerted on the muscle by the weight of an object. Muscle shortens (and moves a load) when tension > load.
- latent pd; contraction pd; relaxation pd
- Maximal contraction shows some overlap of actin & myosin filaments at the beginning of the contraction.
- Heavier load results in slower speed.
- Wave = Temporal Summation: increase in the mechanical response of a fiber to successive APs; complete tetanus is this temporal summation but is so rapid that it is complete contraction without any relaxation. Incomplete tetanus has a bit of relaxation.
- Multiple motor unit summation = spatial summation and many individual motor units combine their contractions for a stronger whole muscle contraction; treppe is warming up; asynchronous motor unit summation is alternating which motor units are working so fatigue doesn’t occur; muscle tone is some motor units contracting but not enough for movement and therefore makes muscles feel firm.
MUSCLE – PART THREE – SMOOTH MUSCLE
- Calcium binds to calmodulin which unblocks the binding sites on actin & permits cross-bridging between actin and myosin and phosphorylates the myosin heads. Cells may contract independently because each receives input from neuron in neurogenic or multiunit; myogenic is automatic in that they work as a single unit with electrical communication between cells.
- Smooth muscle is involuntary, smooth and located in the walls of tubular viscera.
- Fusiform or spindle shaped cells.
- Smooth muscle does have actin and myosin but actin is attached to dense bodies that attach to the cell membrane & myosin then attaches to actin. Not arranged in sarcomeres as with skeletal muscle.
- Neural, mechanical, or hormonal stimulation.
- Calcium leads to depolarization which can lead to contraction without reaching threshold and calcium can be released by things other than voltage changes.
- Myosin phosphorylation is due to MLCK (myosin light chain kinase) and a phosphatase dephosphorylates, or removes, the phosphate group on the myosin head for relaxation.