Ch12 Nervous Tissue Flashcards

Question

Myelin Sheath In CNS, _____ myelinate several _____ in immediate vicinity * push newer layers of ____ under older ones; so _____ spirals ____ towards \_\_\_\_ Myelin sheath is \_\_\_\_ * nodes of ranvier = gap... * axon hillock + initial segment (short section before 1st \_\_\_\_) = ___ zone - important role in initiating....

Answer 1

Myelin Sheath In CNS, **OLIGODENDROCYTES** myelinate several **NERVE FIBERS** in immediate vicinity * push newer layers of **MYELIN** under older ones; so **MYELINATION** spirals **INWARD** towards **NERVE FIBER** Myelin sheath is **SEGMENTED** * nodes of ranvier = gap **BETWEEN SEGMENTS** * axon hillock + initial segment (short section before 1st **SCHWANN CELL**) = **TRIGGER** zone - important role in initiating **NERVE SIGNAL**

Answer 2

* Multiple sclerosis (MS) * Tay-Sachs disease

Answer 3

Schwann cells hold small **NERVE FIBERS** in grooves on their **SURFACE** with only one **MEMBRANE WRAPPING**

Answer 4

Conduction of Speed Nerve Fibers * **SIGNAL CONDUCTION** occurs along surface * Speed depends on **DIAMETER** of **FIBER** * larger **FIBERS** have more **SURFACE AREA**, conduct **RAPIDLY** presence of myelin * small, **UNMYELINATED** fibers * small, **MYELINATED** fibers * large, **MYELINATED** fibers

Answer 5

Regeneration of Nerve Fiber (PNS only) * occurs if **SOMA** and "**TUBE**" intact * distal end of **AXON** and **MYELIN SHEATH** degenerate (soma **SWELLS**, **NUCLEUS** moves off-center) * **AXON STUMP** sprouts several growth processes * **REGENERATION TUBE** guides lucky sprout back to **ORIGINAL** destination (**SCHWANN** cells produce nerve growth factors) * **SOMA** returns to normal

Answer 6

Electrical Potentials and Currents S. Ramon y Cajal's neuron doctrine: nervous pathway not continuous "**WIRE**", but series of **CELLS** separated by **GAPS** called **SYNAPSES** * electrical potential - difference in **CONCENTRATION** of charged particles between one point and another * electrical current - **FLOW** of charged particles from one point to another neurons are **POLARIZED** (charge difference **-70**mV across **PLASMA MEMBRANE**)

Answer 7

Resting Membrane Potential (RMP) * exists because of **UNEQUAL ELECTROLYTE DISTRIBUTION** between ECF and ICF results from 3 factors 1. ions diffuse down their **CONCENTRATION GRADIENT** through membrane 2. plasma membrane is selectively **PERMEABLE** 3. **ELECTRICAL** attraction of cations and anions

Answer 8

RMP * plasma membrane is **MORE** permeable to **K+** than any other ion (**K+** is ~40x as concentrated in ICF as in **ECF**) * Cytoplasmic anions **CANNOT** escape due to **SIZE** or **CHARGE** (PO4-2, SO4-2, organic acids, proteins) * membrane much **LESS** permeable to **Na+** (**Na+** ~12x as concentrated in ECF as **ICF**) * Na+/K+ pumps out **3** Na+ for every **2** K+ it brings in (works **CONTINUOUSLY**, requires great deal of **ATP** ---- much **GLUCOSE** and **O2** needed)

Answer 9

Na+ concentrated **OUTSIDE** (**ECF**) K+ concentrated **INSIDE** (**ICF**)

Answer 10

Local Potentials * Disturbances in **MEMBRANE POTENTIAL** * Occurs when **NEURON** stimulated * Depolarization: **DECREASE** potential across **CELL** membrane because opened **Na+** channels - less **NEGATIVE** value * **NA+** rushes down its concentration gradient * **Na+** diffuses short **DISTANCE** inside **PLASMA** membrane, producing **SHORT-RANGE** change in **VOLTAGE** = local potential

Answer 11

Local Potentials Differences: local potentials vs action potentials * graded: vary in **MAGNITUDE** with **STIMULUS** strength * decremental: get **WEAKER** the **FARTHER** they **SPREAD** * reversible: when **STIMULATION** ceases, **K+** diffusion out of **CELL**, returns **CELL** to normal **RESTING POTENTIAL** * either excitatory or inhibitory: ex) glycine makes membrane potential more **NEGATIVE** = **HYPERPOLARIZED**

Answer 12

Action Potentials * **DRAMATIC** change in **MEMBRANE** produced where high density of **VOLTAGE-GATED** channels occur * if threshold potential (**-55**mV) is reached, voltage-gated **Na+** channels open (**Na+** enters causing **DEPOLARIZATION**) * past 0mV, **Na+** channels close = **DEPOLARIZATION** * slow **K+** gates fully open **K+** exits **REPOLARIZING** cell * negative overshoot produces **HYPERPOLARIZATION** = **EXCESSIVE** exiting of **K+**

Answer 13

Action Potentials * called "**SPIKE**" characteristics * follow **ALL-OR-NONE** law (**VOLTAGE GATES** either open or don't) * nondecremental: do not get **WEAKER** with **DISTANCE** * irreversible: once started, goes to **COMPLETION**, **CANNOT** be stopped

Answer 14

Action Potential Spike Summary * **DIFFUSION** of ions * removal of **ECF K+** by astrocytes * only thin layer of **IONS** close to **MEMBRANE** moved during AP

Answer 15

Refractory Period - period of **RESISTANCE** to **STIMULATION** Absolute refractory period * as long as **Na+** gates **OPEN** * no **STIMULUS** will trigger AP Relative refractory period * as long as **K+** open * only especially **STRONG** stimulus will **TRIGGER NEW** AP * efractory period refers only to **SMALL PATCH** of **MEMBRANE** at one time (quickly **RECOVERS**)

Answer 16

Signal Conduction - Unmyelinated Nerve Fibers AP from **TRIGGER** zone causes **Na+** to enter axon (impulse begins) * **DEPOLARIZATION** excited voltage-regulated gates immediately distal to **AP** * chain reaction of **SEQUENTIAL OPENING** of voltage-gated **Na+** channels down the entire length of axon * impulse (**NON-DECREMENTAL**) travels 2m/sec

Answer 17

Saltatory Conduction - Myelinated Nerve Fibers * voltage-gated channels needed for **APs** * fast **Na+** diffusion occurs between **NODES** * signal seems to jump from node to **NODE** * much faster than **UNMYELINATED** fibers

Answer 18

Synapses * first neuron releases **NEUROTRANSMITTER** onto second that responds to it * 1st neuron in signal path = **PRESYNAPTIC NEURON** (**RELEASES** neurotransmitters) * 2nd neuron = **POSTSYNAPTIC NEURON** (**RESPONDS TO** neurotransmitters)

Answer 19

Synapses * synapses may be **AXODENDRITIC**, **AXOSOMATIC**, or **AXOAXONIC** * number of synapses on **POST-SYNAPTIC** cell quite variable - **SPINAL MOTOR** neuron has ~10,000 - in **CEREBELLUM**, 1 neuron can have as many as many as 100,000 synapses

Answer 20

Discovery of Neurotransmitters * ___________ between neurons discovered through histological observations * Otto Loewi (1921) demonstrated that _____ communicate by ________ "\_\_\_\_\_\_ synapses" - flooded exposed _____ of 2 frogs with \_\_\_\_ - stimulated _____ nerve of first frog, heart \_\_\_\_ - removed saline from that frog found it _____ heart of second frog named it Vagusstoffe "\_\_\_\_\_ substance" ---- later rename ______ 1st known neurotransmitter

Answer 21

Discovery of Neurotransmitters * **ELECTRICAL** synapses do exist - **GAP** junctions join adjacent cells - advantage: **QUICK** transmission (**CARDIAC** and **SMOOTH** muscle, some neurons) - disadvantage: cannot integrate **INFORMATION** /make **DECISIONS** * ability reserved for **CHEMICAL** synapses in which **NEURONS** communicate by releasing **NEUROTRANSMITTERS**

Answer 22

Structure of a Chemical Synapse * presynaptic neurons have vesicles with **NEUROTRANSMITTER** * postsynaptic have **RECEPTORS** and ligand-regulated **ION** channels

Answer 23

Neurotransmitters 4 major categories (by **CHEMICAL** composition) * acetylcholine - from from **ACETIC** acid + choline * amino acid neurotransmitters ex. **GLYCINE** * monoamines - made by removal of -COOH group from AA ex. epinephrine, **NOREPINEPHRINE**, **DOPAMINE** (catecholamines), histamine, **SEROTONIN** * neuropeptides

Answer 24

Neuropeptides * 2-40 AA * act at **LOWER** concentrations * **LONGER** lasting effects * stored in **AXON TERMINAL** as larger **SECRETORY** granules (dense-core vesicles) * some function as **HORMONES** or neuromodulators * some released from **NONNEURAL** tissue (gut-brain peptides cause food cravings (Ghrelin)

Answer 25

Synaptic Transmission 3 kinds of synapses with different modes of **ACTION** * excitatory **CHOLINERGIC** synapse ex) **ACh** * inhibitory **GABA-energic** synapse ex) **GABA** * excitatory **ADRENERGIC** synapse ex) **NE**

Answer 26

Excitatory Cholinergic Synapse - ACh * signal opens **VOLTAGE-GATED CALCIUM** channels in synaptic **KNOB** * triggers release of **ACh**; crosses **SYNAPSE** * ACh receptors trigger opening of **Na+** channels, producing **LOCAL** potential (**POSTSYNAPTIC** potential) * - when -55mV triggers AP in **POSTSYNAPTIC** neuron

Answer 27

Inhibitory GABA-ergic Synapse * signal triggers release of **GABA** into **SYNAPTIC** cleft * GABA receptors trigger opening of **CI-** channels, producing **HYPERPOLARIZATION** (inside more **NEGATIVE** than RMP) * **POSTSYNAPTIC** neuron is inhibited, less likely to reach **THRESHOLD**

Answer 28

Excitatory Adrenergic Synapse * employs **NOREPINEPHRINE (NE)** aka noradrenaline * acts through **SECOND MESSENGER** system (cAMP) -- **RECEPTOR** associated with G protein, which activates adenylate cyclase, coverts **ATP** to **cAMP** * **SLOWER** response than cholinergic and GABA-ergic synapses * advantage = **ENZYME** amplification

Answer 29

Cessation of Signal * Mechanisms to **TURN OFF** stimulation 1. neurotransmitter escapes into **ECF** = **DIFFUSION** (**ASTROCYTES** return it to neurons) 2. synaptic knob reabsorbs AA and monoamines by **ENDOCYTOSIS** = **REUPTAKE** 3. acetylcholinesterase breaks down **ACh** = **DEGRADATION** * Choline reabsorbed and **RECYCLED**

Answer 30

Neuromodulators * modify synaptic **TRANSMISSION** 1. raise or lower **NUMBER** of **RECEPTORS** 2. alter rate of neurotransmitter synthesis, **RELEASE**, **REUPTAKE**, or **BREAKDOWN** * ex) enkephalins - neuromodulator **FAMILY** * small **PEPTIDES** that inhibit **PAIN** signals

Answer 31

Neural Integration * more synapses = greater **INFORMATION-PROCESSING** capability * chemical synapses = **DECISION-MAKING** components of **NERVOUS** system - ability to **PROCESS**, **STORE**, and **RECALL** information due to neural integration

Answer 32

Postsynaptic Potentials - EPSP * neural integration - based on postsynaptic potentials produced by **NEUROTRANSMITTERS** excitatory postsynaptic potential (EPSP) - positive voltage change causing postsynaptic neuron to be more likely to **FIRE** --- results from **Na+** flowing into cell cancelling some **NEGATIVE** charge on **INSIDE** of membrane - glutamate and aspartate = **EXCITATORY** brain neurotransmitters, produce EPSPs - ACh and NE may **EXCITE** or **INHIBIT** depending on receptor on target cell

Answer 33

Temporal and Spatial Summation Net postsynaptic potentials in trigger zone * firing depends on net input of other **CELLS** * typical EPSP voltage = 0.5mV, lasts 20msec * 30 EPSPs needed to reach **THRESHOLD** Temporal Summation * single synapse recieved many EPSPs in **SHORT TIME** Spatial Summation * single synapse receives many EPSPs from **MANY CELLS**

Answer 34

Presynaptic Facilitation One presynaptic neuron **FACILITATES**: * 1st neuron releases NT, opens voltage-gated **Ca+2** channels on 2nd neuron Enhances **NEUROTRANSMITTER** release

Answer 35

Presynaptic Inhibition One presynaptic neuron **SUPPRESSES** another: * 1st neuron releases inhibitory **GABA**, prevents voltage-gated **Ca+2** channels on 2nd neuron from opening * releases **LESS**/no **NEUROTRANSMITTER**

Ch12 Nervous Tissue Flashcards

(60 cards)