Ch12: Nervous Tissue

Front 1

Describe the major structures and functions of the nervous system in the maintenance of homeostasis

Back 1

Brain
Cranial nerves (12 pairs) emerge from base of brain
Nerve (lie outside brain & spinal cord or CNS) follow defined path, serve specific region
Spinal cord: connects to brain through foramen magnum
Spinal nerves (31 pairs) emerge from spinal cord, region-specific
Ganglia: group of neuronal cell bodies, lie outside CNS
Enteric plexuses: extensive network of neurons, in walls of GI tract organs & helps regulate digestive system
Sensory receptor: refers to dendrites of sensory neurons & specialized cells (ie. Photoreceptors in retina)

Front 2

Describe the 3 functions of the Nervous system

Back 2

1 Sensory function
Sensory receptors detect internal stimuli, such as an increase in blood acidity, and external stimuli, such as a raindrop landing on your arm. This sensory info is then carried into the brain & spinal cord through cranial & spinal nerves

2 Integrative function
NS integrates (processes) sensory info by analyzing & storing some of it & by making decisions for appropriate responses. An important integrative function is perception, the conscious awareness of sensory stimuli. Perception occurs in the brain.

3 Motor function
Once sensory info is integrated, NS may elicit an appropriate motor response by activating effectors (muscles & glands) through cranial & spinal nerves.

Front 3

Compare the function of neurons and neuroglia

Back 3

Neurons provide most of the unique functions of the nervous system, such as sensing, thinking, remembering, controlling muscle activity, and regulating glandular secretions.
Neuroglia support, nourish, and protect the neurons and maintain homeostasis in the interstitial fluid that bathes them.

Front 4

Compare the histological characteristics of neuroglia and neurons

Back 4

Neurons
-possess electrical excitability
-3 parts = cell body/soma, dendrites (input ends), axon (output ends; joins to cell body at axon hillock; portion closest to axon hillock = initial segment; trigger zone = junction between axon hillock & initial segment; axon collaterals = branches off axon at 90 angle; axon terminals)

Neuroglia
-smaller but more numerous than neurons
-do NOT generate or propagate action potentials
-can multiply & divide in mature NS

Front 5

Describe the 3 types of neurons based on the number of processes extending from the cell body

Back 5

Multipolar neuron: several dendrites & 1 axon (brain, spinal cord)

Bipolar: 1 main dendrite & 1 axon (eye, ear, olfactory brain region)

Unipolar: dendrites and 1 axon that are fused together to form a continuous process that emerges from cell body (tactile sensory receptors)

Front 6

Describe the major functions of astrocytes (1 of 4 main types of Neuroglia in the CNS)

Back 6

-star-shaped cells = largest, most numerous neuroglia
(1) Contain microfilaments- support neurons
(2) Processes wrapping blood capillaries isolate neurons of CNS from potentially harmful substances in blood by secreting chemicals that maintain blood-brain barrier of endothelial cells - restricts movement of substances between blood & interstitial fluid of CNS
(3) In embryo, secrete chemicals that regulate growth, migration & interconnection among neurons in brain
(4) Help maintain appropriate chemical environment for generation of nerve impulses (ie. K+ concentration); take up excess neurotransmitters; serves as passageway for nutrients & other substances between blood capillaries & neurons
(5) May also play a role in learning & memory by influencing formation of neural synapses

Front 7

Describe the major functions of oligodendrocytes (1 of 4 main types of Neuroglia in the CNS)

Back 7

-resemble astrocytes, but smaller & fewer processes
-processes responsible for forming and maintaining the myelin sheath around CNS axons
-one myelinates several axons
*myelin sheath = multilayered lipid & protein covering around some axons, insulates them & increases speed of nerve impulse conduction

Front 8

Describe the major functions of microglia (1 of 4 main types of Neuroglia in the CNS)

Back 8

=small cells w slender processes w numerous spinelike projections
-function as phagocytes >> remove cellular debris formed during normal development of NS & phagocytize microbes & damaged nervous tissue

Front 9

Describe the major functions of ependymal cells (1 of 4 main types of Neuroglia in the CNS)

Back 9

=cuboidal to columnar cells arranged in a single layer that possess microvilli and cilia
-line ventricles of brain & central canal of spinal cord (filled w cerebrospinal fluid - protects & nourishes brain & spinal cord)
-produce, possibly monitor, and assist in circulation of cerebrospinal fluid
-form the blood-cerebrospinal fluid barrier

Front 10

Describe the major functions of schwann cells and satellite cells (2 main types of Neuroglia in the PNS)

Back 10

SCHWANN CELLS
-encircle PNS axons
-1 schw cell myelinates a single axon
-can enclose as many as 20 or more unmyelinated axons
-participate in axon regeneration (more easily accomplished in the PNS than in CNS)
SATELLITE CELLS
=flat
-surround cell bodies of neurons of PNS ganglia
-provides structural support
-regulate the exchanges of materials between neuronal cell bodies and interstitial fluid

Front 11

Describe myelination in PNS

Back 11

-electrically insulates the axon of a neuron
-increases speed of nerve impulse conduction
-produced by schwann cells & oligodendrocytes
-Outermost layer = schwann cell's cytoplasm & nucleus, only in PNS axons, helps regrowth of damaged axons
-Inner portion (100 layers of Schwann cell membrane) = myelin sheath, found only around axons in the PNS
Nodes of Ranvier = Gaps in the myelin sheath, appear at intervals along the axon

Front 12

Describe myelination in CNS

Back 12

-oligodendrocyte myelinates parts of several axons
-Each oligodendrocyte puts forth about 15 broad, flat processes that spiral around CNS axons, forming a myelin sheath
-neurolemma NOT present bc oligodendrocyte cell body and nucleus do not envelop the axon
-Nodes of Ranvier are present, but fewer in number
-axons display little regrowth after injury (maybe bc of absence of a neurolemma & an inhibitory influence exerted by the oligodendrocytes on axon regrowth

Front 13

Describe what grey and white matter are composed of

Back 13

White: composed primarily of myelinated axons
Gray: contains neuronal cell bodies, dendrites, unmyelinated axons, axon terminals, and neuroglia; little or no myelin in these areas
-Blood vessels are present in both
In the spinal cord, white matter surrounds an inner core of gray matter >> shaped like a butterfly
In the brain, a thin shell of gray matter covers surface of the largest portions of the brain, the cerebrum and cerebellum

Front 14

Compare ganglion and nucleus

Back 14

Ganglia = clusters of neuronal cell bodies in PNS
Nucelus = clusters of neuronal cell bodies in CNS

Front 15

Describe the components and subdivisions of the CNS

Back 15

-brain & spinal cord
-processes incoming sensory info
=souce of thoughts, emotions, memories
-CNS send out most nerve impulses that stimulate muscles to contract and glands to secrete

Front 16

Define Sensory (afferent) and motor (efferent)

Back 16

Sensory (afferent) neurons carry input to the CNS; motor (efferent) neurons carry output from the CNS to effectors in the PNS

Front 17

Describe the components and subdivisions of the PNS

Back 17

PNS = all nervous tissue outside the CNS
>>cranial nerves and their branches, spinal nerves and their branches, ganglia, and sensory receptors
Subdivisions
-somatic nervous system (SNS)
-autonomic nervous system (ANS) >> symp and parasymp NS
-enteric nervous system (ENS) (enter- = intestines)

Front 18

Describe the somatic nervous system

Back 18

>> consists of
(1) sensory neurons that convey info from somatic receptors in head, body wall, and limbs and from receptors for the special senses of vision, hearing, taste, and smell to the CNS
(2) motor neurons: conduct impulses from CNS to skeletal muscles only(voluntary)

Front 19

Describe the ANS

Back 19

consists of
(1) sensory neurons: convey info from autonomic sensory receptors, located primarily in visceral organs (ie. stomach & lungs) to the CNS
(2) motor neurons that conduct nerve impulses from CNS to smooth muscle, cardiac muscle, glands (involuntary)
***motor part of ANS consists of sympathetic division & parasympathetic division. With a few exceptions, effectors receive nerves from both divisions, and usually the two divisions have opposing actions
-ie. sympathetic neurons increase heart rate, parasympathetic neurons slow it down
Generally, symp division helps support exercise or emergency actions, “fight-or-flight” responses; parasymp division takes care of “rest-and-digest” activities

Front 20

Describe the enteric NS

Back 20

= “brain of the gut”
-involuntary
-enteric plexuses function independently from ANS & CNS
-communicate with CNS via symp & parasymp neurons

ENS Sensory neurons- monitor chemical changes within GI tract, stretching of its walls
Enteric motor neurons- govern
>>contraction of GI tract smooth muscle to propel food through
>>secretions of GI tract organs such as acid from stomach
>>activity of GI tract endocrine cells, which secrete hormones

Front 21

Describe the cellular properties that permit communication among neurons and effectors (graded and action potentials; membrane and resting membrane potential)

Back 21

Neurons and Effectors communicate w one another using 2 types of electrical signals:
(1) Graded potentials- used for short-distance communication only
(2) Action potentials: allow communication over long distances w/in body
***Production of graded & action potentials = result of ion channels

Membrane potential = an electrical potential difference (voltage) across membrane
Resting membrane potential = an electrical potential diff (voltage) across membrane of an excitable cell under resting conditions >> exists bc of small buildup of (-) ions in cytosol along inside of membrane & an equal buildup of (+) ions in ECF fluid along outside surface of membrane

Front 22

Compare basic types of ion channels

Back 22

1 Leakage channels: Gated channels that randomly open and close
-Found in nearly all cells, including the dendrites, cell bodies & axons of all types of neurons
2 Ligand-gated channels: Gated channels, open in response to binding of a ligand (chemical) stimulus
-Dendrites of some sensory neurons such as pain receptors, dendrites, cell bodies of interneurons, motor neurons.
3 Mechanically-gated channels: Gated channels, open in response to binding of a mechanical stimulus (such as touch, pressure, vibration, and tissue stretching)
-Dendrites of some sensory neurons such as touch receptors, pressure receptors, and some pain receptors
4 Voltage-gated channels: Gated channels, open in response to a voltage stimulus (change in membrane potential)
-Axons of all types of neurons

Front 23

Describe the 3 major factors that contribute to the generation of a resting membrane potential

Back 23

1 Unequal distribution of ions in ECF & cytosol:
ECF rich in Na+ & Cl- ions
Cytosol rich in K+, phosphates (ATP, amino acids)
-on plasma memb: # of K+ leakage channels > Na+ leakage channels
2 Inability of most anions to leave the cell: Most anions inside cell are not free to leave like K+ bc they are attached to nondiffusible molecules such as ATP & large proteins
3 Electrogenic nature of Na+/K+ ATPases: sodium ions slowly diffuse inward thru the few leakage channels >> small inward Na+ leak & outward K+ leak are offset by the Na+/K+ ATPases (sodium–potassium pumps - help maintain resting membrane potential, pumps out Na+, bring in K+)
***pumps = electrogenic = remove more + charges from cell than they bring in & contribute to negativity of resting membrane potential >> contribution very small

Front 24

Define and describe the 2 kinds of graded potentials
*graded means that they vary in amplitude (size), depending on the strength of the stimulus

Back 24

gp =small deviation from membrane potential >> makes membrane either more polarized (inside more negative) or less polarized (inside less negative)

1 Hyperpolarizing graded potential =When response makes membrane more polarized

Depolarizing graded potential =When response makes membrane less polarized

Front 25

Describe decremental conduction

Back 25

= mode of travel by which graded potentials die out as they spread along the membrane >> charges are lost across the membrane through leakage channels
***graded potentials are useful for short-distance communication only

Front 26

Define and Describe Summation

Back 26

=process by which graded potentials add together
-ie. If 2 depolarizing graded potentials summate, the net result is a larger depolarizing graded potential
-ie. If two hyperpolarizing graded potentials summate, the net result is a larger hyperpolarizing graded potential
-ie. If two equal but opposite graded potentials summate (one depolarizing and the other hyperpolarizing), then they cancel each other out and the overall graded potential disappears

Front 27

Define Action potential and describe the 2 phases plus the extra phase

Back 27

AP/impulse =a sequence of rapidly occurring events that decrease and reverse the membrane potential and then eventually restore it to the resting state
2 main phases
(1)depolarizing phase: neg membrane potential becomes positive
(2) repolarizing phase: membrane potential is restored to resting state of -70 mV
***After repolarizing phase there may be an after-hyperpolarizing phase = membrane potential temporarily becomes more negative than resting level

Front 28

List the sequence of events involved in generation of an action potential (occur on axon plasma membrane and axon terminals)

Back 28

1 Voltage-gated Na+ channels open, allow Na+ influx >> depolarizing phase
2 Voltage-gated K+ channels open, allowing K+ efflux >> repolarizing phase
3 after-hyperpolarizing phase occurs when the voltage-gated K+ channels remain open after the repolarizing phase ends

Front 29

Describe threshold

Back 29

An action potential occurs in the membrane of the axon of a neuron when depolarization reaches a certain level termed the threshold (about -55 mV in many neurons) >> different in Different neurons
-threshold stimulus = stimulus that is just strong enough to depolarize the membrane to threshold
***the greater the stimulus strength above threshold, the greater the FREQUENCY of the action potentials until a maximum frequency is reached as determined by the absolute refractory period

Front 30

Descibe the all-or-none principle

Back 30

An action potential either occurs completely or it does not occur at all

Front 31

Describe the refractory period

Back 31

=period of time after an action potential begins during which an excitable cell cannot generate another action potential in response to a normal threshold stimulus
ASOLUTE refractory period, even a very strong stimulus cannot initiate a second action potential >> Inactivated Na+ channels cannot reopen until they return to the resting state
***In contrast to action potentials, graded potentials do not exhibit a refractory period
RELATIVE refractory period = period of time during which a second action potential can be initiated, but only by a larger-than-normal stimulus >> coincides with the period when the voltage-gated K+ channels are still open after inactivated Na+ channels have returned to their resting state

Front 32

Describe the propagation of nerve impulses of action potentials

Back 32

-NOT decremental (it does not die out)
-an AP keeps its strength as it spreads along memb by a mode of conduction called propagation
-depends on (+) feedback
>>ap regenerates over & over at adjacent regions of memb from trigger zone to axon terminals (in this direction only—it cannot propagate backwards toward the cell body bc any region of membrane that has just undergone an ap is temporarily in absolute refractory period & cannot generate another ap)

Front 33

List and describe the 2 types of propagation

Back 33

1 Continuous conduction
=step-by-step depolarization & repolarization of each adjacent segment of the plasma membr >> ions flow thru their voltage-gated channels in each adjacent segment of memb
-occurs in unmyelinated axons & in muscle fibers
2 Saltatory conduction
=special mode of axn potential propag’n that occurs along myelinated axons
-occur bc of uneven distribution of voltage-gated channels
-When an ap leaps along a myelinated axon, an electric current (carried by ions) flows thru ECF surrounding myelin sheath & thru the cytosol from 1 node to the next. AP at 1st node generates ionic currents in cytosol & ECF >> depolarize membrane to threshold, opening voltage-gated Na+ channels at 2nd node >>ap at 2nd node and so on ***Each node repolarizes after it depolarizes

Front 34

Describe the 3 factors that affect the speed of propagation

Back 34

Amount of myelination: myelinated > nonmyelinated
Axon diameter: Larger-diameter axons propagate action potentials faster than smaller ones due to their larger SAs
Temperature: higher T = higher speed

Front 35

Describe encoding of stimulus intensity

Back 35

1) “Frequency code” – frequency of action potentials that are generated at the trigger zone determines how we sense differing intensities of stimuli
-ie. light touch generates a low frequency of action potentials. A firmer pressure elicits action potentials that pass down the axon at a higher frequency
2) number of sensory neurons recruited (activated) by the stimulus. A firm pressure stimulates a larger number of pressure-sensitive neurons than does a light touch

Front 36

Comparison of the 2 types of electrical signals produced by excitable cells

Back 36

Excitable cells—neurons & muscle fibers—produce 2 types of electrical signals: graded potentials and action potentials (impulses)

Major diff! Propagation of action potentials permits communication over long distances, but graded potentials can function only in short-distance bc they are not propagated
Table 12-2 a summary of the differences between graded potentials and action potentials

Front 37

Explain the events of signal transmission at a synapse

Back 37

1 A nerve impulse arrives at synaptic end bulb (or at a varicosity) of a presynaptic axon
2 Depolarizing phase of nerve impulse opens volt-gated Ca2+ channels on memb of synaptic end bulbs (Ca2+ ions more concentrated in ECF >> Ca2+ influx thru opened channels)
3 Ca2+ increase in presynaptic neuron triggers exocytosis of synaptic vesicles. Each synaptic vesicle contains several thousand mlcls of neurotransmitter - released into synaptic cleft
4 Neurotransmitter mlcls diffuse across syn cleft, bind to receptors in postsynaptic neuron's membrane - ionotropic or metabotropic receptor
5 Binding of neurotransmitter molecules to receptors on ligand-gated channels opens channels & allows specific ions to flow across membrane
6 As ions flow thru opened channels, voltage across membrane changes = postsynaptic potential either a depolarization or a hyperpolarization.
7 When a depolarizing postsynaptic potential reaches threshold, it triggers an action potential in the axon of the post-synaptic neuron

Front 38

Describe a chemical synapse

Back 38

At a chemical synapse, a presynaptic neuron converts an electrical signal (nerve impulse) into a chemical signal (neurotransmitter release).
The postsynaptic neuron then converts the chemical signal back into an electrical signal (postsynaptic potential).

Front 39

Describe an excitatory or an inhibitory graded potential

Back 39

-caused by a neurotransmitter
-depolarizing postsynaptic memb/potential aka. Excitatory postsynaptic potential EPSP (brings membrane closer to threshold- doesn’t necessarily initiate a nerve impulse)
-hyperpolarizing postsynaptic membrane/potential aka. Inhibitory postsynaptic potential IPSP (becomes more negative inside & farther from threshold

Front 40

Describe the 3 ways of Removing of a neurotransmitter

Back 40

Neurotransmitter is removed in three ways:
1 Diffusion. Some of released neurotransmitter molecules diffuse away from the synaptic cleft. Once a neurotransmitter molecule is out of reach of its receptors, it can no longer exert an effect.
2 Enzymatic degradation. Certain neurotransmitters are inactivated through enzymatic degradation. For example, the enzyme acetylcholinesterase AChE breaks down acetylcholine in the synaptic cleft.
3 Uptake by cells. Reuptake (Many neurotransmitters are actively transported back into the neuron that released them. Uptake (Others transported into neighboring neuroglia). ie) Neurons that release norepin rapidly take up norepinephrine & recycle into new synaptic vesicles. The membrane proteins that accomplish such uptake are called neurotransmitter transporters.

Front 41

Distinguish between spatial and temporal summation

Back 41

Spatial summation = summation of postsynaptic potentials in response to stimuli that occur at different locations in the membrane at the same time
-ie. spatial summation results from the buildup of neurotransmitter released simultaneously by several presynaptic end bulbs

Temporal summation = summation of postsynaptic potentials in response to stimuli that occur at the same location in the membrane of the postsynaptic cell but at different times.
-ie. temporal summation results from buildup of neurotransmitter released by a single presynaptic end bulb two or more times in rapid succession.
***Most of the time, spatial and temporal summations are acting together to influence the chance that a neuron fires an action potential.

Front 42

Identify the 2 classes and types of neurotransmitters

Back 42

*divided into two major classes based on size:
1 Small-molecule neurotransmitters: acetylcholine, amino acids, biogenic amines, purines, and nitric oxide
2 Neuropeptides: example (substance P)

Front 43

Describe the functions of ACh/Acetylcholine

Back 43

ACh: in PNS&CNS, excitatory, binds to ionotropic receptors, open cation channels. OR inhibitory, binds to metatropic receptors, open K+ channels

Front 44

Describe the functions of Amino acids:

Back 44

in CNS
ie) Glutamate (glutamic acid) & aspartate (aspartic acid) = powerful excitatory effects, bind to ionotropic receptors, opens cation (Na+) channels >> EPSP. Inactivation of glutamate via reuptake & Glutamate transporters
ie) Gamma aminobutyric acid (GABA) & glycine = inhibitory, bind to ionotropic receptors, open Cl- channels, only in CNS >> Antianxiety drugs like diazepam (Valium®) enhance action of GABA

Front 45

Describe the functions of biogenic amines

Back 45

= modified & decarboxylated (carboxyl group removed) aa's

-Most bind to metabotropic receptors

-excitatory/inhibitory depending on type of metabotropic receptor at synapse
Norepinephrine (NE) involve in arousal (awakening from deep sleep), dreaming, regulating mood ***epin & NE also hormones (released by adrenal medulla)
Dopamine (DA) –emotional responses, addictive behrs, pleasurable experiences, regulate skel musc tone & some skel musc movement
-ie. Parkinson disease: muscular stiffness (degeneration of DA-releasing neurons); One form of schizophrenia = excess DA
***Above 3 ntransmitters classified chemically as catecholamines >> all include an amino group (—NH2) & a catechol ring
-synth from aa tyrosine
-inactivation = reuptake or enzymes(MAO)
Serotonin / 5-hydroxytryptamine (5-HT) in neurons of raphe nucleus in brain, involv in sensory perception, T regulation, control of mood, appetite & induction of sleep

Front 46

Describe the functions of (NO) nitric oxide

Back 46

N2O sometimes used as an anesthetic during dental procedures
-action is brief because NO is a highly reactive free radical
-exists <10 seconds before it combines with oxygen and water to form inactive nitrates and nitrites
-role in memory and learning.
-regulatory molecule
-causes relaxation >> vasodilation >> lower BP, Sildenafil (Viagra®), produced by Phagocytic cells like macrophages and certain wbc’s to kill microbes and tumor cells

Front 47

Describe the types and functions of Neuropeptides

Back 47

-in CNS & PNS, bind to metabotropic receptors, excitatory or inhibitory
-also serve as hormones (regulate physiological responses)
-aka. Opioid peptides, natural painkillers
ENKEPHALINS
-same recptors as opiate drugs (morphine & heroin)
-potent analgesic (pain-relieving) effect (200x stronger vs morphine)
ENDORPHINS
DYNORPHINS
-improved memory & learning; feelings of pleasure / euphoria; control of body T; regulation of pubertal onset hormones, sex drive & reproduction; mental illnesses (depression & schizophrenia)
SUBSTANCE P
-enhances perception of pain
-release is suppressed by Enkephalin & endorphin
-counter effects of certain nerve-damaging chemicals (maybe useful as a treatment for nerve degeneration)

Front 48

Define neural circuit

Back 48

=complicated but functional networks/groups of neurons that process specific types of information

Front 49

Describe the simple series circuit (1of 5 neural circuits in the NS)

Back 49

=a presynaptic neuron stimulates a single postsynaptic neuron. The second neuron then stimulates another, and so on
***most neural circuits are more complex

Front 50

Describe the diverging circuit

Back 50

A single presynaptic neuron may synapse with several postsynaptic neurons >> one presynaptic neuron can simultaneously influence several postsynaptic neurons (or several muscle fibers or gland cells)
=nerve impulse from a single presynaptic neuron causes the stimulation of increasing numbers of cells along the circuit
-ie. Small number of neurons in brain that govern a particular body movement stimulate a much larger number of neurons in the spinal cord
-ie. Sensory impulse relayed to several regions of the brain
*this arrangement amplifies the signal

Front 51

Describe the converging circuit

Back 51

=several presynaptic neurons synapse with a single postsynaptic neuron >> postsynaptic neuron receives nerve impulses from several different sources
-this arrangement permits more effective stimulation or inhibition of the postsynaptic neuron
-ie. A single motor neuron that synapses with skeletal muscle fibers at neuromuscular junctions receives input from several pathways that originate in different brain regions

Front 52

Describe the reverberating circuit

Back 52

=stimulation of the presynaptic cell causes the postsynaptic cell to transmit a series of nerve impulses >> incoming impulse stimulates the first neuron, which stimulates the second, which stimulates the third, and so on
-this arrangement sends impulses back through the circuit again and again.
-output signal may last from a few seconds to many hours, depending on # of synapses & the arrangement of neurons in the circuit
-Inhibitory neurons may turn off a reverberating circuit after some time
-ie. output signals from reverberating circuits = breathing, coordinated muscular activities, waking up, and short-term memory.

Front 53

Describe the parallel after-discharge circuit

Back 53

-a single presynaptic cell stimulates a group of neurons, each of which synapses with a common postsynaptic cell
-A differing number of synapses between the first and last neurons imposes varying synaptic delays, so that last neuron exhibits multiple EPSPs or IPSPs
-If input = excitatory, the postsynaptic neuron then can send out a stream of impulses in quick succession
-ie. involved in precise activities such as mathematical calculations

Front 54

Define Neurogenesis in CNS and identify the two inhibitory factors
Define plasticity

Back 54

=birth of new neurons from undifferentiated stem cells—occurs regularly in some animals
Almost complete lack of neurogenesis in other regions of brain & spinal cord result of 2 factors:
(1) inhibitory influences from neuroglia (oligodendrocytes of myelin sheath)
(2) absence of growth-stimulating cues that were present during fetal development
Plasticity = capability to change based on experience
In the CNS, little or no repair of damage to neurons occurs. Even when the cell body remains intact, a severed axon cannot be repaired or regrown

Front 55

Damage and repair in the PNS

Back 55

In the PNS, damage to dendrites and myelinated axons may be repaired if the cell body remains intact and if the Schwann cells that produce myelination remain active

Front 56

Describe MS (multiple sclerosis)

Back 56

=disease that causes a progressive destruction of myelin sheaths surrounding neurons in the CNS >> multiple regions of myelin sheath deteriorate to scleroses/scars/plaque
=affects 2x more females vs males (most common in whites)

Front 57

Descibe epilepsy

Back 57

=short, recurrent attacks of motor, sensory, or psychological malfunction (hardly affects intelligence)
-initiated by abnormal, synchronous electrical discharges from millions of neurons in the brain (abnormal reverberating circuits)
Partial seizures begin in a small area on one side of brain, produce milder symptoms
Generalized seizures involve larger areas on both sides of brain, loss of consciousness.

Front 58

identify the causes of epilepsy

Back 58

Many causes: brain damage at birth (most common); metabolic disturbances (hypoglycemia, hypocalcemia, uremia, hypoxia); infections (encephalitis or meningitis); toxins (alcohol, tranquilizers, hallucinogens); vascular disturbances (hemorrhage, hypotension); head injuries; tumors & abscesses of brain. Seizures assoc with fever are most common in children under the age of two. However, most epileptic seizures have no demonstrable cause.

Front 59

Identigy the treatments for epilepsy

Back 59

eliminated or alleviated by antiepileptic drugs, such as phenytoin, carbamazepine, and valproate sodium. An implantable device that stimulates the vagus (X) nerve; surgical intervention