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Biology > Bio ch12 Histology of Nervous Tissue > Flashcards

Bio ch12 Histology of Nervous Tissue Flashcards

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1
Q

Nervous tissue comprises of two types of cell

A

Neurons and Neurolgia

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2
Q

Neurons also provide the most unique functions

A

such as sensing, thinking, remembering, controlling muscle activity and regulating gland SECRETION. heheh

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3
Q

NEUROGLIA

A

are smaller than the neurons but they greatly outnumber them by 25 times

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4
Q

NEUROGLIA

A
  • Support, nourish and protect neurons - maintain interstitial fluid that bathes them - continue to divide through out an individuals lifetime
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5
Q

NEURONS(nerve cells)

A
  • possess electrical excitability
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6
Q

Electrical excitability is

A

the ability to respond to stimulus and convert it to potential action

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7
Q

Stimulus is

A

any change in the environment that is strong enough to initiate an action potential

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8
Q

Action potential(nerve impulse)

A

is an ELECTRICAL SIGNAL that travels along the surface of the membrane of the neuron.

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9
Q

Neurons have three parts

A
  • cell body, dendrites, an axon
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10
Q

Cell body

A
  • also known as perikaryon or soma - contains a nucleus surrounded cytoplasm that includes typical organelles such as lysosomes, mitochondria, and a Golgi complex.
  • is location for most protein synthesis which are neurotransmitters and repair proteins
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11
Q

Nissl Bodies

A

are neuronal cell bodies that contain free ribosomes and prominent clusters of rough endoplasmic reticulum

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12
Q

CYTOSKELETONS

A

includes both the NEUROFIBRILS composed of bundles of intermediate filaments that provide the cell shape and support and MICROTUBULES which assists in moving materials between cell body and axon.

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13
Q

Aging NEURONS

A

also contains lipofuscin, a pigment that occurs as clumps of yellowish brown granules in the cytoplasm.

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14
Q

NERVE fibers

A

is a general term for any neuronal process(extension) that emerges from the cell body of a neuron. Again these two are DENDRITES and AXON

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15
Q

Dendrites(or little trees)

A
  • are the receiving or input portions of a neuron(INSIDE IT ARE neurofibrils which provide shape and support)
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16
Q

The single axon (axis)

A

propagates nerve impulses towards another another neuron, a muscle fiber or gland cell.

  • axon is a long thin cylindrical projection(looks like longganisa’s joined together that is attached to the neuron)
  • contains mitochondria, microtubules and neurofibrils.
  • it is joined at the neuron with the axon hillock
  • side branches (collaterals) end in fine processes called axon terminals
  • swollen tips called synaptic and bulbs contain vesicles filled with neurotransmitters
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17
Q

The part closest to the axon hillock is called

A

the initial segment.

In most neurons, most impulses start at thejunction of the axon hillock and the initial segment, an area called the trigger zone, from which they travel along the axon to their destination.

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18
Q

axoplasm

A
  • is the cytoplasm of an axon
  • is surrounded by a plasma membrane known as the axolemma.
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19
Q

What roles do the dendrite, cell body and axon play in communication of signals?

A

Dendrites and the cell body receive input; the axon conducts nerve impulses(action potentials) and transmit the message to another neuron or effector cell by releasing a neurotransmitter at the end of the synaptic end bulbs

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20
Q

The nervous system along with the endocrine system

A

helps to keep controlled conditions within limits to that maintains heath and helps to maintain homeostatis

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21
Q

The nervous system is responsible for

A

all our behaviours, memories and movments.

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22
Q

Neurology is

A

the branch of medical science that deals with the normal functioning and disorders of the nervous system

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23
Q

Axonal transport systems moves substances

A
  • slow axonal flow
  • movement is one direction only - away from cell body
  • movement is 1-5 mm a day
  • fast axonal flow
  • moves organellesand materials along the surface of the microtubules
  • at 200-400 mm a day
  • transport in either direction
  • for use or for recycling in cell body
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24
Q

Axonal transport and diseases

A

Fast axonal transport route by which toxins or pathogens reach neuron cell bodies

  • tetanus(clostridum tetani bacteria)
  • disrupts motor neurons causing painful muscle spasms

Bacteria enter the body through a laceration or puncture injury

  • More serious if wound is in head or neck because of shorter transit time.
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25
Q

Classifications of neurons multipolar, bipolar and unipolar

A

Most neurons inthe body are interneurons and are often named for the histologist who first decribed them or for an aspect of their shape or appearance. examples are purkinje cells or Renshaw cells.

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26
Q

Functional classifications of Neurons

A

Sensory (afferent) neurons - transport sensory information from skin, muscles, joints, sense organs and viscera to CNS.

Motor (efferent) neurons - send motor nerve impulses to muscles and glands

Interneurons - connect to sensory to motor neuraons and its 90% neurons in the body.

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27
Q

Neuroglial cells

A
  • Half the volume of CNS
  • Smaller cells than neurons
  • 50X more numerous
  • Cells can divide
    • rapid mitosis in tumor formation
  • 4 cell types in CNS
    • astrocytes, oligodendocytes, microglia and ependymal
  • 2 cell types in PNS
    • schwann and satellite cells
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28
Q

Astrocytes

A
  • star-shaped cells
  • Form blood-brain barrier by covering blood capillaries
  • metabolized neurotransmitters
  • regulate K+ balance
  • provide structure support
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29
Q

Microglia

A
  • Small cells founds near blood vessels
  • Phagocytic role - CLEAR AWAY DEAD CELLS
  • derived from cells that gave rise to macrophages and monocytes
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30
Q

EPENDYMAL CELLS

A
  • Form epithelial membrane lining cerebral cavities and central canal
  • Produce cerebrospinal fluid(CSF)
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31
Q

Satellite cells

A
  • FLAT cells surrounding neuronal cell bodies iin peripheral ganglia
  • SUPPORT Neurons in PNS ganglia
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32
Q

Oligodendrocytes

A
  • MOST common GLIAL CELL type
  • Each forms MYELIN SHEATH around more than one axons in CNS
  • Analogous to SCHWANN cells of PNS
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33
Q

Myelination

A
  • a MULTI LAYERED lipid and protein covering the myelin sheath and produced schwann cells and oligodendrocytes surrounds the axons of most neurons
  • the SHEATH electrically insulates the AXON and increases SPEED of NERVE IMPULSE CONDUCTION.
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34
Q

Schwann Cells

A
  • Cells encircling PNS axons
  • Each cells produces part of the myelin Sheath surrounding an axon in the PNS
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35
Q

Axon Coverings in PNS

A
  • all axons surrounded by a lipid and protien covering (myelin sheath) produced by Schwann cells
  • Neurilemma is cytoplasm and nucleus of Schwann cell
    • gaps called nodes of Ranvier
  • Myelinated FIBERS appear WHITE
    • jelly-roll like wrappings made of lipoprotein = myelin
    • acts as electrical insulator
    • speed conduction of nerve impulses
  • Unmyelinated fibers
    • slow, small diameter fibers
    • only surrounded by neurilemma but no myelin sheath wrapping
36
Q

Myelination in PNS

A
  • Schwann cells myelinate(wrap around) axons in the PNS during fetal development
  • Schwann cell cytoplasm and nucleus forms outermost layer of neurolemma with inner portion of myelin sheath
  • tube guides growing axons that are repairing themselves
37
Q

Myelination in the CNS

A
  • Oligodendrocytes myelinate axons in the CNS
  • Broad, flat cell processes wrap about CNS axons, but he cell bodies do not surround the axons
  • NO neurilemma is formed
  • Little regrowth after injury is possible due to lack of a distinct tube of neurilemma
38
Q

GRAY AND WHITE MATTER

A
  • WHITE MATTER = myelinated processes
  • GRAY MATTER = nerve cell bodies, dendrites, axon terminals, bundles of unmyelinated axxons and neuroglia (gray color)
    • in the SPINAL cord = gray matter FORMS an H-SHAPE inner core surrounded by WHITE MATTER
    • in the BRAIN = a thin outer shell of gray matter covers the surface and is found in CLUSTERS called NUCLEI inside the CNS
  • A nucleus is a mass of nerve cell bodies and dendrites inside the CNS
39
Q

Electrical signals in the neurons

A
  • Neurons ar electrically excitable due to the voltage difference across their membrane
  • COMMUNICATE with 2 TYPES of electrical signals
    • action potentials that can travel long distances
    • graded potentials that are local membrane changes only
  • Living in cells, a flow of ions occurs through ion channels in the cell membrane
40
Q

Two types of Ion Channels

A
  • Leakage (nongated) channels are alway open
    • nerve cells have more K+ than Na+ leakage channels
    • as a result, membrane potential of - 70mV in nerve tissue
  • Gated channels open and close in response to a stimulus
    • results in neuron excitability
41
Q

Ion Channels

A
  • Gated ion channels respond to voltage changes, ligands(chemicals), and mechanical pressure.
    • Voltage-gated channels respond to a direct change in the membrane potential
    • Ligand-gated channels respond to a specific chemical stimulus
    • Mechanically gated ion channels respond to mechanical vibration or pressure
42
Q

Resting membrane potential

A
  • Negative ions along inside of cell membrane & positive ions along outside
    • potential energy difference at rest is -70mV
    • cell is “polarized”
  • Resting potential exists because
    • concentration of ions different inside & outside
      • extracellular fluid rich in Na+ and Cl
      • cytosol full K+, organic phosphate & amino acids
    • membrane permeability differs for Na+ and K+
    • Na+/K+ pump removes Na+ as fast as it leaks in
43
Q

Graded Potentials

A
  • Small deviations from resting potential of -70mV
    • hyperpolarization = membrane has become more negative
    • depolarization = membrane has become more positive
  • The signals are graded meaning they vary in amplitude(size), depending on the strength of the stimulus and localized.
  • Graded potentials occur most often in the dendrites and cell body of a neuron
44
Q

How do Graded Potential Arise?

A
  • Source of Stimuli
    • mechanical stimulation of membranes with mechanical gated ions channels (pressure)
    • chemical stimulation of membranes with ligand gated ion channels (neurotransmitter)
  • Graded/postsynaptic/receptor or generator potential
    • ions flow through ion channels and change membrane potential locally
    • amount of change varies with strength of stimuli
  • Flow of current (ions) is local change only
45
Q

Generation of an ACTION POTENTIAL

A
  • An action potential(AP) or impulse is a sequence of rapidly occuring events that decrease and eventually reverse the membrane potential (depolarization) and then restore it to its resting state (repolarization)
    • durind and AP, voltage gated Na+ and K+ channels open in SEQUENCE
  • According to the all-or-none principle, if a stimulus reaches threshold, the action potential is always the same.
    • A stronger stimulus will not cause a larger impulse
46
Q

ACTION POTENTIAL

A
  • Series of rapidly occuring events that change and then restore the membrane potential of a cell to its resting state
  • Ions channed open, Na+ rushes in (depolarization), K+rushes out (repolarization)
  • all-or-none principal = with stimulation, either happens one specific way or none at all (lasts 1/1000 of a second)
  • Travels (spreads) over surface of a cell without dying out.
47
Q

Depolarization Phase of Action Potential(AP)

A
  • Chemical or mechanical stimulus caused a graded potential to reach at least (-55mV or threshold)
  • Voltage-gated Na+ channels open & Na+ rushes into cell
    • in resting membrane, inactivation gate of sodium channel is open and activation gate is closed (Na+ cannot get in)
    • when threshold (-55mV) is reached, both open & Na+ enters
    • inactivation gate closes again in few ten-thousands of a second
    • only a total of 20,000 Na+ actually enter the cell, but they change the membrane potential considerably (up to +30mV)
  • Positive feedback process
48
Q

Repolarization Phase of AP

A
  • When threshold potential reach -55mV is reached voltage K+ channels open
  • K+ channel opening is much slower than Na+ channel opening which causes depolarization
  • When K+ channels finally do open, the Na+ channels have already closed(Na+ inflow stops)
  • K+ outflow returns membrane potential to -70mV
  • if enough K+ leaves the cell, it will reach a -90mV membrane potential and enter the after-hyperpolarizing phase
  • K+ channels close and the membrane potential returns to the resitng potential of -70mV
49
Q

Refractory Period of Action Potential(AP)

A
  • Period of time during which neuron can not generate another action potential
  • Absolute refractory period
    • even very strong stimulus with not begin another AP
    • Inactivated Na+ channels must return to the resting state before they can be reopened
    • large fibers have absolute refractory period of 0.4 msec and up to 1000 impulses per second are possible
  • Relative refractory period
    • a suprathreshold stimulus will be able to start an AP
    • K+ channels are still open, but Na+ channels have closed
50
Q

The ACTION POTENTIAL SUMMARIZED

A
  • Resting membrane potential is -70mV
  • Depolarization is the change from -70mV to +30mV
  • Repolarization is the reversal from +30mV back to -70mV
51
Q

LOCAL ANESTHETICS

A
  • Local anesthetics and certain neurotoxins
    • prevent opening of voltage -gated Na+ channels
    • Nerve impulses cannot pass the anesthetized region
  • Examples:
    • Novocaine and Lidocaine
52
Q

Propagation of Action Potential(AP)

A
  • An AP spreads(propagates) over the surface of the axon membrane
    • as the Na+ flows int the cell during depolarization, the voltage of the adjacent areas is effected and their voltage-gated Na+ channels open
    • self propagating along the membrane
    • The traveling action potential is called a nerve impulse
53
Q

Continuous versus Saltatory Conduction

A
  • Continuous conduction (unmyelinated fibers)
    • step by step depolarization of each portion of the length of axolemma
  • Saltatory conduction
    • depolarization only at the nodes of Ranvier where there is a high density of voltage-gated ion channels
    • current carried by ions flow through the extracellular fluid from node to node
54
Q

Speed of Impulse Propagation

A
  • the propagation speed of a nerve impulse is not related to stimulus strength
    • larger, myelinated fibers conduct impulses faster due to size and saltatory conduction
  • Fiber types
    • A fibers largest (5-20 microns & 130 m/sec)
      • myelinated somatic sensory & motor to skeletal muscle
    • B fibers medium (2-3 microns adn 15 m/sec)
      • myelinated visceral sensory & autonomic pregangleonic
    • C fibers smallest (.5-1.5 microns & 2m/sec)
      • unmyelinated sensory and autonomic motor
55
Q

Encoding of Stimulus Intensity

A

The difference from a light touch from a firmer touch

  • Frequency of impulses
    • firm pressure generates impulses at a higher frequency
  • number of sensory neurons activated
    • firm pressure stimulate more neurons that does a light touch
56
Q

Action Potential in Nerve and Muscle

A
  • Entire muscle cell membrane versus only the axon of the neuron is involved
  • Resting membrane potential
    • Nerve is -70mV
    • skeletal and cardiac muscle is closer to -90mV
  • Duration
    • Nerve impulsis 1/2 to 2 msec
    • muscle action potential lasts 1-5msec for skeletal and 10-300 msec for cardiac and smooth muscle
  • Fastes nerve conduction velocity is 18 times faster than velocity over skeletal muscle fiber
57
Q

Signal transmission of synapses

A
  • synapse is the functional junction between one neuron and another OR between a neuron and an effector such as a muscle or gland
58
Q

Signal transmission at Synapses

A
  • 2 types of SYNAPSES
    • electrical
      • ionic current spreads to next cell through gap junctions
      • faster two way transmission & capable of synchronizing groups of neurons
    • chemical
      • one way information transfer from a presynaptic neuron to a postsynaptic neuron
        • axo dentritic - from axon to dendrite
        • axo somatic - from axon to cell body
        • axo axonix - from axon to axon
59
Q

Chemical Synapses

A
  • Action Potential reaches an end bulb and voltage-gated Ca+ 2 channels open
  • Ca+2 flows inward triggering release of neurotransmitter
  • Neurotransmitter crosses synaptic cleft and binding to ligand-gated receptors
    • the more neurotransmitter released the greater change in potential of the postsynaptic cell
  • Synaptic delay is 0.5 msec
  • One way information transfer
60
Q

Removal of Neurotransmitter

A
  • Diffusion
    • move down concentration gradient
  • Enzymatic degradation
    • acetylcholinesterase
  • Uptake by neurons of glia cells
    • neurotransmitter transporters
  • Prozac = serotonin re-uptake inhibitor
61
Q

Three POSSIBLE Responses

A

(this can possibly happen after removal of neurotransmitter)

  • Small EPSP occurs
    • potential reaches -56mV only
  • An impulse is generated
    • threshold was reached
    • membrane potential of at least -55mV
  • IPSP occurs
    • membrane is hyperpolarized
    • potential drops below -70mV
62
Q
A
63
Q

Comparison of Graded and Action Potentials

A
  • origin
    • GPs arise on dendrites and cell bodies
    • APs arise only at trigger zone on axon hillock
  • Types of Channels
    • AP is produced by voltage-gated ion channels
    • GP is produced by ligand or mechanically-gated channels
  • Conduction
    • GPs are localized not propagated
    • APs conduct over the surface of the axon
64
Q

CONTINUED Comparison of Graded and Action Potentials

A
  • Amplitude
    • amplitude of AP is constant (all-or-none)
    • graded potentials vary depending upon stimulus
  • Duration
    • the duration of GP is as long as the stimulus lasts
  • Refractory period
    • The AP has a refractory period due to the nature of the voltage-gated channels, and the GP has none.
65
Q

SUMMATION

A
  • If several presynaptic end bulbs release their neurotransmitter at about the same time, the combined effect may generate a nerve impulse due to summation
  • summation maybe spatial or temporal
66
Q

Spatial summation

A

Summation of effects of neurotransmitters released from several end bulbs onto one neuron

67
Q

Temporal summation

A

summation of effect of neurotransmitters RELEASED from 2 or more firings of the same end bulb in rapid succession onto a second neuron

68
Q
A
69
Q

Summation

A
  • the postsynaptic neuron is an integrator, receiving and intergrating signals then responding
  • if the excitatory effect is greater than the inhibitory effect but less than the threshold level of simulation, the RESULT is a subthreshold EPSP, making it easier to generate a NERVE IMPULSE.
  • if the excitatory effect is greather than the inhibitory effect and reaches or surpasses the threshold level of stimulation, the RESULT is a threshold or SUPRATHRESHOLD EPSP and a nerve impulse
  • If the inhibitory effect dis greater than the excitatory effect the membrane hyperpolarizes IPSP with failure to produce a nerve impulse.
70
Q

Neurotransmitters

A
  • Both excitatory and inhibitory neurotransmitters are present in the CNS and PNS; the same neurotransmitter maybe excitatory in some locations and inhibitory in others
  • Important neurotransmitters include acetylcholine,glutamate,aspartate, gamma aminobutric acide, glycine, norepinephrine, epinephrine, and dopamine
71
Q

Neurotransmitter Effects

A
  • Neurotransmitter effects can be modified
    • synthesis can be stimulated or inhibited
    • release can be blocked or enhanced
    • removal can be simulated or blocked
    • receptor site can be blocked or activated
  • Agonist
    • anything that enhances a transmitters effects
  • Antagonist
    • anything that blocks the action of a neurotransmitter
72
Q

Small-Molecule Neurotransmitter

A
  • Acetylcholine(ACh)
    • released by many PNS neurons & some CNS
    • excitatory on NMJ but inhibitory at others
    • inactivated by acetylcholinesterase
  • Amino Acids
    • glutamate released by nearly all excitatory neurons in the brain — inactivated by glutamate specific transporters
    • GABA is inhibitory neurotransmitter for 1/3 of all brain synapses (valium is a GABA agonist – enhancing its inhibitory effect)
73
Q

Cont. Small molecule Neurotransmitters

A
  • Biogenic Amines
    • modified amino acids (tyrosine)
      • norepinephrine – regulates mood, dreaming, awakening from deep sleep
      • dopamine – regulating skeletal muscle tone
      • serotonin – control of mood, temperature regulation, & induction of sleep
    • removed from synapse & recycled or destroyed by enzymes (mono amine oxidase or catechol-0-methyltransferase)
74
Q

Cont. Small molecule neurotransmitters

A
  • ATP and othe purines (ADP,AMP and adenosine)
    • excitatory in both CNS and PNS
    • released with other neurotransmitters (ACh & NE)
  • Gases (Nitric oxide or NO)
    • formed from amino acid arginine by and enzyme
    • formed on demand and acts immediately
      • diffuses out of cell that produced it to affect neighboring cells
      • may play a role in memory and learning
    • first recognized as VASOLIDILATOR that helps lower blood pressure
75
Q

Neuropeptides

A
  • 3-40 amino acids linked by peptide bonds
  • Substance P – enhances our perception of pain
  • Pain relief
    • enkephalins – pain relieving effect by blocking the release of substance P
    • acupuncture may produce loss of pain sensation because of the release of opiods-like substances such as endorphine or dynorphins
76
Q

Strychnine Poisoning

A
  • In spinal cord, Renshaw cells normally release an inhibitory neurotransmitter (glycine) onto motor neurons preventing excessive muscle contraction
  • Strychnine binds to and blocks glycine receptors in the spinal cord
  • Massive tetanic contractions of all skeletals muscles are produced
    • when the diaphram contracts and remains contracted, breathing cannot OCCUR!
77
Q

Neuronal Circuits

A
  • Neuronal pools are organized into circuits (neural networks) These include simple series, diverging, converging, reverberating, and parallel after discharge circuits (figure 12.18 a-d)
  • A neuronal network may contain thousands or even millions of neurons
  • Neuronal circuits are involved in many important activities
    • breathing
    • short-term memory
    • waking up
78
Q

Cont. Neuronal Circuits

A
  • Diverging – single cell stimulates many others
  • Converging – one cell stimulated by many others
  • Reverberating – impulses from later cells repeatedly stimulate early cells in the circuit (short term memory)
  • Parallel-after-discharge – single cell stimulates a group of cells that ALL stimulate a common postsynaptic cell(math problems)
79
Q

REGENERATION AND REPAIR

A
  • Plasticity maintained throughout life
    • sprouting of new dendrites
    • synthesis of new proteins
    • changes in synaptic contacts with other neurons
  • Limited ability for regeneration (repair)
    • PNS can repair damaged dendrites or axons
    • CNS no repairs are possible
80
Q

Damage and Repair in the Peripheral Nervous System

A
  • When there is damage to an axon, usually there are changes, called chromatolysis, which occur in the cell body of the affected cell; this causes swelling of the cell body and peaks beteween 10 and 10 days after injury
  • By the 3rd to 5th day, degeneration of the distal portion of the neuronal process and myelin sheath (Wallerian degeneration) occurs; afteward, macrophages phagocytize the remains.
  • Retrograde degeneration of the proximal portion of the fiber extends only to the first neurofibral node
  • Regeneration follows chromatolysis; synthesis of RNA and protein accelerates, favoring rebuilding of the axon and often taking several months.
81
Q

Repair within the PNS

A
  • Axons & dendrites maybe repaired if
    • the neuron cell body remain intact
    • schwann cells remain active and form a tube
    • scar tissue does not form too rapidly
  • Chromatolysis
    • 24-48 hours after injury, Nissl bodies break up into fine granual masses
82
Q

Repair within the PNS

A
  • By 3 - 5 days
    • wallerian degeneration occurs(breakdown of axon and myelin sheath distal to injury)
    • retrograde degeneration occurs back one node
  • With in several months regeneration occurs
    • neurolemma on each side of injury repairs tube (schwann cell mitosis)
    • axonal buds grow down the tube to reconnect(1.5mm per day)
83
Q

Neurogenesis in the CNS

A
  • Formation of new neurons form stem cells was not thought to occur in humans
    • 1992 a growth factor was found that stimulates adult mice brain cells to multiply
    • 1998 new neurons found to form within adult human hippocampus (area important to learning)
  • There is a lack of neurogenesis in other regions of the brain and spinal cord
  • Factors preventing neurogenesis in CNS
    • inhibitions by neuroglial cells, absence of growth stimulating factors, lack of neurolemmas, and rapid formation of scar tissue
84
Q

Multiple Sclerosis

A
  • Autoimmune disorder causing destruction of myelin sheaths in CNS
    • sheaths become scars or plaques
    • 1/2 million people in the United States
    • appears between ages 20 and 40
    • females twice as often as males
  • Symptoms include muscular weakness, abnormal sensations or double vision
  • Remissions & relapses result in progressive, cumulative loss of function
85
Q

EPILEPSY

A
  • The second most common neurological disorder
    • affects 1% of the population
  • Characterized by short, recurrent attacks inititated by electrical discharges in the brain
    • lights, noise, or smells maybe sensed
    • skeletal muscles may contract involuntarily
    • loss of consciousness
  • Epilepsy has many causes, including;
    • brain damage at birth, metabolic disturbances, infections, toxins, vascular disturbances, head injuries, and tumors.

Biology (8 decks)

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