Nervous Tissue Flashcards

1
Q

Functions

A
  • controls and integrates all body activities (along with endocrine system)
  • 3 basic functions:
    1. Sensory: sensing changes with receptors
    2. integration: interpreting and remembering those changes
    3. motor: reaction to those changes with effectors
      - muscular contractions
      - glandular secretions
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2
Q

Divisions of Nervous System

A
  1. Central nervous system: brain and spinal cord
  2. Peripheral nervous system: cranial and spinal nerves that contain sensory and motor fibres. Connect CNS to muscles, glands, and all sensory receptors
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3
Q

Subdivisions of the PNS

A
  • somatic (voluntary NS
  • sensory info from sensory receptors to CNS
  • motor neurons to skeletal muscles
  • autonomic (involuntary) nervous system
  • sensory neurons from visceral organs to CNS
  • motor neurons to smooth & cardiac muscle and glands
  • divided into sympathetic & parasympathetic & enteric division (neurons in gut)
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4
Q

Histology of Nervous Tissue

A
  • consists of 2 main cell types
    • neurons
    • neuroglia
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5
Q

Neuroglial Cells

A
  • half the volume of CNS
  • smaller cells than neurons
  • 50x more numerous
  • cells can divide
    • rapid mitosis in tumour formation (gliomas)
  • 4 cells types in CNS
    • astrocytes, oligiodendrocytes, microglia, ependydymal
  • 2 cell types in PNS
    • schwann and satellite cells
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6
Q

Astrocytes

A
  • star shaped cells
  • form blood-brain barrier by covering blood capillaries
  • metabolize neurotransmitters
  • regular K+ balance
  • provide structural support
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7
Q

Oligiodendrocytes

A
  • each forms myelin sheath around more than one axon in CNS

- analogous to Schwann cells of PNS

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8
Q

Microglia

A
  • small cells found near blood vessels
  • phagocytic role: clear away dead cells
  • derived from cells that also gave rise to macrophages and monocytes
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9
Q

Ependymal Cells

A
  • form epithelial membrane lining cerebral cavities and central canal of the spinal cord
  • produces cerebrospinal fluid (CSF)
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10
Q

Satellite Cells

A
  • flat cells surrounding neuronal cell bodies in peripheral ganglia
  • support neurons in PNS ganglia
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11
Q

Shwann Cells

A
  • cells encircling PNS axons

- each cell produces part of the myelin sheath surrounding an axon on the PNS

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12
Q

Neurons

A
  • functional unit of nervous system
  • have capacity to produce action potential (electrical excitability)
  • cell body is a single nucleons with prominent nucleolus
  • cell body contains nissle bodies (chromatophilic substance)
    • rough ER and free ribosomes for protein synthesis
  • neurofilaments give cell shape and support
  • microtubules move material inside cell
  • cell processes: dendrites and axons
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13
Q

Dendrites

A
  • conduct impulses toward the cell body (receptive zone)
  • typically short, highly branched and unmyelinated
  • surfaces specialized for contact with other neurons
  • contains neurofibromas and Nissan bodies
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14
Q

Axons

A
  • conducts impulses away from cell body (conductive zone)
  • long, thin cylindrical process of cell
  • arises at axon hillock
  • impulses arise from initial segment (trigger zone)
  • side branches (collaterals) end in fine processes called axon terminals
  • swollen tips called synaptic end bulbs contain vesicles filled with neurotransmitters
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15
Q

Axon coverings in PNS

A
  • axons surrounded by a lipid & protein covering produced by Schwann cells
  • myelinated axons appear white (jelly-roll like wrapping made of lipoprotein myelin) acts as electrical insulator and speeds up conduction of nerve impulses
  • regular spaces or gaps in myelin sheath called nodes of ranvier
  • unmyelinated fibres: slow, small diameter fibres
    • surround glial cell processes but no myelin sheath wrapping
    • gray and white matter
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16
Q

Myelination in PNS

A
  • Schwann Cells myelinate axons in the PNS during fetal development
  • shwann cell cytoplasm and nucleus forms outermost part with inner portion being myelin sheath
  • tube guides growing axons that are being repaired themselves
17
Q

Parts of synapse

A
  • presynaptic neuron
    • synaptic end bulb
    • synaptic vesicle
    • presynaptic membrane
  • synaptic cleft
  • postsynaptic neuron
    • postsynaptic membrane
    • neurotransmitter receptor sites
18
Q

Transmission of Nerve Impulses

A
  • neuronal excitation and inhibition
    • axon terminals form synapses on dendrites and cell body (excitatory and inhibitory neurotransmitters)
  • Nerve impulse conduction along axon
    • summation takes place at initial segment on axon hillock (concentration of Na ion channels)
  • Nerve impulse conduction along axon
    • at threshold Na channels open and nerve impulse conducted down axon
    • myelinated axon, Na channels open at nodes of ranvier, Salvatore conduction
    • unmyelinated axon, Na channels open on adjacent patch of membrane, slower, continuous conduction
19
Q

Structural classification of neurons

A
  • based on numbers of processes found on cell body
  • multipolar: several dendrites and one axon (most common)
  • bipolar: one main dendrite and one axon (found in retina, inner ear, and olfactory epithelium)
  • unipolar: one process only develops from bipolar (always sensory neurons - dorsal root and ganglia)
20
Q

Functional classification of neurons

A
  • sensory (affrent) neurons: transport sensory information from skin/muscles/joints/sense organs & viscera to CNS)
  • motor (efferent): send motor nerve impulses to muscles and glands)
  • interneurons (association) and projection neurons: connect neuron to neuron
    • 90% of neurons in the body
21
Q

Neuronal Circuits

A
  • diverging: single cell stimulates many others (amplifying the signal)
  • 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 stimulated a group of cells that all stimulate a common postsynaptic cell (precise activities such as math calculations)
22
Q

Regeneration and Repair

A
  • plasticity maintained throughout life
    • sprouting of new dendrites
    • synthesis of 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
23
Q

Repair within PNS

A
  • axons and dendrites may be repairs if:
    • neuron cell body intact
    • Schwann cells remain active and form a tube
    • scar tissue does not form too rapidly
24
Q

Repair within the PNS

A
  • chromatolysis
    • 24-48 hours after injury, nissle bodies break up into fine granular masses
  • by 3-5 days
    • Waller Ian degeneration occurs (breakdown of axon and myelin sheath distal to injury)
    • retrograde degeneration occurs back one node
  • within several months, regeneration occurs
    • neuroglia on each side of injury repairs tube (Schwann cell mitosis)
    • atonal buds grow down the tube to reconnect (1.5mm per day)