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Anatomy > Histoanatomy 1: Neural Tissue > Flashcards

Histoanatomy 1: Neural Tissue Flashcards

1
Q

LO: Describe the basic structural features of neurons

A
  • similar basic components –> uniform basic mechanism of signalling for vision/ touch/ smell/ muscular contraction/ thought (signal origin/ path/ target determines modality vs signal frequency/ pattern determines intensity)
  • neurons are polarized = 2 ends differ in structure/ function
  • dendrites: receive input; graded electrical signals code stimulus strength
  • cell body (soma): input; genetic/ metabolic centre
  • axon (nerve fibre): integrate, output; fixed amplitude APs start at initial segment; usually only 1; vary in length, so may fxn locally/ distantly; can be myelinated/ not; may branch distally –> axon collaterals
  • synaptic terminals: chemical info transfer; target cell type varies (other neuron, muscle, gland)
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2
Q

LO: Describe neuronal function in information transfer

A
  1. unidirectional communication occurs ELECTRICALLY WITHIN neuron via changes in Vm (transmembrane potential)
    - neurons (and muscle cells) are excitable (can generate current flow across membranes –> Vm changes that propagate over cell surface) due to membrane proteins
    - in different parts of neurons, Vm can be graded/ decremental/ all or none/ non-decremental
  2. Unidirectional communications occurs CHEMICALLY BETWEEN cells at synapses via NTs (also due to proteins)
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3
Q

LO: Describe basic structural features of a synapse

A
  1. presynaptic terminal of axon has:
    - voltage gated Ca2+ channels that open when AP arrives
    - active zone where vesicles dock
  2. Synaptic cleft
  3. Postsynaptic membrane of dendrite has:
    - transmitter-gated ion channels/ GPCRs
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4
Q

LO: Describe sequence of steps in synaptic transmission

A
  • AP arrives at terminal
  • voltage gated Ca2+ channels open
  • vesicles dock in active zone
  • NT release by exocytosis
  • membrane retrieved presynaptically by endocytosis
  • postsynaptically, NT binds either ligand-gated ion channels or GPCRs (receptor determines response)
  • NT removed from cleft via reuptake OR enzymatic degradation
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5
Q

LO: Describe structural differences between grey/ white matter

A

Histologically, NS can be subdivided into tissues with/ without neuronal cell bodies in both CNS/ PNS:

  1. White matter (nerves in PNS):
    - axons, glia, vessels, (and CT in PNS)
  2. Grey matter (ganglia in PNS):
    - axons, glia, vessels, AND NEURONAL CELL BODIES
  • glia greatly outnumber!
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6
Q

LO: What are the glial cells of CNS & PNS

A
  1. CNS glia: astrocytes, oligodendrocytes, microglia, ependyma
  2. PNS: satellite cells, Schwann cells
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7
Q

LO: Describe relationships between nerve fibres/ connective tissues in a peripheral nerve

A
  1. Peripheral nerves contain mix of:
    - myelinated/ unmyelinated fibres
    - sensory/ motor (ie. info flows both toward/ away from CNS in given nerve)
    - somatic/ autonomic (ie. somatic motor to skeletal muscle/ sympathetic postganglionic to smooth muscle/ glands in given nerve)
  2. Each axon and its Schwann cell surrounded by ENDONEURIUM: areolar CT including dense, fine capillaries produced by fibroblasts
    - these are bundled together as fascicles and surrounded by PERINEURIUM: more dense, irregular CT
    - larger nerves may consist of multiple fascicles bound together by EPINEURIUM, areolar CT that includes larger vessels/ forms condense sheath surrounding nerve
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8
Q

What are the functions of the nervous system?

A
  1. SENSE: monitor/ detect changes in internal/ external env. = input
  2. INTEGRATE: compare inputs from various senses –> predict outcome of various responses
  3. RESPOND: via control of muscle = output
  • communication = defining function!
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9
Q

Describe two broad categories of neural cells

A
  1. Neurons = specialized for communication
    - electrically within cell via changes in Vm
    - chemically between cells via synaptic transmission
  2. Neuroglia do NOT transfer info, instead:
    - provide structural support (no reticular fibres in neural tissue)
    - chemical support (control CSF/ interstitial fluid composition & mediate metabolic exchange between blood/ neurons)
    - immunologic defence
    - form myelin sheath = insulating
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10
Q

LO: how does neuronal information transfer vary between 3 common classes

A
  1. Multipolar: somatic/ autonomic (visceral) motor neurons, interneurons
    - most common
  2. Bipolar: “special senses” - ie. retina, cochlea, vestibular apparatus
  3. Pseudounipolar: sensory neurons - cell body hangs off axon in sensory ganglion
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11
Q

Graded signal

A
  • a graded signal is proportional in amplitude to the strength of the stimulus that evoked it - ie. strong stimulus = large signal (ie. at receptor/ synaptic potentials)
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12
Q

Decremental signal

A
  • a decremental signal decreases in amplitude as it travels along the membrane away from its point of initiation (ie. at receptor/ synaptic potentials)
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13
Q

All or none signal/ Non-decremental signal

A
  • uniform in amplitude, regardless of stimulus strength
  • constant amplitude; no failure/ distortion of AP over space/ time
  • ie. AP
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14
Q

LO: How does neuronal structure vary between 3 common classes?

A
  1. Multipolar neurons: dendrites/ axon extends from soma
  2. Bipolar: 2 processes from soma - 1 extends peripherally, ending in dendrites, other extends centrally
  3. Pseudounipolar: soma hangs off axon, located in sensory ganglion (ie. DRG, trigeminal ganglion, geniculate ganglion); dendrites/ initial segment in periphery; axon extends to CNS
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15
Q

Describe 2 anatomic subdivisions of NS

A
  1. CNS: brain & SC

2. PNS: all other neural tissue

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16
Q

LO: Describe structure/ function of astrocytes

A

CNS GLIA

  1. Structure:
    - named for star shape
    - 2 major classes: protoplasmic in grey matter, fibrous in white
    - cellular extensions end in “foot processes” (perivascular/ perineural feet) which contact BVs/ neurons
    - rich in intermediate filaments composed of GFAP (glial fibrillary acidic protein)
  2. Function:
    - contact of foot processes with BVs –> tight junctions of BBB
    - structural support: role of reticular CT in CNS
    - maintain ECF chemical homeostasis (ie. buffer K+)
  • think foot on BV –> BBB, foot on neuron –> structural support!
17
Q

LO: Describe basic structure/ function of oligodendrocytes:

A

CNS GLIA

  1. Structure:
    - form myelin sheath in CNS (wrap many layers of O-cyte cell membrane around axon)
    - 1 O-cyte may contribute myelin sheath to up to 50 axons (ie. may wrap its membrane around 50 axons)
    - many O-cites required to myelinated each axon (# determined by length)
    - nodes of Ranvier separate O-cytes along axon (permit exposure of axonal membrane to ECF)
  2. Function:
    - increase AP conduction rate along axon
18
Q

LO: Describe basic structure/ function of microglia

A

CNS GLIA

  1. Structure:
    - few in number (~5% of glia), but proliferate/ become phagocytic when activated by damage/ infection
  2. Function:
    - phagocytic cells of macrophage/ monocyte lineage
19
Q

LO: Describe basic structure/ function of ependymal cells

A

CNS GLIA
1. Structure:
- ciliated cuboidal epithelial cells
2. Function:
- single layer lines free surfaces/ fluid-filled spaces within CNS (ventricle walls, SC central canal)
- cilia propel CSF through ventricular system
- also cover BVs of choroid plexus (brain structure that actively secretes CSF into ventricles)
(CSF fills within CNS (ventricles)/ around CNS (cisterns))

20
Q

LO: Describe basic structure/ function of satellite cells:

A

PNS GLIA (most numerous cell in ganglia)

  1. Structure:
    - surround neuronal cell bodies in PNS (ie. ganglia)
  2. Function:
    - electrically/ chemically insulate cell body –> regulate cell environment (ie. basically myelin on cell bodies)
21
Q

LO: Describe basic structure/ function of Schwann cells

LO: Describe relationships between Schwann cells/ nerve fibres in myelinated/ unmyelinated neurons of the PNS

A

PNS GLIA

  1. form myelin sheath surrounding myelinated PNS axons
    - each Schwann cell wraps itself around a length of axon, squeezing out its cytoplasm –> numerous layers of Schwann cell membrane (appears as thick black layer around axon under microscope)
    - unlike O-cytes, each dedicates itself to SINGLE axon
    - many needed to myelinated given axon
  2. also envelope “unmyelinated” axons in PNS
    - Schwann cells do NOT wrap membrane around axon! Merely enfold it into groove –> axon surrounded by single layer of Schwann cell membrane/ cytoplasm.
    - *# of axons associated with each Schwann cell varies, can be >1!
22
Q

What is GFAP?

A
  • glial fibrillary acidic protein
  • in intermediate filaments of astrocytes (CNS glia)
  • antibodies to GFAP used for identification (ie. fibrous astrocytomas (~80% of adult primary brain tumours) identified by GFAP specificity
23
Q

Initial segment

A
  • part of axon that is most excitable, thus will most easily convert graded signal –> AP

Anatomy (5 decks)

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