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Histology > Nerve & Muscle Tissue > Flashcards

Nerve & Muscle Tissue Flashcards

1
Q

True or False: Involuntary muscle contracts spontaneously, without neural input

A

TRUE

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2
Q

What are the three types of muscle?

A

1) Skeletal/striated voluntary muscle
2) Cardia/striated involuntary muscle
3) Smooth/non-striated involuntary muscle

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3
Q

What are striations a result of?

A

Highly ordered arrangement of the actin and myosin proteins in some muscle tissues

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4
Q

What are characteristics of skeletal muscle?

A
  • Nuclei are at the periphery
  • Cells do not contact adjacent cells directly, but are connected via CT components (no cell junctions)
  • Unbranched, cylindrical cells with striations
  • Multinucleated
  • Very long
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5
Q

Blood vessels and nerves serve a given organ to form a…

A

Neurovascular bundle

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6
Q

What are characteristics of cardiac muscle?

A
  • Incapable of repair following damage
  • Mononuclear; nuclei are centrally-located
  • Striated
  • Involuntary and intrinsically contractile; no neural input needed
  • Cardiocytes form branching networks joined at intercalated discs
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7
Q

What are intercalated discs?

A
  • Found between adjacent cardiocytes to join them
  • Allow for intercellular communication via gap junctions
  • Consists of fascia adherens, which anchors actin filaments of terminal sarcomeres in adjacent cells to provide mechanical strength
  • Desmosomes between adjacent cells provide anchorage for intermediate filaments of the cytoskeleton
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8
Q

What are characteristics of smooth muscle tissue?

A
  • Nonstriated due to irregular arrangement of myofilaments
  • Small, spindle-shaped cells
  • Capable of repair and regeneration
  • Smallest muscle cells
  • Found in respiratory, circulatory, reproductive, GI tracts
  • Contraction modulated by ANS and hormones
  • Involuntary
  • Gap junctions distribute signals
  • Nuclei can be elongated
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9
Q

What are neurons?

A
  • Cells of the NS that are specialized for communication
  • Communicate by chemical or electrical means
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10
Q

What are neuroglia?

A
  • Provide structural support - “replace” reticular fibres
  • Provide chemical support - control the composition of IF and CSF and mediate metabolic exchange
  • Provide immunological defense
  • Form an insulating layer via myelin sheath
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11
Q

Where are multipolar neurons found?

A

Somatic and visceral (autonomic) motor neurons, interneurons

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12
Q

What are bipolar neurons?

A
  • Two process arise from one soma
  • Used for special senses in retina, cochlea, vestibular apparatus
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13
Q

What are pseudounipolar neurons?

A
  • Usually sensory neurons
  • Cell body hangs off of axon
  • Dendrites in the periphery, and axon extends to CNS, with cell bodies located in a sensory ganglion
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14
Q

Describe the organization of skeletal muscle and its CT coverings.

A

Skeletal muscle is surrounded by epimysium and is composed of multiple muscle fascicles ➡️ each muscle fascicle is surrounded by perimysium and is composed of individual muscle cells/fibres ➡️ each muscle fibre is surrounded by endomysium and contains filamentous proteins called myofibrils

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15
Q

Each skeletal muscle fibre has a nerve terminal called the ______.

A

Motor endplate

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16
Q

Describe components of internal organization of skeletal muscle fibres.

A

Sarcoplasm: cytoplasm of muscle fibres
Sarcolemma: cell membrane of muscle fibres
T-tubules: tubular extensions of sarcolemma perpendicular to the cell surface
Sarcoplasmic reticulum: ER of the muscle fibre; acts as a calcium reservoir
Terminal cisternae: expansions of the SR on either side of the T-tubule
Myofibrils: bundles of myofilaments, including actin and myosin
Sarcomere: the contractile unit of striated muscle

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17
Q

What is G actin?

A

Globular actin subunits, each with an active site that binds to myosin heads

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18
Q

What is F actin?

A

Polymer of many actin molecules that form two strands wound around each other

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19
Q

What is tropomyosin?

A

Regulatory molecule that covers the active site of the G actin molecule, preventing crossbridge binding

20
Q

What is troponin?

A

Holds tropomyosin in place and shifts it when there is an increase in calcium, revealing the active site of actin

21
Q

What are thick filaments?

A

Consist of hundreds of myosin molecules, each with a tail and head, which bind the active site of G actin

22
Q

Each thick filament is surrounded by…

A

6 thin filaments

23
Q

What are the three components of the neuromuscular junction?

A

1) Axon terminal
2) Synaptic cleft
3) Motor end plate

24
Q

What is the purpose of junctional folds within the motor end plate?

A

Increases the surface area of the motor end plate to accommodate more AChRs

25
Q

Describe the steps of muscle contraction, beginning with the NMJ.

A

1) A nerve impulse causes ACh to be released at the NMJ, binding AChRs at the motor end plate, and causing depolarization of the sarcolemma
2) This triggers an AP and causes it to spread over the sarcolemma
3) The AP is conducted along the sarcolemma lining the T-tubules, which triggers voltage-sensor proteins to alter their conformation
4) This conformational change triggers the opening of Ca2+ channels in the SR for Ca2+ to flow out
5) Ca2+ binds troponin, causing tropomyosin to shift and expose the active sites of actin
6) Myosin head will bind to the active site, pulling the actin filaments towards the centre of the sarcomere and shortening the muscle fibre as a whole
7) When APs cease and Ca2+ channels in the SR close, Ca2+ is sequestered in the SR by active pumps and active sites are again covered

26
Q

What is a motor unit?

A

A single motor neuron and all the muscle fibres it innervates

27
Q

How is the number of muscle fibres per motor unit related to precision?

A

The smaller the motor units, the more precisely a muscle can be controlled

28
Q

The origin of the signal determines the ____.

A

Modality (vision, touch, smell, etc.)

29
Q

The intensity of signalling is determined by its…

A

Amplitude and frequency, coded by graded potentials

30
Q

Unidirectional communication occurs electrically within a neuron via changes in…

A

Transmembrane potential (Vm)

31
Q

Describe what each of the labels signify.

A

A: Dendrites - receive input
B: Cell body (soma)
C: Axon - integration and output
D: Synaptic terminals - chemical transfer of information
E: Axon hillock - where APs begin

32
Q

What determines the response - the NT or the receptor?

A

The receptor

33
Q

True or False: Glia greatly outnumber neurons.

A

True

34
Q

How does the location of grey vs white matter differ between the brain and the spinal cord?

A

In the brain - grey matter is found primarily in the cortex (outside), whereas white matter is found within that

In the spinal cord - grey matter is located centrally, within the white matter

35
Q

What are the three CT coverings of peripheral nerves?

A

1) Epineurium - outermost layer
2) Perineurium - surrounds individual fascicles
3) Endoneurium - surrounds individual axons within a fascicle

36
Q

What is the role of astrocytes?

A
  • Star-shaped glia within the CNS
  • Protoplasmic astrocytes are mainly in grey matter, and fibrous astrocytes predominate white matter
  • Contribute to the BBB by creating tight junctions with capillary endothelial cells
  • Provide structural support, thus acting like reticular CT in the CNS
  • Maintain the chemical homeostasis of ECF
37
Q

What type of cancer accounts for 80% of brain tumours?

A

Fibrous astrocytomas

38
Q

Astrocytes are rich in intermediate filaments composed of…

A

Glial fibrillary acidic protein (GFAP), which can be used for identification

39
Q

What are the components of the blood-brain barrier?

A

1) Tight junctions of endothelial cells
2) Foot processes of astrocytes
3) Pericytes embedded in endothelial BM

40
Q

What is the role of oligodendrocytes?

A
  • Glial cells within the CNS
  • Make the myelin sheath on axons in CNS
41
Q

What is the role of microglia?

A
  • Phagocytic cells of the CNS
  • Nuclei have a flattended, elongated appearance
  • Normally there are few in # but they proliferate when activated by damage or infection
42
Q

What is the role of ependymal cells?

A
  • Ciliated cuboidal epithelial cells
  • Line fluid-filled spaces within the CNS, such as the ventricle walls and central canal of the spinal cord
  • The cilia help to propel CSF through ventricles
  • Cover the blood vessels of the choroid plexus
43
Q

What is the role of satellite cells?

A
  • Surround neuronal somas in the PNS (ie. in ganglia)
  • Electrically and chemically insulate the cell body
44
Q

What is the role of Schwann cells?

A
  • Make the myelin sheath in axons within the PNS
  • Wrap around the axon to form many layers of Schwann cell membrane and cytoplasm around it
  • Can also “envelope” unmyelinated axons; they enfold multiple axons into a groove so that the axon is surrounded by a single layer of cell membrane
45
Q

How do Schwann cells differ from oligodendrocytes?

A
  • They dedicate themselves to one axon, unlike oligodendrocytes
  • Like oligodendrocytes, many Schwann cells are needed to myelinate a given axon

Histology (4 decks)

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