Nerve & Muscle Tissue

Question 1

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

Answer 1

TRUE

Question 2

What are the three types of muscle?

Answer 2

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

Question 3

What are striations a result of?

Answer 3

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

Question 4

What are characteristics of skeletal muscle?

Answer 4

• 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

Question 5

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

Answer 5

Neurovascular bundle

Question 6

What are characteristics of cardiac muscle?

Answer 6

• 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

Question 7

What are intercalated discs?

Answer 7

• 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

Question 8

What are characteristics of smooth muscle tissue?

Answer 8

• 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

Question 9

What are neurons?

Answer 9

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

Question 10

What are neuroglia?

Answer 10

• 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

Question 11

Where are multipolar neurons found?

Answer 11

Somatic and visceral (autonomic) motor neurons, interneurons

Question 12

What are bipolar neurons?

Answer 12

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

Question 13

What are pseudounipolar neurons?

Answer 13

• 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

Question 14

Describe the organization of skeletal muscle and its CT coverings.

Answer 14

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

Question 15

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

Answer 15

Motor endplate

Question 16

Describe components of internal organization of skeletal muscle fibres.

Answer 16

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

Question 17

What is G actin?

Answer 17

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

Question 18

What is F actin?

Answer 18

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

Question 19

What is tropomyosin?

Answer 19

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

Question 20

What is troponin?

Answer 20

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

Question 21

What are thick filaments?

Answer 21

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

Question 22

Each thick filament is surrounded by…

Answer 22

6 thin filaments

Question 23

What are the three components of the neuromuscular junction?

Answer 23

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

Question 24

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

Answer 24

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

Question 25

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

Answer 25

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

Question 26

What is a motor unit?

Answer 26

A single motor neuron and all the muscle fibres it innervates

Question 27

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

Answer 27

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

Question 28

The origin of the signal determines the ____.

Answer 28

Modality (vision, touch, smell, etc.)

Question 29

The intensity of signalling is determined by its...

Answer 29

Amplitude and frequency, coded by graded potentials

Question 30

Unidirectional communication occurs electrically within a neuron via changes in...

Answer 30

Transmembrane potential (Vm)

Question 31

Describe what each of the labels signify.

Answer 31

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

Question 32

What determines the response - the NT or the receptor?

Answer 32

The receptor

Question 33

True or False: Glia greatly outnumber neurons.

Answer 33

True

Question 34

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

Answer 34

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

Question 35

What are the three CT coverings of peripheral nerves?

Answer 35

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

Question 36

What is the role of astrocytes?

Answer 36

- 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

Question 37

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

Answer 37

Fibrous astrocytomas

Question 38

Astrocytes are rich in intermediate filaments composed of...

Answer 38

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

Question 39

What are the components of the blood-brain barrier?

Answer 39

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

Question 40

What is the role of oligodendrocytes?

Answer 40

- Glial cells within the CNS - Make the myelin sheath on axons in CNS

Question 41

What is the role of microglia?

Answer 41

- 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

Question 42

What is the role of ependymal cells?

Answer 42

- 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

Question 43

What is the role of satellite cells?

Answer 43

- Surround neuronal somas in the PNS (ie. in ganglia) - Electrically and chemically insulate the cell body

Question 44

What is the role of Schwann cells?

Answer 44

- 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

Question 45

How do Schwann cells differ from oligodendrocytes?

Answer 45

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