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Neuroanatomy > 1. Cell structure and function > Flashcards

1. Cell structure and function Flashcards

1
Q

What is the average thickness of a cell membrane

A

7.5 - 10 nm

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2
Q

What are the cell membrane constituents (in decreasing order of importance)?

A

Proteins 55%
Phospholipids 25%
Cholesterol 13%
Other lipids 4%
Carbohydrates 3%

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3
Q

What are the 3 types of lipids in a cell membrane?

A

Phospholipids
Sphingolipids
Cholesterol

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4
Q

What are the two structural portions of a membrane phospholipid?

A
  • Phosphate end: hydrophilic, in contact with extra- and intra-cellular water
  • 2 Fatty acid chains: hydrophobic, forming the middle layer, impermeable to water-soluble substances (ions, glucose, urea) and permeable to fat-soluble substances (O2, CO2, alcohol)
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5
Q

Which cells are most rich in sphingolipids?

A

Neurons.

Note: Sphingolipids have a role in signal transmission, adhesion site for extracellular proteins, and protect from harmful environmental factors.

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6
Q

What are the two main roles of membrane cholesterol?

A

Controls the degree of…
1) Membrane permeability
2) Membrane fluidity

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7
Q

What are the two types of membrane proteins?

A

Integral & surface proteins

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8
Q

What are the three forms of membrane carbohydrates, and where are they usually found?

A

Attached to proteins or lipids, as:
- Glycoproteins
- Glycolipids
- Proteoglycans

Usually attached to integral proteins and form protrude on the outside, forming the glycocalyx

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9
Q

What are the 4 roles of the glycocalyx

A

1) provides a NEGATIVE charge to the outer cell membrane
2) ATTACHMENT site for other cells’ glycocalyx
3) RECEPTOR for hormone bindings (e.g. insulin)
4) involved in IMMUNE reactions

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10
Q

2 types of endocytosis

A

1) PINOcytosis (small molecules)
2) PHAGOcytosis (large molecules)

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11
Q

Name the types of transport across cell membranes

A

1) DIFFUSION - simple vs facilitated (along electrochemical gradient)
2) ACTIVE - primary vs secondary (against electrochemical gradient)

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12
Q

What is the difference between simple vs facilitated diffusion?

A

SIMPLE diffusion:
- Diffusion through protein pores or channels
- No interaction with carrier proteins
- Rate of diffusion is linearly related to substrate concentration

FACILITATED diffusion:
- Interaction with carrier protein
- Saturation: Rate of diffusion is limited (Vmax) by rate of protein conformational changes
- Competition

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13
Q

What is the difference between primary vs secondary active transport?

A

PRIMARY:
- Energy source: high-energy phosphate (e.g. ATP)
- E.g. Na/K ATPase pump (3 Na out, 2 K in)

SECONDARY:
- Energy source: stored energy created by active transport
- Co-transport vs counter-transport
- One solute (usually Na) is transported downhill while other is transported uphill
- E.g. Na-K-2Cl or Na-Glucose cotransporter or Na-H countertransporter

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14
Q

What determines the resting membrane potential?

A

1) equilibrium potential of individual ions (RMP is closest to the equilibrium potential of K+, being the most permeable at rest)
2) relative membrane permeability to individual ions
3) electrochemical gradients
4) fixed, negatively charged organic ions
(…)

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15
Q

What is the RMP of
1) Smooth muscle cell
2) Striated muscle
3) Resting neurons

A

1) Smooth muscle cell: -50mV
2) Striated muscle: -95mV
3) Resting neurons: -65-90 mV

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16
Q

Understand the phases of an action potential

A

1) Membrane depolarizes to threshold potential (-55 mV)
2) Activation of v-gated Na and K channels
3) Na flows in faster than K flows out -> cell depolarizes (rising phase) to +20-30 mV (peak membrane potential).
4) Inward flow of Na spreads to adjacent v-gated channels causing spread to adjacent areas of membrane
5) Nav channels inactivate while K+ continues to flow out -> cell membrane reverses and hyperpolarizes

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17
Q

What is the absolute vs relative refractory period

A

ABSOLUTE:
- Time for Nav channels to de-inactivate (1 ms)
- NO stimulus can generate AP. Prevents overlap of APs.

RELATIVE
- follows refractory period
- Period of hyperpolarization
- Time for K+ channels to close
- STRONGER stimulus needed to generate AP

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18
Q

Other name for cell soma

A

Perikaryon

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19
Q

What is the Nissl substance

A

Rough ER + polysomes

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20
Q

Name given to a cluster of perikarya in the CNS vs PNS

A

CNS: nucleus
PNS: ganglion (synaptic sites for ANS)

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21
Q

Each neuron contains __ axon(s) and __dendrite(s)

A

Single axon
Variable dendrites

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22
Q

3 types of neurons (know how to recognize them)

A

UNIPOLAR (single stem that bifurcates into two)

BIPOLAR (2 stem processes)

MULTIPOLAR (1 axon, multiple dendrites)

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23
Q

Which is the most common neuron type

A

Multipolar

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24
Q

Example(s) of monopolar neurons

A

Primary sensory neurons

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25
Q

Example(s) of bipolar neurons

A

Found in
- Retina
- Olfactory epithelium
- Spiral ganglion (cochlea)
- Vestibular ganglion

26
Q

Example(s) of multipolar neurons

A

Sensory
Motor (α,γ𝛼,𝛾 - to skeletal muscle)
Autonomic, interneurons

27
Q

Name the neuroglia (glial cells) of the PNS vs CNS

A

CNS:
- Microglia (immune/macriphages)
- Oligodendrocytes (myelin)
- Ependymal cells (CSF producing)
- Astrocytes (nutrition, BBB…)

PNS:
- Schwann cells (myelin)

28
Q

Unlike neurons, glial cells..

A

Continue to divide

29
Q

Oligodendrocytes

A

Each contains cell processes that wrap around MULTIPLE axons

30
Q

Schwann cells

A

Concentrically wrap their plasma membrane around ONE axon, forming Nodes of Ranvier -> saltatory conduction

31
Q

Astrocytes

A
  • SEAL outer and inner surfaces of CNS (outer and inner glial limiting membranes)
  • Release neurotropic factors (e.g. NGF)
  • Perivascular end-feet form BBB
  • Reulate extracellular env
  • Repair processes following injury
  • Glutamate metabolism
32
Q

Which 7 areas lack a BBB (slide 35)
= Circumventricular organs, CVO

A

Ependymal CVO
- Choroid plexus
- Subcomissural organ

Paraependymal CVO
- Subfornical organ
- Median eminence/ neurohypophyseal (hypophysis) complex
- Pineal gland
- Area postrema
- Vascular organ of the lamina terminalis

33
Q

Classification of nerve fibers

A

Know table slide 38

34
Q

Where can an axon terminal synapse?

A
  • Perikarya
  • Dendrites
  • Axons
35
Q

2 types of synapses

A

Chemical vs electrical

36
Q

Describe an electrical synapse

A

Ion channels connect the cytoplasm of the pre- and postsynaptic cells at a gap junction

37
Q

Describe a chemical synapse

A

NT released in a synaptic cleft between pre- and post-synaptic cell

38
Q

What is a neuromuscular synapse

A

Between the terminal end of a MOTOR ENDPLATE (specialized effferent endings of an axon terminating on a striated muscle) and a MUSCLE FIBER

39
Q

What is a motor unit

A

1 motor neuron forming NM synapses with a group of skeletal muscles

40
Q

Understand the sequence of events in a neuromuscular synapse

A

1.Presynaptic neuron AP
2.Opening V-gated Ca2+ channels
3.Fusion of ACh vesicle on pre-synaptic membrane
4. Release of ACh
5. Opening of nAChRs, permeable to Na and K
6. Generation of EPP (not AP)
7. Opening of V-gated Na channels on post-synaptic membrane
8. If summation of EPP is large enought – > AP –> propagate along muscle fiber –> contraction

41
Q

Name the neurotransmitters of:
- PNS
- CNS (excitatory vs inhibitory)

A

PNS:
- ACh, NE, Epi

CNS
- Excitatory: glutamate, aspartate
- Inhibitory: GABA, glycine

42
Q

2 mechanisms of NT clearance from synaptic cleft (p 53)

A
  • Enzymatic (AChE)
  • Diffusion (glutamate)
43
Q

Skeletal muscles - define
- Fasciculi
- Epimysium
- Perimysium
- Endomysisum

A
  • Fasciculi: group of myofibers
  • Epimysium: surrounds 1 muscle
  • Perimysium: surrounds 1 fasciulus
  • Endomysisum: surrounds 1 myofiber
44
Q

What are the two types of myofilaments? What are they made of ?

A

THICK
- Myosin
- Has binding sites for ATP and actin

THIN
- Actin, troponin, tropomyosin
- Actin has binding sites for myosin during contraction
- Troponin + tropomyosin block these sites during relaxation

45
Q

What is the smallest contractile unit?

A

Sarcomere
- Repeating units between 2 Z lines
- Microscopically: Alternating dark and light bands –> striated appearance

46
Q

Know the organization of sarcomeres
- A band
- I band
- Z-disk

A
  • A band: superposed myosin + actin filaments
  • I (light) bands: only actin
    -Z disk: ends of actin filaments
47
Q

Name the steps of excitation-contraction coupling (EMG slide 13)

A

1) ACh released from motoneuron binds nAChRs at the motor end plate
2) Na+ & K+ influx –> membrane depolarization –> summation of EPP –> AP –> travels across the sarcolemma
3) AP travels across T-tubules –> activation of ryanodine receptors (RyRs) –> releases Ca2+ from SER into the sarcoplasm (where myofibrils are)
4) Ca2+ binds troponin –> exposes actin-binding site on myosin heads –> cross-bridge formation between thin & thick filaments

48
Q

Name the steps of the sliding filament model (EMG slide 14)

A

5) Phosphate released from myosin head –> pivots towards the center of sarcomere = sliding motion (power stroke) –> shortens sarcomere –> CONTRACTION
6) A new ATP binds myosin –> myosin detaches from actin–> RELAXATION
7) ATP hydrolyzed to ADP + Pi –> myosin returns to neutral position, ready for a next cycle

49
Q

Smooth muscles

A

slides 70-75:)

50
Q

2 types of somatic EFFERENT neurons in the ventral horn?

A

1) SKELETO-MOTOR (Aα) neurons
- Motorneurons
- Innervate EXTRAfusal muscle fibers

2) FUSI-MOTOR (Aγ) neurons
- Innervate INTRAfusal muscle fibers (part of the muscle spindle)

51
Q

What are the two constituents of MUSCLE SPINDLES (muscle proprioceptors)?
(slide 78)

A

1) INTRAFUSAL (4-20) muscle fiber
- Small striated muscle fiber
- Innervated by fusimotor neurons (Aγ)
- Have two contractile regions (a, c) and one central stretchable nuclear region (b)

2) ANNULOSPINAL receptor
- Endings of primary afferent (Ia) neuron, wrapping around the stretchable region of intrafusal muscle fibers
- Activated by stretch of intrafusal muscle fibers → Detecting muscle length

52
Q

What are the 2 types of infrafusal fibers?

A

Based on the distribution of nuclei in the central (nuclear) region
1) nuclear BAG fiber
- Cluster of nuclei
2) nuclear CHAIN fiber
- Single row of nuclei

53
Q

How are muscle spindles activated

A

Receptor is silent at rest, but activated by STRETCHING of the nuclear region, either by:
- Tapping on a tendon/ muscle
- Stimulating fusimotor neurons directly

54
Q

Describe the myotatic (stretch) reflex

A
55
Q

Describe a GOLGI TENDON ORGAN (GTO)

A
  • Encapsulated sensory receptor with branched and unmyeliated nerve endings, embedded at the muscle-tendon junction
  • Meausures muscle TENSION (not lenght)
  • Activates an INHIBITORY interneuron to α the activated motoneurons
  • Prevents muscle overloading
56
Q

Slide 85: spindle vs GTO

A
57
Q

MONOSYNAPTIC (patellar/myotatic) reflex
(slide 86)

A

Synaptic contacts are made between sensory & motor neurons that form a reflex arc

Tapping patellar tendon → stretches extrafusal and intrafusal muscles of the muscle spindle → activate annulospinal receptors (Ia) → excite α motor neurons in the ventral horn → skeletal muscle contracts → Stimulates GTO → feedback inhibition of α motor neurons

Mediated by spinal cord segments L4-L6

58
Q

POLYSYNAPTIC reflex

A

Involves sensory, motor and interneurons

Interneurons =
- Between sensory and motor neurons
- Within gray matter of SC
- Synapse on motor neurons or to other interneurons
- Can cross midline of spinal cord to terminate on contralateral motor neurons
- Excitatory or inhibitory

59
Q

Understand WITHDRAWAL (flexor) reflex

A

Slide 87

60
Q

Undersand PERINEAL reflex

A

Tests the functional integrity of sacral cord segments S1-S3, caudal & pudendal and caudal nerves

contraction of anal sphincter and tail flexion in response to tactile stimulation of perineum

61
Q

Understand CROSS-EXTENSOR reflex

A

Flexing 1 limb -> extension of contralateral limb
- Required to support increasing weight on a limb

Not present in lateral recumbency

UMN (e.g. lateral funiculus lx):
- Opposing tracts in ventral funiculus exert powerful excitatory influence on α and 𝛾 motor neurons supplying extensor muscles → stimulus of flexing limb by pushing pad is sufficient to excite motor neurons in contralateral side of spinal cord → crossed extensor reflex in lateral recumbency

62
Q

Understand CUTANEOUS TRUNCI reflex

A

Stimulus applied to skin → dorsal horn → axons of projection neurons ascent in the fasciculus proprius to reach C8 & T1 → synapse with LMN of the lateral thoracic nerve → panniculus muscle → reflex present bilaterally (stronger on ipsilateral side)

Neuroanatomy (20 decks)

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