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Flashcards in CNS basic physiology Deck (44):
1

Astroglia

integrate/modulate signals
part of BBB
part of synaptic transmission

2

Microglia

blood-borne macrophages
resident immune cells of the brain

3

AP propagation in the brain

1) NaV open, AP generated
2) passive current flows to the next NaV
3) passive current opens next NaV, another AP generated

4

Resistance (AP)

lower in larger axons

5

Capacitance (AP)

larger in larger axons - want to minimize this for faster current propagation
role of myelin sheath

6

Saltatory conduction

AP is not jumping; tunneling under myelin sheath

7

Synapse events

1) AP opens CaV channels
2) Ca influx causes NT-filled vesicles to fuse with the cell membrane
3) NT released into synaptic cleft; binds to receptors, causes opening of ion channels
4) postsynaptic cell depolarizes, AP generated

8

EPSP channels

Na channels

9

IPSP channels

Cl- channels

10

Amino acid NTs

Glutamine - ex
GABA - in
Glycine - in

11

Biogenic amine NTs

Dopamine - D1 ex, D2 in
Norepi, epi, histamine - ex
Serotonin - in or ex

12

Purine NTs

ATP - ex

13

Neuropeptide NTs

Substance P - ex
Met-enkephalin - in
Opioids - in
Adrenocorticotropin - ex

14

Synesthesia

Neurological phenomenon in which stimulation of one sensory pathway --> automatic, involuntary experiences in a second sensory pathway
e.g. Grapheme

15

Pressure receptor types (general)

Exteroceptors
Interoceptors and proprioceptors

16

Meissner's corpuscles

light touch receptors

17

Palcinian corpuscle

deep pressure and vibration receptors
20-60 concentric lamellae composed of fibrous CT separated by gelatinous material
Centre: inner bulb, a fluid-filled cavity with a single afferent unmyelinated nerve ending

18

Ruffini's corpuscle

sensitive to skin stretch sense of position and movement

19

Merkel's disc

sensitive to vibrations at low frequencies

20

Temporal summation

frequency coding
more impulses along a single fiber

21

Spatial summation

population coding
increasing number of parallel fibers that transmit information

22

Adaptation

prolonged presence of a stimulus --> decreased perceived intensity
all sensory receptors adapt to constant stimulation, but rate of adaptation varies

23

2-point discrimination

Helps to assess nerve damage
Depends on receptor density and size of receptive fields

24

Lateral inhibition

Blocks lateral spread of excitatory signals --> increase degree of contrast in sensory pattern

25

Alpha motor neuron

skeletomotor
innervate extrafusal fibers

26

Gamma motor neuron

fusimotor
innervate intrafusal fibers
2 main types

27

Small motor units

small number (e.g. 10) of fibers per motor neuron
fine movements
e.g. eye muscles

28

Large motor units

large number (1000s) of fibers per motor neuron
gross movements
e.g. leg muscles

29

Muscle spindles

stretch-sensitive mechanoreceptors
found in virtually all skeletal muscles
particularly dense in muscles connected with fine, manipulative tasks (intrinsic hand muscles, highest density in neck muscles for direction)
small, elongated structure - scattered among and parallel to contractile extrafusal fibers
CT sheath surrounding intrafusal muscle fibers

30

Intrafusal fibers

modified muscle fibers lacking myofibrils in the centre
1/3 length of extrafusal fibers
Provide information about muscle length and velocity of contraction to the CNS

31

Bag2 intrafusal fibers

largest
most important?
no striations in the middle region and swells to enclose nuclei
"bag"

32

Bag1 intrafusal fibers

smaller than Bag2

33

Bag intrafusal fibers

extend beyond capsule
based upon contraction speed and motor innervation

34

Chain fiber3

half as long as bag, smaller diameter
row of nuclei in the middle
"chain"

35

Typical muscle spindle

1 Bag1, 1 Bag2, 4 chain fibers

36

Muscle spindle - sensory innervation

Large diameter group Ia afferent
- enter capsules and branches
- unmyelinated terminals wrap around fiber
- annulospiral ending on nucleated Bag1, Bag2 and chain intrafusal fibers
- All 3 types of intrafusal fibers receive innervation from Goup Ia afferents

Smaller group II afferents
- enter with Ia afferents; unmyelinated spray terminals on one end of Bag 2 and chain fibers
- no Bag1

37

Muscle spindle - motor innervation

Gamma or fusimotor neurons
2 types of gamma:
1) static - Bag2 and chain
2) dynamic - Bag1 ONLY

38

Muscle spindle function

Sensory neurons fire when centre intrafusal fiber stretches
Opening of spiral endings and initiation of impulses: stretch-operated cation channels; membrane depolarization and action potential firing
Viscoelastic properties affect activation
Ends of intrafusal fibers contract when stimulated by gamma motor neurons --> affect centre of intrafusal fibers, not overall muscle tension
Group Ia: muscle length and velocity info
Group II: length only
Gamma dynamics: increases velocity sensitivity
Gamma static: increases length sensitivity

39

Muscle spindle sensory neurons

tonically active
Fire AP when muscle is at resting length
Signal to alpha motor neurons in ventral horn
tonic excitation --> muscle contraction in extrafusal fibers = resting muscle tension
Firing rates of gamma MN can change in different situations

40

Stretch reflex

Intrafusal fibers stretched --> sensory neurons fire more rapidly
Reflex contraction of muscle to relieve stretch --> stimulus removed (negative FB)
Monosynaptic and polysynaptic excitatory connections between Group Ia and II afferents and alpha motor neurons

41

Myotatic unit

collection of nervous pathways controlling a single joint

42

Reciprocal inhibition

Relaxation of antagonist muscle during agonist contraction
Divergent pathways in spinal cord and inhibitory interneurons

43

Hoffman reflex

electrically evoked analogue of the stretch reflex

44

Ia inhibitory interneuron

receives convergent input from CST and other descending pathways