Module E-04 Flashcards Preview

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Flashcards in Module E-04 Deck (57):
1

what does the Muscle spindle detect?

the length and rate of change of
the length of the muscle

2

What does Golgi Tendon organ detect?

muscular tension (related to contraction)

3

Where are the cell bodies of these muscle afferents located?

the ganglia of spinal dorsal roots or of select cranial nerves (e.g., CN V)

4

Why do neurons with larger diameter axons have faster conduction velocities?

larger axons bear lower intracellular electrical resistance

5

Type of Fiber:Ia
Myelination:?
Receptor:?
Sensitive to:?

Myelination: Yes
Receptor: Primary Spindle Endings
Sensitive to: length and rate of change of length

6

Type of Fiber:Ib
Myelination:?
Receptor:?
Sensitive to:?

Myelination:Yes
Receptor: Golgi Tendon Organ
Sensitive to: Tension

7

Type of Fiber:II
Myelination:?
Receptor:?
Sensitive to:?

Myelination:Yes
Receptor: Secondary Spindle endings
Sensitive to: Length

8

Type of Fiber:II
Myelination:?
Receptor:?
Sensitive to:?

Myelination:Yes
Receptor: Non -Spindle Endings
Sensitive to: Deep Pressure

9

Type of Fiber:III
Myelination:?
Receptor:?
Sensitive to:?

Myelination:Yes
Receptor: Free Nerve Ending
Sensitive to: Pain, chemicals, Temperature

10

Type of Fiber:IV
Myelination:?
Receptor:?
Sensitive to:?

Myelination:NO
Receptor: Free Nerve Ending
Sensitive to: Pain, chemicals, Temperature

11

What is a myotatic reflex?

A reflex whereby stretching of a muscle provokes contraction of the same muscle

12

A _________ connection between __ afferents and _____ motor neurons mediates the myotatic reflex.

monosynaptic; Ia ; alpha

13

What is Inverse myotatic reflex ?

– A reflex whereby heightened tension in the muscle
provokes relaxation of the same muscle.

14

A __________ connections between ___ afferents and _______ motor neurons mediates the inverse myotatic reflex.

polysynaptic; Ib; alpha

15

What is the purpose of gamma motor neuron innervation of muscle spindle fibers?

adjusts sensitivity of the spindle to stretch

16

Muscles involved in fine movements (e.g. of the hand) have a _______ distribution of spindles than those involved in coarse movements

denser

17

What are the Components of a Muscle Spindle?

1) Small group (i.e., 2 – 12) of fine intrafusal muscle fibers.
2) Myelinated sensory axons (large diameter) with receptive endings on the central (noncontractile) regions of intrafusal fibers.
3) Myelinated motor axons (small diameter) that innervate the contractile regions adjacent to the central regions of the intrafusal fibers.

18

Types of Intrafusal Fibers

1) Nuclear bag- numerous large nuclei located in a central bag region
a) Dynamic nuclear bag fiber
b) Static nuclear bag fiber
2) Nuclear chain Fiber- many nuclei arranged in a row

19

What type change are Dynamic nuclear bag fibers sensitive to?

both changes in length but also to rates of change

20

What type change are Static nuclear bag fibers sensitive to?

changes in length

21

What type change are Nuclear chain Fibers sensitive to?

changes in length

22

What are the 2 afferent fibers of the intrafusal FIbers?

1) Group Ia - large , rapid conduction, relay dynamic and static properties
2) Group II - smaller , less rapid conduction, relay only static properties

23

Where on the intrafusal fiber are Group Ia fibers found?

encircle the central (equatorial) zone of each nuclear bag and nuclear chain fiber

24

Where on the intrafusal fiber are Group II fibers found?

communicate with all nuclear chain and static nuclear bag
fibers ONLY (NO dynamic)

25

Motor Innervation of Intrafusal Fibers

1) Dynamic Aγ (Myelinated gamma) motor neurons synapse on dynamic nuclear bag fibers on the contractile portion
2)Static Aγ (Myelinated gamma) motor neurons synapse on static nuclear bag and nuclear chain fibers on the contractile portion.

26

Motor Innervation of Extrafusal Fibers

myelinated and large Group Aα (A alpha) fibers

27

What is Physiological Role of the Muscle Spindle?

• Participates in stretch (myotatic) reflexes
• Provides proprioceptive information to the CNS
• Regulates muscle contraction under the influence
of descending motor pathways and afferent inputs

28

Describe the pathway of the Stretch reflex

1)the muscle spindle is suddenly stretched b
2)Ia afferents conduct action potentials towards excitatory synapses on alpha motor neurons of the stretched muscle and its synergists.
3) These muscles contract immediately.
4) Collaterals of the excited Ia afferents also excite interneurons that inhibit firing of the alpha motor neurons of the antagonist muscle, contributing to a process called reciprocal innervation.

29

During Sustained Stretch what happens to the firing rate of Muscle spindle

muscle spindle afferents fire tonically rather than phasically

30

What happens to Muscle Spindle Activity during Alpha Motor Stimulation

muscle shortens briefly. This shortening may briefly „unload‟ muscle spindles making it inactive, and afferent
discharge ceases, leading to reduced activity of alpha motor neurons. ( not important mechanism as alpha and
gamma motor neurons tend to be co-activated by upper
motor neurons)

31

What happens when Alpha and Gamma Motor Neurons are co-activated?

Both extrafusal and intrafusal muscle fibers contract.
(enables the muscle spindle to measure muscle length continuously)

32

Where are Golgi tendon organs located?

between tendon and extrafusal muscle fibers

33

Golgi tendon organ fibers are in ________ with extrafusal fibers , whereas muscle spindle fibers are in ________ with them

series; parallel

34

Describe the afferent innervation of the Golgi Tendon organ

- innervated by large , myelinated Ib fiber
- Within the capsule of the tendon organ, the Ib fiber branches and loses its myelin sheath
- the naked sensory nerve endings interweaves among chains of collagen fibers

35

How are the Ib fibers activated?

1)Muscular contraction distorts the receptive endings, 2)opening membrane-spanning stretch-sensitive cation channels,
3) the rate of action–potential firing thus increases

36

Physiological role of Golgi tendon Fibers

At great tensions, it mediates inhibition of over-active alpha motor neurons. This distributes tension among
the extrafusal fibers in a muscle.
The Golgi tendon organ is thus part of a reflex (inverse myotatic) that relaxes the homonymous and synergistic muscles and excites the antagonist muscles.
Also continuously active to facilitate rhythmic motor activity (e.g., walking)

37

Describe the synaptic pathway started by Golgi tendon organ

1. High tension in the muscle vigorously activates Ib afferents
2. Ib afferents activate interneurons that inhibit alpha motor neurons communicating with overactive extrafusal fibers
3. Reduced activity in alpha motor neurons relaxes overactive extrafusal fibers, thus reducing chances of injury and/or redistributing load to less strained extrafusal fibers
4. At lower muscular tensions, the apparatus exerts excitatory influences that aid in rhythmic muscular contraction

38

What are the Muscle efferents

1) Aα (alpha motor)
-myelinated
-large-diameter axons ( high conduction velocities)
- innervate extrafusal muscle fibers
- receive inputs from central and peripheral sources
2)Aγ (gamma motor)
- myelinated
- small-diameter axons (lower conduction velocities)
- innervate intrafusal fibers forming the muscle spindles
- receive inputs from central and peripheral sources

39

Which has larger cell body alpha or gamma motor neuron

Alpha motor neuron

40

What are Renshaw cells?

Inhibitory Interneurons that are innervated collateral axons from A alpha motor fibers

41

Location of motor nuclei of distal and proximal muscles in the ventral horn

Proximal (axial) muscle motor neuron nuclei are more medially located and distal muscles are more laterally located

42

Location of motor nuclei of flexor and extensor muscles in the ventral horn

nuclei controlling flexor muscles lie dorsal to the motor nuclei controlling extensor muscles

43

What are the Input to Lower Motor Neurons?

o Muscle spindle afferents
o Local interneurons
o Brainstem and cortical neurons (i.e.upper motor neurons)

44

What is a motor unit?

an alpha motor neuron and the extrafusal muscle fibers that it directly activates

45

Where are motor nuclei located?

1) ventral (anterior) horn of the spinal cord.
2) The brainstem

46

The more Precise the movement, the ______ muscle fibers are in the motor units

fewer

47

3 types of Motor Units

1) Type I
2) Type IIA
3) Type IIB

48

Type I Motor Unit aka

Slow twitch

49

Type IIA Motor Unit aka

Fast Twitch

50

Type IIB Motor Unit aka

Fast Twitch

51

Describe Type I Motor units

low tension; fatigue resistant; aerobic;
innervated by relatively small lower motor neuronal axons

52

Describe Type IIA Motor units

large tension; fatigue resistant (relatively); some aerobic capacity; innervated by relatively large lower motor neuronal axons

53

Describe Type IIB Motor units

large tension; rapidly fatiguing; anaerobic; innervated
by relatively large lower motor neuronal axons

54

What are 2 factors that control contraction, ie increases force produced by muscle?

1. The firing rates of the motor neurons
2. The number of motor units recruited

55

Damage to which fibers causes Hypotonia

either the la afferent pathway or the lower motor neurons will reduce muscle tone, yielding hypotonia and hence flaccid paralysis

56

What cause Lower Motor Neuron Syndrome?

Arises with damage to cells derived from the basal
plate that communicate with somatic muscle cells

57

Features of Lower Motor Neuron Syndrome

– Paresis/paralysis
– Hyporeflexia
– Hypotonia
– Fasciculations (aberrant twitches)
– Fibrillations ( aberrant electrical responses)
– Muscular wasting/atrophy