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Animal Physiology > Nervous System 2.0 (for midterm 2) > Flashcards

Nervous System 2.0 (for midterm 2) Flashcards

1
Q

What is the main function of the somatosensory system?

A

to mediate sensations such as touch, pressure, limb position, vibration, temperature and pain

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2
Q

What senses stimulation? Where are they located?

A

Receptors in the skin, muscle and tendon receive sensations and send information to the CNS

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3
Q

What are the 3 subsystems of the somatosensory system?

A

cutaneous mechanoreceptors

proprioception

pain and temperature

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4
Q

What kind of sensory information do cutaneous mechanoreceptors receive?

A

touch, vibration, pressure on the skin

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5
Q

What kind of sensory information do proprioceptors receive? Where are these?

A

limb positioning
load on joints

located in muscles, tendons and joints

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6
Q

How is sensory information transported from the body (ex. finger tips) to the brain?

A

via sensory receptors with dorsal root ganglia and cranial nerve ganglia

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7
Q

What are dorsal root ganglia?

A

the cell bodies of afferent fibers (sensory receptors for the body)

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8
Q

What are cranial nerve ganglia?

A

the cell bodies of afferent fibers (sensory receptors for the brain)

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9
Q

Explain how a sensory stimulation would be transferred from the finger tip to the brain?

A

dorsal root ganglia extend axons into the finger and up the spinal cord

information travels from the finger tip through the dorsal root ganglia cell body and up the spinal cord

synapse at the top of the spinal cord

synapse in the thalamus

cranial nerve ganglia axon extends into the somatosensory cortex of the cerebral cortex

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10
Q

Where does the dorsal root ganglia synapse with the cranial nerve ganglia?

A

in the thalamus

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11
Q

What part of the brain does the cranial nerve ganglia synapse to transmit the somatosensory information to the brain?

A

the somatosensory cortex of the cerebral cortex

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12
Q

What is a dermatome?

A

the region of the body that is innervated by a single dorsal root ganglion and its spinal nerve

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13
Q

Give an example of a dermatome

A

Cervical nerve 2 innervates the back of the head and neck

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14
Q

What type of membrane receptors are mechanoreceptors?

A

transmembrane cation channels

called PIEZO channels

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15
Q

Explain the transduction of mechanosensory afferents

A

Mechanoreceptors have PIEZO channels closed to both inside and outside of afferent nerve

Na+ is high extracellularly and low intracellularly

  1. mechanoreceptors on the afferent nerve membrane sense a stimulus (ex. pressure on skin)
  2. stretching of the membrane in response to the pressure stimulus opens the PIEZO channels (ie., changes the permeability of the membrane)
  3. Na+ fluxes into the afferent causing a depolarization current across the afferent membrane (generator/receptor current)
  4. if stimulus is strong enough, an AP is generated
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16
Q

How is the firing frequency of APs in mechanosensory afferent nerves related to the stimulus?

A

the frequency of APs is proportional to the magnitude of membrane depolarization or the strength of the stimulus

ex. weak stimulus = weak receptor potential (doesn’t reach threshold)

strong stimulus = receptor potential reaches threshold and causes strong spike potential

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17
Q

What are the cutaneous mechanoreceptors for touch?

A

Merkel cells
Meissner cells
Pacinian cells
Ruffini cells

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18
Q

What type of afferent axons are involved with touch cutaneous mechanoreceptors?

A

Abeta

myelinated, fairly thick

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19
Q

What is the axon diameter of afferents involved with touch cutaneous mechanoreceptors?

A

6-12 um

second largest

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20
Q

What is the conduction velocity of afferents involved with touch cutaneous mechanoreceptors?

A

35-75 m/s

second fastest

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21
Q

Are afferents associated with cutaneous mechanoreceptors for touch myelinated?

A

yes

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22
Q

What are the proprioception receptor types?

A

muscle spindles and Golgi tendon organ

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23
Q

What are the afferent axon types for proprioception?

A

Aalpha
Ia
II
Ib (Golgi organ)

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24
Q

Are afferent axons for proprioception myelinated?

A

yes

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25
Q

What is the axon diameter of afferent nerves for proprioception?

A

13-20 um

largest size

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26
Q

What is the axon conduction velocity of afferent nerves for proprioception?

A

80-120 m/s

fastest

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27
Q

What are the receptor types for pain and temperature?

A

myelinated free nerve endings

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28
Q

What are the afferent axon type(s) of pain and temperature afferent nerves?

A

Adelta

myelinated

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29
Q

What is the axon diameter of afferent nerves for pain and temperature?

A

1-5 um

second smallest

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30
Q

What is the conduction velocity of afferent nerves for pain and temperature?

A

5-30 m/s

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31
Q

What receptors are involved in pain, temperature, and itch?

A

unmyelinated free nerve endings

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32
Q

What is the axon type of afferent nerves for pain, temperature and itch?

A

C

unmyelinated

smallest

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33
Q

What is the axon diameter of afferent nerves for pain, temperature and itch?

A

0.2-1.5 um

the smallest

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34
Q

What is the axon conduction velocity of afferent nerves for pain, temperature and itch?

A

0.5-2 m/s

the slowest

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35
Q

Organize the afferent axon types for the 4 sensory functions in order of fastest-slowest conduction velocities. What contributes to conduction velocity?

A

proprioception afferents

touch afferents

pain, temperature afferents

pain, temperature, itch afferents

myelination and axon diameter contribute to conduction velocity = larger axon diameter contributes, but myelination contributes significantly

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36
Q

How much do myelination and diameter of axons contribute to axon conduction velocity?

A

A lot

ex. afferents for pain, temperature, and itch have unmyelinated axons and CV of 0.5-2 m/s and diameter of 0.2-1.5 um

whereas

afferents for pain, temperature have myelinated axons and CV of 5-30 m/s and diameter of 1-5 um

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37
Q

What attributes differ between somatosensory afferents?

A

axonal diameter
conduction velocity
receptive field sizes
temporal dynamics

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38
Q

What is the main function of sensory receptors?

A

to convert stimulus signals to APs in an afferent neuron

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39
Q

What are receptive fields in afferent nerves? what kind of information do they provide about the stimulus?

A

the area of the body that affects the activity of an afferent nerve when it’s been stimulated

they provide information about stimulus location

the smaller the size of a receptive field, the more precise location of stimulus

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40
Q

How are receptive fields in afferent nerves measured?

A

measured with 2 point discrimination (the smallest distance at which 2 points can still be distinguished)

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41
Q

How do small receptive fields compare to larger ones in terms of precision of stimulus location?

A

small receptive fields can give very precise location information = improved localization

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42
Q

What parts of the body have smaller receptive fields? larger? why?

A

fingers have ~3mm receptive fields
shoulders have 50mm receptive fields

it’s more important for fingers to have precise localization of stimuli for activities such as grabbing and holding objects, this is less important in areas like shoulders or back

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43
Q

What are the two types of temporal dynamics in somatosensory afferents?

A

rapidly adapting afferents

slowly adapting afferents

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44
Q

What kind of stimulus information do rapidly adapting afferents/mechanoreceptors provide?

A

dynamic information about stimulus movement

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45
Q

What frequency do rapidly adapting afferents/mechanoreceptors generate APs?

A

APs are increased when there’s a change of stimulus

ie., APs are initiated only when stimulus is applied and when it is removed, ex. when pressure is applied and when it is removed

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46
Q

What kind of stimulus information do slowly adapting afferents/mechanoreceptors provide?

A

static information about the size and shape of the stimulus

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47
Q

What frequency do slowly adapting afferents/mechanoreceptors initiate APs?

A

APs are generated continuously throughout the duration of the stimulus

ex. they are generated the entire time pressure is applied

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48
Q

What are the 4 mechanoreceptor cell types in the skin? What’s the 5th one that isn’t technically a mechanoreceptor? what makes it different?

A

Meissner cells
Merkel cells
Pacinian cells
Ruffini cells

these cells cap the ends of afferent nerves

free nerve endings are afferent fibers that also receive cutaneous stimulation about pain and temperature but lack specialized receptor cells

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49
Q

Where in the layers of the skin do each of the mechanoreceptors exist?

A

epidermis:
free nerve endings are closest to the surface
Meissner cells

dermis:
Merkel cells are at the interface of epidermis/dermis in pits
Ruffini cells

subcutaneous layer:
Pacinian cells are at the interface of dermis/subcutaneous layer

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50
Q

Where are mechanoreceptor cells located on the afferent nerves?

A

at the endings like caps on the nerves

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51
Q

What is the function of mechanoreceptor cells that encapsulate afferent nerve endings?

A

these cells lower the threshold for initiating APs and increase the afferent nerve’s sensitivity to stimulation

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52
Q

Which mechanoreceptor afferent type is most sensitive to stimulation: encapsulated afferents or free nerve endings?

A

encapsulated afferents because of the specialized mechanoreceptor cells

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53
Q

Describe Meissner afferents (receptive field, temporal dynamics, dermatome, location, sensitivity, sensation type, etc)

A

small receptive field (spatial resolution) - 3mm

rapidly adapting

high innervation of hands

close to skin surface (epidermis)

4x more sensitive than Merkel

sense textured objects moving across skin, grip, low frequency vibrations

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54
Q

Describe Merkel afferents (receptive field, temporal dynamics, dermatome, location, sensitivity, sensation type, etc)

A

highest spatial resolution/smallest receptive field size (0.5mm)

located in the epidermis

slowly adapting

highly concentrated in finger tips

gives info about shape, texture, curvature of objects - sensitive to edges, points, curves

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55
Q

Describe Ruffini afferents (receptive field, temporal dynamics, dermatome, location, sensitivity, sensation type, etc)

A

low spatial resolution/ large receptive field size (>7mm)

deep in the dermis

slowly adapting

sensitive to internally generated stimuli (ex. finger movement)

provides information about finger positions and hand conformation

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56
Q

Describe Pacinian afferents (receptive field, temporal dynamics, dermatome, location, sensitivity, sensation type, etc)

A

lowest spatial resolution/largest receptive field (>10mm)

located deepest in the skin (deep in the dermis)

rapidly adapting

most sensitive

sensitive to high frequency vibrations through an object - ex. using a tool, writing

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57
Q

Which specialized mechanoreceptor cell type has the highest spatial resolution (receptive field)?

A

Merkel cells

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58
Q

Which specialized mechanoreceptor cell type has the lowest spatial resolution (receptive field)?

A

Pacinian

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59
Q

Which specialized mechanoreceptor cell type has the highest sensitivity?

A

Pacinian

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60
Q

Which specialized mechanoreceptor cell type(s) are rapidly adapting?

A

Meissner and Pacinian

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61
Q

Which specialized mechanoreceptor cell type(s) are slowly adapting?

A

Merkel and Ruffini

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62
Q

Describe the cutaneous mechanosensory pathway (how sensory information is transmitted from the body into the brain)

A

cutaneous information is received by a mechanoreceptor/afferent nerve

info is passed into the dorsal root ganglion

info travels ipsilateral up dorsal spinal cord (gracile or cuneate tracts)

synapse in caudal medulla in gracile or cuneate nuclei

crosses over through arcuate fibers to travel up medial lemiscus tract

synapse onto ventral posterior lateral nucleus of thalamus

projects onto somatosensory cortex

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63
Q

Where are the synapses in the cutaneous mechanosensory pathway?

A

at the caudal medulla and the thalamus

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64
Q

What side of the spinal cord does cutaneous mechanosensory information travel up and through what tracts?

A

starts travelling ipsilateral dorsally along either gracile or cuneate tract

when it synapses at the caudal medulla, it crosses to travel up caudally (contralaterally)

travels contralaterally along the medial lemiscus tract to the thalamus where it synapses and projects onto the somatosensory cortex

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65
Q

What are the two receptor types (proprioceptors) for proprioception?

A

Muscle spindle
Golgi tendon organ

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66
Q

What is the main function of proprioceptors?

A

to provide continuous information about limb and other body part position

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67
Q

where are muscle spindles located?

A

in skeletal muscles

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68
Q

What are muscle spindles comprised of?

A

specialized intrafusal muscle fibers

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69
Q

Describe the structure of muscle spindles

A

sensory afferents coiled around intrafusal fibers

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70
Q

What type of afferents are involved in muscle spindles? What type of information do these types provide?

A

Ia and II

Ia is rapidly adapting and provides information about the movement of limbs

II is slowly adapting and provides information about static limb positions

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71
Q

T or F: muscle spindles have only rapidly adapting sensory afferents

A

false, they also have slowly adapting

both Ia and II

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72
Q

What type of information do muscle spindles encode?

A

info about muscle length changes

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73
Q

What type of sensory afferents are found in Golgi tendon organs?

A

group Ib

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74
Q

Where are Golgi tendon organs located?

A

amongst collagen fibers of tendons

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75
Q

What type of info do GTO provide about the stimulus?

A

about the tension (load) on the muscle or tendon

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76
Q

What reflex exists to protect tendons/muscles when the load is too high?

A

reflexes protect the muscles/tendons by forcing the body part (ex. arm) to let go of the weight if the tension (load) is too much on the tendon

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77
Q

Describe the proprioceptive pathway for lower body information

A

lower body proprioceptors send stimulus information through dorsal root and up dorsal spinal cord ipsilaterally

synapse at the Clarke’s nucleus and project signal up the dorsospinocerebellar tract

collaterals travel ipsilaterally to cerebellum and other collaterals cross the caudal medulla

medial lemiscus synapses to ventral posterior lateral nucleus of thalamus which projects to the somatosensory cortex

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78
Q

describe the proprioception pathway for upper body information

A

upper body information follows same pathway as mechanosensory but also sends collaterals ipsilaterally to cerebellum

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79
Q

What side of the spinal cord does lower body information enter and travel?

A

dorsally

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80
Q

Does the lower body proprioceptor information ever cross the spinal cord from dorsal to caudal like the mechanosensory pathway?

A

hmmm unclear

seems like it travels only ipsilaterally? but does it cross at caudal medulla or is that just ‘collaterals’?

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81
Q

Where are the synapses in lower body proprioceptive pathway?

A

Clarke’s nucleus
Dorsal spinocerebellar tract
medial lemiscus/ventral posterial lateral nucleus (thalamus)

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82
Q

What are the major pathways along the spinal cord in proprioception?

A

dorsal column
dorsospinocerebellar

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83
Q

What are the major pathways along the spinal cord in mechanoreception?

A

dorsal column
medial lemiscus

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84
Q

Where does sensory information from the body enter the brain?

A

mechanosensitive and proprioceptive info enters the brain at the Ventral Posterior Complex of the Thalamus

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85
Q

What part of the brain does mechanosensitive and proprioceptive information reaching the thalamus project onto?

A

layer 4 of the primary somatosensory cortex in the cerebral cortex

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86
Q

Which layer of the primary somatosensory cortex is mechanosensitive and proprioceptive information project onto?

A

layer 4 aka the Granular cortex

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87
Q

Which Brodmann’s areas does the primary somatosensory cortex comprise of? where are these in relation to layer 4?

A

layers 3a, 3b, 1, and 2

layer 4 is ventral to layer 3a

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88
Q

Describe the somatotopic organization of the cerebral cortex concept

A

each region of the cerebral cortex corresponds to a specific part of the body which is controlled via motor output or receives sensory input from

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89
Q

When looking at the somatotopic organization of the cerebral cortex diagram, what does the size of the body part drawn represent?

A

the size of the body part drawn represents the size of the brain region that contributes to the body part

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90
Q

Who determined the somatotopic organization of the cerebral cortex diagram?

A

Wilder Penfield and Herbert Jasper from Montreal Neurological Institute

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91
Q

What is nociception?

A

pain detection

92
Q

Which receptor types are involved in nociception?

A

free nerve endings

93
Q

T or F: all free nerve endings have unmyelinated axons

A

false

the ones for pain and temperature are myelinated
the ones for pain, temp, and itch are not

94
Q

Do afferents for nociception have large or small axon diameters?

A

very small

second smallest and smallest

95
Q

How do the conduction velocities of nociception afferents compare to other mechanoreceptors or proprioceptors? why?

A

they’re significantly slower because their axons have much smaller diameters and some of them are unmyelinated (slowest)

96
Q

What afferent types do nociceptors have?

A

Adelta (myelinated)
C (unmyelinated)

97
Q

What are the 2 types of pain? what differentiates them?

A

first and second pain

different velocities of transmission

98
Q

What type of pain is first pain?

A

sharp, rapidly transmitted pain

99
Q

What type of afferent fibers mediate first pain?

A

Adelta fibers (myelinated)

100
Q

What type of pain is second pain?

A

delayed, diffuse and longer-lasting pain sensations

101
Q

What type of afferent fibers mediate second pain?

A

C fibers (unmyelinated)

102
Q

Which of the two pain types is rapid transmission?

A

first pain

103
Q

Describe nociceptors

A

free nerve endings that detect pain

104
Q

Overall, do the axons of nociceptors have fast or slow velocities (think of the diameters and myelination)?

A

slow conduction

Adelta are faster than C fibers because slightly larger diameter and myelinated

C fiber is slowest because very small and no myelination

105
Q

What type of pain stimulation is detected by Adelta fibers in the fast pain pathway?

A

intense mechanical and heat stimuli

106
Q

What type of pain stimulation is detected by C fibers in the slow pain pathway?

A

intense mechanical
warm/cool
chemical

107
Q

What are the channels for pain and temperature stimuli?

A

TRP channels

108
Q

What are TRP channels?

A

Transient Receptor Potential channels for cations

109
Q

Are TRPs selective channels?

A

they’re non-selective cation channels for pain detection

110
Q

Which TRP is involved in sensing noxious thermal stimuli (>43 deg C)? and is also sensitive to what spicy food?

A

TRPV1

capsaicin from chilli peppers

111
Q

Which TRP is involved in sensing mechanical pain?

A

TRPV4 and TACAN

112
Q

Which TRP is involved in sensing chemical pain?

A

TRPA1

113
Q

Which TRP is involved in sensing innocuous temperatures (warm/cool)?

A

TRPV3 and 4 = warm
TRPM8 cool

114
Q

What tract/system does the pain pathway follow in the nervous system?

A

the Anterolateral System

115
Q

Describe the anterolateral pathway

A

pain/temperature information enters spinal cord through dorsal root ganglion on the dorsal horn

information crosses spinal cord at cervical and lumbar spinal cord and travels up spinal cord

synapse to ventral posterior lateral nucleus of the thalamus to project on the somatosensory cortex

116
Q

What is Rexed Laminae? what happens there?

A

layers (laminae) within the spinal cord where free nerve ending afferents synapse

Adelta synapses to neurons in laminae 1 and 5

C synapses to laminae 1 and 2

117
Q

Which layers of Rexed’s laminae do Adelta fibers synapse to?

A

1 and 5

118
Q

Which layers of Rexed’s laminae do C fibers synapse to?

A

1 and 2

119
Q

What are the 2 divisions of the peripheral nervous system?

A

efferent and afferent (sensory)

120
Q

How is the efferent branch of the peripheral nervous system divided?

A

autonomic system and motor division

121
Q

How is the autonomic nervous system of the efferent branch of the peripheral nervous system divided?

A

sympathetic, parasympathetic and enteric systems

122
Q

Describe the autonomic NS

A

involuntary

involved in homeostasis

includes 3 subsystems: parasympathetic, sympathetic, enteric

123
Q

Is the autonomic NS involuntary or voluntary responses?

A

involuntary

124
Q

When is the sympathetic NS most activated?

A

by stress or physical activity

125
Q

What is another term for the sympathetic nervous system?

A

fight or flight

126
Q

When is the parasympathetic NS most activated?

A

during resting periods

127
Q

What is another term for the parasympathetic nervous system?

A

resting and digesting

128
Q

Describe the enteric autonomic nervous system

A

functions independently of the other 2

functions in digestion by innervating organs of alimentary canal

129
Q

How are the para and sympathetic NS involved in homeostasis?

A

the two systems have to work in balance to maintain homeostasis

130
Q

What are the 3 mechanisms for regulating autonomic function/maintaining homeostasis?

A

dual innervation
antagonistic action
basal tone

131
Q

What is dual innervartion in the regulation of autonomic function?

A

both systemsare sending information to most organs simultaneously (ie., most organs are innervated by both systems)

132
Q

What is antagonistic action in the regulation of autonomic function?

A

the systems are acting antagonistically on the organs - one is stimulating while the other is inhibiting

133
Q

What is the basal tone in the regulation of autonomic function?

A

the constant travelling of APs along autonomic neurons even during periods of rest

134
Q

T or F: the neurons that innervate the same organs through different autonomic systems originate from the same parts of the spinal cord

A

false

ex. cranial nerves mediate parasympathetic responses in the eyes, whereas, thoracic nerves mediate sympathetic responses in the eye

135
Q

Where do the sympathetic neurons originate from on the spinal cord?

A

thoracic and lumbar

136
Q

Where do the parasympathetic neurons originate from on the spinal cord?

A

cranial and sacral

137
Q

T or F: all organs have dual innervation from the P and S autonomic systems

A

false, not all do (ex. nasal glands)

138
Q

If the parasympathetic systems stimulates the eye pupil, how might the sympathetic system antagonistically stimulate the pupil?

A

dilate it

139
Q

What are preganglionic neurons?

A

autonomic neurons with cell bodies that originate in the CNS spinal cord and project into the PNS to synapse with postganglionic neurons

140
Q

What are postganglionic neurons?

A

autonomic neurons that synapse in the peripheral nervous system with preganglionic neurons to synapse with target organs and cause a response

141
Q

How many neurons are in series in the sympathetic nervous system? the parasympathetic?

A

2 in both (pre and post-ganglionic)

142
Q

Where do the ganglia run in relation to spinal cord or target organ in the SS?

A

close to the spinal cord

143
Q

Where do the ganglia run in relation to spinal cord or target organ in the PS?

A

close to the target organ

144
Q

Describe the length of the pre- and postganglionic neurons in the SS - why are they like this?

A

preganglionic is short and post is long because the ganglia runs closer to the spinal cord

145
Q

Describe the length of the pre- and postganglionic neurons in the PS - why are they like this?

A

pre are long and post are short because the ganglia run close to the target organ

146
Q

How many synapses are there between the pre and post ganglionic neurons in the SS? how does this compare to the PS?

A

SS = many >10
PS = few <3

147
Q

What type of neurotransmitters are released by the preganglionic neuron at the synapse to the post-ganglionic neuron in the SS?

A

ACh

148
Q

What type of neurotransmitters are released by the preganglionic neuron at the synapse to the post-ganglionic neuron in the PS?

A

ACh

149
Q

What type of receptor does the postganglionic neuron have at the synapse between it and the preganglionic in the SS?

A

Nicotinic ACh receptors

150
Q

What type of receptor does the postganglionic neuron have at the synapse between it and the preganglionic in the PS?

A

Nicotinic ACh

151
Q

What type of neurotransmitters are released by the postganglionic neuron at the synapse to the target organ in the SS?

A

Norepinephrine

152
Q

What type of neurotransmitters are released by the postganglionic neuron at the synapse to the target organ in the PS?

A

ACh

153
Q

What type of receptor does the target organ have to receive the neurotransmitter from the postganglionic neuron in the SS?

A

Adrenergic

154
Q

What type of receptor does the target organ have to receive the neurotransmitter from the postganglionic neuron in the PS?

A

Muscarinic ACh

155
Q

Are the responses caused by the binding of ACh to the nicotinic ACh receptors on postganglionic neurons stimulatory or inhibitory? for SS and PS?

A

stimulatory for both and rapid

156
Q

What kind of response can be triggered in the target organ by the binding of either norepinephrine in the SS or ACh in PS to the receptors on the target organ?

A

either excitatory or inhibitory

157
Q

What does the binding of norepinephrine to adrenergic receptors on target organs cause?

A

a second messenger pathway which triggers multiple responses

158
Q

What does cholernergic mean?

A

neurotransmitters released are ACh

both PS and SS are this

159
Q

What type of movement does the motor pathway of the efferent branch of the peripheral nervous system control?

A

voluntary/somatic movement

160
Q

Where does voluntary movement initiate?

A

in the primary motor cortex of the cerebral cortex

161
Q

What cells are involved in initiating voluntary motor movement in the primary motor cortex?

A

Betz pyramidal cells (huge)
non-Betz pyramidal neurons (small)

162
Q

What is different about the primary motor cortex layers from the somatosensory cortex layers? What does this mean for the primary motor cortex?

A

somatosensory cortex has layer 4 which is where the sensory info is projected onto from the thalamus

the motor cortex does not have a defined 4th layer = does not receive sensory info

163
Q

What is the major CNS tract/pathway for voluntary movement called?

A

Corticospinal tract

164
Q

Describe the corticospinal pathway

A

motor cortex in the brain projects information downwards towards the spinal cord

90% of the fibers cross at the caudal medulla and travel the lateral corticospinal tract

the other 10% travel ipsilaterally in ventral corticospinal tract

lateral corticospinal tract can directly or indirectly innervate alpha motor neurons which innervate distal muscles

ventral corticospinal tract indirectly innervates alpha motor neurons that innervate proximal muscles

165
Q

What are the 2 major tracts within the corticospinal pathway that motor neurons can send information along?

A

lateral corticospinal (90% of efferents)
ventral corticospinal (10% of efferents)

166
Q

What % of fibers from the motor cortex cross at the caudal medulla? which tract do they continue along?

A

90% cross to follow the lateral corticospinal tract

167
Q

What % of fibers from the motor cortex travel ipsilaterally? which tract do they continue along?

A

10% along the ventral corticospinal tract

168
Q

What function do motor neurons along the lateral corticospinal tract have in effecting motor output?

A

they directly or indirectly innervate alpha motor neurons which innervate muscles distal from the spinal cord

169
Q

What function do motor neurons along the ventral corticospinal tract have in effecting motor output?

A

they innervate alpha motor neurons which innervate proximal muscles

170
Q

Where do most lateral corticospinal tract neurons terminate? ie., how do they innervate alpha motor neurons?

A

indirectly: on interneurons in lateral parts of the ventral horn and intermediate grey matter before synapsing on alpha motor neurons

directly: synapse directly onto ventral alpha motor neurons

171
Q

What muscles are innervated by efferent neurons that travel the lateral corticospinal tract?

A

distal muscles via innervated alpha motor neurons

172
Q

What muscles are innervated by efferent neurons that travel the ventral corticospinal tract?

A

proximal muscles via innervated alpha motor neurons

173
Q

What factors can effect muscle tension?

A

the frequency and intensity of stimulation

174
Q

What are the 4 ways muscles can respond to stimuli?

A

single muscle twitches
temporal summation
unfused tetanus
fused tetanus

175
Q

Describe single muscle twitch responses to stimulation rate

A

few, low intensity stimuli cause small contractions at the time stimulus is applied

176
Q

Describe temporal summation

A

3 stimuli are applied consecutively not giving the muscle time to relax between stimuli application causing increased responses each time

177
Q

Describe unfused tetanus

A

stimuli intensity and frequency is increased

allows some relaxation of muscle between applications, but contraction is high until stimuli removed

178
Q

Describe fused tetanus

A

highest stimuli intensity and frequency, no relaxation of muscle at all (contraction is a plateau)

179
Q

Which is the strongest type of muscle contraction? what exercise would cause this response?

A

fused tetanus

ex. weight lifting

180
Q

What exercise would induce unfused tetanus?

A

running

181
Q

Which motor neuron cells synapse directly onto alpha motor neurons?

A

Betz cells

182
Q

Which neurons are involved in the stretch reflex circuitry?

A

sensory afferent neurons - muscle spindles
motor efferent neurons

183
Q

Describe an example of the stretch reflex circuitry

A
  1. a hammer taps the knee at the reflex location causing the tendons to stretch = causes sensory receptors in extensor muscle to stretch

2a. the sensory neuron in the extensor muscle synapses to and stimulates motor neurons in the spinal cord

2b. the sensory neuron in the extensor muscle also stimulates a spinal interneuron

2c. the spinal interneuron synapses to and inhibits motor neurons in the flexor muscle

3a. APs travel along the stimulated motor neuron in the spinal cord to synapse on extensor muscle fibers = contraction of extensor

3b. because the flexor motor neurons have been inhibited, the flexor muscle relaxes

  1. the leg extends
184
Q

in the example of the knee tap reflex, which is the extensor muscle? is this the sensory or motor neuron? is it stimulated or inhibited?

A

the extensor is the quadriceps of the thigh, this is where the sensory afferent neuron originates and where a motor efferent neuron terminates

the sensory neuron is stimulated by the knee tap stretching the tendons, and the muscle contraction is stimulated by motor neurons

185
Q

in the example of the knee tap reflex, which is the flexor muscle? is this the sensory or motor neuron?

A

the flexor is the hamstrings of the thigh, this is where motor efferent neurons terminate

it is inhibited by interneurons in the spinal cord

186
Q

Which type of neuron stimulates the muscle contraction in the extensor muscle in the knee tap reflexes?

A

motor neurons in the spinal cord

187
Q

Explain how the reflex circuit is an example of antagonistic actions from the motor and sensory systems?

A

the sensory neuron synapses and triggers the motor neurons in the spinal cord to both stimulate the extensor muscle and to inhibit the flexor muscle

188
Q

What is flexion?

A

when a limb bends at a joint (muscle shortens)

189
Q

What is extension?

A

when a limb straightens at the joint (muscle lengthens)

190
Q

What causes flexion and extension?

A

they are a response to two antagonistic muscles contracting

191
Q

Explain how biceps and triceps are antagonistic muscles

A

when the bicep contracts to bend the arm at the elbow (flexion), the triceps relax to lengthen

when the bicep relaxes to extend the arm at the elbow (extension), the triceps contract to shorten

192
Q

Explain how the biceps and triceps are involved in stretch reflex circuitry when holding a glass at 90 degrees and then the glass is filled with liquid

A

arm is at 90 degrees holding empty glass

stimulus: liquid added to glass

when the liquid is added, the Ia sensory fibers in the muscle spindles of the bicep send stimulus information to the alpha motor neurons in the spinal cord

the bicep muscle passively stretches in response to the added weight

motor neurons in the spinal cord stimulate the bicep muscle to contract and inhibit the triceps, causing it to relax and allow the bicep to resist the weight of the glass and maintain flexion at 90 degrees

193
Q

What type of feedback loop is maintaining muscle length in the bicep/tricep glass reflex example?

A

negative feedback

194
Q

How is reciprocal innervation connected to the actions of the biceps and triceps when weight is added to the arm?

A

these two muscles are working antagonistically

the bicep is contracting while the tricep is relaxing to maintain flexion

195
Q

What afferent neuron regulates muscle tension?

A

Golgi tendon organ

196
Q

What is the function of regulating muscle tension?

A

to protect muscles and tendons when the load is too heavy by decreasing muscle activity

197
Q

Describe how golgi tendon organs are involved in regulating muscle tension

A

Ib GTO afferents receive information when there is strain on the tendons

send information to the spinal cord where it synapses with motor neurons and inhibitory interneurons

motor neurons inhibit flexor muscle (bicep) and stimulate the extensor muscle (tricep) causing the arm to extend and release weight

198
Q

What is the central pattern generator?

A

a network of neurons in the spinal cord that receive a signal from the brainstem to coordinate motor output signals to generate coordinated movement of limbs

199
Q

Where is locomotion initiated?

A

the motor cortex and mescencephalic locomotor region

200
Q

T or F: studies (such as the one with cats) have shown that sensory feedback is not necessary to cause the rhythmic locomotion observed in animals

A

true

201
Q

How does a lack of sensory input affect the central pattern generator of locomotion?

A

it doesn’t prevent it, it just changes the output of the pattern

202
Q

What did the study on cats with damage to the premotor cortex show?

A

cats can still walk on smooth surfaces but cannot step over objects

203
Q

How do animals move over obstacles while running or walking through dynamic environments? what does this mean for the role of reflexes?

A

stretch receptors (mechanoreceptors) and proprioceptors in limbs receive sensory information about limb position and impact and send information to the pattern generator which can alter the motor outputs

reflexes, and autonomic nervous system, are important in coordinating locomotion

204
Q

T or F: afferent inputs are critical for rhythmic locomotion

A

false

205
Q

What happens if the central pattern generator is stimulated while muscles are paralyzed but there’s no damage to nervous system?

A

if the central pattern generator is stimulated, motor neurons will still be stimulated and produce rhythmic locomotion

206
Q

What 3 parts of the brain have key roles in regulating locomotion?

A

brainstem
cortex
cerebellum

207
Q

What function does the cerebral cortex have in locomotion?

A

it coordinates locomotion in complex environments and uses visual signals

208
Q

What happens to locomotion if there’s damage to the premotor cortex? why?

A

the cat can still walk along even terrain, even if there’s an incline, but it cannot step over obstructions or obstacles

sensory information enters the brain through the thalamus which projects information onto the somatosensory cortex, so if there’s damage to the cerebral cortex, changes to the environment causing sensory input will not be received by the cerebral cortex and motor neurons will not be triggered to move limbs in space

209
Q

What neural structures control movement?

A

in the brain: motor cortex controlled by the basal ganglia and brainstem centers such as the cerebellum

afferent and efferent neurons in the spinal cord

210
Q

What is the basal ganglia?

A

in the motor cortex, it causes initiation of wanted movement and suppression of unwanted movement

basically filters the motor outputs generated by the motor cortex to decide what is appropriate

211
Q

What is the overall function of the motor cortex?

A

to plan, initiate and direct voluntary movement

212
Q

What is the function of brainstem centers in movement?

A

to coordinate (via the cerebellum) rhythmic movements and posture

213
Q

What is the dorsal striatum?

A

the brain region that includes the caudate and putamen

214
Q

What projects onto the dorsal striatum?

A

the substantia nigra pars compacta

215
Q

How is the thalamus affected by the dorsal striatum?

A

the cortex sends information to the dorsal striatum which stimulates medium spiny neurons (MSNs) to disinhibit thalamic neurons through the globus pallidus internal

216
Q

What type of receptor types are on the MSNs and globus pallidal neurons?

A

GABAergic

217
Q

What type of receptors are on cortical neurons?

A

glutamatergic

218
Q

What is Parkinson’s Disease? What causes it? What are it’s symptoms?

A

a neurodegenerative movement disorder that affects 1-2% of 65+ yr olds

progressive loss of dopaminergic neurons in the substantia nigra causes motor symptoms (ex. bradykinesia, resting tremor and muscular rigidity) when >60% of dopaminergic neurons are lost

219
Q

What type of neurons are affected by Parkinson’s Disease?

A

loss of dopaminergic neurons cause motor symptoms

220
Q

When looking at a cross section of a Parkinson’s brain v. non Parkinson’s brain, what is the evident difference?

A

a non-Parkinson’s brain has evident very dark Substantia Nigra regions in the midbrain filled with dopaminergic neurons

a Parkinson’s brain does not have this dark band, it’s very faded due to the loss of dopaminergic neurons

221
Q

What is Huntington’s Disease? What causes it? What are the symptom?

A

a neurodegenerative disease that affects 5-10 people in midlife per 100,000 caused by the HTT gene mutation = huge loss of MSNs in caudate putamen

symptoms:
- cognitive deterioration
- psychiatric impairment
- chorea (abnormal involuntary movement)
- dystonia (sustained muscle contractions = twisting, abnormal posture)
- difficulty initiating movement

222
Q

What gene mutation causes Huntington’s Disease?

A

an autosomal dominant mutation to the HTT gene has 50% transmission

if there’s more than 35 repeats of CAG (polyglutamine), the person will get Huntington’s Disease

223
Q

What is the neural affect of Huntington’s Disease?

A

huge loss of medium spiny neurons in the dorsal striatum (caudate putamen)

224
Q

When looking at a cross section of a Huntington’s Disease brain v. a non Huntington’s Disease brain, what is the evident difference?

A

the Huntington’s Disease brain is severely degraded and has a very reduced dorsal striatum

225
Q

what is cerebellar ataxia?

A

coordination and accuracy of motor activity

Animal Physiology (13 decks)

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