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basal ganglia Flashcards

1
Q

what are basal ganglia involved in?

A

the pathways and centres that are involved in movement

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2
Q

where do signals originate?

A

in the cerebral cortex

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3
Q

what is involved in modulating the signals from the cortex?

A

a variety of subcortical structures such as the basal nuclei

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4
Q

what are LMNs?

A

they are nerve cells whose axons will link the CNS to the muscle

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5
Q

what influences the activity of LMNs in descending pathways?

A

UMNs

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6
Q

what are the control centres that regulate the activity of descending pathways?

A

the cerebellum and the basal ganglia

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7
Q

what does the cortex do?

A

it sens instructions for movement: this can be direct to SC through the cortical spinal tracts, by UMNs - LMNs in SC, the corticonuclear tract to the cranial nuclei, or the extrapyramidal tract in brainstem for movement at level of SC

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8
Q

what is the cerebellum for?

A

coordination, synergy and fine tuning

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9
Q

what are the BG for?

A

cessation of movement, control and normal initiation - is the movement appropriate

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10
Q

where do all information get relayed through?

A

the thalamus

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11
Q

what is the course of information from the thalamus to the response?

A

the motor regions of the cortex will send information to the BG and the cerebellum. The cerebellum will adjust for coordination etc and then either relay back to the thalamus, or to the brainstem. The basal ganglia relays information back to the thalamus. From the thalamus the information travels to the motor regions of the cortex again,and then if appropriate the information from cerebellum and BG goes to the brainstem or SC depending on the pathway. This will result in a motor response in muscles. This then feeds back to sensory receptors which will then give sensory feedback from the muscle to the SC and back to thalamus and brainstem.

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12
Q

what is the primary function of the BG nuclei?

A

it acts to provide feedback mechanism to the cortex for initiation, control and cessation of motor response for movement - modulation of voluntary motor activity

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13
Q

what do the BG do?

A

they receive and interpret information on the plan and sequence of movement from the cortex

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14
Q

once they have received the information what do the BG do?

A

they relay the decision to move through the thalamus - they either excite cerebral cortex to facilitate wanted movement or dampen it to inhibit the unwanted movement

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15
Q

what does lesions of the BG result in?

A

dykinesia - abnormal, involuntary movements that are hypo or hyperkinetic

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16
Q

what will be the result on a structure of an inhibitory neuron acting on an inhibitor of the structure?

A

disinhibition - the structure stays active

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17
Q

what are the anatomical basal ganglia?

A

they are the masses of grey matter in the forebrain that are closely related anatomically and embryologically but are functionally different

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18
Q

what is the lentiform nucleus made of?

A

the putamen and the globus pallidus

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19
Q

what is the C shaped nucleus?

A

the caudate nucleus

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20
Q

what is the amygdala?

A

it is the almond shaped nucleus of which we are unsure of the function that is in the limbic system for emotion

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21
Q

what is the structure near the amygdala of which we are unsure of the function? - it is grey matter

A

the claustrum

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22
Q

what do all the nuclei of the BG do?

A

they all function to coordinate movement for connections

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23
Q

what are the divisions of the BG?

A

the BG split into the corpus striatum and the amygdala. The corpus striatum then splits into the neostriatum known as the striatum and the paleostriatum - the paleostriatum gives rise to the globus pallidus and the neo to the caudate nucleus and the putamen. The putamen and the globus pallidus form the lentiform nucleus

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24
Q

what are the functional basal ganglia?

A

they may not be anatomically related but function as a group

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25
Q

which parts develop later in development?

A

the globus pallidus

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26
Q

which three parts all function as one?

A

the GP, the putamem and the caudate

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27
Q

where is the corpus striatum?

A

in the telencephalon of the brain

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28
Q

how many parts are there of the GP?

A

there are two portions that are functionally different

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29
Q

which part will stain dark and has two parts?

A

the substantia nigra

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30
Q

what structure is in the diencephalon?

A

the subthalamic nucleus

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31
Q

where are the fie structures?

A

3 in the forebrain, one in the midbrain and one in the diencephalon

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32
Q

what are the two portions of the GP?

A

the internus (GPi) and the externus (GPe)

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33
Q

what is the SNr?

A

it is functionally part of the GPi - it is the pars reticulata and is one portion of the substantia nigra

34
Q

where is the substantia nigra?

A

it is mesencephalic

35
Q

what is the other part of the substantia nigra?

A

the pars compacta - SNc

36
Q

what are fusions in the corpus striatum called?

A

the are cellular bridges

37
Q

why are there separations in the corpus striatum?

A

due to the existence of white matter structures such as the internal capsule

38
Q

which part will stain paler of the corpus striatum?

A

the GP

39
Q

what is contained within the internal capsule?

A

there is ascending and descending sensory fibres and perpendicular to these there are projection fibres that can carry information from the GP and thalamus and between the caudate and putamen

40
Q

what are the four division of the thalamus?

A

the epi, hypo, sub and thalamus

41
Q

where is the subthalamic nucleus?

A

it starts below the thalamus and then migrates laterally so is close to the tegmentum of the midbrain and medial to the internal capsule. It forms part of the basal ganglia and is contained within the diencephalon

42
Q

what happens if there are not enough neurons in the substantia nigra?

A

parkinsons results

43
Q

why does the compacta of the nigra stain dark?

A

the neurons produce dopamine and NTs - biproducts of dopamine release melanin which is a dark pigment

44
Q

why does the reticulata not stain dark?

A

the neurons do not produce dopamine

45
Q

what functions similar to the reticulata?

A

the GPi

46
Q

where is the substantia nigra?

A

behind the cerebral peduncles in the mesencephalon

47
Q

what are other functions of the BG?

A

for cognitive processes such as perception, memory, learning, abstract thought and for emotion

48
Q

what is the basic circuitry of the BG?

A

multiple parallel looping circuits from the cerebral cortex and back, through the thalamus to modulate cortical output
the BG have connections within themselves and relay the decision through the thalamus

49
Q

what is the input?

A

the striatum - putamen and caudate

50
Q

what is the output?

A

it is the GPi and SNr that communicate with the thalamus

51
Q

how will the GPi and SNr work?

A

the will tonically inhibit the thalamus if do not want that movement or enhance the movement if do - facilitate movement

52
Q

what is the default process in the GPi and SNr?

A

inhibitory

53
Q

what is the route of the sequence of intended movement from the cortex?

A

sends a copy of sequence of the intended movement to the BG through the cortical striatal neurons which are always excitatory - these influence the neurons in the GP
nigral striatal neurons will influence the striatum which will be inhibitory or excitatory depending on the receptors expressed
inhibitory default neurons from the output nuclei
from the GPi to the thalamus is the pallidothalamic tract

54
Q

what types of neurons come from the cortex or nigra?

A

afferent

55
Q

what are the input nuclei?

A

the striatum - putamen and caudate - they receive afferents

56
Q

what types of afferent projections to the striatum are there?

A

from the cortex - corticostriatal fibres (excitatory) - information about the intended movement
from the substantia nigra pars compacta - striatonigral fibres that release dopamine - excitatory or inhibitory depending on the type of receptor on the post synpatic neuron

57
Q

what are the output nuclei?

A

the GPi and the SNr - send efferent fibres to supply the thalamus

58
Q

what types of efferent fibres are there?

A

the pallidothalamic fibres that are inhibitory - tonically inhibit the thalamus
the thalamocortical fibres that are inherently excitatory to the cortex and facilitate movement

59
Q

what is the function of the thalamus with regards to the BG?

A

to communicate with the motor areas of the cortex especially the premotor and supplementary motor

60
Q

what happens after an excitatory signal?

A

the motor cortex influences LMNs via the corticospinal pathway and extrapyramidal tract

61
Q

how do the basal nuclei primarily function?

A

through inhibition and disinhibition

62
Q

how can BG influence whole packages of movements?

A

the direct pathway - facilitating a specific movement programme

63
Q

what are the types of direct pathways?

A

neurons from the striatum that project directly to the GPi
neurons from the striatum that project to the GPe and then strongly to the subthalamic nucleus and then to the GPi
indirect pathway - inhibit a specific movement programme to allow for the direct pathways programme

64
Q

what is the direct and indirect pathway in the flexion of fingers?

A

indirect - relaxing extensors to allows for the direct pathway of contracting flexors

65
Q

what does the direct pathway aim to do?

A

activate movement - increases the wanted movement

66
Q

how does the direct pathway work?

A

there is an excitatory neuron from the cortex to the putamen which will activate the neuron from the putamen to the GPi which is inhibitory
this will inhibit the inhibitory neuron from the GPi to the thalamus meaning that the excitatory neuron from the thalamus to the cortex is stimulated
movement through the corticospinal tract

67
Q

what does the indirect pathway do?

A

inhibits movement - decreases unwanted

68
Q

how does the indirect work?

A

the neuron from the cortex to the putamen is excitatory - if inappropriate then will go to GPe via inhibitory - enhanced from excitatory
neuron from GPe to subthalmic nucleus is inhibitory and is inhibited so this activity is decreased
neuron from the subthalamic to GPi is activated as less inhibition - more excitatory
excites the neuron from GPi to thalamus which is inhibitory - strong inhibition to excitatory neuron from thalamus to cortex - less stimulation and less unwanted movement

69
Q

what is the role of the SNPC?

A

initiate movement - has a modulatory effect on the indirect and direct pathway to facilitate movement

70
Q

how does the SNPC affect the indirect and direct pathway?

A

direct - dopamine containing neurons come into contact with neurons with the D1 receptor - dopamine acts as excitatory - enhances wanted movement
indirect - inhibits - therefore stops the inhibition of movement - the dopamine containing neurons come into contact with D2 receptors - act as an inhibitory NT and decreases inhibition

71
Q

what will happen with a large burst of dopamine?

A

facilitate movement using both pathways

72
Q

what happens if the SNPC is diminished?

A

cannot initiate movement

73
Q

where do neurons from the SN run and what do they contain?

A

SN to striatum containing dopamine

74
Q

what is the presentation of lesions of the BG?

A

disordered movement on the contralateral side, slow movement, rigidity, tremor

75
Q

what is involved in slow movement and why?

A

there is poor initiation resulting in hypokinesia
there is walking slowly with small steps, external initiation leads to large impacts such as easily falling with a small push and mask face as cannot initiate facial expression and an infrequent blink

76
Q

what is the most common disease of basal ganglia?

A

it is disruption of the nigrostriatal input - parkinsons - decreased movement through both pathways

77
Q

what else can degenerative basal ganglia changes lead to?

A

hyperkinetic disorders, dgeneration of the subthalamic nucleus, degeneration of inhibitory fibres from the striatum to GPe

78
Q

what happens in hyper kinetic disorders?

A

unwanted movements occur

79
Q

what is the result of degeneration of the subthalamic nucleus?

A

there is usually excitatory from the subthalamic to the GPi. Therefore a degeneration will result in this not happening. This means that the inhibitory neuron from the GPi to the thalamus is not activated, therefore the excitatory neuron from the thalamus to the cortex is not inhibited meaning that there is more movement. This results in hemiballismus which is a jerky, violent movement on the contralateral side

80
Q

what is the result of degeneration of inhibitory fibres from the striatum?

A

from striatum to GPe is inhibitory neuron. If these fibres degenerate there will be no inhibition of the inhibitory neuron from the GPe to the subthalamic. Therefore there is inhibition of the excitatory neuron from the subthalamic to the GPi. Therefore there is no stimulation of the inhibitory neuron from the GPi to the thalamus. Therefore there is no inhibition of the excitatory neuron from the thalamus to the cortex - HDD chorea

C&M (36 decks)

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