Neuro Exam 2: Basal Ganglia

Front 1

What does the term basal ganglia refer to?

Back 1

Collection of subcortical nuclei
-Includes caudate, putamen, globus pallidus, subthalamic nucleus, and substantia nigra. Also referred to as extrapyramidal motor system.

Front 2

What does the term striatum refer to?

Back 2

Caudate and putamen

Front 3

What does the term pallidum refer to?

Back 3

Globus pallidus

Front 4

What does the term lenticular nuclei refer to?

Back 4

Putamen and globus pallidus

Front 5

What are the structures of the basal ganglia connected to?

Back 5

Ipsilateral cerebral cortical and diencephalic structures in an orderly topographical fashion

Front 6

What is the caudate?

Back 6

An elongated C-shaped nucleus that is composed of head, body, and tail.
-Head: bulges into lateral aspect of frontal horn of lateral ventricle
-Body/tail: continue posteriorly, then inferiorly, then anteriorly maintaining a lateral relationship to body and temporal horn of lateral ventricle
-Tail of the caudate ends at the amygdala

Front 7

What is the putamen?

Back 7

Largest and most lateral part of the striatum, lying between external capsule and external segment of globus pallidus.
-Microscopicallly, caudate and putamen are identical
-Rostrally, putamen is continuous with head of caudate

Front 8

What is the globus pallidus?

Back 8

Composed of external and internal segments that are separated by thin internal medullary lamina.
-Many bundles of myelinated fibers give it a paler appearance

Front 9

What is the substantia nigra?

Back 9

Largest nuclear mass in midbrain. Located anteriorly and extends length of midbrain into caudal diencephalon.
-2 parts: pars compacta (dorsal, cell-rich that contain melanin pigment giving SN its black appearance) and pars reticulata (ventral, similar to internal segment of globus pallidus).

Front 10

What is the subthalamic nucleus?

Back 10

small, lens-shaped nucleus located in diencephalon inferiorly to the thalamus just above the internal capsule and overlying the substantia nigra

Front 11

Which structures are considered the input nuclei of the basal ganglia?

Back 11

Caudate (for saccadic eye movements, cognitive function, and some motor function) and putamen (for motor function)

Front 12

Which structures are considered the output nuclei of the basal ganglia?

Back 12

Internal segment of the globus pallidus (GPi) and the pars reticulata of the substantia nigra

Front 13

Which area of the basal ganglia is a common area for lacunar infarct?

Back 13

Putamen

Front 14

Which structures of the basal ganglia are considered relay stations?

Back 14

Subthalamic nucleus and the external segment of the globus pallidus (GPe)

Front 15

Where does the output of the basal ganglia project to?

Back 15

Ventral lateral thalamic nucleus (VL) and the midbrain reticular formation

Front 16

Describe the dopamine projections from the substantia nigra to the putamen

Back 16

The dopamine containing neurons synapse on excitatory D1 receptors in the excitatory pathway and inhibitory D2 receptors in the inhibitory pathway.
-Increased activity in pars compacta of substantia nigra leads to increased activity of excitatory pathway and decreased activity of inhibitory pathway. Both of these lead to increased activity of motor cortex.
-Disruption of the dopamine pathways leads to movement disorders with "too little" movement (abnormal stiffness or slowness). Hyperfunction of the dopamine system leads to movement disorders characterized by "too much" movement.

Front 17

What type of interneurons are in the putamen?

Back 17

Excitatory cholinergic interneurons. Drugs that affect acetylcholine transmission are used to treat certain movement disorders.

Front 18

Describe the pathways that give input to the caudate rather than the putamen

Back 18

Cortical inputs come from diffuse cortex. Outputs from BG project back to prefrontal cortex. Pathway involved in saccadic eye movements, cognition, and some motor system.

Front 19

What are the basal ganglia circuits concerned with?

Back 19

Planning and organizing voluntary movement

Front 20

How do you know if you're looking at an anterior or posterior coronal slice of the basal ganglia?

Back 20

If the third ventricle is not present on the slice, it is anterior. If the third ventricle is present, it's a more posterior slice.

Front 21

How can you tell that you're looking at an axial rather than a coronal slice of the basal ganglia?

Back 21

If you can see the whole V of the internal capsule (both anterior/posterior limb) then you are looking at an axial slice.

Front 22

Name the structures on an anterior coronal slice medial to lateral

Back 22

Frontal horn of lateral ventricle, head or body of caudate, anterior limb of internal capsule, globus pallidus (both internal/external), putamen, external capsule, claustrom, extreme capsule, insula.

Front 23

Name the structures on a posterior coronal slice medial to lateral

Back 23

Lateral ventricle and third ventricle (lateral above third), caudate body and thalamus (caudate body above thalamus), posterior limb of internal capsule, globus pallidus, putamen, external capsule, claustrom, extreme capsule, insula (more inferior than these would be substantia nigra in midbrain and caudate tail).

Front 24

What does parkinsonism symptoms and signs results from?

Back 24

-"Lesion" of the substantia nigra pars compacta with decreased DA
-lesion of putamen or globus pallidus

Front 25

What are some ways to alleviate the parkinsonism symptoms/signs?

Back 25

1. Increase dopamine
2. Decrease ACh (Ach found in striatal interneurons)
3. Surgical lesion of GP or VL thalamus
4. Deep brain (electrical) stimulation of GP, VL, STN

Front 26

What is the purpose of the excitatory pathway and what happens if get a lesion there?

Back 26

Purpose is to get the motor system going, dopamine increases movement here.
Lesion = too few movements (hypokinetic)

Front 27

What is the purpose of the inhibitory pathway and what happens if get a lesion there?

Back 27

Put breaks on the motor system (e.g., inhibit movements), dopamine inhibits this pathway which increases movement (aka inhibits inhibition).
Lesion = too many movements (chorea)

Front 28

Describe how a lesion of both the excitatory and inhibitory pathway lead to parkinsonism symptoms

Back 28

Decreased dopamine from SN to putamen. Means excitatory pathway is not getting excited, so it's producing less movements. Means inhibitory pathway is not getting inhibited so it's producing less movements. This leads to the parkinsonism in PD.

Front 29

Which structure is the equivalent of the striatum for the limbic system?

Back 29

Nucleus accumbens (meaning, it's the input nuclei)

Front 30

Which structure is the equivalent of the substantia nigra pars compacta for the limbic system?

Back 30

Ventral tegmental area (meaning it projects dopamine to the nucleus accumbens). Blocking the VTA treats psychosis.

Front 31

What does the nucleus basalis do?

Back 31

Projects ACh to cerebral cortex and is one of the many things that go bad in AD (medications that supplement this aren't really that effective though).

Front 32

What are motor disorders of the basal ganglia called?

Back 32

"Extrapyramidal" disorders (no relation to descending extrapyramidal system)

Front 33

Describe the clinical signs of a basal ganglia disorder

Back 33

Muscle bulk: normal
Muscle tone: hypertonia (rigidity)
Strength: normal (may take longer to turn on strength)
Deep tendon reflexes: normal
Pathological reflexes: none
Movement disorders: Present (in some basal ganglia lesions, may be hypokinetic or hyperkinetic)
Coordination: Appropriate for tone and abnormal movements

Front 34

What is rigidity?

Back 34

Hypertonia that offers uniform resistance throughout the movement.
-Often feels same as spasticity on exam
-Due to increased motor neuron discharge to agonist and antagonist muscles and is unrelated to spasticity.

Front 35

What are akinesia and bradykinesia?

Back 35

Hypokinetic (too little movement) disorders.
-Akinesia: an abnormal slowness in the initiation of voluntary movement
-Bradykinesia: an abnormal slowness in the execution or performance of voluntary movement.
-Often due to basal ganglia dysfunction, but can also be due to other causes (e.g., severe depression, medial frontal lesion)

Front 36

What is stooped posture?

Back 36

An abnormal posture characterized by forward flexion of the head and trunk. Generally associated with decreased arm swing with walking and a tendency to turn all together.

Front 37

What is the term for postural instability in which there is a tendency to fall backward?

Back 37

Retropulsion

Front 38

What is Parkinsonism?

Back 38

A syndrome with many specific causes. Some combination of rigidy, akinesia, bradykinesia, stooped posture, postural instability, and other hypokinetic manifestations (e.g., soft monotonous speech, masked facial appearance, small handwriting). May also have characteristic "Parkinsonian tremor." May be unilateral, but is usually bilateral.

Front 39

Describe the Parkinsonian tremor

Back 39

-Rate of 4-6 Hz
-Pronation/supination of the forearm
-Flexion movements of thumb and fingers ("pill rolling")

Front 40

What does the model of motor basal ganglia function explain and what does it not explain?

Back 40

It explains the hypokinetic features of Parkinsonism, but not the tremor

Front 41

What does the lesion in Parkinsonism involve?

Back 41

Decreased dopaminergic output from subtantia nigra pars compacta.
-May be anatomical (degeneration of neurons in PD) or pharmacological (side-effects of dopamine-blocking drug to treat psychosis). Less commonly, caused by lesion of the putamen or globus pallidus.

Front 42

What are hyperkinetic disorders characterized by and what are the types?

Back 42

Too much movement.
Types: tremor, tic, chorea, hemiballismus, athetosis, dystonia

Front 43

What is a tremor?

Back 43

Involuntary, regular, rhythmic "shaking" movement of a body part. There are different types of tremors and not all are due to lesions of BG (e.g., at rest = Parkinsonian tremor, with activity, physiologic = coffee).

Front 44

What is a tic?

Back 44

Involuntary rapid purposeless but stereotyped (e.g, same every time) movement that may involve face, trunk, extremities, or voice.
-May be due to dysfunction of some parts of BG.

Front 45

What is chorea?

Back 45

Involuntary, rapid, jerk-like, purposeless, non-stereotyped movements that may involve face, trunk, or extremities. Predominately distal.
-Often results from excessive activity in dopaminergic nigrostriatal pathways. Lesions typically in parts of the (contralateral) putamen or caudate, or the (contralateral) subthalamic nucleus.

Front 46

What is hemiballismus?

Back 46

Sudden, involuntary, often violent, flinging movement of one or both extremities of one side.
-Most often seen with lesion of the contralateral subthalamic nucleus.
-May be large amplitude, proximal chorea

Front 47

What is athetosis?

Back 47

Involuntary, slow writhing movement of trunk or extremities.
-Lasts longer, more sustained, most often in cerebral palsy

Front 48

What is dystonia?

Back 48

Slow, sustained abnormal movement (e.g., turning head to one side with torticollis)
-May be focal (one body part, more common in adults) or generalized (most of body, more common in children)