Thalamus and internal capsule (Chapter 16)

Question 1

Name the four regions of the diencephalon:

Answer 1

The diencephalon consists of the:
Epithalamus
Dorsal thalamus
Subthalamus
Hypothalamus

Question 2

What structures are included in the epithalamus?

Answer 2

Pineal gland and habenula.

Question 3

What structures are included in the dorsal thalamus?

Answer 3

Thalamic nuclei.

Question 4

What structures are included in the subthalamus?

Answer 4

Red nucleus and substantial nigra. (Also contains zone incerta and sub thalamic nucleus).

Question 5

What structures are included in the hypothalamus?

Answer 5

Mammillary bodies and infundibular stalk.

Question 6

How is the pineal gland light-regulated?

Answer 6

Contains photoreceptors and receives inputs from retinal cells via the hypothalamus and spinal cord.

Question 7

What is the function of the pineal gland?

Answer 7

Regulates circadian rhythms (+ seasonal sexual cycles in other mammals), secretes melatonin.

Question 8

Where is the habenula located?

Answer 8

2 structures (habenular nuclei) anterior to the pineal.

Question 9

Inputs and outputs of the habenula?

Answer 9

Inputs: globus pallidus, limbic structures.
Outputs: to midbrain/brainstem reticular formation.

Question 10

What is the function of the habenula?

Answer 10

General regulation of emotion-related arousal via the brainstem, may be involved in assigning reward value to stimuli.

Question 11

What type of tracts traverse the subthalamus?

Answer 11

Somatosensory pathways (mostly), also tracts to/from basal ganglia.

Question 12

The subthalamus represents an extension of the __________.

Answer 12

Midbrain tegmentum .

Question 13

What is the general role of the thalamus?

Answer 13

Regulating and directing behavior (arousal & attention), “relay station”, also sensory gating mechanisms (?)

Question 14

What are the three main regions or groups of the dorsal thalamus and how are they defined?

Answer 14

Anterior, medial, and lateral divisions, defined by the internal medullary lamina.

Question 15

What is the internal medullary lamina?

Answer 15

A thin, curved sheet of myelinated fibers that splits and encloses groups of nuclei.

Question 16

Where is the dorsomedial nucleus found?

Answer 16

The DM nucleus is found in the medial division.

Question 17

Where is the anterior nucleus found?

Answer 17

The anterior nucleus is found in the anterior division. It borders on the intraventricular foramen.

Question 18

Where is the pulvinar found?

Answer 18

The pulvinar is posterior.

Question 19

The ______________ wraps all around the dorsal thalamus.

Answer 19

The external sheet of the reticular nucleus wraps all around the dorsal thalamus.

Question 20

Describe the two categories of inputs to the thalamus.

Answer 20

Specific inputs: From periphery. Thalamic nucleus passes on information accurately.
Regulatory inputs: From cortex, other thalamic nuclei, reticular nucleus. Contribute to decisions about the form in which information leaves the thalamus.

Question 21

Name the three types of thalamic nuclei:

Answer 21

Relay nuclei, association nuclei, intralaminar/midline nuclei.

Question 22

What is the function of relay nuclei?

Answer 22

The role of relay nuclei is to deliver information from particular functional areas to appropriate cortical areas (i.e., from and to specific areas).

Question 23

What is the function of association nuclei?

Answer 23

Association nuclei relay/modulate information between cortical regions.
Dorsomedial nucleus: PFC, olfactory, limbic –> PFC.
Pulvinar: Parietal-occipital-temporal association cortex.
Lateral-posterior nucleus: Parietal lobe-parietal lobe.

Question 24

What is the function of the intralaminar and midline nuclei?

Answer 24

Not well understood, but seem to have special role in the function of limbic and motor circuits (limbic system and basal ganglia).

Question 25

Thalamic nuclei have two physiologic states. Name and describe their function.

Answer 25

Tonic mode: Projection neurons act similarly to a typical neuron, where the frequency of a train of action potentials depends on the magnitude of input to that neuron. “Slight additional depolarization causes a train of action potentials, and slight hyperpolarization causes their cessation.”
Burst mode: Burst of AP activity, followed by a period of inactivation (100ms).

Question 26

You would expect to see thalamic nuclei in ________ mode while doing an attention-focused task, and in ________ mode during sleep and when alert but not immediately engaged/waiting for something to happen.

Answer 26

Tonic; burst

Question 27

What causes burst mode?

Answer 27

Controlled by voltage-gated calcium channels. Sustained influx of Ca2+ causes a burst of AP activity followed by a period of inactivation.

More detail:
Burst mode occurs when projection neurons are hyperpolarized beyond the tonic range, which opens a special class of calcium channels, resulting in rhythmic depolarization --> rhythmic burst of action potentials in thalamic projection neurons.

Question 28

What is the general organization of the internal capsule?

Answer 28

5 regions named relative to the lenticular nucleus (i.e., caudate, putamen, globus pallidus).
Anterior limb, posterior limb, genu, retrolenticular (posterior to thalamus), sublenticular nucleus (optic and auditory radiations, connected to lateral and medial geniculates).

Question 29

What part(s) of the internal capsule contains part of the optic radiation?

Answer 29

Retrolenticular part (carries info from inferior portions of visual fields) and sublenticular part (superior visual fields).

Question 30

What part of the internal capsule contains the auditory radiation?

Answer 30

The sublenticular part contains the auditory radiation.

Question 31

What part of the internal capsule carries motor and somatosensory info?

Answer 31

The posterior limb carries motor and somatosensory info (corticospinal, corticobulbar, somatosensory).

Question 32

What are the two principal sources of blood supply to the internal capsule?

Answer 32

Small branches of the MCA