Thalamus 2

Question 1

What are the 2 states of Thalamic projection neurons?

Answer 1

Tonic mode

Burst mode

Question 2

Describe tonic mode

Answer 2

Thalamic projection neurons are slightly depolarized. These neurons behave like typical neurons except a slight depolarization will trigger a train of action potentials. (Class mode–focused)
The magnitude of the input is expressed by the Frequency of the Train of action potentials.
Higher magnitude gets Faster Frequency. (It doesn’t take a lot of depolarization to trigger an action potential)

Question 3

Describe Burst Mode

Answer 3

The state in which projection neurons are Hyperpolarized beyond their tonic state (waking coyote)

1. Special voltage-gated Ca++ channels become available in burst mode. In this state, a slight depolarizatio will trigger a burst of action potentials.
2. Followed by 100ms or greater inactivation period.
3. Bursts can only occur a few per second for a neuron in this state. (Action potentials are right next to each other ( a couple of spike), and the there is a silent period. To bring us out of a restful state and make us attentive very quickly. Can take 15-20 to reset.)

Question 4

What are the 3 functional roles of thalamic tonic and burst modes?

Answer 4

1. FOCUS OF OUR ATTENTION on a stimulus, thought or task is believed to result in a shift of these projection neurons into TONIC MODE.
2. MOST PHASES OF SLEEP are in the BURST MODE so effective information transmission is suspended. (Most info doesn’t get passed through during sleep)
3. THE BURST MODE is often present in some neuronal projections during wakefulness, allowing sudden signaling for an acute awareness of an event.

Question 5

What is the Internal Capsule?

Describe what it is like dorsally and ventrally?

Answer 5

Internal Capsule–(in the diencephalon) is one portion of a continuous massive sheet of projection fibers to and from the cerebral cortex. (white matter) This lets the thalamus, brainstem, and spinal cord communicate with the cortex.

Dorsaly, the internal capsule is continuous with the corona radiata on its way to the cerebral cortex.

Ventrally, this sheet extends as the crus cerebri of the midbrain. The crus cerebri is the anterior part of the cerebral peduncle and is largely made up of descending motor fibers.

Question 6

What is the blood supply to the Thalamus?

Answer 6

Branches of the posterior cerebral artery.
Dorsimedial region is from the posterior choroidal artery.
Remainder is performating arteries of the posterior cerebral artery and posterior communication artery.

Question 7

What is the primary cause of Damage to the Thalamus?

Answer 7

It occurs secondary to a vascular accident.

Question 8

If someone survives a Thalamic stroke, what is the chronic condition that remains? describe.

Answer 8

Thalamic Pain or Central Pain Syndrome.
Occurs if stroke is restricted to posterior thalamus, patient gets intense pain similar to trigeminal neuralgia. (people become siudcidal due to the pain. Light touch sets them off)
This intense pain-inducing signaling is triggered by general somatosensory input.
The pain may spread over the contralateral side of the body. (sensory input has decussated before it hits the thalamus)
Pain is resistant to analgesic drugs.

Question 9

Describe Thalamic Syndrome

Answer 9

The combination of thalamic pain, hemianesthesia (no feeling on a side), and sensory ataxia (really bad coordination) from a contralateral lesion.
The ataxia is due to the medial lemniscus pathway also being affected in the stroke.
(This condition is more common in a rehab center. Goal is to help patient make sense of the inputs they do have…including visual.)