Thalamus

Sagittal view of thalamus

•thalamus extends from the roof of the diencephalon inferiorly to the

hypothalamic sulcus, where it meets the hypothalamus

•this is also a view of the lateral wall of the third ventricle.

•two halves of the thalamus are joined by a bridge across ventricle III

called the massa intermedia or intermediate mass.

•anterior boundary of the thalamus is the interventricular foramen which

is a passageway between the lateral cerebral ventricles and the third ventricle

•posterior boundary is the posterior commissure and mesencephalon

thalamus

relay station by which sensory impulses are relayed from lower pathways to cerebral cortex

pain sensation

pain impulses relayed through thalamus to sensory cortex

thalamic function

1. to relay information directly to cortex

OR

2. to process information and then relay it to cortex

crude sensations begin in thalamus

pain

touch

temperature

some affective sensations (mood)

depression

well-being

feeling of strain or agitation

discrimination

shape

size

texture

movement

cortex is necessary for

recognition

processing is done in the

thalamus

thalamic syndrome symptoms

-first: loss of sensation and pain

-then: hypersensitivity to stimuli as small as tickling or music (clothes are even painful)

thalamic syndrome cause

primarily thrombosis, usually of the posterior cerebral artery

reticular formation (RF)

-Means "net like"

-in mesencephalon, pons and medulla

-RF fills in spaces not otherwise occupied by nuclei and tracts

-not held for anatomy, just grasp general nature of RF

-between tracts and nuclei throughout brain stem and cord

Ascending Reticular Activating System (ARAS) or Reticular activating system (RAS)

1. is necessary for alertness (attention, awareness, sleep-wake cycle)

2. consists of reticular formation AND afferent and efferent connections to the reticular formation

RAS

-the diffuse, net-like reticular formation, plus the connections into and out of it, equals the reticular activating

system

-RAS makes us awake and able to pay attention

all sensory input stimulates the

RAS

power of stimuli the RAS

Olfaction > pain > auditory stimuli > visual Stimuli

Waking-Arousal Mechanisms

-All Sensory Inputs Into The CNS Stimulate The Ras, So, The RAS Is Non-specifically Stimulated By Any Type Of Stimulus

-Activity In The Rf Percolates Upward To The Thalamus And Then Radiates Out Into The Entire Cerebral Cortex And Excites It, Wakes Us Up, Lets Us Focus Attention

-Certain Nuclei Of The Thalamus Are Regarded As An Upper Component Of The Ras, Relaying Excitement To The Entire Cortex

non-specific nature of stimuli activating RAS

1. pathways are polysynaptic

2. pathways to cortex:

a. from non-specific projection of thalamus

b. bypass thalamus going directly to cortex

Anesthesia Blocks _______ But Not

_____ and _____ pathways

RF (reticular formation)

pain

auditory

Locus coeruleus (LC)

-may be part of RAS

-secretes adrenalin and noradrenalin

-sends impulses to every major region

in the CNS

-LC helps to cause behavioral arousal

and alertness

-LC suppresses irrelevant background

stimuli and enhances relevant stimuli

-stimulates alertness

-activated in fear and PTSD