Chapter 12 Diencephalon

diencephalon includes

• epithalamus

• thalamus

• subthalamus

• hypothalamus

• these are all one deep nuclei

location of the diencephalon

cephalic flexure- 80 degree turn from brainstem

interior surface

infundibular stalk & mammillary bodies visible on intact brain

superior border

lateral ventricle

medial border

3rd ventricle

lateral border

internal capsule

the dorsal thalamus is

medial to internal capsule and in the posterior half of brain

diencephalon facts

• hypothalamus- is wedge shaped

• caudal border of hypothalamus- post commissure

• rostral border- anterior commissure & optic chiasm

epithalamus

• pineal gland- endocrine gland involved in seasonal cycles, secretes melatonin—-light to retina signals suprachiasmatic nucleus to inhibit pineal melatonin production

subthalamus

• continuation of midbrain tegmentum

• inferior to thalamus

• lateral to HTh

• medial to cerebral peduncles and internal capsule

• important for basal ganglia motor control

• interconnected with basal ganglia

thalamus

• often called the dorsal thalamus

• 80% of diencephalon

• relay nuclei- sensory relay station

• association nuclei- processing between cortical areas

• intralaminar/midline nuclei- basal ganglia and limbic connections

thalamus sensory relay station

• sensory function- not just to transfer information, a decision site about which form info should reach cortex

• ADHD & autism

dorsal thalamus sensory relay station

• sensory receptors never stop sending sensory information and ALL sensory information is passed along in either TONIC or BURST mode

wrong statements for dorsal thalamus

• “ the function of the sensory relay nuclei of the dorsal thalamus is to decide what sensory information gets to cortex”

• “ the dorsal thalamus decides where to relay the sensory signals”

• the dorsal thalamus is a sensory gatekeeper because it determines which information will be processed and sent to the cortex for use”

what decision does the dorsal thalamus sensory relay nuclei make?

to relay the sensory information in one of two forms- tonic mode & burst mode

tonic mode

info is transmitted faithfully (normally, with fidelity) so we can pay attention to the sensory information

burst mode

info is transmitted but not faithfully (abnormally, without fidelity) so we can ignore the sensory information

thalamus

• each system has its own nuclei

• anterior, medial and lateral divisions separated by internal medullary lamina

• lateral division has a dorsal & central tier

• topographic subdivisions

sensory relay nuclei to remember

• ventral- VPL (posterolateral)

• ventral- VPM (posteromedial)

• medial geniculate- MGN (auditory)

thalamic inputs 2 broad categories

• regulatory thalamic inputs

• specific thalamic inputs

regulatory thalamic inputs

• feedback from cortex, from thalamic reticular nuclei

• processing contributes to the sensory relay station decision about what form the output leaves the thalamus on its way to primary sensory cortex

specific thalamic inputs

• all other thalamic nuclear inputs are specific inputs

• some are motor, many are sensory

thalamic outputs

• relay nuclei: projections to functional area of cortex and limbic system

• association nuclei: projections to cortical association areas; input from cortex and subcortical structures; function is unclear but probably involved in distribution and gating in between cortical areas

what are the two physiological states of projection neurons of dorsal thalamus?

tonic mode & burst mode

tonic and burst mode impact on attention

• it is important that we have both modes and the ability to switch between them rapidly so we don’t suffer from chaotic sensory overload

• most sensory info is in burst mode because our performance skyrockets when we are able to focus on very few stimuli at the same time

most thalamic inputs/outputs move through what?

the internal capsule = white matter, also containing thalamocortical & corticothalamic projections

lesions in the thalamus

can cause motor or sensory losses including thalamic pain and is very difficult to treat

internal capsule 5 sections

• anterior limb

• posterior limb

• genu of internal capsule

• minor ( retrolenticular part, sublenticular part and hypothalamus)

hypothalamus details

• endocrine “general” of the CNS

• promotes homeostasis of internal environment ( autonomic, endocrine, emotional & somatic pathways- sensitive to body temp, blood osmolality, concentration glucose or other hormones

• crucial for motivation in drive-related areas (thirst, hunger, warmth, etc.)

hypothalamic interconnections are diverse including

• interconnections with limbic system and dorsal thalamus, indirectly to cortex

• outputs to pituitary gland

• interconnections with various visceral & somatic nerves of BS& SC, both sensory and motor

• complex and sophisticated

inputs to hypothalamus

• forebrain- septal nucleus, hippocampus, amygdala, orbital gyro & other cortex, retina

• brainstem & spinal cord- from reticular formation, connects to hypothalamus to reticular foramen via peri-aqueductal gray matter

outputs from hypothalamus

• largely reciprocal to inputs via same pathway that carry inputs, two-way traffic

• mammillothalamic tracts (emotion and memory)

hypothalamus control of pituitary gland

• communicates in two ways

• via the supraopticohypophyseal tract

• via hypophyseal portal system

hypothalamus communication with pituitary gland via supraopticohypophyseal tract

neurons of hypothalamus send axons to posterior pituitary gland

hypothalamus communication with pituitary gland via hypophyseal portal system

other neurons secrete releasing or inhibiting hormones into blood vessels that go to the anterior pituitary to control its release of hormones that will circulate to the entire body

pituitary gland 2 sections

• posterior lobe- neurohypophysis

• anterior lobe- adenohypophysis

• both have an effect on the kidney

posterior lobe- neurohypophysis

• antidiuretic hormone (ADH or vasopressin) increases reabsorption of water in kidney, increases peripheral vascular resistance

• oxytocin- uterine & mammary smooth muscle contraction

• antidiuretic hormone prevents hypovolemic shock, blood pressure of blood volume is directly related

anterior lobe adenohypophysis

• hypothalamus gland secretes numerous releasing hormones into hypophyseal portal system, which is a vascular connection carrying hypothalamic releasing or inhibiting hormones for stress, growth, reproduction

adrenocorticotropic hormone

• corticotropin

• symbol- ACTH

• target- adrenal gland

• effect- secretion of glucocorticoids

beta-endorphin hormone

• other names- b-endorphin

• target- mu opioid receptor

• effect- inhibit perception of pain