Chapter 6 (Diencephalon, Basal Ganglia, and Brain Ventricles)

Diencephalon

located between the cerebrum and the brain stem, resting above the midbrain of the brainstem

• its location makes it a prime area for connecting the cerebral cortex to the rest of the body

connects the nervous system to the endocrine system (our hormone system)

consists of four parts

• thalamus

• subthalamus

• hypothalamus

• epithalamus

Thalamus

a greek word meaning “inner chamber” or “bedroom”

sits on top of the midbrain and consists of two halves, or hemispheres, each being the size of a walnut

function: sensory fiber relay station or switchboard between the cerebral cortex and subcortical areas (routes specific information to specific cortical areas)

• processes all sensory information except olfaction

Blood supply to the thalamus

Anterior portion:

• supplied by the tuberothalamic arteries that branch off of the internal carotid artery’s posterior communicating artery

thalamic pain syndrome

also known as Dejerine-Roussy syndrome

involves burning or tingling sensations and possibly hypersensitivity to stimuli that would not normally be painful, such as light touch or temperature change

• this condition can be both severe and debilitating

• a thalamic disorder

hypersomnia

excessive daytime sleepiness

• a thalamic disorder

akinetic mutism

people become passive and do not move or talk

• a thalamic disorder

thalamic aphasia

Three characteristics:

1. fluent verbal output with semantic paraphasias that often result in jargon

2. auditory comprehension that is less severe than one would expect for the severity of verbal output

3. minimally impaired or even intact repetition

• a thalamic disorder

Subthalamus

• lies below the thalamus

• contains a set of specialized cells has more in common with basal ganglia than thalamus

• plays a role in the selection of actions and impulse control

• damage can result in motor problems like hemiballismus(a one-sided involuntary flinging of the limbs sometimes seen in Parkinson’s disease or other neurological disease) 

• damage may also play a role in obsessive-compulsive disorder and general impulsivity

• deep brain stimulation of this area has shown to relieve some types of tremors and other involuntary movements (which demonstrates close connection to the basal ganglia)

Hypothalamus

means “under chamber”

• it is about the size of an almond and lies just under the anterior ventral surface of the thalamus

• its function can be referred to as the linker and a regulator

• linker because it connects the nervous system to the endocrine system through it’s pituitary gland

• a regulator because it controls aspects of metabolism, body temperature, food intake, circadian rhythms, and emotion

Pituitary Gland

connects the nervous system to the endocrine system

Homeostasis

maintaining the body’s status quo

Epithalamus

lies superior and posterior to the thalamus

• consists of the pineal gland, habenula, stria medullaris

Pineal Gland

• an endocrine gland that gets its name from its pinecone shape

• it is about the size and shape of a grain or rice, being about 5 to 8 millimeters in size

• it produces a hormone known as melatonin, which is involved in regulating the sleep-awake cycle, as well as our circadian rhythms, and in gonad development

• after puberty this gland hardens due to a build up of calcium and becomes a useful landmark in nueroimaging because of its dense structure

Basal Ganglia

• a group of structures that make up most of the remaining subcortical gray matter regions of the brain

• consists of three large nuclei: caudate nucleus, globus pallidus, putamen

• functionally has two major pathways that runs through it: 

  • Direct Pathway: from the striatum to the medial globus pallidus to the VA and VL thalamic nuclei, which facilitates movement 

  • Indirect Pathway: runs from the striatum to the lateral globus pallidus to subthalamic nuclei back to the VA and VL thalamic nuclei

• Its connection to cortical motor areas are most significant

  • uses dopamine to regulate important extrapyramidal functions such as posture, balance, arm swinging, and other body movements like walking

• Damage is classified as dyskinesias(involuntary movements) or akinesias(involuntary postures)

  • *Patients can have both at the same time

Caudate Nucleus

• in the shape of an arch

• separated from the globus pallidus and putamen by the internal capsule

• it has a bulbous head anteriorly and a thin tail that leads into a second bulge 

Globus Pallidus

• located with the putamen but separate from the caudate nucleus

• has two nuclei, an external (GPe) and an internal (GPi)

Putamen

• also known as “shell”

• located with the globus pallidus, but separate from the caudate nucleus

Amygdala

• part of the limbic system

Striatum

• functionally the caudate and putamen are one nucleus called the?

• a term that means “striped”

Lenticular Nucleus

• anatomically the putamen and the globus pallidus are lumped together under the name?

• also known as “lens”

Dyskinesias

• involuntary movements

• examples: tremors, athetosis, chorea, ballismus, tics

Akinesia

• involuntary postures

• examples: rigidity, dystonia, bradykinesia

Corona Radiata

• fan-shaped sheet of axons (the fibers between the cortical surface and the thalamus)

• also known as “radiating crown”

• carries nearly all neuron traffic to and from the cerebral cortex

• much cerebral activity takes place in this dense white matter area because disorders involving it result in significant deficits

• those with multiple sclerosis have multiple scars in places like this

Internal Capsule

• a narrow space between the caudate nucleus and the lenticular nucleus

• bends as it passes between the thalamus and the basal ganglia

Genu

• the bend in the internal capsule

• lesions can affect the corticobulbar tract (an important motor pathway for voluntary motor function in the head and neck, and can lead to either hemiplegia or hemiparesis 

Parkinson’s Disease

• a progressive extrapyramidal movement disorder involving degeneration of the substantia nigra and thus the loss of dopaminergic innervation of the striatum

• cause: unknown, though both environmental toxins and genetics have been suggested

• this disease typically begins at 60 years old, usually with increasing tremors being the first symptoms

• signs: bradykinesia, tremor, and rigidity

• diagnosis: made through a neurological exam, no test

• treatment: no cure, dopamine-based drugs, pallidotomy (a surgical procedure in which lesions are made on the medial globus pallidus), deep brain stimulation

• Basal Ganglia Disorders

Huntington’s Disease

• a progressive hereditary neurological disorder, it affects 12 out of every 100,000 people and commonly presents between the ages of 35 and 42 years

• causes: a mutation on chromosome 4, passed to offspring through an autosomal dominant inheritance pattern, when HD appears, it degenerates the basal ganglia and enlarges the brain’s ventricles

• treatment:

• Basal Ganglia Disorder

Choroid Plexus

• “the delicate knot”

• a structure located in each ventricle that produces CSF at a rate of 400 to 500 milliliters each day

• moves between the ventricles via the interventricular foramen and the cerebral aqueduct

Hydrocephalus

• also known as “water brain”

• when CSF accumulates in the brain ventricles causing brain tissue to be compressed against the skull

• two forms:

  • obstructive: a narrowing (stenosis) of the passageways that connect the ventricles can lead to CSF buildup because CSF cannot freely move through the system

  • non-obstructive: involves problems in the absorption of CSF, and in rare cases, the production(may reabsorb old CSF, resulting in swollen ventricles)

• can be congenital or acquired through brain injury, meningitis, or tumor

• if not treated, it can result in increased intracranial pressure, leading to severe brain damage and even death

• less dangerous in infants because their skull is not fused yet

• treatment: surgically inserted shunts (drains CSF)

Habenu

• (“rein”) is a group of nuclei that lies anterior to the pineal gland

• involved in olfactory reflexes, such as when we salivate at the smell of food or gag in response to noxious odor

• also involved in stress responses due to connections to the limbic system as well as our reward processing system 

Stria Medullaris

a white matter tract, connects the habenular nuclei to the limbic system

Dopamine

produced in the midbrain’s substantia nigra

tremors

• rhythmic shaking

• dyskinesia example

athetosis

• slow, writhing movements of the head and hands

• dyskinesia example

Chorea

• quick, abrupt, fidgeting of the hands and/or feet

• dyskinesia example

ballismus

• quick flinging of a limb

• dyskinesia example

tics

• quick, stereotyped motor or vocal behaviors

• a repetitive involuntary behavior

• dyskinesia example

rigidity

• limb resistance to passive movement

• akinesia example

dystonia

simultaneous agonist and antagonist muscle contraction resulting in distorted movements and postures

bradykinesia

slow movements

Characteristics of Parkinson’s Disease

• bradykinesia

• rigidity

• tremor

Characteristics of Huntington’s Disease

• chorea

• dystonia

Characteristics of Tourette syndrome

• motor and vocal tics

Tourette Syndorme

• a neurological disorder characterized by involuntary motor and/or vocal tics

• named after a french neurologist named Georges Gilles

• symptoms emerge in early childhood (age 3 to 9 years)

• the condition affects males three to four times more often than it does females

• about 200,000 people in the U.S. suffer from T.S.

• symptoms are sometimes worse in adolescence and improve with age

• motor tic examples: eye blinking, facial grimacing, or sudden jerks of the head

• vocal tics examples: grunting or barking sounds, throat clearing, or sniffing

• diagnosed through clinical presentation 

• no cure, only neuroleptic drugs

Dopamine

has a dampening effect on motor movement