White Matter Connections

Diencephalon: includes all the “thalamic” structure…named for location to the thalamus & not similarities of function

Cerebrum is composed of the Diencephalon & Cerebral Hemispheres

Functions:

  • Perception
  • Movement
  • Communication
  • Decision making
  • Consciousness
  • Emotion
  • Memory

Diencephalon is composed of the Thalamus, Hypothalamus, Epithalamus, and Sub-thalamus

Thalamus: main functional groups of the nuclei

  • There is a medial, lateral, posterior and anterior region, these are cell bodies (grey matter)…this is where the 3rd axon comes and synapses

    • Relay nuclei: conveys information from the sensory systems, the basal ganglia, or the cerebellum synapses then sends info to the cortex
    • Association Nuclei: processes emotional and integrates sensory information into our memory
    • Nonspecific Nuclei: regulates consciousness, arousal and attention

  • Thalamus Lesions: a lesion will interrupt the ascending pathways, severely compromising the contralateral sensation (2nd and 3rd order neuron will not connect)

    • proprioception is MOST AFFECTED
    • if there is a lot neuronal loss → to moderate to severe disability, even a vegetative state…no way to connect what is happening in the environment to the cortex

  • The thalamus double checks, utilizing the interneurons…self regulation occurs double checking the input of various information

The cortex (as you’ve decided what you want to do) will send it back to the thalamus and compare with the incoming sensory info

  • Red Neuron: confirms that the level of response is equivalent or what is needed for the incoming stimulus
  • once all the info/input is verified & motor plan is composed then it will give the “approval” to proceed
  • helps with the regulating the “amplitude of the response”

   

Lateropulsion aka Pushers Syndrome

Due to damage to the thalamus, unable to feel your body/environment accurately → inaccurate motor response

  • not a voluntary response, they do not realize that they are not centered ( inaccurate understanding of proprioception)

  • powerful pushing away from the less paretic side ( right side damage → left side weakness) in sitting, during transfers, standing and during walking

  • lesion of the posterior thalamus, deficit in sensing postural alignment relative to gravity

  • patient will extend the non-affected arm & leg, pushing → high risk in falls

  • patients will “lose their body” and can unknowingly grab and move limbs that are not their own, no internal sense of their own body

Clinical Correlations

  • Thalamic Syndrome: lesion in the thalamus, will show up as a loss of sensation on the opposite side, pain on the opposite side or hypersensitivity to stimuli that will be felt on the opposite side
    • pain without an injury
    • tendency to repeat or continue unproductive activity
  • Korsakoff’s Syndrome: associated with chronic alcoholism…Patients have degeneration in the medial nuclear group, mammillary bodies. They present as disoriented, having memory disruptions & will hallucinate (visual).
    • These patients can come up with the most wild stories in an attempt to cover the gaps in knowledge or recall
    • It’s a compulsion to make it up, they themselves cannot differentiate b/w reality and what they’ve made up
    • thoughts will be disorganized and tangential, the damage is typically mostly permanent

Projections from the thalamus to the cortex (review image on slides)

  • Lateral Geniculate Nucleus: Visual Stimuli → Occipital Lobe (on the cortex)
  • Pulvinar: sensory association region → Parietal lobe

Hypothalamus: essential for survival, integrates behaviors w/ visceral function

  • electrical stimulation to this region → feeling of hunger (abnormal amount) never satisfied as long as the stimulation is applied
  • bilateral destruction can affect eating behaviors → anorexia, refusal of food, cause starvation
  • Functions include:
    • maintaining homeostasis
    • eating, reproductive and defensive behaviors (primal activities)
    • emotional expression of pleasure, rage, fear and aversion (strong dislike) … can override cognitively based on other cues
    • regulation of circadian rhythms
    • endocrine regulation of growth, metabolism and reproductive organs

The hypothalamus integrates behaviors with visceral function.

  • it receives input/ communicates with the vagus nerve
  • has feedback loops with the pituitary gland, spinal cord & brainstem

  (regulates a lot of daily activities)

Hypothalamus & Sleep

  • neuron in the pre-optic area are active during sleep, responsive environmental stimulation…changes in light
  • some serotonergic neurons are associated with sleep
  • nuclei in the posterior hypothalamus are active during wakefulness…. the opposite anterior region active when you are sleep
  • melatonin has some interaction with the pre-optic area, signals the hypothalamus to make the shift from posterior to anterior activity

Control of Body Temperature

  • Anterior Hypothalamus has thermo-sensitive cells that react to increasing body temperature
  • stimulation of the anterior hypothalamus → cutaneous vasodilation & sweating
  • lesions → hyperthermia (over heating)
  • Posterior Hypothalamic neurons react to lowering body temperature
  • stimulation of the posterior hypothalamus → heat production/ conservation response….cutaneous vasoconstriction & shivering

These 2 areas have to work together to maintain balance

Control of Food & Water Satiety

  • Lateral Zone contains orexin-secreting neurons
  • Increase in orexin increases → increases ones appetite, where they’ll eat way past their capacity
  • Lack of orexin → anorexia
  • Ventromedial Hypothalamus has a satiety center (satisfaction center) that decreases feeding once stimulated
    • destruction or damage → excessive feeding, there is no feeling of being full
  • Leptin is secreted by fat tissues acts on the Hypothalamus Satiety center (still trying to gain an understanding)
  • There are areas that regulate water intake, damage can lead to unquenchable thirst …patients will have to be on fluid restriction

Epithalamus

  • Pineal Gland: main function in the secretion of melatonin
    • regulate circadian rhythms
    • melanocytes are also found in your skin and they go looking for more melanocytes…so melanoma has a high chance of spreading to the brain and why it has such a high mortality rate
    • influences secretion of the pituitary gland, adrenal and parathyroid glands
  • The hypothalamus secrete hormones which stimulate/inhibit production of pituitary hormones…anterior pituitary gland secretes hormones (growth hormone (GH), FSH, LH…) directly into the bloodstream …due to no blood brain barrier
  • Posterior pituitary gland produces adrenocorticotropic & oxytocin …regulation of BP, fluid balance in the kidneys, Aids in childbirth
  • Hypothalamus aids in controlling hormones responsible to control metabolism, reproduction, response to stress and urine production
  • Pituitary Gland controls a lot of endocrine function, pituitary hormones target
    • adrenal cortex
    • thyroid glad
    • ovaries or testes

Hormones released from Anterior Pituitary:

  • Growth Hormone: increases growth in tissues
  • Thyroid-stimulating Hormone: increase in thyroid hormone secretion
  • Adreno-cortiocotropic hormone: stimulates release of glucocorticoids
  • Luteinizing Hormone, Follicle-stimulating hormone & prolactin

Hormones released from the Posterior Pituitary:

  • Antidiuretic hormone
  • Oxytocin

Pituitary Tumors

  • most are benign and slow growing
  • the symptoms seen are due to pressure on the surrounding structures
  • Symptoms = headache, nausea, vomiting, irregular menses and lactation & sexual dysfunction
  • irregular hormone levels (blood test)
  • affects the function of the thalamus and hypothalamus
  • headaches & vision issues due to pressure on the optic nerve
  • possible issues with executive function (related to the pressure build up)

Subcortical White Matter:

Types of fibers (named for where they go & what they carry…)

  • Association fibers: connect cortical region w/in 1 hemisphere…never will cross
    • short association fibers - connect adjacent gyri
    • long association fibers - connect lobes w/in 1 hemisphere (ex: frontal to occipital)
    • all carry very specific information
    • visual pathways is the longest, from the optic region to the thalamus and another back
    • highly myelinated fibers = very quick and high fidelity
    • ASSOCIATION PATHWAY stay on the SAME SIDE
    • damage to association fiber will limit the field that you are able to recognize (if it affects visual pathway)…damage to any of the sensory association pathways have very different symptoms that when fibers cross

This is what gives us….

Perception: interpretation of sensation into meaningful form based on what we know and whats around us…involves memory and actively search for the next bit of info from the environment, helps with anticipation

  • figuring out what you need to do for that next step

  • Long association bundles:

    • Superior Longitudinal: travels from frontal to occipital lobe
    • Inferior Longitudinal: travels from temporal to occipital lobe
    • Uncinate: under the Uncas and Insula from Orbital frontal to temporal
    • Arcuate: bundle that peals from the superior longitudinal to connect Opercular Frontal with Superior Temporal
    • Cingulum: underlies the cingulate gyrus and connects it to the parahippocampal gyrus

  • Projection fibers: Project information out from subcortical region to the cerebral cortex

    • travel vertically, sending information to the body
    • the highway to the spinal cord
    • leaves the cortex → basal ganglia → brainstem → spinal cord
    • fibers create the Internal Capsule
    • big problem if there is a hemorrhage to the internal capsule because is the main highway to relay somatosensory, visual, auditory, & motor information to and from the cerebral cortex
    • Location still plays a role posterior = sensory function & anterior = motor function
    • Basal Ganglia: a lot of information goes to and from (a lot of white matter connections that control movement)
    • vital for normal motor function
    • sequence movements, regulate muscle tone and force
    • helps control how “big” your movements are
    • some white matter fibers provide internal feedback to regulate response being sent out
      • excitatory - produces larger movements
      • inhibitory - produces smaller movements

  • Commissural fibers: connect homologous areas of the cerebral hemispheres

    • travel laterally, so right and left brain can communicate (corpus callosum)
    • Some connect like functions to like functions, few connect different functions
    • Left: auditory language
    • Right: non-verbal language
    • ^ these 2 regions connect through these fibers to communicate so we have an overall understanding

  • Callostomy: corpus callosum is severed (can be partial) due to epilepsy, excessive neuronal activity cannot be controlled by medication or surgical repair ( cuts the short circuit)

    • following patients have trouble with communication (can’t do both) and spatial recognition, interpretation of signals, interpreting maps

  • Tumors: abnormal growth of tissue that form a mass

    • named for the cells involved
    • signs and symptoms are produced by the compression of the surrounding areas, determined by location & size of tumor
    • prognosis depends on history, size, location, patient age and the effectiveness of surgical, chemical & radiation therapy

  • Epilepsy: miss firing of the cortex

    • attacks of excessive cortical neuronal discharge interfering brain function
    • Partial seizures: affect only a restricted area of the cortex
    • Generalized seizures: affect entire cortex
    • after patients are confused for several minutes and have no memory of the seizure
    • Treatments: drug therapy, brain surgery, behavioral adjustments (avoiding specific triggers) and vagus nerve stimulation
    • prevalence of epilepsy is 7 to 10 per 1000 people