biolpsy_04

Biological Psychology Lecture 04: The Physiology of the Brain

Instructor: Dr. Richárd Reichardt Email: reichardt.richard@ppk.elte.hu

Overview of Brain Physiology

• The main functions of the brain are linked to electrical signals generated by neurons.

• Brain physiology also encompasses metabolism, which is dependent on the circulatory and ventricular systems.

Circulation of the Brain

• The circulatory system provides blood to all body organs.

• Blood transports glucose and oxygen essential for cellular energy production.

• Arteries: Carry oxygen-rich blood; Veins: Carry oxygen-depleted blood.

• The brain's oxygen-rich blood supply comes from:

  • Vertebral arteries

  • Internal carotid arteries

The Circle of Willis

• The vertebral and internal carotid arteries lead to the Circle of Willis.

• From the Circle:

  • Anterior, middle, and posterior cerebral arteries supply the forebrain.

  • Branches from the basilar artery supply the brainstem.

The Blood-Brain Barrier

• Capillaries are small blood vessels that release substances into surrounding tissues.

• Brain capillaries are unique due to coverage by:

  • Astrocyte processes

  • Pericytes

• Together, these create the blood-brain barrier, regulating substance passage.

Spinal Cord Blood Supply

• The spinal cord's blood supply mainly arises from branches of the aorta.

• Posterior spinal medulla arteries are interconnected, forming a continuous network.

Stroke

• A stroke occurs due to inadequate blood supply to a brain region.

• Symptoms vary depending on the stroke's location.

Cerebrospinal Fluid (CSF)

• The brain is covered by layers creating the subarachnoid space, filled with cerebrospinal fluid (CSF).

The Ventricular System

• Comprises lateral ventricles, third ventricle, and fourth ventricle.

• Parts of the lateral ventricles extend into all brain lobes.

• The third ventricle lies between the thalami, covered by the hypothalamus at its base.

CSF Production

• Third and fourth ventricles are interconnected via the cerebral aqueduct.

• The fourth ventricle has pathways connecting to the subarachnoid space.

• CSF Volume: ~140 ml, produced by choroid plexuses in ventricles.

• Daily CSF Production: ~500 ml, refreshing contents 3-4 times daily.

Glymphatic System

• Recent discoveries show CSF flows through brain tissue to eliminate debris.

• Functions like the lymphatic system; consists of glial cells.

Glymphatic Flow

• CSF flow depends on arterial pulsation.

• Pulsation reduces with aging due to artery stiffening.

Sleep and Glymphatic Flow

• Glymphatic flow peaks during deep sleep.

• Aging leads to more fragmented sleep and reduced deep sleep duration.

Glymphatic System and Neurodegeneration

• Glymphatic efficacy declines with age, increasing neurodegenerative disease risk.

• Pathology spread in neurodegenerative diseases mirrors CSF flow direction.

Functional Imaging Methods

Positron Emission Tomography (PET)

• Visualizes changes in blood flow.

• Based on CT; uses radioactively labeled chemicals indicating brain activity levels.

Functional MRI (fMRI)

• Based on MRI principles.

• Assesses magnetic properties of oxygenated and deoxygenated hemoglobin, reflecting neural activity ratios.

Electrical Activity of the Nervous System

• The 19th century revealed much about the nervous system's electrical activity.

• It differs from other electrical phenomena; the 20th century clarified its molecular basis via giant squid research.

• Ionic movement through membranes generates electrical signals.

Membrane Potential

• Proper setup allows for measuring electrical potential differences across points.

Physics Behind Membrane Potential

• Diffusion is a physical process; exemplified by mixing coffee and sugar.

• Membranes restrict diffusion within the system.

Resting Membrane Potential

• Key factors include:

  • Potassium channels

  • Na-K pumps

  • Intracellular proteins

• Ion concentration disparities generate electrical potential, with negatively charged proteins creating a net negative internal charge.

Stimulation of Membrane Potential

• Hyperpolarization: Increases potential difference.

• Depolarization: Decreases potential difference.

Action Potential

• Action potentials initiate when membrane potential reaches a threshold.

• Comprised of several phases; primarily driven by ion concentration differences.

• Action potentials are significant as propagating changes through the nervous system.

Electroencephalography (EEG)

• Measures summated brain activity via electrodes on the scalp.

• Essential for sleep studies; evoked potentials are crucial in cognitive neuroscience (ERP).

Next Class:

• Topic: The Cellular Physiology of the Neuron.

• Thank you for your attention!