Large-scale brain structure -- the human brain is quite large for our body size, though not the largest in the animal kingdom. It is highly folded (forming sulci and gyri) to increase the cortical surface area that can fit into the human skull. gyrus is raised, sulcus is indent.

1. Hemispheric division

   1. The brain is divided into right and left hemispheres, which are largely separate from one another and perform separate functions

   2. Divided by the longitudinal fissure, connected by the corpus callosum

   3. The left hemisphere receives sensory information from the right half of the body (except the olfactory/smell system) and sends information to the muscles of the right half of the body… and vice versa

2. Characteristics of the right hemisphere: does not understand language, does recognize faces

3. Characteristics of the left hemisphere: contains the two primary language processing centers (Broca’s and Wernicke’s areas), as well as the seat of consciousness (??)

4. Development of a theory of the brain

   1. Rene Descarte was the first to suggest that the brain was the organ that controlled the body

   2. Luigi Galvani determined that the nerves of the nervous system communicate via electrical impulse

   3. Johannes Muller determined that nerves are capable of sending only one type of message, a binary one: on or off; he also began to collect data via experimental ablation (the systematic removal of brain parts to determine the effect on behavior)

   4. Paul Broca used human subjects who had brain damage of some kind to study brain regions and determined that certain regions of the brain were responsible for specific functions; discovered and named Broca’s area

EEG: electroencephalogram

• Pros:

  • Noninvasive

  • Cheap

  • Easily accessible

• Cons:

  • Average of activity, no specific targeting

PET: Positron emission tomography

• Pros:

  • Detect and view real-time brain activity

  • High resolution

• Cons:

  • Radiation exposure

  • Expensive

CT: computed tomography

• Pros:

  • fast, relatively cheap

  • Good soft tissue imaging

• Cons:

  • X-ray exposure

  • Can't see specific brain activity

MRI: magnetic resonance imaging

• Pros:

  • Can see brain activity but no radioactivity

• Cons:

  • Expensive

  • Takes a long time

  • Some are very uncomfortable

1. Evolution of the human brain

   1. Neoteny: delayed adolescence and a notably juvenile shape to the adult human head allow for longer brain development and a larger brain cavity compared with our cousins the chimps and gorillas.

   2. The obstetrical dilemma: the evolution of upright posture demands that human pelvises be relatively narrow, which limits the width of the birth canal, though human infant heads are quite large to accommodate the large brains, which leads to difficult, painful, and dangerous childbirth

2. Nervous system overview

   1. Functions of the nervous system: sense changes in the external environment and respond to those changes

   2. Organs and organization

      1. CNS = brain and spinal cord

         1. Brain: composed of 100 billion neurons as well as many glial cells

         2. Spinal cord: spans from the brain down through the vertebral column, connecting the brain to the peripheral nerves

      2. PNS = peripheral nerves; composed of bundles of axons surrounded by multiple layers of connective tissue; interspersed in these bundles are the blood vessels that feed the nerves

Tasks of the nervous system

• Conduct messages between the brain and the body

• Generate sensation

• Create motion in the muscles

• Regulate autonomic functions

  • Heart and breathing

  • Digestion

  • Menstrual cycle

  • Etc..

Organs: Brain, brainstem, nerves, spinal cord

Cells: Glia and neurons

Nerves are large bundles of individual neurons.

• Epineurium surrounds the whole structure

• Perineurium surrounds nerve fasicles

• Endoneurium surrounds individual nerves

Efferent nerves conduct messages away from the brain

Afferent nerves conduct messages up to the brain

The dendrites are neurons and receive messages from other neurons.

The cell body (soma) is the main part of the neuron, where the nucleus and most other organelles are.

The axon (of which there is exactly one) sends messages to other neurons.

The axon hillock is a very important region where the axon and soma meet.

The axon can branch at the end to form multiple axon terminals. (aka terminal buttons, synaptic terminals) where the axon meets the dendrites of the next neuron.

3 types of neurons

• Sensory neurons: respond to external changes (i.e. temp, pressure, sound waves, light)

  • Must transduce a physical phenomenon into an electrical impulse

  • Axons project to other neurons

• Interneurons both receive and send messages to/from other neurons

  • Most neurons are interneurons

  • All the neurons in the brain are interneurons

• Motor neurons receive messages from interneurons and project to muscles.

Glial cells are “helper” cells - they support neurons but cannot receive or send messages themselves

Glia add up to about 50% of all brain mass

CNS Glia

• Astrocytes: Metabolic support; clean-up of dead neurons; filtration of blood

• Microglia: immune cells, that destroy bacteria and viruses

• Oligodendrocytes: Form the myelin segments on neural axons; keeps neurons in place

• Ependyma: form the lining of ventricles and fluid chambers; cilia create flow in the cerebral spinal fluid (CSF)

PNS Glia

• Schwann Cells: Each cell forms one myelin segment

  • Myelin is a fatty substance that insulates neural axons and increases signal speed

• Satellite cells: probably metabolic support, but newly discovered and still learning about

The blood-brain barrier is not a single structure but a way that capillaries are organized differently in the brain than elsewhere

• Epithelial cells form overlapping “tight junctions”

• Guard cells, like pericytes and astrocytes, surround the capillaries and filter what diffuses out

Specific regions are exceptions to this and allow for monitoring and homeostasis maintenance
Blood-brain barrier

1. Tight junctions: capillaries in the brain are composed of a single layer of epithelial cells just like capillaries in the rest of the body, but their cell membranes overlap, forming a tighter junction through which it is more difficult for materials to pass

2. Astrocytes: these cells serve as “filters” through which materials must pass as they diffuse from blood to astrocyte to neuron

3. Exceptions: there are regions of the brain whose job it is to monitor the blood for toxins, hydration levels, sugar levels, etc