The Brain Part 2

The Machinery

Learning Goals

From the principles to the parts

  • Last time we established three principles about how the brain works: localization, lateralization, and neuroplasticity.
  • Today:
    • How the brain transmits information
    • Key structures in the brain and their functions

Neurotransmission

How neurons communicate

BrainFacts.org, Society for Neuroscience (1:18). If the player does not load, open it here: youtu.be/hGDvvUNU-cw

The cell that carries information

  • Neurons: Specialized cells that carry information through electrical and chemical signals; the basic building blocks of the nervous system.
  • There are roughly 86 billion of them, and each one connects to thousands of others.

The gap between neurons

  • Synapse: The small gap between two neurons where electrical signals are converted into chemical signals (neurotransmitters) to transmit information.
  • Neurotransmitter: A chemical released into a synapse that carries a signal from one neuron to the next.
  • The signal is electrical inside a cell and chemical between cells.

Repeated signals strengthen a pathway

  • Neural pathway: A series of connected neurons that send signals from one part of the nervous system to another to perform a specific function.
  • The more often a path carries a signal, the more easily it carries it the next time. The processing becomes more automatic.
    • Ex: If you drive, there are specific pathways in your brain that turn the sight of a red light into a foot on the brake and a green light into a foot on the gas.
    • Ex: Every time you hear a certain song, the pathway in your brain is strengthened, making it easier to recognize the next time.

Key Brain Structures and Functions

The cerebral cortex

  • Cerebral cortex: The folded outer surface of the brain, divided into four lobes.
    • It handles perceiving, remembering, using language, planning, and reasoning.
  • Almost everything covered in this course happens here.

The four lobes of the cerebral cortex

  • Occipital lobe, at the back: processes visual information.
  • Temporal lobe, at the sides: processes sound, understands language, and recognizes objects and faces.
  • Parietal lobe, on top: locates things in space and directs attention.
  • Frontal lobe, at the front: plans, makes decisions, and holds back responses.

# Structures beneath the cerebral cortex

Hippocampus

  • Hippocampus: forms new long-term memories. This is the structure surgeons removed from H.M., the patient from last class, which is why he could not form new ones.

Amygdala

  • Amygdala: tags an event as emotionally significant, which is why frightening events are remembered differently.

Thalamus

  • Thalamus: routes incoming sensory signals to the right region of the cerebral cortex. Everything except smell goes through it.

Hypothalamus

  • Hypothalamus: regulates hunger, thirst, temperature, sleep, and hormone release.

Corpus callosum

  • Corpus callosum: the bundle joining the two hemispheres. Cutting it is what produced the split-brain evidence.

Applying the Core Themes

In pairs, take our four core themes. For each one, come up with a way it shows up in what we have covered about The Brain.

Applying the Core Themes

Some examples:

  • Mental Representation → What arrives at your occipital lobe is a pattern of electrical signals. Everything you see is built out of that.
  • Bottom-Up and Top-Down Processing → Signals from your eyes arrive at the occipital lobe from outside you. The frontal lobe sends instructions to the other lobes from inside you.
  • Limited Capacity → Everything passing between the two halves of your brain has to cross one bundle of fibers.
  • Automatic to Controlled Processing → None of the signaling between your neurons is something you decide to do or notice happening.

Practice

Which brain structure is most involved in each one?

  1. You feel a spider on your arm before you look down.
  2. You wake up at 3 a.m. freezing and pull the blanket up.
  3. A month after moving, you can drive to your new job from memory.
  4. You spot your friend’s face in a crowded gym.
  5. Someone puts a key in your left hand while your eyes are closed, and you name it out loud.
  6. You read a text you should not send, and you put the phone down.
  7. Your heart is pounding two seconds after a car horn goes off behind you.
  8. You catch a bottle rolling off the counter.
  9. You notice the streetlight outside turned from red to green.
  10. You work out the tip on a check in your head.

Practice: Answers

  1. Thalamus (routes incoming sensory signals to the correct part of the cortex)
  2. Hypothalamus (regulates hunger, thirst, temperature, sleep, and hormones)
  3. Hippocampus (forms new long-term memories)
  4. Temporal lobe (processes sound, understands language, and recognizes objects and faces)
  5. Corpus callosum (carries signals between the two hemispheres)
  6. Frontal lobe (plans, makes decisions, and holds back responses)
  7. Amygdala (tags an event as emotionally significant)
  8. Parietal lobe (locates things in space and directs attention)
  9. Occipital lobe (processes visual information)
  10. Cerebral cortex (handles higher-level thinking across all four lobes)