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: vision.
  • Temporal lobe, at the sides: hearing, language, and recognizing objects and faces.
  • Parietal lobe, on top: where things are in space, and directing attention.
  • Frontal lobe, at the front: planning, choosing, and holding back a response.

# Structures beneath the cerebral cortex

Hippocampus

  • Hippocampus: forming 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: tagging an event as emotionally significant, which is why frightening events are remembered differently.

Thalamus

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

Hypothalamus

  • Hypothalamus: regulating 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 (hearing, language, recognizing objects and faces)
  5. Corpus callosum (carries signals between the two hemispheres)
  6. Frontal lobe (planning, choosing, holding back a response)
  7. Amygdala (tags an event as emotionally significant)
  8. Parietal lobe (where things are in space, directing attention)
  9. Occipital lobe (vision)
  10. Cerebral cortex (higher-level thinking across all four lobes)