Chapter 4
Neurons, Hormones, and the Brain

Outline
Organization of the nervous system
Structure of a neuron
Communication between neurons
Chemical messengers
Brain structure 


Organization of the nervous system

Central nervous system:  brain and spinal cord (more detail later)

Peripheral nervous system: every thing else

        Somatic nervous system-skeletal nervous system (you control)
              Sensory neurons:  Information from body to CNS (sensing)
              Motor neurons:  Brain to body (action)

        Autonomic nervous system-regulates functioning of internal organs and systems

                biofeedback-process of learning to control the autonomic nervous system

              Control of the autonomic nervous system
                  sympathetic: energizes bodily function
                  parasympathetic:  depresses bodily functions
 

Structure of the neuron

    Dendrites-receiver branches of the neuron

    Cell body
        Contains the nucleus of the cell
        Determines functioning of cell

    Axon
        Messenger branches of the neuron
        Individual branches of an axon which abut (almost) dendrites

    Myelin sheath
        Insulating sheath for larger neurons.
        Derived from glial cells, looks like link sausage
        Speeds up nerve signals
        MS is characterized by deterioration in myelin sheath

Communication between neurons

    synaptic cleft:  microscopic space that separates dendrites from axons

    Nerve impulse:  Dual process

        Electrical: Semipermeable membrane allows flow of Na and K through neuron,
                causes propogation of electrical voltage along the length of neuron.
                This is called the action potential.
        Chemical: Neurotransmitters released by synaptic vessicles flow across synaptic
                cleft to receptor sites and cause either excitatory and inhibitory changes
                membrane of neuron.  Cell body adds excitatory and inhibitory impulses
                to decide whether or not an action potential will be created.

       Chemical messenger types

            neurotransmitters-quick effect, localized at synaptic cleft
           endorphins-localized to synaptic cleft, modulate the effect of neurotransmitters

            hormones-directly to bloodstream, more systemic in effect
              adrenal hormones: Cause or inhibit arousal in the body
                    epiniphrene (adrenaline)  arouses bodily functions
                    norepinephrene depresses bodily functions
                melatonin-Involved in regulating bodily levels throughout the day
              sex hormones-Responsible for sexual maturation and functioning

Brain structure

Measuring the brain
    EEG-Measures electrical output, not very specific
    PET scans- Measures chemical functioning through the use of radioactivity
    MRI-Use of magnetic fields to actually "see" brain structures

Brain structure

Brain stem-Hind brain (Old brain)
    Medulla-responsible for autonomic functioning
    Pons-Sleep cycles and dreaming
    Cerebellum-motor functioning, simple responses

Cerebrum-Forebrain (New brain).   Controls sensory, memory and higher cognitive processes. Covered by the cerebral cortex (gray matter)  Cerebrum is divided into two halves by the corpus callosum, and each hemisphere is further divided into 4 lobes

    occipital lobes-lower back part of brain. vision
    parietal lobes-top of brain, sensory information
    temporal lobes-side of brain, emotion, hearing, memory and language comprehension
    frontal lobes-front of brain, short term memory, complex cognition, social judgment and speech
 



Outline for day 2

Biology of memory
    Atkinson Shiffrin model of memory
    Biological changes associated with memory
    Location of memory
    Hormones and memory
Biology of sleep
    Stages of sleep
    Dreaming
Brain lateralization
    Split brain surgery
       Comparing brain hemispheres


Biology of memory

Atkinson Shiffrin (1968) model of memory  Processing of external stimuli to long term retention broken down into three stages

    Sensory memory:  Takes in stimuli.  Large capacity, short retention (0.5 to 2.0 sec)
    Short term memory:  Storage of stimuli which are attended to.  Small capacity (7+/- items), short retention (30 seconds)
    Long term memory:  Storage of remembered stimuli.  Unlimited capacity, permanent retention

    Items may be forgotten at any stage of processing

Biological changes associated with memory

    Short term retention  Neurons' ability to releas neurotransmitters are temporarily altered
    Long term retention  Permanent changes to neuron structure and functioning occur.  (long-term potentiation)

    Long term potentiation includes:
    1.)  increase in the release of glutamate (neurotransmitter) from transmitting neurons.
    2.)  receiving neurons become more sensitive to glutamate
    3.)  addition of synapse connections in areas where memory is (?)

Hormones and memory

    Adrenaline in moderate amounts improves memory.  Suggested that adrenaline increases glucose level in bloodstream.
    Glucose may impact neurotransmitter functioning.
 

Locating memory

    Memory types:

    Procedural memories:  Memories for tasks, rules (knowing how)
    Declarative memories:  Memories for things (knowing what)  further divided into
        semantic memory-memory of objects
        episodic memory-memory of events

    Procedural memories may be stored within the cerebellum.
    Declarative memories may  be stored within  the cerebral cortex.
    Memories may be processed by the hippocampus

    Story of H.M.
    Severe epilipsies forced doctors to remove H.M.'s hippocampus and amygdala.  H.M.  could still remember things he knew prior to
    surgery but could not store new declarative memories.  He was still able to store new procedural memories.

Biology of Sleep

Nathanial Kleitman  Used EEG methodology to study brain activity during sleep.  Identified the stages of sleep

    Four stages of sleep (and REM)

    Wakefulness
    Stage one:        alpha waves predominate, edge of consciousness
    Stage two:        alpha waves and sleep spindles, definitely asleep
    Stage three:      alpha waves and delta waves, breathing slows down, more asleep
    Stage four:        mostly delta waves, you are "dead to the world".

It takes about 30-45 minutes to progress to stage four.  You then reverse and go back to stage one. (total time 70-90 minutes).
People then enter REM sleep (time to dream).  Process keeps repeating throughout the night in more or less the same order.

Long term sleep deprivation leads to poor physical health, susceptibility to disease!!
 

    REM (Rapid eye movement):  Blood pressure  and breathing speed up, your eyes flutter (couldn't think of a better word!).
    Nobody knows what it's purpose is, but it is important.
 

Dreaming:  What purpose does it serve

    Freud:  Gives the Id an outlet for repressed desires.
    Crick and Mitchison:  "Reverse-learning".  Unused synaptic connections are being cleaned out by the brain.
    Hobson:  "Activation synthesis"  Random neuron firing occurs during sleep.  Cortex attempts to synthesize  these firings into
      meaningful structure.

Brain Lateralization

Lateralization:  Specialization of the two hemispheres of the brain for particular operations
Corpus callosum:  Bundle of fibers that connect the two hemispheres.
Split-brain surgery:  Severing of the corpus callosum.  Decreases the severity of epileptic seizures by mimizing the spread of
random neural firing from the damaged area of the brain.

Myers and Sperry showed that each side of the brain knows things that the other side doesn't.  By cutting the corpus
callosum, experiences may be "trapped" on one side of the brain, disallowing the possibility of responding about certain
qualities of the stimulus.