The Brain's Building Blocks 

Overview: Human Brain

    Genes: are basic, functional units of heredity, each occupying a specific place on a chromosome. 
The instructions contained within them produce "you".

•  The adult brain is a relatively small organ, weighing about 3 pounds. Three major divisions of the brain 
are recognized:   

1. Forebrain - The paired cerebral hemispheres: the cerebrum.   

2. Midbrain -The brain stem, from which the cranial nerves emerge, consisting of the thalamus and hypothalamus, 
the midbrain, the pons, & the medulla oblongata.   

3. Hindbrain - The cerebellum a.k.a. "little brain”, plays an important role in the integration of sensory perception 
& motor output.

Cellular Structure of the brain  

  • Neuron: a cell specialized to conduct and generate electrical impulses and to carry information 
from one part of the brain to another.
   • Glial (GLEE-all) cells: Nerve tissue of the central nervous system other than the signal-transmitting 
neurons. these cells are found interspersed between the neurons (which transmit the nerve signals) 
& provides support & insulation to them.
   • Growth of new neurons in human brains is supported by research!
   • Repairing the brain after injury also occurs through rewiring.
   • The Mind-Body question asks how brain & mind influence each other.

Neurons: Structure & Function

Three basic structures of the neuron:

   • Cell body: In nerve cells, this is the central portion containing the cell nucleus, from which axons 
and dendrites sprout. The cell body is primarily concerned with carrying out the life-sustaining 
functions of a cell.
   • Dendrites: Branched extensions of the nerve cell body which receives signals from other nerve 
cells. Each nerve cell usually has many dendrites.
   • Axon: The long, hair like extension of a nerve cell that carries a message to a nearby nerve cell.

Axon parts:

   • Myelin sheath: A sheath of white, fatty protein (myelin) that covers and acts as an electrical 
insulator for nerve fibers.
   • End bulbs (neurotransmitter)
   • The synapse is a tiny gap between the ends of nerve fibers across which nerve impulses pass 
from one neuron to another; at the synapse, an impulse causes the release of a neurotransmitter, 
which diffuses across the gap and triggers an electrical impulse in the next neuron.

Nervous System - 2 Parts

   • Peripheral nervous system: The nervous system beyond the brain and spinal cord. The nerves in 
this system connect the central nervous system (the brain and spinal cord) to sensory organs, body 
organs, blood vessels, glands and muscles. • Has the ability to re grow.
   • Central nervous system: the portion of the vertebrate nervous system consisting of the brain 
and spinal cord. • Re growth or repair of neurons is very limited.

Sending Information

   • Sequence: action potential:
 
  1. Feeling a sharp object
  2. Axon membrane: chemical gates open
  3. Ions: charged particles
  4. Resting state: Axon's chemical batteries charged by a Sodium pump.
  5. Action potential: sending information
 
   • Sequence: nerve impulse:
 
  6. Sending information is done by nerve impulse down the axon.
  7. All-or-None law states the once started the pulse will go all the way.
  8. Nerve impulse notes:
 
    • Once begun, the impulse goes to end of the axon.
    • The action potential fires at the breaks in the myelin sheath.
 
  9. End bulbs trigger neurotransmitter release. 

Transmitters

    Transmitters (chemical messengers) can be excitatory or inhibitory.

    Neurotransmitters: A special class of transmitters, neurotransmitters are chemical substances 
that carry impulses from one nerve cell to another; found in the space (synapse) that separates 
the transmitting neuron's terminal (axon) from the receiving neuron's terminal (dendrite).

    Neurotransmitters have unique chemical keys and chemical locks.
 
Some better understood neurotransmitters are:
 
 • Serotonin which affects neurons involved in sleep, appetite, sensory perception, temperature 
regulation, pain suppression, & mood.
 
 • Norepinephine which affects neurons involved in increased heart rate, & the slowing of intestinal 
activity during stress, & neurons involved in learning, memory, dreaming, waking from sleep, & 
emotion. Note: Low levels of serotonin & norepinephrine have been associated with severe depression.
 
 • Dopamine which affects neurons involved in voluntary movement, learning, memory, emotion, & 
possibly, response to novelty.
 
 • Acetylcholine which affects neurons involved in muscle action, cognitive functioning, memory , & emotion.
 
 • Glutamate functions as the major excitatory neurotransmitter in the brain.
 
 • GABA functions as the major inhibitory neurotransmitter in the brain. Alcohol mimics GABA neurons 
& opens GABA locks. Oops!

New (other) Transmitters;
 
•   Endorphins: some endorphins function as neurotransmitters, but most act primarily 
by altering the effects of neurotransmitters by limiting or prolonging their effects. The brain's own pain killer. 
  
•   Anandamide (similar to THC the active ingredient of marijuana). May help in the regulation of emotion.
  
•   Nitric oxide (emotional regulator) (a.k.a. laughing gas).
 
Reflex Responses

    Reflex: An involuntary response to a stimulus.

    Reflexes are fast because they are genetically programmed & involve relativity few neural connections.A reflex does 
    not require thinking, in fact reflexes are routed through the spinal cord for action, the brain is only notified of the pain 
    after the reaction to it has occurred.

Steps in a reflex:
 
  1. Sensors detect the pain (alarm).
  2. Afferent [sensory] neurons carry the alarm from the senses to the CNS.
  3. Interneurons make the neural connections necessary to communicate.
  4. Efferent [motor] neurons carry commands from the CNS back to the muscles & organs.
  
 Study Questions:
 
1. How would you decide if a piece of tissue came from the brain or from a muscle?
2. Is it possible to transplant a chimp brain into a human skull?
3. What are some of the ways that nerve gas could cause death?
4. How might the reflexes of professional ball players differ from those of amateurs?
5. What problems might a person have after having their hand amputated?
6. Would you recommend that a family member with Parkinson's be treated with a fetal transplant?
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                           Topics In Psychology
                               Robert C. Gates