Brain structure and the Neuron parts

Organization of Human Nervous System

• Central Nervous System (CNS)

  • Brain and spinal cord

• Peripheral Nervous System (PNS)

  • ALL the nerves that exit the brain and spinal cord, carrying sensory and motor messages to and from the other parts of the body

Neurons

• Cells that make up the brain and the nervous systme 

• Adult brain 100 billion neurons 

• 10^15 synapses 

Representation by Neural Firing

Definition of the mind: The mind creates representations of the world so we can achieve goals

Principle of Neural Representation: All experiences are based on representations in the person’s nervous system

How the brain relates to mind

“Brain cells fire in patters”

• One neuron getting active is referring to a message being transmitted to another neuron

• - Sequences

• “A pattern corresponds to a thought. One pattern causes another pattern”
  The minds is what the brain does!

Materialism

Mind and brain have a casual relationship
“A pattern corresponds to a thought. One pattern causes another pattern”

Explanations of Behavior

• Physiological 

  • describe mechanisms that produce behaviors 

• Activity of the cells of the nervous system 

  • experience is the product of a nervous system made up of an enormous number of discrete cells 

What are discrete cells?

They are just neurons, individual nerve cells, the fundamental structural and functional units that communicate through electrical and chemical signals

Shoulder vs hand squeeze demonstrations

Shoulder is closer to the spine, faster nerve signaling to brain (Rozin and Jonides, 1977)

Three types of Neurons

• Sensory neuron (afferent neuron)

• Interneuron 

• Motor neuron (efferent neuron) 

Sensory neuron (afferent neuron)

• Neuron that detects changes in the external or internal environment

• Sends information about these changes to the CNS

Interneuron

Neuron located entirely within the CNS

Motor Neuron (efferent neuron)

Controls the contraction of muscle or the secretions of a gland

Difference between sensory and motor neuron (AFFERENT) VS (EFFERENT)

The main difference is direction of information flow

• Sensory neurons carry signals from the body’s receptors (like eyes, skin, etc) towards the CNS

• Motor neurons carry signals away from the CNS to cause a response (like by activating muscles or glands) 

Sensation to Reaction

Sensation (Afferent Neurons) → Decision (CNS) → Reaction (Efferent Neurons)

Dendrite 

• bushy, branching extensions fo a neurons

• Receives messages 

• Conduct impulses 

• RECEIVER 

What does the Cell Body/Soma contain?

• Nucleus 

• DNA of the neuron 

• other organelles e.g., mitochondria, ribosomes 

What is the Axon?

• Thin fiber of a neuron

• The cell’s output structure 

• Responsible for transmitting nerve impulses 

• One axon per cell 

• 2 distinct parts 

  • tube-like structure 

  • branches at end that connect to dendrites of other cells 

  • OUTPUT!!!!

What is the brain made up of?

• Gray matter, they are cell bodies 

• White matter, nerve fibers 

Myelin sheath

• Crucial white fatty casing on axon

• Acts as an electrical insulator 

• Increases the speed of neural signals down the axon 

The NEURON

Terminal button

• the bud at the end of a branch of an axon 

• sends information to the next neuron 

• forms synapses with that neuron 

Synapse 

• junction between the terminal button and the membrane of another neuron 

(Vesicle membrane-bound sacs within the axon terminal, neuron store and release neurotransmitters) 

How does a neuron function? (Neuron communication)

Neurons in the CNS

• process information 

• interpret it 

• send commands to muscles, glands, and organs 

Receive and transmit information electrochemically 

Neuron Communication (Action potentials)

Action potentials

• axons convey info by a combination of electrical and chemical processes

  • this combo is called ACTION POTENTIAL

  • signal travels along the axon at a constant strength no matter how far it travels

  • all-or-none process - it’s either happening or not

  • influences receiving neuron

What is the communication process?

1. Action potential travels down axon 

2. Causes neurotransmitter to release from axon terminal

3. Neurotransmitter travels across synapse 

4. Then binds with the receptors on receiving neuron 

Synaptic Activity 

Chemicals released at the synapse excite or inhibit neighboring cells, making action potentials more or less likely 

• traverse between neurons

• … is crucial to brain function

Neurotransmitters

• Chemical that’s released by a terminal button 

• Has an excitatory or inhibitory effect on another neuron 

Acetylcholine (ACh)

• Enables muscle action, learning, and memory 

Dopamine

• Influences movement, learning, attention, and emotion

• excess linked with Schizophrenia 

Serotonin

• affects mood, hunger, sleep, and arousal 

• too little → depression 

Norepinephrine

• controls alertness and arousal 

• too little affects mood negatively 

Nerve cell growth

Neurons constantly grow and lose branches to dendrites and axons

• this growth is related to new experiences and learning

Brain plasticity 

Our brain are plastic 

• Plasticity 

  • brain’s ability to rewire itself

  • relocating info processing functions to different brain areas and/or neural networks

  • the stidy of brain plasticity has profound implications on human learning, behavior, and mental health