Introduction
You cannot totally separate the mind from the body.
Biological psychologists study the linkage and interplay between the body and the mind.
Even more broadly, there is a biopsychosocial component. This concept believes we do the things we do because of (1) our bodies, (2) our minds or thinking, and (3) the culture that we live in.
Neurons
Neurons are nerve cells. There are a few types to know...
Sensory neurons (Afferent) – Take messages from the body, up the spinal cord, to the brain. There are millions of these.
Motor neurons(Efferent) – Take messages from the brain to the body. There are millions of these.
Interneurons – Are neurons within the brain that "talk" to one another while thinking or processing information. There are billions and billions of these.
Parts of a neuron
Cell body with a nucleus in the middle.
Dendrites are feather-like fingers sticking out from the cell body. They bring info in to the cell.
Axons are long "arms" that send info away from the cell body to other neurons or body parts.
Axons are insulated by the myelin sheath. This insulation helps control the impulses and speeds their travel.
Messages travel along neurons at between 2 and 200 mph (depending on the type of neuron). This may seem fast, but is very slow compared to computers.
Neurons "fire" when stimulated by a sense or other chemicals from another neuron. When it fires, it's called the action potential. This is a slight electrical charge.
A chemical reaction generates the electricity, like with a battery.
This is an all-or-nothing event, the neuron either fires or it doesn't fire.
Axons have negatively charged ions inside, positively charged ions outside. There is a selectively permeable membrane in between (it selects what to let in/out).
When firing, a neuron allows the positive ions in. For a moment called the refractory period, it can't fire, until it pushes the positive ions back out and "resets" itself.
Neurons get mixed signals. Excitatory signals tell it to fire. Inhibitory signals tell it to not fire. When the excitatory signals outweigh the inhibitory signals by a certain amount, the neuron fires. This is called the threshold.
How neurons communicate
A synapse is the place where the axon of one neuron meets the dendrites of another. There is a very slight gap in between (the "synaptic gap").
Neurotransmitters are chemical messengers that take the impulse of one neuron across the synaptic gap to another neuron. See chart below.
During what's called reuptake, the extra neurotransmitters return to the original neuron and are ready again.
How neurotransmitters influence us
Neurotransmitters affect people in many ways such as: depression, happiness, hunger, thinking, addictions, and therapy.
An example is acetylcholine (ACh). ACh tells muscles to contract. When it's blocked (as in some anesthetics), the muscles won't contract and we're paralyzed.
Another example is endorphins. These are like natural morphine that our bodies produce. They improve our moods and reduce pain. They're released either in times of pain or heavy exercise.
When a person uses drugs like cocaine, heroine, or morphine, the body will produce less endorphins of its own.
Drugs that act like neurotransmitters and bridge the synaptic gap are called agonist molecules. Opiate drugs produce a "high". Black widow spider poison produces muscle spasms.
Whereas agonists connect the synaptic gap, antagonists block transmission. For example, Botox blocks a muscle from contracting.
The peripheral nervous system
People are said to have two nervous systems:
The central nervous system consists of the brain and spinal cord.
The peripheral nervous system consists of our sensory receptors, muscles, and glands.
The peripheral nervous system has two parts:
The somatic nervous system can be voluntarily controlled, like moving your legs.
The autonomic nervous system runs on its own, like your heartbeat. The autonomic nervous system also has two parts:
The sympathetic nervous system which activates and exerts energy – like preparing to run away or to fight. Specifically, it increases your heartbeat, blood pressure, blood sugar, and slows digestion. It gets you ready for action.
The parasympathetic nervous system kicks in when the "crisis" is over – it calms you down by doing the opposite things. It helps you chill out.
The central nervous system
Our bodies are amazing, but without the brain, we're like robots. The brain is what makes us human. 400 trillion synapses "talk to one another" in our brains.
Neurons group themselves together into neural networks. This helps them communicate even faster.
The spinal cord connects the brain with the peripheral nervous system. Reflexes are a good example of sensory information going to the brain and motor information going from the brain to a muscle.
A single sensory neuron and a motor neuron working together form an interneuron.
A person whose spinal cord is cut and is paralyzed still has the knee-jerk reaction. The brain is not involved with an interneuron.
The endocrine system
The endocrine system secretes hormones which impact interest in sex, food, and aggression.
Like neurotransmitters, some hormones have molecules that act on receptors in the body. Hormones move slower than neurotransmitters, but last longer.
For example, suppose you think you're about to get into a fight. The adrenal glands secrete epinephrine (AKA adrenaline). It increases the pulse, blood pressure, and blood sugar.
After the crisis is over, it takes a while to calm down and return back to normal.
The pituitary gland is the most influential. The pituitary is controlled by the hypothalamus part of the brain. The pituitary's hormones influence growth and secretions by other glands (it's the "master gland"). These hormones, in turn, then influence the brain.
The chain-reaction could be represented as: Brain->Pituitary->Other glands->Hormones->Brain
