Neurons

NERVOUS SYSTEM

Nervous System
1. A body’s electrochemical communication center
  1. Electric: within neurons
  2. Chemical: between neurons
2. 2 parts: CNS vs PNS
  1. Central Nervous System: brain and spinal cord
    1. Sympathetic + Parasympathetic
  2. Peripheral Nervous System: autonomic and somatic
    1. Sensory: afferent (info to brain)
    2. Motor: efferent (info to body)
3. Autonomic Actions = are simple reflexes
  1. Reflex: a simple, autonomic, inborn response to a sensory stimulus. Spinal cord in charge and brain NOT involved because too fast reactions
4. The basic building block of nervous system is called the neuron or a brain/nerve cell
  1. Electrical messenger = inside the neuron
  2. Chemical messenger = outside the neuron
Parts of the Neuron
1. Dendrites: branching extensions that receive incoming messages (neurotransmitters) and conduct messages towards the cell body
2. Soma: is the cell body, which contains the nucleus
3. Axon: extension of a neuron which takes the electrical messages from soma to other neurons: is the longest part of the neuron
  1. (within the neuron)
4. Myelin Sheath: a layer of fatty cells segmentally encasing (insulates) the fibers (axon) of many axons which allows faster transmission speeds in neurons
5. Glial cell: function like glue to hold neurons together. Largest # of cells in the brain. Provides nutrients + protection to all nerves
6. Terminal buttons: located on the end of the axon that release neurotransmitters
  1. Contains sacs (vesicles) that contain neurotransmitters (chemical messengers)

3 Types of Neurons
1. Sensory Neurons
  1. Neurons that carry info from the sensory receptors in the PNS to the brain and spinal cord (CNS)
  2. Also called AFFERENT
2. Interneurons
  1. Neurons within the CNS that internally communicate between sensory and motor neurons
  2. Connectors that allow for info to pass between afferent and efferent neurons.
3. Motor neurons
  1. Take info from the CNS to the muscles and glands within the PNS
  2. Also called EFFERENT

remember**: SAME

SA: sensory-afferent

ME: motor-efferent

Neural Firing (electrochemical communication)
1. Resting potential: refers to the neuron when it is not active (is negatively charged) → –70mv
2. Threshold: refers to the minimal level of stimulation required for a neural impulse to fire → –55mv
3. Electrical Impulse → gated channels open → sodium ions rush in (brief positive charge) → action potential.
  1. Inside of Neuron: more potassium and chloride ions
  2. Outside of neuron: more sodium ions (salt)
  3. Electrical impulse - gated channels open - sodium ions rush in, creating brief + positive - creates action potential [cell fires]
How A Neuron Communicates
1. Action Potential: neural impulse or brief electrical charge that travels down an axon at speeds as fast as 200 mph; is enacted when sense receptors feel something is considered an “ALL OR NOTHING” response.
2. Refractory period: neuron is not able to fire again until it falls back to -70mv. Rest period.
Communication With Other Neurons
1. In order for neurons to communicate with another, it must pass a junction or gap called the synapse between the axon which is sending the signal and the dendrite which is receiving the signal
  1. Charge travels down axon to terminal buttons, releasing neurotransmitters
2. Reuptake: the process of the sending neuron reabsorbing excess neurotransmitters through the synapse
  1. Axon waiting for dendrite to get out of refractory period, axon gone, dendrite cannot fire without neurotransmitters
  2. Axon brings them back/holds on until ready
  3. Some drugs such as cocaine, BLOCK reuptake which leaves the excess neurotransmitters in the synapse
  4. This allows them to continue binding with the receptor sites on the receiving neuron
3. At the ends of the axon, the terminal buttons releases neurotransmitters: which are chemical messengers that bind together neurons and influence whether another neural impulse will take place
  1. 30 total known neurotransmitters, 10 do 90% of the work.
  2. Excitatory → causes neurons to fire
  3. Inhibitory → prevents neurons from firing
Types of Neurotransmitters
1. Acetylcholine: vital role in learning and memory but most well known for its presence in allowing muscle contraction Affects the Somatic, voluntary muscle movement.
  1. Shortage may lead to Alzheimer's disease or muscular disorder. Can also cause Parkinsons.
2. Serotonin: affects mood, hunger, or arousal
  1. Shortage may lead to depression
  2. Excess may lead to OCD/Anxiety/Death
3. Dopamine: influences movement, attention, + emotion
  1. Shortage may lead to Parkinson’s disease (no mobility) + addictive behavior
  2. Excess may lead to schizophrenia
  3. Affects the reward center.
4. Norepinephrine: helps control alertness + arousal when scared or excited (used to treat SNRI: selective norepinephrine reuptake inhibitor)
  1. Fight or flight
  2. Too much = bipolar
  3. Too little = depression
5. Epinephrine: adrenaline: energy in emergencies; formation of traumatic memories (flight or fight)
  1. Shortage may lead to depression
  2. Excess may lead to bipolar
6. Endorphins: called the “morphine within” because of its linked to pain control + pleasure → runner’s high (pituitary gland + minimizes pain)
  1. Shortage may lead to low pain threshold
  2. Excess may lead to high pain threshold
7. GABA: inhibitory neurotransmitter, helps relax and calm down body
  1. Shortage may cause anxiety or epilepsy
  2. Excess may cause no energy
  3. It is a natural tranquilizers + is opposite of Glutamat
8. Glutamate: major excitatory neurotransmitter (speeds brain up)
  1. Shortage may lead to no energy
  2. Excess may cause seizures and migraines
  3. Glutamate is in salt
Agonists vs Antagonists
1. Agonists are chemicals that MIMIC the effects of a neurotransmitter
  1. Ex. opiates (opium) = pain killers ( heroins, meth, morphine)
2. Antagonists are chemicals that BLOCK (sits in the receptor sites) the transmission of a neurotransmitter
  1. Ex. cocaine, haloperidol