2.) 1.3 The Neuron and Neural Firing (#8-18)

#8-18

neuron

• a nerve cell and the basic building block of the nervous system

• carries messages throughout the nervous system

draw a neuron and label each part

dendrite

• receives signals from other neurons

• a neuron’s often bushy, branching extensions that receive and integrate messages, conducting impulses toward the cell body

soma (cell body)

• the part of a neuron that contains the nucleus and DNA

• the cell’s life-support center

axon

• covered in the myelin sheath

• carries signals from one end to the other

• the segmented neuron extension that passes messages through its branches to other neurons, muscles, or glands

axon terminals / terminal buttons

the special endings of a neuron’s amazon that sends signals to the next neuron

myelin sheath

a layer of fatty tissue that insulates and protects the axon of some neurons, which enables greater transmission speed as neural impulses hop from one node to another

• degeneration/deterioration: diminished control and slower reaction time; worse case is the disease multiple sclerosis where communication to muscles and brain regions slow, resulting in diminished muscle control and sometimes impaired cognition

Nodes of Ranvier

the spaces between schwann cells

schwann cells

produce myelin for the myelin sheath

glial cells (“glue cells”)

support cells for the nervous system, providing extra protection and nourishment to neurons

explain the process of neural transmission

1. Neurons transmit messages when stimulated by our senses or by neighboring neurons with a process quicker than a second. When not firing, or at rest, a neuron has a slight negative charge called resting potential.

2. If stimulation reaches the threshold, or the minimum stimulation needed to trigger a neural impulse, a neuron will fire. A neuron sends a message by firing an impulse, called the action potential—a brief charge that travels down its axon.

3. A neuron’s reaction of firing or not firing is not determined by the strength of a stimulation as long as the threshold is met. It will either send a firing or not at all (the all-or-nothing response)

4. Before a neuron can fire again, the ions need to return to their original position or be repolarized. This brief pause between firings is called the refractory period. Once polarized, the neuron is back to its resting potential.

threshold

the minimum stimulation needed to trigger a neural impulse

action potential

a brief electrical charge, or a neural impulse, that travels down an axon to send a message

resting potential

when a neuron is not firing, or is at rest, and has a slightly negative charge

refractory period

• the brief resting pause in neural processing that occurs after a neuron has fired.

• (happens after the action potential and before the resting potential)

• a brief period of time before an action potential happens again until the ions in the axon return to their original position, or gets repolarized

• a brief period of time before an action potential happens again until the axon returns back to its resting state, or gets repolarized

all-or-nothing principle

a neuron’s reaction of either firing with a full-strength response, or not firing at all

synapse / synaptic left

• the meeting point between neurons

• a small space between the neurons

reuptake

• a neurotransmitter’s reabsorption by sending the neuron

• when neurotransmitters finally drift away, to be either broken down by enzymes or reabsorbed by the sending neuron

excitatory neurotransmitters

increases (excites) the likelihood that the next neuron will fire a neural impulse

inhibitory neurotransmitters

decreases (calms) the likelihood that the next neuron will fire a neural impulse, helping to regulate brain activity

acetylcholine (ACh)

• function: a neurotransmitter that enables muscle action, learning, and memory

• malfunctions —> with Alzheimer’s disease, ACh-producing neurons deteriorate

dopamine

• function: a neurotransmitter that influences movement, learning, attention, and emotion

• malfunctions —> oversupply is linked to schizophrenia; undersupply is linked to tremors and decreased mobility in Parkinson’s disease

serotonin

• function: neurotransmitters that affects mood, hunger, sleep, and arousal

• malfunctions —> undersupply is linked to depression. Some drugs that raise serotonin levels are used to treat depression.

norepinephrine

• function: neurotransmitter that helps control alertness and arousal

• malfunction —> undersupply can depress mood

GABA (gamma-aminobutyric acid)

• function: a major inhibitory neurotransmitter

• malfunction —> undersupply is linked to seizures, tremors, and insomnia

glutamate

• function: a major excitatory neurotransmitter (involved in memory)

• malfunction —> oversupply can overstimulate the brain, producing migraines or seizures

endorphins

• function: neurotransmitters that reduce pain or blocks pain signals to the brain

  • the body’s natural pain killers

• oversupply with opioid drugs can suppress the body’s natural endorphin supply

Substance P

• function: a neurotransmitter involved in pain response and transmitting pain signals to the CNS

• malfunction —> oversupply can lead to chronic pain

how does the endocrine system transmit information and interact with the nervous system?

The endocrine system uses hormones that are transmitted through the bloodstream to affect targeted cells at a slower pace, but long-lasting effects. It interacts with the nervous system through the hypothalamus, which controls the pituitary gland. Together, they help regulate things like stress, growth, and mood.

hormones vs neurotransmitters

Neurotransmitters are the chemical messengers of the nervous system and hormones are the chemical messengers of the endocrine system. Hormones are transmitted through the bloodstream slowly, but have long-lasting responses. Neurotransmitters are transmitted across the synaptic gaps between neurons at a rapid pace, but only produce short-lasting results.

adrenaline

• release points: adrenal glands

• function: hormones that prepares the body for emergencies (fight or flight responses)

ghrelin

• release points: cells of especially in the stomach

• function: a hormone that stimulates hunger and signals the brain when it is time to eat

leptin

• release points: adipose tissue

• function: a hormone that regulates body weight, metabolism, and can suppress hunger

melatonin

• release points: pineal gland located in the center of the brain

• function: a hormone that regulates body’s sleep-wake cycle, induces sleep

oxytocin

• release points: pituitary gland

• function: a hormone that facilitates lactation and improves relationships (the bonding hormone)