Chapter 3: Biology and Your Brain: Introduction

neurodiversity

concept that there are a variety of ways that people’s brains process information, function, and present behaviorally

neurons

the messenger cells that receive, integrate, and transmit information using electrical impulses and chemical signals

central nervous system

the “center” line of your body: your brain and spinal cord.

the brain processes information received from the senses, makes decisions, and sends commands out to the rest of the body

spinal cord

long bundle of nerves running down the length of the back

path the brain uses to process messages with the rest of the body

Reflexes

automatic, involuntary responses to a stimulus.

Peripheral Nervous System

consists of neurons that form the communication network between the central nervous system and the body parts

The Somatic Nervous System

controls parts of the body responsible for voluntary movements

Autonomic Nervous System

means that the functions of this system are automatic

sympathetic division

part of the autonomic system that responds to stress and arouses the body for action in response to threats

parasympathetic division

calms the body after the emergency

Sensory/Afferent neurons

detect and respond to stimuli in our environment and relay that information to the spinal cord

Motor neurons

also known as EFFERENT neurons, carry messages from the brain or spinal cord to the muscles

Interneurons

also known as relay neurons, lie between sensory and motor neurons

mirror neurons

Seen by some as a distinct (fourth) type of neuron, but they can also be classified as a type of motor neuron.
Also appear to help explain empathy, our ability to understand and share feelings with others.

Neuron Structure

Dendrites: receive messages from other neurons

Soma: where received messages are processed; contains a nucleus, which controls the cell’s growth and maintenance

Axon: attached to the soma and transmits a message along its entire length using an electrical impulse

Axon terminals: (also called terminal buttons), contain neurotransmitters that send chemical signals to other neurons

Glial Cells

messages would not get communicated without glial cells; help physically hold neurons in place to create nerves

Schwann cells

specialized cells that form the myelin sheath around many neuron axons

Myelin sheath → a protective coat made of fat and protein that surrounds the axon.

Main job of myelin: insulates the axon and helps neural messages travel faster.

Nodes of Ranvier → the small gaps between sections of the myelin sheath.

Neural messages jump from node to node, rather than traveling continuously along the entire axon. This jumping speeds up and regulates the neural message.

semipermeable membrane

covers the neuron.

Allows certain substances to pass through.

Blocks other substances from passing through.

resting potential

a neuron is not transmitting information

Positively charged sodium ions are outside of the cell; negatively charged potassium ions are mostly inside

Action Potential

The sudden arrival of the positive sodium ions while negative potassium ions are pushed out momentarily reverses the charge of the cell from negative to positive; the cell is said to be depolarized.

Electrical Impulse

Neurons operate on an all-or-nothing principle.

A neuron either fires or it doesn’t depending on whether or not the charge in the cell body reaches the threshold.

The movement of this charge along the axon is called an electrical impulse.

The action potential only moves in one direction.

True

The Refractory Period: After the Action Potential

When the sodium channels close, the negatively charged potassium ions reenter the neuron, the positively charged sodium ions are pumped out, and the neuron returns to its resting state of –70 millivolts: ready for the next action potential.

Refractory Period

After an action potential has passed through a section of an axon, the cell membrane in that region cannot admit positive sodium ions again for a few milliseconds. The cell membrane becomes super negatively charged and cannot fire again no matter how much stimulation it receives.

The brain and spinal cord comprise the ______ nervous system.

central

Synapse

The tiny gap where the axon of a presynaptic neuron communicates with the dendrite of a postsynaptic neuron.

Neurotransmitters

When an electrical impulse reaches a neuron’s axon terminals, those sacs (also called vesicles) release neurotransmitters into the synaptic gap. These chemical substances flood the synaptic gap, trying to bind to the dendrites of the next neuron in line, called the postsynaptic neuron.

Excitatory messages

increase the likelihood the receiving neuron will reach the threshold and fire

Inhibitory messages

decrease the likelihood that the receiving neuron will fire

reuptake

When the neurotransmitter's work is completed, it is reabsorbed back into the cell that previously released it (instead of moving along to the next neuron)

Acetylcholine

Brain, spinal cord, and peripheral nervous system

Excitatory or inhibitory

Muscle movement, arousal, attention, memory

Norepinephrine

Brain, spinal cord

Excitatory

Increases alertness

Dopamine

Brain

Excitatory or inhibitory

Control of movement and sensations of pleasure and reward

Serotonin

Brain, spinal cord

Excitatory or inhibitory

Sleep, mood, anxiety, and appetite

Gaba-aminobutyric acid, or GABA

Brain, spinal cord

Inhibitory

Slows central nervous system function

Glutamate

Brain, spinal cord

Excitatory

Learning and memory

Endorphins

Brain, spinal cord

Inhibitory

Pain relief, pleasurable feelings

Oxytocin

Brain, spinal cord

Excitatory or inhibitory

Love, emotional bonding, lactation

Agonists

Increase the presence of neurotransmitters by limiting their reuptake, how well a neuron reabsorbs a particular neurotransmitter.

antagonists

drugs that block neurotransmitters’ effects

selective serotonin reuptake inhibitors

Therapeutic drugs that are typically used as antidepressants and also act on neurotransmitter receptors

Cocaine

Blocks the reuptake of the “feel-good” neurotransmitter dopamine.

Ecstasy/Molly

agonist that stimulates extremely high levels of serotonin, which makes people temporarily feel euphoria, love, pleasure

Hallucinogenic drugs

produce changes in a person’s state of awareness, activate serotonergic systems, and generate hallucinations

alcohol

agonist, it is a depressant and affects our brain by increasing GABA activity

GABA

inhibits much of the central nervous system activity that keeps us conscious, alert, and able to form memories

glutamate synapses

the stimulating effects of nicotine in tobacco come from glutamate synapses

Marijuana

have both agonist and antagonist effects, influenced by other factors such as dose affects both excitatory and inhibitory receptors

Marijuana’s impairment of short-term memory is likely due to THC (the main active ingredient in marijuana) slowing down neurotransmission in the hippocampus, where we normally create memories.

THC can mimic some neurotransmitters and bind to dendrite receptors that inhibit messages associated with feeling pain. Consequently, medical marijuana is primarily used for pain management though also for nausea

Glial Cells

Synaptic pruning is the job of glial cells that target synapses that “have to be removed in a controlled and timely manner” to mature

Specific types of glial cells (microglia and astrocytes) identify and prune excessive synapses at particular stages of development.

In order for neural messages to travel from one neuron to another, they must bridge ______.

the synapse

When a neurotransmitter’s work is completed, what happens to it?

It is reabsorbed into the neuron that released it.

Which of these neurotransmitters inhibits activity by telling the postsynaptic neurons not to fire?

GABA

Hindbrain

Coordinates the many automatic behaviors your body must do to survive

medulla oblongata

Controls the automatic processes of the autonomic nervous system

Regulates our reflexes

Pons

Serving as a bridge between the lower and upper parts of the brain.

Sends signals to your muscles to rest while sleeping

cerebellum

Contains about half of the brain’s neurons and controls movement, balance, and coordination.

Important for athleticism and motor skills required for everyday tasks like texting on your phone or simply walking in a straight line.

Midbrain

Processes information related to hearing, vision, and movement.

The midbrain, the medulla oblongata, and the pons together are called the brainstem.

The brainstem connects the cerebrum (a structure of the forebrain we examine later) to the spinal cord and cerebellum.

reticular formation

a network of nerves that runs through the hindbrain and midbrain

Main functions:

Regulates the sleep–wake cycle

Controls alertness

Affects fatigue

Influences motivation

Helps control basic behaviors such as sleeping, walking, eating, urination, and defecation

Forebrain

Different thoughts and feelings are possible because of the forebrain, the largest part of the brain and the last major region to evolve for humans.

The Limbic System

Processing emotion, motivation, and memory.

Structures of the limbic system: the hippocampus and the amygdala

hippocampus

Involved with the formation and storage of memories.

amygdala

Processes the fear you might experience

Thalamus

Processes a variety of sensory information—hearing, sight, touch, or taste—and routes it to the part of the right part of the forebrain (NO SMELL)

hypothalamus

Body’s coordinating center

Main function is to maintain homeostasis (maintaining stability to survive), regulating hunger, thirst, temperature, and sexual desires

Cerebral Cortex

gray, thin (about 1/10 inch) outer layer of the cerebrum—that “gray matter” on the outermost layer of the brain.

Corticalization describes this prebirth brain-wrinkling process that allows for a lot of brain in a small space.

The Largest Part of the Forebrain: Cerebrum

One hemisphere, usually the left, controls language and speech and processes information sequentially, one bit at a time.

The right hemisphere interprets visual and spatial information and tends to process information as a whole.

The two hemispheres talk to each other through a thick band of white matter called the corpus callosum.

What is his hemisphere responsible for?

The opposite side of the body.

Occipital Lobes

processing visual information

Temporal Lobes

processing hearing

Parietal Lobes

At the top/back of the head are the parietal lobes, which are involved in understanding body position and movement (also called proprioception)

Activated whenever you must draw on sensations and perceptions to judge how far to throw or kick a ball, how much to bend when sitting down in a chair, or how quickly to pull away when a hot comb approaches your scalp.

The frontmost portion of the parietal lobes includes the somatosensory area, which is important for processing and interpreting perception of touch, as well as temperature, body position, and pain.

Frontal Lobes

Responsible for higher-order functions such as attention, planning, impulse control, problem solving, creativity, social interaction, and motor function.

As the last section to fully develop in each of us, we can better understand why children, teenagers, and even some young adults continue to follow foolish impulses.

The most forward part of the frontal lobes is the prefrontal cortex. You can think of the prefrontal cortex as the executive director of your brain.

The frontal lobes also contain the motor area, which is largely responsible for the body’s voluntary movement, such as jumping, running, walking, handwriting, or texting.

Reasoning and wise decision-making are at their peak until around age 25, after which they start decreasing.

False

Which part of the brain develops first during gestation?

hindbrain

Which part of the brain regulates our sleep-wake cycle?

reticular formation

Which part of the brain is known as the “triage” system?

thalamus

Computed Tomography (CT)

Takes X-ray images from different angles and uses software to create cross-sectional images (slices) that map the brain's structure.

Magnetic Resonance Imaging (MRI)

Shows small details that help identify the effects of small strokes, but does not show brain activity.

A person lies on a bed that slides into a tube surrounded by a circular magnet.

Electroencephalography (EEG)

Measures ongoing electrical functioning in the brain by placing electrodes (metal disks attached to wires) on the scalp.

Better at showing WHEN.

Can help detect and identify types of epilepsy.

Positron Emission Tomography (PET)

Measures blood flow to active areas in the brain.

Involves injecting a person with form of radioactive glucose. The computer detects brain activity by looking at which neurons are using up the radioactive glucose.

Used to evaluate brain tumors and alcohol abuse.

Functional MRI (fMRI)

Variation on MRI that indicates brain activity

Does not provide a direct measure of neural activity.

Uses magnets to generate a detailed, three-dimensional computer image of brain structures and activity based on how the brain uses oxygen.

Tend to be clearer than PET scans and avoid exposing brain cells to radiation. Used for early detection of Alzheimer’s disease.

Neuroplasticity

The brain’s ability to adopt new functions, reorganize itself, or make new neural connections as a function of experience.

Neurogenesis

we can form new neurons

Computed tomography (CT) scans are able to show stroke damage in the brain.

True

What is true regarding magnetic resonance imaging (MRI)?

In an MRI, a magnet and radio waves create detailed images of the brain.

endocrine system

Network of glands and organs that release chemicals directly into the bloodstream to communicate messages that influence biological functioning and behavior.

Hormones

The chemicals released in the endocrine system are called hormones. Insulin, cortisol, testosterone, estrogen, and melatonin are hormones you may have heard of.

Neurotransmitters vs Hormones

neurotransmitters send messages almost immediately, whereas hormonal messages may take minutes to reach their destination, and the behaviors and responses affected may not occur until quite a while later

What is the pituitary gland?

controls functioning across the entire endocrine system by acting as a commander sending messages to other glands and organs

Thyroid Gland

releases hormones that control metabolism—the way your body uses energy and regulates vital body functions such as body weight, body temperature, cholesterol levels, and much more.

Adrenal Glands

Produce hormones that help regulate mood and energy and respond to stress.

Cortisol

maintains the activation of bodily systems during prolonged stress

pineal gland

it receives information about the state of the light–dark cycle from the environment and conveys this information to produce and secrete the hormone melatonin

pancreas

regulates blood sugar by secreting insulin and glucagon

thymus

hormones released by this gland are known to be essential to immune function

gonads

produce hormones related to sexual development and reproduction

The pituitary gland is seen as the major gland throughout the body because it ______.

controls the functioning of other glands

Which gland is responsible for controlling metabolism?

thyroid

During reuptake, the neurotransmitters that are left within the synapse ______.

are reabsorbed into the neuron that released them

What is a common example of neurodivergence?

autism

The central nervous system consists of ______.

the brain and spinal cord