Fundamentals of the Brain (psyc 2200, exam 1)

Post Mortem Methods

In vitro cell recording and histology (by staining cells and examining under microscope)

• Often used in animal research

• Used in humans post mortem study

Invasive Methods — In Vivo

Surgically implanted electrodes record or stimulate different areas of the brain

• Also includes tissue removal or tract separation

• Used in animal research

• Sometimes used in humans for medical reasons

Non-Invasive Methods — In Vivo

MRI, PET, fMRI, CAT, MEG, TMS, external/surface recordings

• Required for most experimentation on humans

  • Preferred for medical purposes

• Sometimes used in animal research

CAT

Computer Aided Tomography / CT

A process that uses a series of x-ray scans to the head in order to reconstruct 2D x-ray images into 3D images of internal organs; The subject enters a donut-shaped x-ray machine

Measures Tissue Density by X-Ray

• Very dense tissue (e.g. Bone) blocks x-rays, so it appears white on the scan

• Grey matter blocks some x-rays, so it appears light grey

• White matter blocks less x-rays, so it appears dark grey

• The images produced are not as detailed as MRI scans and there is some radiation, but these scans are cheaper than MRI

• Provides an image for the STRUCTURE of the brain

MRI

Magnetic Resonance Imaging

A scan that uses echo waves (from hydrogen atoms realigned in tissue and then being signaled) to discriminate among grey matter, white matter, and cerebrospinal fluid; Patient enters a donut-shaped giant tube that creates a magnetic field

Measures Atomic Resonance / Energy Release

• White matter appears white

• Grey matter appears grey

• More detailed image than CAT scan

• Shows the STRUCTURE of the brain

MEG

Magnetoencephalography

An imaging technique used to measure magnetic fields produced by electrical activity in the brain; Uses sensitive devices (e.g. Superconducting Quantum Interference Devices, aka SQUIDs)

Measures electromagnetic fields, resulting from neural (ionic flux) activity, at the skull’s surface

• Derive electrical signals from the net effect of ionic currents flowing in the dendrites during synaptic transmission

• Shows the FUNCTION of the brain

EEG

Electroencephalogram

Uses electrodes that attach to the scalp to measure electrical activity in the brain, which is shown as wavy lines on a graph recording

• Finds changes in brain activity that may help diagnose brain conditions

• Better for kids to use because they can move during this imaging process

• Shows the FUNCTION of the brain

PET

Positron Emission Tomography

Measures regional glucose consumption; Subject is injected with a small amount of radioactive glucose, and this scan the absorption of radioactivity outside the head

• If brain cells are more active, they will consume more radioactive glucose, and vice versa

• More commonly used before the fMRI

• Shows the FUNCTION of the brain

fMRI

Functional Magnetic Resonance Imaging

Uses a magnetic field (like an MRI) to create an image, but also measures blood-oxygen (haemodynamic) levels for brain activity

• Brain areas with low blood oxygen (BOLD — blood-oxygen signal) are presumed to be more active

  • Works because the magnetic resonance signal of blood depends on the level of oxygen (More brain activity → More O₂ consumption)

• Doctors ask patients to do something (e.g. opening and closing their hand) while inside the MRI machine to reveal how the brain does tasks

• Shows FUNCTION and STRUCTURE of the brain

Neurons

Transmit information via action potentials and neurochemical release

• A type of cell in the nervous system

Glia

Modulates, supports, and insulates neurons with myelin sheaths

• CNS: Astrocytes and oligodendrocytes

• PNS: Schwann Cells

Astrocytes

A star-shaped glial cell that clears excess neurotransmitters, stabilizes and regulates the blood-brain barrier, and promotes synapse formation

• Found in the CNS

Oligodendrocytes

A glial cell that produces myelin in the CNS

• Commonly found in areas with long axons

Schwann Cells

A glial cell that produces myelin in the PNS

• Commonly found in areas with long axons

Grey Matter

Unmyelinated neurons and parts of neurons

• Found in the outer layer of the brain

White Matter

Myelinated parts of neurons and glia

• Found in subcortical (deeper tissues) areas of the brain

Cell Body

The part of a neuron that contains the nucleus

• the cell’s life-support (metabolic) center

Dendrites

A neuron’s often bushy, branching extensions that receive and integrate messages

• Conducting impulses toward the cell body

Axon

The neuron extension that passes messages through its branches to other neurons or to muscles or glands

• Conducting impulses away from the cell body

Myelin Sheath

Covers axon and insulates the cell

• Speeds up signal

Nodes of Ranvier

Gaps between the myelin sheath

• Essential for the action potential’s speed and timing to the axon terminal

Multipolar Neurons

A neuron with a single axon and many dendrites

• Complex and most common neuron

Bipolar Neurons

A neuron with one axon and one dendrite extending from the cell body

• Rare in humans, but play important roles in the ears, nose, and eyes

Unipolar Neuron

A neuron with an axon that extends into dendrites

• Only has one nerve process extending from the cell body

• Plays a role in touch and pain

Synapse

The junction between the presynaptic and postsynaptic neuron

Vesicles

Stores various neurotransmitters that are released at the synapse

• Located in the axon terminal

Central Nervous System (CNS)

The brain and spinal cord, encased by the blood-brain barrier

Blood Brain Barrier

Surrounds membranes (dura & pia mater) in the brain; A network of “tightened” blood vessel walls for vessels supplying the brain and spinal cord

• Makes it difficult for larger substances to enter the brain

Peripheral Nervous System (PNS)

(Cranial) Nerves outside of the brain and spinal cord

• Includes

  • Somatic system

  • Autonomic system

    • Enteric (Gut / Digestive System)

    • Sympathetic System

    • Parasympathetic System

Olfactory Nerve

Cranial Nerve I

Provides the sense of smell

Optic Nerve

Cranial Nerve II

Provides vision

Oculomotor Nerve

Cranial Nerve III

Opening and moving your eyes and adjusting pupil width

Trochlear Nerve

Cranial Nerve IV

Looking down and moving your eyes toward your nose and away from it

Trigeminal Nerve

Cranial Nerve V

Providing sensations in your eyes, most of your face, and inside your mouth

• Allows you to chew food

Abducens Nerve

Cranial Nerve VI

Moving your eyes from left to right

Facial Nerve

Cranial Nerve VII

Controlling several facial muscles to make facial expressions and providing taste (as a sense) in part of your tongue

Vestibulocochlear Nerve

Cranial Nerve VIII

Providing the sense of hearing and balance

Glossopharyngeal Nerve

Cranial Nerve IX

Providing taste sensations to part of your tongue and controlling muscles for swallowing

• Contains parasympathetic nerve fibers that play a role in blood pressure regulation and saliva production

Vagus Nerve

Cranial Nerve X

The main nerve of the parasympathetic nervous system

• Regulates several autonomic bodily processes:

  • Digestion, blood pressure, heart rate, breathing, mood, saliva production

Spinal Accessory Nerve

Cranial Nerve XI

Controlling neck and shoulder movement

Hypoglossal Nerve

Cranial Nerve XII

Controlling tongue movement, which plays a role in speaking, eating, and swallowing

Spinal Cord

A cylinder-shaped tube of tissue that runs through the center of the spine, from the brainstem to the lower back

• Composed of nerves and cells that carry messages from the brain to the rest of the body (CNS)

• Four Classes of Spinal Nerves: Cervical (Neck), Thoracic (Upper Back), Lumbar (Lower Back), Sacral

• Three Meninges (Protective Tissues):

  • Dura Mater: Outer layer; protects spinal cord from injury

  • Arachnoid Mater (Middle layer)

  • Pia Mater (Deepest inner layer)

Vertebral Cross Section

The horns (ventral and dorsal) are where the spinal nerves synapse are inside the spinal cord

Dorsal (Back): Holds the cell bodies for unipolar somatosensory neurons from the skin — touch and pain — and deep tissue — pain and proprioception

Sensory (Afferent) Neurons

Nervous system cells that receive information from the environment and transmit it to the body

• Travels through the myelinated pathways of the dorsal (back) of the spinal cord

Motor (Efferent) Neurons

Neurons that carry signals from the CNS to the muscles to produce movement

• Travels through the myelinated pathways of the ventral (front) root of the spinal cord

Sympathetic Nervous System

The division of the autonomic nervous system that arouses the body, mobilizing its energy

• Homeostatic functions are put on hold

  • Accelerates heartbeat, raises blood pressure, slows digestion, raises blood sugar, and cools the body

• Prepares body to use all its oxygen and energy; Activates in “Flight or Fight” situations

• Thoracic / Lumbar nerves activated, Ganglia inside spinal column connect nerves

Parasympathetic Nervous System

The division of the autonomic nervous system that calms the body, conserving its energy

• Diverts oxygen and energy to promote homeostatic functions

  • Decelerates heartbeat, lowers blood pressure, stimulates digestion, and processes waste

• Activates in “Rest and Digest” situations

• Cranial / Sacral nerves activated, Ganglia are peripheral to (outside) the spinal column

Chronic Sympathetic Activation Symptoms

• Skin break-outs

• High blood pressure

• Muscle spasms

• Stomach and intestinal upset

• Headaches, anxiety

• Infertility & Impotence

• Hair loss

• Asthma

• Diabetes, weight gain

Horizontal Plane

Rostral (Anterior)

Caudal (Posterior)

Sagittal Plane

Coronal Plane

Basal Ganglia

Structures that play an important role in motivation, reward, and movement; Derived from the forebrain (except substantia nigra)

• Includes:

  • Caudate Nucleus, Globus Pallidus, Putamen, Substantia Nigra (Midbrain), Subthalamic Nucleus, Ventral Pallidum

Limbic System

Plays an important role in modulating emotion and learning / memory; Derived from the forebrain

• Includes:

  • hypothalamus, amygdala, thalamus, hippocampus

Corpus Callosum

A bundle of nerve fibers (white matter tract) that allow the left and right hemisphere’s of the brain to communicate

Cerebrospinal Fluid (CSF)

Derived from the hollow center of the neural tube; Surrounds the brain and spinal cord for protection, metabolic exchange, and waste clearance

• Found in the ventricles of the brain

• Found in sub-arachnoid space of spinal column

Lateral View

Displays 4 lobes — Frontal, Parietal, Temporal, Occipital — and 5 cortices (Frontal and Motor Cortex are found in Frontal Lobe)

Midline View

The majority of brain structures have a left and right component, but the two sides don’t always function identically (especially in higher structures like the cortex)

Wernicke’s Area

Primarily responsible for language comprehension; Helps one understand spoken and written language

Located in the Temporal Lobe

Broca’s Area

Essential for speech production; Allows one to form words and construct grammatically correct sentences

Located in the Frontal Lobe

Laterality

Dominance of one side of the brain in controlling particular activities or functions

Crossed Auditory Pathways

Ascending auditory paths cross the midline, but not 100%

There is a stronger projection from each ear to the other side of the brain

• EX: Hearing something in your left ear is processed in the right side of the brain first, but immediately sent to the left side

Split Brain

Corpus Callosum is severed, disconnecting the left and right hemispheres from each other

Phylogeny

The history of evolution of a species or group, especially in reference to lines of descent and relationships among broad groups of organisms

• EX: Studying humans and primates

Phylogenetic Scale

Examining less evolved species with more evolved species; Comparisons suggest that higher brain structures are more recent products of evolution

• “Lower” structures (that function for basic survival functions) are not that different across species

• “Higher” structures (advanced functions) vary amongst species

  • More complex and elaborate structures in “higher” (more intelligent) species

Brain must be considered as a whole, since different species require different functions for survival

• EX: Bats have an auditory cortex as complex as a dolphins, but other part of their cortex are smaller and not as complex as dolphins

Brain to Body Weight Ratio

A relative measure of brain evolution

Mammals are “higher” species than non-mammals, and humans are on top. However, larger species (e.g. blue whale) are penalized

Cortex/Sub-Cortex Ratio

A relative measure of brain evolution

Favors mammals and humans over other animals

Cortical Enfolding Index

A relative measure of brain evolution

Reflects what is known about “higher” and “lower” species, but as a measurement, it means that dolphins and whales are ‘higher up’ than humans

Ontogeny recapitulates phylogeny

The development of an organism (embryo → adult) reflects its evolutionary history

• EX: The developmental ‘gradient’ of the brain moves from lower structures to higher structures (bottom-up organization) — hindbrain first, midbrain second, forebrain last. This is similar to how the human brain evolved

Ontogeny (Study of Embryos) | Phylogeny (Study of Evolutionary History)

Neurogenesis

aka Neuron Proliferation

Mitotic division of progenitor (mother) cells into dedicated neural or glial precursors, occurring during prenatal infancy at the core of the neural tube, bordering CSF

• Ventricular Zone is where neural progenitors are ‘born’ and start their migration

• First in the neural development sequence

Neuroblastoma

A form of cancer mainly seen in infants and children, since neurons proliferate prenatally and cancer is a disorder of cell-division (run-away mitosis)

• Rates go down as neurons stop dividing

Neuronal Migration

Undifferentiated precursor (daughter) cells migrate to final locations, moving from “inside” of the neural tube outward, occurring from prenatal to infancy

• Second in the neural development sequence

Radial Glia

Supports migrating neurons; helps form the cortical layers (lamination)

Lamination

Each neuronal precursor (daughter cell) has to migrate outward from the ventricle, pass beyond its predecessors and then stop, undergo terminal differentiation and establish its synaptic connections

• aka Inside-Out layering in the cerebral cortex

Neuronal Differentiation

Occurs from prenatal to childhood; a part of neuronal migration

Synaptogenesis

Postnatal elaboration of synapses, occurring from infancy to adolescence

• Proteins in the cytoplasm guide the movement of axonal terminals via attraction and replusion to guide this stage

• Third in the neural development sequence

Myelination

Postnatal myelin forms, occurring from infancy to adolescence

• Causes peak brain weight at ages 12-14

• Fourth in the neural development sequence

Pruning

Getting rid of existing, unwanted synapses and retaining important ones, continuing late into one’s life

• Either loss of neurons or the withdrawal of axons from specific synapses

• EX: Continues into early 20’s for the frontal cortex

Neurotrophic Factors

A factor that promotes neuronal growth

• EX: NGF = Nerve growth factor

Apoptosis

A programmed / genetic neuronal death

Necrosis

An injury-induced neuronal death

Frontal Cortex

The most recently evolved and latest developing structure

• Regulates decision-making, understanding of consequences, planning, and morality