Psych 111 - Chapter 3 - Neuroscience and Behaviour - Part II

By the end of this section you should be able to:

Explain the function of neurons
Outline the components of the neuron
Differentiate the three major types of neurons by their function

Neurons: The Origin of Behaviour

Neurons: cells in the nervous system that communicate w/ each other to perform information-processing tasks

Components of the neuron:

Cell body (aka soma): coordinates the information-processing tasks; keeps the cell alive; contains a nucleus (houses chromosomes that house DNA); surrounded by a cell membrane that allows molecules to flow in and out of the cell
Dendrites: receive information from other neurons and relay that information to the cell body
Axon: carries information to other neurons, muscles, or glands
Covered by a myelin sheath (insulating layer of fatty material); composed of glial cells

Glial cells (support cells)

Digest parts of dead neurons
Provide physical and nutritional support for neurons
Form myelin to help axon carry information more efficiently
Demyelination: deterioration of the myelin sheath; e.g.. multiple sclerosis
Synapse
Region/gap between the axon of one neuron and the dendrites or cell body of another
Fundamental to communication between neurons
Three major types of neurons:
Sensory: receive information from external world and send this information to the brain via the spinal cord

Motor: carry signals from the spinal cord to the muscles to produce movement

Interneurons: connect sensory neurons, motor neurons, or other interneurons; carry information and perform information-processing functions
Specialized by location?
Purkinje cells: interneuron; information from cerebellum to the rest of the brain and the spinal cord; bush-like dendrites
Pyramidal cells: cerebral cortex; triangular cell body and single, long dendrite + other smaller dendrites
Bipolar cells: sensory neuron found in the retinas of the eye; single axon + a single dendrite

The Electrochemical Actions of Neurons:

Information Processing

Learning Outcomes

By the end of this section you should be able to:

Describe how an electric signal moves across a neuron Outline the steps in synaptic transmission Explain how drugs are able to mimic neurotransmitters

The Electrochemical Actions of Neurons

Two stages:
Conduction: movement of an electrical signal within neurons: dendrites -> cell body -> axon
Transmission: movement of a signal from one neuron to another as a result of chemical signalling across the synapse
Two stage process = electro/chemical action of neurons
Conduction
Cell membrane has small pores (channels) that allow small electrically charged molecules (ions) to flow in and out of the cell
lons can carry + or - charge
lons move from high to low [ ]
K* = potassium; Na* = sodium; CI = chlorine
But how?
Resting potential: difference in electric charge between the inside and outside of a neuron's cell membrane; about -70 millivolts
At rest = high [] of positively charged ions (K*) and negatively charged protein ions (A) inside and high [] of positively charged ions (Na*) and negatively charged ion (CI) outside the neuron's cell membrane
Builds potential energy that can be released as a electrical impulse
Action potential
Electric signal conducted along the length of a neuron's axon to a synapse (+40 millivolts)
All or none response where electrical stimulation has to be at or above the threshold
Occurs with same magnitude regardless of whether stimulation is at or above threshold
Occurs because of a change in the state of the membrane channels

Why does an AP occur?

When electrical charge reaches threshold level, sodium-specific channels open and Na* ions rush in; this raises the charge of the inside membrane from (-) to (+): up to +40 millivolts

What happens after an AP?

Sodium channels become inactive (refractory period: the time in which a new AP cannot be initiated)
Potassium-specific channels open causing K+ ions inside to leave the cell; returns electrical charge back to a negative state (then channels close)
Pump helps rebalance of ions to -70 millivolts

Saltatory conduction: electric current passing down the length of a myelinated axon

Myelin facilitates conduction and clumps around the axon with breaks (nodes of Ranvier)
Charge jumps node to node
Steps in synaptic transmission

AP travels down the axon to stimulate release of NTs from vesicles of presynaptic neurons
NTs are released into the synapse
Bind w/ receptor sites on a dendrite of postsynaptic neuron; initiates a new AP
NTs are cleared from the synapse either by reuptake into the presynaptic neuron OR
Being broken down by enzymes in synapse OR
Binding to autoreceptors on the presynaptic neuron

How do NTs know where to go?
Neurons form pathways in the brain that are characterized by specific neurotransmitters; certain neurotransmitters are found in certain parts of the brain
Lock-and-key mechanism: certain neurotransmitters bind to specific receptor sites (based on molecular structure)
Transmission between neurons
Terminal buttons: knoblike structures at the end of an axon and are filled with vesicles containing neurotransmitters (NTs)
Neurotransmitters: chemicals that transmit information across the synapse to a receiving neuron's dendrites
Receptors: parts of the cell membrane that receive neurotransmitters and either initiate or prevent a new electrical signal
How do NTs leave the synapse?
Reuptake: NTs are absorbed by the terminal buttons of the presynaptic neuron's axon or neighbouring glial cells
Enzyme deactivation: NTs are destroyed by enzymes in the synapse; break down NTs
Diffuslon: NTs drift out of the synapse and can no longer reach receptors
Autoreceptors: NTs can bind to receptor sites on presynaptic neurons; release signal to stop releasing NTs if there is excess
Types and Functions of NTs
Acetylcholine (ACh): voluntary motor control; regulation of attention, learning, sleeping, dreaming, memory; deterioration = Alzheimer's
Dopamine: regulates motor behaviour, motivation, pleasure, emotional arousal; role in drug addiction; high levels = schizophrenia; low

'levels = Parkinson's

Serotonin: mood and arousal; regulation of sleep and wakefulness, eating, aggressive behaviour; low levels = mood disorders
Endorphins: act within pain pathways and emotion centers; dulls experience of pain and elevates mood; e.g., runner's high

o L-dopa: when modified, produces dopamine;

ingestion causes neurons to produce more dopamine; agonist for dopamine (Parkinson's)

o Amphetamines: stimulates release and prevents reuptake of norepinephrine and dopamine; excess NTs flood the synapse which increases the activation of the receptors;

agonist

Glutamate: excitatory NT; enhances transmission of info btwn neurons; too much = seizures
GABA: inhibitory NT; stops firing of neurons; too little = seizures
Norepinephrine: mood and arousal; states of vigilance and awareness of dangers; low levels = mood disorders

How do drugs mimic neurotransmitters?

Can alter the production or release of NTs

Can bind to a neuron's receptor

Types:
Agonists: increase the action of a NT; binds to a receptor and activates the NT
Antagonists: diminish the function of a NT; prevents the NT from acting or lessens its effect

o Oplolds: agonists for endorphins; feelings of calm and euphoria; highly effective antagonists that decrease the release of NTs involved in the perception of pain; reduces sensitivity to carbon

dioxide levels in the blood = depresses

breathing

o Naloxone: opioid; antagonist as it binds to opioid receptors blocking agonists (heroin) from effecting neurons

o Prozac: blocks reuptake of serotonin - SSRIs; keeps serotonin in synapse longer to activate more receptors to improve mood; agonist for serotonin (depression)

o Propranolol: beta blockers; blocks receptor sites for norepinephrine in the heart; antagonist for NE as it prevents NE from binding to receptors which slows down the heart; antianxiety, antidepressive

Neurons are the building blocks that form nerves

Nerves: bundles of axons and the glial cells that support them

Nervous system: interacting network of neurons that convey electrochemical information throughout the body

The Organization of the Nervous System

Learning Outcomes

By the end of this section you should be able to:

Differentiate the functions of the central and peripheral nervous systems
Understand the nature of the reflex arc
Demonstrate the hierarchical structure of the central nervous system

_Divisions of the nervous system

Central nervous system (CNS): brain and spinal cord; receives sensory info from external world, and processes/coordinates info to send commands to the skeletal and muscular systems
Peripheral nervous system (PNS): connects CNS to the body's organs and muscles; divided into somatic nervous system and autonomic nervous system
PNS
Somatic nervous system: set of nerves that convey information between voluntary muscles and the CNS
Autonomic nervous system: set of nerves that carry involuntary and automatic commands that control blood vessels, body organs, and glands; divided into sympathetic and parasympathetic nervous system
Subdivisions of ANS
Sympathetic nervous system: nerves that prepare body for action in challenging or threating situations; fight or flight
Parasympathetic nervous system: helps body return to resting state; rest and digest
Components of the CNS
Brain and spinal cord
Spinal reflexes: pathways in the nervous system that generate muscle contractions
Reflex arc: neural pathway that controls reflex actions (e.g., interneurons relay sensory inputs to motor neurons that connect to arm muscles which direct you to retract your hand off a hot stove)
Location of spinal cord injury = extent of abilities lost; the higher up the injury the worse

Structure of the Brain

Learning Outcomes

By the end of this section you should be able to:

Differentiate the functions of the major divisions of the brain
Explain the functions of the cerebral cortex according to organization across hemispheres. within hemispheres, and within specific lobes

Structure of the Brain

Bottom to top approach: higher the level - more complex the function

Side by side approach: one half of the brain specializes in tasks the other half doesn't
Identify the causes and consequences of brain plasticity
Explain the progression of the human brain's evolution

Divisions of the brain

Hindbrain: coordinates information coming into and out of the spinal cord; controls basic functions of life

Medulla: coordinates heart rate, circulation, respiration
Reticular formation: cluster of neurons; regulates sleep, wakefulness, levels of arousal
Cerebellum: "little brain"; controls fine motor skills
Pons: "bridge"; relays information from cerebellum to the rest of the brain

Across hemispheres

Divided into left/right hemispheres
Each hemisphere controls the function of opposite side of the body (contralateral control)
Corpus callosum: connects two hemispheres and supports communication across hemispheres
Within hemispheres
Each hemisphere is divided into four lobes: parietal, temporal, occipital, frontal
Cerebral cortex: responsible for perception, emotion, movement, and thought
Gyri: smooth surfaces of cortex
Sulci: indentations or fissures

Three levels of functioning:

Across hemispheres
Within hemispheres
Within specific lobes
Occipital lobe: back of the cerebral cortex;
processes visual information
Parietal lobe: front of the occipital lobe; processes information about touch; includes somatosensory and motor cortices (strip of brain tissue from top of brain down to the sides)
Represents skins areas on contralateral surface of the body; more sensitive the area the bigger the portion of the cortex dedicated to it
Temporal lobe: lower side of each hemisphere; hearing and language; primary auditory cortex (frequencies of sounds); visual association and interpretation areas
Frontal lobe: behind forehead; specialized areas for movement, abstract thinking, planning, memory, judgment; contains the motor cortex (coordinates muscle movements)

Midbrain: orientation and movement; central location for NTs involved in arousal, mood, and motivation

Tectum: orients an organism in the environment; receives stimulus input and moves organism in coordinated way toward the stimulus

" Tegmentum: movement and arousal; helps to orient an organism toward sensory stimuli

Subcortical (beneath cortex) structures:

Thalamus: relays and filters information from the senses and transmits info to the cerebral cortex; controls incoming sensations (especially during sleep!)
Basal ganglia: set of structures that direct intentional movements; striatum controls posture and movement

Forebrain: controls complex cognitive, emotional, sensory, and motor functions

" Cerebral cortex: outermost layer of the brain;

divided into two hemispheres

Subcortical structures: areas in forebrain near the center of the brain

Hypothalamus: part of limbic system; regulates body temperature, hunger, thirst, and sexual behaviour

Hippocampus: part of limbic system; creates new memories and integrates them for long-term storage
Amygdala: part of limbic system; central role in emotional processes; attaching emotional significance especially fear, punishment, and reward
Endocrine System
Network of glands that produce/secrete into the bloodstream chemical messages (hormones); influence metabolism, growth, sexual development
Includes: thyroid (body temp/HR); adrenals (stress); pancreas (digestion); pineal gland (sleep/wake cycle) and…
Pituitary: master gland; releases hormones to direct the function of other glands

" Brain plasticity

Ability for brain to be molded
Functions assigned to certain areas of the brain can be reassigned to accommodate changing input form the environment
E.g., phantom limb syndrome

Evolutionary development

Invertebrates = those w/o a spinal column
Vertebrates = those w/ a spinal column; hierarchy of CNS: higher levels = more complex functions
Is it genetics (nature) or environment (nurture)
that directs a person's behaviour?
Within specific lobes
Assoclation areas: composed of neurons that help provide sense and meaning to information registered in the cortex
Mirror neurons: active when an animal performs or observes a behaviour being performed; found in frontal lobe and parietal lobe

The Adaptive Brain: Evolution Discussion

Prenatal development
How the nervous system develops/changes within each member of a species
Evolutionary development How the nervous system in humans evolved and adapted from other species

Genes, Epigenetics, and the Environment Learning Outcomes

By the end of this section you should be able to:

Outline the structure of a gene

Differentiate between monozygotic and dizygotic twins
Explain how epigenetic influences work
Give examples of the influence of genetics and the environment to human behaviour
Monozygotic twins: identical twins; splitting of a single fertilized egg; share 100% of genes
Dizygotic twins: fraternal twins; two separate fertilized eggs; share 50% of genes
Twin studies can help researchers understand the role of genetics and environment on behaviour
DNA methylation: adding a methyl group to

DNA; special enzymes (epigenetic writers) add a methyl group which switches off methylated gene to prevent expression

Histone modification: adding chemical modifications to proteins (aka histones) involved in packaging DNA; influence gene expression w/o altering DNA
Genes: unit of heredity transmission; sections on a strand of DNA that code for the protein molecules that affect traits; organized into large threads (chromosomes) Chromosomes: strands of DNA wound around each other in a double-helix configuration; 23 pairs; e.g., XX (female), XY (male) Degree of relatedness: probability of sharing genes
Epigenetics: study of environmental influences that determine whether or not genes are expressed or the degree to which they are expressed, w/o altering the basic DNA sequences that constitute the genes themselves
Epigenetic marks: chemical modifications to DNA that turn genes on or off; two main types

Heritability: measure of the variability of behavioural traits among individuals that can be accounted for by genetics; range of 0 to

1.00 (1.00 = genes are 100% responsible for

individual differences)

" BUT, remember heritability is a(n):

Abstract concept - tells us nothing about specific genes that contribute to a trait
Population concept - tells us nothing about an individual specifically
Dependent on the environment
Not fate - behaviours can be modified

Investigating the Brain

Learning Outcomes

By the end of this section you should be able to:

Identify the three main ways that researchers study the human brain
Compare and contrast advantages and disadvantages of techniques used to study the brain in action

Studying damaged brains

E.g., Phineas Gage
Split-brain procedures (consequences?)
Relating specific psychological and behavioural disruptions to damage helps better understand how the brain area normally functions

" Studying brain's electrical activity

Electroencephalograph (EEG); records electrical activity in the brain
Electrodes placed on the head amplify electrical signals of synapses/APs to produce a visual record of electric activity
Used to record brain activity during different states of consciousness
Types of brain imaging
Neuroimaging: advanced technology used to create images of the brain

Structural imaging: basic structure of the brain; used to find abnormalities (CT scan, MRI, DTI)
Functional imaging: activity of the brain when performing tasks (PET, fMRI, resting state functional connectivity)
Brain injuries: transcranial magnetic stimulation
Brain imaging to study brain structure

CT scan: scanner rotates a device around a person's head that takes x-ray photos at different angles; shows densities of tissue in the brain; tumours are less dense than cortex (appear darker)
MRI: uses a strong magnetic field to line up the nuclei of specific molecules in the brain tissue; pulses of radio waves cause nuclei to rotate out of alignment; mesures energy given off by nuclei when they snap back into alignment; reveals localization of damage but not extent of damage
DTI: special type of MRI; used to visualize white matter pathways (connections btwn brain regions); mesures the rate and direction of diffusion of water molecules; assesses the integrity of a white matter pathway

Brain imaging to study brain function

PET: radioactive substance injected into the bloodstream; brain is scanned by radiation detectors to determine energy/ blood flow (level of activity) while performing tasks; more radiation = more activity
fMRI: detects difference between oxygenated and deoxygenated hemoglobin when exposed to magnetic pulses; active neurons require more blood/oxygen; tells us about levels of activation
Resting state functional connectivity: same fMRI task but at rest; measures the extent to which spontaneous brain activity is correlated over time; higher the correlation, the greater the functional connection

Mimicking brain damage

TMS: magnetic pulse passes through the skull and temporarily deactivates neurons in the cerebral cortex
Can direct TMS pulses to certain brain regions (i.e., turning them off) and measure temporary changes in perception, thought, memory, speech, emotion etc.