Study Notes on Biological Basis of Behaviour

Biological Basis of Behaviour

Chapter 2

A Complex Communication Network
  • Nervous System
    • A complex communication network that conveys messages throughout the body using electrical and chemical processes.
    • Key components:
    • Brain
    • Spinal Cord
    • Nerves
  • Neurons
    • Specialized cells of the nervous system that transmit electrical and chemical signals in the body.
    • The brain consists of approximately 100 billion neurons with an estimated 100 trillion links.
From Bumps to Brain Scans
Part 1
  • Neuroscience
    • Involves the study of the brain and nervous system.
    • Draws upon multiple disciplines, including psychology.
  • Biological Psychology
    • A subfield of psychology focusing on how the brain and other biological systems influence human behavior.
  • Scientific Frontier:
    • The brain is considered the “last frontier of scientific discovery” due to its complexity and the mysteries still surrounding its functions.
Part 2
  • Franz Joseph Gall (1757−1828)
    • Early brain scientist and neuroanatomist; introduced phrenology, suggesting that bumps on the skull correlated with personality traits.
  • Pierre Flourens (1794−1828)
    • Conducted ablation studies, explaining that specific areas of the brain might have particular functions.
Part 3
  • Advancements in technology allow observation of brain activity during various states (e.g., sleep, reading, lying).
  • Questions raised about the admissibility of brain scans in court.
  • Optogenetics
    • Manipulating the activity of individual brain cells for experimental purposes.
Can You Identify the Structure of a Typical Neuron?
  • Components of a Neuron:
    • Cell body
    • Dendrites
    • Receive messages from other neurons.
    • Axon
    • Sends messages from the cell body to axon terminals.
    • Terminal buds
    • Transmit messages to other neurons.
    • Nodes of Ranvier
    • Myelin sheath
    • Speeds up communication.
    • Synapse
The Neuron Structure
  • Dendrites: Receive messages.
  • Axon: Sends messages from cell body to axon terminals.
  • Myelin Sheath: Facilitates faster transmission of impulses.
  • Axon Terminals: Transmit messages to other neurons.
Holding It Together: Glial Cells
  • Glial Cells:
    • Serve as the “glue” of the nervous system, providing support and cohesion for neurons.
    • Types of Glial Cells:
    • Microglia
    • Astrocytes
    • Oligodendrocytes
    • Schwann cells
  • Importance of glial cells emphasized in the context of neuronal injury (e.g., Brandon’s injury).
Communication Within Neurons
Part 1
  • Ion Charges in Neurons:
    • Neurons are surrounded by and filled with positively and negatively charged ions.
    • The overall charge of a neuron is determined by the difference in sum of these charges.
    • Processes directing ion flow:
    • Diffusion
    • Electrostatic Pressure
    • The summation of these processes produces the voltage neuron difference.
Part 2
  • Resting Potential:
    • Represents the electrical potential of a neuron “at rest.”
    • Characteristics include:
    • Negative protein ions are present only inside the cell.
    • Sodium ions (+) are more concentrated outside the cell versus inside.
    • Typical resting potential is around -70 millivolts (mV).
Part 3
  • Action Potential:
    • Initiated when a neuron is stimulated by neighboring cells.
    • Membrane channels start to open at the dendrites, allowing an influx of sodium ions.
    • Changes voltage from -70 mV to -55 mV (threshold potential).
    • Voltage then rises rapidly to +30 mV.
Excitatory and Inhibitory Signals
  • Excitatory Signals:
    • If a neuron receives enough excitatory signals from sending neurons, it will fire.
  • Inhibitory Signals:
    • Inhibit a neuron from releasing a signal through the axon.
  • All-or-None Principle:
    • A neuron either fires or does not fire.
    • The strength of the stimulus is conveyed through the frequency of firing to other neurons.
Myelin Sheath and Information Transmission
  • Function of Myelin Sheath:
    • Envelops and insulates the axon to facilitate faster impulse transmission.
    • Characterized by differences in white matter (myelinated) and gray matter (non-myelinated).
    • Action potentials are transmitted by “skipping” across nodes of Ranvier rather than traversing the entire axon length.
    • Not all axons have myelin.
    • Implications of myelination on information transmission raise important questions.
Communication Between Neurons
  • Neurotransmitters:
    • Chemical messengers used by neurons to communicate at the synapse.
  • Receptor Sites:
    • Specific locations where neurotransmitters attach on the receiving side of the synaptic gap.
    • Follow the “lock and key” model, where neurotransmitter must correspond to receptor site to convey message.
  • Reuptake:
    • Process when neurotransmitters are reabsorbed by the sending axon terminal.
Neurotransmitters and Their Behavioral Roles
Part 1
  • Acetylcholine:
    • Relays messages from neurons to muscles, enabling movement.
    • Excess leads to spasms; deficiency leads to paralysis.
    • Linked to Alzheimer’s disease via low levels in the brain.
  • Glutamate:
    • An excitatory neurotransmitter crucial for learning and memory.
    • Excess may result in strokes; deficiency may lead to schizophrenia symptoms.
Part 2
  • GABA:
    • An inhibitory neurotransmitter involved in regulating sleep and wakefulness.
  • Norepinephrine:
    • Plays multiple roles; notably, prepares the body for stress and regulates arousal and sleep.
    • High levels may cause overarousal and hypervigilance.
Part 3
  • Serotonin:
    • Regulates appetite, aggression, mood, sleep, and breathing.
    • Abnormally low activity may lead to depression; SSRIs are used to enhance serotonin function.
  • Endorphins:
    • Naturally occurring opioids released during pain and exercise, mitigating pain sensations.
Part 4
  • Cortisol:
    • Increases blood sugar (glucose), enhancing brain use of glucose and maintaining substance availability for tissue repair.
    • Slows non-essential functions in stressful situations.
Part 5
  • Dopamine:
    • A critical neurotransmitter involved in attention, reinforcement learning, and movement regulation.
    • Its connection to addiction (e.g., cocaine, amphetamines) and Parkinson’s disease is significant, as the latter involves neuronal loss affecting dopamine production.
Relationships: Your Romantic Brain
  • Dopamine and Love:
    • Increased activity within areas such as the ventral tegmental area (VTA) linked to feelings of love and attraction (as per Aron et al., 2005).
  • Oxytocin:
    • Functions both as a neurotransmitter and a hormone, particularly important in early romantic love and social bonding.
Overview of the Nervous System
  • Central Nervous System (CNS):
    • Major component consisting of the brain and spinal cord.
  • Peripheral Nervous System (PNS):
    • Connects the CNS to the remainder of the body, comprising various neurons.
    • Functions to inform the CNS regarding internal and external environments.
    • Divided into two functional branches:
    • Somatic Nervous System:
      • Controls voluntary movements and conveys sensory information.
    • Autonomic Nervous System:
      • Regulates involuntary bodily processes.
The Spinal Cord and Simple Reflexes
  • Spinal Cord:
    • A crucial bundle of neurons permitting communication between the brain and the PNS.
    • Injury effects: Damage (e.g., through a bullet wound) may disrupt signals between brain and muscles.
Types of Neurons
  • Sensory Neurons:
    • Gather information from sensory systems and convey it to the brain.
  • Motor Neurons:
    • Transmit information from the CNS to enable movement.
  • Interneurons:
    • Found within the brain and spinal cord; function as connectors between sensory and motor neurons.
The Reflex Arc
  • Definition:
    • Automatic response to sensory stimuli, exemplified by the “knee-jerk” reaction.
    • Sensory neurons → interneurons → motor neurons; brain is not involved initially.
  • Evolutionary Significance:
    • Reflexes have developed to enhance human survival throughout evolution.
Peripheral Nervous System
  • Comprises all neurons beyond the CNS.
  • Neurons organized into nerves, which inform the CNS regarding environmental conditions.
  • Two branches:
    • Somatic Nervous System (voluntary control)
    • Autonomic Nervous System (involuntary control)
Autonomic Nervous System
  • Governs involuntary processes within the body.
  • Two major divisions affecting stress response and recovery:
    • Sympathetic Nervous System:
    • Prepares body for action and stress.
    • Parasympathetic Nervous System:
    • Calms the body post-stress.
Endocrine System Overview
  • Key Structures:
    • Pineal gland
    • Hypothalamus
    • Pituitary gland
    • Thyroid gland
    • Adrenal glands
    • Pancreas
    • Ovaries
    • Testes
The Two Hemispheres of the Brain
  • Cerebrum:
    • Largest part of the brain with two distinct hemispheres.
  • Corpus Callosum:
    • Thick band of nerve fibers connecting right and left hemispheres, facilitating communication and coordination.
  • General rule:
    • Right hemisphere controls left body; left hemisphere controls right body.
Split-Brain Personality Effects
Left Brain Functions
  • Traits:
    • Logic, analysis, sequencing, linear thinking, mathematics, language, factual thinking, computation.
Right Brain Functions
  • Traits:
    • Creativity, imagination, holistic thinking, intuition, arts, rhythm, non-verbal feelings, visualization, daydreaming.
Roles of the Left Hemisphere
  • Handedness and Dominance:
    • Language processing is handled by the left hemisphere in 95-99% of right-handed individuals and about 70% of left-handed individuals.
  • Broca’s Area:
    • Critical for speech production.
  • Wernicke’s Area:
    • Key role in language comprehension.
  • Recent research shows these areas may exhibit more complex interactions with various regions.
Roles of the Right Hemisphere
  • Proficient in:
    • Recognizing faces, spatial relationships, processing emotions, directing attention.
  • Prosopagnosia:
    • Condition of “face blindness,” associated with abnormalities in the right fusiform gyrus.
Neuroplasticity
  • The brain's ability to heal, form new connections, and reorganize in response to environmental changes.
  • Example: Learning Braille activates visual-specialized brain regions despite Braille's tactile nature.
  • Children's brains show more plasticity post-injury compared to adults, depending on injury type and severity.
Stem Cells and Neurogenesis
  • Neurogenesis:
    • Certain brain regions can generate new neurons.
  • Important for learning and memory.
  • Current research indicates promise with animal models; however, comprehensive human studies are necessary for understanding safety and efficacy of treatments involving stem cells.
The Cortex
Part 1
  • Cortex Overview:
    • The outermost, wrinkled area of the cerebrum responsible for higher-order mental functions (e.g., decision-making, language).
    • Questions arise regarding the evolutionary advantage of the cortex being wrinkled.
Part 2
  • Sections of the Cortex:
    • Frontal Lobe:
    • Organizes information and is involved in cognitive processes (thinking, perception, impulse control).
    • Parietal Lobe:
    • Processes sensory information (touch, pressure, temperature, spatial orientation).
    • Occipital Lobe:
    • Processes visual information.
    • Temporal Lobe:
    • Processes auditory stimuli and language information.
Lobes of the Brain
  • Example case of Christina's hemispherectomy, removing significant portions of the right frontal lobe and its potential impacts on her cognitive and emotional functions.
Phineas Gage and the Frontal Lobes
  • Incident Summary (1848):
    • Gage was severely injured when a tamping rod penetrated his skull, leading to remarkable personality changes.
    • Modern interpretations suggest the injury might have affected both hemispheres.
The Temporal Lobes and Auditory Cortex
  • Temporal Lobes Functions:
    • Process auditory information, recognize visual objects (especially faces), and play critical roles in language understanding and memory.
  • Auditory Cortex:
    • Located beneath the parietal lobes, responsible for interpreting sounds.
The Occipital Lobes and Primary Visual Cortex
  • Occipital Lobe Functions:
    • Initial processing of visual information occurs here, traditionally located at the lower back of the head.
  • Effects of Damage:
    • If damaged, what changes in visual perception might occur?
The Limbic System
  • A collection of structures that coordinates emotions, basic drives (like hunger), and memory formation.
  • Key components include:
    • Thalamus
    • Hypothalamus
    • Amygdala
    • Hippocampus
The Brainstem
  • Overall Description:
    • Consists of the midbrain, hindbrain, and forebrain.
  • Midbrain:
    • Involved in arousal levels and generating movement patterns in response to sensory stimuli.
  • Hindbrain:
    • Responsible for fundamental life-sustaining processes.
    • Pons:
    • Relay signals from the brain to the cerebellum and medulla.
    • Medulla:
    • Governs autonomic functions such as breathing, heart rate, and blood pressure regulation.
Cerebellum
  • Located behind the brainstem, responsible for muscle coordination and balance.
  • Notably referred to in Latin as the “little brain.”
  • Implications of Damage:
    • Expected challenges would be related to coordination and proprioception.