BIOLOGICAL BASIS OF BEHAVIOUR (Free Access)

  • Neurons: Neurons are the basic building blocks of the nervous system.
    • 100 billion neurons in the human brain.
    • Transmit electrochemical signals
  • Neurons have three basic parts:
  •  Cell body or soma. This main part
    • Contains nucleus for DNA,  endoplasmic reticulum and ribosomes ( for proteins) and mitochondria (for making energy).
    • If the cell body dies, the neuron dies.
  • Axon. This long, cable like projection of the cell.
    • Carries nerve impulse or action potential along the length of the cell.
    • Depending upon the type of neuron, axons can be covered with a thin layer of myelin sheath, like an insulated electrical wire.
    • Myelin is made of fat and protein, and it helps to speed transmission of a nerve impulse down a long axon.
    • Myelinated neurons are typically found in the peripheral nerves (sensory and motor neurons), while non-myelinated neurons in the brain and spinal cord.
  • Dendrites or nerve endings – create connections to other cells and allow the neuron to talk with other cells or perceive the environment.
    • Dendrites can be located on one or both ends of a cell.
  • Axon Terminal  – axon endings that are somewhat enlarged and often club- or button-shaped.
    • Make synaptic connections with another nerve cell or with an effector cell (e.g. muscle cell or gland cell).
    •  contains various neurotransmitters that are released at the small gap between two communicating neurons. This gap is called a synapse
    • The neuron that sends nerve impulses by releasing neurotransmitters via the axon terminal at the synapse is called a presynaptic neuron. In contrast, the neuron that receives the impulse is called a postsynaptic neuron. 
      • Chemical Synapse
      • Electrical Synapse
  • Functional Classification
    • Sensory nervous – carry input messages from sense organs to brain and spinal cord
    • Motor neurons – carry output impulses from the brain and spinal cord to the body’s muscles and organs
    • Interneurons – perform connective or associative functions within the nervous system
      • most in number
    • Glial cells do not send or receive nerve impulses but hold the neurons and their surroundings areas together.
  • Structural Classification
    • Anaxonic neurons are small and have no anatomical clues to distinguish dendrites  from axons; all the cell processes look alike .
      • Anaxonic neurons are located in the brain and in special sense organs.
      • Their functions are poorly understood.
    • Bipolar neurons have two distinct processes—
      • Bipolar neurons are rare but occur in special sense organs, where they relay information about  sight, smell, or hearing from the receptor cells to other neurons.
      • They are smaller than unipolar or multipolar neurons; the largest measure less than 30 mm from end to end.
    • In a unipolar neuron, or pseudounipolar neuron –  the dendrites and axon are continuous-or fused–and the cell body lies off to one side.
      • In such a neuron the initial segment lies where the dendrites converge.
      • Rest is an axon.
      • Most sensory neurons of the peripheral nervous system are unipolar.
    • Multipolar neurons have two or more dendrites and a single axon.
      • Multipolar neurons are the most common type of neuron in the CNS.
      • For example, all the motor neurons that control skeletal muscles are multipolar neurons.
      • Their axons can be as long as those of unipolar neurons.

Nerve Conduction

  • Luigi Galvani first discovered that electrical charges are produced in the muscle cells and nerve cells in the body.
  • Therefore the neurons are capable of generating electrical signals and they transmit information/message to the next neuron by means of these electrical signals.
  • Electrical potential difference: It is the difference in the concentration of the charged particles between axoplasm and interstitial fluid (that is with in the axon of the neuron and outside the axon).
  • Action Potential
    • (1) A stimulus from a sensory neuron causes the target cell to depolarize toward the threshold potential. (-65mv = RMP)
    • (2) If the threshold of excitation is reached, all Na+ channels open and the membrane polarizes. (-55MV)
    • (3) At the peak action potential, K+ channels open and K+ begins to leave the cell. At the same time, Na+ channels close. Reducing the charge leading to repolarization
    • (4) K+ ions continue to leave the cell. The hyperpolarized membrane is in a refractory period and cannot fire.
    • (5) The K+ channels close and the Na+/K+ transporter restores the resting potential.

Neurotransmitters

  • Neurotransmitters transmit messages between neurons, or from neurons to muscles. Neurotransmitters are either small amine molecules, amino acids, or neuropeptides.
    • excitatory, inhibitory or modulatory.
  • An excitatory transmitter promotes the generation of an electrical signal called an action potential in the receiving neuron, while an inhibitory transmitter prevents it.
    • depends on the receptor it binds to.
  • Neuromodulators are not restricted to the synaptic cleft between two neurons, and so can affect large numbers of neurons at once
  • Acetylcholine (Ach) – muscle activity and memory. Reduced when suffering from Alzheimer’s disease
    • Affects areas of the Pons and basal forebrain
  • Norepinephrine
    • excitatory and inhibitory, depending on site
    • neural control of learning, memory, wakefulness, and eating
    • Depression, stress, and panic disorders
  • Serotonin
    • excitatory and inhibitory
    • mood, sleep, eating, arousal
    • Depression, sleeping-eating disorders, OCD
    • secretion – Ralphe nuclei
  • Dopamine
    • excitatory,
    • movement, emotional arousal
    • Parkinson, depression, and schizophrenia
  • GABA
    • inhibitory,
    • motor system
    • Huntington’s disease, loss of motor control, and personality change
  • Endorphin
    • Inhibitory
    • inhibits pain transmission
    • Insensitivity to pain, hypersensitivity, immune problems
  • Histamine –  excitatory neurotransmitter 
    • primarily involved in inflammatory responses, vasodilation, and the regulation of your immune response to foreign bodies such as allergens
    • Otrivin nasal spray stimulates histamine
  • Neuromodulators are messengers released from neurons in the central or peripheral nervous system to affect a group of neurons

They have a more generalized effect on synaptic transmission

The Nervous system

  • Sensory nervous – carry input messages from sense organs to brain and spinal cord
  • Motor neurons – carry output impulses from brain and spinal cord to the body’s muscles and organs
  • Interneurons – perform connective or associative functions within the nervous system
    • most in number
  • Glial cells do not send or receive nerve impulses but hold the neurons and their surroundings areas together.
  • The Nervous System is divided into two major parts
    • Peripheral Nervous System – all neural structure that lie outside the brain and spinal cord
    • Further divided into two parts
      • Somatic nervous system
      • Autonomic nervous system
    • Somatic nervous system – transmits messages from brain & spinal cord to and from voluntary controlled muscles.
  • Autonomic nervous system – Responsible for controlling body’s internal, involuntary (smooth) muscles and glands.
    • Further divided into two categories:
      • Sympathetic nervous system
      • Parasympathetic nervous system
  • Sympathetic nervous system- works on the arousal function and acts as a total unit.
    • Responsible for ‘fight or flight’ response.
    • The response is seen with the following behaviour:
      • Increased sweating,
      • pupil dilation,
      • heartbeat increase,
      • breathing increases,
      • lump digestion
  • Parasympathetic division affects specific organ(s) at a time. In opposition to the sympathetic division it slows down body processes to maintain equilibrium.
    • The responses are opposite to the ‘flight or fight response’.
  • Body and Brain are in constant flux to attain Homeostasis i.e. state of internal balance
  • The Central Nervous System – contains the brain and spinal cord.
    • It connect most parts of the Peripheral Nervous System with the brain.
  • Spinal cord – is 16 to 18 inch long and 1 inch in diameter.
    • It is protected by the vertebrae
    • Spinal reflexes are stimulus response sequences that can be triggered without the involvement of the brain. This reduces reaction time and helps in emergency situations. 
      • 31 pairs of spinal nerves
      • Arranged from top to bottom:
  • Cervical (8)
  • Thoracic (12)
  • Lumbar (5)
  • Sacral (5)
  • Coccygeal (1)
  • 3 meninges protect it as well (arranged innermost-outermost)
    • Pia
    • Arachorid
    • Dura
  • Structure of the Brain
    • The Hindbrain – lowest and the primitive part of the brain;
      • Consists of the areas of the brain stem and the cerebellum
      • Brain stem – supports vital life functions. Consists of the medulla and pons
  • Medulla is responsible for: 
  • Heart rate and perspiration
  • Crossover point for sensory and motor nerves from and to right and left sides of the brain
  • Pons
  • Above the medulla and is responsible for
  • Carrying nerve impulses between the higher and lower levels of nervous system
  • Sleep and respiration
  • Cerebellum
    • Looks like a mini brain
    • Wrinkled cortex of gray matter and is responsible for
      • coordinating muscular movement,
      • learning and memory
    • Alcohol consumption diminishes coordination
    • Trivia: Cats have a highly functional cerebellum
  • The Midbrain
    • Located above the hindbrain
    • Consists of the reticular formation, tectum, the cerebral aqueduct, tegmentum, and the cerebral peduncles. 
    • Contains clusters of sensory and motor neurons
    • Responsible for:
      • Visual and auditory relay centres → forebrain
      • eye movements
  • Reticular formation
    • Finger shaped, deep within forebrain
    • Acts as a sentry, alerting higher centres and allowing or blocking incoming messages
    • Responsible for: Consciousness, sleep and attention
  • The Forebrain
  • The most advanced portion from an evolutionary standpoint
  • Consists of the Cerebrum
  • All parts such as Thalamus, Hypothalamus, Limbic System, Cerebral cortex, are located in the Cerebrum
  • Cerebrum
    • Wraps around the brain stem
    • Two large hemispheres (left and right)
  • Thalamus
    • Located above the midbrain
    • Part of the cerebral spheres
    • Switchboard function: sends sensory nerve impulse to appropriate areas
    • Visual, auditory and body senses (balance and equilibrium)
    • Schizophrenia patients have an abnormally functioning thalamus that relays information to parts that do not need that information.
  • Hypothalamus
    • Located at the base of the brain,
      • below Thalamus
    • Responsible for:
      • Motivation & emotion,
      • temperature regulation,
      • sleeping,
      • eating,
      • drinking and aggression
      • Regulates endocrine and pituitary gland
    • James Olds found that hypothalamus has pleasure areas where dopamine works and is responsible for rewards and punishments
  • Limbic system
    • Located deep within the cerebral hemisphere
    • Responsible for:
      • Satisfying  urges that occur in the hypothalamus related to motivation and emotion
      • Inbred in memory as well
    • Two structures exist within the limbic system:
      • Hippocampus
        • Responsible for the formation and retrieval of memories
          • Damage can lead to severe impairment of recent memories
      • Amygdala
        • Also known as the fear centre
        • Organises motivation and emotional patterns related to aggression and fear
        • Reward and punishment centres for motivation sectors of limbic system
  • The Cerebral Cortex
    • Made up of gray (unmylenated) cells forming the outermost layer of the brain
    • 80% of brain tissue
    • It has fissures that are divided into four lobes based on sensory and motor function
      • The folds of wrinkled cortex looks like a canyon
      • Some division made by the fissures don’t involve sensory or motor function and are known as Association cortex
        • Responsible for mental processes of thought, memory and perception
    • Frontal lobe (planning and execution)
      • self-awareness, planning, initiative and responsibility and emotional experience
      • Prefrontal cortex
        • Located behind forehead,
        • Responsible for:
          • executive functioning,
          • goal setting,
          • judgement,
          • impulse control
      • Motor cortex
        • Responsible for more than 600 voluntary muscles in body
        • Located at the rear end of frontal lobe
        • Body parts are arranged upside down in the motor cortex
          • Information from legs is responded from the top portion of the frontal lobe
          • Information from the upper portions of the body is responded by the lower portion of the frontal lobe
    • Parietal (temperature)
      • The sensory cortex
        • Receives inputs for heat, touch and cold
          • Balance and body movements
        • Located behind motor cortex, and in front of parietal lobe
        • Same upside down principle as motor cortex
    • Temporal lobe is responsible for hearing
    • Occipital is responsible for vision and sight
  • Speech Comprehension and Production
    • Werwick’s area
      • located in the temporal lobe (left hemisphere)
      • Responsible for speech comprehension (written or spoken)
    • Broca’s area
      • located in the frontal lobe (left hemisphere) close to motor cortex
      • Responsible for facial muscle movement and speech production
    • Damage to either leads to:
      • Agnosia – inability to recognise familiar objects
      • Aphasia – inability to comprehend and formulate language due to damage to specific brain regions        
  • Association cortex
    • mental function of perception, language and thought
      • responsible for superior cognitive ability
  • Brain lateralization
    • Refers to the relatively greater localization of functions in each hemisphere
      • Corpus callosum – connects left and right hemisphere
    • Left hemisphere
      • Responsible for speech production, comprehension, math/arithmetic ability, logical abilities, and positive emotions
      • Right portions of the body are controlled by the LH
    • Right hemisphere
      • spatial relations, face recognition, and negative emotions
      • Left portions of the body are controlled by the RH
  • Split Brain – Roger Sperry
    • When the corpus callosum is damaged and the hemisphere begin acting independently of one another
  • Brain Plasticity also known as neuronal plasticity – ability of the neurons to change in structure and function.
  • The production of new neurons in the nervous system is called Neurogenesis.
    • Neural stem cells – uncommitted cells that can mature into any neuron of a degenerative area

Behavioural genetics and environment

  • Behaviour genetics – study how genetics and environment factors influence psychological characteristics
    • Degree of similarity of responses of genetically similar people gives an indication of the impact of genetics
  • Heritability
    • Heritability statistic estimates the extent to which the difference in specific phenotype within a group of people can be attributed to their differing genes.
  • Genetic basis of behaviour
    • Genotype – the specific genetic makeup of an individual
      • compared to a computer software
      • Genes present from birth
      • May or not may not manifest
        • dependent upon other genes which hinder or help this gene activate
    • Phenotype – are the observable characteristics of the individual.
      • The genes that are present and are expressed,
      • Difference between genotype and phenotype is that the genotype has all the genes but not necessary that all will be expressed
  • Major contributor of gene understanding
    • Gregor Mendel
  • Organic factors of genes affect characteristics.
    • Nucleus of all cells constituted by chromosomes
      • 22 identical pairs in humans called autosomes
    • Sex cells are called allosomes as the gene is different in shape, size and length compared to other chromosomes
    • A chromosome is a double stranded, tightly coiled molecule of deoxyribonucleic acid (DNA).
    • All information of heredity are in four chemical bases:
      • adenine
      • thymine
      • guanine
      • cytosine
    • Alleles are alternative characteristics that are developed due to alternative genes/mutation
    • Dominant genes will display characteristics
    • Recessive genes will not display characteristics unless two similar recessive genes are combined.
    • Polygenic transmissions occurs when many genes contribute to make one single dominant trait
  • Experience shapes behaviour in two ways:
    • Fixed action pattern
      • an unlearned automatic response triggered by a particular stimulus
    • Species adaptation
      • learning is not transferred by genes but through natural selection genetically based characteristics that enhance the ability of a species to adapt is transferred
  • Two types of  research studies to test genetics and heritability of behaviours
    • Family studies – Degree of similarity of behaviour of genetically similar relatives in specific traits to the person in question
    • Adoption studies – Degree of similarity of behaviour of adopted children with genetically similar (biological) parents and adoptive parents

Brain and other concepts

  • Intelligence
    • Identical twins reared together
      • correlation is high
    • Identical twins reared apart
      • correlation nearly as high
    • Fraternal twins
      • IQ of adopted children correlate similarly with both their biological parents and adoptive parents
      • (no single gene for intelligence)
      • Genetics/Heredity account for 50-70% change in intelligence
  • Siblings reared together have a high correlation in their IQ
    • Correlation of .32 between unrelated adopted children living together
    • Difference of home environment is more important in lower socio-economic conditions
      • Evidence: children in impoverished homes moving to better homes show increase in IQ by 10-12 points.

Schizophrenia

  • Seymour Ketty
    • Schizophrenia (12% similar genes)
    • Twin studies
      • compared trait similarities in identical and fraternal monozygotic twins
      • Trait similarity a.k.a. high concordance rates
      • High correlation in case of schizophrenia with family members

Personality

  • Genetic differences account for .50 correlation between similar genotype individuals
    • Important finding was that family environment played very limited role in determining personality, except when extremes of neglect and abuse occur.
    • Similar results for twin and adoptive studies.

Gene-environment interaction

  • The environment cannot affect the genotype but only its expression and phenotype
    • Reaction range
      • Is the measure of how much the environment can affect genes
    • Intellectual growth depends on both factors i.e. genes and environment
    • Evocative influence
      • A child’s genetically influenced behaviour may evolve certain responses from others
      • Introvert/extrovert children
    • Gene experimentation
      • Knockout procedure
        • A particular function of a gene is removed.
  • All vertebrates have a bilaterally symmetrical body plan
  • Anatomy of dissected in the following manner
    • Proximal – closer to the trunk
    • Distal – away from the trunk
  • Lateral – away from midline
    • Medial – closer to midline
  • Anterior – front side
    • Posterior – back side

Endocrine system – consists of numerous hormone secreting glands distributed throughout the body.

  • Messages to the body are distributed through hormones secreted via glands
  • Hormones are chemical messengers secreted into the bloodstream
  • Brain decides which impulse to send, between endocrine and nerve impulse, or both
  • Hormones affect us from prenatal stage
    • They affect aggressiveness, sex differences, immune system and so on
  • Immune system
    • foreign substance (antigens) are removed by antibodies
    • Stress, depression, negative thinking reduce immune functioning
    • Candence Pest suggested that the nervous, endocrine and immune system are related
  • Glands are organs in the body that secrete chemicals
    • Endocrine glands
      • secrete enzymes into the ‘bloodstream’ called hormones, usually from sympathetic division of ANS
      • Hormones affect behaviour and emotions through organs like heart, pancreas, sex organs.
    • Pituitary gland also known as Master gland
      • controls all other glands
      • located below hypothalamus
      • influences events related to pregnancy – production of milk, onset of labos, salt and water
  • Growth hormone
    • regulates and controls increase in size of body parts
  • Pineal gland
    • secretes melatonin
    • located nearer to the back of brain
    • regulates sleep wake cycle
  • Thyroid gland
    • secretes thyroxin
    • located inside neck
    • regulates metabolism
  • Pancreas
    •  secretes insulin and glucagon
      • low insulin = diabetes
      • high insulin = hypoglycaemia
    • located in torso
    • regulates blood sugar
  • Gonads
    • secretes androgens, oestrogen, progesterone, and testosterone
    • located in the ovaries (females) and testes (males)
    • regulates sexual behaviour along with the brain
  • Adrenal gland
    • on top of each kidney
    • Two types:
      • Adrenal medulla
        • secretes epinephrine and norepinephrine
        • regulates stress and sympathetic arousal
      • Adrenal cortex
        • secretes 30 different hormones called corticoids (steroids)
        • regulates salt intake, stress reaction, sex hormones
      • Cortisol
        • released under stress 
        • releases glucose into bloodstream
        • provides energy to body and brain by burning fatty acids from fat cells