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.
- Anaxonic neurons are small and have no anatomical clues to distinguish dendrites from axons; all the cell processes look alike .
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
- Further divided into two categories:
- 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
- The Hindbrain – lowest and the primitive part
of the brain;
- 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
- Located at the
base of the brain,
- 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
- Responsible for
the formation and retrieval of 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
- Hippocampus
- 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
- Receives inputs
for heat, touch and cold
- The sensory 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
- Werwick’s area
- Association cortex
- mental function
of perception, language and thought
- responsible for superior cognitive ability
- mental function
of perception, language and thought
- 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
- Refers to the
relatively greater localization of functions in each hemisphere
- 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
- Genotype – the specific genetic
makeup of an individual
- 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
- Nucleus of all cells constituted by
chromosomes
- 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
- Fixed action pattern
- 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
- Identical twins reared together
- 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.
- Knockout procedure
- Reaction range
- 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
- Endocrine glands
- 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
- secretes
insulin and glucagon
- 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
- Adrenal medulla