Brains, Bodies, and Behaviour

Chapter 5: Brains, Bodies, and Behaviour

• Every behaviour stems from biology, influenced by the brain, nerves, muscles, and glands.
• The chapter explores the human biological makeup, focusing on brain structure and how psychologists study it to understand its functions.

Nervous System

• The body is controlled by the nervous system.
• It consists of billions of specialized, interconnected cells.
• Messages are sent between the brain and the body through the nervous system.
• The nervous system comprises the central nervous system (CNS) and the peripheral nervous system (PNS).
• CNS includes the brain and spinal cord.
• PNS consists of neurons linking the CNS to skin, muscles, and glands.

Endocrine System

• Behaviour is also significantly influenced by the endocrine system.
• The endocrine system is a chemical regulator composed of hormone-secreting glands.

The Neuron

• The nervous system contains over 100 billion cells known as neurons.
• A neuron is a cell in the nervous system responsible for receiving and transmitting information.
• Neurons consist of three parts: a cell body (or soma), dendrites, and an axon.
• Soma contains the cell's nucleus and keeps the cell alive.
• Dendrites are branching fibres that collect information from other cells to send to the soma.
• Axon is a long, segmented fibre that transmits information away from the cell body to muscles, glands or other neurons.

Electrical and Chemical Communication of Neurons

• The nervous system operates through an electrochemical process.
• An electrical charge moves through the neuron.
• Chemicals are used to communicate information between neurons.
• A signal received by the dendrites is transmitted to the soma in the form of an electrical signal.
• If the signal is strong enough, it will be transmitted to the axon and then to the terminal buttons.
• Terminal buttons are triggered to emit neurotransmitters that communicate with other neurons across the synapses.
• Axons are protected by a myelin sheath, which insulates and speeds up the transmission of electrical signals.

Action Potential

• Axons remain in a resting potential, where more negatively charged ions are inside than outside.
• The action potential occurs when the axon closest to the soma is stimulated and the electrical signal passes the threshold.
• The cell membrane opens its gates, allowing positively charged sodium ions to enter.
• The number of positive ions exceeds the number of negative ions.
• That particular segment becomes positively charged until it returns to resting potential.
• The action potential operates in an all-or-nothing manner.
• A neuron either fires completely, or not at all.
• Additionally, the neuron enters a refractory period after firing and cannot fire again until it returns to its resting potential.

Neurotransmitters

• Chemicals that relay signals across the synapse between neurons.
• They are released by terminal buttons into the synapse.
• They bind to the dendrites of other neurons.
• Different terminal buttons release different neurotransmitters.
• Receptor sites on dendrites only accept neurotransmitters that fit.
• When a neurotransmitter is accepted by a receiving neuron, its effect is either excitatory or inhibitory.
• Neurotransmitters not accepted by receptor sites are removed from the synapse via enzymes or reuptake, where they are reabsorbed by the transmitting terminal buttons.
• More than 100 chemical substances in the body have been identified as neurotransmitters affecting emotion, cognition, and behaviour.

Agonists and Antagonists

• Drugs can act like neurotransmitters to influence thoughts, feelings, and behaviour.
• Agonists mimic the effects of a neurotransmitter.
• Antagonists reduce or stop the normal effects of a neurotransmitter.
• Some drugs work by blocking reuptake, increasing the neurotransmitter's action in the synapse.
• Acetylcholine controls muscle contractions, memory, sleeping, and dreaming.
• Dopamine is involved in movement, motivation, and emotion.
• Endorphins are released in response to behaviours such as exercise, orgasm, and eating spicy foods.
• GABA is the major inhibitory neurotransmitter in the brain.
• Glutamate is the most common neurotransmitter, found in more than 90% of the brain's synapses.
• Serotonin is involved in functions including mood, appetite, sleep, and aggression.

Brain Structure and Functions

• Animal brains are very similar in overall form.
• In each animal, the brain is layered with basic structures that carry out the same functions.
• The innermost parts of the brain are the oldest regulating basic survival functions and emotions.
• Mammals have developed further brain layers for advanced functions, such as memory and complex social interaction.
• Humans have a large cerebral cortex.

Old Brain

• The brain stem is the oldest, innermost region that controls basic life functions like breathing, attention, and motor responses.
• The medulla controls heart rate and breathing.
• The pons helps control body movements via balance and walking.
• The reticular formation filters stimuli from the spinal cord and relays signals to other brain areas.
• It plays roles in walking, eating, sexual activity, and sleeping.

Thalamus

• The thalamus is an egg-shaped structure above the brain stem.
• Applies more filtering to sensory information from the spinal cord.
• Relays some signals to higher brain levels.
• Receives higher brain replies, forwarding them to the medulla and cerebellum.
• Shuts off incoming sensory signals during sleep.

Cerebellum

• The cerebellum, or "little brain", coordinates voluntary movement.
• Damage to the cerebellum causes difficulty walking, balancing, and holding hands steady.
• Alcohol influences the cerebellum, so people have more difficulty walking when drunk.
• This area Contributes to emotional responses and helps discriminate between sounds and textures.

Limbic System

• The limbic system governs emotion and memory.
• It includes the amygdala, hypothalamus, and hippocampus.
• The amygdala regulates perceptions of and reactions to aggression and fear.
• The hypothalamus regulates hunger, sexual behaviour, and links nervous system to the endocrine system.
• The hippocampus stores information in long-term memory.

Cerebral Cortex

• The cerebral cortex is the outer, bark-like layer of our brain which facilitates language, complex skills, tool creation, and living in social groups.
• The cerebral cortex is wrinkled and folded creating a larger surface area.
• The cerebral cortex is only one-tenth of an inch thick but is 80% of the brain's weight.
• It contains 20 billion nerve cells and 300 trillion synaptic connections with essential glial support cells.
• The cortex is divided into two hemispheres each divided into four lobes separated by folds called fissures.
• Frontal lobe: thinking, planning, memory, and judgment.
• Parietal Lobe: processing information about touch.
• Occipital lobe: processes visual information.
• Temporal lobe: hearing and language

Contralateral Control

• The brain is wired such that in most cases the left hemisphere receives sensations to control the right side and vice versa.

Functions of the Cortex

• Motor cortex: controls and executes body movements by sending signals to the spinal cord.
• Somatosensory cortex: receives information from the skin's sensory receptors and movement of body parts.
• Visual cortex: processes visual information.
• Auditory cortex: responsible for hearing and language.
• Association areas: sensory and motor information is combined with stored knowledge.

Brain Plasticity

• The ability to change its structure and function in response to experience or damage.
• Observed more in young children. Accomplished musicians exhibit a larger auditory cortex.
• After a tumour has impaired language in the left hemisphere, the right hemisphere will begin to compensate.
• New evidence suggests that the brain can engage in neurogenesis, the forming of new neurons.

Brain Lateralization

• The left and right hemispheres specialize to perform different functions.
• The left hemisphere controls the right side of the body and vice versa
• Language in located in the in left hemisphere.
• Left hemisphere is good at judging time, math and rhythm.
• The right hemisphere excels in perceptual, spatial, and facial skills

Nervous System Composition

• The nervous system consists of the central nervous system (CNS) and the peripheral nervous system (PNS).
• CNS consists of the brain and spinal cord, which controls body functions by interpreting sensory information and issuing directives.
• PNS includes bundles of interconnected neurons, which carry messages through sensory, motor, & interneurons.
• Sensory (afferent) neurons carry information from sensory receptors.
• Motor (efferent) neurons transmit information to muscles and glands.
• Interneurons Communicate only with other neurons.
• Signals travel to/from the brain through the spinal cord, or spinal reflexes.

Peripheral Nervous System (PNS)

• PNS is divided into two: the autonomic nervous system (ANS) and the somatic nervous system (SNS).
• The autonomic nervous system (ANS) governs the internal activities of the human body, e.g. heart rate, breathing, digestion, salivation etc.
• The somatic nervous system (SNS) controls the external aspects of the body, including the skeletal muscles, skin, and sense organs.

Autonomic Nervous System

• The ANS is further subdivided into the sympathetic and parasympathetic systems.
• Sympathetic division prepares the body for behaviour, particularly used in high stress situations.
• Parasympathetic division tends to calm the body after periods of stress.

Endocrine System

• The hormone-secreting glands that affect body functions.
• Glands release hormones into the bloodstream and influence behaviour, growth, reproduction, and metabolism.
• The pituitary gland controls body growth and secretes many hormones that affect other glands.
• Pancreas secretes hormones for maintaining a supply of fuel, and also to store energy
• Pineal gland secretes melatonin which regulates the wake-sleep cycle
• Thyroid and parathyroid glands control the speed of usage of energy and hormones.
• Adrenal glands produce hormones to balance salt and water levels, metabolism, the immune system, and sexual development.

Methods of studying the Brain

• Post-mortem examinations of brain tissue.
• Looking for Lesions that affect specific areas of the Brain
• EEG- Electroencephalography is a method that measures the Brains electrical activity.
• Functional Magnetic Resonance Imaging- fMRI-Brain scans that uses a magnetic field to create images of brain activity