Unit 3: The Biological Bases of Behaviour

Transcription

1 Unit 3: The Biological Bases of Behaviour Section 1: Communication in the Nervous System Section 2: Organization in the Nervous System Section 3: Researching the Brain Section 4: The Brain Section 5: Cerebral Laterality Section 6: The Endocrine System Section 7: Heredity and Behaviour Section 1: Communication in the Nervous System Nervous Tissue Neurons receive, integrate, and transmit information Soma is the body of the neuron. Dendrites are the parts of the neuron that receive information The axon transmits signals away from the soma to other neurons, or muscles or glands. The myelin sheath is the insulating material surrounding the axons. Terminal buttons are the ends of the axons that secrete chemicals called neurotransmitters. A synapse is the junction where information is communicated between neurons. The Neuron Impulse Inactive neurons have a resting potential. This is a negative charge. When a neuron activates, it creates an action potential. The neuron's electrical charge changes and becomes less negative or even positive. This shift travels down the axon. After firing, the neuron must rest. This is the neuron's absolute refractory period. After the refractory period, the neurons regain a negative charge. Certain drugs, like anaesthetics, prevent the neurons from firing. The neurons aren't able to reset after the refractory period because the positive ions are blocked. Neurons fire their entire potential. This is the All or None Law. Neurons communicate the strength of a stimulus by how fast they fire. A strong stimulus causes neurons to fire more quickly than a weaker stimulus. The Synapse Neurons don't touch one another. The synaptic cleft is the space between a neuron and the terminal buttons of another neuron. When a neuron's action potential reaches the terminal buttons, they release neurotransmitters. 1

2 Neurotransmitters transmit information from one neuron to another. Neurotransmitters go to receptor sites on the postsynaptic cell membrane of the receiving cell. The postsynaptic potential (PSP) is created when neurotransmitters combine with receptors. It is a voltage change on the postsynaptic cell membrane. Postsynaptic potentials do not follow the All or None Law. They are graded. An excitatory PSP is a positive voltage shift. This increases the probability that the postsynaptic neuron will fire. An inhibitory PSP is a negative voltage shift. This decreases the probability that the postsynaptic neuron will fire. The neurotransmitters then either become inactive or are returned to the presynaptic neuron through reuptake. Neurotransmitters and Behaviour Agonists are chemicals that mimic the effect of neurotransmitters; antagonists are chemicals that oppose the effect of neurotransmitters. Acetylcholine (ACh) is the neurotransmitter found in the motor neurons. Monoamines are neurotransmitters that include dopamine, Norepinephrine, and serotonin. Serotonin, for example, helps to regulate sleep. Dopamine is involved in voluntary movement. Abnormalities in levels of monoamines can cause psychological disorders. For example, low levels of Norepinephrine and serotonin can cause depression and abnormal levels of dopamine can cause schizophrenia. Drugs like cocaine affect people because they affect the levels of dopamine and Norepinephrine. Endorphins are neurotransmitters that reduce pain and produce feelings of exhilaration. They are similar to opiates. Section 2: Organization of the Nervous System The human nervous system consists of the central nervous system and the peripheral nervous system. The Central Nervous System The CNS consists of the brain and the spinal cord. The spinal cord connects the brain to the peripheral nervous system. The CNS is protected by cerebrospinal fluid or CSF (to cushion the brain) and the blood-brain barrier (to screen chemicals from the brain). The Peripheral Nervous System The peripheral nervous system is made up of all the nerves that lie outside the brain and spinal cord. The peripheral nervous system is divided into the somatic nervous system and the autonomic nervous system. The somatic nervous system is made up of nerves connected to voluntary muscles and sensory receptors. 2

3 In the somatic nervous system, afferent nerve fibbers carry information to the CNS. Efferent nerve fibbers carry information from the CNS. The autonomic nervous system is made up of nerves connected to the heart, blood vessels, and glands. The autonomic nervous system is divided into the sympathetic division and parasympathetic division. The sympathetic division controls the body's resources for emergencies, e.g., releasing adrenaline or withdrawing blood from limbs to the vital organs. The parasympathetic division conserves the body's resources, e.g., slowing heart rate. Section 3: Researching the Brain Neuroscientists try to map out the structure and function of the brain. The electroencephalograph (EEC) measures electrical activity in the brain. Different brain wave patterns are associated with different mental activities. Lesioning: When people suffer brain damage, they develop lesions on their brains. Neuroscientists can study the effects of these lesions. Electrical Stimulation of the Brain (ESB) involves sending electrical signals into parts of the brain. Most ESB research is done on animals, but it is also a routine part of brain surgery. Brain Imaging o A Computerized Tomography (CT) scan involves the use of computer enhanced x-rays of the brain. The brain is x-rayed from many angles to produce an image of the brain. o A Positron Emission Tomography (PET) scan images brain function, not structure like a CT scan. Brain activity is imaged by using radioactive chemicals. o A Magnetic Resonance Imaging (MRI) scan uses magnetic fields to map brain structure and activity. Section 4: The Brain The Hindbrain The hindbrain includes the cerebellum, the medulla, and the Pons. The medulla and the Pons are part of the brainstem. The medulla, attached to the spinal cord, controls unconscious functions like circulation, breathing, coughing, and sneezing. The Pons connects the brainstem with the cerebellum. The cerebellum coordinates movement signals from the forebrain and the senses from the body. The Midbrain The midbrain is the top of the brainstem. It is between the hindbrain and the forebrain. The midbrain deals with senses and movement. It is an important centre for dopamine production. The reticular formation deals with reflexes, breathing, pain perception, and sleep. It also is part of the hindbrain. 3

4 The Forebrain The forebrain is the most complex part of the brain. It includes the thalamus, hypothalamus, limbic system, and cerebrum. The thalamus is where all sensory information passes to the cerebral cortex. The hypothalamus controls the autonomic nervous system, connects the brain to the endocrine system, and regulates fighting, fleeing, feeding, and mating. The limbic system is involved in emotion, memory, and motivation. The limbic system is not well understood. It includes the hippocampus be includes the primary somatosensory cortex to process sense stimuli. The cerebrum is divided into four lobes. o The frontal lobe includes the primary motor cortex for movement and the prefrontal cortex for planning, attention, and organizing. o The occipital lobe includes the primary visual cortex. o The parietal lobe includes the somatosensory cortex. o The temporal lobe includes the primary auditory cortex. Section 5: Cerebral Laterality Right and Left Hemispheres of the Brain The left hemisphere is better at verbal processing, such as language, speech, reading, and writing. The right hemisphere is better at nonverbal processing, such as spatial and musical tasks and visual recognition. Although the left hemisphere is better at verbal processing, the right is also involved. Although the right is better at non-verbal processing, the left is also involved. Each hemisphere's primary connections are to the opposite side of the body. Much has been learned through split-brain research, i.e., research on people who have had brain surgery to cut the corpus callosum. Section 6: The Endocrine System The endocrine system consists of glands that release hormones into the bloodstream to control bodily functions, e.g. the pancreas releases insulin to process sugar. Much of the endocrine system is controlled by the hypothalamus. The pituitary gland, connected to the hypothalamus, releases hormones to stimulate other glands. It is sometimes called the "master gland." The endocrine system works with the nervous system. Hormones are also important in physical development. Section 7: Heredity and Behaviour 4

5 Genetics Chromosomes are strands of deoxyribonucleic acid (DNA) molecules that carry genetic information. They are in every cell of your body. Genes are DNA segments on chromosomes that are transmitted from parent to child at conception. Each parent contributes 23 chromosomes. Like chromosomes, genes work in pairs. Some genes are dominant; others are recessive. Genotype is a person's genetic makeup. Phenotype refers to the ways a person's genotype is demonstrated in physical appearance. Polygenic traits require more than two genes, e.g. skin colour. Research Methods and Heredity In family studies, researchers examine heredity by studying the traits of people who are related to one another. In twin studies, researchers examine heredity by studying the traits of identical twins and fraternal twins. In adoption studies, researchers examine heredity by studying traits of children, their biological parents, and their adoptive parents. Genetic mapping is the current research effort to determine the location and function of all human genes. Nature (heredity) and nurture (environment) are important to development. Evolutionary psychology is based on the theory of evolution and knowledge of genetics and heredity. 5