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Chapter Three. The Biological Basis of Behavior. The Nervous System. The Nervous system is living tissue composed of cells. The cells in the nervous system are composed of Neurons and glia cells.
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Chapter Three The Biological Basis of Behavior
The Nervous System • The Nervous system is living tissue composed of cells. The cells in the nervous system are composed of Neurons and glia cells. • Neurons are individual cells in the nervous system that receive, integrate, and transmit information. • Glia cells are found throughout the nervous system . They provide nourishment to the neurons, help remove waste products and provide insulation around many axons. The out number neurons in ten to one.
Parts of the Neuron • The Soma is the cell body containing most of the chemical machinery in the neuron. • Dendrites are part of the neuron which receive information, information flows into the soma. The information then travels away from the soma and along the axon. • The Axon is a long thin fiber that transmits information from the soma to other neurons or muscle glands. Axons are covered with myelin sheaths.
Parts of the Neuron • The Myelin Sheath is a fatty, whit insulating material which covers the axons and speeds up transmission between neurons. • Terminal buttons are at the end of axons and are small knobs that secrete chemicals called neurotransmitters. • Synapses are junctions where information is transmitted from one neuron to another . This is where neurons meet , however they do not actually touch. • The neurons meet at the synaptic cleft. The synaptic cleft is the microscopic gap between the terminal button of one neuron and the cell membrane of another neuron.
Classification of Neurons • Sensory Neurons send signals to the CNS. • Motor Neurons send signals away from CNS. • Interneuron's collect signals within cells.
Neurotransmitters • Neurotransmitters are chemicals that act as messengers that may activate neighboring neurons. Neurotransmitters are fundamental to behavior, playing a key role in everything from muscle movement to moods and mental health.
Neurotransmitters and Behavior • Acetylcholine (Ach)- attention, memory, and arousal • Dopamine (DA)- voluntary movement • Norepinephrine (NE)- mood and arousal • Serotonin- sleep, wakefulness, eating and aggression • GABA- anxiety, sleep and arousal • Glutamate- learning and memory • Endorphins- pain relief and stress
Communication of Neurons • Presynaptic neurons sends signal to postsynaptic neuron. • Messages travel across the gaps between neurons with the arrival of an action potential and the terminal buttons trigger the release of neurotransmitters. • EPSP is an excitatory postsynaptic neuron with positive voltage which increases the likelihood the neuron will fire an action potential. • IPSP is an inhibitory neuron in which there is a negative voltage and decreases the likelihood the neuron will fire an action potential.
Neuron Resting Potential and Action potentials • A neuron at resting potential is at a stable negative charge of about -40mv to -90mv, typically averaging about a -70mv charge. The neuron is inactive at resting potential and contains chloride ions. • An Action Potential is a brief shift in the neurons electrical charge that travels along an axon. During an action potential the charge of the neuron becomes positively charged to about +50mv. During this time the chloride ions flow out of neuron and sodium neurons flow into the cell. A neuron will either fire or not, this is called the “All or Nothing Law”.
The Nervous System • The Nervous System is divided into two different parts. The two parts of the nervous system are the Central Nervous System (CNS)and the Peripheral Nervous System (PNS). • The CNS is the brain and the spinal cord. • The PNS is the cranial and spinal nerves . The PNS contains both sensory and motor neurons. Motor neurons in the PNS are divided into two systems. These two systems are the somatic nervous system, which is the voluntary part of the PNS and the autonomic nervous system, which is the involuntary part of the PNS. • The Autonomic Nervous System (ANS) is divided into two parts. These two parts are the sympathetic nervous system (“flight or fight”) and the parasympathetic nervous system (rest).
The Hindbrain • Medulla oblongata - Attaches to the spinal cord, controls largely unconscious but essential functions, such as; breathing, maintaining muscle tone, and regulating circulation. • Brainstem- is the region of the brain that connects the cerebrum with the spinal cord. Motor and sensory neurons travel through the brainstem allowing for the relay of signals between the brain and the spinal cord.
The Hindbrain • Pons- Bridge of fibers that connects the brainstem with the cerebellum. The pons also contains several clusters of cell bodies involved with sleep and arousal.
The Hindbrain • Cerebellum- Also called the “little brain” that is involved in the coordination of movement and is critical to the sense of equilibrium, or physical balance.
The Midbrain • The Midbrain- segment of brainstem that lies between hindbrain and forebrian. • Reticular formation -Contributes to functions of muscles reflexes, breathing and pain perception. It is best known for its regulation of sleep and wakefulness.
The Forebrain • Thalamus- all sensory information (except smell) must pass through this structure to reach the cerebral cortex. It is the relay station for incoming and out coming signals.
The Forebrain • Hypothalamus - involved in the regulation of biological needs. The hypothalamus lies beneath the thalamus. It is responsible for regulating the needs of; hunger, thirst, and temperature control.
The Forebrain • Hippocampus- part of the limbic system involved in learning and memory. It appears to contain emotion “pleasure centers”.
The Forebrain • Amygdala- part of the limbic system involved in emotion and aggression. The “Fear Center” in the brain.
The Forebrain • Corpus Callosum- bridge of fibers passing information between the two cerebral hemispheres.
The Forebrain • Cerebrum- the largest and most complex part of the human brain. It is responsible for our most complex mental activities, including learning, remembering, thinking and consciousness.
The Forebrain • Cerebral Cortex- is divided into right and left hemispheres. It encompasses about two-thirds of the brain mass and lies over and around most of the structures of the brain. It is the most highly developed part of the human brain and is responsible for thinking, perceiving, producing and understanding language. It is also the most recent structure in the history of brain evolution.
Language areas in the brain • The brain is divided into two halves, a left hemisphere and a right hemisphere. • In human beings, it is the left hemisphere that usually contains the specialized language areas. While this holds true for 97% of right-handed people, about 19% of left-handed people have their language areas in the right hemisphere and as many as 68% of them have some language abilities in both the left and the right hemispheres.
Broca’s Area • The first language area within the left hemisphere to be discovered is called Broca's Area, after Paul Broca. Broca was a French neurologist who had a patient with severe language problems: Although he could understand the speech of others with little difficulty, the only word he could produce was "tan.“ • After the patient died, Broca performed an autopsy, and discovered that an area of the frontal lobe, just ahead of the motor cortex controlling the mouth, had been seriously damaged. He correctly hypothesized that this area was responsible for speech production. • Physicians called the inability to speak aphasia, and the inability to produce speech was therefore called Broca's aphasia, or expressive aphasia. Someone with this kind of aphasia has little problem understanding speech. But when trying to speak themselves are capable only of slow, laborious, often slurred sequences of words. They don't produce complete sentences, seldom use regular grammatical endings such as -ed for the past tense, and tend to leave out small grammatical words.
Wernicke’s Area • The second language area to be discovered is called Wernicke's Area, after Carl Wernicke, a German neurologist. Wernicke had a patient who could speak quite well, but was unable to understand the speech of others. After the patient's death, Wernicke performed an autopsy and found damage to an area at the upper portion of the temporal lobe, just behind the auditory cortex. He correctly hypothesized that this area was responsible for speech comprehension. • This kind of aphasia is known as Wernicke's Aphasia, or receptive aphasia. When you ask a person with this problem a question, they will respond with a sentence that is more or less grammatical, but which contains words that have little to do with the question or, for that matter, with each other. Strange, meaningless, but grammatical sentences come forth, a phenomenon called "word salad." • Like Broca's area is not just about speech production, Wernicke's is not just about speech comprehension. People with Wernicke's Aphasia also have difficulty naming things, often responding with words that sound similar, or the names of related things, as if they are having a very hard time with their mental "dictionaries."
Brain Plasticity • Brain Plasticity is the ability of the brain to change through 1) experience 2) damage to incoming sensory pathways or destruction of brain tissue can lead to neural reorganization and 3) the adult brain can generate new neurons, a process called neurogenesis. • Brain Plasticity shows the brain is flexible and constantly evolving.
The Endocrine System • The Endocrine System consists of glands that secrete chemicals into the bloodstream that help control bodily functioning. • Hormones are the chemical substances released by the endocrine glands. Most of the endocrine system is controlled by the nervous system through the hypothalamus.
The Endocrine Glands • The Pituitary gland secretes growth hormones and regulates secretions of thyroid gland, pancreas, adrenal cortex, and gonads. It is the “master gland” of the endocrine system, however the real power behind it is the hypothalamus. • The Pancreas secretes insulin and glucagon to regulate sugar metabolism. • The Thyroid gland regulates metabolic rates. • The pineal gland is an endocrine gland, like the pituitary gland, it secretes a hormone -- melatonin. • The Adrenal glands consist of the Adrenal cortex Affects (salt and carbohydrate metabolism and inflammatory reactions) and the Adrenal medulla (sleep and emotional arousal). • The Gonads are the Ovaries and the Testes which secrete sex hormones.
Brain Imaging Techniques Magnetic Resonance Imaging (MRI) is a sophisticated software system called Computerized Tomography (CT) converts this information into a three-dimensional picture of any part of the body. A brain scan taken this way looks like a grayish X-ray, the different, clearly delineated types of tissue.
Brain Imaging Techniques • Functional MRI (fMRI) is a brain imaging technique in which neuronal firing is fueled by glucose and oxygen, which are carried in blood. When an area of the brain is fired up, these substances flow towards it, and fMRI shows up the areas where there is most oxygen. The brain takes about half a second to react to a stimulus, so this rapid scanning technique can clearly show the ebb and flow of activity in different parts of the brain as it reacts to various stimuli or undertakes different tasks. fMRI is proving to be the most rewarding of scanning techniques, but it is phenomenally expensive and brain mappers often have to share a machine with clinicians who have more pressing claims to it.
Brain Imaging Techniques Positron Emission Topography (PET) is a technique that achieves a similar end result to fMRI -- it identifies the brain areas that are working hardest by measuring their fuel intake. The pictures produced by PET are very clear (and strikingly pretty) but they cannot achieve the same fine resolution as fMRI. The technique also has a serious drawback in that it requires an injection into the bloodstream of a radioactive marker.
Brain Imaging Technique An electroencephalogram (EEG) is a test used to detect abnormalities related to electrical activity of the brain. This procedure tracks and records brain wave patterns. Small metal discs with thin wires (electrodes) are placed on the scalp, and then send signals to a computer to record the results. Normal electrical activity in the brain makes a recognizable pattern. Through an EEG, doctors can look for abnormal patterns that indicate seizures and other problems.
