Neuroanatomy and Neurophysiology Overview

Neuroanatomy and Neurophysiology

• Science has greatly advanced understanding of the brain in the past 30 years.
• Advances have helped reveal possible reasons brains function differently from each other.
• Psychiatric-mental health nurses require a basic understanding of brain function and current theories of mental illness.
• A lesson represents an overview of the major anatomic structures of the nervous system.
• Current neurobiologic theories regarding what causes mental illness are genetics and heredity, stress and the immune system, and infectious agents.

Structures of the Brain

• The cerebrum has two hemispheres.
• All lobes and structures are in both halves of the cerebrum, except the pineal gland.
• The pineal gland is an endocrine gland.
• The pineal gland influences the activities of the pituitary gland, islets of Langerhans, parathyroids, adrenals, and gonads.
• The left hemisphere controls the right side of the body and is the center for logical reasoning and analytic functions.
• Reading, writing, and mathematical tasks are examples of logical reasoning and analytic functions.
• The right hemisphere controls the left side of the body and is the center for creative processes.
• Cerebral hemispheres are divided into four lobes: frontal, parietal, temporal, and occipital.
• Frontal lobes control thought organization, body movement, memories, emotions, and moral behavior.
• Integration of information regulates arousal, focuses attention, and enables problem-solving and decision-making.
• Abnormalities in the frontal lobes exist.
• Parietal lobes interpret taste and touch sensations and assist in spatial orientation.
• Temporal lobes are centers for smell, hearing, memory, and emotional expression senses.
• The occipital lobe assists in coordinating language generation and visual interpretation, such as depth.
• The cerebellum is located below the cerebrum.
• The cerebellum is the center for coordination of movements and postural adjustments.
• The cerebellum receives and integrates information from all areas of the body and components of the CNS.
• Inhibited dopamine transmission is associated with a lack of smooth coordinated movements in diseases.
• The brainstem includes the midbrain, pons, and medulla oblongata.
• The brainstem includes the nuclei for cranial nerves III through XII.
• The medulla is located at the top of the spinal cord and contains vital centers for respiration and cardiovascular functions.
• The pons are between the medulla and the midbrain, serving as the primary motor pathway.
• The midbrain connects the medulla and the pons with the cerebrum.
• The midbrain includes the reticular activating system, which influences motor activity, sleep, consciousness, and awareness.
• The midbrain includes the extrapyramidal system, which relays information about movement and coordination from the brain to the spinal nerves.
• The locus coeruleus, a small group of norepinephrine-producing neurons in the brain stem, is associated with stress, anxiety, and impulsive behavior.
• The thalamus regulates activity, sensation, and emotion.
• The hypothalamus regulates temperature, appetite, and endocrine function.
• The hypothalamus also regulates sexual drive and impulse behavior associated with anger, rage, or excitement.
• The hippocampus and amygdala are involved in emotional arousal.
• Disturbances in the limbic system are implicated in a variety of mental illnesses.
• Memory loss that accompanies dementia is an example of a disturbance in the limbic system.
• Poorly controlled emotions and impulses seen with psychotic or manic behavior are an example of a disturbance in the limbic system

Neurotransmitters

• Approximately 100 billion brain cells form groups of neurons arranged in networks.
• Neurons communicate via electrochemical messages from neuron to neuron.
• Electrochemical messages pass from the dendrites through the soma or cell body, down the axon, and across synapses to the dendrites of the next neuron.
• In the nervous system, electrochemical messages cross the synapses between neural cells via neurotransmitters, which are special chemical messengers.
• Neurotransmitters are chemical substances manufactured in the neuron.
• Neurotransmitters aid in transmitting information throughout the body.
• Neurotransmitters either excite or stimulate an action in the cells (excitatory) or inhibit or stop an action.
• There are more than 100 neurotransmitters in the body.
• Neurotransmitters regulate appetite, memory, and emotions.
• Neurotransmitters regulate as well as muscle action and movement.
• An agonist is a drug that has chemical properties similar to a neurotransmitter.
• Agonists mimic the effects of a neurotransmitter.
• Antagonists are drugs that reduce or stop the effects of a neurotransmitter.
• Acetylcholine (ACh) is either excitatory or inhibitory.
• Acetylcholine stimulates muscle contractions and regulates memory, sleeping, and dreaming.
• Alzheimer's disease is associated with an undersupply of acetylcholine.
• Nicotine is an acetylcholine agonist.
• Dopamine is excitatory.
• Dopamine is involved in movement, motivation, and emotion.
• Dopamine produces feelings of pleasure when released by the brain's reward system.
• Schizophrenia is linked to increases in dopamine.
• Parkinson's disease is linked to reductions in dopamine.
• Endorphins are released in response to behaviors such as vigorous exercise, orgasm and eating spicy foods.
• Endorphins are natural pain relievers related to compounds found in opium, morphine and heroin.
• Endorphin release creates a sense of euphoria.
• Gamma-aminobutyric acid (GABA) is the major inhibitory neurotransmitter in the brain; it lowers arousal and is involved in sleep.
• A lack of GABA causes can lead to involuntary motor actions, including tremors and seizures.
• Alcohol stimulates the release of GABA, inhibiting the nervous system and causing drunkenness.
• Low GABA levels can produce anxiety, and GABA agonists are used to reduce anxiety.
• Glutamate is the most common neurotransmitter and is excitatory.
• Glutamate is in more than 90% of the brain's synapses and is involved in learning.
• Excess glutamate can cause overstimulation, migraines, and seizures.
• Serotonin is inhibitory.
• Serotonin is involved in many functions, including mood, appetite, sleep, and sexual behaviors.
• Low serotonin levels are associated with depression.
• Some drugs used to treat depression are selective serotonin reuptake inhibitors (SSRIs).
• Epinephrine/Adrenaline is excitatory and controls the fight-or-flight response.
• High levels of epinephrine lead to high blood pressure, anxiety, and insomnia; and an increased risk of stroke.
• Low levels of epinephrine leads to diminished excitement and not being able to react appropriately in dangerous situations.
• Norepinephrine/Noradrenaline is excitatory.
• Norepinephrine helps in activating the body and brain to take action during times of stress or in dangerous situations.
• Norepinephrine acids in alertness and concentration.
• High levels of norepinephrine lead to high blood pressure, excessive sweating, and anxiety.
• Low levels of norepinephrine mean that energy levels are lower and concentration is lacking.

Neurobiologic Causes of Mental Illness

• Origins of mental disorders are not that simple and are not always hereditary like physical illnesses.
• Several mental disorders may be linked to a specific gene or combination of genes but are not solely genetic.
• Non-genetic factors also play essential roles.
• Certain infections have been linked to brain damage and the development of mental illness or the worsening of its symptoms.
• Pediatric autoimmune neuropsychiatric disorder (PANDAS) associated with streptococcus bacteria has been linked to obsessive-compulsive disorders.
• Defects in or injury to certain areas of the brain have been linked to mental illnesses.
• Disruption of early fetal brain development or trauma at the time of birth may play a part in certain conditions, such as autism.
• Long-term substance abuse has been linked to anxiety, depression, and paranoia.
• Poor nutrition and exposure to toxins, such as lead, may play a role in mental illnesses.