Biological Bases of Behavior Notes

Biological Bases of Behavior

Basic Neuroscience

• All behavior results from activity in the cells of the nervous system.

• The nervous system has two main divisions:

  • Central Nervous System (CNS): Brain and spinal cord.

  • Peripheral Nervous System (PNS): Nerves to/from the brain and spinal cord (cranial nerves, spinal nerves, and peripheral ganglia).

Outline of the Nervous System

• I. Peripheral Nervous System (PNS)

  • A. Somatic Nervous System

  • B. Autonomic Nervous System (ANS)

    • Sympathetic Nervous System

    • Parasympathetic Nervous System

• II. Central Nervous System (CNS)

  • A. Spinal Cord

  • B. Brain

    • B1. Cerebrum

      • Cerebral Cortex

      • Subcortical Brain Areas

    • B2. Cerebellum

    • B3. Brain Stem

The Peripheral Nervous System

• Two main subdivisions: somatic nervous system and autonomic nervous system.

• A. The Somatic Nervous System

  • Sends and receives sensory messages.

  • Controls voluntary motor movement of skeletal muscles.

• B. The Autonomic Nervous System (ANS)

  • Controls automatic or involuntary bodily functions (smooth muscles and glands).

  • Includes digestion, heart rate, and breathing.

  • Main function: maintain homeostasis.

  • Subdivided into:

    • The Sympathetic Nervous System (SNS): The body's mobilizing system; "fight or flight"; dominant during stress; hormones released increase respiration, heart rate, and blood pressure, and decreases digestion and elimination.

    • The Parasympathetic Nervous System (PNS): The energy conserving system; dominant when relaxed; main function is basic body maintenance by slowing heart rate, blood pressure, and respiration, while increasing digestion and elimination.

• Healthier to have the parasympathetic system dominant.

The Central Nervous System (CNS)

• Consists of the spinal cord and brain.

• Sensory (afferent) neurons carry information into the CNS.

• Motor (efferent) neurons carry information away from the CNS to muscles and glands.

• A. The Spinal Cord

  • Divided into four regions:

    • Cervical: C1-C7 vertebrae.

    • Thoracic: T1-T12 vertebrae.

    • Lumbar: L1-L5 vertebrae.

    • Sacral: $1$ vertebra.

  • Damage leads to muscle dysfunction below the damaged area.

    • C1-C5 severing: quadriplegia.

    • C6-C7 severing: paraplegia and partial arm paralysis.

    • T1 or below severing: paraplegia only.

  • Incomplete severing: paresis (muscle weakness).

  • Reflexes may remain intact, even with damage (e.g., knee jerk reflex).

• B. The Brain

  • Control center for voluntary and most involuntary behavior.

  • Major divisions: cerebrum, cerebellum, and brain stem.

The Cerebrum

• Involved with complex thought, perception, and action.

• Two main layers: the cerebral cortex (outer) and the subcortical areas (inner).

• Analogy: The cortex is like the rind of an orange, and the subcortical areas are like the fruit.

The Cerebral Cortex

• The outside surface of the brain; the least developed part of the brain at birth (more developed in humans than in other animals).

• Highly convoluted with folds (gyri) for expansion of cortical surface area.

The Hemispheres

• Divided into the left and right hemispheres, connected by the corpus callosum..

• Left hemisphere controls the right side of the body, and vice versa.

• The left hemisphere is dominant in about 97% of all people.

  • Dominance refers to control over language, including reading, writing, speaking, spelling, and naming.

  • Also involved in verbal memory and rational, analytical, logical, and abstract thinking.

  • Damage may result in aphasia, agraphia, anomia, apraxia, and/or difficulties with the right side of the body.

• The Right Hemisphere

  • Involved with perceptual, visuospatial, artistic, musical, and intuitive activities.

  • Associated with body image and comprehension/expression of visual, facial, and verbal emotion.

  • Damage may result in left side hemi-neglect, prosopagnosia, visual-perceptual disturbances, agnosia for musical sounds, indifference, euphoria, hysteria, depression, mania, disinhibition, impulsivity, and abnormal sexual behavior.

The Lobes

• Each hemisphere is divided into four lobes: frontal, parietal, temporal, and occipital.

• Separated by elongated grooves (sulci).

  • The central sulcus separates the frontal and parietal lobes.

  • The lateral sulcus separates the temporal lobes from the frontal and parietal lobes.

The Frontal Lobes

• Located at the top front portion of each hemisphere; about 1/3 of the entire brain.

• Three main divisions: prefrontal cortex, premotor area, and motor area.

  • Prefrontal cortex: critical to personality, emotionality, inhibition, planning, initiative, abstract thinking, judgment, and higher mental functions.

  • Premotor area: involved in planning movement.

  • Motor area: instigates voluntary muscle movement.

  • Broca's area (left frontal lobe): controls the muscles that produce speech.

• Damage: loss of movement/paralysis, personality changes, emotional lability, perseveration, inattention, difficulty with problem solving, and inability to express language (Broca's Aphasia).

The Parietal Lobes

• Located just behind the frontal lobes.

• Contain the primary sensory areas that process somatosensory information.

• Integrate sensations of touch (shape, size, weight, texture) into 3D experiences.

• Process sensations of pain, heat, and proprioception (body position and movement).

• Right parietal lobe: directs attention and visual/spatial skills.

• Left parietal lobe: overlearned motor routines and linguistic skills (reading, writing, naming objects).

• Damage: anomia, agraphia, alexia, acalculia, difficulty drawing objects or distinguishing right from left, lack of awareness of body parts, problems with eye-hand coordination, and problems with attending to more than one object at a time.

• Gerstmann's syndrome (lesions of the left parietal lobe): agraphia, acalculia, right-left disorientation, and finger agnosia.

The Temporal Lobes

• Located on the outsides of each hemisphere (around the temples).

• Contain the primary auditory cortex.

• Connected to the limbic system (amygdala and hippocampus) and involved in emotional behavior and memory.

• Left temporal lobe: verbal memory and language comprehension (Wernicke's area).

• Right temporal lobe: visual memory.

• Damage: increased aggressive behavior, increased/decreased interest in sexual behavior, interference with memory, and problems understanding speech (Wernicke's aphasia).

The Occipital Lobes

• Located at the back of the brain.

• House the primary visual cortex: involved in sight, reading, and visual images.

• Damage: difficulty recognizing drawn objects or identifying colors, hallucinations and illusions, inability to recognize words (word blindness), and problems with reading or writing.

Subcortical Brain Areas

• Include the corpus callosum, the limbic system, and the basal ganglia inside the cerebrum. Subcortical connections.

• The Corpus Callosum

  • Bundle of nerve fibers that serves as a bridge between the left and right hemispheres.

  • Allows for communication between the two hemispheres for language expression or rational analysis.

  • Split-brain patients have undergone severing of the corpus callosum to reduce severe epileptic seizures.

• The Limbic System

  • Set of brain structures that form the inner border of the cortex.

  • Involved in emotions (fear, anger, pleasure), basic drives (sex, hunger), learning, olfaction, and memory.

  • Influences autonomic nervous system and endocrine system.

  • Structures: thalamus, hypothalamus, hippocampus, amygdala, and septum.

  • Thalamus:

    • Below the corpus callosum.

    • Major sensory relay center (except olfaction).

    • Integrates and processes sensory information before projecting it to the appropriate cortical areas.

    • Critical in the perception of pain.

    • Abnormalities linked to schizophrenia (misperceptions of sensory input).

  • Hypothalamus:

    • Below the thalamus.

    • Role in homeostasis through connections to the endocrine system and autonomic nervous systems.

    • Regulates temperature, hunger, thirst, sex, cyclic sex hormone secretion, aggression, and the sleep-wake cycle.

    • Suprachiasmatic nucleus (SCN): circadian clock.

    • Secretes hypothalamic releasing and inhibiting hormones that influence pituitary gland hormone secretion.

  • Hippocampus:

    • Primary function is memory, specifically consolidation of conscious memories.

    • New lasting information and events of lasting memories are stored here.

  • Amygdala:

    • Attaches emotional significance to sensory input.

    • Implicated in fear (startle response), aggression, and emotional memory.

    • Controls the fear response and has been linked to PTSD.

    • Stimulating the amygdala increases aggression, while removal/destruction diminishes it.

    • Klüver-Bucy syndrome (caused by bilateral temporal lobectomies with complete removal of the amygdala) results in placidity, apathy, hypersexuality, hyperphagia, and agnosias.

  • Septum:

    • Moderates or decreases aggression.

    • Damage can result in septal rage syndrome.

• The Basal Ganglia

  • In regulation and coordination of movement and establishing posture.

  • They are inhibitory, and dysfunction results in extraneous unwanted movements or difficulty with intended movement.

  • Caudate nucleus, Putamen, Substantia Nigra, Globus Pallidus, Subthalamic Nucleus.

The Cerebellum

• The second largest structure in the brain, located at the base of the brain stem.

• Provides excitatory inputs for smooth movement and coordinate motor activity.

• Controls posture, muscle tone, and balance.

• Hallmark of cerebellar disease is ataxia, defined as a lack of coordination of voluntary movements.

• Symptoms: problems with posture, gait, incorrect timing, disequilibrium, vertigo, inability to reach out and grab objects, difficulty making rapid movements, and coordinating fine movements.

The Brain Stem

• Below the subcortical regions and in front of the cerebellum.

• The most primitive part of the brain and is an extension of the spinal cord.

• Of the 12 cranial nerves, 10 begin in the brain stem. The pons, medulla, and reticular formation.

• Pons and Medulla
  * The pons (upper portion) and the medulla (bottom) are involved in sleep, respiration, movement, and cardiovascular activity. Damage can lead to failure of bodily functions and death.
  * Cranial nerve XII (hypoglossal nerve) originates in the medulla; damage can cause articulation problems similar to Broca's aphasia.

• The Reticular Formation

  • Interconnected nuclei in the brainstem, especially important in awareness, attention, and sleep.

  • Reticular activating system (RAS): projects to the thalamus; involved in the sleep-wake cycle, serves as a filter for incoming sensory information, and mediates alertness.

Neurons

• All behavior results from neuronal activity.

• Neurons communicate with each other, glands, muscles, and other body organs by releasing chemical neurotransmitters.

• Parts of a Neuron

  • Dendrites: receive information from other neurons by capturing neurotransmitters released into the synaptic cleft at their receptor sites.

  • Cell body/soma: integrates information from the dendrites; contains the nucleus, which regulates all cell activity.

  • Axon: a tube-like structure that transmits information to other neurons.

• Action Potential

  • Plays a vital role in cell-to-cell communication.

  • At rest: excess of sodium ions ($Na^+$) on the outside of the cell and potassium ions ($K^+$) on the inside.

  • Stimulus of sufficient charge: sodium ($Na^+$) rushes into the cell, creating an action potential (electrochemical impulse), then potassium ($K^+$) moves outside the cell.

  • Action potential travels the length of the axon to the boutons (terminal buttons), releasing neurotransmitters into the synaptic cleft (synapse).

  • Neurotransmitters in the synaptic cleft bind to receptor sites on dendrites of adjacent neurons, continuing the communication chain. Neurotransmitters in the synaptic cleft are taken up by the pre-synaptic neuron's terminal buttons and therefore never reach the adjoining neuron.

• All or None Principle

  • A neuron either fires to its fullest extent or does not fire at all.

  • After firing: absolute refractory period (neuron cannot fire) followed by a relative refractory period (intense stimulation needed).

  • During the refractory period: $Na^+$ and $K^+$ ions are returned to original sides.

Neurotransmitters

• Divided into the classical neurotransmitters and the peptide neurotransmitters.

• Agonist is applied to any substance that enhances the effect of the neurotransmitter, while antagonist refers to any substance that inhibits the neurotransmitter effect.

• If they increase the likelihood of an action potential, they are classified as Excitatory (e.g., acetylcholine, norepinephrine, glutamate).

• If they decrease the likelihood of an action potential, they are classified as Inhibitory (e.g., GABA, endorphins).

• The Classical Neurotransmitters include acetylcholine, the catecholamines (dopamine, norepinephrine), serotonin, and the amino acids.

  • Acetylcholine (ACh):

    • One of the most common neurotransmitters.

    • Involved in voluntary movement and memory/cognition.

    • Believed that the poison of the black widow spider, which causes paralysis, directly affects acetylcholine.

    • Deficiencies are observed in Alzheimer's disease.

  • Catecholamines:

    • Dopamine (DA):

      • Involved in thought, movement, and emotion.

      • Linked to the reward system.

      • Psychotic symptoms of schizophrenia result from excess dopamine.

      • Parkinson's Disease involves a degeneration of neurons in the substantia nigra, resulting in a decrease in dopamine.

      • L-Dopa (Levodopa), a precursor to dopamine, is used to treat the movement components of Parkinson's.

    • Norepinephrine (NE):

      • Involved in mood, pain perception, and sleep.

      • Depression is associated with a relative deficiency of norepinephrine, while mania is associated with a relative norepinephrine excess.

      • Released as a hormone into the bloodstream, where it causes blood vessels to contract and heart rate to increase.

  • Serotonin (5-HT)

    • Significantly involved in mood, sleep, appetite, aggression, sexual activity, and pain perception.

    • Deficiencies are implicated in mood disorders.

    • Levels of norepinephrine play a role in whether the mood disorder is expressed as mania (too much norepinephrine) or depression (too little norepinephrine).

      • Low serotonin and low norepinephrine are linked to depression.

      • Low serotonin and high norepinephrine are linked to mania.

  • The Amino Acids: GABA (gamma-aminobutyric acid) & Glycine and Glutamate.

    • GABA and glycine: major inhibitory neurotransmitters in the CNS, having a calming effect.

      • Anxiety and epileptic seizures are associated with insufficient levels of GABA.

      • Benzodiazepines are GABA agonists, increasing the levels of GABA to reduce levels of overarousal.

    • Glutamate: the most common neurotransmitter in the CNS and a major mediator of fast transmission.

      • Abnormal glutamate transmission is suspected in Schizophrenia, OCD, Autistic Disorder, and depression.

• The Peptide Neurotransmitters:

  • Long chains of amino acids, including enkephalins and endorphins (endogenous opioids) to regulate stress and pain, and Substance P (pain regulation).

Endocrine Disorders

• Disruption of endocrine functioning can result in medical conditions with accompanying psychological symptoms.

• Pituitary gland: master endocrine gland releasing hormones that activate other endocrine glands; regulated by the hypothalamus.

• Thyroid Disorders (controls metabolism through secretion of the hormone thyroxin)

  • Hyperthyroidism (excess secretion of thyroxin):

    • Weight loss despite increased appetite, heat sensitivity, sweating, diarrhea, tremor and palpitations, fatigue, agitated depression, insomnia, impaired memory and judgment, and hallucinations and delusions.

    • The most common form of hyperthyroidism is Grave's disease.

  • Hypothyroidism (undersecretion of thyroxin):

    • Unexplained weight gain, sluggishness, fatigue, impaired memory and intellectual functioning, and sensitivity to cold.

• Diabetes

  • The pancreas produces and secretes insulin, which regulates blood sugar levels.

  • Diabetes occurs when the pancreas does not produce insulin (Type I Diabetes), the body develops a resistance to insulin (Type II Diabetes), or may develop during pregnancy (Gestational Diabetes).

  • The hallmark of diabetes is hyperglycemia (excessive glucose or blood sugar levels), with classic symptoms (