Unit 2: The Biological Perspective

Learning Objectives

  • Identify the parts of a neuron and their function

  • Explain electrical communication within neurons: the action potential

  • Describe chemical communication between neurons: neurotransmitters

  • Compare and contrast methods to study the brain

  • Identify basic brain structures and their function

  • Describe the peripheral and central nervous systems

  • Explain the role of the neuroendocrine system: hormones

Localization of Function

  • Notable Quote:
    "For thirty years I have studied crania and living heads from all parts of the world and have found in every instance that there is a perfect correspondence between the conformation of the healthy skull of an individual and his known characteristics."

Key Terms

  • Nervous System: A network of cells that carries information to and from all parts of the body.

  • Neuroscience: A branch of life science that deals with the structure and functioning of the brain and the neurons, nerves, and nervous tissue that form the nervous system.

  • Biological Psychology (Behavioral Neuroscience): A branch of neuroscience that focuses on the biological bases of psychological processes and behavior.

The Nervous System’s Building Block

  • Neuron: The basic cell that makes up the nervous system and receives and sends messages within that system.

Structure of the Neuron

  • Dendrites: Branch-like structures that receive messages from other neurons.

  • Soma (Cell Body): Responsible for maintaining the life of the cell.

  • Axon: Long, tube-like structure that carries the neural message to other cells.

  • Axon Terminals: Located at the end of the axon and are responsible for neural communication.

Other Cells in the Nervous System

  • Glial Cells:

    • Provide support for neurons to grow.

    • Deliver nutrients to neurons.

    • Clean up waste products and dead neurons.

    • Produce myelin to coat axons (Myelin is a fatty substance that coats the axons of neurons to insulate, protect, and speed up the neural impulse).

Electrical Communication: Key Terms

  • Ions: Charged particles.

    • The balance of ions inside and outside of the neuron determines charge:

    • Inside neuron: Negatively charged

    • Outside neuron: Positively charged.

  • Diffusion: Process of ions moving from areas of high concentration to areas of low concentration.

  • Resting Potential: State of the neuron when not firing a neural impulse.

Electrical Communication: The Neural Impulse

  • Action Potential: The release of the neural impulse consisting of a reversal of the electrical charge within the axon.

    • Allows positive sodium ions to enter the cell.

    • All-or-None Phenomenon: Refers to the idea that a neuron fires completely or not at all; there is no partial firing.

Electrical Communication: Review

  • Electrical Charge (millivolts):

    • Resting potential: -70 ext{ mV}

    • Threshold: -55 ext{ mV}

    • Hyperpolarization: A state when the neuron is more negatively charged than its resting state.

Visual Representation of Electrical Communication

  • Diagram illustrating various elements such as resting potential, action potential, and the involvement of positively charged sodium ions as well as axon terminals in neurotransmitter release.

Chemical Communication: Neurotransmission

  • Synaptic Vesicles: Sac-like structures found inside the axon terminal containing chemicals (neurotransmitters).

  • Neurotransmitter: Chemicals found in synaptic vesicles which, when released, have an effect on the next cell.

  • Receptor Sites: Three-dimensional proteins on the surface of dendrites or certain cells of muscles and glands shaped to fit only certain neurotransmitters.

  • Synapse/Synaptic Gap: Microscopic fluid-filled space between the axon terminals of one cell and the dendrites of the next cell.

Neuron Activation

  • Excitatory Synapse: A neurotransmitter that causes the receiving cell to fire.

  • Inhibitory Synapse: A neurotransmitter that causes the receiving cell to stop firing.

Chemical Communication: Neurotransmitters and Their Functions

  • Acetylcholine (ACh):

    • Functions: Excitatory or inhibitory; involved in arousal, attention, memory, and controls muscle contractions.

  • Norepinephrine (NE):

    • Functions: Mainly excitatory; involved in arousal and mood.

  • Dopamine (DA):

    • Functions: Excitatory or inhibitory; involved in control of movement and sensations of pleasure.

  • Serotonin (5-HT):

    • Functions: Excitatory or inhibitory; involved in sleep, mood, anxiety, and appetite.

  • Gamma-Aminobutyric Acid (GABA):

    • Functions: Major inhibitory neurotransmitter; involved in sleep and inhibits movement.

  • Glutamate:

    • Functions: Major excitatory neurotransmitter; involved in learning, memory formation, nervous system development, and synaptic plasticity.

  • Endorphins:

    • Functions: Inhibitory neural regulators involved in pain relief.

Neurotransmission: Agonism/Antagonism

  • Agonists: Chemicals that mimic or enhance the effects of a neurotransmitter on receptor sites on the next cell, increasing or decreasing the activity of the cell.

  • Antagonists: Chemicals that block or reduce a cell’s response to the action of other chemicals or neurotransmitters.

Cleaning Up the Synapse

  • Reuptake: Process by which neurotransmitters are taken back into the synaptic vesicles.

    • Example: Drugs like cocaine block the reuptake process.

  • Enzymatic Degradation: Process by which the structure of a neurotransmitter is altered so it can no longer act on a receptor.

Brain Methods: Planes of Section

  • Planes of Section: Divisions used to help describe the location of brain structures.

Brain Methods: Lesioning Studies

  • Lesioning Studies: Involves the insertion of a thin, insulated wire into the brain through which an electrical current is sent that destroys the brain cells at the tip of the wire.

  • Brain Stimulation:

    • Electrical Stimulation of the Brain (ESB): A milder electrical current that causes neurons to react as if they had received a message.

Brain Methods: Non-Invasive Techniques

  • Transcranial Magnetic Stimulation (TMS): Magnetic pulses applied to cortex using special copper wire coils that are positioned over the head.

  • Transcranial Direct Current Stimulation (tDCS).

Brain Methods: Invasive Techniques

  • Deep Brain Stimulation (DBS): Impulse generator implanted that sends impulses to implanted electrodes, stimulating brain areas of interest.

  • Optogenetics: Involves modifying genes of neurons so they are sensitive to light and then using light devices inserted in the brain to modify brain activity.

Neuroimaging Techniques: Mapping Structure

  • Computed Tomography (CT): Brain-imaging method using computer-controlled X-rays of the brain.

  • Magnetic Resonance Imaging (MRI): Brain-imaging method using radio waves and magnetic fields of the body to produce detailed images of the brain.

  • Diffusion Tensor Imaging (DTI): Uses MRI data to estimate the location and orientation of the brain’s white matter tracts.

Neuroimaging Techniques: Mapping Function

  • Electroencephalogram (EEG): A device that records the electrical activity of cortical neurons using scalp electrodes.

  • Magnetoencephalography (MEG): Detects small magnetic fields generated by the electrical activity of neurons.

  • Positron Emission Tomography (PET): Radioactive sugar is injected into the subject, and a computer compiles a color-coded image of brain activity.

  • Functional MRI (fMRI): Detects changes in the activity of the brain over different time periods.

  • Near-Infrared Spectroscopy (NIRS): Uses infrared light to determine changes in blood oxygen levels in the brain.

Anatomical Directions

  • Sagittal Plane: Divides the body into left and right halves.

  • Coronal Plane: Divides the body into anterior (front) and posterior (back) parts.

  • Horizontal Plane: Divides the body into superior (top) and inferior (bottom) parts.

  • Common terms used for directional localization:

    • Anterior: Toward the front.

    • Posterior: Toward the rear.

    • Superior: Above.

    • Inferior: Below.

    • Medial: Toward the middle or midline.

    • Lateral: Away from the middle or midline.

    • Ventral: Toward the belly.

    • Dorsal: Toward the top of the head (brain) or back (spinal cord).

Parts of the Brain

  • Major Structures of the Human Brain:

    • Basal Ganglia: Involved in the coordination of movement.

    • Amygdala: Regulates emotions such as fear.

    • Cerebellum: Controls balance and organizes muscle activity.

    • Cerebral Cortex: Registers complex thought processes.

    • Corpus Callosum: Connects the left and right hemispheres.

    • Thalamus: Relays sensory signals to the cerebral cortex.

    • Hypothalamus: Regulates body functions such as thirst and aggression.

    • Pituitary Gland: Influences other endocrine glands.

    • Pons: Connects the brain's top and bottom; involved in sleep regulation.

    • Hippocampus: Plays a crucial role in memory formation.

    • Reticular Formation: Involved in arousal and attention.

    • Medulla: Controls involuntary functions like heartbeat and breathing.

Parts of the Human Brain: The Hindbrain

  • Medulla: Responsible for essential life-regulating functions (breathing, swallowing, heart rate).

  • Pons: Connects the brain's upper and lower parts; plays a part in sleep and left-right coordination.

  • Reticular Formation: Responsible for selective attention, filtering background noises.

  • Cerebellum: Coordinates involuntary movements and balance control.

Parts of the Human Brain: The Limbic System

  • Limbic System: Involved in emotion, memory, and motivation.

    • Thalamus: Relays sensory information.

    • Hypothalamus: Governs motivational behaviors such as hunger and thirst.

    • Hippocampus: Facilitates long-term memory formation.

    • Amygdala: Processes feelings of fear and the memory of fear.

    • Cingulate Cortex: Plays roles in cognition and emotion processing.

Parts of the Human Brain: The Cortex

  • Cortex: The outer layer responsible for higher-level reasoning and sensory interpretation.

  • Corticalization: Refers to the wrinkling of the cortex which allows more neurons to fit within the skull.

  • Cerebral Hemispheres: The two halves of the brain.

  • Corpus Callosum: Connective tissue that links the left and right hemispheres.

Lobes and Cortical Areas of the Brain

  • Frontal Lobe:

    • Higher mental processes and decision-making.

    • Motor Cortex: Commands muscle movement.

  • Parietal Lobe:

    • Processing sensory information such as touch and temperature.

    • Somatosensory Cortex: Receives messages from the skin and body.

  • Temporal Lobe:

    • Associated with auditory processing and meaningful speech.

    • Auditory Cortex: Processes sound information.

  • Occipital Lobe:

    • Contains the primary visual cortex that processes visual data.

The Motor and Somatosensory Cortex

  • Represents various body parts in terms of motor and sensory function.

  • Highly detailed representation across their respective cortical areas.

The Association Areas of the Cortex

  • Critical for coordination and interpretation of information, as well as advanced mental processing.

Broca’s Aphasia

  • Characterized by difficulties in speech production while comprehension remains intact.

Wernicke’s Aphasia

  • Condition resulting from damage to Wernicke’s area; leads to issues in understanding or creating meaningful language.

Spatial Neglect

  • Condition resulted from damage to the right hemisphere’s association areas; inability to recognize objects in the left visual field.

The Cerebral Hemispheres

  • Cerebrum: Comprises the upper brain including left and right hemispheres.

  • Split-Brain Research: Involves examination of patients with a severed corpus callosum, leading to unique information processing and specialization.

The Cerebral Hemispheres Specialization

  • Left Hemisphere:

    • Controls language, logical thought, analysis, and mathematics.

  • Right Hemisphere:

    • Governs emotional expression, spatial perception, and pattern recognition.

Structure of the Nervous System

  • Nervous System:

    • Central Nervous System (CNS): Comprising the brain and spinal cord, interprets messages and coordinates responses.

    • Peripheral Nervous System (PNS): Transmits information to and from the CNS; consists of somatic and autonomic nervous systems.

Peripheral Nervous System (PNS)

  • Somatic Nervous System: Controls voluntary movements and carries sensory information.

  • Autonomic Nervous System (ANS): Regulates involuntary functions (e.g., heart rate, digestion).

    • Sympathetic Division: Activates the body in stress-related situations.

    • Parasympathetic Division: Oversees rest and digest processes.

The Central Nervous System (CNS)

  • Central part of the nervous system encompassing the brain and spinal cord; responsible for fast reflexes and information processing.

The Spinal Cord Reflex

  • Sensory (Afferent) Neuron: Carries information from senses to the CNS.

  • Motor (Efferent) Neuron: Sends information from the CNS to muscles.

  • Interneuron: Connects afferent neurons to efferent neurons in reflex actions.

  • Reflex Arc: The pathway that the reflex takes from sensory input to motor response.

The Peripheral Nervous System (PNS)

  • Encompasses all nerves outside of the CNS; facilitates communication within the body.

  • Characteristics: Comprises somatic and autonomic nervous systems, crucial for sensory and motor functions.

Functions of the PNS and SNS

  • Parasympathetic Division:

    • Enhances salivation, constricts bronchi, slows heart rate, and promotes digestion.

  • Sympathetic Division:

    • Increases heart rate, dilates bronchi, reduces salivation, and prepares the body for action.

The Endocrine System

  • Endocrine Glands: Secrete hormones into the bloodstream; affect bodily functions and behaviors.

  • Hormones: Chemical messengers influencing emotions and physical responses.

The Master Gland: The Pituitary

  • Pituitary Gland: Known as the master gland; regulates other endocrine glands and releases critical hormones such as oxytocin (involved in reproductive behaviors) and vasopressin (regulates water levels).

Other Endocrine Glands

  • Pineal Gland: Produces melatonin which regulates sleep patterns.

  • Thyroid Gland: Controls metabolism.

  • Pancreas: Regulates blood sugar levels by secreting insulin.

  • Gonads:

    • Ovaries: Female gonads regulating female reproductive hormones.

    • Testes: Male gonads regulating male reproductive hormones.

  • Adrenal Glands: Secrete hormones to manage stress and regulate bodily functions during adolescent developmental changes.