Chapter 3 - The Biological Component PDF

Chapter 3 The Biological Component Dr. Kimberley Campbell  Chapter Outline Neurons Electrical signal transmission Chemical signal transmission The Nervous System Central nervous system Peripheral nervous system The Endocrine System Hemispheric Lateraliz...

Chapter 3 The Biological Component Dr. Kimberley Campbell  Chapter Outline Neurons Electrical signal transmission Chemical signal transmission The Nervous System Central nervous system Peripheral nervous system The Endocrine System Hemispheric Lateralization  Neurons Communication at the Cellular Level  What Are Neurons? Neurons: cells that convey sensory information from the body into the brain, carry out operations within our central nervous system, and transmit commands from the brain to the body Part of our nervous system Basic structures of behaviour  Types of Neurons Motor neuron: carries commands to the muscles and organs Sensory neurons: Carry information from the body and outside world into brain and spinal cord Interneurons: neurons which connect one neuron to another in the same part of brain or spinal cord Cell Membrane Energy and the Cell Membrane Polarization: a state in which there is a difference in electrical charge between the inside and outside of the neuron Voltage: measure of the difference in electrical charge between two points Resting potential: difference in charge between inside & outside of membrane of a neuron at rest Energy and the Cell Membrane Ions: atoms that have lost or gained electrons Positive: Na+, K+ Negative: Cl-, A-  What Moves the Ions? Force of diffusion: tendency of ions to move through membrane to less concentrated side K+ K+ K+ K+ K+  What Moves the Ions? Electrostatic pressure: force where ions are repelled from similarly charged, attracted to oppositely charged K+ Cl- K+ Cl- K+ Cl- K+ Cl-  What Moves the Ions? Sodium potassium pump: large protein molecules that move sodium ions through cell membrane to outside, potassium ions back inside  Ion Channels Ion channels: gated pores in the membrane formed by proteins; limit the flow of ions into and out of the cell Can be chemically gated or electrically gated Chemically: neurotransmitters or hormones Electrically: change in electrical potential of the membrane  Depolarization Local potential: partial depolarization Polarity in an area shifts toward zero when disturbed Local potential is a graded potential Varies in magnitude with the strength of the stimulus that produced it  Depolarization If local potential exceeds the threshold for activating electrically gated channels, then an action potential occurs  Depolarization Action potential: abrupt depolarization of membrane that allows neuron to communicate  Depolarization Action potential: abrupt depolarization of membrane that allows neuron to communicate Action potential is ungraded All-or-none law: occurs at full strength or it does not occur at all Action potential is nondecremental Travels down the axon without any decrease in size Propagated at each successive point along the way Nerve Impulse  Hyperpolarization Increase in electrical charge across a membrane (more negative) Usually due to the inward flow of chloride ions or outward flow of potassium ions  Refractory Periods Absolute refractory period: sodium ion channels are unresponsive to further stimulation A new action potential cannot occur Relative refractory period: sodium ion channels could support another action potential, but potassium channels are still open A new action potential can occur, if the stimulation is sufficiently strong enough to overcome the charge  Rate Law Rate law: axon encodes stimulus intensity not in the size of its action potential but in its firing rate  Myelin Sheath Fatty, insulating layer that wraps around the axon Speeds transmission by forcing signals to “jump” ahead to nodes of Ranvier Made up of glial cells Schwann cells in peripheral nervous system One bundle per cell Oligodendrocytes in the central nervous system Multiple bundles per cell Glial Cells  Glial Cells Make up the myelin sheath Break down dead neurons Bring in nutrients for neurons Provide physical support to keep neurons in place and form scaffolding for development  The Synapse End of axon terminals are terminal buttons Vesicles are bubbles containing neurotransmitters Synapse is fluid-filled space between neurons  Neurotransmitters Chemical substances that carry messages across the synapse to either excite other neurons, or inhibit their firing Excitation vs. Inhibition Neurotransmitters and Receptors  Drugs and Receptors Agonist – drug increases activity at receptor Antagonist – drug decreases activity at receptor  Drugs and Receptors Agonist – drug increases activity at receptor Antagonist – drug decreases activity at receptor Direct – drug binds at same site Indirect – drug binds at different site Drugs and Receptors Pre and Postsynaptic Potential Voltage change at receptor site – postsynaptic potential (PSP) Not all-or-none Changes the probability of the postsynaptic neuron firing Positive voltage shift – excitatory PSP Negative voltage shift – inhibitory PSP 44  Excitation and Inhibition Excitatory postsynaptic potential (EPSP): when receptors open sodium channels to produce a partial depolarization of the dendrites and cell body Inhibitory postsynaptic potential (IPSP): when receptors open potassium channels, chloride channels, or both to produce a hyperpolarization of the dendrites and cell body  Postsynaptic Integration Spatial summation: combines potentials occurring simultaneously at different locations on the dendrites and cell body Temporal summation: combines potentials arriving a short time apart, from either the same or separate inputs Temporal Summation Spatial Summation Postsynaptic Integration The Nervous System  Directional Terms Dorsal: toward the back Ventral: toward the stomach Anterior: toward the front Posterior: toward the rear Superior: above another structure Inferior: below another structure Lateral: toward the side Medial: toward the middle  Important Terminology An important note: nerve ≠ neuron Neuron: a single neural cell Nerve: a bundle of axons running together Term only used in the peripheral nervous system Tract: a bundle of axons running together in the CNS Organization of the Nervous System Organization of the Nervous System Peripheral nervous system – nerves that lie outside the central nervous system Somatic nervous system – voluntary muscles and sensory receptors Autonomic nervous system (ANS) – controls automatic, involuntary functions Sympathetic – Go (fight-or-flight) Parasympathetic – Stop Organization of the Nervous System Organization of the Nervous System Central nervous system (CNS) – brain and spinal cord Afferent = toward the CNS Efferent = away from the CNS  Early History of Brain Studies Invention of the microscope allowed scientists to separate out individual neurons by hand (1800s) Staining techniques allowed scientists to visualize neurons in preserved tissues Improved understanding of structures, but what about functions? Early 1900s – started to see reliable methods of recording electrical activity in the brain  Damage Studies & Lesioning Damaging areas to alleviate symptoms e.g., epilepsy e.g., prefrontal lobotomy disconnect frontal lobe and thalamus side-effects Lesion studies What happens when this part is damaged? Transcranial Magnetic Stimulation (TMS) A technique that allows scientists to enhance or depress activity in specific parts of the brain Metal coil produces a magnetic field that can penetrate up to 2 cm into the brain Pulse timing and duration can be modified to increase firing or decrease firing Also used as a treatment technique Transcranial Magnetic Stimulation (TMS) Computerized Tomography (CT or CAT) Produces computer-enhanced X-ray of the brain Builds 2D picture of the brain based on differential absorption of X-rays Tissue density affects absorption Control which axis we take images on Can stitch multiple images together Reveals gross features of the brain Does not resolve brain structure well Computerized Tomography (CT or CAT) Magnetic Resonance Imaging (MRI) Uses strong magnetic field to align certain molecules, then a quick and strong burst of radio waves to disrupt alignment Measure energy released when the molecules snap back into alignment with magnetic fields Different molecules release different levels of energy Allows us to resolve soft tissues much better than CAT scans Magnetic Resonance Imaging (MRI)  Functional Magnetic Resonance Imaging (fMRI) Detects changes in blood oxygenation, blood flow Tied to neural activity High activity = high oxygen use and high blood flow Specifically, hemoglobin Need to consider background activity Better spatial and temporal resolution than a PET scan  Diffusion Tensor Imaging (DTI) Builds a picture of water movement (diffusion) in the brain using an MRI scanner Observe blood flow along specific neural tracts Measure rate and direction High spatial resolution and directionality Helps us understand connectivity Positron Emission Tomography (PET) Tracks levels of a harmless radioactive material that is injected into the subject’s bloodstream Higher activity in brain areas = more blood flow, higher concentration of the radioisotope Similar logic to fMRI Positron Emission Tomography (PET) Near Infrared Spectroscopy (NIRS) Measures changes in blood oxygenation Shines near IR light through the skull Detects attenuation of reemerging light Indirect measure of brain activity Electroencephalography (EEG) Measures electrical activity via electrodes Can be Inter- or Intra-cranial Electrodes either on or in the skull Very good time resolution Milliseconds Electroencephalography (EEG) Organization of the Nervous System  The Spinal Cord Nerve bundles in spinal cord carry information to and from brain Nerves in each section connect with different areas in body  The Spinal Cord Back Dorsal horn contains afferent endings (axons) of sensory nerves Ventral horn contains cell bodies (and dendrites) of efferent nerves Both connected by interneurons (aka relay neurons) Front Organization of the Nervous System The Brain  The Brain Hindbrain Vital functions and coordinating movements Midbrain Reflex actions and voluntary movements Forebrain Highly developed, numerous functions  The Hindbrain Regulation of basic life functions Connects peripheral and central nervous system  The Medulla Controls heart activity and circulation Regulates breathing Involved in coordinating swallowing and digestion All sensory and motor nerve tracts ascend from the spinal cord and descend from the brain  Pons Relay station for signals between higher levels of the nervous system and lower levels Coordinates with the cerebellum and rest of the brain Connects to muscles and glands in face and neck  Cerebellum Controls bodily coordination, balance, and muscle tone Active in fine motor control and smoothing out movements Helps with sequences of actions Involved in procedural memory Memory of motor skills The Brain Organization of the Nervous System  The Midbrain Reticular formation Superior and inferior colliculi Red nucleus Substantia nigra Tectum vs tegmentum  Reticular Formation Helps to regulate awareness and attention Filter out irrelevant stimuli Regulates sleep and wakefulness Aka arousal Coordinates several brain areas Organization of the Nervous System  The Forebrain Basal ganglia Limbic system Thalamus Hypothalamus Cerebral cortex  Basal Ganglia Controls voluntary and involuntary movement Principal structures: Caudate nucleus Putamen Globus pallidus  Limbic System Principal structures: Amygdala Hippocampus Cingulate cortex Limbic system regulates: Emotional and sexual behaviors Memory Spatial navigation The Limbic System  The Limbic System Amygdala - increases electrical activity in its neurons when we are under threat Fight or flight response Remember events tied to strong emotions Receives sensory input to determine emotional value/intensity of a stimulus  The Limbic System Hippocampus - activated when we form memories Assists the process of memory formation Cingulate gyrus - helps focus our attention and thoughts on things that are unpleasant to us Physical and emotional pain  Thalamus Relays incoming sensory information through groups of neurons that project to the appropriate region in the cortex Also actively filters incoming sensory information  Hypothalamus Regulates the autonomic and endocrine systems Involved in hunger responses, sexual behavior, temperature control, and aggression Homeostasis  Geography of the Brain Cerebral Cortex: outer layer of frontal lobe Cerebral hemispheres: large, wrinkled structures dominating brain’s appearance The dorsal or superior part of the brain and that are covered by the cortex  Surface Features Cortex: outer surface of brain; literally, “bark” Mostly made up of the cell bodies of neurons Gyrus: each ridge in surface of the brain Plural = gyri Sulcus: groove or space between two gyri Plural = sulci Fissure: large groove or space between two gyri  Interior Features Lateral ventricles: winged-shaped cavities Filled with cerebrospinal fluid (CSF) made by a network of interconnected blood vessels CSF: suspends the brain, acts as shock absorber Provides stable environment for optimal function  Hemispheric Divisions Each hemisphere is divided into four lobes: Frontal (executive function) Parietal (sensory integration) Temporal (auditory, taste, smell, memory) Occipital (visual) The Brain  Temporal Lobes Temporal lobes: Regions containing the auditory projection area, visual and auditory association areas, an additional language area, and structures important in learning and memory Inferior temporal cortex: plays major role in visual identification of objects  Other Interesting Concepts Aphasia Difficulty processing or producing language Mirror neurons Our actions and the actions of others Plasticity Making new connections Adapting after damage The Endocrine System  The Endocrine System A series of glands throughout the body that release hormones Hormones: chemical messengers in the bloodstream Serves as a secondary control system Feedback to the NS  Endocrine Glands Pituitary: “the director,” growth hormone Thyroid: metabolic rate Adrenal: salt and carbohydrate metabolism Pancreas: sugar metabolism Gonads: sex hormones CNS Endocrine Control Centers Hypothalamus: secretes hormones and controls the pituitary gland via direct nerve stimulation and chemicals Pineal Gland: secretes melatonin to regulate sleep cycles Pituitary Gland: secretes hormones that affect sexual behavior, reproduction, circulatory function, hunger, and responses to aggression  The HPA Axis and Stress Hypothalamic-Pituitary- Adrenal (HPA) Axis Activated in time of stress How the brain affects the immune system Hemispheric Lateralization And Split Brain Patients  Hemispheric Lateralization Handedness Footedness Ocular dominance Aural dominance  Hemispheric Lateralization Right Hemisphere: feelings, intuition, humour aesthetic, colour relationships, rhythm, physical senses, motor skills the left side of the body  Hemispheric Lateralization Left Hemisphere: analytical thinking, rules, logic structure, mathematics, planning speech, language, time the right side of the body Corpus Callosum Visual Lateralization Left visual field – processed in right hemisphere of brain Right visual field – processed in left hemisphere of brain  Split Brain Video https://www.youtube.com/watch?v=ZMLzP1VCANo