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Chapter 48: Nervous System

Chapter 48: Nervous System. 2.e.2 – Timing and coordination of physiological events are regulated by multiple mechanisms (11.1). 3.b.2 – A variety of intercellular and intracellular signal transmissions mediate gene expression (11.1 & 11.4).

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Chapter 48: Nervous System

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  1. Chapter 48: Nervous System

  2. 2.e.2 – Timing and coordination of physiological events are regulated by multiple mechanisms (11.1). 3.b.2 – A variety of intercellular and intracellular signal transmissions mediate gene expression (11.1 & 11.4). 3.d.1 – Cell communication processes share common features that reflect a shared evolutionary history (11.2 & 11.2). 3.d.2 – Cells communicate with each other through direct contact with other cells or from a distance via chemical signaling (11.1 & 11.2). Essential Knowledge

  3. 3.d.3 – Signal transduction pathways link signal reception with cellular response (11.3). 3.d.4 – Changes in signal transduction pathways can alter cellular response (11.4). Essential knowledge

  4. Two types of cells: • Glia (supporting) • Neurons • Nervous system is comprised of two parts: • Central (spinal cord, brain) • Peripheral (outlying nerves) • Nervous system is a system of circuits of neurons and supporting cells that work together to communicate with rest of the body Introduction

  5. Cnidarians: • Ex: hydra • Nerve net (simplistic concentration of nerves) • Echinoderms: • Ex: Seastar • Radial nerves and central nerve ring • Flatworms: • Cephalization (concentration of nervous system in anterior/head region) • Central nervous system: simple brain with 2 nerve cords Diversity of Nervous Systems

  6. Annelids/Arthropods: • Ex: insects, crayfish • Cephalization with complicated brain with ventral nerve cord • Also contain clusters of neurons called ganglia • Vertebrates: • Brain, dorsal spinal cord make up CNS • Nerves and ganglia make up PNS Diversity of Nervous Systems

  7. High degree of cephalization in vertebrates Spinal cord: integrates simple responses to stimuli and transports info to and from brain Cerebrospinal fluid: fluid cushions brain and carries out circulatory functions White matter: Axon in bundles (named for color of their myelin sheaths) Gray matter: Neuron cell bodies, dendrites, and unmyelinated axons Nervous System Organization

  8. Cell body: • Contains nucleus and organelles • Extensions: • Dendrites: received signals from other neurons, highly branched • Axon: transmits signals to other cells, longer • Contains terminal branches called synaptic terminals which release neurotransmitters (relay of signals across synapse) • Myelin sheath: • Many axons wrapped in this insulating layer Neuron Structure

  9. Neurons communicate with other cells at synapses • Electrical synapses: allow electrical current to flow directly from cell to cell (via gap junctions) • Chemical synapses: involves release of neurotransmitters Neuron Communication

  10. Very numerous • Give structural integrity and physiological support to nervous system • Astrocytes: • in CNS, facilitate info transfer at synapse (learning/memory), induce formation of blood-brain barrier, can act as stem cells • Radial glia: • Guide embryonic growth of neurons, act as stem cells • Oligodendrocytes (CNS) and Schwann cells (PNS): • Insulate axons in mylein sheath by wrapping around them Supporting Cells (Glia)

  11. Three steps: • 1) Sensory input • Detection of external stimuli or internal conditions • Sensory neurons transmit this info to CNS • 2) Integration • Completed by interneurons • Send output through motor neurons to effector cells (muscle and endocrine cells) • 3) Motor output • Response to signal/output • Ex: reflex, hormone production and secretion Processing Information

  12. Membrane potential: • Electrical potential difference • Exists across the plasma membrane of all cells • Dependent upon concentration of certain ions on either side of the cell membrane • Outside cell: Na+ and Cl- • Inside cell: K+ and a number of negatively charged amino acids and other molecules • Sodium-potassium pumps maintain the concentration gradient/difference Membrane Potential

  13. In addition to the ungated K+ and Na+ ion channels, neurons also have gated ion channels • Open and closed in response to stimuli • Stretch-gated ion channels: found in stretch sensors, open in response to mechanical stimuli • Ligand/Chemically-gated ion channels: found in synapses, respond to chemical stimuli • Voltage-gated ion channels: found in axons, respond to change in membrane potential Gated Ion Channels

  14. Resting potential: • Nontransmitting neuron • Ions continually diffuse (without energy use) through channels down their concentration gradient until balanced • Equilibrium potential: • The membrane voltage when the concentrations are balanced • Neurons at rest have more K+ channels open than Na+ Resting Potential

  15. Action potential: when a neuron is transmitting a signal due to the reception of a stimuli • Stimuli that open/close gated ion channels may increase or decrease membrane potential • Graded potential: the stronger the stimuli = more channels opens (and vice versa) • Hyperpolarization: the result of a stimuli that OPENS K+ channels (K+ flows OUT and membrane potential shifts) • Depolarization: the result of a stimuli that OPENS Na+ channels (Na+ flows OUT and membrane potential shifts) Action Potential

  16. Once depolarization reaches a certain membrane potential (called the threshold) an action potential is triggered • Stronger stimuli = higher frequency of action potentials • Involves BOTH Na+ and K+ ion channels • Na+ channels open quickly in response to depolarization • K+ channels open more slowly Action Potential

  17. Sequence of events: • 1) Stimulus depolarizes membrane to threshold • 2) Na+ gates open causing influx of Na+ (causing further depolarization) • 3) More Na+ activation gates open, causing membrane potential to be shifted towards Na+ concentration (rising phase) • 4) Falling phase: when Na+ inactivation gates close and K+ activation gates open (bring membrane potential towards K+ concentration) • 5) Undershoot: membrane’s permeability towards K+ is higher (than at rest), continual OUTFLOW of K+ temporarily hyperpolarizes membrane Action Potential

  18. Carries information to and from the CNS • Regulates movement and homeostasis • Made of: • Paired cranial nerves and spinal nerves • Associated ganglia • Contains BOTH sensory and motor neurons • Two parts: • 1) Somatic nervous system • Carries signals to and from skeletal muscles • 2) Autonomic nervous system • Maintains internal environment (by controlling smooth/cardiac muscles) Peripheral Nervous System

  19. Autonomic NS (three divisions): • 1) Sympathetic division • Accelerates heart and metabolic rate • Generates energy • 2) Parasympathetic division • Carries signals for self-maintenance activities (digestion and slow heart rate) • Conserves energy • 3) Enteric division • Networks of neurons that control secretions of digestive tract, pancreas, gallbladder • Control contractions of smooth muscles (peristalsis) Peripheral Nervous System

  20. Embryonic development • Forms three portions (midbrain, hindbrain, forebrain) – called cephalons • As fetus develops, these three portions specialized further into 5 regions • Forebrain: becomes cerebrum (outer portion of which becomes cerebral cortex) • Cerebral cortex: extends out and around brain • Mid/Hindbrain: become brainstem, cerebellum • Brainstem: consists of midbrain, pons, medulla oblongata Brain

  21. Controls (in part): • Attention span • Alertness • Appetite • Motivation • Homeostasis • Medulla oblongata (medulla): • Control center for homestatic functions (breathing, swallowing, heart and blood vessel action, digestion) • Pons: • Functions w/ medulla in above activities • Conducts information between the rest of the brain and spinal cord • Midbrain: • Receives and integrates sensory information Brainstem

  22. Controls learning, remembering motor skills, coordination, error-checking (during perception, cognitive functions) Integrates information from auditory and visual systems together with input from joints and muscles Provides automatic coordination of movement and balance Cerebellum

  23. Includes: • Epithalamus • Includes pineal gland and choroid plexus • Clusters of capillaries produces cerebrospinal fluid • Thalamus • Major input and sorting center for sensory information • Major output center for motor information from cerebrum • Receives input from cerebrum and other brain parts to regulate emotion and arousal • Hypothalamus • Major brain region for homeostatic regulation • Produces posterior pituitary hormones and releases hormones that control anterior pituitary • Contains regulating centers for survival functions and sexual/mating behaviors, alarm response and pleasure Diencephalon

  24. Functions: • Determines Intelligence • Personality • Interpretation of Sensory Impulses • Motor Function • Planning and Organization • Touch Sensation • Divided into right and left hemispheres • Communicate to each other via the corpus callosum (thick band of axons) • Each hemisphere: • Covered with gray matter (called cerebral cortex) • Contains inner white matter (that includes group of neurons important to planning and learning movements) Cerebrum

  25. Largest and most complex part of mammalian brain • Divided into lobes: • Frontal Lobe- associated with reasoning, planning, parts of speech, movement, emotions, and problem solving • Parietal Lobe- associated with movement, orientation, recognition, perception of stimuli • Occipital Lobe- associated with visual processing • Temporal Lobe- associated with perception and recognition of auditory stimuli, memory, and speech Cerebrum

  26. Schizophrenia: • Characterized by psychotic episodes involving hallucinations and delusions • Both genetic and environmental components • Treatments: focus on drugs that blocking dopamine receptors • Bipolar disorder: • Involves swings of mood from high to low • Includes major depression (a persistent low mood) • Both bipolar and depression have genetic and environmental components CNS Injuries and Diseases

  27. Alzheimer’s disease: • Dementia characterized by confusion, memory loss, personality changes • Age-related (more frequency with higher age) • Progressive disease • Involves death of neurons in large areas of the brain CNS Injuries and Diseases

  28. Parkinson’s Disease: • Progressive, age-related motor disorder • Characterized by difficulty in movements, rigidity, muscle tremors • Death of neurons lead to motor issues (from the accumulation of a particular protein) CNS Injuries and Diseases

  29. The types of nervous systems, development of the human nervous system, details of the various structures and features of the brain parts, and details of specific neurologic processes are beyond the scope of the course and the AP Exam. Exclusion statements

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