Introduction BI 212 BI 213 BI 211 Ecosystems Organs / organ systems Cells Organelles Communities Tissues Molecules Populations Organisms Campbell et al. Figure 1.4 Introduction What is Anatomy and Physiology? Anatomy: Study of internal / external structure and the physical relationships between body parts Microscopic Anatomy (requires magnification ) Cytology = Study of cells Histology = Study of tissues Gross Anatomy (visible to naked eye ) Regional Anatomy = Study of structures in particular region (e.g., limb) Systemic Anatomy = Study of organ systems Physiology: Study of how living organisms perform vital functions Physical / chemical factors Cell physiology Special physiology System physiology The two disciplines are interrelated (structure dictates function...) Introduction 1) Cellular level Molecular interactions 2) Tissue level Similar cells specific function 3) Organ level 2 tissues specific function 5) Organism level Organ systems = life 4) Organ system level 2 organs specific function 1
Feedback Introduction Primary Tissue Types: Campbell et al. Figure 40.5 Introduction Regulatory System Function: For life to continue, precise internal body conditions must be maintained regardless of external conditions The principle function of regulatory systems is to maintain Homeostasis Homeostasis: The process of maintaining a relatively stable internal environment (Bernard 19 th century) Not a static process (dynamic equilibrium) Requires energy (unlike a true equilibrium state) Conditions maintained via feedback systems Introduction Feedback System: Information Input (Set Point) Control Center Nervous System Endocrine System Receptor (transducer) Output Effector (Change in system) Effect Negative Feedback: Drives system toward set point Positive Feedback: Drives system away from set point 2
Chapter 48 / 49: Fundamentals of the Nervous System Histology: Neurons Specialized excitable cells Allow for communication throughout body (via electrical impulses) Neuron Anatomy: Glial cells: Support cells that nourish, insulate, and protect neurons 1) Dendrites: Receive information (environment / other neurons) 2) Cell body (soma): Integrates information / initiate response 3) Axon: Conducts action potential (AP electrical impulse) 4) Synaptic terminals: Transmit signal (other neurons / effector organs) Axon hillock (AP generation) Dendrites Axon Synaptic terminals Centrioles (Can not divide) Cell body Histology: Neurons Specialized excitable cells Allow for communication throughout body (via electrical impulses) Neural Processes: AP Action potentials never travel retrograde AP Anterograde AP Dendrites AP Retrograde 3
Histology: Neurons Specialized excitable cells Allow for communication throughout body (via electrical impulses) Neural Processes: Synapse Neurotransmitter: Chemicals released by one neuron that affect the activity of a second neuron Campbell et al. Figure 48.4 Information Processing: Monitor internal / external environment Control Center (interneurons) (sensory neurons) Issue commands (maintain homeostasis) (motor neurons) Campbell et al. Figure 48.3 4
Organization of Nervous Systems: Nerve Net Nerves Cephalization Cephalization: Clustering of sensory neurons / interneurons at anterior end Central Nervous System Peripheral Nervous System Campbell et al. Figure 49.2 Neurons are highly irritable If adequately stimulated, an electrical impulse (action potential) is conducted along the axon... Setting the Stage... Amplifier Electrode At rest, the inside of a neuron is (-) compared to the outside () (Polarized) Oscilloscope Resting Membrane Potential WHY? 5
Resting Membrane Potential: Membrane Proteins: (Passive) K Channel (Passive) Na Channel (Active) Na /K Pump K Na Anion (Cl - or Protein) Ions Resting Membrane Potential: >> Na outside In the beginning... Charge equal across membrane >> K inside Resting Membrane Potential: Equilibrium Potential (Nernst / Goldman equation) () - - 3 Na ATP Leaky 2 K Net effect: More () ions move out than in (neg. charge develops inside cell) 6
Neurons use changes in membrane potential to communicate: Stimulus opens ion gates: 1) Open Na gates 2) Open K gates Na K 70 mv 0 mv Depolarization 70 mv 0 mv Hyperpolarization Inside becomes less negative Inside becomes more negative Neurons use two primary types of signals to communicate: 1) Graded Potentials (Short-range communication) Local changes in membrane potential (limited range) Na Magnitude of potential depends on stimulus strength 70 mv 0 mv (e.g., brief opening of gate) Weak stimulus 70 mv 0 mv (e.g., prolonged opening of gate) Strong stimulus Magnitude of potential decreases with distance from source 7
Neurons use two primary types of signals to communicate: 1) Graded Potentials (Short-range communication) Graded potentials initiate action potentials Axon Hillock Types of Signals used by Neurons: 2) Action Potentials (Long-range communication) Short-lived, self-propagating depolarization event Occurs only along axon of neuron (or muscle sarcolemma) Cell interior goes from (-) to () Magnitude of signal independent of signal strength (all-or-none principle) Types of Signals used by Neurons: 2) Action Potentials (Long-range communication) Action Potential Events: Na 30 mv 0 mv Threshold 1) Graded potential (depolarization) reaches axon hillock 2) Event reaches threshold; Na gates open (voltage-gated) Positive feedback cycle (all-nor-none event) 3) Membrane reverses polarity; Na gates close (~ 30 mv) 8
Types of Signals used by Neurons: 2) Action Potentials (Long-range communication) Action Potential Events: 30 mv 0 mv Threshold 3 Na K 2 K 4) K gates open (voltage gated); cell repolarizes 5) Cell returns to resting membrane potential Na / K pumps re-establish solute concentrations Refractory Period: Cell can not fire additional APs... Needs to recharge Max APs ~ 750 / sec Tetrototoxin (TTX) How does an action potential move down an axon? 1) Continuous Conduction (unmyelinated axons) Chain-reaction along membrane of axon (slow 10 m/s) Campbell et al. Figure 48.11 9
How does an action potential move down an axon? 2) Saltatory Conduction (myelinated axons) Protects / electrically insulates neurons from one another Increases speed of impulse transmission (1 m/s vs. 150 m/s) Nodes of Ranvier Schwann Cells Action potential jumps from node to node Demyelination: Loss of myelination Multiple Sclerosis Campbell et al. Figure 48.13 Coding for Stimulus Intensity: Remember: Magnitude of action potential is independent of signal strength (signal fixed all-or-none) However: Rate is not fixed AP frequency = stimulus (the stronger the stimulus, the more AP s per second) How Do Neurons Communicate Together? Synapse: Functional point of contact between two neurons or between a neuron and an effector cell Electrical Synapse: Gap junctions connect cells allowing for direct transfer of ions Chemical Synapse: Neuotransmitters (chemicals) mediate signal transfer (unidirectional ) 10
Events at a Chemical Synapse: Synaptic vesicles (neurotransmitter) (30 50 nm) Synaptic cleft Receptor proteins Presynaptic cell Postsynaptic cell (e.g., dendrite) Events at a Chemical Synapse: 1) Action potential arrives at synaptic terminal 2) Ca voltage gates open; Ca enters cell 3) Synaptic vesicles fuse with plasma membrane Ca Presynaptic cell Ca Postsynaptic cell (e.g., dendrite) Events at a Chemical Synapse: 1) Action potential arrives at synaptic terminal 2) Ca voltage gates open; Ca enters cell 3) Synaptic vesicles fuse with plasma membrane Ca 3) Neurotransmitter released into synaptic cleft (exocytosis) 4) Neurotransmitter binds with postsynaptic receptors 5) Neurotransmitter removal Enzyme degradation Presynaptic cell reuptake Diffusion from cleft Presynaptic cell Ca Depolarization event (excitatory) Hyperpolarization event (inhibitory) Postsynaptic cell (e.g., dendrite) 11
Neuron activity depends on a balance of excitatory and inhibitory input: EPSP (Excitatory Postsynaptic Potential) A single EPSP cannot induce an action potential EPSPs add together (summate) to trigger postsynaptic cell Marieb & Hoehn Figure 11.18 Types of Summation: Spatial Summation: Simultaneous stimulation from separate synapses Temporal Summation: Repeated stimulation from a single synapse Neuron activity depends on a balance of excitatory and inhibitory input: IPSP (Inhibitory Postsynaptic Potential) - Cell bodies / dendrites may have > 10,000 connections 12
At present, ~100 neurotransmitters identified (1) (2) Feel Good Effects (3) (4) (5) (natural opiates) 13