A&P Chapter 12 - Lecture notes 10 PDF

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Biol 2401 with Prof. Vasefi...

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Endocrine System: slow, prolonged response, hormones Functions of Nervous System: communicates w/t & regulates other body systems for homeostasis  works in conjunction w/t endocrine system  also involved in perception, memory, emotion, voluntary movement, behavior Nervous System: rapid brief response, action potentials & neurotransmitters  complex structure: brain, 12 pairs of cranial nerves, spinal cord, 31 pairs of spinal nerves, o ganglion, enteric plexuses, sensory receptors 3 Components of Nervous System: 1. sensory: detect internal & external stimuli o sensory info carried to brain & spinal cord via sensory neurons 2. integrative: processes sensory info (analysis, integration & storage (memory)) o association neurons (interneurons) 3.

motor: respond appropriately to sensory info o response info carried to effector (muscles & glands) via motor neurons 2 Major Parts of Nervous System: 1. Central NS: brain & spinal cord 2. Peripheral NS: cranial & spinal nerves & branches, ganglion & sensory receptors, A. Somatic Nervous System:  sensory neurons from sensory organs, body wall, limbs, etc.  motor neurons lead to skeletal muscle = voluntary control B. Autonomic Nervous System:  sensory neurons from visceral organs, 2 major parts: a. parasympathetic: generally inhibitory, rest & digest activities b. sympathetic: generally excitatory, fight/flight response  most effectors receive neurons for both activities  motor neurons lead to smooth, cardiac muscle & glands = involuntary control Functional divisions of Peripheral Nervous System: 1. Afferent  Brings sensory info to the CNS through receptors  Receptors: sensory structures that detect changes 2. Efferent  Carries motor commands from the CNS to muscle & gland  Effectors: target organs that carry commands from CNS A. Somatic Nervous System o Controls skeletal muscle contractions o Voluntary & involuntary actions B. Automatic Nervous System o Visceral motor system, automatically regulates smooth muscle, cardiac, & glandular secretion Neurons: electrically excitable, nervous tissue part, A. cell body: nucleus, cytoplasm, typical organelles

B. C. D.

E.

o Perikaryon: contains organelles that provide energy and synthesize organic materials dendrites: multiple nerve fibers, short & branched o input section, gets signal from axon of other cell axon: single nerve fiber, long & branched only at end o output section of neuron, delivers signal to other cell or telodendria Synapse o Communication between neuron and the target cell o Postsynaptic cell: neuron o Postsynaptic cell: target o Synaptic cleft: space between two cells o Postsynaptic membrane: receptors for the neurotransmitter o Axoplasmic Transport  Anterograde: flow from cell body to axon terminal by kinesia  Retrogade: axon terminals toward cell body by dynein telodendria: end in synaptic terminals, neurotransmitters stored in synaptic vessels

Classification of Neuron A. Structural Classification 1. Anaxonic Neurons o Small and numerous dendrites, with no axon o Located in the brain and special sense organs 2. Bipolar Neurons o One dendrite that branches extensively into dendrite branches at its distal tip, and one axon with the cell body between the two 3. Unipolar Neurons o Dendrite & axon are continuous(fused) & cell body lie off to the side 4. Multipolar Neurons o Two or more dendrites and a single axon B. Functional Classification 1. Sensory (Afferent) o Deliver info from sensory receptors to CNS o Somatic sensory neurons: monitor outside world and our position in it o Visceral sensory neurons: monitor internal conditions o 3 Categories a. Interoceptors: monitor internal systems;  Provide sensations of distension (stretch) b. Exteroceptors: provide info about enviornment c. Proprioceptors: monitor position & movement of skeletal and joints 2. Motor Neurons (Efferent) o Carry instructions from the CNS to peripheral effectors 3. Interneurons

4 Types of Neuroglia in CNS: support, nourish & protect neurons, part of nervous tissue  astrocytes: support neurons, maintain appropriate chemical environment around neurons o maintain blood-brain barrier: extensions wrap around blood vessels o extensions of astrocyte wrap around blood vessels  oligodendrocyte: produces & maintains myelin sheath around CNS axons  microglia: phagocytize microbes & damaged neurons’ tissue  ependymal cell: line ventricles of brain & spinal cord, make cerebrospinal fluid 2 Types of Neuroglia in PNS:  satellite cells: surround cell bodies of neurons in PNS ganglia, support & exchange materials  Schwann cells: encircle axons of neurons in PNS, produce myelin sheath Myelin Sheath:  made of lipids & proteins  electrically insulates axon (produces generation of action potential) 2 Types of Tissues in CNS:  white matter: made of myelinated axons  gray matter: has neural cell bodies, dendrites, unmyelinated axons, a.terminals & neuroglia Axons of neurons often bundled together, forming nerves & tracks Nerves: bundles of axons, in PNS Tracks: bundles of axons, in CNS Resting Membrane Potential of Neurons:  happens b/c of unequal concentration of cations across plasma membrane o slight positive charge outside & slight negative charge inside  

separation of pos./neg. electrical charges = form of potential energy typical resting potential for neurons: -70 mV, negative sign means negative inside o neurons are polarized

exists b/c of high concentration of Na+ outside cell o Na+/K+ pumps in plasma membrane actively transport Na+ outside cell -few Na+ leakage channels in plasma membrane Electrical Signals in Neurons:  depends on existence of resting membrane potential & presence of specific ion channels  happen due to flow of ions across plasma membrane via ion channels Ion Channels: allow specific ions to cross plasma membrane  ion movement makes flow of electrical current that changes resting membrane potential  4 Types of Ion Channels: 1. leakage channel: randomly open & close, more K+ leakage channels than Na+ channels  plasma membrane more permeable to K+ than Na+ 2. chemically gated channel: open in response to specific chemical stimulus (ligand)  neurotransmitters, hormones, ions 3. mechanically gated channel: open in response to mechanical stimulus,  found in sensory receptors 4. voltage gated channel: open in response to change in membrane potential (voltage)  participate in generation & propagation of action potentials 

Types of Mechanical Stimuli: vibration, pressure, mechanical stretching Changing resting membrane potential generates electrical signals. Neurons produce 2 types of electrical signals: graded & action potentials Graded Potential: small deviation from resting potential b/c of ion movement  vary in amplitude depending on stimulus strength  generated when stimuli causes ligand/mechanically gated channels to open/close  happen in dendrites & cell body of sensory receptors & neurons  can initiate nerve action potential/trigger full action potential at -55 mV Action Potential: large deviation from resting potential b/c of ion movement  always same ultimate strength/amplitude/size, propagate along axon, 4 steps to occur  series of rapid events that take place in 2 phases: depolarization & repolarization  4 Steps to Generate Action Potential: 1. depolarization of threshold  stimulus (graded potential) causes depolarization (becomes -55 mV) 2. activation of sodium channels & rapid depolarization  threshold triggers fast-acting voltage gated Na+ channels to open  Na+ moves down electrochemical gradient into cell cell inside becomes positively charged (depolarized) +10 mV 3. inactivation of sodium & activation of potassium channels  membrane potential peaks -> +30 mV  Na+ voltage gated channels start closing  slow-acting voltage gated K+ channels open (in response to threshold of -55 mV)  K+ moves down its chemical gradient out of cell 4. closing of potassium channels  sodium channels become reactivated  potassium channels close again  membrane potential reacts to resting potential (-70 mV Polarization A. Depolarization:  cell inside positively charged -> +30 mV  fast acting Na+ channels open B. Repolarization:  cell inside negatively charged again -> -70 mV  fast acting Na+ channels inactivated  slow acting K+ channels open C. After Hyper-polarizing Phase:  outflow of K+ may make membrane potential -90 mV  Na+/K+ pumps restore membrane potential to normal (-70 mV) via active transport Refractory Period: period that excitable cell cannot generate action potential 1. Absolute Refractory Period:  Na+ channels need time to return to resting state before opening again

 no stimulus can generate second action potential  ensures action potential moves in single direction 2. Relative Refractory Period:  K+ channels are open  2nd action potential can be generated if stimulus is longer than normal Propagation of Nerve Impulse:  action potential generated at specific point on plasma membrane, continuous, saltatory  not across plasma membrane at once, localized events  movement of action potential along neuron o from trigger zone at junction of cell body & axon to axon terminals Continuous Propagation: slow rate of propagation, happens in myelinated axons  action potential at 1 point stimulates generation of action potential at next point  step by step polarization & depolarization of each axon region Saltatory Propagation: much faster propagation than continuous, in myelinated axons,  few Na+ & K+ channels under myelin sheath  action potentials can not be generated, action potentials jump from 1 Ranvier node to next Signal Transmissions of Synapses:  synapses b/t neurons, presynaptic neuron sends signal, postsynaptic neuron receives signal  2 types: 1. Electrical Synapse: action potential conducted directly from cell to cell via gap junctions  faster communication & greater synchronization among cells 2. Chemical Synapse: action potential conducted across synaptic cleft indirectly via neurotransmitters  pre & post synaptic cells separated by synaptic cleft, filled w/t interstitial fluid Dopamine: CNS; control of movement Seratonin: CNS; attention and emotional status Norepinephrine: sympathetic nervous system; arousal, dreaming, & moods Acetylcholine: parasympathetic; neuromuscular junctions...