Nervous System Chapter 10 PDF

Nervous System Chapter 10  Divisions of the Nervous System Central Nervous System- Brain and Spinal Cord Peripheral Nervous System- nerves General Functions of the Nervous System Sensory - impulses are sent to the CNS; detect changes inside and outside of the body Integration...

Nervous System Chapter 10  Divisions of the Nervous System Central Nervous System- Brain and Spinal Cord Peripheral Nervous System- nerves General Functions of the Nervous System Sensory - impulses are sent to the CNS; detect changes inside and outside of the body Integration - occurs within CNS; processes incoming sensory input (decision making) Motor - impulses are sent from CNS to effectors (muscles or Cells of the Nervous System Neurons- nerve cells; conduct impulses Neuroglia- surrounds nerve cells; do not conduct impulses Neurons- conducting cells  Parts of a neuron- 1. Cell Body- contains cytoplasm, mitochondria, lysosomes, microtubles, golgi apparatus and a nucleus - Nissl bodies- chromatophilic substance that consists mainly of RER. 2. Dendrites- receive input; highly branched and provide many receptors; can be one or more 3. Axon- transmits input and carries the input away from the cell body; usually one long fiber  Impulses travel to dendrite  cell body  axon in ONE WAY! Neuron http://www.youtube.com/watch?v=i- NgGKSNiNw&NR=1&feature=fvwp&safe ty_mode=true&persist_safety_mode=1 Neuron Classification Structural Functional Classification Classification 1. Multipolar- 1 axon 1. Sensory and MANY (afferent) dendrites Neurons- carry 2. Bipolar- 1 axon impulses from and 1 dendrite peripheral body parts to the CNS 3. Unipolar- 1 2. Interneurons- lie process which splits into 2 within the CNS and branches, the form links with peripheral process other neurons and the central 3. Motor (efferent) process Neurons- carry impulses from the Neuroglia- nonconducting cells  Provide structural support, nourish neurons, and remove clutter from between neurons  2 types of Neuroglial cells in the PERIPHERAL NERVOUS SYSTEM: 1. Schwann Cells 2. Satellite Cells  4 types of Neuroglial cells in the CENTRAL NERVOUS SYSTEM: 1. Astrocytes 2. Oligodendrocytes 3. Microglia 4. Ependyma Neuroglial Cells in the PNS SCHWANN CELLS- produce the myelin on myelinated neurons; wrap around the processes in one of 2 ways: 1. Tightly wrap around fibers, forming a myelin sheath -Neurilemma- the outermost layer of wrapping has cytoplasm & nucleus 2. Just neurilemma with no myelin sheath SATELLITE CELLS- clusters of neuron cell bodies called ganglia Myelinated fiber - fiber that has a myelin sheath; impulse travels faster Unmyelinated fiber - fiber that does not have a myelin sheath; impulse travels slower Gray matter - nervous tissue containing lots of cell bodies and unmyelinated fibers White matter - nervous tissue Neuroglial Cells in the CNS ASTROCYTES- large star shaped cells between neurons and blood vessels; structural support, communication, and transportation between blood vessels and neurons OLIGODENDROCYTES- shaped like astrocytes with fewer processes, occur in rows along axons; form myelin sheath in the CNS ( NO neurilemma) MICROGLIA-small cells with few processes found throughout CNS; structural support and phagocytosis EPENDYMA- cuboidal and columnar cells in Neuron Regeneration In CNS - no regeneration, since there is no endoneurial tube, and no neurilemma In PNS - regeneration MIGHT occur, because the endoneurium’s presence may prevent scar tissue from coming in before the process can regrow If the cell body of a neuron (CNS or PNS) is destroyed, regeneration will never occur. Synapse A synapse is the junction between the axon of one neuron and the dendrite or cell body of another neuron 2 Types: 1. Presynaptic Fiber- the neuron which sends impulse to synapse - It releases neurotransmitters into the synaptic cleft 2. Postsynaptic Fiber- the neuron which has receptors for the neurotransmitters Synaptic Transmission 1. Presynaptic knob of 4. Neurotransmitters cross axon contains cleft and bind to vesicles filled with receptors on neurotransmitters. postsynaptic membrane of neuron (either 2. When impulse dendrite or cell body) reaches knob, Ca++ 5. If enough diffuses into neurotransmitters are cytoplasm. present, an action 3. Vesicles move to potential will occur. membrane and 6. Neurotransmitters are release either decomposed or neurotransmitters they move back into into cleft. presynaptic knob. Synapse http://www.youtube.com/watch?v=HXx9 qlJetSU&feature=related&safety_mode= true&persist_safety_mode=1 Neuron Potentials  A nerve impulse is a chain reaction of permeability changes along a neuron’s membrane. The concentration of ions on either side of the membrane affects its charge distribution (known as its potential). Resting Potential The charge distribution when a nerve is at rest. No impulse being conducted, so membrane is not very permeable to POTASSIUM (K+) and even less permeable to SODIUM (Na+). Active transport has to be used to pump K+ in and Na+ out. More negatively charged ions on the inside of the cell so more positive particles are going to move in (attraction): - More Na+ on outside, K+ on inside - Membrane is positive on the outside, Changes in Potentials When a stimulus encounters a neuron, it responds by changing its permeability to various ions, which affects the potential (charge distribution). 1. Hyperpolarized- the resting membrane becomes more negative 2. Depolarized-the resting membrane becomes more positive Resting Potential Nerve Impulse If the stimulus is strong enough (threshold) it causes Na+ gates to open Na+ flows into the cell, depolarizing the membrane. An action potential is reached at +30 mV. Depolarization Nerve Impulse Immediately, K+ gates open K+ moves out, repolarizing the membrane It even hyperpolarizes (less than -70) for a brief moment. Repolarization Nerve Impulse Then the active transport pumps reestablish the resting potential by pumping Na+ out and K+ in. ACTION POTENTIAL- the rapid sequence of Na+ and K+ movements - It triggers a chain reaction of action potentials all down the length of the neuron. - Nerve Impulse- the chain reaction of action potentials Terms  All-or-None Response- if a neuron responds at all, it responds COMPLETELY or conducts COMPLETELY or not at all  Refractory Period- a short time period after a nerve impulse where a stimulus will not conduct the neuron  Saltatory Conduction- type of impulse conduction along myelinated fibers Impulse “jumps” from node to node (the nodes of Ranvier are the areas of exposed neuron fiber between myelinated regions) Speed of Nerve Impulse Thick fibers transmit faster than thin. Myelinated fibers transmit faster than unmyelinated. Fastest - thick and myelinated Ex: motor fibers leading to muscles (120 meters/sec) Slowest - thin and unmyelinated Ex: sensory fibers in skin (0.5 meters/sec) Synaptic Potentials- Change in voltage in localized area of dendrite or cell body 2 Types: 1. Excitatory Postsynaptic Potential - neurotransmitter triggers Na+ gates to open and membrane is depolarized (more likely reach action potential) 2. Inhibitory Postsynaptic Potential - neurotransmitter triggers K+ gates to open and membrane is hyperpolarized (less likely to reach action potential)  Many synaptic knobs contact each neuron… some excitatory, some inhibitory. - The summation of their effects (usually occurs at the trigger zone) determines if the action potential occurs or not.  Facilitation - if a neuron receives a net excitatory stimulation, but is subthreshold, it is more susceptible to an action potential the NEXT time. Types of Neurotransmitters Monoamines- modifications of amino acids - Ex: Epinephrine, Dopamine, Serotonin Amino Acids- unmodified amino acids - Ex: Glycine, Gamma-aminobutyric acid (GABA) Peptides- short chains of amino acids - Ex: Substance P, Endorphins Pg. 373, Table 10.4 and 10.5  Convergence When a neuron receives impulses from 2 or more other neurons Allows the brain to receive information from different regions of the body and respond in a special way Divergence When 1 neuron sends impulses to 2 or more other neurons - results in an amplified response Nerve Classification Types of Fibers Origin Sensory- contains Cranial only sensory fibers Spinal (afferent) Motor- contains only motor fibers(efferent) Mixed- contains both sensory and motor fibers Groups of General Nerve Fibers Within Nerves General Somatic Efferent Fibers -carry impulses from CNS to skeletal muscles General Visceral Efferent Fibers-carry impulses from CNS to smooth muscles and glands General Somatic Afferent Fibers-carry impulses from skeletal muscles and skin to CNS General Visceral Afferent Fibers-carry impulses from smooth muscles and glands to CNS Reflex Arc - simple impulse pathway during a reflex (automatic unconscious response to a stimulus) Receptor - specialized nerve endings stimulated by change Sensory neuron - carries impulse from receptor to CNS Interneuron - connects sensory to motor neuron Motor neuron - carries impulse away from CNS Effector - smooth muscle or gland that responds