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Nervous System - Coggle Diagram
Nervous System
Communication Methods
The Chemical Synapse
Excitatory and Inhibitory synapses
An Inhibitory Postsynaptic Potential (IPSP) is a graded hyperpolarization due to net influx of negative ions
or net efflux of positive ions.
An Excitatory Postsynaptic Potential (EPSP) is a graded depolarization due to influx of positive ions.
Neuronal Networks
Lateral Inhibition
Cholinergic Synapses
Acetylcholine (ACh) = neurotransmitter
Nicotinic- ligand gated ion channel (skeletal muscle and brain)
Muscarinic- G protein coupled (heart, smooth muscle, glands, brain)
Adrenergic Synapses
Catecholamines = neurotransmitters (tyrosine based)
Norepinephrine
Epinephrine
Alpha and beta adrenergic receptors-G protein coupled act via second messengers (heart, smooth muscle, glands)
Key Concepts
Neurons process incoming information in dendrites and the soma by summing the post-synaptic membrane potential changes (graded potentials).
Spatial summation is the addition of inputs occurring simultaneously within neighboring synapses.
Temporal summation is the addition of inputs occurring very close to one another in time within the same synapse.
Neurotransmitters transmit signals within milliseconds by binding receptors on the postsynaptic cell.
Organization
Nervous System Organization
Afferent Neurons
are sensory (transmit information to the CNS).
Efferent Neurons
“cause” change (transmit information away from the CNS).
Peripheral Nervous System: cranial nerves, spinal nerves
Central Nervous System: spinal cord, brain
PNS Sensory Input
Sensory Systems
: Vision, Hearing, Taste, Equilibrium, Olfaction, Somatosensation, (also visceral stimuli like pH and O2 content of blood, osmolarity, blood glucose)
Somatosensation
receptors in skin, muscle and bones & visceral receptors (in organs) detect pain, temperature, touch, pressure, and proprioception (joint capsule, tendon, and muscle stretch).
PNS Input & Output
CNS (Integrative)
Autonomic
(Efferent)
Parasympathetic
Sympathetic
Enteric
Somatic
(Efferent)
Sensory
(Afferent)
Input Signal: touch, temperature, pain or visceral sensory signals
Sympathetic & Parasympathetic Nervous System
PNS Output
Key Concepts
The CNS and PNS constitute a reflex arc. The CNS (brain & spinal cord) integrates sensory input (PNS) and provides appropriate output to effectors (PNS).
The efferent portion of the PNS is divided into somatic and autonomic nervous systems.
The nervous system is composed of the brain, spinal cord, cranial nerves and spinal nerves. The first two make up the CNS, the latter two constitute the PNS.
Somatic innervates skeletal muscle to cause contraction.
Autonomic nervous system (ANS) is divided into sympathetic, parasympathetic and enteric.
Sympathetic (SNS) and parasympathetic act reciprocally and in opposition (accelerator & brake).
Enteric division acts independently in the gut but can be modulated by the other divisions of the ANS. SNS is “fight or flight”; ParaSNS is “rest or digestion”.
Introduction & Cell Types
Neuron
Glial Cells
Peripheral Nervous System
Schwann Cells: one cell myelinates a portion of an axon
Central Nervous System
Oligodendrocytes: one cell myelinates many different axons
Microglial Cells: immune cells of CNS
Astrocytes: support neurons
Key Concepts
Neurons transmit information by ion conduction.
Glia provide structural and metabolic support for neurons.
Neurons and glia are the principal cells of the nervous system.
Methods of Communication
Action Potentials
Voltage Gated Na+ & K+ Channels
Depolarization of the membrane is the stimulus which leads to both channels opening. To reset the Na+ channel from inactive to closed need to repolarize the membrane. Refractory period is when Na+ channels are inactivated.
Action Potentials
Action Potentials: are rapid, “all or none” and do not decay over distances
Unidirectional Propagation of AP
Action potentials move one-way along the axon because of the absolute refractory period of the voltage gated Na+ channel.
Integration of Signals
Input
Dendrites: ligand gated ion channels, some voltage gated channels; graded potentials.
Cell body (Soma): ligand gated ion channels; graded potentials.
Output
Axon: voltage gated ion channels, action potentials
Axon initial segment: highest density of voltage gated ion channels & lowest threshold for initiating an action potential, “integrative zone”
Saltatory Conduction
Large diameter, myelinated axons transmit action potentials very rapidly.
Voltage gated channels are concentrated at the nodes.
Inactivation of voltage gated Na+ channels insures uni-directional propagation along the axon.
Key Concepts
An action potential is a wave of depolarization followed immediately by a wave of repolarization. During an action potential, depolarization is due to the movement of Na+ into the nerve cell. Repolarization is due to the movement of K+ out of the cell.
Action potentials are electrical signals that propagate without decrement along axons, are “all or none”, have refractory periods, and uni-directional propagation in neurons.
Membrane Potentials
Equilibrium Potential
ion channels
Gated
Bidirectional
Specific
Resting Membrane Potential
Na+/K+ ATPase establishes the chemical concentration gradient for Na & K and sets up a small electrical gradient by pumping more positive ions (Na) out.
Greater net movement of K+ leaving (K+ leak) than Na+ entering
makes the resting membrane potential negative on the inside.
Changes in Membrane Potential
Overshoot = inside more + relative to outside (i.e., reversal of polarity)
Repolarizing = becoming more negative but still above resting potential
Depolarization = less negative than resting membrane potential (i.e., closer to zero)
Hyperpolarization = more negative than resting potential (further from zero)
Graded Potentials
Key Concepts
The Na/K+ ATPase re-equilibrates the resting membrane potential. Inactivation of the Na/K+ ATPase will lead to depolarization over time as K+ leaks out and Na+ enters, dissipating the resting membrane potential.
Graded potentials are electrical signals that are local, vary with intensity of the stimulus, can summate, can be stimulatory or inhibitory, and have no refractory period.
The equilibrium potential of an ion is when the chemical gradient and the electrical gradient are equal in magnitude but opposite in direction.
Electrochemical Gradient
