8Anatomy of the Neuron Soma The cell body of the neuron; contains the nucleus and other organelles necessary for survival of the cellDendriteBranches of the neuron that receive chemical messages (neurotransmitters) from another neuronAxonLong “arm(s)” of the neuron that propagate electrical messages (action potentials) from within the neuronAxon hillockThe site of the soma where the axon stems from and most often the site of action potential origination
9Neuroglia Functions: Example: Astrocytes, Oligodendrocytes Surround neurons and hold them in placeSupply nutrients and oxygenInsulate one neuron from anotherDestroy pathogens and remove dead neurons
10Types of Neurons Sensory (afferent) Transmits signals from sensory receptors to the spinal cord/brain.Motor (efferent)Transmit signals from the brain/spinal cord to muscle fibers, resulting in muscle contractions, and affect glands.Interneurons (association)Connect neurons to other neurons within the same region of the brain or spinal cord.
12Action PotentialElectrochemical message that can stimulate or inhibit another neuron
13The Action Potential Electrochemical changes that occur along the axon Voltage change caused by migration of sodium and potassium ions across the cell membrane of the axonAction potentials may be excitatory (EPSP’s) or inhibitory (IPSP’s) of the next neuron
14Schwann Cells & MyelinThe axons of many neurons are wrapped in glial tissue called Schwann cellsSchwann cells produce a fatty tissue called myelin that wraps around regions of the axonThe spaces between the wrapped layers of myelin are called Nodes of Ranvier
15Saltatory ConductionThe myelin sheaths insulate the axon, preventing excessive leakage of K+ ionsDepolarization at one Node of Ranvier is sufficient to propagate the action potential at an adjacent node.As less gated channels need to be opened and closed along the axon, the effective speed of the action potential is greater
17NeurotransmittersNeurotransmitters (NT) are endogenous chemicals that transmit signals from a neuron to a target cell across a synaptic cleftSynthesis of the NT can take place in the cell body, in the axon, or in the axon terminal.Storage of the NT in storage granules or vesicles in the axon terminal.
19Synaptic Transmission Calcium enters the axon terminal during an action potential, releasing the neurotransmitter (NT) into the synaptic cleft.The NT binds to and activates a receptor in the postsynaptic membrane.The neurotransmitter is either destroyed enzymatically, or taken back into the terminal from which it came, where it can be reused, or degraded and removed.
25Central v. Peripheral Divisions Central (CNS)Form: Brain, Spinal Cord, Optic NerveForm: Protected by bone and/or blood-brain barrierFunction: Integrates messages received from extremities, sensory organs and internal organsPeripheral (PNS):Form: Nerves and Ganglia outside of CNS. Includes 10 of 12 cranial nervesForm: Not protected by bone or blood-brain barrierFunction: Relays messages between CNS and extremities.
26Autonomic v. Somatic Divisions of PNS Autonomic Divison (ANS)Function: Involuntary control over heart rate, breathing, perspiration, salivation, pupillary dilation and digestionForm: Afferent (sensory) & Efferent (motor) neuronsSubdivided in Sympathetic and Parasympathetic DivisionsSomatic Division (SoNS)Function: Voluntary control of body via efferent motor neuronsSoNS also encompasses reflex arcs, which do NOT travel to brain but instead rely on association neuronsForm: Comprised of three types of nervesSpinalCranialAssociation
27Somatic Division (SoNS) The SoNS is responsible for controlling voluntary movements, using efferent (motor) neurons, and reflex arcs, using association (inter-) neurons.Three types of nerves:Spinal: Innervate much of the body, and connect through the spinal column to the spinal cord. (letter-number designations according to the vertebra through which they connect to the spinal column)Cranial: Innervate the head, and connect directly to the brain (especially the brainstem). (Roman Numerals descriptive names).Association: Connects other neurons (not “projection” neurons)
28Somatic Reflex ArcsA reflex arc is a neural pathway that controls action reflexes (ex: patellar reaction) by synapsing in the spinal cord (not the brain).This allows for faster response time. Sensory information is still relayed to your brain, as the reflex action occurs.
29Autonomic Division (ANS) The ANS is responsible for controlling involuntary movements, such as heart rate, breathing, perspiration, salivation, pupillary dilation,digestion.It is composed of afferent (sensory) and efferent (motor) neurons.The ANS is further subdivided two divisions:The Sympathetic Division (“Fight or Flight”)The Parasympathetic Division (“Feed & Breed”)
31Sympathetic and Parasympathetic Divisions of the ANS Sympathetic (Fight or Flight)Elevates blood pressure via vasoconstrictionIncreases respiratory volume via dilation of bronchiolesInhibition of peristalsisDilation of pupilParasympathetic (Feed & Breed)Decreased blood pressure via vasodilationDecreased respiratory rateIncreased digestion, urination and defecation