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| helps to keep controlled conditions within limits that maintain health and helps to maintain homeostasis. |
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| responds rapidly using electrochemical changes called nerve impulses (action potentials) |
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| is responsible for all our perceptions, behaviors, memories, and movements. |
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| hundreds/thousands of axons + connective tissue + blood vessels, all located outside brain and spinal cord |
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| 31 pairs emerge from the spinal cord |
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| are masses of cell bodies of neurons associated with cranial and spinal nerves |
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| are extensive networks of neurons that help regulate the digestive system |
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| are either parts of neurons or specialized cells that monitor changes in the internal or external environment, e.g. photoreceptors in retina of eye |
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nsenses changes in the internal and external environment through sensory receptors.
qInternal = stretching of stomach when full.
External = smell of smoke, changes in light |
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| analyzes the sensory information, stores some aspects, and makes decisions regarding appropriate behaviors |
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| occurs in the brain and is the conscious awareness of sensory stimuli |
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nis the response to stimuli by initiating action by activating effectors.
qMuscle contraction
Secretion of glands |
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nCentral nervous system (CNS) |
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qConsists of the brain and spinal cord |
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| Peripheral nervous system (PNS) |
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qAll nervous tissue outside of CNS
nConsists of cranial, spinal nerves and peripheral nerves
nConnects CNS to muscles, glands and all sensory receptors |
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nSomatic nervous system (SNS) (Voluntary)
nAutonomic nervous systems (ANS) (Involuntary)
nEnteric nervous system (ENS) (Involuntary) |
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nSomatic nervous system (SNS) (Voluntary) |
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nControls skeletal muscle contraction
qSensory neurons that convey information from skin, joints and special sensory receptors (vision, hearing, taste and smell) to the CNS
qMotor neurons to skeletal muscle tissue |
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nAutonomic nervous systems (ANS) (Involuntary) |
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qControls “automatic functions” (BP, heart rate)
qSensory neurons from visceral organs to CNS
qMotor neurons to smooth & cardiacmuscle and glands |
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nEnteric nervous system (ENS) (Involuntary) |
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qControls GI tract; “Brain of the gut”
qSensory & motor neurons control GI tract
qMany enteric plexus neurons function independently of ANS & CNS |
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nConsists of two cell types:
Neurons and Neuroglia |
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| Generate and conduct action potentials (nerve impulse) in response to stimuli |
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| Support, nourish and protect neurons. |
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n1) Cell Body
n2) Dendrites
n3) Axons |
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| Most neurons have three parts |
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qContains nucleus and typical organelles |
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| (“little trees”): receive input from sensory receptors or other neurons. |
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qCarry nerve impulse towards cell body
qThey are usually short and highly branched.
Most neurons have many |
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nsend nerve impulse toward another neuron, to a muscle or to a gland.
qConducts nerve impulse away from cell body |
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| cone-shaped elevation where axon joins cell body |
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qjunction of axon hillock and initial segment (part of axon closest to axon hillock). |
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| part of axon closest to axon hillock |
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| contain and release neurotransmitters. |
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| general term for dendrite or axon of neuron; usually an axon |
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nMany processes extending from cell body
nSeveral dendrites and one axon.
qMost neurons in brain and spinal cord (CNS)
qTypical motor neuron |
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nTwo processes extending from cell body
nOne axon and one dendrite extending from either end of cell body.
qRare and small
qFound in retina of eye, inner ear, olfactory area of brain. |
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nOne process extending from cell body.
qThe dendrites function as sensory receptors (detect touch, pressure, pain, or thermal stimuli)
qTypical sensory neurons
qMost unipolar neurons are located in PNS
qCell bodies located in ganglia of spinal and cranial nerves |
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nSensory/afferent neurons |
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qAssociated with sensory receptors
Send action potentials toward CNS |
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qSend action potentials away from CNS to effectors (muscles or glands) in the periphery |
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nInterneurons/association neurons |
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qLocated within CNS between sensory and motor neurons.
qProcess incoming sensory information from sensory neurons and elicit motor response by activating appropriate motor neurons |
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| Neuroglial cells (Glial cells |
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Definition
nMake up half of volume of CNS.
nCells are smaller than neurons, but 50x more numerous.
nDo NOT generate or propagate action potentials
nUnlike neurons, neuroglial cells can divide in adult!
qWhen neurons die, neuroglia divide to fill in spaces |
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qare brain tumors derived from glia
nHighly malignant and grow rapidly |
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qAstrocytes, oligodendrocytes, microglia, ependymal cells |
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nStar-shaped cell that is the largest and most numerous of neuroglia
nContribute to blood-brain barrier (restricts movement of substances between blood and interstitial fluid of CNS)
nConduct nutrients and other substances to and from blood capillaries and neurons |
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| restricts movement of substances between blood and interstitial fluid of CNS |
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nSmaller and contain fewer processes than astrocytes
nForm and maintain myelin sheath around CNS axons
nAnalogous to Schwann cells of PNS |
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nSmallest and least numerous neuroglia in CNS
nFunction as phagocytes
qPhagocytize microbes, clear away dead cells and waste products |
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nArranged in single layer, cells have cilia or microvilli.
nForm epithelial membrane lining of ventricles of brain and central canal of spinal cord.
nProduce, circulate, and monitor cerebrospinal fluid (CSF) |
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nCompletely surrounds axons of PNS.
nMakes myelin that insulates axons of PNS.
nParticipates in regeneration of injured PNS axons |
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nElectrically insulates axon and increases speed of nerve impulse conduction.
nProduced by Schwann cells in PNS and oligodendrocytes in CNS |
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| myelin sheath = myelinated |
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| Layers of lipid and protein around axon form a |
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nAmount of myelin increase from birth to adulthood |
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nSchwann cells begin to form myelin sheaths during fetal development
nEach Schwann cell spirals many times around an axon, wrapping it in multiple layers of plasma membrane.
nThe inner portion of the wrapping forms the myelin sheath.
nThe nucleus and cytoplasm of the Schwann cell lie outside the myelin sheath, forming the neurolemma(found only in axons of PNS). |
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nSchwann cells can also wrap around several adjacent axons.
However, only one layer of the plasma membrane of a Schwann cell surrounds the axon; there are no multiple layers, and so no myelin is produced |
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nunmyelinated gaps between Schwann cells.
Nerve impulse “jumps” from node to node, increasing speed of conduction. |
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nOligodendrocytesmyelinate axons of CNS neurons.
qCell processes wrap around the axon, but the cell body and nucleus of the oligodendrocyte does not surround it, so no neurilemma is formed!
qNodes of Ranvier are present, but fewer in number |
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| masses of myelinated axons in CNS (brain and spinal cord) |
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| masses of neuron cell bodies, dendrites, unmyelinated axons in CNS |
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qLooks gray due to Nissl bodies and lack of myelin |
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qLooks white due to whitish color of myelin |
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nLoss or destruction of myelin sheaths around axons in CNS or PNS
qCan be caused by disease, radiation, chemotherapy, heavy-metal (arsenic, lead, mercury) poisoning
qResults in loss of sensation and motor control that leaves affected regions numb and paralyzed |
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nAutoimmune disease – the body’s own immune system attacks and destroys the myelin sheaths (demyelination) of CNS neurons.
qThe myelin sheaths deteriorate to scleroses which are hardened plaques or scars.
qDestruction of myelin sheaths slows and then short-circuits propagation of nerve impulses. |
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nAffects 350,000 in U.S.; 2 million worldwide
nUsually appears between 20 – 40 years of age
nAffects females 2X more than men
nSymptoms of MS: bowel and bladder dysfunction, difficulty walking, balancing, fatigue, dizziness, emotional and cognitive changes
qRelapsing-remitting MS: attack of symptoms followed by period of remission in which symptoms temporarily disappear
nCause of MS uncertain
qGenetic susceptibility and environmental exposure (virus)
No cure |
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| Neuron Repair and Regeneration |
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nIf PNS dendrites or axons are severed, regrowth may be possible if neuron cell body is intact, and if Schwann cells remain active.
qNeurolemma of Schwann cell forms “regeneration tube.” |
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| Neuron Repair and Regeneration |
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nIf CNS nerve fibers are severed, little or no regrowth occurs.
qNo neurolemma to form “regeneration tube.” |
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| Neuron Repair and Regeneration |
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nWhen a PNS neuron is injured, the part of the axon distal to the damaged region degenerates; however, the neurolemma remains.
nSchwann cells on either side of the injured site multiply by mitosis and grow toward each other, forming a regeneration tube across the injured area (if the gap is not too large).
nThe tube guides the growth of a new axon, a slow process that may take several months.
qIn time, Schwann cells will form new myelin sheath |
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nNeurons are terminally differentiated
qThey do not undergo mitosis |
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nIn adults, neurons cannot be replaced if destroyed by injury or disease
nNeural stem cells are found in adult nervous system |
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| Neural stem cells are active in human |
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| area of brain involved in learning and memory; and olfactory bulb, involved in sense of smell |
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qThere is a lack of neurogenesis in other regions of the brain and spinal cord. |
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Ganglion/Ganglia Nucleus/Nuclei
Nerve
Tract |
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| Collections of Nervous Tissue |
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| cluster of neuron cell bodies in PNS |
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| cluster of neuronal cell bodies in CNS |
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nbundle of axons in PNS
qCranial nerves connect brain to periphery
qSpinal nerves connect spinal cord to periphery |
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nbundle of axons in CNS
qTracts interconnect neurons in spinal cord and brain |
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