Structure and Structure and Function of the Function of the Nervous SystemNervous System

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Central Nervous System:

Brain

Spinal cord

Peripheral Nervous System:

Cranial nerves (12 pairs)

Spinal nerves (31 pairs)

Afferent (ascending) – sensory

Efferent (descending) – motor

Central Nervous SystemCentral Nervous System

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Peripheral Nervous System

Somatic Nervous Autonomic Nervous System System

Operates with conscious control              Usually without conscious control

Controls skeletal muscle Regulates body’s internal environment

Releases Acetylcholine at synapses               Releasesacetylcholine or norepinephrine at

                                                                           synapses

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Autonomic Nervous System

Sympathetic Parasympathetic Nervous System Nervous System

Originates in the thoracic Originates in the brain stemand lumbar segments         (cranial nerves) and sacralof the spinal cord : segments of the spinal Thoracolumbar system cord: Craniosacral system

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Sympathetic Parasympathetic Nervous System Nervous System

Effect is wide spread            Effect is local

"Fight-or-Flight" - Bear           "Feed and Breed” - Book emergency, excitement, exercise,            salivation, lacrimation, urination,   embarrassment defecation

                                                                                     Postganglionic fibers Postganglionic fibers release norepinephrine     release Ach

Preganglionic fibers of both release ACh

Cells of the Nervous Cells of the Nervous SystemSystem

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Neurons – the primary cell of the nervous system

Supporting cells – Neuroglial cells

NeuronsNeurons

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Each neuron is adapted for a specialized function.

Detect environmental changes

Process information

Initiate body responses

Fuel source is mostly glucose

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Saltatory conductionSaltatory conduction

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Neuroglia – “Nerve Neuroglia – “Nerve glue”glue”

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Schwann cells form the myelin sheathes of axons in the peripheral nervous system.

AstrocytesOligodendrocytesMicrogliaEpendymal cells are found in the CNS

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Generation of nerve Generation of nerve impulsesimpulses

Action potentials are generated when Action potentials are generated when stimulus is greater than threshold.stimulus is greater than threshold.

Action potential is an all-or-none Action potential is an all-or-none responseresponse

Axon has a resting potentialAxon has a resting potential Opening of voltage gated channels Opening of voltage gated channels

propagates current down axonpropagates current down axon At end of axon, neurotransmitters At end of axon, neurotransmitters

released from synaptic knobs into released from synaptic knobs into synaptic cleftsynaptic cleft 2121

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Neurons interact with other Neurons interact with other neuronsneurons

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Synapse – region between two neurons

Presynaptic → Postsynaptic

Neurotransmitters:

Excitatory – Excitatory postsynaptic potentials (depolarize)

Inhibitory – Inhibitory postsynaptic potentials (hyperpolarize –more difficult to reach threshold)

NeurotransmittersNeurotransmitters

At least 30 knownAt least 30 known AcetylcholineAcetylcholine Amino acids – GABAAmino acids – GABA Biogenic amines – catecholamines – Biogenic amines – catecholamines –

norepinephrine, epinephrine, dopaminenorepinephrine, epinephrine, dopamine– Also serotonin and histamineAlso serotonin and histamine

Neuropeptides – opiates such as Neuropeptides – opiates such as enkephalins and endorphinsenkephalins and endorphins

Gases – Nitric oxide (NO)- vasodilationGases – Nitric oxide (NO)- vasodilation

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BrainBrain

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Divisions of BrainDivisions of Brain

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Forebrain - cerebral hemispheres, thalamus and hypothalamus

Midbrain - corpora quadrigemina and cerebral peduncles

Hindbrain - cerebellum, pons, medulla oblongata

Reticular formation

Reticular activating system

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Gyri - convolutions

Sulci - grooves

Gray matter – nerve cell bodies and dendrites (unmyelinated)

White matter – myelinated axons

Spinal cordSpinal cord

Lies in vertebral canal protected Lies in vertebral canal protected by vertebral columnby vertebral column

Connects brain and bodyConnects brain and body Somatic and autonomic reflexesSomatic and autonomic reflexes Begins at medulla oblongata and Begins at medulla oblongata and

ends at conus medullaris at L1 or ends at conus medullaris at L1 or L2L2

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Protective StructuresProtective Structures

CraniumCranium Meninges:Meninges:

– Dura Mater – “Tough mother”Dura Mater – “Tough mother” Periosteum and meningeal layerPeriosteum and meningeal layer Falx cerebri, Falx cerebelli, and Falx cerebri, Falx cerebelli, and

Tentorium cerebelliTentorium cerebelli– Arachnoid – “Spider web-like”Arachnoid – “Spider web-like”

Subarachnoid space – CSF flowsSubarachnoid space – CSF flows– Pia mater – “Gentle mother”Pia mater – “Gentle mother”

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Blood-Brain BarrierBlood-Brain Barrier

Capillaries have tight junctionsCapillaries have tight junctions Aided by astrocytesAided by astrocytes Selectively permeableSelectively permeable Important when we want to get Important when we want to get

antibiotics or other antibiotics or other chemotherapeutic agents into chemotherapeutic agents into the brain.the brain.

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