1.Nervous Sys Org - Lecture
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Transcript of 1.Nervous Sys Org - Lecture
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Anatomy and Physiology, Sixth Edi tion
Lecturer: Dr. D. Fisher
Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Overview
Of the
Nervous System
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The Nervous System
Components Brain, spinal cord, nerves, sensory receptors
Responsible for
Sensory perceptions, mental activities,stimulating muscle movements, secretions ofmany glands
Subdivisions Central nervous system ( CNS ) Peripheral nervous system ( PNS )
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Central Nervous System
Consists of Brain
Located in cranial vault
of skull Spinal cord
Located in vertebralcanal
Brain and spinal cord Continuous with each
other at foramenmagnum
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Brain and Cranial Nerves
Brain Part of CNS contained in cranial cavity Control center for many of bodys functions Much like a complex computer but more
Parts of the brain Brainstem Cerebellum Diencephalon Cerebrum
Cranial nerves Part of PNS arise directly from brain
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Brainstem
Connects spinal cord to brain Parts
Medulla oblongata Pons
Midbrain
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Brainstem
Medulla oblongata or medulla Regulates: Heart rate, blood vessel diameter,
respiration, swallowing, vomiting, hiccupping,coughing, and sneezing
Pyramids: Decussate
Pons Sleep and respiratory center
Midbrain Integral part of auditory pathways in CNS
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Cerebellum
Involved in control of: balance, posture,locomotion, and finemotor coordination
producing smoothflowing movements
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Diencephalon
Components Thalamus, Subthalamus, Epithalamus, Hypothalamus
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Diencephalon
Thalamus Largest part ofdiencephalon
Most sensory input projectsto here
Influences mood andactions as fear or rage
Subthalamus Involved in controlling
motor functions
Epithalamus Pineal gland may influence
sleep-wake cycle
Hypothalamus Functions
ANS control Endocrine control Muscle control Temperature regulation Regulation of food and
water intake
Emotions Regulation of sleep-
wake cycle
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Cerebrum
Largest portion of brain Divisions
Right
Left Lobes: Frontal, parietal,
occipital, temporal,insula
Cortex: Outer surface Medulla: Center
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Basal Nuclei and Limbic System
Basal nuclei Motor function control
Limbic system Basic survival
functions as memory,
reproduction, nutrition Emotions
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Meninges
Connective tissuemembranes
Dura mater: Superficial Arachnoid mater Pia mater: Bound
tightly to brain
Spaces Subdural: Serous fluid Subarachnoid: CSF
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Meninges
Connective tissuemembranes surroundingspinal cord and brain
Dura mater Arachnoid mater Pia mater
Spaces
Epidural: Anesthesia injected Subdural: Serous fluid Subarachnoid: CSF
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Ventricles
Ventricles: Lateral ventricles (2), third ventricle, fourthventricle
Choroid plexuses produce CSF which fills ventricles andother parts of brain and spinal cord Blood-cerebrospinal fluid barrier: Substances do not pass between
cells but through due to tight junctions of blood endothelial cells
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Cerebrospinal Fluid (CSF)
Similar to serum with most of proteinsremoved
Bathes brain and spinal cord Provides a protective cushion around CNS Provides some nutrients to CNS tissues
Produced by ependymal cells
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Flow of CSF
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Brain Blood Supply
Brain Requires tremendous amount of blood Receives 15-20% of blood pumped by heart Interruption can cause unconsciousness and irreversible
brain damage High metabolic rate and dependence on constant supply
of oxygen and glucose Receives blood through arteries
Blood-Brain barrier Capillary endothelial cells along with astrocytes and
basement membrane To be considered when developing drugs
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Cranial Nerves
Indicated by Romannumerals I-XII fromanterior to posterior
May have one or more of3 functions Sensory (special or general) Somatic motor (skeletal
muscles)
Parasympathetic (regulationof glands, smooth muscles,cardiac muscle)
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Cranial Nerves
Olfactory (I) Optic (II)
Oculomotor (III) Trochlear (IV) Trigeminal (V)
Abducens (VI)
Facial (VII) Vestibulocochlear (VIII)
Glossopharyngeal (IX) Vagus (X) Accessory (XI)
Hypoglossal (XII)
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What are NERVES?
Nerves are distinct peripheral extensionsof the central nervous system (CNS).
Within the CNS (brain and spinal cord)nerve fibers are grouped together to formdistinct tracts (eg spinothalamic tract orthe dorsal lemniscal tract).
Nerve fibers are simply the axons ofvarious neurons.
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Cells of Nervous System
Neurons or nerve cells Receive stimuli and
transmit action potentials
Organization Cell body or soma Dendrites: Input Axons: Output
Neuroglia or glial cells Support and protect
neurons
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Types of Neurons
Functional classification Sensory or afferent: Action potentials toward CNS
Motor or efferent : Action potentials away from CNS Interneurons or association neurons : Within CNS from one
neuron to another
Structural classification Multipolar, bipolar, unipolar
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Morphology of NeuronsAny Neuron can be dividedup into a cell body and a setof neurites (dendrites andaxons).In terms of the position ofthe cell body relative to theneurites neurons can bedivided into three main
groups: (Pseudo)unipolar, bipolar and multipolarneurons.
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Bodian Definitions
That part of the neuron that is specialised toreceive stimuli is called the dendritic zone. That part of the neuron specialized to
conduct the stimuli is called the axoniczone.
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Neuroglia of CNS
Astrocytes Regulate extracellular brain fluid composition Promote tight junctions to form blood-brain barrier
Ependymal Cells Line brain ventricles and spinal cord central canal Help form choroid plexuses that secrete CSF
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Neuroglia of CNS
Microglia Specialized macrophages
Oligodendrocytes Form myelin sheaths if surround axon
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Neuroglia of PNS
Schwann cells or neurolemmocytes Wrap around portion of only one axon to form myelin sheath
Satellite cells Surround neuron cell bodies in ganglia, provide support and nutrients
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Peripheral Nerves
Consist of Axon bundles Schwann cells
Connective tissue Endoneurium Perineurium: Surrounds
axon groups to formfascicles
Epineurium
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Spinal Nerves
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SPINAL NERVES
31 pairs
Named & numberedaccording to region & levelof spinal cord from whichthey emerge
Roots of lower lumbar,sacral, & coccygeal spinal
nerves (i.e. cauda equina)descend at angle to reachrespective intervertebralforamina before emergingfrom vertebral column
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SPINAL NERVES Anterior (ventral) rami, except
thoracic nerves T 2-T12, formnetworks on both right & left sidesof body = called plexuses (named
by general regions they serve or
routes they follow)
Anterior rami of spinal nerves T 2-T12 do not enter into formation of
plexuses
These are calledintercostal/thoracic nerves travel directly to structures theyinnervate in intercostal spaces
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Peripheral Nervous System
Two subcategories Sensory or afferent Motor or efferent
Divisions
Somatic nervoussystem
Autonomic nervoussystem ( ANS )
Sympathetic Parasympathetic Enteric
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Spinal Cord and Spinal Nerves
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Cross Section of Spinal Cord
White matter Myelinated axons
forming nerve tracts Fissure and sulcus Three columns or
funiculi Ventral Dorsal Lateral
Gray matter Neuron cell cell bodies,
dendrites, axons
Horns Posterior (dorsal) Anterior (ventral) Lateral
Commissures Gray: Central canal White
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Cervical Plexus
C1-C4
Phrenic nerve From C3-C5 cervical and
brachial plexus Innervate diaphragm
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Brachial Plexus
C5-T1 Major nerves
Axillary Radial Musculocutaneous Ulnar
Median
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Structure General Innervation Representative Nerves
Cervical Plexus(C1-C4)
Mm and skin of neck &shoulder; diaphragm
phrenic innervatesdiaphragm
Brachial Plexus(C5-T1)
upper extremity Mm &skin
axillary,musculocutaneous,ulnar, median, radial
Lumbar Plexus (L1-L4)
lower extremity Mm &skin, perineal Mm/skin;some abdominal Mm
femoral, obturator,saphenous
Sacral Plexus(L4-S4) lower extremity Mm &skin, perineal Mm/skin sciatic, tibial, fibular,gluteal, pudendal
Intercostal/Thoracic Nerves
Intercostal & AbdominalMm, skin
Intercostal nerve branches (rami)
SPINAL NERVE PLEXUS
SUMMARY
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Nervous System Organization