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Nervous System II

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Title: Nervous System II


1
Chapter 11
  • Nervous System II

2
PROTECTION OF THE CNS
  • The brain and spinal cord are protected
    (surrounded) by bones, membranes, and fluid.

3
Meningies
  • membranes surrounding and protecting CNS
  • three layers
  • dura mater outer, tough
  • DM splits into two layers where it encloses the
    dural sinuses (that collect venous blood from the
    brain)
  • arachnoid mater thin, weblike
  • Beneath the arachnoid mater lies a wide space
    called the sub-arachnoid space
  • This space is filled with cerebrospinal fluid
    (CSF) and serves as a cushion for the brain
  • pia mater inner, very thin
  • dips into grooves contours
  • The space between the dura mater and the bone is
    called the epidural space and is filled with
    loose CT and fat
  • CSF fills the subarachnoid space and central
    canal

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Ventricles of the Brian
  • (interconnected cavities) within the cerebral
    hemispheres and brain stem
  • The Ventricles
  • are continuous with central canal of spinal cord
  • are filled with cerebrospinal fluid (CSF)
  • are lined by ependymal cells
  • neuroglial cell in CNS

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Cerebrospinal Fluid
  • secreted by choroid plexus
  • circulates in ventricles, central canal of
    spinal cord, and subarachnoid space
  • completely surrounds brain and spinal cord
  • clear liquid
  • provides nutrition and protection
  • helps maintain stable ion concentrations in CNS

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THE SPINAL CORD
  • The spinal cord is a nerve column that passes
    downward from brain into the vertebral canal.
    Recall that it is part of the CNS

10
Structure of the Spinal Cord
  • Length about 17 inches
  • Start foramen magnum
  • End tapers to point (conus medullaris) and
    terminates near the intervertebral disc that
    separates the 1st - 2nd lumbar (L1-L2) vertebra
  • Contains 31 segments (and therefore gives rise to
    31 pairs of spinal nerves)
  • Note cervical and lumbar enlargements

11
Structure of the Spinal Cord cont.
  • cauda equina (horses tail) in which the lower
    lumbar and sacral nerves travel downward
  • i.e. lower spinal nerves must chase their
    points of exit)
  • filum terminale that represents distal portion of
    the tail (pia mater)
  • No actual nerve tissue
  • A cross-section of the spinal cord resembles a
    butterfly with its wings outspread (gray matter)
    surrounded by white matter

12
Functions of the Spinal Cord
  • Nerve Pathway the route traveled by a nerve
    impulse through the nervous system
  • Reflex arc the simplest demonstration of a
    nerve pathway (spinal reflexes)
  • involves 2-3 neurons
  • involuntary response
  • often does not involve the brain
  • Examples include
  • knee-jerk or patellar reflex

13
Spinal Nerves
  • Spinal nerves extend to/from the spinal cord and
    are part of the PNS
  • Ganglion a bundle of cell bodies outside the
    CNS
  • Dorsal Root Ganglion contains the cell bodies of
    sensory (afferent) neurons bringing impulses to
    the CNS
  • The fusion of the dorsal and ventral roots
    designates the beginning of the spinal nerve
    which then passes through its intervertebral
    foramen

14
Ascending and Descending Tracts
  • The white matter of the spinal cord represents
    the location of our major nerve pathways called
    "nerve tracts"
  • provide a 2-way system of communication
  • ascending tracts conduct sensory (afferent)
    impulses from body parts to brain
  • descending tracts conduct motor (efferent)
    impulses from brain to effectors
  • All pathways are paired (right and left)

15
BRAIN
  • The brain is the largest and most complex portion
    of the nervous system.

16
Introduction
  • It occupies the cranial cavity and is composed of
    one hundred billion multipolar neurons.
  • The brain oversees the function of the entire
    body and also provides characteristics like
    personality
  • The brain is composed of 5 major portions
  • cerebrum, cerebellum, diencephalon, basal nuclei
    and brain stem

17
Structure of the Cerebrum
  • Cerebrum the largest portion of the brain,
    which is divided into two cerebral hemispheres.
  • Hemispheres are connected by a deep bridge of
    nerve fibers called the corpus callosum
  • Surface ridges are called convolutions (gyri)
  • Convolutions are separated by two types of
    grooves. (Sulci and Fissures)
  • Each hemisphere is divided into lobes, which are
    named for the bones that cover them including
    frontal, parietal, temporal, and occipital lobes

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20
Structure/Function of the Cerebrum
  • Composition
  • Bulk of cerebrum is white matter.
  • bundles of myelinated nerve fibers (by
    oligodendrocyte)
  • Cerebral cortex or the outer portion of cerebrum
    is composed of gray matter
  • bundles of neuron cell bodies
  • contains 75 of all neurons in nervous system
  • Functional Regions of the Cerebral cortex
  • Responsible for all conscious behavior by
    containing three kinds of functional areas, which
    include motor, sensory and association areas

21
Sensory Areas
  • Sensory Areas are concerned with conscious
    awareness of sensations and are located in the
    parietal, occipital, and temporal cortex
  • The include the
  • Cutaneous Sensory Area
  • Visual Area
  • Auditory Area
  • Sensory Area for Taste
  • Sensory Area for Smell

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24
Association Areas
  • regions that are not primary motor or primary
    sensory areas
  • widespread throughout the cerebral cortex
  • Association traits include
  • analyzing interpreting sensory experiences
  • help provide memory, reasoning, verbalizing,
    judgment and emotions

25
Hemisphere Dominance
  • The left hemisphere is dominant is most
    individuals
  • Dominant hemisphere controls
  • speech
  • writing
  • reading
  • verbal skills
  • analytical skills
  • computational skills
  • Nondominant hemisphere controls
  • nonverbal tasks
  • motor tasks
  • understanding and interpreting musical and
    visual patterns
  • provides emotional and intuitive thought
    processes

26
Memory
  • Memory is the consequence of learning. Whereas
    learning is the acquisition of new knowledge,
    memory is the persistence of that learning, with
    the ability to access it at a later time
  • Two types of memory
  • Short Term working memory
  • Long Term changes structure or function of
    neurons

27
Motor Areas
  • Motor Areas are located in the frontal cortex
  • Primary motor cortex
  • initiates all voluntary muscle movements
  • Broca's area
  • motor speech area
  • Frontal Eye Field
  • controls voluntary movements of eyes and eyelids

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Basal Nuclei
  • masses of gray matter located deep within the
    white matter of the cerebral hemispheres
  • Release dopamine, which inhibits excess movements
  • control certain muscular activities
  • primarily by inhibiting motor functions
  • caudate nucleus, putamen, globus pallidus

31
Diencephalon
  • includes two important areas of gray matter
  • Thalamus
  • gateway for sensory impulses heading to cerebral
    cortex
  • receives all sensory impulses (except smell)
  • channels impulses to appropriate part of
    cerebral cortex for interpretation
  • Hypothalamus
  • maintains homeostasis by regulating visceral
    activities
  • links nervous and endocrine systems

32
Limbic System
  • Limbic System involved in Emotional response
  • interprets sensory impulses
  • includes structures in the frontal and temporal
    cortex, basal nuclei, thalamus, hypothalamus, and
    deep nuclei
  • controls emotional experience and expression
  • produces feelings
  • recognizes life threatening upsets in a person's
    physical or psychological condition and counters
    them

33
Brain Stem
  • The brain stem is composed of three major parts
  • midbrain, pons, and medulla oblongata
  • The brain stem serves as a pathway for fiber
    tracts running to (sensory impulses) and from
    (motor impulses) the cerebrum and is the sight
    where many cranial nerves (PNS) arise

34
Midbrain
  • Corpora quadrigemina 4 dome-like protrusions on
    the dorsal midbrain surface
  • centers for visual and auditory reflexes
  • Cerebral peduncles bundles of nerve fibers
  • acts in reflex actions (visual and auditory)
  • also contains areas associated with reticular
    formation
  • contains bundles of fibers that join lower parts
    of brainstem and spinal cord with higher part of
    brain
  • cerebral aqueduct

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Pons
  • "bridge" or pathway of conduction tracts
  • helps regulate rate and depth of breathing
  • also contains areas associated with reticular
    formation
  • relays nerve impulses to and from medulla
    oblongata and cerebellum

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Medulla Oblongata
  • conducts ascending and descending impulses
    between brain and spinal cord
  • contains an autonomic reflex center involved in
    maintaining homeostasis of important visceral
    organs
  • contains cardiac, vasomotor, and respiratory
    control centers
  • contains various nonvital reflex control centers
    (coughing, sneezing, swallowing, vomiting)

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Reticular Formation
  • complex network of nerve fibers scattered
    throughout the brain stem
  • controls brains alertness
  • inhibited sleep, alcohol, tranquilizers
  • extends into the diencephalon
  • connects to centers of hypothalamus, basal
    nuclei, cerebellum, and cerebrum
  • filters incoming sensory information
  • arouses cerebral cortex into state of
    wakefulness
  • Types pf Sleep
  • Slow wave (90min) overall decrease in reticular
    formation activity
  • person is tired
  • restful
  • reduced blood pressure and respiratory rate
  • Rapid eye movement sleep (REM) certain areas of
    brain are active
  • responsible for dreaming
  • lasts 15 minutes
  • some areas of brain active
  • heart and respiratory rates irregular

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Cerebellum
  • note pattern of white matter (within gray matter)
    "arbor vitae"
  • integrates sensory information concerning
    position of body parts
  • coordinates skeletal muscle activity
  • maintains posture

43
PERIFERAL NERVOUS SYSTEM
44
PSN Introduction
  • The peripheral nervous system (PNS) consists of
    nerves that extend to and from the CNS organs
  • Cranial nerves arising from the brain
  • Somatic fibers connecting to the skin and
    skeletal muscles
  • Autonomic fibers connecting to viscera
  • Spinal nerves arising from the spinal cord
  • Somatic fibers connecting to the skin and
    skeletal muscles
  • Autonomic fibers connecting to viscera
  • The PNS is divided into a sensory and motor
    branch
  • The motor branch of the PNS is further subdivided
    into a somatic nervous system (from CNS to skin
    and skeletal muscles) and autonomic nervous
    system (from CNS to smooth muscle, cardiac muscle
    and endocrine glands)

45
Structure Of Peripheral Nerves
  • A nerve is a cord-like bundle of axons wrapped in
    CT
  • Structure of a Nerve
  • Three types of CT wrappings (similar to muscle)
  • endoneurium around each axon (and myelin)
  • perineurium around each fascicle (bundle) of
    axons
  • epineurium around each nerve

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Nerve Fiber Classification
  • Mixed Nerves
  • Nerves that carry impulses both to and from the
    CNS
  • contain both sensory and motor axons
  • most common 2-way communication
  • Sensory (afferent) Nerves
  • Nerves that only carry sensory impulses toward
    the CNS
  • rare (only three pairs of cranial nerves)
  • Motor (efferent) Nerves
  • Nerves that only carry motor impulses away from
    CNS
  • rare (only five pairs of cranial nerves)

48
Nerve Fiber Classification cont.
  • General somatic efferent fibers
  • carry motor impulses from CNS to skeletal
    muscles
  • General somatic afferent fibers
  • carry sensory impulses to CNS from skin and
    skeletal muscles
  • General visceral efferent fibers
  • carry motor impulses away from CNS to smooth
    muscles and glands
  • General visceral afferent fibers
  • carry sensory impulses to CNS from blood vessels
    and internal organs
  • Special somatic efferent fibers
  • carry motor impulses from brain to muscles used
    in chewing, swallowing, speaking, and forming
    facial expressions
  • Special visceral afferent fibers
  • carry sensory impulses to brain from olfactory
    and taste receptors
  • Special somatic afferent fibers
  • carry sensory impulses to brain from receptors
    of sight, hearing, and equilibrium

49
Cranial Nerves
  • 12 pairs
  • 2 pairs to/from forebrain
  • 10 pairs to/from brain stem
  • Memorize by using one of many mnemonic devices
  • One example is "Oh, Oh, Oh, To Touch And Feel
    Very Good Velvet AH!"
  • See www.medicalmnemonics.com for more.

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52
Spinal Nerves
  • Introduction
  • Recall that a spinal nerve is formed from the
    fusion of a dorsal and ventral root
  • Then the spinal nerve passes through its
    intervertebral foramen
  • Spinal nerves are associated with the spinal cord
    and are named for the region of the spinal cord
    from which they arise

53
Spinal Nerves cont.
  • General Characteristics
  • 31 pairs
  • 8 cervical nerves, 12 thoracic nerves, 5 lumbar
    nerves, 5 sacral nerves, 1 coccygeal nerve
  • Composition all mixed nerves

54
Spinal Nerve cont.
  • Dorsal root (posterior or sensory root)
  • axons of sensory neurons in the dorsal root
    ganglion
  • Ventral root (anterior or motor root)
  • axons of motor neurons whose cell bodies are in
    spinal cord
  • Spinal nerve
  • union of ventral root and dorsal root

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Dermatome
  • an area of skin that the sensory nerve fibers of
    a particular spinal nerve innervate

57
Distribution of Spinal Nerves
  • A short distance after passing through its
    intervertebral foramen, a spinal nerve branches
    into several branches
  • A posterior branch (dorsal ramus)
  • A large anterior branch (i.e. ventral ramus)
  • Branches to paravertebral (autonomic) ganglia
    rami communicans

58
Nerve plexus
  • Definition a branching network (of the anterior
    branches) of spinal nerves
  • The nerves do not extend directly to the body
    part they innervate, instead they form networks.
  • present in all spinal nerves except T2 - T12
  • cervical plexus neck muscles and diaphragm
    (breathing)
  • brachial plexus upper limb
  • lumbar plexus anterior and medial thigh
  • sacral plexus posterior lower limb, leg

59
Nerve plexus cont.
  • Each resulting branch of the plexus contains the
    fibers from several spinal nerves
  • Fibers from each spinal nerve are carried to the
    body periphery via several different routes or
    branches.
  • Therefore, damage to one spinal segment cannot
    completely paralyze any limb muscle

60
Intercostal Nerves
  • Nerves T2-T11 run in intercostal spaces
  • Supply skin (sensory) and muscles (motor) in the
    surrounding area

61
AUTONOMIC NERVOUS SYSTEM (ANS)
62
Autonomic Nervous System
  • functions without conscious effort
  • controls visceral activities
  • regulates smooth muscle, cardiac muscle, and
    glands
  • efferent fibers typically lead to ganglia
    outside CNS
  • Controlled largely by CNS
  • Two Divisions
  • sympathetic prepares body for fight or flight
    situations
  • parasympathetic prepares body for resting and
    digesting activities

63
Sympathetic Division
  • thoracolumbar divison location of
    preganglionic neurons
  • preganglionic fibers leave spinal nerves through
    white rami and enter paravertebral ganglia
  • paraverterbral ganglia and fibers that connect
    them make up the sympathetic trunk

64
Sympathetic Division cont.
  • postganglionic fibers extend from sympathetic
    ganglia to visceral organs
  • postganglionic fibers usually pass through gray
    rami and return to a spinal nerve before
    proceeding to an effector

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Parasympathetic Division
  • craniosacral division location of
    preganglionic neurons
  • ganglia are near or within various organs
  • terminal ganglia
  • short postganglionic fibers
  • continue to specific muscles or glands
  • preganglionic fibers of the head are included in
    nerves III, VII, and IX
  • preganglionic fibers of thorax and abdomen are
    parts of nerve X

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Autonomic Neurotransmitters
  • Cholinergic Fibers
  • release acetylcholine
  • preganglionic sympathetic and parasympathetic
    fibers
  • postganglionic parasympathetic fibers
  • Adrenergic Fibers
  • release norepinephrine
  • most postganglionic sympathetic fibers

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