Chapter 7 nervous system
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Chapter 7 – Nervous system. Ms. Harborth Anatomy and physiology. Structural classification. Central nervous system (CNS) – consists of the brain and spinal cord. Command center Peripheral nervous system (PNS) – part of body outside of CNS.

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Chapter 7 – Nervous system

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Chapter 7 – Nervous system

Ms. Harborth

Anatomy and physiology


Structural classification

  • Central nervous system (CNS) – consists of the brain and spinal cord. Command center

  • Peripheral nervous system (PNS) – part of body outside of CNS.

    • Spinal nerves – carry impulses to and from spinal cord

    • Cranial nerves – carry impulses to and from the brain


  • PNS

    • Sensory (afferent) – carries impulses FROM sensory organs TO the brain

    • Motor (efferent) – carries impulses FROM the brain TO effector organs, muscles, and glands.

      • Somatic nervous system – control skeletal muscles

      • Autonomic nervous system – regulates automatic events (smooth and cardiac muscle)

        • Sympathetic

        • Parasympathetic


Nervous tissue

  • Supporting cells of CNS “neuroglia”

    • Astrocytes – barrier between neurons and capillaries

    • Microglia – phagocytes that “clean”

    • Ependymal cells – beat cilia to circulate cerebrospinal fluid

    • Oligodendrocytes – form myelin sheaths

      Supporting cells of PNS:

    • Schwann cells – form myelin sheaths

    • Satellite cells – protective, cushioning cells

  • Neurons

    • Cell body (Nissl substance & neurofibrils)

    • Processes (fibers)

      • Myelin sheath, Schwann cells (PNS), nodes of Ranvier

    • Dendrites (toward cell body)

    • Axons (away from cell body)

      • Axonal terminals, neurotransmitters, synaptic cleft, synapse


Astrocyte

Ependymal cells

Oligodendrocyte

Microglial cell


Multiple sclerosis

  • Immune system gradually destroys myelin sheaths, converting to scleroses (hardened processes)


Vocab

  • Nuclei – clusters of cell bodies in the CNS

  • Ganglia – small collections of cell bodies found in the PNS.

  • Tracts – bundles of nerve fibers in the CNS

  • Nerves – bundles of nerve fibers in the PNS

  • Whitematter – myelinated fibers in the CNS

  • Graymatter – unmyelinated fibers and cell bodies in the CNS


Classification of neurons

  • Functional (direction of nerve impulse)

    • Sensory (afferent) neurons – neurons carrying impulses from sensory receptors to the CNS. Cell bodies are found in ganglion outside of CNS.

      • Cutaneous sense organs, proprioceptors

    • Motor (efferent) neurons – neurons carrying impulses to viscera and/or muscles and glands. Cell bodies are in the CNS.

    • Association neurons (interneurons) – connect motor and sensory neurons in neural pathways.


Classification of neurons

  • Structural

    • Multipolar neuron – several processes extending from cell body.

      • All motor and association neurons

    • Bipolar neuron – axon and dendrite extend from cell body

      • Rare. Found in some special sense organs.

    • Unipolar neuron– short, single process that usually divides into proximal and distal fibers. Axon conducts nerve impulses both toward AND away from the cell body.

      • Sensory neurons found in PNS ganglia


Neuron physiology

  • Nerve impulse –

    • Irritability

      • 1. Inactive neuron is polarized (more negative inside)

      • 2. Stimulus excites neuron, permeability increases

      • 3. Depolarization Action Potential

      • 4. Repolarization

      • Saltatory conduction – occurs on myelinated nerves FASTER

      • Cold and continuous pressure hinder conduction

    • Conductivity

      • When action potential reaches axonal endings, tiny vesicles fuse with axonal membranes, rupture, and releases neurotransmitters which start impulse in next neuron

      • Electrochemical event

    • animation


Neuron physiology

  • Reflex Arc

    • Autonomic reflexes

      • Regulate activity of smooth muscles, heart, and glands.

      • Ex: salivary reflex and pupillary reflex.

    • Somatic reflexes

      • Reflexes that stimulate skeletal muscles

    • Minimum of five elements:

      • Sensory receptor

      • Afferent neuron

      • Integration center

      • Efferent neuron

      • Effector organ


Central Nervous System

  • Embryonic development:

    • Neural tube develops

    • 4th week – anterior end of neural tube expands and brain formation begins. Central canal of neural tube becomes 4 ventricles


Functional Anatomy of the Brain

  • Cerebral Hemispheres

  • Diencephalon

  • Cerebellum

  • Brain Stem


Cerebral Hemispheres

  • Gyri: elevated ridges of tissue

  • Sulci: shallow grooves

  • Fissures: deeper grooves which separate large regions of the brain

  • Hemispheres separated by longitudinal fissure

  • Lobes are named for cranial bones that surrounding them


Cerebral Hemisphere

  • Parietal lobe: posterior to central sulcus

    • Somatic sensory area – localizes and interprets impulses from sensory receptors. Sensory pathways cross (left -> right, right -> left)

  • Occipital lobe: visual area

  • Temporal lobe: auditory and olfactory area

  • Frontal lobe: Higher intellectual reasoning in anterior part

    • Primary motor area - Axons of motor neurons form pyramidal (corticospinal) tract which descends to spinal cord. Pathways are crossed.

    • Broca’s area – speech. Only found in one hemisphere

    • Speech area – junction of temporal, parietal, and occipital lobes. Sound out words. One hemisphere.

  • Gray matter (cerebral cortex): cell bodies of neurons

  • White matter: fiber tracts carrying impulses to or from the cortex

  • Corpus callosum: large fiber tract that connects cerebral hemispheres. Allows halves to communicate with one another.

  • Basal nuclei: “islands” of gray matter buried in white matter. Modify instructions sent to muscles.


Diencephalon

  • Thalamus

    • Encloses third ventricle

    • Relay station for sensory impulses

  • Hypothalamus

    • Regulation of temperature, water balance and metabolism. Regulates pituitary

    • Limbic system – “emotional-visceral brain”. Thirst, appetite, sex, pain, pleasure centers.

    • Mammillary bodies – reflex involved in olfaction

  • Epithalamus

    • Pineal body

    • Choroid plexus of third ventricle


Diencephalon


Brain stem

  • Midbrain

    • Cerebral aqueduct – canal that connects third ventricle of diencphalon to fourth ventricle below

    • Cerebral peduncles – convey ascending and descending impulses

    • Corpora quadrigemina– reflex centers for vision and hearing

  • Pons

    • Mostly fiber tracts, but does have some nuclei involved in controlling breathing

  • Medulla oblongata

    • Merges into spinal cord.

    • Regulate vital visceral activities. Controls heart rate, blood pressure, breathing, swallowing, and vomiting

  • Reticular formation

    • Neurons involved in motor control of the visceral organs. RAS (reticular activating system) plays a role in consciousness and awake/sleep cycles. Damage to this area results in coma.


Brain Stem


Cerebellum

  • Two hemispheres

  • Timing for skeletal muscle activity and controls balance/equilibrium

  • Takes info from eyes, ears and muscles to coordinate movements in a smooth fashion


meninges

  • Three connective tissue membranes covering and protecting brain and spinal cord

  • Dura mater – outermost layer. Double-layered, forms periosteum and meningeal layer.

  • Arachnoid mater – span subarachnoid space to attach to innermost membrane

    • Subarachnoid space filled with cerebrospinal fluid. Arachnoid villi protrude through dura mater. Dural sinuses absorb fluid into blood through arachnoid villi.

  • Pia mater – delicate layer clings tightly to surface of brain and spinal cord.

  • Meningitis – inflammation of meninges


  • Cerebrospinal fluid (CSF)

    • similar to blood plasma.

    • continually formed from blood by choroid plexuses

    • continually moving.

  • Blood-brain barrier – any changes in fluid around brain could be detrimental. Barrier composed of the LEAST permeable capillaries in whole body. Water, glucose and essential amino acids can pass through.


Spinal Cord

  • 17 inches long, thickness of a thumb

  • Extends from foramen magnum to 1st or 2nd lumbar vertebrae, right below ribs

  • Caudaequina


Peripheral Nervous System

  • Endoneurium

  • Perineurium

  • Fascicles

  • Epineurium

  • Nerves are classified by which direction they transmit

    • Mixed nerves

    • Afferent (sensory)

    • Efferent (motor)


Cranial nerves

  • 12 pairs (table 7.1)

  • Serve head and neck (except vagus nerves – extend to thoracic and abdominal cavities)

  • I. Olfactory

  • II. Optic

  • III. Oculomotor

  • IV. Trochlear

  • V. Trigeminal

  • VI. Abducens

  • VII. Facial

  • VIII. Vestibulochochlear

  • IX. Glossopharyngeal

  • X. Vagus

  • XI. Accessory

  • XII. Hypoglossal


Spinal Nerves/ Nerve Plexuses

  • 31 pairs of spinal nerves formed by combo of ventral and dorsal roots of spinal cord. Named for region of spinal cord from which they arise.

  • Each spinal nerve divides into dorsal and ventral rami

  • Dorsal rami serve skin and muscles of posterior body trunk

  • Ventral rami of T1 – T12 form intercostal nerves

  • Ventral rami of other spinal nerves form 4 plexuses (Table 7.2)


Autonomic nervous system

  • Motor subdivisions that control automatic activities (cardiac and smooth muscle, and glands)

  • Sympathetic and parasympathetic

    • Sympathetic – mobilizes body during extreme situation (fear, exercise, rage, etc.)

    • Parasympathetic – allows us to “unwind” and conserve energy


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