2/28/18 nervous system - rob kelly seminarsperipheral nervous system • cranial nerves: exit brain...

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Copyright © 2016 by Elsevier Inc. All rights reserved.

Nervous System

Chapter 23

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Introduction

• Nervous system uses transmitted electrical signals called impulses to relay messages and to stimulate change

• Body’s master communication and regulating system

• Every thought, action, and sensation reflects nerve activity

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Anatomy

• Brain• Spinal cord• Cranial and spinal nerves• Sense organs• Neurotransmitters

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Physiology

• Sensory input• Interpretive functions• Motor output• Higher mental functioning and

emotional responsiveness

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Organization of the Nervous System

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From Patton KT, Thibodeau GA: Anatomy & physiology, ed 7, St. Louis, 2010, Mosby.


Central Nervous System

• Interprets sensory information⎼ Issues instructions in the form of motor

responses• Governs thoughts and emotional

responses• Surrounded by bones of skull and spinal

column

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Major Components of the Central Nervous System

• Brain • Spinal cord• Meninges• Cerebrospinal fluid (CSF)

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Peripheral Nervous System

• Cranial nerves: Exit brain• Spinal nerves: Exit spinal cord• Subdivisions of PNS are:

⎼ SNS: Voluntary (responses consciously controlled)

⎼ ANS: Involuntary • ANS contains sympathetic and

parasympathetic divisions

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Cells of the Nervous System

• Nervous system made up of billions of cells

• Two types: ⎼ Neurons⎼ Neuroglia

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Neuroglia

• Supports, protects, and insulates neurons

• Smaller and more numerous than neurons⎼ Makes up more than 50% of CNS

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Neuroglia

• Glial cells in CNS are:⎼ Astrocytes⎼ Microglia⎼ Oligodendrocytes

• Glial cells in PNS are:⎼ Schwann cells⎼ Satellite cells

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Neurons

• Impulse-conducting cells • Properties include:

⎼ Excitability: Converts stimulus into impulse⎼ Conductibility: Transmits impulses to

neurons, muscles, and glands⎼ Secretion: Secretes neurotransmitters

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Parts of a Neuron

• Cell body⎼ Contains nucleus and other organelles

• Dendrite⎼ Transmits impulses to cell body

• Axon⎼ Transmits impulses away from cell body

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Structures Associated with Axons

• Synaptic bulbs⎼ Located at end of telodendron ⎼ Contain synaptic vesicles

• Synaptic vesicles⎼ Contain neurotransmitters

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Parts of a Neuron

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From Applegate E: The anatomy and physiology learning system, ed 4, St. Louis, 2011, Saunders.

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Functional Classification of Neurons

• Afferent (sensory): Carry impulses to CNS

• Efferent (motor): Carry impulses from CNS to muscles or glands

• Interneurons (association): Carry impulses between sensory and motor neurons and perform integrative functions

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Connective Tissue Layers of Nerves

• Epineurium⎼ Outer layer around entire nerve

• Perineurium⎼ Surrounds fascicles

• Endoneurium ⎼ Surrounds individual neurons and their

extensions

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Nerve Impulses

• Electrical signals that convey information along neurons

• Action potential• Change in the electrical charge of a cell

membrane ⎼ Needed to conduct an impulse⎼ Caused by movement of charged particles

(ions)

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Polarization

• Neuron is resting and not conducting an impulse⎼ Inside has negative (–) charge⎼ Outside has positive (+) charge

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Sodium-Potassium Pump

• Produces and maintains polarization• Pumps ions in opposite directions at an

unequal rate• Ions are:

⎼ Sodium (Na+)⎼ Potassium (K+)

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All-or-None Response

• Impulse is conducted along entire neuron at maximum capacity⎼ No fluctuations or decrease in magnitude

• Impulse continues until it reaches end of neuron

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Refractory Period

• Inability of a neuron to conduct another impulse ⎼ Essentially, a neuron's unresponsive

period

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Nerve Impulse

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Synapse

• Junction between:⎼ Neuron and neuron⎼ Neuron and muscle⎼ Neuron and gland

• Impulses are transmitted across synapse by with help of neurotransmitters

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Synaptic Structures

• Synaptic bulbs ⎼ Located at end of axon⎼ Contain neurotransmitters

• Synaptic gap (cleft)⎼ Space between synaptic bulb and plasma

membrane

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Neurotransmitters

• Chemical messengers involved in synaptic transmission

• Stored in vesicles of presynaptic neuron• Can be excitatory or inhibitory

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Examples of Neurotransmitters

• Acetylcholine is most common• Epinephrine and norepinephrine• Serotonin• Dopamine• Endorphins

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Synapse

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Central Nervous System

• Brain and spinal cord• Protected by

⎼ Skull ⎼ Vertebral column⎼ Meninges⎼ Cerebrospinal fluid (CSF)

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Brain

• It interprets sensory information and governs intellectual activity, consciousness, memories, and emotions

• Uses glucose as an energy source⎼ Cerebrum⎼ Diencephalon⎼ Cerebellum ⎼ Brainstem

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Regions of Brain

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From Herlihy B: The human body in health and illness, ed 4, St. Louis, 2011, Saunders.


Cerebrum

• Largest area of brain• Language centers interpret

written/spoken words as well as speech• Cerebral cortex covers outer region of

cerebrum⎼ Sulci and gyri separate cerebrum into

lobes

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Cerebral Hemispheres

• Cerebrum contains right and left hemispheres ⎼ Research indicates they possess

specialized functions• Longitudinal fissure

⎼ Separates hemispheres• Corpus callosum

⎼ Transverse fibers connecting hemispheres

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Hemispheric Specialization

• Left hemisphere

⎼ Language: Receptive and expressive

⎼ Governs many mathematical abilities, as

well as reasoning and analytical skills

• Right hemisphere specializes in sounds

⎼ Melodies

⎼ Art

⎼ Emotional expression

⎼ Spatial relationships

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Copyright © 2016 by Elsevier Inc. All rights reserved. 35


Cerebral Lobes

• Frontal lobe⎼ Motor function⎼ Personality/mood⎼ Intellect ⎼ Speech

• Parietal lobe⎼ Sensation ⎼ Speech⎼ Understanding

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Cerebral Lobes

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Cerebral Lobes

• Temporal lobe⎼ Auditory ⎼ Naming⎼ Memory

• Occipital lobe⎼ Vision ⎼ Whole object integration

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Brain Waves and States of Consciousness

• Consciousness: Degree of mental alertness and responsiveness

• Levels of consciousness recorded as brain wave patterns⎼ Beta⎼ Alpha⎼ Theta⎼ Delta

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Brain Wave Patterns

• Beta⎼ Wakeful consciousness and mental activity⎼ High-intensity waves are associated with

extreme stress• Alpha

⎼ Awake and relaxed

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Brain Wave Patterns

• Theta⎼ Drowsiness and dreamlike awareness,

subconscious, out-of-body experiences• Delta

⎼ Deep sleep from which the subject is not easily aroused

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Diencephalon

• Located in center of brain• Contains two primary structures:

⎼ Thalamus ⎼ Hypothalamus

• Also contains two glands: ⎼ Pituitary⎼ Pineal

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Diencephalon


Thalamus and Hypothalamus

• Thalamus

⎼ Relays sensory information (except

olfaction) to appropriate parts of cerebrum

• Hypothalamus

⎼ Regulates ANS

⎼ Controls hunger and thirst, anger and

aggression, hormones, sexual behavior,

and sleep patterns

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Pituitary and Pineal Glands

• Pituitary ⎼ Sits in sella turcica of sphenoid bone

• Pineal ⎼ Located below corpus callosum⎼ Produces and secretes melatonin

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Diencephalon, Cerebellum, and Brainstem

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Cerebellum

• Located posterior and inferior to cerebrum⎼ Concerned with muscle tone⎼ Coordinates complex muscular movements⎼ Regulates posture and balance

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Cerebellum

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Brainstem

• Vegatative function• Continuous with spinal cord • Three divisions:

⎼ Midbrain⎼ Pons⎼ Medulla oblongata

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Brainstem


Midbrain and Pons

• Midbrain⎼ Conducts nerve impulses from cerebrum to

pons ⎼ Conducts sensory impulses from spinal

cord to thalamus• Pons

⎼ Connects cerebellum and cerebrum with spinal cord

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Medulla Oblongata

• Transmits sensory and motor impulses between brain and spinal cord

• Contains: ⎼ Respiratory center⎼ Cardiovascular center⎼ Vasomotor center

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Spinal Cord

• Exits skull via foramen magnum • Integrating center and information

highway• Cauda equina

⎼ Lower portion of cord fans out like a horse tail

• Filum terminale⎼ Fibrous extension of cauda equina;

anchored to the coccyx

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Spinal Cord

• Cross section reveals:⎼ White matter: Located on periphery⎼ Gray matter: Located in deeper regions

• H-shaped

• Central canal⎼ Center of spinal cord; contains circulating

CSF

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Spinal Cord

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Spinal Cord: Tracts

• Two types: ⎼ Ascending

• Sensory (afferent) impulses travel up cord⎼ Descending

• Motor (efferent) impulses travel down cord

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Meningeal Layers

• Pia mater⎼ Innermost delicate layer⎼ Attaches to surface of CNS

• Arachnoid⎼ Middle layer; forms loose covering around

CNS• Dura mater

⎼ Outermost dense layer; lies against bones of CNS

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Meningeal Spaces

• Subdural space⎼ Located between dura and arachnoid⎼ Filled with serous fluid

• Epidural space⎼ Located between dura and vertebral canal⎼ Contains adipose tissue, connective tissue,

and blood vessels

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Meninges in Skull Region

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From Leonard P: Building a Medical Vocabulary, ed 7, St. Louis, 2009, Saunders.


Cerebrospinal Fluid

• Fluid circulating around brain and spinal cord

• Functions include:⎼ Supplies oxygen and nutrients to tissues of

brain and spinal cord⎼ Removes metabolic waste during sleep⎼ Acts like a shock absorber

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Peripheral Nervous System

• Cranial nerves⎼ Arise from inferior surface of brain⎼ 12 pairs

• Spinal nerves⎼ Arise from spinal cord ⎼ 31 pairs

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Cranial Nerves

• CN I: Olfactory - smell• CN II: Optic - sight• CN III: Oculomotor - eye movement• CN IV: Trochlear - eye movement• CN V: Trigeminal - face sensation and

chewing • CN VI: Abducens - eye movement • CN VII: Facial - facial expression

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Cranial Nerves

• CN VIII: Vestibulocochlear - hearing and equilibrium

• CN IX: Glossopharyngeal - oral sensation, taste and salivation

• CN X: Vagus - 90% of parasympathetic nervous system

• CN XI: Accessory (spinal accessory) -trapezius and SCM

• CN XII: Hypoglossal - tongue movement63

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Cranial Nerves

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Spinal Nerves

• 31 pairs⎼ 8 cervical nerves ⎼ 12 thoracic nerves⎼ 5 lumbar nerves⎼ 5 sacral nerves⎼ 1 coccygeal nerve

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Structure of Spinal Nerves

• Part of spinal nerve that connects to spinal cord

• Two types:⎼ Ventral (anterior)

• Contains motor neurons⎼ Dorsal (posterior)

• Contains sensory neurons

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Ganglion

• Cluster of nerve cell bodies • Ventral and dorsal roots merge to form

a single nerve

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Nerve Plexuses

• Network of intersecting nerves in PNS• Major plexuses:

⎼ Cervical⎼ Brachial⎼ Lumbosacral

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Dermatomes

• Area of skin supplied by specific sensory nerve root

• Dermatomes are named by their corresponding nerve

• Distribution called a dermatome map⎼ Each map has its own variations

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Dermatome Map

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From Habif: Clinical dermatology: a color guide to diagnosis and therapy, ed 5, St. Louis, 2010, Mosby.


Myotomes

• Group of skeletal muscles supplied by specific motor spinal nerve root

• Distribution is called a myotome map• Sometimes used in muscle tests

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Myotome Map

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Reflexes

• Involuntary and predictable• Cranial reflex means the brain mediated

the reflex⎼ Primitive reflexes may reappear in people

with dementia• Spinal reflex means the spinal cord

mediated the reflex

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Stretch (Patellar) Reflex

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Autonomic Nervous System

• Innervates cardiac and smooth muscles/glands, thus regulating:⎼ Heart and respiration rates⎼ Blood circulation⎼ Body temperature⎼ Gastrointestinal activity and metabolism

• Two divisions: ⎼ Sympathetic and parasympathetic

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Autonomic Nervous System

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Dual Innervation

• Innervated by both sympathetic and parasympathetic divisions

• Some have only sympathetic innervation ⎼ Example: Adrenal glands

• Some have only parasympathetic innervation ⎼ Example: Lacrimal apparatus

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Parasympathetic Division

• Supports functions that conserve and restore energy

• Regulates digestion⎼ "Housekeeping" division

• Nerves emerge from the brainstem and sacrum

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Sympathetic Division

• Dominates during physical exertion or emotional stress⎼ Effects include raises in heart rate, blood

pressure, and respiration• Suppresses activity of the digestive and

urinary systems• Also called the thoracolumbar division

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The Senses

• The five senses:⎼ Touch⎼ Taste⎼ Smell⎼ Vision⎼ Hearing

• Special senses • General senses

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Touch

• Many different types of many receptors, such as: ⎼ Pressure⎼ Movement⎼ Temperature⎼ Nociception and pain perception

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Taste

• Chemoreceptors activated when a molecule from a particular size and shape fits into a particular receptor site

• Five primary tastes:⎼ Salty⎼ Sweet⎼ Bitter⎼ Sour⎼ Savory

• Strongly influenced by smell82


Taste Buds on the Tongue

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From Applegate E: The anatomy and physiology learning system, ed 4, St. Louis, 2011, Saunders.


Smell

• Olfaction: Sense of smell• Scent receptors located in superior

nasal cavity⎼ Molecules fit into receptor sites;

information travels into olfactory bulb and the brain

• Plays important role in sexual behavior

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Structures Involved in Smell

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Vision

• Photoreceptors transmit visual information and send to retina

• Rods are active in dim light, responsible for night vision

• Cones are active in bright light, specialized for detecting color

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Vision: The Retina

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Vision: Rods and Cones

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B: From Patton KT, Thibodeau GA: Anatomy & physiology, ed 7, St. Louis, 2010, Mosby. C: Courtesy Dr. Scott Mittman, Johns Hopkins Hospital, Baltimore, MD.


Hearing

• Mediated by mechanoreceptors ⎼ Detect sound waves and vibrations

• Sound waves vibrate tympanic membrane, causing it to vibrate⎼ Transmitted through three small bones in

middle ear• Oval window covers opening to cochlea

⎼ Sound waves travel until they reach brain

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The Ear

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Pitch and Volume

• Pitch⎼ Quality of tone or sound⎼ Depends on vibration speed

• Volume⎼ Loudness of sound ⎼ Can change without altering pitch

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Balance and Equilibrium

• Fluid-filled canals contain mechanoreceptors that resemble hair⎼ These cells move when we move⎼ Information is sent along nerves, notifying

brain of body movements

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Receptors

• Respond to stimuli by creating a nerve impulse⎼ Our bodies avert harm and seek nourishment

• Specific receptors generally detect specific stimuli

• Perception: Organization, identification, and interpretation of sensory information

• Adaptation: Decrease in sensitivity to prolonged stimulus

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Exteroceptors and Interoceptors

• Exteroceptors⎼ Located on or near surface of the body⎼ Detect touch, pressure, nociception, and

temperature• Interoceptors

⎼ Respond to stretching of blood vessels and gastrointestinal tract movements

⎼ Involved in sensations, such as hunger, thirst, and the urge to defecate and urinate

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Proprioceptors

• Found in muscles, joints, fascia, and ears

• Detect body movements, body position, and muscle stretch

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Receptors Classified by Type of Stimuli Detected

• Chemoreceptors detect chemical stimuli or changes in chemical concentrations of fluids

• Osmoreceptors detect changes in electrolyte concentrations

• Nociceptors detect noxious stimuli, such as excessive heat and cold or tissue damage

• Mechanoreceptors detect mechanical stimuli

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Muscle Spindles

• Stretch receptors wrapped around intrafusal fibers

• Monitor changes in muscle length and rate of change

• Cause reflexive contraction when muscles are overstretched

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Muscle Spindle

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Golgi Tendon Organs

• Activated by muscle tension • Located at musculotendinous junctions• If tension is too great, motor efferent

neurons are inhibited ⎼ Causes inverse stretch reflex

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