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Anatomy and Physiology > Peripheral Nervous System and Special Senses > Flashcards

Peripheral Nervous System and Special Senses Flashcards

1
Q

PNS Structural Classification

A

o Nerves extending from the brain and spinal cord
 Spinal nerves  carry impulses to and from the spinal cord
 Cranial nerves  carry impulses to and from the brain

o Functions
 Serve as communication lines among sensory organs, the brain and spinal cord, and glands or muscles

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2
Q

PNS Functional Classification

A

Motor (efferent) division (continued)

Two subdivisions
Somatic nervous system = voluntary
• Consciously (voluntarily) controls skeletal muscles

Autonomic nervous system = involuntary
• Automatically controls smooth and cardiac muscles and glands
• Further divided into the sympathetic and parasympathetic nervous systems

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3
Q

PNS Glial Cells

A

Schwann cells
 Form myelin sheath around nerve fibers in the PNS

Satellite cells
 Protect and cushion neuron cell bodies

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4
Q

Nervous Tissue: Schwann Cell, Nodes of Ranvier, Oligodendocytes

A

Myelin sheaths

Schwann cells
 Wrap axons in a jelly roll–like fashion (PNS) to form the myelin sheath
 Neurilemma
• Part of the Schwann cell external to the myelin sheath
• Important in nerve fibre regeneration

 Nodes of Ranvier
• Gaps in myelin sheath along the axon
• Speed up propagation of nerve impulses

Oligodendrocytes
 Produce myelin sheaths around axons of the CNS
 Lack a neurilemma

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5
Q

Structure of a Nerve

A
  • Nerves are bundles of neurons found outside the CNS
  • Endoneurium is a CT sheath that surrounds each fiber (surrounds neurolemma and node of Ranvier
  • Perineurium wraps groups of fibers bound into a fascicle
  • Epineurium binds groups of fascicles (cord like strength)
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6
Q

Nerve Types

A

Mixed nerves
o Contain both sensory and motor fibers
o All spinal nerves

Sensory (afferent) nerves
o Carry impulses toward the CNS

Motor (efferent) nerves
o Carry impulses away from the CNS`

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7
Q

Cranial Nerves

A
  • 12 pairs of nerves serve mostly the head and neck from the left and right side of the brain
  • Only the pair of vagus nerves extends to thoracic and abdominal cavities
-	Most are mixed nerves, but three are sensory only 
o	Optic (sight) 
o	Olfactory (sight)
o	Vestibulocochlear (hearing and balance)
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8
Q

Distribution of Cranial Nerves

A
  • Olfactory  sensory impulses for smell
  • Optic  sensory impulses for sight
  • Oculomotor, Trochlear and Abducens  sensory/motor impulses for eye movements
  • Trigeminal  sensory/motor impulses for jaw motion and facial sensation
  • Facial  sensory/motor impulses for facial sensation and taste
  • Vestibulocochlear  sensory impulses relating to hearing and balance
  • Glossopharyngeal  sensory/motor impulses for taste and movement of throat muscles
  • Vagus  Sensory/Motor relating to many autonomic functions
  • Accessory  nerve impulses related to moving of neck muscles
  • Hypoglossal  motor/sensory for tongue movement and sensation
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9
Q

Spinal Nerves

A
  • 31 pairs from right and left side of spinal cord
  • Formed by the combination of the ventral and dorsal roots of the spinal cord
  • Named for the region of the spinal cord from which they arise
  • Spinal nerves divide soon after leaving the spinal cord into a dorsal ramus and a ventral ramus
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10
Q

Rami

A

All rami are mixed nerves

o Ramus
 Branch of a spinal nerve; contains both motor and sensory fibers

o Dorsal rami
 Serve the skin and muscles of the posterior trunk

o Ventral rami (T1–T12)
 Form the intercostal nerves that supply muscles and skin of the ribs and trunk

o Ventral rami (except T1–T12)
 Form a complex of networks (plexus) for the anterior

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11
Q

Plexus

A

o Networks of nerves serving motor and sensory needs of the limbs
o Form from ventral rami of spinal nerves in the cervical, lumbar, and sacral regions

o Four plexuses
 Cervical

Brachial
• 5 separate nerves branch out
• Transmit information to and from the skin and muscles of the shoulder, upper arm, forearm and hand

Lumbar
• 3 main nerves branch out
• Transmit information to and from the anterior and medial thigh and lower leg and thigh and hip

Sacral
• 3 main nerves branch out
• Transmit impulses to and from the skin of the posterior thigh and lower leg, gluteal muscles, hamstring muscles and those that control the foot

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12
Q

Autonomic Nervous System

A

Motor subdivision of the PNS
o Consists only of motor nerves
o Controls the body automatically (and is also known as the involuntary nervous system)
o Regulates cardiac and smooth muscles and glands

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13
Q

ANS vs SNS

A

Somatic nervous system
o Motor neuron cell bodies originate inside the CNS
o Axons extends to skeletal muscles that are served

Autonomic nervous system
o Chain of two motor neurons
 Preganglionic neuron is in the brain or spinal cord
• Those found in spinal cord  begin at the lateral horn
 Postganglionic neuron extends to the organ

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14
Q

Anatomy of the Parasympathetic Division

A
  • Parasympathetic division is also known as the craniosacral division
  • Preganglionic neurons originate in:
    o Cranial nerves III, VII, IX, and X
    o S2 through S4 regions of the spinal cord
  • Preganglionic neurons synapse with terminal ganglia.
    o From there, postganglionic axons extend to organs that are served
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15
Q

Anatomy of the Sympathetic Division

A
  • Sympathetic division is also known as the thoracolumbar division
  • Preganglionic neurons originate from T1 through L2
    o Axons pass through a ramus communicans to enter a sympathetic trunk ganglion
    o Sympathetic trunk, or chain, lies near the spinal cord
  • After synapsing at the ganglion, the axon may synapse with a second neuron at the same or different level
  • Or the preganglionic neuron may pass through the ganglion without synapsing and form part of the splanchnic nerves
    o Splanchnic nerves travel to the collateral ganglion
    o Collateral ganglia serve the abdominal and pelvic organs
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16
Q

Anatomic Functioning

A
  • Body organs served by the autonomic nervous system receive fibers from both divisions
    o Exceptions: blood vessels, structures of the skin, some glands, and the adrenal medulla
    o These exceptions receive only sympathetic fibers
  • When body divisions serve the same organ, they cause antagonistic effects due to different neurotransmitters
    o Parasympathetic (cholinergic) fibers release acetylcholine
    o Sympathetic postganglionic (adrenergic) fibers release norepinephrine
    o Preganglionic axons of both divisions release acetycholine
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17
Q

Sympathetic - Fight or Flight

A 
o	Response to unusual stimulus when emotionally or physically stressed or threatened
o	Takes over to increase activities 
o	Remember as the “E” division
	Exercise
	Excitement
	Emergency 
	Embarrassment
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18
Q

Parasympathetic - Rest and Digest

A 
o	“Rest-and-digest” system
o	Conserves energy 
o	Maintains daily necessary body functions 
o	Remember as the “D” division
	Digestion
	Defecation
	Diuresis
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19
Q

Special Senses

A 
-	Special senses include:
o	Smell
o	Taste
o	Sight
o	Hearing 
o	Equilibrium
  • Special sense receptors
    o Large, complex sensory organs
    o Localized clusters of receptors
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20
Q

The Eye and Vision

A
  • 70 percent of all sensory receptors are in the eyes

- Each eye has over 1 million nerve fibers carrying information to the brain

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21
Q

Anatomy of the Eye - Accessory Structures

A 
-	Accessory structures include the:
o	Extrinsic eye muscles
o	Eyelids 
o	Conjunctiva
o	Lacrimal apparatus
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22
Q

External and Accessory Structures - Explained

A
  • Eyelids
    o Meet at the medial and lateral commissure (canthus)
  • Eyelashes
    o Tarsal glands produce an oily secretion that lubricates the eye
    o Ciliary glands are located between the eyelashes
  • Conjunctiva
    o Membrane that lines the eyelids and eyeball
    o Connects with the transparent cornea
    o Secretes mucus to lubricate the eye and keep it moist
  • Lacrimal apparatus = lacrimal gland + ducts
    o Lacrimal gland—produces lacrimal fluid (tears); situated on lateral end of each eye
    o Tears drain across the eye into the lacrimal canaliculi, then the lacrimal sac, and into the nasolacrimal duct, which empties into the nasal cavity
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23
Q

Tears

A 
-	Tears contain: 
o	Dilute salt solution
o	Mucus 
o	Antibodies
o	Lysozyme (enzyme that destroys bacteria)
  • Function of tears
    o Cleanse, protect, moisten, lubricate the eye
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24
Q

Extrinsic Eye Muscles

A
  • Six muscles attach to the outer surface of the eye

- Produce gross eye movements

25
Q

Internal Structures: The Eyeball

A
  • Three layers, or tunics, form the wall of the eyeball
    o Fibrous layer: outside layer
    o Vascular layer: middle layer
    o Sensory layer: inside layer
  • Humors are fluids that fill the interior of the eyeball
  • Lens divides the eye into two chambers
26
Q

Fibrous Layer: Eyeball

A

Fibrous layer = sclera + cornea
o Sclera
 White connective tissue layer
 Seen anteriorly as the “white of the eye”

o	Cornea
	Transparent, central anterior portion 
	Allows for light to pass through
	Repairs itself easily 
	The only human tissue that can be transplanted without fear of rejection (no blood supply)
27
Q

Vascular Layer: Eyeball

A
  • Choroid is a blood-rich nutritive layer that contains a pigment (prevents light from scattering)
  • Choroid is modified anteriorly into two smooth muscle structures
    o Ciliary body
    o Iris
     Regulates amount of light entering eye
     Pigmented layer that gives eye colour
     Pupil  Rounded opening in the iris
28
Q

Sensory Layer: Eyeball

A

Sensory layer
o Retina contains two layers
 Outer pigmented layer absorbs light and prevents it from scattering
 Inner neural layer contains receptor cells (photoreceptors)
• Rods – dim light
• Cones – bright light and colour vision

o Electrical signals pass from photoreceptors via a two neuron chain
 Bipolar neurons
 Ganglion cells
o Signals leave the retina toward the brain through the optic nerve

o Optic disc (blind spot) is where the optic nerve leaves the eyeball
 Cannot see images focused on the optic disc

29
Q

Rods

A

 Most are found toward the edges of the retina
 Allow vision in dim light and peripheral vision
 All perception is in gray tones

30
Q

Cones

A

 Allow for detailed color vision
 Densest in the center of the retina
 Fovea centralis (area of sharpest vision)–lateral to blind spot
• Area of the retina with only cones
• Visual acuity (sharpest vision) is here
 No photoreceptor cells are at the optic disc, or blind spot

31
Q

Cone Sensitivity

A

 Three types of cones

 Each cone type is sensitive to different wavelengths of visible light

32
Q

Optic Disc

A

 Blind spot on the retina
 Junction between optic nerve and eye
 Cannot transmit optic information

33
Q

Internal Structures: Lens

A
  • Flexible, biconvex crystal-like structure
  • Held in place by a suspensory ligament attached to the ciliary body

Lens divides the eye into two chambers
o Anterior (aqueous) segment
 Anterior to the lens
 Contains aqueous humor, a clear, watery fluid
 Maintains intracochlear pressure and provides nutrients for lens and cornea

o Posterior (vitreous) segment
 Posterior to the lens
 Contains vitreous humor, a gel-like substance
 Prevents eye from collapsing by maintaining intracochlear pressure

34
Q

Physiology of Vision - Visual Pathway to Brain

A

Visual fields and visual pathways to the brain
o Optic nerve
 Bundle of axons that exit the back of the eye carrying impulses from the retina

o Optic chiasma
 Location where the optic nerves cross
 Fibers from the medial side of each eye cross over to the opposite side of the brain

o Optic tracts
 Contain fibers from the lateral side of the eye on the same side and the medial side of the opposite eye
 Synapse with neurons in the thalamus

o Optic radiation
 Axons from the thalamus run to the occipital lobe
 Synapse with cortical cells, and vision interpretation (seeing) occurs

35
Q

Summary of the pathway of impulses from the retina to the point of visual interpretation

A 
	1. Optic nerve
	2. Optic chiasma
	3. Optic tract 
	4. Thalamus 
	5. Optic radiation 
	6. Optic cortex in occipital lobe of brain
36
Q

Visual Fields

A

o Each eye “sees” a slightly different view
o Field of view overlaps for each eye

  • Binocular vision results and provides:
    o Depth perception (three-dimensional vision)
37
Q

Emmetropia

A

(harmonious vision)

o Eye focuses images correctly on the retina

38
Q

Myopia (Nearsightedness)

A

o Distant objects appear blurry
o Light from those objects fails to reach the retina and are focused in front of it
o Results from an eyeball that is too long

39
Q

Hyperopia (farsightedness)

A

o Near objects are blurry, whereas distant objects are clear
o Distant objects are focused behind the retina
o Results from an eyeball that is too short or from a “lazy lens”

40
Q

Astigmatism

A

o Images are blurry
o Results from light focusing as lines, not points, on the retina because of unequal curvatures of the cornea or lens
o Corrective lenses can partially or completely correct astigmatism

41
Q

The Ear: Hearing and Balance

A
  • Ear houses two senses
    o Hearing
    o Equilibrium (balance)
  • Receptors are mechanoreceptors
  • Different organs house receptors for each sense
42
Q

Anatomy of the Ear: External (outer) Ear

A

 Auricle (pinna)
 External acoustic meatus (auditory canal)
• Narrow chamber in the temporal bone
• Lined with skin and ceruminous (earwax) glands
o Cleans and protects the ear
• Ends at the tympanic membrane (eardrum)
o Separates outer ear from inner ear
 External ear is involved only in collecting sound waves

43
Q

Anatomy of the Ear: Middle Ear

A

 Air-filled, mucosa-lined cavity within the temporal bone
 Involved only in the sense of hearing
 Located between tympanic membrane and oval window and round window

 Tympanic Cavity
• Three bones (ossicles) span the cavity
o Malleus (hammer)
o Incus (anvil)
o Stapes (stirrup)
o Connect tympanic membrane to the membrane of oval window
o Transmit and amplify soundwaves
• Function
o Transmit vibrations from tympanic membrane to the fluids of the inner ear
o Vibrations travel from the malleus → incus → stapes → oval window of inner ear

 Pharyngotympanic tube (auditory tube)
• Links middle ear cavity with the throat
• Equalizes pressure in the middle ear cavity so the eardrum can vibrate

44
Q

Internal (inner) ear

A

 Includes sense organs for hearing and balance
 Bony labyrinth (osseous labyrinth) consists of:
• Cochlea
• Vestibule
• Semicircular canals
 Bony labyrinth is filled with perilymph
• Membranous labyrinth is suspended in perilymph and contains endolymph

45
Q

Equilibrium

A
  • Equilibrium receptors of the inner ear are called the vestibular apparatus
  • Vestibular apparatus has two functional parts
46
Q

Static Equilibrium

A

Maculae—receptors in the vestibule
• Report on the position of the head
• Help us keep our head erect
• Send information via the vestibular nerve (division of cranial nerve VIII) to the cerebellum of the brain

47
Q

Anatomy of the Maculae

A
  • Hair cells are embedded in the otolithic membrane
  • Otoliths (tiny stones) float in a gel around hair cells
  • Movements cause otoliths to roll and bend hair cells
  • Impulse transmitted via vestibulocochlear nerve
48
Q

Dynamic Equilibrium

A

Crista ampullaris
• Responds to angular or rotational movements of the head
• Located in the ampulla of each semicircular canal
• Tuft of hair cells covered with cupula (gelatinous cap)
• If the head moves, the cupula drags against the endolymph
• Hair cells are stimulated, and the impulse travels the vestibular nerve to the cerebellum

49
Q

Hearing: Spiral Organs of Corti

A

o Located within the cochlear duct
o Receptors = hair cells on the basilar membrane  extend into endolymph of cochlear duct
o Gel-like tectorial membrane is capable of bending hair cells
o Cochlear nerve attached to hair cells transmits nerve impulses to auditory cortex on temporal lobe

50
Q

Pathway of Vibrations from Sound Waves

A

Pathway of Vibrations from Sound Waves
o Move by the ossicles from the eardrum to the oval window
o Sound is amplified by the ossicles
o Pressure waves cause vibrations in the basilar membrane in the spiral organ of Corti
o Hair cells of the tectorial membrane are bent when the basilar membrane vibrates against it
o An action potential starts in the cochlear nerve (cranial nerve VIII), and the impulse travels to the temporal lobe

  • High-pitched sounds disturb the short, stiff fibers of the basilar membrane
    o Receptor cells close to the oval window are stimulated
  • Low-pitched sounds disturb the long, floppy fibers of the basilar membrane
    o Specific hair cells further along the cochlea are affected
51
Q

Hearing Deficits

A
  • Deafness refers to any loss of hearing
    o Results from injury, loud sounds, excessive earwax, scarring of the tympanic membrane
  • Tinnitus refers to ringing in the ear
    o Results from damage to hair cells in the inner ear
    o Ringing caused by random movement of hair cells
52
Q

Chemical Senses: Smell and Taste

A

Chemoreceptors
o Stimulated by chemicals in solution
o Taste has five types of receptors
o Smell can differentiate a wider range of chemicals

  • Both senses complement each other and respond to many of the same stimuli
53
Q

Olfactory Receptors and Sense of Smell

A
  • Olfactory receptors are in roof of nasal cavity
    o Olfactory receptor cells (neurons) with long cilia known as olfactory hairs detect chemicals
    o Chemicals must be dissolved in mucus for detection by chemoreceptors called olfactory receptors
  • Impulses are transmitted via the olfactory filaments to the olfactory nerve (cranial nerve I)
  • Smells are interpreted in the olfactory cortex
  • When suffering a cold , olfactory receptors are partially blocked
  • Nerve pathway between nose and brain travel through the limbic system
    o Part of brain responsible for emotion
54
Q

Taste Buds and Sense of Taste

A
  • Taste buds house the receptor organs
  • Locations of taste buds
    o Most are on the tongue
    o Soft palate
    o Superior part of the pharynx
    o Cheeks
  • The tongue is covered with projections called papillae that contain taste buds
55
Q

Gustatory Cells

A

Gustatory cells are the taste receptors
o Possess gustatory hairs (long microvilli)
o Gustatory hairs protrude through a taste pore
o Hairs are stimulated by chemicals dissolved in saliva

56
Q

Areas in which Taste Buds are found

A

Impulses are carried to the gustatory complex by several cranial nerves because taste buds are found in different areas
o Facial nerve (cranial nerve VII)
o Glossopharyngeal nerve (cranial nerve IX)
o Vagus nerve (cranial nerve X)
- Taste buds are replaced frequently by basal cells (every 7 to 10 days)

57
Q

Five Basic Taste Sensations

A
  • Sweet receptors respond to sugars, saccharine, some amino acids
  • Sour receptors respond to H+ ions or acids
  • Bitter receptors respond to alkaloids
  • Salty receptors respond to metal ions
  • Umami receptors respond to the amino acid glutamate or the beefy taste of meat
58
Q

Disorders of the Nose and Tongue

A
  • Rhinitis is inflammation of the mucous membranes in the nasal passage
    o Caused by infections, allergies, strong chemical odours and certain drugs
  • Septum problems
  • Infections, injuries and abnormal tissue growth affect the tongue
    o Inadequate oral hygiene can lead to growth of hairs on the tongue

Anatomy and Physiology (14 decks)

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