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Anatomy & Physiology > Chapter #13: Peripheral Nervous System > Flashcards

Chapter #13: Peripheral Nervous System Flashcards

1
Q

Function of PNS

A

-The PNS links the CNS to the outside world
-Nerves extend from every area of the body: provide the brain with sensory input & allows for motor output to reach effector organs

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2
Q

General Structures of the PNS

A

-any nervous system tissue that is not the brain or spinal cord, including
1) Sensory receptors
2) Afferent fibers: carry sensory info (sends in)
3) Efferent fibers: carry motor info (sends out)

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3
Q

Two subdivisions of the PNS

A
  1. Afferent division
  2. Efferent division
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4
Q

Afferent division

A

-carry impulses from the body to the central nervous system
-concerned with sensory input
-Function: impulses allow CNS to interpret information & send out a response

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5
Q

Efferent division

A

-carry impulses from CNS to the effector organs
-concerned with motor output
-Function: impulses activate muscle or glands to carry out response
-Somatic division: skeletal muscle tissue is the effector
-Autonomic division: cardiac muscle, smooth muscle, & glands are effectors

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6
Q

Sensory receptors

A

Function: specialized structures that respond to changes in the environment (internal or external) called stimuli

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7
Q

How can sensory receptors be classified?

A

1) Stimulus type: what change in the environment activates the receptor
2) Location: either location in the body or the location of the source of the stimulus (inside or outside the body)
3) Receptor structure: nonencapsulated vs. encapsulated

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8
Q

Classification by Stimulus Type

A

1) Mechanoreceptors: respond to mechanical force (body-wide)
2) Thermoreceptors: respond to temperature changes (body-wide)
3) Photoreceptors: respond to light (localized; only found in eyes)
4) Chemoreceptors: respond to chemicals in solution (sense of smell, taste, blood pH, changing nutrient levels)
5) Nociceptors: respond to damaging stimuli (harm receptor; extreme pressure, temperature, pain)

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9
Q

Classification by Stimulus Location

A

1) Exteroceptor: mostly found at or near the body surface (close to surface of skin)
-Receptor is sensitive to stimuli that arise outside the body (ex. photoreceptors, mechanoreceptors)
2) Interoceptor: found deeper in the body
-Receptor responds to stimuli that arise deep in the body (ex. chemoreceptors, mechanoreceptors)
3) Proprioceptors: found in skeletal muscle, tendon, joints, ligaments (highly localized)
-Receptor responds to changes in body movement/position (mechanoreceptors)

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10
Q

Classification by Receptor Structure

A

-Receptors of the general senses
-Composed mostly of nerve endings: modified dendritic endings of sensory neurons; respond to change
-Two types of nerve endings:
1) Non-encapsulated (free) nerve ending
2) Encapsulated nerve ending

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11
Q

Non-encapsulated (free) Nerve Endings

A

-Dendritic ends of sensory receptors have no capsule or covering
-Mostly abundant in epithelia and connective tissue
-Function: respond mostly to pain (nociceptors) and temperature (thermoreceptors)

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12
Q

Other sensations allowed by free nerve endings

A

1) Itch (chemoreceptor): histamine release activates free nerve endings
2) Light pressure (mechanoreceptor): Merkel cells in the integument
3) Light touch specifically for hair (mechanoreceptor): free nerve endings wrap around hair follicle, respond to change in position of the hair & hair follicle

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13
Q

Encapsulated nerve endings

A

-Dendritic endings are enclosed in a capsule
-Most mechanoreceptors are encapsulated
1) Tactile corpuscles: found in dermal papillae of hairless skin
-Function: important for light touch sensation
2) Lamellar corpuscles: located deep in dermis
-Function: stimulated by onset of deep pressure
3) Bulbous corpuscles: located in dermis, subcutaneous tissue, and joint capsules
-Function: respond to deep, continuous pressure
4) Muscle spindles: proprioceptors found in tissue wrapped around skeletal muscle
-Function: detect muscle stretch & initiates reflexes to resist excessive stretching forces
5) Tendon organs: proprioceptors of tendons
-Function: initiates reflex that relaxes skeletal muscle to prevent damage to tendon
6) Joint kinesthetic receptor: proprioceptor monitoring stretch in joints
-Function: provide information about joint position and motion (prevent dislocation)

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14
Q

Sensation vs. Perception

A

-Sensation: awareness of a change in external/internal environment
-Perception: how we interpret the stimuli (do we like the change?)

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15
Q

Somatosensory system

A

-sensory system that specifically serves body wall and limbs
-Receives input from exteroceptors, proprioceptors, and interoceptors

-Three levels of integration operate to allow perception to occur:
1) Receptor level
2) Circuit level
3) Perceptual level

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16
Q

Processing at the Receptor Level

A

-sensation will only occur if a stimulus activates a receptor and if the action potentials reach the CNS.
-For this to happen:
1) Stimulus energy must match receptor specificity
-ex. mechanoreceptor will not respond to light
2) Stimulus must be applied within receptor’s receptive field
-dendrites only extend out so far; smaller receptor field is easier for your brain to figure out where it came from
3) The stimulus energy must be converted to a graded potential
4) Graded potentials must reach threshold for sensory receptor to generate an action potential

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17
Q

Processing at the Circuit Level

A

-delivering impulses to appropriate region of the cerebral cortex

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18
Q

Processing at the Perceptual Level

A

-sensory input is interpreted at the cerebral cortex
-Identifying and appreciating sensation does not depend on the message: it depends on the target neurons of the cerebral cortex (this is why some people have different perceptions of pain)

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19
Q

Perception of Pain

A

-No one likes to feel pain, but it is important
-pain is a warning to prevent you from damaging yourself more than you already have
-you can’t measure pain
-individuals interpret pain differently; different levels of pain tolerance
-What triggers pain?
-Excessive temperature & excessive pressure, chemicals released by damaged cells of injured tissue, histamine, K+, ATP, acids, bradykinin, etc.

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20
Q

Two types of pain

A

1) Sharp pain: usually occurs at onset of injury (shorter pain)
-Impulses carried by small, myelinated fibers
2) Burning pain: occurs after sharp pain (longer pain)
-Impulses carried by small, nonmyelinated fibers

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21
Q

Suppression of pain perception

A

-This occurs most often during times of stress: coping/escape mechanism (if you do not suppress the pain there will be a worse consequence)
-Endorphins and enkephalins suppress feeling of pain (ex. high stress-survival situations like car accidents, sprained ankles in times where you need to run)
-shut off the brain from responding to painful messages when the pain is too much

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22
Q

Pain arising from inside the body

A

1) Visceral Pain: noxious stimulation of receptors of the thorax and abdominal cavity
-Stimuli that result in visceral pain: extreme stretching of tissue, ischemia, muscle spasms/cramps, irritating chemicals (ex. over stretched stomach from eating too much)
2) Referred pain: pain stimuli arising from one part of the body are perceived as coming from another part
-Why does this occur? Visceral pain afferents travel along similar route as some somatic pain fibers (ex. heart attacks: first symptom is pain from the left arm)
-The brain is “confused” by the signal: cannot determine exact location of source

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23
Q

Nerves

A

-cordlike organ that is part of the peripheral nervous system consisting of parallel bundles of peripheral axons enclosed by connective tissue wrappings (reaches parts of the body in shorter distances
-Classification of nerves:
-Type of information the nerve carries: sensory or motor (some send both)
-Direction in which the information is carried:
-Afferent nerves: carry information toward CNS
-Efferent nerves: carry information away from CNS
-Mixed nerves: carry information to and from the CNS

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24
Q

Structure of a nerve

A

-Nerves are bundles of axons enclosed by connective tissue wrappings
-A single axon is surrounded by endoneurium
-Groups of axons are bundled together by perineurium
-Bundles are called fascicles
-Fascicles are bundled together by epineurium
-Bundles of fascicles form the actual nerve
-Also has blood vessels and lymphatic vessels (keeps all fascicles healthy; immune defenses)

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25
Q

Nerve Damage & Regeneration

A

-Remember: mature neurons do not divide!
-In the CNS: severed/damaged axons do not regenerate
-When damaged, the neuron dies (all nerves enclosed by bone)
-In the PNS: severed/damaged axons are capable of regeneration (small regenerative capacity; but do not replace)
-But for regeneration to occur:
1) The cell body must remain undamaged
2) The distance between severed ends must be short
-Regenerated axons do not ”behave” as before the injury (a regenerated neuron in the PNS is not as good as the original)

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26
Q

Axon Regeneration Steps

A
  1. Injury occurs
  2. Clean-up
  3. Axon regeneration begins
  4. Completion of regeneration
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27
Q

Step 1: Injury occurs

A

-The axon is damaged/torn during the injury
-Proximal portion of axon will seal itself off (so that cell body remains protected)
-The distal portion of the cell will degenerate

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28
Q

Step 2: Clean-up

A

-small amount of immune system access
-Macrophages invade area of damaged axon
-Dead/dying portion of neuron is destroyed
-if you do not clean up dead neurons, they would physically get in the way of regeneration

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29
Q

Step 3: Axon regeneration begins

A

-Schwann cells release growth factor to stimulate axon growth
-Proximal end of axon grows filaments
-Schwann cells form a “tube” (place limit on where the axon can grow; ensures the filaments to grow/sprout in the correct manner)

30
Q

Step 4: Completion of regeneration

A

-Axon filaments continue to growforms complete axon
-Schwann cells form new myelin sheath around new axon
-Overall diameter of new axon is smaller than the original causing a lower conduction speed and slower messages

31
Q

Cranial Nerves

A

-Twelve pairs of cranial nerves extend from the brain (24 nerves total)
-Cranial nerves serve head and neck structures (11 nerves)
-Exception: the vagus nerve (X) extends into the abdomen

32
Q

I: Olfactory Nerve

A

-Function: nerves associated with olfaction (smell)
-Sensory nerve

33
Q

II: Optic Nerve

A

-Function: nerves associated with vision
-Sensory nerve

34
Q

III: Oculomotor Nerve

A

-Function: supplies four of the six extrinsic eye muscles the move the eyeball
-Motor Nerve

35
Q

IV: Trochlear Nerve

A

-Function: innervates extrinsic eye muscle that depresses eye and turns it laterally and downward (called the superior oblique)
-Motor Nerve

36
Q

V: Trigeminal Nerve

A

-Function: supplies sensory fibers to the face and motor fibers to the chewing muscles (largest of the cranial nerves)
-sensation of pain, touch, temperature on face
-if damaged, sensory deficits to face &. mouth & changes eating habits
-Both

37
Q

VI: Abducens Nerve

A

-Function: controls extrinsic eye muscle (6th eye muscle) that abducts the eye (the lateral rectus muscle)
-Motor nerve

38
Q

VII: Facial Nerve

A

-Function: innervates muscle for facial expression, contributes to taste (sends info to gustatory cortex)
-Both

39
Q

VIII: Vestibulocochlear Nerve

A

-Function: contributes to hearing and balance (sends info to auditory & vestibular cortex)
-Sensory nerve

40
Q

IX: Glossopharyngeal Nerve

A

-Function: innervates tongue for taste & general senses, innervates pharynx for general senses, innervates muscles of pharynx for swallowing
-Both

41
Q

X: Vagus Nerve

A

-Longest cranial nerve and is the only cranial nerve that serves more than head and neck structures
-Function: fibers extend to and supply sensory & motor fibers to the organs of the thorax and abdomen
-Both

42
Q

XI: Spinal Accessory Nerve

A

-Function: supplies motor fibers to muscles that move the head and neck
-Motor nerve

43
Q

XII: Hypoglossal Nerve

A

-Function: innervates muscles of the tongue and under the tongue to allow movement of tongue for chewing, speech, swallowing
-Motor nerve

44
Q

Mnemonic Mechanism for Nerve names

A

Oh oh oh to touch and feel a girl’s very soft hair

45
Q

Mnemonic Mechanism for Sensory motor or both

A

Some say marry money but my brother says big brains matter more

46
Q

Spinal Nerves

A

-31 pairs of spinal nerves branch from the spinal cord (62 total)
-Function: supply all parts of the body not served by the cranial nerves
-Remember: nerves connect to spinal cord via dorsal (sensory) and ventral (motor) roots
-all spinal nerves serve mixed functions
-Spinal nerves divide to form dorsal ramus and ventral ramus
-Each ramus provides fibers to specific parts of the body

47
Q

Dorsal Ramus

A

-Function: provides sensory and motor fibers to the skin and muscles of the back

48
Q

Ventral ramus (ventral rami)

A

-Function: provides sensory and motor fibers to lateral and ventral body walls (front and side of body) and to the upper & lower limbs
-structurally much more complex
-Ventral rami branch to form nerve networks called nerve plexuses
-Ventral serves most of the body

49
Q

How is a nerve plexus formed?

A

-As ventral rami extend away from from the spinal cord, they branch several times
-Branches from neighboring rami join one another to form a “weaving network” of nerves

50
Q

Effect of nerve plexus formation

A

1) Each branch of the plexus contains fibers from multiple spinal nerves
2) Fibers from each ramus travel to body via several routes
-if you suffer trauma to one part of your body and lose one plexus, you still have others; you can damage one part of your plexus & not have a complete lose of function to the limb overall

51
Q

Nerve plexuses in body:

A

1) Cervical plexus
2) Brachial plexus
3) Lumbosacral plexus

52
Q

Cervical Plexus

A

-Main function: cutaneous nerves that supply the neck, ear, back of the head, and shoulders
-only supplies skin
-C1-C4

53
Q

Brachial Plexus

A

-Function: provides fibers that supply the upper body limbs
-C5-C8 and T1

54
Q

Lumbosacral Plexus

A

-Lumbar plexus and sacral plexus have large degree of overlap
-Lumbar plexus
-Function: innervates parts of abdominal wall muscle, major branches innervate anterior & medial thigh
-Sacral plexus
-Some fibers of lumbar plexus contribute to sacral plexus via lumbosacral trunk
-Function: innervates buttocks and posterior aspect of lower limbs, pelvic structures and perineum
-ex. sciatic nerve (pain in lower back down leg)

55
Q

Anterolateral Thorax and Abdominal Wall

A

-Ventral rami in the thorax do not form plexuses, but are arranged in segmental pattern
-Function: serve intercostal muscles between ribs, skin of anterolateral thorax, and most of abdominal wall

56
Q

Back

A

-Dorsal rami innervate posterior body trunk in segmental pattern
-Function: each dorsal ramus innervates narrow strip of muscle & skin at same area where it emerges from spinal column

57
Q

Skin (Dermatomes)

A

-Area of skin innervated by a single spinal nerve
-Function: provides sensory details (pressure, temperature, pain, etc.) of the skin to the brain

58
Q

Reflex Arc

A

response that enables rapid and predictable responses by the body (automatic, response is almost the same each time; ex. losing your balance)

59
Q

Types of reflexes

A

1) Intrinsic reflex: unlearned, unpremeditated, and involuntary: ”built-in” response
-Rapid, predictable motor response to a stimulus
-Can still be modified according to circumstance
-Ex: making fast adjustments to body posture after losing balance
2) Acquired reflex: results from practice or repetition: ”learned” responses
-Ex: driving a car

60
Q

Components of a reflex arc

A

1) Receptor: site of stimulus action (afferent)
2) Sensory neuron: transmits afferent impulses to the CNS
3) Integration center: synapses found in the CNS (decides motor response)
4) Motor neuron: conducts efferent impulses from the integration center to the effector organ (travel to effector organ)
5) Effector: muscle fiber or gland that responds to the efferent impulse

61
Q

Spinal Reflex

A

-any somatic reflex that is mediated by the spinal cord
-Most occur without any higher CNS involvement

62
Q

Types of spinal reflexes

A

1) Stretch reflex
2) Tendon reflex
3) Flexor and Cross-Extension reflexes

63
Q

Stretches reflexes

A

-ensure that a muscle stays at its optimal length
-Function: prevents damage to muscle and tendon by causing a muscle to contract when the muscle is stretched too far

64
Q

All stretch reflexes are:

A

1) Monosynaptic: have only a single synapse (no interneurons involved) between the sensory neuron and a motor neuron
2) Ipsilateral: the stimulus and response occur on the same side of the body

65
Q

All stretch reflexes are:

A

1) Monosynaptic: have only a single synapse between the sensory neuron and a motor neuron
2) Ipsilateral: the stimulus and response occur on the same side of the body

66
Q

What is involved in stretch reflexes?

A

-Muscle spindles: provide information about the length of a particular muscle
-Muscle spindles function as proprioceptors
-When stretched, muscle spindle sends impulses at higher frequency to spinal cord
-Example: the knee-jerk reflex
-inhibitory; contracting quad and relaxing hamstring

67
Q

Function of tendon reflexes

A

prevents damage to muscle by causing the muscle to relax when tension force (during muscle contraction) becomes so great it can damage the muscle
-almost the opposite of a stretch reflex

68
Q

Tendon Organs

A

-provide information about the amount of tension in a muscle and its associated tendons
-Muscles relax and lengthen in response to tension
-Importance: helps prevent damage due to excessive stretch
-Tendon organs are involved in the tendon reflex
-Tendon reflexes are polysynaptic: involve multiple synapses with chains of interneurons
-excitatory; relax quad and contracting hamstring

69
Q

Flexor & Crossed-Extensor Reflexes

A

-in many instances, these reflexes occur together

70
Q

Flexor reflex (withdrawal reflex)

A

-initiated by painful stimuli
-Causes automatic withdrawal of body part from the stimulus source
-Ipsilateral and polysynaptic
-Importance: protection/survival mechanism
-this reflex can be overridden consciously; ex. piercings or tattoos, blood is drawn, vaccines, etc.

71
Q

Crossed-Extensor Reflex

A

-often accompanies flexor reflex
-Prevalent in weight-bearing limbsmaintains balance
-Reflex is contralateral: the stimulus and response occur on opposite sides of the body
-Ex: stepping on a Lego
-The leg/foot that steps on the Lego has an ipsilateral withdrawal reflex; you pick your foot up off the floor
-Opposite leg has contralateral extensor reflex: you shift your weight to the opposite side of your body

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