9 - Peripheral Nervous System Flashcards
1
Q
What are Sensory receptors?
A
- Specialized to respond to changes in their envmt
2
Q
How are Sensory recpetors classified
A
- Functionally by type of stimulus detected
- Location of stimulus
- Structural complexity
3
Q
What are Nociceptors
A
- pain receptors
- myelinated type A - fast pain
- unmyelinated type C - slow pain
4
Q
What are Thermoreceptors
A
- temperature receptors
5
Q
What are chemoreceptors
A
- respond to water-soluble & lipid-soluble substances dissolved in body fluids
6
Q
What are Mechanoreceptors?
A
- sensitive to stimuli that distort their plasma membranes
- proprioceptors - position of joints & muscles
- Baroreceptors - pressure changes
- tactile receptors - touch, pressure & vibration
7
Q
How are Sensory receptors classified by Location of stimulus?
A
- Exteroceptors - stimuli arising outside body
- Interoceptors (visceroceptors) - stimuli arising in internal viscera & blood vessels
- Proprioceptors - stretch in skeletal muscles, tendons, joints, ligaments & connective tissue coverings of bones & muscles
8
Q
How are Sensory recpetors classified by structural complexity
A
- Unencapsulated nerve endings:
○ Not protected by accessory structures
○ Present throughout body
○ Mainly Group C fibers - Encapsulated nerve endings:
○ All are mechanoreceptors
○ Enclosed by connective tissue capsule
9
Q
What are examples of Unencapsulated Nerve endings
A
- hair follicle receptors
- merkel discs
10
Q
What are examples of Encapsulated Nerve endings
A
- Messiner’s corpuscles
- Pacinian corpuscles
- Ruffini endings
- Muscle spindles
- Golgi (tendon) organs
- Joint kinesthetic receptors
11
Q
Sensation vs. Perception
A
- Sensation - awareness of changes in internal & external environment
- Perception - conscious interpretation of those stimuli
12
Q
What are the 3 basic levels of neuronal integration in sensory systems
A
- Receptor level > circuit level > perceptual level
13
Q
Processing at Receptor level
A
- Generating a signal - for sensation to occur, stimulus must excite a receptor & AP must reach CNS
- Graded potential must reach threshold -> AP
14
Q
What is Adaptation in Receptors
A
- change in sensitivity in presence of constant stimulus
- Receptor membranes become less responsive
- Receptor potentials decline in frequency or stop
15
Q
What are Phasic receptors
A
- fast-adapting, send signals at beginning or end of stimulus
- Ex. Receptors for pressure, touch & smell
16
Q
What are Tonic receptors
A
- adapt slowly or not at all
- Ex. Nociceptors & most proprioceptors
17
Q
Processing at Circuit Level
A
- pathways of 3 neurons conduct sensory impulses from receptors to cortical regions
18
Q
Processing at Perceptual level
A
- Interpretation of sensory input depends on specific location of target neurons in sensory cortex
19
Q
What is the Perception of pain
A
- Warns of actual or impending tissue damage
- Stimuli - Extreme pressure & temp & Chemicals release by tissues - histamines
- Impulses travel on:
- Thinly myelinated AS fibers release glutamate
- Unmyelinated C fibers release glutamate + substance P
20
Q
What is the Gate Control Theory
A
- Non-painful inputs (AB) inhibit pain transmission (C fibers)
21
Q
What is Descending Pain Control
A
- Some pain impulses are blocked by inhibitory endogenous opioids (endorphins & enkephalins)
- Descending fibers from cortex & hypothalamus release inhibitory NTs that suppress pain signals
22
Q
Long Lasting/intense pain can lead to…
A
- hyperalgesia (pain amplification), chronic pain & phantom limb pain
23
Q
What is Visceral pain
A
- Visceral pain results from stimulation of visceral organ receptors
Felt as vague aching, gnawing, burning
24
Q
What is referred pain?
A
- pain from one body region perceived as coming from different region
25
Q
What are the Steps to Nerve Fiber Regeneration
A
- axon becomes fragmented at injury site
- Macrophages clean out dead axon
- axon sprouts grow through regeneration tube formed by schwann cells
- axon regenerates & new myelin sheath forms
26
Q
What are the 2 classifications of peripheral nerves?
A
- cranial nerves
- spinal nerves
27
Q
What is cranial nerve 1
name, function, pathway
A
- Olfactory nerves
- Sensory - olfaction
- Olfactory receptors of nasal cavity > cribriform plates > synapse in olfactory bulbs > primary olfactory cortex
28
Q
What is CN 2
A
- optic nerves
- Sensory - vision
- Retinas > optic canals > cross at optic chiasma > thalamus (LGN) > visual cortex
29
Q
What is CN 3
A
- Motor
- Somatic - raising eyelid (levator palpebrae superioris), directing eyeball (4 extrinsic eye muscles)
- PSNS - sphincter pupillae & ciliary muscle
- Exits through superior orbital fissure to various muscles around/ in eye
30
Q
What is CN 4
A
- Trochlear nerves
- Motor - superior oblique muscle
Exit through superior orbital fissures
31
Q
What is CN 5
A
- Trigeminal nerves
- Ophthalmic (V1) - passes through superior orbital fissure
- Maxillary (V2) - passes through foramen rotundum
- Mandibular (V3) - passes through foramen ovale
- V1 & V2 - sensory ONLY
- V3 - sensory & motor
32
Q
What is CN 6
A
- abducens nerves
- Motor - lateral rectus muscle
- Exit through superior orbital fissures
33
Q
What is CN 7
A
- facial nerves
- Motor - Muscles of facial expression & stapedius, PSNS to glands
- Sensory - Taste from anterior 2/3 of tongue, Skin external acoustic meatus & auricle
- internal acoustic meatuses to exit skull via stylomastoid foramina
34
Q
What is CN 8
A
- Vestibulocochlear nerves (aka Auditory nerves)
- Sensory - hearing (cochlear division) & eqbm/balance (vestibular division)
- pass from inner ear to brainstem through internal acoustic meatus
35
Q
What is CN 9
A
- glossopharyngeal nerves
- Motor - PSNS fibers to parotid gland (salivary gland), Stylopharyngeus (elevates pharynx during swallowing)
- Sensory - Taste - posterior 1/3 tongue , Sensory - posterior 1/3 tongue, oropharynx, tympanic membrane, middle ear, auditory tube, Impulses from carotid chemoreceptors & baroreceptors
- Exit skull through jugular foramen
36
Q
What is CN 10
A
- vagus nerve
- Motor - PSNS innervation of heart, lungs & abdominal viscera, Muscles of larynx & pharynx
- Sensory - Sensory info from thoracic/abdominal viscera & posterior ear/external acoustic meatus, Baroreceptors & chemoreceptors, Taste from posterior tongues & pharynx
- Exit skull via jugular foramen
37
Q
What is CN 11
A
- Spinal Accessory Nerve
- Motor - trapezius & sternocleidomastoid
- Rootlets of spinal cord > Foramen magnum > cranium > accessory nerves exit skull through Jugular foramina
38
Q
What is CN 12
A
- Hypoglossal Nerves
- Motor - tongue muscles contributing to swallowing & speech
- Exit skull via hypoglossal canal
39
Q
What are spinal nerves?
A
- 31 pairs of mixed nerves
- Named according to point of issue from spinal cord
40
Q
What is Dermatome
A
- Area of skin innervated by cutaneous branches of a single spinal nerve
- All spinal nerves except C1
- Way of determining site of spinal cord damage
41
Q
What is the flow of spinal nerves? from cord to rami
A
spinal cord > rootlets > root > spinal nerve > rami
42
Q
What are the 4 mixed rami?
A
- Meningeal branch - to spinal meninges & blood vessels
- Dorsal ramus - to posterior body trunk
- Ventral ramus - form plexuses
- Rami communicantes - autonomic pathways
43
Q
Why do we have a plexus of ventral rami
A
- each muscle in a limbreceives its nerve supply from more than 1 spinal nerve
- damaging one spinal segment will not completely paralyze a limb
44
Q
What is the Cervical Plexus? Purpose?
A
- Innervated skin & muscles of neck, ear, back of head & shoulders
- Phrenic nerve - C345 keeps diaphragm alive
- Keeps you breathing
45
Q
What is the Brachial Plexus?
A
- Formed by ventral rami of C5-T1
- Gives rise to nerves that innervated upper limb & pectoral girdle (motor & sensory)
46
Q
What are the 5 Terminal branches (peripheral nerves) of the Brachial Plexus
A
- radial (P)
- axillary (P)
- musculocutaneous (A)
- median (A)
- ulnar (A)
47
Q
What is function of Radial Nerve
A
- M - posterior muscles of arm
- S - posterior skin of arm
48
Q
What is function of Axillary Nerve
A
- M - deltoid, teres minor
- S - skin & joint capsule of shoulder
49
Q
What is function of Musculocutaneous Nerve
A
- M - anterior arm muscles
- S - skin of lateral forearm
50
Q
What is function of Median Nerve
A
- M - lateral flexors & pronators in forearm & some intrinsic muscles of hand
- S - skin of lateral aspect of hand
51
Q
What is function of Ulnar Nerve
A
- M - anterior medial forearm muscles & medial intrinsic muscles of hand
- S - skin of medial aspect of hand
52
Q
What does the Lumbar plexus innervate? What are the nerves?
A
- Innervated thigh, abdominal wall & psoas muscles
- Obturator nerve - passes through obturator foramen to innervate adductor muscles
- Femoral nerve - innervated anterior thigh muscles & skin of anterior/medial thigh & medial leg
53
Q
What does the Sacral plexus innervate? What are the nerves?
A
- Serves buttock, lower limb, pelvic structures, & perineum
- Pudendal nerve - skin/muscles of perineum
- Sciatic nerve - longest/thickest nerve of body
○ Innervates hamstrings, adductor magnus, & most muscles in leg & foot
○ Composed of tibial & common fibular nerves
54
Q
What is a muscle spindle
A
- Composed of 3-10short intrafusal muscle fibers in a CT capsule
- Intrafusal fibers - noncontractile in central regions (lack myofilaments)
55
Q
Sensory Innervation of muscle spindles
A
- Intrafusal muscle fibers wrapped w/ 2 types of afferent (sensory) endings
- Primary sensory endings (type Ia fiber) - rate & degree of stretch
- Secondary sensory endings (type II fiber) - degree of stretch
56
Q
Motor Innervation of muscle spindles
A
- Contractile end regions are innervated by gamma (y) efferent fibers that maintain spindle sensitivity
- Just the ends of spindles have contractile unit
57
Q
If only motor neurons of muscle spindle are activated…
A
- only extrafusal muscle fibers contract
- muscle spindle becomes slack & no APs are fired
- unable to signal further length changes
58
Q
if a-y Coactivation of muscle spindle occurs …
A
- both extrafusal & intrafusal muscle fibers contract
- muscle spindle tension is maintained
- can signal changes in length
59
Q
What are the parts to a spinal reflex
A
- Integration center is in spinal cord
- Effectors are skeletal muscle
- receptor > sensory neuron > integration center > motor neuron > effector
60
Q
What is a stretch reflex
A
- Maintain muscle tone in large postural muscles
- Cause muscle contraction in response to increased muscle length (stretch)
- All stretch reflexes are monosynaptic & ipsilateral
61
Q
What is a Golgi tendon reflex
A
- Polysynaptic reflexes
- Help to prevent damage due to excessive stretch
- Produce muscle relaxation in response to tension
- Contracting muscle relaxes & antagonist contracts (reciprocal activation)
62
Q
What is a flexor reflex
A
- Painful stimulus causes automatic withdrawal of threatened body part
- Ipsilateral & polysynaptic
Reciprocal inhibition
63
Q
What is a crossed-extensor reflex
A
- Occurs w/ flexor reflexes in weight-bearing limbs to maintain balance
- Consists of ipsilateral flexor reflex & contralateral extensor reflex
○ Stimulated side is withdrawn (flexed)
○ Contralateral side is extended
