Peripheral Nervous System - Flashcards
1
Q
What are the two major divisions of the peripheral nervous system?
A
Somatic and Autonomic
2
Q
What are the two divisions of the autonomic nervous system?
A
Sympathetic and para-sympathetic
3
Q
What are sensory receptors classified by?
A
- Functionality by type of detected stimulus
- Location of stimulus
- Structural complexity
4
Q
How does transduction occur in sensory receptors?
A
stimulus energy is converted into a graded potential which must reach threshold for nerve impulse
5
Q
What are pain receptors called and what type of fibers carry impulses there?
A
Nociceptors
- type A (myelinated) fibers carry fast pain sensations
- type C (unmyelinated) fibers carry slow pain sensations
6
Q
What do chemoreceptors do?
A
Respond to water soluble and lipid soluble substances dissolved in body fluids
7
Q
What do mechanoreceptors do and what are the subtypes of mechanoreceptors (3)?
A
Sensitive to stimuli that distort the plasma membrane –> mechanically gated ion channels
- Proprioceptors –> watch positions of joints
- Baroreceptors –> detect changes in pressure (inside stimulus, changes in blood vessels)
- Tactile receptors –> sensations of touch, pressure and vibrations (outside stimulus)
8
Q
What are the three classifications of sensory receptors according to location?
A
- Externoreceptors –> response to stimuli from outside the body (skin and most special sense organs)
- Internoceptors –> respond to stimulus from internal viscera and blood vessels; sensitive to chemical changes, tissue stretch and temperature changes)
- Proprioceptors –> Respond to stretch in skeletal muscles, joints, tendons, ligaments and connective tissues covering bones and muscles (lets the brain know what is happening)
9
Q
What are the anatomical classifications of sensory receptors according to structural complexity?
A
- Unencapuslated nerve endings
2. Encapsulated nerve endings
10
Q
Where would you find unencapsulated nerve endings and what type of fibers are they usually made of?
A
Found abundantly in epithelial and connective tissue, mainly group C fibers and they are not protected by accessory structures
11
Q
What type of receptors have encapsulated nerve endings and what are they enclosed by?
A
Mechanoreceptors –> enclosed by connective tissue capsule
12
Q
What is the classification of hair follicle receptors?
A
- unencapsulated dendritic endings
- mechanoreceptors wrapped around air
- rapidly adapting
13
Q
What unencapsulated receptors have free nerve endings?
A
- thermoreceptors (cold receptors 10-40 degrees are superficial while heat receptors 32-48 degrees are deeper)
- Mechanoreceptors
- Nocioreceptors
14
Q
What is a Merkel disk and where are they found?
A
Mechanoreceptors for light steady pressure –> found in the basal layer of epidermis
*slowly adapting
15
Q
What are Meissner’s corpuscles, what do they do and where are they found?
A
–> ENCAPSULATED dendritic endings
–> detects light pressure, discriminative touch, low frequency vibrations
–> found in dermal papillae of hairless skin
16
Q
What are Pacinian corpuscles, what do they do and where are they found?
A
–> ENCAPSULATED dendtritic endings
–> sense deep pressure, stretch, high frequency vibratiion
–> found in the dermis and hypodermis
17
Q
What are Ruffini endings, what do they do and where are they found?
A
–> ENCAPSULATED dendritic endings
–> receptive to continuous pressure and stretch
–> found in the dermis, hypodermis and joint capsule
18
Q
What are the superficial and deep fast adapting dendritic endings?
A
Superficial: Miessner corpuscles
Deep: Pacinian corpuscles
19
Q
What are the superficial and deep slow adapting dendritic endings?
A
Superficial: Merkel cells
Deep: Ruffini endings
20
Q
What is the difference between sensation and perception?
A
Sensation: awareness of changes in the internal and external environment
Perception: conscious interpretation of the stimuli
21
Q
What are the 3 basic levels of neural integration in sensory systems?
A
- Receptor level
- Circuit level
- Perceptual level
22
Q
What must happen in order for a sensation to occur?
A
Stimulus must excite the receptor (must match receptor specificity and applied in receptive field), transduction occurs (changing stimulus energy into graded potential) and the action potential has to reach the CNS (graded potential must reach threshold)
23
Q
What does adaptation mean in terms of sensory receptors?
A
Change in sensitivity to a constant stimulus –> receptor membranes become less responsive and potentials decline or stop
24
Q
What is a phasic receptor?
A
Fast-adapting –> sends signals at the beginning or end of a stimulus
Ex: receptors for pressure, touch and smell
- think about a smell being in a room, you stop noticing it after a while
- think clothes, you don’t feel your clothes on your body all day
25
What is a tonic receptor?
Adapt slowly or not at all
Ex: nociceptors and most proprioceptors --> you need pain in order for these to actually "turn on"
26
What happens when stimulus is being processed at a circuit level?
Pathways of 3 NEURONS conduct sensory impulses received from receptors towards appropriate cortical regions
27
What does feature abstraction mean as an aspect of sensory perception?
Identification of more complex aspects of multiple stimuli properties --> being able to describe properties of something without knowing what it is
Ex: velvet is compressible and smooth but not completely continuous
28
Pain impulses travel on what type of fibers? What do they release?
Thinly myelinated α fibers --> release glutamate
Unmyelinated C fibers --> release glutamate and substance P
29
What does pain warn?
Actual or impending tissue damage
30
What is gate control theory?
Non-painful inputs (AB) inhibit pain transmission (C fibers)
--> less of the information is actually going through but only while there is an application of stimulus
31
What is involved in descending pain control?
- some pain impulses are blocked by inhibitory endogenous opioids (endorphins and enkephalins)
- Descending fibers from cortex & hypothalamus release INHIBITORY neurotransmitters which suppress pain signals
32
What does hyperalgesia mean?
pain amplification
33
How do we "learn" pain and what does this mean?
NDMA receptors allow the spinal cord to "learn" hyperalgesia (as this is used more, the body gets better at feeling pain and this can lead to chronic pain)
34
What is referred pain?
Pain that is coming from a different region in the body but it actually comes from somewhere else.
35
What is the criteria for a neuron to be able to regenerate?
If the body is still intact but the axon is damaged, it can regenerate using coordinated activity between macrophages, Schwaan cells, and axons
36
What supporting neural cells have growth-inhibiting proteins?
ogliodendrocytes
37
What supporting neural cells cause scarring?
Astrocytes form scar tissues --> prevents the CNS fiber regeneration
38
What are the steps in regenerating an axon?
1. Wallerian degeneration: Sheath breaks down distally (towards axon terminal)
2. Macrophages clean out the dead axon distal to the injury
3. Axon sprouts grow through the regeneration tube made by the Schwaan cells
4. Axon regenerates and new myelin sheath is formed
39
What are the two classifications of PNS nerves?
Cranial and spinal nerves
40
What is CN I?
Olfactory --> special sensory; smell
- comes from the olfactory receptor cells of nasal cavity
- go through ciribriform plate
- fibers synapse in olfactory bulbs
- pathway reaches to primary olfactory cortex
41
What is CN II?
Optic --> special sensory; sight
- come from retinas, pass through optic canal, converge and partially cross in optic chiasma
- continue to thalamus
42
How can you test CN II?
Holding up fingers and asking them to tell you how many fingers you're holding up
43
What is CN III?
Oculomotor --> motor nerve
- somatic: raises eyelid - levator palpabrae superioris
- PSNS: sphinter pupillae & cilliary muscle
Exits through superior orbital fissure to muscles around the eye
44
What is CN IV?
Trochlear --> motor
Innervates superior oblique muscle, lever system
Exits through superior orbital fissure
45
What is CN V?
Trigeminal --> both motor and sensory
46
What are the three divisions of the CN V, where do they pass through and are they sensory or motor?
CN V = Trigeminal nerve
1. Opthalmic (V1) --> passes through superior orbital fissure
- sensory only
2. Maxillary (V2) --> passes through foramen rotundum
- sensory only
3. Mandibular (v2) --> passes through foramen ovale
- sensory and motor
- muscles of mastication, tensor tympani, and tensor celi palatine
47
How would you test for functioning of CN V?
CN V = Trigeminal
Touching the forehead (V1)
Touching the cheek (V2)
Touching the jaw and watching mastication movements (V3)
48
What is CN VI?
Abducens --> motor
- innervates lateral rectus muscle
- exits through superior orbital fissure
49
Explain the mnemonic LR6SO4 and all the rest are 3
Lateral rectus is innervated by CN VI
Superior oblique is innervated by CN IV
all the other eye muscles are innervated by CN III
50
What is cranial nerve VII?
Facial --> both sensory and motor
- travels through internal acoustic meatuses, exits skull at stylomastoid foamina
Motor: muscles of facial expressions and stapedius, PSNS to glands
Sensory: taste from anterior 2/3 of the tongue, skin external acoustic meatus and auricle
51
What is cranial nerve VIII?
Vestibulocochlear/Auditory --> special sensory; hearing
Cochlear division - hearing
Vestibular division - equilibrium and balance
Afferent fibers go from inner ear to brainstem through internal acoustic meatuses
52
What is cranial nerve IX?
Glossopharyngeal --> both sensory and motor
Motor: PSNS to parotid gland, stylopharyngeus which elevates pharynx during swallowing
Sensory: taste on posterior 1/3 of tongue, sensor for pressure (how much blood is going into the brain and the chemical composition of it)
53
What is Cranial nerve X?
Vagus --> both sensory and motor
Motor: PSNS innervation of heart, lungs and abdominal viscera, muscles of larynx and pharynx
Sensory: thoracic/abdominal viscera, external acoustic meatus, and taste from posterior tongue and pharynx
--> baroreceptors and chemotrceptors
54
What does vagus mean?
Wanderer --> the nerve wanders from the brain all the way to the viscera (liver, stomach, kidneys, intestines)
55
What is cranial nerve XI?
Spinal Accessory --> motor
- innervates trapezius and sternocleidomastoid
Formed from ventral rootlets from C1-C5 region of spinal cord (NOT THE BRAIN), enters brain through foramen magnum and exits through jugular foramen
56
How do you test CN XI?
CN XI = Spinal accessory nerves
Test the surrounding muscles for function
57
What is cranial nerve XII?
Hypoglossal --> motor
- innervates majority of tongue muscles contributing to swallowing and speech
Exits skull through hypoglossal canal
58
How would you test for CN VII?
CN VII = facial nerve
If a person can open their eyes and mouth really wide and shut them really tight
Also testing for symmetry - do both sides of the lips move up when smiling?
59
What is a dermatome and what is it used for?
Area of skin innervated by cutaneous branches of a single spinal nerve --> used to determine spinal cord damage
60
What is Hilton's law?
Any nerve serving a muscle that produces movement at a joint also innervates the joint and the skin over the joint
61
What is the organization of the spinal cord to rami?
Spinal cord --> rootlets --> root --> spinal nerve --> rami
62
Each spinal nerve branches into 4 mixed rami, what are these rami?
1. Meningeal branch: to spinal meninges and blood vessels
2. Dorsal ramus: to posterior body trunk
3. Ventral ramus: form plexuses
4. Rami communicantes: autonomic pathways (join to ventral rami in thoracic region)
63
What are the exceptions of ventral ramus forming plexuses?
T2-T12: they act as intercostal nerves --> muscles of ribs, anerolateral thorax & abdominal walls
64
Why do we have plexuses of ventral rami?
Plexus of ventral rami allows each limb to receive nerve supply from multiple spinal cords --> the benefit is that damaging one spinal segment or root will not completely paralyze any limb muscle
65
What does the cervical plexus do and where is it?
What is the very important nerve in the plexus?
Cervical plexus runs from C1-C5 --> it innervates skin and muscles of neck, ear, back of the neck and shoulders
C345 = Phrenic nerve
This nerve keeps the diaphragm alive, very important for breathing
66
What happens if you damage the spinal cord above C1 or C2? What about below that?
Above C1, C2 --> could be fatal
Just below that you would still be able to breathe but not move
67
What ventral rami forms the brachial plexus and what does it do?
Brachial plexus is made from C5-C8 and T1 --> innervates upper limb and pectoral girdle
68
Be able to draw the brachial plexus
What is the easy way to do this?
Three Y's men went bowling. One got a strike and one got a spare
1. Draw the sideways Y's, the open end of the top and bottom one at the right side of the page
2. the M (for men) goes between the sticks at the ends of the first and second Y
3. the strike (X) goes in between the first and second Y
4. the spare (\) goes between the second and the third Y
69
What are the branches of the brachial plexus?
Musculotaneous, axillary, median, radial, and ulnar
| in descending order according to the brachial plexus map
70
What are the general functions of the radial branch?
Motor: post posterior muscles of limb
Sensory: posterior skin of limb
71
What are the general functions of the Axillary branch of the brachial plexus?
Motor: deltoid, teres minor
Skin: skin & joint capsule of the shoulder
72
What are the general functions of the musculocutaneous branch of the brachial plexus?
Motor: anterior arm muscles
Sensory: skin of lateral forearm
73
What are the general functions of the median branch of the brachial plexus?
Motor: most lateral flexors & pronators in forearm + some lateral intrinsic muscles muscles of hand
Sensory: skin of lateral aspect of hand
74
What are the general functions of the of the ulnar branch of the brachial plexus?
Motor: anterior medial forearm muscles and most medial intrinsic muscles of hand
Sensory: skin of medial aspect of hand
75
What nerves make up the lumbar plexus and what is its function?
L1-L4 make up the lumbar plexus --> innervates thigh, abdominal wall and psoas major
76
Which nerves make up the lumbar plexus and what do they innervate?
Obturator nerve --> innervates adductor muscles
Femoral nerve --> innervates anterior thigh muscles and skin of anterior/medial thigh and medial leg
Pudendal nerve --> skin and muscles of perineum
Siatic nerve --> innervates hamstrings, adductor magnus and most muscles in leg and foot
77
What is a muscle spindle?
Made of 3-10 short intrafusal muscle fibers in a connective tissue capsule
78
What is an intrafusal fiber?
Non-contractile in central regions (lack myofilaments) --> contractile components at the end and they sense the stretch in the muscles
79
What are the 2 different types of afferent endings in intrafusal fibers?
Primary/anulospiral --> sensory endings that innervate spindle centre and are stimulated by rate and degree of stretch
Secondary/flower spray --> sensory endings of type 2 fibers that innervate spindle ends and degree of stretch
80
What fibers maintain spindle sensitivity?
gamma efferent fibers --> innervate contractile end regions
81
What innervates extrafusal fibers
α efferent fibers
Extrafusal fibers are also called contractile muscle fibers
82
What are the two ways to excite muscle spindles?
1. External stretch of muscle and muscle spindle
2. internal stretch of muscle spindle --> activating gamma motor neurons stimulates ends to contract and stretches muscle spindle
83
Explain co-activation of muscle spindles
Both intrafusal and extrafusal muscle fibers contract --> muscle spindle tension is maintained and it can still signal the changes in length of the muscle
*if we did not have this function, activity would be lost - co-activation is necessary to determine sensitivity (we would know that there was a contraction but have no idea how much of a contraction)
84
What are the two types of reflexes?
1. Inborn/intrinsic --> rapid, involuntary, predictable motor response to stimulus
2. Learned/acquired reflexes --> resulting from practice or repetition
85
How do spinal reflexes work and why are they important?
Spinal somatic reflexes have an integration center in the spinal cord and the effectors are skeletal muscle
These are important because they can clinically evaluate sensorimotor function of body
86
What is a Golgi tendon organ and what does it do?
Golgi tendon organ is the inside of a tendon and has afferent sensory neurons that tell the brain the amount of tension in muscle and tendons
87
What is the importance of stretch reflexes?
They maintain muscle tone in large postural muscles and cause muscle contraction in response to increased muscle length
These reflexes are monosynaptic and ipsilateral
88
Explain the steps in the patellar reflex
1. tapping the ligament excites the muscle spindles in the quadriceps femoris
2. Afferent impulses (la primary sensory endings) travel to the spinal cord where they synapse with α motor neurons and interneurons
3. α motor neurons send activating impulses to quads and cause them to contract (extends the knee)
- -> interneurons make inhibitory synapses with ventral horn neurons that stop the contraction of antagonist muscles (hamstrings)
89
Explain reciprocal inhibition
the way interneurons will make inhibitory synapses with ventral horn neurons that stop contracting antagonist muscles
90
What does a Golgi tendon reflex do?
Helps prevent damage due to excessive stretch and is important for smooth onset and termination of muscle contraction
Produces muscle RELAXATION in response to tension
- afferent impulses transmitted to spinal cord
- contracting muscle relaxes and antagonist contracts (reciprocal activation)
- information transmitted simultaneously to cerebellum is used to adjust muscle tension
91
What is the purpose of flexor reflexes?
Flexor reflex = withdrawal reflex
Painful stimulus causes automatic withdrawal of threatened body part --> ipsilateral
92
What is a crossed-extensor reflex and why is it important?
Occurs with flexor reflexes in weight-bearing limbs to MAINTAIN BALANCE
need this to be able to walk --> stimulated side is withdrawn and the contralateral side is extended (reflex consists of ipsilateral flexor reflex and contralateral extensor reflex)
93
What is a superficial reflex? What are some examples?
Excited by gentle cutaneous stimulation --> polysnaptic reflexes that depend on upper motor pathways & cord-level reflex arcs
Ex: plantar reflex, abdominal reflexes, cremaster reflex
