12 - NS Sensory Systems Flashcards
What do spinal nerves consist of
millions of axons that exit the vertebral column
Where do spinal nerves exit through
intervertebral foranima
What does the ventral spinal root do
sends out automatic and somatic motor signals
Where does sensory information return to the spinal cord
dorsal sensory root
What is the DRG
contains cell bodies of sensory neurons
Where are the axons of sensory neurons
all over the body - joints and muscles
When do mixed spinal nerves become peripheral nerves
When it exits the vertebral column
- because outside nervous system domain
What is a ventral ramus
innervate all the large flexor muscles of the front of the body
motor and sensory
mixed spinal nerves
Dorsal Ramus
innervate all the muscles that have an action on the spine
motor and sensory
mixed spinal nerves
Sympathetic Chain Ganglia
part of ventral ramus
Autonomic in nature
lie really close to vertebral column
Where does the spinal cord end
L2-L3
conus medullaris
What are the parts of the vetebral canal
cervical (8)
thoracic (12)
lumbar (5)
sacral (5)
What is the cauda equina
What is its importance
formed by the end (ish) spinal nerve roots
where to put needle for CSF collection (no spinal cord, get out of the way when needle is poked in)
What is the nerve plexus
mixed spinal nerve bundles
innervate structures of the upper limb and lower limb
composed of axons from the ventral ramus of several spinal levels in strategic areas of the body (large muscle groups)
What is the brachial plexus
C5-T1
motor and sensory to upper limbs
intercostal nerves
t1-t11
motor and sensory to the body wall
What is the lumbosacral plexus
L2-S4
motor and sensory to lower limbs
What do plexuses give rise to
named peripheral nerves that innervate specific structures within the upper and lower limbs
often named for regions they serve or the course that they take (eg. ulnar, fibular nerve)
What are dermatones
thin segments of skin
represent different spinal nerves that bring information back to spinal cord
(represent regions of the skin supplied somatic sensory neurons from discrete levels of the spinal cord)
Quantatative Sensations
can put number on (objective)
- touch & pressure
- proprioception
qualatative sensations
subjective
- temperature
- nocioception (pain)
How do all the sensations get into the spinal cord
which type of sensations are sent
dorsal sensory root
mechanoreception (touch, pressure)
- mechemically gated ion channel to generate action potentials
proprioception
nociception (pain)
thermoception (hot/cold sensations)
Where are the cell bodies of the sensory neuron
dorsal root ganglion
how is pain tested
pin prick
how is pressure tested
standardized monofilament
How is temperature tested
cold/hot turning fork
How is touch tested
q tip
Where does proprioception (position sense) come from
- muscle (generate enough force to pull tendon right off bone/protective) - know length of muscle for balance
- tendons (detecting tension generated/transmitted)
- joints (kinesthetics receptors that detect joint position and movement)
What are the two major proprioceptors
muscle spindle (length)
tendon organ
Where does the receptions of sensory symptoms (nocioception, mechanoreception and proprioception) lead to
dorsal sensory root of spinal cord
Proprioception
detect position sense
synapse in ventral horn of spinal cord
cell bodies of motor neurons
generate reflexes
Describe the intraspinal organization
nociception & thermoreception: small afferents with no or little myelin
mechanoreception: medium afferents with light-heavy myelin
proprioception: large afferents with heavy myelin
Describe how reflexes are generated in response to nociception
- sensory receptor (responds to stimulus by producing a generator or receptor potential –> sends action potentials down dorsal sensory root)
- sensory neuron (axon conducts impulses from receptor to integrating center)
- Integrating Center (one or more regions w/in CNS that relay impulses from sensory to motor neurons) –> interneuron: determines if it important to send out a muscle
- Through ventral root to motor neuron to generate reflex
What are reflexes
a fast, involuntary, unplanned sequence of actions in response to a particular stimulus
can be somatic or automatic (constriction of pupil)
can be monosyaptic (one synapse) or polysynaptic (multiple synapse)
What is the spinal cords role in reflexes
acts as integrating centre
What is a monosynaptic reflex
What is an example
One synapse
Testing proprioception
Spinal cord reflex elicited by stretching muscle
1. hit tendon, muscle stretches
2. muscle spindles are activated (tells that muscles are lengthening)
3. spinal cord thinks you’re falling over –> generates reflex that contracts that muscle to oppose the stretch
4. ventral motor nerves –> knee jerks forwards
5. knee jerks forwards by hamstrings relaxing at the same time by reciprocal innervation (talks to interneuron talking to other neuron)
What is an example of a polysnaptic reflex
l o l
what are stretch reflexes and what are they used for
used to clinically test the integrity of specific levels of the spinal cord
S1, 2
achilles tendon reflex (reflexively contract)
1, 2 buckle my shoe
innervate muscles of the calf
L3,4
3,4, kicking the door
patellar tendon reflex
stretching quadricep muscles, causing extension in the knee
sensory and motor aspects
C5, 6
5,6, pick up sticks
biceps brachii tendon reflex
allows you to flex elbows
brachioradialis tendon reflex
arm to radialis outside
C7,8
put the sticks back down
triceps tendon reflex
extends elbow, triceps contract
How does the crossed-extensor reflex work
- painful stimulus activates nociceptor
- primary sensory neuron enters spinal cord and diverges
- one collateral activates ascending pathways for sensation (pain) and postural adjustment (shift in centre of gravity)
- Withdrawal reflex pulls foot away from painful stimulus
- crossed extensor reflex supports body as weight shifts away from painful stimulus
Dorsal Colum (medial limniscal pathway)
white matter at the back of the spinal cord
touch, pressure, propriocetpion
fasciculus cutaneatus: upper limb
fasciulus gracilis: lower limb
How does information travel through the dorsal column
comes in through the primary sensory neuron
sends axons to synapse through spinal cord to brainstem
touch, pressure, proprioception
Anterolateral pathway
out front, off to the side
from spine to thalamus (spinothalamic tract, no stops)
pain and temperature
from dorsal sensory route, neuron ends there and synapses with the secondary sensory neuron
crosses spinal cord to get to opposite anterior lateral tract
pain and temperature
How does pain and temperature travel up
contralateral
How does touch, pressure and proprioception travel
ipsilateral
Where do all the sensations end up
passes through the thalamus to terminate in the
primary somatosensory cortex
What does the middle cerebral artery sense
lateral cortex
face
What does the anterior cerebral artery (medial cortex) sense
lower limb
What is the path of the dorsal column/medial lemniscal pathway (touch and pressure)
- right side of body –> touch and pressure receptors
- right dorsal route
- goes up appropriate wedge of white matter
- upper limb: cuneatous
- lower limb: gracile - medulla, synapse with secondary neuron
- crosses over through the medulla and pons
- passes through midbrain to thalamus to cortex
medial lemniscal: conscious pathway
What is the path of the dorsal column/spinocerebellar tract (proprioception)
same as touch and pressure
cerebellum has dedicated line –> white matter b/c axons of neuron carrying information straight up to cerebellum to help carry out muscular movements
info crosses at the medulla
spinocerebellar tract: subconscious
also receives information from inner ear
what is the path for pain and temperature
- comes in on right, synapses immediately at the grey matter
- secondary neuron corsses hte spinal cord to travel up the lateral spinothalamic tract
- goes from spine to thalamus
- axon splits and talk to reticular portion of the brain, keeps you awake
- talks to midbrain (periaqueductual grey matter) - primary somatosensroy cortex to know where pain is located (localized)
What are the three types of pain
nociceptive pain
neuropathic pain
centralized pain
What is nociceptive pain
activation of nociceptors as a result of damage or trauma to tissues
free nerve endings detect trauma
What is neuropathic pain
abnormal activation of sensory neurons
perceive pain even though no injury to tissue itself
(back pain = pain across leg, buttocks to thigh –> because pinched neuron/nerve before entering spinal cord has been pinched (irritated muscle, irritation from…)
What is centralized pain
abnormal perception of painful stimuli
signals coming from CNS being decoded and perceived by you –> has to do with past experiences with pain
could have wound up pain reception by CNS
What are the types of central sensitization
hyperalgesia:
- truly have pain in tissue because of damage, but pain signals are amplified
Allodynia:
- CNS takes other sensory modalities (touch adn pressure) and make into pain signal to perceive as pain (touch being painful)
What does endogenous pain control do
Where are they located
How does it work
Pathways to limit the amount of pain signals that make their way up to the cerebral cord
Spinal cord ‘gate’ mechanism of pain control
- proprioceptive and touch sensation take preccendent over pain (block it out)
- person touching their knee after hitting it to feel less pain
Inhibitory neuron activated by stimulating it with other sensory modalities (touch and proprioception)
- blocks messages from spinal cord
Which structures have a role in central control of pain
Reticular Formation (not so much)
PAG (mostly): send descending axons down SC to release endorphins and enkephalins on primary and secondary sensory neurons to inhibit pain tramission
What are the types of therapy for exogenous pain relief
nonpharmacologic therapy
- exercise
- multidisciplinary rehabilitation
- acupuncture
- tai-chi, yoga
pharmacologic therapy
- nonsteroidla anti-inflammatory drugs (act peripherally)
- transmadol or duloxetine
- opiods (act centrally)
