somatosensory Flashcards
Gray matter
neuron cell bodies with little myelin
site of information processing, synaptic integration
White matter
abundantly myelinated axons
carry signals from one part of the CNS to another
posterior (dorsal) root of spinal nerve only carries ____ ____
sensory fibers
anterior (ventral) root of pinal nerve carries only ___ ____
motor fibers
What are columns or funiculi of white matter?
three pairs of these white matter bundles
ascending tracts carry..
sensory information up the spinal cord
descending tracts carry…
motor information down the spinal cord
What is decussation?
as the fibers pass up or down the brainstem and spinal cord they cross over from the left to the right side and vice versa
What is contralateral?
when the origin and destination of a tract are on opposite sides of the body
What is ipilateral?
when the origin and destination of a tract are on the same side of the body;does not decussate
What are the ascending tracts?
gracile fasciculus cuneate fasciculus spinothalamic tract spinoreticular tract posterior and anterior spinocerebellar tracts
What are the two neurons involved in descending tracts?
upper motor neuron- originates in cerebral cortex or brainstem and terminates on a lower motor neuron
lower motor neuron- in brianstem or spinal cord
What is the cause of chickenpox?
varicella-zoster virus
Where does the chickenpox virus remain for life?
posterior root ganglia
What is shingles?
localized disease caused by the virus traveling down the sensory nerves by fast axonal transport when immune system is comprimised
What are symptoms of shingles?
painful trail of skin discoloration and fluid-filled vesicles along path of nerve, usually in chest and waist on one side of the body, pain and itching
What is meningitis? what is the cause?
inflammation of the meninges
- most serious between ages of 3 months and 2 years
- caused by bacterial and/or viral invasion of the CNS
- Pia mater and arachnoid ar emost often affected
Signs of meningitis
high fever, stiff neck, drowsiness, intense headache
- may progress to coma then death within hours of onset
how is meningitis diagnosed?
by examining CSF for bacteria
- lumbar puncture draws fluid from subarachnoid space between two lumber vertebrae
What is spina bifida?
congenital defect in whihc one or more vertebrae fail to form a complete vertebral arch for enclosure of the spinal cord
When does spina bifida occur?
first 4 weeks of development, so folic acid supplementation must begin 3 months before contraception
What is a complete transection?
complete severance of cord
-immediate loss of motor control below level of injury
Where along the spine would spinal cord trauma pose the threat of respiratory failure?
above C4
What doe sthe medulla oblongata control?
caridac center- adjusts rate and force of heart
vasomotor center- adjusts blood vessel diameter
respiratory centers- control rate and depth of breahting
reflex centers- for coughing, sneezing, gagging, swallowing, vomiting, etc.
Pyramids of the medulla oblongata contain descending fibers called corticospinal tracts, what do they carry?
motor signals to skeletal muscles
In the medulla oblongata, what does the inferior olivary nucleus do?
relay center for signals to cerebellum
What is the reticular formation of the medulla oblongata?
loose network of nuclei extending throughout the medulla, pons, and midbrain
- contains cardiac, vasomotor and respiratory centers
Metencephalon
develops into the pons and cerebellum
Pons
anterior bulge in brainstem, rostral to medulla
cerebral peduncles
connnect cerebellum to pons and midbrian
Characterisitics of the pons
ascending sensory tracts, descending motor tracts, pathways in and out of cerebellum, cranial nerves V VI VII VIII, reticular formation whcih contains additional nuclei concerned with sleep, respiration, posture
Parts of midbrain & function
- substantia nigra- dark gray to black nucleus, motor center that relays inhibitory signals to thalamus and basal nuclei preventing unwanted body movement
- cerebral crus- bundles of nerve fibers that connect the cererbrum to the pons, carries corticospinal tracts
What part of the brain leads to tremors of parkinson’s?
the midbrian- degeneration of neurons
Where is the reticular formation?
loosely organized web of gray matter that runs vertically through all levels of the brianstem, clusters of gray matter scattered throughout pons, midbrain and medulla, occupies space between white fiber tracts and brianstem nuclei, and many connections with many areas of cerebrum
What does the reticular formation control?
somatic motor control (motor coordinaiton), cardiovascular control, pain modulation, sleep and consciousness, habituation (brain ignores repetitive, incosequential stimuli)
What is the largets part of the hindrbain? (second largest part of the brain as a whole)
cerebellum
What deos the cerebellum consist of?
right and elft cerebellar hemispheres connected by vermis
Characteristics of cerebellum
cortex of gray matter with folds and four deep nuclei in each hemisphere
What is the arbor vitae?
white matter branching pattern of the cerebellum
cerebellar peduncles
three pairs of stalks that connect the cerebellum to the brianstem
inferior peduncles
connected to medulla oblongata
middle peduncles
connected to the pons
superior peduncles
connencted to the midbrian
functions of cerebellum
monitors muscle contractions and aid sin motor coordination, evaluation of sensory input, timekeeping center, hearing, planning and scheduling
What might lesions of the cerebellum result in?
emotional overreactions and troubel with impulse control
What are the two parts of the forebrain?
- diencephalon- enclose thrid ventricle, most rostral part of the brianstem
- telencephalon- develops cheifly into the cerebrum
What are the three embryonic derivatives of the diencephalon?
thalamus, hypothalamus, epithalamus
What is the thalamus?
ovoid mass on each side oft he brian perched at the superior end of the brainstem beneath the cerebral hemispheres
What are the functions of the hypothalamus?
hromone secretion, autonomic effects (heart rate, bp, etc.), thermoregulation, food and water intake, rhythm of sleep and waking, memory, emotional behavior
What part of the forebrain is the cerebrum a part of?
telencephalon
What is the cerebrum and functions?
largest and most conspicuous part of human brian
-seat of sensory perception, memory, thought, judgement, and voluntary motor actions
What si the white fibrous tract that connects the two cerebral hemispheres?
corpus callosum
What is the gyri and sulci of the cerebrum?
gyri- increases SA for information-processing capability
sulci- some divide each hemispheres into five lobes named cranial bones overlying them
What are the 5 lobes of the cerebrum?
frontal lobes, parietal lobe, occipital lobe, temporal lobe, insula (hidden by other regions)
frontal lobe
voluntary motor functions, motivation, foresight, planning, memory, mood, emotion, social judgement, and aggression
parietal lobe
receives and intergrates general sensory info, taste, and soem visual processing
occipital lobe
primary visual center of brain
temporal lobe
areas for hearing, smell, learning, memory, and some aspects of vision and emotion
insula
understanding spoken language, taste and sensory information form visceral receptors
what is the sensory homunculus?
diagram of the primary somesthetic cortex which resebles an upside-down sensory map of the contralateral side of the body
somatotopy
point-topoinnt correspondence between an area of the boyd and an area of the CNS
What are somatic senses?
mechanoreceptive- tactile (touch, pressure, vibration, ticle), position (static and rate of movement of body parts)
thermoreceptive- hot and cold
pain- damage to tissue
what is touch?
stimulation of tactile receptors in the skin
What is pressure?
deformation of deep tissue
what is vibration?
rapid repetitive sensory signals
What are the types of mechanoreceptors in the hand?
meissner, merkel, pacinian corpuscle, ruffini endings
What is the iggo dome receptor?
gorup of merkel discs, which create a very sensitive recptor, concentrated in the finger tips
nerve signal transmission of the iggo dome receptor
alpha beta myelinated fibers (msot specialized endings)- fast transmission
alpha delta myleinated fibers (free nerve endings) - slower
Sensory nerve characterisitcs
C- slow pain
alpha delta
alpha beta- fast pain
Where is the cell body located?
dorsal root ganglia
The doral root ganglion cell has an axon wiht 2 branches, what are they?
peripheral- terminates in specialized receptors
central- terminates in dorsal honr of the spinal cord
Spinal pathways for somatic signal; dorsal column-meidal lemniscal
large, myelinated fibers
somatotropic organization
fine touch, proprioception, pressure, vibraiton
spinal pathways for somatic signals; anterolateral pathways
small, myelinated fibers
pain, temp, crude touch, itch
the medial branch of the dorsal column pathway
ascends through dorsal columns to brain stem
lateral branch of the dorsal column pathway
many divisions and synapses within SC
- local neuron activation which will eventually enter DC
- spinal reflec mediation
- spinocerebellar tract
- spinocervical tract
spinocerebellar in the dorsal column pathway
convey proprioceptive information to the cerebellum (ipsilateral tract)
- dorsalp muscle spindle information
- ventral- golgi tendojn organ information
spino-olivary in dorsal column pathway
proprioceptive information to the olivary nucleus then to cerebellum
spinocervical in dorsal column pathway
vestigial in humans
Dorsal column-medial lemniscal pathway is responsible for what?
deep touch, vibration, and proprioception are carried in the dorsal cavities
What are the 1st, 2nd, and 3rd order neurons responsible for in the dorsal column-medial lemniscal pathway?
1st order neuron travels up the ipsilateral SC terminating in th emedulla oblongata
decussation of 2nd order neuron in medulla
3rd order neuron in thalamus carries signal to cerebral cortex
In DCML pathway; where do third order neurons project to?
1 and 2 somatosensory cortex
In DCML; what is 1 somatosensory cortex?
brodmann’s area 1,2,3
In DCML; what is 2 somatosensory cortex?
brodmann’s area 5 and 7A
What is the somatosensory area and where?
- arranged as a sensory homunculus
- very discrete localization in 1 somatosensory cortex
- 2 somatosensory cortex organization is not as defined
Where does input first arrivein the somatosensory cortex?
at layer IV
What layers receive diffuse, nonspecific input?
I and II
control overall level of excitability
What do layer II and III in the somatosensory cortex do?
send information to related sutes on opposite sites on opposite sides of the brain
axons travel thru corpus callosum
What do layers V and VI of the somatosensory cortex do?
regulation of signal transmission
output to basal ganglia, spinal cord, brain stem and thalamus
what are the functions of the primary somatosensory cortex?
Localize different sensations in different body parts Judge degrees of pressure Judge object weights Determine object shapes Determine material textures
Fucntions of the somatosensory association cortex
deciphers meaning from sensory input
Where does the somatosensory assocaition cortex receive signals from?
1 somatosensory cortex
thalamus
visual cortex
auditory cortex
What happens when the somatosensory association cortex is inhibted?
Amorphosynthesis
-inability to recognize complex objects and forms on the opposite side of the body
What is a dermatome?
specific area of the skin taht receives sensory input from a pair of spinal nerves
A diagram of the cutaneous regions innervated by each spinal nerve
dermatome map
Up to how much do dermatomes overlap their edges?
as much as 50%
Why must you anesthetize three successive spinal nerves?
to produce a total loss of sensation in one dermatome
Why does 2 point discrimination occur?
because of laterl inhibition
Where does lateral inhibiton occur?
at each level of DCML pathway
- gracile and cuneate nuclei
- VPL of thalamus
- somatosensory cortex
What are the 3 stimuli types for pain?
mechanical, themral and chemical (bradykinin, acid, ACh, prostaglandin, substance P)
Painreceptors are non-adapting. Increase in sensitivity is called what?
hyperalgesia
What sensations are carried in the spinothalamic pathway?
pain, pressure, temp, light touch, tickle, and itch
When do most people feel temperature as pain?
45 degree C, tissue damage
What does pain from heat correlate with?
rate of tissue damage and NOT the total damage
Intensity of pain correlates with what?
rate of tissue damage and NOT total damage
First order pain fibers alpha delta account for what?
fast pain
- excite 2nd order neurons that travel in the neospinothalamic tract
- highly somatotropic organization
- 2nd order neurons terminate in VPL of thalamus
First order pain fibers C account for what?
slow pain
- excites 2nd order neurons that travel in the paleospinothalamic tract
- poor localizaiton
- 2nd order neurons terminate in VPL of thalamus
Where is the termination of most paleospinothalamic tract neurons?
brainstem
- reticular nuclei
- tectal area of mesencephalon
- periaqueductal grey
What are the NTs of endogenous pain modulation?
enkephalin and serotonin
What are the brainstem areas effect in endogenous pain modulation?
- Periaqueductal grey
- Periventricular nuclei
- Raphe magnus nucleus
- Nucleus reticularis paragigantocellularis
What NT is involved in both pre and post synaptic inhibition of C and alpha delta fibers?
enkephalin
What are the causes of referred pain?
ischemia, chemical stimuli, cramps, over distention
Hyperalgesia
excessive pain receptor sensitivity
sunburned skin
Tic Douloureux
‘suicide disease’
severe, lancinating/stabbing pain in the sensory distribution of the trigeminal nerve
Brown-Sequard syndrome
transection of spinal cord on only one side
-motor- ipsilateral–> motor function lost below the site of injury
-sensory- ipsilateral–> DCML sensations lost
contralateral–> spinothalamic sensations lost
Headache
- menengitis- inflammation of the meninges
- low CSF pressure- distortion of dural surfaces due to the brain not floating freely in the CSF
- Migraines- vascualr headache, nausea, loss of vision, visual/auditory hallucinations
