unit 3a Flashcards
somatosensory disorders
Cutaneous senses
perception of touch & pain f/ stimulation of skin
proprioception
ability to sense position of body & limbs
Kinesthesis
ability to sense mvmt of body & limbs
skin
Largest organ of body , both in surface & weight
Provides many funcs. incl:
- protection (germs, trauma, UV, toxins)
-excretion (water, waste)
-endrocrine processes (vitamin D production)
-regulation of body temp. & water loss
- sensation (tactile info)
*3 layers: Epidermis, Dermis, Subcutaneous Tissue.
Epidermis
Outermost, protective layer of skin,
-composed mostly of dead cells
Basement membrane
Specialized structure that lies b/t epidermis & dermis
Includes various protein structures linking basal layer of keratinocytes (skin cells) to basement memb. & basement memb. to underlying dermis
Once skin-cancer cells cross this boundary, they can begin to spread thru the body thru vascular syst. of dermis
Dermis
Middle layer of skin
- below epidermis
-forms true skin
-contains blood capillaries, nerve endings, sweat glands, hair follicles & other structures
Subcutaneous tissue
Deepest layer of skin
- made up of vessels, fat, & connective tissue
hairy skin
Most of our skin has hair.
- Primary somatosensory receptor in hairy skin = follicle receptor
→ which is a mechanoreceptor triggered by distortion of hair shaft
Glabrous skin
Hairless skin
- contains more specialized types of mechanoreceptors
- ex: on palms, soles, lips
Mechanoreceptor
A sensory receptor that responds to mechanical pressure/distortion (stretching, vibration) via mechanotransduction: mvmt of cell membrane, physically pulls open/pushes closed ion channels in the membrane,→ leading to changes in cell signaling
Normally, there are 4 main types in glabrous mammalian skin
-* Pacinian corpuscles
- Meissner’s corpuscles
- Merkel’s discs (AKA Merkel’s receptors)
-Ruffini cylinders (AKA Ruffini endings)
*
These differ along several factors, incl.: morphology, skin location, rate of adaption, frequency selectivity, spatial receptive field, & perceptual task
Slowly adapting fibers (SA)
Fire continuously as long as pressure is applied to provide detailed high acuity tactile info
- Found in Merkel’s disks (upper dermis) & Ruffini cylinders (lower dermis)
Rapidly adapting fibers (RA)
Fire at onset & offset of stimulation to provide info abt start & stop of a sensation
- found in Messier’s corpuscles (upper dermis) & Pacinian corpuscles (lower dermis)
Acute nociceptive pain
-Part of rapid warning relay instructing motor neurons of CNS to minimize detected physical harm. Mediated by nociceptors on A-δ & C fibers
nociceptors
-(pain sensors) free nerve endings that terminate just below the skin in tendons, joints & organs. Serve to detect cutaneous pain, somatic pain & visceral pain.
-Specialized for heat, chemicals, severe pressure, + cold. Hot & cold sensations are carried via thermoreceptors
-Threshold of eliciting receptor response must be balances to warn of damage but not affected by normal activity
Chronic inflammatory pain
Inflammatory nociceptive pain assoc. w/ tissue damage & resulting inflamm. process
- adaptive in that it elicits physiologic responses that promote healing
Chronic neuropathic pain
neuropathic pain produced by damage to neurons in peripheral & Central nervous systems, involves sensitization of these systems
- Peripheral sensitization: increase in stimulation of peripheral nociceptors that amplifies pain signals to CNS
-Central sensitization: neurons (originating in dorsal horn of spinal cord) become hyperstimulated, incr. pain signals to brain & → incr pain sensation
Spinal cord
a long, thin, tubular bundle of nervous tissue + support cells (like glia) that extends f/ medulla oblongata (in brainstem) to lumbar region of the vertebral column
the brain + spinal cord =CNS
In contrast to the cortex, grey mater is inside of spinal cord & surrounded by white matter.
Spinal cord has 3 major functions:
- Acts as conduit for motor info → travels down the spina cord, as a conduit for sensory info in the reverse direction & ~ as center for coordinating certain reflexes
Vertebral Column
bony structure made of multiple vertebrae that protect the relatively shorter spinal cord.
- Spinal nerves project thru small opening in the vertebral bones
Dorsal root ganglion
the sensory nerves of the peripheral nervous system (PNS) have their cell bodies in the dorsal root ganglion
ganglion = group of cell bodies
These cells have projections (like dendrites) that carry info f/ peripheral sensory receptors - peripheral nerve- & also projections (axons) that carry info into spinal cord - dorsal root
Ventral root
the motor nerve exiting the spinal cord to innervate muscle fibers
Fascicle
a bundle of neuronal axons surrounded by connective tissue
- a component of a nerve
Spinal Reflex Pathway
neural pathway that controls a reflex action
As most sensory neurons synapse in spinal cord before going to cortex, spinal motor neurons can rapidly activate w/o waiting for signals to go to/come f/ brains 1st.
Sensory input is sent to brain while the reflex is being carried out
Posterior Columns
A set of somatosensory white matter tracts in posterior spinal cord that carry info abt fine touch, vibration, pressure, & joint position f/ the spinal cord to thalamus (→ then to S1)
name turns into ‘medical lemniscus’ when tracts reach the brainstem (where dorsal root ganglion axons then synapse & cross to opposite side. -Organized somatotopically.
Spinocerebellar tract
set of somatosensory white matter tracts in the POSTERIOR/ LATERAL spinal cord that carries info abt joint position & muscle fiber tension f/ spinal cord → cerebellum
- projections do NOT cross to opposite side
-Organized somatotopically
Anterior Spinothalamic tract
set of somatosensory white matter tracts in ANTERIOR spinal cord that carries info abt crude touch & pressure f/ spinal cord → thalamus
-dorsal root gang axons synapse & cross immediately to opposite side
- organized somatotopically
Lateral Spinothalamic tract
a set of somatosensory white matter tracts in the lateral spinal cord that carries info abt pain & temp f/ spinal cord → thalamus
-dorsal root gang axons synapse & cross immediately to opposite side
- organized somatotopically
Thalamus
Sensory ‘relay station’ in brain (located sub cortically) to which all sensory neuronal pathways project prior to entering cortex, EXCEPT those involved in olfaction
Primary somatosensory cortex (S1)
a strip of cortex just posterior to central sulcus, where primary ctrl of sensation occurs
-S1 contains a somatotropin (body map) representation
- S2 = 2nd somatosensory area located just inferior & posterior to S1.
Somatotopy
the pt-for-pt correspondence of an area of the body to a specific pt on the CNS
- somatotopic organization is present in both S1 & M1
Pain matrix
a number of diff. areas of the brain involved in pain perception
Signal f/ nociceptors travel up the spinothalamic pathway & activate many of these areas.
-New research demonstrates that S1 & S2 are also directly involved in pain perception
Tactile agnosia
a disorder characterized by inability to identify by touch an object (or characteristics of an object)
-possibly caused by damage to S1
-much like visual agnosia, but symptoms now apply to touch
- Specific tactile agnosia may rise f/ damage to higher-order regions of the somatosensory system, including inability to identify object’s weight/size (but still identify object w/ tactile info)
Cotard syndrome
delusional belief that one is dead, DNE, is putrefying or has lost blood or internal organs (‘walking corpse syndrome’)
paradoxical delusions of immortality may also occur (‘I am dead already, so now I can’t be killed’)
Assoc. w/ depression, schizo., capers syndrome, bipolar disorder, migraine, herpes medication.
May arise f/ disconnection b/t high-order sensation/face perception (?) & emotional processing of limbic cortex
Treatments may include electro-convulsive shock therapy (ECT)
Congenital analgesia
AKA congenial insensitivity to pain (CIP)
A set of rare conditions in which a person can’t feel (has never felt) physical pain.
Condition may be cause by
1. increased endorphins/natural opioids or
2. mutation in sodium channel in pain receptors
Cause high risk of serious injury, illness, & death
Insensitivity to pain
painful stimulus not perceived
- patient can’t describe intensity/type of pain
Indifference to pain
patient CAN perceive stimulus but LACKS approp. response
- dont flinch or withdraw when exposed to pain
Chronic pain
pain that extends beyond expected period of ealing
-Affects 1/3 of all Americans
-major impacts on quality of life
-creates large economic burden on society
Patients severely underrated, yet it affects more ppl than heart disease, cancer, & diabetes COMBINED
Affective (mood) & emotional effects on pain perception exist but chronic pain is NOT ‘all in patient’s head’
Phantom limb syndrome
disorder characterized by having sensations (usually pain) in a limb that is no linger attached to body
Mirror therapy or virtual reality may provide some relief
Although phantom pain can be debilitation, sensation of a phantom limb can improve a person’s ability to use a prosthetic.
