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.
