lecture 12 Flashcards
somatic sensation
sensation from the skin, skeletal muscles, bones, tendons and joints -will give us rise to touch, pressure, awareness of the body’s position and movements, temperature and itch -responsible for : cutaneous sensation (touch), proprioception (sense of limb in space), kinesthesis (sense of limb during movement)
skin types
- hairy
- glabrous (no hair eg. palms)
layers
epidermis : outer layer gets washed off every day
dermis : inner layer where sensors are located
mechanoreceptors
mechanically-gated ion channels open in response to mechanical deformation (pressure) on skin
types of mechanoreceptors
- Merkel’s corpuscle
- meissne’s corpuscle
- ruffini corpuscle
- pacinian corpuscles
merkels corpuscle
- furthest on exterior
- disk shaped
- small receptive field
- slow adapting to stimulus
meissners corpuscle
- 2/4 second most posterior
- flattened cells
- small receptive field
- rapidly adapts to stimulus
ruffini corpuscle
- ¾ second most interior
- branched fibers in a cylindrical capsule
- large receptive field
- slow adapting to stimulus
pacinian corpuscle
- 4/4 deepest
- layered, onion-like capsule
- large receptive field
- rapidly adapt to stimulus
high tactile acuity
small receptive fields (eg. hands and lips)
responsible for posture and movement
muscle spindle, golgi tendon organ, and vestibular organs
muscle spindle
stretch receptors
- spindles located parralel with the regular muscle fibers
- undergo the same length changes as the rest of the muscles thus,
- they are in an ideal location to sense changes in muscle length
-1a afferent neuron grup 2 afferent neuron
golgi tendon organ
muscle tension monitor
- located in the tendon of the muscle in series with the muscle fibers
- they become stretched when the muscle contracts thus
- they sense the force the muscle exerts
muscle receptors (proprioception)
a) muscle stretch
- stretch, spindles stretching, action potentials throughout stretch
b) extrafusal fiber contraction
- cant fire as well, less action potentials
c) alpha-gamma coactivation
- gama motor neuron detect contraction and lead to AP’s occuring
thermoreceptors
sense temperature change
- small in diameter
- slow adapting (allow to get hands off hot stove)
- have little myelin
- originate as free neuron endings
- seperate receptors for hot and cold
nociceptors
sense pain stimuli
- free axon endings
- small diameter
- little myelin
- respond to extreme mechanical deformation, temperature and many chemicals
non-steroidal anti-inflammatory drugs (NSAiDS)
alleviate pain
- inhibit activity of cyclooxygenase enzyme
- important enzyme for production of prostaglandis
- prostaglandins are significant chemical stimulators of nociceptors
- blocking production= reducing firing rate of pain receptors
referred pain
sensation of pain is experienced at a site other than the injured or diseased tissues (eg. heart attack0
afferent neurons converting on the same spinal nerve
hyperalgesia
increased sensitivity to pain
-can last for hours after stimulus is gone
analgesia
inability to sense physical pain
- can’t sense it is burning you
- leads to injuries etc.
itch
thought to be a somatic sensation
- are free neuron ending
- slow adapting (why if you dont scratch it right away it persists)
- activate by mechanical stimulation or chemical mediators
2 pathways of the somatosensory system
anterolatteral/spinothalamic pathway and dorsal column
anterolateral/spinothalamic pathway
- crosses over sooner
- for pain and temperature
- goes through brainstem, then thalamus, ends up in somatosensory cortex
dorsal column
- doesnt cross over right away, goes up towards brainstem and then secondary neuron crosses from brainstem to thalamus
- for movement, limb position, fine touch, pressure
- ends up in somatosensory cortex
somatosensory cortex
right side of body is perceived on left side of somatosensory cortex
dermatomes
area of skin supplied by given spinal cord segment
-sensory
myotomes
group of muscles supplied by a given spinal cord segment
-motor
