Lecture 7/8: Sensory Receptors and Reflexes

Question 1

Define dermatomes and feature extraction

Answer 1

dermatomes are regions of skin that are supplied by a given dorsal root

feature extraction: some cortical neurons signal stronger when stimulus is in a certain direction, i.e. wrist to fingers, or from ulna to radius

Question 2

Describe the different sensory receptor types

Answer 2

Meissner: light touch/vibration, fast adapting, surface, small receptive area
Merkel: pressure, slow adapting, surface, small receptive area
Ruffini: skin stretch, slow adapting, deep, large receptive field
Paccini: vibration, , deep, large receptive field

Question 3

Describe the DCML pathway

Answer 3

1st order neurons go up to medulla, project to 2nd order neurons. they decussate in the medulla and go up to the thalamic nuclei. thalamic nuclei project to the somatosensory cortex

carries info on fine touch, vibration, proprioception

Question 4

Describe the spinothalamic pathway

Answer 4

1st order neurons go in through dorsal root and project to secondary neurons. these cross over in the spinal cord and project to the thalamus. tertiary neurons carry info to the somatosensory cortex

carries info on temperature, pain, coarse touch

Question 5

Discuss the structure and function of muscle spindles and golgi tendon organs

Answer 5

muscle spindles. carried by 1a and 2 neurons. sense information about length/stretch of muscle fibers. 1a senses dynamic changes in stretch. 2 fibers sense tonic stretch (length and duration). Lie parallel to extrafusal muscle fibers, composed of bag and chain fibers. 1a fibers warp around all fibers, group 2 fibers wrap around everything except bag 1 fiber. Innervated by gamma motor neurons which prevent slack and have alpha-gamma coactivation

GTOs sense force/tension in the muscle. wrap around connective tissue in the tendons, lie in series. information from GTOs carried by 1b afferents.

Question 6

Describe the myotactic reflex

Answer 6

tendon-tap reflex. Tendon stretched, sensed by muscle spindle. carried by 1a afferent, directly synapses to alpha motor neurons, causes extensors to contract. also synapses with inhibitory interneuron, causes flexor to relax. one side is monosynaptic, other side is disynaptic

Question 7

Describe the inverse myotactic reflec

Answer 7

prevents hyperextension. When 1b afferents sense tension through GTO, goes to spinal cord. both pathways are disynaptic. Causes inhibition of extensor, contraction of the flexor.

Question 8

Describe the crossed-extensor reflex

Answer 8

through nociceptor (pain), stepping on a nail. Polysynaptic pathway through type 3 and 4 afferents. causes contraction of flexor on ipsilateral side, and relaxation of extensor on ipsilateral side. on the contralateral side, there is contraction of extensor, relaxation of flexor. contralateral side is through commisural interneurons

Question 9

discuss recurrent inhibition and reciprocal innervation

Answer 9

Recurrent inhibition is Renshaw cells. when the flexor is activated, it also innervates the Renshaw cells. Renshaw cells inhibit the agonist, while also inhibiting the inhibitory interneuron for the antagonist. This disinhibition excites the antagonist/extensor and prevents muscle damage/tetany

reciprocal innervation where innervating agonist also inhibits antagonist through inhibitory interneurons