Week 1 (lecture 4)- Sensory Receptors and Ascending Pathways

Question 1

what are the ascending pathways?

Answer 1

neural pathways by which sensory information from peripheral nerves is transmitted to the CNS

Question 2

what are the 4 steps of ascending pathways? (3rd order)

Answer 2

receptor
SC
decussation, and ascends thalamus
projects to cortex

(each order is between each stage)

Question 3

define receptors?

Answer 3

specialised cells that respond to environmental stimuli

Question 4

what are the 3 classifications of receptors?

Answer 4

function 
location
structure

Question 5

what are the 4 types of receptors under functional classification, and what do they detect?

Answer 5

mechanoreceptors (deformation e.g. touch, pressure; subcategory of proprioceptors)

photoreceptors (light)

thermoreceptors (heating/cooling)

chemoreceptors (substances released by cells; subcategory of nociceptors)

Question 6

what are the 3 types of receptors under location classification, and what do they detect?

Answer 6

externoreceptors (detect environmental stimuli)

internoreceptors (detect internal stimuli)

proprioceptors (detect static position/movement; found in muscles, tendons etc)

Question 7

what can be used to subdivide receptors based on structure?

Answer 7

complexity (most are simple; complex ones typically found at sensory organs)

Question 8

name 3 unencapsulated receptors, and what they do?

Answer 8

free dendric endings (small diameter allows sensation of ‘crude touch’)

modified free (e.g. merkel disks- light touch)

root hair plexuses (detects displacement of hair)

Question 9

name 3 types of unencapsulated receptors at skin level, and their role?

Answer 9

Meismers corpuscles (light touch/vibration; small receptive field)

Pacinian Corpsucles (subcutaneous fine touch/vibration; large receptive field)

Ruffinis corpuscles (stretch)

Question 10

name 3 proprioceptors that are responsible for detecting muscle/joint related actions?

Answer 10

muscle spindles (muscle length/speed of lengthening)

golgi tendon organs (muscle/tendon tension)

joint kinaesthetic receptors (modified receptors in joint capsule/ligaments)

Question 11

describe joint kinaesthetic receptors in joint capsule?

Answer 11

Ruffini type endings detect extremities of joint range; Pacinian corpuscles detect movement

Question 12

describe joint kinaesthetic receptors in ligaments?

Answer 12

receptor stimuli similar to golgi tendon organs detect tension

Question 13

what are the 5 steps of a simple reflex arc?

Answer 13

detection of stimulus by receptors

activation of afferent neurone (by an AP starting in the PNS and entering the CNS via dorsal root ganglion into the dorsal horn of grey matter)

information processing/integration (within grey matter of SC)

activation of efferent neurone (via anterior horn of grey matter)

effector response (i.e. muscles)

Question 14

what 2 ways can the automatic function of the reflex arc be?

Answer 14

somatic (e.g. spinal reflexes leading to muscle movement)

visceral (e.g. activating glands)

Question 15

what is the difference between inborn and learned reflex activity?

Answer 15

inborn= rapid, involuntary and stops us having to think about it i.e. to get out of danger quicker

learned= developed over repetitive practice (e.g. driving)

Question 16

what are 3 examples of spinal (somatic) reflexes?

Answer 16

stretch reflex (muscle spindle proprioceptors)

tendon reflex (golgi tendon organs proprioceptors)

flexor reflex+ crossed exterior reflex

Question 17

what is the stretch reflex and why is it so important as an inborn reflex?

Answer 17

involve stimulation of muscle spindle, which can detect change in muscle length/speed of lengthening= critical to create a rapid movement when instructed by a reflex arc

Question 18

what are the 3 orders of the dorsal column pathways (medial lemniscal system), and what is its function?

Answer 18

1st: receptor -> dorsal horn -> medulla
2nd: medulla (decussation)-> thalamus
3rd: thalamus -> somatosensory cortex

function= transmission of info regarding discrimination of touch/vibration
(fasciculus cuneatus-above t6; fasciculus gracilis- below t6)

Question 19

what are the 3 orders of the lateral and anterior spinothalamic pathways, and what is its function?

Answer 19

1st: receptor -> dorsal horn
2nd: dorsal horn (decussation)-> thalamus
3rd: thalamus -> cortex

function: lateral=pain/temp
anterior= touch/pressure

Question 20

what are the 2 orders of the anterior and posterior spinocerebellar pathways, and what is its function?

Answer 20

1st: proprioceptive receptor -> dorsal horn
2nd: dorsal horn -> cerebellum

function= carry proprioceptive information

anterior= partial decussation 
posterior= no decussation

Question 21

what are sensory homunculi, and where are the most represented parts of the body?

Answer 21

cortical tissue body map representation

face and hand have more tissue designated than the trunk for example