Chapter 6 - Somatosensory

Question 1

muscle spindle

Answer 1

the sensory organ in muscle

- consists of muscle fibers, sensory endings, and motor endings

Question 2

sensory endings of spindle

Answer 2

• respond to stretch(changes in muscle length)
• respond to velocity of length change
  Type 1a afferents(primary endings) = quick and tonic stretch of the spindle
  
  • wrap around the central region of each intrafusal fiber
    Type 2 afferents(secondary endings) = tonic stretch of the muscle
  • end on nuclear chain fibers

Question 3

intrafusal fibers

Answer 3

fibers inside the spindle
- contractile only at their ends
Types: 1) nuclear bag fibers 2) nuclear chain fibers

Question 4

nuclear bag fibers

Answer 4

intrafusal fibers

- have a clump of nuclei in the central region

Question 5

nuclear chain fibers

Answer 5

intrafusal fibers

- have nuclei arranged in single file

Question 6

primary endings

Answer 6

type 1a

• wrap around the central region of the intrafusal fiber
• also called annulospiral endings
• discharge is phasic and tonic

Question 7

secondary endings

Answer 7

type 2

• end mainly on nuclear chain fibers adjacent to the primary endings
• also called flower-spray endings
• respond only tonically

Question 8

phasic discharge

Answer 8

maximal during quick stretch and fades quickly

Question 9

tonic discharge

Answer 9

sustained during constant stretch

- rate of firing is proportional to the stretch of spindle fibers

Question 10

Golgi tendon organs

Answer 10

encapsulated nerve endings woven among the collagen strands of the tendon

• relays tension in tendons(very sensitive)
• responds to tension exerted by active contraction and passive stretch
• type 1b afferents

Question 11

joint receptors

Answer 11

• respond to mechanical deformation of the capsule and ligaments
  Types:
  1) ligament receptors(type 1b)
  2) Ruffini’s and paciniform endings(type 2)
  3) free nerve endings

Question 12

Ruffini’s endings

Answer 12

in the joint capsule

• signal extremes of joint range
• respond more to passive than active movement

Question 13

paciniform corpuscles

Answer 13

respond to movement, but not when joint position is constant

Question 14

ligament receptors

Answer 14

signal tension

Question 15

free nerve endings

Answer 15

stimulated by inflammation

Question 16

discriminative touch

Answer 16

localization of touch and vibration

- ability to discriminate between two closely spaced points touching the skin

Question 17

conscious proprioception

Answer 17

awareness of movements and of the relative position of body parts

Question 18

stereognosis

Answer 18

ability to use touch and proprioception to identify an object

Question 19

pathway for discriminative touch and conscious proprioception

Answer 19

• dorsal column/medial lemniscus system
  1) 1st order = neuron conveys information from the receptors to the medulla
  2) 2nd order = neuron conveys information from the medulla to the thalamus
  3) 3rd order = neuron conveys information from the thalamus to the cerebral cortex

Question 20

Discriminative touch and conscious proprioceptive information pathways from the body

Answer 20

1st order = dorsal root ganglion —–> 2nd order = nucleus cuneatus or gracilis —–> VPL(ventral posterolateral) nucleus of thalamus

Question 21

Discriminative touch and conscious proprioceptive information pathways from the face

Answer 21

1st order = trigeminal ganglion —-> main sensory nucleus of trigeminal nerve ——> VPM(ventral posteromedial) nucleus of thalamus

Question 22

SPG

Answer 22

Stepping Pattern generator

• adaptable networks of spinal interneurons that activate lower motor neurons to elicit alternating flexion and extension of the hips and knees
• for walking

Question 23

H-reflex

Answer 23

monosynaptic reflex elicited by electrically stimulating a nerve

• testing substitutes cutaneous electrical stimulation of a peripheral nerve for tendon percussion of the myotatic reflex
• faster than the tendon tap reflex because it does not require activation of spindle receptors

Question 24

UMNs

Answer 24

upper motor neurons

• provide all motor signals from the brain to the spinal cord and from the cerebrum to the cranial nerve lower motor neurons in the brainstem
• ones projecting to the spinal cord are classified according to where they synapse: medially, laterally, or throughout the ventral horn

Question 25

Medial UMNs

Answer 25

``` signal lower motor neurons that innervate postural and girdle muscle 3 tracts from the brainstem: - reticulospinal - medial and lateral vestibulospinal - medial corticospinal ```

Question 26

Lateral UMN's

Answer 26

signal lower motor neurons that innervate muscle used for fractionated movement and muscles in face and neck

Question 27

UMNs throughout the ventral horn

Answer 27

contributes to background levels of excitation in the cord and facilitates local reflex arcs

Question 28

reticulospinal tract

Answer 28

begins in the reticular formation - facilitate bilateral lower motor neurons innervating postural and gross limb movement muscles throughout the entire body - involved in anticipatory postural adjustments and reaching - for neck reflexes in response to visual and auditory input

Question 29

medial vestibulospinal tract

Answer 29

receive information about head movement and position from the vestibular apparatus in the inner ear - project to cervical and thoracic levels and affect activity in lower motor neurons controlling neck and upper back muscle

Question 30

lateral vetibulospinal tract

Answer 30

respond to gravity information from the vestibular apparatus - facilitate lower motor neurons to extensors while inhibiting lower motor neurons to flexors - continuously active to maintain the center of gravity over the base of support, responding to destabilization

Question 31

medial corticospinal tract

Answer 31

direct connection from cerebral cortex to the spinal cord - project to the ipsilateral, contralateral, and bilateral spinal cord - synapse with lower motor neurons that control neck, shoulder and trunk muscles

Question 32

fractionation

Answer 32

the ability to activate individual muscles independently of other muscles - lateral spinal cord - 2 tracts: 1) rubrospinal(minimal contribution) 2) lateral corticospinal

Question 33

lateral corticospinal tract

Answer 33

most important in controlling voluntary movement - fractionates movement by activating inhibitory neurons to prevent unwanted muscles from contracting - arise in the primary motor, premotor, and supplementary motor cortex

Question 34

raphespinal tract

Answer 34

releases serotonin - modulates the activity of spinal lower motor neurons - part of the emotional motor system

Question 35

ceruleospinal tract

Answer 35

releases norepinephrine - produces tonic facilitation of spinal lower motor neurons - part of the emotional motor system