T1L18 physiology of the spinal chord

Question 1

spinal nerves

Answer 1

highways of both somatosensory (afferent) pathways to sc and motor (efferent) pathways from sc to muscles

Question 2

sensation;

perception;

Answer 2

sensation- detection by receptors

perception- interpretation by sc and brain

Question 3

convergence and divergence

Answer 3

• receptors transduce energy generated by externals stimuli
• receptors specific to a narrow range of input
• signal events by combination of RATE, SPATIAL AND TEMPORAL codes
• high spatial resolution required (eg cones in retina) > low convergence
• detection of weak signals (eg rods in retina) > high convergence

Question 4

2 kinds of primary sensory recpetors

Answer 4

pic s6

most the stimulus directly forms ap in neurone
in some (taste, eqbm, hearing), a separate cell is effected by the stimulus which causes chemical transmission to sensory neuron

Question 5

modaility, receptor, afferent fibre type and velocity:

touch, pressure, vibration

Answer 5

• mechanorecptors eg Pacinian corpuscle
  fibres: Abeta, wide diameter, fast
• bare nerve endings (as in uncovered)
  fibres: Adelta, medium diameter and speed

Question 6

modaility, receptor, afferent fibre type and velocity:

pain

Answer 6

fast, pricking pains > bare nerve endings
fibres: Adelta, medium speed and diameter

slow, burning pains, itch
fibres: C fibes, low diameter and velocity

Question 7

receptors for:
shear
contact
pricking
tension, folding
deep pressure, vibration
hair movement

Answer 7

shear- Meissner's corpuscle
contact- merkel disk
pricking- free nerve endings
tension, folding- ruffinis corpuscle
deep pressure, vibration- Pacinian corpuscle
hair movement- idk

Question 8

Pacinian corpuscle

Answer 8

pressure and vibration

afferent signals to dorsal root ganglion

pressure starts> generator potential > ap
pressures stops> generator potential> ap

on/off system

Question 9

density of mechanoreceptor

Answer 9

• much denser on hand and face
• greater spatial resolution
• measured by 2 point discrimination

Question 10

the spinal chord can —– independently to the brain

Answer 10

generate complex motor patterns independently of the brain

Question 11

motor neurons in spinal chord are called

Answer 11

lower motor neurons

Question 12

lower motor neurons

Answer 12

• first common path for all signals from cns to muscles
• in longitudinally organised columns

each column contains:
- large alpha fibres (thick and fast)
- small gamma fibres (thin and slow)
and goes to a muscle or functionally similar tissues

each muscle receives motor fibres through more than one ventral root in spinal nerve, so destruction of one ventral root or spinal nerve causes weakness rather than paralysis

Question 13

motor unit

Answer 13

a single alpha motor neuron and the muscle fibres it innervates

• each motor neuron synapses to multiple fibres

Question 14

more = more spatial resolution

Answer 14

• higher density of mechanoreceptors

eg on face and hand

Question 15

simple reflexes

Answer 15

• interaction between a proprioceptive sensory and a motor unit

proprioception = self detection

proprioceptive sensory organs:

• muscle spindles (-ve feedback loop by muscle length (eg to catch a ball, force is exerted as the ball exerts force)
• Golgi tendon organs (-ve feedback loop by muscle tension)

Question 16

clasp knife and knee jerk reflexes

Answer 16

s20, 21

• muscle spindles (-ve feedback loop by muscle length (eg to catch a ball, force is exerted as the ball exerts force) eg KNEE JERK
• Golgi tendon organs (-ve feedback loop by muscle tension) eg CLASP-KNIFE

Question 17

stretch reflex circuitry

Answer 17

• monosynaptic reflex pathway

A) muscle spindle- sensory receptor initiates reflex

B) stretch > increase Ia afferent > increased alpha motor neuron > contraction of muscle

C) stretch reflex- negative feedback loop to the desired muscle length. the desired length is set by descending pathways

s22

Question 18

flexion reflex

eg standing on a lego

Answer 18

polysynaptic reflex pathway

Stimulation of cutaneous pain receptors in the foot leads to activation of spinal cord local circuits that withdraw (flex) the stimulated extremity and extend the other extremity to provide compensatory support.

s23

Question 19

origins of different motor neurons in spinal chord

Answer 19

medial = middler muscles eg abdominals
lateral = extremities eg hands
s24

Question 20

homunculus

Answer 20

figure with proportions based on density of neuronal coverage

s25

Question 21

anterior chord syndrome

Answer 21

bilateral lower motor neuron paralysis:

• muscular atrophy
• bilateral spastic paralysis below lesion level due to cut of anterior descending tracts
• bilateral loss of pain, temperature control, light touch sensations due to loss of anterior and lateral spinothalamic tracts

Question 22

cord hemisection syndroms (brown-sequard syndrome)

Answer 22

ipsilateral lower motor neuron paralysis:

• ipsilateral cutaneous anaesthesia in the segment of the lesion (complete sensation loss)
• ipsilateral loss of vibration, proprioception and tactile discrimination below level of lesion
• contralateral loss of paint, temp and light touch

contralateral = other side
ipsilateral = same side

Question 23

complete cord transection syndrome

Answer 23

complete loss of sensation and voluntary movement below level of lesion

• bilateral spastic paralysis below lesion due to descending tracts
• bilateral loss of all sensation below lesion due to ascending tracts
• bladder and bowel no longer under voluntary control due to loss of descending autonomic fibres