Physiology of the spinal cord

Question 1

Sensation

Answer 1

Detection by receptors

Question 2

Perception

Answer 2

Interpretation by spinal cord and brain circuits

Question 3

Receptors

Answer 3

Neurones specialised in the transduction of energy generated by external stimuli

Specific for a narrow range of input

Question 4

Mechanoreceptors

Answer 4

Touch, pressure and vibration

Aβ fibre type

Wide diameter, fast

Question 5

Bare nerve endings

Answer 5

Aδ

Medium diameter and speed

Question 6

Bare nerve endings

- fast ‘pricking’ pain

Answer 6

Aδ

Medium diameter and speed

Question 7

Bare nerve endings

- slow burning pain, itch

Answer 7

C-fibres

Thin diameter, slow

Question 8

Pacinian corpuscle

Answer 8

Fast adaption

On-off response

Question 9

Two point discrimination

Answer 9

To measure variation in the sensitivity of tactile discrimination as a function of location on the body surface

Question 10

Spatial distribution of receptors

Answer 10

The density of mechanoreceptors is much greater on the hand and face than elsewhere, allowing the detection of stimuli at a much greater spatial resolution

Question 11

Motor system

Answer 11

Our muscles and the neurones that command them

This is the system that actually gives rise to behaviour

Question 12

Lower motor neurones

Answer 12

Final common path for all signals from the CNS to skeletal muscles

Collected in longitudinally organised columns

Question 13

Lower motor neurone columns

Answer 13

Contains larger, alpha and smaller, gamma motor neurones to one muscle

Each column extends through more than one segment of the cord

Question 14

The motor unit

Answer 14

A single α motor neurone and the muscle fibres it innervates

Question 15

Proprioceptive sensory organs

Answer 15

Muscle spindles- negative feedback regulation of muscle length

Golgi tendon organs- negative feedback regulation of muscle tension

Question 16

Tendon organs

Answer 16

Respond to muscle tension (due to contraction), spindles respond to length (due to passive stretch), but in a manner modified by the activity of their own contractile elements

Question 17

Stretch reflex circuit: a monosynaptic reflex pathway

Answer 17

Muscle spindle: sensory receptor that initiates the reflex

Stretch -> increased la afferent activity -> increased α motor neurone activity -> contraction of same muscle

Stretch reflex: negative feedback loop to regulate muscle length

Question 18

Somatotopic organisation of lower motor neurones

Answer 18

Motor neurones innervating axial musculature (e.g. postural trunk muscles) located most medially

Those innervating distal muscles (e.g. in the hands) located most laterally

Question 19

Somatotopic order in the human primary somatic sensory cortex

Answer 19

Electrical activity recorder following mechanosensory stimulation of different parts of the body

Somatotopic representation of body parts from medial to latleral

Amount of sensory cortex to hands and face much larger than relative amount of body surface

Question 20

Anterior cord syndrome

Answer 20

Bilateral lower motor neurone paralysis and muscular atrophy in segment of lesion

Bilateral spastic paralysis below level of lesion

Bilateral loss of pain, temperature and light touch sensations below level of lesions

Tactile discrimination and vibratory and proprioceptive sensations preserved because posterior white column on both sides are undamaged

Question 21

Brown- Sequard or cord hemisection syndrome

Answer 21

Ipsilateral lower motor neurone paralysis and muscular atrophy in segment of lesion

Ipsilateral spastic paralysis below level of lesion

Ipsilateral band of cutaneous anaesthesia in segment of lesion

Ipsilateral loss of tactile discrimination and vibratory and proprioceptive sensations below lesion

Contralateral loss of pain, temperature and light touch

Discriminative touch pathways travelling in ascending tracts in contralateral dorsal white column remain intact

Question 22

Complete cord transection syndrome

Answer 22

Complete loss of sensation and voluntary movement below level of lesion

Bilateral lower motor neurone paralysis and muscular atrophy in segment of lesion

Bilateral spastic paralysis below level of lesion

Bilateral loss of all sensations below level of lesion

Bladder and bowel functions no longer under voluntary control