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Question 1

Physiological functions of the spinal cord

Answer 1

-Initial processing of somatosensory input by the CNS

Final processing of motor output by the CNS

Question 2

what is Sensation

Answer 2

Detection by receptors

Question 3

what is Perception

Answer 3

Interpretation by spinal cord and brain circuits

Question 4

rate

Answer 4

frequency of APs

Question 5

Spatial code

Answer 5

relative position relative to how event is signalled

Question 6

temporal

Answer 6

How neuron is firing

Question 7

example of convergence

Answer 7

• High spatial resolution required: low convergence (e.g., cones and bipolar cells in retina).
  
  • Detection of weak signals required: high convergence
    (e. g., rods and bipolar cells in the retina).

Question 8

example of divergence

Answer 8

Input is used for complex or multiple functions: high divergence (e.g., vestibulo-ocular reflex).

Question 9

the lowest TH provides

Answer 9

Stimulus specificity

Question 10

give an example of different types of receptors for same modality

Answer 10

Merkel disks- sensitive to light contact

Free nerve endings- prickly sensations

Question 11

mechanisms of sensory stimulus discrimination 2: spatial distribution

Using an example of a compass

Answer 11

Two-point discrimination: to measure variation in the sensitivity of tactile discrimination as a function of location on the body surface.
Principle: the higher the density of mechanoreceptors the smaller the distance at which two tactile stimuli can be discriminated.

Question 12

where is the density of receptors much greater on ? & what does that result in :

Answer 12

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 13

what is the 3rd mechanism of sensory stimulus discrimination

Answer 13

Windows of response intensity

Question 14

what does the spinal cord represent and why

Answer 14

the simplest motor system because it can produce motor function with independence of the brain

Question 15

Evidence for the simplest motor system

Answer 15

After cord transection of a dog: The hindlimbs are still able to walk on a treadmill
Patterned electrical activity can be recorded from the muscles

Question 16

What are the lower mototr neurons

Answer 16

motor neurons present in the spinal cord

: Final common path for all signals (neuronal information) from the CNS to skeletal muscles (“keys on a piano”)

Question 17

how are lower motor neurons organized

Answer 17

Longitudinal organized columns

Question 18

What are Alpha motor neurons

Answer 18

the larger, alpha (thick axon, high conductance velocity)

Question 19

What are gamma motor neurons

Answer 19

gamma (thin axon, low conductance velocity), motor neuron

Question 20

why does destruction of a single ventral root or a single spinal nerve will not produce paralysis, only weakness

Answer 20

Bc esach muscle receives motor fibres through more than one ventral root and spinal nerve

Question 21

what is a motor unit

Answer 21

a single  motor neuron and the muscle fibres it innervates

Question 22

what is proprioception

Answer 22

Self detection stimulus

Question 23

What are the 2 main types of proprioceptive stimulus

Answer 23

Muscle spindles – negative feedback regulation of muscle length
Golgi tendon organs – negative feedback regulation of muscle tension

Question 24

clasp-knife reflex

Answer 24

protects muscles from being torn of from bones and muscles; when there is a lot of force on muscles, it well fire and synapse onto inhibitory neuron, in the spinal cord which results in the muscles being de-activated

Question 25

clasp-knife reflex

Answer 25

protects muscles from being torn of from bones and muscles; when there is a lot of force on muscles, it well fire and synapse onto inhibitory neuron, in the spinal cord which results in the muscles being de-activated

Question 26

what 2 elements do each muscles have

Answer 26

Contractrile and stretch-sensitive (non-contractile) elements in muscle

Question 27

How are muscle spindles arranged

Answer 27

In parallel connection to tendon organs: therefore they can respond to changes in length due to passive stretch

Question 28

relation of spindles to stretch organ

Answer 28

Tendon organs 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 29

what is the stretch reflex circuitry

Answer 29

A monosynaptic reflex pathway

Question 30

explain the stretch reflex circuitry

Answer 30

) Muscle spindle: the sensory receptor that initiates the reflex.

(B) Stretch  increased Ia afferent activity  increased α motor neuron activity leading to contraction of the same muscle.

(Ia afferents also excite motor neurons that innervate synergistic muscles, and inhibit motor neurons of the antagonist muscles).

(C) Stretch reflex: negative feedback loop to regulate muscle length. ‘Desired’ length is preset by descending pathways.

Question 31

What is the spinal circuitry responsible for the flexion reflex

Answer 31

Polysynaptic reflex pathway

Question 32

Explain the polysynaptic reflex pathway

Answer 32

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.

Question 33

what is somatotopic organisation of lower motor neurons

Answer 33

Motor neurons innervating axial musculature (i.e., postural trunk muscles) are located most medially, whereas those innervating distal musculature (e.g., in the hands) are located most laterally.

Question 34

Effects of lesions to the spinal cord

Answer 34

Anterior cord syndrome:

Bilateral lower motor neuron paralysis and muscular atrophy in the segment of the lesion (due to damage to lower motor neurons).
Bilateral spastic paralysis below the level of the lesion (due to loss of anterior descending tracts).
Bilateral loss of pain, temperature and light touch sensations below the level of the lesion (due to loss of anterior and lateral spinothalamic tracts).

But: Tactile discrimination and vibratory and proprioceptive sensations are preserved because the posterior (dorsal) white columns on both sides are undamaged.

Question 35

Brown-seguard- cord hemisection syndrome

Answer 35

Ipsilateral lower motor neuron paralysis and muscular atrophy in the segment of the lesion (due to damage to lower motor neurons).
Ipsilateral spastic paralysis below the level of the lesion (due to loss of anterior descending tracts).
Ipsilateral band of cutaneous anesthesia in the segment of the lesion (due to loss of dorsal root).
Ipsilateral loss of tactile discrimination and of vibratory and proprioceptive sensations below the level of the lesion (due to loss of ascending tracts in the dorsal white column on the side of the lesion).
Contralateral loss of pain, temperature and light touch (due to loss of crossed lateral spinothalamic tracts on the side of the lesion).

But: Discriminative touch pathways travelling in the ascending tracts in the contralateral dorsal white column remain intact.

Question 36

III. Complete cord transection syndrome.

Answer 36

Complete loss of sensation and voluntary movement below the level of the lesion.
Bilateral lower motor neuron paralysis and muscular atrophy in the segment of the lesion.
Bilateral spastic paralysis below the level of the lesion (due to loss of descending tracts).
Bilateral loss of all sensations below the level of the lesion (due to loss of ascending tracts).
Bladder and bowel functions no longer under voluntary control (due to loss of descending autonomic fibres)