Physiology of the Spinal Cord

Question 1

4 physiological functions of the spinal cord:

Answer 1

• acts as a conduit between the brain
  and the rest of the body
• initial processing of somatosensory
  input to the CNS
• final processing of motor output from
  the CNS
• can act without brain signals; reflex
  activity

Question 2

Sensation definition:

Answer 2

the detection of a stimulus by a receptor

Question 3

Perception definition:

Answer 3

the interpretation of that stimulus by the brain with existing emotions and memories

Question 4

Sensory Receptors:
- are
- two types

Answer 4

• specialised endings of the peripheral
  process of the sensory neuron
• mechanoreceptors (pressure or
  distortion)
• nociceptors: chemical, thermal,
  mechanical

Question 5

Mechanoreceptors in skin:

Answer 5

• hair follicle receptors
• merkell’s receptor

Question 6

Receptors Mediating Tactile Senses:

Answer 6

insert diagram

Question 7

All somatosensory processing receptors are located in the

Answer 7

dermis
epidermis = dead skin = no sensory fibers

Question 8

Pancinian Corpuscle:

Answer 8

• distortion due to pressure = stimulus
• causes all or nothing action potential
• depolarisation of dorsal root ganglion
• deep pressure, fast vibration

Question 9

What are C fibre pains?

Answer 9

slow pain, might have a delay
slow phase

Question 10

Mechanosensory (proprioception/vibration/light touch): ascend in dorsal columns on the

Answer 10

same side to ssynapse with second order neuron in medulla

Question 11

Pain & temperature: synapse at level of entry with second order neuron which

Answer 11

crosses midline and ascends in lateral spinothalamic tract

Question 12

Sensory information is integrated at all levels of the nervous system;

Answer 12

excitatory and inhibitory modulation

whether stimulus is passes to brain

Question 13

Descending pathways can modulate sensory input:

Answer 13

green and red are descending trunks
different neurotransmitters modulate the transmission at spinal level

Question 14

Mechanisms of sensory stimulus discrimination:

Answer 14

• different receptor types allow
  differentiation between different
  sensations
• spatial distribution of receptors
• windows of response intensity

Question 15

Spatial Distribution of Receptors:

Answer 15

• two point discrimination to measure
  variation in the sensitivity of tractile
  discrimination as a function of location
  on the body surface
• the higher the density of the
  mechanoreceptors,
  the smaller the distance at which two
  tactile stimuli can be discriminated

eg higher density of mechanoreceptors on the
hand and face, allowing the detection of
stimuli at a much greater spatial resolution

Question 16

Motor Processing:

Answer 16

descending pathway, short dendrons, long axons, decussation at brain level

Question 17

Ventral horn of the cord has anterior motor neurons: give rise to nerve fibers innervating muscles:

Answer 17

• alpha motor neurons
• gamma motor neurons

Question 18

What is a motor unit?

Answer 18

a motor neuron and the muscle fibres it synapses with

Question 19

Merkell’s receptor:
- type of receptor
- what sensory information

Answer 19

• mechanoreceptor
• touch and pressure; low threshold

Question 20

Meissner’s Corpuscle:
- type of receptor
- what sensory information

Answer 20

• mechanoreceptors
• texture, slow vibration
• just under the epidermis

Question 21

Painless burns

Answer 21

can be deeper than dermis

Question 22

Ruffini’s Ending:
- type of receptor
- what sensory information

Answer 22

• mechanoreceptor
• skin stretch
• superior dermis

Question 23

Mechanisms of Sensory Stimulus Discrimination:

Answer 23

insert diagram

Question 24

How are lower motor neurons collected?

Answer 24

longitudinally in organised columns

Question 25

No muscle is innervated by a single spinal cord level:

Answer 25

each column of lower motor neurons extend through more than one segmented each muscle receives motor fibers through more than one ventral root hence damage to a single nerve will not cause complete paralysis

Question 26

Renshaw Cells:

Answer 26

groups of cells sitting close to motor neurons inhibitory to motor neurons affected by descending pathways through the spinocerebellar tract lateral inhibition of lower motor neurons; preventing innervation of muscles that are not needed

Question 27

Can more than one muscle be innervated by the same spinal nerve root? Link with lateral inhibition.

Answer 27

more than one muscle can be innervated by the same spinal nerve root lateral inhibition via renshaw cells prevents for example 2 muscles moving when not needed

Question 28

Effect of lateral inhibition on signals?

Answer 28

Lateral inhibition sharpens or focusses signals

Question 29

2 types of reflex integration:

Answer 29

- simple reflex - complex polysynaptic reflex causes bilateral withdrawal both occur solely in the spinal cord

Question 30

Muscle Sensory Organs: Mechanoreceptors:

Answer 30

- detect proprioception = forces generated within the body - sensory nerve fibers - muscle spindles - golgi tendon organs - continuous feedback; integrate between several muscles - control muscle at conscious and unconscious levels: spinal cord, cerebellum, cerebral cortex

Question 31

What do Muscle Spindles do?

Answer 31

Muscle sensory organs found in bodies of muscle, which respond to muscle length

Question 32

What do Golgi Tendon Organs do?

Answer 32

Muscle sensory organs found in bodies of muscle, which respond to tension of muscle

Question 33

Muscle Spindles: - are - when are impulses created

Answer 33

- sensory fibers stimulated by stretch - spindles emit impulses continually!!! - with stretch = impulses increase - with contraction = impulses decrease

Question 34

Muscle Spindles: - dynamic response

Answer 34

a sudden increase in length, causes impulses to suddenly increase

Question 35

Muscle Spindles: - gradual increase

Answer 35

impulses increase proportionally to the stretch

Question 36

Muscle Spindles: - static response

Answer 36

impulses continue after stretch

Question 37

What is shown in the diagram below?

Answer 37

Muscle spindle

Question 38

Monosynaptic Pathway:

Answer 38

interaction of sensory and motor nerves at a spinal cord level: simple circuit

Question 39

Knee Jerk Reflex:

Answer 39

- dynamic stretch reflex - sudden stretch leads to strong reflex contraction - static stretch reflex, leads to weaker, more prolonged phase - due to muscle spindles

Question 40

Golgi Tendon Organ: - is - does - effect - function

Answer 40

- sensory receptor through which muscle tendon fibers pass - detects muscle tension - effect is inhibitory - protects against excess tension due to prolonged contraction of muscle

Question 41

What is show below?

Answer 41

Golgi Tendon Organ

Question 42

Clasp Knife Reflex:

Answer 42

- golgi tendon organ responds to tension, not passive stretch - activation inhibits the alpha motor neuron - leads to reduction in activity in the same muscle - sometimes called the inverse stretch reflex

Question 43

What is the reflex circuitry for the contraction of muscle below?

Answer 43

- bicep contract, triceps relax to flex elbow to maintain distance - stretch of muscle leads to lengthening of muscle spindle - activates the alpha motor neuron to contract the muscle - negative feedback loop regulates muscle length - desired length set by descending pathways; circuits do not exist in isolation

Question 44

The flexor reflex is a monosynaptic or polysynaptic reflex pathway?

Answer 44

Polysynaptic

Question 45

Flexor Reflex:

Answer 45

- pain leads to flexion of muscle - allows muscle withdrawal - other circuits are also activated to inhibit antagonistic muscles - effects on opposite side of the body: crossed extensor reflex

Question 46

Knee Jerk Reflex can assess how senstive the

Answer 46

stretch reflexes are

Question 47

If a reflex is reduced, then which motor neurons are afffected?

Answer 47

lower motor neurons

Question 48

If a reflex is exaggerated, then which motor neurons are affected?

Answer 48

upper motor neurons