Sensory & Motor Neurons

Question 0

Describe Aa sensory fibres

Answer 0

Largest diameter, myelinated, proprioceptors of skeletal muscle

Question 1

How do sensory neurons encode stimulus intensity?

Answer 1

Through amplitude of receptor potential within their dendrites (EPSP) and transformation into a digital pulse code

Question 2

Describe Ab sensory fibres

Answer 2

Large diameter, myelinated, mechanoreceptors of skin

Question 3

Describe A& sensory fibres

Answer 3

Smaller diameter, lightly myelinated, receptors for pain and temperature

Question 4

Describe C sensory fibres

Answer 4

Smallest diameter, unmyelinated, slowest transmission speed, receptors for temperature, pain and itch (e.g. burning sensation)

Question 5

What are the types of sensory receptors?

Answer 5

Thermoreceptors, chemoreceptors, mechanoreceptors and photo (electromagnetic) receptors.

Nociceptors fall under all 4 categories

Question 6

What are the outputs of chemoreceptors?

Answer 6

Chemical outputs e.g. taste, smell, CO2, O2 etc.

Question 7

What is the output of photoreceptors?

Answer 7

Electromagnetic radiation (light)

Question 8

What are the four types of temperature recognised by thermoreceptors?

Answer 8

Cold, cool, warm and hot

Question 9

What are thermoreceptors driven by?

Answer 9

Transient receptor potential (TRP) channels

Cold: TRP(A)1 (cold/frigid) and TRP(M)8 (cold/cool)

Warm: TRP(V)1/TRP(V)2 (hot/burning) and TRP(V)3 (warm)

Question 10

What are the three hypotheses regarding how mechanoreceptors work?

Answer 10

A: Direct physical stretching open channels
B: Second messenger system initiated by force detection/chemical stimuli
C: Force conveyed through structural proteins

Question 11

What do mechanoreceptors respond to?

Answer 11

Physical distortion - touch, deformation and proprioception

Question 12

What are the four types of mechanoreceptors and what do they detect?

Answer 12

1) Meissner corpuscle: Initial contact (motion/stroking/slippage)
2) Merkel’s disks: Pressure/texture
3) Pacinian corpuscle: Vibration
4) Ruffini endings: Skin stretch

Question 13

Which mechanoreceptors adapt
A) rapidly
B) slowly

Answer 13

A) Meissner corpuscle and Pacinian corpuscle

B) Merkel’s disks and Ruffini endings

Question 14

What are the two classes of nociceptors?

Answer 14

Class 1: Innervated by A& fibres, respond to sharp/prickly pain

Class 2: Innervated by C fibres, respond to dull/burning pain, not localised, poorly tolerated

Question 15

What is sensory receptor adaptation?

Answer 15

When a continuous stimulus is applied, receptor response decreases over time until extinction

Question 16

What are tonic receptors and what is their function?

Answer 16

Slowly adapting receptors that transmit impulses for long periods of time (hours/days) while a stimulus is present.
Keep the brain informed about the status of the body and indicate the duration of a stimulus

Question 17

What are phasic receptors and what is their function?

Answer 17

Rapidly adapting receptors that only respond to change, indicating if there is a change in stimulus strength or a new stimulus.
Important for balance and movement

Question 18

What is the dorsal column-medial lemniscal responsible for? Describe its pathway.

Answer 18

Touch and proprioception.

1) Signal enters through the dorsal root and synapses with interneurons in the dorsal horn
2) Signal travels in the ipsilateral dorsal column to the medulla, where it synapses with second order neurons and decussates
3) Signal travels in the medial lemniscal pathway to the thalamus and synapses with ventrobasal complex
4) Signal travels to somatosensory cortex via internal capsule

Question 19

What is the anterolateral system responsible for? Describe its pathway.

Answer 19

Pain, itch and thermal sensation.

1) Signal enters through the dorsal root and synapses with interneurons in the dorsal horn
2) Signal decussates to the contralateral side and enters the anterolateral pathway
3) Signal travels to the thalamus and synapses with ventrobasal complex
4) Signal travels to somatosensory cortex via internal capsule

Question 20

Describe the anatomy of the sensory cortex.

Answer 20

Located in the precentral gurus, highly organised, receives information from the opposite sides of the body and gives an unequal representation of the body

Question 21

What is the medial brain stem pathway responsible for?

Answer 21

Posture

Question 22

What is the lateral brain stem pathway responsible for?

Answer 22

Self-movement of distal limbs

Question 23

What are the primary motor pathways?

Answer 23

Medial/lateral brain stem pathways, corticobulbar pathway, ventral/lateral corticospinal pathway, rubrospinal pathway

Question 24

What is the corticobulbar pathway responsible for?

Answer 24

Facial movements

Question 25

What is the corticospinal pathway responsible for?

Answer 25

Spinal movements

Question 26

What do muscle spindles respond to?

Answer 26

Muscle tone and length and the rate of change in muscle tone and length

Question 27

What fibres are muscle spindles composed of?

Answer 27

Intrafusal muscle fibres

Question 28

What are the two types of intrafusal fibres?

Answer 28

Nuclear bag and nuclear chain

Question 29

What are the two types of sensory receptor endings and what do they respond to?

Answer 29

Primary (Type 1A): Static tone and sudden dynamic changes Secondary (Type 2): Static tone

Question 30

How is a muscle spindle activated to increased muscle tone?

Answer 30

Weight added to muscle, type 1A neurons increase firing, alpha motor neurons are activated, muscle contracts, intrafusal fibres lose tension, gamma motor neurons are activated, intrafusal fibres become tense again

Question 31

What do Golgi tendon organs respond to and what is their function?

Answer 31

Stretching of the tendon - inhibition of anterior motor neurons - deforms terminals of sensory receptors (opens calcium channels to allow for action potential) Protect against excessive tension of the muscle and tendon

Question 32

What fibres do alpha neurons innervate and what do they control?

Answer 32

Extrafusal fibres Muscle tone and contraction

Question 33

What fibres do gamma motor neurons innervate and what do they control?

Answer 33

Intrafusal fibres Intrafusal tone and allow sensitivity to changes in length

Question 34

What is the function of lateral inhibition and through what cells does it occur?

Answer 34

Used to strengthen/sharpen signals, occurring through Renshaw cells

Question 35

What is an example of a monosynaptic reflex?

Answer 35

Stretch reflex

Question 36

What is an example of a polysynaptic reflex

Answer 36

Pain reflex

Question 37

What pathways are stimulated in a pain reflex?

Answer 37

Motor neurons (withdrawal reflex and reciprocal inhibition) Reverberating circuits Anterolateral pathway