Week 2

Question 1

Functional part of the neurone

Receives input from other neurones and conveys graded electrical signals passively to the soma

Answer 1

Dendrite

Question 2

Functional part of the neurone

Synthetic and metabolic centre of the neurone. Contains the nucleus ribosomes, mitochondria and endoplasmic reticulum

Answer 2

Cel body (soma)

Question 3

Functional part of the neurone

Sight of initiation of the “all or nothing” action potential

Answer 3

Axon hillock and initial segment

Question 4

Functional part of the neurone

Conducts output signals as action potentials to the presynaptic terminal, and vice versa, by slow and fast axonal transport

Answer 4

Axon

Question 5

Functional part of the neurone

Point of chemical communication between neurones (or other cells)

Answer 5

Synapse

Question 6

What are the four morphologies of neurone?

Can you provide an example of each?

Answer 6

Unipolar (one dendrite) - peripheral autonomic neurone

Pseudounipolar (one dendrite that bifurcates) - dorsal root ganglion neurone

Bipolar - retinal bipolar neurone in the eye

Multipolar (3 or more dendrites) - lower motor neurone

Question 7

Action potential of neurones

Resting potential?

At what voltage is the threshold for the all or nothing action potential?

Answer 7

Resting potential = -70mV

Threshold for action potential generation = -60mV

Question 8

Action potential of neurones

What ion channel is involved in the upstroke of the action potential?

What does this influx of ions result in?

Answer 8

Na+ channels are open in the upstroke period of the action potenial

This influx of Na+ ions results in hyperpolarisation of the membrane and a resting membrane potential of +40mV

Immediately after Na+ channels open, K+ channels also open

Question 9

Action potential of neurones

What ion channel is open in the downstroke of the action potential?

What does this result in?

Answer 9

K+ channels are opened as soon as Na+ channels are opened, and after the initial overshoot there is a drop in voltage, resulting in an undershoot where the membrane potential is briefly at -80mV

Question 10

What are the 3 morphological types of synapse?

Which is the most common?

Answer 10

Axodendritic (most common)

Axosomatic (relatively common)

Axoaxonic (uncommon)

Question 11

Most frequent excitatory neurotransmitter in the CNS

Answer 11

Glutamate

Question 12

Most frequent inhibitory neurotransmitter in the CNS

Answer 12

GABA or glycine

Question 13

Define the terms spatial and temporal summation

Answer 13

Spatial summation - many inputs converge on a neurone to determine its output i.e. if more EPSPs then excitatory, if more IPSPs then inhibitory

Temporal summation - a single input may modulate output by variation in action potential frequency. This occurs over time

Question 14

Low threshold units respond to non-damaging and innocuous/potentially damaging and noxious stimuli. Examples of these units are ___

High threshold units respond to non-damaging and innocuous/potentially damaging and noxious stimuli. Examples of these units are ___

Answer 14

Low threshold units respond to non-damaging and innocuous stimuli i.e. low intensity - increasing the strength of the stimulus increses the rate of firing. Examples include mechanoreceptors mediating fine discriminatory touch and thermoreceptors mediating cold, cool, warm and hot

High threshold units respond to potentially damaging and noxious stimuli i.e. high intensity. Examples include high threshold mechanoreceptors, thermal nociceptors that respond to extreme degrees of temperature, chemical nociceptors and polymodal nociceptors (respond to multiple stimuli)

Question 15

Organise these fibres based on speed of conduction…

C

A alpha

A beta

A delta

Answer 15

A alpha (slowest)

A beta (slightly faster)

A delta (faster)

C (fastest)

Question 16

C fibres are involved in…

Answer 16

temperature, pain and itch

Question 17

A alpha fibres are involved in…

Answer 17

Proprioceptors of skeletal muscle

Question 18

A beta fibres are involved in…

Answer 18

Mechanoreceptors of skin

Question 19

A delta fibres are involved in…

Answer 19

Pain and temperature

Question 20

What does ‘adaptation’ refer to, with regards to sensory units?

Answer 20

Adaptation - feature of sensory units that determines whether they change their firing rate only in response to a stimulus of changing intensity, OR if they fire continuously throughout a constant stimulus

Can be classified into…

1. Slowly Adapting. Continuous info is sent to CNS while terminal is deformed, meaning continued firing. Example - stretch receptors
2. Fast/Rapid Adapting. Detects changes in stimulus strength, with the number of impulses changing proportionally. Example – some muscle spindle afferents, hair follicle afferents
3. Very Fast Adapting. Respond only to very fast movements e.g. rapid vibration. Example – Pacinian corpuscle

Question 21

What does the term ‘receptive field’ refer to?

What is its relation to sensory acuity?

Answer 21

Peripheral terminals of cutaneous afferent fibres branch into many fine processes, the tips of which can be…

• Free nerve endings
• Associated with specialised structures

RF is the territory from which a sensory unit can be excited, and RF size varies greatly across the body. “RF is the particular region of the sensory space (e.g., the body surface, or the visual field) in which a stimulus will modify the firing of that neuron”

RF varies inversely with sensory acuity, meaning that the smaller the RF the finer the degree of discriminatory touch

Question 22

Mechanoreceptors can be physiologically classified based on their rates of adaptation (either Slow or Fast Adapting, SA and FA) and the size of their receptive field (small field or wide field, type 1 and type 2)

Provide an example of each of the following…

FA1

FA2

SA1

SA2

Answer 22

FA1 - Meissner corpuscles

FA2 - Pacinian corpuscles

SA1 - Merkel cell-neurite complexes

SA2 - Ruffini endings

Question 23

Which sensory receptor is located in the basal epithelium of skin areas with high sensory acuity e.g. finger pads, and is sensitive to stroking, fluttering and low frequency vibrations?

How is this receptor physiologically classified?

Answer 23

Meissner corpuscles

Classified as FA1 (fast adapting, small receptive field)

Question 24

Which sensory receptor appears as large “onion-like” structures found close to the periosteum of bone, and are very sensitive to higher frequency vibrations?

How is this sensory receptor physiologically classified?

Answer 24

Pacinian corpuscles

Classified as FA2 (fast adapting, large receptive field)

(Bottom box in diagram)

Question 25

Which sensory receptor is located in the basal epithelium of skin areas with high sensory acuity (e.g. finger pads), formed from many expanded nerve terminals each associated with a Merkel cell, and is extremely sensitive to the edges of objects? How is this sensory receptor physiologically classified?

Answer 25

**Merkel cell-neurite complexes** Classified as SA1 (slow adapting, small receptive field)

Question 26

Which sensory receptor is a collagenous core with branching axons, found in the dermis and joint capsules of both glabrous and hairy skin, and is especially sensitive to dragging/shearing forces? How is this sensory receptor physiologically classified?

Answer 26

**Ruffini endings** Classified as SA2 (slow adapting, large receptive field)

Question 27

Which of the following sensory receptors is NOT present in hairy skin? - Ruffini endings - Meissner corpuscles - Pacinian corpuscles - Merkell cell-neurite complexes

Answer 27

**Meissner corpuscles** are NOT found in hairy skin

Question 28

How is the grey matter of the spinal cord subdivided?

Answer 28

Into dorsal and ventral horns, and **10 distinct laminae or Rexed**

Question 29

What are the 3 types of afferent fibre found within the laminae of Rexed?

Answer 29

Nociceptors (laminae I and II) Low threshold mechanoreceptors (laminae III to VI) Proprioceptors (laminae VII, VIII and IX)

Question 30

Describe the dermatome distribution of the upper limb

Answer 30

C4 - deltoid C5 - bag patch C6 - lateral forearm and thumb C7 - middle three fingers and posterior middle forearm C8 - 5th finger and posterior medial forearm T1 - medial arm and medial bicep

Question 31

Describe the dermatome distribution of the lower limb

Answer 31

L1 - pocket area L2 - lateral thigh L3 - medial thigh L4 - medial leg and big toe L5 - lateral leg and toes 2, 3 and 4 S1 - 5th toe and lateral ankle S2 - back of leg S3 - glutes

Question 32

DCML tract - ascension of the first order neurone is ipsilateral/contralateral Where does the synapse between the first and second order neurone in this tract take place?

Answer 32

Ascension is **ipsilateral** Synapse occurs either in the dorsal column **gracile nucleus (GN)** or **cuneate nucleus (CN)**

Question 33

Where does decussation occur in the DCML tract?

Answer 33

In the brainstem (**medulla, great sensory decussation)**

Question 34

What sensations does the DCML tract provide?

Answer 34

Discriminatory touch Fine touch Pressure Vibration detection (via Pacinian corpuscles) _Conscious_ proprioception

Question 35

Spinothalamic tract - ascension of the first order neurone is ipislateral/contralateral Where does decussation occur in the spinothalamic tract?

Answer 35

Ascension is **contralateral** Decussation occurs **at the spinal level of the first order neurone**

Question 36

What sensations does the spinothalamic tract provide?

Answer 36

Pain Thermosensation Crude touch Itch Tickle

Question 37

In what clinical presenation are the differences in the level of decussation between the DCML and spinothalamic tracts particularly relevant?

Answer 37

Brown-Sequard Syndrome Paralysis and loss of proprioception (hemiparaplegia) is seen on the ipsilateral side of the body (DMCL), while loss of pain and temperature sensation is seen on the contralateral side of the body (spinothalamic tract)

Question 38

What are the two components of the dorsal column ascending tracts? What does each do?

Answer 38

Dorsal column ascending tracts are made up of the **Fasciculus gracilis** and **Fasciculus cuneatus** FG is more medial and controls the lower limbs and trunk (T6 and below) FC is more lateral and controls the upper limbs and upper trunk (everything above T6)

Question 39

State the location and subdivisions of the primary somatosensory cortex Which of these subdivisions does the majority of input go to?

Answer 39

Location - post central gyrus of the parietal lobe, immediately posterior to the central sulcus Subdivisions - **Brodmann areas (BA)** **1, 2, 3a** and **3b** The majority of input goes to BAs **3a and 3b** BAs 3a and 3b are closer to the central sulcus than BAs 1 and 2

Question 40

What are the modality sensitivities of Brodmann Areas 3a and 3b?

Answer 40

3a - proprioceptors, so modality is **body position** 3b - cutaneous (e.g. Merkel cells) and Fast Adapting (e.g. Meissner's corpuscles) receptors, modality is **touch** (texture, shape, stimulus size)

Question 41

The somatosensory cortex is layered (made up of 6 cell layers, I – VI). Thalamic inputs to SI (somatosensory cortex) terminate mainly on neurones within which layer?

Answer 41

**Layer IV**

Question 42

What is the posterior parietal cortex important for? How might damage to this area present?

Answer 42

Important for **deciphering deeper meaning** from the information provided by the somatosensory cortex e.g. telling the difference between a coin and a key in your pocket, just by touch Damage can result in some bizarre neurological symptoms e.g. **agnosia** (inability to interpret sensations and as a result being unable to recognise things), **astereognosia** (inability to identify an object by active touch of the hands) and **hemispatial neglect syndrome** (patient believes the contralateral side to the area affected (usually the right, so left is the contralateral side) no longer exists

Question 43

Regarding drug action on neurotransmission, how does a local anaesthetic such as lidocaine work?

Answer 43

Local anaesthetics such as lidocaine are **Na+ channel antagonists**, meaning they prevent Na+ from entering through channels, which prevents depolarisation and excitation, meaning they have an **inhibitory affect**

Question 44

Describe the release of a neurotransmitter from a synapse

Answer 44

Action potential **depolarises** the axon terminal This depolarisation opens voltage-gated Ca2+ channels = **Ca2+ enters the cell** Calcium entry triggers **exocytosis of synaptic vesicle contents** (pre-formed neurotransmitters) Neurotransmitter then diffuses across the synaptic cleft and binds with receptors on the post-synaptic cell, which initiates response

Question 45

What are the 3 ways in which neurotransmitters can be deactivated?

Answer 45

1. can be taken back up into the presynaptic cell and reused, or taken into glial cells 2. can be inactivated by enzymes 3. neurotransmitters can diffuse out of the synaptic cleft

Question 46

How do channels for GABA/glycine/nicotinic ACh and glutamate differ structurally?

Answer 46

GABA/glycine/nicotinic ACh channels are **pentamers** Glutamate channels are **tetramers**

Question 47

Non-NMDA ionotropic receptors (AMPA and kainate) mediate slow/fast excitatory synaptic transmission NMDA receptors mediate slow/fast excitatory synaptic transmission

Answer 47

Non-NMDA receptors mediate **fast excitatory synaptic transmission** NMDA receptors mediate **slow excitatory synaptic transmission**

Question 48

How do the following drugs affect GABA receptors? Which GABA receptors do they affect? - Benzodiazepines - Barbiturates - Baclofen

Answer 48

Benzodiazepines - positive allosteric modulator of GABAa receptor, **enhance Cl- entry, decrease resting membrane potential** and **enhance inhibition in the presence of GABA** Barbiturates - similar to BZDs and **potentiates the effect of GABA at the GABAa receptor** Baclofen - **agonist of the GABAb receptor**, so enhances the K current and increases inhibition

Question 49

Major excitatory neurotransmitter? What ions does it allow into the cell? What effect does this have?

Answer 49

**Glutamate** Allows **Na+** and **K+** into the cell, resulting in EPSP, depolarisation and excitation

Question 50

Major inhibitory neurotransmitter? What ions does it allow into the cell? What effect does this have?

Answer 50

GABA Allows **Cl-** into the cell, resulting in an IPSP, hyperpolarisation and inhibition

Question 51

Lower Motor Neurones (LMNs) are comprised of both alpha and gamma motor neurones - what is the role of each?

Answer 51

Alpha motor neurones - innervate the **bulk of skeletal muscle fibres** Gamma motor neurones - innervate a sensory organ within the muscle, known as the **muscle spindle**

Question 52

How do axons from LMNs exit the spinal cord?

Answer 52

Exit in the **ventral roots** which join with dorsal roots to form mixed spinal nerves, or via **cranial nerves**

Question 53

Are motor neurones distributed evenly across the spinal cord?

Answer 53

No - greater number in the **cervical enlargement (C3-T1)** and in the **lumbar enlargement (L1-S3)**

Question 54

# Define the following terms... - motor unit - motor neurone pool

Answer 54

Motor unit - an alpha motor neurone and all of the skeletal muscle fibres that i innervates Motor neurone pool - a collection of alpha motor neurones that innervate a single muscle

Question 55

What are the two major types of skeletal muscle fibre? Describe each

Answer 55

Two major types - **Fast** and **Slow** **Slow (Type I) Fibres** * ATP derived from oxidative phosphorylation * Slow contraction and relaxation - **fatigue resistant** * Appears as **red fibres** ("dark meat") due to higher myoglobin content **Fast (Type II) Fibres** * **Type IIa** * ATP derived from oxidative phosphorylation * Fast contraction and relaxation - **fatigue resistant** * Red, and reasonably well vascularised * **Type IIb** * **​**ATP derived from glycolysis * Fast contraction but **not fatigue resistant** * Pale in colour, poorly vascularised - "white meat"

Question 56

What is the Henneman Size Principle?

Answer 56

**Susceptibility of an alpha motor neurone to discharge action potentials is a function of its size** Smaller alpha-MNs (part of slow motor units) have a lower threshold than larger ones (part of fatigue resistant or fast fatiguing motor units). Slow motor units are more easily activated and "trained" by activities that affect the muscle

Question 57

What is the myotactic reflex? What is the clinical relevance?

Answer 57

When a skeletal muscle is pulled, **it pulls back** (monosynaptic reflex arc) Change of length and the rate of this change is registered by **muscle spindles** Clinical relevance - striking the patellar tendon to cause a knee jerk reflex is underpinned by this reflex

Question 58

Which neurotransmitter is released by hair cells in the ear when they bend?

Answer 58

Potassium, K+

Question 59

Describe the 3 cell types that light passes directly (vertical pathway) through when it hits the retina What is the function of horizontal cells and amacrine cells?

Answer 59

Ganglion cells \> bipolar cells \> photoreceptors Horizontal cells - interconnect a group of "surround neurones" which sample the total amount of excitation in the surrounding area and respond by releasing **GABA** to influence signal processing Amacrine cells - receive input from bipolar cells and project to ganglion cells, bipolar cells and other amacrine cells. Also influence signal processing

Question 60

In light, less/more glutamate is released from photoreceptors In dark, less/more glutamate is released from photoreceptors

Answer 60

Light = **less glutamate released** Dark = **more glutamate released**

Question 61

Describe the ON and OFF pathways, along with which receptors are involved

Answer 61

OFF pathway - bipolar cells express **ionotropic gluR receptors** In the light (less glutamate available), this results in a more negative V(m) being passed on to the ganglion cell In the dark (more glutamate available), this results in a more positive V(m) being passed on to the ganglion cell ON pathway - bipolar cells express **metabotropic gluR receptors** In the light (less glutamate available), this results in a more positive V(m) being passed on to the ganglion cell, and the converse is seen in the dark

Question 62

What are the 4 types of photoreceptor in the human eye, and which colour is sensed by each?

Answer 62

Short-wavelength cones = blue Medium-wavelength cones = green Long-wavelength cones = red Rods (black and white)

Question 63

Rods/cones allow us to see **dim light** Rods/cones allow us to see in **normal daylight** Which displays more convergence and thus increases sensitivity while decreasing acuity?

Answer 63

Rods = dim light Cones = normal daylight **Rods** display more convergence

Question 64

What type of spinal interneurones are involved in the following... - reciprocal inhibition - flexor reflex - crossed extensor reflex

Answer 64

**Reciprocal inhibition** - voluntary contraction of an extensor will stretch the antagonistic flexor, initiating the myotactic reflex. Descending pathways that activate the alpha motorneurones controlling the extensor muscles will also inhibit the alpha motorneurones supplying the antagonistic flexor muscles, allowing unopposed extension. Important in the initiation of movement by the motor cortex. This is done via **inhibitory spinal interneurones** **Flexor reflex** - noxious stimuli causes a limb to flex, mediated by **excitatory spinal interneurones** **Crossed extensor** - noxious stimuli causes a limb to extend, also mediated by **excitatory spinal interneurones**

Question 65

Where do the descending spinal tracts originate? What are they involved in?

Answer 65

Originate in the **cerebral cortex** and the **brain stem** 1. Control of movement 2. Muscle tone 3. Spinal reflexes 4. Spinal autonomic functions 5. Modulation of sensory transmission to higher centres

Question 66

What are the two important descending pathways to be aware of? Which parts of the brain control both? What does each do?

Answer 66

**Lateral pathways** (**lateral corticospinal tract** and rubrospinal tract) - under control from the **cerebral cortex.** Important for **voluntary control of distal musculature esp discrete skilled moves of the hands and fingers** **Ventromedial pathways** (pontine reticulospinal tract, medullary reticulospinal tract, lateral vestibulospinal tract and tectospinal tract) - under control from the **b****rainstem.**Important for the**control of posture and locomotion**

Question 67

Which is the major lateral descending tract? Where do fibres in this tract decussate?

Answer 67

The corticospinal (pyramidal) tract Most fibres (75-90%) decussate at the pyramidal decussation to form the lateral corticospinal tract, however 10-25% stay ipsilateral to form the ventral corticospinal tract and decussate more caudally **NB - irrespective of level of decussation, left hemisphere controls musculature on the right side and vice versa**

Question 68

What effects might lesions of the lateral descending pathways have on a patient?

Answer 68

Loss of 'fractionated' movements i.e. shoulders, elbows, wrists and fingers cannot be moved independently Slowing and impairment of accuracy of voluntary movements Posture is not really affected

Question 69

Which of the following is a maladaptive response? Nociceptive pain Inflammatory pain Pathological pain

Answer 69

**Pathological pain is maladaptive** (no physiological purpose, persists over months to years)

Question 70

Nociceptors are first order/second order neurones

Answer 70

**First order**

Question 71

What are the two types of nociceptor and what kind of stimuli does each respond to?

Answer 71

**Að fibres** - mechanical/thermal nociceptors. Mediate **fast pain** (stabbing, pricking etc.) **C fibres** - unmyelinated, collectively respond to all noxious stimuli (polymodal). Mediate **slow pain** (burning, throbbing, cramping etc.)

Question 72

What family of receptors is activated by noxious heat?

Answer 72

**Transient receptor potenial (TRP) family**, particularly **TRPA1, TRPC3** and **TRPV1**

Question 73

What receptors are activated by chemical stimuli?

Answer 73

H+ ions activate acid sensing ion channels (**ASICs**), ATP activates **P2X and P2Y receptors** and bradykinin activates **B2 receptors**

Question 74

Try and explain referred pain!

Answer 74

Visceral afferents from nociceptors follow sympathetic pathways before entering the dorsal horn Some visceral and skin afferents **converge** upon the same spinothalamic neurones. **The brain interprets the nociceptive information arising from the viscera as originating from an area of skin that may be distant to the internal organ**

Question 75

What are the two major nociceptive tracts?

Answer 75

Spinothalamic tract Spinoreticular tract