Q1

Please describe a monosynaptic stretch reflex.

Muscle spindle and its reflex connections are involved in proprioception

CNS 1

Essential to pass

Monosynaptic, sensory organ, effector

 


Q2

Draw & label the action potential in a nerve cell.

 

cns 2

 

Pass Criteria:

Resting membrane potential

Movement of sodium potassium ions

 

Discuss the factors that affect conduction.

  • Myelinated vs demyelinated
  • Saltatory vs non-saltatory
  • Size
  • Direction of the conduction

 

What are the ion fluxes that occur during the action potential?

  • Fast Na+ influx
  • Slow K+ efflux

 


Q3

Describe the synthesis and release of acetyl choline at the neuro-muscular junction?

cns 3

Once it is released, how is the effect terminated?

  • Diffusion
  • Acetylcholinesterase

 


Q4

Draw a nerve action potential.

Resting membrane potential (-70m V);

Firing potential (-55mV);

Depolarises to positive level(+35mV)

cns 4

Pass Criteria:

  • (Concept, not exact figures)

What are the ion fluxes that occur during an action potential?

Fast sodium influx; slow potassium efflux

 


Q5

Describe the sequence of events in transmission of a motor nerve impulse to a muscle.

  • Motor neuron action potential;
  • end-plate potential;
  • Acetylcholine release;
  • Ach binding to nicotinic receptors;
  • muscle end-plate potential.

How does the muscle become depolarised?

T tubules and release of Ca2+ from sarcoplasmic reticulum

 


Q6

Describe the withdrawal reflex.

Reflex arc consisting of sense organ afferent and efferent nerve and effector

Noxious stimulus to skin or sub cut

Response of flexor muscle contraction and extensor relaxation

Result in withdrawal of limb from stimulus

Cross extensor response


Pass criteria:

3 out of 5

What is meant by the term polysynaptic reflex?

One or more interneurons and interposed between the afferent and efferent neurons

What are the effects of a polysynaptic reflex?

Prolonged effect as different time for stimulus to reach effector

Reverberation circuit as some interneurons turn back on themselves further prolonging the effect.

 


Q7

Describe the sequence of events in contraction and relaxation of skeletal muscle.

Steps in contraction

Discharge of motor neuron.

Release of transmitter (acetylcholine) at motor end-plate.

Binding of acetylcholine to nicotinic acetylcholine receptors.

Increased Na+ and K+ conductance in end-plate membrane.

Generation of end-plate potential.

Generation of action potential in muscle fibers.

Inward spread of depolarization along T tubules.

Release of Ca2+ from terminal cisterns of sarcoplasmic reticulum and diffusion to thick and thin filaments.

Binding of Ca2+ to troponin C, uncovering myosin-binding sites on actin.

Formation of cross-linkages between actin and myosin and sliding of thin on thick filaments, producing movement.

Steps in relaxation

Ca2+ pumped back into sarcoplasmic reticulum.

Release of Ca2+ from troponin.

Cessation of interaction between actin and myosin.

Pass Criteria:

  • Bolded

What is summation of contractions?

  • The electrical response of a muscle fibre to repeated stimulation
  • Contractile mechanism does not have a refractory period, so repeated stimulation before relaxation has occurred produces additional activation and a response added to the contraction already present
  • With rapidly repeated stimulation, individual responses fuse into one continuous contraction (tetanus; tetanic contraction).
  • Complete tetanus: no relaxation between stimuli; tension developed ~ 4 times that of an individual twitch contraction
  • Incomplete tetanus: periods of incomplete relaxation between summated stimuli

 


Q8

What happens to acetylcholine when released into a synapse?

  • Binds to post-synaptic cholinergic receptors
  • Catabolism by acetylcholinesterase at the postsynaptic membrane
  • Reuptake of choline –  No acetylcholine reuptake
  • Catabolism by pseudocholinesterase in the circulation

3/5 to pass

Describe the differences between the two types of acetylcholine receptors.

  • Divided on basis of pharmacological properties into muscarinic and nicotinic

needed to pass

 

  • Muscarinic–actions mimicked by muscarine and blocked by atropine. Found in smooth muscle, glands and brain. G- protein coupled to adenylyl cyclase and/or phospholipase.

2 sites to pass

 

  • Nicotinic–actions mimicked by nicotine. Found in neuromuscular junction, autonomic ganglia and the central nervous system. Ligand-gated sodium ion channels.

2 sites to pass

 


Q9

Describe the resting membrane potential of a cell.

  • There is difference in electronic charge across a cell membrane. The inside is negative compared to the outside. Resting MP results from separation of positive and negative charges across a cell membrane. Neuron average RMP -70 mV.

What conditions are required to create a resting membrane potential?

  • Lipid bilayer, unequal distribution of ions, membrane must be permeable to ions, concentration gradient.

In a neuron what ions are involved and how is the concentration gradient produced?

  • Na and K. Na is primarily extracellular and K intracellular. Passive movement of ions occur via selective ion channels. Na-K ATPase actively move ions against their electrochemical gradient.

 


Q10

What is clonus?

  • Regular, repetitive, rhythmic contractions of a muscle subjected to sudden, sustained stretch.

Why does ankle clonus occur with upper motor neuron lesions?

  • Loss of descending cortical input to inhibitory neurons called Renshaw cells, and therefore loss of inhibition of antagonists, resulting in repetitive sequential contractions of ankle flexors and extensors.

What are the components of the stretch reflex?

  • Sensor, afferent nerve, Monosynaptic at spinal level, efferent nerve, effector

 


Q11

Describe how pain is transmitted from the periphery to the brain.

Sensory organ or nerve ending

Transmission via 2 fibre types

  • Small fast myelinated A-delta fibers
  • Large slow unmyelinated C fibers

Spinal Cord: both fiber groups end in the doral horn of the spinal cord (“gate”)

  • A delta on neurons in laminas 1 and 4
  • C fibers on laminas 1&2

From spinal cord to brain via ventrolateral system – (second order neurons), lateral spinothalamic tract to the thalamus, then to the cerebral cortex (third order neurons)

Must mention dorsal horn of the spinal cord and at least 3 others in bold to pass

How can Acute pain be modulated?

  • Gate theory” eg stimulation of large touch/pressure afferents causing inhabitation of pain pathways in the dorsal horn of the spinal cord.
  • Stress induced analgesia
  • Drugs (eg opoids)
  • Higher centre interpretation

Must get gate theory and 1 other.

What sites do opioid peptides act on?

  • Receptors in the afferent nerve fibres
  • Dorsal horn region of the spinal cord
  • Periaqueductal grey matter in the brain

Supplementary Question

 


Q12

In the synapse, where can inhibition occur?

  • Post synaptic: direct or indirect (refractory periods, after hyperpolarisations)
  • Pre-synaptic: mediated by neurons that end on excitatory endings (axo-axonal synapses)

Must give presynaptic and post synaptic to pass

What are the mechanisms involved?

  • Increased Cl- conductance – reduces Ca2+ influx and amount of excitatory transmitter released.
  • Voltage gated K+ channels – K+ reduces Ca2+ entry
  • Direct inhibition of excitatory transmitter release, independent of Ca2+ influx.

Must give reduction in Ca2+ influx.

 


Q13

Describe the structure and function of the sodium potassium ATPase pump.

  • Function
    • Antiport: catalyses hydrolysis of ATP to ADP to move 3 Na out cell in exchange for 2 K in.
    • Maintains electrochemical gradient ECF (Electrogenic pump 3+ out / 2+ in = net 1+ out) and is large part of basal energy consumption – 33% energy use by cells (70% neurons)
    • When Na binds to alpha subunit, ATP also binds. ATP is converted to ADP causing change in protein configuration extruding Na out of cell.
    • Coupled to transport other substances (secondary active transport) e.g.glucose in SI mucosa,
    • K then binds extracellularly dephosphorylating alpha subunit which returns to original configuration releasing K into cytoplasm

 

  • Structure
  • alpha and ß subunits which pass through cell membrane
  • Both heterogeneous
    • alpha subunit intracellular binding sites for Na & ATP alpha subunit extracellular binding sites for K & ouabain ß subunit has no binding sites Na / K Variable distribution of alpha 1 + 2 and ß 1+2 subunits

 


Q14

What is the function of the reticular activating system?

  • Network of centres in the brain that regulate respiratory, cardiovascular, vegetative and endocrine functions
  • Non-specific activation from any modality
  • Sends signals mostly to the thalamus
  • Increases cortical electrical activity
  • Increased consciousness, alert state, heightened sensory perception – Essential

Describe its location and structure.

  • Complex polysynaptic network
  • Mid ventral portion of medulla + midbrain
  • Converging sensory fibres from long tracts and cranial nerves

 


Q15

Describe the sequence of events in the contraction of skeletal muscle.

  • Discharge of the motor neurone
  • Release of Ach at the motor endplate
  • Ach binds nicotinic Ach receptors
  • Increase in Naand K conductancein the end plate membrane
  • End plate potential
  • Muscle action potential
  • Depolarization along T tubules
  • Ca release at SR
  • Ca binds Trop C and uncovers myosinbinding sites on actin
  • Actin myosin cross links and thin filaments slide on each other.

How does tetanic contraction occur?

  • Contractile mechanism has no refractory period
  • Repeated stimulation before relaxation has occurred – summation of contractions
  • Fast repeated stimulation causes a fused continuous tetanic contraction. Can be complete or incomplete.
  • Series of maximal stimuli at a frequency just below tetanizing causes increasing tension between each twitch, due to increased calcium availability.

 


Q16

Can you give an example of a stretch reflex?

  • Knee jerk
  • Ankle jerk

Describe elements of a stretch reflex.

  • Sensor from afferent limb (1a fibre from muscle spindle, monosynaptic neurone and excite the motor neurone, so the muscle contracts.

What is an inverse stretch reflex?

  • Following prolonged stretch or muscle contraction, the muscle suddenly relaxes. This stimulates the Golgi tendon organ.
  • Integrator (Synapse on the motor neurone for stretch and inhibitory interneuron for the inverse stretch)
  • Efferent limb (ventral root for both)
  • Effector (muscle fibers)

 


Q17

Describe the characteristics of nerve fibers responsible for transmission of 'fast pain'?

  • myelinated A delta fibers
  • 2-5 um diameter
  • conduction rates 12-30 m/s
  • end in dorsal horn (lamina 1 and 5)
  • neurotransmitter is glutamate

Pass=myelinated plus 2/4 others

What differences are there between these nerve fibers and those responsible for transmission of “slow” or second pain?

  • unmyelinated C fibers
  • smaller 0.4 – 1.2 um diameter
  • slower 0.5 – 2.0 m/s
  • also dorsal horn but lamina 1 and 2
  • neurotransmitter is substance P
  • different sensation – dull / intense / diffuse
  • different locations as less A delta fibers in deeper structures

Pass = 4 bolded points

What do you understand by the term referred pain?

  • Same embryonic segment or dermatome
  • Give an example
    • eg diaphragmatic pain referred to shoulder tips.

 


Q18

Describe or draw the synthesis and release of noradrenaline at a synapse?

cns 5

How is the noradrenaline effect at the synapse terminated?

  • Diffusion
  • Reuptake
  • Monoamine Oxidase
  • COMT

What types or noradrenergic receptors are there?

  • Alpha
  • Beta

 


Q19

How is visual acuity measured? What does the fractions of a VA of 6/24 represent?

  • Measurement from Snellen chart viewed at a distance of 6 metres or 20 feet
  • 6/24 indicates reduced VA

Pass Criteria:

  • Numerator is the distance at which the chart is read
  • The denominator is the smallest line that can be read
  • 6/6 indicates normal vision

What factors influence visual acuity?

  • Optical factors – the state of the image forming mechanisms/sharpness of focus
  • Retinal factors – the state of the cones
  • Stimulus factors – illumination, brightness of the stimulus, contrast between stimulus and background, legnth time exposed to stimulus
  • Sensitivity and interpretative ability of the brain
  • Resolving power of the eye, property of the cones

Pass Criteria:

  • 2/3 to pass

Why is the fovea important for visual acuity?

  • Fovea is the point where visual acuity is greatest
  • Fovea is the centre of the macula, a thinned out rod free portion of the retina where the cones are densely packed and each synapses on a single bipolar cell

Pass Criteria:

  • One of bold 

 


Q20

What factors affect cerebral blood flow?

  • Intracranial pressure
  • Mean arterial pressure
  • Mean venous pressure
  • Local factors: pH, pCO2, cause constriction and dilatation of cerebral arteries
  • Blood viscosity

Pass Criteria:

  • Bold + 1

Describe autoregulation of cerebral blood flow. You can draw a diagram if you wish.

  • The process by which cerebral blood flow is maintained at a constant level despite variation in perfusion pressure.
  • Average cerebral blood flow is 54mL/100g/min between MAP 65-140mmHg

Pass Criteria:

  • Able to draw a plateau region with a range for MAP of 50 – 150 mmHg

What is the Monroe-Kellie doctrine?

  • Due to the fact that brain tissue and spinal fluid are essentially incompressible, the volume of blood, spinal fluid and brain tissue must be relatively constant. So when ICP rises, the cerebral vessels are compressed resulting in reduced cerebral blood flow.

Pass Criteria:

  • Need to pass 2/3 part to pass

 


Q21

What are upper motor neurons?

  • Upper motor neurons usually refer to corticospinal neurons that innervate spinal motor neurons (also include brain stem neurons that control spinal motor neurons)

Pass Criteria:

  • Bold

What clinical features are seen when they are injured?

  • Damage initially causes muscles to become weak and flaccid but eventually leads to spasticity, hypertonia, hyperactive stretch reflexes and an abnormal plantar extensor reflex (upwards)

Pass Criteria:

  • 2 of bold findings

What is the physiological basis to clonus?

  • Loss of descending cortical input to inhibitory neurons called Renshaw cells, and therefore loss of inhibition of antagonists, resulting in repetitive sequential contractions of ankle flexors and extensors.

Pass Criteria:

  • Bold

List the long term complications of spinal cord injury.

  • Ulcers
  • Protein/muscle degradation
  • Hypercalcaemia
  • Renal stones (calcium)
  • Urinary tract infection

Pass Criteria:

  • 2 to pass

Q22

Define the resting membrane potential of a neuron.

  • Potential difference across cell at rest, as a result of separation of positive and negative electronic charges across cell membrane
  • Inside negative relative to outside of cell
  • Normal RMP of neuron = – 70 mv

Pass Criteria:

  • Bold

Explain how resting membrane potential is created.
Prompt: Why is RMP negative on the inside of a cell?

  • Main ions involved Na+ & K+
  • Na+ K+ ATPase pump creates electrochemical gradient by pumping out 3 Na+ for every 2 K+ pumped in
  • Na+ & K+ diffuse down concentration gradient across permeable cell membrane (K+ diffuses from inside to outside of cell; opposite for Na+)
  • Cell membrane more permeable to K+ at rest –> that’s why RMP is close to equilibrium potential for K+
  • RMP represents an equilibrium state; driving force for ions down concentration gradient = driving forces down electrical gradient

Pass Criteria:

  • Bold

Why is a cell more excitable in hyperkalaemia?

  • RMP moves closer to threshold potential for eliciting action potential (becomes less negative on the inside of cell

Pass Criteria:

  • Bold

Q23

Draw a skeletal muscle action potential.

 

Pass Criteria:

  • Correct shape, axes, resting membrane potentials and durations (+/- 25%)

What is the sequence of events in the contraction of a skeletal muscle fibre, starting at the motor end-plate?

  1. Discharge of motor neuron
  2. Release of transmitter (acetylcholine) at motor endplate
  3. Binding of ACh to NIcotinic ACh receptors
  4. Increased NA+ & K+ conductance in end plate membrane
  5. Generation of end plate potential
  6. Generation of action potential in muscle fibers
  7. Inward spread of depolarisation along T tubules
  8. Release of Ca2+ from terminal cisterns of sarcoplasmic reticulum and diffusion to thick and thin filaments
  9. Binding of Ca2+ to troponin C, uncovering myosin-binding sites on actin
  10. Formation of cross-linkages between actin and mysoin and sliding of thin on thick filaments, producing movement

Pass Criteria:

  • 5 of 10 to pass

What is the sequence of events in the relaxation of a skeletal muscle fibre?

  1. Ca2+ pumped back into sarcoplasmic reticulum
  2. Release of Ca2+ from troponin
  3. Cessation of interaction between actin and mysoin

Pass Criteria:

  • Bold to pass

 

Q24

What factors affect cerebral blood flow?

  • MAP at brain level
  • MVP at brain level
  • ICP
  • Viscosity of the blood
  • Local constriction/dilatation of cerebral arterioles

Pass Criteria:

  • 3 of 5 to pass

What is the mechanism of the Cushing response?

  1. Increase in ICP results in decreased CBF
  2. Ischaemia of VMA
  3. SNS output increases
  4. Increased systemic BP
  5. Stimulation of baroreceptors
  6. Stimulation of vagal outflow
  7. Decreased HR and RR

Pass Criteria:

  • Explains concept

What is the Monro-Kellie doctrine?

  • The volume of blood (75 mL), CSF (75 mL) and brain (1400g) in cranium must be relatively constant
  • Negative effects on these therefore if additional intracranial volume (ie: SDH/EDH) occurs

Pass Criteria:

  • Explains concept