NEURO W1

Neurones, neuron physiology, CNS Embryology & Neurological Diagnosis

What are the 4 functional units of a neuron?

• Cell body

• Dendrite

• Axon

• Synapse

How signalling in a neuron work?

• Cell fires action potential

• Signal transmits down the neuron

• Leads to release of neurotransmitter at synaptic cleft

What is the function of the myelin sheath?

Increase the speed of neuronal transmission

What sized fibres have a faster speed of conduction and are generally more brain friendly?

Large diameter fibres

What is the charge on the outside of a neuron?

Positive

What is the charge on the inside of a neuron?

Negative

What is responsible for the large amount of negative charge within a neuron?

Protein

What else besides protein maintains the electrical differential in a neuron?

Sodium Potassium pumps

What happens to a neuron if it synthesises less protein?

Will become more positive (closer to 0mV)

What is required for a neuron to produce energy?

• Mitochondria

• Protein replication

• Gene expression

• Fuel supply

• Oxygen

What will failure to trigger gene expression and protein replication cause in the cell?

Cell will become closer toward 0mV electrical potential, causing it to spontaneously fire

Define Resting Membrane Potential

The sum of all excitatory and inhibitory influences on the neuron at a given moment

What is the standard Resting Membrane Potential (RMP) of a neuron?

-70mV

What does hyperpolarisation mean?

More inhibition/less excitation

What does hypopolarisation mean?

Less inhibition/more excitation

At what RMP will a neuron fire (depolarise)?

-55mV

What is long term potentiation?

• The process of neuroplasticity

• Building health and functional capacity within a neuron

• Involves repeated firing through temporal and spatial summation which causes NMDA receptor activation

• DNA transcription and protein synthesis occurs

What happens if long term potentiation doesn’t occur?

Replication process wont happen as much, causing dysfunction in the neuron

What happens if long term potentiation occurs in the “wrong” systems?

OCD. Failing to inhibit systems within the brain

What is the first 4 steps in the embryology of the nervous system?

1. Notochord, precursor of neural crest, precursor of neural tube formed

2. Precursor neural tube folds in on itself

3. Forms neural tube—> Precursor of CNS—> If no join happens=Spina Bifida

4. Neural crest cells migrate out to form the PNS

What will the Telencephalon become through embryology?

Rhinencephalon, amygdala, hippocampus, neocortex, basal ganglia, lateral ventricles

What will the Diencephalon become through embryology?

Epithalamus, thalamus, hypothalamus, subthalamus, pituitary gland, pineal gland, third ventricle

What will the Mesencephalon become through embryology?

Midbrain

What will the Rhombencephalon become through embryology?

Metencephalon→ Pons, cerebellum

Myelencephalon→ Medulla oblongata

What do Rostral and Caudal mean?

Superior and inferior

Depending on orientation, Rostral can mean ANT, Caudal can mean POST

What do Ventral and Dorsal mean?

Anterior and Posterior

What nerve fibre types are there, from fastest conducting to slowest?

Larger diameter:

Type Ia, Ib, II

Alpha motor neurons

A delta

Smaller diameter:

C fibres

What 7 levels of the nervous system are there to consider in the neurological differential diagnosis?

• Effector/receptor/neurological junction

• Peripheral nerve & nerve roots

• Spinal cord

• Brainstem

• Cerebellum

• Thalamus/Basal Ganglia

• Cerebral cortex

What should you be thinking about when considering Effector/receptor/neurological junction differential diagnosis?

• Receptor/neurological junction→ muscle spindle degeneration w/ age

• Effector= gland or muscle→ output of nervous system

What should you be thinking about when considering Peripheral nerve & nerve root differential diagnosis?

• Anatomy of the nerves and roots

• Peripheral nerve→ thinking pain/temp fibres, changes in LDA fibres

• Sensory loss will match dermatome

• Motor loss will match myotome

What should you be thinking about when considering spinal cord differential diagnosis?

• Sensory loss will not match particular dermatome or myotome

• UMN/LMN

• Consider distinctive pattern of loss due to involved tract

• i.e. corticospinal→ hemiplegic signs, UMN signs ipsilateral to lesion

• i.e. ANT spinothalamic tract→ P/T loss contralateral to lesion. POST→ light touch, proprioception, 2 point discrimination, vibration loss is all ipsilateral

What should you be thinking about when considering brainstem differential diagnosis?

• Sensory and motor findings from long tract involvement (patterns differ to spinal cord)

• Cranial nerve signs as well

• IF spasticity one side of body and CN signs, you will not get CN signs from spinal cord lesion

What should you be thinking about when considering cerrebellum differential diagnosis?

• Rhythm, coordination and timing changes

• Assess through function tests→ Finger to nose, rapid alternating movements, nystagmus test

What should you be thinking about when considering thalamus/basal ganglia differential diagnosis?

• Sensory and motor changes (non-dermatomal)

• Hyperkinetic disorders (ballistic movements, dystonic posturing, ticks, myoclonic bradykinesia, rigidity, resting tremors)

What should you be thinking about when considering cerebral cortical differential diagnosis?

• Consider the 4 lobes

• Frontal→ problems with planning, decision making, motivation, speech

• Parietal→ complex movements

• Temporal→ Hearing, memory, smell, naming things, identifying objects, seizure type activity

• Occipital- Vision

When assessing light touch for a patient, what neurological structure is being assessed?

Posterior columns

When assessing sharp touch for a patient, what neurological structure is being assessed?

Corticospinal tracts

Dermatomes- Upper limbs

Dermatomes- Lower limbs

List the upper and lower limb reflexes

C5- Biceps→ Elbow flexion

C6- Brachioradialis→ Elbow flexion

C7- Triceps→ Elbow extension

L4- Patella→ Knee extension

L5- Medial hamstring→ Knee flexion

S1- Achillies- Dorsiflexion

Please state all grades in the Muscle Stretch Reflex results

0= Absent (Possible LMN lesion)

1= Reduced (Possible LMN lesion

2= Normal

3= Increased (Hyper-reflexia)

4= Increased (Hyper-reflexia with clonus)

What does the positive test for clonus look like at the ankle?

Sustained beats (5 or more)

List the myotomes of the upper limb

C3 – neck lateral flexion

C4 – shoulder shrug

C5 - deltoid

C6 – Wrist extension

C7 – Wrist flexion

C8 – Finger abduction

List the myotomes for the lower limb

L2 – hip flexion

L3 – knee extension

L4– ankle dorsiflexion

L5 – big toe extension

S1 – ankle dorsiflexion

Please state all grades in recording muscle strength

0= Total paralysis, no evidence of contraction

1 (Trace)= Palpable/visible contraction (no joint movement)

2 (Poor)= Full ROM with gravity eliminated

3 (Fair)= Full ROM against gravity

4 (Good)= Full ROM against gravity with moderate resistance

5 (Normal)= Full ROM against gravity with full resistance