ILA8 - Brown Sequard Syndrome

Question 1

What does the central nervous system consist of?

Answer 1

Brain and spinal cord. Myelination by oogliodendrocytes

Question 2

What does the peripheral nervous system consist of?

Answer 2

Everything else. Myelination by Schwann cells.
Sensory body in dorsal root ganglion, motor body in ventral horn of spinal cord
Cranial nerves except optic and olfactory are peripheral

Question 3

Describe the somatic nervous system.

Answer 3

• Voluntary &involuntary reflexes
• Peripheral NS
• Myelinated by Schwann

Question 4

What are the three neurons in the somatic NS?

Answer 4

• Alpha (extrafusal fibres=movement, cell body in ventral horn)
• Beta (intrafusal with collaterals to extra)
• Gamma (intrafusal fibre, regulate the sensitivity of the spindle to muscle stretching, contract intrafusal fibres when muscle relaxes so only small stretch will activate sensory neurons and stretch reflex

Question 5

Whats the difference between autonomic and somatic nerve fibres?

Answer 5

Somatic have no ganglia but autonomic do

Question 6

Most of the time, which neurotransmitters are used at the 2 synapses in sympathetic nerve fibres?

Answer 6

ACh to nicotinic receptors at ganglia

Noradrenaline to adrinergic receptors at target organ

Question 7

Most of the time, which neurotransmitters are used at the 2 synapses in parasympathetic nerve fibres?

Answer 7

ACh onto nicotinic receptors at ganglia

ACh onto muscarinic receptors at target

Question 8

Describe autonomic NS.

Answer 8

• Involuntary
• Regulates function of internal joints
• Myelinated preganglionic synapses to autonomic ganglia
• Sympathetic and parasympathetic

Question 9

Describe the Parasympathetic NS.

Answer 9

• Cn 3, 7, 9, 10, sacral 1-4 and ganglia near organ
• Single preganglionic fibre
• Longer pathways so a slower system

Question 10

Describe the sympathetic NS.

Answer 10

• C1-L1/2 (end of spinal cord), sympathetic trunk except Splachnic nerves
• Multiple preganglionic fibres
• Ganglion near spinal cord

Question 11

What is the resting potential?

Answer 11

Inside is negative (-70mV)

Question 12

How is the neuronal membrane semi permeable at rest?

Answer 12

Cl and K pass freely

Na there low permeability

Question 13

What are the two forces determining the concentration of ions?

Answer 13

Diffusion and electrochemical gradient?

Question 14

What is the action of the Na+/K+ ATPase pump?

Answer 14

• 3 Na+ out for 2 K+ in
• Maintains Na+ outside cell
• K+ diffuses out via channels
• Requires energy

Question 15

When does a neurone fire?

Answer 15

When potential across membrane is suddenly and temporarily reversed, which transmits info

Question 16

What are the forces acting on K+ at rest?

Answer 16

Diffusion =outwards

Electrochemical =in

Question 17

What are the forces acting on Na+ at rest?

Answer 17

Diffsion =in

Elecrtochemical =in

Question 18

What are the forces acting on Cl- at rest?

Answer 18

Diffusion =in

Electrochemical =out

Question 19

What are the events involved in producing an action potential?

Answer 19

Threshold and depolarisation
Reversal of membrane potential
Repolarisation (and hyper)
Refractory period (absolute then relative)

Question 20

Describe the generation of an action potential.

Answer 20

• Neurotransmitter binds to receptor on dendrites and activates
• Receptor opens ion channels
• Ions (Na+) cross plasma membrane changing potential
• The potential change spreads through the cell
• If the potential change at the axon hillock are above the threshold an action potential is triggered, more Na+ channels opened

Question 21

What do excitatory neurotransmitters cause?

Answer 21

Depolarise the membrane, increasing the probability of an action potential occurring. So causes an Excitatory Post Synaptic Potential (EPSP)

Question 22

What do inhibitory neurotransmitters cause?

Answer 22

Hyperpolarisation of membrane, so decrease probability of action potential occurring, so Inhibitory Post Synaptic Potential (IPSP)

Question 23

How are EPSPs involved in action potential?

Answer 23

1) EPSP begins to depolarise membrane
2) If threshold met (-55mV) then voltage gated Na+ channels open causing membrane potential to go to +30mV (depolarisation)
3) Repolarisation by Na+ closing and K+ open, K+ moves out down conc gradient
4) K+ channels take too long to close, slight overshoot (hyperrepolarisation), Na+/K+ ATPase pump
5) Refractory period as Na+ channels can’t open

Question 24

What is the difference between the absolute and relative refractory periods?

Answer 24

Absolute is when no other action potential can be produced no matter how strong the stimulus (1-2ms).
Relative is when another action potential can be produced (as some Na+ channels become re activated) but the stimulus must be stronger than previous.

Question 25

Describe how the action potential is conducted along the neuron.

Answer 25

a) Ions diffuse to neighbouring region of Axon
b) AP depolarizes neighbouring region up to threshold
c) Na+ voltage gated channels open→ AP triggers
d) Unidirectional due to the refractory period
e) Saltatory conduction:
- Same as normal axonal propagation but jumps from node to node due to myelination

Question 26

What are the 4 aspects of a stimulus?

Answer 26

• Modality (type)
• Intensity
• Location
• Duration

Question 27

Name some modalities?

Answer 27

Photoreception, mechanoreception, thermoreception, proprioception, nocioception, chemoreception

Question 28

What is a sub-modality?

Answer 28

Different variations within the same stimulus.

Question 29

How is a stimulus sensed?

Answer 29

a) Sensory receptor activity triggered by a specific stimulus. Results in the opening of ion channels:
- Sensory receptors are either specialised endings of afferent neurons or separate cells which signal the neuron by releasing Neurotransmitter
- Stimulus must be sufficient to reach the receptor potential→ Stimulus results in graded potential, this must be sufficient to flow to area with voltage gated channels to trigger an AP
b) Afferent neurons have two processes (Dorsal ganglion=cell body)
- One to site of reception
c) One to spinal cord where they synapse with interneurons
d) Interneurons synapse with ascending neurons in specific ascending pathways (1 sense from 1 area)
e) Decussation occurs at the interneuron or at the brainstem (usually in medulla)
f) Pass to brainstem and thalamus and then onto the somatosensory cortex (posterior to central sulcus) for processing

Question 30

Describe the knee jerk reflex.

Answer 30

a) Striking patellar ligament just below patellar stretched spindles in quadriceps (gamma neuron)
b) Afferent signal travels to spinal cord and synapses at L4 with:
- Interneurone, which synapses with to motor neurone for hamstring, has inhibitory effect
- alpha motor neuron to quads, exitatrory
c) Extensor muscle contracts and flexor relaxes

Question 31

What is Brown Sequard Syndrome?

Answer 31

Incomplete spinal cord lesion, usually in cervical region

Damage or loss of asc. or desc. spinal cord tracts on one side

Question 32

Name some causes of Brown Sequard Syndrome.

Answer 32

Trauma (eg. stabs)

Non-traumatic (eg. tumour, MS)

Question 33

What is the clinical presentation of Brown Sequard Syndrome?

Answer 33

• Ipsilateral (to lesion) motor neurone paralysis (motor0
• Ipsilateral loss of fine touch, vibration, proprioception and 2 point descrimination (DCML)
• Contralateral loss of pain and temp (ST)