ILA8 - Brown Sequard Syndrome Flashcards
What does the central nervous system consist of?
Brain and spinal cord. Myelination by oogliodendrocytes
What does the peripheral nervous system consist of?
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
Describe the somatic nervous system.
- Voluntary &involuntary reflexes
- Peripheral NS
- Myelinated by Schwann
What are the three neurons in the somatic NS?
- 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
Whats the difference between autonomic and somatic nerve fibres?
Somatic have no ganglia but autonomic do
Most of the time, which neurotransmitters are used at the 2 synapses in sympathetic nerve fibres?
ACh to nicotinic receptors at ganglia
Noradrenaline to adrinergic receptors at target organ
Most of the time, which neurotransmitters are used at the 2 synapses in parasympathetic nerve fibres?
ACh onto nicotinic receptors at ganglia
ACh onto muscarinic receptors at target
Describe autonomic NS.
- Involuntary
- Regulates function of internal joints
- Myelinated preganglionic synapses to autonomic ganglia
- Sympathetic and parasympathetic
Describe the Parasympathetic NS.
- Cn 3, 7, 9, 10, sacral 1-4 and ganglia near organ
- Single preganglionic fibre
- Longer pathways so a slower system
Describe the sympathetic NS.
- C1-L1/2 (end of spinal cord), sympathetic trunk except Splachnic nerves
- Multiple preganglionic fibres
- Ganglion near spinal cord
What is the resting potential?
Inside is negative (-70mV)
How is the neuronal membrane semi permeable at rest?
Cl and K pass freely
Na there low permeability
What are the two forces determining the concentration of ions?
Diffusion and electrochemical gradient?
What is the action of the Na+/K+ ATPase pump?
- 3 Na+ out for 2 K+ in
- Maintains Na+ outside cell
- K+ diffuses out via channels
- Requires energy
When does a neurone fire?
When potential across membrane is suddenly and temporarily reversed, which transmits info
What are the forces acting on K+ at rest?
Diffusion =outwards
Electrochemical =in
What are the forces acting on Na+ at rest?
Diffsion =in
Elecrtochemical =in
What are the forces acting on Cl- at rest?
Diffusion =in
Electrochemical =out
What are the events involved in producing an action potential?
Threshold and depolarisation
Reversal of membrane potential
Repolarisation (and hyper)
Refractory period (absolute then relative)
Describe the generation of an action potential.
- 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
What do excitatory neurotransmitters cause?
Depolarise the membrane, increasing the probability of an action potential occurring. So causes an Excitatory Post Synaptic Potential (EPSP)
What do inhibitory neurotransmitters cause?
Hyperpolarisation of membrane, so decrease probability of action potential occurring, so Inhibitory Post Synaptic Potential (IPSP)
How are EPSPs involved in action potential?
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
What is the difference between the absolute and relative refractory periods?
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.
Describe how the action potential is conducted along the neuron.
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
What are the 4 aspects of a stimulus?
- Modality (type)
- Intensity
- Location
- Duration
Name some modalities?
Photoreception, mechanoreception, thermoreception, proprioception, nocioception, chemoreception
What is a sub-modality?
Different variations within the same stimulus.
How is a stimulus sensed?
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
Describe the knee jerk reflex.
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
What is Brown Sequard Syndrome?
Incomplete spinal cord lesion, usually in cervical region
Damage or loss of asc. or desc. spinal cord tracts on one side
Name some causes of Brown Sequard Syndrome.
Trauma (eg. stabs)
Non-traumatic (eg. tumour, MS)
What is the clinical presentation of Brown Sequard Syndrome?
- 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)
