Nervous System Physiology Flashcards
Compare Na and K concentration inside and outside nerve cell at resting membrane potential?
Na concentration low inside, high outside
K concentration high inside, low outside
What pump maintains the RMP of a nerve cell?
Na/K ATPase pump
Describe the movement of ions via the Na/K/ATPase pump?
3Na OUT
2K IN
What equation can be used to calculated the electrical potential across the cell membrane for a specific ion?
Nernst equation
What is ACh broken down by at the synaptic cleft?
Acetylcholinesterase
What combines to make acetylcholine?
Choline and Acetyl-SCoA –> ACh and CoA
What does acetylcholinesterase break down ACh into?
Acetate and Choline
Where does ACh bind on a nicotinic receptor?
Binds to the alpha subunits (2 out of 5 units within the nicotinic receptor are alpha)
What ion does the nicotinic receptor channel into the cell when ACh binds to it?
Na+
Describe the 4 phases of a nerve fibre membrane potential?
Phase 0 - RMP
Phase 1 - Depolarisation
Phase 2 - Repolarisation
Phase 3 - Overshoot
Movement of what ion causes depolarisation of a nerve cell membrane potential?
Na influx
Movement of what ion causes repolarisation of a nerve cell membrane potential?
K efflux
What is the Nernst equation?
E = 61/ValenceCharge. log(Xout/Xin)
How many ACh vesicles are released by an action potential at the NMJ?
125
Where is acetylcholinesterase found at the synaptic cleft?
Bound to the basal lamina of connective tissue within the cleft
What modality is served by A-alpha nerve fibres?
1) Motor
2) Sensory Type Ia - Proprioception
3) Sensory Type Ib - Proprioception
Are A (alpha, beta, gamma, delta) nerve fibres myelinated?
yes
What modality is served by A-beta nerve fibres?
Sensory Type II - Touch, pressure proprioception
What modality is served by A-gamma nerve fibres?
Motor to muscle spindle/golgi
What modality is served by A-delta nerve fibres?
Sensory Type III - Pain, temperature, touch
What modality is served by B nerve fibres?
Preganglionic sympathetic autonomic fibres
Are B nerve fibres myelinated?
Mostly
What modality is served by C dorsal root fibres?
Sensory type IV - Pain, temperature, touch
Are C (dorsal root and sympathetic) fibres myelinated?
No
What modality is served by C sympathetic nerve fibres?
Post-ganglionic autonomic fibres
What speed do unmyelinated C fibres conduct at?
1m/s
What happens to diameter of nerve fibre as you move from A->B–>C–>D fibres?
Diameter decreases
What ion channel inactivation results in the absolute refractory period of a nerve impulse?
Inactivation of Na channels
As diameter of nerve fibre increases (from C–>B–A) what happens to the conduction speed?
Increases
Why do myelinated fibres conduct faster than unmyelinated fibres?
Saltatory conduction via nodes of ranvier
What happens to conduction speed as a nerve fibre is cooled?
Conduction speed slows
What is the maximum velocity of nerve fibres?
Up to 120m/s (A fibres are the fastest)
What are the 4 ascending pathways?
1) Dorsal columns
2) Lateral spinothalamic tracts
3) Anterior spinothalamic tracts
4) Spinocerebellar tracts
What 2 tracts make up the dorsal columns?
Gracilis fasciculus
Cuneatus fasciculu
What modalities do the dorsal columns carry?
Touch, vibration, proprioception
What modalities do the lateral spinothalamic tracts carry?
Pain and temperature
What modalities do the anterior spinothalamic tracts carry?
Light touch and pressure
What modalities do the spinocerebellar tracts carry?
Proprioception
Which ascending pathways are ipsilateral vs contralateral?
Ipsilateral:
Dorsal columns
Contralateral:
Lateral spinothalamic,
anterior spinothalamic,
spinocerebellar
What are the 2 main groups of descending pathways?
1) Pyramidal tracts
2) Extrapyramidal tracts
Describe the 2 pyramidal tracts? Where do they decussate?
Lateral corticospinal tract - decussated in the medulla
Anterior corticospinal tract - will go onto decussate at the spinal level
What do the anterior corticospinal tract predominantly innervate?
Motor function of trunk
Where do the extrapyramidal tracts originate from?
Brainstem nuclei
What is the primary role of extrapyramidal tracts?
Postura and muscle tone
Immediately after spinal cord transection what happens to motor power and reflexes?
Flaccid paralysis and loss of limb reflexes
How long after complete spinal cord transection does it take for hyper-reflexia to develop?
2-6 weeks
What nerve fibres are involved in the pain pathway?
A (delta) and C
Where do the cell bodies of A (delta) and C dorsal root fibres reside?
Dorsal root ganglion of the spinal cord
A(delta) fibres of the pain pathway, synapse with cells in which laminae of the dorsal horn?
Laminae I and V
C fibres of the pain pathway, synapse with cells in which laminae of the dorsal horn? What is the name of this area?
Laminae II and III (Substantia gelatinosa)
Where are the cell bodies of 1st order neurones of sensory pathways located?
Dorsal root ganglion
Where do 1st order neurone of pain sensory pathways synapse?
Dorsal horn
Where do spinothalamic tracts cross?
1-2 spinal segments above entry
Where do 2nd order neurones of the pain sensory pathway via spinothalamic tracts synapse?
Ventral posterior nucleus of thalamus
Where do the 3rd order neurones of the pain sensory pathway synapse?
Sensory cortex of the brain
Where are the cell bodies of 1st order neurones of the vibration sensory pathways located?
Dorsal root ganglion
Where do the 1st order neurones of the vibration pathway synapse?
Travel via but do not synapse at dorsal horn
Ascend up dorsal columns
Synapse at nucleus cuneatus in medulla with 2nd order neurone cell body
Where do dorsal columns cross?
Do NOT cross in spinal cord ‘ipsilateral’
But 2nd order neurone crosses in the medulla
Where do 2nd order neurones of the vibration sensory pathway via dorsal columns synapse?
Ventral posterior nucleus of thalamus
Where do 3rd order neurones of the vibration sensory pathway via dorsal columns synapse?
Primary somatosensory cortex of brain
Where do corticospinal tracts start?
Midbrain
Where do lateral and anterior corticospinal tracts cross?
Lateral CST: Cross in medulla
Anterior CST: Cross at spinal level
Where do upper motor neurons synapse with lower motor neurones? (travel via corticospinal tracts)
Ventral horn
In brown-sequard syndrome what are the implications for motor function at level and below level of lesions?
Ipsilateral hemiplegia
At level: Flaccid (injury to LMN at ventral horn)
Below level: Spastic (injury to UMNs only)
In brown-sequard syndrome what are the implications for fine touch, vibration and proprioception at level and below level of lesions?
Ipsilateral loss of fine touch, vibration and proprioception (dorsal columns) at level and below level of lesion
In brown-sequard syndrome what are the implications for pain, temperature, crude touch at level and below level of lesions?
Ipsilateral pain, temperature and crude touch at the level of lesions
Contralateral pain, temp and crude touch below the level of the lesion
If the sympathetic chain is involved in Brown-Sequard syndrome (lesion must be above T1) - does horners syndrome occur ipsilaterally or contralaterally to lesion?
Ipsilateral
What is the afferent and efferent nerve supply for:
1) Intrafusal muscle
2) Extrafusal muscle
1) Intra-fusal - contains muscle spindle.
Afferent:
A(alpha - sensory type 1A) + A(beta - sensory type II).
Efferent motor: A(gamma)
Extra-fusal - doesn’t contain muscle spindle.
Only efferent motor: A(alpha)
What is the function of golgi tendon organs?
Respond to overstretch of a muscle and produce an inhibitory impulse
What is the afferent and efferent nerve supply of golgi tendons?
Afferent: A (alpha - Sensory Type 1b)
Efferent: A (gamma)
At what spinal levels is sympathetic outlow from?
T1-L2
Where do sympathetic pre-ganglionic nerves synapse?
Sympathetic chain
What nerves supply the parasympathetic outflow?
cranial nerves III, VII, IX, X and S2-S4
Which neurotransmitters do parasympathetic pre-ganglionic nerve fibres transmit?
ACh
ACh released from pre-ganglionic parasympathetic nerve fibres binds to which receptors?
Nicotinic (N)
Which neurotransmitters do parasympathetic post-ganglionic nerve fibres transmit?
ACh
ACh released from parasympathetic post-ganglionic nerve fibres bind to which receptors?
Muscarinic (M2)
Which neurotransmitter do sympathetic pre-ganglionic nerve fibres transmit?
ACh
ACh released from sympathetic pre-ganglionic nerve fibres bind to which receptors?
Nicotinic (N)
What neurotransmitter do sympathetic post-ganglionic nerve fibres which supply the heart and blood vessels transmit?
Noradrenaline
What neurotransmitter do sympathetic post-ganglionic nerve fibres which supply sweat glands transmit?
ACh
ACh from sympathetic post-ganglionic nerve fibres which supply sweat glands bind to which receptor?
Muscarinic (M2)
Where does parasympathetic innervation of the bladder come from?
S2 S3 S4 pelvic nerves
What does parasympathetic stimulation of the bladder result in?
Detrusor contraction and sphincter relaxation
Compare the fasciculus gracilis and fasciculuc cuneatus dorsal columns?
Fasciculus gracilis is more medial, sensory afferents from lower trunk and legs
Fasciculus cuneatus is more lateral, sensory afferents from upper trunk and arms
