Neuro physiology Flashcards
What type of neurone are most:
a) sensory neurones
b) motor neurones
a) unipolar/pseudounipolar, with cell bodies lying in the dorsal root ganglion
b) multipolar
Cells which myelinate axons in a) the CNS and b) the PNS
a) oligodendrocytes
b) Schwann cells
Which cells are the “macrophages” of the CNS?
Microglia
What are the main support cells in the CNS?
Astrocytes- wide range of functions including maintenance of the BBB
Epithelial cells which line the ventricles?
Ependymal cells
What is the resting transmembrane potential of a neurone?
Around -70mV
Equilibrium potential for a) K+ and b) Na+
a) -90mV- cell is permeable to potassium
b) 66mV- cell is not very permeable to sodium
What are the main cations and anions of a) the ICF and b) the ECF
a) cation- potassium, anions- phophate and proteins
b) cation- sodium, anion- chloride
Describe how an action potential is generated (3)
Opening of a sodium channel brings an area of membrane to threshold (-60mV)
Voltage-gated sodium channels are opened causing an influx and depolarisation
Voltage gated sodium channels are inactivated at 30mV, and voltage gated potassium channels are opened causing K+ efflux, repolarizing the membrane potential
What is the transmembrane potential during the relative refractory period?
Hyperpolarized- needs a greater than normal stimulus to become depolarized again
Two main factors which influence speed of AP propagation
myelination of the axon and axon diameter
What information is carried by the fastest axons?
Proprioception
Describe how an AP is transmitted at a cholinergic synapse (5)
Arrival of AP depolarizes the synaptic knob opening calcium channels and causing an influx of calcium
Calcium causes the exocytosis of neurotransmitter vesicles (ACh)
ACh diffuses across,binds to receptors and induces a depolarizing potential
ACh is removed by acetylcholinesterase inhibitors
Types of acetylcholine receptors (2)
Nicotonic-initiate a fast epsp at skeletal muscle by direct ion gating
Muscarinic-initiate a slow epsp by closing Potassium channels (in parasympathetic axons)
Neurotransmitters in the CNS:
a) main excitatory
b) main inhibitory and its mechanism
c) inhibits antagonist motoneurone in spinal reflexes
a) glutamate
b) GABA- opens chloride and potassium channels to hyperpolarize the membrane
c) glycine
Receptors which sense
a) light touch
b) pressure
c) pain
a) Meissners, Merkel
b) Pacinian, Ruffini
c) noiceptors
Types of nociceptor (4)
Mechanoreceptors
Thermal (heat/cold)
Chemical (prostaglandin/bradykinin/histamine)
Polymodal- respond to at least two of the above
A-delta fibres respond to…and mediate….
Respond to noxious mechanical and thermal stimuli- mediate first pain
C-fibres respond to….and mediate…
Respond to all noxious stimuli- mediate second pain
How can receptive field be demonstrated?
Two point discrimination test
What does a motor unit consist of?
A motor neurone and all the muscle fibres it innervates
What does a motor pool consist of?
A muscle and all the motor neurones that innervate it
How is excitation coupled to contraction?
ACh binds to nicotinic receptors
This causes release of calcium from the sacroplasmic reticulum
Calcium binds troponin, unveiling cross-bridging sites on actin
Actin-myosin cross bridges are formed and ATP powers filament sliding, shortening the muscle
What is the muscle stretch reflex also known as?
The myotatic reflex
What is the organ responsible for detecting muscle stretch?
The muscle spindle
What is reciprocal inhibition?
Relaxation of the antagonist muscle during the stretch reflex e.g. in the knee jerk reflex, the relaxation of the hamstring muscles
What name is given to the reflex which opposes excessive muscle tension rather than stretch?
Golgi reflex
Which type of motor neurones
a) keep the muscle spindle fom going “slack”
b) contact the muscle being stretched to oppose the stretch
a) gamma
b) alpha
