IC2&3: Neurophysiology Flashcards
Compare the threshold MP to the resting MP
The threshold membrane potential is more positive than the basal/resting membrane potential
Explain the processes in depolarising stimulus
AP begins when a graded potential (depolarising potential) reaching the trigger zone (-40mV) depolarises the membrane, which is generated by the opening of the ligand-gated channels by the excitatory neurotransmitter released at the NMJ
Explain depolarisation
As the cell depolarises, voltage-gated Na+ channels are activated, making the membrane much more permeable to Na+ (The Na+ is more concentrated outside of the cell).
Rapid Na+ entry into the cell through voltage-gated sodium channels depolarises the cell, peaking at 50mV
How does hypokalemia affect the body in general
hypokalemia affects the resting MP and impairs the ability to generate AP at the NMJ, leading to muscle weakness and paralysis
What is the neuromuscular joint (NMJ)?
NMJ is the synapse between the axon terminal of a motorneuron with the motor end plate
highly excitable region of muscle fibre plasma responsible for initiation of action potentials across the muscle’s surface, ultimately causing the muscle to contract
Explain how the application of intense heat (above 43 ºC) to the skin is perceived (3)
The application of heat leads to sensory transduction by nociceptors (free nerve endings)
involves the depolarisation of the receptor membrane from the receptor to the trigger zone to generate an AP
axons generally associated with nociceptors are the C- and Aδ- fibers
What are the 4 features of pain?
Quality (nature of stimulus like touch, noxious, warmth),
Intensity (perceived strength of the stimulus),
Duration and Location (perceived duration for which the stimulus was applied and the location of the stimulus)
Explain where afferent and efferent nerves originate and carry signal towards.
- Afferent nerves carry signals from the periphery to the CNS (A = into the CNS)
- Efferent nerves carry signals from the CNS to the periphery (E = exit the CNS)
After being processed by the CNS, which 2 areas can the signal go towards (and what functions do these systems serve)?
via the efferent division that may affect either:
somatic NS (for movement via skeletal muscles)
autonomic NS (homeostasis such as heart contraction)
What is a Pacinian corpuscle?
the enclosed nerve ending with layers of connective tissue are at the area of the skin such as the fingertip (receptor region)
State the types of fibres involved in touch and pain and describe their thickness.
Touch: Aβ thick myelinated
Pain: unmyelinated axons (C fibre) or with thin myelin (Aδ fibre)
What is a possible cause for congenital insensitivity to pain with anhidrosis (CIPA)
absence of NGF-dependent C or Aδ fibres from loss of function mutations in the NTRK1 gene
(NGF = nerve growth factor)
What are the postsynaptic targets for excitatory and inhibitory synapses?
dendrite for an excitatory synapse
soma for an inhibitory synapse
Explain what happens in a synapse (4)
AP depolarises the membrane (negative to positive),
triggers the opening of voltage-gated Ca channels
Ca enters the presynaptic terminal, triggering the vesicles to fuse with the membrane of the presynaptic terminal, releasing excitatory neurotransmitters
they bind to receptors on the postsynaptic terminal to transmit the signal to a dendrite and depolarise the postsynaptic membrane
What two regions can the grey and white matter be divided into?
Grey matter: dorsal horn and the ventral horn
White matter: dorsal column and ventrolateral column (or ventrolateral quadrant)
Where are efferents particularly located in?
ventral horn of the grey matter
(VHGM)
Describe the balance of ions at RMP
at RMP:
Outside: Na+, Cl- and Ca2+ are high
Inside: K+ is high
Describe the movement of K+ at RMP and equilibrium MP
At the RMP of -65mV, there is more K+ inside of the cell
Conc gradient causes K+ to move out of the cell
Electrical gradient causes K+ to move in of the cell
The pull in either direction is balanced at -97mV (equilibrium potential), which is more negative than RMP
Explain how hypokalemia results in paralysis (with relation to K+ movement)
hypokalemia (for example with the use of diuretics) leads to hyperpolarisation of the membrane, making the cell less excitable,
when the K+ outside the cell is depleted, the electrochemical gradient becomes sharper, causing K+ to diffuse out
as K+ leaves the cell, the membrane becomes hyperpolarised (more negative)
Explain what may happen if a patient takes too many multivitamins containing K+
Increased serum K+, leading to depolarisation
& Describe the events that occur at the Pacinian corpuscle (and its structure) that lead to the generation of an AP (4)
The Pacinian corpuscle has channels that are interlinked at the skin
Upon pressure, the interlinked channels unlink slightly and allow positive ions to pass through them, causing depolarisation
This initial depolarisation travels down the axon and reaches the trigger zone (at the start of the first myelinated area)
When it reaches the trigger zone, an AP is generated
Describe how touch signals are sensed through contralateral representation (4)
The first order neuron (afferent) receives the signal,
transmitting it to the second order neuron in the medulla (that crosses over to the other side)
this is sent to a third order neuron in the thalamus and
sent to the somatosensoty cortex for sensation
How does the pain signal sensation differ from touch signal sensation?
Touch: 2nd order neuron in medulla
Pain: 2nd order neuron in dorsal horn of spinal cord
Where is the primary somatosensory cortex located
Post central gyrus
(neurons are arranged in a somatosensory homunculus)
What are the 4 principles underlying sensory processing?
- The relay uses AP as a signal to relay properties of the stimulus
- The signal travels along topographic lines
- The signal travels along a labelled line (between receptor and its primary afferent)
- The signal along the relay line encodes for properties of the stimuli such as intensity
Describe the pain pathophysiology:
where does the signal go after the free nerve endings receive the painful stimulus? (2)
Free nerve endings (painful stimulus) lead to a C fibre (first order neuron) which then synapses with the spinothalamic neuron (second order neuron)
In the touch pathophysiology:
Which fibre takes which path to relay signal to the brain
The touch fibres lead to a Aβ fibre (first order neuron) and leads to the spinal cord where it turns upwards along the doral column pathway
What are the two places that the Aβ fibre is in contact with
Spinal cord
inhibitory neuron
How does inhibition work? (3)
The inhibitory transmitter GABA acts on the spinothalamic tract neurons,
this opens up Cl- channels, causing Cl- to move from the outside to the inside of the cell
and hyperpolarise the spinothalamic tract neuron (becomes less excited)
How does pain modulation work?
(2 locations, 1 interneuron)
Context suppresses pain and excites neurons in the prefrontal cortex which will excite neurons in the midbrain (periaqueductal grey, PAG) which then inhibits the pain pathway
The E interneuron (enkephalin) within the spinal cord is the one that ultimately inhibits the spinothalamic neuron
What are the 3 types of generated movement?
- Reflexes (involuntary) (eg. removing hand in response to hot surface)
- Rhythmic motor patterns (require voluntary initiation and termination) (eg. walking)
- Voluntary (goal-directed) (of own desire)
Which part of the brain controls voluntary movement?
Cortex
Which part of the brain controls rhythmic motor patterns?
Brain stem
Which two areas in the brain are important for voluntary behiaviour
Primary motor cortex
Premotor area
Explain the function of the cerebellum (involves 2 other brain parts)
It indirectly affects movement by adjusting the output of the efferents via the cortex and the brain stem
State the function of the basal ganglia
initiation of movement and selection of appropriate motor programme
What are some effects of basal ganglia damage? (2 classes)
movement disorders (tremors at rest, rapid flicking movements, violent flailing/ballism, slow writhing or twisting, bradykinesia)
posture disorders (rigidity)
What are the 4 ingredients for voluntary movement?
- knowledge where the body is in space,
- where it intends to go
- selection of a plan to get it there, plan held in memory until the appropriate time
- instruction to implement the plan
Which part of the brain controls “knowledge where the body is in space”
posterior parietal cortex
Which part of the brain controls “Where it intends to go and what to do”
anterior frontal lobes
Which part of the brain controls “Selection of a plan and holding it until execution”
premotor cortical areas
Which part of the brain controls “implementation”
primary motor complex
