Physiology Flashcards
What are the four components into which a cell is divided?
Dendrite
Soma
Axon
Synapse
What does the soma of a nerve cell contain?
Mitochondria, ribosomes, ER, nucleus
What does the soma of a nerve cell do?
Integrates all the signals until an AP is generated
What does an axon do?
Conducts output signals to presynaptic terminals
What is a synapse?
Point of chemical communication between neurones
What are the four types of neuron?
Unipolar
Pseudounipolar
Bipolar
Multipolar
Which type of neuron is a peripheral autonomic neuron?
Unipolar
Which type of neuron is a dorsal root ganglion neuron?
Psuedounipolar
Which type of neuron is a retinal neuron?
Bipolar
Which type of neuron is a lower motor neuron?
Multipolar
Which Golgi type of neurons have short /no axon?
Golgi type II
Why does a membrane potential “leak”?
Ion channels along the axon which lets current out
What is lambda in terms of the nervous system?
The distance which a change in membrane potential can travel before diminishing to 37% of the original
What equation defines lambda
Rm/Ri ^0.5
How can Ri be decreased and what effect does this have on lambda?
Increases lambda
Increase axon diameter (not viable in vertebrae)
How can Rm be increased and what effect does this have on lambda?
Increases lambda
Add myelin
How do Schwann cells myelinate cells?
Send out processes to wrap around the axon several times, many surround one axon
How do oligodendrocytes myelinate cells?
Each oligodendrocyte surrounds many axons
What is a chemical synapse, structurally?
Matric of fibrous extracellular proteins within the cleft that holds synaptic membranes together
What are the three classifications of presynaptic terminal, based on structure?
Axodendritic
Axosomatic
Axoaxonic
What is an axodendritic synapse?
Axon synapses with a dendrite (most common)
What is an axosomatic synapse?
Axon synapses with the soma
What is an axoaxonic synapse?
Axon synapses with another axon
What are the classifications of synapse based on function?
Excitatory
Inhibitory
How does an excitatory synapse work?
Uses glutamate
When released, generates a brief excitatory post-synaptic potential (EPSP)
How does an inhibitory synapse work?
Uses GABA and glycine (GABA higher in brain)
Released these to generate a hyperpolarising response or inhibitory post-synaptic potential (IPSP)
What are the two types of synaptic integration?
Spatial summation
Temporal Summation
Describe spatial summation
Several inputs converge on one neuron to determine its output (whichever type there is more of)
Describe temporal summation
Single input of the same type, if enough occur in a short enough time frame it changes the membrane potential
What are the 5 sensations (not including special sensory) ?
Fine touch Proprioception Thermosensation Nociception Pruriception
Where does the “exteroceptive” division pick up sensation from?
Cutaneous sense, from surface of body
What does the proprioceptive division sense?
Posture and movement through sensors in muscles, tendons and joints
Where does the enteroceptive division pick up sensation from?
Internal body
Where are the first order neurons in the somatosensory pathway found?
Dorsal root ganglia
or
Cranial ganglia
Where are the 2nd order neurons in the somatosensory pathway found?
Dorsal horn of spinal cord
or
Brainstem nuclei
Where are the 3rd of neurones in the somatosensory cortex found?
Thalamic nuclei
How is the signal passed from the first order neuron to the second order neuron in the somatosensory pathway
Stimulus opens cation selective ion channels in peripheral terminal or primary sensory afferent, creating depolarising receptor potential
Triggers an AP, frequency is increased with increased membrane potential
APs arrive at central terminal causing graded released of neurotransmitter on second order neurons
What is the sensory unit for touch, pressure and vibration?
Skin mechanoreceptors
What is the sensory unit for proprioception?
Joint and muscle mechanoreceptors
What is the sensory unit for temperature?
Thermoreceptors
What is the sensory unit for pain?
Mechanical, thermal and polymodal nociceptors
What is the sensory unit for itch?
Itch receptors
Which receptors mediate fine discriminatory touch?
Low threshold mechanoreceptors
Which receptors respond to cold, cool, warm and hot but not dangerous stimuli?
Low threshold thermoceptors
Which receptors respond to high pressure mechanical stimuli?
High threshold mechanoreceptors
Which temperatures do thermal nociceptors respond to?
> 45 or
What do chemical nociceptors respond to?
Substance in tissue
Which type of receptors constantly fire signals?
Stretch receptors
Which type of receptor (based on adaption rate) gives continuous information to the CNS?
Slow adaption
What kind of information do fast adaption fibres give to CNS?
Acute change
What do very fast adapting fibres respond to?
Rapid movement such as vibration
Describe the myelination on A-alpha axons
Thick
Describe the myelination on A-beta axons
Moderate
Describe the myelination on A-delta axons
Thin
Describe the myelination on C fibres
None
What is the approx. conduction velocity of A-alpha axons?
80-120m/s
What is the approx. conduction velocity of A-beta axons?
35-75m/s
What is the approx. conduction velocity of A-delta axons?
5-30m/s
What is the approx. conduction velocity of C axons?
0.5-2m/s
What is the sensory receptor of A-alpha axons?
Proprioceptors of muscle
What is the sensory receptor of A-beta axons?
Mechanoreceptors of skin
What is the sensory receptor of A-delta axons?
Pain and temp
What is the sensory receptor of C axons?
Temperature, pain, itch
What is the receptive field?
Territory from which a sensory unit can be excited defined by a “two-point” threshold
Give an example of where receptive field is small on the body
Fingertips
Describe the relationship between receptive field and acuity
Inversely proportional
What are the four types of low threshold mechanoreceptors?
Fast adapting 1 (small RF)
Fast adapting 2 (wide RF)
Slow adapting 1
Slow adapting 2
What is a slow adapting 1 unit otherwise known as?
Merkel cell - neurite complex
Where are slow adapting 1 units found?
Basal epithelium on hands and soles of feet mostly
Describe the sensory acuity of slow adapting 1 units?
High
What are fast adapting 1 units otherwise known as?
Meissner corpuscles
What do fast-adapting 1 units sense?
Low frequency vibration, stroking and flutter
Describe the acuity of fast-adapting 1 units?
High
What are slow adapting 2 units otherwise known as?
Ruffini endings
Where are slow adapting 2 units found?
Dermis and joint capsules
Describe the core of slow adapting 2 units?
Collagenous so axons can branch into it
Where are fast adapting 1 units found?
Close to basal epithelium
What is the role of slow adapting 1 units?
Signal sustained pressure, sense texture
What are fast-adapting 2 unit otherwise known as?
Pacinian corpuscles
Where are fast-adapting 2 units found?
Close to periosteum
What do fast adapting 2 units sense?
High frequency vibration
Describe the acuity of fast-adapting 2 units
Low
Which receptors does hairy skin contain?
FA2, SA1, SA2
Which two types of fibre do hair units have?
Circumferential fibres
Palisade fibres
What does grey matter make up in the spinal cord?
Dorsal and ventral horns and laminae of Rexed
In which laminae of Rexed do nociceptors terminate?
Laminae I and II
In which laminae of Rexed do low threshold mechanoreceptors terminate?
Laminae III, IV, V, VI
In which laminae of Rexed do proprioceptors terminate?
Laminae VII, VIII, IX
Describe who fine touch, pressure, vibration and proprioception get to brain via dorsal column medial lemniscal pathway
Enters dorsal horn and synapses with 2nd order neurons
Ascends cord on same side
Synapses in either dorsal column gracile nucleus or cuneate nucleus
Desiccates from 2nd order neuron
Travels to medial lemniscus and ascends to ventral posterior lateral nucleus of thalamus
Synapses in 3rd order neurons
Signal travels to somatosensory cortex via posterior internal capsule
What is stereognosis?
Ability to recognise an object through touch
Describe who crude touch, itch, tickle gets to brain via spinal cord
Enters spinal cord, immediately crosses
Ascends spinal cord to synapse in thalamus
Where does input from T6 and below run in the dorsal column?
Fasciculus gracilis
Where does input from T5 and above run in the dorsal column?
Fasciculus cuneatus
Which is more lateral in the dorsal column, fasciculus gracillis or cuneatus?
Fasciculus cuneatus
What is lateral inhibition?
When one neuron is active, it inhibits the activity of the adjacent neurons via inhibitory interneurons
How is somatic information from the anterior head mediated?
By two trigeminothalamic pathways
Describe the trigeminothalamic pathways
Impulses originate at terminal of trigeminal nerves
Synapse on second order neurons in spinal nucleus (pain, temp) or chief sensory nucleus
Projected to the ventroposteriomedial nucleus of the thalamus via trigeminal lemniscus
Sent to cortex via thalamocortical neurons
Where is the somatosensory cortex located?
Post central gyrus of the parietal cortex posterior to central sulcus and adjacent to posterior parietal cortex
What is the central sulcus split into?
Brodmann areas 1, 2, 3a, 3b
Where does Brodmann area 3a get information from?
Muscle spindles
What type of information does Brodmann area 3a receive?
Proprioceptive information
Where does Brodmann area 3b get it’s information from?
Cutaneous receptors: Merkel cells and Meissner’s corpuscles and area 3a
What type of information does Brodmann area 3b receive?
Touch
Where does Brodmann area 1 get information from?
Cutaneous mechanoreceptors and area 3b
What type of information does Brodmann area 1 receive?
Texture discrimination
Where does Brodmann area 2 get information from?
Joint afferent, Golgi tendon organs, areas 3a and 3b
What type of information does Brodmann area 2 receive?
Object perception
What would be the affect of a lesion in Brodmann area 3b?
Deficits in texture, shape and dsicrimination
What would be the affect of a lesion in Brodmann area 1?
Loss of texture discrimination
What would be the affect of a lesion in Brodmann area 2?
Impaired grasping and size and shape discrimination
How many cell layers does the somatosensory cortex have?
6
Where does most of in the information in the somatosensory cortex terminate?
Layer IV
What is the role of the posterior parietal cortex?
Receive and integrate information from cortical and sub-cortical areas
Interprets all of the sensory information to give a full picture of the environment
What can damage to the posterior parietal cortex cause?
Agnosia, astereognosis, hemi-spatial neglect
Which drugs are examples of Na channel antagonists?
Local anaesthetics
How are transmitters released at cell synapses?
AP depolarises axon terminal
Causes opening of voltage gated Ca2+ channels
Ca2+ enters cell and triggers exocytosis of synaptic vesicle content
Diffuses across synaptic cleft and binds with post synaptic cell
What happens to neurotransmitters after response is initiated in post-synaptic cell?
Either:
Returned to axon terminal or transported into glial cells
Inactivated by enzymes
Diffuse out of synaptic cleft
What is the major inhibitory neurotransmitter?
GABA
On which receptors does GABA act?
Ionotropic (to allow Cl into cell)
Which neurotransmitter do interneurons typically use?
GABA
What neurotransmitters do projection neurons typically use?
Glutamate (excitatory)
What is the resting membrane potential normally?
-70mV
What effect do K channel agonist have?
Inhibitory
As opens K channel, causes outflow, makes cell more negative
What effect do K channel antagonists have?
Excitatory
As closes K channel, causes retention, makes cell more positive
What type of receptor is responsible for direct gating?
Ionotropic receptor
What type of receptor is responsible for indirect gating?
GPCR
What do GPCR do with regards to gating?
Modulate neurotransmitter release
Regulate the size of the post-synaptic potential
Modulate channels in soma
What is the structure of a glutamate channel?
Tetrameric
What is the structure of GABA, glycine and nicotinic ACh receptors?
Pentameric
What are the two GABA receptors in the CNS?
GABA(A) - activates Cl- channels
GABA(B) - activates K channels
Name a drug which can enhance the action of GABA?
Benzodiazepines, baclofen
What is “quanta”?
Release of neurotransmitter from a single cell
What is quanta released by?
Purkinje cell - Olivary neuron synapses
Inhibitory basket cell
Where are upper motor neurons located?
In the motor cortex
Where are lower motor neurons located?
In spinal cord or brainstem
Where are the two enlargements of motor neurons in the spinal cord?
Cervical C3-T1
Lumbar L1-S3
What is a motor unit?
Single alpha-neuron and all of the skeletal muscle is innervates
What are smaller motor units for?
Fine movements, eg fingers and EO eye muscles
What is each muscle fibre innervated by?
Single motor axon at the endplate/NMJ, usually at the centre of the fibre
What is the motor neuron pool?
Collection of alpha-motor neurons which innervate a single muscle
How is muscle contraction graded?
Through the recruitment of additional synergistic motor units
or
Chance in frequency of AP discharge from alpha motor neuron
Which lower motor neurons are more dorsal, flexor or extensor?
Flexor
Where do lower motor neurones receive input from?
Central terminal of dorsal root ganglion
UMNs in motor cortex
Spinal interneurons
What does muscle strength depend on?
Firing rates of LMNs, number of LMNs and co-ordination of movement
Fibre size and phenotype
Which alpha motor neurons are larger, for fast or slow type muscles?
Fast type
Describe the myotatic reflex
Muscle is stretched
Activates Ia afferent stimulating excitatory post-synaptic transmission
Activates alpha motor neuron
Contraction of muscle
What are intrafusal fibres?
Non-contractile equatorial regions in muscle innervated by Ia (sensory afferent)
What supply intrafusal fibres?
Gama motor neurons
How are intrafusal fibres subdivided?
Bag 1/dynamic
Bag 2/static
Describe a dynamic intrafusal fibre
Sensitive to the rate of change of muscle length, innervated by gamma motor neurons
Describe a static intrafusal fibre
Sensitive to current length of muscle, innervated by static gamma motor neurons
Where do Ia afferent fibres come from?
Annulospinal nerve
Which is the slower afferent fibre, Ia or II?
II
What do type II afferent fibres form on intrafusal fibres?
Flowerspray endings
Which type of intrafusal fibre do type II afferent fibres NOT innervate?
Bag 1
What do static motor neurons sense?
Slow muscle length changes ie sitting -> standing
What do dynamic motor neurons sense?
Fast muscle length changes like shaking hands
Where are Golgi tendon organs found?
Between collage fibres between tendon and bone
What happens when tension is applied to Golgi tendon organs?
Mechanoreceptors are activated
What innervated Golgi tendon organs?
Groub Ib fibres
What is the function of the Golgi tendon organs?
To protect muscle from overload
Where are proprioceptive axons found?
In connective tissue of joints
What do proprioceptive axons respond to?
Changes in angle, direction, velocity of movement
What do horizontal cells in the eye receive input from?
Photoreceptors
Where do horizontal cells in the eye project to?
Other photoreceptors and bipolar cells
What do amacrine cells in the eye receive input from?
Bipolar cells
Where do amacrine cells in the eye project to?
Ganglion cells, bipolar cells and other amacrine cells
What does “the Dark Current” refer to?
When light stimulus hits the retina, membrane potential is inhibited and there is an influx of sodium
What does light convert 11-cis-retinal to?
All-trans-retinal
What does all-trans-retinal activate?
Rhodopsin
What does rhodopsin activate?
G proteins which activate phosphodiesterase
If there is more light is there more or less cGMP?
Less because phosphodiesterase hydrolyses it
Where are cones located?
In the fovea
What are cones for?
Fine and colour vision, seeing in daylight
Where are rods found?
Along the whole retina excluding fovea
What are rods for?
Seeing in dim light (ie night)
Why is parallel processing important?
Compared in the cortex to perceive depth
If there is a lesion on the optic tract what is the visual defect?
Monocular blindness
If there is a lesion at the optic chiasm what is the visual defect?
Bitemporal hemianopia
If there is a lesion at the striate cortex what is the visual defect?
Contralateral hemianopia with foveal sparing
If there is a lesion at the optic radiation what is the visual defect?
Quadrantanopia
Where do spinal interneurons receive input from?
Primary sensory axons
Descending axons from the brain
Collaterals of LMNs
Other interneurons
What is reciprocal inhibition?
When muscles which antagonise the desired movement are inhibited to allow agonist movement to be unopposed
What can inhibit Renshaw cells?
Strychnine
What are Renshaw cells?
Inhibitory collateral cells
What is pain?
An unpleasant, sensory and emotional experience a/w actual tissue damage or described in such terms
What are the 3 classifications of pain?
Nociceptive, inflammatory and pathological
Describe the characteristic of pain which originates in the skin
Well localised, pricking, stabbing, burning
Describe the characteristic of pain which originates in the muscle
Poorly localised, aching, tender, cramping, stabbing
Describe the characteristic of pain which originates in the viscera
Very poorly localised, dull, vague, nauseating
What are nociceptors?
Peripheral primary sensory afferent neurons normally activated by intense stimuli
What happens when nociceptors relay pain to second order neurons?
AP causes voltage activated Ca2+ channels to open
Ca2+ influx causes glutamate release which activates post-synaptic AMPA and NMDA receptors
Influx of Na and Ca into postsynaptic cell
EPSP occurs opening voltage activated Na+ channels
What information do A-delta fibres receive?
Mechanical and thermal
Stabbing, pricking, lancinating sensation
What temperatures do type I and II A-delta fibres activate at?
Type I - very hot, 53
Type II - hot, 43
What information do C-fibres receive?
All noxious stimuli
What is hyperalgesia?
Increased response/perception of a painful stimulus
What is allodynia?
Perception of pain with a non-painful stimulus
Which receptors perceive noxious heat?
TRPA1, TRPC3, TRPV1
What pathology can affect TRPV1 receptors?
Activated by inflammatory conditions and become sensitised to normal body temperature
How do afferent C-fibres carry information to the CNS?
Via glutamate release and peptides in the dorsal horn
What effect does long term stimulation have on C-fibres?
Increases overall excitability
What do efferent C-fibres do when stimulated?
Release pro-inflammatory mediators from peripheral terminal
Where do C-fibres synapse in the spinal cord?
Laminae of Rexed I and outer part of II
What do C-fibres in laminae of Rexed I do?
Excite nociceptive cells
What do C-fibres in laminae of Rexed II do?
Synapse on interneurons and travel to V to synapse at the wide dynamic range neuron
When does viscerosomatic pain occur?
When internal organs ruptures and exudate comes into contact with a body wall structure
