Peter's Physiology Flashcards
List the main components of neuronal structure
Dendrites Soma (cell body) Axon hillock + initial segment Axon Synapse
What is the main function of dendrites?
Receive neuronal inputs and convey graded signals towards the soma
The soma of the neurone is the metabolic centre. List the structures it contains
Nucleus Ribosomes Mitochondria Endoplasmic reticulum Nissl substance
What is Nissl substance?
Rough endoplasmic reticulum (ER with ribosomes)
Which part of the neurone is the site of initiation of an action potential?
Axon hillock + initial segment
What is the main function of an axon?
Conducts action potentials to other neurones or cells from soma to presynaptic terminal
Electrical info/material can travel from the soma to presynaptic terminal (anterograde) and vice versa (retrograde). True/False?
What can retrograde transport facilitate?
True
Retrograde travel can welcome viral infection (e.g. polio, herpes, rabies)
What is a synapse?
Point of chemical communication between 2 neurones
List the 4 main types of neurone, classified by shape
Unipolar
Pseudounipolar
Bipolar
Multipolar
Describe a unipolar neurone and give an example of where it may be found
No dendrite; soma only gives off axon
e.g. peripheral autonomic neurone
Describe a pseudounipolar neurone and give an example of where it may be found
Short axon bifurcates into soma and central axon
e.g. dorsal root ganglion neurone
Describe a bipolar neurone and give an example of where it may be found
Dendrite + soma + axon
e.g. retinal bipolar neurone
Describe a multipolar neurone and give an example of where it may be found
3 or more neurites attached to soma
e.g. lower motor neurone
What is the difference between Golgi type I and type II axons?
Golgi type I = long axon
Golgi type II = short axon
Which channels open in neurones when membrane polarity reaches threshold to cause the upstroke of the action potential? What direction do the ions move?
Which channels open in neurones to cause the downstroke of the action potential? What direction do the ions move?
Na channels - IN TO THE CELL
K channels - OUT OF THE CELL
Which 2 factors determine the distance over which electrical current spreads in a neurone?
Membrane resistance
Axoplasm resistance
Increasing membrane/axoplasm resistance increases the distance travelled by electrical current
Increasing membrane resistance increases the distance travelled by electrical current
(less current leaks out)
A narrow axon provides high/low resistance to conduction velocity
A narrow axon provides high resistance to conduction velocity
Which insulating material can help increase conduction velocity in neurones by reducing current leak and increasing membrane resistance?
Myelin
Which cells produce myelin for neurones?
Schwann cells in PNS
Oligodendrocytes in CNS
Many schwann cells and oligodendrocytes surround axons. True/False?
False
Many schwann cells surround one axon but usually only one oligodendrocyte surrounds many axons
Which region does the action potential “jump” from to get between neurones in myelinated axons?
Nodes of Ranvier
What are the 3 main morphological classifications of a synapse?
Axodendritic (most common) - between axon + dendrite
Axosomatic - between axon + soma
Axoaxonic (least common) - between axon + axon
Synapses can be excitatory or inhibitory. Respectfully, what are the main transmitters involved for each?
Glutamate for excitatory CNS
GABA or glycine for inhibitory CNS
The excitatory postsynaptic potential (epsp) is depolarizing and the inhibitory postsynaptic potential (ipsp) is hyperpolarizing. True/False?
True
If an epsp is too weak to cause synapse, how can excitation be achieved?
Converge multiple epsp’s to cause net excitation (synaptic summation)
List the sensory modalities that come under the somatosensory system
Fine discriminatory touch (light touch, pressure, vibration, flutter) Proprioception Temperature (thermosensation) Pain (nociception) Itch (pruriception)
What happens to the energy generated by a stimulus at a sensory nerve cell terminal?
Transduced into electrical activity which creates depolarizing (generator) potential which, if strong enough, can trigger action potential
Which receptors aid with proprioception?
Joint and muscle mechnoreceptors
Adaptation determines the firing rate of sensory neurones in response to changing stimuli. Describe the slow-adapting response and give an example
Continuous information whilst nerve being stimulated
Gives info about position, stretch, force
Stretch receptors
Adaptation determines the firing rate of sensory neurones in response to changing stimuli. Describe the rapid-adapting response and give an example
Detects change in stimulus strength and rate of movement
Muscle spindle/ hair follicle afferents
Adaptation determines the firing rate of sensory neurones in response to changing stimuli. Describe the very-rapid-adapting response and give an example
Responds only to very fast movement (vibration)
Pacinian corpuscle
Primary sensory afferent fibres are grouped I-IV or Aα, Aβ, Aδ, C. Order the groups from thickest-least thickest myelination, i.e. from fastest conduction velocity to slow
Group I, group II, group III, group IV
AKA: Aα, Aβ, Aδ, C
What is meant by the receptive field of a sensory neurone? What is it inversely related to?
The region which, when stimulated, produces a response in that neurone
Innervation density sensory acuity (size of RF is smaller with higher acuity)
Which type of sensory receptor do Aα primary sensory afferents conduct?
Proprioceptors
Which type of sensory receptor do Aβ primary sensory afferents conduct?
Mechanoreceptors of skin
Which type of sensory receptor do Aδ primary sensory afferents conduct?
Nociceptors
Thermoreceptors
Which type of sensory receptor do C primary sensory afferents conduct?
Nociceptors
Thermoreceptors
Itch receptors
What do free nerve endings in skin help sense?
Pain
Temperature
What do Meissner’s corpuscles in skin help sense? What are they subclassified as?
Touch/vibration (low frequency)
FA1 (High sensory acuity)
What do Merkel’s discs in skin help sense? What are they subclassified as?
Touch
SA1 (High sensory acuity)
What do Ruffini endings in skin help sense?
Pressure (sensitive to drag and shearing forces)
SA2 (Low sensory acuity)
What do Pacinian corpuscles in skin help sense?
Pressure (sensitive to high frequency vibration)
FA2 (Low sensory acuity)
Two point discrimination is being able to distinguish 2 stimuli separately without overlap. Which corpuscles have higher 2 point discrimination - Pacinian or Meissner’s?
Meissner’s corpuscles
less overlap of receptive fields
Meissner’s corpuscles, Ruffini endings, Merkel discs, Pacinian corpuscles and long hair are all supplied by which sensory fibre type?
Aβ
Short hair is supplied by which sensory fibre type?
Aδ
What is a dermatome?
Area of skin innervated by left and right dorsal roots of a spinal nerve
The spinal cord consists of grey and white matter. Ascending the cord, the proportion of which matter increases?
Proportion of white matter increases as you ascend the spinal cord
Nociceptors (fibre class ___) terminate at laminae _ and _ of grey matter
Nociceptors (fibre class Aδ/C) terminate at laminae I and II
Low-threshold mechanoreceptors (fibre class ___) terminate between laminae _ and _ of grey matter
Low-threshold mechanoreceptors (fibre class Aβ) terminate between laminae III and VI
Proprioceptors (fibre class ___) terminate between laminae _ and _ of grey matter
Proprioceptors (fibre class Aα) terminate between laminae VII and IX
What are the 2 main tracts of the somatic sensory pathway?
Dorsal column medial leminscal pathway
Spinothalamic tract
The dorsal column of the somatosensory pathway conveys Aα/Aβ sensory fibre info (proprioception, touch). Where does the 1’ neurone synapse in the spinal cord?
All fibres synapse in brainstem (MEDULLA) and crossover to opposite side onto 2’ neurone
The spinothalamic tract of the somatosensory pathway conveys Aδ/C sensory fibre info (pain, temperature). Where does the 1’ neurone synapse in the spinal cord?
Synapses shortly after entry into spinal cord; fibres crossover to opposite side at different points along the cord in 2’ neurone
Where do the 2’ neurones in the somatosensory tracts synapse?
VPL nucelus of thalamus
Dorsal columns of the somatosensory pathway consist of which 2 tracts?
Medial fasciculus gracilis
Lateral fasciculus cuneatus
Sensory input from which spinal regions travels in fasciculus gracilis?
From T6 and below (legs and lower trunk)
Sensory input from which spinal regions travel in fasciculus cuneatus?
From T6 and above (arms and upper trunk)
What is meant by contrast enhancement in the sensory pathway?
As information is conveyed between neurones, differences in activity between adjacent neurones are amplified
Which part of the brain receives the sensory information from the somatosensory pathway (dorsal column medial lemniscus pathway + spinothalamic tract)?
Post-central gyrus (primary somatosensory cortex) via the thalamus
What is stereognosis?
Ability to recognise an object by feeling it
Which cranial nerve provides sensory innervation to the face?
Trigeminal nerve
trigeminothalamic pathway
Outline (roughly) the sensory facial areas innervated by divisions of the trigeminal nerve
Ophthalmic: nose upwards
Maxillary: ala, cheeks, lateral forehead, upper lip
Mandibulary: lower lip, jaw, earline
Once central terminals of the trigeminal synapse, in what do they travel to the thalamus?
Trigeminal lemniscus (runs parallel to dorsal column medial lemniscus)
Where is the somatosensory cortex located?
In the post central gyrus of the parietal cortex, posterior to central sulcus
What is the name of the areas contained within the somatosensory cortex? Where are they located anatomically?
Broadmann areas (1, 2, 3a, 3b) Posterior to central sulcus (S1)
The somatosensory cortex receives input from the ventral posterolateral thalamus. What proportion of input goes to each Broadmann area?
70% to Broadmann 3a + 3b
30% to Broadmann 1 + 2
What input and information does Broadmann area 3a receive?
Proprioceptors (muscle spindles)
Info: body position
What input and information does Broadmann area 3b receive?
Cutaneous receptors, rapid-adapting receptors, BA 3a
Info: touch (texture, shape, size)
What input and information does Broadmann area 1 receive?
Cutaneous receptors, mechanoreceptors, BA 3b
Info: texture discrimination
What input and information does Broadmann area 2 receive?
Joint afferents, Golgi tendons, BA 3a, BA 3b
Info: object perception (stereognosis)
What is the name of the somatotropic map of the body surface present on the somatosensory cortex? What does it represent?
Sensory homunculus
Reveals relative sensory cortical power devoted to each body part
There are 6 cell layers (I-VI) to the somatosensory cortex - upon which layer do thalamic inputs usually terminate?
Layer IV neurones
Give an explanation for phantom pain experienced following amputation
Cortical remapping involves the area formerly represented by the amputated body part being stimulated by adjacent body part as per the somatotropic map (homunculus)
What is a motor unit’ and a ‘motor neurone pool’?
Alpha motor neurones and all of skeletal muscle fibres it innervates
Collection of alpha-motor neurones that innervate a single muscle
What is the myotatic reflex? What is its role?
When a skeletal muscle is pulled, a reverse (protective) force in the muscle spindle pulls it back
Involved in proprioception
What is contained within a muscle spindle?
Fibrous capsule
Intrafusal muscle fibre
Innervation of intrafusal fibres
- Ia sensory afferents (non-contractile region)
- Gamma-motor neurone efferents (contractile polar end)
What is the benefit of stimulating intrafusal and extrafusal fibres (alpha and gamma -motor neurones) at the same time?
Fibres run parallel to each other
Prevents the muscle spindle from going slack (1a response is maintained)
What is the function of Golgi tendon organs?
Monitor changes in muscle tension to protect from overload
Where are Golgi tendon organs located?
At the junction between tendon and muscle and run in series with extrafusal fibres
What is the ultimate reflex that occurs in golgi tendon organs?
Reverse myotatic reflex that maintains muscle tension within safe limits
Inhibitory interneurons mediate which reflexes in flexion/extension of muscle?
Reverse myotatic response
Reciprocal inhibition
The myotatic reflex and reciprocal inhibition occur to produce desired movement. Outline the process using quadriceps + hamstring muscle
Quadriceps contraction requires hamstring relaxation - Ia fibre supplying the alpha-motor neurone of the quadriceps (MONOSYNAPTIC) inhibits the alpha-motor neurone of the hamstring VIA an inhibitory interneuron (POLYSYNAPTIC)
Excitatory interneurons mediate which reflexes in flexion/extension of muscle? What is the function of this?
Flexor reflex
Crossed extensor reflex
Postural support
What is the main lateral pathway for descending spinal tracts?
Corticospinal tract
Nociceptors are primary afferent/efferent neurones comprising __ fibres and __ fibres
Nociceptors are primary afferent neurones comprising Aδ fibres and C fibres
Which fibres - Aδ or C - mediate first/fast pain and are myelinated? Do they act on all nociceptors?
Aδ fibres
No - only mechanical/ thermal
Which fibres - Aδ or C - mediate second/slow pain and are unmyelinated? Do they act on all nociceptors?
C fibres
Yes
List the 4 functional regions of a neurone
Input
Integrative
Conductile
Output
Where does a sensory neurone travel from and to?
Skin
Dorsal horn of spinal cord
Where does a motor neurone travel from and to?
Ventral horn of spinal cord
Skeletal muscle
What is a local interneurone?
Between neurones in CNS
What is a projection neurone?
From dorsal horn of spinal cord to brain structures
What is the threshold required for an action potential to fire in neurones in mV?
-60mV
What are the four main stages, in order, involved in firing of an action potential? The stimulus for an AP is depolarizing/ hyperpolarizing.
Upstroke
Overshoot
Downstroke
Undershoot
Depolarizing
What happens to the polarity of the membrane during the overshoot phase of an action potential?
Polarity reversed to inside positive
Membrane potential change, in abscence of an ___, is an active/passive process that increases/reduces with distance. Why is this?
Action potential
Passive
Reduces
Passive signals do not spread far because the nerve cell membrane is ‘leaky’
What type of channels cluster at Nodes of Ranvier during saltatory conduction?
Na voltage-gated channels
Summarise the eight stages of chemical neurotransmission
- Uptake of transmitter (T)
- Synthesis of T
- Storage of T
- Depolarisation by AP
- Ca influx through Ca voltage-gated channels
- Channel induced release of T (exocytosis)
- Receptor activation on post-synaptic membrane
- Enzyme mediated inactivation of T or reuptake of T
What are the two types of summation?
SPATIAL: Many inputs converge upon a neurone to determine it’s output
TEMPORAL: Single input may modulate output by variation in action potential frequency of that input
What are the three divisions of the somatosensory system?
EXTRACEPTIVE: registers info from surface of body by receptors
PROPRIOCEPTIVE: maintains posture and movement through muscles, tendons, jonts
ENTEROCEPTIVE: internal state of body controlled by ANS
Where would you find a 1st order sensory neurone?
PNS: From receptor to the spinal cord
PRIMARY AFFERENT
Where would you find a 2nd order sensory neurone?
CNS: From spinal cord - cell bodies in a ganglion - to thalamus
Where would you find a 3rd order sensory neurone?
CNS: From thalamus to cerebral somatosensory cortex
The amplitude at which an AP is conducted, and NT release is graded and depends on what factor?
Intensity of stimulus - whether receptor is low threshold (non-damaging stimulus) or high ihreshold nociceptors (damaging stimulus)
How is receptive field measured?
Two point discrimination - apply two sharp stimuli at different sites - being able to distinguish 2 stimuli separately without overlap = receptive field
How are low threshold mechanoreceptors classified?
Rates of adaption (FA, SA)
Size of receptive field (small = type 1, wide = type 2)
In hairy skin, what sensory receptors do hair units replace?
Meissner corpuscles
What are the functions of the DCML pathway?
Discriminatory touch Pressure Vibration Conscious proprioception/ kinaesthesia Stereognosis
What are the functions of the spinothalamic pathway?
Pain Thermosensation Crude touch Itch Tickle
How do 3rd order neurones in the DCML pathway reach the cortex?
Via posterior internal capsule
What are the two possible routes that can occur after branching of the first order neurone in the dorsal horn of the DCML pathway?
Synapse onto secondary order neurones
Pass onto ascending axon via gracile or cuneate tract and synapse in the gracile or cuneate nucleus
Where do crossed fibres of the DCML pathway travel to before reaching the thalamus?
Medial lemniscus
What is meant by lateral inhibition in the sensory pathway?
One active neurone inhibits activity of neurones adjacent to it via inhibitory interneurones
What is the role of lateral inhibition in the DCML pathway?
Sharpens stimulus perception, occurs at transferring of information at DCML synapses
How many trigeminal nerves are there in the trigeminal system? How many divisions do they have?
2 (some neurones in trigeminal sensory ganglion)
3 (V1, V2, V3)
Where do secondary order neurones synapse in the trigeminal system?
Chief sensory nucleus (general tactile stimuli) Spinal nucleus (pain, temperature)
How many layers are in the somatosensory cortex, and what is interspaced between them?
6
Vertical columns
What is the role of the posterior parietal cortex? What can result if damage occurs to it?
Receives and integrates information from S1 and other cortical areas (visual, auditory) and sub-cortical areas (thalamus)
Neurological disorders that have simple sensory skills intact
Give some examples of disorders that can result from damage to the posterior parietal cortex?
Agnosia
Astereognosia
Hemispatial neglect syndrome (typically on right parietal cortex causing inattention to the left)
What is the somatic motor system composed of? Where would you find UMNs and LMNs?
Skeletal muscles and elements of nervous system that control them
Brain
Brainstem and ventral horns
Give the two types of LMNs
Alpha MNs: bulk of muscle fibres that produce force
Gamma MNs: sensory organ in muscle spindle
Where in the spinal cord would you find a larger ventral horn area? Why?
Cervical enlargemet (C3-T1) Lumbar enlargement (L1-S3) Larger quantity of motor neurones
Outline the somatotopic distribution of the ventral horn in terms of the location of motor units
Axial muscles medial to distal muscles
Flexors dorsal to extensors
What are the 3 synaptic inputs of motor units?
Dorsal root ganglion cells
UMNs in motor cortex
Brainstem spinal interneurones
What is the role of temporal summation in muscle strength?
Combines twitches from a single AP of a motor unit to sustained contraction due to summation of further APs
List the factors that contribute to muscle strength?
Neuromuscular activation (firing rate of LMNs, number of motor units, coordination of movement) Force production by innervated muscle fibres (fibre size and phenotype (fast or slow))
How do fast (type II) and slow (type I) skeletal muscle fibres differ?
How fast myosin ATPase splits ATP to provide energy for cross bridge formation
For slow skeletal muscle fibres, ATP is derived from ________ and they are ___ in colour due to ____
Oxidative phosphorylation
Red
High myoglobin
What are the two types of fast skeletal muscle fibres?
IIa and IIb
For fast skeletal muscle fibres, ATP is derived from ________ (IIa) and ________ in IIb and they are ___ and _____ in colour, respectively
Oxidative phosphorylation
Glycolysis
Red (well vascularised)
White
List the three types of motor units, the relative tension for each and their associated skeletal muscle fibre
FAST FATIGUING - very high tension - type IIb/x
FATIGUE RESISTANT - high tension - type IIa
SLOW - low tension - fatigue resistant - type I
What is meant by the ‘Henneman size principle’
Susceptibility of alpha motor neurone to discharge APs is a function of it’s size
(smaller alpha MNs have a lower threshold e.g. slow type 1 SkM fibres are more easily activated and trained)
Alpha motor neurones are recruited from smallest to largest. True/ False?
True
This allows fine and graded development of muscle force
What type of reflex arc is the myotatic reflex? What neurotransmitter is it mediated by?
Monosynaptic
Glutamate (excitatory synaptic transmission) that activates the alpha motor neurone for contraction to occur
Intrafusal fibres can be divided into…
What do they control)
Nuclear bag fibres
(bag 1/dynamic which control rate of change)
(bag 2/ static - control absolute muscle length)
Chain fibres (control absolute muscle length)
What innervates intrafusal fibres and controls rate of change (dynamic response) AND absolute muscle length (static response)? What are they sensitive to?
Ia afferents
Stretch
What innervates intrafusal fibres and controls rate of change (static response)? What are they sensitive to?
II fibres
Stretch
If muscle length changes slowly and predictably, what fibres are active?
Static gamma motor neurones
If muscle length changes rapidly and unpredicatably, what fibres are active?
Dynamic gamma motor neurones
Group __ afferents innervate Golgi tendon organs and synapse with alpha-motor neurones via ____ of the contracted muscle.
1b
Inhibitory interneurones
Where are inhibitory interneurones located in golgi tendon organs?
Between 1b afferent and the alpha motor neurone
What is the role of free nerve endings as a joint receptor?
Nociceptive action
What is the role of golgi-type endings as a joint receptor?
Protective function
What is the role of paciniform endings as a joint receptor?
Acceleration detector
What is the role of ruffini endings as a joint receptor?
Position and speed of movements
What is reciprocal inhibition?
Relaxation of another muscle needed to allow another to contract
In the flexor reflex and crossed extensor reflex, _____ stimuli cause limb to flex/extend by contrcaction of muscles via _______ interneurones and relaxation via ______ and ________ interneurones.
Noxious
Excitatory
Excitatory and inhibitory
Describe the heirarchy of motor control, giving the function and structure for each of the 3 levels.
HIGH LEVEL - strategy - neocortical associated areas and basal ganglia structures
MIDDLE LEVEL - tactics - motor cortex and cerebellum
LOW LEVEL - execution - brainstem and spinal cord
Where do the lateral and ventral pathways originate respectively?
Cerebral cortex
Brainstem
What is the role of the lateral pathways?
Voluntary control of distal muscles, especially discrete skilled movements
What is the role of the ventromedial pathways?
Control of posture and locomotion
Which minor lateral pathway has cell bodies in the red nucleus?
Rubrospinal tract
Where do the axons of the rubrospinal tract decussate?
At ventral tegmental decussation
What does the rubrospinal tract control?
Control over limb flexor muscles, exciting LMNs of muscles
What tracts compose the venteromedial pathways of the spinal cord?
Vestibulospinal tract
Tectospinal tract
Reticulospinal tract
List and define the three types of pain
NOCICEPTIVE - immediate protective response, short-lived
INFLAMMATORY - assists in healing, persists day - weeks
PATHOLOGICAL - no physiological purpose, months - years
List the characteristics of pain affecting the skin
Well localised, pricking, stabbing, burning
List the characteristics of pain affecting muscle
Poorly localised, aching, soreness/ tenderness, cramping, stabbing, burning
List the characteristics of pain affecting viscera
Poorly localised, dullness, vagueness, fullness, nausea
Nociceptors are what type of sructural neurone?
Pseudounipolar
What type of nociceptor stimuli act on transient receptor potential receptors?
Thermal
Acid-sensing chemical receptors are activated by what ion? Give some examples
H+
ASIC, P2X, P2Y
B2 chemical receptors are activated by what chemical?
Bradykinin
Activation of polynodal nociceptors causes the influx of what ions, causing depolarisation?
Na+
Ca 2+
What channels are activated in polynodal receptors, eliciting an AP in the CNS
Na+ voltage channels
Describe the nociceptive pathway from a peripheral site to the dorsal horn of the spinal cord
Free nerve endings (C or A) activated
— Depolarisation —>
Axon of nociceptor (primary neurone) —>
Soma in DRG or trigeminal G —>
Dorsal horn of spinal cord —>
Axon of projection neurone (secondary neurone —>
STT and SRT tracts —> PAIN
Polymodal nociceptors are a subset of _ fibres
C
Peptidergic C fibres have both afferent and efferent functions. True/ False?
True
What is released from free nerve endings of peptidergic nociceptors due to tissue damage or inflammatory mediators, in neurogenic inflammation? What are their functions?
Peptides (Substance P and CGRP)
SUBSTANCE P: vasodilatation of plasma proteins, release of histamine for mast cells, sensitizes surrounding receptors
CGRP: vasodilatation
What two processes can result if noxious stimuli is applied in the long term, enhancing spinal excitablility?
HYPERALGESIA: a person develops an increased sensitivity to pain
ALLODYNIA: individuals with allodynia, however, feel pain when something is ordinarily painless.
The primary excitatory neurotransmitter in neurotransmission is ____ and it release after ____ inlux via voltage gated channels. The epsp generated is typically fast/ slow
Glutamate
Calcium
Fast
In what situation, are NMDA receptors activated in neurotransmission? How is this achieved?
Only in intense stimuli
By relieving voltage dependant block with magnesium
Where do primary afferent axons terminate in dorsal horn of spinal cord?
Laminae of Rexed
What laminae do C and A fibres in?
I, III, (V for A)
How does referred pain come about, in terms of visceral and skin afferents?
They converge upon the same spinothalamic neurones - brain interprets viscera as coming from soma
When does visceral become viscerosomatic pain?
When inflammatory exudate from a diseased organ contacts a somatic structure
What is meant by the ‘gate control theory’?
Non-painful input closes the “gates” to painful input, which prevents pain sensation from travelling to the central nervous system.
How does the gate control theory work?
Both thin (A and C) and large diameter (AB) nerve fibers carry information from the site of injury to two destinations in the dorsal horn of the spinal cord:
Activity in both thin and large diameter fibers excites transmission cells, carry signals to brain. Thin fibre activity impedes the inhibitory cells (tending to allow the transmission cell to fire) and large diameter fibres activity excites the inhibitory cells (tending to inhibit transmission cell activity).
So, the more large fibres activity relative to thin fibre activity at the inhibitory cell, the less pain is felt.
What are the two major nociceptive tracts, and what fibres do they project?
STT: Fast fibre A pain from lamina 1 and WDR neurones from lamina V
SRT: Transmits slow C fibre pain
Temperature sensitivity is not uniform across the body surface. Why is this?
Thermoreceptor neurones do not respond to both hot and cold sensitive spots
