Peters 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
Electrical info/material can travel from the soma to presynaptic terminal (anterograde) and vice versa (retrograde). True/False?
True
Retrograde travel can welcome infection (e.g. polio)
What is a synapse?
Point of chemical communication between 2 neurones
List the 4 main types of neurone
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 (-60mV) to cause the upstroke of the action potential?
Na channels
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?
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)
Axosomatic
Axoaxonic (least common)
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
Touch Proprioception Temperature Pain Itch
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
Continuous information whilst nerve being stimulated
Gives info about position, stretch, force
Adaptation determines the firing rate of sensory neurones in response to changing stimuli. Describe the rapid-adapting response
Detects change in stimulus strength and rate of movement
Adaptation determines the firing rate of sensory neurones in response to changing stimuli. Describe the very-rapid-adapting response
Responds only to very fast movement (vibration)
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?
The region which, when stimulated, produces a response in that neurone
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?
Touch/vibration
What do Merkel’s discs in skin help sense?
Touch
What do Ruffini endings in skin help sense?
Pressure
What do Pacinian corpuscles in skin help sense?
Pressure
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 _
Nociceptors (fibre class Aδ/C) terminate at laminae I and II
Low-threshold mechanoreceptors (fibre class ___) terminate between laminae _ and _
Low-threshold mechanoreceptors (fibre class Aβ) terminate between laminae III and VI
Proprioceptors (fibre class ___) terminate between laminae _ and _
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 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?
Thalamus
Dorsal columns of the somatosensory pathway consist of which 2 tracts?
Fasciculus gracilis
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 median 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?
Broadmann areas (1, 2, 3a, 3b)
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 neurone pool’?
Collection of alpha-motor neurones that innervate a single muscle
What is the myotatic reflex?
When a skeletal muscle is pulled, a reverse (protective) force in the muscle spindle pulls it back
What is contained within a muscle spindle?
Intrafusal muscle fibre
Ia sensory afferents
Gamma-motor neurone efferents
What is the benefit of stimulating intrafusal and extrafusal fibres (alpha and gamma -motor neurones) at the same time?
Prevents the muscle spindle from going slack
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
Group Ib afferents innervate Golgi tendon organs and synapse with alpha-motor neurones via inhibitory interneurons of the contracted muscle. What is the ultimate reflex that occurs?
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 inhibits the alpha-motor neurone of the hamstring VIA an inhibitory interneuron
Excitatory interneurons mediate which reflexes in flexion/extension of muscle?
Stretch reflex
Crossed extensor reflex
What is the main lateral pathway for descending spinal tracts?
Corticospinal tract
Nociceptors are primary afferent 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?
Aδ fibres
Which fibres - Aδ or C - mediate second/slow pain?
C fibres
