Physiology Flashcards
what is the function of the axon hillock in a neuron
site of action potentials
what is the function of a dendrite in a neuron
receives input from other regions and conveys electrical signals to soma
what is the function of an axon
conducts output signals as action potentials to presynaptic terminals
what are the 4 types of neuron present
unipolar
bipolar
multipolar
pseudounipolar
what is resting membrane potential value
-70
conductance in myelinated/non-myelinated neurons is faster
myelinated neurons is faster
action potentials jump between what structures
nodes of ranvier
outline the steps in synaptic transmission
uptake of precursor - synthesis of transmitter - depolarisation by action potentials - Ca influx - Ca induced release of neurotransmitter - receptor activation - enzyme mediated inactivation of transmitter - reuptake of transmitter
what is the main excitatory neurotransmitter in the CNS
glutamine
what is the action of glutamine in the CNS
activated post synaptic, cation selective inotropic glutamine receptors causing graded excitatory depolarising response, Na moves in to get more positive
what is the main inhibitory neurotransmitter in the CNS
GABA or glycine
what is the action of GABA in the CNS
generates a local inhibitory, hyperpolarising response, Cl moves into the cell and it becomes more -ve
fast excitatory post synaptic potentials is due to activation of nicotinic ACh or muscarinic G protein
nicotinic ACh
muscarinic G protein produces a slow excitatory response
what are the 5 different receptors for different sensory modalities in the body
fine touch - pressure, vibration proprioception pain - nociception itch - pruriception temperature
what is proprioception
body’s awareness of its own space, controlled by posture and movement
describe a first order neuron
within PNS
primary sensory afferent
usually in dorsal root ganglia
describe a second order neuron
within CNS
located in dorsal horn of spinal cord or brainstem nuclei
describe a third order neuron
within CNS
in thalamic nuclei
outline the receptors/sensory unit that pick up each sensory modality
skin mechanoreceptors - touch and pressure
joint/muscle mechanoreceptors - proprioception
thermoreceptors - temperature
nociceptors - pain
itch receptors - itch
what is the threshold a stimulus must reach
the intensity required to excite a sensory unit
low threshold for fine touch
high threshold for pain and high temperature
primary sensory afferent fibres differ in axon diameter, extent of myelination, conduction velocity and associated sensory receptor, state which one is group I-IV
I - A alpha
II - A beta
III - A delta
IV - C
outline the order of sensory fibres from bigger diameter to smallest diameter
I, II, III, IV
describe A alpha fibres
biggest diameter
thick myelination
very fast conduction
receptor for proprioception of muscles
describe A beta fibres
moderate diameter
moderate myelination
fast conduction
receptor for mechanoreceptors of skin
describe A delta fibres
small diameter
thin myelination
moderate conduction
receptor for pain and temperature
describe C fibres
smallest diameter
no myelination
slow conduction
receptor for pain, temperature and itch
what is a receptive field
target territory from which a sensory unit can be excited
what is sensory acuity
fineness of discrimination
sensory acuity is proportional or inversely proportional to receptive field
inversely proportional
what do Meissners and Merkels endings sense
vibration
merkels disc has same distribution as meissners but also on hairy skin
what do Ruffini endings and pacinian corpuscles sense
pressure
ruffini is in joint capsules and dermis
pacinian is in fascia and dermis
in the spinal cord, what is within grey matter
cell bodies and sensory afferent terminals
in the spinal cord what is within white matter
fibre tracts
the grey matter in the spinal cord is divided into dorsal and ventral horns with how many laminae of Rexed
10
nociceptors are __ fibre class and terminate at __ laminae
A delta and C
I and II laminae
low threshold mechanoreceptors are __ fibre class and terminate at __ laminae
A beta
III and IV
proprioceptors are __ fibre class and terminate at __ laminae
A alpha
VII to IX
what are the 2 tracts that convey sensory information back to the brain
dorsal column medial lemniscus
spinothalamic tract
what tract conveys fine touch and proprioception to the brain
DCML
what tract conveys pain, itch and thermosensation to the brain
spinothalamic
outline what the 1st, 2nd and 3rd order neuron do in the DCML
1st - fibres from feeling of touch to the dorsal horn of spinal cord
2nd - decussation in the medulla to the thalamus
3rd - thalamus to the primary somatosensory cortex in post central gyrus
outline what the 1st, 2nd and 3rd order neuron do in the spinothalamic tract
1st - immediately decussate at the level of the spinal cord
2nd - travel up contralateral side to the medulla
3rd - synapse in thalamus and travel to post central gyrus
where is the primary somatosensory cortex located
post central gyrus in the parietal lobe
what is the clinical relevance of spinothalamic fibres crossing but DCML not crossing
in spinal injury Brown-Sequard can develop where both tracts are affected from opposite sides
what are the 2 areas of the DCML tract and where do they supply
fasciculus cuneatus (more laterally) - above T6 fasciculus gracilis (medially) - T6 and below
what is lateral inhibition
when one neuron is active, it inhibits the activity of its neighbours via inhibitory neurons to strengthen the stimulus perception
in the trigeminal system what does the chief sensory nucleus sense
general tactile stimuli
in the trigeminal system, what does the spinal nucleus sense
pain and temperature
describe the 2nd order neuron in the trigeminal system
once in chief or sensory nucleus, the fibres decussate and project via trigeminal lemniscus to ventroposteriomedial nucleus of the thalamus
what is Brodmanns area
where the somatosensory system is located, receive input from the VP nucleus
divided into 1, 2, 3a and 3b
outline what sensory information goes to which area of Brodmanns areas
3a - proprioceptors
3b - cutaneous slow and fast receptors
1 - cutaneous fast mechanoreceptors
2 - joint afferents
what is the function of the posterior parietal cortex
receives and integrates information from somatosensory cortex and other areas to decifer the deeper meaning of it
damage can cause bizarre neurological disorders
what are the 2 components of the somatic motor system
skeletal muscles and the elements of the nervous system that control them
what are the 2 types of motor neuron in the body
upper motor neuron and lower motor neuron
where are UMNs and LMNs found
UMNs - within the brain
LMNs - soma of the brainstem or ventral horn of the spinal cord
what is the function of UMNs and LMNs
UMNs supply input to LMNs
LMNs modulate their activity and command muscle contraction
what is the function of alpha motor neurons
LMN that innervates the bulk of fibres within a muscle
what is the function of gamma motor neurons
LMN that innervates a sensory organ within a muscle called spindle fibre
what is the function of axial muscles
control posture, muscles around the trunk
what is the function of proximal muscles
control locomotion, muscles around the pelvic girdle
what is the function of distal muscles
control fine movement of the hands
axons of the LMNs exit the spinal cord though what structures
ventral rootlets then ventral root - form a spinal nerve with sensory fibres
why is there a greater distribution of motor neurons in the cervical and lumbar enlargements of the spinal cord
more motor neurons are required to innervate the distal and proximal musculature
what is a motor unit
functional unit of motor system
an alpha MN and all the skeletal muscle fibres it innervates
what is a motor pool
an alpha motor neuron and all the fibres required to innervate a single muscle
what 2 mechanisms are the force of muscle contraction graded by
frequency of action potential discharge of alpha MN
the recruitment of additional synergistic motor units
the LMNs innervating axial muscles in the ventral horn are more medial/lateral compared to LMNs innervating distal muscles
more medial
the LMNs innervating flexors are more dorsal/ventral in the ventral horn compared to LMNs innervating extensors
dorsal
what muscle in the body has very few muscle fibres per LMN
extra-ocular muscles
very fine movements
what muscle in the body has hundreds of muscle fibres per LMN
quadriceps muscles
anti-gravity requirements
what are the 3 types of muscle fibres and describe the difference between them
slow (type I) - slow contraction and relaxation, fatigue resistant, ATP from phosphorylation, red meat due to myoglobin levels
fast (type IIa) - fast contraction and fatigue resistant, ATP from phosphorylation, red meat
fast (type IIb) - fast contraction but can fatigue, ATP from glycolysis, white meat - not found in humans
outline the order of recruitment of LMNs during an activity
recruited in order of the physical task, the slow type is always activated before the fast type etc as the exercise builds
what is the myotatic reflex
when skeletal muscle is pulled, it is pulled backwards to regulate the length of the muscle preventing damage
what organ senses the change in length of muscle during the myotatic reflex
muscle spindle
what is the function of the muscle spindle
proprioceptors of intrafusal muscle fibres that sense a change in muscle length and stretch to help the change
state 4 things that are present in spindle fibres
fibrous capsule
intrafusal muscle fibres
sensory afferents
gamma motor neuron efferents
state the deep tendon reflexes and the nerves they test
biceps C5-6 supinator C5-6 triceps C7 quads L3-4 gastrocnemius S1
where are golgi tendons located
between muscle and tendons
what is the function of golgi tendons
regulate muscle tension and protect muscles from overload
what is reciprocal inhibition
when an extensor eg quad contracts in the knee jerk the hamstring relaxes to prevent damage
where do descending spinal tracts arise from
cerebral cortex or brainstem
what are the two divisions of the descending pathway and explain the difference between them
lateral pathway - control from cerebral cortex, controls distal musculature such as skilled hand movements
ventromedial pathway - control from brainstem, function is controlling posture and locomotion
the lateral pathway is divided into which 2 tracts
corticospinal/pyramidal tract
rubrospinal tract
outline the course of the corticospinal tract
axons course to the base of the medulla, most of the fibres cross at the pyramidal decussation (lateral corticospinal tract) and the rest decussate more caudally, known as the ventral corticospinal tract
what does the corticospinal tract control
distal musculature particularly flexors
where do cell bodies of the rubrospinal tract originate
red nucleus
where do fibres decussate in the rubrospinal tract
ventral tegmental decussation
rubrospinal tract descends ventrolaterally to the corticospinal tract
what is the function of the rubrospinal tract
exerts control over limb flexor muscles
how would a lesion of the lateral pathway present
loss of fractionated movements, joints cannot move independently
slowing and impairment of accuracy of movements
what is the function of the vestibulospinal tract
hold body upright and maintain posture
controls extensor MNs
do fibres of the vestibulospinal tract decussate
no
where does the tectospinal tract begin
superior colliculus, receives input from the retina and visual cortex
where do the fibres of the tectospinal tract decussate
dorsal tegmental decussation at the midbrain
what is the function of the tectospinal tract
controls muscles of the neck, upper trunk and shoulders based on eye movements
what is reticular formation
diffuse mesh of neurons that are located along the length and core of the brainstem
where does the reticulospinal tract originate from
reticular formation
describe the difference between the pontine/medial reticulospinal tract and the medullary/lateral reticulospinal tract
pontine/medial - contracts flexors of lower limb
medullary/lateral - opposes the action of medial tract
innocuous signals are transmitted by which fibres
A beta fibres
nociceptive signals are transmitted by which fibres
C and A delta fibres
what are the three types of pain signals
nociceptive
inflammatory
pathological
what are the two types of nociceptors in the body
A gamma fibres - mechanical and thermal only, mediate first fast pain
C fibres - all types of noxious stimuli, mediate second or slow pain such as throbbing or cramping
what is the gate control theory
the gate either blocks pain signals or allows them through depending on the stronger signal that is felt
if A beta fibres firing exceeds C and A gamma fibres is nociception perceived
no as more innocuous signals are being perceived than nociceptive signals
