physiology Flashcards
what is the type of skin called that is not covered by hair and has skin ridges
glabrous skin
4 types of mechanoreceptors in glabrous skin
Meissner corpuscles
Merkel complexes
Ruffini organs
Pacinian corpuscles
where are Meissner corpuscles located
in the epidermis
where are Merkel complexes located
in the epidermal-dermal ridges
where are Ruffini corpuscles?
in the dermis
where are Pacinian corpuscles
in the subcutaneous layer
how do the mechanoreceptors of the skin create an AP
the distortion of the skin causes an opening of Na channels –> AP
what is the difference between slow and rapid adapting fibres?
slow - have an ongoing response - tells you about the ongoing stumulus
rapid - fire only with a change in stimulus
what do pacinian corpuscles respond to, and how big are their receptor fields
vibration - relatively large R fields compared to Meissners corpuscles
which mechanoreceptors of the skin are slow adapting and which are rapidly adapting
merkel complexes and Ruffini endings - slow
meissner and pacinian - fast
what do merkel complexes respond to
indentation of the skin
what do ruffini endings respond to
skin movement - tells you about posture
what do meissner receptors respond to
transient response to skin movement
which mechanoreceptors are superficial and which are deep
superficial - meissner and merkel
deep - ruffini and pacinian
which mechanoreceptors have a high density of receptors and which have a low density
high - merkel and meissner
low - pacinian and ruffini
when picking up an object with your hand… which receptors convey what information
meissner - encode rate of force
merkel - encode grip force
pacinian - encode vibrations
ruffini encode hand posture
what is a receptor field
a measure of how much territory a single receptor is responsive to
in which areas of the body are the receptor fields in a high density
in the hands, feet and face
what is the approx conduction velocity of sensory fibres for touch
~50m/s - fast (highly myelinated)
how many dermatomes do we have
31
why are the dermatomal patterns and the peripheral nerve patterns different at the periphery
due to the formation of plexuses
in what “column” does sensory (touch) information travel in?
the posterior/dorsal columns
what is the gross regional topography of the posterior columns in the spinal cord
lower body is more medial and upper body is more lateral
where does the decussation of somatosensory (touch) neurons occur?
in the caudal medulla (at the top of the posterior columns)
what are the 2 general areas of the posterior columns called that take information from the lower limbs and the upper limbs
lower limbs = gracile fasiculus
upper limbs = cuneate fasiculus
how many neurons are involved in the chain for the somatosensory pathway
3 (first to caudal medulla, second to thalamus and third to cortex)
in what area of the caudal medulla do somatosensory information synapse with the 2nd neuron of the sequence for upper and lower limb information
upper limb = cuneate nucleus
lower limb = gracile nucleus
somatosensory pathway: after decussating, what is the tract called in which they ascend?
the medial lemniscus
what is the change in orientation of the areas corresponding for the upper and lower limb somatosensory information through the medial lemniscus (anatomy)
at decussation - on the ventral side (lower limb info lower than upper limb info) then twist laterally to the R side with lower limb more lateral then twist again so in the cortex - the lower limb is above the upper limb info
what are the internal arcuate fibres of the somatosensory pathway?
the neurons that decussate in the caudal medulla
where does the medial lemniscus go to?
the ventral posterolateral nucleus of the thalamus
where can lesions be if you have lost touch sensation on the left side
- epsilateral side of the spinal cord or peripheral nerve
- contralateral part of the brain
where is the primary somatosensory cortex located
in the postcentral gyrus
what are the 4 subdivisions of the primary somatosensory cortex
1, 2, 3a, 3b
where does information come from for the secondary somatosensory cortex
from both the primary somatosensory cortex and the thalamus directly
which region of the primary somatosensory pathway does the majority of information go to
3b
which region of the primary somatosensory pathway goes on to give info to the posterior parietal cortex
region 2
what is neuroplasticity
changes in neural pathways and synapses which are due to changes in behavior, environment and neural processes, as well as changes resulting from bodily injury (cortex does not waste space)
where is the site for lumbar puncture
L3-L4
what is the composition of the spinal cord (in terns of white and grey matter) as you move up the spinal cord
more and more white matter (more fibres have joined the spinal cord)
what are alpha motor neurons
motor neurons that directly innervate skeletal muscle and have connections to sensory inputs
what is the topography of the motor neurons in the ventral horn
the more lateral –> the more distal and the further away from the midline
what is a motor neuron pool
all of the neurons that innervate a certain muscle
what detects stretch of the muscle
specialised sensory fibre in the muscle encapsulated in a protective sheath
what innervates the specialised sensory fibres for stretch in muscle and why?
gamma motor neurons - to allow it to adjust its position in accordance to movement of the muscle
what are the only muscles of the body without specialised sensory fibres for stretch?
intraocular muscles
what detects force of the muscle
Golgi Receptors
explain the monosynaptic reflex mechanism
1) tap on the tendon of extensor muscle –> causes stimulation of a sensory neuron
2) stimulates the motor neuron of the extensor muscle (excitatory) –> contraction
3) stimulates the inhibitory interneuron to cause relaxation of the flexor muscle
what is the monosynaptic reflex needed for
in order to maintain postural tone
explain the force (Golgi) reflex of muscle
1) Golgi receptor detects force on the extensor muscle
2) stimulates sensory neuron
3) stimulates inhibitory interneuron to cause inhibition and therefore relaxation of the extensor
4) stimulates excitatory interneuron to cause stimulation and therefore contraction of the flexor (excites the antagonistic muscle)
what is a lower motor neuron
the cholinergic motor neuron in the ventral horn that innervate skeletal muscle
what is an upper motor neuron
any neuron that effects the excitability of the LMN
what are the UMN lesion symptoms
hyper-reflexes and spastic contraction
what are the LMN lesion symptoms
muscle atrophy and no contraction and no reflexes
why do you get hyper-reflexes and spastic contraction when you have a UMN lesion
because the UMN is usually providing primarily inhibitory signals to the LMN, and therefore with a lesion - this inhibition is lost and the LMN is therefore over excited
what are the 4 types of pain
nociceptive pain - physiological
inflammatory pain - physiological
neuropathic pain - pathological
functional pain syndromes - pathological
what is the difference between nocioception and pain?
nocioception is the pathway from transduction the cortex pain is the higher order process that occurs in the cortex to tell you its painful
what types of things do nocioceptors detect
Protons
high levels of heat
noxious cold
intense mechanical force/pressure
chemical irritants
what are the fibres involved in nocioception? and what are their difference from each other
C fibres - not myelinated, go only to the most superficial layers of the dorsal horn laminae
A-delta - myelinated, go down to the deep layers of laminae of the dorsal horn (also superficial)
what is the difference between nocioceptors and pacinian corpusles in regards to transduction?
pacinian corpusles only send signals when the stimulus is still there nocioceptors continue to send signals when the stimulus is removed to signal tissue damage
what is the timeline of signals sent by C fibres and A-delta fibres with a stimulus
A-delta signal sent initially = sharp pain, precisely localised Then followed by slow, burning, throbbing pain by the C fibres
which pathway carries nocioception to the brain
anterolateral system (cross over in the spinal cord)
what are the two synapses made by fibres carrying nocioception
1) reflex pathway in the spinal cord through interneuron and motor neuron to remove body from the stimulus
2) anterolateral system to the cortex for “pain” recognition
why can inflammatory pain by spontaneous and continuous
due to the inflammatory mediators released by the tissue damage –> pain
which receptor does capsaicin activate
TRPV1 (heat receptor)
how does capsaicin cause “heat”
TRPV1 opened –> drops the threshold for activation so that the channels is always open, so that you detect the heat at normal temperatures
what can sensitisation of the fibres carrying nocioception ultimately cause
allodynia - painful response to a normally innocuous stimulus hyperalgesia - an increased response to a normally painful stimulus
what is secondary hyperalgesia
when sensitisation has occured in the level of the spinal cord –> there is an expansion of the area that is sensitised
what is maladaptive pain
pain that does not respond to drug treatment
what is neuropathic and dysfunctional pain
neuropathic pain - some kind of damage to the somatosensory system itself
dysfunctional pain - no neural leasions and no identifiable tissue or physiological pathology can be identifed
what causes peripheral neuropathic pain
when the nerve has been damaged –> causes generation of pain signals when there is no stimulation of these terminals
what is the major system in which emotions can influence pain, and how does it work?
through the PAG system - relays through the ventral medulla down to the dorsal horn of the spinal cord and vice versa
explain the “top down psychological modulation of pain”
fear through amygdala, anterior cingulate, prefrontal cortex and insula –> engages the descending pain modulation system (PAG) –> pain desensitivity
the ANS innervates everything except
CNS tissue and skeletal muscle
what is the anatomical difference of the SNS and PNS
SNS fibres originate from the thoraco-lumbar spinal cord and have ganglia close to the spinal cord/far away from organs
PNS fibres originate from the cranial and sacral spinal cord and have ganglia close to the organs/far from the spinal cord
what are the two ganglia associated with the SNS
para-vertebral
pre-vertebral
what are the NTs associated with the PNS and SNS
SNS - ACh (N) (pre) –> NA mostly with ACh (M) to glands PNS - ACh (N) (pre) –> ACh (M)
what is the difference in myelination in the autonomic nervous system
pre ganglionic fibres are lightly myelinated or unmyelinated while postganglionic are all unmyelinated
what are extra-junctional responses
where receptors for a NT can be expressed remotely from the synapse (and therefore can be affected by exogenous agonists)
what parts of the spinal cord do the pre-ganglion fibres of the SNS and PNS come from
SNS - intermediolateral cell column
PNS - intermediate grey column (sacral fibres), brainstem (cranial)
what is the purpose of having ganglia for the SNS
essential for integration and coordination of sympathetic control between organs/tissues
what are the primary purposes of the prevertebral ganglia and the paravertebral ganglia
pre - innervate non-vascular smooth muscle
para - innervation for vasoconstriction of BVs
explain the concepts of divergence and convergence of postganglionic Sympathetic fibres
divergence - one post ganglionic fibre can activate many, many neurons
convergence - lots of preganlionic fibres converge and integrate their message onto one post-ganglionic fibres
is the adrenal medulla innervated by pre or postganlgionic SNS fibres
pre
what are the 4 parasympathetic nuclei in the brainstem
Edinger Westphal
salivatory nucleus
dorsal motor nucleus of vagus
nucleus ambiguus
what is the rule breaking of the pelvic plexus
- many of the parasympathetic ganglion neurons have unusually long axons contain many sympathetic neurons = mixed ganglia
true or false - the typical autonomic reflex does not involve the brain
False (most autonomic reflexes involve the brain)
where is the central processing centre for the afferent signals of the autonomic nervous system
the nucleus of the solitary tract
what are the projections of the nucleus of the solitary tract for the autonomic system
- provide feedback to the local reflexes
- provide information to higher centres to drive more complex responses
what is the central processing centre for the efferent output of the autonomic nervous system from the brain
the hypothalamus
what is the action of the hypothalamus in the ANS
compares situations to biological set points and if there is a deviation, it initiates and coordinates an appropriate response
what is the advantage of having a large motor end plate of LMNs
they can innervate multiple muscle fibres = motor unit
What is Henneman’s size principle
As you want a bigger force you recruit larger and larger motor units (leave the largest motor units until last)
Why is the neuromuscular synapse described as “secure” and 1:1?
because as soon as a signal impulse comes down the fibres, it will contract impulse=contraction
what type of Receptor is used at a neuromuscular endplate
Nicotinic ACh receptor
What causes fibrillations of a muscle
- hypersensitivity of the R - increased ACh R expression
what are fibrillations
tiny contraction caused by activity of a single muscle cell
what are fasciculations
groups of muscle fibres contracting involuntarily
what causes fasciculations
probably due to spontaneous activation of a degenerating motor neuron
what are the two receptors involved in the monosynaptic reflex
intrafusal muscle fibre Rs - encode length
Golgi tendon organs - encode force
LMN signs
weakness/paralysis
decreased superficial reflexes
hypoactive deep reflexes
decreased tone
fasiculations and fibrilaltions
severe muscle atrophy
what are the two spinal cord pathways involved in motor control
lateral corticospinal tract
ventromedial pathways
explain the topography of the LMNs synapse to the UMN in the ventral horn
lateral = distal muscles
medial = proximal muscles
what is the major role of the lateral and medial vestibulospinal tracts
postural control - role in ongoing postural maintenance
what is the major role of the reticulospinal tract
role in maintaining muscles in the midline - role in the position of the body
what is the major role of the colliculospinal tract
role in orientation reflexes also initiates the reflex that prevents falling
UMN signs
spasticity
increased tone
hyperactive deep reflexes
clonus
babinskis sign
loss of fine voluntary movement
explain the body positioning of decerebrate and decorticate rigidity
decerebrate - both upper and lower limbs are extended
decorticate - upper limbs flexed while lower limbs are extended
what is the use of looking at whether someone has decerebrate or decorticate rigidity
tells you where abouts the disconnection is between the brain and the spinal cord
what structures in the brain influence decerebrate and decorticate ridigity? and where are they?
Red nucleus - midbrain
reticular formation - medulla and pons
why do you get decorticate rigidity
loss of inhibitory control over the red nucleus and the reticular formation
- red nucleus - causes flexion of upper limbs
- reticular formation - causes extension of both upper and lower limbs
- (flexion wins in the upper arms)
why do you get decerebrate rigidity
loss of inhibitory control over the reticular formation and no longer influenced by the midbrain
- reticular formation - causes extension of both upper and lower limbs
what does babinski’’s sign mean
that the brain is no longer in normal control of the motor neurons originating in the spinal cord that control the muscles of the foot
why is there different patterns of motor loss to the face
because some cranial nuclei receive bilateral innervation while others dont (lower facial muscles and hypoglossal nuclei)
what are the UMN and LMN signs on the face
UMN - weakness of inferior facial muscles only
LMN - weakness of both superior and inferior facial muscles
what are the two “outputs” for motor control
anticipation and movement
what spinal “tract” is presumably involved in the anticipation of a movement
the ventral corticospinal tract that does not cross (ipsilateral)
where does the locomotion pattern generator originate
in the lumbar-sacral spinal cord
what initiates the swing phase of locomotion
the sensory feedback from extensor muscles
how is the cortex involved in the pattern generator
its not its only responsible for altering it in anticipation of a change
where is the division between information traversing the gracile and cuneate fasiculi
gracile - T7 and below
cuneate - T6 and above
what is the topographical arrangment of UMN-LMN synapses to do with flexors and extensor, and proximal and distal muscles
proximal - medial
distal - lateral
flexors - dorsal
extensors - ventral
how do sensory neurons traverse from the lateral ventroposterior nucleus of the thalamus to S1
through the internal capsule
what three pathways are in the anterolateral system
spinothalamic (anterior and lateral)
spinoreticular
spinotectal
What is the Tract of Lissauer
the fibres carrying pain, temp and crude touch that enter the dorsal horn go into the tract of lissauer where they ascend or descend 1-2 spinal nerve segments where they synapse at the dorsal horn of that level
explain the second order neuron of the spinothalamic pathway
starts off from its synapse within the dorsal horn and then decussates to the contralateral side via the anterior white commissure and then travels up the anterolateral segment of the spinal cord in the lateral funiculus until it reaches the lateral ventroposterior nucleus and synapses with 3rd order neuron
explain the route of the 3rd order neuron of the spinothalamic pathway
travels from the lateral ventroposterior nucleus of the thalamus up the internal capsule to S1
what are the 2 types of LMN
alpha motor neuron
gamma motor neuron
