Physiology Flashcards
Function of dendrites Soma (perikaryon) Axon hillock and initial segment Axon Synapse
Received input from other neurones and conveys graded electrical signals passively to the soma
Integrated incoming signal that are then conducted passively to the axon hillock
site of initiation of the all or none AP
Conducts output signal as action potentials to other neurones. between soma and presynaptic terminal (anterograde direction) vice versa is retrograde direction
Point of chemical communication between neurones or other cells
What do viruses take advantage of in axons
retrograde direction is used to infect neurones - herpes, polio, rabies
Give examples of unipolar neurones
pseudo unipolar neurone
bipolar
multipolar
peripheral autonomic neurone
dorsal root ganglion
retinal bipolar neurone
LMN
Input
Integrative
Conductive
Output
dendrites
soma
axon
leading to secretion of neurotransmitter
Golgi type 1
Type 2
long axon
short axon
how does an action potential work
sodium channels open for sodium influx for the upstroke
potassium channels open up for a potassium outflow for the downstroke
normal resting membrane potential
threshold
peak
undershoot
-70mV
-60mV
+40mV
-80mV
Why does an undershoot take place in AP
Some potassium channels remain open for a small period of time
What is the problem with passive conduction
leaky membrane - passive signals do not spread far from their site of origin due to current loss across the membrane
How can passive conduction be improved
decreasing axial resistance of the axoplasm by increasing axon dm
increasing membrane resistance by adding an insulating material
How does an AP move forward
at the peak of the AP outside is negative and the inside is positive - cyclic current which generates an AP -> AP moves forward
The difference between larger dm axon and smaller dm axon
larger has low resistance so more APs can be produced and vice versa
What are the insulating materials in CNS
PNS
Oligodendrocytes - one surrounds many axons
Schwann cells - many surround one axon
What is saltatory conduction
AP jump from one nice of ranvier to the next rather than flowing constantly
Give three types of synapses in order of frequency
axodendritic - very common
axosomatic - common
axoaxonic - uncommon
Describe an excitatory synapse
glutamate activates postsynaptic cation selective inotropic glutamate receptors generating a local graded excitatory depolarising response - excitatory postsynaptic potential
describe an inhibitory synapse
GABA or glycine activates postsynaptic anion selective inotropic GABA or glycine receptors generating a local graded inhibitory hyperpolarizing - inhibitory postsynaptic potential
what are the three major amino acid neurotransmitters in the CNS
glutamate
GABA
glycine
What separates pre and post synaptic membranes
synaptic cleft
what stores NT within the presynaptic terminal
vesicles
difference between pre synaptic membrane and post
pre - active zones around which vesicles cluster
post- NT receptors
what holds the post and pre synaptic membranes together
a matrix of fibrous extracellular protein within the cleft
What are amino acids and amines released from
What are peptides released from
synaptic vesicles
secretary vesicles
Give examples of amino acids
Glutamate, GABA, glycine
gives examples of amines
Each, DA, NA, 5-HT
give examples of peptides
CCK, Enk, Neuropeptide Y, somatostatin, TRH, VIP
What ion channels fores glutamate, GABA, glycine, ACh and 5-HT activate
inotropic which mediate fast neurotransmission
what do all except glycine activate
metabrotropic G protein coupled receptors
mediate slow neurotransmission
exteroceptive sensations
proprioeceptive sensations
visceral sensations
deep sensations
from the surface of the body
concerning posture and movement
from the internal organs
from fascia, muscles and bone
the higher the amplitude of the stimulus and the longer the duration means what
more APs fired and more neurotransmitter released
list the stimulus and physiological receptor for the following touch, pressure, vibration proprioception pain itch
mechanical forces on skin. skin mechanoreceptors
mechanical forces on joins and muscles. joint and muscle mechanoreceptors
heat. thermoreceptors
strong mechanical force on skin, viscera, heat. mechanical, thermal and polydymas nociceptors
irritant. itch receptors
list the two types of low threshold units
low threshold mechanoreceptors - mediate touch, vibration, pressure
low threshold thermoreceptors - medical cold, cool, indifferent, warm, hot
list the 4 kinds of high threshold units (nociceptors)
high threshold mechanireceptors- high intensity mechanical stimuli
thermal nociceptors - extreme degrees of heat >45 or <10
chemical - substances in tissues
polymodal - respond to at least two of the above
Slowly adapting neurones
rapidly adapting
very rapidly adapting
carry on firing APs - stretch receptors
number of impulse proportional to rate of change of stimulus - some muscle spindles, hair follicle afferents
only 1 - vibration - responds to very fast movement
A alpha
A beta
A weird one
C
thick myelinated - proprioceptors of skeletal muscle
moderately myelinated - mechanoreceptors of skin
think - pain, temp
none - temp, pain, itch
what is receptive field
region that when stimulated with an adequate stimulus causes a response in that neurone
list what the skin is innervated with
free nerve endings
meissners corpuscles - esp where 2 point disc is, not in hair skin
merkels - same as meis, but only in hairy skin
hair end organs
krause end bulbs
pacinial corpuscles
Meissners merkel pacinial ruffini hair G - guard(long) hair d - down (short) c mechanoreceptor
Ab - stroking, fluttering RA Ab - pressure, texture SA Ab - vibration , VRA Ab - skin stretch - SA Ab - stroking, fluttering A weird one - light stroking C - stroking, social and erotic touch
What is grey matter divided into
dorsal and ventral horn and 10 laminae of rexed
where are these afferent terminals in the dorsal horn
nociceptors A weird one/C
LTMs Ab
Proprioceptros Aa
laminae 1-2
laminae 3-6
laminae 6-9
dorsal column first order neurone carries what
spinothalmic tract carries what
touch, pressure, vibration, conscious proprioception
pain, thermosensation, crude touch, itch, tickle
what is the dorsal column divided into and then further divided into
medial fasciculus gracilis (lumbar and sacral)
lateral fasciculus cuneatus (cervical and thoracic)
what are the capabilities of the dorsal column (5)
stereogenesis fine touch conscious proprioception vibration detection weight discrimination
where is the somatosensory cortex located
in the post central gyrus of the parietal cortex immediately posterior to the central sulcus and adjacent to the posterior parietal cortex
list the inputs for brodmans area 1
2
3a
3b
1-cutaneous mechanoreceptors, BA 3b [texture discrimination]joint afferents, golgi tendon organs, deep tissues, BA 3a and 3b [object perception]
2-joint afferents, golgi tendon organs, deep tissues, BA 3a and 3b [object perception]
3a-proprioreceptors [body position]
3b - cutaneous SA and RA, BA 3a [touch]
list the layers from the surface to white matter of the somatosensory cortex
molecular external granular external pyramidal internal granular internal pyramidal multiform -white matter -
loss of a receptive field - finger is cut off (e.g. D3)
area formerly representing D3 will respond to stimulation of the adjacent digits - their cortical representation expands into what was D3
Na channels open
Ca channels
Cl channels
K channels
flows inwards (depolarization, excitatory) flows inwards (depolarisation, excitatory) flows inwards (hyperpolariazation, inhibitory) flows outwards (hyper, inhibitory)
where does the AP depolarise?
what channels does the depolarisation open?
entry of the substance then triggers what?
where does the NT diffuse and bind?
what does the binding do?
axon terminal
Ca channels
calcium entry triggers exocytosis
synaptic cleft and receptors on the post synaptic cell
initiates a response in the post synaptic cell
what are the three ways of inactivating neurotransmitters
NT can be returned to axon terminals for reuse or transported into glial cells
enzymes inactivate them
Nt can diffuse out of the synaptic cleft
what are the two modes of action by NT on ion channels
direct by inotropic receptors
indirect by activation of metabrotropic receptors
what are the two major families of ligand gated channels and the difference between the two
GABA, glycine and Ash - pentamers
Glutamate receptors channels are tetramers
what packages are NT released in and how can this affect the outcome of neurotransmission
quanta’s - varying quanta may be released
difference between spatial summation and temporal
spatially distributed by times together
EPSPs occur in temporal sequence such that threshold is triggered
nociceptive pain
inflammatory pain
pathological pain
acute pain
prolonged
neurogenic (IBS, fibromyalgia)
what order neurones are nociceptors
first order neurones
two fires in nociceptors
A delta - mechanical/thermal, thinly myelinated, mediate first or fast pain
C fibres - unmyelinated, polymodal, mediate second or slow pain
describe the two types of A delta fibres
Type 1 - HTM - strong mechanical stimuli, activated by noxious heat >53, show sensitisation to prolonged stimuli, mediated first pain to mechanical stimuli
Type 2 - mechanical, heat 43-47, sensative to capsaicin. shows adaption. mediated first pain to heat
describe the 4 types of C fibres
C-MH - mechanical stimuli and heat 39-51, capsaicin, shows sensitisation to repeated stimuli
C-M - mechanical just
C-H - heat, sensative to capsaicin
C-MiHi-normally insensitive to both but acquires sensitivity following sensitisation by inflammatory mediators. sensitive to capsaicin and other algesic or pro algesic substances
difference between central terminal and peripheral in bidirectional nociceptors
central - not responsive to environmental stimuli. Ca dependant transmitter release. targeted by endogenous molecules that regulate activity
peripheral - responsive to environmental stimuli, site of release of molecules that influence local tissue environment. targeted by endogenous molecules that regulate sensitivity
where do nociceptive A delta and C fibres terminate
superficially in lamina I and II and also V for A delta
what cells receive input form only A beta fibres
proprioceptive
peripheral sensitisation
central
mediated by nociceptors at site of injury
causes primary hyperalgesia
major role in heat and lesser of a role in mechanical sensitivity
reflects an increase in CNS neurones activity and properties
causes secondary hyperalgesia and allodynia
plays a major role in mechanical sensitivity
physiological controlling of the gate
medical
open - C/a delta
closed - A beta fibres active
open - extent of injury, insufficient medication
closed - sufficient medication
thermosensation at the skin
is it uniform over the body
no - hot and cold spots
what kind of potential has been implicated in thermosensation
transient receptor potential (TRP)
input of LMNs
UPMs
proprioceptors and internuroens
what do LMNs compromise of
alpha MNs - innervate bulk of fibres within muscle that generate force
Gamma MNs - inneverate sensory organ within muscle known as a muscle spindle
biceps brachii and brachialis work together how
what group of muscles are these antagonists to
synergists
triceps brachii and anconeus
where do axons of the LMNs exit
spinal cord in ventral roots or via CNs
where are the nerves that innervate distal and proximal musculature
and where are the ones that innervate the axial musculature
mainly in the cervical and lumbar sacral segments of the spinal cord
all levels
what does alpha MN and all of the muscle fibres it innervates called
motor unit
what is a collection of alpha MNs that all supply a single muscle called
motor neurone pool
how is force of muscle contraction graded by alpha MNs
frequency of AP discharge of alpha MN
recruitment of additional, synergistic, motor units
LMNs innervating axial muscles are what to those innervating distal muscle
LMNs innervating flexors are what to those supplying extensors
medial
dorsal
sources of input to alpha MNs
central terminals of dorsal root ganglion cells whose axons innervate the muscle spindles
UMNs in the motor cortex and brain stem
spinal interneurones
what does muscle strength depend on
firing of LMNs
number of LMNs that innverate the muscle
co ordination of the movement
fibre size
fibre phenotype
what are small motor units innervated by
small alpha MNs and vice versa
what if the force of contraction of each motor unit dependant on
the size
where is the motor axon innervating a muscle fibre
at endplate (neuromuscular junction) which is usually at the centre of the fibre
slow fibres
fast fibres
slow - aerobic, red, slow contraction, fatigue resistant
fast - type 2A fast contraction, aerobic, fatigue resistant
type 2B - anaerobic, fast contraction but not fatigue resistant, white
the three types of motor units
slow - most numerous - lowest threshold
fatigue resistant
fast fatiguing - large and have a high threshold
what is the myotonic reflex
when a skeletal muscle is pulled it pulls back
how does a myotonic reflex occur
change in length and rate of change is registered by a sensory organ within the muscle - contributes to non conscious proprioception
what do muscle spindles consist of
fibrous capture intramural muscle fibres
sensory afferents - innervate intrafusal fibres
gamma MNs - efferents - innervate intrafusal fibres
stretch of muscle spindle - what happens next
activation of la afferent - activation alpha MN - contraction of muscle
supinator - wrist biceps triceps quadriceps ankle
C5-C6 C5-C6 C7 L3-L4 S1
what consists of intrafusal fibres
stimulation from what causes the spindle to contract
non contractile region - innervated by la
contractile - receive efferents from alpha MNs
gamma MNs
what happens during voluntary movement in intrafusal fibres
alpha and gamma MNs co activated so intrafusal fibres contract in parallel with the extra fusal fibres
where are golgi tendon organs
what do they monitor
what are they innervated by
how do they act to regulate muscle tension
junction of muscle and tendon
changes in muscle tension - in series with extrafusal fibres
lb
protect muscle from over load and regulate muscle tension to an optimal range
where do lb enter and synapse under what and where and what do they lead to
spinal cord
synapse under inhibitory interneurone which then synapse on alpha MNs of the homonymous muscle forming the basis of the reverse myotonic reflex
what is the polysynaptic pathway
in which an inhibitory internueone is interposed between the lb afferent and alpha MN
where are proprioceptive axons
what do they respond to
free nerve endings
golgi type endings
paciniform
ruffini
CT of joints
angle, directions nd velocity of movement in a joint
HT SA, nociceptive function
HT SA protective role
LT SA acceleration detectors
LT SA static position and speed of movements
where does proprioceptive information arise form
muscle spindles
golgi tendon organs
joint receptors
what do inhibitory interneurones mediate
inverse myotonic response
reciprocal inhibition between extensor and flexor muscles
