Theme 2 Flashcards
Properties of Nerve cells
Name the different cellular compartments in a neurone
Dendrites: Receive and process information and bring it to the soma.
Axon: Conducts signals to other neurones via synapses at the axon terminal.
Soma: Cell body
Define the following terms: 1. Ganglion 2. Nerve 3. Nerve tract/pathway
- Ganglion: group of neurone cell bodies in the peripheral nervous system (PNS).
- Nerve: bundle of axons in the PNS.
- Nerve tract or pathway: bundle of axons in the CNS.
What is a multipolar neurone? - examples?
Neurones that have multiple dendrites emanating from it’s cell body allowing it to receive impulses from multiple neurones Motorneurones & interneurones
What is the function of an interneurone?
Communicates between afferent and efferent neurones in the CNS
How is a bipolar sensory neurone different to most neurones?
Has two axons, with a cell body in the middle. One axon attaches to the sensory organ, the other communicates with the CNS.
How does myelination of nerve cells differ in the PNS and CNS?
CNS: Oligodendrocytes –> provide myelin to several axons PNS: Schwann cells –> provide myelin only to one axon
What proportion of nerve cells are stained by the ‘Golgi Silver Impregnation method’?
1%
What are glial cells?
nerve cells that do not carry nerve impulses
Where does an axon emerge from a cell body?
Axon Hillock
When observed under a microscope, how can you tell the difference between an axon and a dendrite?
Dendrites:
- Spines covering
- Taper the further they travel from the cell body
Axon: axon will not taper and features no spines.
Why are spines useful for dendrites?
Spines increases the SA on dendrites to send somatic information
Why is the diameter of an axon constant?
Conduction velocity of impulses of axons depend on the diameter
What are the different Types of connections between axon terminals and postsynaptic cells?
- AXOSOMATIC
- AXOAXONIC
- AXODENDRITIC
What are the three axonal transport mechanisms?
- Fast anterograde
- Slow anterograde
- Fast retrograde
Define the terms Anterograde & Retrograde
Anterograde: Cell body to terminal
Retrograde: terminal to cell body
What type of axonal transport is likely to be used for the transport of organelles or neurotransmitters towards the synaptic terminal?
Fast anterograde
Which protein is involved in this type of transport along the microtubule?
Kinesin
What type of axonal transport is likely to be used to transport surplus membrane particles and metabolites to the cell body?
Fast anterograde
How does Slow anterograde axonal transport work?
Moves soluble substances along the axon at two different rates
How are electrical signals generated?
All electrical signals are generated by an influx of ions – a change in potential between the two sides of the membrance
What is the Nernst equation used to calculate?
Electrical potential across a membrane, when that membrane is permeable to only one ion. Reflects the electrochemical gradient acting on a given ion
How does the Goldman equation expand on the Nernst equation?
takes into account different ion species to work out an overall membrane potential
In terms of relative proportion, which ion leak channels are the most frequent in the membrane of a neurone? Na+, K+, or Cl-
K+
What type of signal propagation do nerve cells use? How does this allow conduction?
Active propagation
Non-decrements: The signal (action potential) does not change with distance
What are the advantageous properties of electrical responses?
Graded bigger stimulus = bigger response
Summation multiple stimuli = summed response (2 stimuli in short sequence, will add up)
What gates do Na ions have?
internal (h) (inactivation) and external (m) (activation)
What gates do K ions have?
n
What are the two type of synapses?
Electrical: no chemical transduction involved (bidirectional) Chemical (unidirectional)
What type of synapse is found in Cardiac cells?
Electrical synapses
What is a gap junction? What protein forms the structure of a gap junction?
Protein pores that bridge the gap between two cells Connexin
What is the advantage of electrical synapses?
NO synaptic delay
What are the two types of neurotransmitter receptors?
Ionotrophic: directly linked to an ion channel which opens when neurotransmitter attaches
Metabotrophic: activates a G-protein which then activates an ion channel
Step by step of a neurotransmitter release
- AP in presynaptic neurone
- Ca ions into synaptic bulb
- Release of neurotransmitter by exocytosis
- Binding of neurotransmitter to postsynaptic
- Opening of ion channels on post synaptic
Which protein cuts a vesicle from the membrane?
Dynamin
Which protein coats vesicles involved in the exocytosis of neurotransmitter into the synaptic cleft?
Clathrin
What is an EPSP?
Excitatory Post-Synaptic Potential
What are the conduction properties of an AP and an EPSP?
AP = Non-decremental
EPSP: decremental
What is temporal summation?
Adding together of EPSP’s by firing at the same presynaptic terminal at a high frequency to generate an action potential.
What is Spatial Summation?
Adding together of EPSP’s generated by firing of two or more presynaptic neurones simultaneously to generate an action potential in the post-synaptic neurone
What is an IPSP? When may IPSP be required?
Inhibitory Post-synaptic Potential Inhibition of motor neurones for antagonistic muscles
What are the different order neurones?
First order neurone carry signals from the periphery to the spinal cord
Second order neurone carry signals from the spinal cord to the thalamus
Third order neurone carry signals from the thalamus to the primary sensory cortex
Define Afferent & Efferent Nerves
Afferent: Towards CNS
Efferent: Away from CNS
S - ensory
A - fferent
M - ptor
E - fferent
What is the nerve classification of Motor and sensory nerves? Where are their cell bodies found? Are they always Myelinated?
Motor = Multipolar - ventral root ganglion –> Myelinated
Sensory = Unipolar - Dorsal root ganglion –> Myelinated, unmyelinated
In terms of types of nerve cells, how do the Roman numeral and letter system of classifying nerve fibres differ?
Numerals - Sensory neurones
Letters - Sensory and motor neurones
As you go down the Numerals table, what fibre property changes?
↓Diameter
↓ Conduction
Which RN fibre is responsible for:
- Slow pain
- Fast Pain
- III
- IV
What is crude touch?
non discriminate nature of touch – something is touching us but do not know where or what is is
What is fine touch?
can tell what it is
In the letter system of classifying nerve cells, which type of fibre has the slowest conduction velocity?
C
Which type of nerve fibre is responsible for solely the Golgi Tendon Organ?
Ib fibre
What fibres are part of the Parasympathetic nervous system?
C & B
What fibres are part of the Sympathetic nervous system?
Aa & Ay
Define Perception
Interpretation of sensation (in cortex)
Define somatic
Relating to the body
Proprioceptors
helping to understand where the limbs are in terms of space
What’s the 3 main classification types of Sensory receptors?
- Microscopic Features
- Receptor location and activating stimuli
- Type of stimulus detected
What is a Nociceptor?
pain receptors
Define Decussation?
crossing over
What are the Spinal pathways?
Pain/temp: Anterolateral
Fine touch/Proprioception: Dorsal column medial lemiscus
What are the Trigeminal Pathways?
Pain/temp: Trigeminothalamic
Fine touch/Proprioception: Double Trigeminothalamic
What is the Dorsal Column-Medial Lemniscus pathway?
Where does it synapse and cross over?
What thalamus nucleus does it synapse in?
- Enters dorsal root
- Ascends dorsal column - ipsilaterally
- Synapses in medulla, gracile & cuneate nucleus and crosses over
- Ascends to synapse in thalamus: Ventral Posterior Lateral Nucleus
- Ascend to sensory cortex (Post Central gyrus)
How do fibres from Dorsal Column-Medial Lemniscus travel up the spinal cord the the medula?
Travel via 2 fibre bundles (in dorsal columns)
Cuneate fasciculus - upper
Gracile fasciculus - lower
What is the Anterolateral system?
Where does it synapse and cross over?
What thalamus nucleus does it synapse in?
Enters dorsal column
Synapse & crosses over in spinal cord –> Thalamus
synapses in Ventral posterior lateral nucleus
What is the Pain/temp Trigeminothalamic pathway?
Enters pons through trigeminal ganglion, synapses & crosses over
Synapses in Thalamus: Ventral posterior medial nucleus
What is the Fine touch/Proprioception Trigeminothalamic pathway?
Double:
Enters pons through trigeminal ganglion
Decends to Rostral Medulla & other to Medulla
Synapse and cross over
Synapses in Thalamus: Ventral posterior medial nucleus
What is a noxious stimuli?
anything that can cause harm to the body
What are pain receptors?
Nociceptors - Free nerve endings
Which two types of fibres relay pain sensation, and how does the type of pain differ?
A-Delta fibres: Sharp Fast pain —> Myelinated
C-Fibres: Slow, Dull ache —> Non-myelinated
What do C-fibres respond to?
Mechanical stimulation (same as A-delta)
+ substances from Damaged tissue –> chemicals being released & Cytokines from immune cells
Where do C fibres & A-delta fibres synapse?
A-Delta: synapse in the top (1 lamina) and further down in the grey matter (5 lamina)
C-fibres: generally in the top layers (1 & 2 lamina)
What is Peripheral Sensitisation?
Lowering of sensation = threshold lowered = responsiveness increased
List some chemicals responsible for increased sensitisation of Nociceptors following damage or inflammation to the body.
- ATP
- Histamine
- Serotonin (5-HT)
- Cytokines
- Bradykinin
- Neuropeptides
Which cell surface receptors on the postsynaptic membrane are responsible for increased central sensitisation of pain?
AMPA and NMDA
How does increased stimulation of these receptors increase the central sensitisation of pain?
- Increased activity of pathways
- Activating receptors
- Nerve cells increase calcium levels
- Activate secondary messenger system
- Triggers transcription factors
- Up regulate certain proteins
- Adds more receptors to membranes
more receptors = more responsiveness to released neurotransmitters = strengthening synapse
What does the gate theory of pain suggest about the inhibition of pain pathways?
Pain pathways can be inhibited by the activation of (touch) A-alpha, and A-beta (Ia, Ib, and II) pathways in the same area. E.g. rubbing an injury makes it feel better.
What is Deafferentation?
Changes to the pathways, could be a reason for chronic pain
What is referred pain?
Feeling pain away from area of damage, caused by a convergence of pain pathways to one neuron that travels to the thalamus - have the same neuron, so brain can’t tell where the pain is coming from
What is the function of the descending centrifugal pathway?
Pain inhibition from central control points in the CNS.
List some neurotransmitters that activate the descending centrifugal pathway
- Enkephalin
- Endorphin
- Dynorphin
- Serotonin
- Glutamate
How do opioids reduce pain sensations?
Inhibits the pathways that inhibit the centrifugal pathway of pain inhibition (double negative action)
What are the main decending pathways?
Lateral corticospinal tract:
- Voluntary control of distal musculature
Anterior corticospinal tract:
- Voluntary control of proximal musculature
Reticulospinal tracts (pontine and medullary):
- Regulate flexor reflexes and initiate patterned activity e.g. locomotion
Rubrospinal tract:
- Motor control
- excitation of flexor muscles
Vestibulospinal tracts:
- Lateral - maintaining of balance and posture
Medial - maintaining of head position and fixation of gaze
Tectospinal tract:
- control head movements in response to visual stimuli
