Neuro wrap up Flashcards
What is a neurone?
Conduction relays of the nervous system, transmit information in the form of action potential.
Found throughout the body and brain, broadly categorised as motor or sensory.
Structural divisions of the CNS
brain and spinal cord
Structural divisions of the peripheral nervous system
nerves outside the CNS, including spinal nerves and cranial nerves
Functional divisions of the PNS
somatic and autonomic nervous systems
autonomic is further subdivided into sympathetic and parasympathetic nervous systems
subdivisions of the autonomic nervous system
sympathetic and parasympathetic
Which nerves carry parasympathetic information?
CN 3, 7, 9 and 10
Pelvic nerve (S2, 3, 4)
Which nerves carry sympathetic information?
T1-L2 spinal ganglia
List some roles of the parasympathetic nervous system:
Broadly - rest and digest.
Pupil constriction, salivation, slows heartbeat, bronchoconstriction, gastric peristalsis and secretion, release of bile, bladder contraction, erection/arousal
Parasympathetic functions of CN3
pupil constriction and accommodation
Parasympathetic functions of CN 7
flow of saliva from sublingual and submandibular gland
lacrimal gland
Parasympathetic functions of CN 9
flow of saliva from the parotid gland
Parasympathetic functions of CN 10
slows heartbeat, constricts bronchi, stimulates gastric peristalsis and secretion, stimulates release of bile
Parasympathetic functions of pelvic nerve (S2, 3, 4)
contracts bladder
stimulates intestinal motility
Roles of the sympathetic nervous system
Broadly: fight or flight.
Dilates pupil, inhibits saliva, accelerates heartbeat, dilates bronchi, inhibits gastric peristalsis and secretion, conversion of glycogen to glucose in liver, secretion of adrenaline and noradrenaline, inhibits bladder contraction, orgasm/ejaculation.
Structure of the sympathetic nervous system:
location of preganglionic bodies? Postganglionic bodies?
Preganglionic cell bodies in T1-L2 spinal ganglia, transmit to sympathetic chain.
Post ganglionic cell bodies in the sympathetic chain –> target structure
Sympathetic nervous system:
Preganglionic neurotransmitter and receptors
Postganglionic nervous system and receptors
Preganglionic: acetylcholine, nicotinic receptors
Postganglionic: noradrenaline, alpha and beta adrenoreceptors (beta 1 = heart, beta 2 = lungs, beta 3 = bladder)
Structure f the parasympathetic nervous system:
Location of preganglionic cell bodies
Postganglionic cell bodies
Preganglionic cell bodies in the brainstem –> just outside target organ
Postganglionic cell bodies just outside target organ –> target
Parasympathetic nervous system neuro transmitters:
pre ganglionic
postganglionic
Pre = nicotinic ACh Post = Muscarinic ACh
What three main parts form a neurone?
Cell body containing nucleus and organelles
Axon conducting the impulse
Dendrites - projections receiving information
What 3 main categories do neurones come under in terms of direction of information transmitted?
- Afferent: info from sensory receptors to CNS
- Efferent: info from CNS to target tissues
- Interneurones: contained entirely within the CNS
Myelin - purpose and composition
Fatty substance contributed by oligodendrocytes (CNS) or Schwann cells (PNS) wrapping themselves around the axon of a neurone.
Acts as an electrical insulator, prevents ion movement, and forms a protective cushioning barrier
Where do neurones of the CNS get their myelin sheath compared with neurones of the PNS?
CNS = oligodendrocytes PNS = Schwann cells
Briefly describe saltatory conduction
Schwann cell insulation means ion movement can occur only at the nodes of Ranvier (gaps between Schwann cells).
The electrical signal must therefore ‘hop’ from one node to the next in saltatory conduction.
This is faster than the continuous conduction taking place in unmyelinated neurones.
3 factors affecting conduction velocity
- Nerve diameter: larger = faster
- Temperature (hotter = faster, up to a point)
- Myelination
All or nothing - what determines the intensity of the signal perceived by the brain?
the frequency, not the strength, of the signal: neurones can either be firing or not firing, depending on wether the threshold potential is exceeded
6 steps of axonal transmission
- Resting potential: the nerve is unstimulated, -70mV
- Generator potential: stimulus causes a slight depolarisation
- Threshold potential: slight depolarisation reaches -55mV
- Depolarization: massive Sodium influx, peaks at +30mV
- Repolarisation (absolute refractory period)
- Hyperpolarisation (Relative refractory period)
How is resting potential maintained?
Channels:
Na+/K+ pump actively pumps 3Na+ out for every 2K+ in.
Voltage gated potassium channels are open.
Voltage gated sodium channels are closed.
How does the arrival of a stimulus alter the potential of an axon?
Arrival of a stimulus from a synapse destabilises some of the sodium channels.
A small amount of sodium leaks in, leading to a slight depolarisation.
If the depolarisation is enough to reach the threshold potential, an action potential is triggered.
Describe the sequence of events if threshold potential is reached in a neurone.
What is happening to each channel?
- all voltage gated sodium channels now open
- massive influx of positively charged sodium ions causes membrane potential to become positive.
Na+/K+ pump stops.
Voltage gated potassium channels close.
Voltage gated sodium channels open.
Following depolarisation, how is resting potential restored in the repolarisation period?
+30mV reached and the impulse has been spread down the length of the axon
Resting potential must be restored:
- Sodium channels close: no more sodium may enter axon
- Potassium channels open: potassium starts leaving axon
- Na+/K+ pump actively pumping 3Na+ out and for every 2K+ in
What are the 2 parts of a refractory period and when do they take place?
- Absolute refractory period, takes place during repolarisation
- Relative refractory period, takes place during hyperpolarisation
How does absolute vs relative refractory period affect transmission of a new action potential?
absolute - neurone cannot generate a new action potential
relative - neurone can generate a new action potential only in response to a stimulus stronger than previous stimulus (raises threshold potential)
In synaptic transmission, what is convergence?
divergence?
Convergence = many Presynaptic knobs pass impulse to one postsynaptic membrane Divergence = one presynaptic knob at many postsynaptic membranes
What are the 5 fundamental processes of synaptic transmission?
- Manufacture (intracellular biochemical process)
- Storage
- Release (triggered by AP)
- Elicit a post-synaptic response (diffuse across cleft, bind to receptor)
- Inactivation (breakdown or reuptake)
Sequence of events following the arrival of an action potential at the presynaptic knob
- Action potential arrives at the presynaptic knob
- Entry of Na+ ions causes voltage gated calcium channels to open, Ca2+ influx
- Calcium ions cause vesicles to fuse with the cell membrane and release preformed neurotransmitters into the synaptic cleft (exocytosis)
- Neurotransmitter diffuses across the synapse and binds with receptors on the postsynaptic membrane
Neurotransmitter breakdown - what are the 3 main mechanisms by which neurotransmitters re removed following synaptic transmission?
- Active transport back into the presynaptic knob (reuptake)
- Diffusion away from receptor sites
- Enzymatically broken down and recycled
Definition of pain
“an unpleasantsensory andemotional experienceassociated with actual or potential tissue damage”
Define:
1. Acute pain
- Chronic pain
- Short term pain of less than 12 weeks
- Continuous long term pain of more than 12 weeks OR lasting longer than would be expected
Divided into chronic cancer pain and chronic non cancer pain
Define nociceptive pain
pain arising from actual or threatened damage to non-neural tissue
due to the activation of nociceptors
Define neuropathic pain
pain arising as a direct consequence of a lesion/disease in the somatosensory system
painkillers -
what are analgesics?
what are anaesthetics?
analgesics - selectively suppresses pain without an effect on consciousness or other senses, e.g. paracetamol
anaesthetic - induces insensitivity to pain with reversible loss of all sensation e.g. local anaesthetics
What are the 4 types of nerve fibres in the PNS?
A-alpha, A-beta, A-delta and C fibres
which of the 4 types of nerve fibres in the PNS are nociceptive?
A-delta and C fibres
Describe A-delta nerve fibres
- info transmitted
- diameter
- myelination
- speed of conduction
- type of pain
- nociceptive, transmit mechanical and thermal pain information
- myelinated, large diameter
- rapid conduction
Initial sharp pain
describe C-fibres - info transmitted - diameter - myelination - speed of conduction type of pain
- nociceptive, transmit mechanical, thermal and chemical pain
- unmyelinated, small diameter
- slow conduction
Only activated by very strong painful stimuli, dull aching pain
What information does the spinothalamic tract carry?
Ascending
pain, temperature and crude touch
Describe the route of information travelling via the spinothalamic tract:
- primary, secondary and tertiary neurones
- primary neurones enter via dorsal root ganglion, travel up 1/2 spinal segments
- synapse with secondary neurones which decussate in the spinal cord and continue to the thalamus
- tertiary neurones in the thalamus carry info to the primary somatosensory cortex via the internal capsule
Briefly describe the Melzack-Wall Pain Gate theory?
- non-noxious stimuli can prevent noxious stimuli from eliciting pain sensation
- Non noxious stimuli in the same region carried by A-beta fibres cause inhibitory interneurones to fire, reducing sensation of pain
(rub it better)
what is a motor unit?
a single alpha motor neuroe and all the muscle fibres it inervates
what is a motor neurone pool?
a collection of motor neurones innervating a single skeletal muscle
what is a motor end plate?
region of the cell membrane of the muscle fibre which lies directly beneath an axon terminal