lecture 3 and 4: NS (function, organization and cellular components) Flashcards
1
Q
what does the human NS do
A
system that conducts stimuli from sensory receptors to brain and spinal cord and conducts impulses back to other parts of the body
2
Q
what underlies the nerve impulse code
A
frequency and pattern of AP firing
3
Q
what facilitates the conduction of AP
A
neurons specialised morphology and gene expression
4
Q
the 2 major control systems are the NS and…
A
endocrine system
5
Q
what kind of signalling
A
electrochemical
6
Q
CNS
A
brain and spinal cord
-control centres
7
Q
PNS
A
12 pairs of cranial nerves and 31 pairs of spinal nerves
-comms between CNS and rest of body
8
Q
basic spinal reflex arc
A
- receptor
- afferent sensory neuron
- interneuron
- efferent motor neuron
- effector
9
Q
somatic NS
A
innervates skeletal muscle and responsible for voluntary movement
10
Q
autonomic NS
A
innervates cardiac muscle, smooth muscle and glands- regulates involuntary bodily functions
11
Q
sympathetic
A
fight or flight
12
Q
parasympathetic
A
rest and digest- regulates automatic body functions
13
Q
enteric
A
division of ANS (little brain)
-lining of GI tract
-control processes involved in transport and digestion of food
14
Q
what is the PNS divided into
A
afferent division
(somatic sensory, visceral sensory, spatial sensory)
efferent division
(SNS, ANS)
- ANS contains sympathetic, parasympathetic. enteric)
15
Q
neurons (nerve cells)
A
functional unit of NS specialised for electrochemical signalling
- 85 billion
- neutrites (dendrites and axons)
16
Q
glia (support cells)
A
maintenance of NS but don’t directly participate in relaying electrochemical signals
17
Q
soma
A
- high demand for protein synthesis
- many proteins packaged into vesicles and transported to axons
18
Q
axons
A
- originates from axons hillock
- <1mm to >1m
- branch off at right angles to form collaterals
- conduct AP’s
19
Q
axon terminals and synapses
A
PREsynaptic axon terminal rich in synaptic vessles (neurotransmitters) and mitochondria (high energy demands of synaptic transmission)
POSTsynaptic have receptors (allow signal transmission)
20
Q
dendrites
A
- dendritic arbours (complex branching networks)
- 2mm
- synaptic input
- many postsynaptic membrane components
- can have spines
21
Q
afferent neurons
A
- info INTO CNS from receptors at peripheral endings
- single process from cell body splits into long peripheral process (axon) that’s in the PNS and a short central process (axon) that enters the CNS
22
Q
efferent neurons
A
- info OUT OF CNS to effector cells (muscles, glands, neurons)
- many dendrites
- most of axon in PNS, small bit in CNS
23
Q
interneurons
A
- integrators and signal changers
- reflex circuits
- lie entirely within CNS
- account for >99% of all neurons
24
Q
neurons classified based on:
A
- no of neurites
- complexity of dendritic branching
- axon length
- NS use
- location
25
how is myelin sheath formed
glial membrane wraps around axonal membrane
26
what do oligodendrocytes and schwann cells do
myelinate axon membranes (increasing speed of AP propagation)
-schwann cells myelinate axons in PNS
27
what does myelination do
- restricts nerve impulse generation
- increases conduction velocity by up to 100-fold
28
astrocytes
- most abundant glial cell
- star like
- formation and maintenance of synapses
- regulate neural chemical environment
- regulate blood flow and form part of blood-brain-barrier
29
microglia
- innate immune cells of CNS
- 15% of cells in brain
- 1st responders to injury and infection
- secrete cytokines and growth factors (neurons)
30
ependymal cells
- line ventricles of CNS
- ciliated (squamous or columnar)
- form choroid plexus which generates CSF
31
what does CSF do
- flows through ventricular system into subarachnoid space and bathes brain and spinal cord
- supplies CNS with metabolites and clears waste products as it's reabsorbed into blood
32
what is grey matter
collections of neuronal cell bodies
33
what is white matter
collections of axons
34
4 main parts of brain
1. cerebrum (cerebral cortex)
2. diencephalon
3. brainstem
4. cerebellum
35
frontal lobe
motor cortex
36
parietal lobe
somatosensory cortex
37
temporal lobe
auditory cortex
38
occipital lobe
visual cortex
39
cerebrum
medial temporal lobe and hippocampus
40
alzheimer's
- leading cause of dementia
- progressive degeneration of cerebrum- initially localised to medial temporal lobe
- neuropathology characterised by beta-amyloid plaques and neurofibrillary tangles (hyper-phosphorylated tau)
41
diencephalon
- consists of epithalamus, thalamus, subthalamus, hypothalamus
- thalamus functions as sensory integration hub of brain
- hypothalamus involved in regulation of emotional behaviour and whole-body homeostasis
- regulates ANS and endocrine function by innervating pituitary gland
42
brainstem
- continuous with spinal cord
- midbrain, pons, medulla oblongata
- origin of 12 pairs of cranial nerves
- regulation of motor function and processes e.g. breathing, blood circulationa and consiousness
43
parkinsons
- 2nd most prevelnt neurodegenerative disease
- movement disorder (loss of dopaminergic neurons in substantia nigra parts compacta (SNpc) of midbrain and impaired innervation of striatum
- neuropath characterised by proteinaceous aggregates (Lewy bodies) which contain misfolded alpha-synuclein
44
cerebellum
- largest structure of hindbrain
- outer cortical layer of grey matter (cerebellar cortex) surrounds inner white matter
- involved entirely in uncouncious regulation of movement
45
limbic system
- regulating mood and emotion
- cerebrum and diencephalon
- structures anatomically interconnected
46
spinal cord
-segmented structure within vertebral canal of vertebral column
-origin of 31 pairs of spinal nerves
-receives sensory info from skin + viscera and relays to brain (ascending pathways)
-sends somatic + autonomic motor efferents to periphery
47
motor neurone disease (amyotrophic lateral sclerosis)
-impaired skeletal muscle innervation, progressive loss of ability of speak, move, swallow, breath
- caused by loss ventral horn motor neurons in spinal cord or upper motor neurons in brain
- neuropath characterised by proteinaceous aggregates/inclusions
48
CNS protective elements
- CNS tissue encased in bone
- tissues protected by 3 associated membranes (meninges)
1. dura mater
2. arachnoid membrane
3. pia mater
49
subarachnoid space
contains CSF- produced by ventricular system and bathes tissues of CNS
50
PNS nerve structure
- individual axons surrounded by endoneurium
- perineurium binds groups of axons by fasicles
- epineurium encloses fasicles to form a nerve
51
what is a nerve
collection of myelinated axons enclosed in layers of connective tissue
52
nerves can be...
afferent (sensory)
efferent (motor)
mixed
53
PNS: spinal nerves
- 31 pairs of spinal nerves emerge from spinal cord
- spinal nerves are mixed (sensory and motor)
- sensory fibres project to the CNS via dorsal roots of spinal cord
- motor fibres project from CNS via ventral roots
54
what do sensory receptors do
transduce mechanical, thermal, chemo and noxious (painful) stimuli into nerve impulses that are transmitted to CNS
55
exteroceptors (skin)
respond to pain (nociceptive) stimuli, temp, touch and pressure
56
interoreceptors (viscera)
respond to mechanical and chemical stimuli
57
proprioceptors (muscles, joints and tendons)
promote postural awareness and movement
58
what type of pathway is SNS
monosynaptic
- neuron in CNS (ventral spinal cord) projects directly to skeletal muscle cell
59
what type of pathway is ANS
disynaptic pathway
- neuron in CNS projects to peripheral ganglionic neuron, which projects to visceral cell
60
where are cell bodies of (lower) autonomic motor neurons located
outside CNS in autonomic ganglia (postganglionic neurons)
61
what are postganglionic neurons innervated by
preganglionic neurons, located in the CNS
62
where do preganglionic axons of the SNS emerge from
the thoracic and lumbar potions of the spinal cord
63
where do preganglionic axons of the PNS emerge from
the brainstem and sacral portion of the spinal cord
64
electrical PD (voltage)
forced exerted on a charged particle which arises due to the difference in electrical potential between 2 charged points
65
electrical conductance
relative ability of an electrical charge to migrate from 1 point to another (i.e. ability for a current to be generated)
66
electrical resistance
relative inability of an electrical charge to migrate from 1 point to another (inverse of conductance)
67
what is an AP
self-regenerating wave of electrochemical activity that allows nerve cells to carry signals throughout the NS
- reversal in the voltage across the axonal membrane that's instigated by a rapid change in membrane permeability to Na+ ions and the resulting flow of +ve current into the cell
68
structure of the cellular microenvironment
2 polar environments (extracellular fluid and cytosol) seperated by a non-polar barrier (hydrophobic core of the phospholipid bilayer)
69
what restricts the movement of ions in the cellular microenvironment
membranes
70
what happens if ions move across the membrane
electrical currents aren't conducted
71
what do ion pumps do
use energy dervied from ATP hydrolysis to transport ions against their concentration gradients
72
why do neurons need to conduct electricity
1. ionic concentration gradients across the cell membrane
2. voltage across the membrane
3. membrane permeability
73
AP properties
- only fired when threshold met (all or nothing)
- self propagating
- size + duration don't change along axon
- stronger stimuli increase FREQUENCY of AP firing, not size of AP
74
stages of AP
1. resting membrane potential (-65mv)
2. depol - more +ve than resting (rising phase)
3. repol- returns to -ve (falling phase)
4. hyperpol- more negative than resting (undershoot/refractory period)
75
molecular basis of depol
voltage gated Na channels open, rapid influx of Na+ ions (inward +ve current)
76
molecular basis of repol
voltage gated Na channels inactivate at peak of AP (prevent more Na+ influx) while delayed opening of voltage gated K+ channels causes efflux of K+ and outward flow of +ve current
77
molecular basis of resting potential
-Na+ and K+ ions unevenly distributed across neuronal membrane, with K+ more concentrated in cytosol and Na+ more concentrated in extracellular fluid
-Resting membrane more permeable to K+ than Na+ (more +ve charge is lost from the cell from K+ efflux, than is brought into the cell from Na+ influx
-Active transport maintains conc gradients (3 Na+ ions pumped out of the cell and 2 K+ ions pumped into the cell per molecule of ATP hydrolysed)
-The resting membrane potential is negative because relatively more +ve charge flows out of cell than into it
78
undershoot/refractory period
-K+ efflux continues beyond RP
-prevents stimuli depolarizing membrane to critical threshold and prevents new AP firing
- followig this, RP re-established by Na/K pump
79
how does the sum of all inputs determine if a neuron generates an AP
the post neurons recieves thousands of presynaptic inputs from other neurons, the sum of all excitatory and inhibitory inputs determines whether the post neuron will be depolarized to the critical threshold needed for firing an AP
80
symptomatic management of AD
therapeutic targeting of dysfunctional cholinergic and glutamatergic neurotransmitter pathways
81
cholinergic pathway
- acetylcholine in synaptic vesicles
- acetylcholinesterase (donepezil, galantamine, rivastigmine) on post converts acetylcholine to choline and acetate
- nicotinic receptor
- Na+
82
glutamatergic pathway
- glutamate in synaptic vesicles
- NMDA receptor (memantine)
- Na+/Ca2+
