synapse

Question 1

action potential

Answer 1

rapid, large depolarisation from threshold mem potential

threshold potential more +ve > basal (RMP)

Question 2

when does AP occur?

Answer 2

1) when external stimulus applied
2) info is transferred to neuron

Question 3

steps to Action potential depolarisation

Answer 3

1) rest mem potential of -80/60mV (based on K, Na, Cl distribution)

2) AP begins: excitatory neurotransmitter, open ligand -gated channels (NMJ, synapse of CNS)

depolarising potential reach trigger zone, depolarise mem

3) voltage gated Na channels activated, mem more permeable to Na (EXTRACELL –> INTRA)

4) Na entry, depolarise cell

5) inside more +ve > outside, reverse mem potential polarity

6) voltage gated Na+ channels inactivated. VG K+ channels open, mem potential more permeable to K+

K+ move out, mem potential repolarises

7) VG K+ channels close. mem potential returns to normal (Na-K pump: 2 Na+ out and 3K+ in)

Question 4

electrochemical gradient

Answer 4

ionic distribution across mem at rest (resting mem potential)

K+ (intracell > extracell)

Ca2+ (intracell < extracell)
Na+ (intracell < extracell) ** ASM
Cl- (intracell < extracell)

electrochemical gradient determines equilibrium potential

Question 5

resting mem potential is usually +/-ve ??

Answer 5

more neg than threshold mem potential

mem must be depolarised –> threshold mem for AP signal to be evoked

Question 6

forces acting on K that affects its movement

Answer 6

1) conc gradient favour EFFLUX of K (intracell –> extracell)

2) electrical gradient PULLS +ve K+ (extracell –> intracell)

2 gradients oppose each other

Question 7

equilibrium potential

Answer 7

equilibrium potential (where OUT = INWARD gradients, no net movement of ion across mem

balanced at eg: -97mV, no net movement of K+

Question 8

eqm potential eqn

Answer 8

E = 58 log (conc of ION outside/ conc of ION inside)

specific for each ion: K, Na. Given ion will either move IN/OUT cell to push mem potential towards E value

different from mem potential

Question 9

mem potential

Answer 9

reflects conc and permeability of K, Na, other ions that are distributed across the mem

Question 10

at rest, normal state movement

Answer 10

K move outward (push mem potential towards -97mV)

Na move inward (push mem potential towards +75mV)

mem potential maintained at -80/60mV (more neg reflects greater permeability for K+ = leak K channels)

Question 11

alter K conc outside (incr extracell conc)

Answer 11

E value = 58 log (50/ 140) = -25mV vs -97mV

favour K outflow but now less steep than before
less K move out since E is more +ve now

greater accumulation of +ve charges inside mem.
Resting mem potential becomes less negative, closer to threshold

Depolarisation easier as less stimulus needed to initiate action potential

Question 12

hypernatremia

Answer 12

still favour inflow of Na+ intracellularly

more positive rest mem potential

reach threshold easier, depolarisation easier as less stimulus needed to initiate AP

Question 13

hypokalemia

Answer 13

low extracell K

more -ve E value. still favour K outflow, more steep now, more K move out

less accumulation of +ve charges inside mem.
Resting mem potential becomes MORE negative, further from threshold

Depolarisation harder as more stimulus needed to initiate action potential (less excitable)

Question 14

synaptic transmission

Answer 14

communication b. cells (b. neurons, nerves, muscles)

3 components:
1) presynaptic terminal
2) postsynaptic cell
3) synaptic cleft

Question 15

2 types synaptic transmission

Answer 15

electrical – current generated in presynaptic neuron FLOWS DIRECTLY into postsynaptic cell through gap-junction channels

chemical – has synaptic cleft, neurotransmitters released, receptors on postsynaptic cleft

Question 16

chemical synapse

Answer 16

has synaptic cleft 20-40nm

1) action potential in presynaptic cell release chemical transmitters in cleft

2) transmitter diffuse across cleft, interact with specific receptors

3) depolarise/ hyperpolarise postsynaptic cell

4) depo: reach threshold mem, leads to generation of action potential in postsynaptic cell

Question 17

neuromuscular junction definition

Answer 17

NMJ synapse/ junction of axon terminal of motoneuron with motor end plate (motor neuron excites skeletal muscle fiber)

highly excitable region of muscle fiber

plasma mem: initiates AP across muscle surface = contract muscle

CHEMICAL SYNAPSE

Question 18

how depolarisation occurs at neuromuscular junction

1) transmitting (AP presynaptic)
2) receptive (Ach)

Answer 18

1) synaptic transmission involve release of acetylcholine from presynaptic axon terminal (open VG Ca2+ channel)

2) Ach binds to nicotinic receptor (postsynaptic mem/ muscle mem – ligand gated)

3) initiate depol of postsynap mem (influx of Na+) result in muscle contraction (motor end plate)

Question 19

release of Ca2+ in presynaptic axon

Answer 19

presence of Ca2+ in axon terminal cause synaptic vesicles to fuse with mem

Ca2+ act on Ca2+ sensitive vesicle mem poteins (VAMPs) –> vesicle docking to presynapse –> fuse with presynaptic mem –> exocytosis

Question 20

transmitters for diff synapse and their effects

Answer 20

Ach – excitatory at NMJ
glutamate – excitatory in CNS

GABA – inhibitory in CNS & NMJ

Question 21

facilitate depolarisation at threshold mem potential

Answer 21

block efflux of intracell K+
incr influx of extrcell Na+
decr influx of extracell Cl-

release Ach at NMJ
incr nicotinic receptor agonist at NMJ

Question 22

type of channels at membrane

Answer 22

ligand-gated channels (AP begins, NMJ to motor end plate)

voltage-gated channels (depol, repol)

Question 23

sensation

Answer 23

conscious awareness of external stimuli (touch, pressure)

signal generated: external stimulus reach sensory cortex (along label line)

Question 24

sensory receptor embedded in skin

Answer 24

specialised sensory nerve ending/ specialised epithelial cells – recognise stimulus

initiate sensory transduction by action potential in same cell/ adjacent one

sensory receptor send info –> CNS via afferent nerve fibers (1* afferents)

Question 25

pacinian corpuscle
enclosed nerve ending has layers of connective tissue

Answer 25

1) receptive field: specific area of receptor that monitors non pain frequencies (vibration)

2) converts physical energy to signal

Question 26

1* afferent

Answer 26

carry nerve impulses from receptors/ sense organs –> CNS

Question 27

mechanoreceptor sensory receptors

Answer 27

sensitive to mechanical energy

touch, pressure (vibration), stretch, sound

Question 28

nociceptor

Answer 28

free nerve ending, sensitive to tissue damage

noxious stimuli

eg: capsaicin (chemical) – Trpv1 receptor

Question 29

chemoreceptor

Answer 29

sensitive to chemicals

O2, pH, various organic molecules – glucose

Question 30

photoreceptor

Answer 30

responsive to light

photos of light

Question 31

thermoreceptor

Answer 31

sensitive to hear and cold

varying degrees of heat
(> 44-45*C = noxious stimuli)

Question 32

proprioceptor

Answer 32

sense position of body in space

Question 33

types of 1* afferent

Answer 33

A: skeletal muscle within body
Ab: mechanoreceptor of skin

Ad: pain, temp
C: temp, pain itch

Question 34

degree of myelination

Answer 34

A, Ab: largest diameter, thickest myelin

Ad: thinly myelinated
C: free nerve ending, unmyelinated

Question 35

sensory transduction

Answer 35

sensory receptor converts energy (in a STIMULUS) –> AP (change in electrical potential across mem)

cause receptor mem to depolarise = AP generation (signal relayed to brain)

Question 36

steps in sensory transduction

Answer 36

1) Application of stimulus to receptor in periphery that generally results in depolarisation of receptor mem

2) Receptor potential travels to trigger zone of associated primary afferent
a. Depolarisation, when it reaches trigger zone generates action potential generation adzone

3) Action potential discharge propagated along the axon

4) Action potential discharge reaches the axon terminal stimulate the release of transmitter
a. Affect next neuron in line in the CNS

Question 37

Trigger zone

Answer 37

axon hillock

sum of total signals (inhibitory & excitatory)
if > threshold = trigger AP

Question 38

label lines

Answer 38

the brain perceives the info arriving from specific neuronal tract as the adequate stimulus of the 1st order sensory receptor (afferent),

only respond to one type of stimulus even if diff stimulus activates it

Question 39

common somatosensory pathways

Answer 39

1* afferent (peripheral axon) –> 2* afferent (spinal cord or brain stem nucleus)

decussation (cross to other side below thalamus)

all have thalamic nucleus

end in parietal lobe of cerebral cortex

Question 40

nociceptors (C, Ad 1* afferents)

Answer 40

sensory receptor that responds to potential damaging stimuli

BY send nerve signals to spinal cord and brain
- nociception = perception of pain

internal and external nociceptors

Question 41

external nociceptors

Answer 41

cell bodies of these neurons located in either Dorsal root ganglion/ Trigeminal ganglia

TGM ganglia: specialised nerves for face
DR ganglia: associated with rest of body

axons extend into PNS, terminate in branches (receptive fields)

Question 42

intensity of stimulus incr when incr in

Answer 42

number of AP generated/ unit time

freq/ rate of AP from nociceptors activation

Question 43

impaired sensory

Answer 43

loss of large diameter Ab fibers (less non-painful sensations)

absence of C/Ad fibers (loss of pain receptors)

Question 44

what happens at efferent?

Answer 44

neurons in CNS will generate another signal

efferent distinct by location

usually in ventral horn of spinal cord (controls movement).

doral arm (mostly cell bodies on sensory neurons)

Question 45

depolarise

Answer 45

membrane depolarizes above the threshold voltage, and the influx of sodium ions

Question 46

Repolarise, hyperpolarise

Answer 46

change in a cell’s membrane potential that makes it more negative.

inactivate Na, open K+ channels

Question 47

generation of sensation signal

Answer 47

1) receptors transduce external stimuli to electrical charge

2) electrical charge depolarises = action potential ***

3) relay action potential to CNS, processed in cortex to understand the sensation

Question 48

how action potential is relayed

Answer 48

myelinated > faster > unmyelinated

jumps over myelin sheath, nodes of ranvier is shorter distance than through nerve

Question 49

AP in neuron

Answer 49

requires excitatory neurotransmitter (efferent converts to electrical energy)

transfer signals from 1 neuron –> another
evokes synaptic potential (EPSP, IPSP –> evokes AP)

• An EPSP has a reversal potential more positive than the action potential threshold = DEPOL
• an IPSP has a reversal potential more negative than threshold = HYPERPOL

Question 50

hyperexcitability in neurons

Answer 50

eg rhythmic firing of large pop of neurons ==> SEIZURE ===> epilepsy (multiple, unprovoked)

• abnormal activity in small areas of cortex –> trigger for seizures –> spread to other synaptically connected region

uncontrolled movement (jerking)

Question 51

control of seizure

Answer 51

1) enhance inhibitory synapse (limit AP firing, act on VG-Na+ channels)

2) hyperpolarisation (GABA, IPSP)

3) decr excitatory (glutamate, CNS)

Question 52

contralateral pathway where for touch and pain?

Answer 52

□ Pain: spinothalamic/ anterolateral
* Touch: Dorsal column – cross at medulla