6 - neurophysiology

Question 1

compare the effects of the sympathetic vs parasympathetic nervous systems on cardiac muscle

Answer 1

PARASYMPATHETIC
• in cardiac muscle, there are M2 receptors
• activated by ACh released from vagus nerve
• causes activation of G(l) protein —> inhibits adenyl cyclase —> inhibits production of cAMP —> activation of K+ channels —> K+ out of cell (hyperpolarisation) —> takes longer to reach threshold —> lower HR

SYMPATHETIC
• noradrenaline from sympathetic nerve activates beta-1 receptors
• activates G(s) protein
• different second messenger to increase HR

Question 2

using a diagram, describe the effect of sympathetic and parasympathetic activation on the following organs: heart, brain, lungs, blood vessels, urinary bladder, liver.

Answer 2

redraw that diagram he used a billion times in the leccys

Question 3

draw the structure of the ANS

Answer 3

CNS
pre-ganglionic fibre
autonomic ganglion (neurotransmitters + modulation of signal)
post-ganglionic fibre
varicosity (neurotransmitter)
effector organ

Question 4

using a diagram, describe how specific receptors control

heart rate

Answer 4

:P

Question 5

what is the function of the autonomic ganglia

Answer 5

to either enhance or reduce a signal

Question 6

list the different forms of motility in the GIT and with one sentence for each describe the functional importance.

Answer 6

1) gastric mixing

2) segmentation
– move chyme in both directions which allows greater mixing with the secretions of the intestines

3) peristalsis
– propulsion of bolus

4) migrating motor complex
– moves undigested remains to large intestine in between meals to empty stomach for next meal
– responsible for the rumbling experienced when hungry

Question 7

describe the mechanism of defecation

Answer 7

parasympathetic nerve involved in contraction of smooth muscle (internal sphincter) which results in defection —> automatically controlled (early development)

later in development, gain control over external sphincter using skeletal muscle and motor neurons —> voluntary control

Question 8

using a simple diagram explain how stress affects the sympathetic nervous system and the HPA axis

Answer 8

XD

Question 9

using a diagram explain how olfaction affects different structures within the brain

Answer 9

B~D

Question 10

justify this statement: the sympathetic nervous system and pituitary gland maintain homeostasis

Answer 10

hypothalamus and pituitary gland function to maintain homeostasis

they respond to changes in the body by releasing hormones and activating sympathetic/parasympathetic NS

Question 11

how does negative feedback fail during chronic stress?

Answer 11

• more and more cortisol release
• neg. feedback begins to fail
• glucocorticoid receptors on hippocampus

• hippocampus logically controls stress response —>
suppresses cortisol

• over-excitation due to cortisol = suppression form hippocampus fails
• chronic stress leads to destruction of hippocampus —> memory loss + alzheimers + dementia

Question 12

draw and described in order - the molecular events from motor neuron action potential generation through to the generation of a muscle action potential

Answer 12

1) AP arrives at motor nerve terminal
2) AP triggers the opening of VG Ca2+ channels = entry of Ca2+
3) Ca2+ dependant release of acetylcholine (ACh) from synaptic vesicles (exocytosis)
4) ACh traverses the synaptic cleft to bind to its receptor a ligand gated Ion channel (AChRs)
5) binding causes opening of this ion channel = large movement of Na+ in and a small movement of K+ out of the muscle cell = depolarisation
6) current flow between the depolarised post-synaptic membrane and adjacent membrane of muscle
7) local current flow opens voltage gated Na+ channels in the adjacent membrane
8) the resulting entry of Na+ causes the resting MP to rise from ~ -70 mV to -60mV = generation of a muscle action potential
9) ACh is subsequently destroyed by acetylcholine-esterase (enzyme in synaptic cleft)

Question 13

what is the latent period?

Answer 13

muscle APs last for only 1 to 2 ms, whereas the muscle contraction that results can last about 50 ms

latent period = time delay between stimulation and contraction

Question 14

what is myasthenia?

Answer 14

disease which causes the drop in the number of post-synaptic AChRs to such a level that causes muscle weakness

Question 15

what is lambert-eaton syndrome?

Answer 15

auto immune self antibodies to the pre- synaptic voltage gated calcium channels

poor pre-synaptic release of neurotransmitter - leads to neuromuscular block

causes muscle weakness

Question 16

what is spinal muscular atrophy ?

Answer 16

an autosomal recessive disease caused by a genetic defect in the SMN1 gene, which encodes SMN, a protein
widely expressed in all eukaryotic cells

SMN1 is apparently selectively necessary for survival of motor neurons

causes muscle weakness

Question 17

what is the consequence of a mutation in the dystrophin gene

Answer 17

mutation in the dystrophin gene = no dystrophin (anchors muscle fibre to extracellular matrix)

dystrophin supports muscle fibre strength

absence of dystrophin reduces muscle stiffness, increases sarcolemmal deformability, and compromises mechanical stability

Question 18

what is a motor unit?

briefly compare small and large motor units

Answer 18

motor unit = 1 motor neuron the number of muscle fibres it innervates

small motor units = fine control but weaker muscle contraction

large motor units = larger muscle contraction

Question 19

state and explain henneman’s size principle

Answer 19

for a given synaptic input, motor neurons with the smallest cell bodies are activated 1st & large motor neurons are activated last

smaller neurons have higher membrane resistance and require lower depolarising current to reach spike threshold

small motor-neurons innervate small motor unit
large motor-neurons innervate large motor unit

Question 20

compare the three types of motor fibres

Answer 20

TYPE I:
– small MN
– slow twitch
– fatigue resistant
– slow oxidative
– low myosin ATPase activity

TYPE IIA:
– medium MN
– fast twitch
– fatigue resistant
– fast oxidative

TYPE IIX:
– large MN
– fast twitch
– fatigable 
– fast glycolytic 
– high myosin ATPase activity

Question 21

how does chronic denervation–reinnervation of muscle lead to fibre type grouping, type I in particular?

Answer 21

chronic denervation re-innervation events lead to type 1 fibre predominance

fast motor neurons die first

de-inervated tissue pumps out GFs

∴ local sprouting and expansion of surviving slow MNs

type I now dictates fast-twitch fibres

Question 22

what do muscle spindles detect?

how are muscle spindles kept taut?

Answer 22

muscle spindles detect ∆length of muscle

spindle must always remain taut to maintain sensitivity to ∆length

gamma MN act on spindles to maintain their sensitivity during muscle contraction

Question 23

what are golgi tendon organs and what do they detect?

Answer 23

golgi tendon organs are located in the tendinous insertions of muscle

detect changes in muscle tension

activated by increases in muscle tension and thus measure the degree of tension/load that the muscle is under

Question 24

draw and briefly describe five types of interneuronal circuits

Answer 24

DIVERGENCE
black MN excite inhibitory MN —> no firing
white MN excite excitatory MN —> firing
withdrawal reflex

CONVERGENCE
many motorneurons excite the same MN
brain stem / cortex inputs

REVERBRATING
excited for longer by exciting self

FEED FORWARD INHIBITION
interneuron does not allow MN to fire
rhythmic activity

GATING
excitation and reciprocal inhibition
stretch reflex

Question 25

draw a diagram of the patella reflex

Answer 25

:P

Question 26

draw a diagram of how the crossed extensor and withdrawal reflex work together during locomotion

Answer 26

:^O

Question 27

why is a patient with a spinal cord injury and supported by a harness able to walk on a tread mill ?

Answer 27

i don’t actually know the answer to this can any1 help :(

Question 28

name and briefly describe two mechanisms used for postural adjestments

Answer 28

feed forward:
– anticipatory
– preprogrammed from experience
– unlike reflexes

feedback:
– compensatory 
– stereotyped 
– show a space time organisation
– like reflexes

Question 29

describe the reflex(es) controlled by the vestibular nuclei

Answer 29

vestibular nuclei receive afferents which signal head postion WRT gravity

signals via vestibulospinal tract to control multiple relfexes

lateral nuclei = controls proximal limbs to maintain stance

medial + superior = coordination of eye with head movements

inferior = integrates afferents + cerebellum to higher areas

Question 30

describe the reflex(es) controlled by the reticular formations

Answer 30

maintaining posture via feed-forward mechanisms

medullary (lateral) reticular formation = inhibitory to extensor muscle tone

pontine (medial) reticular formation = facilitates extensor muscle tone

Question 31

describe the reflex(es) controlled by the superior collucli

Answer 31

receives visual input

outputs to reticular formation then to motoneurons of ocular motor nucleus + outputs to cervical motoneurons of head and neck (tectospinal)

controls saccadic eye movements

Question 32

describe the reflex(es) controlled by the red nuclei

Answer 32

red nuclei increases flexor muscle tone to facilitate grabbing behaviour

Question 33

describe the function of the cerebellum

Answer 33

Functions as a COMPARATOR

compares intended movement with performance of movement and makes adjustment

1) internal feedback (corollary discharge)
2) external feed back (reference)
3) input to lower motor neurons
1 & 2 allow for comparisons, 3 for correction

Question 34

list the functional lobes of the cerebellum (function, input, output)

Answer 34

VESTIBULOCEREBELLUM
• structural = folcculonodular lobe
• input: vestibular apparatus
• output: lateral vestibular nucleus
function: maintenance of balance, control of eye movements

SPINOCEREBELLUM
• input: spinal cord
• output: back down to spinal cord via fastigial nucleus (proximal muscles) or interposed nucleus (distal muscles)
• function: regulation of muscle tone, coordination of skulled voluntary movement

CEREBROCEREBELLUM
• input: cerebral hemispheres (motor cortices)
• output: back to hemispheres
• function: planning and initiation of voluntary activity, storage of procedural memories

Question 35

what fibres control the deep cerebellar nuclei?

are they inhibitory or excitatory?

Answer 35

climbing fibres (excitatory)

mossy fibres (excitatory)

purkinje fibres (excitatory)

Question 36

what is hypotonia?

Answer 36

diminished resistance to passive limb displacements

e.g. after knee-jerk reflex, leg may oscillate 6-8 times before coming to rest (compared to immediately in healthy patients)

Question 37

what is ataxia

Answer 37

lack of coordination

errors in the range of movement

errors in the rate and regularity of movements

Question 38

what is the main difference between an upper and lower motor neuron lesion?

Answer 38

LMN lesion = flaccid paralysis (reflexes lost)

UMN lesion = spasticity (reflexes intact)

Question 39

what is the function of the premotor cortex?

from where does it receives inputs?

what are the consequences of a lesion in the PMC?

Answer 39

function:
– setting up the motor programs for learned sequences
– coordination of bilateral movements
– active when told to dream movement (planning)

inputs:
– sensory cortex
– visual inputs

lesion:
impaired ability to execute purposeful movements

Question 40

what is Broca’s area?

where is it located?

what are the consequences of a lesion to this area?

Answer 40

function:
– production of speech

location:
– inferior frontal gyrus in frontal cortex

lesion:
– speech = non-fluent, effortful
– comprehension = preserved for single words and sentences
– repetition = impaired

Question 41

what is Wernicke’s area?

where is it located?

what are the consequences of a lesion to this area?

Answer 41

function:
– comprehension of language

location:
– left posterior, superior and middle temporal cortex

lesion:
– speech = fluent
– comprehension = impaired
– repetition = impaired

Question 42

what in conduction aphasia?

Answer 42

conduction aphasia = damage to left supramarginal gyrus

speech = fluent with some articulatory defects

comprehension = intact / largely preserved

repetition = impaired

Question 43

TRUE OF FALSE

NPY, NA and ATP are all released from same nerve terminal

Answer 43

TRUE

NPY, NA and ATP are all released from same nerve terminal

All act to increase contractility of smooth muscle by acting on ⍺-1 (NA +NPY) and P2X (NPY + ATP) receptors → induce calcium release