9.2- the mammalian nervous system

Question 1

2 divisions of the nervous system

Answer 1

1.CNS- brain and spinal cord
2.PNS-sensory and motor neurons

Question 2

the peripheral nervous system

Answer 2

-made up of somatic and autonomic
-autonomic is further divided into sympathetic (arousing) and parasympathetic (calming)
-somatic is further divided into sensory and motor

Question 3

autonomic- sympathetic Vs parasympathetic

Answer 3

symp= speeds up activity
para=slows down/ inhibits activity

Question 4

function of sensory Vs motor neuron

Answer 4

-sensory carries impulses from receptors towards CNS
-motor carries nerve impulses away from the CNS to effectors

Question 5

motor nervous system sub divisions

Answer 5

1.voluntary- carries nerve impulses to the bodies muscles under conscious control
2.autonomic- carries nerve impulses to glands smooth or cardiac muscle and is involuntary

Question 6

autonomic nervous system sub divisions

Answer 6

-sympathetic and parasympathetic
-these systems act antagonistically

Question 7

functional comparison parasympathetic Vs sympathetic

Answer 7

symp
-produces noradrenaline at synapses
-often involved in fight or flight
-activated in times of stress
para
-slower inhibitory effect
-acetylcholine produced
-maintains normal functions, rest and digest

Question 8

brain functions- cerebrum

Answer 8

-controls voluntary behaviour including movement, intelligence, memory, personality and ability to reason

Question 9

brain functions- cerebellum

Answer 9

-coordinates smooth movements, using info from muscles and ears the maintain balance and posture

Question 10

brain functions- medulla oblongata

Answer 10

-contains reflex centres that control functions such as breathing and heart rate

Question 11

brain functions- hypothalamus

Answer 11

-thermoregulation and osmoregulation
-coordinates autonomic nervous system
-involved in thirst, hunger etc

Question 12

sensory neuron structure

Answer 12

-cell body in centre
-synaptic bulbs at end to pass on impulses
-receptor e.g. pressure receptor at other end connected to dendrites
-direction of nerve impulse is from receptor end to bulb end

Question 13

relay neuron structure

Answer 13

-cell body in centre
-very short axon either side
-not myelinated
-no Schwann cells or nodes
-impulse travels from dendrites end to synaptic bulbs

Question 14

motor neuron structure

Answer 14

-cell body on end
-other end has synaptic bulbs attached to effector e.g. muscle
-dendrites coming off cell body
-myelinated axon
-nodes and Schwann cells

Question 15

myelination and its purpose

Answer 15

-means they are wrapped in a Schwann cell
-this cell forms a fatty layer
-protects nerve from damage
-speeds up transmission of impulse by stimulating it
-gaps between are nodes of ranvier

Question 16

what is resting potential?

Answer 16

-when the inside of the axon is negatively charged compared to the outside
-we describe the axon as polarised
-resting potential is around -70mV

Question 17

when does an action potential occur

Answer 17

-when a neuron sends information from its cell body down its axon

Question 18

stages of action potential

Answer 18

1.depolarisation- movement of Na+ ions into neuron reduces potential difference across the membrane +40mV
2.repolarisation- movement of K+ ions out of neuron reduces depolarisation
3.hyperpolarisation- K= channels stay open too long, gradually ion concs go back to resting

Question 19

the sodium potassium pump

Answer 19

-requires ATP
-3 Na+ ions move out for every 2K+ in
-ATPase in pump uses ATP to move ions

Question 20

how resting potential happens

Answer 20

1.Na ions are actively transported out by Na-K pump
2. K ions actively transported in by pump
3. active transport of Na is greater than K 3-2
4. Na will naturally diffuse back into axon and potassium out
5. however, most Na channels are closed and most K channels more permeable
6. so gradient maintained

Question 21

steps of AP in detail

Answer 21

-stimulus causes some Na gates to open so sodium ions diffuse in, they trigger depolarisation, becomes +
-as Na diffuses in, more Na channels open increasing diffusion (pos feedback)
-once around +40mV, sodium ion channels close and excess pumped out by Na K pump
-K channels open so they diffuse out of axon moving down conc gradient axon is repolarised
-outward diffusion of K ions causes overshoot, with inside being more neg that usual (hyper)
-gates on K channels close and once again Na pumped out and K in
-RP -70mV again

Question 22

refractory period

Answer 22

-recovery time of an axon
-neurons can generate nerve impulses at many frequencies, limited by;
1.absolute refractory period- neuron inexcitable
2.relative refractory period- less excitable than normal
-when line on graph lies flat

Question 23

absolute refractory period

Answer 23

-left part of graph before AP
-sodium channels completely blocked and RP has not been restored
-milliseconds
-second stimulus will not trigger second AP no matter how strong

Question 24

relative refractory period

Answer 24

-when potassium channels are open to repolarise the membrane
-normal RP cannot be restored until these are closed
-greater then normal stimulus required to initiate AP

Question 25

purpose of refractory periods

Answer 25

• ensures APs are only propagated in one direction
  -produces discrete impulses so Aps are separate
  -limits number of Aps

Question 26

transmission in unmyelinated axons

Answer 26

-current occurs in part of the neuron
-this is detected in an adjacent part of membrane
-causes voltage gated channels to open when threshold is reached
-nerve impulse is transmitted as self propagating wave of depolarisation

Question 27

propagation in myelinated axons

Answer 27

-myelin sheath acts as electrical insulator
-current can only be set up between adjacent nodes of ranvier
-more sodium channels are open at these nodes
-depolarisation leaps from one node to next (saltatory conduction)
-therefore nerve impulses can be transmitted very quickly and efficiently

Question 28

factors affecting nerve impulses- myelination

Answer 28

-only vertebrates have this
-increases speed
-100 times faster

Question 29

factors affecting nerve impulses- axon diameter

Answer 29

-wider axon can transmit impulses faster
-myelination means there is no need for wide axons
-therefore takes up less space

Question 30

factors affecting nerve impulses- temperature

Answer 30

-higher temp means faster conduction, within limits
-this is because propagation involves diffusion of ions and rate of diffusion increases with temperature
-therefore ions have more kinetic energy
-temp also effects enzymes involved in active trasnport to maintain RP
-at very high temps, they denature, disrupting nerve conduction

Question 31

events at a synapse

Answer 31

-Action potential depolarises the presynaptic neuron.
-Calcium channels open and calcium diffuses in.
-Synaptic vesicles move to and fuse with the pre-synaptic membrane.
-The neurotransmitter is released into the synaptic cleft.
-Neurotransmitter moves across cleft by diffusion.
-Neurotransmitter binds to specific protein receptors on the sodium channel on the post synaptic membrane..
-Sodium channels open and sodium diffuses in.
-This causes a change in the potential difference of the membrane and an excitatory post-synaptic potential (EPSP) to be set up.
-If there are a sufficient number of these EPSPs, the positive charge in the post-synaptic cell exceeds the threshold level and an action potential will occur.

Question 32

inhibitory post synaptic potential

Answer 32

-kind of synaptic potential that makes postsynaptic neuron less likely to generate AP
-different channels open in membrane allowing inward movement of neg ions
-makes it more neg than RP
-means AP less likely to occur

Question 33

synapse- breakdown of neurotransmitters

Answer 33

-broken down by hydrolytic enzymes
-they then move back across the cleft, back into synaptic knob and are recycled

Question 34

acetylcholine

Answer 34

-neurotransmitter found at majority of synapses
-it is broken down by an enzyme called acetylcholinesterase.
-acetyl and choline diffuse back across the cleft into presynaptic
-this allows neurotransmitter to be recycled

Question 35

2 types of synapses

Answer 35

1.adrenergic
-often found in sympathetic nervous system
-uses noradrenaline as neurotransmitter
2.cholinergic
-mostly found in parasympathetic
-only uses Acth

Question 36

specific drug examples need to know

Answer 36

-nicotine -cobra venom
-lidocaine

Question 37

effects of drugs- nicotine

Answer 37

-mimics effects of acetylcholine
-triggers dopamine release which can be associated with pleasure sensations
-triggers AP in post synaptic but receptors remain unresponsive for a while
-has stimulating effect at low doses but lethal in high doses

Question 38

effects of drugs- lidocaine

Answer 38

-used as local anaesthetic by dentists
-blocks voltage gated Na channels so preventing AP
-also prevents some heart arrhythmias so preventing early action potentials

Question 39

effects of drugs- cobra venom

Answer 39

-toxic and often fatal
-binds reversible to acetylcholine receptors, preventing an impulse
-can be used to relax trachea muscles in low doses
-means muscles are not stimulated to contract so person becomes paralysed

Question 40

function of eye parts- cilliary muscle

Answer 40

-pulls lens for focusing

Question 41

function of eye parts- cornea

Answer 41

-lets light in eye and begins focusing

Question 42

function of eye parts- iris

Answer 42

-controls amount of light entering eye

Question 43

function of eye parts- lens

Answer 43

• focuses light onto retina

Question 44

function of eye parts- optic nerve

Answer 44

-sends signals to brain

Question 45

function of eye parts-pupil

Answer 45

-lets light through to lens

Question 46

function of eye parts-retina

Answer 46

-light sensitive layer, sends messages to optic nerve

Question 47

function of eye parts- suspensory ligaments

Answer 47

-holds lens in plae

Question 48

transduction in the eye

Answer 48

-converts light into pattern of nerve impulses
-takes place in retina by layer of photosensitive cells at back of eye

Question 49

rod cells

Answer 49

-spread evenly across retina except fovea
-show black and white images
-cannot distinguish between different wavelengths of light
-detect light at very low intensity
-threshold must be detected before potential can occur
-generator potential is generated in bipolar cell
-multiple to one bipolar (retinal convergence), threshold more likely to be reached through summation

Question 50

rod cells- visual acuity

Answer 50

-cannot distinguish 2 close together dots
-because light received only generates one impulse
-

Question 51

rod cells in low light

Answer 51

-rhodopsin must be broken down to create generator potential
-low light intensity has enough energy to break this down

Question 52

cone cells

Answer 52

-tightly packed at fovea
-3 diff types for diff wavelengths
-own seperate bipolar neurons
-only respond to high light intensity as summation cannot occur
-brain can distinguish between separate light sources
-iodopsin requires higher light intensity to break down
-contain diff types od iodposin for diff light wavelengths

Question 53

the fovea

Answer 53

-part of the retina which light is focused on
-receives greatest intensity of light
-therefore cone cells found here

Question 54

how does rhodopsin work?

Answer 54

-Rhodopsin is formed from opsin and retinal.
-Retinal exists as 2 different isomers: cis-retinal & trans-retinal.
-In the dark all retinal is in the cis form.
-When a photon of light hits the rhodopsin, it converts from cis to trans form.
-This changes the shape of the retinal and puts strain on the bonding between opsin and retinal, breaking up the molecule.
-This is known as ‘bleaching’.

Question 55

bleaching

Answer 55

-Rod cells are usually quite permeable to sodium ions.
-When rhodopsin is bleached, this causes the -Na ion channels to close, making it less permeable to sodium.
-However, the sodium pump continues to work and so sodium ions are removed from the cell.
-This makes the inside of the rod cell more negative than normal.
-This hyperpolarisation is known as the ‘generator potential’.

Question 56

HR control by baroreceptors

Answer 56

-found in carotid arteries in neck and aorta, when exercise starts;
1.blood vessels dilate in response to adrenaline, bp falls
2.reduces stretch in baroreceptors
4.cardiac control centre sends messages along sympathetic nerve to stimulate heart rate and increase bp by vasoconstriction

Question 57

HR control by chemoreceptors

Answer 57

-found in walls of carotid arteries
-sensitive to CO2 levels which cause changes in pH
1.when blood has high CO2 conc, pH is lowered
2.they detect this and inc frequency of impulses to medulla
3.this increases frequency of impulses via sympathetic to SAN so hr increases
4.inc blood flow means more CO2 is removed from lungs

Question 58

HR control by hormones

Answer 58

-when stressed, sympathetic nerve stimulates adrenal medulla to release adrenaline
-binds to receptors on target organ, including SAN
-increases excitation and so increasing hr
-more oxygen and glucose are supplied to muscles for fight or flight

Question 59

cardiac output calculation

Answer 59

stroke volume* heart rate