9.2 The Nervous System Flashcards
CNS
Brain + spinal cord
PNS
Pairs of nerves which originate form spinal cord
What is PNS made up of
Autonomic NS - communication with internal organs + glands
Voluntary NS - communication with sense organs + voluntary muscles
What is the Autonomic NS made up of
Sympathetic NS - Produces noradrenaline at synapse/ speeds up
Parasympathetic NS - Produces acetylcholine at synapse/ slows down
What is voluntary NS made up of
Sensory Neurones
Motor Neurones
Brain
Hypothalamus
Cerebellum
Cerebrum
Medulla Oblongata
Hypothalamus
Hormone secretions
Thermoregulation
Osmoreguation
Cerebellum
Smooth movements
Balance Posture
Cerebrum
Voluntary Behaviour
Personality
Medulla Oblongata
Breathing
Heart Rate
Schwann cell
Forms a fatty layer arounnd the neurone
Nodes of Ranvier
Gaps between the Schwann cell
Function of myelin sheath
Protects the nerve from damage
Speeds up transmission
Types of neurones
Sensory
Motor
Relay
Sensory neurones
Transmits impulses from receptors to the CNS
Motor Neurones
Transmits impulses from CNS to muscles + glands
Relay Neurones
Transmits impulses from sensory to motor neurones
Reflex Arc Steps
1) Stimulus is detected by a receptor
2) SN sends impulses to the spinal cord
3) Impulses are passed on to a RN in the spinal cord
4) RN connects to the MN + passes the impulse on
5) MN carries impulse to the muscle
What is Resting State
Outside the membrane is +vely charged compared to the inside
Membrane becomes polarised
Resting state = -70mV
How is resting state achieved
Caused by the Na - K pump
pumps 3 Na ions out
for every 2 K ions pumped in
Active state
Depolarisation
Repolarisation
Hyperpolarisation
Refractory Period
What happens in depolarisation
Na channels open
Na ions move into axon
causes -ve feedback
What happens in repolarisation
Na channels close
K channels open
K ions move out of axon
What happens in hyperpolarisation
K channels stay open for too long
Charge goes below -70mV
What is the refractory period
The recovery time of an axon
What happens in the absolute refractory period
Na channels are blocked
What happens in the relative refractory period
K channel is open to repolarise
neuron is less excitable than normal
What happens in the synapse to generate an EPSP
1) AP depolarises the presynaptic neuron
2) Ca channels open + Ca ions diffuse in
3) Synaptic vesicles move to + fuse with the presynaptic membrane
4) A neurotransmitter is released into the synaptic cleft
5) The neurotransmitter moves across the cleft by diffusion
6) Neurotransmitter binds to specific protein receptors on the postsynaptic membrane
7) Na channels open + Na ions diffuse in
8) This causes a change in the pd of the membrane + an EPSP to be generated
What is an IPSP
Makes a postsynaptic neuron less likely to generate an AP
Allows the movement of -ve ions into the membrane
makes the postsynaptic neuron more -ve than normal RP
AP is less likely to occur
How is acetylcholine recycled
After it attaches to the receptors on the Na channels
it is broken down by acetylcholinesterase
this hydrolyses acetylcholine into acetate + choline
they diffuse back across the cleft into the presynaptic neuron to be recycled
How does nicotine affect the synapse before stimulation
Binds to a type of acetylcholine receptor on the postsynaptic membrane
This initiates an AP
How does nicotine affect the synapse after stimulation
Causes receptors to be unresponsive to other stimulation
triggers a release of dopamine
this increases heart rate + blood pressure
How does lidocaine affect the synapse
Blocks gated Na channels
prevents an influx of Na ions in the postsynaptic neuron
prevents an AP from being generated
Uses of lidocaine
Local anaesthetic
Regulate heart beat
How does cobra venom affect the synapse
Binds to acetylcholine receptors on the postsynaptic membrane
prevents an influx of Na ions + generation of an AP
Uses of Cobra venom
A muscle relaxant during asthma attacks
Cilary muscles
Pulls the lens for focusing
Cornea
Lets light into eye + begins focusing
Iris
Controls the amount of light entering he eye
Lens
Focuses light onto the retina
Optic Nerve
Sends signals to the brain
Pupil
Lets light through to the brain
Retina
Sends signals to the optic nerve
Suspensory Ligaments
Holds the lens in place
What is Transduction
Takes place in the retina
Converts light into a pattern of nerve impulses
Rod cells
Spread across the retina except at fovea
Images in black + white
More of them than cone cells
Used to detect light at low intensities
Summation in Rod Cells
Multiple rod cells are connected to 1 bipolar neuron
much more likely that the threshold value will be reached by summation
Low light in Rod cells
Rhodopsin is broken down to create a generator potential
low light intensities have enough energy to break it down
rod cells can work in low light
Visual Acuity in Rod Cells
Rod cells can’t distinguish 2 dots close together
light received by different rod cells only generates 1 impulse
brain can’t distinguish between separate sources of light
Cone Cells
Found at fovea
Connected to their own separate bipolar neurone
Can only respond to high intensity light
summation doesn’t occur
Brain can distinguish between separate sources of light
high visual acuity
Fovea
part of retina where light is focused on
It receives the highest intensity of light
Rhodopsin
Formed from opsin + retinal
retinal exists as trans + cisretinal
retinal in the dark
All retinal is in the cis form
retinal in the light
All retinal is in the trans form
Change of shape puts a strain on bonding between opsin +retinal
breaks the molecule - known as bleaching
Bleaching
When rhodopsin is bleached
Na channels close making it less permeable to Na
Na pump still works
Na ions are removed from the cell
inside the rod cell is more -ve than normal
this hyperpolarisaion is known as the generator potential
Chemoreceptors
Control Blood CO2
High CO2 = low pH of blood
Low blood CO2 (High pH)
Receptors send impulse to medulla
Medulla sends impulses along the parasympathetic NS
This secretes acetylcholine which binds to receptors on SAN
Heart rate decreases
High blood CO2 (Low pH)
Receptors send impulse to medulla
Medulla sends impulses along the sympathetic NS
This secretes noradrenaline which binds to receptors on SAN
Heart rate increases
Baroreceptors
Control blood pressure
High blood pressure
Receptors send impulse to medulla
Medulla sends impulses along the parasympathetic NS
This secretes acetylcholine which binds to receptors on SAN
Heart rate decreases
Low blood pressure
Receptors send impulse to medulla
Medulla sends impulses along the sympathetic NS
This secretes noradrenaline which binds to receptors on SAN
Heart rate increases
Hormones
When stressed the sympathetic nerves stimulate the adrenal medulla to release adrenaline
this binds to receptors on SAN
this increase the frequency of excitation
this increases the heart rate
so more oxygen + glucose are supplied to the muscle
