The Nervous System Flashcards
What is a dendrite?
To receive impulses
What is a synaptic bulb?
To pass on impulses
What is myelination?
-Most neurons in the spinal cord are myelinated
-They are wrapped in a specialised cell called the Schwann cell
-This cell forms a fatty layer around the neuron (myelin sheath)
-This protects the nerve from damage
-Speeds up the transmission of the impulse by insulating it
What are the general events of a reflex arc?
- Stimulus
- Receptors
- Sensory neurone passes impulses to spinal cord
- Co ordinator links sensory neurone to motor neurone
- Motor neurone carries impulses from spinal cord
- Effector (a muscle or gland)
- Response
What makes up the central nervous system (CNS)?
The brain and spinal cord
What makes up the peripheral nervous system (PNS)?
Pairs of nerves which originate from either the brain or spinal cord
-Made up of sensory or motor neurons
What can the PNS be split into?
The automatic nervous system and the somatic/voluntary nervous system
What is the automatic nervous system?
Communicates with internal organs and glands
What is the somatic/voluntary nervous system?
Communicates with sense organs and voluntary muscles
What can the automatic nervous system be split into?
-Sympathetic = positive stimulation/speeds up activity
-Parasympathetic = inhibitor/slows down activity
What does a sensory neuron do?
Carries impulses from the receptor toward the CNS
What does a motor neuron do?
Carries nerve impulses away from the CNS to effectors
What does the sympathetic nervous system do?
-Produces noradrenaline (a type of neurotransmitter) at the synapses
-Often involved in fight or flight response
-Activated in times of stress or activity
What are some examples of what the sympathetic nervous system does?
-Dilates pupils
-Dilates bronchi
-Accelerates heartbeat
-Stimulates production of adrenaline and noradrenaline
-Inhibits flow of saliva
-Stimulates conversion of glycogen to glucose
What does the parasympathetic nervous system do?
-Slower, more inhibitor effect on organ systems
-Produces acetylcholine (Ach, a type of neurotransmitter)
-Maintains normal functioning of the body (rest and digest)
What are some examples of what the parasympathetic nervous system does?
-Constricts pupil
-Constricts bronchi
-Stimulates release of bile
-Slows heartbeat
-Stimulates flow of saliva and tears
What does the cerebellum do?
Controls balance and co ordination of movement
What does the medulla oblongata do?
Controls breathing and heart rate (autonomic functions)
What does the hypothalamus do?
Used for temperature regulation and osmoregulation
What does the cerebrum do?
Initiates movement, controls sight and speech
What does the node of Ranvier do?
Allows impulse to jump from node to node
What is the resting state?
The neuron isn’t being stimulated
What happens in the resting state?
-Outside the membrane is positively charged compared to the inside
-Membrane is polarised
-Voltage across the membrane when at rest is called the resting potential
What is the resting potential?
(-70mV) and is the difference between the inside and outside of axon membrane
What is the sodium potassium pump?
-Requires energy (active transport)
-3 sodium ions (Na+) are moved out the membrane
-2 potassium ions (K+) are moved in
What are the steps of action potential?
-Resting potential (-70mV)
-Depolarisation (+40mV)
-Repolarisation
-Refractory period
-Hyperpolarisation
What is depolarisation?
Movement of sodium ions into the neuron reduces the potential difference across the membrane
(the sodium channels open so sodium ions move into the axon and increase voltage to +40mV)
What is re-polarisation?
Movement of potassium ions out of the neuron to reverse the depolarisation
(potassium ions open and potassium ions move out)
What is hyperpolerisation?
Potassium channels stay open a bit too long
What are the voltages of action potential?
-70mV, -55mV, +40mV
(stimulus must be at least -55mV)
What is depolarisation an example of?
Positive feedback (when one sodium channel opens it makes more open)
What is a synapse?
A gap between two neurones
What are the events at a synapse?
-Action potential depolarised the presynaptic neurone
-Calcium channels open and calcium diffuses in
-Synaptic vesicles move and fuse with presynaptic membrane
-The neurotransmitter is released into the synaptic cleft
-Neurotransmitter moves across cleft by diffusion
-Neurotransmitter binds to specific protein receptors on the sodium channels on the post synaptic membrane
-Sodium channels open and sodium diffuses in
-Causes a change in the potential difference of the membrane and an excitatory post synaptic potential (EPSP)
What is the inhibitory post synaptic potential (IPSP)
-A synaptic potential that makes a post synaptic neurone less likely to generate an action potential
-Different ion channels open in the membrane, allowing inward movement of negative ions
-Makes the post synaptic cell more negative than normal resting potential
-This means an action potential is less likely to occur
How are neurotransmitters broken down?
-Broken down by hydrolytic enzymes
-Move back across the cleft into the synaptic knob to be recycled
What the two types of synapses?
-Adrenergic
-Cholinergic
What is the acetylcholine example?
-Attaches to receptors on the sodium channels and is broken down by the enzyme acetylcholinease
-It hydrolyses acetylcholine into separate acetate and choline
-The acetyl and choline diffuse back across the cleft into the presynaptic neuron
-This allows the neurotransmitter to be recycled
What is an adrenergic synapse?
-Found in the sympathetic nervous system
-Uses noradrenaline and adrenaline as a neurotransmitter
What is a cholinergic synapse?
-Found in the parasympathetic nervous system
-Uses acetylcholine as a neurotransmitter
What is the general effect of drugs increasing the response at a synapse?
-Increases the amount of neurotransmitter synthesised
-Increases the release of neurotransmitter from the vesicles at the presynaptic membrane
-Binds to post synaptic receptors and activates them or increases the effect or the normal neurotransmitter
-Prevents break down of neurotransmitter
What is the general effect of drugs decreasing the response at a synapse?
-Blocks the synthesis of neurotransmitter
-Causes neurotransmitter to leak from vesicles and be destroyed by enzymes
-Prevents the release of neurotransmitter from vesicles
-Blocks receptors and prevents neurotransmitter binding
What does nicotine do to the synapse?
-Mimics the effect of acetylcholine
-Triggers the release of dopamine (pleasure sensations)
-Triggers an action potential in post synaptic neurone
-Low doses = stimulating effect, high doses = lethal
What does lidocaine do to the synapses?
-Blocks voltage gated sodium channels
-Prevent heart arrhythmias by preventing early or extra action potentials
What do the ciliary muscles do?
Pulls lens for focusing
What does the cornea do?
Lets light into the eye and begins focusing
What does the iris do?
Controls the amount of light entering the eye
What does the lens do?
Focuses light onto the retina
What does the optic nerve do?
Sends signal to the brain
What does the pupil do?
Lets light through the lens
What does the retina do?
Light sensitive layer and sends signal to the optic nerve
What does the suspensory ligament do?
Holds lens in place
What are the rod and cone cells?
Photo-receptors (detect light)
What is transduction in the eye?
-Converts light into pattern of nerve impulses
-Takes place in the retina by photosensitive cells
-Rods and cone cells are attached to nerves
What does the rod cell do?
-Provide images in black and white (greyscale)
-Can’t distinguish between different wavelengths of light
-Used to detect light at a low intensity
-A certain threshold must be detected before a generator potential can occur
How do rod cells work?
-A pigment called rhodopsin must be broken down to create a generator potential
-Low light intensity has enough energy to break this down
What is the link between rod cells and visual activity?
-Rod cells cannot distinguish two dots close together
-Light received by different rod cells will only generate one impulse
-So the brain cannot distinguish between separate sources of light
What does the cone cell do?
-Found tightly packed at the fovea
-There are three types of cone cells all responding to different wavelengths of light
-They are connected to separate bipolar neurones
-Only respond to high light intensities
-The brain can distinguish between different separate sources of light
How do cone cells work?
-A pigment called iodospin requires a higher intensity of light to break it down
-Cone cells contain different types of iodospin which is why they respond to different wavelengths of light
What are the three types of cone cells?
-Red
-Green
-Blue
What is the fovea?
-The part of the retina that light is focused on
-Receives the greatest intensity of light
-Cone cells are found here
-Rod cells are found at the edges of the fovea where light intensity is lower
How does rhodopsin work?
-Formed from opsin and retinal
-Retinal can be: cis retinal or trans retinal
-In the dark retinal is in its cis form
-When light hits the the rhodopsin it converts to the trans form
What is bleaching?
-When light hits the rhodopsin the shape of the retina and puts strain on the bonding between opsin and retinal
-This breaks up the molecule
What happens in bleaching?
-When rhodopsin is bleached it causes the sodium ion channels to close making it less permeable to sodium
-The sodium pump continues to work so sodium ions are removed from the cell
-This makes the inside of the rod cell more negative
-This is a type of hyperpotential called the generator potential
How does the generator potential happen in the rod cell?
-The generator potential is generated in the bipolar cell connected to the rod cell
-There are multiple rods connected to one bipolar neuron so it is more likely that the threshold value will be reached by summation
