The Nervous System Flashcards
What are the two systems that make up the nervous system?
What do each consist of?
Central nervous system:
- Brain
- Spinal cord
Peripheral nervous system
- Sensory nerves
- Motor nerves
What systems make up the peripheral nervous system?
Autonomic nervous system
- Involuntary
- Stimulates smooth muscle, cardiac muscle and glands
Somatic nervous system
- Voluntary
- Stimulates skeletal muscle
What two systems can the autonomic nervous system be divided into?
Sympathetic nervous system
-‘fight or flight’ responses
Parasympathetic nervous system
-‘rest and digest’ responses
When would a gland be stimulated?
- When there is a change in the concentration of a specific substance
- If they receive an electrical impulse
What do hormones bind to?
Target cells
What is a nervous system receptor like in the resting state?
- Difference in charge between the inside and outside of the cell
- This means there is a voltage across the membrane
- The membrane is said to be polarised
What is potential difference?
The voltage across the membrane
What happens in a receptor when a stimulus is detected?
- Permeability of the cell membrane to ions changes
- This stops the movement of ions in or out of the cell
- This causes a change in the potential difference, which, if large enough, will trigger an action potential
What is an action potential?
An electrical impulse along a neurone
What pigment do rod cells contain?
Rhodopsin
What is rhodopsin made from?
Retinal and opsin
What happens when rod cells are stimulated?
- Light energy causes rhodopsin to break down into retinal and opsin in a process called bleaching
- The bleaching of rhodopsin causes the sodium ion channels to close
- Sodium ions are moved out of the cell via active transport but can’t diffuse back in
- Na+ ions build up outside the cell making the inside of the membrane more negative than the outside
- The cell membrane is hyperpolarised
- This stops the cell releasing neurotransmitters which means there is no inhibition of the bipolar molecule
- The bipolar molecule depolarises which causes a change in potential difference
- If the change in potential difference is large enough, an action potential is transmitted to the brain via the optic nerve
What do dendrites do?
Carry nerve impulses towards the cell body of a neuron
What do axons do?
Carry nerve impulses away from the cell body of a neuron
Describe the structure of a motor neuron
- Many short dendrites
- One long axon
Describe the structure of a sensory neuron
- One long dendrite
- One short axon
Describe the structure of a relay neuron
- Many short dendrites
- Many short axons
What is the voltage across the membrane when it’s at rest?
-70 mV
How is the resting potential created and maintained?
- Sodium-potassium pumps move Na+ ions out of the neuron and K+ ions into the neuron
- This creates a sodium ion electrochemical gradient as the sodium ions can’t re-enter the neuron
- Membrane is permeable to K+ ions so they diffuse back out of the neuron through potassium ion channels
Describe the sequence of events that make up an action potential
Stimulus
- Neuron cell membrane becomes excited causing sodium ion channels to open
- The membrane becomes more permeable to sodium, so Na+ ions diffuse into the neuron down the sodium ion electrochemical gradient
- This makes the inside of the neuron less negative
Depolarisation
- If the potential difference reaches the threshold, around -55 mV, more sodium ion channels open
- This causes more Na+ ions to diffuse into the neuron
Repolarisation
- When the potential difference is around +30 mV, the sodium ion channels close and the potassium ion channels open
- K+ ions diffuse out of the neuron down the potassium ion concentration gradient
- Membrane starts to return to its resting potential
Hyperpolarisation
- Potassium ion channels are slow to close so too much K+ ions diffuse out of the neuron
- The potential difference becomes more negative than the resting potential (less than -70 mV)
Resting potential
- The ion channels are reset
- The sodium-potassium pump returns the membrane to its resting state
What happens in the refractory period?
- The sodium and potassium ion channels are recovering and can’t open again for a while
- Therefore the neuron cell membrane can’t become excited again straight away
How does the action potential move along a neuron?
In a wave of depolarisation
Compare nerve impulses and hormones
Nervous communication:
- Uses electrical impulses
- Fast response
- Localised response
- Short acting
Hormonal communication:
- Uses chemical messengers in the blood
- Slower response
- Widespread response
- Longer acting
Describe the sequence of events from the action potential arrival at the presynaptic membrane of a synapse to the generation of a new action potential at the postsynaptic membrane (6)
- Action potential arriving at the presynaptic membrane stimulates voltage gated Ca2+ ion channels to open
- Ca2+ ions diffuse into the neuron
- This causes synaptic vesicles, containing neurotransmitter, to move the to the presynaptic membrane
- The vesicles fuse with the membrane and release the neurotransmitter into the synaptic cleft via exocytosis
- The neurotransmitter diffuses across the synaptic cleft and binds to specific receptors on the postsynaptic membrane
- This causes Ca2+ ion channels to open in the postsynaptic membrane
- There is an influx of Ca2+ ions which causes depolarisation
- This triggers a new action potential to be generated at the postsynaptic membrane
What is a reflex?
A rapid, involuntary response to a stimulus
Describe the reflex arc
- Receptors detect a stimuli and generate an impulse
- Sensory neurons conduct the impulse to the centre nervous system (CNS) by entering the spine through the dorsal route
- Sensory neurone forms a synapse with a relay neurone
- Relay neurone forms a synapse with a motor neurone
- Motor neurone carries the impulse out of the spinal cord through the ventral route to effectors
- Effectors produce a response
What is the advantage of the reflex pathways?
- They produce rapid responses
- Important for survival
Describe the nervous pathways involved in the increase of heart rate when starting to exercise
- Cardiovascular control centre in brain detects increase in CO2 and lactate in the blood
- Sensory receptors in muscles send impulses to cardiovascular control centre along sensory neurons
- Impulses sent from cardiovascular control centre to SAN via sympathetic nerve
- Impulses from SAN to heart muscles increases in frequency, causing heart rate to rise
Where are dendrons found?
Before the cell body in a sensory neuron
Where are axons found in neurons?
- After the cell body
- Carrying the impulse away
Where are the cell bodies of sensory neurons found?
-In the Ganglia
What is the Ganglia? Where is it?
- The place where cell bodies of sensory neurons are found
- Near the spinal cord
What are on the ends of sensory neurons?
Dendrites
Compare and contrast the structure of motor and sensory neurones
- Both have a long nerve fibre
- In a motor neurone this nerve fibre is an axon
- In a sensory neurone it is a dendron
- Sensory neurones have their cell body in the middle of neurone while motor neurones have the cell body at the start of the neurone
Explain how the parasympathetic and sympathetic branches of the autonomic nervous system work antagonistically
- Antagonistic means working in opposition to each other
- Changes made by the sympathetic system can be reversed by the parasympathetic system
- They allow changes to be made, for example when regulating heart beat
What is the motor-end plate?
Where a neurone and muscle meet
What are Schwann cells? What do they do?
-Forms a myelin sheath around an axon
Where are nodes of Ranvier found?
In between Schwann cells on the myelin sheath
How does a myelin sheath increase the speed of impulses?
- Acts as an electrical insulator
- Ensures depolarisation only happens at the nodes of Ranvier
- Impulse travels from node to node, decreasing the points at which depolarisation can take place along an axon
What is it called when an impulse is insulated by a myelin sheath?
Saltatory conduction
Why is an impulse along a non-myelinated neurone slower than an impulse along a myelinated one?
- In a non-myelinated neurone the impulse travels as a wave along the whole length of the axon membrane
- In a myelinated neurone, the impulse can only travel from node to node, reducing the amount of axon membrane that the impulse travels along
Why is the refractory period important?
- In the refractory period, an impulse cannot travel along a neuron until the resting potential has been reached
- This keeps the wave of depolarisation moving forward as the membranes behind the impulse cannot carry the impulse as they have not reached the resting potential yet
