Chapter 13 The Nervous System Flashcards
What is homeostasis?
Maintaining a stable equilibrium of the conditions within the body, in spite of external changes
Why is coordination needed?
Few body systems work in isolation
Each system is specialised for one function, so coordination ended for cell and system to operate efficiently.
What is cell signalling?
Communication at a cellular level
Cells secreting chemicals such as hormones or neurotransmitters, to elicit a response of another cell
What is the general pathway of a nervous system response?
Stimulus- Sensory neurone - Spinal Cord - Brain - Spinal Cord - Motor neurone - effector
What are neurones?
Specialised nerve cells that transmit electrical impulses around the body
What are the structural differences between a motor neurone and sensory neurone?
Motor neurones have the cell body at the start of the neurone, and they do not have a dendron, only an axon and dendrites
Sensory neurones have the cell body in the middle of the neurone, contain 1 axon and 1 dendron, and many dendrites/ axon terminals
Both usually have myelin sheath and nodes of ranvier
What is the structure of a relay neurone?
A large cell body with many dendrons and dendrites, and 1 short axon and axon terminals
What is the myelin sheath and what is its function?
Schwann cells wrapped along the axon, more than 20 times, producing thick layers of phospholipid bilayer
An insulating layer, meaning ion movement can only occur at the nodes of ranvier, increasing the speed of impulse transmission and reducing the energy demands as less sodium potassium pumps are needed
What is the role of a sensory receptor? What is a transducer?
Acts as a transducer, converting a certain type of stimulus into electrical impulses,
Transducer- converts one form of energy into another
What are the different types of receptors?
Mechano
Chemo
Thermo
Photo
What is the structure of the Pacinian Corpuscle?
Neurone ending covered into layers of connective tissue, with viscous gel in between
Capsule on the outside
Blood capillary inside
Contain stretch mediated sodium channels
How does the Pacinian Corpuscle transfer pressure to an electrical impulse?
1) Normally, the stretch-mediated channels are closed, they are too narrow to allow Na+ through at resting potential
2) When pressure applied, the shape of the corpuscle changes. The deformation allows the sodium channels to wides, allowing Na+ to diffuse in.
3) Na+ increases potential difference, causes depolarisation of the membrane. This creates a generator potential, which can be propagated into an action potential along the axon.
How is the resting potential of a cell membrane established?
Sodium potassium pump- 3Na+ actively pumped out and 2K+ actively pumped in
Voltage gated Na+ channels closed, membrane less permeable to Na+ movement
Potassium channels shut, but leaky, so so K+ continues to diffuse out
So more positive outside than in, -70mV resting, electrochemical gradient
What is an action potential? What is a nerve impulse?
Action potential- Change in potential difference across the neurone membrane of the axon when stimulated
Nerve Impulse- Action potential that starts at one end and is propagated along the axon to the other end
What is the process of an action potential?
1) The stimulus (normally Na+) cause some voltage-gated Na+ channels to open, increasing the membranes permeability, and so Na+ diffuse making the membrane less negative
2) When the threshold of -55mV is reached, more Na+ channels open, causing a rapid increase in membrane potential, to +40mV as Na+ keeps diffusing in
3) At 40mV, the voltage gated Na+ channels shut, and K+ channels open. K+ rapidly diffuse out, causing the membrane potential to fall to below the resting
4) In this state of hyperpolarisation, the sodium potassium pump reestablishes the resting potential. The neurone enters its refractory period
How is the action potential propagated?
Depolarisation of the axon membrane acts as the stimulus for voltage gated Na+ channels to open slightly further down the axon
This will cause depolarisation along the axon and thus propagate as an impulse
Na+ diffuse down the axon due to the electrochemical gradient, this is more specifically what acts as the stimulus
How do refractory periods occur?
Hyperpolarisation occurs in the membrane before the one being stimulated
This means it cannot be excited as the Na+ channels will not open
What are the benefits of neurones having refractory periods?
It prevents backward propagation- unidirectional
It enables discrete impulses so they do not overlap
What is saltatory conduction?
Action potentials jump between the nodes of Ranvier
The myelin sheath is impermeable to ion movement
What are the benefits to saltatory conduction?
There are longer localised circuits
This speeds up transmission as less Na+ channel need to open/ close
And less energy is needed by having fewer sodium potassium pumps
Prevents depolarisation across the whole length of the axon
What factors affect the speed of impulse transmission?
Axon diameter- larger, faster, as less resistance to the flow of ions
Temperature- higher, faster diffusion of ions, until too high and sodium/potassium pumps denature
Presence of myelin sheath
How does the size of stimulus affect action potentials?
All or nothing response - as long as the threshold value is exceeded, an action potential of the same size is triggered
However, larger stimuli increase the rate/frequency action potentials stimulated
What are the components of a synapse? What is the gap size?
Synaptic cleft- gap between
Synaptic knob- swollen end of presynaptic
Neurotransmitter
20-30nm
What are the two types of neurotransmitter, give an example?
Excitatory- results in depolarisation of the post synaptic neurone , e.g Acetylcholine
Inhibitory- results in hyper polarisation of the post synaptic neurone, effectively refractory period eg GABA, Gamma Amino Butyric Acid
