Nervous system Flashcards
structure of NS
CNS
- brain + spinal cord
PNS
- spinal + cranial nerves
function of NS
mainatain homeostasis
receive, coordinate and respond
divisions of the NS
function of PNS
Caries sensory information from body to CNS vis sensory nerves
Carries motor information from CNS to body via motor nerves
structure of PNS
cranial and spinal nerves
Autonomic NS
controls involuntary actions
Somatic NS
Controls voluntary skeletal movements
Sympathetic NS
prepares for flight or fight responses
Parasympathetic NS
prepares the body for rest and repair by returning body to homeostasis after threat has been subsided
what are glial cells?
- provide structural support, insulation, and nutrients for neurons
- non conductive –> do not transmit electrical impulses
examples of glial cells
- Schwann cells
- Oligodendrocytes
- Microglial cells
- Ependymal cells
- Astrocytes
neuron
nerve cell that transmits electrical impulse signals for communication
properties of neurons
- excitability
- conductivity
- synaptic transmission
- plasticity
excitablility
respond to stimuli and generate action potentials in response to stimuli
conductivity
transmit electrical impulse over long distances (dendrite —> axon terminal)
synaptic transmission
neurotransmitters relay signals from one neuron to another
plasticity
ability to change and adapt in response to experience, learning and memory formation
What is A?
Dendrite
what is B?
cell body
what is C?
nucleus
what is D?
Schwann cell
what is E?
myelin sheath
what is F?
node of Ranvier
what is G?
axon terminal
what is H?
axon
What is the function of the nucleus of a neuron?
To provide DNA of cell
What is the function of a dendrite?
To RECEIVE information FROM other neurons and carry information TOWARDS the cell body
What is the function of the axon?
To carry information FROM the cell body TO other neurons
What is the function of an axon terminal?
To stores and secretes neurotransmitters which carry chemical messages to other neurons/cells
What is the function of the myelin sheath?
To insulate axon which increases the rate at which nerve impulses are conducted along the axon
What is the function of the nodes of Ranvier?
Gaps in the myelin sheath that allow for depolarisation of nerve impulse
axon hillock
site where the action potential is
generated
4 stages of an action potential
resting, threshold, depolarisation, repolarisation
2 types of nervous tissue
neurons and neuroglia
3 types of neurons
sensory, motor, interneurons
synapse
The connection between adjacent neurons.
2 types of neural messages
within neurons: electrical (action potential)
between neurons: chemical (neurotransmitters)
neurotransmitter
The chemical secreted into the gap between neurons at a synapse.
Nerve impulse
The high speed signals that pass along the axons of nerve cells.
multipolar
bipolar
unipolar
sensory (afferent) neurons
conduct impulses from sensory receptors into CNS
motor (efferent) neurons
conduct impulses away from the CNS to the effector organs (muscles and glands)
interneurons
lie between sensory and motor neurons or other interneurons
Resting membrane potential
- neuron maintains -70mV inside the cell
- high [K+] inside
- high [Na+] outside
- at rest, more permeable to K+ through leak channels
Sodium potassium pump: process
(1) Initially there is a lower concentration of Na+ ions outside versus those inside the cell.
(2) Three cytoplasmic sodium (Na+) ions bind to the pump.
(3) This promotes hydrolysis of ATP into ADP, releasing energy.
(4) The Na+ / K+ pump changes shape within the membrane and releases Na+ outside of the cell.
(5) The new shape of the channel binds two potassium ions.
(6) This triggers release of phosphate and the dephosphorylated pump resumes its original shape.
(7) K+ is released inside the cell.
Action potential
Rapid change in the permeability of the neuronal membrane to Na+ and K+
Threshold initiation
Signals from the dendrites and cell body reach the axon hillock.
As the axon hillock depolarises, voltage-gated channels for sodium open rapidly, increasing membrane permeability to sodium.
Sodium diffuses down its concentration gradient into the cell.
If the stimulus at the axon hillock is great enough, the neuron depolarises by about 15 mV to a point called ‘threshold’ (-55 mV).
At threshold, an action potential is generated.
Depolarisation
More sodium voltage-gated channels open.
This causes more sodium to flow into the cell, which in turn causes the cell to depolarise further and opens more voltage-gated sodium channels.
This positive feedback loop produces the rising phase of the action potential.
This ends with the inactivation of the Na+ voltage-gated channels and the opening of K+ voltage-gated channels.
Repolarisation
Potassium diffuses out of the cell as the potassium voltage-gated channels open.
With less sodium moving into the cell and more potassium moving out of the cell, the membrane potential becomes more negative, moving back towards the resting value.
Repolarisation restores the electrical
balance.
Hyperpolarisation
Excessive potassium continues to diffuse out of the cell, causing the membrane potential to become more negative than the resting membrane potential.
All the potassium channels are closed and the sodium-potassium pump redistributes the ions to their original, resting state levels.
Absolute refractory period
Occurs after the generation of an action potential and sodium voltage gated channels are open:
- Neuron cannot generate another action potential
- All Sodium channels are inactive regardless of stimulus
- Potassium channels are open allowing diffusion of potassium
out of the cell - Can only go in the forward direction
Relative refractory period
Occurs after the absolute refractory period:
- Cell can generate action potential but only if it is depolarised to a value more positive than normal threshold
- Can occur since some sodium channels are still inactive but others have reset and returned to their resting state
- Some potassium channels are still open
How does the central nervous system tell the difference between a weak stimulus and a strong one?
How does the central nervous system control different strengths of muscle contraction?
Neurons code the intensity of information by the frequency of action potentials.
Conduction velocity
· the speed that an action potential is propagated along an axon
Fast:
· essential neural pathways
· Reflexes
Slow
· Serve internal organs
. Digestive tract, glands and blood vessels
What 2 factors effect conduction velocity?
Axon Diameter –> longer axons conduct more rapidly b/c offer less resistance to flow of local current, bringing adjacent areas of the membrane to threshold quicker
Myelination –> insulation: proventing almost allleakage of the charge from the axon and allowing the membrane potentials to change more rapidly
SALTATORY PROPAGATION
- Conduction within a myelinated axon.
- Jump between nodes.
CONTINUOUS PROPAGATION
- Conduction within an unmyelinated axon.
- Charge leaks through channels
- Separate opening of voltage gated channels = slow.
SYNAPTIC TRANSMISSION
- AP arrives at axon terminals.
- Voltage gates calcium channels open and calcium enters the axon terminal.
- Calcium causes the vesicles to migrate towards presynaptic membrane, which fuse with membrane.
- Diffuse across synaptic cleft.
- Binds to receptors, chemically gated channels.
- Ion channles open to postsynaptic membrane.
- Potential of postsynaptic membrane changes.
- If enough excitatory – AP GENERATES.
NT effects are terminated by
- Reuptake - NT’s re-enter presynaptic cell to be reused.
- Degradation - enzymes breakdown NT into a substance that cant be received by post synaptic
receptors. - Diffuse away from the synapse.
An axon is connected to the neuron cell body at the
axon hillock
Ion channels that are always open are called
leak channels
Excitatory Postsynaptic Potential (EPSP)
Excitatory ion channels are permeable to sodium and potassium
- More sodium moves into the cell, than potassium moves out of the cell.
- Membrane becomes more positive, stimulating depolarisation of the membrane
Inhibitory Postsynaptic Potential (IPSP)
Involve inhibitory ion channels that are permeable to chloride and potassium ions
- Chloride ion moves into the cell whilst potassium moves out
- Inside of cell becomes more negative causing hyperpolarisation
- Effect makes it more difficult for the cell membrane potential to reach threshold
- Makes it less likely for an action potential to be generated
