Biology SL chapter 6.5 (Nerves, hormones and homeostasis)

Structure of the nervous system.
Central nervous system: brain and spinal cord. Peripheral nervous system: peripheral nerves which links CNS to the body's receptors and effectors.
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State the parts of a motor neuron
Nucleus, dendrite, Soma (cell body), axon (covered in a myelin sheath which is made from schwann cells), nodes of ranvier and motor end plate
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Three types of neurons in nervous system
Sensory neurons: nerve impulses from receptors to CNS (afferent pathway). Relay neurons: impulses within CNS. Motor neurons: impulses from CNS to effects (efferent pathway)
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Stimulus-response pathway
Stimulus -> receptor -> sensory neuron -> CNS -> relay neuron -> CNS -> motor neuron -> effector -> response
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Define resting potential
The charge difference across the membrane when a neuron is not firing (-70 mV), as maintained by the sodium-potassium pump
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Define action potential
The charge difference across the membrane when a neuron is firing
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Define depolarisation
The change from a negative resting potential to a positive action potential (caused by opening of sodium channels)
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Define repolarisaiton
The change from a positive action potential back to a negative resting potential (caused by opening of potassium channels)
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Generating resting potential
Sodium-potassium pump maintains electrochemical gradient of resting potential. Is a transmembrane protein that uses active transport to exchange Na and K across membrane. 3Na out per 2K in. Makes neuron negatively charged compared to outside
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Transmission of action potential pt1
Na and K channels are voltage gated, meaning they open/close depending on voltage in membrane. In response to signal, sodium channels open and sodium enters neuron. This causes membrane to become positive.
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Transmission of action potential pt2
If sufficient change is achieved (threshold potential), adjacent sodium gates open, generating a wave of action potential, which spreads down axon.
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Regaining resting potential (refractory period)
The electrical charge also activates potassium channels, causing K to exist the neuron. This causes membrane potential to be negative again (repolarisation). before neuron can fire again, original levels of Na/K must be achieved by the pump.
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Synaptic transfer
1. Action potential reaches axon terminal. 2. Calcium channels open. 3. Ca ions cause vesicles to release neurotransmitter. 4. neurotransmitter crosses synapse. 5. neurotransmitter binds to neuroreceptors. 6. triggers signal in post-synaptic neuron.
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What is the endocrine system?
Edocrine gland is a ductless gland in the body that manufactures chemical messengers called hormones and secretes them directly into blood.Hormones act on distant sites (target cells) to control activities such as growth and sex development
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What is homeostasis?
The tendency of an organism or cell to maintain constant internal environment within certain limits, such as body temperature, blood pH, co2 and o2 concentration, blood glucose and water balance.
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Negative feedback loop
Stimulus - >change detected -> receptor -> input sent via afferent pathway -> control centre (hypothalamus) ->output via efferent pathway -> effector -> response opposes change -> balance restored
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Explain the control of body temperature (when temperature rises)
Vasodilation: skin arterioles dilate, bringing blood closer to body surface and allowing for heat transfer (convective cooling). Sweating: sweat glands release sweat, which is evaporated, removing heat from body (evaporative cooling)
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Explain the control of body temperature (when temperature drops)
Vasoconstriction: skin arterioles constrict, moving blood away from body surface, retaining heat. Shivering: muscles shake in small movements, expending heat through cell respiration (which produces heat as by-product)
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Thermoregulation by the nervous system
Increase in temp -> detected by thermorceptors in skin+hypothalamus -> cooling mechanisms (sweating, vasodilation) -> normal temp. Decrease ->detected by thermoreceptors+hypothalamus->heating mechanisms(shivering, vasoconstriction) ->normal body temp
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Explain control of blood glucose concentration pt1 (when glucose levels are high)
Insulin is released from beta cells in pancreas, which stimulates glyocen synthesis in liver and increase rate of cell respiration to decrease blood glucose concentration
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Explain control of blood glucose concentration pt2 (when glucose levels are low)
Glucagon is released from alpha cells in pancreas which stimulates glycogen breakdown in liver, and decreasing rate of cell respiration. This ensures glucose is released into blood stream and less is used, increasing glucose levels.
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Other cards in this set

Card 2

Front

State the parts of a motor neuron

Back

Nucleus, dendrite, Soma (cell body), axon (covered in a myelin sheath which is made from schwann cells), nodes of ranvier and motor end plate

Card 3

Front

Three types of neurons in nervous system

Back

Preview of the front of card 3

Card 4

Front

Stimulus-response pathway

Back

Preview of the front of card 4

Card 5

Front

Define resting potential

Back

Preview of the front of card 5
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