C6 Flashcards
(32 cards)
What is homeostasis
“The maintenance of the body’s internal environment
despite changes in the external environment or changes in the body’s rate of activity.”
Example of a negative feedback loop effector
Organs, glands, muscle or other any other structure that responds to bring the variable back to the setpoint.
Receptors (4)
- Electromagnetic receptors (Photoreceptors Thermoreceptors)
- Mechanoreceptors: detect a range of sensory stimulus (sound, pressure, balance)
- Chemoreceptors: chemicals detected from food +
environment - Nociceptor: detects pain
Nervous system (2 main parts)
Central nervous system (C.N.S)
Peripheral nervous system (P.N.S)
What makes up the C.N.S.?
Brain - protected by skull
Spinal Cord - protected by vertebrae
Made up of interneurons, which relay information
What makes up the P.N.S. (2)
Somatic - voluntry + sensory perceptions
(experiences)
Automatic - Parasympathetic (rest and digest)
- Sympathetic (fight or flight)
- Enteric (GI)
What are action potentials + 4 steps?
How a message travels through neurons.
- Axon stimulation
- Depolarisation
- Repolarisation
- Hyperpolerisation
V.G.C
- Protein channels in the neural membrane that are usually closed (at -70 mV)
- open ( + close) depending on the electrical potential to access the membrane
Action potentials - Step 1
Axon stimulation
- occurs (e.g. environmental stimulus or through a neurotransmitter binding to the dendrite) - causes a Na V.G.C to open
- Na+ ions rush down concentration gradient into neuron.
- causes the neuron to be less negative on the inside
Action potentials - Step 2
Depolarisation
- triggers more Na V.G.C to open.
- If the potential difference reaches -55 mV (threshold value), more channels open, causing rapid depolarisation due to↑ Na+ inside the neuron.
- causes the potential difference to be +30 mV
Action potentials - Step 3
Repolarisation
- After ~1 millisecond, all Na V.G.C close (therefore Na+ stops moving into the neuron) and K V.G.C. open; therefore, it diffuses out of the axon (down con-gradient).
- This decrease in K+ results in the potential difference dropping back down
Action potentials - Step 4
Hyperpolarisation
- This occurs as there is a lag in closing the K.V.G.C.
- More K+ is moved out of the axon.
- Membrane potential drops to -80 mV
-Na/k pump works to restore the resting potential (-70mv)
Oscilloscope trace
Look at nicolas notes for this
Propagation of Action Potentials
- An A.P. travels down the neuron as the A.P. at one point in the neuron/cell membrane triggers an A.P. in the next portion of the cell membrane - due to
increase in Na+ - A.P. travels in one direction along axon as once the membrane has repolarised, the Na.V. G. C. are shut + cannot be opened for a period of time (refractory period) :. The transmission of messages by A.P. are discrete events.
Myelinated Neurons
- Have a Myelin sheath + nodes of Ranvier
- Na V.G.C and K V.G.C are only in nodes of Ranvier
- A.P. ‘Jumps’ between nodes of Ranvier
- this increases the speed of transmission by 100x
How does the brain interpret action potentials?
Brain interprets - frequency of A.P.
- Number of neurons carrying A.P.
- Nature of stimulus (e.g. light/heat/pain) is deduced by the position of the sensory neuron in the brain
What is a synapse?
- The gap between the axon terminal and the next neuron (or cell)
- Usually, the A.P. is converted to a chemical message (neurotransmitter) that crosses the synapse (the gap).
A.P. is transferred across synapse (8 steps)
- A.P. arrives & axon terminal
- V.G.C - Ca2+ - open target cell)
- Ca2+ enter the presynaptic neuron
- Ca2+ interact with neurotransmitter vesicles
- Cause vesicles to move to membrane + dock
- Neurotransmitter leaves neuron, into synapse.
- N.T. binds to receptor on postsynaptic neuron (or open target cell)
- Signal initiated in postsynaptic cell
Types of neurotransmitters (2)
Excitatory neurotransmitters -
stimulate an A.P. or trigger some action in the cell
Inhibitory neurotransmitters -
cause hyperpolarisation/flow of K+ out or Cl- into nerve cell -> reduce the message
Fates of neurotransmitters
- Detach from receptor protein and are reabsorbed back into the postsynaptic neuron
OR
-Diffuse away from the site
OR - Broken down by enzymes, so the receptor protein is not continually opened.
Examples of neurotransmitters
- Acetylcholine: released by motor neurons, binds to Muscle fibres to trigger muscle contractions
-Dopamine: often referred to as the pleasure chemical, makes you happy.
Which part of the brain is responsible for thermoregulation?
Hypothalamus acts as a ‘thermostat’
- Receptor cells detect changes in temperature (in skin, organs + blood vessels)
- Receptors send nerve impulse to hypothalamus that temperature has deviated from set point.
Means of Thermoregulation (4)
- Vasodilation/Vasoconstriction
- Sweating
- Piloerection
- Shivering (or other rapid muscle contractions)
How does Vasodilation/Vasoconstriction affect body temperature?
Vasodilation: ↑ in blood flow to skin as arteries expand, causing more heat to be lost to the environment via radiation
Vasoconstriction:↓ in blood flow to skin, causing less heat ot be lost via radiation
