neural communication Flashcards
(actually in animal responses) until i say so
what is the central nervous system?
-brain
-spinal cord
what is the peripheral nervous system?
-sensory neurones carrying sensory information from the receptors to the CNS
-motor neurones
what does the peripheral nervous system branch into?
-somatic nervous system
-autonomic nervous system
what is the somatic nervous system?
-voluntary, conscious activities eg. running
-most neurones are myelinated
-stimulates skeletal muscle
what is the autonomic nervous system?
-involuntary, unconscious activities eg. digestion
-most neurones are non-myelinated
-stimulates smooth muscle in the gut wall, cardiac muscle and glands
what is the autonomic nervous system branched into?
-sympathetic nervous system
-parasympathetic nervous system
what is the sympathetic nervous system?
-prepares body for ‘fight or flight’ response eg increases heart rate
-neurones secrete the neurotransmitter noradrenaline at the synapse between the neuron and the effector
what is the parasympathetic nervous system?
-calms the body down and prepares it for ‘rest and digest’ eg. decreased heart rate
-parasympathetic neurones secrete the neurotransmitter acetylcholine between the neurone and effector
what is the hypothalamus?
-automatically maintains body temperature and homeostasis at the normal level
-produces hormones that control the pituitary gland
what is the pituitary gland?
-controlled by the hypothalamus
-releases hormones and stimulates other glands to release their hormones
what is the medulla oblongata?
-at the top of the spinal cord
-automatically controls breathing rate and heart rate
what is the cerebrum?
-the largest part of the brain
-it’s divided into two cerebral hemispheres
-the cerebrum has a thin outer layer called the cerebral cortex which is highly folded
-the cerebrum is involved in vision, hearing, learning and thinking
what is the cerebellum?
-the cerebellum has a folded cortex
-important for muscle coordination, posture and coordination of balance
(now in neural communication)
what do sensory neurons carry?
structure?
myelinated or non-myelinated?
-carry impulses from the sensory receptor to relay and motor neurons
-long dendron that carries the impulse from the sensory receptor cell to the cell body and then an axon carries it from the cell body to the next neurone
-myelinated
what is a myelin sheath?
what kind of biological molecule is it?so?
what is saltatory conduction?
what does this mean?
-Schwann cells wrap around the axon to form a myelin sheath
-a lipid so doesn’t allow charged ions to pass through it
-when the impulse just from node to node (from each node of Ranvier which are the gaps between the myelin sheath).
-that the action potential travels along the axon faster as it doesn’t have to generate an action potential along the entire axon, just the nodes of Ranvier = increasing the speed of impulse transmission
what do relay neurons carry?
structure?
-carry impulses between the sensory and motor neurons
-multiple short axons and dendrons
what do motor neurons carry?
structure?
and transmit the impulse where?
-carry the impulse from relay or sensory neurons to effectors (muscle or glands)
-have a long axon and multiple short dendrons and an axon terminal
-away from the cell body
what are sensory receptors?
what do they carry?
what are the 3 types of sensory receptors? and what do they detect?
-they detect a stimulus, these cells are transducers, converting different types of stimuli into electrical nerve impulses
-impulses from a receptor to the CNS
-photoreceptors (rods and cone cells) = light
-thermoreceptors (skin) = heat
-mechanoreceptor (pacinian Corpuscle in skin) =pressure
what is the Pacinian Corpuscle?
where are they?
what does it consist of?
what do the channel proteins allow?
what will the channels do?
-receptors that respond to pressure changes
-deep in the skin, mainly fingers and feet
-a single sensory neurone wrapped with layers of tissue separated by gel and the sensory neurone in the pacinian corpuscle has special channel proteins in its plasma membrane
-allow ion transportation and the membrane’s surrounding the sensory neurones have stretch-mediated sodium channels
-they will open and allow sodium ions to diffuse into the sensory neurone ONLY when they are stretched and deformed.
sensory neurone resting state?
when pressure is applied?
-the sodium-ion channels are too narrow for the sodium ions to diffuse into the sensory neurone so the resting potential is maintained
-when pressure is applied = the stretch-mediated sodium ion channels are deformed and widen = allowing sodium ions to diffuse in which leads to the establishment of a generator potential
explain resting potential-
-when a neurone is not conducting an impulse there is a difference between the electrical charge inside and outside of the neurone = this is resting potential
-there are more sodium and potassium ions outside of the neurone compared to the inside so the inside is more negative at -70mV
-the resting potential is maintained by a sodium-potassium pump which uses active transport and therefore ATP
-the pump moves 2 potassium ions in and 3 sodium ions out, creating an electrochemical gradient causing potassium to diffuse out and sodium to diffuse in
-however the membrane is more permeable to potassium so more potassium diffuses out resulting in the -70mV
what is an action potential?
what is the refractory period?
An action potential is when the neuron’s voltage increases beyond a threshold from resting potential. This generates a nervous impulse. The increase in voltage (depolarisation) is due to the neurone membrane becoming more permeable to sodium ions
-during repolarisation and hyperpolarisation the neuron cell membrane cannot respond to another stimulus
describe an action potential (mark scheme)-
-generator potential causes first sodium ion channels to open
-if enough sodium ions move into the axon to reduce the potential difference to the threshold value
-which is -55mV
-then, voltage dependent sodium channels open and sodium ions move into the axon
-more sodium ions move in, so more sodium ion channels open, this is an example of positive feedback
-this is called the ‘all or nothing’ principle as all the sodium ion channels open if the threshold is reached
-the potential difference is now +40mV as it becomes more positive inside the axon compared to the outside
-this is depolarisation
-the sodium voltage dependent channels close which is the absolute refractory period
-voltage dependent potassium channels open and potassium ions move out of the axon
-the membrane repolarises
-the potassium ion ‘overshoot’ causes hyperpolarisation
-the voltage is now more negative than resting potential
-enabling the impulse to only flow in one direction
-the resting potential is re-established because potassium ions diffuse back into the cell as sodium-potassium pump switches back on
-this wave of depolarisation-repolarisation- hyperpolerisation repeats itself down the axon
-the myelin sheath speeds up conduction as it is an electrical insulator
-because the current can jump between the nodes of Ranvier, this is the saltatory effect
what is a wave of depolarisation?
what does this cause?
-when an action potential happens, some of the sodium ions that enter the neurone diffuse sideways = causing the sodium ion channels in the next region of the neurone to open and sodium ions diffuse into that part
-a wave of depolarisation to travel along the neurone
-and then the wave moves away from the parts of the membrane in the refractory period because these parts can’t fire an action potential
what happens once the threshold is reached?
if the threshold isn’t reached?
what will a bigger action potential cause?
-an action potential will always fire with the same change in voltage
-an action potential won’t fire = this is the ‘all or nothing’ principle of action potentials
-cause them to fire more frequently
what is a cholinergic synapse?
-synapses that use the neurotransmitter acetylcholine, they bind to cholinergic receptors and are broken down by an enzyme called acetylcholinesterase which breaks the acetylcholine into choline and acetate to be recycled in the presynaptic neurone.
-action potential arrives at the synaptic knob of the presynaptic neurone
-the depolarisation of the synaptic knob stimulates voltage-gated calcium ion channels in the presynaptic neurone to open.
-calcium ions diffuse into the synaptic knob, from tissue fluid surrounding the neurone
-the influx of calcium ions into the synaptic knob causes the synaptic vesicles to move towards and fuse with the presynaptic membrane
-the neurotransmitters are then released into the synaptic cleft by exocytosis
-the neurotransmitter diffuses down a concentration gradient across the synaptic cleft, to the post synaptic membrane
-the acetylecholine then binds to specific cholinergic recepters on the postsynaptic membrane
-this causes sodium ion channels in the postsynaptic neurone to open and sodium ions diffuse in, if enough neurotransmitter binds, and enough sodium ions diffuse in to raise the membrane potential above the -55mV threshold then the neurone becomes depolarised and an action potential is generated
-neurotransmitter is removed from the synaptic cleft so the response doesn’t keep on happening
what is an excitatory synapse?
-neurotransmitters depolarise the post synaptic membrane, making it fire an action potential if the threshold is reached
what is an inhibitory synapse?
this is because?
-when the neurotransmitters bind to receptors on the post synaptic membrane, they hyperpolarise the membrane (make the potential difference more negative), preventing an action potential from being fired
-chloride ions move into the postsynaptic membrane and potassium ions move out
what is synaptic divergence?
what is synaptic convergence?
-when one neurone connects to many neurones, information can be dispersed to different parts of the body
-when many neurones connect to one neurone, information can be amplified (made stronger)
summation in the synapse-
what is summation?
why is it needed?
-the rapid build up of neurotransmitters in the synapse to help generate an action potential by two methods: spatial or temporal summation
-because some action potentials do not result in sufficient concentrations of neurotransmitters being released to generate a new action potential
spatial summation-
three possibilities?
so what does spatial summation allow?
-when neurones converge, the small amount of neurotransmitter released from each neurone can be enough all together to reach the threshold in the postsynaptic neurone and trigger an action potential
-if some neurones released an inhibitory neurotransmitter then the total effect of all the neurotransmitters might be no action potential
-stimuli may arrive from different sources
-signals from multiple stimuli to be coordinated into a single response
what is temporal summation?
what happens?
what do both types of summation mean?
-where two or more nerve impulses arrive in quick succession from the same presynaptic neurone
-it makes action potential more likely because more neurotransmitter is released into the synaptic cleft
-that synapses accurately process information, finely tuning the response
one way-
-receptors for neurotransmitters are only on the postsynaptic membranes, so impulses can only travels in one direction.
