3.5.1-3 Nervous System Flashcards
What is the ‘coordinator’ in the CNS?
The network of inter-neurones connecting the sensory and motor systems. It’s job is to receive impulses from sensory neurones and transmit impulses to motor neurones
What are effectors in the CNS?
Effectors are the cells which effect a response.
What are the only two effectors in humans?
Muscles and Glands
What are the two types of glands and what to they do differently?
- Exocrine Glands, which secrete liquids to the outside like sweat.
- Endocrine Glands, which secrete hormones to the bloodstream
What is another name for a nerve cell?
Neurone
What is the composition of a neurone?
A cell body with extensions leading off of it in opposite directions
What is the side of the nerve called which carries nerve impulses toward the cell body and what are the ends called?
Dendrons, ending with dendrites
What is the name of the extension in a neurone which carries nerve impulses away from the cell body?
an Axon
What is the difference between a neurone and a nerve?
A neurone is a nerve cell, a nerve is a bundle of neurones.
What is the name of the point at which impulses are passed from one neurone to another?
Synapse
What are Schwann cells and what do they do?
Companion cells to the neurones which wrap around the axon to form a thick lipid layer called the myelin sheathe which electrically insulates the axon by preventing diffusion of ions out of the axon
What are the gaps in the myelin sheathe called?
Nodes of Ranvier
What are the three types of neurones in Humans?
- Sensory neurones
- Effector Neurones
- Interneurones
What does a sensory neurone look like?
Long dendrons on one side, an axon on the other, with a cell body in the middle
What do effector neurones look like?
Dendrites surrounding the cell body and long axons to connect to effectors
What do Interneurones look like?
(For recognition in exam, not specific vocab) Short axons and dendrons, big looking cell body
What is a stimulus?
Changes in the external or internal environment
What protein pump do all animal cell membranes have, which maintains the membrane potential?
Na+K+ATPase Protein Pump
How does the sodium potassium protein pump work to maintain an ion gradient across cell membranes?
It uses energy from ATP to simultaneously pump 3 sodium ions out of the cell and 2 potassium ions into the cell, whilst potassium and sodium channels allow leakage of potassium and sodium back down their concentration gradients. This causes a potential difference across the cell membrane
What is the potential difference across all animal cell membranes called?
Membrane potential
Is the membrane potential always negative/positive inside the cell?
The membrane potential is always negative inside the cell
How are the channels in nerve and muscle cells gated?
They are voltage gated which means that they can open and close based on the size of the voltage across the membrane
What does it mean for a muscle or nerve cell to be electrically excitable?
They can change their membrane potential
What is the resting membrane potential of a nerve cell?
-70mV
What are the two phases of an action potential?
Depolarisation and Repolarisation
What is an action potential, in relation to membrane potential?
A reversal of the membrane potential for about a millisecond
What occurs during the depolarisation phase of an action potential?
The sodium channels open, causing sodium ions to diffuse into the cell down their concentration gradient, making the inside of the cell more positive.
What occurs during the Repolarisation stage of an Action Potential?
Potassium channels open, causing potassium ions to diffuse out of the cell, down their concentration gradient, making the inside more negative again.
At what voltage do voltage gated sodium channels open, causing depolarisation?
-30mV
At what voltage do the voltage gated potassium channels open, causing Repolarisation?
0V
What voltage activates the Sodium potassium pump?
It is active constantly, regardless of voltage across the membrane
How are nerve impulses started?
Appropriately gated sodium channels in their respective receptor cells opening due to their respective stimulus, which causes depolarisation of the membrane potential which affects the voltage gated sodium channels nearby, causing an action potential.
How are nerve impulses propagated?
Once an action potential has started on one end of an axon, it moves along it automatically s nearby voltage gated sodium channels are opened in response to the reversal of the membrane potential
What is the refractory period?
The amount of time after a sodium channel has opened that is necessary for it to close and open again
Why do action potentials travel only in one direction?
Because the refractory period of ion channels means they cannot open again in time to start the action potential in the direction from which it originated
How can we determine the different strengths of nerve impulses if they all have a fixed amplitude?
The strength of a stimulus is indicated by the frequency of nerve impulses
How fast do nerve impulses travel?
0.1 - 100 m/s
What 3 factors are the speed of nerve impulses limited by?
Temperature, Axon Diameter and the Myelin sheathe
How does temperature affect the speed of action potentials?
Higher temperatures increase the speed of action potentials and vice versa
How does the axon diameter affect the speed of an action potential?
The larger the axon diameter the faster the action potential
How does the myelin sheathe affect the speed of an action potential?
Is a good electrical insulator, so it allows for a process known as saltatory propagation where the action potential can jump from node to node in between myelin sheathes which greatly speeds up the action potential
What is a node of Ranvier?
The area between myelin sheathes which is the location of the voltage gated ion channels
What are Pacinian corpuscles?
Mechano receptors found in skin (and joints, ligaments etc.) that detect strong pressure and vibrations, made of a sensory neurone surrounded by a capsule of many flattened layers of Schwann cells and fluid called lamellae.
How do Pacinian corpuscles work?
Pressure distorts the neurone cell membrane, which opens mechanically gated sodium ion channels, which causes a local depolarisation as sodium ion diffuse in called a generator potential, which if above a threshold, it will trigger an action potential
What is a synapse?
The junction between the end of an axon and the dendrite of the next neurone.
What is the presynaptic membrane?
Membrane of the axon terminals
What is the post synaptic membrane?
Membrane of the dendrites
What do synaptic vesicles carry?
Neurotransmitters, e.g. Acetylcholine
What is Acetylcholine?
The neurotransmitter released by motor nerves at the neuromuscular junction.
At a resting membrane potential, which side has more sodium ions, and consequently what direction do they flow when their respective channel is opened during depolarisation?
The outside of the cell, and they flow into the cell during depolarisation
At a resting membrane potential, which side has more potassium ions, and consequently what direction do they flow when their respective channel is opened during Repolarisation
More on the inside of the cell, and they diffuse out of the cell during Repolarisation
What are neuroreceptors?
Chemical gated ion channels
Explain what happens when an action potential reaches a synapse?
- The arrival of the action potential stimulates voltage gated calcium channel to open and ions diffuse into the cell down their concentration gradient
- The ions cause the synaptic vesicles to release their contents through the presynaptic membrane by exocytosis
- The neurotransmitters diffuse across the synaptic cleft, which then bind to the neuroreceptors in the post synaptic membrane, causing the ion channels to open.
- This causes depolarisation of the post synaptic membrane, called the PSP (post synaptic potential), which may start an action potential.
- The neurotransmitter is removed by breaking it down with an enzyme, and the products are reabsorbed by the presynaptic membrane by endocytosis, to synthesise more neurotransmitter using energy from mitochondria.
What are the five types of synapses?
Excitatory Ion Channel Synapses Inhibitory Ion Channel Synapses Non-Channel Synapses Neuromuscular Junctions Electrical Synapses
What are Excitatory Ion Channel Synapses?
These synapses have neuroreceptors that are sodium channels, cussing depolarisation when they open and diffuse ions into the cell, making an action potential more likely.
What are inhibitory Ion Channel Synapses?
Synapses with chloride ion channels, which cause hyper polarisation when opened and negative ions diffuse into the cell, making an action potential less likely.
What are non-channel synapses?
Synapses with membrane bound enzymes instead of channels, which catalyse the production of a “messenger chemical” inside the cell which can alter the number and sensitivity of ion channels in the cell.
What are neuromuscular junctions?
Synapses between effector neurones and muscle cells, which always use the neurotransmitter acetylcholine and are always excitatory.
What are electrical synapses?
Synapses in which the cells touch and share proteins, allowing direct transfer of action potential without neurotransmitter. Found only in the heart and eye.
What is axon convergence?
Where one neurone can have many synapses on its cell body and dendrites.
What is a post synaptic potential?
The local voltage change in the cell body caused by each synapse
What is the grand post synaptic potential?
The sum of the excitatory and inhibitory PSPs.
What is a drug called which stimulates a synapse?
An Agonist
What is a drug which inhibits a synapse?
An antagonist
What is temporal summation?
The summing of a sequence of PSPs from a single synapse
What is spatial summation?
The summing of PSPs from different synapses over the cell body and dendrite tree
How can drugs affect synapses?
They can stimulate or inhibit synapses through various methods e.g. Mimicking neurotransmitter or blocking neuroreceptors.
What is the somatic nervous system responsible for?
Voluntary responses
What is the autonomic nervous system responsible for?
Involuntary responses and output to smooth muscles and glands
What are parasympathetic neurones responsible for?
Relaxing responses; Feed and Breed
What are sympathetic neurones responsible for?
Fight or flight responses
What is the part of the brain responsible for heart rate?
Medulla Oblangata
What is the part of the medulla that is responsible for heart rate?
Cardiovascular Centre
What are the two nerves connecting the cardiovascular centre and the sino atrial node?
Sympathetic nerve, which speeds up the heart rate
Parasympathetic nerve which slows the heart rate down
How does cardiovascular centre affect stroke volume?
By sending nerve impulses to the Arterioles, causing vasoconstriction or vasodilation, to increase or decrease blood pressure/stroke volume respectively.
What changes occur in the body during exercise which can be regulated by the autonomic nervous system?
Oxygen concentration, pH (carbonic acid from CO2) and temperature
What are pH changes in the blood detected by and where is it found?
Chemoreceptors found in the walls of the aorta, the walls of the carotid arteries and the medulla
What happens what chemoreceptors in the aorta and carotid arteries detect decreasing pH?
The chemoreceptors send impulses to the cardiovascular centre, which then send signals along the sympathetic nerve to the SAN in order to increase heart rate
What is the paracrine system?
Chemical mediators that are released locally that travel by diffusion by tissue fluid.
What is the autocrine system?
Released by a cell to act upon the same cell
What are the Key features of reflexes?
Involves few neurones Immediate Involuntary Invariable, Same every time Innate, not learned
Why is no image perceived when light hits the optic nerve
There are no rods or cones
Why are images perceived by the fovea more detailed than those perceived by the rest of the retina?
The fovea contains mainly cones which each synapse connected to a single neurone so there is no retinal convergence
How does the number and distribution of rods and cones across the retina differ in nocturnal animals than humans
Nocturnal animals have more rods in the fovea as rods are more sensitive due to retinal convergence
Explain how someone feels pain when they prick their finger on a thorn
Impulses are sent to the sensory areas of the brain in the cerebral hemispheres which is then interpreted as pain
Humans produce a large number of different hormones but only a small number of different neurotransmitters. Explain the significance of this difference.
Hormones reach all cells via the blood. Neurotransmitters are released directly onto a target cell and different hormones are specific to different target cells
A myelinated axon conducts impulses faster than a non-myelinated axon. Explain this difference.
An action potential/depolarisation only occurs at node
and the impulse jumps from node to node/saltatory;
so action potential/impulse does not travel along whole length of the axon
