3.8 - The Nervous System Flashcards
What is acetylcholine?
A type of neurotransmitter that is used for communication between neurones.
Define action potential
The temporary change in electrical potential across the membrane of an axon in response to the transmission of a nerve impulse.
Explain the term all-or-nothing
A principle that states that all stimuli above a certain threshold value will generate the same size action potential, regardless of the strength of the stimulus.
What is an axon?
A long fibre that conducts nerve impulses away from the cell body
What are axon terminals?
Branched endings of an axon that approach the muscle fibre
What is cell body?
The region of the neuron that contains the organelles, notably the nucleus and the rough endoplasmic reticulum.
What is the central canal?
A cerebrospinal fluid-filled space that lies in the centre of grey matter.
Define the central nervous system (CNS)
The brain and spinal cord
What are cholinesterase?
An enzyme responsible for the hydrolysis of acetylcholine in the postsynaptic neuron
What are dendrites?
Short, branched extensions of the cell body that receive nerve impulses from other neurons.
Explain depolarisation
A sudden, temporary change in the membrane potential of a neuron in response to the transmission of a nerve impulse. The inside of the axon is less negative than the outside and the potential difference reaches approximately +40 millivolts (mV)
What is the dorsal root ganglion?
A group of sensory neuron cell bodies in the dorsal root of a spinal nerve
What is an effector?
An organ, tissue, or cell that produces a response to a stimulus
What is grey matter?
The darker tissue of the central nervous system which ties centrally and consists of relay and motor neuron cell bodies
What is hyperpolarisation?
A decrease in the membrane potential of an axon (due to the opening of K+ channels), so that it is even more negative than the resting potential.
Explain what meninges are
Three membranes that cover the brain and spinal cord: the pia mater, arachnoid mater and dura mater.
Define what a motor neuron is
A neuron that carries nerve impulses from the CNS to the effectors via the ventral root
What is the myelin sheath?
An electrically insulating layer consisting of the membranes of Schwann cells. It decreases the speed of nerve impulses.
What is a nerve impulse?
A wave of depolarisation that travels across an axon membrane. It is self-propagating.
What is a nerve net?
The simplest form of of nervous system found in Cnidarians. It consists of interconnected nerve cells with short extensions allowing a response to a limited number of stimuli
What are neurotransmitters?
Chemicals that are used for communication between neurones and their target cells. Neurotransmitters are stored in synaptic vesicles in the presynaptic neuron and released into the synaptic cleft
Explain what the Nodes of Ranvier are
Gaps between adjacent Schwann cells in the myelin sheath at which action potentials can occur
What are organophosphates?
Chemical substances that act as cholinesterase inhibitors, preventing the hydrolysis of acetylcholine in the postsynaptic neurone and resulting in continuous stimulation of the neuron. Organophosphates can be used as insecticides.
What is an oscilloscope trace?
A trace showing the change in electrical potential across the membrane of an axon at each stage of an action potential.
What is the peripheral nervous system (PNS)?
Pairs of nerves that originate from the CNS and carry nerve impulses into and out of the CNS.
What is the postsynaptic neuron?
The neuron after the synapse which contains specific receptor proteins on its membrane, complementary to the neurotransmitter.
What is the presynaptic neuron?
The neuron before the synapse which releases neurotransmitters from synaptic vesicles into the synaptic cleft
What are psychoactive drugs?
Excitatory drugs (e.g. amphetamine) that stimulates the release of neurotransmitters such as noradrenaline
What is a receptor?
A specialised structure that detects a specific type of stimulus
What is a reflex?
A rapid, automatic response to a sensory stimulus by the body. It serves as a protective mechanism.
What is the reflex arc?
The pathway of neurones involved in a reflex action:
Stimulus > Receptor > Sensory neuron > Relay neuron > Motor neuron > Effector > Response
What is the refractory period?
The time period after an action potential during which further action potentials are prevented. This ensures that action potentials can only be propagated in one direction.
What is a relay neuron?
A neuron located in the spinal cord that links the sensory neurone o the motor neurone
What is repolarisation?
The re-establishment of the resting potential (-70 mV)
What is the meaning of resting potential?
The potential difference across the cell membrane of a neuron at rest which is typically -70 millivolts (mV)
What is saltatory propagation?
The process by which a nerve impulse is propagated along a myelinated neuron. Depolarisation occurs at the nodes of Ranvier and action potentials jump from node to node, speeding up transmission
Explain what Schwann cells are
cells that from the myelin sheath around nerve cells in the peripheral nervous system
What is a sensory neuron?
A neuron that carries nerve impulses from the receptors to the CNS via the dorsal root
What is the sodium-potassium pump?
A carrier protein found in the plasma membrane of an axon. It actively transports three sodium ions (Na+) out of the axon for every two potassium ions (K+) that it pumps into the axon.
Define what a stimulus is
A change in an organism’s internal or external environment that can be detected
What is a synapse?
the junction between two nerve cells or a nerve cell and an effector
What is a synaptic cleft?
A small gap between neurones across which a nerve impulse is transmitted via neurotransmitters
Explain what synaptic end bulbs are
the end of an axon that is bulbous shaped and contains synaptic vesicles filled with neurotransmitters
What are synaptic vesicles?
Secretory vesicles located in the presynaptic neuron that store neurotransmitters. upon fusion with the presynaptic membrane, their contents are released into the synaptic cleft
What is white matter?
The lighter tissue of the central nervous system which surrounds grey matter and consists of myelinated axons
