Unit 3: Chapter 3 - Nerve Cells and Nerve Impulses Flashcards
Central Nervous System
Consists of the brain and spinal cord. It is the control centre for the whole nervous system.
Peripheral Nervous System
The nerves that connect the CNS with the receptors muscles and glands.
Neurons
Nerve cells. The basic structural and functional unit of the whole nervous system. They can very in shape and size but all consist of a cell body and two extensions from the body; the dendrites and the axon.
Interneurons
Have many branches that are able to send or receive messages to or from adjacent neurons
Cell body
The central part of a neuron containing the nucleus and other basic cell organelles
Dendrites
Short extensions of the cytoplasm of the cell body. They are highly branched and carry messages (nerve impulses) into the cell body.
Axon
Often a single, long extension of the cytoplasm. Usually carries nerve impulses away from the cell body
Nerve impulses
A signal transmitted along a nerve fibre. It consists of a wave of electrical depolarization that reverses the potential difference across the nerve cell membranes.
Myelin sheath
A layer of fatty material that may cover the axon of a neuron. If it covers the axon these neurons are referred to as myelinated.
Nerve fibre
Any long extension of cytoplasm of a nerve cell body.
Myelinated fibres
Any nerve fibre thats axon is covered in myelin sheath
Grey matter
Areas of the brain that that consist of nerve cell bodies and unmyelinated fibres.
White matter
Areas of the brain that consist of myelinated fibres (the lipid myelin that covers these fibres is white)
Schwann Cells
Outside the brain and spinal cord, the myelin sheath is formed by these special cells.
Nodes of Ranvier
The intervals (gaps) along the axon in the myelin sheath
Sensory (receptor) neuron
These neurons carry messages from receptors in the sense organs, or in the skin to the central nervous system.
Motor (effector) neuron
These neurons carry messages from the central nervous system to the muscles and glands (the effectors).
Multipolar neurons
These neurons have one axon and multiple dendrites extending from the cell body. Most common neuron found in the NS. Includes most of the interneurons in the brain and the spinal cord and also the motor neurons that carry messages to the skeletal muscles.
Bipolar neurons
Have one axon and one dendrite, both axon and dendrite may have branches at their ends. Bipolar neurons occurs in the eye, ear and nose, where they take impulses from the receptor cells to other neurons.
Unipolar neurons
Just have one extension, the axon. The cell body is to one side of the axon. Most sensory neurons that carry messages to the spinal cord are of this type.
Synapse
The junction between dendrites and axon terminal of adjacent neurons (a small gap).
Neuromuscular junction
A similar junction where an axon meets a skeletal cell
Nerve impulse
The message that travels along the neuron
Potential
When a group of oppositely charged particles are separated and have the potential to come together and released energy. Measured in volts or millivolts.
Membrane potential
A difference of electrical charge between the inside and the outside of a neuron
Resting membrane potential
Membrane potential of unstimulated nerve cell. Usually -70mV.
Inside of the membrane is 70mV less than outside (0)
This is due mainly to differences in K+ (30 times greater inside cell) and Na+ (10 times greater outside cell) ions.
Sodium Potassium Pump
Active transport using energy of 3 Na+ OUT of cell and 2 K+ INTO cell.
Depolarisation
When Na+ surge into cell at a greater rate of K+ moving out.
All or none response
There must be enough current to pass the threshold (-55mV) to cause a stimulus. If there isn’t enough energy, nothing happens.
Repolarisation
The restoration in membrane potential that returns it to a negative value just after the depolarization phase of an action potential has changed the membrane potential to a positive value.
Action potential
Cells taking action. Rapid polarisation and depolarisation. A short-term change in the electrical potential on the surface of a cell (e.g. a nerve cell or muscle cell) in response to stimulation, and then leads to the transmission of an electrical impulse (nerve impulse) that travels across the cell membrane.
Refractory period
Briefly after an action potential that part of the nerve fibre can’t be stimulated again (short period)
Polarised
The act or process of producing a positive electrical charge and a negative electrical charge such that between a nerve cell internal electrical charge, which is negative, and the surrounding environment of a nerve cell, which is positive.
Saltatory conduction
Nerve impulses jumping from one Node of Ranvier to another
Postsynaptic
The receiving end of a discharge across a synapse
Presynaptic neuron
A neuron from the axon terminal of which an electrical impulse is transmitted across a synaptic cleft to the cell body or one or more dendrites of a postsynaptic neuron by the release of a chemical neurotransmitter.
Stimulus intensity
The size of a nerve impulse is always the same, regardless of the size of stimulus, and does not become weaker.
How can we distinguish intensity?
- Depolarisation of more nerve fibres with strong stimuli
2. More impulses in a given time than a weak stimulus
Synapse transmission
At the synapse, there is no membrane. Another method of transmission must be involved.
Neurotransmitters
Neurotransmitters
(Special chemicals that nerve impulses are converted into at the synapse) are released from the ends of the axon from vesicles.
Synaptic vesicle
A small secretory vesicle that contains a neurotransmitter, is found inside an axon near the presynaptic membrane, and releases its contents into the synaptic cleft after fusing with the membrane.
Synaptic cleft
The space between neurons at a nerve synapse across which a nerve impulse is transmitted by a neurotransmitter. — called also synaptic gap
Depressant
A drug tending to, slow lower or depress functioning of the nervous system (nerve impulses.) (alcohol)
Stimulant
A drug that tends to speed up or raises levels of nerve impulses, nervous activity (Cocain)
