Chapter 3 A- Nerve Cells & Nerve Impulses Flashcards
What is a neuron?
A nerve cell, basic structural and functional units of the nervous system
What do all neurons consist of?
- cell body
- two extensions: axon and dendrites
Neuron: cell body
- contains nucleus, organelles and cytoplasm
Neuron: dendrites
- fairly short extensions of the cytoplasm
- highly branched
- carry nerve impulses into the cell body
Neuron: axon
- single, long extension of the cytoplasm
- length varies greatly, can be very long
- most covered with layer of fatty material called the myelin sheath
What is a nerve fibre?
Term used for any long extension of a neuron, usually refers to an axon
Neuron: myelinated fibre
- axon with myelin sheath
Neuron: unmyelinated fibre
- axon with no myelin sheath
What does grey matter consist of?
Cells with unmyelinated fibres
What does white matter consist of?
Cells with myelinated fibres
Neuron: Schwann cells
- wrap around myelin sheath
- forms myelin sheath
Neuron: nodes of Ranvier
- gaps in the myelin sheath
Neuron: neurilemma
- outermost coil of the Schwann cell
- helps repair injured fibres
What are the functions of the myelin sheath?
- acts as an insulator
- protects axons from damage
- speeds up movement of nerve impulses along axon
What are the three functional types of neurons?
- sensory (receptor) neurons
- Motor (effector) neurons
- Inter neurons
What is the function of sensory neurons?
- carry messages from the receptors in the sense organs, or skin, to the central nervous system
What is the function of motor neurons?
- carry messages from the central nervous system to muscles and glands - the effectors
What is the function of interneurons?
- located in the central nervous system and are the link between sensory and motor neurons
What are the structural types of neurons?
- Multipolar neurons
- Bipolar neurons
- Unipolar neurons
Structure of multipolar neurons:
- have one axon and multiple dendrites extending from the cell body
Where are multipolar neurons found?
- most of the interneurons in the CNS
- motor neurons
Structure of bipolar neurons:
- one axon and one dendrite
- both axon and dendrite may have many branches
Where are bipolar neurons found?
- sensory neurons in the eye, ear and nose, where they take impulses from receptor cells to other neurons
Structure of unipolar neurons:
- have just one extension: an axon
- the cell body is to the side of the axon
Where are unipolar neurons found?
- sensory neurons that carry impulses to the spinal chord
What is a synapse?
The junction between the branches of adjacent neurons
What is a neuronmuscular junction?
The synapse that exists where an axon meets a skeletal muscle cell
What is the all-or-none response?
A stimulus is either strong enough to trigger an impulse, or it is not. The magnitude of an impulse is always the same.
How are we able to distinguish stimuli of different intensities?
- a strong stimulus causes depolarisation of more nerve fibres than a weak stimulus
- a strong stimulus produces more nerve impulses in a given time than a weak stimulus
What ions are found in high concentration inside the membrane?
- K+
- variety of negative ions that come from organic substances made by the cell
What ions are found in high concentration outside the membrane?
- Na
- Cl
The cell membrane is highly permeable to __________
- K
- Cl
The cell membrane is slightly permeable to __________
- Na
How does the cell membrane maintain the potential difference?
- actively moves ions across the membrane (sodium-potassium pump)
- there are a large number of negatively charges ions trapped inside the cell
Where are unipolar neurons found?
Sensory neurons
Where are bipolar neurons found?
Sensory neurons in the eye, ear and nose
Where are multipolar neurons found?
Connector neurons, motor neurons
Which way does the nerve impulse travel?
Axon to dendrites
