UNIT A (NERVOUS AND ENDORCRINE SYSTEM) Flashcards
What does the nervous system do in regard to homeostasis?
The nervous system regulates body structures and processes to maintain homeostasis despite fluctuations in the internal and external environment.
What are the two divisions of the nervous system?
Central nervous system (CNS)
Peripheral nervous system (PNS)
CNS
Consists of the nerves of the brain and spinal cord and acts as a coordinating centre for incoming and outgoing information.
PNS
Consists of nerves that carry information between the organs of the body and the central nervous system. Further subdivided into somatic and autonomic
nerves.
Division on the Nervous System (Diagram)
Gilial Cells
Neuroglial cells, are nonconducting cells and are important for the structural support and metabolism of the nerve cells. Has different types of myelin sheath. (Schwann cells are a type of gilial cell that form the myelin sheath around axon).
Neurilemma
Outer layer of Schwann cells in the PNS.. Delicate membrane that surrounds the axon of some nerve cells. Formed by the Schwann cells and promotes the regeneration of damaged axons. Not all nerve cells that have a myelin sheath have a neurilemma.
Nerves within the brain that contain myelinated fibres are called white matter because the myelinated axons are whitish in appearance. Other nerve cells within the brain and spinal cord, referred to as the grey matter, lack a myelin sheath.
Myelin Sheath
Insulated covering over the axon of a nerve cell, located in the PNS, made up of Schwann cells that form neurilemma.
Neuron
Nerve cell that conducts nerve impulses
Dendrite
Projection of cytoplasm that carries impulses toward the cell body. Conduct nerve impulses towards cell body.
Axon
Extension of cytoplasm that
carries nerve impulses away from
the cell body
Nodes of Ranvier
Regularly occurring gaps between sections of myelin sheath along the axon.
Sensory Neurons
Located in the PNS, neurons that
carries impulses to the central
nervous system; also known as
afferent neuron.
Ganglia
The cell bodies of sensory neurons are
located in clusters called located outside of the spinal cord.
Interneurons
Located in the CNS, link neurons to other neurons. Found only in the brain and spinal cord, the interneurons (also known as association neurons) integrate and interpret the sensory information and connect sensory neurons to outgoing motor neurons.
Motor Neurons
(also known as efferent neurons) relay information to the effectors, which is the cell or organ that responds to the stimulus. Muscles, organs, and glands are classified as effectors because they produce responses.
Reflex Arc
Before it reaches your brain, sensation detected by receptors and a nerve impulse carried to the spinal cord. The sensory neuron passes the impulse on to an interneuron, which, in turn, relays the impulse to a motor neuron. The motor neuron causes the muscles in the hand to contract and the hand to pull away. All this happens in less than a second, before the information even travels to the brain.
Pupillary Reflex
Check for reflexes, healthy nervous system!
All or nothing
No matter what the intensity or duration of a stimulation, a nerve or muscle will respond completely or not at all. No such thing as a too big or less impulse.
BUT threshold level is not a fixed value and can be influenced by ion concentration, neurotransmitters, diseases, disorders or conditions.
Action Potential
The voltage difference across a nerve cell
membrane when the nerve is excited. The resting membrane normally had a potential somewhere near -70 mV (millivolts); however, when the nerve became excited, the potential on the inside of the membrane registered -55mV. This reversal of potential is described as an action potential.
Resting Potential
Voltage difference across a nerve cell membrane when it is not transmitting a nerve impulse (usually negative).
Plasma Membrane During Resting Potential
Higher concentration of
potassium ions (K+) inside the cell and a higher concentration of sodium ions (Na+) outside the cell. The movement of K+ is mainly responsible for creating the electrical potential. Sodiuum-Potassium exchange pump exchanges 3 Na+ ions for 2 K+ ions. Plasma membranes are selectively permeable; ions cannot cross the bilayer by simple diffusion. Instead, they enter cells by facilitated diffusion, passing through gated ion channels that span the bilayer. (If ion concentrations were determined only by diffusion, eventually the concentrations of sodium and potassium would equalize across the membrane. This does not happen because the sodium-potassium pump in the membrane moves potassium back into the cell and sodium back out of the cell through active transport.)
Polarized Membrane
Excess positive ions accumulate along the outside of the nerve membrane, while excess negative ions accumulate along the inside of the membrane. The resting membrane is said to be charged and is called a polarized membrane. A charge of -70 mV indicates the difference between the number of positive charges found on the inside of the nerve membrane relative to the outside. (A charge of -90 mV on the inside of the nerve membrane would indicate even fewer positive ions inside the membrane relative to the outside.)
Impulse Order
- Resting Potential: -70mV
- Action Potential: -55mV
- Depolarization: Diffusion of sodium ions into the nerve cells, resulting in a charge reversal. Cell membranesare more permeable to Na+ than K+, opening sodium channels while potassium channels remain closed. All the way to +35mV
Repolarization: The process of restoring the original polarity of the nerve membrane, Na+ channels close and K+ channels open. As K+ leaves from the inside of the cell, the inside becomes more negative, outside becomes more positive, and because K+ channels are slow to close, causes hyperpolarization! - Hyperpolarization: Condition in
which the inside of the nerve cell
membrane has a greater negative
charge than the resting membrane;
caused by excessive diffusion of
potassium ions out of the cell. - Refractory Period: Recovery time
required before a neuron can
produce another action potential. MUST return to resting potential before generating another action potential!