Week 25 - Introduction to the Nervous system

• Both the nervous and endocrine systems play a key role in homeostasis by responding to input signals and generating an output signal/response.
• Information flow through the nervous system is coordinated through electrical signals and the release of regulatory molecules.
• The nervous system consists of neurons which directly contact most organs, and hormones which are transported by the blood to body organs.
• The endocrine system consists of hormones which are transported by the blood to body organs, and receptors which must be present on the target cell for a response to occur.
• The Nernst equation describes equilibrium potential.
• Resting membrane potential is similar (but not identical) to the K+ equilibrium potential because at rest cells are much more permeable to K+ than to other ions.
• Membrane potential is an electrical potential difference across the cell membrane.
• Equilibrium potential is the potential, for any ion, at which there is no net flux of that ion across the membrane because the chemical and electrical forces that tend to move the ion exactly balance.
• Resting membrane potential is the membrane potential of excitable cells (e.g. neurons) at rest.
• Neurons use both electrical and chemical (neurotransmitters) signals, while the endocrine system uses only chemical signals (hormones).
• Control in the nervous system is very specific as neurons contact target organs directly, while in the endocrine system control is more general as hormone is secreted into blood and can reach many organs.
• Ganglia are collections of nerve cell bodies outside the Central Nervous System (CNS).
• The Peripheral Nervous System (PNS) includes all neurons that lie outside or partially outside the CNS.
• The Central Nervous System (CNS) includes the brain and spinal cord.
• The brain sits in the bony cranium and the spinal cord runs down the back (dorsal side) inside the vertebral column.
• The bones of the cranium and vertebral column, membranes (meninges) and fluid (cerebrospinal fluid) protect the nervous tissue.
• Afferent or sensory neurons carry information about light, temperature, pressure and other stimuli from sensory receptors throughout the body into the Central Nervous System (CNS).
• Neurons are the functional unit of the nervous system, with approximately 100 billion in the human brain.
• Dendritic spines vary from thin spikes to mushroom shaped knobs and increase the surface area of dendrites.
• If charges can not move through the material it is known as an insulator.
• All living cells in the body maintain a potential (voltage) difference across the cell membrane, this is the cell’s membrane potential.
• The axon cytoplasm is filled with many types of fibres and filaments but lacks ribosomes and endoplasmic reticulum.
• The membrane potential at rest (cells not actively signalling) is the resting membrane potential.
• The cell body of a neuron is small, generally making up one-tenth or less of the total cell volume.
• Glial cells are essential for the functioning of the nervous system, as without them the nervous system would not function.
• Neurons and muscles (excitable cells) can alter their membrane potential in response to stimulation.
• When separated positive and negative charges can move freely toward each other, the material through which they move is called a conductor.
• Separating positive charges from negative charges requires energy.
• The law of conservation of electrical charge states that the net amount of electrical charge produced in any process is zero, meaning that opposite charges (+ and -) are attracted to each other and like repel.
• The human CNS contains electrical synapses where the presynaptic and postsynaptic cells are connected by gap junction channels, allowing for bidirectional cell to cell communication that is faster than chemical synapses.
• Neurons vary in structure and function, with different types having different numbers and lengths of axons and dendrites.
• Interneurons, or interconnecting neurons, lie entirely within the CNS where they integrate information and often have complex branching processes to connect them with many other neurons.
• The Nernst equation is used for a cell that is freely permeable to only one ion at a time.
• Membrane Potential depends on the uneven distribution of positively and negatively charged ions on each side of the membrane (electrical gradient/force) and the ion permeability of the plasma membrane.
• The chemical force for an ion moves K+ out as present at higher concentration inside.
• Na+ and K+ diffuse in and out of cells through leak channels (open channels) in the membrane.
• Na+ and K+ pumps, which are present in the membrane of all cells, pump Na+ out and K+ in.
• Membrane potential is non-zero when K+ diffuses in and out of cells through leak channels (open channels) in the membrane.
• When the chemical and electrical forces exactly balance there will be no net movement of K+.
• Living cells, however, have limited permeability to several ions.