Nervous Histology and Impulse Transmission
|Nervous tissue|| Highly cellular (densely packed) tissue with two principle cells: Glial cells and Neurons---|
Glial cells: Supporting Cells that include:
Neurons: excitable cells that transmit electrical signals
|Microglia|| - small glial cells act as phagocytes,|
clearing debris and invading infections from the nervous system.
|Astrocytes||Star shaped glial cells that provide both physical and nutritional support to neurons.|
|Glial cells||Supporting cells of the nervous system.|
|Neurons|| Excitable cells that transmit electrical signals; highly specialized cells that conduct/transmit messages.|
The have extreme longevity (< 100 yrs)
They are amitotic meaning they do not divide (except for olfactory and hippocampal neurons).
They have an exceptionally high metabolic rate, requiring abundant supplies of oxygen and glucose.
|Oligodendrocytes||Specialized cells in the CNS that wrap around the axons of neurons to make myelin.|
|Satellite cells||Surround neuron cell bodies with ganglia, but their function is unknown.|
|Schwann cells||Surround and form myelin sheaths around the larger nerve fibers (similar to oligodendrocytes).|
|Dendrites||Arm-like processes that extend from the cell body of all neurons which receive signals. They are short, tapering, and have branching extensions and are usually found close to the cell body. Dendrites are unmyelinated (slow conductors).|
|Axon||A single arm-like process that extends from the cell body of all neurons which generate and transmit nerve impulses. They can be long (up to ~ 1 meter) or short with diffuse branching at the end. Axons are myelinated (fast conductors).|
|Excitable cells|| Those cells that can be stimulated to create a tiny electric current. |
Muscle cells and
nerve cells (neurons) are excitable.
Excitable cells are excitable because of the special ability to briefly alter the resting membrane potential.
|Electrical potential|| In the simplest terms, an electrical potential is a separation of different charges. |
So, if the inside of a compartment has more negative particles than positive particles, it will be negatively charged.
This creates potential movement.
|Large Negatively Charge Molecules||Really big molecules that are trapped inside the cell and have a negative charge. This is why the inside of the cell is negatively charged.|
|Potassium Ions (K+)||Small particles of potassium that carry a positive charge. These can go through the cell membrane whenever they want.|
|Sodium Ions (Na+)||Small positively charged particles of sodium that are stuck on the outside of the cell looking in.|
|Action potential||Each Impulse sent down an axon by a nerve cell. A nerve cell transmits a signal when it receives an impulse from another neuron.|
|Myelin sheath|| protects and electrically insulates nerve fibers. It increases the speed of impulse transmission. Axons are myelinated (fast conductors).|
Dendrites are unmyelinated (slow conductors).
|Sensory Input||Monitoring changes occurring inside and outside of the body.|
|Integration||Processing information from senses and deciding how to react to it.|
|Effector Output||Responding or reacting to sensory out put.|
|Central nervous system (CNS)||Consists of the brain and spinal cord.|
|Peripheral nervous system (PNS)|| Any part of the nervous system outside of the CNS.|
Spinal nerves carry impulses to and from the spinal cord.
Cranial nerves carry impulses to and from the brain.
|Afferent||Generally refers to anything going toward a specific area.|
|Efferent||Generally refers to anything being carried away from an area.|
|Effectors||Any organ or structure that creates an effect in response to a signal from the nervous system.|
|Afferent division||Consists of nerve fibers which carry impulses to the CNS from sensory receptors throughout the body.|
|Somatic afferent fibers||Fibers that convey impulses from the skin, skeletal muscles, and joints.|
|Visceral afferent fibers||Fibers that convey impulses from the visceral organs.|
|Efferent division||Transmits impulses from the CNS to effector organs.|
|Somatic nervous system||Allows us to control our skeletal muscles.|
|Autonomic nervous system (ANS)||Consists of visceral motor nerve fibers that regulate the activity of glands, and smooth and cardiac muscles.|
|Sympathetic Division||Reacts to exciting stimuli - fight or flight.|
|Parasympathetic Division||Reacts to stimulations from the viscera and other areas to prepare the body for non-voluntary processes - house keeping.|
|Amitotic||Cells do not divide.|
|High Metabolic Rate||Requiring abundant supplies of oxygen and glucose.|
|Concentration gradient||When there are more particles of an ion on one side of the membrane than the other; The unequal distribution of ions across the membrane; potassium more highly concentrated inside and sodium more concentrated outside. Sodium/potassium pump keeps sodium concentration higher outside.|
|Electrostatic force|| Like those of a magnet.|
Opposite charges attract (+ moves toward -)
Same charges push away from each other.
|Ion pump||A special membrane protein that can move ions in a direction against the normal flow of equilibrium.|
|Voltage-Gated Sodium Channels|| Open in response to a slight change in the membrane potential.|
Only allow sodium ions through.
|Voltage Gated Potassium Channels|| Open in response to a massive positive change in membrane potential.|
Only allow potassium ions through.
|Voltage-gated channels|| Found at the beginning of the nerve cell axon and all the way down the length of the axon. |
They are arranged in pairs: 1 of each type of channel at different points on the axon.
|Absolute refractory period|| Time during which no action potential can be formed. |
Lasts about 1 millisecond or .001 seconds.
|Relative refractory period||Time when a particularly strong amount of stimulation can force an action potential.|
|Synapses||the gaps between neurons, across which chemical messages are sent, small gaps, or spaces, between nerve cells, neurons, through which information is transmitted from one neuron to the next.|
|pre-synaptic axon terminal||Releases synaptic vesicles carrying neurotransmitters.|
|post-synaptic dendrite||Has special receptors to receive specific neurotransmitters.|
|synaptic cleft||The space between pre and post synaptic neurons.|