Nervous System Flashcards
Organization of the nervous system
In 2 parts:
Central Nervous System - brain and spinal cord
Peripheral Nervous System - spinal and cranial nerves
Divisions of the PNS
Afferent - conducts towards the CNS
Efferent - conducts away from the CNS
Somatic Division of the PNS
Nerves that supply the skeletal muscles. Usually under conscious control
Autonomic Division of the PNS
Nerves that supply smooth muscle, heart muscle, and glands. Not under conscious control. 2 parts: parasympathetic and sympathetic
3 Functions of the Nervous System
- Monitor (Sensory Input)
- Integration
- Response (Motor Input)
Nerve
A bundle of neuronal processes found in the PNS
Nerve Tract
The same as the nerve, a bundle of neuronal processes, but found in the CNS
Ganglion
A collection of cell bodies and synapses which is found in the PNS
Nucleus
A collection of cell bodies and synapses found in the CNS
Center
A synaptic area in the CNS with a specific function (vision center, speech center, etc)
Gray Matter
A general term for unmyelinated nervous tissue.
White Matter
A general term for myelinated nervous tissue
Neurons
The structural and functional units of the nervous system, they conduct actions potentials. They are long lived, amitotic (don’t divide) and have a high metabolic rate.
Structure of a Neuron
Have 3 general regions: input region, conducting region, and output region. Consist of a cell body and one or more slender processes.
Plasma Membrane of the Neuron
This is the site of electrical signaling
Nissl Bodies
Condensations of the rough ER. Composed mainly of RNA and proteins, and function in protein synthesis.
Dendrites
Highly branched cell processes. They are the receptive regions of the neuron. They conduct signals toward the cell body and contain Nissl bodies
Axons
Processes that generate and conduct the AP away from the cell body. Do not contain Nissl bodies, rough ER, or Golgi apparatus. Have a plasma membrane called an axolemma.
Axon Hillock
The region of the cell body which extends into the axon. It is here that the AP is initiated.
Collaterals
Branching of the axons along it’s length.
Telodendria
The terminates of the axon. Each axon can have 10,000 or more. Here is where the neurotransmitter is released.
Myelin Sheath
A white envelope which surrounds the axons of many nerve cells. Made mostly of a white lipid known as myelin. It protects, insulate, and increases the speed of the AP.
Myelination in the PNS
The sheath is formed by Schwann cells which wrap around the axons many times creating many layers of membrane.
Satellite Cell
Regulate the chemical environment of the cell.
Nodes of Ranvier
Small gaps where adjacent Schwann cells meet.
Neurilemma
The nucleus and cytoplasm of Schwann cells wrapped around the myelin sheath forming a tube. When an axon is cut, it forms a regeneration tube which secretes chemicals to help repair the damage which is why most PNS nerve damage is repairable.
Myelination in the CNS
Myelin sheaths are formed by oligodendrocytes. They have nodes of Ranvier, but no neurilemma because each oligodendrocyte myelinates up to 60 different processes. Repair of damaged neurons in the CNS is very limited.
Motor Neurons
Efferent - Conduct impulses away from the CNS.
Sensory Neurons
Afferent - Conduct impulses towards the CNS
Association Neurons
Interneurons - Found within the CNS. Connect the motor and sensory neurons.
Multipolar Neurons
Have more than 2 processes coming off the cell body. Mostly motor and interneurons, most common type found in the CNS.
Bipolar Neurons
Two processes coming off the cell body, one axon and one dendrite. Often associated with special senses like hearing and the retina of the eye.
Unipolar Neurons
There is a single major process coming off the cell body. THis process usually divides into two parts. Most sensory neurons are of this type.
Anaxonic Neurons
Found in the brain
Astrocytes
Most numerous glial cells in the CNS. Have long extensions, hence the star like appearance. They metabolize neurotransmitters, and help control the ionic environment around the neurons.
Oligodendrocytes
Form the myelin sheaths for axons in the CNS
Ependymal Cells
Line the cavities of the CNS and cushion the brain and spinal cord. Have microvilli that circulate the CSF.
Microgliocytes
Small phagocytotic cells, play a role in the destruction of dead tissue and defense against microorganisms
Resting Membrane Potential
Averages about -70mv
Neuronal Responses
First response is the action potential. The second response is the release of the neurotransmitter.
Threshold Point
The weakest stimulus needed to produce an AP.
Subthreshold
Insufficient stimulus. No impulse is produced.
Absolute Refractory
When a membrane patch is generating an AP, that neuron cannot respond to another stimulus
Synapses
The junctions between two or more neurons.
Presynaptic
The neuron which conducts the impulse towards the synapse
Postsynaptic
The neuron which conducts the impulse away from the synapse.
Depolarization
The plasma membrane is becoming less negative. When there is an influx of Na+
Repolarization
The plasma membrane is becoming more negative. K+ is diffusing out, there is a membrane change in permeability.
Second Impulse
A second impulse cannot be generated until the membrane potential is reestablished.
EPSP
Excitatory postsynaptic potential. Causes Na+ and K+ passage. It’s only function is to trigger an AP.