Flashcards in MNSR 13 - Nervous system: Neurons, Myelin, Nerves Deck (21)
What are the functions of the nervous system?
There are four functions of the nervous system:
1. coordinate muscle activity
2. Regulate the organs
3. Control input from the senses
4. Initiate actions
What are receptors and effectors?
Receptors are cells that receive sensations, while effectors are cells that make the appropriate response to the sensations.
What are the two subdivisions of the nervous system?
1. Central Nervous System (brain & spinal cord)
2. Peripheral Nervous System
- Autonomic Nervous System (Sympathetic, Parasympathetic, Enteric)
- Somatic Nervous System
What is neurulation?
Neurulation is the formation of the Neural Tube from a specialized region of ectoderm called the neural plate.
1. Neural plate forms from the ectoderm and begins to fold.
2. Neural plate binds dorsally to form the neural crest.
3. Closure of the neural tube disconnects the neural crest from the epidermis.
4. Neural crest cells differentiate to form the PNS.
What is a Neural Tube Disorder? Give examples.
Neural Tube Disorders are malformations of the neural tube. Tube defects include:
1. Anencephaly (head)
2. Encephalocele (head)
3. Spina Bifida (spine)
Why do pregnant women take folic acid supplements?
Folic acid is the synthetic version of the vitamin B9 that all pregnant women and pre-pregnant women should take to prevent Neural Tube Defects for their baby. Folic acid:
1. is needed to synthesize DNA bases
2. reduces the chance of NTDs by 70% with 400mg/day preconceptional use and 12 weeks post-conceptional use
3. allieviates side-effects of some immunosuppressant drugs
What does the somatic nervous system do and include?
1. Includes all neurons connected with muscles, sense organs, and skin
2. Deals with sensory information (afferent nerves: receptors to the spinal cord)
3. Controls the movement of the body (efferent nerves: spinal cord to muscles)
What does the Neuron consist of?
1. Dendrites (less than 1mm in length)
2. Soma (contains nucleus, Nissl bodies, neurofilaments, neurotubules)
3. Axon (could be 1m in length)
4. Synaptic terminal
What is the Sciatic nerve?
The longest nerve in the body.
What are the three types of neurons?
1. Pseudounipolar (PNS):
- connects sensory organs to the spinal cord
- one long dendrite, one short axon
- dendrite is structurally and functionally an axon
2. Bipolar (PNS):
- specialized sensory neurons found in the retina, inner ear, and olfactory mucosa
- one dendrite, one axon
3. Multipolar (CNS):
- large amounts of information received
- many dendrites, one axon that is long and branched
- has motor neurons
What are ganglia?
Ganglia is a mass of nerve cell bodies and dendrites. The brain is a fusion of many ganglia.
What is a plexus?
A complex system of ganglia that provide relay points between different neurological structures in the body.
What is Brachial Plexus Injury?
Brachial Plexus Injury is a paralyzed arm causing lack of sensation in the arm, hand, and wrist. Usually occurs during the birth process because a baby's shoulder becomes impacted during the birth process, causing the brachial plexus to shear or tear.
What do axons divide into, in the Central Nervous System?
Axons divide into two things:
- grey matter: contains somata, dendrites, and a few axons
- white matter: contains just axons
What are glial cells?
Glial cells are non-nervous cells that surround nerve cells. In the CNS, they are called OLIGODENDROCYTES (neuroglial cells), while in the PNS they are called SCHWANN CELLS. They both wrap around axons to form layers of the myelin sheath that provide insulation to the axon.
Myelination begins in the fourth month of fetal life and continues after birth. As the process continues, the cytoplasm from the Schwann cells is excluded, forming just layers of plasma membrane around the axon.
What is found between each Schwann cell?
Between each Schwann Cell are gaps called the nodes of Ranvier, where the axon is not myelinated and the axolemma shows.
What are non-myelinated nerve fibers?
Many axons are embedded in grooves of the cytoplasm of a Schwann Cell, which fuses to form a mesaxon.
What are peripheral nerves? Explain its structure.
Anatomical structures consisting of many nerve fibers called fascicles.
1. The axons of a fascicle remain a matrix of loose collagen fibers and capillaries called the ENDONEURIUM.
2. Each fascicle is bound by dense collagen fibers called the PERINEURIUM.
3. All fascicles of a peripheral nerve remain in a layer of connective tissue called the EPINEURIUM.
What is Multiple Sclerosis?
Multiple Sclerosis is the loss of the myelin sheath of the oligodendrocytes of the CNS. It can lead to partial or complete blindness, motor disorders of the limbs, and 80% of cases lead to total disability.