L8: Organization of nervous system Flashcards
What is the nervous system composed of?
The nervous system is formed of 2 types of cells and their processes:
Nerve cells: called neurons.
Supporting cells: called glial cells or neuroglial cells or neuroglia.
What is the structure of the cell body (soma)?
consists of the nucleus and cytoplasm.
The nucleus is usually central and contains nucleolus.
The cytoplasm contains organelles & inclusions
What are the processes of the nerve cell?
single axon and dendrites.
Compare between axon and dendrites Acc to:
Length
Function
It is the largest process of the nerve cell
Through which the nerve cell communicates with other nerve cells
Short and highly branched processes
Receive impulses from other neurons and transmit them toward the cell body
What are neurons classified according to?
the number of their processes into 3 types:
1) Unipolar Neurons: they have one process:
a. True unipolar neurons
b. Pseudounipolar neurons
2) Bipolar Neurons: 2 processes, one axon, and one dendrite. located in the sense organs (olfactory epithelium of nose, retina)
3) Multipolar Neurons: one axon and several dendrites. They form most of the nerve cells in the nervous system
What are synapses?
Sites of communication between nerve cells or between a nerve cell and muscle or gland.
What is the structure of the synapse?
- Presynaptic element: axon terminal containing synaptic vesicles.
- Synaptic cleft: 20-nm space.
- Postsynaptic element: usually dendrite.
What are the types of synapses?
1) Axodendritic synapse: between axon and dendrite.
2) Axonaxonic synapse: between axon and axon.
3) Axosomatic synapse: between axon and cell body.
4) Neuromuscular junction: between axon and muscle fiber
What are the types of neuroglia cells
A. CENTRAL NEUROGLIA: in the central nervous system(CNS)
B. PERIPHERAL NEUROGLIA: in the peripheral nervous system
What are examples of central neuroglia?
a. Astrocytes: for support and protection.
b. Oligodendrocytes: for the formation of myelin.
c. Microglia: for phagocytosis and defense against infection.
d. Ependymal cells: lining ventricles of the brain
What are examples of peripheral neuroglia?
a. Schwann cells: formation of myelin
b. Satellite cells: surrounding nerve cells
What are the divisions of the NS?
1) Central nervous system (C.N.S): Brain Spinal cord
2) Peripheral somatic nervous system
3) Peripheral autonomic nervous system
What are the divisions of the brain?
1) Cerebrum: formed of:
a. Two cerebral hemispheres: contain higher motor and sensory centers.
b. Diencephalon: formed mainly of thalamus and hypothalamus
2) Cerebellum: for coordination of muscles movements and maintaining equilibrium.
3) Brain stem: formed of the midbrain, pons, and medulla oblongata.
What is another division of the brain?
Forebrain: two cerebral hemispheres and diencephalon
midbrain: midbrain
hindbrain: cerebellum, pons, and medulla
What are the ventricles of the brain?
Lateral ventricle in each cerebral hemisphere
3rd ventricle in the diencephalon
4th ventricle in the hindbrain
What is the length of the spinal cord?
Length: 45 cm in the male and 42 cm in the female.
What is the location of the spinal cord?
in the upper two-thirds of the vertebral canal.
Where does the spinal cord begin?
as the continuation of the medulla oblongata.
Where does the spinal cord end?
It ends at:
o In the newborn: at the level of the third lumbar vertebra (L3).
o In the adult: at the level of the lower border of (L1).
What is the number of spinal cord segments?
31 segment
What is the distribution of spinal nerves?
Distribution: the 31 pairs of the spinal nerves are distributed as follows:
8 cervical 12 thoracic 5 lumbar 5 sacral 1 coccygeal
How are spinal nerves formed?
- Each spinal nerve arises by 2 roots
- The 2 roots unite at the intervertebral foramen to form spinal nerve trunk
What does the ventral root contain?
Axons of anterior horn cells supply skeletal muscles.
Axons of lateral horn cells (autonomic) supply smooth muscles.
What is attached to the dorsal root?
The spinal ganglion is attached to it; so it is called dorsal root ganglion.
What is the dorsal root formed from?
It is formed of processes of pseudounipolar cells of the spinal ganglion
Ventral root
Motor (efferent)
Dorsal root
Sensory (afferent)
What are the branches of spinal nerves?
Anterior (Ventral) Primary Ramus
Posterior (Dorsal) Primary Ramus
What are the characters of ventral primary rami?
Large in size.
Run anteriorly
May join each other to form plexuses
Connected to the sympathetic chain
What are the characters of dorsal primary rami?
Smaller in size
Run backward supply muscles & skin of the back.
Does not share in the formation of plexuses.
Not connected to the sympathetic chain
What is attached to the sympathetic ganglion?
Ventral ramus is attached to sympathetic ganglion by 2 rami communicantes: white ramus (myelinated) and gray ramus (unmyelinated)
What is the number of cranial nerves and from where do they arise?
Consists of 12 pairs (I to XII).
All arise from the brainstem except The first (I, olfactory), which arises from the nose, and the second (II, optic), which arises from the retina
What do both of the autonomic systems consist of?
Each system is formed of 3 components:
Preganglionic fibers: arise from a nucleus in the brain stem or spinal cord.
These fibers relay in the autonomic ganglia.
Autonomic ganglia: sympathetic, or parasympathetic.
Postganglionic fibers: arise from the ganglia to supply the organs.
Peripheral somatic nervous system
Cranial nerves: 12 pairs, from brain .
Spinal nerves: 31 pairs, from spinal cord .
Associated ganglia: spinal & cranial ganglia
Peripheral autonomic nervous system
Sympathetic part: thoracolumbar part .
Parasympathetic part: craniosacral part .
Associated ganglia: autonomic ganglia
What are the sympathetic and parasympathetic nerves?
