BSC2085 ASSIGNMENT 4 PART 1
1. Name subdivisions of the Nervous System (NS)
The nervous system is composed of two major anatomical subdivisions: the central nervous
system (CNS) and the peripheral nervous system (PNS). The central nervous system is
composed of the brain and spinal cord, which are enclosed and protected by the cranium and
vertebral column. The peripheral nervous system is composed of all the rest, except the brain
and spinal cord. It is composed of nerves and ganglia.
2. What are the 2 major subdivisions of the PNS and name their neurotransmitters.
The peripheral nervous system is functionally divided into sensory and motor divisions, and
each of these is further divided into somatic and visceral subdivisions. The sensory (afferent)
division carries sensory signals from various receptors (sense organs and simple sensory nerve
endings) to the CNS. This is the pathway that informs the CNS of stimuli within and around the
body. The motor (efferent) division carries signals from the CNS to gland and muscle cells that
carry out the body’s responses. Cells and organs that respond to commands from the nervous
system are called effectors. The somatic motor division carries signals to the skeletal muscles.
This output produces muscular contractions that are under voluntary control, as well as
involuntary muscle contractions called somatic reflexes. The visceral motor division (autonomic
nervous system) carries signals to glands, cardiac muscle, and smooth muscle. We usually have
no voluntary control over these effectors, and this system operates at an unconscious level.
3. Name and describe function of 4 types of neuroglia cells in CNS.
There are four types of neuroglia that occur in the central nervous system.

Oligodendrocytes somewhat resemble an octopus; they have a bulbous body with as
many as 15 armlike processes. Each process reaches out to a nerve fiber and spirals
around it like electrical tape wrapped repeatedly around a wire. This spiral wrapping is
called the myelin sheath, insulates the nerve fiber from the extracellular fluid and
speeds up signal conduction in the nerve fiber.

Ependymal cell resembles a cuboidal epithelium lining the internal cavities of the brain
and spinal cord. Unlike epithelial cells, however, they have no basement membrane,
and they exhibit rootlike processes that penetrate the underlying nervous tissue.
Ependymal cells produce a significant fraction of the cerebrospinal fluid (CSF), a clear
liquid that bathes the CNS and fills its internal cavities. Some of them have patches of
cilia on their apical surfaces that help to circulate the CSF.

Microglia are small macrophages that develop from stem cells related to the white
blood cells called monocytes. They wander through the CNS and phagocytize dead
nervous tissue, microorganisms, and other foreign matter. They become concentrated
in areas damaged by infection, trauma, or stroke. Pathologists look for clusters of
microglia in histological sections of the brain as a clue to sites of injury.

Astrocytes are the most abundant glial cells in the CNS and constitute over 90% of the
tissue in some areas of the brain. They cover the entire brain surface and most non
synaptic regions of the neurons in the gray matter of the CNS. They are named for their
many-branched, somewhat starlike shape. They form a supportive framework for the
nervous tissue. They have extensions called perivascular feet, which contact the blood
capillaries and stimulate them to form a tight seal called the blood–brain barrier. This
barrier isolates the blood from the brain tissue and limits what substances can get to the
brain cells, thus protecting the neurons. They convert blood glucose to lactate and
supply this to the neurons for nourishment. They secrete proteins called nerve growth
factors that promote neuron growth and synapse formation. They communicate
electrically with neurons and may influence future synaptic signaling between neurons.
They regulate the chemical composition of the tissue fluid. When neurons transmit
signals, they release neurotransmitters and potassium ions. Astrocytes absorb these
substances and prevent them from reaching excessive levels in the tissue fluid. When
neurons are damaged, astrocytes form hardened scar tissue and fill space formerly
occupied by the neurons. This process is called astrocytes or sclerosis.