Nervous Tissue Flashcards
List the 2 anatomical subdivisions of the nervous system.
- Central nervous system (CNS) [consists of the brain and spinal cord. It is primarily responsible for integrating, processing and coordinating sensory data and motor commands. It is also the seat of higher functions such as intelligence, memory, learning and emotions]
- Peripheral nervous system (PNS) [includes all of the neural tissue outside of the CNS through 12 pairs of cranial nerves, 33 pairs of spinal nerves and peripheral nerves conducting impulses to and from the CNS and ganglia that are small aggregates of nerve cells outside the CNS]
Briefly elaborate on the PNS’ afferent and efferent divisions in terms of what they do.
The PNS provides sensory information from receptors to the CNS (afferent division); and carries motor commands from the CNS to peripheral tissues and systems (efferent division).
The efferent division has somatic nervous system and visceral motor system/autonomic nervous system. Explain their functions.
- The somatic nervous system (SNS) controls skeletal muscle contraction that may be voluntary or involuntary . [Mainly controls voluntary activities]
- The autonomic nervous system (ANS) regulates smooth muscle, cardiac muscle and glandular (exocrine and endocrine) activity. [Controls involuntary activities]
a) The autonomic nervous system provides almost every organ with a double set of nerves that make up the sympathetic and parasympathetic systems. State the functions of those systems.
b) The autonomic nervous system has a third component. What third system is that and what does it do?
a) The sympathetic system activates and prepares the body for vigorous muscular activity, stress and emergencies [arouses body to expend energy]. The parasympathetic system lowers activity, operates during normal situations, permits digestion, and conservation of energy [calms body to conserve and maintain energy].
b) The enteric (gut) nervous system (ENS). It has parasympathetic ganglia [because of digestion] and interneurons for the involuntary control over smooth muscle and glands of digestive system.
Briefly describe each of the following types of neurons as classified according to the number of processes extending from the cell body. [classification of neurons according to structure]
1. multipolar neurons
2. bipolar neurons
3. unipolar/pseudounipolar neurons
4. anaxonic neurons
- multipolar neurons: each has one axon and two or more dendrites
- bipolar neurons: one dendrite and one axon [comprise sensory neurons of retina, olfactory epithelium, inner ear]
- pseudounipolar neurons: each have a single process that bifurcates close to the perikaryon, with the longer branch extending to a peripheral ending and the other towards the CNS [includes all other sensory neurons]
- anaxonic neurons: many dendrites but no true axon [do not produce action potentials, but regulate electrical changes of adjacent CNS neurons]
- unipolar neurons: only has the axon and cell body
For illustrations see Junqueria page 165.
NB: Pseudounipolar neurons are called so because there is a dendrite besides the axon.
What are Nissl bodies?
They are large masses of free polysomes and RER indicating the cell’s high rate of protein synthesis.
Notes:
What are polysomes? A polysome (polyribosome) is a group of ribosomes bound to an mRNA molecule like “beads” on a “thread”.
What is the function of dendritic spines?
They are the first processing site for synaptic signals arriving on a neuron.
Further notes:
These are mushroom shaped structures with an expanded head connected to the dendrite shaft by a narrower neck. Their processing apparatus is contained in a complex of proteins attached to the cytosolic surface of the postsynaptic membrane. They participate in the plastic changes that underlie adaptation, learning, and memory.
The axon is a long cylindrical process that varies in length and diameter according to the type of neuron. They all originate from a short pyramid-shaped tapered region called the ____(a)____ which arises from the ____(b)____. The plasma membrane of the axon is called ____(c)____, and its contents are the ____(d)____. In neurons with a myelinated axon, the portion of the axon between the ____(a)____ and the point at which myelination begins is called the ____(e)____. It contains several types of ion channels that generate the change in electrical potential, which constitutes the action potential.
Axons of interneurons and some motor neurons also have major branches called ____(f)____ that end at smaller branches with synapses influencing the activity of many other neurons. Each small axonal branch ends with a dilation called a ____(g)____ that contacts another neuron or non-nerve cell at a synapse to initiate an impulse in that cell.
(a) axon hillock
(b) perikaryon/cell body
(c) axolemma
(d) axoplasm
(e) initial segment
(f) collaterals
(g) terminal button
Lively bidirectional transport of molecules large and small occurs within axons. Organelles and macromolecules synthesized in the cell body move by ____(a)____ transport along axonal microtubules via ____(b)____ from the perikaryon to the synaptic terminals. ____(c)____ transport in the opposite direction along microtubules via ____(d)____ carries other macromolecules, such as materials taken up by endocytosis (including viruses and toxins), from the periphery of the cell to the body.
(a) anterograde transport
(b) kinesin
(c) retrograde transport
(d) dynein
Pyramidal neurons (also known as pyramidal cells) are ____(a)____ neurons [classification according to number of processes] found in areas of the brain including the ____(b)____, ____(c)____ and ____(d)____.
(a) multipolar
(b) (c) (d) cerebral cortex, hippocampus and amygdala
Where are stellate neurons found?
- cerebral and cerebellar cortices
- gray matter of spinal cord
- motor nuclei of cranial nerves of the brain stem
Purkinje neurons: They form one of the characteristic features of the cerebellar cortex. They have a profuse dendritic arborization in the ____(a)____ layer of the cerebral cortex. The finer dendritic branches bear thousands of regularly spaced projections or spines. The axons of the purkinje cells traverse the ____(b)____ layer of the cerebellum, acquire myelin sheaths on entering the white matter and terminate in the ____(c)____.
(a) molecular
(b) granular
(c) central cerebellar nuclei
How are neurons classified according to function?
a) Motor (efferent) neurons: control effector organs e.g. muscle fibres and glands
b) Sensory (afferent) neurons: involved in the reception of sensory stimuli from the environment and from within the body
c) Interneurons: transmit impulses between other neurons
State the embryonic origin and main functions of 4 types of glial cells found in the Central Nervous System.
Oligodendrocyte
Origin: neural tube
Main functions: myelin production
Astrocyte
Origin: neural tube
Main functions: structural support, repair processes, blood-brain barrier, metabolic exchanges
Ependymal cell
Origin: neural tube
Main functions: lining the cavities of the CNS
Microglia
Origin: bone marrow
Main functions: macrophagic activity
State the origin, location and main functions of Schwann cells.
Origin: neural crest
Location: Peripheral nervous system
Main functions: myelin production
