Answers-2, BIO 3220, Nervous System


1. Review the general function of the nervous system.
Its overall function is to collect information about the external conditions in relation to the body’s internal state (sensory/receptors), to analyze this information (integration/memory), and to initiate appropriate responses to satisfy certain needs (response).

2. Compare and contrast the central and peripheral nervous system.
The Central Nervous System (CNS) consist of the brain and the spinal cord. The spinal cord carries messages from the body to the brain, where they are analyzed and interpreted. Response messages are then passed from the brain through the spinal cord and to the rest of the body. The Peripheral Nervous System (PNS) consists of the neurons not included in the brain and spinal cord. Some peripheral neurons collect information from the body and transmit it toward the CNS. These are called afferent neurons. Other peripheral neurons transmit information away from the CNS. These are called efferent neurons. The PNS is responsible for the body functions which are not under conscious control, like the heartbeat or the digestive system. The smooth operation of the PNS is achieved by dividing it into sympathetic and parasympathetic Systems.

3. Describe the parts of a neuron.
A neuron consists of three main parts:
Cell body – the largest part, contains the nucleus and much of the cytoplasm (area between the nucleus and the cell membrane), most of the metabolic activity of the cell, including the generation of ATP (a compound that stores energy) and synthesis of protein
Dendrites – short branch extensions spreading out from the cell body; dendrites receive stimulus (action potentials) and carry impulses from the environment or from other neurons and carry them toward the cell body
Axon – a long fiber that carries impulses away from the cell body; each neuron has only one axon; the axon ends in a series of small swellings called axon terminals

4. Define neuroglia. Give some examples of neuroglial cells.
Within the brain and spinal cord, both myelinated and unmyelinated parts of neurons may be in contact with cells called neuroglia (“nerve glue”). These cells are responsible for various functions, including potassium transport, nutrition, excretion, regeneration, and repair. About half of the bulk of the brain is neuroglia.

5. Discuss the development of the nervous system. Include neurulation, neural tube, germinal layer, mantle layer, marginal layer, neuroblast, spongioblast, alar plate, basal plate.
Neurulation is the process that establishes the central nervous system. As seen in cross section, the embryonic neural tube forms three layers; from neurocoel outward, these are an internal or ependymal/germinal, an intermediate or mantle, and an external or marginal. The ependymal layer is ultimately converted into the ependyma of the central canal; the processes of its cells pass outward toward the periphery. The marginal layer is devoid of nuclei, and later forms the supporting framework. The mantle layer represents the whole of the future gray columns; in it the cells are differentiated into two sets, spongioblasts or young neuroglia cells, and germinal cells, which are the parents of the neuroblasts or young nerve cells. The widest part of the canal serves to subdivide the lateral wall of the neural tube into a dorsal or alar, and a ventral or basal lamina, a subdivision which extends forward into the brain.

6. Identify the location of the spinal cord.
The spinal cord is a column of millions of nerve fibers (axons) that run through your spinal canal. It extends from the brain to the area between the end of your first lumbar vertebra and top of your second lumbar vertebra. At the second lumbar vertebra, the spinal cord divides into several different groups of fibers that form the nerves that will go to the lower half of the body. For a small distance, the nerves actually travel through the spinal canal before exiting out the neural foramen. This collection of nerves is called the cauda equina (horse’s tail) while it is still inside the spinal canal.

7. Define meninges. Name the specific components and describe their function.
Meninges are layers of tissue that support and protect the spinal cord. In fish, the protective layer is called the meninx primitiva. The inner membrane in higher vertebrates is called the leptomeninx. The outer membrane in higher vertebrates is called the dura matter. Mammals posses pia matter, an inner splitting of leptomeninx, and arachnoid and subarachnoid space, an outer layer splitting from leptomeninx. The subarachnoid space contains cerebrospinal fluid.

8. Define cauda equina.
Cauda equina is the bundle of spinal nerve roots running through the lower part of the subarachnoid space within the vertebral canal below the first lumbar vertebra; the caudal most set of spinal nerves resembling a horse’s tail.

9. Contrast the location and function of gray matter versus white matter in the spinal cord.
Gray Matter is internal and has an irregular shape resembling the letter H. Dorsal Gray Columns form the upper arms or “horns” of the H. Nerve cell bodies of association neurons that synapse with sensory fibers are on the dorsal column. Ventral Gray Columns form the shorter, broader, lower arms of the H. Nerve cell bodies of somatic motor neurons fill the ventral columns. Gray commissure, centrally located, surrounds the central canal and makes up the cross arm of the H; it transmits fibers from one side of the cord to the other. The white matter are tracts peripheral to the gray matter and carry ascending or descending messages.

10. Describe spinal nerves. Name the hole that allows them to exit the vertebrae. Explain dorsal and ventral roots and dorsal and ventral rami as they relate to the spinal cord.
The nerve joins the cord by separate dorsal and ventral roots through the intervertebral foramen, The dorsal root contains sensory information and the ventral root contains motor information. Just distal to the union of the two roots, the spinal nerve divides into a dorsal ramus that goes to muscles of epaxial origin and a relatively large ventral ramus that goes to the appendages and structures of hypaxial origin.

11. Define plexus.
A plexus is a network of successive spinal nerves that supply limbs.

12. Define occipitaspinal nerve.
A pair of extra nerves in anamniotes that innervate hypobranchial muscles

13. Discuss the functions of spinal nerves.
All of the spinal nerves are “mixed”; that is, they contain both sensory and motor neurons. Touch sensation from the body is transmitted upward to the brain and instructions for body movement from the brain are transmitted downward to the body through specialized nerve pathways in the spinal cord. Simple reflexes requiring no higher mental processes, e.g., the lower leg jerking when the knee is tapped with a hammer, are performed by spinal nerves going in and out of the spinal cord.

14. Explain what a ventricle is in the nervous system. Name and locate the ventricles. Explain how the ventricles interconnect.

A ventricle is a cavity containing CSF. The cerebrum has 2 lateral ventricles that connect to the 3rd ventricle via the interventricular foramen. The third ventricle is in the diencephalon. The third ventricle connects to the fourth ventricle via the cerebral aqueduct which courses through the mesencephalon. The fourth ventricle is in the hindbrain and separates the medulla oblongata from the cerebellum.

15. Name the three parts of the embryonic brain.
Prosencephalon (forebrain), mesencephalon (midbrain), rhombencephalon (hindbrain)

16. Describe the telencephalon, rhinencephalon and cerebral hemispheres.

The Prosencephalon gives rise to the Telencephalon. It in turn gives reise to the olfactory portion of the brain – the rhinencephalon – and the cerebral hemispheres. The cerebral hemispheres are small in lower vertebrates and very large in higher vertebrates. Mammals have such large cerebral hemispheres that it covers the rhinencephalon and contains convolutions.

17. Describe the paleostriatum, neostriatum, hyperstriatum and basal nuclei.

These describe the cerebral hemispheres in vertebrates. The paleostriatum is the cerebrum of fish and it mainly coordinates olfactory reflexes. Starting with reptiles, the paleostriatum becomes buried and the neostriatum becomes an area of more nuclei, neuroglia and various tracts. The hyperstriatum is seen primarily in birds responsible for certain behaviors such as courting, the Basal nuclei = Corpus striatum are the remants of the paleostriatum and neostriatum in the mammal brain.

18. Locate the cerebral cortex and discuss its functions.

The cerebral cortex starts in reptiles and is the outer gray matter of the cerebral hemispheres. It contains billions of neurons and is responsible for voluntary movement, and conscious sensations (seeing, touching…), thinking, memory…

19. Describe the diencephalon – including the functions of the epithalamus, thalamus and hypothalamus.

The other part of the embryonic prosencephalon is the diencephalon. It contains the epithalamus which includes the pineal body. The pineal body is endocrine in gnathostomes, helping to monitor various cycles related to length of daylight. The thalamus is the center part of the diencephalon and is the primary sensory relay center for virtually all sensory (except smell) information going to the cerebral hemispheres. The hypothalamus is obviously located below the thalamus and regulates the Autonomic Nervous System, various homeostasis functions (temperature, thirst….) and makes hormones.

20. Locate the mesencephalon. Lists its parts and functions.

The mesencephalon is the midbrain. It is an embryonic and an adult therm. It contains the optic lobes associated with visual reflexes, the auditory lobes associated with hearing reflexes and the cerebral peduncles which are primary motor tracts descending from the cerebrum.

21. Locate the parts of the rhombencephalon and discuss their functions.

The rhombencephalon is the embryonic hindbrain. It contains the myelencephalon, or medulla oblongata. The medulla is responsible for being a connection between brain and spinal cord and regulates vital reflexes such as breathing and blood pressure. The metencephalon is the cerebellum (coordination & balance headquarters) and the pons (assists in breathing regulation and “bridges” other parts of the brain).

22. List the 12 cranial nerves per your nerve handout. Describe the sensory and motor functions. Locate where they emerge from the brain. Discuss any phylogenetic differences amongst the vertebrates. Name the cranial nerves unique to amniotes.

Refer to this link for the 12 cranial nerves. Only amniotes have cranial nerves XI and XII.

23. Compare the Autonomic Nervous System to the somatic efferent system.

Somatic efferent is part of the Peripheral Nervous systm and contains one neuron going to skeletal muscles. The ANS is also Peripheral Nervous system and efferent, but contains a preganglionic and a postganglionic neuron going to smooth muscle, cardiac, muscle and glands.

24. Name the two divisions of the A.N.S. and briefly compare their functions and structures.

Sympathetic is fight or flight; Parasympathetic is rest and relaxation. Both tend to innervate smooth muscle, cardiac muscle and glands, however, sympathetic begins in the thoracolumbar region of the spinal cord and parasympathetic begins in the sacral region of the spinal cord Plus the brainstem and runs along with cranial nerves III, VII, IX, and most importantly, X.

25. Name the two A.N.S. neurons.

Pregangionic and postgangionic neurons. A ganglion is a group of neuron cell bodies found in the peripheral nervous system.

26. Define autonomic ganglia. List three types.

Specific names of ganglia containing synapsing in the ANS. Three types are paravertebral, collateral and terminal.

27. Contrast adrenergic and cholinergic.

Adrenergic neurons release norepinephrine as the neurotransmitter. These are found in the postganglionic neurons of the Sympathetic division. Cholinergic neurons release acetylcholine as the neurotransmitter and are found at the neuromuscular junction and at the preganglionic neurons of both sympathetic and parasympathetic divisions as well as the postganglionic neurons in the parasympathetic divisions.

28. Describe the location and function of the adrenal medulla. What does it secrete?

This gland is above the kidney and releases epinephrine to prolong and exaggerate the fight or flight response.