Chapter 3 - Anatomy of the Nervous System

What are the three important principles regarding the respective functions of the sympathetic and parasympathetic systems?

1. Sympathetic nerves stimulate, organize, and mobilize energy resources in threatening situations. Whereas, parasympathetic nerves act to conserve energy. 2. Each autonomic target organ receives opposing sympathetic and parasympathetic input, and its activity is thus controlled by relative levels of sympathetic and parasympathetic activity. 3. Sympathetic changes are indicative of psychological arousal, whereas parasympathetic changes are indicative of psychological relaxation. Ex: Think of sympathetic as instigators. The nerves get scared when you get scared, so they wind you up. Parasympathetic as empathy. The nerves are empathetic and they help you to conserve.

Golgi Complex

A connected system of membranes that packages molecules in vesicles.

Myelin Sheath

A layer of fatty tissue segmentally encasing the fibers of many neurons; enables vastly greater transmission speed of neural impulses as the impulse hops from one node to the next. Increase speed and efficiency of axonal conduction.

Blood Brain Barrier

A mechanism that impedes the passage of many toxic substances from the blood into the brain. Its a consequence of the special structure of cerebral blood vessels. The cells of the blood vessels are tightly packed, thus forming a barrier to the passage of many molecules - particularly proteins and other large molecules. The degree to which therapeutic or recreational drugs can influence brain activity depends on the ease with which they penetrate the blood-brain barrier. It doesn't impede the passage of ALL large molecules. Some large molecules are critical for normal brain function (e.g., glucose) and actively transported through cerebral blood vessel walls. The blood vessel walls in some areas of the brain allow certain large molecules to pass through them unimpeded. Many CNS disorders are associated with impairment of the blood-brain barrier.

Cerebral Aqueduct

A narrow channel that connects the third and fourth ventricles. Found in midbrain (mesencephalon), and a structure located in the division of the tegmentum. The periaqueductal gray is situated around it.

Golgi Stain

A neural stain that completely darkens a few of the neuron in each slice of tissue, thereby revealing their silhouettes in great detail but internal details are invisible. Most commonly used when the overall shape of a neuron is of interest. Discovered when C.Golgi saw the silver chromate create a chemical reaction of potassium dichromate and silver nitrate.

Nissl Stain

A neural stain that has an affinity for structures in neuron cell bodies. Under low magnification, the stains provide a gross indication of brain structure by selectively staining groups of neural cell bodies, and under higher magnification one can distinguish individual neural cell bodies and thus count the number of neurons in various areas. The most common dye used in the method is cresol violet. This and other dyes penetrate all cells on a slide, but they bind effectively only to structures in neuron cell bodies.

Electron Microscopy

A neuroanatomical technique the provides information about the details of neuronal structure. Because of the nature of light, the limit of light magnification is about 1,500X, which is insufficient to reveal the fine anatomical design of neurons. Greater detail can be seen by first coating thin slices of neural tissue with an electron-absorbing substance that is taken up by different parts of neurons to different degrees, then passing a beam of electrons through the tissue onto a photographic film. The result is an electron micrograph; capturing the neuronal structure in great detail. A scanning electron microscope provides micrographs in three dimensions but is not capable of as much magnification as conventional electron microscopy. Its weakness is because the images are so detailed, they can make it difficult to visualize general aspects of neuroanatomical structure.

Multipolar Neuron

A neuron with MORE than two processes (axons) extending from its cell body. Most neurons are multipolar.

Unipolar Neuron

A neuron with one process (axons) extending from its cell body.

Bipolar Neuron

A neuron with two processes (axons) extending from its cell body.

Midsagittal Section

A section cut down the centre of the brain, between the two hemispheres.

Central Canal

A small central channel that runs the length of the spinal cord.

Endoplasmic Reticulum

A system of folded membranes in the cell body. Rough portions (those with ribosomes) play a role in the synthesis of proteins. Smooth portions (those without ribosomes) play a role in the synthesis of fats.

Which cranial nerve is number (VI) ?

Abducens; motor; eye movements Abducens; sensory; sensory signals rom certain eye muscles Abducens: Controls the movement of the lateral rectus muscle in humans, responsible for outward gaze

Hydrocephalus

Accumulation of fluid in the spaces of the brain. (Water Head). Hydrocephalus is treated by draining the excess fluid from the ventricles and trying to remove the obstruction. Often congenital (present from birth).

Glial Cells

Also called glia; they are several classes of non-neural cells of the nervous system. The physiological effects are numerous, but exact nature of their function is largely debatable. New discoveries have suggested that they are more varied than implied (not just 4 different types). At least 9 different astrocytes have been identified; each with its own structure and physiology.

Frontal Sections

Also termed coronal sections; any sections of brain tissue cut in a plane that is parallel to the face.

What are the three axes of the vertebrate nervous system?

Anterior-Posterior; Dorsal-Ventral; Medial-Lateral

What are the two types of neuroanatomical tracing techniques?

Anterograde and retrograde tracing methods.

Horizontal Sections

Any slices of brain tissue cut in a plane that are parallel to the top of the brain.

Sagittal Sections

Any slices of brain tissue cut in a plane that is parallel to the side of the brain.

Which cranial nerve is number (VIII) ?

Auditory-Vestibular; sensory; audition, sensory signals from the organs of balance in the inner ear

Lateral

Away from the midline, toward the body's lateral surfaces.

Subarachnoid Space

Beneath the arachnoid membrane. The space which contains many large blood vessels and cerebrospinal fluid.

Tracts

Bundles of axons in the CNS.

Nerves

Bundles of axons in the PNS.

Efferent Nerves

Carry motor signals from the CNS to the skeletal muscles.

Afferent Nerves

Carry signals from the skin, skeletal muscles, joints, eyes, ears, etc to the CNS.

Neurons

Cells that specialized for reception, conduction and transmission of electrochemical signals. Come in a variety of shapes and sizes.

Neuron Cell Membrane

Composed of a lipid bilayer, or two layers of fat molecules. Embedded in the lipid bilayer are numerous protein molecules that are the basis of many of the cell membranes functional properties. Some membrane proteins are "channel proteins" through which certain molecules can pass. Others are "signal proteins" which transfer a signal to the inside of the neuron when particulate molecules bind to them on the outside of the membrane.

Which cranial nerve is number (VII) ?

Facial; sensory; taste from anterior two-thirds of tongue Facial; motor; facial expression, secretion of tears, salivation, cranial blood vessel dilation

Microglia

Glial cells that respond to injury or disease by engulfing cellular debris or even entire cells and trigger inflammatory responses. They are smaller than other glial cells. Been shown to play more than a supportive role such as a role in the regulation of cell death, synapse formation and elimination.

Oligodendrocytes

Glial cells with extensions that wrap around the axons of some herons of the CNS. These extensions are rich in myelin. Glial cells that myelinate the CNS axons of the CNS.

Which cranial nerve is number (IX) ?

Glossopharyngeal; sensory; taste from posterior third of tongue Glossopharyngeal; motor, salivation, swallowing Glossopharyngeal: A mixed nerve that carries afferent sensory and efferent motor information

How do you tell the difference between efferent and afferent nerves?

Going toward the CNS - begin with an A. Going away from the CNS - begin with an E.

Which cranial nerve is (XII) ?

Hypoglossal; motor, tongue movements Hypoglossal; sensory, sensory signals from tongue muscles Hypoglossal: Innervates all the extrinsic and intrinsic muscles of the tongue, except for the palatoglossus which is innervated by the vagus nerve. It is a nerve with a solely motor function

What happens when the flow of cerebrospinal fluid is blocked by a tumor near one of the narrow channels that link the ventricles?

If for example, near the cerebral aqueduct which connects the 3rd and 4th ventricles, if there is a build up of fluid in the ventricles, it causes the walls of the entries and the entire brain to expand and produces a condition called: hydrocephalus (Water Head). Hydrocephalus is treated by draining the excess fluid from the ventricles and trying to remove the obstruction.

How are directions in the vertebrate nervous system described?

In relation to the orientation of the spinal cord.

Sympathetic Nerves

In the Autonomic Nervous System; autonomic motor nerves that project from the CNS in the lumbar (small of he back) and thoracic (chest) regions of the spinal cord.

Parasympathetic Nerves

In the Autonomic Nervous System; autonomic motor nerves that project from the brain and sacral (lower back) region of the spinal cord.

Ribosomes

Internal cellular structure on which proteins are synthesized; they are located on the endoplasmic reticulum.

What are the two different neuroanatomical meanings of nucleus?

It is a structure in the neuron cell body AND and cluster of cell bodies in the CNS.

Astrocytes

Large, star shaped glial cells that play multiple roles in the CNS. The extensions of some cover the outer surfaces of blood vessels that course through the brain; they also make contact with other neurons. These particular astrocytes appear to play a role in allowing the passage of some chemicals from the blood into the CNS neurons and in blocking other chemicals, and they have the ability to contract or relax blood vessels based on the blood flow demands of particular brain regions. Have been shown to exchange chemical signals with neurons and other astrocytes, control establishment and maintenance of synapses between neurons, modulate neural activity, form functional networks with neurons and other astrocytes, control the blood-brain barrier, and to respond to injury.

Proximal

Means "close" to something. In the CNS, it means closer to it.

Distal

Means "far" from something. In the CNS, it means farther from it.

Arachnoid Membrane

Middle layer of the three membranes (meninges) that surround the brain and spinal cord. Its spider web like.

Neurotransmitters

Molecules that are released from active neurons and influence the activity of other cells.

Cranial Nerves

Nerves which project from the brain. There are 12 pairs. They are numbered in sequence from front to back. They include purely sensory nerves like olfactory nerves (I), and the optic nerves (II), but most contain both sensory and motor fibres. The longest cranial nerves are the vagus nerves (X), which contain motor and sensory fibres travelling to and from the gut. Because the functions and locations of the cranial nerves are specific, disruptions of a particular cranial nerve functions provide excellent cues about the location and extent of tumors and other kinds of brain pathology.

Interneurons

Neurons with a short axon or no axon at all.

Which cranial nerve is number (III) ?

Oculomotor; motor; eye movement and pupillary constriction. Oculomotor; sensory, sensory signals from certain eye muscles. Oculomotor: Motion of the eye.

Which cranial nerve is number (I) ?

Olfactory; sensory; smell

What are the four kinds of glial cells?

Oligodendrocytes, Schwann Cells, Astrocytes and Microglia.

How is the nervous system divided?

On the most basic level, it can be divided into 2 parts: the central nervous system (brain and spinal cord) and the peripheral nervous system which is made up of nerves that connect to sensory receptors and the body's muscles and glands. The PNS can be divided into the somatic nervous system which connects to skeletal muscles and skin, and the autonomic nervous system which includes activities such as breathing. The autonomic system connects the sensory system to the central nervous system as well as the CNS to non-skeletal muscles and glands. The autonomic nervous system can be further divided into the sympatric nervous system which controls responses to emergency or stressful situations and parasympathetic nervous system which controls all routine functions such as breathing rate..

Which cranial nerve is number (II) ?

Optic; sensory; vision

Choroid Plexuses

Produces cerebrospinal fluid. The network of capillaries that protrude into the ventricles from the pia mater.

Cerebrospinal Fluid (CSF)

Protects the CNS and fills the subarachnoid space (beneath arachnoid membrane) the central canal of the spinal cord, and the cerebral ventricles of the brain. Supports and cushions the brain. Patients who have had some of their fluid drained away often suffer raging headaches and experience stabbing pain each time they jerk their heads. Its produced by the choroid plusses (networks of capillaries or blood vessels that protrude into the ventricles from the pia mater). Excess fluid is continuously absorbed from the subarachnoid space into large blood-filled spaces (dural sinuses).

How are Schwann Cells and Oligodendrocytes different?

Schwann cells myelinate axons in the PNS, while Oligodendrocytes myelinate axons in the CNS. Another interesting difference is that when Schwann cells myelinate, their cell body's actually wrap around the axon. Oligodendrocytes secrete the myelin sheaths around the axons. Schwann cells constitute one myelin segment, whereas each oligodendrocyte provides several myelin segments, often on more than one axon. Another difference is that only Schwann Cells can guide axonal regeneration (regrowth) after damage. Thats why effective axonal regeneration in the mammalian nervous system is restricted to the PNS.

Mitochondria

Sites of aerobic (oxygen consuming) energy release.

Synaptic Vesicles

Spherical membrane packages that store neurotransmitter molecules ready for release near synapses.

Which cranial nerve is (XI) ?

Spinal Accessory; motor, movement of neck, shoulders and head Spinal Accessory; sensory, sensory signals from muscles of the neck

Dural Sinuses

Sublayers of the dura that have divided to form a route for blood. The purpose of this structure is to drain blood away from the brain and scalp.

Buttons

The button-like endings of the axon branches, which release chemicals into synapses.

Cytoplasm

The clean internal fluid of the cell.

Nuclei

The clusters of cell bodies in the CNS.

Ganglia

The clusters of cell bodies in the PNS. (Singular: Ganglion).

Axon Hillock

The cone shaped region at the junction between the axon and the cell body.

Peripheral Nervous System (PNS)

The division located outside the skull and spine. Composed of two divisions: The Somatic Nervous System, and the Autonomic Nervous System. Most of the nerves of the peripheral nervous system project from the spinal cord, but there are 12 pairs of exceptions.

Central Nervous System (CNS)

The division of the nervous system located within the skull and spine. Composed of two divisions: Brain and Spinal Cord.

Myelin

The fatty insulation around many neurons.

Cerebral Ventricles

The four large internal chambers of the brain: the two lateral ventricles, the third ventricle, and fourth ventricle.

Synapses

The gaps between adjacent neurons which chemical signals are transmitted.

Nodes of Ranvier

The gaps between the sections of myelin.

Schwann Cells

The glial cells that compose the myelin sheaths of PNS axons and promote the regeneration of PNS axons.

Pia Mater

The innermost meninx. Its delicate, and adheres to the surface of the CNS.

Axon

The long, narrow process that projects from the cell body.

Cell Body

The metabolic centre of the neuron; also called the soma.

Somatic Nervous System (SNS)

The part of the PNS that interacts with the external environment. Composed of afferent nerves that carry sensory signals from the skin, skeletal muscles, joints, eyes, ears and so on to the CNS and efferent nerves that carry motor signals from the CNS to the skeletal muscles.

Autonomic Nervous System (ANS)

The part of the Peripheral Nervous System that regulates the body's internal environment. Its composed of different nerves that carry signals from internal organs to the CNS and efferent nerves that carry motor signals from the CNS to internal organs. Has two kinds of efferent nerves: sympathetic (projecting from the CNS) and parasympathetic (project from the brain and sacral region of spinal cord). All sympathetic and parasympathetic nerves are two-stage neural paths.

Cell Membrane

The semipermeable membrane that encloses the neuron.

Dendrites

The short processes emanating from the cell body, which receive most fo the synaptic contacts from other neurons.

Nucleus

The spherical DNA containing structure of the cell body.

What is special about the two kinds of efferent nerves in the ANS?

They are two stage neural paths. The sympathetic and parasympathetic neurons project from the CNS and only go part of the way to the target organs before they synapse on other neurons (second-stage neurons) that carry the signals the rest of the way. The sympathetic and parasympathetic systems differ in that the sympathetic neurons that project from the CNS synapse on second-stage neurons are at a substantial distance from their target organs, whereas the parasympathetic neurons that project from the CNS synapse are near their target organs on very short second-stage neurons.

Dura Mater

Thick, tough, outermost layer of the meninges surrounding and protecting the brain and spinal cord. (Tough mother).

What two kinds of gross neural structures are in the nervous system?

Those composed primarily of cell bodies and those composed primarily of axons.

Meninges

Three protective membranes that cover the brain and spinal cord (singular meninx). The outer meninx, is a tough membrane called dura mater (tough mother). Inside the dura mater is the fine arachnoid membrane (spider web like). Beneath the arachnoid membrane is a space called the subarachnoid space, which contains many large blood vessels and cerebrospinal fluid; then comes the innermost meninx, the delicate pia mater (pious mother) which adheres to the surface of the CNS.

Inferior

Toward the bottom of the primate head or brain.

Medial

Toward the midline of the body.

Anterior

Toward the nose end (anterior end) of the head. Also called rostral.

Dorsal

Toward the surface of the back or top of the head (Dorsal surface). Superior is often used to refer to the top of the primate head.

Ventral

Toward the surface of the chest or bottom of the head (Ventral surface). Sometimes called Inferior, which is used to refer to the bottom of the primate head.

Posterior

Toward the tail end (posterior end) of the head. Also named caudal.

Superior

Toward the top of the primate head.

Which cranial nerve is number (V) ?

Trigeminal; sensory; facial sensations Trigeminal; motor; chewing Trigeminal: Responsible for sensation in the face and motor functions such as biting and chewing.

Which cranial nerve is number (IV) ?

Trochlear; motor; eye movement Trochlear; sensory; sensory signals from certain eye muscles. Trochlear: Relating to a part of the body resembling a pulley.

Microtubules

Tubules responsible for the rapid transport of material throughout neurons.

What is the vertebrate nervous system composed of?

Two divisions: the central nervous system and the peripheral nervous system.

Anterograde Tracing Methods

Used when you want to trace the paths of axons projecting AWAY from cell bodies located in a particular area. Inject chemicals, which are then taken up by cell bodies and transported FORWARD along their axons to the terminal buttons. A few days later remove the brain, slice it, and treat to reveal the location of injected chemical.

Which cranial nerve is number (X) ?

Vagus; sensory, sensations from abdominal and thoracic regions Vagus; motor, control over abdominal and thoracic organs and muscles of the throat Vagus: Interfaces with parasympathetic control of the heart, lungs, and digestive tract

Retrograde Tracing Methods

Works in reverse, used to trace the paths of axons projecting INTO a particular area. Inject chemicals, which are take up by terminal buttons and transported BACKWARD along their axons into their cell bodies. A few days later remove the brain, slice it, and treat to reveal the location of injected chemical.