BIO100 Chptr 11 Nervous System II Divisions of the Nervous System Flashcards
(178 cards)
1
Q
cephal-
A
cephal-, head: encephalitis
—inflammation of the brain.
2
Q
chiasm-
A
chiasm-, cross: optic chiasma
—X-shaped structure produced by the crossing over of optic nerve fibers.
3
Q
funi-
A
funi-, small cord or fiber: funiculus
—major nerve tract or bundle of myelinated axons within the spinal cord.
4
Q
gangli-
A
gangli-, swelling: ganglion
—mass of neuron cell bodies.
5
Q
mening-
A
mening-, membrane: meninges
—membranous coverings of the brain and spinal cord.
6
Q
plex-
A
plex-, interweaving: choroid plexus
—mass of specialized capillaries associated with spaces in the brain.
7
Q
central nervous system (CNS)
A
consists of the brain and the spinal cord
8
Q
The brain
A
is the largest and most complex part of the nervous system. It oversees many aspects of physiology, such as sensation and perception, movement, and thinking.
9
Q
The brain includes
A
the two cerebral hemispheres, the diencephalon, the brainstem, and the cerebellum
10
Q
The brain contains
A
about one hundred billion (1011) multipolar neurons as well as countless branches of the axons by which these neurons communicate with each other and with neurons elsewhere in the nervous system.
11
Q
UNmyelinated axons - appear gray
A
are called gray matter - grey/gray nerves
12
Q
areas containing myelinated axons appear white
A
are called white matter - white nerves
13
Q
Where is the white and gray matter in the brain & spinal cord?
A
In the brain, the outer layers of the cerebral hemispheres and cerebellum are largely gray matter.
White matter, representing interconnecting axons, is found deeper, with islands of gray matter located throughout. In the spinal cord, in contrast, gray matter (the cell bodies of neurons) is found more centrally, with white matter more peripheral and consisting of axons extending up to the brain or down from the brain.
14
Q
The brain connects
A
to the spinal cord through the brainstem. Axons conducting impulses up to the brain are bundled in ascending tracts. Those conducting impulses down through the spinal cord are in descending tracts. Both the brain and the spinal cord connect to the peripheral nervous system (PNS) via peripheral nerves.
15
Q
The brain lies in
A
the cranial cavity of the skull, and the spinal cord occupies the vertebral canal in the vertebral column. Beneath these bony coverings, membranes called meninges, located between the bone and the soft tissues of the nervous system, protect the brain and spinal cord
16
Q
meninges
A
the three membranes (the dura mater, arachnoid, and pia mater) that line the skull and vertebral canal and enclose the brain and spinal cord.
17
Q
nerve fiber
A
another term for the axon of a neuron. A nerve is formed of a bundle of many such fibers, with their sheaths.
18
Q
dura mater
A
the tough outermost membrane enveloping the brain and spinal cord.
19
Q
dural sinuses
A
dural venous sinuses are spaces between the endosteal and meningeal layers of the dura. They contain venous blood that originates for the most part from the brain or cranial cavity. The sinuses contain an endothelial lining that is continuous into the veins that are connected to them
20
Q
pia mater (denticulate ligaments)
A
denticulate ligaments are triangular shaped ligaments that anchor the spinal cord along its length, at each side, to the dura mater. The bases of the ligaments arise in the pia mater and they are firmly attached to the arachnoid mater and dura mater at the apex. They have 21 attachments per side.
21
Q
epidural space
A
is the area between the dura mater (a membrane) and the vertebral wall, containing fat and small blood vessels. The space is located just outside the dural sac which surrounds the nerve roots and is filled with cerebrospinal fluid.
22
Q
subdural hematoma
A
subdural hematoma (SDH) is a type of bleeding in which a collection of blood—usually associated with a traumatic brain injury—gathers between the inner layer of the dura mater and the arachnoid mater of the meninges surrounding the brain. It usually results from tears in bridging veins that cross the subdural space.
23
Q
arachnoid mater
A
is one of the three meninges, the protective membranes that cover the brain and spinal cord. The arachnoid mater is a derivative of the neural crest mesectoderm in the embryo.
24
Q
subarachnoid space
A
is the interval between the arachnoid membrane and the pia mater. It is occupied by delicate connective tissue trabeculae and intercommunicating channels containing cerebrospinal fluid (CSF).
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cerebrospinal fluid (CSF)
is a clear, colorless body fluid found in the brain and spinal cord. It is produced by specialised ependymal cells in the choroid plexuses of the ventricles of the brain, and absorbed in the arachnoid granulations.
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pia mater
the delicate innermost membrane enveloping the brain and spinal cord.
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Partitions Formed by the Dura Mater
Falx cerebelli -Separates the right and left cerebellar hemispheres
Falx cerebri - Extends downward into the longitudinal fissure, and separates the right and left cerebral hemispheres
Tentorium cerebelli - Separates the occipital lobes of the cerebrum from the cerebellum
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Meningitis
an inflammation of the meninges usually caused by bacterial or viral infection of the CSF, affects the arachnoid and pia maters and sometimes the dura mater, mostly in children. Complications include visual loss, hearing loss, paralysis, and intellectual disability. Meningitis may be fatal. Children are vaccinated against Haemophilus influenza type b, which was once the most common bacterial cause of meningitis.
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ventricles
a hollow part or cavity in an organ.
each of the four connected fluid-filled cavities in the center of the brain.
each of the two main chambers of the heart, left and right.
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traumatic brain injury (TBI)
results from mechanical force such as from a fall, accident, attack, or sports-related injury to the brain.
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The two lateral ventricles
The first ventricle is in the left cerebral hemisphere and the second ventricle is in the right cerebral hemisphere. They extend anteriorly and posteriorly into the cerebral hemispheres.
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third ventricle
A narrow space that constitutes the third ventricle is in the midline of the brain beneath the corpus callosum, which is a bridge of axons that links the two cerebral hemispheres. This ventricle communicates with the lateral ventricles through openings (interventricular foramina) in its anterior end.
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corpus callosum
a broad band of nerve fibers joining the two hemispheres of the brain.
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interventricular foramina
the interventricular foramina (or foramina of Monro) are channels that connect the paired lateral ventricles with the third ventricle at the midline of the brain.
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The fourth ventricle
is in the brainstem, just anterior to the cerebellum. A narrow canal, the cerebral aqueduct (aqueduct of Sylvius), connects the third ventricle to the fourth ventricle and passes lengthwise through the brainstem. This ventricle is continuous with the central canal of the spinal cord and has openings in its roof that lead into the subarachnoid space of the meninges.
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cerebral aqueduct (aqueduct of Sylvius)
The cerebral aqueduct (aqueductus mesencephali, mesencephalic duct, sylvian aqueduct or aqueduct of Sylvius) is within the midbrain. It contains cerebrospinal fluid (CSF) and connects the third ventricle to the fourth ventricle, located dorsal to the pons and ventral to the cerebellum.
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choroid plexuses
a network of blood vessels in each ventricle of the brain. It is derived from the pia mater and produces the cerebrospinal fluid.
Choroid plexuses are tiny, reddish, cauliflower-like masses of specialized capillaries from the pia mater, covered by a single layer of specialized ependymal cells
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blood-brain barrier
The blood–brain barrier (BBB) is a highly selective semipermeable border of endothelial cells that prevents solutes in the circulating blood from non-selectively crossing into the extracellular fluid of the central nervous system where neurons reside.
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blood-CSF barrier
The blood–cerebrospinal fluid barrier (BCSFB) is a fluid–brain barrier that is composed of a pair of membranes that separate blood from CSF at the capillary level and CSF from brain tissue. The blood–CSF boundary at the choroid plexus is a membrane composed of epithelial cells and tight junctions that link them.
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The brain contains neural centers -
associated with sensory functions and is responsible for sensations and perceptions. It issues motor commands to skeletal muscles and carries on higher mental functions, such as memory and reasoning. The brain also contains neural centers and pathways that coordinate muscular movements, and others that regulate visceral activities. In addition to overseeing the function of the entire body, the brain is responsible for characteristics such as personality.
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The basic structure of the brain
The brain is made of three main parts: the forebrain, midbrain, and hindbrain. The forebrain consists of the cerebrum, thalamus, and hypothalamus (part of the limbic system). The midbrain consists of the tectum and tegmentum. The hindbrain is made of the cerebellum, pons and medulla.
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The brain forms early on -
brain development begins a few weeks after conception and is thought to be complete by early adulthood. The basic structure of the brain is laid down primarily during the prenatal period and early childhood, and the formation and refinement of neural networks continues over the long term.
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cerebrum
the principal and most anterior part of the brain in vertebrates, located in the front area of the skull and consisting of two hemispheres, left and right, separated by a fissure. It is responsible for the integration of complex sensory and neural functions and the initiation and coordination of voluntary activity in the body.
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basal nuclei
The basal ganglia (or basal nuclei) are a group of subcortical nuclei, of varied origin, in the brains of vertebrates, including humans, which are situated at the base of the forebrain and top of the midbrain.
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diencephalon
the caudal (posterior) part of the forebrain, containing the epithalamus, thalamus, hypothalamus, and ventral thalamus and the third ventricle.
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midbrain
also called mesencephalon, region of the developing vertebrate brain that is composed of the tectum and tegmentum. The midbrain serves important functions in motor movement, particularly movements of the eye, and in auditory and visual processing.
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cerebellum
the part of the brain at the back of the skull in vertebrates. Its function is to coordinate and regulate muscular activity.
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pons
the part of the brainstem that links the medulla oblongata and the thalamus.
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medulla oblongata
the continuation of the spinal cord within the skull, forming the lowest part of the brainstem and containing control centers for the heart and lungs.
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brainstem
is the distal part of the brain that is made up of the midbrain, pons, and medulla oblongata. Each of the three components has its own unique structure and function. Together, they help to regulate breathing, heart rate, blood pressure, and several other important functions.
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Anencephaly
is the absence of a major portion of the brain, skull, and scalp that occurs during embryonic development. It is a cephalic disorder that results from a neural tube defect that occurs when the rostral (head) end of the neural tube fails to close, usually between the 23rd and 26th / 28th day following conception.
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spina bifida
is a birth defect that occurs when the spine and spinal cord don't form properly. It's a type of neural tube defect. The neural tube is the structure in a developing embryo that eventually becomes the baby's brain, spinal cord and the tissues that enclose them.
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corpus callosum
a broad band of nerve fibers joining the two hemispheres of the brain.
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Structural Development of the Brain
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Forebrain (prosencephalon)
Anterior portion (telencephalon)
Posterior portion (diencephalon)
Midbrain (mesencephalon)
Hindbrain (rhombencephalon)
Anterior portion (metencephalon)
Posterior portion (myelencephalon)
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gyri (ji′ri) (gyrus)
is one of the prominent rounded elevations or convolutions that form the cerebral hemisphere. Gyri and sulci create the folded appearance of the brain in human and other mammals. The gyri serve to increase surface area for information processing capability.
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sulcus
a groove or furrow, especially one on the surface of the brain. somewhat deep groove
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fissure in relation to the brain
The longitudinal fissure (or cerebral fissure, median longitudinal fissure, interhemispheric fissure) is the deep groove that separates the two cerebral hemispheres of the vertebrate brain. Lying within it is a continuation of the dura mater (one of the meninges) called the falx cerebri.
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fissure
* verb - split or crack (something) to form a long, narrow opening. - "the skin becomes dry, fissured, and cracked"
* noun - a long, narrow opening or line of breakage made by cracking or splitting, especially in rock or earth.
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frontal lobe
forms the anterior portion of each cerebral hemisphere. It is bordered posteriorly by a central sulcus (fissure of Rolando), which passes out from the longitudinal fissure at a right angle, and inferiorly by a lateral sulcus (fissure of Sylvius), which exits the undersurface of the brain along its sides.
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parietal lobe
is posterior to the frontal lobe and is separated from it by the central sulcus.
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temporal lobe
lies inferior to the frontal and parietal lobes and is separated from them by the lateral sulcus.
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occipital lobe
forms the posterior portion of each cerebral hemisphere and is separated from the cerebellum by a shelflike extension of dura mater called the tentorium cerebelli. The occipital lobe and the parietal and temporal lobes have no distinct boundary.
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tentorium cerebelli
tentorium or tentorium cerebelli (Latin for "tent of the cerebellum") is an extension of the dura mater that separates the cerebellum from the inferior portion of the occipital lobes.
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insula
The insula (island of Reil) is a lobe deep within the lateral sulcus of each hemisphere and is so named because it is covered by parts of the frontal, parietal, and temporal lobes. A circular sulcus separates the insula from the other lobes.
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limbic lobe -
Some sources include a sixth lobe, the limbic lobe, which is deeper than the other lobes. This area is discussed as the “limbic system” - The limbic lobe is an arc-shaped region of cortex on the medial surface of each cerebral hemisphere of the mammalian brain, consisting of parts of the frontal, parietal and temporal lobes.
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cerebral cortex
The cortex constitutes the outermost portion of the cerebrum. It covers the gyri, dipping into the sulci and fissures. The cerebral cortex contains nearly 75% of all the neuron cell bodies in the nervous system. -
All lobes of the cerebrum have a thin layer of gray matter (2 to 5 millimeters thick
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Functions of the Cerebral Cortex
The cerebral cortex provides higher brain functions: interpreting impulses from sense organs, initiating voluntary muscular movements, storing information as memory, and retrieving this information in reasoning. The cerebral cortex is also the part of the brain responsible for intelligence and personality.
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somatosensory cortex
The primary somatosensory cortex is located in a ridge of cortex called the postcentral gyrus, which is found in the parietal lobe. It is situated just posterior to the central sulcus, a prominent fissure that runs down the side of the cerebral cortex.
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visual cortex
The primary visual cortex is the most studied visual area in the brain. In mammals, it is located in the posterior pole of the occipital lobe and is the simplest, earliest cortical visual area. It is highly specialized for processing information about static and moving objects and is excellent in pattern recognition.
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auditory cortex
The auditory cortex is the part of the temporal lobe that processes auditory information in humans and many other vertebrates. It is a part of the auditory system, performing basic and higher functions in hearing, such as possible relations to language switching.
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gustatory cortex
The primary gustatory cortex is a brain structure responsible for the perception of taste. It consists of two substructures: the anterior insula on the insular lobe and the frontal operculum on the inferior frontal gyrus of the frontal lobe.
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olfactory cortex
Sense of smell -
The olfactory cortex is a structurally distinct cortical region on the ventral surface of the forebrain, composed of several areas that receive input from the olfactory bulb (anterior olfactory nucleus, piriform cortex, olfactory tubercle, anterior cortical amygdaloid nucleus, periamygdaloid cortex, and entorhinal
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Association Areas of the Cortex
Association areas are neither primarily sensory nor motor. They connect with each other and with other brain structures. Association areas occupy the anterior portions of the frontal lobes and are widespread in the lateral portions of the parietal, temporal, and occipital lobes. Association areas analyze and interpret sensory experiences and help provide memory, reasoning, verbalizing, judgment, and emotions
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Motor Areas of the Cortex
primary motor areas (motor cortex) of the cerebral cortex lie in the precentral gyri of the frontal lobes just in front of the central sulcus and in the anterior wall of this sulcus (fig. 11.8). The nervous tissue in these regions contains many large pyramidal cells, named for their pyramid-shaped cell bodies.
Impulses from the pyramidal cells move downward through the brainstem and into the spinal cord on descending tracts. Most of the nerve fibers in these tracts cross over from one side of the brain to the other within the brainstem.
Impulses conducted on these pathways in special patterns and frequencies are responsible for movements in skeletal muscles. More specifically, as figure 11.9 shows, cells in the upper portions of the motor areas send impulses to muscles in the thighs and legs; those in the middle portions control muscles in the arms and forearms; and those in lower portions activate muscles of the head, face, and tongue.
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Functions of the Cerebral Lobes
* Frontal lobes - Association areas carry on higher intellectual processes for concentrating, planning, complex problem solving, and judging the consequences of behavior. Motor areas control movements of voluntary skeletal muscles.
* Parietal lobes - Sensory areas provide sensations of temperature, touch, pressure, and pain involving the skin. Association areas function in understanding speech and in using words to express thoughts and feelings.
* Temporal lobes - Sensory areas are responsible for hearing. Association areas interpret sensory experiences and remember visual scenes, music, and other complex sensory patterns.
* Occipital lobes - Sensory areas are responsible for vision. Association areas combine visual images with other sensory experiences.
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long-term potentiation
In neuroscience, long-term potentiation (LTP) is a persistent strengthening of synapses based on recent patterns of activity. These are patterns of synaptic activity that produce a long-lasting increase in signal transmission between two neurons.
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memory consolidation
is defined as a time-dependent process by which recent learned experiences are transformed into long-term memory, presumably by structural and chemical changes in the nervous system (e.g., the strengthening of synaptic connections between neurons).
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basal nuclei
Basal nuclei: A region located at the base of the brain composed of 4 clusters of neurons, or nerve cells. This area of the brain is responsible for body movement and coordination. - The basal nuclei are also called the basal ganglia.
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diencephalon
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-is largely composed of gray matter.
the caudal (posterior) part of the forebrain, containing the epithalamus, thalamus, hypothalamus, and ventral thalamus and the third ventricle.
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thalamus
either of two masses of gray matter lying between the cerebral hemispheres on either side of the third ventricle, relaying sensory information and acting as a center for pain perception.
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hypothalamus
The hypothalamus is a small region of the brain. It's located at the base of the brain, near the pituitary gland. While it's very small, the hypothalamus plays a crucial role in many important functions, including: releasing hormones. regulating body temperature
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Other parts of the diencephalon
(1) the optic tracts, which originate from the optic chiasma (formed by some of the optic nerve fibers crossing over);
(2) the infundibulum (pituitary stalk), which is a conical process behind the optic chiasma to which the pituitary gland is attached;
(3) the posterior pituitary gland, which hangs from the floor of the hypothalamus, attached to the infundibulum;
(4) the mammillary (mam′ĭ-lar″e) bodies, which are two rounded structures behind the infundibulum; and
(5) the pineal gland, which is a cone-shaped projection from the roof of the diencephalon
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optic tracts
The optic tract (from the Latin tractus opticus) is a part of the visual system in the brain. It is a continuation of the optic nerve that relays information from the optic chiasm to the ipsilateral lateral geniculate nucleus (LGN), pretectal nuclei, and superior colliculus.
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optic chiasma
noun: optic chiasma
1.
ANATOMY
the X-shaped structure formed at the point below the brain where the two optic nerves cross over each other.
2.
BIOLOGY
a point at which paired chromosomes remain in contact during the first metaphase of meiosis, and at which crossing over and exchange of genetic material occur between the strands.
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infundibulum (pituitary stalk)
infundibulum or pituitary stalk, the infundibular stalk is a tube-like structure that connects the posterior pituitary to the hypothalamus. It allows for hormones synthesized in the hypothalamus to be sent to the posterior pituitary for release into the bloodstream.
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posterior pituitary gland
The back portion of the pituitary, a small gland in the head called the master gland. The posterior pituitary secretes the hormone oxytocin which increases uterine contractions and antidiuretic hormone (ADH) which increases reabsorption of water by the tubules of the kidney.
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mammillary bodies
are a pair of small round bodies, located on the undersurface of the brain that, as part of the diencephalon, form part of the limbic system. They are located at the ends of the anterior arches of the fornix.
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pineal gland
is a small endocrine gland in the brain of most vertebrates. The pineal gland produces melatonin, a serotonin-derived hormone which modulates sleep patterns in both circadian and seasonal cycles. The shape of the gland resembles a pine cone from which it derived its name.[1] The pineal gland is located in the epithalamus, near the center of the brain, between the two hemispheres, tucked in a groove where the two halves of the thalamus join
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The hypothalamus regulates:
1. heart rate and arterial blood pressure
2. body temperature
3. water and electrolyte balance
4. control of hunger and body weight
5. control of movements and glandular secretions of the stomach and intestines
6. production of neurosecretory substances that stimulate the pituitary gland to release hormones that help regulate growth, control various glands, and influence reproductive physiology
7. sleep and wakefulness
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Substantia nigra
“large black area,” named for the dark pigment that the neurons release as a by-product of synthesizing the neurotransmitter dopamine.
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imaging technology called SPECT (single photon emission computed tomography)
uses a chemical compound similar to cocaine that binds specifically to dopamine transporter molecules in the striatum, marking them. This compound used with SPECT is called a DaTscan. It distinguishes tremors that are specifically due to PD, which is useful both for diagnosis and in research to ensure that people in clinical trials to evaluate PD treatments actually have PD.
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thalamotomy
Thalamotomy is a surgical procedure in which an opening is made into the thalamus to improve the overall brain function in patients. - usually performed on patients with PD
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pallidotomy
Pallidotomy is a neurosurgical procedure whereby a tiny electrical probe is placed in the globus pallidus, which is then heated to 80 °C for 60 seconds, to destroy a small area of brain cells.
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cerebral peduncles
are the two stalks that attach the cerebrum to the brainstem. They are structures at the front of the midbrain which arise from the front of the pons and contain the large ascending (sensory) and descending (motor) nerve tracts that run to and from the cerebrum from the pons.
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corpora quadrigemina
corpora quadrigemina (Latin for "quadruplet bodies") are the four colliculi—two inferior, two superior—located on the tectum of the dorsal aspect of the midbrain. They are respectively named the inferior and superior colliculus. The corpora quadrigemina are reflex centers involving vision and hearing.
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red nucleus
Near the center of the midbrain is a mass of gray matter called the red nucleus. This nucleus communicates with the cerebellum and with centers of the spinal cord, and it plays a role in reflexes that maintain posture. It appears red because it is richly supplied with blood vessels.
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pyramids
The medullary pyramids are paired white matter structures of the brainstem's medulla oblongata that contain motor fibers of the corticospinal and corticobulbar tracts – known together as the pyramidal tracts. The lower limit of the pyramids is marked when the fibers cross (decussate).
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olive - in the brainstem
Olives of Medulla. The olives of the medulla, also known as the olivary bodies, are located on the ventral surface of the medulla oblongata of the brainstem, lateral to the medullary pyramids. - The olives contain the inferior olivary nucleus (the superior olivary nucleus is actually located in the pons).
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nucleus gracilis and the nucleus cuneatus,
receive sensory impulses from fibers of ascending tracts and pass them on to the thalamus or the cerebellum.
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Other nuclei in the medulla oblongata control vital visceral activities. These reflex centers include the following:
1. Peripheral nerves conduct impulses originating in the cardiac center to the heart, where they increase or decrease heart rate.
2. Certain cells of the vasomotor center initiate impulses that affect smooth muscle in the walls of blood vessels and stimulate them to contract, constricting the vessels (vasoconstriction) and thereby raising blood pressure. A decrease in the activity of these cells can produce the opposite effect—dilation of the blood vessels (vasodilation) and a consequent drop in blood pressure.
3. The respiratory center maintains the basic rhythm of breathing and works with other brainstem areas to adjust the rate and depth of breathing to meet changing needs.
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reticular formation
Sleep and consciousness – The reticular formation has projections to the thalamus and cerebral cortex that allow it to exert some control over which sensory signals reach the cerebrum and come to our conscious attention. It plays a central role in states of consciousness like alertness and sleep.
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non-rapid eye movement (non-REM) 1 of 2 types of sleep
is dreamless sleep. During NREM, the brain waves on the electroencephalographic (EEG) recording are typically slow and of high voltage, the breathing and heart rate are slow and regular, the blood pressure is low, and the sleeper is relatively still.
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rapid eye movement (REM) 2 of 2 types of sleep
is a unique phase of sleep, distinguishable by random/rapid movement of the eyes, accompanied with low muscle tone throughout the body, and the propensity of the sleeper to dream vividly.
The REM phase is also known as paradoxical sleep (PS) and sometimes desynchronized sleep because of physiological similarities to waking states, including rapid, low-voltage desynchronized brain waves. Electrical and chemical activity regulating this phase seems to originate in the brain stem and is characterized most notably by an abundance of the neurotransmitter acetylcholine, combined with a nearly complete absence of monoamine neurotransmitters histamine, serotonin, and norepinephrine.
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spinal cord
is a slender column of nervous tissue that is continuous with the brain and extends downward through the vertebral canal. The spinal cord originates where nervous tissue leaves the cranial cavity at the level of the foramen magnum. The cord tapers to a point and terminates near the intervertebral disc that separates the first and second lumbar vertebrae
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Structure of the Spinal Cord
The spinal cord consists of thirty-one segments, each of which gives rise to a pair of spinal nerves. Spinal nerves are grouped according to the level of the vertebra with which they are associated. Within each group, the pairs of nerves are numbered in sequence from superior to inferior. They're eight pairs of cervical spinal nerves - C1 passes superior to the vertebra C1, and each of the remaining seven pairs of cervical spinal nerves, C2 through C8 pass below the vertebra above them, through the intervertebral foramina. Therefore, although there are seven cervical vertebrae, there are eight pairs of cervical nerves (numbered C1 to C8). Below the cervical region, spinal nerves are named for the vertebra above them. There are twelve pairs of thoracic nerves (numbered T1 to T12), five pairs of lumbar nerves (numbered L1 to L5), five pairs of sacral nerves (numbered S1 to S5), and one pair of coccygeal nerves (Co). These nerves branch to various body parts and connect them with the CNS.
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cervical enlargement
corresponds with the attachments of the large nerves which supply the upper limbs. It extends from about the fifth cervical to the first thoracic vertebra, its maximum circumference (about 38 mm.) being on a level with the attachment of the sixth pair of cervical nerves.
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lumbar enlargement
or lumbosacral enlargement- is a widened area of the spinal cord that gives attachment to the nerves which supply the lower limbs. It commences about the level of T11 and ends at L2, and reaches its maximum circumference, of about 33 mm.
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conus medullaris
(Latin for "medullary cone") or conus terminalis is the tapered, lower end of the spinal cord. It occurs near lumbar vertebral levels 1 (L1) and 2 (L2), occasionally lower.
This structure serves to stabilize the spinal cord by connecting the conus to the coccyx via the coccygeal ligament. The lumbosacral nerve roots continue inferiorly to this as the cauda equina.
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filum terminale
("terminal thread") is a delicate strand of fibrous tissue, about 20 cm in length, proceeding downward from the apex of the conus medullaris. It is one of the modifications of pia mater.
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posterior median sulcus
a longitudinal division on each side of the spinal cord comprising white matter between the dorsal root and the posterior median sulcus — compare lateral funiculus, ventral funiculus.
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posterior horns
(also dorsal horn, posterior cornu, dorsal cornu) may refer to: - Posterior horn of spinal cord, the dorsal (towards the back) grey matter section of the spinal cord that receives several types of sensory information from the body including light touch, proprioception, and vibration.
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anterior horns
are the ventral extensions of the H-shaped gray matter and contain the large anterior horn cells (lower motor neurons) and smaller gamma motor neurons, which innervate muscle spindles.
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lateral horn
A column of neuron cell bodies and unmyelinated cell processes (ie, gray matter) running through the lateral quadrant of spinal cord segments C8–L2 In stained cross-sections of spinal cord, the lateral horns form a small bulge of gray matter between the dorsal and ventral horns.
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posterior root ganglia (singular, ganglion)
All the posterior roots of spinal nerves contain a ganglion. As the dorsal or posterior root of a spinal nerve is primarily sensory, the dorsal root ganglion contains cell bodies of these sensory nerve fibers.
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gray commissure
is a thin strip of grey matter that surrounds the central canal of the spinal cord and, along with the anterior white commissure, connects the two halves of the cord. It comprises lamina X in the Rexed classification.
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reflex
nerve pathway
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reflex arc
the nerve pathway involved in a reflex action, including at its simplest a sensory nerve and a motor nerve with a synapse between.
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Reflex Behavior
is a reflex action: an involuntary and rapid response to a stimulus, or cue. One example of a human reflex action is the knee-jerk reflex.
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segmental innervation
refers to the distribution (innervation) of nerves within an organ or muscle. These nerves are attached to a segment of the spine. Segmental innervation can be mapped through stimulation of the nerve at the spinal segment.
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Parts of a Reflex Arc
* Receptor - The receptor end of a dendrite or a specialized receptor cell in a sensory organ - Sensitive to a specific type of internal or external change
* Sensory neuron - Dendrite, cell body, and axon of a sensory neuron - Conducts an impulse from the receptor into the brain or spinal cord
* Interneuron - Dendrite, cell body, and axon of a neuron within the brain or spinal cord - Serves as processing center; conducts an impulse from the sensory neuronto its synapse with a motor neuron
* Motor neuron - Dendrite, cell body, and axon of a motor neuron - Conducts an impulse from the brain or spinal cord out to the synapse with an effector
* Effector - A muscle or gland - Responds to stimulation by the motor neuron and produces the reflex or behavioral action
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ascending tracts
refer to the neural pathways by which sensory information from the peripheral nerves is transmitted to the cerebral cortex. In some texts, ascending tracts are also known as somatosensory pathways or systems. - Unconscious tracts – comprised of the spinocerebellar tracts.
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descending tracts
are the pathways by which motor signals are sent from the brain to lower motor neurones. The lower motor neurones then directly innervate muscles to produce movement. ... Pyramidal tracts - These tracts originate in the cerebral cortex, carrying motor fibres to the spinal cord and brain stem.
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spinothalamic tract
begins at various levels of the spinal cord and conducts sensory impulses associated with the sensations of pain and touch to the thalamus.
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corticospinal tract
originates in the cerebral cortex and conducts motor impulses on so-called upper motor neurons downward through the spinal cord.
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Fasciculus gracilis
- fiber bundle that carries tactile and proprioceptive information from the lower half of the body, the fasciculus gracilis is part of the posterior columns and terminates in the nucleus gracilis.
- either of a pair of nerve tracts of the posterior funiculus of the spinal cord situated on opposite sides of and immediately adjacent to the posterior median septum and carrying nerve fibers from the lower part of the body
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fasciculus cuneatus
- fiber bundle that carries tactile and proprioceptive information from the upper limbs and torso, the fasciculus cuneatus is part of the posterior columns and terminates in the nucleus cuneatus.
- fiber bundle that carries tactile and proprioceptive information from the upper limbs and torso, the fasciculus cuneatus is part of the posterior columns and terminates in the nucleus cuneatus.
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spinothalamic tracts
are in the lateral and anterior funiculi, respectively. The lateral tracts conduct impulses from various body regions to the brain and give rise to sensations of pain and temperature. Impulses conducted on fibers of the anterior tracts are interpreted as touch and pressure. Impulses in these tracts cross over in the spinal cord
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spinocerebellar tracts
lie near the surface in the lateral funiculi of the spinal cord). Fibers in the posterior tracts remain uncrossed, whereas those in the anterior tracts cross over in the medulla. Impulses conducted on their fibers originate in the muscles of the lower limbs and trunk and then travel to the cerebellum. These impulses are used by the cerebellum to coordinate muscular movements.
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corticospinal tracts
occupy the lateral and anterior funiculi, respectively. Most of the fibers of the lateral tracts cross over in the lower medulla oblongata. Some fibers of the anterior tracts cross over at various levels of the spinal cord. Axons in the corticospinal tracts conduct motor impulses from the brain and synapse either directly or through interneurons with lower motor neurons, whose axons continue through spinal nerves to various skeletal muscle. Thus, fibers of the corticospinal tracts conduct motor commands that control voluntary movements.
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reticulospinal tracts
are in the lateral funiculi, whereas the anterior and medial reticulospinal tracts are in the anterior funiculi. Some fibers in the lateral tracts cross over, whereas others remain uncrossed. Those of the anterior and medial tracts remain uncrossed. Motor impulses conducted on the reticulospinal tracts originate in the brain and control muscular tone and activity of sweat glands.
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rubrospinal (roo″bro-spi′nal) tracts
cross over in the brain and pass through the lateral funiculi. They conduct impulses from the brain to synapses with lower motor neurons, and help to coordinate muscle actions.
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Peripheral Nervous System PNS
consists of the nerves that branch from the CNS, connecting it to other body parts. The PNS includes the cranial nerves that arise from the brain and the spinal nerves that arise from the spinal cord.
The PNS can also be subdivided into somatic and autonomic nervous systems.
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somatic nervous system
consists of the nerve fibers that connect the CNS to the skin and skeletal muscles, so it plays a role in conscious activities.
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autonomic nervous system
includes fibers that connect the CNS to viscera such as the heart, stomach, intestines, and various glands. The autonomic nervous system controls subconscious actions. outlines the subdivisions of the nervous system.
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endoneurium
A small amount of loose connective tissue called endoneurium surrounds individual axons.
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Structure of Peripheral Nerves
Nerves are essentially bundles of axons, but they have specific levels of organization. A small amount of loose connective tissue called endoneurium surrounds individual axons. Axons are organized in bundles called fascicles. Each fascicle is enclosed in a sleeve of loose connective tissue called the perineurium. A group of bundled fascicles, surrounded by an outermost layer of dense connective tissue called the epineurium, constitutes a nerve. Blood vessels in the epineurium and perineurium give rise to a network of capillaries in the endoneurium that provides oxygen and nutrients to the neurons.
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Nerve and Nerve Fiber Classification
Recall that nerves are bundles of nerve fibers, or axons.
Nerves that have only fibers of sensory neurons, conducting impulses into the brain or spinal cord, are called sensory nerves.
Nerves that have only fibers involved in motor control are motor nerves.
Most nerves include both sensory and motor fibers and are called mixed nerves.
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Nerve Tracts of the Spinal Cord
* Ascending Tracts - 1. Fasciculus gracilis and fasciculus cuneatus - Posterior funiculi. 2. Spinothalamic tracts (lateral and anterior) - Lateral and anterior funiculi. 3. Spinocerebellar tracts (posterior and anterior) - Lateral funiculi
* Descending Tracts - 1.Corticospinal tracts (lateral and anterior) - Lateral and anterior funiculi 2.Reticulospinal tracts (lateral, anterior, and medial) - Lateral and anterior funiculi 3. Rubrospinal tracts - Lateral funiculi
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Subdivisions of the Nervous System
Central nervous system (CNS)
Brain
Spinal cord
Peripheral nervous system (PNS)
Cranial nerves arising from the brain
(1)Somatic afferent and efferent
fibers connecting to the skin and skeletal muscles
(2)Autonomic efferent fibers connecting to viscera
(3)Visceral afferent fibers connecting to viscera
Spinal nerves arising from the spinal cord
(1)Somatic afferent and efferent fibers connecting to the skin and skeletal muscles
(2)Autonomic efferent fibers connecting to viscera
(3)Visceral afferent fibers connecting to viscera
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Nerves originating from the brain that communicate with other body parts are called
cranial nerves - Twelve pairs of cranial nerves are located on the underside of the brain.
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whereas nerves originating from the spinal cord that communicate with other body parts are called
spinal nerves
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The nerve fibers in the cranial and spinal nerves can be subdivided further into four groups as follows:
General somatic efferent fibers
General visceral efferent fibers
General somatic afferent fibers
General visceral afferent fibers
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General somatic efferent fibers
conduct motor impulses outward from the brain or spinal cord to skeletal muscles and stimulate them to contract.
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General visceral efferent fibers
conduct motor impulses outward from the brain or spinal cord to smooth muscle and glands associated with internal organs.
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General somatic afferent fibers
conduct sensory impulses inward to the brain or spinal cord from receptors in the skin and skeletal muscles.
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General visceral afferent fibers
conduct sensory impulses to the CNS from blood vessels and internal organs.
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Three other groups of fibers, found only in cranial nerves, are associated with more specialized, or special, structures:
Special somatic efferent fibers
Special visceral afferent fibers
Special somatic afferent fibers
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Special visceral afferent fibers
conduct sensory impulses inward to the brain from the olfactory and taste receptors.
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Special somatic afferent fibers
conduct sensory impulses inward to the brain from the receptors of sight, hearing, and equilibrium.
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Special somatic efferent fibers
conduct motor impulses outward from the brain to the muscles used in chewing, swallowing, speaking, and forming facial expressions.
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Twelve pairs of cranial nerves are located on the underside of the brain.
I Olfactory Nerve Smell
II Optic Nerve Vision
III Oculomotor Nerve Eye movement; pupil constriction
IV Trochlear Nerve Eye movement
V Trigeminal Nerve Somatosensory information (touch, pain) from the face and head; muscles for chewing.
VI Abducens Nerve Eye movement
VII Facial Nerve Taste (anterior 2/3 of tongue); somatosensory information from ear; controls muscles used in facial expression.
VIII Vestibulocochlear Nerve Hearing; balance
IX Glossopharyngeal Nerve Taste (posterior 1/3 of tongue); Somatosensory information from tongue, tonsil, pharynx; controls some muscles used in swallowing.
X Vagus Nerve Sensory, motor and autonomic functions of viscera (glands, digestion, heart rate)
XI Spinal Accessory Nerve Controls muscles used in head movement.
XII Hypoglossal Nerve Controls muscles of tongue
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cauda equina (horse’s tail)
is a bundle of spinal nerves and spinal nerve rootlets, consisting of the second through fifth lumbar nerve pairs, the first through fifth sacral nerve pairs, and the coccygeal nerve, all of which arise from the lumbar enlargement and the conus medullaris of the spinal cord.
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anterior root (ventral, or motor, root)
of each spinal nerve consists of axons from the motor neurons whose cell bodies lie within the gray matter of the cord.
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posterior root (dorsal, or sensory, root)
can be identified by an enlargement called the posterior root ganglion. This ganglion contains the cell bodies of the sensory neurons whose axons (peripheral processes) conduct impulses inward from peripheral body parts. The axons (central processes) of these neurons continue through the posterior root and into the spinal cord, where they form synapses with other neurons or ascend to the brain. An anterior root and a posterior root unite to form a spinal nerve, which extends outward from the vertebral canal through an intervertebral foramen (the posterior root is usually absent from the first pair of spinal nerves).
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Cervical Plexuses
The anterior branches of the first four cervical nerves form the cervical plexuses, which lie deep in the neck on either side
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phrenic nerves
Fibers from these plexuses supply the muscles and skin of the neck. In addition, fibers from the third, fourth, and fifth cervical nerves pass into the right and left phrenic (fren′ik) nerves, which conduct motor impulses to the muscle fibers of the diaphragm.
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Brachial Plexuses
The anterior branches of the lower four cervical nerves and the first thoracic nerve give rise to brachial plexuses. These networks of nerve fibers are deep in the shoulders between the neck and the axillae (armpits).
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Brachial Plexuses Nerves
Musculocutaneous nerves supply muscles of the arms on the anterior sides and the skin of the forearms.
Ulnar nerves supply muscles of the forearms and hands and the skin of the hands.
Median nerves supply muscles of the forearms and muscles and skin of the hands.
Radial nerves supply muscles of the arms on the posterior sides and the skin of the forearms and hands.
Axillary nerves supply muscles and skin of the anterior, lateral, and posterior regions of the arm.
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Other nerves associated with the brachial plexus that innervate various skeletal muscles include the following:
The lateral and medial pectoral nerves supply the pectoralis major and pectoralis minor muscles.
The dorsal scapular nerve supplies the rhomboid major and levator scapulae muscles.
The lower subscapular nerve supplies the subscapularis and teres major muscles.
The thoracodorsal nerve supplies the latissimus dorsi muscle.
The suprascapular nerve supplies the supraspinatus and infraspinatus muscles.
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Lumbosacral Plexuses
The ventral branches of the lumbar and first four sacral nerves form the lumbosacral (lum″bo-sa′kral) plexuses. The lumbar portions are in the lumbar regions of the abdomen and the sacral portions are in the pelvic cavity. These networks of nerve fibers give rise to a number of nerves associated with the lower abdominal wall, external genitalia, buttocks, thighs, legs, and feet.
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The major branches of these plexuses include the following
he obturator nerves supply the adductor muscles of the thighs.
The femoral nerves divide into many branches, supplying motor impulses to muscles of the anterior thighs and receiving sensory impulses from the skin of the thighs and legs.
The sciatic nerves are the largest and longest nerves in the body, formed by the common fibular nerve and the tibial nerve wrapped in a connective tissue sheath. They pass downward into the buttocks and descend into the thighs, where they re-emerge as the tibial and common fibular nerves. The many branches of these nerves supply muscles and skin in the thighs, legs, and feet.
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Other nerves associated with the lumbosacral plexus that innervate various skeletal muscles include the following:
the pudendal nerve supplies the muscles of the perineum.
The inferior and superior gluteal nerves supply the gluteal muscles and the tensor fasciae latae muscle.
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intercostal nerves
are the somatic nerves that arise from the anterior divisions of the thoracic spinal nerves from T1 to T11. These nerves in addition to supplying the thoracic wall also supply the pleura and peritoneum.
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The autonomic nervous system (ANS)
is an efferent (motor) part of the PNS that functions independently (autonomously) and continuously, without conscious effort. This system controls visceral activities by regulating the actions of smooth muscles, cardiac muscles, and various glands. It oversees heart rate, blood pressure, breathing rate, body temperature, and other visceral activities that aid in maintaining homeostasis. Portions of the autonomic nervous system also respond during times of emotional stress and prepare the body to meet the demands of strenuous physical activity.
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The autonomic nervous system includes two divisions,
the sympathetic (sim″pah-thet′ik) and parasympathetic (par″ahsim″pah-thet′ik) divisions.
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preganglionic fiber
In the autonomic nervous system, fibers from the CNS to the ganglion are known as preganglionic fibers. All preganglionic fibers, whether they are in the sympathetic division or in the parasympathetic division, are cholinergic (that is, these fibers use acetylcholine as their neurotransmitter) and they are myelinated.
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What is the difference between preganglionic and postganglionic fibers?
The first set, called preganglionic neurons, originates in the brainstem or the spinal cord, and the second set, called ganglion cells or postganglionic neurons, lies outside the central nervous system in collections of nerve cells called autonomic ganglia.
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postganglionic fiber
In the autonomic nervous system, these are the fibers that run from the ganglion to the effector organ. cholinergic: Pertaining to, activated by, producing, or having the same function as acetylcholine. adrenergic: Containing or releasing adrenaline.
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sympathetic chain ganglia (paravertebral ganglia)
The bilaterally symmetric sympathetic chain ganglia, also called the paravertebral ganglia, are located just ventral and lateral to the spinal cord. The chain extends from the upper neck down to the coccyx, forming the unpaired coccygeal ganglion.
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sympathetic trunks
The sympathetic trunk is a fundamental part of the sympathetic nervous system, and part of the autonomic nervous system. It allows nerve fibres to travel to spinal nerves that are superior and inferior to the one in which they originated.
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gray rami
Each spinal nerve receives a branch called a gray ramus communicans (plural rami communicantes) from the adjacent paravertebral ganglion of the sympathetic trunk. The gray rami communicantes contain postganglionic nerve fibers of the sympathetic nervous system and are composed of largely unmyelinated neurons.
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norepinephrine (20%)
- a hormone that is released by the adrenal medulla and by the sympathetic nerves and functions as a neurotransmitter. It is also used as a drug to raise blood pressure.
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epinephrine (80%)
also epinephrin. A hormone secreted by the adrenal medulla that is released into the bloodstream in response to physical or mental stress, as from fear or injury.
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epinephrine (80%)
| norepinephrine (20%)
The chromaffin cells release catecholamines: ~80% of adrenaline (epinephrine) and ~20% of noradrenaline (norepinephrine) into systemic circulation for systemic effects on multiple organs (similarly to secretory neurones of the hypothalamus), and can also send paracrine signals.
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Autonomic Neurotransmitters
The different postganglionic neurotransmitters (mediators) are responsible for the different effects that the sympathetic and parasympathetic divisions have on organs
The preganglionic neurons of the sympathetic and parasympathetic divisions all secrete acetylcholine, and for this reason they are called cholinergic. The parasympathetic postganglionic fibers are also cholinergic (one exception, parasympathetic neurons that secrete nitric oxide, is described in section 22.2, Organs of the Male Reproductive System, Erection, Orgasm, and Ejaculation). Most sympathetic postganglionic neurons, however, secrete nor-epinephrine (noradrenalin) and are called adrenergic. Exceptions to this include the sympathetic postganglionic neurons that stimulate sweat glands and a few sympathetic neurons to blood vessels in skin (which cause vasodilation); these neurons secrete acetylcholine and therefore are cholinergic (adrenergic sympathetic fibers to blood vessels cause vasoconstriction).
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cholinergic
Cholinergic agents are compounds which mimic the action of acetylcholine and/or butyrylcholine. In general, the word "choline" describes the various quaternary ammonium salts containing the N, N, N-trimethylethanolammonium cation.
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adrenergic
Adrenergic means "working on adrenaline or noradrenaline". Adrenergic nervous system, a part of autonomic nervous system that uses epinephrine or norepinephrine as its neurotransmitter Regarding proteins:
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sympathetic tone
The condition of a muscle when the tone is maintained predominantly by impulses from the sympathetic nervous system. / partial contraction
