4. Tuberculous meningitis is also known as TB meningitis or tubercular meningitis. Tuberculous
meningitis is Mycobacterium tuberculosis infection of the meninges—the system of membranes
which envelops the central nervous system. It is the most common form of CNS tuberculosis.
Fever and headache are the cardinal features. Confusion is a late feature and coma bears a poor
prognosis. Meningism is absent in a fifth of patients with TB meningitis. Patients may also have
focal neurological deficits.
Causes are Tension headaches are due to contraction (tightness) of the muscles in your
shoulders, neck, scalp, and jaw. They are often related to stress, depression, or anxiety.
Overworking, not getting enough sleep, missing meals, and using alcohol or street drugs can
make you more susceptible to headaches. Foods that can trigger a headache include chocolate,
cheese, and monosodium glutamate (MSG), a flavor enhancer. People who drink caffeine can
have headaches when they don't get their usual daily amount.
Mycobacterium tuberculosis of the meninges is the cardinal feature and the inflammation is
concentrated towards the base of the brain. Infection begins in the lungs and may spread to the
meninges by a variety of routes.
The signs and symptoms are: fever, seizures, restlessness, loss of appetite, severe headache,
nausea and vomiting, stiff neck, sensitivity to light (photophobia) and loss of consciousness.
Blood-borne spread certainly occurs and 25% of patients with miliary TB have TB meningitis,
presumably by crossing the blood-brain barrier; but a proportion of patients may get TB
meningitis from rupture of a cortical focus in the brain; an even smaller proportion get it from
rupture of a bony focus in the spine. It is rare and unusual for TB of the spine to cause TB of the
central nervous system, but isolated cases have been described. Diagnosis of TB meningitis is
made by analyzing CSF collected by lumbar puncture. When collecting CSF for suspected TB
meningitis, a minimum of 1ml of fluid should be taken (preferably 5 to 10ml).The CSF usually
has a high protein, low glucose and a raised number of lymphocytes. Acid-fast bacilli are
sometimes seen on a CSF smear, but more commonly, M. tuberculosis is grown in culture. A
spider web clot in the collected CSF is characteristic of TB meningitis, but is a rare finding.
More than half of cases of TB meningitis cannot be confirmed microbiologically, and these
patients are treated on the basis of clinical suspicion only. The culture of TB from CSF takes a
minimum of two weeks, and therefore the majority of patients with TB meningitis are started on
treatment before the diagnosis is confirmed.
Imaging studies such as CT or MRI may show features strongly suggestive of TB meningitis, but
cannot diagnose it.
The treatment of TB meningitis is isoniazid, rifampicin, pyrazinamide and ethambutol for two
months, followed by isoniazid and rifampicin alone for a further ten months. Steroids are always
used in the first six weeks of treatment (and sometimes for longer). A few patients may require
immunomodulatory agents such as thalidomide. Treatment must be started as soon as there is a
reasonable suspicion of the diagnosis. Treatment must not be delayed while waiting for
confirmation of the diagnosis. Hydrocephalus occurs as a complication in about a third of
patients with TB meningitis and will require a ventricular shunt.
6. Name: R.H.P.
Address: Blk 15 Lot 20 Phase 3 Paliparan, Dasmariñas, Cavite
Date of Birth: October 8, 1990
Birthplace: Manila
Age: 18 years old
Sex: Female
Civil Status: Single
Nationality: Filipino
Religion: Catholic
Occupation: Sales lady
Admission Date/Time: January 8, 2009 – 1:39 am
Attending Physician: Dr. L.M.G.
ADMITTING HISTORY
This is a case of an 18 year old, female patient who was admitted at San Lazaro Hospital
last January 8, 2009 – 1:39 am with chief complaints of fever.
• 21 days PTA: fever, low – mod grade, tolerable headache and vomiting
• 14 days PTA: patient had a fever; consult was done at a private clinic. Patient was
diagnosed to have UTI, was given unrecalled antibiotics.
• 13 days PTA: (+) High grade fever 39°C, vomiting, colds.
• 12 days PTA: Patient was confined at Emilio Aguinaldo Hospital in Cavite, and was
diagnosed to have UTI and migraine, was discharged after 2 hospital days.
• 11 days PTA: given Levofloxan once a day times 7 days →vomiting.
• 8 days PTA: patient complains of pain on nape area with neck rigidity and headache,
fever, no convulsion.
• 5 days PTA: dizziness, anorexia, HA, with pain at her back characterized as pricking
sensation.
x-ray was done revealing ® apical densities.
Tramadol, Metoclopromide, Vitaplus and Demachlor were given. Patient was
then referred to this institution for evacuation and management.
• Few hours PTC: generalized body weakness
PHYSICAL ASSESSMENT
• GS: weak looking, conscious, coherent
• Skin: (-) jaundice, (-) pallor, (-) cyanosis, no active dermatoses
• HEENT: (+) dry lips, NAD
• C/L: SCE, (-) retractions, (-) crackles, no wheezes noted
• AP: no murmur
• Heart: Normal Rate Regular Rhythm, (-) murmurs
• Abdomen: (-) BM from 12-27-08 to present, no mass palpated, no tenderness
• GUT: Unremarkable
• IE: Unremarkable
7. • Extremities: no atrophy noted
• Neuro:
o (+) neck rigidity
o (+) brudzinki’s sign
o (+) kernig’s sign
o (-) babinski reflex
• Vital Signs:
o B/P= 90/70
o PR=76
o RR=18
o T=38 OC
Admitting Impression: TB Meningitis t/c typhoid fever
Final Diagnosis: TB Meningitis
FAMILY HISTORY
FATHER MOTHER
DIABETES (-) (-)
HYPERTENSION (-) (-)
ASTHMA (-) (-)
PTB (-) (+)
The patient had no family history of diabetes, hypertension, as well as respiratory disease
such as asthma but had family history of PTB on mother’s side.
9. Central Nervous System
The central nervous system (CNS) is the largest part of the nervous system, and includes
the brain and spinal cord. The spinal cavity holds and protects the spinal cord, while the head
contains and protects the brain. The CNS is covered by the meninges, a three layered protective
coat. The brain is also protected by the skull, and the spinal cord is also protected by the
vertebrae.
The central nervous system (CNS) is the part of the nervous system that functions to
coordinate the activity of all parts of the bodies of multicellular organisms. In vertebrates, the
central nervous system is enclosed in the meninges. The meninges (singular meninx) is the
system of membranes which envelops the central nervous system. The meninges consist of three
layers: the dura mater, the arachnoid mater, and the pia mater. The primary function of the
meninges and of the cerebrospinal fluid is to protect the central nervous system. It contains the
majority of the nervous system and consists of the brain (in vertebrates which have them), and
the spinal cord.
10. The meninges (singular meninx) is the system of membranes which envelops the central
nervous system. The meninges consist of three layers: the dura mater, the arachnoid mater, and
the pia mater. The primary function of the meninges and of the cerebrospinal fluid is to protect
the central nervous system. The space between these membranes is bathed with a spinal fluid
much like lymph, which serves as a protective cushion for the delicate nerve tissue, and allows
some expansion space for the brain when its blood supply is increased.
3 layers of meninges:
• Dura mater - (also rarely called meninx fibrosa, or pachymeninx) is a thick, durable
membrane, closest to the skull. It consists of two layers, the periosteal layer, closest to the
calvaria and the inner meningeal layer. It contains larger blood vessels which split into the
capilliaries in the pia mater. It is composed of dense fibrous tissue, and its inner surface is
11. covered by flattened cells like those present on the surfaces of the pia mater and arachnoid.
The dura mater is a sac which envelops the arachnoid and has been modified to serve
several functions. The dura mater surrounds and supports the large venous channels (dural
sinuses) carrying blood from the brain toward the heart.
The falx cerebri separates the hemispheres of the cerebrum. The falx cerebelli separates the
lobes of the cerebellum.
The tentorium cerebelli separates the cerebrum from the cerebellum.
The epidural space is a potential space between the dura mater and the skull. If there is
hemorrhaging in the brain, blood may collect here. Adults are more likely than children to bleed
here as a result of closed head injury.
The subdural space is another potential space. It is between the dura mater and the middle layer
of the meninges, the arachnoid mater. When bleeding occurs in the cranium, blood may collect
here and push down on the lower layers of the meninges. If bleeding continues, brain damage
will result from this pressure. Children are especially likely to have bleeding in the subdural
space in cases of head injury.
• Arachnoid mater - The middle element of the meninges is the arachnoid membrane, so
named because of its spider web-like appearance. It provides a cushioning effect for the
central nervous system. The arachnoid mater exists as a thin, transparent membrane. It is
composed of fibrous tissue and, like the pia mater, is covered by flat cells also thought to
be impermeable to fluid. The arachnoid does not follow the convolutions of the surface of
the brain and so looks like a loosely fitting sac. In the region of the brain, particularly, a
large number of fine filaments called arachnoid trabeculae pass from the arachnoid through
the subarachnoid space to blend with the tissue of the pia mater.
The arachnoid and pia mater are sometimes together called the leptomeninges.
The subarachanoid space lies between the arachnoid and pia mater. It is filled with
cerebrospinal fluid. All blood vessels entering the brain, as well as cranial nerves pass through
this space. The term arachnoid refers to the spider web like appearance of the blood vessels
within the space.
• Pia mater - The pia or pia mater is a very delicate membrane. It is the meningeal envelope
which firmly adheres to the surface of the brain and spinal cord. As such it follows all the
minor contours of the brain (gyri and sulci). It is a very thin membrane composed of
fibrous tissue covered on its outer surface by a sheet of flat cells thought to be
impermeable to fluid. The pia mater is pierced by blood vessels which travel to the brain
and spinal cord, and its capillaries are responsible for nourishing the brain.
Cerebrospinal fluid - is a clear liquid produced within spaces in the brain called ventricles.
Like saliva it is a filtrate of blood. It is also found inside the subarachnoid space of the meninges
which surrounds both the brain and the spinal chord. In addition, a space inside the spinal chord
12. called the central canal also contains cerebrospinal fluid. It acts as a cushion for the neuraxis,
also bringing nutrients to the brain and spinal cord and removing waste from the system.
Choroid Plexus
All of the ventricles contain choroid plexuses which produce cerebrospinal fluid by allowing
certain components of blood to enter the ventricles. The choroid plexuses are formed by the
fusion of the pia mater, the most internal layer of the meninges and the ependyma, the lining of
the ventricles.
The Ventricles
These four spaces are filled with cerebrospinal fluid and protect the brain by cushioning it and
supporting its weight.
The two lateral ventricles extend across a large area of the brain. The anterior horns of these
structures are located in the frontal lobes. They extend posteriorly into the parietal lobes and their
inferior horns are found in the temporal lobes.
The third ventricle lies between the two thalamic bodies. The massa intermedia passes through
it and the hypothalamus forms its floor and part of its lateral walls.
The fourth ventricle is located between the cerebellum and the pons.
The four ventricles are connected to one another.
The two foramina of Munro, which are also know as the interventricular foramina, link the
lateral ventricles to the third ventricle.
The Aqueduct of Sylvius which is also called the cerebral aqueduct connects the third and
fourth ventricles.
The fourth ventricle is connected to the subarachnoid space via two lateral foramina of Luschka
and by one medial foramen of Magendie.
ANATOMY OF THE CNS
BRAIN
The center of the nervous system. The brain is located in the head, protected by the skull
and close to the primary sensory apparatus of vision, hearing, balance, taste, and smell.
13. • The frontal lobe is concerned with higher intellectual functions, such as abstract
thought and reason, speech (Broca's area in the left hemisphere only), olfaction, and
emotion. Voluntary movement is controlled in the precentral gyrus (the primary motor
area).
• The parietal lobe is dedicated to sensory awareness, particularly in the postcentral
gyrus (the primary sensory area). It is also concernes with abstract reasoning,
language interpretation and formation of a mental egocentric map of the surrounding
area.
• The occipital lobe is responsible for interpretation and processing of visual stimuli from
the optic nerves, and association of these stimuli with other nervous imputs and
memories.
• The temporal lobe is concerned with emotional development and formation, and also
contains the auditory area responsible for processing and discrimination of sound. It is
also the area thought to be responsible for the formation and processing of memories.
The brain can be subdivided into several distinct regions:
1. Brainstem – consists of medulla oblongata, pons and midbrain.
• Medulla oblongata - is the lower portion of the brainstem. It deals with autonomic
functions, such as breathing and blood pressure. The cardiac center is the part of the
medulla oblongata responsible for controlling the heart rate.
• Pons - relays sensory information between the cerebellum and cerebrum; aids in
relaying other messages in the brain; controls arousal, and regulates respiration (see
respiratory centres). In some theories, the pons has a role in dreaming.
• Midbrain (mesencephalon) - The mesencephalon is considered part of the brain stem.
Its substantia nigra is closely associated with motor system pathways of the basal
ganglia.
The human mesencephalon is archipallian in origin, meaning its general architecture is shared
with the most ancient of vertebrates. Dopamine produced in the substantia nigra plays a role in
motivation and habituation of species from humans to the most elementary animals such as
insects.
2. Cerebellum - is a region of the brain that plays an important role in the integration of
sensory perception, coordination and motor control. In order to coordinate motor control,
there are many neural pathways linking the cerebellum with the cerebral motor cortex (which
sends information to the muscles causing them to move) and the spinocerebellar tract (which
provides proprioceptive feedback on the position of the body in space). The cerebellum
integrates these pathways, like a train conductor, using the constant feedback on body
position to fine-tune motor movements.
3. Diencephalon - (or interbrain) is the region of the brain that includes the thalamus,
hypothalamus, epithalamus, prethalamus or subthalamus and pretectum. The diencephalon is
located at the midline of the brain, above the mesencephalon of the brain stem. The
diencephalon contains the zona limitans intrathalamica as morphological boundary and
signalling center between the prethalamus and the thalamus.
• Thalamus - plays an important role in regulating states of sleep and wakefulness.
Thalamic nuclei have strong reciprocal connections with the cerebral cortex, forming
thalamo-cortico-thalamic circuits that are believed to be involved with consciousness.
14. The thalamus plays a major role in regulating arousal, the level of awareness, and
activity. Damage to the thalamus can lead to permanent coma.
• Epithalamus – is a dorsal posterior segment of the diencephalon (a segment in the
middle of the brain also containing the hypothalamus and the thalamus) which
includes the habenula, the stria medullaris and the pineal body. Its function is the
connection between the limbic system to other parts of the brain.
• Hypothalamus - is a small part of the brain located just below the thalamus on both
sides of the third ventricle. Lesions of the hypothalamus interfere with several
vegetative functions and some so called motivated behaviors like sexuality,
combativeness, and hunger. The hypothalamus also plays a role in emotion.
Specifically, the lateral parts seem to be involved with pleasure and rage, while the
medial part is linked to aversion, displeasure, and a tendency to uncontrollable and
loud laughing. However, in general the hypothalamus has more to do with the
expression of emotions
4. Cerebrum - or top portion of the brain, is divided by a deep crevice, called the longitudinal
sulcus. The longitudinal sulcus separates the cerebrum in to the right and left hemispheres. In
the hemispheres you will find the cerebral cortex, basal ganglia and the limbic system. The
two hemispheres are connected by a bundle of nerve fibers called the corpus callosum. The
right hemisphere is responsible for the left side of the body while the opposite is true of the
left hemisphere.
PHYSIOLOGY OF THE CNS
Medulla
The medulla is the control center for respiratory, cardiovascular and digestive functions.
Pons
The pons houses the control centers for respiration and inhibitory functions. Here it will interact
with the cerebellum.
Cerebrum
The cerebrum, or top portion of the brain, is divided by a deep crevice, called the longitudinal
sulcus. The longitudinal sulcus separates the cerebrum in to the right and left hemispheres. In the
hemispheres you will find the cerebral cortex, basal ganglia and the limbic system. The two
hemispheres are connected by a bundle of nerve fibers called the corpus callosum. The right
hemisphere is responsible for the left side of the body while the opposite is true of the left
hemisphere. Each of the two hemispheres are divided into four separated lobes: the frontal in
control of specialized motor control, learning, planning and speech; parietal in control of somatic
sensory functions; occipital in control of vision; and temporal lobes which consists of hearing
centers and some speech. Located deep to the temporal lobe of the cerebrum is the insula.
15. Cerebellum
The cerebellum is the part of the brain that is located posterior to the medulla oblongata and
pons. It coordinates skeletal muscles to produce smooth, graceful motions. The cerebellum
receives information from our eyes, ears, muscles, and joints about what position our body is
currently in (proprioception). It also receives output from the cerebral cortex about where these
parts should be. After processing this information, the cerebellum sends motor impulses from the
brainstem to the skeletal muscles. The main function of the cerebellum is coordination. The
cerebellum is also responsible for balance and posture. It also assists us when we are learning a
new motor skill, such as playing a sport or musical instrument.
The Limbic System
The Limbic System is a complex set of structures found just
beneath the cerebrum and on both sides of the thalamus. It
combines higher mental functions, and primitive emotion, into
one system. It is often referred to as the emotional nervous
system. It is not only responsible for our emotional lives, but also
our higher mental functions, such as learning and formation of
memories. The Limbic system explains why some things seem so
pleasurable to us, such as eating and why some medical
conditions are caused by mental stress, such as high blood
pressure. There are two significant structures within the limbic
system and several smaller structures that are important as well.
They are:
1. The Hippocampus
2. The Amygdala
3. The Thalamus
4. The Hypothalamus
5. The Fornix and Parahippocampus
6. The Cingulate Gyrus
Structures of the Limbic System
Hippocampus
The Hippocampus is found deep in the temporal lobe, shaped like a seahorse. It consists of two
horns that curve back from the amygdala. It is situated in the brain so as to make the prefrontal
area aware of our past experiences stored in that area. The prefrontal area of the brain consults
this structure to use memories to modify our behavior. The hippocampus is responsible for
memory.
Amygdala
The Amygdala is a little almond shaped structure, deep inside the anteroinferior region of the
temporal lobe, connects with the hippocampus, the septi nuclei, the prefrontal area and the
medial dorsal nucleus of the thalamus. These connections make it possible for the amygdala to
play its important role on the mediation and control of such activities and feelings as love,
16. friendship, affection, and expression of mood. The amygdala is the center for identification of
danger and is fundamental for self preservation. The amygdala is the nucleus responsible for
fear.
Thalamus
Lesions or stimulation of the medial, dorsal, and anterior nuclei of the thalamus are associated
with changes in emotional reactivity. However, the importance of these nuclei on the regulation
of emotional behavior is not due to the thalamus itself, but to the connections of these nuclei with
other limbic system structures. The medial dorsal nucleus makes connections with cortical zones
of the prefrontal area and with the hypothalamus. The anterior nuclei connect with the mamillary
bodies and through them, via fornix, with the hippocampus and the cingulated gyrus, thus taking
part in what is known as the Papez's circuit.
Hypothalamus
The Hypothalamus is a small part of the brain located just below the thalamus on both sides of
the third ventricle. Lesions of the hypothalamus interfere with several vegetative functions and
some so called motivated behaviors like sexuality, combativeness, and hunger. The
hypothalamus also plays a role in emotion. Specifically, the lateral parts seem to be involved
with pleasure and rage, while the medial part is linked to aversion, displeasure, and a tendency to
uncontrollable and loud laughing. However, in general the hypothalamus has more to do with the
expression of emotions. When the physical symptoms of emotion appear, the threat they pose
returns, via the hypothalamus, to the limbic centers and then the prefrontal nuclei, increasing
anxiety.
The Fornix and Parahippocampal
These small structures are important connecting pathways for the limbic system.
The Cingulate Gyrus
The Cingulate Gyrus is located in the medial side of the brain between the cingulated sulcus and
the corpus callosum. There is still much to be learned about this gyrus, but it is already known
that its frontal part coordinates smells and sights, with pleasant memories of previous emotions.
The region participates in the emotional reaction to pain and in the regulation of aggressive
behavior.
Memory and Learning
Memory is defined as: The mental faculty of retaining and recalling past experiences, the act or
instance of remembering recollection. Learning takes place when we retain and utilize past
memories.
Overall, the mechanisms of memory are not completely understood. Brain areas such as the
hippocampus, the amygdala, the striatum, or the mammillary bodies are thought to be involved
in specific types of memory. For example, the hippocampus is believed to be involved in spatial
learning and declarative learning (learning information such as what you're reading now), while
the amygdala is thought to be involved in emotional memory. Damage to certain areas in patients
and animal models and subsequent memory deficits is a primary source of information.
However, rather than implicating a specific area, it could be that damage to adjacent areas, or to
17. a pathway traveling through the area is actually responsible for the observed deficit. Further, it is
not sufficient to describe memory, and its counterpart, learning, as solely dependent on specific
brain regions. Learning and memory are attributed to changes in neuronal synapses, thought to
be mediated by long-term potentiation and long-term depression.
There are three basic types of memory:
1. Sensory Memory
2. Short Term Memory
3. Long Term Memory
Sensory Memory
The sensory memories act as a buffer for stimuli through senses. A sensory memory retains an
exact copy of what is seen or heard: iconic memory for visual, echoic memory for aural and
haptic memory for touch. Information is passed from sensory memory into short term memory.
Some believe it lasts only 300 milliseconds, it has unlimited capacity. Selective attention
determines what information moves from sensory memory to short term memory.
Short Term Memory
Short Term Memory acts as a scratch pad for temporary recall of the information under process.
For instance, in order to understand this sentence you need to hold in your mind the beginning of
the sentence as you read the rest. Short term memory decays rapidly and also has a limited
capacity. Chunking of information can lead to an increase in the short term memory capacity,
this is the reason why a hyphenated phone number is easier to remember than a single long
number. The successful formation of a chunk is known as closure. Interference often causes
disturbance in short term memory retention. This accounts for the desire to complete a task held
in short term memory as soon as possible.
Within short term memory there are three basic operations:
1. Iconic memory - the ability to hold visual images
2. Acoustic memory - the ability to hold sounds. Can be held longer than iconic.
3. Working memory - an active process to keep it until it is put to use. Note that the goal is
not really to move the information from short term memory to long term memory, but
merely to put it to immediate use.
The process of transferring information from short term to long term memory involves the
encoding or consolidation of information. This is not a function of time, that is, the longer the
memory stays in the short term the more likely it is to be placed in the long term memory. On
organizing complex information in short term before it can be encoded into the long term
memory, in this process the meaningfulness or emotional content of an item may play a greater
role in its retention in the long term memory. The limbic system sets up local reverberating
circuits such as the Papaz's Circuit.
Long Term Memory
Long Term Memory is used for storage of information over a long time. Information from short
to long term memory is transferred after a short period. Unlike short term memory, long term
memory has little decay. Long term potential is an enhanced response at the synapse within the
18. hippocampus. It is essential to memory storage. The limbic system isn't directly involved in long
term memory necessarily but it selects them from short term memory, consolidates these
memories by playing them like a continuous tape, and involves the hippocampus and amygdala.
There are two types of long term memory:
1. Episodic Memory
2. Semantic Memory
Episodic memory represents our memory of events and experiences in a serial form. It is from
this memory that we can reconstruct the actual events that took place at a given point in our
lives. Semantic memory, on the other hand, is a structured record of facts, concepts, and skills
that we have acquired. The information in the semantic memory is derived from our own episode
memory, such as that we can learn new facts or concepts from experiences.
There are three main activities that are related to long term memory:
1. Storage
2. Deletion
3. Retrieval
Information for short term memory is stored in long term memory by rehearsal. The repeated
exposure to a stimulus or the rehearsal of a piece of information transfers it into long term
memory. Experiments also suggest that learning is most effective if it is distributed over time.
Deletion is mainly caused by decay and interference. Emotional factors also affect long term
memory. However, it is debatable whether we actually ever forget anything or whether it just
sometimes becomes increasingly difficult to retrieve it. Information may not be recalled
sometimes but may be recognized, or may be recalled only with prompting. This leads us to the
third operation of memory, information retrieval.
There are two types of information retrieval:
1. Recall
2. Recognition
In recall, the information is reproduced from memory. In recognition the presentation of the
information provides the knowledge that the information has been seen before. Recognition is of
lesser complexity, as the information is provided as a cue. However, the recall may be assisted
by the provision of retrieval cues which enable the subject to quickly access the information in
memory.
19. ANATOMY OF THE PNS
The peripheral nervous system includes 12 cranial nerves 31 pairs of spinal nerves. It can be
subdivided into the somatic and autonomic systems. It is a way of communication from the
central nervous system to the rest of the body by nerve impulses that regulate the functions of the
human body.
The twelve cranial nerves are
I Olfactory Nerve for smell
II Optic Nerve for vision
III Oculomotor for looking around
IV Trochlear for moving eye
V Trigeminal for feeling touch on face
VI Abducens to move eye muscles
VII Facial to smile, wink, and help us taste
VIII Vestibulocochlear to help with balance, equilibrium, and hearing
IX Glossopharengeal for swallowing and gagging
X Vagus for swallowing, talking, and parasympathetic actions of digestion
XI Spinal accessory for shrugging shoulders
XII Hypoglossal for tongue more divided into different regions as muscles
The 10 out of the 12 cranial nerves originate from the brainstem, and mainly control the
functions of the anatomic structures of the head with some exceptions. CN X receives visceral
sensory information from the thorax and abdomen, and CN XI is responsible for innervating the
sternocleidomastoid and trapezius muscles, neither of which is exclusively in the head.
Spinal nerves take their origins from the spinal cord. They control the functions of the rest of the
body. In humans, there are 31 pairs of spinal nerves: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral
20. and 1 coccygeal. The naming convention for spinal nerves is to name it after the vertebra
immediately above it. Thus the fourth thoracic nerve originates just below the fourth thoracic
vertebra. This convention breaks down in the cervical spine. The first spinal nerve originates
above the first cervical vertebra and is called C1. This continues down to the last cervical spinal
nerve, C8. There are only 7 cervical vertebrae and 8 cervical spinal nerves.
Peripheral nervous system
The PNS is a regional term for the collective nervous structures that do not lie in the CNS. The
bodies of the nerve cells lie in the CNS, either in the brain or the spinal cord, and the longer of
the cellular processes of these cells, known as axons, extend through the limbs and the flesh of
the torso. The large majority of the axons which are commonly called nerves, are considered to
be PNS.
The peripheral nervous system (PNS) resides or extends outside the central nervous system
(CNS), which consists of the brain and spinal cord. The main function of the PNS is to connect
the CNS to the limbs and organs. Unlike the central nervous system, the PNS is not protected by
bone or by the blood-brain barrier, leaving it exposed to toxins and mechanical injuries. The
peripheral nervous system is divided into the somatic nervous system and the autonomic nervous
system.
Physiological division
A less anatomical but much more functional way of dividing the human nervous system is
classification according to the role that the different neural pathways play, regardless of whether
or not they cross through the CNS/PNS:
• The somatic nervous system is responsible for coordinating voluntary body movements
(i.e. activities that are under conscious control).
• The autonomic nervous system is responsible for coordinating involuntary functions,
such as breathing and digestion.
In turn, these divisions of the nervous system can be further divided according to the direction in
which they conduct nerve impulses:
• Afferent system by sensory neurons, which carries impulses from a somatic receptor to
the CNS
• Efferent system by motor neurons, which carries impulses from the CNS to an effector
• Relay system by interneurons (also called "relay neurons"), which transmit impulses
between the sensory and motor neurons (both in the CNS and PNS).
• The junction between two neurons is called a synapse. There is a very narrow gap (about
20nm in width) between the neurons called the synaptic cleft. This is where an action
potential (the "message" being carried by the neurons, also known as the nerve impulse)
is transmitted from one neuron to the next. This is achieved by relaying the message
across the synaptic cleft using neurotransmitters, which diffuse across the gap. The
neurotransmitters then bind to receptor sites on the neighboring (postsynaptic) neuron,
which in turn produces its own electrical/nerve impulse. This impulse is sent to the next
synapse, and the cycle repeats itself.
21. • Nerve impulses are a change in ion balance between the inside and outside of a neuron.
Because the nervous system uses a combination of electrical and chemical signals, it is
incredibly fast. Although the chemical aspect of signaling is much slower than the
electrical aspect, a nerve impulse is still fast enough for the reaction time to be negligible
in day to day situations. Speed is a necessary characteristic in order for an organism to
quickly identify the presence of danger, and thus avoid injury/death. For example, a hand
touching a hot stove. If the nervous system was only comprised of chemical signals, the
nervous system would not be able to signal the arm to move fast enough to escape
dangerous burns. Thus, the speed of the nervous system is evolutionarily valuable, and is
in fact a necessity for life.
The Somatic System
The somatic nervous system is that part of the peripheral nervous system associated with the
voluntary control of body movements through the action of skeletal muscles, and also reception
of external stimuli. The somatic nervous system consists of afferent fibers that receive
information from external sources, and efferent fibers that are responsible for muscle contraction.
The somatic system includes the pathways from the skin and skeletal muscles to the Central
Nervous System. It is also described as involved with activities that involve consciousness.
The basic route of the efferent somatic nervous system includes a two neuron sequence. The first
is the upper motor neuron, whose cell body is located in the precentral gyrus (Brodman Area 4)
of the brain. It receives stimuli from this area to control skeletal (voluntary) muscle. The upper
motor neuron carries this stimulus down the corticospinal tract and synapses in the ventral horn
of the spinal cord with the alpha motor neuron, a lower motor neuron. The upper motor neuron
releases acetylcholine from its axon terminal knobs and these are received by nicotinic receptors
on the alpha motor neuron. The alpha motor neurons cell body sends the stimulus down its axon
via the ventral root of the spinal cord and proceeds to its neuromuscular junction of its skeletal
muscle. There, it releases acetylcholine from its axon terminal knobs to the muscles nicotinic
receptors, resulting in stimulus to contract the muscle.
The somatic system includes all the neurons connected with the muscles, sense organs and skin.
It deals with sensory information and controls the movement of the body.
The Autonomic System
The Autonomic system deals with the visceral organs, like the heart, stomach, gland, and the
intestines. It regulates systems that are unconsciously carried out to keep our body alive and
well, such as breathing, digestion (peristalsis), and regulation of the heartbeat. The Autonomic
system consists of the sympathetic and the parasympathetic divisions. Both divisions work
without conscious effort, and they have similar nerve pathways, but the sympathetic and
parasympathetic systems generally have opposite effects on target tissues (they are antagonistic).
By controlling the relative input from each division, the autonomic system regulates many
aspects of homeostasis. One of the main nerves for the parasympathetic autonomic system is
Cranial Nerve X, the Vagus nerve.
Ten out of the twelve cranial nerves originate from the brainstem, and mainly control the
functions of the anatomic structures of the head with some exceptions. The nuclei of cranial
22. nerves I and II lie in the forebrain and thalamus, respectively, and are thus not considered to be
true cranial nerves. CN X (10) receives visceral sensory information from the thorax and
abdomen, and CN XI (11) is responsible for innervating the sternocleidomastoid and trapezius
muscles, neither of which is exclusively in the head.
Spinal nerves take their origins from the spinal cord. They control the functions of the rest of the
body. In humans, there are 31 pairs of spinal nerves: 7 cervical, 12 thoracic, 5 lumbar, 5 sacral
and 1 coccygeal. In the cervical region, the spinal nerve roots come out above the corresponding
vertebrae (i.e. nerve root between the skull and 1st cervical vertebrae is called spinal nerve C1).
From the thoracic region to the coccygeal region, the spinal nerve roots come out below the
corresponding vertebrae. It is important to note that this method creates a problem when naming
the spinal nerve root between C7 and T1 (so it is called spinal nerve root C8). In the lumbar and
sacral region, the spinal nerve roots travel within the dural sac and they travel below the level of
L2 as the cauda equina.
Cervical spinal nerves (C1-C4)
The first 4 cervical spinal nerves, C1 through C4, split and recombine to produce a variety of
nerves that subserve the neck and back of head.
Spinal nerve C1 is called the suboccipital nerve which provides motor innervation to muscles at
the base of the skull. C2 and C3 form many of the nerves of the neck, providing both sensory and
motor control. These include the greater occipital nerve which provides sensation to the back of
the head, the lesser occipital nerve which provides sensation to the area behind the ears, the
greater auricular nerve and the lesser auricular nerve. See occipital neuralgia. The phrenic nerve
arises from nerve roots C3, C4 and C5. It innervates the diaphragm, enabling breathing. If the
spinal cord is transected above C3, then spontaneous breathing is not possible.
Brachial plexus (C5-T1)
The last four cervical spinal nerves, C5 through C8, and the first thoracic spinal nerve,
T1,combine to form the brachial plexus, or plexus brachialis, a tangled array of nerves, splitting,
combining and recombining, to form the nerves that subserve the arm and upper back. Although
the brachial plexus may appear tangled, it is highly organized and predictable, with little
variation between people.
Neurotransmitters
The main neurotransmitters of the peripheral nervous system are acetylcholine and
noradrenaline. However, there are several other neurotransmitters as well, jointly labeled Non-
noradrenergic, non-cholinergic (NANC) transmitters. Examples of such transmitters include non-
peptides: ATP, GABA, dopamine, NO, and peptides: neuropeptide Y, VIP, GnRH, Substance P
and CGRP.
23. The Sympathetic System
The Sympathetic Division
The sympathetic nervous system activates what is often termed the fight or flight response, as it
is most active under sudden stressful circumstances (such as being attacked). This response is
also known as sympathetico-adrenal response of the body, as the pre-ganglionic sympathetic
fibers that end in the adrenal medulla (but also all other sympathetic fibers) secrete acetylcholine,
which activates the secretion of adrenaline (epinephrine) and to a lesser extent noradrenaline
(norepinephrine) from it. Therefore, this response that acts primarily on the cardiovascular
system is mediated directly via impulses transmitted through the sympathetic nervous system and
indirectly via catecholamines secreted from the adrenal medulla.
Neurons
Neurons are electrically excitable cells in the nervous system that process and transmit
information. Neurons are the core components of the brain, the vertebrate spinal cord, the
invertebrate ventral nerve cord, and the peripheral nerves. A number of different types of
neurons exist: sensory neurons respond to touch, sound, light and numerous other stimuli
effecting sensory organs and send signals to the spinal cord and brain, motor neurons receive
signals from the brain and spinal cord and cause muscle contractions and affect glands,
Interneurons connect neurons to other neurons within the brain and spinal cord.
24. There are three types of directions of the neurons:
• Sensory system by sensory neurons, between the sensory and motor neurons. However,
there are relay neurons in the CNS as well.
• By function, the peripheral nervous system is divided into the somatic nervous system,
autonomic nervous system and the enteric nervous system. The somatic nervous system
is responsible for coordinating the body movements, and also for receiving external
stimuli. It is the system that regulates activities that are under conscious control. The
autonomic nervous system is then split into the sympathetic division, parasympathetic
division, and enteric division. The sympathetic nervous system responds to impending
danger or stress, and is responsible for the increase of one's heartbeat and blood pressure,
among other physiological changes, along with the sense of excitement one feels due to
the increase of adrenaline in the system. The parasympathetic nervous system, on the
other hand, is evident when a person is resting and feels relaxed, and is responsible for
such things as the constriction of the pupil, the slowing of the heart, the dilation of the
blood vessels, and the stimulation of the digestive and genitourinary systems. The role of
the enteric nervous system is to manage every aspect of digestion, from the esophagus to
the stomach, small intestine and colon.
Glial cells
Glial cells are non-neuronal cells that provide support and nutrition, maintain homeostasis, form
myelin, and participate in signal transmission in the nervous system. In the human brain, glia are
estimated to outnumber neurons by about 10 to 1.
Glial cells provide support and protection for neurons. They are thus known as the "glue" of the
nervous system. The four main functions of glial cells are to surround neurons and hold them in
place, to supply nutrients and oxygen to neurons, to insulate one neuron from another, and to
destroy pathogens and remove dead neurons.
Organization
Sympathetic nerves originate inside the vertebral column, toward the middle of the spinal cord in
the intermediolateral cell column (or lateral horn), beginning at the first thoracic segment of the
spinal cord and extending into the second or third lumbar segments. Because its cells begin in the
thoracic and lumbar regions of the spinal cord, the SNS is said to have a thoracolumbar outflow.
Axons of these nerves leave the spinal cord in the ventral branches (rami) of the spinal nerves,
and then separate out as 'white rami' (so called from the shiny white sheaths of myelin around
each axon) which connect to two chain ganglia extending alongside the vertebral column on the
left and right. These elongated ganglia are also known as paravertebral ganglia or sympathetic
trunks. In these hubs, connections (synapses) are made which then distribute the nerves to major
organs, glands, and other parts of the body.
In order to reach the target organs and glands, the axons must travel long distances in the body,
and, to accomplish this, many axons link up with the axon of a second cell. The ends of the
axons do not make direct contact, but rather link across a space, the synapse.
In the SNS and other components of the peripheral nervous system, these synapses are made at
sites called ganglia. The cell that sends its fiber is called a preganglionic cell, while the cell
25. whose fiber leaves the ganglion is called a postganglionic cell. As mentioned previously, the
preganglionic cells of the SNS are located between the first thoracic segment and the second or
third lumbar segments of the spinal cord. Postganglionic cells have their cell bodies in the
ganglia and send their axons to target organs or glands.
The ganglia include not just the sympathetic trunks but also the superior cervical ganglion
(which sends sympathetic nerve fibers to the head), and the celiac and mesenteric ganglia (which
send sympathetic fibers to the gut).
Relationship to sympathetic
While an oversimplification, it is said that the parasympathetic system acts in a reciprocal
manner to the effects of the sympathetic nervous system; in fact, in some tissues innervated by
both systems, the effects are synergistic.
The Parasympathetic Division
The parasympathetic nervous system is part of the autonomic nervous system. Sometimes called
the rest and digest system or feed and breed. The parasympathetic system conserves energy as it
slows the heart rate, increases intestinal and gland activity, and relaxes sphincter muscles in the
gastrointestinal tract.
Receptors
The parasympathetic nervous system uses only acetylcholine (ACh) as its neurotransmitter. The
ACh acts on two types of receptors, the muscarinic and nicotinic cholinergic receptors. Most
transmissions occur in two stages: When stimulated, the preganglionic nerve releases ACh at the
ganglion, which acts on nicotinic receptors of the postganglionic nerve. The postganglionic nerve
then releases ACh to stimulate the muscarinic receptors of the target organ.
The three main types of muscarinic receptors that are well characterised are:
• The M1 muscarinic receptors are located in the neural system.
• The M2 muscarinic receptors are located in the heart, and act to bring the heart back to
normal after the actions of the sympathetic nervous system: slowing down the heart rate,
reducing contractile forces of the atrial cardiac muscle, and reducing conduction velocity
of the atrioventricular node (AV node). Note, they have no effect on the contractile forces
of the ventricular muscle.
• The M3 muscarinic receptors are located at many places in the body, such as the smooth
muscles of the blood vessels, as well as the lungs, which means that they cause
vasoconstriction and bronchoconstriction. They are also in the smooth muscles of the
gastrointestinal tract (GIT), which help in increasing intestinal motility and dilating
sphincters. The M3 receptors are also located in many glands that help to stimulate
secretion in salivary glands and other glands of the body.
Nervous Tissue
The nervous system coordinates the activity of the muscles, monitors the organs, constructs and
also stops input from the senses, and initiates actions. Prominent participants in a nervous system
include neurons and nerves, which play roles in such coordination.Our nervous tissue only
26. consists of two types of cells. These cells are neurons and neuroglia cells. The neurons are
responsible for transmitting nerve impulses. Neuroglia cells are responsible for supporting and
nourishing the neuron cells.
Types of neurons
There are three types of neurons in the body. We have sensory neurons, interneurons, and motor
neurons. Neurons are a major class of cells in the nervous system. Neurons are sometimes called
nerve cells, though this term is technically imprecise, as many neurons do not form nerves. In
vertebrates, neurons are found in the brain, the spinal cord and in the nerves and ganglia of the
peripheral nervous system. Their main role is to process and transmit information. Neurons have
excitable membranes, which allow them to generate and propagate electrical impulses. Sensory
neuron takes nerve impulses or messages right from the sensory receptor and delivers it to the
central nervous system. A sensory receptor is a structure that can find any kind of change in it's
surroundings or environment.
Structure of a neuron
Neurons have three different parts to them. They all have an axon, a cell body and dendrites. The
axon is the part of the neuron that conducts nerve impulses. Axons can get to be quite long.
When an axon is present in nerves, it is called a nerve fiber. A cell body has a nucleous and it
also has other organelles. The dendrites are the short pieces that come off of the cell body that
receive the signals from sensory receptors and other neurons.
Myelin Sheath
Schwann cells contain a lipid substance called myelin in their plasma membranes. When
schwann cells wrap around axons, a myelin sheath forms. There are gaps that have no myelin
sheath around them; these gaps are called nodes of Ranvier. Myelin sheathes make excellent
27. insulators. Axons that are longer have a myelin sheath, while shorter axons do not. The disease
multiple sclerosis is an autoimmune disease where the body attacks the myelin sheath of the
central nervous system.
Information transmission
Messages travel through the SNS in a bidirectional flow. Efferent messages can trigger changes
in different parts of the body simultaneously. For example, the sympathetic nervous system can
accelerate heart rate; widen bronchial passages; decrease motility (movement) of the large
intestine; constrict blood vessels; increase peristalsis in the esophagus; cause pupil dilation,
piloerection (goose bumps) and perspiration (sweating); and raise blood pressure. Afferent
messages carry sensations such as heat, cold, or pain.
The first synapse (in the sympathetic chain) is mediated by nicotinic receptors physiologically
activated by acetylcholine, and the target synapse is mediated by adrenergic receptors
physiologically activated by either noradrenaline or adrenaline. An exception is with sweat
glands which receive sympathetic innervation but have muscarinic acetylcholine receptors which
are normally characteristic of PNS. Another exception is with certain deep muscle blood vessels,
which have acetylcholine receptors and which dilate (rather than constrict) with an increase in
sympathetic tone. The sympathetic system cell bodies are located on the spinal cord excluding
the cranial and sacral regions. The preganglonic neurons exit from the vertebral column and
synapse with the postganglonic nerouns in the sympathetic trunk.
The parasympathetic nervous system is one of three divisions of the autonomic nervous system.
Sometimes called the rest and digest system, the parasympathetic system conserves energy as it
slows the heart rate, increases intestinal and gland activity, and relaxes sphincter muscles in the
gastrointestinal tract.
