NERVOUS SYSTEM: NERVOUS TISSUE
CHAPTER OBJECTIVES
When you have completed this chapter you should be able to:
 Describe the anatomy of a neuron.

Classify the different types of neuron according to their structure and direction of the action
potential.

Describe the types and functions of neuroglia.

Understand and describe how a nerve impulse is generated and propagated.
The nervous system along with the endocrine system work together to coordinate all of the body
systems. It does this by detecting, storing, transmitting and responding to information or stimui.
The nervous system can be anatomically subdivided into the central nervous system (CNS) and the
peripheral nervous system (PNS). The central nervous system consists of the brain and spinal cord
and the peripheral nervous system consists of the spinal nerves and ganglia.
Nervous tissue
Neurons or nerve cells are the basic components of the nervous system and our bodies contain
billions of them. Supporting and protecting the neurons are neuroglia cells which form a type of
connective tissue around the nerve cells.
Neurons
Neurons come in various shapes and sizes but they all contain a cell body and usually two processes;
a dendrite and an axon. Dendrites are short, thin branched projections (the word dendrite is derived
from the Greek word "dendron", which means tree) that receive signals and transmit them towards
the cell body. They form synapses with other neurons and respond to neurotransmitters. Axons are
long straight projections which transmit signals (action potentials) away from the cell body. Their
ends branch to form presynaptic terminals which contain neurotransmitters to send signals away
from the cell.
Components of a
Description
Neuron
Cell body
Contains a large nucleus and granular protoplasm.
Axon
Axons are long straight processes which transmit signals (action potentials) away
from the cell body. Their ends branch to form presynaptic terminals which
contain neurotransmitters.
Dendrite
Dendrites are short, thin branched processes which receive signals and transmit
them towards the cell body.
Neurons can be classified according to their structure or by the direction in which the action
potentials travel.
Structure
Neuron Types Neuron Structure
Unipolar
Has an axon but no dendrites.
Mostly sensory fibres.
Bipolar
Has an axon and a dendrite.
Part of specialised sensory organs.
Multipolar
Has one axon and numerous dendrites. Motor and interneurons.
Direction of Action Potential
Neuron Types
Sensory (Afferent) Neurons
Direction of the Action Potential
Conduct signals to the CNS.
Motor (Efferent) Neurons
Conduct signals from the CNS to the muscles.
Interneurons (Association Neurons) Conduct signals from one neuron to another.
Neuroglia
Neuroglia are essential for the normal functioning of the nervous system. They have a number of
supporting roles throughout the nervous system and there are 5 different types of neuroglia cells
which carry out these functions.
Neuroglia
Astrocytes
Location Function
Star shaped cells that help keep the neurons in place as well as
CNS
regulating the composition of the surrounding extracellular fluid.
Ependymal cells CNS
Microglia
CNS
Oligodendrocytes CNS
PNS
Schwann Cells
Myelin Sheaths
Secrete and move the cerebral spinal fluid.
They engulf unwanted tissue in the CNS, e.g. microorganisms and
damaged tissue.
Each cell forms myelin sheaths around multiple axons in the CNS.
Each cell forms a myelin sheath around a single axon in the PNS.
The lipid rich membrane of the oligodendrites or schwann cells tightly wrap around a section of an
axon several times like a swiss roll. It is this tightly packed membrane that forms the myelin sheath
around an axon, which is now known as a myelinated fibre. Cells line up in rows along the axon and
between each adjacent oligodendrite or schwann cell is a tiny gap called a node of Ranvier. The
myelin sheath acts like as an insulator between the nodes of Ranvier, only allowing the action
potential to leap from node to node rather than to travel along the entire length of the axon. This
means that axons with a myelin sheath conduct action potentials quicker along their length than
unmyelinated axons. The myelin sheath also prevents the action potential from being passed to
adjacent neurons as well as protecting the fibre.
Clinical Considerations
It is unclear exactly what causes multiple sclerosis, but it is thought to be an autoimmune
disease. The immune system attacks its own cells (oligodendrocytes, schwann cells)
resulting in the demyelination of axons throughout the nervous system as well as the
Multiple formation of scar tissue. Demyelination interferes with the ability of the nerve to send
Sclerosis signals, and the scarring can cause damage to the nerves themselves.
Multiple sclerosis causes muscle weakness, double vision, problems with balance and
coordination, and problems with memory and problem solving.
Action Potentials
In every part of our body are electrically charged particles known as ions which can be positively or
negatively charged. Neurons rely on these differently charged ions to create and conduct electrical
impulses (action potentials).
Name
Sodium ions
Symbol Electrical Charge
(Na+) Plus 1 positive charge.
Plus 1 positive charge.
Potassium ions (K+)
Calcium ions (Ca++) Plus 2 positive charge.
Chloride ions (Cl-)
Minus 1 negative charge.
All cells have a 'resting potential', meaning when at rest the overall charge of ions inside the cell are
negative compared to the ions outside the cell in the extracellular fluid. The difference in charge
across the cell membrane of a neuron creates a potential electrical difference of about -70 milivolts
(mV). The cell membrane maintains this resting potential by selectively allowing some ions to pass
into the cell via special channels or gates and by blocking the entry of other ions. Due to the
electrochemical gradients Na+ slowly diffuses into the neuron and K+ slowly diffuses out of the
neuron. Because of this natural diffusion the resting neuron must actively pump Na+ out of the cell
and take K+ in to maintain its resting potential of -70 mV.
When a neuron is stimulated a section of its membrane becomes depolarised by the exchange of ions
across it. A section of the cell membrane opens its sodium channels allowing sodium ions to move
inside the cell. The sodium ions are positively charged and are attracted into the cell by the
negatively charged ions inside, as well as the lower sodium concentrations. The influx of positive
ions reverses (depolarises) the resting potential and the inside of the neuron becomes more
positively charged. When depolarisation reaches a certain level or threshold, i.e. the voltage inside
the cell reaches at least -55 milivolts, it triggers the opening of more sodium channels which in turn
triggers the opening of sodium channels in the adjacent cell membrane. Thus depolarisation is spread
along the entire cell membrane in a wave; this is an action potential and conducts the nerve impulse
along the axon. Once the action potential reaches the end of the axon the action potential is
converted to a chemical signal by the release of a neurotransmitter. The inside of the cell continues
to depolarise until the voltage peaks at about +35 milivolts, at which point the cell membrane closes
its sodium channels so that no more Na+ can enter, and opens its K+ channels to allow the positively
charged K+ ions to leave the cell. This process reverses the depolarisation (repolarisation) and
allows the neuron to return to its original resting potential of -70 milivolts.
SELF-TEST
Complete the following questions before you go onto the next section:
 Draw and label a typical neuron.

What is the significance of myelin sheaths.

Describe how an action potential is propagated.
NERVOUS SYSTEM: CENTRAL NERVOUS
SYSTEM
CHAPTER OBJECTIVES
When you have completed this chapter you should be able to:

Describe the difference between the CNS and PNS.

Locate and identify the forebrain, midbrain and hindbrain .

Identify the major gyri and sulci of the brain.

Describe the main parts of the forebrain and describe its function.

Describe the main parts of the midbrain and describe its function.

Describe the main parts of the hindbrain and describe its function.

Describe the main parts of the spinal cord.
The central nervous system (CNS) consists of the brain and spinal cord and the peripheral nervous
system (PNS) consists of the spinal nerves and ganglia.
Brain
The brain occupies the cranial cavity and can be divided into three main parts. The forebrain,
midbrain and hindbrain. The midbrain and hindbrain are collectively know as the brain stem and
contain the nuclei from which the cranial nerves originate.
Name
Description
Forebrain
Prosencephalon
Largest part of the
brain.
Midbrain
Mesencephalon (brain
stem)
1.5 cm in length.
Hindbrain
Rhombencephalon (brain
stem)
Important named parts


Telencephalon (cerebrum).
Diencephalon (thalamus, hypothalamus, pineal
body).

Quadrigeminal bodies - cerebral peduncles.



Pons.
Medulla oblongata.
Cerebellum.
Forebrain
Telencephalon (Cerebrum)
The cerebrum is the largest part of the brain and is divided into left and right hemispheres by a
longitudinal fissure that runs along the median sagittal plane. Inferiorly the hemispheres are
connected together by a band of white matter called the corpus collosum. The outer layer of the
cerebrum is composed of grey matter and called the cerebral cortex. It is responsible for the analysis
of sensory input, memory, learning and cognitive thought. Each hemisphere is greatly folded
forming gyri (folds) and sulci (grooves) which increases the surface area of the cerebral cortex.
Although the exact location of the sulci and gyri varies between different individuals, there are a
number of large gyri and deep sulci which can be identified as constant landmarks. The main ones
have been listed below;
Name
Description
Longitudinal
fissure
A large fissure running from back to front along the median sagittal plane; it divides the
cerebrum into left and right cerebral hemispheres.
Central sulcus
Descending downwards and forwards from the top of the hemisphere. It divides the
frontal and parietal lobes.
Parietal-occipital Descending downwards and forwards mainly inside the longitudinal fissure, it divides the
sulcus
parietal and occipital lobes.
This is found at the posterior border of the frontal lobe, in front of the central sulcus. It
Precentral gyrus descends downwards and forwards from the top of the hemisphere. Forms the primary
motor area (cortex).
Postcentral
gyrus
This is found at the anterior border of the parietal lobe, behind the central sulcus. It
descends downwards and forwards from the top of the hemisphere. Forms the primary
sensory area (cortex).
Lateral sulcus
Found on the lateral side of the brain it ascends almost horizontally from the front of the
brain to the angular gyrus and separates the temporal lobe from the frontal lobe above.
Each hemisphere can be further divided into lobes, their names of which correlate with the
surrounding bones that protect them.
Lobe of the
Description
Cerebrum
Function

The largest lobe found at the front of the brain
undercover of the frontal bone. It contains the
Frontal lobe precentral gyrus posteriorly. It is separated from the
parietal lobe posteriorly by the central sulcus and from
the temporal lobe inferiorly by the lateral sulcus.






Temporal
lobe
Found at the side of the brain undercover of the
temporal bone. It is separated above from the frontal
lobe by the lateral sulcus.


The primary motor area
(cortex).
Motor association area
(motor control).
Brocha's area - motor speech
(production)
Cognitive thought and
memory.
Personality
Primary olfactory cortex.
Primary auditory area
(hearing).
Auditory association area
(hearing).
Wernicke area (speech
comprehension).



Parietal
lobe
Found at the top of the brain undercover of the parietal
bone. Anteriorly it contains the postcentral gyrus and is
separated from the frontal lobe by the central sulcus.
Posteriorly it is separated from the occipital lobe by the
parietal-occipital sulcus.
Occipital
lobe
Found at the back of the brain undercover of the
occipital bone.
Insula
The smallest lobe of the brain found deep in the
cerebrum between the lips of the lateral sulcus.




Special senses (hearing,
smelling).
Learning and memory
(retrieval).
Emotions
Primary sensory area
(cortex).
Sensory association area
(general senses).
Body orientation.
Primary gustatory cortex
(taste).


Primary visual area (cortex).
Visual association area
(vision) - visual
interpretation.

Special senses (taste,
hearing).
Visceral sensation.

LOBES AND MAJOR LANDMARKS OF THE CEREBRUM
Diencephalon
The diencephalon consists of two thalami, two hypothalami and a single pineal body.
Thalamus
The thalami are the largest parts of the diencephalon and are located in the centre of the brain in the
outer walls of the third ventricle. They are often connected to each other across the third ventricle by
a small interthalamic adhesion.
The thalamus receives sensory and motor input as well as influences mood. It receives mostly
sensory input including auditory and visual input and relays the signals to the cerebral cortex.
Sensory Nuclei of the Thalamus Sensory input from
Medial geniculate nucleus
Auditory
Lateral geniculate nucleus
Visual
Ventral posterior nucleus
Other sensory input
Pineal body
This is a small pine-cone shaped gland projecting from the posterior of the third ventricle by a mid
line stalk. Its role is not fully understood but it is thought to be involved in the sleep-wake cycle and
the onset of puberty.
Hypothalamus
The hypothalamus is located at the very bottom of the diencephalon below the thalamus and behind
the optic chiasma. It is very important and is often referred to as the 'master gland' as it controls a
large number of bodily functions, one of the most important being that of homeostasis. Homeostasis
is the maintenance of the bodies physiology, i.e. the maintenance of blood pressure, body
temperature, weight and the chemical composition of the body's fluids. Other regulatory roles of the
hypothalamus are control of our mood and emotions, autonomic functions, food and water intake,
sleep wake cycle and endocrine function.
Name
Description
Function
Mammillary
bodies
A pair of small white bodies protruding
from the front of the hypothalamus.
Emotional responses to smells.
Infundibulum
A stalk which connects the hypothalamus
with the pituitary gland (hypophysis).
Through its connection the hypothalamus
regulates the function of the pituitary gland.
Mesencephalon (midbrain)
The smallest part of the brainstem measuring 1.5 cms it consists of the tectum, tegmentum, cerebral
peduncles and the substantia nigra. It is responsible for the visual and gustatory response as well as
the coordination of movement.
Name
Description
Roof of the midbrain, consisting of four nuclei which form 4 mounds, collectively
know as quadrigeminal bodies, on the dorsal surface of the brain stem.
Tectum
The 2 superior nuclei are called the superior colliculi the 2 inferior nuclei are called
the inferior colliculi. The superior colliculi control the visual response and the
inferior colliculi control the auditory response.
Tegmentum
Is the floor of the midbrain and consists of ascending tracts from the spinal cord to the
brain. It controls motor functions.
Substantia
nigra
A pigmented lamina located between the tegmentum and cerebral peduncles which helps
to coordinate movement.
Cerebral
peduncles
Located inferior to the tegmentum and consist of descending (motor) tracts from the
cerebrum to the spinal cord and cerebellum.
Cranial nerve
nuclei
The nuclei of the trochlear and oculomotor cranial nerves are located in the midbrain.
Brainstem
The midbrain and hindbrain are collectively know as the brain stem. It is the lowest part of the brain
and is continuous inferiorly with the cervical spinal cord at the foramen magnum. Its fibres connect
the peripheral nervous system (spinal nerves and cranial nerves) to the central nervous system (brain
and spinal cord).
The brain stem is extremely important because it contains the nuclei from which most cranial nerves
originate as well as the vital centres necessary for survival; breathing, digestion, heart rate, blood
pressure and for consciousness (being awake and alert).
Retinacular Formation
The retinacular formation is a series of important nuclei that span the brainstem and receive the
majority of the sensory information from the body and the motor signals from the cerebrum. The
nuclei also play an integral role in the maintenance of the conscious state.
Rhombencephalon (hindbrain)
The hindbrain consists of the pons superiorly, the cerebellum posteriorly and the medulla oblongata
inferiorly. The medulla oblongata is continuous inferiorly with the spinal cord.
Pons
Located in front of the cerebellum, the pons is only 2.5 cm in length and bulges anteriorly. It consists
of descending fibres travelling to the spinal cord and ascending fibres to the cerebellum. It also
contains the nuclei of four of the cranial nerves and the respiratory centre which controls expiration.
Name
Description
Pontine nuclei
Located anteriorly in the pons they connect the cerebrum to the cerebellum and
coordinate voluntary movement.
Respiratory
centre
Controls respiratory (expiration) movements.
The nuclei of the following cranial nerves are located in the posterior part of the pons;
Cranial nerve
nuclei




Trigeminal (V)
Abducens (VI)
Facial (VII)
Vestibular cochlear (VIII)
Medulla Oblongata
The medulla oblongata is only 3 cm in length and is the most inferior portion of the brainstem being
continuous with the spinal cord inferiorly. It consists of the pyramids and olives and contains
ascending and descending nerve tracts, several nuclei and importantly the 'vital centres', which
regulate heart rate, respiration and blood vessel diameter. It also contains some non-vital centres
involved in swallowing, vomiting, sneezing and coughing.
Name
Description
Function
Pyramids
Two enlargements on the anterior surface of the length of the medulla;
they taper towards the spinal cord. Here the descending nerve tract
Conscious voluntary
fibres (corticospinal fibres) cross over to the other side to form the
movements.
'pyramidal decussation'.
Olive
Two protrusions found on the anterolateral side of the medulla just
lateral to the pyramids. It consists of an olivary complex of nuclei.
Balance Coordination
of sound from the ear.
The medulla is the centre for several important regulatory reflexes;
Vital
Centres



Cardiac centres
Respiratory centres
Vasomotor centres
Heart rate.
Respiratory
(inspiration). Blood
vessel diameter.
The nuclei of the following cranial nerves are located in the medulla
oblongata;
Cranial
nerve
nuclei




Glossopharyngeal (IX)
Vagus (X)
Accessory (XI)
Hypoglossal (XII)
Cerebellum
The cerebellum is the lobe of the brain situated in the posterior cranial fossa. Its surface is folded
into folia and consists of two hemispheres connected in the mid line by the vermis. It is separated
from the pons and medulla oblongata anteriorly by the fourth ventricle. The cerebellum is
responsible for coordination of movement and sends information to the thalamus and cortex.
Grey and white matter
The brain and spinal cord contain both grey and white matter.
In the Brain
The grey matter can be found in the cerebral cortex, the basal ganglia and the limbic system. It is
made up of the cell bodies, dendrites and synapses of the neurons and are grouped into functionally
important nuclei.
The white matter is made up of the myelinated fibres (axons) which connect the different parts of the
brain to each other as well as to the spinal cord.
In the Spinal Cord
The spinal cord is oval in cross section and consists of white and grey matter. The grey matter lies
centrally and is arranged into ventral, dorsal and lateral grey horns (anterior and posterior horns). It
consists of neurons and neurites, neuroglia and blood vessels. It appears grey because of the
abundance of neuronal cell bodies.
The white matter surrounds the grey mater and is white in colour due to the presence of myelin,
which insulates the nerve fibres.
Ventricles
Inside the brain are four interconnected cavities filled with cerebral spinal fluid; two lateral
ventricles, a single third ventricle and a single fourth ventricle. The two lateral ventricles are the
largest ventricles and lie one in each cerebral hemisphere. They are approximately C-shaped (wish
bone), each communicating with the thin mid line third ventricle via an intraventricular foramen.
The third ventricle communicates inferiorly with the fourth ventricle via the cerebral aqueduct and
descends in the mid plane through the midbrain. The fourth ventricle is a small, triangular chamber
found between the pons in front and the cerebellum behind. Inferiorly it narrows to form the central
canal which descends though the medulla oblongata and spinal cord.
Each ventricle contains a choroid plexus which secretes cerebral spinal fluid (CSF) into the
ventricles. The third ventricle contains the thalamus and hypothalamus in its lateral walls and the
infundibulum, tuber cinereum and the mammillary bodies in its floor. The corpus collosum forms the
roof of the lateral and third ventricles.
Cerebral Spinal Fluid (CSF)
The CSF is a clear fluid produced by the choroid plexuses of the ventricles. It circulates within the
ventricles as well as in the subarachnoid space between the pia mater and arachnoid mater
surrounding the brain and spinal cord. CSF baths the brain and spinal cord in a chemically stable
environment and provides it with nutrients. It also allows the brain to be buoyant and protects the
brain from jolting into the cranium.
Meninges
Surrounding the brain and spinal cord are three membranous layers;
In the Brain
Around the brain these three layers are collectively known as the meninges;
Outermost layer;
The outermost layer, the dura mater is dense and consists of two layers, a periosteal layer and a
meningeal layer. The periosteal layer adheres to the internal surface of the cranium and for the
majority of its course lies directly touching the meningeal layer. At certain locations the periosteal
and meningeal layers are pulled away from each other to create a space, a dural sinus. The sinuses
are filled with venous blood from the brain via the cerebral veins. They drain blood into the internal
jugular vein.
Dural Sinuses
Superior sagittal sinus
Cavernous sinus
Inferior petrosal sinus
Superior petrosal sinus
Transverse sinus
Sigmoid sinus
Occipital sinus
The meningeal layer folds inwards to form two double thickness sheets which help to hold the brain
in place. The falx cerebri is the fold of dura which projects vertically into the longitudinal fissure
between the cerebral hemispheres. The tentorum cerebelli is the fold of dura which projects
horizontally between the cerebellum below and the cerebrum above.
Middle layer;
The middle layer, the arachnoid mater, is thin and transparent and lines the inner surface of the dura
mater. It possesses arachnoid trabeculae (granulations) which project into the pia mater and villi
which project into the dura mata.
Innermost layer;
The innermost layer, the pia mater lies directly on the surface of the brain. This layer is very thin
and transparent and closely follows all of the gyri and sulci. Between the pia mater and the arachnoid
mater is the subarachnoid space in which the CSF is circulated. CSF is returned to the blood via the
arachnoid trabeculae (granulations).
In summary;
Name
Location
Description
Pia Mater
Innermost
layer.


Thin and transparent.
Invests the surface of the brain and spinal cord.
Arachnoid Mater
Middle layer.


Thin and transparent.
Project villi through the dura into the venous sinuses to
absorb CSF.
Dura Mater
Outermost
layer.



Thick and fibrous.
Made up of two layers; periosteal and meningeal.
Contains the venous sinuses.

Folds inwards to form the falx cerebri and tentorum cerebelli.
CROSS SECTION OF THE SCALP
In the Spine
The spinal cord meninges are a continuation of the cranial meninges and are connected to the
foramen magnum. Like the cranial meninges the fibrous dura mater is the thick outermost layer and
is connected posteriorly to the posterior longitudinal ligament. The arachnoid mater lines the inner
surface of the dura mater and the pia mater lies directly on the spinal cord itself. The pia mater
attaches to the dura mater via the denticulate ligament.
DENTICULATE LIGAMENT
The spinal cord terminates at the level of L2, but the dura continues to the level of S2 creating a
cistern into which the the lower spinal roots hang.
SELF-TEST
Complete the following questions before you go onto the next section:

Describe the important structures of the midbrain.

Name three structures related to the third ventricle.

Describe the functions of CSF.
Spinal cord
The spinal cord is continuous with the medulla oblongata at the foramen magnum, and descends in
the vertebral canal. It consists of 31 segments corresponding to the 31 spinal nerves; 8 cervical, 12
thoracic, 5 lumbar, 5 sacral and 1 coccygeal.
At the level of the second lumbar vertebrae the spinal cord terminates by tapering to a conus
medullaris. From the conus medullaris is a long thin filament called the filum terminale. The
vertebral canal below the second lumbar vertebra is filled with the nerve roots from the lumbosacral
spine; this bunch of nerve roots resembles a horses tail and so is known as the cauda equina.
Along its course the spinal cord has two enlargements, the cervical enlargement and the lumbosacral
enlargement, in the cervical and lumbar regions respectively. These swellings are due to the large
spinal nerves which emerge from these parts of the cord to supply the upper and lower limbs.
The spinal cord is made up of a column of grey matter (contains cell bodies) surrounded by a
cylinder of white matter (myelinated neurons). The neurons of the grey matter are arranged into
ventral, dorsal and lateral horns. The fibres of the white matter travel longitudinally along the spinal
cord in designated columns.
SELF-TEST
Complete the following questions before you go onto the next section:

How many segments does the spinal cord have?

Which vertebral level does the spinal cord terminate?

Why does the spinal cord have a number of enlargements along its course?
NERVOUS SYSTEM: PERIPHERAL
NERVOUS SYSTEM
CHAPTER OBJECTIVES
When you have completed his chapter you should be able to:

Name all 12 cranial nerves and describe their functions.

Describe the anatomy of a typical spinal nerve.

Identify the cervical, lumbar, sacral and coccygeal plexuses.

Name the main branches of each plexus and describe their course and function.

Describe the difference between the parasympathetic and sympathetic nervous systems.
The peripheral nervous system (PNS) consists of the spinal nerves and ganglia and the cranial
nerves. The nerves of the PNS contain sensory fibres which relay signals to the central nervous
system (CNS) and motor fibres which relay signals from the CNS to the effector muscles/glands.
The PNS can be divided into sensory somatic and autonomic systems. The sensory somatic nervous
system is voluntary and relays sensory information, of which we are conscious, from the external
environment to the CNS and relays motor signals from the CNS to operate the muscles of the body.
The autonomic nervous system is involuntary and relays sensory information about the internals of
the body to the CNS and relays motor signals from the CNS to regulate the internal environment of
the body, e.g. vessel diameter.
Sensory somatic system
The sensory somatic system consists of 12 pairs of cranial nerves and 31 pairs of spinal nerves.
Cranial nerves
The cranial nerves all originate or terminate in the brain stem. All cranial nerves, apart from the first
two, which are purely sensory, contain motor as well as sensory fibres and can be described as
'mixed' nerves. However, for descriptive terms each nerve is usually described in terms of its
predominant fibres. The motor (afferent) fibres originate in the brain stem and terminate in muscles
or glands, and the sensory (efferent) fibres originate in the sensory organs and receptors and
terminate in the brain stem.
Cranial Nerve
Fibres
Course
Olfactory (I)
Sensory
Origin: mucosa of the
nasal cavity.
Terminates: olfactory
Function

Smell.
bulb.
Optic (II)
Sensory
Origin: retina of the
eyeball.
Terminates: lateral
geniculate body of the
thalamus.
Oculomotor (III)
Origin: midbrain.
Predominantly
Terminates: extrinsic
motor
muscles of the eye.
Trochlear (IV)
Origin: midbrain
Predominantly
Terminates: extrinsic
Motor
muscle of the eye.
Trigeminal (V)
Abducens (VI)
Facial (VII)
Mixed
Origin: middle and
upper face and the
pons.
Terminates: pons and
the muscles of
mastication.
Motor
Origin: pons.
Terminates: extrinsic
muscle of the eye.
Mixed
Origin: taste buds and
pons.
Terminates: thalamus
and muscles of facial
expression and
salivary glands.
Origin: cochlear and
Vestibulocochlear Predominantly semicircular canals of
(VIII)
sensory
the inner ear.
Terminates: pons and

Vision.

Extrinsic muscles of the eyeball
(superior, medial and inferior rectus
and inferior oblique and levator
palpebrae superioris).
Parasympathetic: intrinsic muscles of
the eyeball (sphincter of the pupil and
the ciliary muscle of the lens).


Extrinsic muscle of the eyeball
(superior oblique).

Sensory (ophthalmic, maxillary and
mandibular nerves): scalp, face and
mouth.
Motor (mandibular nerve): muscles of
mastication (chewing) and soft palate
and the middle ear.


Extrinsic muscle of the eyeball (lateral
rectus).


Sensory: taste, external ear and palate.
Motor (temporal, zygomatic, buccal,
mandibular and cervical nerves):
muscles of facial expression and middle
ear.
Parasympathetic: salivary and lacrimal
glands.



Hearing.
Balance.
medulla oblongata.
Glossopharyngeal
Mixed
(IX)
Vagus (X)
Accessory (X)
Hypoglossal (XII)
Origin: pharynx,
middle ear and
tongue and the
medulla oblongata.
Terminates: medulla
oblongata, parotid
gland and pharynx.
Mixed
Origin: viscera,
tongue, pharynx and
larynx; medulla
oblongata.
Terminates: medulla
oblongata; viscera,
tongue, pharynx and
larynx.
Motor
Origin: medulla
oblongata
Terminates: muscles
of the neck and
swallowing
Motor
Origin: medulla
oblongata
Terminates: tongue
and hyoid muscles.









Sensory: taste, tongue, pharynx, tonsils
and middle ear.
Motor: muscles of the pharynx
(swallowing).
Parasympathetic: parotid gland.
Sensory: pharynx, larynx, thoracic and
abdominal organs and taste.
Motor: soft palate, pharynx, intrinsic
laryngeal muscles (voice) and extrinsic
tongue muscle.
Parasympathetic: to the thoracic and
abdominal viscera - digestive tract,
heart and lungs, kidneys, spleen liver
and pancreas.
Neck muscles (sternocleidomastoid
and trapezius).
Muscles of swallowing (pharynx and
soft palate).
Extrinsic and intrinsic muscles of the
tongue and hyoid muscles.
SELF TEST
Complete the following questions before you go onto the next section:

Name in order all 12 cranial nerves.

Name the cranial nerves that innervate the extrinsic muscles of the eyeball.

Name the cranial nerves that carry parasympathetic fibres.
Spinal nerves
There are 31 pairs of spinal nerves each arising from dorsal and ventral rootlets from the
corresponding 31 segments of the spinal cord. There are 8 pairs of cervical spinal nerves, the first set
arising above the atlas (C1) and the last arising below the seventh cervical vertebra (C7). There are
12 pairs of thoracic spinal nerves, 5 sets of lumbar spinal nerves, 5 sets of sacral and spinal nerves
and 1 set of coccygeal spinal nerves.
The dorsal roots arise from the posterolateral sides of the cord and carry sensory fibres from the
cord. The ventral roots arise from the anterolateral sides of the cord and carry motor fibres from the
cord. The dorsal and ventral roots unite to form the mixed (sensory and motor) spinal nerves. Just
before the ventral and dorsal roots join, there is a small swelling known as the dorsal root ganglion.
It is formed by the cell bodies of the sensory neurons.
With the exception of the 1st cervical, the sacral and the coccygeal spinal nerves, all of the spinal
nerves exit the vertebral canal via the intervertebral foramina. The intervertebral foramina are found
along the sides of the vertebral column, formed between the pedicles of adjacent vertebrae. The first
cervical spinal nerve exits above the atlas, between it and the occipital bone, and the sacral spinal
nerves exit via the ventral and dorsal sacral foramina.
After exiting through the intervertebral foramina the spinal nerves soon divide into dorsal and
ventral rami (branches). The dorsal branches supply the deep muscle and the skin of the back of the
trunk. The ventral branches supply the rest of the body. The ventral branches of the thoracic spinal
nerves form the intercostal nerves which supply the muscles of the thoracic cage. The ventral
branches of the rest of the spinal nerves interlink to form specialised nerve plexuses which supply
the rest of the body.
Cervical Plexus
The ventral branches of the 1st-4th cervical spinal nerves (C1-C4) interlink to form the cervical
plexus. The cervical plexus gives off many branches which supply the superficial muscles of the
neck and the skin over the neck and back of the head. An important branch of the cervical plexus is
the phrenic nerve which travels through the thorax to innervate the movement of the diaphragm;
without it we would not be able to breath.
Brachial Plexus
The ventral branches of the 5th-8th cervical and the 1st thoracic spinal nerves (C5-T1) interlink to
form the brachial plexus. The brachial plexus supplies the entire upper limb with motor and sensory
innervation. The brachial plexus divides into lateral, posterior and medial cords before dividing into
a number of large branches;
Brachial plexus (C5Origin
T1)
Course
Musculocutaneous
Nerve (C5-C7)
It descends between biceps and
brachialis to the elbow where it
A branch of the
lateral cord.
Innervates

Motor: flexors of the
elbow joint;
coracobrachialis,
becomes the lateral cutaneous
nerve of the forearm.


Axillary Nerve (C5C6)
A branch of the
posterior cord.
Descends behind the axillary artery
winds around the surgical neck of
the humerus.
It exits the axilla under teres minor
and runs around the back of the
A continuation of
humerus in the radial groove with
Radial Nerve (C5-T1) the posterior
the arteria profunda brachii. From
cord.
here it runs down the lateral side
of the forearm to the wrist.






Runs down the medial side of the
arm in front of the medial head of
A continuation of
the triceps to reach the elbow. It
Ulnar Nerve (C7-T1)
the medial cord.
enters the flexor compartment of
the forearm to travel to the wrist.



Median Nerve (C5T1)
It leaves the axilla with the
Arises from the
brachial artery and travels to the
medial and lateral elbow. In the forearm it travels to
cords of the
the wrist where it enters the
carpal tunnel and divides into
brachial plexus.
medial and lateral branches.

biceps and brachialis
muscles.
Sensory (cutaneous):
Skin over the radial
(lateral) border of the
forearm.
Motor: deltoid and
teres minor muscles.
Sensory: shoulder
joint
Sensory (cutaneous):
Skin over the shoulder
and lateral arm.
Motor: extensors of
the elbow, wrist and
hand.
Sensory: elbow, wrist
and hand joints.
Sensory (cutaneous):
Skin over the dorsum
of the hand.
Motor: a few of the
flexors of the wrist
and hand and most of
the intrinsic muscles
of the hand.
Sensory: hand joints.
Sensory (cutaneous):
Skin of the ulnar
(medial) aspect of the
hand.
Motor: most of the
long flexors of the
forearm and the
thenar muscles.
Sensory (cutaneous):
Skin of the elbow,
wrist, and radial
aspect of the palm of
the hand.
DIAGRAM OF THE BRACHIAL PLEXUS
Lumbar Plexus
The ventral branches of the 1st to 4th lumbar spinal nerves interlink to form the lumbar plexus. The
lumbar plexus supplies the thigh and skin of the buttocks and genitals;
Lumbar plexus
(L1-L4)
Origin
Femoral nerve
The largest nerve of the lumbar plexus, it
Posterior
arises with in the substance of the psoas
divisions of
muscle. It passes into the thigh under the
Course
Innervates

Motor: iliopsoas,
sartorius and quadriceps
femoris muscles.
L2-L4.
Iliohypogastric
Ilioinguinal
Anterior
division of
T12-L1
Arises within the substance of psoas
emerging laterally to travel over quadratus
lumborum. It pierces transversus abdominis
to travel between it and internal oblique.
Anterior
division of
L1
Emerges from the superolateral border of
psoas major, passes over quadratus
lumborum and pierces transversus
abdominis and internal oblique. It
continues underneath external oblique and
enters the inguinal canal.
Lateral femoral
L2-L3
cutaneous
Genitofemoral
Obturator
inguinal ligament, where it divides into
anterior and posterior branches.
Emerges from the lateral aspect of psoas
major travels along iliacus to enter the
surface of the thigh under the inguinal
ligament. Here it divides into anterior and
posterior branches.
Passes through the substance of psoas
Anterior
major and emerges from its anterior
divisions of
surface where it divides into genital and
L1-L2
femoral branches.
It ascends through psoas major to emerge
Anterior
at the pelvic brim medial to the muscle. It
divisions of descends along the lateral wall of the pelvis
to enter the thigh through the obturator
L2-L4
foramen.

Sensory (cutaneous):
Skin over the anterior
and lateral thigh and the
medial leg and foot.

Motor: abdominal
muscles.
Sensory (cutaneous):
Skin of the anterior
buttocks and abdominal
wall above the pubis.


Sensory (cutaneous):
Skin of the superomedial
thigh and genital area.

Sensory (cutaneous):
Skin over the lateral
aspect of the thigh
down to the knee.

Sensory (cutaneous):
Skin over the femoral
triangle and genital
area.

Motor: Adductors of the
thigh.
Sensory: hip and knee
joints and cruciate
ligaments.
Sensory (cutaneous):
Skin of the medial side
of the thigh.


Sacral Plexus
The ventral branches of the 4th lumbar to the 4th sacral spinal nerves (L4-S4) interlink to form the
sacral plexus. Because there is an overlap between the lumbar and sacral plexuses they are often
described together as the lumbosacral plexus. A large division known as the lumbosacral trunk
arises from the ventral branches of the L4-L5 and joins with the ventral branches of S1 to supply the
lower limb.
Sacral
Plexus
Sciatic
nerve
Origin
Course
Anterior
divisions of
the L4-S3
The largest nerve in the body, it is really two
nerves bound together with connective tissue;
the medially placed tibial nerve and laterally
placed common (fibular) peroneal nerve. It
exits the pelvis, through the greater sciatic
foramen, underneath piriformis and runs down
the back of the leg to the knee where its two
components split from one another.
Larger of the
two divisions
Tibial nerve
of the sciatic
nerve (L4-S3)
Arises as a separate division in the popliteal
fossa, and descends into the flexor
compartment of the leg (calf) in which it travels
to the ankle. On reaching the ankle it divides
into medial and lateral plantar nerves which
enter the sole of the foot.
Innervates


Motor: hamstrings.
Sensory: hip joint.

Motor: flexors of the
leg.
Sensory: knee and foot
joints.
Sensory (cutaneous):
skin over the back of
the leg and on the sole
of the foot.



Motor: peroneal
muscles and extensors
of the ankle.
Sensory: knee, foot and
ankle joints.
Sensory (cutaneous):
skin over the anterior,
lateral and posterior
aspect of the leg and
skin of the dorsum of
the foot and toes.
Common
(fibular)
Peroneal
nerve
Smaller of
the two
divisions of
the sciatic
nerve (L4-S2)
Arises as a separate division in the popliteal
fossa and travels laterally around the neck of
the fibula to enter the peroneus longus muscle
where it divides into deep and superficial
branches.

Superior
Gluteal
Nerve
Posterior
divisions of
L4-S1
It exits the pelvis through the greater sciatic
foramen, above piriformis to reach the gluteal
region.

Motor: gluteus medius
and minimus and
tensor fasciae latae.
Inferior
Gluteal
Posterior
divisions of
It exits the pelvis through the greater sciatic
foramen, below piriformis to reach the gluteal

Motor: gluteus
maximus.

Nerve
L5-S2
region.
Pudendal
Nerve
Anterior
divisions of
S2-S4
It exits the pelvis through the greater sciatic
foramen, between piriformis and coccygeus
and enters the pelvis again through the lesser
sciatic foramen.


Motor: perineal
muscles.
Sensory (cutaneous):
skin of the perineum.
Coccygeal Plexus
The ventral branches of the 4th to 5th sacral spinal nerves and the coccygeal spinal nerve (S4-Co1)
interlink to form the coccygeal plexus. It pierces the anococcygeal ligament to supply sensory
innervation to the skin of that region.
SELF TEST
Complete the following questions before you go onto the next section:

Beginning at the spinal cord describe the formation of a spinal nerve.

Which nerve roots contribute to each plexus?

Name 3 nerves from each of the cervical, brachial and lumbar plexuses.
Autonomic nervous system
The autonomic nervous system (ANS) maintains our internal bodily functions without us being
aware of it. It consists of afferent (sensory) fibres that transmit sensory information from the
periphery (viscera) to the CNS, and efferent (motor) fibres that send motor signals from the CNS to
the periphery. This loop of autonomic sensory and motor fibres allows the body to monitor and
control such functions as heart rate, vessel diameter, smooth muscles surrounding organs and the
secretions of glands.
The ANS can be divided into two separate systems, sympathetic and parasympathetic, both of
which contain motor and sensory fibres. The fibres in both systems arise in the central nervous
system (brain and spinal cord) as preganglionic fibres. These synapse in ganglia with postganglionic
fibres, which then travel to the target organ.
Most organs are innervated by fibres from both divisions of the ANS; the sympathetic system
generally prepares the body for activity while the parasympathetic prepares it for rest.
Sympathetic
The sympathetic system controls our 'fight or flight' responses, i.e. quickly activates our body
preparing it for action by increasing the heart rate, dilating the pupils and vessels to the muscles,
increases skin sweating and suppresses digestion.
The motor (efferent) sympathetic fibres (preganglionic motor neurons) arise from the
intermediolateral column in the thoracic spinal cord and travel to the sympathetic ganglia listed
below, where they synapse with postganglionic neurons before reaching their target organs. The
sympathetic chain is found on either side of the vertebral column and consists of a number of
sympathetic ganglia strung together by sympathetic trunks.
Sympathetic Ganglia
Chain ganglia
Middle cervical ganglia
Superior cervical ganglia
Stellate ganglia
Aortic ganglia
Celiac ganglia
Renal ganglia
Mesenteric ganglia
White and grey rami connect the sympathetic trunks to the spinal nerves. Fibres emerge from the
chains to form sympathetic plexuses around the internal organs.
Sympathetic plexuses
Oesophageal plexus
Aortic plexus
Gastric plexus
Cardiac plexus
Superior hypogastric plexus
Inferior hypogastric plexus
The sensory (afferent) sympathetic fibres carry sensory information from the viscera to the CNS.
The afferent fibres enter the dorsal horn of the spinal cord alongside the sensory afferents from the
skin, this can cause confusion with referred pain.
Referred pain
Because the afferent fibres enter the dorsal horn of the spinal cord alongside the sensory afferents
from the skin, pain from the viscera can be perceived as originating from elsewhere in the body. This
is known as referred pain and must be understood when investigating the condition of a patient, for
example, when a person is experiencing a heart attack they will often feel pain in their left shoulder,
neck and arm. This is due to the sensory fibres from the heart and those areas of the arm entering the
spinal cord at the same level where the signals get confused.
Parasympathetic
The parasympathetic system controls the opposite responses to 'fight or flight' responses, i.e.
depresses the activity of the body preparing it for rest by decreasing the heart rate, constricting the
pupils and vessels to the skeletal muscles and stimulating digestion (peristalsis and salivary
production).
Parasympathetic cells are located in specialised nuclei throughout the brainstem and the sacral
spinal cord. Its fibres travel in four of the cranial nerves chiefly the vagus nerve as well as the
splanchnic and pelvic nerves. The majority of sensory (afferent) parasympathetic fibres return to the
medulla oblongata via the vagus nerve where the fibres then travel in the solitary tract to the
solitary nucleus which receives sensory information about the blood pressure, CO2/O2 levels and
digestive tract distension.
Parasympathetic nerves Targets
Vagus nerve
Heart, stomach, small intestine, parts of the large intestine.
Oculomotor
Sphincter of pupil and ciliary muscle.
Facial nerves
Lacrimal, nasal, submandibular and sublingual glands.
Glossopharyngeal nerve Parotid gland.
Pelvic splanchnic nerves Parts of the large intestine, rectum, bladder, penis or clitoris.
The motor (efferent) parasympathetic fibres travel to parasympathetic ganglia before reaching their
target organ.
Parasympathetic Ganglia Targets
Ciliary ganglia
Sphincter of pupil and ciliary muscle.
Pterygopalatine ganglia
Lacrimal and nasal glands.
Submandibular ganglia
Submandibular and sublingual glands.
Otic ganglia
Parotid gland.
Mesenteric ganglia
Parts of the large intestine and rectum.
Pelvic ganglia
Bladder, penis or clitoris.
Autonomic Reflexes
A reflex is a pathway with an afferent (sensory) signal that evokes an immediate efferent response
(motor) without the signal being transmitted to the brain.
e.g. afferent fibres from the viscera baroreceptors and chemoreceptors in the carotid sinus and arch
of the aorta are carried to the CNS by the major autonomic nerves where they control heart rate,
blood pressure and respiration.
Summary of ANS Function;
Structure
Sympathetic Action
Parasympathetic Action
Heart Rate
Increase.
Decrease.
Heart Contraction
Increase force.
Decrease force.
Blood Vessels
Directs blood to the skeletal muscles (away from
the skin and viscera).
Directs blood to the to the skin and
viscera.
Sweat Production
Increases production.
Decreases production.
Pupil Aperture
Dilates.
Constricts.
Trachea and
Bronchi
Dilates.
Constricts.
Blood Pressure
Increases.
Lowers.
Salivary Gland
Decreases production.
Increase production.
Gastrointestinal
Tract
Decreases peristalsis, reduced digestion.
Increases peristalsis, increases
digestion.
Liver
Stimulates the conversion of glycogen to glucose.
Inhibits the conversion of glycogen
to glucose.
Kidney
Decreased urine production.
Increased urine production.
Bladder
Wall relaxed, sphincter closed.
Wall contracted, sphincter relaxed.
SELF TEST
Complete the following questions before you go onto the next section:

Describe the functions of the sympathetic and parasympathetic nervous systems.

Name and locate five sympathetic ganglia.

Name and locate four parasympathetic nerves.