NEURO: Structure Of The Nervous System

Question 1

What is the human nervous system?

Answer 1

The human nervous system is comprised of the central nervous system (CNS) and the peripheral nervous system (PNS).

The human nervous system is a complex collection of neurones including glial cells that allow the transmission of signals between different parts of the body. The coordinated actions of the NS is responsible for a diverse range of functions such as see, hear, move, feel, dream, memory etc.

Afferent sensory fibres carry sensory information from the periphery to the brain. Efferent motor fibres carry motor instructions from the brain to the periphery.

Question 2

What is the Central Nervous System?

Answer 2

The CNS refers to the regions of the nervous system that are encased in bone - namely the brain and spinal cord.

The brain plays a central role in the control of most bodily functions, including awareness, movements, sensations, thoughts, speech, and memory. Some reflex movements can occur via spinal cord pathways without the participation of brain structures.

Question 3

What is the Peripheral Nervous System and describe its subdivisions?

Answer 3

The PNS refers to all parts of the nervous system other than the brain and spinal cord. These nerves form the communication network between the CNS and the body parts. The PNS is divided into the:

• Somatic NS
• Autonomic NS

The somatic NS provides innervation to the skin joints, skeletal muscle and commits the voluntary control of movement and locomotion.

The Autonomic NS provides innervation to the cardiovascular system, internal organs and smooth muscles to control for example heart rate, blood pressure, breathing and digestion.

The ANS can be divided into the sympathetic and parasympathetic NS.

Sympathetic NS - involved in fight and flight responses. Includes increased heart and blood pressure, and decreased digestion function.

Parasympathetic NS - involved in rest and digest responses. Includes decreased heart and blood pressure, and increased digestion function.

Question 4

Briefly describe the brain and some of its functions.

Answer 4

The brain is the most complex organ in the human body. It contains billions of neurones and trillions of synapses (signals travelling between neurones at up to 268mph.)

It controls ‘basic’ fundamental life processes such as:

• breathing
• organ function
• movement

It also controls more complex processes such as:

• thought
• behaviour and emotions
• creating memories

Question 5

What are the 3 major regions of the brain?

Answer 5

1. Forebrain
   - Cerebrum (telencephalon)
   - Diencephalon
2. Brainstem
   - Midbrain
   - Pons
   - Medulla Oblongata
3. Cerebellum

Question 6

What are the 3 orientations for brain scans and the axes of the brain?

Answer 6

- sagittal (divides brain into the left and right hemisphere) - this can also be midsaggital (at the midline)
or parasagittal (more lateral)
- coronal (divides into anterior and posterior)
- transverse/horizontal/axial (divides into superior and inferior)

Side note:
Anterior = Front
Posterior = Behind

Rostral = Nose
Caudal = Tail

Dorsal = Top
Ventral = Bottom

Superior = Above
Inferior = Below

Question 7

Describe the hippocampus.

Answer 7

The hippocampus (derived from the Greek for ‘seahorse’) is a region of the cerebral cortex embedded deep within the temporal lobe.

Its functions include:

• Learning
• Memory formation and retrieval.
• Regulation of hypothalamus-pituitary-adrenal (HPA) axis.

Hippocampal dysfunction:
In 1985, Clive Wearing (a composer and musician) contracted a virus that caused damage to his hippocampus causing him memory problems.

• Anterograde amnesia = unable to create new memories
• Retrograde amnesia = generally unable to recall past memories.

Question 8

What can the 3 orientations for brain scans reveal?

Answer 8

Coronal, horizontal and sagittal sections can reveal regions within the forebrain, including various sub-cortical structures (e.g. the hippocampus.)

Question 9

What are the cranial nerves and list all 12 of them.

Answer 9

The cranial nerves describe the 12 nerves (I-XII) pairs of nerves arising from the brainstem that perform a diverse range of functions.

The cranial nerves are numbered from anterior to posterior.

I. Olfactory
II. Optic
III. Oculomotor
IV. Trochlear
V. Trigeminal
VI. Abducens
VII. Facial
VIII. Auditory-vestibular (vestibulocochlear)
IX. Glossopharyngeal
X. Vagus
XI. Spinal accessory
XII. Hypoglossal

Cranial nerves 1 and 2 are part of the CNS. 3 to 12 are part of the PNS.

Acronym to help remember:
Oh! Oh! Oh! To Touch And Feel Virgin Girls Vagina Such Heaven!

Note: see summary pic

Question 10

Describe the Olfactory nerve (CN I).

Answer 10

The olfactory nerve is a special sensory nerve - responsible for the sensation of smell.
Olfaction = smell

In our noses, there is olfactory epithelium, which contains olfactory receptor cells. They transmit information to the olfactory bulb.

The olfactory bulb then transmits the smell information to 3 different places:

• Frontal cortex: where we have the conscious perception of the smell
• Hippocampus: where we have odour memory, and it decides if an action is to be induced because of the smell
• Hypothalamus amygdala: where we store the motivational and emotional factors of smell

The olfactory nerve function is to mediate the transmission of information to the olfactory bulb where it is subsequently conveyed to other brain regions allowing for different aspects of the sensation of smell.

Question 11

Describe the Optic nerve (CN II).

Answer 11

The optic nerve is a special sensory nerve - important in vision.

It transmits information from our rods and cones in our retina to the visual cortex in our occipital lobes (in the brain).

It does this via:
the retinal ganglion cells transmits information to –> the lateral geniculate nucleus (in the thalamus) –> to the visual cortex (in the occipital lobe.)

This allows us to interpret colour and contrast.

Question 12

Describe the the Oculomotor nerve (CN III).

Answer 12

The Oculomotor nerve is involved in somatic motor function to control the eye and eyelid movement. (CN III + IV + VI all involved in this.)

It is also involved in the parasympathetic control (visceral autonomic motor control) of pupil size - concerned with pupillary constriction and accommodation.

Question 13

Describe the Trochlear nerve (CN IV).

Answer 13

It conveys motor information.

It is involved in the somatic motor control of eyeball movement (CN III + IV + VI).

Question 14

Describe the Trigeminal nerve (CN V).

Answer 14

The Trigeminal nerve is both somatic sensory and motor.

Somatic sensory function - involved in the sensation of touch to the face.

Somatic motor function - involved in the movement of muscles of mastification (chewing).

It is involved in receiving signals from our facial skin regions. It has three divisions:

• opthalmic (sensory)
• maxillary (sensory)
• mandibular (sensory)

Question 15

Describe the Abducens nerve (CN VI).

Answer 15

The Abducens nerve is a somatic motor nerve. It is involved in controlling eye movements like cranial nerves III and IV.

Question 16

Which parts of the eye do the different cranial nerves control?

Answer 16

• The palpebrae muscles are controlled by the Optic nerve (CN II), and are used for opening the eyelid.
• The inferior rectus, medial rectus, superior rectus and the inferior oblique is controlled is controlled by the Oculomotor nerve (CN III).
• The superior oblique is controlled by the Trochlear nerve (CN IV).
• The lateral rectus is controlled by the Abducens nerve (CN VI).

These are the 6 extraocular muscles. They eye control movement and the levator palpebrae muscle controls eyelid elevation.

Question 17

Describe the facial nerve (CN VII).

Answer 17

The Facial nerve is a special sensory nerve. It has a somatic sensory function in the movement of muscles and facial expressions. The special sensory function includes the sensation of taste in the anterior tongue.

It conveys sensory, motor and parasympathetic information.

For the sensory part, it helps with taste on the anterior two-thirds of the tongue.

For the motor part, it controls the facial expression muscles. It also controls the stapedius muscle, a muscle in our ear which blocks it when we need to dull down information that is either harmful or useless.

For the parasympathetic part, it controls the salivary glands, the lacrimal glands, the glands of the nose and palate.

Question 18

Describe the vestibulocochlear nerve (CN VIII).

Answer 18

The vestibulocochlear nerve
(a.k.a auditory-vestibular nerve) conveys sensory information - hearing and balance.

With hearing, the cochlea cells project to the medial geniculate nucleus (in the thalamus), then to the auditory cortex (in the temporal lobe).

With balance, the vestibular hair cells project to the ventral posterolateral nucleus (in the thalamus), then to the vestibular cortex (in the temporal lobe).

Question 19

Describe the glossopharyngeal nerve (CN IX).

Answer 19

The glossopharyngeal nerve has sensory, motor and parasympathetic functions.

• Special sensory function - involved in the sensation of taste in posterior tongue.
• Visceral sensory - detection of blood pressure in the aorta
• Somatic motor - movement of muscles in the throat
• Visceral motor - parasympathetic control of salivary glands.

It has a variety of sensory functions. It plays a sensory role with the pharynx, the auditory tube, the middle ear, the posterior third of the tongue, and detects blood pressure changes in the aorta.

With its motor functions, it controls swallowing.

With its parasympathetic functions, it stimulates the salivary glands.

Question 20

Describe the vagus nerve (CN X).

Answer 20

It has sensory, motor and parasympathetic functions.

• Visceral sensory function - its involved in the sensation of pain with associated viscera (internal organs).
• Somatic motor function - it controls muscles used for speech and swallowing in the throat.
• Visceral motor function - involved in the parasympathetic control of the smooth muscle in the heart, lungs and abdominal organs.

Question 21

Which cranial nerves are involved in the sensation of taste and what is the brief mechanism?

Answer 21

The anterior tongue (controlled by CN VII), posterior tongue (controlled by CN IX), and epiglottis (controlled by CN X) send signals –> Glustatory nucles (medulla) –> Ventral posterior medial nucleus (thalamus) –> Gustatory cortex

Question 22

Describe the accessory nerve (CN XI).

Answer 22

The accessory nerve (CN XI) conveys motor information from our brain to the periphery; it does it cranialy and via the spine.

Somatic motor function - movement of muscles in the throat and neck.

Cranialy, it controls the muscles of the pharynx, larynxa and soft palate.

Via the spine, it controls the head and neck muscles.

Question 23

Describe the hypoglossal nerve (CN XII).

Answer 23

The hypoglossal nerve (CN XII) conveys motor information.

Somatic motor function - controls tongue movement for swallowing and speech.

Question 24

What are the meninges?

Answer 24

The meninges describe the 3 membranes that cover the brain and spinal cord. They ensure the nervous system encased in the skull and the vertebral column do not come into direct contact with overlying bone.

The 3 meninges (from superficial to deep) are the:
- dura mater: tough, in-elastic layer surrounding the brain and spinal cord. Adheres tightly to the brain.

The subdural space separate the dura matter and arachnoid space

• arachnoid membrane: adheres the two layers together

The subarachnoid spaces separates the arachnoid membrane and pia matter.

• pia mater: a thin membrane that adheres closely to the brain

The subarachnoid space is filled with cerebrospinal fluid (CSF).

Question 25

What is the function of the meninges?

Answer 25

• The primary function of the meninges is the protection of the brain and spinal cord.
• Passage of CSF - ventricular system.
• Supports the cerebral and spinal blood vessels - vasculature system.

Question 26

What is the ventricular system and what is its function?

Answer 26

The ventricular system comprises a series of interconnected, cerebrospinal fluid (CSF)-filled spaces that lie at the core of the forebrain and brainstem.

The ventricular system comprises:

• lateral ventricles
• third ventricle
• fourth ventricle

The choroid plexus is responsible for producing the cerebrospinal fluid that fits these ventricular spaces.

Functions:

• Protection of the brain (e.g. cushion for physical shock)
• Transport e.g. nutrients, waste products
• Other functions include regulation of buoyancy.

Question 27

How is the CSF (cerebrospinal fluid) made?

Answer 27

The CSF is made in the choroid plexus.

• CSF flows from the cerebrum ventricles down to the brainstem and spinal cord.
• CSF enters the subarachnoid space via apertures near the cerebellum.
• CSF is absorbed by blood vessels in the arachnoid space.

Question 28

What are the functions of the CSF?

Answer 28

• it protects the brain from physical and chemical injury
• it regulates intracranial pressure
• it is essential in exchanging nutrients and waste products between the blood and the CNS

Question 29

What is the vasculature system of the brain?

Answer 29

2 pairs of arteries supply blood to the brain: the internal carotid arteries (from the common carotid artery) and the vertebral arteries (from the subclavian artery). Branches from these arteries supply blood throughout the brain.

• Another circulation to the brain is derived from the internal carotid arteries - supplies the forebrain (cerebrum and diencephalon).
• Posterior circulation to the brain is derived from the vertebral arteries - supplies the brainstem, cerebellum and upper spinal cord.

They also form an interconnected structure called the Circle of Willis.

Question 30

What is the function of the vasculature system of the brain?

Answer 30

• Delivery of oxygen (O2) to brain tissue.
• Removal of carbon dioxide (CO2)
• Transport (e.g. nutrients, waste products)

Question 31

Describe the vertebral arteries.

Answer 31

Vertebral arteries converge near base of pons to form the basilar artery.

The basilar artery splits into the right and left superior cerebellar arteries and the posterior cerebral arteries at the level of the midbrain.

Posterior cerebral arteries send branches – posterior communicating arteries – that connect to the internal carotid arteries.

Question 32

Describe the Internal Carotid Arteries.

Answer 32

The internal carotid arteries branch to form middle cerebral arteries and the anterior cerebral arteries.

The anterior cerebral arteries are connected by the anterior communicating artery.

The anterior communicating arteries form a ring of connected arteries at the base of the brain known as the circle of Willis.

Question 33

Which artery supplies the lateral surface of the cerebrum and which artery supplies the medial wall of the cerebral hemisphere?

Answer 33

Most of the lateral surface of the cerebrum is supplied by the middle cerebral artery.

Most of the medial wall of the cerebral hemisphere is supplied by the anterior cerebral artery.

Question 34

Glossary.

Answer 34

Afferent – Nerves that are conducting information to a location
Anterior – Nearer the front
Arachnoid membrane - A fine, delicate membrane, the middle one of the three membranes or meninges that surround the brain and spinal cord, situated between the dura mater and the pia mater.
Brain - An organ of soft nervous tissue contained in the skull of vertebrates, functioning as the coordinating centre of sensation and intellectual and nervous activity.
Brain stem - The central trunk of the mammalian brain, consisting of the medulla oblongata, pons, and midbrain, and continuing downwards to form the spinal cord.
Caudal – At or near the tail or the posterior part of the body
Central nervous system - The complex of nerve tissues that controls the activities of the body. In vertebrates it comprises the brain and spinal cord.
Cerebellum - The part of the brain at the back of the skull in vertebrates, which coordinates and regulates muscular activity.
Cerebrospinal fluid - Clear watery fluid which fills the brains ventricles and the space between the arachnoid membrane and the pia mater.
Cerebrum - The principal and most anterior part of the brain in vertebrates, located in the front area of the skull and consisting of two hemispheres, left and right, separated by a fissure.
Choroid plexus - A network of blood vessels in each ventricle of the brain, producing the cerebrospinal fluid
Contralateral - Relating to or denoting the side of the body opposite to that on which a particular structure or condition occurs.
Coronal – Relating to the crown of the head
Cranial nerve - Each of twelve pairs of nerves which arise directly from the brain, not from the spinal cord, and pass through separate apertures in the skull.
Dorsal - On or relating to the upper side or back of an animal, plant, or organ.
Dura mater - The tough outermost membrane enveloping the brain and spinal cord.
Efferent – Nerves that are conducting information from a location
Ipsilateral - Belonging to or occurring on the same side of the body
Lateral – Of, at, towards, or from the side
Lymphatic system - The network of vessels through which lymph drains from the tissues into the blood.
Medial – Situated in the middle
Meninges - The three membranes (the dura mater, arachnoid, and pia mater) that line the skull and vertebral canal and enclose the brain and spinal cord.
Midline - A median line or plane of bilateral symmetry, especially that of the body.
Midsagittal plane - The median vertical longitudinal plane that divides a bilaterally symmetrical animal into right and left halves — called also median plane.
Pia mater - The delicate innermost membrane enveloping the brain and spinal cord.
Posterior – Further back in position
Rostral - Situated or occurring near the front end of the body, especially in the region of the nose and mouth
Sagittal - Relating to the suture on top of the skull which runs between the parietal bones in a front to back direction.
Spinal cord - The cylindrical bundle of nerve fibres and associated tissue which is enclosed in the spine and connects nearly all parts of the body to the brain, with which it forms the central nervous system
Ventral - On or relating to the underside of an animal or plant; abdominal
Ventricular system - A set of four interconnected cavities (ventricles) in the brain