Topic 1- The nervous system

Question 1

What is a body system?

Answer 1

Body systems are groups of organs and tissues that work together to perform a specific set of functions.

Question 2

Explain the divisions of the nervous system.

Answer 2

The nervous system divides into the central nervous system (CNS) and the peripheral nervous system (PNS). These are a geographical division - the central nervous system is very much within the central plane in the body, whilst the peripheral nervous system is towards the extremities.

The central nervous system consists of the brain and spinal cord. The brain, of course, receives and processes all sorts of information. It also stores information and generates original thoughts and emotions in responses to different scenarios. The spinal cord has more limited functions. It is critical for the control of movement and relaying motor signals from the brain to muscle and transmitting sensory information from the body to the brain.

The peripheral nervous system is considerably more complex in its divisions. It shows a division into motor neurons and sensory neurons but the most critical divisions for you to be aware of are those of the motor neurons- these divide into the somatic nervous system, which is about the control of the skeletal muscles, and the autonomic nervous system which controls involuntary responses such as the fight or flight response.

Question 3

Explain the external structural divisions of the brain.

Answer 3

There are two cerebral hemispheres. The wrinkly outer surface is the cerebral cortex. The cerebellum
The cerebellum is located in the back of your brain as you can also see part of the brain stem which is continuous with the spine.

Question 4

Explain the internal structural divisions of the brain.

Answer 4

The inner view of the brain shows a more complex picture. You can see variations in text and shape. The overall divisions notable here are:
Forebrain
Midbrain
Hindbrain

Within these three categories there are further sub-divisions.

Question 5

Explain the further subdivisions of the forebrain and it’s principle structure.

Answer 5

Telencephalon and diencephalon

Telecephalon’s principle structure: cerebral cortex, basal ganglia, limbic system

Diencephalon’s principle structure: thalamus, hyothalamus

Question 6

Explain the further subdivision of the midbrain and it’s principle structure.

Answer 6

mesencephalon

mesencephalon’s principle structure: tectum and tegmentum

Question 7

Explain the further subdivisions of the hindbrain and it’s principle structure.

Answer 7

myelencephalon

myelencephalon’s principle structure: medula oblongata

Question 8

Explain the different functions associated with the different lobes.

Answer 8

Frontal: motor control, executive function

Parietal: bodily sensations, spatial relationships

Temporal: hearing

Occipital: vision

Question 9

What is the function of the basal ganglia?

Answer 9

Movement

Question 10

What is the function of the limbic system?

Answer 10

Motivation and emotion

Question 11

What is the function of the thalamus?

Answer 11

Relay and integration of sensory information

Question 12

What is the function of the hypothalamus?

Answer 12

Controls Autonomic Nervous System and Endocrine Systems

Question 13

What is the function of the tectum?

Answer 13

visual and auditory processing

Question 14

What is the function of the tegmentum?

Answer 14

sleep, arousal, movement

Question 15

What is the function of the cerebellum?

Answer 15

motor coordination, muscle tone and balance

Question 16

What is the function of the pons and medulla?

Answer 16

sleep and arousal

Question 17

What is the function of the medulla oblongata?

Answer 17

control of vital functions

Question 18

Where does the brain get information from?

Answer 18

The brain receives inputs from a 12 different nerves, called the cranial nerves.

These nerves sit outside the brain and spinal cord and are therefore part of the Peripheral Nervous System.
The first two (olfactory and optic) link directly to the cerebrum.
The remaining nerves link to the brainstem.

Vestibulocochlear nerve (Sensation and Perception)
Optic nerve (Sensation and Perception)

Another source of information to the brain is the spinal cord.

Question 19

Explain the structure of the spinal cord.

Answer 19

Eight cervical segments for cervical nerves C1 – C8, innervating neck, shoulders, arms and hands.

Twelve thoracic segments for thoracic nerves T1 – T12, innervating trunk and arms.

Five lumber segments for lumber nerves L1 to L5, innervating lower back and front below waist (including legs but not genitals).

Five sacral segments for sacral nerves S1 to S5, innervating bottom and back of legs and genitals.

The spinal cord itself divides into white and grey matter. The grey matter can then be divided into a series of layers. Importantly for our understanding:

Incoming sensory information travels to the spinal cord via the dorsal root (blue pathway)

Outgoing motor information travels to the rest of the body via the ventral root (red pathway)

Just outside the spinal cord, the two pathways combine to form a spinal nerve.
Information also travels up and down the spinal cord to and from the brain. It can also cross from one side of the spinal cord to the other (e.g. left and right)

Question 20

What are the key functions of the spinal cord?

Answer 20

Because of the pathways travelling to the brain via the spinal cord, we know that the spinal cord is responsible for relaying key information:

Sensory information from our bodily senses (touch, pain, temperature, proprioception)

Motor signals to the body.

Question 21

Explain how the location of a spinal cord injury relates to the impairment.

Answer 21

The higher the location of the injury the more severe the impairment.

Cervical:

• Paralysis in arms, hands, trunk and legs
• May not be able to breathe independently, cough, or control bowel or bladder.
• Ability to speak impaired.

Thoracic:

• Injuries affect the trunk and legs.
• Can stand in a standing frame, while others may walk with braces.
• Little or no control of bowel or bladder.

Lumber:

• Little or no control of bowel or bladder.
• Depending on strength in the legs, may need a wheelchair and may also walk with braces.

Sacral:

• Little or no voluntary control of bowel or bladder, but can manage on their own with special equipment
• Most likely will be able to walk

Question 22

Explain using the midline for mapping.

Answer 22

When describing different parts of the nervous system it is important to make sure we do so using certain conventions – a bit like map reading. The following terms are important:

Relative to the midline (red): contralateral (opposite side) and ipsilateral (same side)

Relative to the midline: medial (closer to the midline) and lateral (further from the midline)

Question 23

Explain using planes for mapping.

Answer 23

The brain can be considered in different planes as well and this is particularly important to understand when viewing brain images:

Coronal – sliced front to back or vice versa

Horizontal – sliced top to bottom or vice versa

Sagittal – slices from side to side

Question 24

Explain the mapping terminology used to describe areas of the brain in relation to each other.

Answer 24

Dorsal/superior
Rostral + Caudal
ventral

In the human brain, this is flipped 90 degrees with rostral at the top as we stand upright.

Question 25

Explain blood supply in the CNS.

Answer 25

The central nervous system and the brain have a remarkable blood supply:

Brain is 2% of body mass but receives 15% of blood supply.

Faster rate of blood circulation in the brain means it receives 20% of body’s oxygen.

Brain cell is never more than 50µm from a blood vessel.

This impressive blood supply forms the basis of the signal used in several brain imaging techniques.

Question 26

Explain the meningeal layers.

Answer 26

There are three different meningeal layers:
Dura Mater
Arachnoid
Pia Mater

Together they perform three key functions:

1. Protecting the brain and spinal cord from mechanical injury
2. Providing blood supply to the skull and to the hemispheres
3. Providing a space for the flow of cerebrospinal fluid.

Question 27

Explain the dura mater.

Answer 27

Means ‘hard mother’, tough and inflexible – divided into several layers.

Within the PNS this layer is fused with the arachnoid layer.

Question 28

Explain the arachnoid.

Answer 28

Delicate, impermeable and avascular with a web-like appearance.

Within the PNS this layer is fused with the dura mater.

Question 29

Explain the pia mater.

Answer 29

Means ‘tender mother’, adheres closely to the brain and fuses with lining of the ventricles to form structures which produce cerebrospinal fluid.

Question 30

Explain cerebrospinal fluid.

Answer 30

The CNS is bathed in fluid called cerebrospinal fluid. This fluid circulates through ventricular system of the brain.

CSF is produced largely by a structure called the choroid plexus and we around 500ml produced per day.
CSF is a clear, colourless fluid.
It provides structural support.

Question 31

Explain the development of the neural tube.

Answer 31

At 22 days post gestation the neural tube develops in the process called neurulation:

The ectoderm layer at the top of the embryo starts to thicken into a structure called the neural plate.

This plate starts to fold in the middle so that a groove is created.

The groove then closes and is completely separated from the area above it which forms the epidermis.

The neural tube is the basis of the CNS whilst the neural crest, the topmost edge of the neural tube, forms the PNS.

Question 32

What happens when the neural tube fails to close?

Answer 32

The formation of the neural tube is a key process in the development of the nervous system. However, it does not always close as it should, and this can give rise to neural tube defects:

One of the most common of these is Spina Bifida

There are three main types of Spina Bifida, of differing severity.

The most common location for the failure of the tube to close is the lower back region.

Question 33

Explain the three different types of spina bifida.

Answer 33

Occulta:

• most common and mildest type
• 1 or 2 vertebrae in the spine are affected
• most people have no symptoms and are unaware they have it

Meningocele:

• the meninges protrude out through the spine
• the spinal cord itself develops normally
• surgery can be carried out to remove the membranes without spinal cord damage

Myelomeningocele:

• most severe for where several vertebrae are affected
• the spinal cord and meninges protrude out of the back

Question 34

What are the symptoms of spina bifida?

Answer 34

Movement problems: weakness of paralysis in lower limbs, deformed or dislocated bones

Bladder and bowel problems: urinary incontinence, UTI, kidney problems, bowel incontinence

Associated hydrocephalus: a short attention span, difficulty solving problems, difficulty reading, difficultly understanding some spoken language, difficulty planning

Question 35

What is a risk factor?

Answer 35

The WHO define a risk factor as:

“any attribute, characteristic or exposure of an individual that increases the likelihood of developing a disease or injury.”

Even before a cause is known risk factors can be identified. Where people at risk can be identified it may be possible intervene either to prevent a condition arising by a change in behaviour or situation or to ensure appropriate support is available and accessed.

Question 36

What are the risk factors of spina bifida?

Answer 36

Race: increased in white population

Diabetes: increased risk is mother has uncontrolled diabetes

Obesity: Increased risk is mother was obese before pregnancy

Sex: increased in girls

Folate deficiency: increased risk is mother lacks folate (vitamin B9) during pregnancy

Medications: increased risk for some medications eg anti-seizure medications

Question 37

How does the neural tube develop once closed?

Answer 37

The tube begins to curl into a backwards C shape

Some bulbous regions start to develop: the top becomes the forebrain, the middle the midbrain and the bottom the hindbrain.

Beneath the hindbrain remains a tube which forms the spinal cord.

This produces three primary brain vesicles and happens when the embryo is about 3-4 weeks old.

After the primary differentiation, there is a secondary period of differentiation at five weeks old.

The forebrain divides into the telencephalon and diencephalon, the midbrain into the mesencephalon and the hindbrain into the metencephalon and myelencephalon.

The telencephalon goes on to form the cerbrum.

The diencephalon goes on to form the eye cup and the thalamus, hypothalamus and epithalamus region.

The metencephalon goes on to form the pons and cerebellum

the myelencephalon goes on to form the medulla oblongata.

Question 38

Explain how different animals have contributed to our understanding of humans.

Answer 38

Sea slug: Much has been learnt about basic types of learning from the aplysia or sea slug.

Cats: Work on cats has contributed a great deal to our understanding of sensory processing including vision.

Rodents: Work on rodents (rats and mice) has taught us a great deal about motivation and in particular drug addiction.

Question 39

Explain homology when studying animals.

Answer 39

Whole brains can vary considerably but the key for researchers is whether there is homology between key structures:

What are the key structures I am interested in within the human brain?
Are there similar structures in another species?
Similar connections to other areas
Similar chemical compositions
Similar gene expression
Similar function