Functional Anatomy of the CNS

Question 1

What comprises the CNS?

Answer 1

Brain
Spinal cord

Question 2

What are the three regions of the brain that it can be divided anatomically?

Answer 2

Brain stem
Cerebellum
Forebrain (cerebrum and diencephalon)

Question 3

What is the brain stem and where is it found?

Answer 3

The brainstem is a stalk like projection that extends cadually from the cerebrum comprised of both grey (neuronal cell bodies making up brainstem nuclei) and white matter (axons projecting from cell bodies elsewhere in the nervous system). The brainstem connects the cerebrum, the cerebellum and the spinal cord.

Question 4

What are the three sections of the brain stem?

Answer 4

In descending order:
Midbrain
Pons
Medulla oblangata

Question 5

What are the functions of the brain stem?

Answer 5

The brain stem structurally connects the brain and the spinal cord. They are the site of exit for cranial nerves.

As a relay centre it is responsible for transmission of neuronal activity between the higher areas of the brain and the spinal cord. This is an active process in which synapses within the pathway enables the initial processing stages to where thousands of neuronal inputs from pre-synaptic neurons begin to integration - known as neuronal integration.

Question 6

Explain reticular formation as an example of neuronal integration in the brain stem.

Answer 6

Reticular formation is a complex network of brainstem nuclei and neurons found within the brainstem that are responsible for being a major integration and relay center to enable the co-ordination the function of many different brain functions.
One aspect of this is integrating sensory input from the periphery and filtering off unnecessary information.

Question 7

What are some of the functions reticular formation is able to modulate?

Answer 7

Blood pressure
Heart rate
Respiratory rate
Postural reflexes (balance and posture)
Neuro-vegetative reflexes
Taste
Sleep-wakefulness cycles

Question 8

Explain the significance of reticular formation in the sleep and wake cycle.

Answer 8

Neurons of specifically the ascending reticular activating system within reticular formation play a crucial role in arousal and consciousness. These project to nuclei within the thalamus and cerebral cortex and are able to exert some control over/have a selection process of which sensory signals reach the cerebrum and come to our conscious attention.

Question 9

What is the function of the medulla oblangata?

Answer 9

The medulla oblangata is responsible for involuntary functions (without being conscious) and contains both vital and non-vital reflex centres.

Vital reflex centres include those the respiratory control centre (for breathing), digestion and circulation

Non-vital reflex centres include those that initiate the cough reflex, and also contained here is the chemoreceptor trigger zone which when stimulated induces vomiting.

Question 10

What is found in the midbrain (crucial to the pathophysiology of Parkinsons)?

Answer 10

Substantia nigra, crucial for the production of dopamine and initiating movement

Question 11

What is the cerebellum and where is it located?

Answer 11

The cerebellum is located at the base of the brain connected by fibres to the brain stem, specifically pons. It is separated from the cerebrum above by a tough layer of dura mater, however like the cerebral cortex the cerebellum is also divided into two hemispheres and contains a narrow midline zone called the vermis.

Question 12

What is the main function of the cerebellum?

Answer 12

Co-ordination of voluntary movement. Again this is achieved by the integration of all sensory input from the body to establish the position of the body. This then enables the precise execution of voluntary movement.
For example integration of information from sensory receptors in the periphery and motor areas from the cerebrum enables the precise, voluntary movement of selectively picking up an item for example with the awareness of the position of the arm/hand in relation to the item.

Question 13

What are some examples of sensory inputs from the periphery?

Answer 13

Muscles
Joints
Eyes
Skin
Ears
Viscera

Question 14

Aside from its role in the co-ordination of voluntary movement, what are some of the other functions of the cerebellum?

Answer 14

It is also involved in the planning and initiation of movement, by the transmission of information to motor areas to initiate movement.
Also involved in procedural memory - memory associated with movements enabling subconscious movement, such as learning a dance
Also involved in balance and eye movements which correspond, as the eyes remain focus as the body continues to move

Question 15

What is the diencephalon and where is it located?

Answer 15

The diencephalon is centrally located within the brain sitting at the top of the brain stem above the midbrain and under the cerebrum and alongside the cerebrum forms part of the forebrain.
There are two crucial components of the diencephalon - the thalamus and hypothalamus among others.

Question 16

What is the function of the thalamus?

Answer 16

All sensory pathways pass through the thalamus and again acts as relay centre, responsible for preliminary processing, filtering information and ensuring the information is directed to the correct part of the brain.
By filtering sensory information this ensures that our attention is drawn appropriately.

The thalamus is also responsible for motor control.

Question 17

What is the function of the hypothalamus?

Answer 17

It is a major homeostatic control centre and therefore ensures integration of all homeostatic input and then regulates an appropriate response to the integration of homeostatic input.
This is achieved by regulating the autonomic nervous system and endocrine system to mediate the response.

In relation to the endocrine system, the hypothalamus is connected to the pituitary gland. The hypothalamus controls secretion of hormones from the pituitary gland.

The hypothalamus also forms part of the limbic system which is responsible for memory, behavioural patterns and emotion.

Involved in the sleep wakefulness cycle.

Question 18

What are examples of homeostatic control systems by the hypothalamus?

Answer 18

Heart rate
Blood pressure
Blood oxygen
Blood glucose
Body temeprature

Question 19

Describe the structure of the limbic system.

Answer 19

The limbic system is an aggregation of brain structures that are generally located lateral to the thalamus (within the forebrain), underneath the cerebral cortex (sub-cortical), and above the brainstem.
This includes both the thalamus and hypothalamus.

Question 20

What is the main function of the limbic system?

Answer 20

The limbic system is involved in lower order emotional processing of input from sensory systems and therefore can be said to be responsible for programming basic emotions such as fear, anxiety, anger, pleasure associated with survival.

The limbic centre also mediates the neural centres which will control basic responses such as preparing for attack, laughing and crying are pre-programmed by the limbic system. Therefore it co-ordinates feelings of fear/anxiety with fight/flight response in the hippocampus which then stimulates the sympathetic nervous system.

The limbic system is also linked to reward pathways, when we do something for survival such as eating, drinking, sex - we feel good motivating us to do it again, so hence is also linked to motivational pathways. If drugs stimulate these same ways this can result in addiction. In contrast activities that cause fear, anxiety or distress result in the formation of punishment pathways leading to their avoidance.

Question 21

Provide an examples of a component of the limbic system that associated with a specific emotion.

Answer 21

Stimulation of the amygdala is associated with the expression of feelings of fear and anxiety. In patients with anger-management issues is also associated with over-activation of the amygdala.
The septal nuclei stimulation is responsible for feelings of pleasure and satisfaction.

Question 22

How is the limbic system linked to olfaction?

Answer 22

Olfactory bulbs (responsible for sense of smell) is also connected to the limbic system which is why smell is associated with basic emotions.
The hippocampus responsible for memory is also linked to the limbic system which in the context to olfaction is why a smell can be associated closely with a memory.

Question 23

What are the two components of the cerebrum?

Answer 23

Cerebral cortex
Basal nuclei also known as basal ganglia

Question 24

What are basal nuclei?

Answer 24

They are a cluster of cell bodies within the subcortical region of the brain. They form a part of the extrapyramidal motor system and work in tandem with the pyramidal and limbic systems.

Question 25

What are the five pairs of nuclei that comprise of the basal ganglia?

Answer 25

Caudate nucleus
Putamen
Globus pallidus
Subthalamic nucleus
Substantia nigra

These can then be grouped into broader groups:
Striatum: Dorsal striatum (caudate nucleus and putamen which are interconnected) and ventral striatum
Globus pallidus
Subthalamic nucleus in the brainstem
Substantia nigra

Question 26

What is the role of basal ganglia?

Answer 26

Involved in movement as part of the extrapyramidal motor system.
They have an overall inhibitory role in modulating motor activity, inhibiting muscle tone - preventing contraction.
They also have a role in initiating purposeful movement
Involved in posture and support, with sustained contraction of muscle facilitating this.