Overview of the Nervous System

Question 1

How many pairs of nerves arise from the brain and spine?

Answer 1

12 cranial nerves

31 spinal nerves (8C, 12T, 5L, 5S, 1C)

Question 2

There are two types of peripheral motor nerves - somatic and autonomic. What is another term for autonomic?

Answer 2

Visceromotor

Question 3

How is sensory info transmitted from internal organs?

Answer 3

Via visceral afferent fibres

Question 4

Name all 12 cranial nerves

Answer 4

Olfactory, optic, occulomotor, trochlear, trigeminal, abducens, facial, vestibulocochlear, glossopharyngeal, vagus, accessory, hypoglossal

Question 5

What is the transmitter used in the somatic nervous system?

Answer 5

Acetylcholine

Question 6

Where does the ultimate control of the autonomic nervous system reside?

Answer 6

Hypothalamus - ‘head ganglion of the ANS’, maintains homeostasis by regulating autonomic and endocrine systems (and modulating behaviour)

Question 7

What are neurones?

Answer 7

• the principal specialised cell-type of the nervous system
• responsible for sensory, integrative and motor activities
• approximately 100 billion neurons in the brain
• can be classified as excitatory (often using glutamate as their neurotransmitter) or inhibitory (primarily using gamma-aminobutyric acid/GABA as a neurotransmitter)

Question 8

What are neuroglia?

Answer 8

Glial cells.

• outnumber neurons 10:1, but represent only 50% of the brain volume because they are generally smaller
• main types: astrocytes, oligodendrocytes, microglia (plus Schwann cells in the PNS)
• the term glia comes from the Greek word for glue, but it is now known they offer much more than just structural support to nerve cells

Question 9

What is a unipolar neurone and where are they found?

Answer 9

Unipolar neurons have a single long process, where the original two processes have fused to become one, so they are also referred to as pseudounipolar.

These include the first order sensory neurons that have cell bodies in the dorsal root ganglia and cranial nerve ganglia.

Question 10

What is a bipolar neurone and where are they found?

Answer 10

Bipolar neurons have 2 processes coming from the cell body, tend to be found in special sensory structures (e.g. the ear, nose and eye)

Question 11

What is a multipolar neurone and where are they found?

Answer 11

Multipolar neurons which have numerous processes (called neurites) make up the majority of nerve cells in the brain.

Question 12

What is an astrocyte?

Answer 12

The main glial cell - star shaped, important for:

• brain energy metabolism
• neurotransmission (constant ionic env)
• detoxification of ammonia
• inflammation and repair
• learning and memory (?)
• blood-brain barrier (BBB)

Question 13

Why do neurones prefer lactate to glucose and how do astrocytes contribute to this?

Answer 13

Neurones prefer lactate as energy extraction from this substrate produces less oxidative stress which can potentially harm nerve cells because they are so active.

The astrocytes ‘pre-digest’ lactate (metabolic coupling).

Question 14

What is the blood-brain barrier?

Answer 14

Highly selective permeability barrier that separates the circulating blood from the brain extracellular fluid in the central nervous system (CNS).

Lots of tight junctions between capillary endothelial cells in the brain, spinal cord and retina which restrict extracellular passage of molecules. This is due to an inductive interaction between astrocytic feet processes (end feet) which induce changes in the capillary endothelial cells.

Question 15

What are microglial cells?

Answer 15

• Resident immune and phagocytic cells of the CNS
• Derived from the bone marrow
• Related to monocytes and macrophages

Involved in:

• inflammation
• immune responses
• removing dead cells / debris (by phagocytosis)

Question 16

What are microglial nodules?

Answer 16

Clusters of activated microglia also surround and destroy nerve cells that have been infected by viruses and must be sacrificed.

Question 17

What is neuronophagia?

Answer 17

the process by which the microglial cells digest the dead neurons

Question 18

What are oligodendrocytes?

Answer 18

Responsible for myelination of CNS axons. Provide multiple cytoplasmic processes that extend to several neighbouring axons and provide a single myelin segment to each of them.

Analogous to Schwann cells in the peripheral nervous system. Degenerate in demyelinating disorders such as multiple sclerosis

Question 19

What is grey matter?

Answer 19

Grey matter consists of neuronal cell bodies, dendrites, synaptic connections and glial cells, especially astrocytes.

Question 20

What are the two main types of grey matter?

Answer 20

• *Cerebral cortex**
• superficial layer of grey matter (2-4mm thick)
• forms the superficial surface of the brain
• has six layers in most areas
• *Subcortical nuclei**
• collections of neuronal cell bodies in the CNS
• buried in hemispheric white matter / brain stem
• not to be confused with the nuclei inside cells

Question 21

What is white matter?

Answer 21

White matter is made up of myelinated axons and glial cells, especially oligodendrocytes.

Question 22

Describe the three main types of subcortical white matter

Answer 22

1. Association fibres - link areas of the cortex within a cerebral hemisphere
2. Commisural fibres - link matching areas in the left and right cerebral hemispheres, eg. the corpus callosum.
3. Projection fibres - either (i) leave the cerebral cortex and project downwards towards the brain stem or spinal cord (eg. corticospinal motor tract) or (ii) project upwards towards the cortex via a synaptic relay in the thalamus (eg. the ascending sensory pathways for touch, pain and temperature are projection fibres). The large bundle of projection fibres that passes between the basal ganglia and thalamus is the internal capsule

Question 23

Why is the internal capsule clinically important?

Answer 23

as damage here (e.g. due to a stroke) may cause contralateral paralysis or sensory loss by interrupting the motor and sensory projection fibres

Question 24

What is the cerebrum responsible for?

Answer 24

The cerebrum is responsible for sensation, movement, thought, behaviour, personality, language, memory and learning. Diseases of the cerebral hemispheres (e.g. stroke, tumours) can therefore affect any of these functions. The cerebral hemispheres are linked across the midline by the corpus callosum, which is a massive bundle of around 300 million nerve fibres.

Question 25

What is the cerebellum responsible for?

Answer 25

The cerebellum is involved in the control of balance, posture, muscle tone, coordination and dexterity (including fine control of the tongue muscles). Disease in this part of the brain therefore leads to clumsiness, erratic motor control (called ataxia) and slurred speech (called dysarthria). Some types of learning probably also rely on the cerebellum, most probably the acquisition of complex motor skills (e.g. learning to juggle, play the piano or touch-type).

Question 26

What is the brainstem responsible for?

Answer 26

The brain stem is involved in “life support” functions including the regulation of breathing, control of the heart rate and blood pressure, airway-protective reflexes (e.g. cough, sneeze, gag) that help to prevent choking and inhalation of fluids (aspiration) which can cause pneumonia. The brain stem is also critical for maintaining wakefulness (consciousness) and regulating normal sleep-wake cycles. Brain stem damage may therefore result in coma or death.

Question 27

What is the frontal lobe important for?

Answer 27

Contains the primary motor cortex and is therefore important for movement (but also behaviour and language).

Question 28

What is the temporal lobe important for?

Answer 28

Contains the primary auditory cortex and is important for hearing

Question 29

What is the occipital lobe important for?

Answer 29

The primary visual cortex

Question 30

What is the parietal lobe important for?

Answer 30

in sensations of touch and pain but also contributes to visuospatial ability