29-10-21 - Introduction to the Nervous System

Question 1

Learning outcomes

Answer 1

• Review the function and general organisation of the central and peripheral nervous systems
• Summarise the differences between gray and white matter with regard to location, composition, and nomenclature.
• Contrast the general features of the sympathetic and parasympathetic nervous systems.
• Briefly describe the meningeal layers of the brain and spinal cord.
• Identify the major areas of the ventricular system.
• Identify the different lobes and divisions of the brain and their associated functions.
• Describe the features of a transverse section of spinal cord.
• Briefly describe the basic anatomy of a typical spinal nerve.

Question 2

What does the CNS consist of?

What is it covered by?

What is it suspended in?

What does the PNS consist of?

Answer 2

• The CNS consists of the encephalon (brain) and the spinal cord
• The CNS is covered with a system of membranes called meninges
• It is suspended in CSF
• The PNS consists of 12 pairs of cranial nerves, 31 pairs of spinal nerves, and their ganglia

Question 3

What are the 4 different parts of the Central Nervous system?

What parts make up the encephalon?

Answer 3

• The 4 parts of the CNS:

1. Spinal cord
2. Brain stem (contains nuclei of all cranial nerve, except the first 2) – consists of the midbrain, medulla, and pons
3. Cerebellum
4. Cerebrum – consists of the telencephalon (cerebral hemispheres) and the diencephalon (between cerebral hemispheres – consists of thalamus and hypothalamus - black)

• 2+3+4 makes up the encephalon

Question 4

What are neurons?

How do they transmit information?

What is their structure?

Answer 4

• Neurons are the functional unit of the nervous system (CNS and PNS)
• Neurons excitable nerve cells that transmit information through electrical signals or action potentials
• A typical neuron has a cell body (soma - red) and neurite(s).
• A neurite can either be an axon or dendrite.
• Axon (blue) is single, can be as long as 1m, covered with a myelin or Schwann sheath.
• Dendrites (green) are multiple, thing, short extensions.

Question 5

What is the function of glial cells (neuroglia)?

How do they compare in numbers to neurons?

How do they differ to neurons in terms of regeneration?

What are the 4 glial cells of the CNS?

What is their function?

What are the 2 glial cells of the PNS?

What is their function?

Answer 5

• Specialized cells called neuroglia support neurons
• Neurons are far outnumbered by glial cells
• Glial cells can regenerate, while neurons hardly generate, if ever.
• The 4 types of glial cells of the CNS:

1. Oligodendrocytes - myelin production in the CNS
2. Astrocytes – reinforce the blood brain barrier between the blood system and substances of the brain. It is a selectively permeable membrane. Brain uses glucose, but cant metabolise proteins, so a barrier is needed
3. Microglia – scavengers that tidy up dead cells and pathogens
4. Ependymal cells – CSF production, which is important in protection, support, and providing nutrition to the CNS

• The 2 types of glial cells of the PNS:

1. Satellite cells – take away excess metabolites and regulate nutrition to cell bodies
2. Schwann cells – Myelin production in the PNS

Question 6

What is myelin?

What is it made from?

Where is myelin found in the nervous system?

What is the purpose of myelination of neurons?

What cells are responsible for myelination in the CNS and PNS?

How do these cells differ?

Answer 6

• Myelin is an insulation material
• It is rich in lipid and protein
• Many neurons have insulating layers of myelin around the internodes of axons, with nodes of Ranvier between these internodes.
• Myelination makes conduction of action potentials faster, and makes them require less energy, as the depolarization jumps to nods of Ranvier between internodes
• Oligodendrocytes are responsible for myelination in the CNS
• Schwann cells are responsible for myelination in the PNS
• Oligodendrocytes can produce myelin for many internodes along the axon
• Schwann cells can only produce myelin for 1 internode along the axon

Question 7

How do neurons communicate between each other?

Describe the 5 steps in this process.

What can differ between synapses?

What does this allow to be involved?

Answer 7

• Neurons communicate with each other at synapses using neurotransmitters
• The process of communication between neurons:

1. Action potential comes down the axon till they reach the plasma membrane at the nerve terminal (synaptic boutons) of the axon, where synapses are located
2. This stimulates the release of neurotransmitters
3. Vesicles make their way down the axon and fuse with the plasma membrane causing neurotransmitters to be exocytosed into the synaptic cleft
4. Neurotransmitters diffuse across the synaptic cleft and binds with receptors on the dendrites of the next neuron
5. This binding can either cause inhibition or stimulation of a further action potential

• Different synapses have different neurotransmitters, meaning there are different shapes of molecules.
• This can allow pharmacology o be involved

Question 8

What is a nucleus in the CNS?

What is a ganglion?

Where do synapses exist?

Answer 8

• A nucleus is a collection of nerves cell bodies within with the CNS
• A ganglion (plural is ganglia) is a collection of nerve cell bodies outside of the CNS in the PNS
• Synapses exist where there are short dendrites close to cell bodies, which exist in ganglia

Question 9

What are the 2 gross appearances of the nervous system?

What do they each consist of?

Where are they found?

What are they each usually responsible for?

Answer 9

1. Grey matter

• Predominantly neuron cell bodies, neuroglia, and unmyelinated neurites (grey because they don’t have myelin)
• In CNS – nucleus, in PNS – ganglion
• Grey matter is on the surface of the cerebral and cerebellar hemispheres, as well as in the depths of the cerebrum
• Also found in the centre of the spinal cord
• Grey matter is mostly processing

1. White matter

• Consists of axons (usually myelinated)
• Found underneath grey matter in the cortex of the brain, and in the periphery of the spinal cord
• White matter is mostly transmission

Question 10

What scan can be used to generate a 3D model of the brain?

What else does this scan show?

What does dense tracks represent?

Where direction is a vast amount of communication?

Answer 10

• A diffusion tensor imaging (MRI) is used to generate 3D models of the brain
• This also shows the axons connecting to specific areas of the CNS, and what direction they are going in.
• Dense tracks of axons are mostly where white matter is (mostly concerned with transmission)
• There is a vast amount of communication downwards into the spinal cord and periphery.

Question 11

Describe the map of divisions of the nervous system

Answer 11

Question 12

What are the 2 functional divisions of the nervous system?

What are they comprised of?

What is the function of these divisions?

Describe how these divisions link together in the nervous system

Answer 12

1. Sensory (afferent) division

• Comprises sensory (aka afferent) neurons
• These neurons convey information from receptors in the peripheral tissues and organs to the CNS
• Afferent neurons also convey information from one part of the nervous system to another

1. Motor (efferent) division

• Comprises motor (aka efferent) neurons
• These neurons transmit signals from the CNS to the effects cells
• This includes skeletal and smooth muscles, organs, and glands

1. Sensory (afferent) info goes into the CNS where it is integrated and processed
2. Decision of motor output is decided open and sent through the efferent nervous system to effector cells via cranial and spinal nerves, which are part of the PNS

Question 13

What are the efferent (motor) divisions of the nervous system?

Where do they innervate?

Are they voluntary or involuntary?

Answer 13

1. Somatic motor nervous system

• Innervation of skeletal muscles
• Voluntary and conscious movements and sensation

1. Autonomic/visceral motor nervous system

• Innervation of cardiac and smooth muscles, and glands
• Important for homeostasis
• Involuntary (e.g high CO2 – increase respiratory rate, BP is high – dilate blood vessels)

Question 14

What are the 2 divisions of the autonomic nervous system (PNS)?

Where do they each leave the CNS?

Answer 14

1. Sympathetic Nervous System (SNS)

• Responsible for fight or flight in conditions of emergency
• Thoracolumbar outflow - leaves the CNS via thoracic and upper lumbar spinal cord
• Specifically, pre-ganglionic sympathetic neurons are at the lateral horn of the T1-L2 spinal cord segments

1. Parasympathetic Nervous System (PNS)

• Responsible for rest, digest, and homeostasis
• Craniosacral outflow - leaves CNS from the brainstem and sacral spinal cord
• Specifically, pre-ganglionic parasympathetic neurons are at the brain stem, or S2-S4 spinal cord segments (lateral horn only found in thoracic and upper lumbar segments)

Question 15

How is the sympathetic nervous system activated?

What is it responsible for?

What 7 physiological changes does activation of the SNS cause?

What does the SNS to do blood flow during exercise?

Answer 15

• The sympathetic nervous system is activated in emergency situations, and is responsible for fight or flight
• 7 physiological changes upon activation of SNS:

1. Dilated pupils
2. Dilates the bronchial smooth muscles
3. Increases blood pressure (constricts vascular smooth muscles)
4. Increases respiratory rate
5. Increases heart rate
6. Increases blood glucose levels
7. Increases sweating

• During exercise, sympathetic vasoconstriction shunts blood from the skin and digestive viscera to the heart, brain, and skeletal muscles (the shits)

Question 16

What is the Parasympathetic nervous system responsible for?

What 6 things is the PNS responsible for in the body?

How are the SNS and PNS complementary?

Answer 16

• The parasympathetic nervous system is responsible for rest, digest, and homeostasis
• The PNS is responsible for:

1. Conserving body heat, and maintaining body activities at basal levels (homeostasis)
2. Pupillary constriction
3. Glandular secretion
4. Increases digestive tract mobility
5. Elimination of faeces and urine
6. Decreases HR and respiratory rate

• The SNS and PNS generally have opposite/complementary effects
• During fight or flight, there is more SNS and less PNS
• During normal activities or rest, there is more PNS and less SNS

Question 17

What is the enteric nervous system?

What is it influenced by?

How does it report back?

What is unique about the enteric nervous system?

Answer 17

• The enteric nervous system is the self-contained, semi-autonomous nervous system of the gut
• The enteric system is still heavily influenced by the visceral motor system
• The enteric nervous system reports back via the visceral sensory system
• The enteric system has enough neurons to almost control itself without outside input

Question 18

Where are ganglia located in the SNS?

Describe the connections of the 2-neuron chain in the SNS.

How long are each of the neurons in the 2-neuron chain?

What are some effectors in the SNS?

Answer 18

• In the SNS, ganglia are located in chains that run down either side of the vertebral column
• These are known as paravertebral chains
• In the 2 neurons chain of the SNS, the pre-ganglionic (pre-synaptic) neuron synapses with the post-ganglionic neuron (post-synaptic) neuron in a ganglion
• In the SNS, the axon of pre-ganglionic neurons are short, and the axons of post-ganglionic neurons that go out to effectors are long
• The effectors in the SNS could be blood vessels in the limbs vasoconstricting, heart, gut.

Question 19

Where are ganglia located in the PNS?

Describe the connections of the 2-neuron chain in the PNS.

How long are each of the neurons in the 2-neuron chain?

Where does the PNS innervate?

What could effectors be?

Answer 19

• In the PNS, ganglia are located in the periphery and in, near, or on the organ that is their effector
• In the 2 neurons chain of the PNS, the pre-ganglionic (pre-synaptic) neuron synapses with the post-ganglionic neuron (post-synaptic) neuron in a ganglion
• In the PNS, the axon of pre-ganglionic neurons are long, and the axons of post-ganglionic neurons that go out to effectors is short, and very close to the effector
• The cranial nerves innervate in the skull to around 2/3rds of the transverse large intestine
• The Sacro spinal nerves innervate the remaining /3^rd of the transverse colon and the reproductive organs
• Effectors of the PNS could be the heart, gut, or reproductive organs

Question 20

What are the different neurotransmitters used in the Somatic nervous system and Autonomic nervous system?

What does the use of different neurotransmitters allow for?

Answer 20

• The somatic nervous system neurons use acetylcholine as a neurotransmitter at the neuromuscular junction for its effector e.g skeletal muscles
• The pre-synaptic neurons in the sympathetic nervous system use Acetylcholine
• The post-synaptic neurons in the sympathetic nervous system use noradrenaline (norepinephrine) as a neurotransmitter
• The pre-synaptic and post-synaptic neurons in the parasympathetic nervous system use acetylcholine as a neurotransmitter
• Different neurotransmitters allow for pharmacology to be used to potentially utilise different neurotransmitters for different effects

Question 21

What are the 3 things that protect the Encephalon and the spinal cord?

What is present outside of the meninges?

What are the 3 layers of Meninges from top to bottom?

Answer 21

• The brain and spinal cord are protected by:

1. Bones (skull bones for brain and vertebrae for spinal cord)
2. Meninges – membranous linings of CNS
3. CSF

• Outside of meninges n the head there is the skull
• Outside of meninges in the vertebral column, there are vertebral bones
• The 3 layers of meninges from top to bottom:

1. Dura mater
2. Arachnoid mater
3. Pia mater

Question 22

Where is the dura located?

How strong is it?

What are the 2 layers of the dura?

How are Dural partitions formed?

What is the role of the falx cerebri?

What is the role of Dural partitions?

Answer 22

• The dura layer is the most superficial, and the toughest layer
• The dura has 2 layers:

1. Inner meningeal layer (close to brain)
2. Outer periosteal layer (close to skull)

• The meningeal dura mater invaginates between brain regions to form Dural partitions (Dural septae) e.g falx cerebri
• The falx cerebri separates the cerebral hemispheres and provides channels, known as Dural sinuses, where the blood and CSF can drain from the brain
• The Dural partitions have 3 main roles:

1. Secure the brain to skull
2. Dampen movement of the brain in the cranial cavity
3. Divide the cranial cavity into freely communicating parts.

Question 23

What are the names of 4 important Dural septae?

What are their roles?

Answer 23

1. Falx cerebelli - runs between the 2 cerebral hemispheres
2. Tentorium cerebelli – separates cerebellum from the rest of the encephalon
3. Diaphrama sellae – diaphragm over the top of pituitary gland

Falx cerebri - separates the cerebral hemispheres and provides channels, known as Dural sinuses, where the blood and CSF can drain from the brain

Question 24

How is the arachnoid mater positioned in relation to the Dural mater?

Why is it like this?

What is it appearance liked?

Where is the Pia mater located?

What is it in contact with?

What does it enter into?

How vascularized is it?

Answer 24

• The arachnoid mater adheres closely to the dura, as there is CSF in the sub-arachnoid space
• The arachnoid is web-like in appearance
• The pia mater is the deepest layer, and in contact with CNS tissue (encephalon) – can’t tell the difference between pia mater and the surface of the brain
• The pia mater enters into every sulci (gaps between folds of brain)
• The pia mater is highly vascularized

Question 25

What are the 3 potential spaces regarding the meninges? Where are they located? Where is there no potential space and why?

Answer 25

* 3 potential spaces of meninges: 1. Epidural space – between dura and skull. Goes down spinal cord too 2. Subdural space – potential space between dura and arachnoid 3. Subarachnoid space – between arachnoid and pia. Contains CSF and cerebral arteries * There is no potential space between the pia mater and encephalon surface, as the pia mater is in direct contact with the encephalon.

Question 26

What are cerebral ventricles? What do they contain? What do they produce? Where are all 4 located?

Answer 26

* The cerebral ventricles are interconnected spaces in the brain and spinal cord * The cerebral ventricles contain CSF * CSF is mainly produced by the choroid plexus in the lateral, 3^rd and 4^th ventricles, with most of it being produced in the choroid plexus of the lateral ventricles

Question 27

What is CSF? Where is it produced? What does CSF surround and fill? Where does the CSF pass to from here? Where does CSF circulate? How does CSF drain and re-circulate? What are the 5 functions of CSF?

Answer 27

* CSF is a clear, cell free fluid * CSF is mainly produced by the choroid plexus in the lateral, 3rd and 4th ventricles, with most of it being produced in the choroid plexus of the lateral ventricles * CSF surrounds the entire nervous system and fills the cerebral ventricles * CSF passes from the 4^th cerebral ventricles to the subarachnoid space via 3 holes – 1 midline and 2 lateral * CSF circulates in the cisterns (where CSF can collect) and sub-arachnoid space * CSF is absorbed via arachnoid granulations and drained into the Dural venous system where it re-circulates * The 5 functions of the CSF: 1. Support – cushions brain in skull 2. Shock absorber 3. Nutrient supply 4. Homeostasis 5. Immune function

Question 28

What is found on the external surface of the cerebrum? Why is it like this? What are these separated by?

Answer 28

* On the external surface of the brain, there are infoldings of the grey matter on the cerebral hemisphere (convulsions) called gyri (singular is gyrus) * This increases the surface area of grey matter (which primarily processes), which increases the processing power of the brain * Gyri are separated from each other by sulci (singular – sulcus)

Question 29

What are the 2 hemispheres of the cerebrum divided by? What does this also separate? What does each hemisphere consist of? Label these parts of the brain and describe what these structures do

Answer 29

* The 2 hemispheres of the brain are divided incompletely by the median longitudinal fissure * This separates the cerebral cortex into two cortices * Each hemisphere consists of a cerebral cortex, cerebral white matter and nuclei (collection of cell bodies) * Examples of sub-cortical nuclei are the caudate and putamen

Question 30

What are cerebral lobes? What are they formed by? What are they separated by? What are the 6 different lobes of the brain? What are the names of the different sulci that divide the lobes of the brain? What is a unique sulci and why?

Answer 30

* Cerebral lobes are part of the hemispheres (telencephalon) * They are formed by gyri, and separated by sulci * 6 different lobes of the brain: 1. Frontal lobe 2. Parietal lobe 3. Occipital lobe 4. Temporal lobe 5. Limbic lobe – found buried under the cortex between the frontal and temporal lobes 6. Insula – small region of cerebral cortex deep in lateral surface of brain * Names of different sulci between lobes: * Lateral sulcus – separates temporal lobe from the frontal and parietal lobe * Parieto-occipital sulcus – separates parietal and occipital lobes * Central sulcus - separates the frontal and parietal lobes. This sulcus is unique as it is the only sulcus that goes from the temporal lobe into the median longitudinal fissure

Question 31

What is an important delineation for responsibilities in different parts of the cerebrum? What are the main parts of the cerebrum responsible for: * Motor function * Sensory function * Vision * Auditory

Answer 31

* The central sulcus is important delineation for responsibilities in different parts of the brain * Motor (red)– primary motor and premotor areas in frontal lobe * Sensory function (blue) – primary somatosensory and somatosensory association areas in parietal lobe * Vision function (green) – Primary visual and visual association areas in occipital lobe * Auditory function (black) – primary auditory and auditory association areas in temporal lobe

Question 32

Where is cortical function found in the hemispheres of the cerebrum? What is each side of the cerebrum specialised for? Why is the left-hemisphere considered dominant? What are the areas of the left hemisphere of the cerebrum responsible for motor function and sensory interpretation of language? What happens if these areas are damaged?

Answer 32

* The hemispheres show literalisation of cortical function * The left hemisphere – specialised for language and maths skills * The right hemisphere – for visual-spatial skills and creativity * The left-hemisphere is widely considered the dominant hemispheres as it controls the right hand * In the left-hemisphere of the brain, there is a motor area called Broca’s areas in the frontal lobe, and a sensory interpretation area called Wernicke’s area in the parietal lobe * If damage is done to the Broca’s area (e.g stroke), this can result in the loss of ability to speak * If damage is done to Wernicke’s area, this will cause loss of sensory interpretation * The brain can’t give the right words to sent out to motor areas, resulting in an inability to answer simple questions, which causes a word salad (mixture of seemingly random words and phrases)

Question 33

What does each cerebral hemisphere receive and send out? How is this represented? What is a homunculus?

Answer 33

* Each cerebral hemisphere receives sensory information from, and sends motor impulses to, the opposite side of the body * The body is represented in an upside-down fashion in sensory and motor cortices * The areas of sensory and motor cortices in the brain responsible for limbs are more medial * The areas of sensory and motor cortices in the brain responsible for the head and mouth are more lateral * A homunculus is the representation of human body parts on top of the part of the cortex that is responsible for them.

Question 34

What are the two parts of the diencephalon? What are the 2 functions of the thalamus? What does it enclose? What 2 things does the hypothalamus control? What 4 things does the hypothalamus regulate?

Answer 34

* The diencephalon consists of the thalamus and the hypothalamus * Functions of the thalamus: 1. The thalamus is a major sensory relay station for sensory impulses ascending to the sensory cortex (comes from pretty much all of the body) 2. The thalamus is a major sensory relay station for Inputs from subcortical motor nuclei and cerebellum travelling to the cerebral motor complex * The hypothalamus is responsible for: 1. Autonomic control 2. Endocrine control (along with pituitary gland) * The hypothalamus regulates: 1. Thirst – fluid electrolyte balance 2. Eating – energy balance 3. Sexual behaviour – reproduction 4. Body temperature

Question 35

Where is the midbrain located? What 3 things does the midbrain contain? What are these areas used for? Which of these areas is affected in Parkinson’s? What does the midbrain surround?

Answer 35

* The midbrain is located at the top part of the brainstem The midbrain contains: 1. The superior and inferior colliculi (bumps at the back of the midbrain) - Visual and auditory reflex centres Important in coordinating head and eye movement in response to visual and auditory stimuli (allows head to move while eyes stay on target) 2. The red nucleus – subcortical motor function 3. Substantia nigra – involved in reward-seeking and motor learning * In Parkinson’s, the substantia nigra neurons are lost, which affects motor movement * The midbrain surrounds the cerebral aqueduct

Question 36

Where is the pons located? What 2 things is the pons responsible for? Where is the medulla oblongata located? What occurs with axons here? What 3 things does the vital centres of the medulla oblongata regulate? What 4 things does the non-vital centres regulate?

Answer 36

* The pons is a round bump below the midbrain on the brainstem 1. The pons is a conduction area, and contains connections between the forebrain and the cerebellum 2. The pons contains several cranial nuclei that contribute to the regulation of respiration, hearing and balance * The medulla oblongata is where pyramidal decussation (crossing of corticospinal axons) occurs before entering the spinal cord * Vital centres regulate: 1. Respiratory rhythm 2. Heart rate 3. Blood pressure * Non-vital centres regulate: 1. Coughing 2. Sneezing 3. Swallowing 4. Vomiting

Question 37

What is the cerebellum split into? Where is it located? What are the 3 layers of cerebellum from outermost layer to inside? How does the cerebellum connect to the brainstem? What are the 2 functions of the cerebellum? What are these functions important for?

Answer 37

* The cerebellum consists of 2 hemispheres with a Vertus in the middle * It is located in the cerebellar fossa (depression in the occipital bone) * The cerebellum is convoluted with: 1. An outer cortex of grey matter 2. White mater 3. Sub-cortical grey matter nuclei * The cerebellum is connected to the brain stem by 3 cerebellar peduncles (superior, middle inferior) * The 2 functions of the cerebellum: 1. Processes and interprets impulses from motor cortex and sensory pathways 2. Coordinates motor activity for smooth, well time movements * These functions are very important for balance

Question 38

What is the spinal cord? What 3 things is the spinal cord protected by? Where does the spinal cord extend to? What is the spinal cord like 3 months in utero? What happens as the foetus grows? What is the spinal cord like in a new born? How does this change by the time we learn to walk?

Answer 38

* The spinal cord is a two-way impulse conduction pathway and reflex centre * The spinal cord is protected by vertebrae. Meninges, and CSF * Extends from the skull base (foramen magnum) to the level of L1/L2 intervertebral disc or mid L2 vertebrae * It does not extend the length of the vertebral column * At 3 months of pregnancy, the spinal cord fills the entire length of the vertebral column * As the foetus grows, the vertebral column gets longer, but the spinal cord doesn’t grow at the same rate, resulting in it being let behind (differential growth rates) * In a newborn, the spinal cord is at the level of L3 * By the time we learn to walk, the spinal cord ends at around L1 or L2 vertebrae

Question 39

What are 4 external features of the spinal cord?

Answer 39

1. Cervical and lumbosacral enlargements (red) – areas involved in the innervation of limbs 2. Conus medullaris (purple) – end of the spinal cord 3. Posterior medial sulcus (green) 4. Anterior median fissure (blue)

Question 40

What is the shape of grey matter in the spinal cord? What does it contain? What are the 3 different types of horns? What neurons do they contain? What does white mater in the spinal cord contain? What are the 3 different types of columns does it contain?

Answer 40

* The grey matter of the spinal cord is H shaped, and contains neuron cell bodies within horns 1. Dorsal/posterior horns (blue) – interneurons 2. Lateral/posterior horns (only in thoracic and upper lumbar region) (green) – visceral (autonomic) motor neurons 3. Ventral/anterior horns (red) – somatic motor neurons * White mater of the spinal cord consists of columns containing a number of ascending and descending tracts. * All tracts are paired, and most decussate (cross to form an X) * The 3 columns the spinal cord contains are the: 1. Ventral (anterior) columns (red) 2. Lateral columns (green) 3. Dorsal (posterior) columns (blue)

Question 41

What is the spinal cord divided into? How many segments and nerve pairs are in each part of the spinal cord? How do nerves get down to lower limbs despite the spinal cord ending at around the L1 vertebrae of the vertebral column? What does this form? What nerves does this consist of?

Answer 41

* The spinal cord is divided into segments that are associated with one pair of spinal nerves * 8 Cervical segment and nerve pairs * 12 Thoracic * 5 Lumbar * 5 Sacral * 1 Coccygeal * Neurons leave the spinal cord, travel down the vertebral canal, before coming out at the appropriate vertebrae * This leaves neurons coming out of the vertebral column, which looks like a horse’s tail * This is called the caude equina, which consists of roots of the lumbar and lower spinal nerves