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Branches of the nervous system

Central Nervous System (CNS)
Peripheral Nervous System (PNS)


Branches of the CNS and PNS

- Brain
- Spinal Cord

- Motor Neurons (from CNS to muscles and glands)
- Sensory Neurons (from sensory organs to CNS)


Branches of motor neurons

Somatic Nervous System
- voluntary movements

Autonomic Nervous System
- involuntary responses


Branches of the Autonomic Nervous system

Sympathetic Division
- Fight or Flight

Parasympathetic Division
- Rest or Digest


Anatomical Planes (5)

Medial Plane
Lateral Plane
Horizontal Plane
Coronal Plane
Sagittal Plane


Ipsilateral and Contralateral

Ipsilateral items lie on the same lateral side
Contralateral items lie of different sides of the body


Anatomical Relationships (spatial) (4)

Rostral = up (beak)
Caudal = down (tail)

Ventral (anterior) = belly
Dorsal (posterior) = back

These axes line up when you look up, so in normal anatomical position, for the head:
Dorsal = superior
Ventral = inferior


Basic Divisions of the brain (3)



10% of brain volume but 50% of the brain's cells



Divisions of the Forebrain

- Telencephalon
> olfactory bulbs (for olfactory stimuli)
> cerebral hemispheres (regulation of sensory and motor function)

- Diencephalon (sensory gateway / regulation of internal environment)


Divisions of the Hindbrain

- Cerebellum
(movement coordination / learning of motor skills)

- Pons
(relay point between cerebellum and cerebral cortex in mammals)

- Medulla
(regulation of internal environment)


Divisions of the Midbrain

- Optic Tecta
(processing of sensory {mainly visual} stimuli)

- Tegmentum
(aspects of motor control)


Divisions of the cortex into lobes (forebrain)

Frontal Lobe
- motor control
- executive functions

Temporal Lobe
- hearing

Parietal Lobe
- bodily sensations
- spatial relationships

Occipital Lobe
- vision


Brodmann's areas

Divided the brain into areas according to structural divisions
However an apparent difference in structure does not mean a difference in function


Cranial Nerves

The structures that carry information into the brain
There are 12 cranial nerves in humans, the first 2 emerge from the cerebrum and the other 10 emerge from the brainstem

Cranial Nerves are part of the Peripheral Nervous System (sensory neurons)


Overview of brain functions:
- cerebral cortex
- basal ganglia
- thalamus, hypothalamus
- cerebellum
- pons and medulla
- midbrain

Cerebral cortex
- cognition
- sensory processing
- motor control
- learning

Basal Ganglia
- voluntary and learnt motion

Thalamus, Hypothalamus
- sensory integration and relay
- attention
- consciousness
- emotion
- homeostasis

- motor coordination
- muscle tone and balance

Pons and Medulla
- involuntary body functions (i.e. sleep)
- cognitive motor skills (i.e. typing)

- audio/visual relay
- posture
- alertness



A group of related nuclei


Divisions of the spinal cord and what they innervate

8 Cervical nerves
- neck / shoulders / arms / hands

12 Thoracic nerves
- trunk of the body / arms

5 Lumbar nerves
- lower back / front of the legs

5 Sacral nerves
- back of legs + ass / genitals


Dorsal column-medial lemniscal pathway

Transmits sensory information but NOT pain
- from proprioceptors or mechanoreceptors

- Afferent (first-order) neuron from the receptor goes into the dorsal root ganglion of the spinal cord
- Passes up the Dorsal Column to the Medulla Oblongata, where it synapses onto a second-order
- 2nd order neuron travels out of the Dorsal Column and passes over the Medial-Lemniscus to the other side of the Medulla Oblongata and up into the Thalamus
- In the Thalamus, it synapses onto a third-order neuron and terminates in the Primary Somatosensory Cortex


Spinothalamic Tract (a pathway)

Transmits pain information
- from nociceptors or thermoreceptors

- Afferent neuron from the receptor goes into the dorsal root ganglion of the spinal cord
- Immediately synapses onto an interneuron in the dorsal horn and passes into the other side of the spinal cord
- This travels up to the thalamus where it synapses onto an efferent neuron and onto the Primary Somatosensory Cortex


What the dorsal column-medial lemniscal pathway and spinothalamic tract tell you about spinal damage

If damaged on one side of the spina cord:
- sensory information from below that same side will not travel up
- pain information from that opposite side will not travel up
- due to the way each pathway passes over to the other side of the spinal cord


Sympathetic vs Parasympathetic effects of the Autonomic Nervous System

- dilates pupils and inhibits tears
- relaxes airways
- increases heart rate
- inhibits salivation and digestion / stimulates glucose release from the liver
- relaxes bladder and rectum
- stimulates orgasm
- stimulates release of adrenalin and noradranalin

- constricts pupils an stimulates tears
- constricts airways
- slows heart rate
- stimulates salivation and digestion / stimulates insulin release from the liver
- constricts bladder and rectum
- stimulates sexual arousal


Changes to the Autonomic Nervous system (by exercise and trauma)

- recreational athletes show a shift towards the sympathetic nervous system
> if persistent this can cause high blood pressure and cardiovascular disease
- long term intensive athletic training causes a shift towards the parasympathetic nervous system

- PTSD causes a heightened sensitivity in the autonomic nervous system
- tends to have persisting effects


Brain facts

- Brain is 2% of the body mass but receives 15% of the body's blood supply and receives 20% of the body's oxygen
- no brain cell is further than 50 um (micrometers)



Dura mater
- tough and inflexible, divided into several layers

Arachnoid mater
- delicate, impermeable and avascular

Pia mater
- adheres closely to the brain
- fuses with the lining of the ventricles to form structures that produce cerebrospinal fluid (CSF)

The Peripheral Nervous System (PNS) has no pia mater, only 2 layers



Produced mainly by the Choroid Plexus, about 500ml daily



Structures can be considered as homologous if they have similar:
- structure
- connections
- chemical signalling
- gene expression
- function


Three R's in animal research

All research should aim to:
- Reduce the total number of animals used
- Replace live animal testing with anything else where possible
- Refinement (minimise suffering and distress to the animal)


Development of the body from 3 plates

- forms the skin and nervous system

- forms bones and muscles

- forms the lining of internal organs


Development of the Ectoderm

- After 22 days from gestation, the neural plate forms the neural tube via Neurulation:
> Neural plate folds at the Neural plate borders, forming a Neural Groove
> When the Neural Folds fuse together, this groove becomes the Neural Tube and the folds form the Neural Crest
+ The Central Nervous System develops from the Neural Tube
+ The Peripheral Nervous System develops from the Neural Crest


Birth defects of nervous system maldevelopment (spina bifida)

Spina Bifida
- the most common birth defect associated with live birth
- occurs when the neural groove doesn't properly close up to form the neural groove, so there is a gap

- Occulta
> asymptomatic, normally a tuft of hair at the location
- Meningocele
> a sack containing spinal fluid at the location of non-fusing
- Myelomeningocele (80-90% of cases)
> a sack containing spinal cord, nerves and spinal fluid

- depend on the severity and location
- High on the spine could cause paralysis
- Lower down could cause incontinence

- Movement problems:
> weakness or paralysis of lower limbs
> deformed bones
- Bladder and bowel problems
> incontinence / UTI
- Associated Hydrocephalus (enlarged head) [least common]
> with many associated learning difficulties


Risk factors for Spina Bifida

- being white
- being a girl
- the mother has diabetes
- the mother is obese
- the mother has a folate (folic acid / vitamin B6) deficiency
- certain medications (i.e. anti-seizure)


Differentiation of the Neural Tube

- firstly into 3 Primary Brain Vesicles
> Forebrain, Midbrain, Hindbrain
> Prosencephalon, Mesencephalon, Rhombencephalon
- then these further differentiate:
> Forebrain differentiates into 2 Telencephalic Vesicles, 2 Optic Vesicles and the Diencephalon
> Midbrain differentiates into the Mesencephalon, which differentiates into the Tectum, Aqueduct and Tegmentum which form a layered tube (around the Cerebral Aqueduct)
> Hindbrain differentiates into the Cerebellum, Pons and Medulla (also the 4th ventricle which is continuous with the aqueduct)