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Nervous System 2 Notes

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This is an extract of our Nervous System 2 document, which we sell as part of our Pre Clinical Systems Based Teaching Notes collection written by the top tier of Bristol University students.

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Nervous System Introduction Organisation CNS = brain within skull & spinal cord within vertebral column PNS = 12 pairs of cranial nerves & 31 pairs of spinal nerves

Peripheral Nervous System A named and identifiable collection of thousands of neuronal axons bundled together - sciatic nerve Nerves divided smaller but axons are continuous - tibial nerve Nerves can fuse together and then divide to redistribute axons at a plexus - cervical plexus Clumps of cell bodies are called ganglia

Afferent Neurones Sensory Enter the spinal cord through the dorsal horn Some are somatosensory - from the body wall and skin Some are viscerosensory - from internal organs

There are 6 types of peripheral neurone General Somatic Afferent - GSA General Somatic Efferent - GSE General Visceral Afferent - GVA General Visceral Efferent - GSE Special Somatic Afferent - SSA Special Visceral Efferent - SVE

Efferent Neurones Motor Exit the spinal cord through the ventral horn Some are somatomotor - controlling the skeletal muscles Some are visceromotor, the ANS - controlling internal organs

Visceromotor System - Autonomic Nervous System Two divisions - sympathetic and parasympathetic Innervates visceral organs Both systems have a 2 neurone chain and ganglia The cell bodies of the pre-ganglionic neurones are in the CNS Post-ganglionic cell bodies are in the ganglia Post-ganglionic neurones innervate the smooth muscle The sympathetic chain runs the length of the vertebral column Splanchnic nerves branch off the chain to innervate abdominal organs

Development Forms in 3rd week of embryonic life from the ectodermal layer A neural groove develops in the midline and neural cells proliferate to form a neural tube The tube forms the spinal cord and swells to form the brain Hindbrain - rhombencephalon Forms the medulla, pons and cerebellum Midbrain - mesencephalon Tectum and cerebral peduncle Forebrain - diencephalon Thalamus and hypothalamus
- telencephalon Cerebral hemispheres and basal nuclei

The cerebra hemisphere is made up of 4 lobes: Frontal, parietal, occipital &

The tissues of the brain are surrounded by cavities known as ventricles that are derived from the lumen of the neural tube The space is filled with cerebrospinal fluid (CSF), which acts as a cushion

Meninges There are 3 enveloping membranes

Dura The dura is the outermost and toughest layer The dura is folded to help support the brain The falx cerebri - a midline sickle shaped fold extending into the longitudinal fissure separating the hemispheres The tentorium cerebelli - a tent shaped arching fold dividing the cranium into a posterior fossa, below containing the brainstem and cerebellum and middle and anterior fossae, above occupied by the forebrain

Arachnoid The arachnoid layer is a fibrocellular layer lining the dura. The subarachnoid space contains the CSF Larger spaces in the subarachnoid space are named cisterns CSF emerges into the subarachnoid space from the 4th ventricle and drains into the Superior Sagittal Sinus

Pia The pia matter is a thin fibrocellular layer closely covering the surface of the brain The pia allows passive exchange of water and small molecules between the brain ECF and CSF

CSF About 500ml is secreted each day, mainly by the choroid plexuses in the lateral, 3rd and 4th ventricles The circulation of CSF is indicated by the blue arrows Secretions begins with the ultrafiltration of plasma but has a different composition to blood due to selective reabsorption CSF contains no RBC and a few WBC in health Arachnoid villi (granulations) project into the venous sinuses and act as one-way valves allowing CSF into the blood whenever the pressure is greater in the subarachnoid space than the venous sinus Unwanted metabolites are removed by selective absorption by the choroid plexuses and being dumped into the venous blood by arachnoid villi The brain floats in the CSF, therefore dampening forces produced by head movement

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