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Lecture

BIOD27H3 Lecture Notes - Central Nervous System, Arachnoid Mater, Pia Mater


Department
Biological Sciences
Course Code
BIOD27H3
Professor
Catherine Nash

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Physiology Midterm 2 Review
Lecture 9
oCentral Nervous System = brain & spinal cord (contains neurons that communicate within the CNS
and the rest of the body)
oPeripheral Nervous System = Autonomic (involuntary) Nervous System (cardiac, smooth
muscle(liver), adipose tissue(fat), endocrine system), Enteric Nervous System(digestive) & Somatic
Motor Division(skeletal muscles)
Evolution of the Brain
oLines of the Jellyfish represent the nervous system; In jelly fish the nerve net functions together to co-
ordinate movement
oIn flat worms, nerve cords represent bundles of nerves in the brain and the primitive brain is a
collection of cell bodies within the head; Flat worms = simple nervous system. Nerve cell bodies
restricted to the head.
oAnnelids and segmented worms have clusters of nerve cells (ganglia = swellings where synapse are)
through the body
oAllows functions equivalent to spinal reflexes(involuntary) in humans to be carried out
o In vertebrates the forebrain is more complex e.g structures like cortex and cerebellum
o Animals increase in complexity and specialisation as move up phylogenetic tree
oThe cortex increases in size in higher mammals. Thicker cortexs help us to perform higher
processes(awareness, analysis of perception) the cortex decodes information and decides how it will
respond
Development of the Nervous System
oDuring the developmental stage in the fetus, 2 cells divide and form the neural tube( which ultimately
becomes the CNS
oNeural Plate: region in the embryo that forms the CNS
oOn day 20 of the embryonic stage, cells in the neural plate move upwards towards the neural crest and
what this does is it causes a neural groove to form
ocells migration elevates the neural crest and deepens the neural groove
oThe neural crest eventually increases in size until it flops over onto each other and makes a neural tube
oLumen forms the central cavity (ventricles or gaps/spaces) of the CNS
o Lining of lumen becomes gap function cells and neural stem cells
o Outer layers become neurons and glia(supportive cells) (central nervous system (CNS))
o Neural crest becomes sensory and motor neurons of
(peripheral nervous system (PNS))
oStem cells are cells that can take on any form that are
present or developing through a lifetime
oAt week 4 cerebrum (cortex) is similar in size to other
brain regions and by week 6, 7 major regions of the CNS
have formed
oBy week 11, the CNS look similar to that that we see at
birth
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oWeek 11: Growth of cerebrum (cortex) accelerates
oAt birth the cerebrum surrounds the diencephalon, midbrain and pons
oCranial nerves: Carry information to and from brain from entire body
oAt birth, the cerebrum becomes invaginated which creates a large surface area for neurons etc.. to be
maintained in our brain
How the Brain is Protected and Maintains its Function
1.Bone protects the Central Nervous System (CNS): CRANIUM protects the brain and VERTICAL
COLUMN protects the spinal cord
* 3 protective layers surround the brain:
Bone
Connective tissue
Fluid
2. Meniges(connective tissue) support and protect the CNS
*3 layers:
1. Dura mater (thickest). Contains veins that drain blood (away from the brain) through sinuses (cavities);
forms the outside protective layer
2. Arachnoid mater (loose)
3. Pia mater (thin); Tightly associated with the brain. Contains arteries that supply blood to the brain.
Beneath pia matter is EC fluid that bathes neurons
3.Cerebrospinal fluid (CSF) cushions the CNS
oProvides physical and chemical protection
oCompared to EC and plasma, the CSF has a Lower [K+] and [Ca2+], higher [H+], same [Na+]
oLittle protein; no red blood cells; red blood cells are toxic to neurons because of high Iron
concentration
oCSF is secreted from the choroid plexus into ventricles
oflows through subarachnoid space to cushions brain and spinal cord
oCSF and EC communicate through pia mater and ventricle membranes
oCSF flows through the subarachnoid space between pia mater and arachnoid membrane
oCSF is reabsorbed into blood villi (hair-like structures) on arachnoid membrane
oAllows removal of wastes (toxins, metabolites)
o Entire volume of CSF (approx 400ml) is replaced 3 times / day
oTo discover any type of illness occurring in the CNS, doctors perform a lumbar puncture:
removal of CSF from subarachnoid space at lower end of spinal column
4.Ventricles of the brain
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5.The Blood-Brain Barrier protects the brain from harmful substances in the blood (barrier between CSF
and the blood)
oActs as a barrier between cerebrospinal fluid (CSF) and blood
o Protects against fluctuations in hormones and chemicals (e.g neurotransitters)
o Prevents pathogens e.g. Blood born bacteria entering CNS
o Formed by tight junctions and glial cells that prevent solute movement
o Selectivity of membrane carriers and channels enables nutrients, O2 to enter the CSF
6.Blood Supply to the Brain
oBrain constitutes 2% of total body weight; receives 15% of cardiac output; 20% total body
oxygen and 50% total glucose consumption
oBlocking of blood supply (e.g. cardiac arrest) can cause unconsciousness within 10 seconds
oGrey matter and white matter are the 2 main types of matter within the brain and both types
are located in the brain and spinal cord
oGrey matter = dendrites, cell body & synapse; White matter = axons of neurons, glial cells
and myelin sheath
The Spinal Cord
oMajor pathway for information flowing between brain, skin, joints, muscles
oCarries neural network for locomotion
oProvides communication between the brain and the rest of the body
oDivided into 4 regions:
- cranial
- thoracic
- lumbar
- sacral
oEach region subdivided into segments each gives rise to a bilateral pair of spinal nerves
oWhere spinal nerve joins spinal cord = root
oIn ALS, the spinal cord degenerates
oSpinal cord is divided into 2 portions: the ventral(front) and the dorsal(back)
oThe dorsal root receives afferent (entering the brain) nerves; terminate (end) in the dorsal horn
o Efferent (leaving the brain) nerves originate in the ventral horn; terminate on different body parts
outside the brain
Functions of the Brain Stem
oConsists of: Medulla Oblongata & Pons
oMedulla Oblongata(involuntary/unconscious)
Arousal and sleep
Muscle tone and muscle stretch reflexeswww.notesolution.com
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