PHGY 210 Study Guide - Final Guide: Arachnoid Granulation, Pia Mater, Dura Mater

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Published on 17 Sep 2014
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Nervous system:
Major divisions:
1) Afferent (Cell bodies outside of CNS)
2) Efferent (Cell bodies in CNS)
3) Cranial nerves (somatic, visual, olfactory, taste, auditory)
4) Spinal nerves (somatic sensation: Touch, temperature, pain, proprioception)
5) Somatic efferent (innervates only skeletal, only excitatory, motor neurons)
6) Autonomic efferent (innervates motor neurons, smooth & cardiac muscle, excitatory/inhibitory)
7) Enteric
Divisions of spinal cord:
Thoracic nerves: (12 segments) shoulders, chest, upper abdomen
Cervical: (8 segments) that innervate neck, shoulders, arms, hand
Lumbar nerves: (5 segments) for lower abdominal wall hips, and legs
Sacral nerves: (5 segments) genitals and lower digestive tract
Coccygeal nerves: 1 segment
Cranial nerves: (12 of them)
10/12 go into brain stem
Olfactory nerve and optic nerve do not go into the brain stem
Development of nervous system:
Egg--dividing into ball of cells--inner cell mass (blastocyst)--structures/cavities--week 3--blastocyst
contains embryonic disc-top layer=neural plate
Development of neural tube:
Ectoderm->CNS and PNS
Mesoderm-->Dura layers
Endoderm-->Digestive system
3-4 week: Neural groove pinches off to form neural tube-->ectoderm layer-->Tube becomes CNS and
part of PNS
Neural tube:
Tubes form neural tubes forms vesicles (fore, mid, hindbrain)
Forebrain-->cerebral and thalamus
Midbrain-->midbrain
Hind-->Pons, Medulla, and cerebellum
Tail becomes the spinal cord
Cavity in neural tube becomes the ventricles and the central canal
CSF and ventricles:
2 circulatory system in brain: CSF (ventricle) and the BLOOD
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CSF:
-Produced in ventricles; 150mL of in head at any time
-2 biggest ventricles=lateral ventricles
-Lining of ventricles (Choroid plexus) produces CSF takes blood-secrete CSF into ventricles
CSF:
Brain floats in CSF, produces 500ml /day
CSF functions:
1) Cushions the CNS; specific gravity of CSF and the brain are equal
2) Provides nourishment to the brain
3) Removes metabolic waste through absorption at arachnoid villi
Composed of sterile, colourless, acellular fluid that contains glucose
Passive circulation; no pumping
Circulation: Foramen of monro—3rd ventricle--cerebral aqueduct--4th vent--central canal—Exit routes:
3 openings (foramen of lushka (2 lateral) and magendie) --CSF goes out to subarachnoid space--comes up to the
top--arachnoid villi suck and empty CSF into dural sinus which is connected to venous blood supply
Hydrocephalus (Build up of CSF):
Intracranial pressure-->Leads to expansion of head
2 types:
1) Communicating=
Ventricles can communicate with each other, Problem in subarachnoid space, potentially with arachnoid
villi; problem is outside CNS
2) Non-communicating=
Blockage between ventricles; usually in cerebral aqueduct cause it's small-->pressure built up inside
ventricles pushes brain against skull
Meninges of CNS:
Cover spinal cord and the brain
1) Dura mater= protects brain and spinal cord, tough leather membrane
--Dura layer opens up in a space along the midline at the top of the brain (dural sinus)
2) Arachnoid membrane
3) Pia mater= stuck to surface of gray matter (cerebral cortex)
Trabeculae are pillars between the Pia and arachnoid that allow CSF to flow in between
Subarachnoid space=space between pia and arachnoid membrane
Blood vessels in the subarachnoid space
Blood supply to the brain:
1) Brain metabolizes a lot of glucose
2) Very little glycogen in the brain
3) Brain needs continuous supply of glucose and oxygen; does not require insulin
4) Disrupt supply can lead to loss of consciousness, few minutes-death)
5) Receives 15% of total blood but only 2% of body mass since it requires continuous supply of blood and O2
Blood flow to the brain:
Mainly going up carotid artery--divides into internal/external--internal goes to the brain
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Vertebral artery also carries blood to brain
Close to base of brain, 2 vertebral come together to form basilar artery
Basilary and 2 internal carotid (Left and right) form “Circle of Willis”
(Circle of Willis)=safety factor
-->if problem in one of internal arteries (blood clot in one side)
-->blood from the other internal artery can be shunted to the other side and reach the brain
Blood brain barrier:
Mediated by endothelial cells which form these tight junctions
Diffusion across endothelial cells (only H2O, CO2, O2, and lipid soluble, ions)
If not lipid soluble, active transport of glucose and some amino acid
Astrocytes= (glial cells=non neural cells of CNS)
Functions of astrocytes:
1) Foot processes of these cells induce tight junctions
2) Regulate environment around neurons by maintaining ion concentration in ECF
3) Suck up loose neurotransmitters
4) Provide structural support to brain
5) Are garbage collectors; phagocytosis of debris
Perception of external world:
Sensation=awareness of sensory stimulation
Perception=understanding of sensation's meaning
We do not perceive the energy of a sensory stimulus directly
We only perceive neural activity produced by sensory stimulation, NOT energy
LAW OF SPECIFIC NERVE ENERGIES
~Regardless of how you activate receptors, what you receive is what that receptor is specialized for
E.g. By rubbing eyes, you increase intraocular pressure-->AP-->must be receiving light
LAW OF PROJECTION:
~Sensation is always felt at receptor's location, regardless of where in the brain you stimulate the sensation
E.g. Phantom limb pain
Sensory receptors:
~In order to perceive sensory energy, it has to interact with receptor membrane and has to be
specific to the receptor membrane
~Sensory transduction=opening or closing of ion channel due to stimulus
~Receptor cell receives energy and releases neurotransmitter->AP to the brain
*** Stimulus--receptor membrane—transduction--channel activation--AP to CNS***
Magnitude of neurotransmitter release depends on the frequency of action potentials
Adaptation:
Most afferents show adaptation; allows us to be sensitive to changes in sensory input
1) Non-adapting =encode stimulus intensity and slow changes
2) Slowly-adapting=some stimulus intensity and moderate stimulus change-emphasizes the change
3) Rapidly adapting =just tell you the change only, not the stimulus intensity; fast stimulus changes; called
ON OFF response
Receptive Fields (RF):
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