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Nervous System

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Classification

Anatomically

CNS

Brain

Spinal cord

PNS

Peripheral nerves

Functionally

Somatic nervous system (SNS)

Skeletal or voluntary muscles

Autonomic nervous system (ANS)

Automatic functions

Nervous system Computer

Sensory receptors and nerves

Effectors and motor nerves

Spinal cord

Brain and spinal cord

Control mechanisms in lower brain

Input circuit

Output circuit

Simple computers (output directlycontrolled by input)

Complex computers (input and previousmemory)

CPU (sequence of informationprocessing)

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CNS: Brain and SpinalCord

PNS: Cranial Nerves (12)

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PNS: Spinal Nerves (31)

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Spinal cord : Slender structurecontinuous with the brain

Descends into the vertebral canaland ends around the level of the firstor second lumbar vertebra

31 spinal segments:

8 cervical segments

12 thoracic segments

5 lumbar segments

5 sacral segments

1 coccygeal segment

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Martini 13-11

Comparison of Somatic and Autonomic Systems

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Freeman 45-20

Meninges

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CNS: Brain

Four sections and three levels

Cerebrum (higher brain):Thoughts and memory

Diencephalons (subcortical or lowerbrain):subconcious activities like arterial pressure,emotions, feeding reflexes

Brain stem (lower and mid brain): respiration,visual and auditory reflexes

Cerebellum (lower brain) :Coordination inmovement

Space Restriction and Brain Development

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CNS: Brain – Cerebrum

Largest section

Two cerebral hemispheres

Connected by a thick bundle of nerve fiberscalled the corpus callosum

Longitudinal fissure between hemispheres

Sulci – grooves on surface

Gyri or convolutions – bumps of brain matterbetween sulci

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Previous slide

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Cortex

Outer layer – graymatter

Contains about 75%of all neurons

Inner layer – white matter

Functions

Interpret sensory information

Initiate body movements

Stores memories and creates emotions

Ventricles

Interconnectedcavities within thebrain

Filled with CSF

CNS: Brain – Cerebrum (cont.)

Ventricles of the Brain

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Diencephalon: Thalamus and Hypothalamus

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Between the cerebral hemispheres superior to thebrain stem

Thalamus

Relay station for sensory information going to thecerebral cortex for interpretation

Hypothalamus

Maintains homeostasis by regulating vital activities

CNS: Brain – Diencephalon

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Connects the cerebrum to the spinal cord

Midbrain (mesencephalon, amygdala)

Just beneathdiencephalon

Controls both visualand auditory reflexes, eg.feeding reflexes

Pons

Rounded bulge onunderside of brain stem

Between midbrain andmedulla oblongata

Regulates respiration

Medulla oblongata

Inferior portion of brainstem

Directly connected tospinal cord

Controls many vitalactivities, such as heartrate, blood pressure,and breathing

CNS: Brain – Brain Stem

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Location

Inferior to the occipital lobes of the cerebrum

Posterior to the pons and medulla oblongata

Coordinates

Complex skeletal muscle contractions that areneeded for body movements

Fine movements

Brain

CNS: Brain – Cerebellum

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Lobes

Frontal

Motor areas for voluntary bodymovements

Parietal

Somatosensory – interpretssensations

Temporal

Auditory – interprets sounds

Occipital

Interprets what a person sees

Frontal

Parietal

Occipital

Temporal

CNS: Brain – Cerebrum (cont.)

Spinal Cord

Marieb 12.29a

Gray Matter and Spinal Roots

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Cross-Sectional Anatomy of the Spinal Cord

Anterior median fissure – separates anterior funiculi

Posterior median sulcus – divides posterior funiculi

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Gray Matter: Organization

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Alberts 18-26

USB DRIVE:Anat & Phys 1 (day):Powerpoint Slides:

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Neuron Structure (cont.)

White matter – axons withmyelin sheath

Schwann cells – neurological cells

Wrap around some axons

Cell membranes contain myelin

Myelin insulates axons and enablesaxons to send nerve impulses morequickly

Gray matter – axons withoutmyelin sheath

Schwanncells

Axon

Dendrites

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Image result for neuroglial cells histology, cerebrum

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Myelin Sheath and Neurilemma: Formation

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Freeman 45-12a

Comparison of Structural Classes of Neurons

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Martini 12-4

Saltatory Conduction

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Dendrites

Cell body

Nucleus

Axon hillock

Axon

Signaldirection

Synapse

Myelin sheath

Axonterminals

Presynaptic cell

Postsynaptic cell

Campbell 48.5

Structure of a Nerve

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Nerve Impulse

Impulse travels down axon to synaptic knob

Vesicles or small sacs in synaptic knob

Produce chemicals called neurotransmitters

Neurotransmitters are released by synaptic knob

Allow impulse transmission to postsynapticstructures

Dendrites

Cell bodies

Axons of other neurons

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Nerve Impulse

Functions of neurotransmitters

Cause muscles to contract or relax

Cause glands to secrete products

Activate or inhibit neurons

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Nerve Impulse

Membrane potential

Neuron cell membrane at rest is in a polarized state

Inside of cell membrane is negative (-90 mV)

Outside of cell membrane is positive due to more Na+ and K+

As Na+ and K+ move into the cell, the membrane becomesdepolarized

Inside becomes more positive (+ 45 mV)

Action potential (nerve impulse) is created

Repolarization occurs when K+ and later Na+ move to theoutside of the cell membrane

Return of the cell to polarized (resting) state

Synaptic Cleft: Information Transfer

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Type of Synapses

Chemical , Electrical

In electrical synapses, ionic current spreads directly from one cell to anotherthrough tubular structures called connexons. A cluster of 100 or so connexonsforms a pathway (connection) called a GAP JUNCTION between adjacentcells. Gap junctions are common between cardiac muscle cells (shown below,left) and between smooth muscle cells

Excitatory , inhibitory

GABA, glycine- inhibitory, to lower anxiety

Acetyl choline, serotonin, glutamine- Excitatory

Epenepherin, Norepinepherin, dopamine are both excitatory and inhibitory

Postsynapticneuron

Synapticterminalsof presynapticneurons

5 µm

Campbell 48.16

Freeman 45-17a

CSF

Cerebrospinal fluid (CSF) is a clear, colorless body fluid found inthe brain and spine. It is produced in the choroid plexuses of the ventricles ofthe brain. It acts as a cushion or buffer for the brain's cortex, providing basicmechanical and immunological protection to the brain inside the skull. TheCSF also serves a vital function in cerebral autoregulation of cerebral bloodflow.

The CSF occupies the subarachnoid space (between the arachnoid mater andthe pia mater) and the ventricular system around and inside the brain and spinalcord. It constitutes the content of the ventricles, cisterns, and sulci of the brain,as well as the central canal of the spinal cord.

http://massagemag.com/massage-blog/craniosacral-therapy/files/2008/11/csf-blogedit1.jpg

The CSF has two major pumps thathelp to establish healthy flow. Thepump at the top of the spine is theocciput bone which makes up thelower portion of the skull. Flexionand extension motions of theoccipital bone upon the atlas helpto pump CSF through the brain andspinal cord

The other pump is at the bottom ofthe spine in the sacrum. Flexionand extension of the sacrum is alsocritical to help pump the CSF

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1. Lateral ventricle

2. Interventricular foramen

3. Third ventricle

4. Cerebral aqueduct

5. Fourth ventricle

6a. Median aperture

6b. Lateral aperture

6c. Central canal (spinal cord)

7. Subarachnoid space

8. Arachnoid villi

9. Dural sinuses

Marieb 12.26b

http://www.apsubiology.org/anatomy/2010/2010_Exam_Reviews/Exam_4_Review/CSF.fig.12.22b.jpg

Composition

CSF composition is similar to serum composition, besidesprotein, calcium and protein concentrations which are lower

CSF is normally as clear as water and does not contain any bloodcell (leukocytes, aka white blood cells and erythrocytes, aka redblood cells).

However, in infections such as meningitis, leukocytes may passinto the CSF and after hemorrhage, red blood cells may be foundin CSF.

Protein concentration in the CSF, usually very low, is increased incase of infection and if CSF reabsorption at the level of thearachnoïd villi is impaired.

In a reverse way, glucose concentration is decreased in somepathological conditions (tumor, acute bacterial infection, fungalinfections...)

Substance

Cerebrospinal Fluid

Serum

Water Content (%)

Protein (mg/dL)

7000

Glucose (mg/dL)

Osmolarity(mOsm/L)

295

Sodium (mEq/L)

138

Potassium (mEq/L)

2.8

4.5

Calcium (mEq/L)

2.1

4.8

Magnesium (mEq/L)

0.3

1.7

Chloride (mEq/L)

119

102

7.33

7.41

Comparison of Average Serum and CerebrospinalFluid [7]

Function of CSF

Buoyancy: The actual mass of the human brain is about 1400 grams; however, thenet weight of the brain suspended in the CSF is equivalent to a mass of25 grams.[18] The brain therefore exists in neutral buoyancy, which allows the brain tomaintain itsdensity without being impaired by its own weight, which would cut offblood supply and kill neurons in the lower sections without CSF.[19]

Protection: CSF protects the brain tissue from injury when jolted or hit. In certainsituations such as auto accidents or sportsinjuries, the CSF cannot protect the brain fromforced contact with the skull case, causing hemorrhaging, brain damage, and sometimesdeath.

Chemical stability: CSF flows throughout the inner ventricular system in the brain andis absorbed back into the bloodstream, rinsing the metabolic waste from the centralnervous system through the blood–brain barrier. This allows for homeostatic regulationof the distribution of neuroendocrine factors, to which slight changes can causeproblems or damage to the nervous system. For example,high glycine concentration disrupts temperature and blood pressure control, and highCSF pH causes dizziness andsyncope.[19]

Blood Brain Barrier

Because the brain is so specialized many of the chemicals found in the bloodare actually toxic to the neurons in the brain. With such a specialized job onewould think that the brain itself should actually have its own separatecirculatory system.

Unlike other parts of the body where the arteries and veins and capillaries bringnutrients to cells and move waste out of cells, the neurons in the brain arecreated with specialized capillaries made of protein fibers called “astrocytes”.These specialized capillaries essentially filter out harmful toxins and onlyallow through to the specialized brain cells healthy nutrients the brain needs.

Alcohol too passes the Blood Brain Barrier as easily as water and that can bevery bad for brain tissue. Prescription drugs however, because they are mostlysynthetic have great difficulty in passing through this Blood Brain Barrier.The body recognizes the synthetic material as foreign and won’t let it passthrough.

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http://medcell.med.yale.edu/systems_cell_biology_old/nervous/images/myelin_cartoon.jpg

C) Myelination process

D) Unmelinated neuron