Download The Nervous System

The Nervous System
Mark Olson, Ph.D.
I'd take the awe of understanding over the awe of ignorance any day. ~Douglas Adams
Nervous System
• 100 billion neurons in humans (bees: 1 million), each averaging 10,000 connections. 20 billion in neocortex.
o
Covers 4 soccer fields when laid flat.
o
More possible neural connections than number of stars in the universe.
o
Glial Cells: support neurons. 10-50x the number of glial cells than neurons.
• 1 neuron lost every second.
• 2% of body weight (3lbs). 78% water.
• 20% of body oxygen supply goes to brain. Supply is kept constant.
• 100% utilized. The “10% used” idea is simply ridiculous.
Three Functional Neuron Types
• Afferent/Sensory: From sensory receptors to the brain
o
Receptors: beginning of first sensory neuron (c 91)
 Exteroceptors (all senses: sight, hearing, touch (light/deep/temp/pain), taste, smell, etc)
 Proprioceptors (joint position detected by measuring stretch in muscles and tendons)
 Interoceptors (visceral)
• Efferent/Motor: From brain to effectors
o
Effectors (muscles or glands): end of last motor neuron
• Interneurons: short neurons in spinal cord that connect afferent
and efferent neurons
Neurons (c 71)
• Cell body: contains the nucleus, keeps cell alive
• Dendrites: receive chemical signals from other neurons
• Axon: carries electrical signal, 1 or 0
• Myelin: insulates some axons
• Terminal: releases neurotransmitters into synapse
• Synapse: fluid-filled space between neurons
• Neurotransmitters: chemicals released into synapse
o Serotonin (mood/depression, sleep, perception, digestion)
o Dopamine (movement/Parkinsons, pleasure/addiction)
o Noradrenaline (energy, alertness)
o Acetylcholine (muscle contraction, memory)
• Receptor Sites: location on receiving neuron’s dendrites where neurotransmitters are absorbed. Excitatory vs Inhibitory.
• “Neurons that fire together, wire together”
White and Grey Matter
• White matter (insulated wire): contains only myelinated axons; signals transported. Faster signal
• Grey matter (exposed wire): no myelin; mostly cell bodies and dendrites. Signals processed, neurons interact.
A Structural Division is a "geographical" division (e.g. the telephone wire inside vs outside your house: same wire, two locations. A
neuron can travel from the PNS to the CNS: same neuron, two locations).
A Functional Division is based on purpose (e.g. the electric wires inside your house versus the telephone wires inside your house:
same location, different functions). Note that most textbooks list the ANS as a subdivision of the PNS, which is to say that it only
exists in the periphery, which is not actually true. SNS and ANS neurons can run side by side each other in the CNS or the PNS.
Nervous System: Two Structural Divisions (c 70)
• Central nervous system (CNS)
o Brain and spinal cord
o Integration and command center
• Peripheral nervous system (PNS)
o Paired spinal and cranial nerves
o Carries messages to/from the spinal cord & brain
• CNS and PNS separated by Meninges (see next page)
Nervous System: Two Functional Divisions
• Somatic nervous system (SNS)
o Sensory (afferent): from sensory receptors in skin,
eyes, tongue, skeletal muscle, and joints to CNS
o Motor (efferent): from CNS to muscles
• Autonomic nervous system (ANS)
o Sensory: from visceral organs to CNS
o Motor: from CNS to smooth muscle, cardiac
muscle, and glands
o Divisions: sympathetic & parasympathetic
Central Nervous System (CNS)
Major Structures
• Brain
o Cerebrum: largest part. contains outer layer of cortex (neocortex)
o Cerebellum: integrates motor and proprioceptive signals
o Brain stem
 Midbrain: orienting behavior
 Pons: projects proprioceptive fibers to cerebellum
 Medulla oblongata: survival functions
• Spinal Cord
Cerebrum (c 73)
• Site of significant growth in humans
• Composed of both white matter and grey matter (incl neocortex)
• 2 Hemispheres, each with 4 pairs of cortical lobes
o Occipital (visual)
o Temporal (auditory, memory, object recognition)
o Parietal (touch, spatial, body position, math, attention)
o Frontal (motor, planning, time, personality, social,
inhibitions, attention, memory, affected most by alcohol,
40% of human cortex)
o 5th inner lobe: Limbic (emotions, see below)
• Cortical regions, highly organized
o Primary somatosensory cortex (sensory homunculus)
o Primary motor cortex (motor homunculus)
o Primary visual cortex
o Prefrontal cortex
• Corpus callosum
o White matter tract that connects the two hemispheres. 250 million fibers.
• Thalamus
o Little brain; All sensory information (except smell) goes through the thalamus on the way to the cerebral neocortex
• Pineal gland (within the brain but not part of the brain)
o Input directly from eyes
o Excretes melatonin, regulates sleep cycle
o Light-sensitive thru the skull in birds
• Ventricles (c 80)
o Spaces in the brain where CSF is produced (.5 liter daily—total replaced 4 times/day). Moves through all 4 lobes.
• Limbic System
o Part of the Cerebrum (overlaps medial temporal lobe)
o “Mammalian Brain”: Region of significant growth in humans, comparable to that of the neocortex
o Seat of Memory and Emotions
• Pleasure, attachment, desire, love, anger, fear
o Structures:
• Nucleus accumbens (pleasure center)
• Amygdala (fear center) in medial temporal lobe
• Hippocampus (memory storage) in medial temporal lobe
• [Note: no such thing as muscle memory]
• Hypothalamus (autonomic controls)
Meninges (c 77, 81)
 Three layers of connective tissue that encase and protect CNS and separate it from the PNS
o Dura mater: like leather, next to skull
o Arachnoid: weblike material
 Subarachnoid space: Contains Cerebral Spinal Fluid (CSF) which serves as a liquid cushion
o Pia mater: like plastic-wrap (clear and thin), follows gyri and sulci
 Meningitis: Inflammation of the Meninges
Effects of Tobacco: doubles risk for Alzheimers and dementia. Decreased sense of smell. Increased stress. Hearing and vision loss,
including cataracts. Addiction and reduced capacity for pleasure.
Peripheral Nervous System (PNS)
PNS Spinal Nerves (c 84)
• 31 pairs exit between vertebrae, from Cervical to Coccygeal nerve roots
o 8C’s, 12T’s, 5L’s, 5S’s, 1Co’s: One extra nerve in cervical spine
• Each spinal nerve carries sensory & motor neurons. Each nerve separates just outside the spinal
cord into the Dorsal (Sensory) and Ventral (Motor) Roots
• Dermatomes: area of skin innervated by one pair of spinal nerves (c 90)
• Myotomes: area of muscles innervated by one pair of spinal nerves
Plexuses: Cervical, Brachial, Lumbar, Sacral (c 86)
Proprioception: Sensory neurons (proprioceptors) in muscles
(muscle spindle) and tendons (golgi tendon organ) detect the
amount of stretch in those tissues and provide “position sense”.
Signals are processed in the spinal cord and cerebellum.
Pain and Stretch Reflexes (c 85)
• Reflexes involve only the spinal cord, not the brain
• Afferent (Pain or Proprio) to Spinal Cord to Efferent
PNS Cranial Nerves (c 83)
• 12 pairs from brainstem (sensory, motor, mixed)
• OOOTTAFVGV-AH!! (ooo,ooo,ooo, to touch and feel…)
1. Olfactory: S: smelling
2. Optic: S: seeing (38% of all axons to brain)
3. Oculomotor: M: moving eyes
4. Trochlear: M: moving eyes
5. Trigeminal: S: touch from face
6. Abducens: M: moving eyes
7. Facial: SM: moving face muscles, and tasting
8.
9.
10.
11.
12.
Vestibulo-Cochlear: S: hearing, balance
Glossopharyngeal: SM: mouth and throat; tasting
Vagus: SM: to/from viscera (autonomic); tasting
Accessory: M: moving SCM and Trapezius
Hypoglossal: M: moving tongue
Autonomic Nervous System (ANS) (c 92-94)
ANS Function (see note about Functional/Structural divisions on page 1)
• Innervates visceral organs, smooth muscles, and glands
• Controlled by Hypothalamus, which is influenced by other limbic centers
• Two Divisions
o Sympathetic
 ‘fight or flight (or freeze?)’
 Stress response (increased heart rate, pupil dilation, bronchial dilation, vasodilation of blood to muscles,
vasoconstriction of blood to skin and digestive organs, sweat, adrenaline release from adrenal glands, shallower
and faster breathing)
 note: prolonged sympathetic response has widespread negative
systemic effects and is the basis for most diseases in the USA
o Parasympathetic:
 Relaxation response (increased blood to digestive organs and
skin, slower and deeper breathing, pupil constriction, decreased
heart rate)
 note: a parasympathetic response IS the basis for most of the
healing effects of massage!
ANS Anatomy
• Sympathetic (not illustrated)
o Hypothalamic signals descend spinal cord. Exit spinal cord along T1L2. Enter ganglia anterior and lateral to spinal cord. Continue to all
organs, including blood vessels and sweat glands.
• Parasympathetic (see illustration)
o Hypothalamic signals enter brain stem and exit via cranial nerves
 Cranial Nerve X (Vagus) innervates all nonpelvic visceral organs
o Others descend spinal cord and exit at S2-S4 to innervate lower
abdominal organs (bladder, large intestines, reproductive organs)
Endocrine System (c 151-153)
 Endocrine – ductless secretions into circulatory vessels
[NOT Exocrine – secretions through ducts (sweat, tears,
saliva, oil, milk, digestive secretions, mucous)]
 Hormones produced in special glands
 Regulates body functions, maintains homeostasis
 Hypothalamus --> Pituitary --> Glands
 Negative Feedback
Hypothalamus
Brain nuclei relaying messages to glands via
• Direct Autonomic Neural signal --> Adrenal Medulla
• Secretion of Hormones (Oxytocin and
Vasopressin/ADH) --> Posterior Pituitary -->
Reproductive and Kidneys
• Secretion of Regulatory Hormones (e.g. GnRH) -->
Anterior Pituitary --> (Para)Thyroid, Adrenal Cortex,
Reproductive Organs
Endocrine Glands & Hormones
• Pituitary – 9 hormones
• Pineal – Melatonin
• Thyroid – Thyroxin
• Parathyroid – Parathormone
• Thymus – Lymph cells & Hormones
• Adrenals
o Cortex -- Glucocorticoids, androgens
o Medulla -- Epinephrine & Norepinephrine (NE)
• Pancreas – Insulin & Glucagon
• Gonads – (FSH & LH)
o Ovaries – Estrogen, Progesterone, & Inhibin
o Testes – Testosterone & Inhibin
Pituitary Hormones
• Anterior Pituitary (7)
o TSH --> Thyroid --> Thyroid hormones --> bone,
kidneys, Ca+2, growth
o ACTH --> Adrenal Cortex --> Glucocorticoids
o FSH --> Gonads --> Inhibin, Estrogen / Inhibin
o LH --> Gonads --> Progesterone, Estrogen /
Androgens
o PRL --> Mammary Glands
o GH --> Liver --> Bone, Muscle, Etc
o MSH --> Skin
• Posterior Pituitary (2)
o ADH (Vasopressin) --> Kidneys
• Made in Hypothalamus, Reduces ion
concentration, Increases blood pressure, Inhibited
by alcohol
o Oxytocin --> Reproductive organs
• Made in Hypothalamus, rises during sexual
arousal, peaks at orgasm, smooth muscle
contraction during sex in uterus, vagina, sperm
ducts, prostate gland
Pineal Hormone: Melatonin
• Produced in Pineal Gland
• Inhibits Reproductive Function, lowest during puberty
• Antioxidant
• Circadian Rhythms
Adrenals
• Sympathetic Nervous System Response
• Two Divisions
o Cortex: Secretes Glucocorticoids and Androgens
o Medulla: Secretes Epinephrine and Norepinephrine
General Adaptation Syndrome (GAS)
• Alarm Phase
o “Fight or Flight”
o Increase in heart rate, respiratory rate, cell energy use
o Mobilization of glucose reserves
• Resistance Phase
o Mobilization of remaining lipid energy reserves
o Conservation of glucose
o Elevation of blood glucose concentrations
o Conservation of salts and H2O, loss of K+ and H+
o Increase in blood volume and pressure from ADH
o Increased susceptibility to infections
• Exhaustion Phase
o Exhaustion of lipid reserves
o Inability to produce glucocorticoids
o Failure to maintain electrolyte balance
o Cumulative structural or functional damage to vital
organs
Endocrine System Pathologies
• Diabetes
• GAS
• Hyper/hypothyroidism
Chakras (?)
• Chakras = Endocrine glands?
• Chakras = Autonomic Plexuses?
Effects of Tobacco:
• Reduces estrogen levels (thus increasing risk for
osteoporosis and disrupting female cycle, including
irregular periods and earlier menopause)
• Alters hormonal regulation of body weight and fat
distribution
• Increases risk of several endocrine diseases, including
diabetes, the symptoms of which are worsened by
smoking
• Doubles risk of pancreatic cancer (80% death rate within
1 year)
• Arsenic in cigarettes is an endocrine disruptor.
Reproductive System
Reproductive System (c 157, 160)
• Gonads
o Ovaries: product ovum (egg)
o Testes: produce spermatoza and testosterone
• Accessory Glands and Organs
o Greater vestibular (Bartholin’s) glands, Cervical
mucous glands, Uterus, Vagina
o Seminal vesicles, Prostate gland, Bulbourethral
(Cowper’s) glands
• Ducts
o Uterine tubes, fallopian tubes
o Epidiymis, vas deferens, urethra
• External Genitalia
o Vulva: Clitoris, Labia (major, minor)
o Penis, Scrotum
• Hormones
o Estrogen, Progesterone, Testosterone
o Testosterone
Homologous Structures
The difference a little timely testosterone makes…
• Ovary -> Testes
• Glans Clitoris -> Glans Penis (Head)
• Clitoral Hood -> Foreskin
• Clitoral Body/Crura -> Corpus cavernosa
• Vestibular Bulbs -> Corpus spongiosum
• Minor Labia -> Skin of penis
• Major Labia -> Scrotum
• Greater Vestibular (Bartholin’s) Glands ->
Bulbourethral (Cowper’s) Glands
• Skene’s Gland -> Prostate Gland
Testosterone
• Increases metabolism (bone and muscle growth)
• Impedes development of breasts, ovaries
• Establishment and maintenance of male secondary sex
characteristics (facial hair, muscle mass, quality and
location of adipose tissue deposits)
• Stimulates spermatogenesis and maintains other male
reproductive glands and organs
• Effects on CNS (Promotes aggression; Impedes
development of left hemisphere, which in turn impedes
immune functioning; Increases libido, especially in males)
Male Reproductive System (c 157)
• Male gonads produce sperm and testosterone
• Scrotum keeps testes 3°C lower than core body temp
• Sperm are delivered to the exterior through a system of
ducts: epididymis, ductus deferens, ejaculatory duct, and
the urethra
• Accessory sex glands empty their secretions into the ducts
at ejaculation
Accessory Glands
• Seminal Vesicles
o Lie on the posterior wall of the bladder
o Alkaline secretions containing fructose for sperm,
prostaglandins (smooth muscle stimulus), fibrinogen
o Join the ductus deferens to form the ejaculatory duct
o Sperm and seminal fluid mix in the ejaculatory duct and
enter the prostatic urethra during ejaculation
• Prostate Gland
o Doughnut-shaped gland that encircles part of the
urethra inferior to the bladder
o Milky, slightly acid fluid, contains citrate, enzymes,
and prostate-specific antigen (PSA)
o Seminalplasmin--antibiotic prevents UTIs in males
o Plays a role in the activation of sperm
o Enters the prostatic urethra during ejaculation
• Bulbourethral Glands (Cowper’s Glands)
o Pea-sized glands inferior to the prostate
o Produce thick, clear, alkaline mucus prior to ejaculation
that neutralizes traces of acidic urine in the urethra and
lubricates tip of penis
Semen
• 2-5 ml of semen are ejaculated (20-130 million sperm/ml)
• pH of 7.2 to 8.0
• Provides a transport medium. Protects and activates sperm
• Prostaglandins in semen decrease the viscosity of mucus in
the cervix and stimulate reverse peristalsis in the uterus
• Semen Composition (60% from Seminal vesicles, 30%
from Prostate gland, 5% from Bulbourethral glands)
Estrogens
• Increase metabolism, bone formation, endometrial growth,
vaginal lubrication and wall thickness, HDL
• Decrease height growth, muscle mass, LDL, bowel
motility
• Promote female secondary sex characteristics (body hair
and location of adipose tissue)
• CNS effects (possibly increased libido)
• Excess estrogen can cause numerous problems. Plastics
and parabens mimic estrogen
Female Reproductive Cycle (c 163)
• Follicular phase --> Ovulation (14) --> Luteal Phase
• GnRH, LH, FSH, and Estrogen peak day before ovulation
• At ovulation, pulse frequency of GnRH is every 30
minutes (down from 90 minutes earlier in cycle, and once
per day later in cycle)
• Sudden rise in LH results in ovulation (release of ovum
into Fallopian Tubes)
• Temp: lowest at ovulation, highest during Luteal Phase
• Progesterone rises at ovulation and dominates during
Luteal Phase
• Fertile 5 days before ovulation and 1 day after (approx
week 2). Sperm can live for 6 days and must fertilize egg
during the day it’s in the fallopian tube.
Neurophysiology of Sexual Intercourse
• Parasympathetic activity leads to
o Blood engorgement (erection) of penis, clitoris,
nipples. Makes these structures more sensitive
o Release of lubricating fluid from cervical mucous,
vagina, and greater vestibular glands (female)
• Sympathetic activity leads to
o Inhibition of parasympathetic activity above
o Emission of male fluids into ducts (pre-ejaculation)
o (Automatic) loss of male erection after orgasm
Sexual Arousal
• Involves
o Blood engorgement of penis and clitoris
o Vaginal secretion
o Requires dominant parasympathetic activation
• Problems
o Stress--Sympathetic dominance results in impotence
and vaginal dryness
o Alcohol--damages blood vessels
o Smoking—see “Effects of Tobacco”
Orgasm
• Involves rhythmic contractions of skeletal muscles
(ischiocavernosus and bulbospongiosus) innervated by
lumbar spinal nerves
• Not sympathetic or parasympathetic
• Usually involves ejaculation in males, sometimes in
females (Skene’s Gland?)
• Increase in heart rate and blood pressure
• Pleasure derives from activity in CNS (limbic), unrelated
to muscle contractions
• Requires rhythmic stimulus + focused attention
• Same neural design utilized to attain other spiritual states
(ritual, meditation, chanting, etc.)
STDs
Most STDs are asymptomatic, and most people don’t test
themselves for anything besides HIV. See detailed chart.
• Bacteria
o Chlamydia: most commonly treated
o Gonorrhea: males always have symptoms
o Syphilis: rare
• Viruses
o HIV: “AIDS virus”, weak
o Hepatitis (A, B, C): only virus with treatment. 50100x more contagious than HIV
o Herpes: most prevalent: 20-25%, skin transmission,
rarely tested for
o HPV: most commonly acquired: 80%, skin
transmission, untestable in males and easily missed in
females, asymptomatic strains cause cervical cancer
STD Risk Chart Listing Known Risks
[Least to greatest, Possible or unknown risks in brackets]
• Performing oral sex on a woman: Herpes, [HPV]
• Receiving oral sex, women: Herpes, [HPV]
• Receiving oral sex, men: Chlamydia, Gonorrhea, Herpes,
NGU, Syphilis, [HPV]
• Performing oral sex on a man: Chlamydia, Gonorrhea, Hep
A, Herpes, HPV, Syphilis, [Hep B, HIV, Hep C]
• Anal sex, top or bottom: Chlamydia, Gonorrhea,
Crabs/Scabies, Hep B, Herpes, HIV, HPV, NGU (top
only), Syphilis, [Hep C]
• Vaginal sex, man or woman: Chlamydia, Gonorrhea,
Crabs/Scabies, Hep B, Herpes, HIV, HPV, NGU (male
only), Syphilis, Trichomoniasis, [Hep C]
Effects of Tobacco
• Impotence: nicotine reduces nitric oxide (which is THE chemical responsible for erection), increases ET-1 (which causes
vasoconstriction), thickens artery walls thru increased plaque production, and increases clot formation. Erection is all about blood
supply. Smoking is the #1 physical cause of impotence, and increases the risk of it by 50%.
• Decreased fertility rates: smoking reduces sperm count and motility in males and fertility rates for both males and females.
Reduces likelihood of conception by 30%, not counting impotence issue.
• Premature menopause
• Cervical cancer: 4x risk
• Breast cancer: 2x risk with 10 cig/day and 5x risk with 15 cig/day
• Reduced effectiveness of oral contraceptives (the pill)
• Effects on fetus include altered brain chemistry in regards to pleasure and pain regions (child will likely cry more), decreased
oxygen supply, reduced development (lower body weight) due to decreased blood flow to placenta… Increased risk of Sudden
Infant Death Syndrome (SIDS), spontaneous abortions, stillbirths, cleft palettes and lips, respiratory disorders, leukemia, ADHD,
etc,