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Nervous System. The Brains of the Operation. Functions. Three major functions: 1 . Receive sensory input Gather info by monitoring changes or stimuli from inside & outside body 2. Integration of input Process & interpret sensory input & determine action 3. Motor output

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nervous system

Nervous System

The Brains of the Operation

functions
Functions
  • Three major functions:
    • 1. Receive sensory input
      • Gather info by monitoring changes or stimuli from inside & outside body
    • 2. Integration of input
      • Process & interpret sensory input & determine action
    • 3. Motor output
      • Carry out response decided by integration usually by muscles (movement) or glands (secretion)
organization
Organization
  • Two major parts of nervous system:
    • Central nervous system (CNS)
      • Brain
      • Spinal cord
    • Peripheral nervous system (PNS)
      • All nerves (spinal & cranial) outside of CNS
      • Two components:
        • Sensory (afferent) division
          • Info going TOWARD CNS
        • Motor (efferent) division
          • Impulses EXIT from CNS
slide5

Two subdivisions of motor (efferent):

    • Somatic nervous system – voluntary
      • Conscious control of skeletal muscles
    • Autonomic nervous system - involuntary
      • Controls smooth/cardiac muscle & glands
slide6

Two subdivisions of autonomic that often bring about opposite effects:

    • Parasympathetic – stimulate rest & digest activities
      • Ex: stimulate flow of saliva
    • Sympathetic – stimulate flight or fight activities
      • Ex: inhibit flow of saliva
structure of nervous tissue
Structure of Nervous Tissue
  • Classified into two types of cells:
    • Neurons – transmit nerve impulses; no cell division (amitotic)
    • Support cells (called neuroglia or glia) that can not transmit nerve impulses; cell division (mitotic)
      • Astrocytes
      • Microglia
      • Ependymal cells
      • Oligodendrocytes
      • Satellite cells
      • Schwann cells

Central nervous system (CNS)

Peripheral nervous system (PNS)

neurons
Neurons
  • Also known as nerve cells
  • Structure allows them to receive & transmit messages or impulses
  • All have same basic structures
  • Cell body – usual cell organelles including nucleusexcept no centrioles (no mitosis)
  • Processes/fibers – arms that extend to/from body
    • To body = dendrites (1-100s)
    • From body = axon (only 1)
slide10

Must know cell parts:

    • Soma - cell body
    • Nucleus – metabolic center of cell
    • Dendrite(s) – one or more processes that conducts impulses TOWARD cell body
    • Axon hillock – where cell branches out to axon
    • Axon – process that conducts impulses AWAY from cell body
    • Myelin – whitish, fatty substance found on long axons in CNS; speeds up transmission rate
    • Schwann cells – cells that myelinate axons in PNS
    • Myelin sheath – membranes wrapped around myelin
    • Nodes of Ranvier– gaps in between Schwann cells
    • Axon terminal – branched end of axon in which neurotransmitters are stored in vesicles
slide11

Large concentrations of cell bodies in CNS are in clusters & called nuclei

  • Small concentrations are called ganglia (pl) or ganglion (sing) – found in CNS & PNS
  • Bundles of nerve fibers in CNS called tracts, but in PNS are called nerves
    • Myelinated nerve fibers/tracts in CNS called white matter
    • Unmyelinated fibers and cell bodies called gray matter
slide12

Three types of neurons based on function or direction of nerve impulse:

    • Sensory (afferent) neurons
      • Carry impulses from sensory receptors TOWARD CNS
        • Nerve endings – pain & temperature receptors
        • Meissner’s corpuscle – touch receptor
        • Pacinian corpuscle – deep pressure receptor
        • Proprioceptors – stretch or tension in tendons & muscles
    • Motor (efferent) neurons
      • Carry impulses FROM CNS to organs or muscles
    • Association neurons/interneurons
      • Connect motor & sensory neurons
slide14

Three types of neurons based on structure or how many processes extend from body

    • Unipolar
      • Single, very short process from cell body
      • Immediately breaks into peripheral & central axon
        • Unique: dendrites at peripheral end, so axon conducts impulses away and TO cell body
    • Bipolar
      • One axon, one dendrite
      • Very rare, only seen sense organs (eye & nose)
      • Act as receptor cells
    • Multipolar
      • Several processes extend from cell body
      • All motor neurons are multipolar so they are most common
2 support cells 2a astrocytes
2. Support Cells2a. Astrocytes
  • Star-shaped
  • Account for ~ 50% of neural tissue
  • Form living barrier between capillaries & neurons therefore make exchanges between them
  • Help protect neurons from harmful substances
  • Pick up extra ions
  • Recapture released neurotransmitters
2b microglia
2b. Microglia
  • Spiderlike phagocytes (cell eaters)
    • Dispose of debris like dead brain cells & bacteria
2c ependymal cells
2c. Ependymal Cells
  • Covered with cilia
  • Line cavity of brain & spinal cord
    • Beating of cilia help circulate cerebrospinal fluid that fills brain & spinal cord cavity
    • Forms protective cushion around CNS
2d oligodendrocyte
2d. Oligodendrocyte
  • Wrap flat extensions tightly around nerve fibers
    • Produces fatty insulating covering of axons called myelin sheaths in CNS
2e schwann cells
2e. Schwann Cells
  • Form myelin around axons in PNS
2f satellite cells
2f. Satellite Cells
  • Protective, cushioning cell body in PNS
d nerve impulse
D. Nerve Impulse
  • Recall a neuron has two distinct properties that differentiate it from any other cell in the human body:
    • Irritability - ability to respond to stimuli & convert it to a nerve impulse
    • conductivity - ability to transmit an impulse to other neurons, muscles, or glands
  • Most CNS neurons receive chemical stimulus at plasma membrane (everywhere on neuron), transmits it as electrical signal along axon, & ends as chemical signal at axon terminals
  • Most PNS neurons (sensory organs) receive stimulus as light (eyes), sound waves (ears), pressure (touch), chemicals (taste), or chemicals (smell)
slide24

plasma membrane is where nerve impulse begins

  • Plasma membrane at rest is polarized
    • fewer positive ions (K+) are inside cell than positive ions (Na+) outside cell
    • More negative (Cl-) ions inside cell than outside

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slide25

a stimulus depolarizes neuron’s membrane by opening up Na+ gates on membrane, allowing Na+ inside

  • initial exchange of ions is a local depolarization
    • Inside is more + than outside
  • Depolarization starts an action potentialin entire neuron
slide26

Once action potential (nerve impulse) starts, it’s propagated over entire axon (all or nothing principle)

  • K+ ions rush out of the neuron after Na+ ions rush in, which repolarizes the membrane
  • Na+/K+pump on membrane restores original configuration by shoving Na+ back out and allowing K+ back in
    • requires ATP
slide27

Impulse travels faster when fibers have a myelin sheath

  • Once electrical action potential reaches axon terminals, excites vesicles containing neurotransmitters
  • Vesicles move toward axon terminal membrane & releases neurotransmitter into synaptic cleft
    • Neurons NEVER touch other neurons
    • Neurotransmitters bind to receptors on neighboring neuron’s dendrites
    • New action potential will start on THAT one
slide29

The human body uses 50 different neurotransmitters depending on the need

  • Neurotransmitters either excite or inhibit neurons
    • Many drugs act to mimic the effect of neurotransmitters on the brain
e reflexes
E. Reflexes
  • Much communication between neurons on everyday basis is done via reflexes
    • Reflex: rapid, predictable, involuntary responses to stimuli
  • Reflex always occurs in same manner using same neural pathways of both CNS & PNS so they are called reflex arcs
slide33

Two types of reflexes:

    • Somatic: stimulates skeletal muscles
      • Ex: pull hand away from hot object, blinking when air burst aimed at eyes
    • Autonomic: regulate smooth & cardiac muscles, & glands
      • Ex: secretion of saliva, change in pupil size
slide34

Reflex arcs have at least 5 elements involved in same arc or pattern:

    • Sensory receptor – react to stimulus
    • Sensory neuron – connect receptor & CNS
    • Integration center – connect neurons
    • Motor neuron – connect CNS & effector
    • Effector organ – muscle/gland to be stimulated
slide35

patellar (knee-jerk) reflex is simplest type of reflex – two neurons involved

  • Withdrawal reflex (remove from painful stimulus) is more complicated – three neurons involved utilizing association neuron
f brain structure functions
F. Brain Structure & Functions
  • Average adult brain weighs 3 lbs
  • Divided into 4 regions:
    • Cerebrum – largest region, broken into left & right hemispheres
    • Diencephalon – interbrain atop brain stem
    • Brain stem – stalk on which brain sits, connects to spinal cord
    • Cerebellum – bulbous projection at occipital region, broken into two hemispheres
1 cerebrum
1. Cerebrum
  • Made of two hemispheres together called cerebrum
  • Encloses other three parts of brain
  • Entire surface made of peaks and valleys
    • Gyrus (gyri) – peaks of ridges
    • Sulcus (sulci) – shallow valleys
    • Fissures – deep grooves separating large regions
slide38

Function of cerebrum is vast

    • speech, memory, logical & emotional response, consciousness, interpretation of sensation, voluntary movement
  • Sulci & fissures divide cerebrum into lobes (named after cranial bones)
    • Parietal lobe
    • Frontal lobe
    • Temporal lobe
    • Occipital lobe
slide39

Parietal Lobe

    • Somatic sensory area located just posterior to central sulcus receives & interprets impulses from body’s sensory receptors (NOT special senses)
      • Pain, cold, light touch
slide40

Spatial map depicting region on body where senses come from and how much brain power is devoted to them is called sensory homunculus

Model depiction showing areas of body given more brain “power” than others

slide41

Sensory pathways are crossed pathways, meaning left side of brain receives impulses from right side of body & vice versa

    • Itch on right hand interpreted on left side of somatic sensory area.
slide42

Occipital lobe

    • Visual area located in posterior part
  • Temporal lobe
    • Auditory area bordering lateral sulcus
    • Olfactory (smell) area deep inside
slide43

Frontal lobe

    • Contains primary motor area, just anterior to central sulcus, which allows us control of skeletal muscles
    • Spatial map region called

motor homunculus

    • Broca’s area – located in

left hemisphere gives

ability to speak

    • Higher intellectual reason
    • Socially acceptable

behavior

    • Language comprehension
slide46

Two layers of cerebral hemisphere:

    • Gray matter (cerebral cortex)
      • Outermost layer made out of cell bodies of neurons (no myelin)
      • Ridges allow greater surface area, increasing amount of neurons
      • Several islands of gray matter that jut inward called basal ganglia
    • White matter
      • Deeper cerebral layer made from fiber tracts (bundles of nerve fibers)
      • Major tract called corpus callosumconnects right & left cerebral hemisphere
2 diencephalon
2. Diencephalon
  • AKA interbrain, made of 3 areas:
    • Thalamus – relay station for sensory impulses going up to sensory cortex
      • Get rough idea if sensation will be pleasant or unpleasant – sensory cortex figures it out
    • Hypothalamus – regulates body temperature, water balance (thirst), metabolism (appetite), sex, pain, pleasure, pituitary gland
      • Pituitary gland is attached & secretes hormones
    • Epithalamus – pineal gland(secretes hormones) & choroid plexus (knots of capillaries that form cerebrospinal fluid)
3 brain stem
3. Brain Stem
  • Made of 3 structures:
    • Midbrain – reflex centers for vision & hearing
    • Pons – fiber tracts that control breathing
    • Medulla oblongata – control heart rate, blood pressure, breathing, swallowing, vomiting
  • Many small gray matter areas that control breathing, blood pressure
  • Running along length is reticular formation which regulates consciousness, awake/sleep cycles
    • Damage here results in permanent unconsciousness or coma
4 cerebellum
4. Cerebellum
  • Two hemispheres & wrinkly (convoluted) surface
    • Outer cortex is gray matter while inner region is white matter called arbor vitae (tree of life)
  • Provides timing for muscle activity, controls balance & equilibrium
    • Constantly monitors body position & makes adjustments to keep balance
g protection of cns
G. Protection of CNS
  • As nervous tissue is very soft and delicate, injury to irreplaceable neurons can be catastrophic
  • Three methods of protection:
    • Bony skull & vertebral column
    • Membranes
    • Cerebrospinal fluid
membranes
Membranes
  • Top: Dura mater (“tough mother”)
    • Periosteal layer (touches skull)
    • Meningeal layer
  • Middle: Arachnoid mater (“spider mother”)
    • Looks like a cobweb
  • Bottom: Pia mater (“gentle mother”)
    • Clings gently but tightly to brain surface
  • Three connective tissue membranes called meninges cover & protect CNS
csf cerebrospinal fluid
CSF (Cerebrospinal Fluid)
  • Watery broth similar to blood plasma
  • Constantly formed by choroid plexuses
    • Little protein, lots of vitamin C, lots of ions
  • Always circulating among ventricles, canals, & aqueducts in brain
    • Spinal tap removes CSF from lumbar area
slide57

Brain can not handle tiniest fluctuations of chemicals (all kinds) as other organs can

  • As result, neurons are kept separated from blood borne substances by “blood-brain barrier” which is composed of least permeable capillaries in human body
    • Only water, glucose, essential amino acids, fats, respiratory gases, and fat-soluble alcohols, nicotine, caffeine, and anesthetics can pass
    • Metabolic wastes (urea), toxins, proteins, most drugs are prevented
    • Nonessential amino acids & K, are always pumped from brain
h spinal cord
H. Spinal Cord
  • The other component of CNS, it’s a two-way conduction pathway from PNS & brain composed of neurons with long axons
  • Reflex center where reflexes are determined
slide60

17” long spinal cord is continuation of brain stem ending at L2

  • Starting at L3, branched into 31 pairs of spinal nerves exit vertebral column called caudaequina(horse’s tail)
    • Cervical – 8 pairs
    • Thoracic – 12 pairs
    • Lumbar – 5 pairs
    • Sacral – 5 pairs
  • Covered by meninges for protection
slide61

Gray matter of spinal cord resembles butterfly

    • Posterior projections = posterior/dorsal horns
    • Anterior projections = ventral/anterior horns
    • Gray matter surrounds central canal which contains CSF
    • Spinal (nerve) fibers entering spinal cord
slide62

White matter composed of myelinated fiber tracts

    • Divided into three regions: posterior, lateral, anterior columns
    • Two types of tracts
      • Sensory/afferent tracts: conduct sensory impulses TO the brain
      • Motor/efferent tracts: carry impulses FROM brain to skeletal muscles
i peripheral nervous system pns
I. Peripheral Nervous System (PNS)
  • Consists of nerves & scattered groups of ganglia found outside CNS
  • Nerve is bundle of neuron fibers not in CNS
    • Neuron fibers (processes) surrounded by endoneurium
    • Groups of fibers bound by perineurium
    • Whole bundles called fascicles
    • Fascicles bound together by epineurium
slide64

Nerves carrying both sensory & motor fibers called mixed nerves

    • All spinal nerves are mixed
    • Sensory (afferent) nerves – toward CNS
    • Motor (efferent) nerves – away from CNS
  • Cranial nerves – 12 pairs that serve head and neck
slide65

Spinal nerves – 31 pairs formed by both dorsal & ventral roots of spinal cord

    • Ventral rami (extension) forms four plexuses (network of nerves) which are both sensory & motor
slide66

Three nerves to know:

    • Sciatic nerve
      • part of sacral plexus
      • Largest nerve in body
      • Serves lower trunk & posterior thigh/leg
      • Inflammation or damage causes sciatica
slide67

Median nerve

    • Part of brachial plexus
    • Allows flexion of forearm & some hand muscles
    • Pressure on nerve from tendon causes carpal tunnel syndrome
      • Inability to pick up small objects, fine motor control
slide68

VII Facial nerve

    • 7th cranial nerve
    • Serves muscles for facial expression, salivary & lacrimal (tear ducts) glands, taste buds
    • Weakening or paralysis causes Bell’s palsy
j autonomic nervous system
J. Autonomic Nervous System
  • Involuntary motor branch of PNS that controls smooth muscles, cardiac muscles, glands
  • Information from CNS activates nerves that release neurotransmitters which then signal appropriate muscle/gland
slide70

Recall two divisions of ANS that have opposite effects:

    • Sympathetic – extreme situations (fear, exercise, rage)
    • Parasympathetic – rest & conserve energy
  • Three neurotransmitters in ANS:
    • Acetylcholine – both sympathetic & parasympathetic
    • Epinephrine – sympathetic division
    • Norepinephrine – sympathetic division
k development
K. Development
  • Formation
    • Nervous system formed during first 4 weeks of embryonic development
    • Maternal infection or poor health habits may cause permanent damage
      • Measles causes deafness
      • Smoking decreases oxygen causing low birth weight, others
      • Drugs (OTCs & illegal) can permanently damage
slide72

Maturation

    • Last areas of CNS to mature is hypothalamus
      • Preemies have problems controlling body temperature
    • Throughout childhood, no neurons grow but in fact become myelinated, allowing neuromuscular control
slide73

Aging

    • Brain at maximum weight as young adult
    • Next 60+ years, neurons get damaged & die
      • Other unused pathways can take over & be developed
    • Sympathetic nervous system becomes less efficient
    • Premature shrinking of brain occurs when individuals accelerate normal process with lifestyle
      • Boxers, alcoholics, drug abusers
l diseases injuries
L. Diseases/Injuries
  • Huntington’s Disease
    • Dominant genetic disease (one dominant allele needed) for 50% chance of acquiring it
    • Strikes in middle age (around 50)
    • Massive degeneration of basal nuclei then cerebral cortex
    • Initial symptoms are wild, jerky movements termed chorea (Latin for dance)
    • Usually fatal within 15 years of onset
    • Treated with neurotransmitter (dopamine) blockers
slide75

Parkinson’s Disease

    • Degeneration of dopamine-releasing neurons in substantianigra(in midbrain) so basal nuclei dopamine targets becomes overactive, causing tremors
    • Treatment with L-dopa drugs helps some symptoms, but after more neurons are affected, it is ineffective
    • Newer (albeit controversial) treatments include transplanting embryonic substantianigra tissue, or genetically engineered (stem cells), or cells from fetal pigs
slide76

Alzheimer’s

    • Progressive degenerative disease that results in dementia (mental deterioration)
    • Nearly 50% of all people in nursing homes have Alzheimer’s
    • Begins with short-term memory loss, short attention span, disorientation, loss of language
    • Result of shortage of acetylcholine & structural changes in brain (areas of cognition & memory)
    • Microscopy of tissue shows abnormally large deposits of protein
    • About 5-15% of people over 65 will get this
slide77

Stroke (Cerebrovascular Accident/CVA)

    • Blood circulation to brain area is blocked resulting in tissue death
      • Blood clot
      • Ruptured blood vessel
    • Area of tissue is initially located by looking at patient’s symptoms
      • Left cerebral hemisphere results in aphasia (language impairment)
    • Severe strokes kill 2/3 people almost immediately, and remaining 1/3 die within 3 years
    • Mild strokes do not cut off blood flow completely
      • Called temporary brain ischemia or transient ischemic attack (TIA)
      • Not permanent but offer warning signs of CVA later
slide78

Spinal Cord injuries (SCI) & Paralysis

    • Any damage to the spinal cord resulting from crushing or severing.
    • Cervical injuries
      • Cervical (neck) injuries usually result in full or partial tetra/quadriplegia.
    • Thoracic injuries
      • Injuries at or below the thoracic spinal levels result in paraplegia.
      • T1 to T8 : inability to control the abdominal muscles.
      • T9 to T12 : partial loss of trunk and abdominal muscle control.
    • Lumbar and sacral injuries
      • Decreased control of the legs and hips, urinary system, and anus.

There are about 11,000 new cases of spinal cord injury in the U.S. every year.

Males account of 82% of all spinal cord injuries and females for 18%.

slide79

Multiple Sclerosis

    • Autoimmune disease in which myelin sheaths around axon fibers in CNS are gradually destroyed by own immune system
    • Myelin converts to hardened sheaths called scleroses
    • Lack of insulation leads to inability to control muscles
    • Treatment today includes hormone-like substance called interferon
    • Will result in complete inability to function
slide80

Meningitis

    • Inflammation of meninges due to viruses or bacteria
    • Can be life threatening since can spread to nervous tissue of CNS
    • Diagnosed by spinal tap to look at CSF
m diagnosing problems
M. Diagnosing Problems
  • EEG (electroencephalogram)
    • Assess electric activity of brain impulses
    • Many electrodes are placed on scalp and measurement of activity pattern is recorded
    • Used to diagnose epileptic lesions, tumors
slide82

PEG (pneumoencephalography)

    • Detection of hydrocephalus (water on brain)
    • Cerebrospinal fluid is drained via spinal tap, air is injected into subarachnoid space
    • Provides clear picture of ventricles
    • Extremely painful for patients – recovery takes 2-3 months for CF to return back to normal
    • Not used since 1980s
slide83

Cerebral angiogram

    • Used to assess condition of cerebral arteries
    • Dye is injected into artery & disperses into brain
    • X-ray is then taken which highlights dye so blood flow can be assessed
      • Stroke victims
slide84

Computed (Computer- Aided) Tomography (CT or CAT) scan

    • Series of X-rays grouped together by a computer.
    • Used to see tumors, lesions, MS or Alzheimer’s plaques, infarcts (dead brain tissue)
    • Important in mapping brain prior to surgery
slide85

MRI scan (Magnetic Resonance Imagery)

    • Used to see tumors, lesions, MS or Alzheimer’s plaques, infarcts (dead brain tissue)
    • Similar to CT scan but 3D image capabilities
slide86

PET scan (Positron Emission Tomography)

    • Used to determine sugar (glucose) uptake/usage of cells
      • Faster growing cells (cancer) use sugar faster
      • Active brain areas also use sugar faster
        • Alzheimer, Parkinson, epilepsy, tumors, dementia
    • Patient drinks glucose solution, areas of fast uptake show up on image