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The Brains of the Operation

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1 The Brains of the Operation
Nervous System The Brains of the Operation

2 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)

3 Remember this from Intro Unit?

4 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

5 Two subdivisions of motor (efferent):
Somatic nervous system – voluntary Conscious control of skeletal muscles Autonomic nervous system - involuntary Controls smooth/cardiac muscle & glands

6 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

7 Overview (yes, copy this down)

8 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)

9 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 nucleus except no centrioles (no mitosis) Processes/fibers – arms that extend to/from body To body = dendrites (1-100s) From body = axon (only 1)

10 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

11 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

12 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

13 Functional Neuron Types

14 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

15 Structural Neuron Types

16 2. Support Cells 2a. 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

17 2b. Microglia Spiderlike phagocytes (cell eaters)
Dispose of debris like dead brain cells & bacteria

18 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

19 2d. Oligodendrocyte Wrap flat extensions tightly around nerve fibers
Produces fatty insulating covering of axons called myelin sheaths in CNS

20 2e. Schwann Cells Form myelin around axons in PNS

21 2f. Satellite Cells Protective, cushioning cell body in PNS

22 Nerve Cells of CNS

23 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)

24 - - - - - - - - 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 - Na+ K+ - Na+ Na+ Na+ Na+ Na+ - - - K+ K+ K+ K+ - K+ - - Na+

25 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 potential in entire neuron

26 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

27 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


29 Recap

30 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

31 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

32 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 (brain) – connect neurons Motor neuron – connect CNS & effector Effector organ – muscle/gland to be stimulated

33 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

34 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

35 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

36 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

37 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

38 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

39 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.

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

41 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

42 Sensory & Motor Areas of Cerebral Hemisphere


44 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 callosum connects right & left cerebral hemisphere


46 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)

47 Diencephalon

48 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

49 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

50 Brain Structure Recap Structure Subdivision Function Cerebrum
Frontal Lobe Speech, logic/reason, social behavior, language comprehension Parietal Lobe Receives sensory input (pain, cold, light touch) Temporal Lobe Auditory cortex, olfactory cortex Occipital Lobe Visual cortex Diencephalon Thalamus Sensory impulse relay station Hypothalamus Regulates body temp, water balance, metabolism, sex, pain, pleasure, pituitary gland Epithalamus Regulates pineal gland, choroid plexus (cerebrospinal fluid) Brain Stem Midbrain Reflex center for vision & hearing Pons breathing Medulla oblongata Controls heart rate, blood pressure, breathing, swallowing, vomiting Cerebellum none Muscle coordination, balance, equilibrium

51 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

52 Membranes Three connective tissue membranes called meninges cover & protect CNS 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

53 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


55 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


57 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

58 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 cauda equina (horse’s tail) Covered by meninges for protection

59 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

60 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

61 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

62 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

63 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

64 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

65 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

66 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

67 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

68 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

69 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

70 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

71 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

72 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

73 Parkinson’s Disease Degeneration of dopamine-releasing neurons in substantia nigra (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 substantia nigra tissue, or genetically engineered (stem cells), or cells from fetal pigs

74 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

75 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

76 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%.

77 Multiple Sclerosis Will result in complete inability to function
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

78 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

79 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

80 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

81 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

82 Computed Tomography (CT or CAT) scan
Used to see tumors, lesions, MS or Alzheimer’s plaques, infarcts (dead brain tissue) Important in mapping brain prior to surgery

83 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

84 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

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