Ch. 7 Lecture - Nervous System (marieb).ppt (2024)

• Overview & Organization of the Nervous System

• Functions of the Nervous System

The master controlling & communicating system of the body…

• Sensory input —gathering information
• To monitor changes occurring inside and outside the body
• Changes = stimuli
• Integration
• To process and interpret sensory input and decide if action is needed
• Motor output
• A response to integrated stimuli
• The response activates muscles or glands

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• Structural Classification �of the Nervous System

• Central nervous system (CNS) – dorsal body cavity; integrating and command centers; interpret sensory information & give out instructions
• Brain
• Spinal cord
• Peripheral nervous system (PNS) – outside of CNS
• Nerves outside the brain and spinal cord
• Spinal nerves – carry impulses to and from spinal cord
• Cranial nerves – carry impulses to and from brain

• Functional Classification of �the Peripheral Nervous System

• Sensory (afferent) division
• Nerve fibers that carry information to the CNS
• Somatic sensory fibers – deliver impulses from skin, skeletal muscle, and joints
• Visceral sensory fibers (afferents) – deliver impulses from viscera
• Motor (efferent) division
• Nerve fibers that carry impulses away from the CNS
• Somatic (voluntary) NS – voluntary control of skeletal muscles
• Autonomic (involuntary NS – involuntary control of smooth & cardiac muscle and glands
• Divided into sympathetic and parasympathetic NS

• Structure & Function of Nervous Tissue

• Support Cells
• Support cells in the CNS are grouped together as neuroglia (AKA glia or glial cells) = “nerve glue”
• Functions: support, insulate, and protect neurons
• Cannot transmit nerve impulses (as can neurons)
• Never lose their ability to divide (as neurons do)
• Most brain tumors are gliomas
• Types:
• Glia of the Central Nervous System:
• Astrocytes
• Microglia
• Ependymal cells
• Oligodendrocytes
• Glia of the Peripheral Nervous System:
• Schwann cells
• Satellite cells

• Astrocytes
• Abundant (~1/2 of neural tissue)
• Star-shaped cells
• Brace & anchor neurons to capillaries
• Form living barrier between capillaries and neurons (exchange) (blood-brain barrier)
• Control brain’s chemical environment
• Absorb leaked K⁺ ions
• Absorb released neurotransmitters
• Microglia
• Spiderlike phagocytes
• Protect from infection
• Dispose of debris
• Dead brain cells & bacteria

• Ependymal cells
• Line cavities of the brain and spinal cord
• Beating cilia circulate cerebrospinal fluid (CSF)
• CSF fills brain & spinal cord cavities & serves as cushion
• Oligodendrocytes
• Wrap around nerve fibers in the CNS
• Produce fatty insulating coverings = myelin sheaths
• Satellite cells
• Protect neuron cell bodies
• Schwann cells
• Form myelin sheath around nerve fibers in the PNS

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Answer Did You Get It? #’s 2-3

• Neurons

• Neurons = nerve cells
• Cells specialized to transmit nerve impulses from one part of body to another
• Two major regions of neurons:
• Cell body
• Metabolic center: contains nucleus, large nucleolus
• No centrioles = no mitosis
• Nissl substance = specialized RER
• Neurofibrils (intermediate cytoskeleton)
• Maintain cell shape

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• Processes outside the cell body
• Microscopic to 3-4 ft in length
• Longest = from lumbar region of spine to great toe
• Dendrites—conduct impulses toward the cell body
• A neuron may have hundreds
• Axons—conduct impulses away from the cell body
• Arises from cone-like region of cell body called axon hillock
• Collateral branches
• End in highly branched axon terminals
• Axon terminals contain vesicles with neurotransmitters
• Axonal terminals are separated from the next neuron by a synaptic cleft
• Synapse—junction between nerves (syn = clasp/join)

• Myelin sheath—whitish, fatty material covering axons
• Protects & insulates fibers
• Increases rate of nerve impulse transmission
• Schwann cells—produce myelin sheaths in jelly roll–like fashion
• Schwann cells in the PNS; oligodendrocytes in the CNS
• Neurilemma – portion of cell membrane on outer layer of coil where most of its cytoplasm resides
• Nodes of Ranvier—gaps in myelin sheath along the axon
• Aid in speeding up nerve impulses – saltatory conduction
• Homeostatic imbalance – multiple sclerosis = gradual destruction of myelin sheaths (become hardened = sclerosis), autoimmune disease (sheath protein)
• Visual & speech disturbances, loss of muscle control, increasingly disabled
• Interferon injections provide relief; no cure

• Terminology of Neurons

• Most neuron cell bodies are found in the CNS
• Nuclei—clusters of cell bodies within the white matter of the CNS (protected within the brain case and vertebral column)
• Ganglia—small collections of cell bodies in the PNS
• Tracts = bundles of nerve fibers in CNS
• White matter – myelinated tracts in CNS
• Gray matter—cell bodies and unmyelinated tracts in CNS
• Nerves = bundles of nerve fibers in PNS

• Functional Classification of Neurons

Direction of nerve impulse with respect to CNS

• Sensory (afferent) neurons
• Carry impulses from the sensory receptors to the CNS
• Ganglion outside of CNS
• Dendrite endings associate with receptors
• Cutaneous sense organs in muscles and tendons
• Proprioceptors—detect stretch or tension

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Naked nerve ending; pain/temp

Meissner’s corpuscule: touch

Pacinian corpuscule: deep pressure

Golgi tendon organ & muscle spindle;: proprioception

• Motor (efferent) neurons
• Carry impulses from the central nervous system to viscera, muscles, or glands
• Cell bodies always in CNS
• Interneurons (association neurons)
• Connect sensory and motor neurons in neural pathways
• Cell bodies always in CNS

• Structural Classification of Neurons

• Multipolar neurons—many extensions from the cell body
• most common
• Bipolar neurons—one axon and one dendrite
• Rare in adults
• Act in sensory processing – eye, nose
• Unipolar neurons—have a short single process leaving the cell body
• Divides into proximal (central) and distal (peripheral) processes
• Dendrites only at peripheral end
• Conducts action potentials both ways
• Found in sensory neurons of PNS ganglia

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• Physiology of the Nervous System

• Functional Properties of Neurons
• Irritability - ability to respond to stimuli and convert to nerve impulses
• Conductivity - ability to transmit an impulse to other neurons, muscles, or glands
• Nerve Impulses
• Electrical conditions of a resting neuron’s membrane
• Polarized – resting/inactive neuron
• Fewer positive ions on inner face of plasma membrane than on outer face
• Depolarized – stimulated neuron
• More positive ions inside the cell than outside

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• Action Potential Initiation and Generation
• Stimuli excite neurons: light, sound, pressure, mostly neurotransmitters released by other neurons
• Cause a temporary change in the cell membrane’s permeability
• Stimulus causes sodium channel gates to open, and sodium to rush in
• Causes depolarization of the neuron’s membrane
• Inside more positive, outside less positive = graded/local potential
• If stimulus is strong enough, a long distance signal called an action potential or nerve impulse occurs
• Nerve impulses are all-or-nothing responses – they are either propagated over the entire axon or not at all

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• Repolarization
• Membrane immediately becomes impermeable to sodium, but permeable to potassium ions
• K⁺ ions rush out of the neuron, restoring electrical conditions to polarized = repolarization
• Repolarization must occur before another impulse can be conducted
• The sodium-potassium pump, using ATP, restores the original concentrations of Na⁺ and K⁺.
• Saltatory conduction = In myelinated fibers, propagation occurs more quickly since the nerve impulse jumps from node to node.

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• Homeostatic imbalance: factors that impair impulse conduction:
• Sedatives & anesthetics block sodium entry
• Cold & continuous pressure interrupt blood circulation (nutrients & O₂) – e.g. ice creates numbness, foot “goes to sleep”; prickly feeling caused by impulse transmission starting back up

• Transmission of the Signal at Synapses
• Neurotransmitter is released from vesicles within the axon terminal
• Neurotransmitter molecules diffuse across the synapse
• Neurotransmitters bind to receptors in the membrane of the next neuron
• If enough neurotransmitters are released, another nerve impulse will be generated in this neuron
• Enzymes remove the neurotransmitters from the receptors
• Impulse transmission is an electrochemical event – electrical along the neuron’s membrane; chemical within the synapses

Axon�terminal

Vesicles

Synaptic�cleft

Action�potential�arrives

Synapse

Axon of�transmitting�neuron

Receiving�neuron

Neurotrans-�mitter is re-�leased into�synaptic cleft

Neurotrans-�mitter binds�to receptor�on receiving�neuron’s�membrane

Vesicle�fuses with�plasma�membrane

Synaptic cleft

Neurotransmitter�molecules

Ion channels

Receiving neuron

Transmitting neuron

Receptor

Neurotransmitter

Na⁺

Na⁺

Neurotransmitter�broken down�and released

Ion channel opens

Ion channel closes

• Reflexes

• Reflex — rapid, predictable, and involuntary response to a stimulus
• Always travel in one direction
• Occurs over pathways called reflex arcs
• Reflex arc — direct route from a sensory neuron, to an interneuron, to an effector
• Neural pathway involving the CNS and PNS

Stimulus at distal�end of neuron

Skin

Interneuron

Receptor

Effector

Sensory neuron

Motor neuron

Integration�center

(a)

• Types of Reflexes
• Somatic reflexes
• Reflexes which stimulate the skeletal muscles
• Example: moving hand away from a hot stove
• Autonomic reflexes
• Regulate the activity of smooth muscles, heart, and glands
• Examples: salivary reflex, pupillary reflex
• Regulate: digestion, elimination, blood pressure, and sweating

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• Parts of a reflex arc
• Sensory receptor – reacts to a stimulus
• Sensory neuron
• Integration center
• Motor neuron
• Effector organ – muscle or gland which is stimulated

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Stimulus at distal�end of neuron

Skin

Interneuron

Receptor

Effector

Sensory neuron

Motor neuron

Integration�center

(a)

• Patellar (knee-jerk) reflex is an example of a two-neuron reflex arc

Spinal cord

Sensory (afferent)�neuron

Motor�(efferent)�neuron

Sensory receptors�(stretch receptors�in the quadriceps�muscle)

Effector�(quadriceps�muscle of�thigh)

Synapse in�ventral horn�gray matter

Figure 7.11b–c

Inter-�neuron

Motor�(efferent)�neuron

Sensory (afferent)�neuron

Sensory receptors�(pain receptors in�the skin)

Effector�(biceps�brachii�muscle)

(c)

• Flexor (withdrawal) reflex is an example of a three-neuron reflex arc
• Withdrawal reflex arc has an interneuron
• The more neurons involved, the slower the communication because of the time it takes for neurotransmitters to diffuse
• Many spinal reflexes do not involve the brain
• Other reflexes require the brain to evaluate different types of information
• Reflex testing evaluates condition of the nervous system
• Exaggerated, distorted, and absent reflexes indicate nervous system disorders

Answer Did You Get It? #’s 8-11

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• Central Nervous System (CNS)

• CNS develops from the embryonic neural tube
• Runs along the dorsal median plane
• 4^th week – anterior end expands = brain formation
• Rest of tube = spinal cord
• The central canal of the neural tube enlarges into 4 chambers = ventricles
• Filled with cerebrospinal fluid

• Functional Anatomy of the Brain

• ~3 lbs, wrinkled, texture similar to cold oatmeal
• 4 major regions:
• Cerebral hemispheres (cerebrum)
• Diencephalon
• Brain stem
• Cerebellum

• Cerebrum (cerebral hemispheres)
• Paired, superior parts of the brain
• Includes more than half of the brain mass; obscures most of the brain stem
• The surface is made of ridges (gyri = “twisters”) and grooves (sulci = “furrows”)
• Fissures (deep grooves) divide the cerebrum into lobes
• Occipital lobe
• Temporal lobe

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• Cerebral Cortex
• Functions: speech, memory, logic, emotion, consciousness, sensation interpretation, & voluntary movement
• Cell bodies of neurons in cerebral cortex in outermost gray matter
• Primary somatic sensory area
• In parietal lobe posterior to central sulcus
• Receives & interprets impulses from the body’s sensory receptors
• Detects: pain, cold, light touch

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• Visual area in occipital lobe
• Auditory area in temporal lobe
• Olfactory area deep in temporal lobe
• Primary motor area in frontal lobe
• Conscious movement of skeletal muscle
• Axons of these motor neurons form the corticospinal or pyramidal tract
• Descends to spinal cord

• Broca’s area at base of precentral gyrus
• Involved in our ability to speak
• Only located in one (usually left) hemisphere
• Damage here can cause inability to speak – conscious of what you want to say, but unable to do it
• Frontal association areas – higher intellectual reasoning & socially acceptable behavior
• Complex memories stored in temporal and frontal lobes

• Speech/language (Wernicke’s) area – junction of temporal, parietal, & occipital lobes
• Allows us to sound out words
• Usually in just one hemisphere
• Damage: Wernicke’s aphasia – lack of language comprehension; clear speaking though
• Frontal lobes – language comprehension (word meaning)
• Gustatory area – taste – base of primary somatic sensory area (parietal)
• General interpretation area – temporal & parietal

• Cerebral White Matter
• White matter—fiber tracts carrying impulses to, from, and within the cortex
• Corpus callosum – large tract connecting hemispheres; allows hemispheres to communicate with one another
• Called commisures
• Association fiber tracts connect areas within hemispheres; projection fiber tracts connect cerebrum to lower CNS centers
• Basal nuclei (basal ganglia) — islands of gray matter buried within the white matter
• Regulate voluntary

motor activities

• Homeostatic Imbalance:
• Problems with basal

nuclei cause difficulty in

walking or other voluntary

movements: Huntington’s

disease & Parkinson’s

disease

Answer Did You Get It? #’s 12-13

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• Regions of the Brain: Diencephalon (Interbrain)

• Sits on top of brain stem; enclosed by the cerebral hemispheres
• Made of three parts: Thalamus, Hypothalamus, Epithalamus
• Thalamus – relay station for sensory impulses traveling up to sensory cortex
• Crude awareness of a pending sensation being pleasant or not
• Hypothalamus – floor of diencephalon

• Autonomic NS center: helps body temp, water balance, & metabolism
• Limbic system – “emotional-visceral brain” where thirst, appetite, sex, pain, and pleasure centers are
• Regulates the pituitary gland; secretes hormones
• Mammillary bodies – reflex centers involved in olfaction

• Epithalamus
• Forms the roof of the third ventricle
• Houses the pineal body (an endocrine gland)
• Includes the choroid plexus—complex of capillaries which form cerebrospinal fluid

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• Regions of the Brain: Brain Stem

• Small: ~thumb in diameter & ~3” long
• 3 regions: midbrain, pons, & medulla oblongata
• Provides a pathway for ascending & descending tracts
• Contains nuclei with rigidly programmed autonomic behaviors necessary for survival
• Some connected to cranial nerves controlling breathing & blood pressure

• Midbrain
• From mammilary bodies to pons
• Cerebral aqueduct – canal connecting 3^rd ventricle of diencephalon to 4^th ventricle
• Has two bulging fiber tracts — cerebral peduncles: convey ascending & descending impulses
• Mostly composed of tracts of nerve fibers
• Has four rounded protrusions— corpora quadrigemina (“gemini” = twins)
• Reflex centers for vision and hearing

• Pons (“bridge”)
• Rounded part of brain stem just below midbrain
• Mostly composed of fiber tracts
• Includes nuclei involved in the control of breathing
• Medulla Oblongata
• Most inferior part of the brain stem
• Merges into the spinal cord
• Includes important fiber tracts
• Contains nuclei which control:
• Heart rate
• Blood pressure
• Breathing
• Swallowing
• Vomiting
• Fourth ventricle

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• Reticular Formation
• Diffuse mass of gray matter along the length of the brain stem
• Involved in motor control of visceral organs
• Reticular activating system (RAS) plays a role in awake/sleep cycles and consciousness
• Damage here can cause a coma (permanent unconsciousness)

• Regions of the Brain: Cerebellum

• Cauliflower-like, dorsally projecting from under the occipital lobe
• Two hemispheres with convoluted surfaces
• Outer cortex composed of gray matter; inner region composed of white matter
• Provides precise timing for skeletal muscle activity and controls balance & equilibrium
• “Automatic pilot” – compares brain’s intentions with body’s actual performance; initiates appropriate corrective measures

• Homeostatic Imbalance:
• Ataxia – damage to cerebellum can result in clumsy & disorganized movements; appear to be drunk

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Answer Did You Get It? #’s 14-16

• Protection of the Central Nervous System

• Nervous tissue is soft and delicate; neurons injured easily
• Brain and spinal cord protected by
• Scalp and skin
• Skull and vertebral column
• Meninges (membranes)
• Cerebrospinal fluid (watery cushion)
• Blood-brain barrier – protection from harmful substances in the blood

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• Meninges

• Connective tissue membranes which cover & protect the CNS
• Dura mater
• Double-layered, outermost layer; leathery
• Periosteal layer (periosteum)—attached to inner surface of the skull
• Meningeal layer—outer covering of the brain; fuses with the dura mater of the spinal cord
• Layers are fused except in dural venous sinuses where venous blood is collected
• Inward folds attach brain to cranial cavity
• Falx cerebri & tantorium cerebelli

• Arachnoid mater (“spider”)
• Middle layer
• Web-like
• Attached to the pia mater, forming the subarachnoid space
• Filled with cerebrospinal fluid (CSF)
• Arachnoid villi – projections of arachnoid mater; protrude through dura mater
• CSF passes into dural sinuses through these structures
• Pia mater (“gentle mother”)
• Innermost membrane
• Clings tightly brain and spinal cord surfaces

• Epidural injections – “upon the dura”

• Homeostatic Imbalance:
• Meningitis – inflammation of the meninges
• Bacterial or vial infections
• Serious threat to brain if spreads into CNS
• Encephalitis – inflammation of the brain
• Diagnosed by sampling CSF

• Cerebrospinal Fluid (CSF)

• Similar to blood plasma composition
• Less protein, more vitamin C, different ion composition
• Formed from blood by choroid plexuses
• Clusters of capillaries hanging from each of brain’s ventricles
• Forms a watery cushion to protect the brain from trauma
• Circulated in arachnoid space, ventricles, and central canal of the spinal cord

• CSF continually circulates in brain
• From two lateral ventricles, to 3^rd ventricle, through cerebral aqueduct, to 4^th ventricle
• Some CSF continues to spinal cord
• Normally circulates at a constant rate
• Changes to CSF composition may indicate meningitis, tumors, or MS
• Lumbar/spinal tap – sample the CSF
• Remain lying down for 12 hrs or “spinal headache”

• Homeostatic Imbalance - Hydrocephalus

• If something obstructs CSF drainage, it accumulates and exerts pressure on the brain
• “Water on the brain”
• Results in enlarged head in newborns with increasing brain size
• Would cause brain damage in adults
• Treated by surgically inserting a shunt (plastic drain); drains excess fluid into a vein

• Blood-Brain Barrier

• Brain is super sensitive to having a constant internal environment
• Neurons kept separated from bloodborne substances by the blood-brain barrier
• Composed of least permeable capillaries of the body
• Bound by tight junctions
• Allowed to enter:
• Water, glucose, and essential amino acids pass easily through
• Excludes
• Metabolic wastes (urea, toxins, proteins, most drugs), nonessential amino acids, K⁺
• Useless as a barrier against some substances
• Fats and fat soluble molecules
• Respiratory gases
• Alcohol
• Nicotine
• Anesthesia

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Answer Did You Get It? #’s 17-19

• Traumatic Brain Injuries

• Head injuries are leading cause of accidental death in US; caused by damaging blow to head
• Further damage caused by brain ricocheting on opposite end of skull
• Concussion
• Slight brain injury
• Dizzy/”see stars,” briefly lose consciousness
• No permanent brain damage
• Contusion
• Marked tissue destruction occurs
• May remain conscious if cerebral cortex injury; may be in coma if brain stem is injured severely (especially RAS)
• Nervous tissue does not regenerate
• Intracranial hemorrhage
• Bleeding from ruptured vessels
• May cause death
• Cerebral edema
• Brain swelling from the inflammatory response
• May compress and kill brain tissue – neurological deterioration

• Cerebrovascular Accident (CVA/Stroke)

• 3^rd leading cause of death in US
• Blood circulation to brain is obstructed by a blood clot or ruptured blood vessel
• Brain tissue supplied with oxygen from that blood source dies
• Loss of some functions or death may result; undamaged neurons can spread into damaged areas and take over some lost functions (=neuroplasticity)
• Hemiplegia – one-sided paralysis (e.g. right-sided paralysis = damage to left motor cortex)
• Apahsia – damage to language areas
• Motor/Broca’s aphasia – loss of ability to speak
• Sensory/Wernicke’s aphasia – loss of ability to understand written & spoken language
• Transient ischemic attack (ITA) – temporary restriction of blood flow (ischemia) to brain
• Last 5-50 min; numbness, temporary paralysis; impaired speech
• Warning of impending, more serious CVA

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Answer Did You Get It #20

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• The Terrible Three

• Alzheimer’s Disease
• Progressive degenerative brain disease, results in dementia (mental deterioration)
• Mostly seen in the elderly, but may begin in middle age
• Victims experience: memory loss, short attention span, disorientation, eventual loss of language, irritability, moodiness, confusion, sometimes violent, and ultimately, hallucinations.
• Structural changes in the brain include: low Ach, shrinking gyri, brain atrophy (especially in areas of thought and memory), abnormal protein (senile plaque – beta amyloid peptide) deposits, and twisted tau fibers within neurons
• Treat with acetylcholinesterase inhibitors

• Parkinson’s Disease

• Problem associated with basal nuclei; cause not known
• Typically affects people in 50’s-60’s
• Degeneration of dopamine-releasing neurons in the substantia nigra, causing basal nuclei to become overactive
• Symptoms: persistent tremor (even at rest), head nodding, “pill-rolling” of fingers, forward-bent walking posture, shuffling gait, stiff facial expressions, difficulty in initiating movements
• Treatments: L-dopa for some symptoms (bad side effects); deprenyl to slow degeneration; thalamic stimulation via electrodes alleviates tremors; implants of embryonic tissue promising

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• Huntington’s Disease

• Genetic disorder (dominant) – typically occurs at middle-age
• Massive degeneration of basal nuclei and later of the cerebral cortex
• Progressive symptoms: wild, jerky movements (chorea), later marked mental deterioration
• Typically fatal within 15 years
• Overstimulation of motor cortex
• Treat with drugs that block dopamine; fetal tissue implants are promising

• Spinal Cord

• 2-way conduction pathway to and from the brain
• Major reflex center (spinal reflexes)
• Extends from the foramen magnum of the skull to the first or second lumbar vertebra
• Cushioned & protected by meninges
• 31 pairs of spinal nerves arise from the spinal cord
• Cervical & lumbar enlargements – origin of upper & lower limb nerves
• Cauda equina (horse’s tail) is a collection of spinal nerves at the inferior end

• Gray matter of Spinal Cord and Spinal Roots
• Gray matter surrounds the central canal (filled with CSF)
• Dorsal (posterior) horns – project posteriorly
• Contain interneurons
• Sensory neuron cell bodies in dorsal root ganglia; enter spinal cord through dorsal root
• Anterior (ventral) horns – project anteriorly
• Motor neuron cell bodies in ventral horns; axons exit spinal cord through ventral root
• hom*oeostatic imbalance – flaccid paralysis – damage to ventral root = no stimulation of muscles
• Spinal nerves – fusion of dorsal and ventral roots

• White matter of the Spinal Cord
• Myelinated fiber tracts (see 7.22)
• Dorsal, lateral, ventral columns
• Sensory/afferent tracts – conduct sensory impulses to brain
• Motor/efferent tracts – conduct impulses from brain to skeletal muscles
• Dorsal column tracts are all ascending carrying sensory input to brain
• Lateral & ventral tracts contain both ascending & descending tracts
• Homeostatic imbalance – spastic paralysis: transected (cut crosswise) or crushed spinal cord – affected muscles stay healthy b/c still stimulated, but moments become spastic; loss of feeling below injury
• Quadriplegic = 4 limbs affected
• Paraplegic = legs only

Answer Did You Get It? #’s 21-23

• Peripheral Nervous System (PNS)

• Nerves and ganglia outside CNS
• Structure of a Nerve
• Nerve = bundle of neuron fibers outside the CNS
• Neuron fibers are bundled by connective tissue
• Delicate endoneurium surrounds each fiber
• Groups of fibers are bound into fascicles by coarser perineurium
• Fascicles are bound together by tough, fibrous epineurium
• Forms cordlike nerve

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• Nerves are classified according to the direction in which they transmit impulses:
• Mixed nerves – nerves with both sensory and motor fibers
• Sensory (afferent) nerves – nerves carrying impulses toward the CNS
• Motor (efferent) nerves – nerves carrying impulses away from the CNS

• Cranial Nerves

• 12 pairs of nerves that mostly serve the head and neck
• Only the pair of vagus nerves extend to thoracic and abdominal cavities
• Numbered in order; names typically match the structures they control
• Most are mixed nerves, but three are sensory only (optic, olfactory, & vestibulocochlear)

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• Olfactory nerve — sensory for smell
• Optic nerve — sensory for vision
• Oculomotor nerve — motor fibers to eye muscles (most movements, lens shape, & pupil size)
• Trochlear nerve — motor fiber to eye muscle (superior oblique)
• Trigeminal nerve — sensory for the face, nose, & mouth; motor fibers to chewing muscles
• Abducens nerve — motor fibers to eye muscles (lateral movement)
• Facial nerve — sensory for anterior taste buds; motor fibers for facial expression and lacrimal & salivary glands
• Vestibulocochlear nerve — sensory for balance and hearing
• Glossopharyngeal nerve — sensory for posterior taste buds; motor fibers to the pharynx (swallowing & saliva production); carotid artery pressure sensors
• Vagus nerves — sensory and motor fibers for pharynx, larynx, and thoracic & abdominal viscera (mostly parasympathetic = promote digestion & regulate heart activity)
• Accessory nerve — motor fibers to sternocleidomastoid & trapezius
• Hypoglossal nerve — motor fibers for tongue movements; sensory impulses from tongue
• Oh Once One Takes The Anatomy Final Very Good Vacations Are Heavenly.
• Only Owls Observe Them Traveling And Finding Voldemort Guarding Very Secret Horcruxes

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• Spinal Nerves & Nerve Plexuses

• There are 31 pairs formed by the combination of the ventral and dorsal roots of the spinal cord
• Named for the region from which they arise
• Spinal nerves divide after leaving the spinal cord
• Dorsal rami — serve the skin and muscles of the posterior trunk
• Ventral rami — for nerves T₁ -T₁₂ forms intercostal nerves (muscles between ribs & skin and muscles of anterior trunk); for rest of nerves forms a nerve networks (plexus) for limb sensory & motor

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• Cervical plexus – from C₁–C₅ ventral rami
• Phrenic nerve – diaphragm; shoulder/neck muscles
• Brachial plexus – from C₅–C₈ and T₁ ventral rami
• Axillary nerve – deltoid muscle, shoulder skin; superior thorax muscles & skin
• Radial nerve – triceps & extensor muscles; upper limb posterior skin
• Median nerve – flexor muscles; forearm skin; some hand muscles
• Musculocutaneous nerve – arm flexor muscles; lateral forearm skin
• Ulnar nerve – some forearm flexor muscles; wrist & hand muscles; hand skin
• Lumbar plexus – from L₁–L₄ ventral rami
• Femoral nerve – lower abdomen , hip flexors & knee extensors; leg & thigh anteromedial skin
• Obturator nerve – adductor & small hip muscles; medial thigh & hip joint skin
• Sacral plexus – from L₄–L₅ and S₁–S₄ ventral rami
• Sciatic nerve – largest nerve in body; splits into two nerves; lower trunk & posterior thigh surface (hip extensors & knee flexors)
• Common fibular nerve – lateral leg & foot
• Tibial nerve – posterior leg & foot
• Superior & inferior gluteal nerves – gluteal muscles

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• Motor subdivision of the PNS
• Controls body activities automatically
• Special neurons that regulate cardiac muscle, smooth muscle (visceral organs & blood vessels), and glands
• Helps to maintain homeostasis – constantly makes adjustments to keep internal conditions stable
• Consists only of motor nerves

• Somatic vs. Autonomic nervous systems (both PNS)
• Different effector organs and neurotransmitters
• Somatic NS has cell bodies in CNS and an axon that extends to the effector organ
• Autonomic NS has a chain of two motor neurons
• Preganglionic axon – 1^st neuron; in the CNS (“before the ganglion”)
• Postganglionic axon – 2^nd neuron; outside of CNS; goes to organ

• Two divisions of ANS
• Sympathetic & parasympathetic division
• Regulate the same organs, but with opposite effects (counterbalance one another)
• Sympathetic division – mobilizes body during extreme situations (“fight vs. flight”)
• Parasympathetic division – rest and digest; unwind & conserve

CNSPNS

Brain & Spinal Cord Cranial & Spinal Nerves

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Sensory Division Motor Division

(Periphery → CNS) (CNS → Periphery)

Afferent/Incoming Efferent/Outgoing

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Cranial Spinal Somatic Motor NSAutonomic NS

NervesNerves Voluntary Involuntary

(Reflexes)

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Sympathetic Parasympathetic Enteric

Stimulatory Inhibitory GI

• Anatomy of the Parasympathetic Division
• Originates from brain nuclei of cranial nerves (III, VII, IX, & X) and S₂-S₄
• AKA craniosacral division
• Cranial neurons synapse with ganglionic motor neuron in terminal ganglia (basically are at the effector organs)
• Sacral preganglionic neurons form pelvic splanchnic nerves (pelvic nerves) – pelvic cavity
• Always uses acetylcholine as a neurotransmitter

• Anatomy of the Sympathetic Division
• Originates from gray matter in spinal cord from T₁ through L₂
• AKA thoracolumbar division
• Ganglia are at the sympathetic trunk (near the spinal cord)
• Short pre-ganglionic neuron and long post-ganglionic neuron transmit impulse from CNS to the effector
• Norepinephrine and epinephrine are neurotransmitters to the effector organs

• Sympathetic Functioning —“fight or flight”
• Response to unusual stimulus
• Takes over to increase activities
• Remember as the “E” division
• Exercise, excitement, emergency, and embarrassment
• Homeostatic Imbalance – excessive sympathetic NS stimulation
• Type A personality – never slows down; may be susceptible to heart disease, high blood pressure, ulcers
• Parasympathetic Functioning —“housekeeping” activites
• Conserves energy (rest & digest)
• Maintains daily necessary body functions
• Remember as the “D” division
• digestion, defecation, and diuresis

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Answer Did You Get It? #’s 28-30

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• Tracking Down CNS Problems

• EEG – electroencephalography
• Recording of brain neuron’s electrical impulse transmission
• Attach electrodes on scalp
• Record speed of brain waves (unique to each individual)
• Alpha = awake, relaxed state
• Beta = awake, alert state
• Theta = common in children, not normal adults
• Delta = deep sleep

• CT, MRI & PET scans
• CT (computed axial tomography) & MRI (magnetic resonance imaging) – easily identify tumors, intracranial lesions, MS plaques & areas of dead brain tissue (infarcts)
• PET scans – localize lesions that cause epileptic sezures; used for Alzheimer’s diagnosis, and in cancer tumor activity

• Cerebral angiography
• Used to visualize arteries in brain
• Used to guide a catheter carrying clot-busting drugs (tPA)

• Development Aspects of the Nervous System

• The nervous system is formed during the first month of embryonic development; therefore, any maternal infection can have extremely harmful effects
• Maternal measles (rubella) = deafness
• Lack of O₂ for minutes can cause neuron death
• Smoking decreases amount of O₂ in blood; less O₂ to developing fetus’s brain (potentially brain damage)
• Radiation & drugs (alcohol, opiates, cocaine, etc.) can all damage fetal nervous system development

• Development Aspects of the Nervous System

• Homeostatic imbalances:
• Cerebral palsy – poor control and spastic movements of voluntary muscles, seizures, mental retardation, impaired hearing & vision
• Can be caused by lack of O₂ during difficult delivery
• Anencephaly – failure of the cerebrum to develop; cannot hear, see, or process sensory inputs
• Spina bifida – “forked spine”; vertebra fail to completely form; can result in varying degrees of paralysis & loss of bowel and bladder control

• The hypothalamus is one of the last areas of the brain to develop (regulates body temperature_
• Premature babies can’t thermoregulate well
• Continued growth & maturation of nervous system through childhood
• Myelination: cranial to caudal; proximal to distal
• Brain is maximum weight as young adult
• Neurons then continue to get damaged and die
• Steady decline of brain weight and volume
• Can still learn throughout life; unlimited neural pathways available
• Sympathetic NS becomes less efficient (especially in constricting blood vessels)
• Orthostatic hypotension – pooling of blood in the feet due to lack of activation of vasoconstrictor fibers and lightheadness; common in elderly when they stand up quickly

• Arteriosclerosis (plaque build up in arteries) and high blood pressure result in less O₂ supply to brain
• Can causes senility – forgetfulness, irritability, confusion, and difficulty in concentrating and thinking clearly
• Some drugs, low blood pressure, constipation, poor nutrition, depression, dehydration, and hormone imbalances can cause “reversible senility”
• Professional boxers (& other high impact sports) and chronic alcoholics hasten the effects of aging on the brain
• “Punch drunk” – slurred speech, tremors, abnormal gait, dementia in retired boxers
• Reduced brain size in both

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Answer Did You Get It? #’s 31-32