Lecture 6: Nervous System Flashcards Preview

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Flashcards in Lecture 6: Nervous System Deck (84):
1

Neuron

aka cyton or soma (cell body) with one or more nerve process
processse include dendrites conducting impulses to the cell body, and axons conducting them away

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synapse

junction of axon of one neuron with another neuron's cell body or dendrite

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Groups of cell bodies

within the CNS=nuclei
outside the CNS=ganglia

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bundle of nerve processes

inside the CNS=fasciculi or tracts
outside the CNS=nerves

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Central Nervous System comprised of

the dorsal cavity, aka the brain and spinal cord
protected by cranial skull, vertebrae, and dura matter

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Peripheral nervous system is comprised of

cranial and spinal NERVES;
split into the autonomic nervous system and the somatic portion

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autonomic nervous system comprised of

sympatheic (thoraco-lumbar outflow) and parasympathetic (cranio-sacral outflow)

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brain

includes cerebrum, cerebellum, and brain stem
has four ventricles filled with cerebrel spinal fluid

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brain is divided into three parts

forebrain=telencephalon (cerebrum) and diencephalon
midbrain=mesencephalon (thalamus)
hindbrain=metencephalon (pons and cerebellum) and myelencephalon (medulla oblongata)

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telencephalon

cerebral cortex, corpora callosum and smell centre
-encloses the cavities of the lateral ventricles

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cerebrum

two hemispheres with ridges (gyri) and furrows (sulci); gray matter on the surface, white at center, and used for voluntary muscle control, interpretation of sensations, and reasoning

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corpus striatum/callosum

connects each cerebral cortex with another part of CNS

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Rhiencephalon

smell/olfactory brain

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diencephalon

thalamus, epithalamus, hypothalamus, most of the third ventricle, and entry site for optic nerves

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thalamus

relay centre for nerve fibers connecting cerebrum to brain stem and spinal bord

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hypothalamus

includes the hypohysis and pituitary gland; ANS and hormone control

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mesencephalon

cerebral peduncles and 4 quadrigeminal bodies=anterior for vision and caudal for hearing

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cerebral peduncles

continuations of the spinal cord and the brain stem into the respective cerebral hemispheres, containing fiber tracts and nuclei

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metencephalon

cerebellum and pons

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cerebellum

many folds, two hemispheres
gray matter surface, white matter center
coordination of voluntary movements

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pons

bridge of fibers between hemispheres
otehr fiber tracts and nuclei

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4th ventricle

part of the metencephalon, between the cerebellum and pons and brain stem

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myelencephalon

aka medulla oblongata, it is a continuation of the spinal cord
control respiration, circulation, digestion, and helps relay signals between brain and spinal cord

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brain stem

=medulla oblongata, pons, and midbrain, many cranial nerves are hosted here
-controls respiration and circulation

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ventricles

chambers filled with CSF
each has a CHOROID PLEXUS: a network of capillaries
connected with subarachnoid space of brain/spinal cord

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meninges

covering of brain and spinal cord
consists of dura matter, arachnoidea, and pia matter: site of infection for meningitis

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spinal cord

continuation of medulla oblongata
distinct segments: pairs of spinal nerves, usually one per vertebra
-sensory=afferent fibers from DORSAL roots
-motor=efferent fibers from VENTRAL roots
central gray matter (gray horns), of mainly nerves cell bodies and processes and white external

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tracts of spinal cord: peripheral white matter

on each side: doral white column, lateral white column, and ventral white column

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dorsal white column

afferent tracts: give sense of position

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lateral white ventral column

1. dorsal and ventral spinocerebellar
2. rubrospinal
3. lateral spinothalamic
4. lateral corticospinal

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dorsal and ventral spinocerebellar

to the cerebellum, aid in coordiation of movements

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rubrospinal

from red nucleus in the midbrain to motor cells in the opposite side verntal gray horn: receive feedback from cerebellum

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lateral spinothalamic

fibers from dorsal gray horn (opposite side) to the thalamus: monitor pain and temperature

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lateral corticospinal

from motor area of cerebrum to ventral gray horn: aid voluntary movement

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ventral white column

direct vestibulospinal tract
crossed vestibulospinal tract
ventral corticospinal tract
-their impulses are associated with voluntary motor activity

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direct vestibulospinal tract

from the lateral vestibular nucleus to motor nuclei in spinal cord
-set the tone of the extensor muscle

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crossed vestibulospinal tract

from the descending vestibular nucleus to motor centres of the opposite side of spinal cord

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ventral corticospinal/cerebrospinal tract

connects motor area of cerebrum with spinal cord (same and opposite sides)

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Spinal Nerves

supply sensory and motor fibers to regions of body in area where they emerge from the spinal cord
-limbs are supplied with sensory and motor fibers by nerve bundles called plexuses

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brachial plexus

supplies nerves to forelimbs
derived from last 3 or 4 cervical and first 1 or 2 thoracic spinal nerves

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lumbosacral plexus

supplies hind limbs
derived from ventral branches of last few lumbar and first 1, 2, or 3 sacral nerves

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ventral root

carries efferent motor neurons to muscles and glands

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dorsal root

carries afferent sensory info to CNS

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gray matter

consists of cell bodies of interneurons and some motor/efferent neurons

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white matter

consists of axons carrying info through spinal cord to brain (afferent/sensory neurons)

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cranial nerves

12 cranial nerves, no dorsal or ventral roots, emerge through various foramina of skull
-some are strictly sensory/afferent, and some mixed (while all spinal nerves are mixed)

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cranial nerve list

olfactory, optic, occulomotor, trochlear (eye movement), trigeminal (chewing), abducens (eye move), facial, auditory (acoustic or vestibulocochlear), glossopharyngeal (taste/swallow), vagus (internal organs), spinal accessory (shoulders and neck) and hypoglossal (tongue)

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Autonomic Nervous System

-visceral part of PNS
-innervates the smooth muscle, cardiac muscle, and glands
-sympathetic/parasympathetic
most auto efferent nerves synapse outside CNS:
-preganglionic neurons from CNS
-ganglions, and post ganglionic neurons to viscera
-afferent nerves have no cell bodies or synapses outside CNS

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sympathetic nervous system

-from thoracic and lumbar spinal nerves
-efferent fibers from lateral gray column of t&l, along ventral root
-preganglionic sympathetic neurons=myelinated synapse with secondary neurons (post-ganglionic) in ganglions close to spinal column

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ganglionated sympathetic trunk

symp. ganglia interconnected, receives white rami communications from spinal nerves
-contains fibers to nerve trunks and plexuses to viscera, ie. greater and lesser splanchnic nerves, preganglionic fibers to adrenal medulla

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Parasympathetic nervous system

-4 cranial nerves and sacral spinal nerves
-includes occulomotor (3), facial (7), glossopharyngeal (9), which control smooth muscle and glands of head region
-vagus (10) controls heart, lungs, and most viscera
-sacral nerves control last part of digestive system, most urogenital; synapse with secondary/postganglionic neurons in ganglion near to organs, making postganglionic parasymp neurons short

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Summary of Sympatheic NS

-derived from thoracic and lumbar segments of spinal cord
-preganglionic fibers are relatively short
-post ganglionic fibers from sympathetic ganglia to organs are LONG
-prepares for high activity
-release of norepinephrine (adrenaline)

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summary of parasympathetic

-derived from cranial nerves and sacral portion of the spine
-preganglionic fibers are LONG
-postganglionic fibers are short
-prepares for low activity
-release of acetylcholine

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supporting tissue in CNS and PNS

CNS=neuroglia
PNS=ordinary white fibrous connective tissue

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Structure of neuron

processes:thin, few organelles
cell body: large mass of cytoplasm, nucleus, and one or more nucleoli
other: mitochondria, fibrils, golgi network, and centrosome, endoplasmic reticulum

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neuron class by processes

pseudo unipolar neuron: cell body aside processes
dipolar neuron: body between processes, one dendrite, one axon, used for smell, sight, and balance
multipolar neurons: several dendrites but one axon

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motor nerves end in

each terminal branch supplying a single muscle fiber

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Myelinated nerve fibers

white: sheath of fatty material with many layers of schwann cells wrapped around the nerve fiber

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Unmyelinated nerve fibers

gray: surrounded, not wrapped, by ONE layer of schwann cells

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functions of neurons

irritabilty and conductivity of signals
-perception of changes in exterior environment
-perception of changes in interior environment
-ability to adapt to these changes

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resting potential

-electrical difference between neg. charges inside membrane next to axoplasm and pos. charges outside
-produced by diff in ions and their charges inside and outside membrane
-unequal distribution of charges produces voltage diff across membrane=membrane potential
-mem. pot. varies cell to cell
-plasma membrane in resting stage is impermeable to sodium and permeable to potassium and chloride

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action potentials

nerve fiber capable of converting mechanical and chemical stimulus to electrical energy
-results from reversal of polarity on plasma membrane created by adequate stimulus, a stim capable of significantly increasing membrane permeability of Na+

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AP stimulus

-any changes in environment large enough will depolarized the rest potential, causing the nerve to produce an AP (nerve impulse; series of AP)
-impulse is a wave of electrical charge moving down the membrane of nerve fiber
-stimuli can be physical (pressure, temp, light), or chemical (parts of body fluids, osmotic pressure)
-any change in environment either internal or external can act as stimulus

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threshold stimulus

when a stimulus is barely enough to initiate an AP and therefore and impulse

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depolarization

rapid increase in membrane permeability to sodium

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repolarization

getting back to resting potential

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conductance

overall process of AP, depolarization, and repolarization depends on changes in membrane conductance to sodium and potassium

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nerve impulse

propagation of AP in one direction

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conductance velocities

-speed of conduction of an impulse remains constant
-different nerve fibers vary in speed of conductance
-myelinated fibers conduct impulses more rapidly

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Neuronal synapse

-electrochemical transmission site
-usually specialized junction between two neurons
-similar junctions of neurons with muscle and gland cells

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presynaptic neuron

conducts impulse toward synapse

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postsynaptic neuron

conducts impulse away from synapse
-excitability is either increase, if excitatory synapse, or decreased, if inhibitory synapse

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transmitting sybstances/neurotransmitters btw synapses

acetylcholine, norepinephrine, dopamine, seratonin (stim), glycine, and gamma-aminobutyric acid (GABA)

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type 1 synapse s type 2

1: axo-dendritic
2: axo-somatic

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factors affecting transmission

-synaptic junction is weakest link in neuron chain, it is here that changes affect transmission of impulses
-many drugs act at the synapse: morphine, strychnine, and tranquilizers
-alkalosis (increased pH of body fluids) neuron excitability increases
-acidosis (decreased pH): neuron excitability decreases
-decreased oxygen in body fluids, decrease excitability of neurons

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Reflexes

-autonomic or unconscious response of an effector organ (muscle or gland) to an appropriate stimulus
-

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two neurons involved in reflex arc

afferent/sensory or receptor neuron
efferent/motor or effector neuron
-usually one or more connector neurons

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spinal reflex=

stretch reflex

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visual reflex=

production of salivary and gastric secretion by a dog when it sees food

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conditioned reflex=

let down of milk, etc.

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reflex centers

located throughout the CNS, spinal cord has less complex
-more complex reflexes mediated through reflex centers found in brain: medulla oblongata=heart, resp, swallowing, vomiting, coughing; cerebellum=locomotion and posture

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Role of ANS

maintain stable internal body environment: homeostasis, by regulating activity of cardiac, smooth muscles, and glands
-activation of ANS occurs by cerebrocortical input or by other afferent input to hypothalamus

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hypothalamus acts as major integrator of ANS

-caudal part integrates symp division
-rostral part integrates parasymp. division
fight/flight activity: symp
relaxed vegetative activity: parasympathetic

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Chemical transmitters

postganglionic sympathetic: nor-epinephrine
all other: acetylcholine