Lecture 6: Nervous System Flashcards
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
synapse
junction of axon of one neuron with another neuron’s cell body or dendrite
Groups of cell bodies
within the CNS=nuclei
outside the CNS=ganglia
bundle of nerve processes
inside the CNS=fasciculi or tracts
outside the CNS=nerves
Central Nervous System comprised of
the dorsal cavity, aka the brain and spinal cord
protected by cranial skull, vertebrae, and dura matter
Peripheral nervous system is comprised of
cranial and spinal NERVES;
split into the autonomic nervous system and the somatic portion
autonomic nervous system comprised of
sympatheic (thoraco-lumbar outflow) and parasympathetic (cranio-sacral outflow)
brain
includes cerebrum, cerebellum, and brain stem
has four ventricles filled with cerebrel spinal fluid
brain is divided into three parts
forebrain=telencephalon (cerebrum) and diencephalon
midbrain=mesencephalon (thalamus)
hindbrain=metencephalon (pons and cerebellum) and myelencephalon (medulla oblongata)
telencephalon
cerebral cortex, corpora callosum and smell centre
-encloses the cavities of the lateral ventricles
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
corpus striatum/callosum
connects each cerebral cortex with another part of CNS
Rhiencephalon
smell/olfactory brain
diencephalon
thalamus, epithalamus, hypothalamus, most of the third ventricle, and entry site for optic nerves
thalamus
relay centre for nerve fibers connecting cerebrum to brain stem and spinal bord
hypothalamus
includes the hypohysis and pituitary gland; ANS and hormone control
mesencephalon
cerebral peduncles and 4 quadrigeminal bodies=anterior for vision and caudal for hearing
cerebral peduncles
continuations of the spinal cord and the brain stem into the respective cerebral hemispheres, containing fiber tracts and nuclei
metencephalon
cerebellum and pons
cerebellum
many folds, two hemispheres
gray matter surface, white matter center
coordination of voluntary movements
pons
bridge of fibers between hemispheres
otehr fiber tracts and nuclei
4th ventricle
part of the metencephalon, between the cerebellum and pons and brain stem
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
brain stem
=medulla oblongata, pons, and midbrain, many cranial nerves are hosted here
-controls respiration and circulation
ventricles
chambers filled with CSF
each has a CHOROID PLEXUS: a network of capillaries
connected with subarachnoid space of brain/spinal cord
meninges
covering of brain and spinal cord
consists of dura matter, arachnoidea, and pia matter: site of infection for meningitis
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
tracts of spinal cord: peripheral white matter
on each side: doral white column, lateral white column, and ventral white column
dorsal white column
afferent tracts: give sense of position
lateral white ventral column
- dorsal and ventral spinocerebellar
- rubrospinal
- lateral spinothalamic
- lateral corticospinal
dorsal and ventral spinocerebellar
to the cerebellum, aid in coordiation of movements
rubrospinal
from red nucleus in the midbrain to motor cells in the opposite side verntal gray horn: receive feedback from cerebellum
lateral spinothalamic
fibers from dorsal gray horn (opposite side) to the thalamus: monitor pain and temperature
lateral corticospinal
from motor area of cerebrum to ventral gray horn: aid voluntary movement
ventral white column
direct vestibulospinal tract
crossed vestibulospinal tract
ventral corticospinal tract
-their impulses are associated with voluntary motor activity
direct vestibulospinal tract
from the lateral vestibular nucleus to motor nuclei in spinal cord
-set the tone of the extensor muscle
crossed vestibulospinal tract
from the descending vestibular nucleus to motor centres of the opposite side of spinal cord
ventral corticospinal/cerebrospinal tract
connects motor area of cerebrum with spinal cord (same and opposite sides)
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
brachial plexus
supplies nerves to forelimbs
derived from last 3 or 4 cervical and first 1 or 2 thoracic spinal nerves
lumbosacral plexus
supplies hind limbs
derived from ventral branches of last few lumbar and first 1, 2, or 3 sacral nerves
ventral root
carries efferent motor neurons to muscles and glands
dorsal root
carries afferent sensory info to CNS
gray matter
consists of cell bodies of interneurons and some motor/efferent neurons
white matter
consists of axons carrying info through spinal cord to brain (afferent/sensory neurons)
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)
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)
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
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
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
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
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)
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
supporting tissue in CNS and PNS
CNS=neuroglia
PNS=ordinary white fibrous connective tissue
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
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
motor nerves end in
each terminal branch supplying a single muscle fiber
Myelinated nerve fibers
white: sheath of fatty material with many layers of schwann cells wrapped around the nerve fiber
Unmyelinated nerve fibers
gray: surrounded, not wrapped, by ONE layer of schwann cells
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
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
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+
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
threshold stimulus
when a stimulus is barely enough to initiate an AP and therefore and impulse
depolarization
rapid increase in membrane permeability to sodium
repolarization
getting back to resting potential
conductance
overall process of AP, depolarization, and repolarization depends on changes in membrane conductance to sodium and potassium
nerve impulse
propagation of AP in one direction
conductance velocities
- speed of conduction of an impulse remains constant
- different nerve fibers vary in speed of conductance
- myelinated fibers conduct impulses more rapidly
Neuronal synapse
- electrochemical transmission site
- usually specialized junction between two neurons
- similar junctions of neurons with muscle and gland cells
presynaptic neuron
conducts impulse toward synapse
postsynaptic neuron
conducts impulse away from synapse
-excitability is either increase, if excitatory synapse, or decreased, if inhibitory synapse
transmitting sybstances/neurotransmitters btw synapses
acetylcholine, norepinephrine, dopamine, seratonin (stim), glycine, and gamma-aminobutyric acid (GABA)
type 1 synapse s type 2
1: axo-dendritic
2: axo-somatic
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
Reflexes
two neurons involved in reflex arc
afferent/sensory or receptor neuron
efferent/motor or effector neuron
-usually one or more connector neurons
spinal reflex=
stretch reflex
visual reflex=
production of salivary and gastric secretion by a dog when it sees food
conditioned reflex=
let down of milk, etc.
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
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
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
Chemical transmitters
postganglionic sympathetic: nor-epinephrine
all other: acetylcholine
