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Nervous Tissue
Nervous System Organization
Chapter 11
Histology of Nervous Tissue
• Made of two different varieties of cells
1. Neuroglia or supporting cells
2. Neurons
Quiz Pic
p.390
11.3a-e
QUIZ PIC p. 392
11.4b
Axons
• Myelinated and unmyelinated
• CNS covered by olidodendocytes
• PNS Schwann cells
Change in Membrane Potential
• Two types of signals are produced
1. Graded Potentials- signal over short
distances
2. Action Potentials- long distance signals
Types of Membrane Changes
A. Graded Potentials- short lived, local
changes in the membrane
• depolarization or hyperpolarization
• cannot travel all the way to an effector
organ
• dies out over time
Steps of Potential Creation
A. Depolarization- change in which inner
membrane becomes more positive
compared to resting membrane
B. Repolarization- membrane going back to
the resting state
C. Hyperpolarization- change in which
membrane becomes more negative
compared to resting membrane
Change in Membrane Potential
• Changes in membrane potential are used to
send, receive, and integrate information
• Can be produced by anything that
1. changes permeability to an ion
2. alters ion concentration on both sides of
the membrane
What changes membrane
Potential?
• Heat, light, pressure
• Chemical
• Little bit of the unknown
Homeostatic Imbalance
• Anesthetics
• Prevent Na+2 channels from opening
• Prevent oxygen needed to function
Continuous Propagation of AP
• This occurs in unmyelinated axons
– If enough stimulus is applied to the membrane,
an action potential is generated; the in rush of
sodium ions at the site of the stimulus causes
local changes in the membrane that cause more
voltage gated channels to open and depolarize
more and more membrane until threshold is
reached and the action potential moves along
the membrane
Saltatory Conduction of AP
• Occurs only on myelinated axons
• all voltage gated sodium channels are
concentrated between the nodes of Ranvier
• when a stimulus causes the AP the AP will
not stimulate neighboring membrane but
jump from node to node
• much faster travel time than continuous
conduction
Homeostatic Imbalance
•
•
•
•
•
Multiple Sclerosis (MS)
Myelin sheaths destroyed
Become hard scleroses
Current can not jump nodes
Axons are fine and try to fix by making more
Na+2 pumps
• Causes major irregularity in impluses
Synapse
• The location or junction between 2 neurons
where the transmission of information occurs
- the neuron sending information is the
presynaptic neuron
- the neuron receiving information is the post
synaptic neuron
Chemical Synapses
• Specialized for release and reception of chemical
neurotransmitters
• Contains 3 parts
1. Axon Terminal- filled with vesicles containing
neurotransmitter
2. Synaptic Cleft- space between the neurons
3. Neurotransmitter Receptor Region- located on the post
synaptic neuron
Electrical Synapses
• Far less common than chemical synapses
• Provide a means to synchronize activity
between neurons
• Gap junctions
Termination of Neurotransmitter Effects
• Degradation by enzymes associated with the
post synaptic membrane (Can you think of
where you have already seen this?)
• Reuptake of the neurotransmitter at the
presynaptic terminal
• Diffusion away from the synapse
Neurotransmitter types
•
•
•
•
p. 415-417 (skim through)
ACh acetylcholine ????
AChe acetylcholinesterase ????
Dopamine  inhibitory, cocaine blocks
uptake
• Serotonin  Prozac blocks uptake, LSD
blocks
Mechanism of Action of Neurotransmitter
• Direct- neurotransmitters that open ion
channels
• Indirect- act through Second Messenger
molecules
• Excitatory- cause depolarization of the
membrane
• Inhibitory- cause hyperpolarization of the
membrane
Central Nervous
system
Bio 105
Chapter 12
Quiz
Picture
Ventricles
Homeostatic
Imbalance
Hydrocephalus
•Water on the brain
•Ventricles have to
much cerebral fluid
Three Regions of Cerebral
Hemispheres
• Cortex- Conscious mind
Gray matter containing cell bodies
Dendrites
Unmyelinated axons
• Cerebral White Matter- Myelinated fibers bundled
into fiber tracts
- Communication between
cortex and lower CNS
structures
• Basal Ganglia- complex role in motor control
attention, and cognition
Brodmann Areas
Brodmann Areas
Somatotopy
Cerebral Cortex Continued
Premotor Cortex- just anterior to the
precentral gyrus
• controls learned motor skills of
patterned nature
• planned movements
Broca’s Area- special motor speech area;
planning of motor activities
Frontal Eye Field- controls voluntary
motor movement of the eyes
Homeostatic Imbalance
Stroke
Stoppage of blood flow to brain
Ex:
• Damages region of primary motor cortex,
body parlayed
• Damage to premotor cortex relearnable
Cerebral Cortex
•
Sensory Areas- conscious awareness
of sensation; located in parietal,
temporal and occipital lobes
Primary somatosensory cortex
• Spatial discrimination
Somatosensory Association cortex
Visual areas
Auditory areas
Gustatory areas
Brodmann Areas
Somatotopy
Homeostatic Imbalance
• Damage to primary visual or auditory stop
sight or hearing
• Damage to the association area allow sight
or hearing, but lack comprhension
Multimodal Association Areas
• Rest of cerebral cortex
• Front and side of cerebral cortex
• Pulls together all info received from primary
somatosensory cortex and passes on to
primary motor cortex
• Helps in judgment, reasoning, persistence
Cerebral White Matter
• Commissures- connect corresponding
hemispheres gray matter enabling coordinated
function; largest is corpus callosum
• Association Fibers- connect different parts of
same hemisphere
• Projection Fibers- fibers that enter brain from
cord; fibers that leave brain for cord
Diencephalon- three parts
• 1.Thalamus- 80% of total; gets sensory inputs,
regulates emotion & visceral function
• 2. Hypothalamus- responsible for several functions
including body temperature regulation; regulation food
intake; emotional response, autonomic control, thirst,
sleep-wake cycle; endocrine system function
• 3. Epithalamus- pineal secretes melatonin; choroid
plexus for CSF
Brain Stem
• Produce the autonomic functions necessary
for survival
• provides pathway for fiber tracts between
cord and hemispheres
• contain the nuclei for 10 of 12 pairs of cranial
nerves
• Three parts- midbrain, pons, and medulla
oblongata
1. Midbrain
• Contains the substantia nigra which
produces the precursor for dopamine which
is a neurotransmitter
• degeneration of these neurons causes
Parkinson's Disease
2. Pons
• Contains mostly projection fibers
• contains centers for breathing
3. Medulla Oblongata
• Most inferior part of brain stem
• decussation of the pyramids -the fibers cross
over to the opposite side of the cord
3. Medulla: Centers
Contains important centers of AUTONOMIC
nervous system:
– respiratory center
– cardiac center
– vasomotor center
– vomiting
– swallowing
– hiccuping
– coughing
– sneezing
Cerebellum
• 11 % of total brain mass
• Located under cerebral hemispheres
posterior to pons and medulla
• Provides precise timing and appropriate
patterns for smooth, coordinated smooth
muscle contractions
• Activity occurs subconsciously
A. Limbic System
• consists of parts of cerebrum (limbic lobe,
hippocampus and amygdaloid body) and
diencephalon (thalamus, hypothalamus)
• parts linked by white tracts (fornix connects
hippocampus to hypothalamus)
Protection for Brain
• Bone
• Meninges
• Cerebral Spinal Fluid inside ventricles
Layers of Meninges
• Dura Mater- strongest, thickest, tough external membrane
- 2 layers with outer forming periosteum of bone
and inner covering the brain
- extends to cord but, no periosteal layer
• Arachnoid Mater- middle layer
- subdural space between it and the dura
- subarachnoid space below it filled with CSF
• Pia Mater- delicate CT that clings to the brain into every sulci
Blood Brain Barrier
• Produced by the characteristics of the
capillaries that supply the brain which
include:
– Thick basal lamina
– Continuous endothelium of vessel walls
Provide selection of substances that reach the
neurons
Spinal Cord
• Gray/white matter reversed compared to the
hemispheres
• Gray is on the inside and white is on the
outside
• Enclosed in vertebral column
• 18 inches long; ¾ inch thick
Spinal Cord
• Meninges- same as brain except no periosteal
layer on outside of the dura
• CSF- fills the space between the pia and
arachnoid meninges
- these layers extend beyond the end
of the cord at L1
- space here is for spinal tap or
lumbar puncture
Quiz
Picture
Categories of Memory
1. Declarative memory (factual knowledge)
– Explicit information
– Related to our conscious thoughts and our
language ability
– Stored in LTM with context in which it was
learned
Categories of Memory
2. Nondeclarative memory
– Less conscious or unconscious
– Acquired through experience and repetition
– Best remembered by doing; hard to unlearn
– Includes procedural (skills) memory, motor
memory, and emotional memory
Thalamus
Basal forebrain
Touch
Prefrontal cortex
Hearing
Vision
Taste
Smell
Hippocampus
Sensory
input
(a) Declarative
memory circuits
Association
cortex
Thalamus
Medial temporal lobe
(hippocampus, etc.)
Prefrontal
cortex
ACh
ACh
Basal
forebrain
Figure 12.23a
Sensory and
motor inputs
Association
cortex
Basal
nuclei
Thalamus
Dopamine
Premotor
cortex
Premotor
cortex
Substantia
nigra
Thalamus
Basal nuclei
Substantia nigra
(b) Procedural (skills) memory circuits
Figure 12.23b
Molecular Basis of Memory
• During learning:
– Altered mRNA is synthesized and moved to axons and
dendrites
– Dendritic spines change shape
– Extracellular proteins are deposited at synapses involved
in LTM
– Number and size of presynaptic terminals may increase
– More neurotransmitter is released by presynaptic
neurons
PNS
Bio 105 Chapter 13
Organization of the
Nervous System
Peripheral Nervous System
• 12 pairs of Cranial nerves
• 31 pairs of Spinal nerves
Quiz
Picture
Reflex Arc
The Eye
• Sphere with a 1 inch diameter
• Accessories to eye include:
– Eyebrows
– Eyelids- palbebrae fissure, lacrimal punctum,
eyelashes, Meibomian glands
– Conjunctiva- mucous membrane covering
– Lacrimal apparatus (tears)  lacrimal gland,
lacrimal canal, nasolacrimal duct
– Extrinsic Eye Muscles
Layers of the eyeball
• Fibrous Tunic- outermost layer; dense
avascular CT
– Sclera- white part; posterior; continuous with
dura
– Cornea- clear, anterior part; part of light
refraction apparatus
Layers of the eyeball
• Vascular Tunic (Uvea)- highly pigmented; 3
regions
– Choroid- highly vascular; posterior part
– Ciliary body- smooth muscle to control lens
shape; ciliary process to make fluid of anterior
chamber
– Iris- most anterior; colored part of eye; round
opening is pupil
Layers of the eyeball
• Sensory Tunic (Retina)- contains the
neurons that allow for vision; 2 layers
including the outer pigmented layer and inner
neural layer
• Optic disc- Optic Nerve II leaves the eye;
also called blind spot
• Macula Lutea- area of sharpest vision
• Rods- dim light, peripheral vision
• Cones- bright light, high acuity vision
Eye Chambers
• Posterior Segment- behind lens; contains
gel like vitreous
• Anterior Segment- filled with fluid; plasma
like; forms and circulates continuously; made
from capillaries in ciliary process
Lens Changes for focusing
• Close vision– Accommodation- ciliary muscles contract; lens
bulges and gets fat
– Constriction of pupils- circular muscles of iris
contract; pupil gets small
– Convergence of eyeballs- both eyes move
medially to see object
Lens changes for focusing
• Distant Vision
– Ciliary muscles are completely relaxed; lens is
as thin and flat as it can get
– Eyes are best adapted for this type of vision
Physiology of seeing
• Pigmented layer absorbs light
• Photoreceptors (Rods and Cones) have
visual pigments
• Retinal and opsins (Rods=rhodopsin)
• Rhodopsin (and other proteins) control
nuerotransmitter release
• Light breaks down rhodopsin, release
neurotransmitter, cause Na+1 release starts
action potential
Homeostatic Imbalances Eye
• Glaucoma  fluid build up
• Detached retina  neural layer separates
from pigmented layer
• Cataract  under nourishment of lens
• Strabismus  weakness of eye muscle
• Watery eyes  lacrimal apparatus
• Conjunctivitis  inflammation of conjunctiva