Download Ch 48-50 CVHS Nervous System

Nervous System, Sensory
Mechanisms and Motor
Mechanisms
 CVHS
 Chapters
48, 49 & 50
Organization of the Nervous System

Central Nervous System
(CNS)


brain and spinal cord
Peripheral Nervous
System (PNS)


nerves outside of CNS
cranial nerves
• connect brain w/ upper
body

spinal nerves
• Connect spine w/ regions
of the body below the
head
Peripheral Nervous System
(PNS)

PNS


Sensory/Afferent
Division


sense stimuli inside
and outside the body, helps
to control internal
environment
send impulses to the CNS
Motor/Efferent Division


send impulses away from
the CNS
effectors: control voluntary
and involuntary muscles
Autonomic Nervous System

Involuntary: smooth
and cardiac muscle

Sympathetic
• increases energy
consumption and
prepare for action
• Fight or Flight response

Parasympathetic
• Enhance activity to gain
and conserve energy
Neuron
cell body
myelin sheath
synaptic terminal
dendrites
Schwann cells
synapse
axon (hillock)
nodes of Ranvier
terminal branches
Neuron Structure

Cell body:


Dendrites:


produce myelin in the PNS
synaptic terminal:


Holes in myelin where Na can
move into the cell
Schwann Cell:


lipid layer surrounding nerve
cell
Nodes of Ranvier:


Point @ which impulse starts
when threshold is exceeded
myelin sheath:


Receive information
Axon (hillcock):


performs cellular functions
End of axon
Synapse:

communication junction
between 2 nerve cells, where
neurotransmitters move
Functional Organization of
Neurons
3 Classes of Neurons
• sensory neurons
convey impulse from
sensory receptors to CNS
• interneurons
integrate sensory input
and motor output
• motor neurons
convey impulses from
CNS to effector cells
• Function as a reflex arc:
• Sensory neuron,
to interneuron, to motor
neuron
The Knee-jerk Reflex
1. Tap patellar tendon
2. Sensory receptors sense
stretch in quadriceps
3. Sensory neurons convey
info. to spinal cord
4. Synapses with motor
neuron in spinal cord
5. Motor neuron conveys
signal to quadriceps
6. Synapse with interneuron in spinal cord
7. Interneurons inhibit other
motor neurons (hamstring)
8. Prevents the hamstring
from contracting (no resistance
to quads contracting).
The Nature of Neural Signals
Membrane Potential
• the difference in voltage across the plasma membrane
+ arises from differences in ionic composition (Na+/K+ pump)
- normal: positive outside; negative inside (-70mV)
48_06RestingPotential_A.swf
Excitable Cells
Action Potential
• cells that have the ability to change their membrane potentials
• neurons and muscle cells
• Resting potential (unexcited)
• Change from resting potential can result in active electrical
impulse
• Gated ion channels open or close in response to stimuli
• Hyperpolarization
• increase in the electrical gradient opens K+ channel;
• increase outflow of K+; more negative, no impulse
• Depolarization
• reduction in the electrical gradient
• opens Na+ channel
• increase inflow of Na+; less negative, can cause nerve
impulse
• action potential: a brief reversal of membrane polarity
Graded Potentials and the
Action Potential in a Neuron
Propagation of the Action Potential

Membrane becomes
depolarized by reacting to a
stimulus.
 Must cross a threshold of
-55 mV
Action potential – all or none
response
 Increase frequency =
increased stimulus
Na+ rushes into the axon
causing the charge reversal from
– to + inside the axon
K+ leaves the axon after the
action potential is finished
 Refractory period – another
action potential can not occur
yet
 Resting potential is restored



Action Potential
48_10ActionPotential_A.swf
Saltatory Conduction
Saltatory Conduction
• speeds the propagation of action potential
+ nodes of Ranvier: gaps between myelinated regions
- action potentials “jump” from node to node
Conversion of Signal:
Electrical to Chemical
• Depolarization causes
influx of Ca2+
• Release of synaptic
vesicle contents
• Neurotransmitter released into cleft
• Molecules bind to
receptors
• Opens ion channels
•48_15Synapse_A.swf
Diversity of Nervous Systems
The Brain

Structures
Cerebrum




Brainstem





Cerebral cortex – outer portion of the cerebrum – gray matter
Cerebral hemispheres – left and right sides
Corpus callosum – allows communication between the left and right
hemispheres
Medulla oblongata – controls autonomic and homeostatic functions
Pons – regulates breathing
Midbrain – large scale body movements - walking
Cerebellum – coordination, learning, and decision making
Diencephalon


Thalamus – input center for sensory info and output center for motor info
Hypothalamus – homeostasis – links to the endocrine system
Cerebral Hemispheres
Left
 Language
 Math
 Logical operations
 Visual and auditory
details
Right
 Pattern recognition
 Face recognition
 Spatial relations
 Nonverbal thinking
 Emotional processing
 Understanding and
reacting to stress
 Music
Cerebral Cortex

Frontal lobe


Speech
Temporal lobe



Smell
Hearing
Occipital lobe


Vision
Parietal lobe



Speech
Taste
Reading
Sensory Receptors
 Detect
stimuli
 Externorecptors – detect external stimuli

Heat, light, pressure, chemicals etc.
 Internoreceptors

– detect internal stimuli
Blood pressure, body position etc.
Sensory Receptors
 Mechanoreceptors

– detect physical stimuli
Pressure, touch, stretch, motion, and sound
 Chemoreceptors
– detect solute
concentration

Osmolarity, glucose, oxygen, carbon dioxide, and
amino acids
 Photoreceptors

– detect visible light
Rods and cones
 Thermoreceptors

– detect temperature
Hot and cold
 Nocieceptor
– detect pain
Senses
Cold
Light touch
 Sight
Pain
Hair
Heat
 Sound
 Touch
Epidermis
 Taste
 Smell
Dermis
Nerve
Connective tissue
Hair movement
Strong pressure
Hearing
 Outer

ear – pinna and auditory canal
Tympanic membrane separates middle ear and
vibrates in response to sound
 Middle

Oval window (detects vibrations from the stapes)
and Eustachian tube
 Inner


ear – malleus, incus, and stapes
ear –
semicircular canals - detect balance and
equilibrium
cochlea – contains hair cells which send the
message to the brain
Sight
 Eye







Sclera – white connective tissue
Choriod – layer inside the sclera
Conjucnctiva – mucous membrane over the sclera
Cornea – transparent part of the eye where light enters
Iris – color of eye – regulates pupil – amount of light entering
Pupil – hole in the center of the iris
Retina – contains photoreceptors – internal layer of eye
• Rods – detect light intensity
• Cones – detect color




Lens – focuses light on the retina
Cilliary body – move the lens
Aqueous humor – liquid in the front of the eye – focus light onto
retina
Vitreous humor – liquid in the back of the eye – focus light onto
retina
Recall: Muscle Tissue

Muscle Tissue
muscle fibers capable of
contracting when
stimulated by nerve
impulses
Skeletal Muscle


- striated (striped)
- voluntary movements
- multinucleated
Smooth Muscle
- branched, tapered
- involuntary actions
Cardiac Muscle
- striated, branched
Muscle Contraction
Skeletal Muscle
• two kinds
• fast-twitch (white meat)
• Tend to go anaerobic
• slow-twitch (dark meat)
• myoglobin-rich
• “twitch”
• contraction of protein filaments causes
muscles to shorten
- thin (actin) and thick (myosin) bands
- interleaved with each other
myosin grabs actin and pulls
- sliding filament theory of muscle
contraction
Muscle Contraction
Sliding Filament Theory
• relaxed muscle
+ length of each sarcomere is greater
- Z-line to Z-line
• Contracting Muscle
+ actin/myosin slide past each other
- shortening the sarcomere
• Contracted Muscle (maximum)
+ actin filaments overlap each other
- sarcomere is very short
Myosin & Actin Interactions
Regulation of Muscle Contraction







ACh released @ synaptic
terminal, diffuse across cleft &
bond to muscle cell receptors
Action potential moves down PM
along T-tubule
Action Potential triggers Ca 2+
release from sarcoplasmic
reticulum
Ca2+ bond to troponin in thin
filament
Myosin cross bridges alternative
attach to actin pulling thin
filament toward sarcomere
Cystolic Ca 2+ removed
Tropomyosin blocks myosin
binding sites, contraction ends
and muscle relaxes