Transcript Axon - Denver School of Nursing

Denver School of Nursing – ADN & BSN Programs
No Laboratory component for this class
BIO 206 / 308 – Unit 2 Ch 12 & 13, NeuroPhysiology

Lets start at the basics
and pull this brain
system apart…

What is the purpose of the Nervous system?

Just as always make it simple…

The crazy complexity of the Nervous system
can be be broken down to THREE words…
 What are the basic 3 Functions of the NS?
▪ 1) ?
▪ 2) ?
▪ 3) ?

The nervous system is organized to:
1)

Detect
2)

Evaluate
3)

Respond

The nervous system is organized to:
1) DETECT changes (from stimuli) in the internal
and external environment,
2) EVALUATE the level and type of stimuli, &
3) RESPOND by initiating changes in muscles or
glands or not initiating change

CNS vs PNS

Autonomic vs Somatic


Central Nervous System (CNS)
 Brain and spinal cord
Peripheral Nervous System (PNS)
 Cranial nerves (12)
 Spinal nerves (31)
 Pathways –
▪ Afferent (ascending) – sensory
▪ Efferent (descending) – motor


Neuron
Glia (glial cells)


Dendrites
Axon




Neuron – Single unit of the NS
Glia (glial cells) – supportive cells to neurons
Dendrites – Receptor arms of the neuron
Axon – delivery arm of the neuron
•
Three components
– Cell body (soma)
• Mainly in the CNS
• Densely packed in CNS → NUCLEI
• Densely packed in PNS → GANGLIA
– Dendrite
• Receptive portion of neuron
– Axon
• Carries nerve impulse away from the cell
body
• One per neuron
•
Axon
– Hillock
• Leaves the cell body, Nissl free
• Lowest threshold for stimulation so → AP begins here
– Myelin
• Insulating layer of lipid material segmented: ↑ speed of
conduction
• Multiple sclerosis, Guillain-Barre’
– Endoneurium
• Delicate layer of connective tissue around each axon
– Neurilemma
• Thin membrane between the myelin sheath and the
endoneurium
Functional classification
– Sensory
• Receptors to CNS
• Afferent
– Associational
• Interneurons
• Sensory to motor
– Motor
• Form CNS to effector organ*
• Efferent
*(skeletal muscle or organs)

Support cells: 50% brain and spinal
column volume: 5 – 10 x more
numerous than neurons

Oligodendrocytes

Schwann cells

Ependymal cells

Astrocytes

Microglia


Neurons generate and conduct
electrical and chemical impulses by
selectively changing the electrical
portion of their
plasma membranes and influencing
other nearby neurons by the release
of neurotransmitters.

RESTING Electric Potential:
 1) K+ > INside
 2) Na+ > OUTside
 3) Ca2+ > OUTside
Electrical Action Potential:
 Initially, the inside of the cell is negative.
 Chemical / Charge imbalance creates the Resting
Potential
▪ INSIDE of the CELL - High K, Low Na / Ca
▪ OUTSIDE of the Cell - High Na / Ca, Low K
 “Excitable cells” have the capability of changing their
membrane charge, when the NET charge changes other
transporters (Voltage gated channels) open causing a
chain reaction of increasing positive and then negative
charge.
 The Action Potential – is the name of the rapid change
and propagation of a chemical membrane potential.

Net membrane electrical potential is determined by:
 1) The concentration gradients for K+, Na+, and Ca2+ across
the membrane.
 2) The relative permeability (electrical conductance) of the
membrane to each of these ions)
▪ Therefore the NET electrical potential is determined by multiplying
each individual ion equilibrium potentials multiplied by their
membrane permeability and added together.
▪ (DON’T Panic this pink bullet point will not be on any exam)

Movement of these ions according to
concentration gradient


Summary of Ion pumps
These are ACTIVE Transport Pumps to set the
cells back up to “Resting Potential”
 1) Na/K ATPase (3Na+ OUT (/2K+ IN)
 2) Ca ATPase (Ca2+ OUT)
 3) Na/Ca Exchanger (3Na+ IN /1Ca2+ OUT)
Summary of Cardiac
Ion pumps:
 1) Na/K ATPase
(3Na+/2K+)
 2) Ca ATPase
(Ca2+ OUT)
 3) Na/Ca Exchanger
(3Na+/1Ca2)
Action Potential of a nerve cell:
 Here the
Resting Potential
would be -60
Action Potential of a nerve cell:
 Resting Phase (-60)
 Threshold (-45)
 Rising Phase = Depolarization
(Facilitated transport of Na in)
 Falling Phase = Repolarization
(Facilitated transport of K out)
 Refractory Period - Hyperpolarization(Na/K ATPase)
So how do these nerves
actually talk to each other??
The answer is in the…
“Synaptic Cleft”
Electrochemical regulation
of neurotransmitter
release…
Electrochemical regulation
of neurotransmitter
release…
LETS Break it down:
1) “Electricity” (change in
charge of the nerve)
2) Open or closed gate
3) Release of messenger
4) Messenger received
5) New message delivered
Synaptic Cleft – Intersection for delivery and acceptance of Info…
what are the messengers called?
Do NOT panic, you do
NOT need to
memorize detailed
names… this is just a
pictures to help
visualize the 
“chemical intersection”
Which is called
the 
Synaptic Cleft



Neurons are not physically continuous
with one another
Region between adjacent neurons –
synapse
Impulses are transmitted across the
synapse by neurotransmitters.

Presynaptic neurons and postsynaptic
neurons – “to and from the synapse”

Synaptic bouton – vesicles containing
neurotransmitters
 More than 30 substances
 Excitatory (excitatory postsynaptic potential)
 Inhibitory (inhibitory postsynaptic potential)

Synaptic cleft
 Space between neurons
Principles of Human Anatomy and Physiology, 11e
38

Astrocytes

Oligodendrocytes

Schwann cells

Astrocytes (only in CNS) – surround and deliver
nutrients and blood supply to neurons.

Oligodendrocytes (CNS) – structural support
&produce myelin sheath to multiple CNS nerve
fibers (Stroke recovery)

Schwann cells (PNS) – Mylinate single axon
regions of the same neuron. (lack of healing)
Image from Iowa State University: http://www.public.iastate.edu
A. Afferent
neuron
A. Efferent
neuron
A. Interneuron
Image from Iowa State University: http://www.public.iastate.edu
Image from BIOPRO Baden-Württemberg Institute of Physiology: http://www.biovalley.com
Does anyone know what the Blood Brain Barrier is??
Any guesses?

Blood Brain Barrier- is a tight web of astrocytes
around the brain capillaries that form the BBB

The concept of the blood brain barrier was first
introduced by Paul Ehrlich. He found that
intravenous injection of dyes into the bloodstream
stained all the tissues in most organs except the
brain. Using electron microscopy and electrondense tracers such as horseradish peroxidase
(HRP) a group of scientists demonstrated that the
blood- brain barrier is located in endothelial cells of
capillaries of the brain.
Spinal Nerves:
~ 8 Cervical nerves
~ 12 Thoracic nerves
~ 5 Lumbar nerves
~ 5 Sacral nerves
~ ONE Coccygeal nerve
Total of 31 Paired Spinal Nerves
Image from: http://kalibneil.tripod.com
Neuromuscular Junction
 Motor unit – neuron and
skeletal muscle
 Junction – axon and plasma
membrane of muscle

Grey vs White Matter
Protective Structure

Meninges
 Protective membranes surrounding the
brain and spinal cord
▪ Dura mater
▪ subdural space – veins
▪ Arachnoid
▪ CSF
▪ Pia mater

Cerebrospinal fluid (CSF) and the
ventricular system

CSF – clear, colorless similar to blood
plasma and interstitial fluid
 125 to 150 ml
 Produced by choroid plexus (ependymal
cells) within the ventricles (lateral, 3rd & 4th)
 Reabsorbed through the arachnoid villi

Cranial Nerves

Cranial Nerves (PNS)
 Olfactory (I)
 Optic (II)
 Oculomotor (III)
 Trochlear (IV)
 Trigeminal (V)
 Abducens (VI)
 Facial (VII)
 Vestibulocochlear (VIII)




(acoustic)
Glossopharyngeal (IX)
Vagus (X)
Accessory (XI)
Hypoglossal (XII)

How to memorize the cranial nerves…
Image from: http://efildenimaxenu.blogspot.com
 Optic (II) – Sensory Vision
 Oculomotor (III) – Motor control superior, medial, inferior
rectus, + inferior oblique (Also controls pupil constriction)
 Trochlear (IV) – Motor control of superior oblique
 Abducens (VI) – Motor control of lateral rectus
CN IV
Image from: http://www.ncbi.nlm.nih.gov
CN III
CN VI
Reflex Arc




Receptor
Afferent (sensory) neuron
Efferent (motor) neuron
Effector – muscle/gland

Spinal Cord nerve roots
 Dorsal nerve root  localized / specific cord level
afferent sensation (dermatomes)
 Ventral nerve root  localized / specific cord level
efferent motor control (myotomes)
Image from: http://www.whiplash101.com / Apparelyzed.com

Figure 8-17
Anterior
With SC comparison


Posterior
List of Myotomes of Commonly Injured Nerve Roots
C5 – The deltoid muscle (abduction of the arm at the shoulder).
C6 – The biceps (flexion of the arm at the elbow).
C7 – The triceps (extension of the arm at the elbow).
C8 – The small muscles of the hand.
L4 – The quadriceps (extension of the leg at the knee).
L5 – The tibialis anterior (Dorsiflexion).
S1 – The gastrocnemius muscle (Plantarflexion).
Image from: http://neurotalk.psychcentral.com
Image from: http://neurotalk.psychcentral.com

Divisions of the Nervous System
 Central Nervous System (2 main components)
 Peripheral Nervous System (All the REST)
▪ Autonomic (What is an example of this function?)
▪ Somatic (What is an example of this function?)
▪ Sensory nerves (What is an example of their function?)

A) Autonomic = Involuntary control of nerves (ANS)
 THE ANS is further divided into: (p.212)
▪ i) Sympathetic NS
▪ ii) Parasympathetic NS
 Autonomic NS controls everything we take for
granted…

A) Autonomic = Involuntary control of nerves (ANS)
 THE ANS is further divided into: (p.212)
▪ i) Sympathetic NS – “FIGHT or FLIGHT”
▪ ii) Parasympathetic NS - “REST and DIGEST”
 Autonomic NS controls everything we take for
granted… if it was up to us we would stop breathing
as soon as we fall asleep in class, but the autonomic
NS keeps you alive!!

“Fight or Flight”
 Accelerates heart rate
 Constricts blood vessels to smooth muscle
 Dilates blood vessels to skeletal muscle
 Decreases GI movement
 Dilation of pupil
 Effects on glands: Increases epinephrine, sweat
secretion and decreases digestive secretion

“Fight or Flight”
  HR
 Vasoconstriction to Smooth Ms
 Vasodilatation to Skeletal Ms
  peristalsis
 Mydriasis
 Effects on glands: Increases epinephrine, sweat
secretion and decreases digestive secretion

“Rest and Digest”
 Slows heartbeat
 NO effect on blood vessels to smooth muscle
 NO effect on blood vessels to skeletal muscle
 Increases peristalsis
 Contraction of pupil
 Effects on glands: No effect on adrenal medulla or
sweat glands, but increases secretion of digestive
enzymes

“Rest and Digest”
  HR
 NO Δ smooth muscle vasculature
 NO Δ skeletal muscle vasculature
  peristalsis
 Miosis
 Effects on glands: No effect on adrenal medulla or
sweat glands, but increases secretion of digestive
enzymes

SNS “Fight or Flight”
 Short Preganglionic Fibers
▪ “Cholinergic” (Acetylcholine signal)
 Long Postganglionic fibers
▪ “Adrenergic” (Norepinephrine signal)

PNS “Rest & Digest”
 Long Preganglionic Fibers
▪ “Cholinergic” (Acetylcholine signal)
 Short Postganglionic fibers
▪ ALSO “Cholinergic” (Acetylcholine signal)

SNS “Fight or Flight”
 Primary chemical signal
▪ Epinephrine / Norepinephrine

PNS “Rest & Digest”
 Primary chemical signal
▪ Acetylcholine

B) Somatic= Voluntary control of motor
nerves (SNS)
 This is the division that provides nervous control
of the musculoskeletal system

Distal to the injury
 Wallerian degeneration
▪ Swelling
▪ Neurofilaments hypertrophy
▪ Myelin sheath shrinks and
disintegrates
▪ Axon portion degenerates
▪ Myelin sheath ⇨ Schwann cell
pathway

Limited to myelinated axons
 Generally only in the PNS (Schwann cells)
 CNS limited by ↑ scar formation and
different type of myelin(oligodendrocytes)

Depends upon location, type of injury
(crush vs. cut), inflammatory response
and scar tissue formation
What is the smallest bone in the HUMAN Body??
AND what sense is it involved in??
Sense Organ
Specific Receptor
Type of Receptor
Sense
Eye
Rods and Cones
Photoreceptor
Vision
Ear
Organ of Corti
Mechanoreceptor
Hearing
Inner Ear
Cristae ampullares
Mechanoreceptor
Balance
Nose
Olfactory cells
Chemoreceptor
Smell
Taste Buds
Gustatory Cells
Chemoreceptor
Taste
Thermoreceptor
Temperature
Nociceptors
Pain
Peripheral NS
Acute – Fast (Type A)
Chronic – Slow (Type B)
Hypothalamus Detects Osmotic /
Osmoreceptor
electrolyte balance of blood.
a) Muscles
b) Tendons
a) Muscle spindles
b) Golgi tendon receptors
Thirst
a + b = Proprioceptors Proprioception
(stretch+mechano)
Retina is made of two specialized photoreceptors:
RODS and CONES
Do you know the specific function of these two receptors??
The Average human eye has 125 Million Rods and Cones
Rods are the photoreceptors that detect monochromatic
image and image quality (black and white)
Cones are the photoreceptors that detect detailed images and
have three subgroups to detect the array of color images.
Humans have 18 times as many rods as cones, however the
cones are not evenly distributed, instead they are
concentrated in the Fovea centralis and center of the retina