Human Anatomy Unit 5b - Peripheral Nervous System

Peripheral Nervous System

All nerves lateral to CNS

Subdivisons of PNS

1. Somatic system

2. Autonomic system

Somatic system

• Regulates skin & skeletal muscles

• Usually voluntary response

• Includes reflexes

• Protect body from harm

Autonomic System

• Regulates cardiac & smooth muscles, and glands

• Functions automatically, usually involuntary

Subdivisions of Autonomic

1. Sympathetic

2. Parasympathetic

Sympathetic

• Emergency situations: “fight or flight”: increased heart rate & respiration, digestion & excretion inhibited, pupils dilated

• Neurotransmitter = norepinephrine (NE)

• Similar effects of adrenaline

Parasympathetic

• Responses during relaxation: digestion, regular heart rate, pupils contracted

• Neurotransmitter = acetylcholine (ACh)

Functions of Nervous System

1. Gathers info (sensory input)

2. Interprets info & determines response (integration)

3. Causes response (motor output)

Sub-divisions ofNervous System

• Central Nervous System (CNS): brain and spinal cord

• Peripheral Nervous System (PNS): all neurons lateral to CNS

Neurons

Nerve cells that communicate

Characteristics of Neurons

1. Long life span

2. Amitotic (do not reproduce)

3. High metabolic rate (require constant energy and O2)

Neuroglia

Nerve cells that do NOT communicate

Characteristics of Neuroglia

• Nourish neurons to promote growth & health

  • Scaffolding for cells to climb

  • Remove debris from dead cells (after injury)

  • Role in neuron maturation (add myelin)

2 Types of Neuroglia

1. Astrocytes

2. Schwann cells

Astrocytes

• Nourish neurons

• Maintain appropriate chemical environment for neurons (“mop up” toxins)

Schwann cells

• Form myelin sheaths around axons

Myelin sheath

• Made of lipids and proteins

• Surrounds axon of neuron

• Allows for quick nerve impulse transmission

Multiple Sclerosis

• Autoimmune disorder:

  • WBC fight cells of myelin sheath —> causes scarring

  • Results in delayed or blocked signals that control muscle coordination, strength, sensation & vision

Types of neurons

1. Sensory

2. Interneuron

3. Motor neuron

Sensory neurons

(afferent, PNS): receives info from outside and takes it to CNS

Interneuron

(CNS): coordinates info & determines response

Motor neuron

(efferent, PNS): causes response

Dendrites

Receive neurotransmitters

Axon

Send neurotransmitters away to next neuron

Nodes of Ranvier

• Periodic gaps along the axon (no myelin)

• Allows for rapid conduction of nerve impulses

Synapse

• Space in between neurons

• Allows for instantaneous communication throughout body

Axon Terminals

• Change electrical impulses or action potentials within into chemical messages

Soma

• The main cell body

Nucleus

• Controls the cell

Nerve Impulses

• Necessary for ALL functions of nervous system

• Occur due to bioelectric currents (movement of Na+, K+, Ca+2, Cl-)

Resting Potential

• Resting axons are POLARIZED (outside of axon is +, inside of axon is - )

Action Potential

• Must occur to conduct a nerve impulse

• The polarity inside the axon changes:

  1. Inside of axon becomes positive (depolarization)

  2. Then the inside of axon quickly becomes negative again (repolarization)

• All or None response (once it begins, it will complete)

• Intensity of message: depends on frequency of action potentials

• Speed: depends on diameter of axon & if axon is myelinated

Action Potential Image

How many Impulse Transmission steps?

3 Steps

Impulse Transmission: Step 1

Axon branches at the end into axon terminals

Impulse Transmission: Step 2

Axon terminals release neurotransmitters across synapse

Impulse Transmission: Step 3

Neurotransmitters received by dendrite of next neuron

Impulse Transmission Image

Hearing Step 1

Pinna (outer ear) “catches” sound waves

Hearing Step 2

Sound travels through auditory canal and hits tympanic membrane (ear drum)

• Located between canal & middle ear

• Muscles keep membrane very taut – therefore membrane vibrates when hit by sound waves

Hearing Step 3

The cochlea (inner ear) must conduct sound through fluid

• Requires more pressure to “push” sound waves

• Pressure is generated by 3 ossicles

  • Malleus (hammer)

  • Incus (anvil)

  • Stapes (stirrup)

Hearing Step 4

• The stapes pushes on the basilar membrane (part of cochlea) causing vibrations in different locations

• Cochlea has to convert physical sound waves into electrical signals for the brain to understand

  • The cochlea is made of 3 separate coiled tubes separated by thin membranes

Hearing Step 5

• Organ of Corti (on basilar membrane) contains 1000s of tiny hairs – when vibrations are strong enough, the hairs move and send an electrical impulse to the vestibulocochlear nerve

Hearing Step 6

VB-Cochlear nerve transmits info to brain

Cochlear Implants

The implant device sends its own electrical signals to the cochlear nerve – thus allowing a patient to hear

Ear Image

Cornea

• < 1/50 of an inch thick

• Cornea must stay clear for light to enter

For the cornea to stay clear:

1. Stem cells around the cornea produce corneal daughter cells

2. Daughter cells migrate to center of cornea & form a protective, transparent coat

   • Replaced every few days

If stem cells are destroyed:

• Daughter cells aren’t produced and

  blood vessels & sclera grows over

  cornea

Corneal Transplants

• Discovered by accident

• Donor eyes preferably not over 50 years old

Transplanting Stem Cells: Step 1

• Surgeon scrapes away growth over recipient’s cornea

Transplanting Stem Cells: Step 2

• Surgeon cuts stem cells away from donor cornea & thins from 1 mm to 1/3 mm

Transplanting Stem Cells: Step 3

• Place ring of stem cells on recipient’s eye & suture in place

Transplanting Stem Cells: Aftermath

• Transplanting stem cells does not result in vision

• Takes ~ 4 months for the patient to produce daughter cells & for the daughter cells to forge paths

Transplanting Cornea

• Surgeon removes damaged cornea

• Transplants new cornea

Laser Eye Surgery

Reshapes cornea to allow light to be better focused on retina (clearer vision)

1. Make flap in cornea

2. Remove microscopic amount of corneal tissue with laser (laser uses a cool UV beam to remove tissue and reshape cornea)

   • Ex: near sighted: goal is to flatten cornea

   • Ex: far sighted: goal is to make cornea steeper

   • Ex: astigmatism: goal is to make cornea a more normal shape

Bionic Eye

• Uses retinal implant, converts images to mini-video camera in glasses

  • Not highly detailed vision

Artificial Corneas (Kpro)

• A synthetic material that is transparent, regenerates, has high water content, and a unique biomechanics system

Transplanting CNS Stem Cells

• Transplant stem cells from olfactory region to spine region, stem cells grew and stimulated regeneration