intro nervous system ap150

How information travels from receptors to the CNS to effectors through neurons

1. Sensory receptors detect stimulus

2. Sensory neurons (afferent) in PNS carry information toward CNS

3. Intraneurons in CNS process sensory output and connect sensory neurons to motor neurons and initiate response
4. Signal is sent to motor neuron which is efferent and sends command to stimulate effector (muscle/gland)

Sensory deff.

any aspect of the N.S involved with transmitting sensory information

Motor def.

any part of the N.S that transmits motor information

Afferent def.

toward CNS

Efferent def.

away from CNS

CNS

• processes/integrates sensory info and generates responses

• Brain and spinal cord

PNS

• Detects sensory input with receptors

• sends/conducts sensory info to CNS

• Carry commands to effectors from CNS

• Links CNS to sensory info and effector

Special sensory

5 senses, equilibrium, is conscious

Visceral sensory

internal organs, blood vessels, not conscious

Somatic sensory

skin, muscle, bone, joints, is conscious

Autonomic motor system of PNS

• Smooth muscle, cardiac muscle, glands

• Involuntary control

• 2 divisions

  • sympathetic and parasympathetic division

Somatic motor system

• Skeletal muscle

• Voluntary control

Sympathetic division

• Prepares body for physical activity/energy expending

• fight/flight

Parasympathetic division

• Regulates resting or vegetative functions/energy assimilation

• Rest and digest

Cell body

• One

• Receptive: receives input/stimuli or are stimulated directly

• Graded potentials input

Axon

• From one cell body

• Branches = collaterals

• Synaptic knobs w/ synaptic vesicles

• Generates output: transmitted impulses to other cells (action potentials)

Dendrites

• Many

• Receptive: receives input/stimuli or are stimulated directly

• Graded potentials

• input

Neuron general characteristics

• Transmit information as electrical impulses

  • Receive input (graded potentials)

  • Generate output (action potentials)

• Do not divide

• Long, large

  • Requires effective transport, axoplasmic transport mechanism to transport structures throughout cell

  • Consumes large amount of energy (O2)

• Ion pumps/gated channels on PM

  • Enables electrical impulses

  • Consumes large amount of energy (O2)

Why do neurons have high metabolic need and use lots of oxygen

• Many mitochondria

• High oxygen demand making neurons sensitive to lack of O2

• NS function/mental status are often earliest signs of dysfunction/loss of homeostasis

Graded potential

occur on dendrites and cell bodies

• Strength and spread is proportional to stimulus

Action potential

occur on axons

• “All or non” either happen completely or not at all

structural category of neuron: multipolar

most neurons in CNS with dendrites attached to cell body and one long axon, motor neurons

structural category of neuron: Unipolar

single processes that divides into two branches, part that extends into periphery has dendrite like sensory receptors
- eg. sensory neurons

structural category of neuron: Bipolar

sensory in retina of eye and nose, has two processes, one dendrite and axon

What are the combinations of cells that can form chemical synapses with one another?

• Receptor and neuron

• Neuron and neuron (e.g axon to cell bodies and dendrites)

• Neuron and effector

Two cells of a chemical synapse

Presynaptic cell:

• Synaptic knob and axon

Postsynaptic cell:

• dendrite or cell body

Presynaptic cell structures

• Synaptic knob

  • Has gated calcium channels

  • Synaptic vesicles in knob with neurotransmitters

Synaptic cleft in chemical synapse

Space between presynaptic and postsynaptic cells

Postsynaptic cell structures

• Postsynaptic membrane

  • Has receptors for neurotransmitters

  • Also has gated ion channels

  • Sometimes receptors and channels are part of same membrane

Describe the basic sequence of events that take place during the function of a chemical synapse including cause and effect relationships.

1. Electrical impulses (action potentials) of presynaptic cell reach synaptic cleft

2. Neurotransmitters diffuse across synaptic cleft

3. Neurotransmitters bind to receptors of post synaptic cell, causing inhibition or excitation

4. Neurotransmitter is either broken down by enzymes or transmitted back into presynaptic cell

   1. Synaptic activity ends

   2. Takes place in half a millisecond to one millisecond

Excitatory effects (epsp)

promotes formation of chemical impulse

Inhibitory effects (ipsp)

inhibits formation of electrical impulse

NMJ

motor neuron + synaptic cleft + motor end plate

Motor neuron structures

• Synaptic knob

  • Gated Ca+ channels

  • Synaptic vesicles in knob contain neurotransmitters (ACh)

Synaptic cleft in NMJ

Space between motor neuron and muscle cell

Motor end plate

• Skeleton muscle cell adjacent to cleft

• Contains ACh receptors

Glial cells in PNS

1. schwann cells

2. satellite cells

Glial cells in CNS

1. oligodendrocytes

2. astrocytes

3. microglia

4. ependymal cells

Schwann cells

1. Surround portion of single axon

2. Electrically insulates axon

3. Axon repair 

4. Myelinated or unmyelinated

Satellite cells

1. Surround neuron cell bodies in ganglia

2. protects/regulatees chemical environment around neuron

3. Regulates nutrients

Oligodendrocytes

1. Produce myelin in CNS neurons

2. Myelinate multiple axons

Astrocytes

1. Covers surface of blood vessels within the CNS

2. Promote tight junctions to form blood-brain barrier

3. Regulate extracellular brain fluid composition

4. Neurotransmitter movement/recycling

5. Assist in neuron repair

6. Guide development of neural connections

Microglia

1. Phagocytic

2. Defends against pathogens

3. Removes debris and dead  tissue

4. Removes waste

Ependymal cells

1. Line the ventricles and central canal

2. form /secrete cerebral spinal fluid (csf)

   1. Form part of choroid plexuses (which make CSF)

Myelinated axons

• Myelin sheath = repeated wrapping, creating later of lipid proteins rich in plasma membrane over the axon surface

  • Speeds transmission of action potential

  • Not continuous

    • Nodes of ranvier

What factors affect how fast an action potential travels down an axon

 Myelination:

• Myelinated axons are faster than unmyelinated

2. Diameter/thickness

• The larger in diameter the axon the faster it carries an impulse

White matter:

• structures/regions rich in myelinated axons

• Carries electrical impulses from one place to another

Gray matter:

• Areas of predominantly cell bodies, dendrites, neuroglia, and/or unmyelinated axons

• Typically integrative in function

What component of the nervous system is nerves located in

PNS

Anatomy of nerve:

• A bundle of axons and their CT sheaths

  • Endoneurium: surrounds individual neurons, areolar CT 

  • Perineurium: surrounds fascicles, contain blood vessels

  • Epineuron: surrounds entire nerve, dense CT