Bio 30 - Unit 4 - Topic 1-2

Peripheral Nervous System (PNS)

Peripheral Nervous System (PNS)

• Carry sensory messages to CNS, CNS to muscles/glands

• Somatic (voluntary)

  • Sensory (receiving) and motor (carrying & muscle) neurons

• Autonomic (non-voluntary)

  • Sympathetic (fight or flight) and parasympathetic (rest + digest)

  • Motor and sensory

Central Nervous System (CNS)

• Processes information

  • Brain

  • Spinal Chord

Somatic Nerves

• Voluntary

• Sensory receptors, carry info to CNS, CNS to skeletal glands (in control)

Autonomic Nerves

• Involuntary

• Controls glandular secretions & functioning of smooth and cardiac muscles (not in control)

Sympathetic & Parasympathetic Nervous System

• Work in opposition of each other

• Regulate involuntary processes of the body

  • ex. heartbeat, peristalsis, etc

Glial

• Supporting cell (structural - like “glue”)

• Non-conducting

• Nourishes neurons, removes waste & defends

Neuron Cells

• Conducting info via nerve (electrochemical) impulse

• Responds to physical and chemical stimuli

• Individuals neurons organized together to form “nerves”

  • neurons can “fire” (aka. depolarize)

Sensory Neurons

• Found in PNS

• Receive stimuli and begin the action

• Carries impulse to the CNS

Interneurons

• CNS

• Receive impulse from sensory neurons

• Interpret and process the impulse (brain)

Motor Neurons

• PNS

• Receive impulse from interneurons

• Causes the response in the effectors (muscles)

General Features of Neurons

• Dendrites

• Cell Body

• Axon

• Branding Ends (Axon Terminals)

Dendrites

• Start of every neurons

• Receptors (receive stimuli) and begin the action

• Relay impulse towards cell body and axon

Cell Body

• Contains nucleus (processes info)

• Filled with neuroplasm (goo)

Axon

• Conducts impulse away from cell body

• Long and skinny, length range from 1mm to 1m

Schwann Cells (Glial Cells)

• Found on PNS neurons only

• Supporting cell made of 2 parts

  • Neurilemma (thin OUTER membrane)

  • Myelin (INNER sheath)

Neurilemma

• Thin OUTER membrane

• Regenerates damaged PNS axons

  • CNS interneurons have none of these, their damage is permanent

Myelin

• INNER Sheath (schwann cells put together)

• Made of white fatty protein

• Allows action potentials (pulses) to move faster along axon (by preventing the loss of charge)

• Insulates axon

Nodes of Ranvier

• Space between Schwann cells

• Contain ion channels (Na+ and K+)

• Impulse “jumps” to allow faster conduction

  • Called saltatory conduction

Neurilemma/Myelin

• White Matter: myelinated neurons

  • Faster transmission

• Grey Matter: unmyelinated neurons

  • slower transmission

Axon Terminals

• “Feet”

• Contain vesicles that release chemicals (called neurotransmitters)

  • which diffuse across the synapse

• Where one neuron communicates with another

Reflex Arc

Neurons organized to make your body react even before you’re consciously aware of the threat

Affector

• Sensory receptor

• Senses/detects stimulus and nerve impulse initiated

Effector

• Muscle or gland that responds

Polarized

• Resting state - non conducting an impulse

• Resting membrane potential of -70 mV

• More Na+ outside than K+ inside, proteins inside make the inside charge negative

• Na/K pump maintains this

Na/K Pump

• More K+ channels than Na+ (K+ diffuses out more)

• K+ is more permeable and leaky, dominates membrane potential

• 3 Na+ out, 2 K+ in

Depolarization

• Nerve impulse (action potential) (stimulated)

• Reversal charge of +40 mV

• Na+ channels open, Na+ diffuses in

  • once voltage is positive inside, gates close

    • K+ gates are closed

Repolarization

• Back to rest

• K+ channels open, K+ diffuses out, charge becomes -70 mV again

• K+ gates close slower, causing extra negative charge (-80 - 90 mV), called hyper-polarized

• Na/K pump transports ions to correct location

Refractory Period

• Depolarization completed, nerve is repolarized, before a 2nd action potential can be done

  • will not respond to stimuli

• Caused by hyperpolarization

Threshold Potential

• Minimum stimulus level, -55 mV is the average threshold value

Summation

• Neuron’s working together to reach the threshold

Synapse

• Small space between neurons or between neurons and effectors

Presynaptic Neuron

• Before the synapse

Postsynaptic Neuron

• After the synapse

• Neurotransmitters releases from presynaptic neuron, diffuses across synapse

  • Bind to postsynaptic neuron receptor proteins

• Excitatory neuro-tranmission binding causes depolarization of the dendrites

Neurotransmitters

• Specific chemicals substances, neuron communication

• Stored in synaptic vesicles in axon terminals

• Cause excitement or inhibition of postsynaptic neuron

Excitatory Neurotransmitters

1. Action potential causes vesicles to fuse with presynaptic membrane (because Ca+ enters), releases neurotransmitters into the synapse

2. Neurotransmitters bind to receptor proteins on postsynaptic neuron

3. Initiates depolarization (opens Na+ channels)

4. Enzyme enters synapses, breaks down neurotransmitters, stopping impulse

5. Neurotransmitters reabsorbed by presynaptic neuron

Inhibitory Neurotransmitters

• Bind to different receptor proteins on postsynaptic neuron

• K+ gates open, K+ diffuses out

• Opens negative ion channels (Cl-), rushing into neuron - causing hyper-polarization