Ch 12-Nervous System3% of your body weight

2 divisions•Central Nervous System (CNS)- brain & spinal cord

•Peripheral Nervous System (PNS)- nerves in rest of bodyAfferent- brings sensory information to CNS from peripheral tissues & organs

Efferent- carries motor from CNS to muscles, glands, & adipose

1. Somatic NS- sensory receptors for senses, motor from skeletal2. Autonomic NS- sensory for visceral, motor CNS to smooth &

cardiac muscle & glands1. Sympathethic- fight or flight2. Parasympathetic- rest & digest

Nervous Tissue

•Neurons- structural & functional units- react to physical & chemical changes- send nerve impulses along nerve fibers

•Neuroglia- supporting cells (protect, nourish, cleanup, regulate)

Parts: Pg 3761. cell body- nucleus surrounded by

cytoplasm, rough ER called Nissl bodies

2. dendrites- receiving portions of neurons, usually not myelinated

3. axon- moves nerve impulses toward another neuron, muscle fiber, or gland

Others:- joins cell body at axon hillock- first part called initial segment- axoplasm- cytoplasm- axolemma- plasma membrane- axon collateral- branch & axon

terminal- end- Trigger zone- initial segment meets

axon hillock, where impulse arises

Synapse

•site of communication b/w two neurons, must have at least 2 neurons for a reflex

•Presynaptic cell-sends a message• Synaptic end bulb- tips of axon terminal• contain synaptic vesicles that store neurotransmitters

*Separated by synaptic cleft*

•Postsynaptic cell-receives the message

•If receiving cell is a: muscle = Neuromuscular junctionGland = neuroglandular junction

Structural Classes of Neurons• 1. Anaxonic- not distinguishing dendrite from axon• 2. Bipolar- 2 distinct processes(1 dendrite & 1 axon)

• Rare- in special sense organs for sight, smell, hearing• small

• 3. Unipolar- dendrites & axons are continuous, cell body inbetween• Peripheral nervous system, long

• 4. Multipolar- 2 or more dendrites & an axon• Most common in CNS, control skeletal muscles, long

Functions

1.Sensory- “afferent neurons” (to brain), at the ends of neurons-gather info if something changes & convert to impulses• Interoceptors- inside

• systems (digestive, respiratory, cardiovascular)• senses (deep pressure, pain)

• Exteroceptors- outside• touch, temp, pressure, sight, smell, hearing

• Proprioceptors- body position from muscles & joints

2. Integrate- “interneurons” (in brain), signals are sent to brain- create sensation, memory, produce thoughts

3. Motor- “efferent neurons” (away from brain), act upon impulseseffectors- response structures (muscles & glands)

*SAME*

Myelination•Myelin Sheath- multilayered lipid & protein covering, insulate the axon & increases speed- more myelin = faster impulse- Neurolemma- outer layer of Schwann cell, aids in regeneration of

injury- Internodes-where myelin occurs- Nodes of Ranvier- gaps in myelin sheath

Conduction- how it travels1. Continuous- straight line2. Saltatory- myelinated fibers, jumps, fastest

Disorders of Myelin-all can lead to paralysis

• Chronic exposure to heavy-metals (lead, arsenic, mercury) leads to demyelination

• Diphtheria- from bacterial infection, toxin damages myelin, we have a vaccine

• Multiple Sclerosis- affects axons in the optic nerve, brain, & SC• Loss of vision, problems with speech, balance, coordination• Can be progressive, 30-40yrs of age, more in women

• Guillain-Barre Syndrome- autoimmune, demyelination of PNS• Weakness & tingling > paralysis• Triggered by virus• Most fully recover

MS-http://www.youtube.com/watch?v=qgySDmRRzxY

What’s the Matter?•White Matter- has myelin, axons•Gray Matter- little or no myelin- cell bodies, dendrites, unmyelinated axons, axon terminals,

neuroglia

• Separate/protect neurons• Provide framework for neural tissue• Regulate composition of interstitial fluid• Act as phagocytes

Classification of Neuroglia of CNS1. Astrocytes- (star), most numerous

maintain blood-brain barrier, structural support, regulate ions, absorb & recycle neurotransmitters, form scar tissue

2. Oligodendrocytes- form myelin in CNS, structural framework

3. Microglia- janitors/police (eat bacterial cells & debris), smallest, least numerous

4. Ependymal- lines central canal of sc and ventricles of brain, regulate the composition of cerebrospinal fluid

Classification of Neuroglia of PNS1. Schwann- produce myelin in the PNS2. Satellite- regulate exchange of material b/w

neuronal cell bodies & interstitial fluid

Neural Response to Injury

Wallerian Degeneration- PNS• 1. fragmentation of axon &

myelin occurs in distal stump

• 2. Schwann cells form cord, grow into cut, & unite stumps• Macrophages engulf debris

• 3. Axon sends buds into network of Schwann cells and then starts growing along cord of Schwann cells

• 4. Axon grows

CNS- more complicated

• More axons are likely involved• Astrocytes produce scar tissue that can prevent growth• Astrocytes release chemicals that block growth

How does a nerve impulse happen?Ion movements & electrical signals:• All plasma membranes produce electrical signals by

ion movement

• Transmembrane potential is particularly important to neurons

• Main membrane processes:1. Resting Potential- work it may do, difference in

electrical charge• Inside- negative (K+), Outside- positive (Na+) & (Cl-)

2. Graded potential- temporary, change in resting potential caused by stimulus

3. Action potential- electrical impulse produced by graded potential propagated along axon to synapse

4. Synaptic activity- releases neurotransmitters producing graded potentials in postsynaptic cell membrane

5. Information processing- response of postsynaptic cell

ElectrochemicalGradients-Sum of chemical and electrical forces acting on ion across membrane

Why is the inside -?1. Negatively charged proteins inside the cell are too large to cross2. it is easier for K+ to diffuse out than Na+ to enter

Membrane channels

Passive/Leakage channels- always open Active/Gated channels- open or close in response to stimuli• Chemically/Ligand gated-

response to chemicals (hormones, neurotransmitters)• Ex: Ach receptors at

neuromuscular junction

• Voltage gated- response to changes in transmembrane potential• Mechanically gated- response to

physical distortion of membrane surface by touch, pressure or vibration

Action potentialwhen a nerve detects a change

1. Resting state- all channels closed-Threshold- gates open

2. Depolarizing phase- Na channel opens and Na comes in

- makes more positive

3. Repolarizing phase- Na channel closes, K channel opens and K flows out, makes more negative until

4. Resting state*exception- can go from #1 to Hyperpolarized = more negative

-happens if K+ opens right away

Refractory Period- short gap in time b/w impulses

All or None – if nerve responds, it is completely

http://www.youtube.com/watch?v=ifD1YG07fB8

Excitatory-promote action potentialInhibitory- suppress action potential

1. Acetylcholine (Ach)- skeletal muscles2. Norepinephrine- consciousness & attention, body temp3. Dopamine- emotions, addictions, pleasure, subconscious motor

function4. Serotonin- senses, temperature, mood (lack of=depression), appetite5. Glutamate & Aspartate- memory, learning, excitatory6. GABA- inhibitory, anti-anxiety

Neuromodulators

• Other chemicals released by synaptic terminals• Similar in function to neurotransmitters• Alter rate of neurotransmitter release or change post-synaptic cell’s

response

• Opioids like endorphins- relieve pain

Drugs & Addiction• Drugs can release two to 10 times the amount of dopamine that

natural rewards do, and they do it more quickly and more reliably• brain responds by producing less dopamine naturally or eliminating

dopamine receptors

• Alcohol: increases GABA & decreases glutamate=increase in dopamine

• Cocaine: inhibits removal of dopamine from synapses = “high”

• THC: stimulates release of dopamine = euphoria, drowsiness, appetite

• Ecstasy: targets serotonin receptors > mood

Parkinson’s Disease

• damage/degeneration of dopamine producing neurons• Usually after 50, more in men, can be genetic

Symptoms:• Problems with balance and walking• Rigid or stiff muscles• Difficulty swallowing• Drooling• Slowed, quieter speech and monotone voice• No expression in your face (like you are wearing a mask)• Tremors

Epilepsy

• short, recurrent attacks of motor, sensory, or psychological malfunction

• http://www.youtube.com/watch?v=6NcqQkKjqTI