Ch 12-Nervous System3% of your body weight

2 divisions

•Central Nervous System (CNS)-

•Peripheral Nervous System (PNS)- Afferent-

Efferent-

1. sensory receptors for senses, motor from skeletal2. sensory for visceral, motor CNS to smooth &

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

Nervous Tissue

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

•Neuroglia-

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

•Presynaptic cell-• Synaptic end bulb- tips of axon terminal

• contain synaptic vesicles that store neurotransmitters

*Separated by synaptic cleft*

•Postsynaptic cell-

•If receiving cell is a: muscle = Gland =

Structural Classes of Neurons

• 1. Anaxonic- • 2. Bipolar-

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

• 3. Unipolar- • Peripheral nervous system, long

• 4. Multipolar- • Most common in CNS, control skeletal muscles, long

Functions

1.Sensory- -gather info if something changes & convert to impulses• Interoceptors-• systems (digestive, respiratory, cardiovascular)• senses (deep pressure, pain)

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

• Proprioceptors-

2. Integrate- - create sensation, memory, produce thoughts

3. Motor- effectors- response structures (muscles & glands)

*SAME*

Myelination

•Myelin Sheath-

- more myelin = - Neurolemma-

- Internodes- - Nodes of Ranvier-

Conduction- how it travels1. Continuous- 2. Saltatory-

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

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

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

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

What’s the Matter?

•White Matter- •Gray Matter- - cell bodies, dendrites, unmyelinated axons, axon terminals,

neuroglia

N e u ro g lia - N o u ris h e s n e u ro n s

• F(x):

Classification of Neuroglia of CNS1. Astrocytes-

2. Oligodendrocytes-

3. Microglia-

4. Ependymal-

Classification of Neuroglia of PNS1. Schwann- 2. Satellite-

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-

• Inside- Outside- 2. Graded potential-

3. Action potential-

4. Synaptic activity-

5. Information processing-

ElectrochemicalGradients-

Membrane channels

Passive/Leakage channels-

Active/Gated channels-

• Chemically/Ligand gated-

• Ex: Ach receptors at

neuromuscular junction

• Voltage gated-

• Mechanically gated-

Action potentialwhen a nerve detects a change

1. Resting state- -Threshold-

2. Depolarizing phase-

- makes more

3. Repolarizing phase-

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

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

Refractory Period-

All or None –

N e u ro tra n s m itte rs

Excitatory- Inhibitory-

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-

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