Nervous System

Endocrine System

communicates through hormones (chemical messengers) secreted into the blood

Nervous System

employs electrical (action potentials) and chemical (neurotransmitters) means to send messages from cell to cell

Central Nervous System

brain and spinal cord enclosed in bony coverings; enclosed by cranium and vertebral column

Peripheral Nervous System

composed of nerves and ganglia

Nerves

bundles of nerve fibers (axons) wrapped in fibrous connective tissue

Ganglia

concentration of neuron cell bodies

Afferent PNS

carries sensory signals from receptors TO the CNS; divided into somatic and visceral divisions

Somatic Sensory Division

carries signals from receptors in the skin, muscles, bone, and joints

Visceral Sensory Division

carries signals from the viscera (organs, glands, and involuntary muscle) in the thoracic and abdominal cavities

Efferent/Motor Division

carries signals FROM the CNS to glands and muscle cells that carry out the body’s response

Effectors

cells and organs that respond to commands from the CNS

Somatic Motor Division

carries signals to skeletal muscles

Somatic Reflexes

involuntary muscle contractions

Visceral Motor Division Name

Autonomic Nervous System

Autonomic Nervous System

carries signals to glands, cardiac muscle, and smooth muscle

Visceral Reflexes

involuntary responses

Sympathetic Division of ANS

Fight or Flight; Norepinephrine/adrenaline; arouses body for action (increase breathing and heart rate, decrease digestive and renal function)

Parasympathetic Division of ANS

Rest and Digest; Ach; calming effect; Slows heart and breathing; activates digestion and renal function

Afferent Neurons

impulses TO the CNS; detect stimuli;

Efferent Neurons

Impulses OUT of CNS; most lead to muscles

Association Neurons

located entirely within CNS; integrate NS activity; process, store, and retrieve information to determine how the body will respond to stimuli; 90% of all neurons;

Properties of Neurons

Excitability, Conductivity, and Secretion

Excitability

respond to environmental changes and stimuli

Conductivity

respond to stimuli by producing electrical signals that are quickly conducted to other cells at distant locations

Secretion

chemical neurotransmitters secreted to cross gaps between nerve fibers and stimulate the next cell

Nuclei

groups of cell bodies in the CNS

Ganglia

Groups of cell bodies in the PNS

Neurosoma

Cell body with a centrally located nucleus; No centrioles (amitotic)

Dendrites

branches coming from the soma; primary site for receiving signals from other neurons;

Axon

originates from axon hillock/trigger zone; specialized for rapid conduction of nerve signals to points far from soma; one per neuron;

Axon collaterals

branches of axon

Axoplasm

cytoplasm of axon

Axolemma

plasma membrane of axon

Terminal arborization

extensive complex of fine branches at distal end of axon;

Synaptic knob

swelling that forms a synapse junction with the next cell; contains synaptic vesicles full of neurotransmitters

Multipolar Neuron

One axon and multiple dendrites; neurons in the brain and spinal cord

Bipolar Neuron

one axon and one dendrite; olfactory cells, retina, inner ear

Unipolar neuron

single process leading away from the soma; sensory from skin and organs to spinal cord

Anaxonic Neuron

many dendrites but no axon; help in visual processes

Neuroglia

glial cells; support and protect neuron; form framework for nervous tissue; gives precision to conduction pathways

Oligodendrocytes

from myelin sheaths in CNS; can wrap around multiple neurons; produce proteins that inhibit regrowth and form glial scar tissue

Ependymal Cells

lines internal cavities of the brain; cuboidal epithelium with cilia; secretes and circulates CSF

Microglia

small, wandering macrophages that search for cellular debris to phagocytize

Astrocytes

Most abundant glial cell in CNS; form a supportive framework of nervous tissue; perivascular feet wrap capillaries to form blood brain barrier;

CNS Glia cells

Oligodendrocytes, astrocytes, microglia, and ependymal cells

PNS Glia Cells

Schwann Cells, and Satellite cells

Astrocytosis/Sclerosis

Astrocytes from hardened scar tissue and fill damaged space

Schwann Cells

envelope nerve fibers in PNS; produces a myelin sheath; assist in the regeneration of damaged fibers

Satellite Cells

Surround somas in ganglia of PNS; provide electrical insulation around the soma; regulate the chemical environment of neurons;

3 Sources of Brain Tumors

Meninges; Metastasis from other organ tumors; glial cells that are mitotically active throughout life

Gliomas

grow rapidly and are highly malignant; blood-brain barrier decreases the effectiveness of chemotherapy; treatment consists of radiation or surgery

Myelin Sheath

insulating layer around neurons, formed by oligodendrocytes and Schwann cells; segmented; electrically insulates axon

Nodes of Ranvier

gap between myelin segments

Internodes

myelin covered segments of neuron

Initial Segment

short section of nerve fiber between the axon hillock and the first glial cell

Conduction Speed of Nerve FIbers

speed at which a nerve signal travels along a nerve fiber; dependent on diameter of the fiber and presence or absence of myelin

Cable Properties

Ability to conduct current; cytoplasm resistance decreases as axon diameter increases; electrical current leaks out through ion channels

Multiple Sclerosis

Myelin sheaths in the CS deteriorate; myelin replaced by hardened scar tissue; nerve conduction is disrupted; cause may be autoimmune triggered by a virus

Tay-Sachs Disease

a hereditary disorder of infants of Jewish ancestry; Abnormal accumulation of glycolipid GM2 in the myelin sheath; enzyme missing causing blindness, loss of coordination and dementia

Regeneration of PNS nerves

soma must be intact and some neurilemma must remain; fibers distal to the injury cannot survive; regeneration tube is formed by schwann cells, basal lamia, and the neurilemma;

Denervation

atrophy of muscle due to loss of nerve contact by damaged nerve

Electrophysiology

cellular mechanisms for producing electrical potentials and currents; basis for neural communication and muscle contraction

Electrical Potential

difference in concentration of charged particles between one point and another

Electrical current

flow of charged particles from one point to another

Resting Membrane Potential

charge difference across the plasma membrane; -70mV; exists because of unequal electrolyte distribution between ECF and ICF; Na+ concentrated in ECF; K+ concentrated in ICF

Action Potential

dramatic change produced by voltage-regulated ion gates in the plasma membrane;

Threshold

critical voltage to which local potentials must rise to open the voltage-regulated gates (-55 mV);

Small unmyelinated Fibers Conduction Speed

0\.5 - 2.0 m/sec

Large myelinated fibers conduction speed

up to 120 m/sec

Luigi Galvani

discovered the role of electricity in muscle contraction

Camillo Golgi

developed important method for staining neurons with silver

Santiago Ramon y Cajal

neuron doctrine creator

Neuron Doctrine

nervous pathway is not a continuous tube but a series of cells separated by gaps called synapses

Cytoplasmic Anions

Can not escape due to size or charge

Depolarization

Na+ flows into the cell

Repolarization

K+ gates open and K+ exit the cell

Hyperpolarization

K+ gates stay open longer than the Na+ gates

Nondecremental

do not get weaker with distance

Irreversible

once started goes to completion and cannot be stopped

Step 1 of Action Potential

Local potential - Na+ into the cell from stimulus

Step 2 of Action Potential

Threshold - action potential proceeds, voltage gated channels open

Step 3 of Action Potential

Depolarization - sodium influx

Step 4 of Action Potential

Peak Potential - slow K+ gates open, and Na+ Close

Step 5 of Action Potential

Repolarization - potassium eflux (exit the cell)

Step 6 of Action Potential

Hyperpolarization/Afterpotential - excessive K+ eflux

Step 7 of Action Potential

Return to RMP through Na+K+ Pumps

Refractory Period

the period of resistance to stimlation

Absolute Refractory Period

no stimulus will trigger AP

Relative Refractory Period

New trigger possible but unlikely; K+ gates still open

Saltatory Conduction

the nerve signal jumps from node to node

Presynaptic Neuron

releases neurotransmitter

Postsynaptic Neuron

responds to neurotransmitter

Axodendritic Synapse

Dendrite postsynaptic neuron

Axosomatic Synapse

Soma postsynaptic neuron

Axoaxonic Synapse

Axon postsynaptic neuron

Synapse step 1

Arrival of AP at synaptic knob

Synapse step 2

Voltage-Gated Calcium channel opens and calcium diffuses into synaptic knob

Synapse step 3

Vessicles secrete neurotransmitter via exocytosis

Synapse step 4

Neurotransmitters diffuse across synaptic cleft and bind to post synaptic receptors

Synapse step 5

Neurotransmitter causes opening of ion-channels in postsynaptic cell; can be excitatory or inhibitory