Neural Tissue

endocrine and nervous systems maintain what?

homeostasis

endocrine system

communicates by means of chemical messengers (hormones)secreted into the blood

nervous syestem

employs electrical and chemical means to send messages from cell to cell

Three steps of nervous system

1. receive information

2. process information

3. issue commands

what are the two major subdivisions of the nervous system?

Central Nervous System (CNS) and Peripheral Nervous System (PNS)

Central Nervous System (CNS)

brain and spinal cord

Peripheral Nervous System (PNS)

the entire nervous system except the brain and spinal cord; composed of nerves and ganglia

nerve

a bundle of nerve fibers (axons) wrapped in fibrous connective tissue

Ganglia

a knot-like swelling in a nerve where neuron cell bodies are concentrated

two major divisions of the PNS

Sensory (afferent) division

Motor (efferent) division

sensory division

carries signals from receptors to CNS

motor division

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

two major subdivisions of the motor division

visceral motor and somatic motor

visceral (Autonomic nervous system) motor system

carries signals to glands, cardiac and smooth muscle. Its involuntary responses are visceral reflexes

somatic motor system

carries signals to skeletal muscles leading to muscular contraction and somatic reflexes (involuntary muscle contractions).

two components of the autonomic system

sympathetic and parasympathetic

sympathetic nervous system

a set of nerves that prepares the body for action in challenging or threatening situations

parasympathetic nervous system

a set of nerves that helps the body return to a normal resting state

3 major subdivisions of the sensory division of the PNS

special senses, visceral sensory, somatic sensory

special senses

monitor smell, taste, vision, balance, and hearing

visceral sensory

monitors internal organs

somatic sensory

monitors external environment, skin, body wall, limbs

cells of nervous tissue

neurons and neuroglia

Neurons

cells used for communication by the nervous tissue

Neuroglia

cells that support and protect neurons

Three classes of neurons

sensory neurons, interneurons, motor neurons

sensory neurons

Detect stimuli and transmit information about them toward the CNS

Interneurons

Receive signals from many neurons, integrates, processes, and determines the appropriate response. Lie entirely within the CNS connecting motor and sensory pathways (about 90% of all neurons).

motor neurons

Send signals out to muscles and gland cells (the effectors)

components of a neuron

Soma, dendrites, axon, axon hillock, axon terminal

soma

cell body of a neuron

dendrites

Branchlike parts of a neuron that are specialized to receive information.

Axon

A threadlike extension of a neuron that carries nerve impulses away from the cell body.

axon hillock

Cone shaped region of an axon where it joins the cell body; controls the initiation of an electrical impulse based on the inputs from other neurons or the environment

axon terminal

swellings that form contact points (synapses) with other cells, contains synaptic vesicles full of neurotransmitters

structural classification of neurons

multipolar, bipolar, unipolar, anaxonic

multipolar neuron

Multiple processes coming from cell body usually one axon and multiple dendrites

bipolar neurons

Two processes coming out of cell body of the neuron usually one axon and one dendrite

unipolar neuron

a neuron with one process extending from its cell body

anaxonic neuron

many dendrites but no axon

axonal transport

The transportation of materials from the neuronal cell body to distant regions in the dendrites and axons, and from the axon terminals back to the cell body.

anterograde transport

down the axon away from the soma

retrograde transport

up the axon toward the soma

kinesin

motor proteins in anterograde transport

Dynein

motor proteins in retrograde transport

Neuroglia of the CNS: Ependymal Cells

cuboidal epithelium with cilia on apical surface that line internal cavities of the brain. They secrete and circulate cerebrospinal fluid (CSF).

Neuroglia of the CNS: Astrocytes

most abundant glia in CNS. Star shaped cells that covers brain surface and most non synaptic regions of neurons

Neuroglia of the CNS: Oligodendrocytes

octopus like cells with arm-like processes that wrap around nerve fibers forming myelin sheathes in CNS that speed signal conduction.

Neuroglia of the PNS: Schwann cells

wind around the axon and form myelin sheaths. It also assist in regeneration of damaged fibers

Neuroglia of the PNS: Satellite cells

surround the somas of PNS neurons inside ganglia. They also provide electrical insulation and regulate the chemical environment.

myelin sheath

made up of the plasma of glial cells, made up of 20% protein and 80% lipid. It provides insulation around the axon and increases action potential conduction velocity.

Parts of a myelinated neuron

nodes of Ranvier, internodes, initial segment, trigger zone

disease of myelin sheath

multiple sclerosis and tay-sachs disease

multiple sclerosis

myelin sheath destruction. disruptions in nerve impulse conduction

Tay-Sachs disease

the abnormal accumulation of glycolipid called Gm2 in the myelin sheath which disrupts conduction of nerve signals

factors that can affect the speed on conduction

diameter of fiber (larger=faster) & presence of myelin (absent myelin=slower)

Regeneration of Nerve Fibers in CNS vs PNS

Mature neurons are amitotic, but if the soma (cell body) of the damaged nerve is intact, the peripheral axon may regenerate in PNS; does not occur in CNS

Process of regeneration of nerve fibers

1. Nerve cut; debris cleaned.

2. Swollen soma, broken ER, nucleus shift; axon sprouts growths; muscle shrinks.

3. Regeneration tube guides growth back.

4. Contact made; soma shrinks; muscle regrows.

What is a resting membrane of the neuron and how is the resting membrane potential created?

The resting membrane potential is the voltage across the membrane of a neuro it is created within the membrane

Na/K ATPase

3 Na out, 2 K in; helps create and maintain the sodium and potassium ion concentration gradients across the membrane

Na gradient

only allow sodium ions through, and so on

K gradient

only allow potassium ions through

What is a local potential and how is it established?

Change in membrane potential at an nearby point of stimulation may be a depolorization or a hyperpolarization.

What is an action potential and how is it established?

Rapid up-and-down shift in membrane potential that can travel a long distance down an axon

What is the difference between an action potential and a local potential?

Local potentials can either excite or inhibit the membrane while action potentials are all excitatory

What are the events of an action potential?

1. a triggering event

2. slow depolarization from -70mV to -55 mV

3. -55mV is the threshold point and rapid depolarization to +30mV occurs

4. repolarization

5. frequently over shoot to -80mV before repolarizaing at -70mV

relative refractory period

the time when a cell is unresponsive to a stimulus of greater strength, but may still respond to a weaker one.

absolute refractory period

the time frame during which a cell is unresponsive to any external stimulus, regardless of strength or duration

propagation vs. saltatory propagation

Saltatory propagation is faster than continuous propagation because it uses fewer channels and less energy

synapse

junction between two nerve cells consisting of a minute gap across which impulses pass by diffusion of a neurotransmitter

presynaptic junction

stops releasing neurotransmitter

post-synaptic neuron

less likely to fire action potential

What are the events of a chemical synapse?

1. Action potential in pre-synaptic neuron.

2. Action potential reaches axon terminal (synaptic knob).

3. Voltage-gated Ca++ channels open.

4. Ca++ enters the knob.

5. Ca++ triggers neurotransmitter release via exocytosis into the synaptic cleft.

Nuerotransmitters

Chemical messangers released from nueron to nueron.

neurotransmitter: Acetylcholine

is involved in muscle contractions and memory. in a class by itself, formed from acetic acid and choline

amino acid neurotransmitters

glycine, aspartate, g-aminobutyric acid (GABA)

neurotransmitters: monoamines

Epinephrine, norepinephrine, dopamine (catecholamines) Histamine and serotonin

synthesized from amino acids

neurotransmitters: neuropeptides

Enkephalin, cholecystokinin, substance p, B-endorphins

stored in secretory granules

Compare and contrast excitatory cholinergic synapse, inhibitory GABA-ergic synapse, excitatory adrenergic synapse

• Cholinergic synapses use ACh and nicotinic receptors for depolarization.

• GABA-ergic synapses use GABA and its receptors for hyperpolarization.

• Adrenergic synapses use norepinephrine/epinephrine and adrenergic receptors for fight-or-flight responses.

three kinds of synapses with different modes of action

Excitatory cholinergic synapse