Nervous System
Oranismal S&F
Tony Serino. Ph.D.
Biology Dept.
Misericordia University
Nervous System
• Controls and/or modifies all other systems
• Rapid response time
• Usually short duration
Lecture Outline:
• General anatomy and physiology of neurons
Functional Areas
Divisions of the Nervous System
Nervous Tissue
• Non-excitable Tissue (Supportive cells)
– Neuroglia –present in CNS
– Schwann and Satellite cells –present in PNS
– Create myelin, protect and nurture neurons
• Neurons (excitable tissue)
– Initiate and conduct electrical signals (action potentials)
Neuron Anatomy
Axonal terminal
Nerve ending
Synaptic boutons
Synaptic knobs
Functional Zones of a Neuron
Receptor Zone
Initial segment of Axon
(trigger zone)
Nerve
endings
Axon
Node of Ranvier: gaps in myelin sheath
Synapses
• Areas where neurons communicate with
other cells
• Can be chemical (with neurotransmitters)
or electrical (gap junctions)
Anatomy of Synapse (chemical)
Neurotransmission ends when NT diffuses away,
re-absorbed by presynaptic neuron, or NT metabolized
(degraded) by enzymes in cleft
Membrane Potentials
• Produced by the unequal distribution of ions
across a selectively permeable membrane
• The inside of the cell is called negative by
convention
• The intensity of the ion difference is
expressed as voltage (measured in
millivolts (mV))
Measuring Membrane Potentials
Resting Membrane Potential
Parameters necessary to create a resting membrane potential:
•A semi-permeable membrane
•Distribution of ions across membrane
•Presence of large non-diffusible anions in interior
•Na-K pump (3 Na+ out for every 2 K+ in)
Gated Channel Proteins
• Opening gate allows ions to travel into or
out of the cell thereby changing the
membrane potential
• Can be controlled chemically or electrically
Chemically Gated Channel Protein
Voltage (electrically) Gated
Channel Protein
Graded Potentials
Depolarization
Inside of cell becomes
less negative
•Transient
•Decremental
•Due to chemically
gated channels opening
•Can be summated
•May be excitatory or
inhibitory
Will only trigger AP if the
threshold of the neuron is
reached.
Hyperpolarization
Inside of cell becomes
more negative
Graded potentials magnitude vary
with stimulus strength
Action Potentials
• Wave-like, massive depolarization
with rapid repolarization
• Propagated down entire length of
axon or muscle cell membrane
• All or none
• No summation possible
• Due to opening of voltage gated
channels and corresponding
positive feedback cycle established
Endocrine System
• Controls and modifies the internal
environment by releasing chemicals
(hormones) into the blood
• Slower response time but longer duration
of action compared to nervous system
Chemical Messengers (hormones)
• Hormone –secreted by cell into blood and
acts on another cell some distance away
• Neurohormone –secreted by neuron into
blood to affect a target cell some distance
away
• Local hormones –secreted by cell into
interstitial fluid to affects cells nearby
– Paracrines –affect neighboring cells
– Autocrines –affect the secreting cell
• Pheromones –secreted by cell onto body
surface to affect cells of another individual
Hormones
• Chemical Classification
– Amines –single or few amino acids, most water soluble
• Epinephrine, Thyroxine (but water insoluble), Melatonin
– Proteins –short to long chains of amino acids; water
soluble
• GH, FSH, LH, Insulin, Glucagon, ADH, etc.
– Steroids –derivatives of cholesterol; water insoluble
• Estrogen, Testosterone, Progesterone, Cortisol, Aldosterone
Steroid Hormones
Characteristics Common to all Hormones
• Must have target cell with appropriate
receptor molecules
• Receptor-hormone complex must trigger
events in target cell that changes its
physiology
• Mechanisms for deactivating the hormone
response must be present
Controlling Hormone Response
• Half-life of the hormone
• Physiological range
• Modifying target cell response
– Up and down regulation
• Turning off secretion
– Negative feedback
– Control by other hormones, neurons and
metabolites
Control of Hormone Secretion
Mechanisms of Hormone Action
2nd messengers
Water
Soluble
Water
Insoluble
Carrier protein
nd
2
Messengers: cAMP
2nd Messengers: IP3 and Ca++-Calmodulin
Steroid Hormone Transduction
Different Styles of Secretion
• Prohormone –a hormone that is made as a
larger (inactive form) that must be changed
prior to secretion (allows for storage of
hormone in secreting cell)
Ex.: proinsulin, pro-opiomelanocortin
• Prehormone –a hormone that is secreted in
an inactive form that must be changed near
or in the target cell
Ex.: Thyroxine, Angiotensinogen
Proinsulin
Types of Endocrine Disorders
• Hypersecretion
– Too much secretion of the hormone
• Hyposecretion
– Too little secretion of hormone
• Hyporesponsiveness
– Normal secretion, but little to no response by
target cells
Endocrine Glands