Nervous System

Oranismal S&FTony Serino. Ph.D.

Biology Dept.Misericordia University

Nervous System• Controls and/or modifies all other systems• Rapid response time• Usually short duration

• General anatomy and physiology of neurons

Lecture Outline:

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 terminalNerve endingSynaptic boutonsSynaptic knobs

Functional Zones of a Neuron

Receptor Zone

Initial segment of Axon(trigger zone)

Axon

Nerve endings

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

• 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)

Parameters necessary to create a resting membrane potential:

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

Hyperpolarization

• Transient• Decremental• Due to chemically

gated channels opening• Can be summated• May be excitatory or

inhibitory

Will only trigger AP if thethreshold of the neuron isreached.

Inside of cell becomes less negative

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

Water Soluble

WaterInsoluble

Carrier protein

2nd messengers

2nd 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 cellEx.: 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