Term 2 Flashcards
Nervous System
Controls homeostasis through nerve impulses (action potentials) conducted along axons of neurons. At axon terminals, impulses trigger release of neurotransmitter molecules. The result is either excitation or inhibition of specific other neurons, muscle fibers (cells), or gland cells.
Nervous System
Types of cells of the nervous system
Neurons( Nerve cells) Neuroglia
Nervous System
Neurons (nerve cells) properties
Excitability: ability to RESPOND to a stimulus
Conductivity: ability to TRANSMIT a signal
Nervous System
Neuroglia properties
Specialized cells that support the neurons in some way
Ex. They phagocytize foreign substances, produce cerebrospinal fluid, and form myelin sheaths around axons
Nervous System organization
Central nervous system (CNS)
Peripheral nervous system (PNS)
Nervous system organization
Central nervous system (CNS)
Consists of the brain & spinal cord which are surrounded and protected by the skull and vertebral column respectively
May be thought of as the central control center of the body, receiving and interpreting or integrating all stimuli and relaying nerve impulses to muscles and glands where the designated actions take place
Nervous system organization
Peripheral nervous system
Includes all of the neural tissue outside the CNS. it delivers sensory information to the CNS and carries motor commands to peripheral tissues and systems.
Somatic nervous system (SNS)
Automatic (autonomic) nervous system (ANS)
Nervous system organization
Peripheral nervous system
Somatic nervous system
Division of the PNS composed of:
Somatic Afferent SENSORY division - which receives sensory information and conveys it to the spinal cord and brain via nerves.
Somatic Efferent MOTOR division - which regulates the contraction of skeleton via neuronal pathways that descend from the brain and spinal cord to lower motor neurons
Nervous system organization
Peripheral nervous system
Autonomic nervous system
Consists of sensory neurons that convey information from receptors in the viscera to the CNS and motor neurons from the CNS that conduct impulses to smooth muscle, cardiac muscle, and glands. Since its motor responses are not normally under conscious control, the ANS is involuntary.
Motor portion: sympathetic and parasympathetic division. With a few exceptions, the viscera receives instructions from both.
Sympathetic neurons - involve expenditure of energy
Parasympathetic neurons - restore and conserve body energy
Nervous System
Neurons - Three principled parts
The cell body
Dendrites
An axon
Nervous System
Neurons
Cell body
Vary in shape and size Has a large nucleus which contains a nucleolus, as well as several structures that are responsible for metabolism, growth and repair of the neuron - endoplasmic reticulum, lysosomes, mitochondria, neurofilaments, neurotubules, and Golgi apparatus
Neurofilaments: provide a skeletal framework for the axon
Neurotubules: function in the intracellular transport of the proteins and other substances, in both directions between the cell body and the ends of the processes
Nervous System
Neurons
Dendrites
Thread-like projections which are actually extensions of the cell body
Conduct nerve impulses towards the cell body
Nervous System
Neurons
Axons
A neuron generally has just one axon which extends from the cell body Carries nerve impulses away from the cell body to the next neuron, muscle or gland
Originates from the AXON HILLOCK
The initial segment, the site where the nerve impulse is initiated, lies immediately after the axon hillock
May have side processes called COLLATERAL BRANCHES end in a spray of small axon branches or TELODENRIA which end I tiny swellings called end bulbs
Nervous System
Neurons
Synapse
The junction between the end bulb of one axon and the cell body, dendrite, or axon of another neuron
A site where information is transferred from one cell to another
Ex. Neuron, muscle,gland
Nervous System
Neurons
Neurolemmocyte
Schwann cells
Form myelin sheaths around axons in the PNS
Nervous System
Neurons
Oligodendryte
Form myelin sheaths in the CNS
Nervous System
Myelination of axons
Some axons are covered with layers of a lipid sheath called myelin
Myelin sheath is formed by specialized non-neural cells called SCHWANN CELLS in the PNS and OLIGODENROCYTES in the CNS
The outer layer, or sheath, of the cells is the NEUILEMMA sheath
A myelin sheath is segmented, interrupted at regular intervals by gaps called NODES OF RANVIER. The distance between nodes is the INTERNODE.
There are myelinated and unmyelinated axons
A myelinated nerve fiber transmits a nerve impulse faster
Nervous System
Types of Neurons - Structural Classification
Multipolar Neurons
Have many processes consisting of many dendrites and a single axon
Ex. association (interneurons) and motor neurons
Nervous System
Types of Neurons - Structural Classification
Bipolar Neurons
have two processes: a dendrite and an axon which conducts action potentials to the CNS
Sensory neurons
Relatively Rare but play an important role in relaying information concerning sight, smell, and hearing
Nervous System
Types of Neurons - Structural Classification
Unipolar Neurons
Have one process, an axon Most sensory neurons are unipolar
Their peripheral ends have dendrite-like processes that respond to stimuli, producing action potentials that are conducted by the axon to the CNS
The branch that extends from the periphery to the neuron cell body, conducts action potentials to the cell body. According to a functional definition of a dendrite, it could be classified as a dendrite
Nervous System
The Reflex Arc - Location
Afferent Neurons
Convey information from the tissues and organs of the body to the CNS
Unipolar neurons are the most common in the PNS
Nervous System
The Reflex Arc - Location
Efferent or Motor Neurons
Convey nerve impulses away from the CNS to effectors (muscles and glands)
All motor neurons that control skeletal muscles are multipolar neurons
Nervous System
The Reflex Arc - Location
Interneurons (Association) Neurons
Lie between sensory and motor neurons in the neural pathways of the CNS
Responsible for the distribution of sensory information and the coordination of motor activity
Multipolar neurons
Endocrine System
Releases its messenger molecules, called hormones into the bloodstream. The cardiovascular system then delivers hormones to virtually all cells throughout the body
Nervous VS Endocrine
The __ system causes muscles to contract and glands to secrete their product
VS
The __ system alters metabolic activities, regulate growth and development, and guides reproductive processes.
The NERVOUS system causes muscles to contract and glands to secrete their product
The ENDOCRINE system alters metabolic activities, regulate growth and development, and guides reproductive processes.
Nervous VS Endocrine
__ most often produce their effects within a few milliseconds.
__ generally take several hours to bring about their responses.
NERVE IMPULSES most often produce their effects within a few milliseconds.
HORMONES generally take several hours to bring about their responses.
Nervous VS Endocrine
The effects of activating the __ system are generally briefer than the effects produced by the __ system
The effects of activating the NERVOUS system are generally briefer than the effects produced by the ENDOCRINE system
Endocrine System organization
Endocrine glands
Exocrine glands
Endocrine System organization
Endocrine Glands
Endocrine glands and specific cells are ductless, secreting products called hormones into extracellular spaces from which they enter the blood stream and circulate throughout the body to their target areas
Endocrine System organization
Exocrin glands
Exocrine gland secretions, such as sweat and salivary glands, empty directly into ducts that transport them to specific locations
Endocrine System
Hormones
Specialized chemical substances produced and secreted by an endocrine cell or organ
Effective only at specific target cells
Like neurotransmitters, they influence their target cells by chemically binding to integral proteins or glycoprotein molecules called receptors
Endocrine System
Hormones
Circulating
Hormones that can pass into the blood and act on distant target cells ENDOCRINES
Endocrine System
Hormones
Local
Hormones that act locally without first entering the bloodstream.
PARACRINES act on neighboring cells
AUTOCRINES act on the same cell that secreted them
Endocrine System
Chemical Signal Classification
Autocrines
Released by cells and have a local effect on the same cell that released it
Endocrine System
Chemical Signal Classification
Paracrine
Released by cells and affect other cell types locally without being transported in the blood
Endocrine System
Chemical Signal Classification
Hormone
Secreted into the blood to reach their target
Endocrine System
Chemical Signal Classification
Neurohormone
Produced by neurons and function like hormones
Endocrine System
Chemical Signal Classification
Neurotransmitter
Released by neurons at a synapse and influences a postsynaptic cell
Endocrine System
Chemical Signal Classification
Pheromone
A chemical signal secreted into the environment that modify the behavior of other individuals
Endocrine System
Chemical Signal Classification
Autocrine example
Prostaglandins
Endocrine System
Chemical Signal Classification
Paracrine examples
Histamine prostaglandins
Endocrine System
Chemical Signal Classification
Hormone examples
Thyroxine
Insulin
Endocrine System
Chemical Signal Classification
Neurohormone example
Oxytocin
Antidiuretic hormone
Endocrine System
Chemical Signal Classification
Neurotransmitter/neurohumor example
Acetylcholine
Epinepherine
Endocrine System
Chemical Signal Classification
Pheromones example
Sex pheromones are released by humans and many other animals. they are released in the urine of animals, such as dogs and cats. Pheromones produced by women influence the length of the menstrual cycle of other women
Endocrine System
Chemical Classification
Amines
Polypeptides and Proteins
Steroids
Ecosanoids
Endocrine System
Chemical Classification
Amines
Hormones derived from the amino acids Tyrosine and Tryptophan.
They include hormones secreted by the adrenal medulla and thyroid
Ex. Epinephrine, thyroid hormones, serotonin
Endocrine System
Chemical Classification
Polypeptides and Proteins
Consist of chains of amino acids
Synthesized on rough endoplasmic reticulum and exported from the cell
Ex. Insulin (pancreas), erythropoietin (kidney), antidiuretic hormone (posterior pituitary)
Endocrine System
Chemical Classification
Steroids
Lipids derived from cholesterol
Ex. Testosterone, progesterone, estrogens and cortisol
Endocrine System
Chemical Classification
Ecosanoids
Derived from arachidonic acid, a fatty acid
Exert control over many body systems
Ex. Thromboxane A2 is made by platelets. it causes vasoconstriction and promotes platelet aggregation. these actions prevent excessive blood loss when a blood vessel is damaged or severed
Endocrine System
Hormone Transport in Blood
Water-soluble
Catecholamines, peptide, and protein hormones are water-soluble hormones They circulate in watery blood plasma, and in free form (not attached to plasma proteins)
Endocrine System
Hormone Transport in Blood
Steroid and Thyroid
On entering the blood, steroid and thyroid hormones attache to specific transport proteins, which are synthesized by the liver.
The (shuttle) proteins have 3 functions
- they improve the transportability of the lipid-soluble hormones by making them temporarily water-soluble
- retard passage of the small hormone molecules through the filtering mechanisms in the kidney, thus slowing the rate of hormone loss in the urine
- provide a ready reserve of hormones already present in the bloodstream
Endocrine System
Mechanism of Action
Water-soluble
Peptides, proteins, and catecholamines (water-soluble hormones) exert at least some of their physiological responses through the increased synthesis of cAMP. These include anitidiuretic hormone (ADH), oxytocin (OT), calcitonin (CT), epinepherine, and norepinephrine
Besides cAMP, several other substances are known as second messengers. These include calcium ions (Ca2+), cyclic guanosine monophate (cGMP), inositol trisphosphate (IP3) and diacylglycerol (DAG)
The hormonal mechanism called the FIXED-MEMBRANE-RECEPTOR MECHANISM, involves the formation of second messengers
Endocrine System
Mechanism of Action
Water-soluble
Fixed-Membrane-Receptor Mechanism
Catecholamines, peptides, and proteins hormones are water-soluble. their receptors are integral proteins on the plasma membrane of target cells
Since these hormones can deliver their message only to the plasma membrane, they are called FIRST MESSENGER.
a SECOND MESSENGER, commonly cyclic (cAMP), is needed to relay the message inside the cell where hormone-stimulated response can take place. cAMP is synthesized from ATP by adenylate cyclase, an enzyme attached to the inner surface of hte plasma membrane.
cAMP and other second messengers alter cell function in specific ways.
Ex. elevated cAMP increses cardiac muscle contraction
Endocrine System
Mechanism of Action
Lipid-soluble (Steroid and Thyroid)
Because steroid hormones are lipid-soluble and pass easily through the plasma membrane, their receptors are inside the target cells. The hormone mechanism called the MOBILE-RECEPTOR MECHANISM, involves stimulus of protein synthesis.
Cortisol, aldosterone, thyroid hormones, testosterone, estrogen and progesterone are mobile-receptor hormones and have their receptor hormones and have their receptors localized in the cytoplasm
All other hormones usually use the fixed-membrane-receptor mechanism
Endocrine System
Control of Secretion
Negative Feedback Mechanism
A hormone is release in response to a specific stimulus and usually, its action reverses or negates the stimulus through a negative feedback mechanism
Ex. control of insulin secretion by blood glucose levels
Endocrine System
Control of Secretion
Positive Feedback Mechanism
The effect of a positive feedback mechanism is amplification of the stimulus and increasing release of the hormone until a particular process in complete and the stimulus ceases.
Ex. during child birth, the hormone oxytocin stimulates contraction of the uterus. uterine contractions, in turn, stimule more oxytocin release.
