UNIT A (NERVOUS AND ENDORCRINE SYSTEM) Flashcards
What does the nervous system do in regard to homeostasis?
The nervous system regulates body structures and processes to maintain homeostasis despite fluctuations in the internal and external environment.
What are the two divisions of the nervous system?
Central nervous system (CNS)
Peripheral nervous system (PNS)
CNS
Consists of the nerves of the brain and spinal cord and acts as a coordinating centre for incoming and outgoing information.
PNS
Consists of nerves that carry information between the organs of the body and the central nervous system. Further subdivided into somatic and autonomic
nerves.
Division on the Nervous System (Diagram)
Gilial Cells
Neuroglial cells, are nonconducting cells and are important for the structural support and metabolism of the nerve cells. Has different types of myelin sheath. (Schwann cells are a type of gilial cell that form the myelin sheath around axon).
Neurilemma
Outer layer of Schwann cells in the PNS.. Delicate membrane that surrounds the axon of some nerve cells. Formed
by the Schwann cells and promotes the regeneration of damaged axons. Not all nerve cells that have a myelin sheath have a neurilemma.
Nerves within the brain that contain myelinated fibres are called white matter because the myelinated axons are whitish in appearance. Other nerve cells within the brain and spinal cord, referred to as the grey matter, lack a myelin sheath.
Myelin Sheath
Insulated covering over the axon of a nerve cell, located in the PNS, made up of Schwann cells that form neurilemma.
Neuron
Nerve cell that conducts nerve impulses
Dendrite
Projection of cytoplasm that carries impulses toward the cell body. Conduct nerve impulses towards cell body.
Axon
Extension of cytoplasm that
carries nerve impulses away from
the cell body
Nodes of Ranvier
Regularly occurring gaps between sections of myelin sheath along the axon.
Sensory Neurons
Located in the PNS, neurons that
carries impulses to the central
nervous system; also known as
afferent neuron.
Ganglia
The cell bodies of sensory neurons are
located in clusters called located outside of the spinal cord.
Interneurons
Located in the CNS, link neurons to other neurons. Found only in the brain and spinal cord, the interneurons (also known as association neurons) integrate and interpret the sensory information and connect sensory neurons to outgoing motor neurons.
Motor Neurons
(also known as efferent neurons) relay information to the effectors, which is the cell or organ that responds to the stimulus. Muscles, organs, and glands are classified as effectors because they produce responses.
Reflex Arc
Before it reaches your brain, sensation detected by receptors and a nerve impulse carried to the spinal cord. The sensory neuron passes the impulse on to an interneuron, which, in turn, relays the impulse to a motor neuron. The motor neuron causes the muscles in the hand to contract and the hand to pull away. All this happens in less than a second, before the information even travels to the brain.
Pupillary Reflex
Check for reflexes, healthy nervous system!
Action Potential
The voltage difference across a nerve cell
membrane when the nerve is excited. The resting membrane normally had a potential somewhere near -70 mV (millivolts); however, when the nerve became excited, the potential on the inside of the membrane registered -55mV. This reversal of potential is described as an action potential.
Resting Potential
Voltage difference across a nerve cell membrane when it is not transmitting a nerve impulse (usually negative).
Plasma Membrane During Resting Potential
Higher concentration of
potassium ions (K+) inside the cell and a higher concentration of sodium ions (Na+) outside the cell. The movement of K+ is mainly responsible for creating the electrical potential. Sodiuum-Potassium exchange pump exchanges 3 Na+ ions for 2 K+ ions. Plasma membranes are selectively permeable; ions cannot cross the bilayer by simple diffusion. Instead, they enter cells by facilitated diffusion, passing through gated ion channels that span the bilayer. (If ion concentrations were determined only by diffusion, eventually the concentrations of sodium and potassium would equalize across the membrane. This does not happen because the sodium-potassium pump in the membrane moves potassium back into the cell and sodium back out of the cell through active transport.)
Polarized Membrane
Excess positive ions accumulate along the outside of the nerve membrane, while excess negative ions accumulate along the inside of the membrane. The resting membrane is said to be charged and is called a polarized membrane. A charge of -70 mV indicates the difference between the number of positive charges found on the inside of the nerve membrane relative to the outside. (A charge of -90 mV on the inside of the nerve membrane would indicate even fewer positive ions inside the membrane relative to the outside.)
Impulse Order
- Resting Potential: -70mV
- Action Potential: -55mV
- Depolarization: Diffusion of sodium ions into the nerve cells, resulting in a charge reversal. Cell membranesare more permeable to Na+ than K+, opening sodium channels while potassium channels remain closed. All the way to +35mV
Repolarization: The process of restoring the original polarity of the nerve membrane, Na+ channels close and K+ channels open. As K+ leaves from the inside of the cell, the inside becomes more negative, outside becomes more positive, and because K+ channels are slow to close, causes hyperpolarization! - Hyperpolarization: Condition in
which the inside of the nerve cell
membrane has a greater negative
charge than the resting membrane;
caused by excessive diffusion of
potassium ions out of the cell. - Refractory Period: Recovery time
required before a neuron can
produce another action potential. MUST return to resting potential before generating another action potential!
Movement of Action Potential is through
When axons are myelinated, nerve impulses travel by saltatory conduction. The flow of ions across the cell membrane can only happen at the nodes and so action potentials have to “jump” from node to node. This causes a nerve signal to be transmitted down an
axon much faster.
Order of travel
Dendrites, cell body, axon hillock, axon, myelin sheath, nodes of Ranvier, axon terminals, synapse.
Threshold Level
Minimum level of a
stimulus required to produce a
response
All-or-none-response
A nerve or muscle fibre responds completely or not at all to a stimulus.
Synapse
A region between neurons, or between neurons and effectors; also known as the synaptic cleft. Rarely involve just two neurons!
Neurotransmitters
Chemical messenger released by the
presynaptic neuron that binds to receptors on the postsynaptic neuron.
Presynaptic Neuron
A neuron that carries impulses to the synapse.
Postsynaptic Neuron
Neuron that carries impulses away from the synapse.
Diffusion of Neurotransmitters
Begins by Exyocytocis of Neurotransmitter. Diffusion is a slow process. Not surprisingly, the greater the number of synapses over a specified distance, the slower the speed of transmission. This may explain why you react so quickly to a stimulus in a reflex arc, which has few synapses, while solving biology problems, which involves many more synapses, requires more time.
Acetylcholine
Acts as an excitatory neurotransmitter on many postsynaptic neurons by opening the sodium ion channels. With the sodium channels open, the postsynaptic neuron would remain in a constant state of depolarization. Constant state of contraction!!
Although acetylcholine can act
as an excitatory neurotransmitter on some postsynaptic membranes, it can act as an inhibitory neurotransmitter on others.
Cholinesterase
An enzyme, which breaks down acetylcholine, that is released from presynaptic membranes in the end plates of neurons shortly after acetylcholine. Once acetylcholine is destroyed, the sodium channels close, and the neuron begins its recovery phase. Many insecticides take advantage of the synapse by blocking cholinesterase.
Excitatory Neurotransmitter (depolarization)
Increase membrane permeability to Na+; sodium gates open and sodium ions rush into the axon; the membrane becomes depolarized; action potential generated. (Acetylcholine, adrenaline/ epinephrine which stimulates sympathetic neurons).
Inhibitaory Neurotransmitter (hyperpolarization)
Increase membrane permeability to K+; potassium channels open, and membrane becomes hyperpolarized which means it is more difficult to generate an action potential. The inside of the axon becomes even more negatively charged. Prevent postsynaptic neurons from becoming active (GABA).
Can an action potential be generated by both excitatory and inhibitory?
No. The production of an action potential in neuron D requires the sum of two excitatory neurons. This principle is referred to as summation.
Parkinson’s disease
Involuntary muscle contractions and tremors is caused by inadequate production of dopamine.
Alzheimer’s disease
Associated with the deterioration of memory and mental capacity, has been related to decreased production of acetylcholine.
Meninges
Protective membranes
that surround the brain and spinal
cord
Cerebrospinal fluid
Cushioning fluid that circulates between the innermost and middle membranes of the brain and spinal cord; it provides a connection between neural and endocrine systems.
Spinal Cord
Carries sensory nerve messages from receptors to the brain and relays motor nerve messages from the brain to muscles, organs, and glands. Emerging from the skull through an opening called the foramen magnum, the spinal cord extends downward through a canal within the backbone.
Dorsal Root
Brings sensory information into the spinal
cord.
Ventral Root
Carries motor information from the spinal cord to the peripheral muscles, organs, and glands (effectors).
Grey Matter
Cell bodies, dendrites, short unmyelinated axons. Outside areas of the brain forms the H-shaped core of the spinal cord (inside).
White Matter
Myelinated axons that run together in tracts. Inner region of some areas of the brain and outer area of the spinal chord.
Brain divisions
- Hindbrain
- Midbrain
- Forebrain
Layers of Mengies, outside to inside
- Dura mater
- Archnoid Master
- Pia mater
What makes up the forebrain?
Cerebrum
Cerebral Cortex
Corpus Callosum
Thalamus
Hypothalamus
Olfactory Bulbs
(frontal lobe, parietal lobe, occipital lobe, temporal lobe).
What makes up the hindbrain?
Cerbellum
Medualla Oblongata
Pons
What makes up the midbrain?
Found above the pons
Directs and processes visual and auditory info between hindbrain and forebrain
Cerebrum
Divided into left and right hemispheres. Largest and most highly developed part of the human brain, which stores sensory information and initiates voluntary motor
activities.
Cerebral Cortex
Outer layer of the cerebral hemispheres
Corpus Callosum
Nerve tract that joins the two cerebral hemispheres.
Thalamus
Area of brain that coordinates and interprets sensory information and directs it to the cerebrum.
Hypothalamus
Area of the brain that coordinates many nerve and hormone functions. Plays a large role in maintaining the body’s internal equilibrium. A direct connection between the hypothalamus and the pituitary gland unites the nervous system with the endocrine system.
Regulates internal environment, blood pressure, hunger, thirst, sleep, body temperature, water balance and plays a role in the fight or flight response!
Olfactory Bulb
Area of the brain that processes information about smell; one bulb in each hemisphere.
Cerebellum
Part of the hindbrain that controls limb movements, balance, and muscle tone.
Pons
Region of the brain that acts
as a relay station by sending nerve
messages between the cerebellum
and the medulla.
Medulla Oblongata
Region of the hindbrain that joins the spinal cord to the cerebellum base of brainsteam, connects brain with spinal cord; one of the most important sites of autonomic nerve control. Involuntary muscle action, breathing movements, the diameter of the blood vessels, heart rate, swallowing, coughing.
